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[1] Arctic amplification decreases temperature variance in northern mid - to high-latitudes

Changes in climate variability are arguably more important for society and ecosystems than changes in mean climate , especially if they translate into altered extremes .
There is a common perception and growing concern that human-induced climate change will lead to more volatile and extreme weather .
Certain types of extreme weather have increased in frequency and/or severity , in part because of a shift in mean climate but also because of changing variability .
In spite of mean climate warming , an ostensibly large number of high-impact cold extremes have occurred in the Northern Hemisphere mid-latitudes over the past decade .
One explanation is that Arctic amplification -- the greater warming of the Arctic compared with lower latitudes associated with diminishing sea ice and snow cover -- is altering the polar jet stream and increasing temperature variability .
This study shows , however , that subseasonal cold-season temperature variability has significantly decreased over the mid - to high-latitude Northern Hemisphere in recent decades .
This is partly because northerly winds and associated cold days are warming more rapidly than southerly winds and warm days , and so Arctic amplification acts to reduce subseasonal temperature variance .
Previous hypotheses linking Arctic amplification to increased weather extremes invoke dynamical changes in atmospheric circulation , which are hard to detect in present observations and highly uncertain in the future .
In contrast , decreases in subseasonal cold-season temperature variability , in accordance with the mechanism proposed here , are detectable in the observational record and are highly robust in twenty-first-century climate model simulations .

[2] Elevation-dependent influence of snow accumulation on forest greening

Rising temperatures and declining water availability have influenced the ecological function of mountain forests over the past half-century .
For instance , warming in spring and summer and shifts towards earlier snowmelt are associated with an increase in wildfire activity and tree mortality in mountain forests in the western United States .
Temperature increases are expected to continue during the twenty-first century in mountain ecosystems across the globe , with uncertain consequences .
Here , we examine the influence of interannual variations in snowpack accumulation on forest greenness in the Sierra Nevada Mountains , California , between 1982 and 2006 .
Using observational records of snow accumulation and satellite data on vegetation greenness we show that vegetation greenness increases with snow accumulation .
Indeed , we show that variations in maximum snow accumulation explain over 50 % of the interannual variability in peak forest greenness across the Sierra Nevada region .
The extent to which snow accumulation can explain variations in greenness varies with elevation , reaching a maximum in the water-limited mid-elevations , between 2,000 and 2,600 m .
In situ measurements of carbon uptake and snow accumulation along an elevational transect in the region confirm the elevation dependence of this relationship .
We suggest that mid-elevation mountain forest ecosystems could prove particularly sensitive to future increases in temperature and concurrent changes in snow accumulation and melt .

[3] Greenhouse gas mitigation can reduce sea-ice loss and increase polar bear persistence

On the basis of projected losses of their essential sea-ice habitats , a United States Geological Survey research team concluded in 2007 that two-thirds of the world 's polar bears ( Ursus maritimus ) could disappear by mid-century if business-as-usual greenhouse gas emissions continue .
That projection , however , did not consider the possible benefits of greenhouse gas mitigation .
A key question is whether temperature increases lead to proportional losses of sea-ice habitat , or whether sea-ice cover crosses a tipping point and irreversibly collapses when temperature reaches a critical threshold .
Such a tipping point would mean future greenhouse gas mitigation would confer no conservation benefits to polar bears .
Here we show , using a general circulation model , that substantially more sea-ice habitat would be retained if greenhouse gas rise is mitigated .
We also show , with Bayesian network model outcomes , that increased habitat retention under greenhouse gas mitigation means that polar bears could persist throughout the century in greater numbers and more areas than in the business-as-usual case .
Our general circulation model outcomes did not reveal thresholds leading to irreversible loss of ice ; instead , a linear relationship between global mean surface air temperature and sea-ice habitat substantiated the hypothesis that sea-ice thermodynamics can overcome albedo feedbacks proposed to cause sea-ice tipping points .
Our outcomes indicate that rapid summer ice losses in models and observations represent increased volatility of a thinning sea-ice cover , rather than tipping-point behaviour .
Mitigation-driven Bayesian network outcomes show that previously predicted declines in polar bear distribution and numbers are not unavoidable .
Because polar bears are sentinels of the Arctic marine ecosystem and trends in their sea-ice habitats foreshadow future global changes , mitigating greenhouse gas emissions to improve polar bear status would have conservation benefits throughout and beyond the Arctic .

[4] Decrease in CO2 efflux from northern hardwater lakes with increasing atmospheric warming

Boreal lakes are biogeochemical hotspots that alter carbon fluxes by sequestering particulate organic carbon in sediments and by oxidizing terrestrial dissolved organic matter to carbon dioxide ( CO2 ) or methane through microbial processes .
At present , such dilute lakes release ~ 1.4 petagrams of carbon annually to the atmosphere , and this carbon efflux may increase in the future in response to elevated temperatures and increased hydrological delivery of mineralizable dissolved organic matter to lakes .
Much less is known about the potential effects of climate changes on carbon fluxes from carbonate-rich hardwater and saline lakes that account for about 20 per cent of inland water surface area .
Here we show that atmospheric warming may reduce CO2 emissions from hardwater lakes .
We analyse decadal records of meteorological variability , CO2 fluxes and water chemistry to investigate the processes affecting variations in pH and carbon exchange in hydrologically diverse lakes of central North America .
We find that the lakes have shifted progressively from being substantial CO2 sources in the mid-1990s to sequestering CO2 by 2010 , with a steady increase in annual mean pH. We attribute the observed changes in pH and CO2 uptake to an atmospheric-warming-induced decline in ice cover in spring that decreases CO2 accumulation under ice , increases spring and summer pH , and enhances the chemical uptake of CO2 in hardwater lakes .
Our study suggests that rising temperatures do not invariably increase CO2 emissions from aquatic ecosystems .

[5] Increased future ice discharge from Antarctica owing to higher snowfall

Anthropogenic climate change is likely to cause continuing global sea level rise , but some processes within the Earth system may mitigate the magnitude of the projected effect .
Regional and global climate models simulate enhanced snowfall over Antarctica , which would provide a direct offset of the future contribution to global sea level rise from cryospheric mass loss and ocean expansion .
Uncertainties exist in modelled snowfall , but even larger uncertainties exist in the potential changes of dynamic ice discharge from Antarctica and thus in the ultimate fate of the precipitation-deposited ice mass .
Here we show that snowfall and discharge are not independent , but that future ice discharge will increase by up to three times as a result of additional snowfall under global warming .
Our results , based on an ice-sheet model forced by climate simulations through to the end of 2500 ( ref .
8 ) , show that the enhanced discharge effect exceeds the effect of surface warming as well as that of basal ice-shelf melting , and is due to the difference in surface elevation change caused by snowfall on grounded versus floating ice .
Although different underlying forcings drive ice loss from basal melting versus increased snowfall , similar ice dynamical processes are nonetheless at work in both ; therefore results are relatively independent of the specific representation of the transition zone .
In an ensemble of simulations designed to capture ice-physics uncertainty , the additional dynamic ice loss along the coastline compensates between 30 and 65 per cent of the ice gain due to enhanced snowfall over the entire continent .
This results in a dynamic ice loss of up to 1.25 metres in the year 2500 for the strongest warming scenario .
The reported effect thus strongly counters a potential negative contribution to global sea level by the Antarctic Ice Sheet .

[6] Reconciliation of halogen-induced ozone loss with the total-column ozone record

The observed depletion of the ozone layer from the 1980s onwards is attributed to halogen source gases emitted by human activities .
However , the precision of this attribution is complicated by year-to-year variations in meteorology , that is , dynamical variability , and by changes in tropospheric ozone concentrations .
As such , key aspects of the total-column ozone record , which combines changes in both tropospheric and stratospheric ozone , remain unexplained , such as the apparent absence of a decline in total-column ozone levels before 1980 , and of any long-term decline in total-column ozone levels in the tropics .
Here we use a chemistry-climate model to estimate changes in halogen-induced ozone loss between 1960 and 2010 ; the model is constrained by observed meteorology to remove the effects of dynamical variability , and driven by emissions of tropospheric ozone precursors to separate out changes in tropospheric ozone .
We show that halogen-induced ozone loss closely followed stratospheric halogen loading over the studied period .
Pronounced enhancements in ozone loss were apparent in both hemispheres following the volcanic eruptions of El Chichon and , in particular , Mount Pinatubo , which significantly enhanced stratospheric aerosol loads .
We further show that approximately 40 % of the long-term non-volcanic ozone loss occurred before 1980 , and that long-term ozone loss also occurred in the tropical stratosphere .
Finally , we show that halogen-induced ozone loss has declined by over 10 % since stratospheric halogen loading peaked in the late 1990s , indicating that the recovery of the ozone layer is well underway .

[7] Land-atmosphere coupling and climate change in Europe

Increasing greenhouse gas concentrations are expected to enhance the interannual variability of summer climate in Europe and other mid-latitude regions , potentially causing more frequent heatwaves .
Climate models consistently predict an increase in the variability of summer temperatures in these areas , but the underlying mechanisms responsible for this increase remain uncertain .
Here we explore these mechanisms using regional simulations of recent and future climatic conditions with and without land-atmosphere interactions .
Our results indicate that the increase in summer temperature variability predicted in central and eastern Europe is mainly due to feedbacks between the land surface and the atmosphere .
Furthermore , they suggest that land-atmosphere interactions increase climate variability in this region because climatic regimes in Europe shift northwards in response to increasing greenhouse gas concentrations , creating a new transitional climate zone with strong land-atmosphere coupling in central and eastern Europe .
These findings emphasize the importance of soil-moisture-temperature feedbacks ( in addition to soil-moisture-precipitation feedbacks ) in influencing summer climate variability and the potential migration of climate zones with strong land-atmosphere coupling as a consequence of global warming .
This highlights the crucial role of land-atmosphere interactions in future climate change .

[8] Agricultural Green Revolution as a driver of increasing atmospheric CO2 seasonal amplitude

The atmospheric carbon dioxide ( CO2 ) record displays a prominent seasonal cycle that arises mainly from changes in vegetation growth and the corresponding CO2 uptake during the boreal spring and summer growing seasons and CO2 release during the autumn and winter seasons .
The CO2 seasonal amplitude has increased over the past five decades , suggesting an increase in Northern Hemisphere biospheric activity .
It has been proposed that vegetation growth may have been stimulated by higher concentrations of CO2 as well as by warming in recent decades , but such mechanisms have been unable to explain the full range and magnitude of the observed increase in CO2 seasonal amplitude .
Here we suggest that the intensification of agriculture ( the Green Revolution , in which much greater crop yield per unit area was achieved by hybridization , irrigation and fertilization ) during the past five decades is a driver of changes in the seasonal characteristics of the global carbon cycle .
Our analysis of CO2 data and atmospheric inversions shows a robust 15 per cent long-term increase in CO2 seasonal amplitude from 1961 to 2010 , punctuated by large decadal and interannual variations .
Using a terrestrial carbon cycle model that takes into account high-yield cultivars , fertilizer use and irrigation , we find that the long-term increase in CO2 seasonal amplitude arises from two major regions : the mid-latitude cropland between 25degrees N and 60degrees N and the high-latitude natural vegetation between 50degrees N and 70degrees N .
The long-term trend of seasonal amplitude increase is 0.311 + / - 0.027 per cent per year , of which sensitivity experiments attribute 45 , 29 and 26 per cent to land-use change , climate variability and change , and increased productivity due to CO2 fertilization , respectively .
Vegetation growth was earlier by one to two weeks , as measured by the mid-point of vegetation carbon uptake , and took up 0.5 petagrams more carbon in July , the height of the growing season , during 2001-2010 than in 1961-1970 , suggesting that human land use and management contribute to seasonal changes in the CO2 exchange between the biosphere and the atmosphere .

[9] The effect of climate change on ozone depletion through changes in stratospheric water vapour

Several studies have predicted substantial increases in Arctic ozone depletion due to the stratospheric cooling induced by increasing atmospheric CO2 concentrations .
But climate change may additionally influence Arctic ozone depletion through changes in the water vapour cycle .
Here we investigate this possibility by combining predictions of tropical tropopause temperatures from a general circulation model with results from a one-dimensional radiative convective model , recent progress in understanding the stratospheric water vapour budget , modelling of heterogeneous reaction rates and the results of a general circulation model on the radiative effect of increased water vapour .
Whereas most of the stratosphere will cool as greenhouse-gas concentrations increase , the tropical tropopause may become warmer , resulting in an increase of the mean saturation mixing ratio of water vapour and hence an increased transport of water vapour from the troposphere to the stratosphere .
Stratospheric water vapour concentration in the polar regions determines both the critical temperature below which heterogeneous reactions on cold aerosols become important ( the mechanism driving enhanced ozone depletion ) and the temperature of the Arctic vortex itself .
Our results indicate that ozone loss in the later winter and spring Arctic vortex depends critically on water vapour variations which are forced by sea surface temperature changes in the tropics .
This potentially important effect has not been taken into account in previous scenarios of Arctic ozone loss under climate change conditions .

[10] Increased polar stratospheric ozone losses and delayed eventual recovery owing to increasing greenhouse-gas concentrations

The chemical reactions responsible for stratospheric ozone depletion are extremely sensitive to temperature .
Greenhouse gases warm the Earth 's surface but cool the stratosphere radiatively and therefore affect ozone depletion .
Here we investigate the interplay between projected future emissions of greenhouse gases and levels of ozone-depleting halogen species using a global climate model that incorporates simplified ozone-depletion chemistry .
Temperature and wind changes induced by the increasing greenhouse-gas concentrations alter planetary-wave propagation in our model , reducing the frequency of sudden stratospheric warmings in the Northern Hemisphere .
This results in a more stable Arctic polar vortex , with significantly colder temperatures in the lower stratosphere and concomitantly increased ozone depletion .
Increased concentrations of greenhouse gases might therefore be at least partly responsible for the very large Arctic ozone losses observed in recent winters .
Arctic losses reach a maximum in the decade 2010 to 2019 in our model , roughly a decade after the maximum in stratospheric chlorine abundance .
The mean losses are about the same as those over the Antarctic during the early 1990s , with geographically localized losses of up to two-thirds of the Arctic ozone column in the worst years .
The severity and the duration of the Antarctic ozone hole are also predicted to increase because of greenhouse-gas-induced stratospheric cooling over the coming decades .

[11] Circulation response to warming shaped by radiative changes of clouds and water vapour

The atmospheric circulation controls how global climate change will be expressed regionally .
Substantial circulation changes are expected under global warming , including a narrowing of the intertropical convergence zone , a slow down and poleward expansion of the tropical circulation , and a poleward shift of mid-latitude stormtracks and jets .
Yet , climate model projections of the circulation response to climate change remain uncertain .
Here we present simulations with two different aquaplanet climate models and analyse these simulations using the cloud and water-vapour locking method .
We find that radiative changes of clouds and water vapour are key to the regional response of precipitation and circulation to global warming .
Model disagreement in the response of key characteristics of the atmospheric circulation -- the intertropical convergence zone , the strength of the Hadley circulation , and the trade winds -- arises from disagreement between the models in radiative changes of tropical ice clouds and their coupling to the circulation .
We find that cloud changes amplify a poleward shift of the extratropical jet , whereas water vapour changes oppose such a shift , but the degree of compensation is model-dependent .
We conclude that radiative changes of clouds and water vapour are not only integral to the magnitude of future global-mean warming but also determine patterns of regional climate change .

[12] Complex forest dynamics indicate potential for slowing carbon accumulation in the southeastern United States

Over the past century forest regrowth in Europe and North America expanded forest carbon ( C ) sinks and offset C emissions but future C accumulation is uncertain .
Policy makers need insights into forest C dynamics as they anticipate emissions futures and goals .
We used land use and forest inventory data to estimate how forest C dynamics have changed in the southeastern United States and attribute changes to land use , management , and disturbance causes .
From 2007-2012 , forests yielded a net sink of C because of net land use change ( +6.48 Tg C yr-1 ) and net biomass accumulation ( +75.4 Tg C yr-1 ) .
Forests disturbed by weather , insect/disease , and fire show dampened yet positive forest C changes ( +1.56 , +1.4 , +5.48 Tg C yr-1 , respectively ) .
Forest cutting caused net decreases in C ( -76.7 Tg C yr-1 ) but was offset by forest growth ( +143.77 Tg C yr-1 ) .
Forest growth rates depend on age or stage of development and projected C stock changes indicate a gradual slowing of carbon accumulation with anticipated forest aging ( a reduction of 9.5 % over the next five years ) .
Additionally , small shifts in land use transitions consistent with economic futures resulted in a 40.6 % decrease in C accumulation .

[13] Analogous nutrient limitations in unicellular diazotrophs and Prochlorococcus in the South Pacific Ocean

Growth limitation of phytoplankton and unicellular nitrogen ( N2 ) fixers ( diazotrophs ) were investigated in the oligotrophic Western South Pacific Ocean .
Based on change in abundances of nifH or 23S rRNA gene copies during nutrient-enrichment experiments , the factors limiting net growth of the unicellular diazotrophs UCYN-A ( Group A ) , Crocosphaera watsonii , gamma-Proteobacterium 24774A11 , and the non-diazotrophic picocyanobacterium Prochlorococcus , varied within the region .
At the westernmost stations , numbers were enhanced by organic carbon added as simple sugars , a combination of iron and an organic chelator , or iron added with phosphate .
At stations nearest the equator , the nutrient-limiting growth was not apparent .
Maximum net growth rates for UCYN-A , C. watsonii and gamma-24774A11 were 0.19 , 0.61 and 0.52 d-1 , respectively , which are the first known empirical growth rates reported for the uncultivated UCYN-A and the gamma-24774A11 .
The addition of N enhanced total phytoplankton biomass up to 5-fold , and the non-N2-fixing Synechococcus was among the groups that responded favorably to N addition .
Nitrogen was the major nutrient-limiting phytoplankton biomass in the Western South Pacific Ocean , while availability of organic carbon or iron and organic chelator appear to limit abundances of unicellular diazotrophs .
Lack of phytoplankton response to nutrient additions in the Pacific warm pool waters suggests diazotroph growth in this area is controlled by different factors than in the higher latitudes , which may partially explain previously observed variability in community composition in the region .

[14] Rising CO2 and increased light exposure synergistically reduce marine primary productivity

Carbon dioxide and light are two major prerequisites of photosynthesis .
Rising CO2 levels in oceanic surface waters in combination with ample light supply are therefore often considered stimulatory to marine primary production .
Here we show that the combination of an increase in both CO2 and light exposure negatively impacts photosynthesis and growth of marine primary producers .
When exposed to CO2 concentrations projected for the end of this century , natural phytoplankton assemblages of the South China Sea responded with decreased primary production and increased light stress at light intensities representative of the upper surface layer .
The phytoplankton community shifted away from diatoms , the dominant phytoplankton group during our field campaigns .
To examine the underlying mechanisms of the observed responses , we grew diatoms at different CO2 concentrations and under varying levels ( 5-100 % ) of solar radiation experienced by the phytoplankton at different depths of the euphotic zone .
Above 22-36 % of incident surface irradiance , growth rates in the high-CO2-grown cells were inversely related to light levels and exhibited reduced thresholds at which light becomes inhibitory .
Future shoaling of upper-mixed-layer depths will expose phytoplankton to increased mean light intensities .
In combination with rising CO2 levels , this may cause a widespread decline in marine primary production and a community shift away from diatoms , the main algal group that supports higher trophic levels and carbon export in the ocean .

[15] Nitrogen and phosphorus addition impact soil N2O emission in a secondary tropical forest of South China

Nutrient availability greatly regulates ecosystem processes and functions of tropical forests .
However , few studies have explored impacts of N addition ( aN ) , P addition ( aP ) and NxP interaction on tropical forests N2O fluxes .
We established an N and P addition experiment in a tropical forest to test whether : ( 1 ) N addition would increase N2O emission and nitrification , and ( 2 ) P addition would increase N2O emission and N transformations .
Nitrogen and P addition had no effect on N mineralization and nitrification .
Soil microbial biomass was increased following P addition in wet seasons .
aN increased 39 % N2O emission as compared to control ( 43.3 mugN2O-N m-2h-1 ) .
aP did not increase N2O emission .
Overall , N2O emission was 60 % greater for aNP relative to the control , but significant difference was observed only in wet seasons , when N2O emission was 78 % greater for aNP relative to the control .
Our results suggested that increasing N deposition will enhance soil N2O emission , and there would be NxP interaction on N2O emission in wet seasons .
Given elevated N deposition in future , P addition in this tropical soil will stimulate soil microbial activities in wet seasons , which will further enhance soil N2O emission .

[16] Climate variation explains a third of global crop yield variability

Many studies have examined the role of mean climate change in agriculture , but an understanding of the influence of inter-annual climate variations on crop yields in different regions remains elusive .
We use detailed crop statistics time series for ~ 13,500 political units to examine how recent climate variability led to variations in maize , rice , wheat and soybean crop yields worldwide .
While some areas show no significant influence of climate variability , in substantial areas of the global breadbaskets , > 60 % of the yield variability can be explained by climate variability .
Globally , climate variability accounts for roughly a third ( ~ 32-39 % ) of the observed yield variability .
Our study uniquely illustrates spatial patterns in the relationship between climate variability and crop yield variability , highlighting where variations in temperature , precipitation or their interaction explain yield variability .
We discuss key drivers for the observed variations to target further research and policy interventions geared towards buffering future crop production from climate variability .

[17] Moderate changes in nutrient input alter tropical microbial and protist communities and belowground linkages

We investigated the response of soil microbial communities in tropical ecosystems to increased nutrient deposition , such as predicted by anthropogenic change scenarios .
Moderate amounts of nitrogen and phosphorus and their combination were added along an altitudinal transect .
We expected microorganisms and microbial grazers ( testate amoebae ) to significantly respond to nutrient additions with the effect increasing with increasing altitude and with duration of nutrient additions .
Further , we expected nutrients to alter grazer-prey interrelationships .
Indeed , nutrient additions strongly altered microbial biomass ( MB ) and community structure as well as the community structure of testate amoebae .
The response of microorganisms varied with both altitude and duration of nutrient addition .
The results indicate that microorganisms are generally limited by N , but saprotrophic fungi also by P. Also , arbuscular mycorrhizal fungi benefited from N and/or P addition .
Parallel to MB , testate amoebae benefited from the addition of N but were detrimentally affected by P , with the addition of P negating the positive effect of N .
Our data suggests that testate amoeba communities are predominantly structured by abiotic factors and by antagonistic interactions with other microorganisms , in particular mycorrhizal fungi , rather than by the availability of prey .
Overall , the results suggest that the decomposer system of tropical montane rainforests significantly responds to even moderate changes in nutrient inputs with the potential to cause major ramifications of the whole ecosystem including litter decomposition and plant growth .

[18] Dissolved organic carbon trends resulting from changes in atmospheric deposition chemistry

Several hypotheses have been proposed to explain recent , widespread increases in concentrations of dissolved organic carbon ( DOC ) in the surface waters of glaciated landscapes across eastern North America and northern and central Europe .
Some invoke anthropogenic forcing through mechanisms related to climate change , nitrogen deposition or changes in land use , and by implication suggest that current concentrations and fluxes are without precedent .
All of these hypotheses imply that DOC levels will continue to rise , with unpredictable consequences for the global carbon cycle .
Alternatively , it has been proposed that DOC concentrations are returning toward pre-industrial levels as a result of a gradual decline in the sulphate content of atmospheric deposition .
Here we show , through the assessment of time series data from 522 remote lakes and streams in North America and northern Europe , that rising trends in DOC between 1990 and 2004 can be concisely explained by a simple model based solely on changes in deposition chemistry and catchment acid-sensitivity .
We demonstrate that DOC concentrations have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined .
We conclude that acid deposition to these ecosystems has been partially buffered by changes in organic acidity and that the rise in DOC is integral to recovery from acidification .
Over recent decades , deposition-driven increases in organic matter solubility may have increased the export of DOC to the oceans , a potentially important component of regional carbon balances .
The increase in DOC concentrations in these regions appears unrelated to other climatic factors .

[19] Effects of climate change on US grain transport

The United States is a global grain supplier .
Agriculture uses 22 % of all US transported tonnage with grain being the largest component .
Crop mix shifts are an often cited consequence of climate change and such shifts may change the demands grain places on the transport system .
Studies also find that climate change could decrease Great Lakes water levels , shorten the duration of ice cover in the winter and alter grain supplies in grain-exporting countries .
This study investigates the effects of such phenomena on US grain transportation movements both in volumes and modes .
Specifically we examine the effects of possible shifts in : crop production patterns ; Great Lakes water levels ; winter navigation possibilities ; and foreign grain production .
We find that crop mix shifts reduce the importance of Lower Mississippi River ports , but increase the role of Pacific Northwest ports , Great Lakes ports and Atlantic ports .
We also find a shift from barge to rail and truck transport .
Conversely , a longer navigation season or a reduction in Great Lake water levels increases grain shipments to the ports in the Lower Mississippi River .
Higher use of Great Lakes ports occurs under a reduction of grain production in European exporting countries that compete with Great Lakes ports .

[20] Pace of shifts in climate regions increases with global temperature

Human-induced climate change causes significant changes in local climates , which in turn lead to changes in regional climate zones .
Large shifts in the world distribution of Koppen-Geiger climate classifications by the end of this century have been projected .
However , only a few studies have analysed the pace of these shifts in climate zones , and none has analysed whether the pace itself changes with increasing global mean temperature .
In this study , pace refers to the rate at which climate zones change as a function of amount of global warming .
Here we show that present climate projections suggest that the pace of shifting climate zones increases approximately linearly with increasing global temperature .
Using the RCP8 .5 emissions pathway , the pace nearly doubles by the end of this century and about 20 % of all land area undergoes a change in its original climate .
This implies that species will have increasingly less time to adapt to Koppen zone changes in the future , which is expected to increase the risk of extinction .

[21] Reduced methane growth rate explained by decreased Northern Hemisphere microbial sources

Atmospheric methane ( CH4 ) increased through much of the twentieth century , but this trend gradually weakened until a stable state was temporarily reached around the turn of the millennium , after which levels increased once more .
The reasons for the slowdown are incompletely understood , with past work identifying changes in fossil fuel , wetland and agricultural sources and hydroxyl ( OH ) sinks as important causal factors .
Here we show that the late-twentieth-century changes in the CH4 growth rates are best explained by reduced microbial sources in the Northern Hemisphere .
Our results , based on synchronous time series of atmospheric CH4 mixing and 13C/12C ratios and a two-box atmospheric model , indicate that the evolution of the mixing ratio requires no significant change in Southern Hemisphere sources between 1984 and 2005 .
Observed changes in the interhemispheric difference of 13C effectively exclude reduced fossil fuel emissions as the primary cause of the slowdown .
The 13C observations are consistent with long-term reductions in agricultural emissions or another microbial source within the Northern Hemisphere .
Approximately half ( 51 + / - 18 % ) of the decrease in Northern Hemisphere CH4 emissions can be explained by reduced emissions from rice agriculture in Asia over the past three decades associated with increases in fertilizer application and reductions in water use .

[22] Contribution of ice sheet and mountain glacier melt to recent sea level rise

Changes in global mean sea level primarily reflect the sum of three contributions : water mass changes in the oceans , water density changes , and variations in the volume of the ocean basins .
Satellite altimetry data suggest that sea level rose by about 2.39 + / -0.48 mm yr-1 between 2005 and 2011 .
However , previous estimates of sea level rise from density and ocean mass changes were lower than the altimeter data indicate .
Here we show that the gap in the sea level budget disappears when we combine gravity data from the GRACE ( Gravity Recovery and Climate Experiment ) satellite mission and temperature and salinity observations from the Argo programme collected between 2005 and 2011 .
The Argo data indicate a density-driven sea level rise of 0.60 + / -0.27 mm yr-1 throughout this period .
To estimate ocean mass change from the gravity data , we developed a forward modelling technique that reduces the bleeding of terrestrial signals into the ocean data .
Our reassessment suggests an ocean mass contribution of 1.80 + / -0.47 mm yr-1 , for a total sea level rise of 2.40 + / -0.54 mm yr-1 , in agreement with the altimeter-based estimates .
On the basis of the GRACE data , we conclude that most of the change in ocean mass is caused by the melting of polar ice sheets and mountain glaciers .
This contribution of ice melt is larger than previous estimates , but agrees with reports of accelerated ice melt in recent years .

[23] Pre-exposure to drought increases the resistance of tropical forest soil bacterial communities to extended drought

Global climate models project a decrease in the magnitude of precipitation in tropical regions .
Changes in rainfall patterns have important implications for the moisture content and redox status of tropical soils , yet little is known about how these changes may affect microbial community structure .
Specifically , does exposure to prior stress confer increased resistance to subsequent perturbation ?
Here we reduced the quantity of precipitation throughfall to tropical forest soils in the Luquillo Mountains , Puerto Rico .
Treatments included newly established throughfall exclusion plots ( de novo excluded ) , plots undergoing reduction for a second time ( pre-excluded ) and ambient control plots .
Ten months of throughfall exclusion led to a small but statistically significant decline in soil water potential and bacterial populations clearly adapted to increased osmotic stress .
Although the water potential decline was small and microbial biomass did not change , phylogenetic diversity in the de novo-excluded plots decreased by ~ 40 % compared with the control plots , yet pre-excluded plots showed no significant change .
On the other hand , the relative abundances of bacterial taxa in both the de novo-excluded and pre-excluded plots changed significantly with throughfall exclusion compared with control plots .
Changes in bacterial community structure could be explained by changes in soil pore water chemistry and suggested changes in soil redox .
Soluble iron declined in treatment plots and was correlated with decreased soluble phosphorus concentrations , which may have significant implications for microbial productivity in these P-limited systems .

[24] Holocene Southern Ocean surface temperature variability west of the Antarctic Peninsula

The disintegration of ice shelves , reduced sea-ice and glacier extent , and shifting ecological zones observed around Antarctica highlight the impact of recent atmospheric and oceanic warming on the cryosphere .
Observations and models suggest that oceanic and atmospheric temperature variations at Antarctica 's margins affect global cryosphere stability , ocean circulation , sea levels and carbon cycling .
In particular , recent climate changes on the Antarctic Peninsula have been dramatic , yet the Holocene climate variability of this region is largely unknown , limiting our ability to evaluate ongoing changes within the context of historical variability and underlying forcing mechanisms .
Here we show that surface ocean temperatures at the continental margin of the western Antarctic Peninsula cooled by 3-4 degreesC over the past 12,000 years , tracking the Holocene decline of local ( 65degrees S ) spring insolation .
Our results , based on TEX86 sea surface temperature ( SST ) proxy evidence from a marine sediment core , indicate the importance of regional summer duration as a driver of Antarctic seasonal sea-ice fluctuations .
On millennial timescales , abrupt SST fluctuations of 2-4 degreesC coincide with globally recognized climate variability .
Similarities between our SSTs , Southern Hemisphere westerly wind reconstructions and El Nino/Southern Oscillation variability indicate that present climate teleconnections between the tropical Pacific Ocean and the western Antarctic Peninsula strengthened late in the Holocene epoch .
We conclude that during the Holocene , Southern Ocean temperatures at the western Antarctic Peninsula margin were tied to changes in the position of the westerlies , which have a critical role in global carbon cycling .

[25] Glacial greenhouse-gas fluctuations controlled by ocean circulation changes

Earth 's climate and the concentrations of the atmospheric greenhouse gases carbon dioxide ( CO2 ) and nitrous oxide ( N2O ) varied strongly on millennial timescales during past glacial periods .
Large and rapid warming events in Greenland and the North Atlantic were followed by more gradual cooling , and are highly correlated with fluctuations of N2O as recorded in ice cores .
Antarctic temperature variations , on the other hand , were smaller and more gradual , showed warming during the Greenland cold phase and cooling while the North Atlantic was warm , and were highly correlated with fluctuations in CO2 .
Abrupt changes in the Atlantic meridional overturning circulation ( AMOC ) have often been invoked to explain the physical characteristics of these Dansgaard-Oeschger climate oscillations , but the mechanisms for the greenhouse-gas variations and their linkage to the AMOC have remained unclear .
Here we present simulations with a coupled model of glacial climate and biogeochemical cycles , forced only with changes in the AMOC .
The model simultaneously reproduces characteristic features of the Dansgaard-Oeschger temperature , as well as CO2 and N2O fluctuations .
Despite significant changes in the land carbon inventory , CO2 variations on millennial timescales are dominated by slow changes in the deep ocean inventory of biologically sequestered carbon and are correlated with Antarctic temperature and Southern Ocean stratification .
In contrast , N2O co-varies more rapidly with Greenland temperatures owing to fast adjustments of the thermocline oxygen budget .
These results suggest that ocean circulation changes were the primary mechanism that drove glacial CO2 and N2O fluctuations on millennial timescales .

[26] Carbon balance of Arctic tundra under increased snow cover mediated by a plant pathogen

Climate change is affecting plant community composition and ecosystem structure , with consequences for ecosystem processes such as carbon storage .
Climate can affect plants directly by altering growth rates , and indirectly by affecting predators and herbivores , which in turn influence plants .
Diseases are also known to be important for the structure and function of food webs .
However , the role of plant diseases in modulating ecosystem responses to a changing climate is poorly understood .
This is partly because disease outbreaks are relatively rare and spatially variable , such that that their effects can only be captured in long-term experiments .
Here we show that , although plant growth was favoured by the insulating effects of increased snow cover in experimental plots in Sweden , plant biomass decreased over the seven-year study .
The decline in biomass was caused by an outbreak of a host-specific parasitic fungus , Arwidssonia empetri , which killed the majority of the shoots of the dominant plant species , Empetrum hermaphroditum , after six years of increased snow cover .
After the outbreak of the disease , instantaneous measurements of gross photosynthesis and net ecosystem carbon exchange were significantly reduced at midday during the growing season .
Our results show that plant diseases can alter and even reverse the effects of a changing climate on tundra carbon balance by altering plant composition .

[27] Focus on poleward shifts in species ' distribution underestimates the fingerprint of climate change

Species are largely predicted to shift poleward as global temperatures increase , with this fingerprint of climate change being already observed across a range of taxonomic groups and , mostly temperate , geographic locations .
However , the assumption of uni-directional distribution shifts does not account for complex interactions among temperature , precipitation and species-specific tolerances , all of which shape the direction and magnitude of changes in a species ' climatic niche .
We analysed 60 years of past climate change on the Australian continent , assessing the velocity of changes in temperature and precipitation , as well as changes in climatic niche space for 464 Australian birds .
We show large magnitude and rapid rates of change in Australian climate over the past 60 years resulting in high-velocity and multi-directional , including equatorial , shifts in suitable climatic space for birds ( ranging from 0.1 to 7.6 km yr-1 , mean 1.27 km yr-1 ) .
Overall , if measured only in terms of poleward distribution shifts , the fingerprint of climate change is underestimated by an average of 26 % in temperate regions of the continent and by an average of 95 % in tropical regions .
We suggest that the velocity of movement required by Australian species to track their climatic niche may be much faster than previously thought and that the interaction between temperature and precipitation changes will result in multi-directional distribution shifts globally .

[28] Deglacial pulses of deep-ocean silicate into the subtropical North Atlantic Ocean

Growing evidence suggests that the low atmospheric CO2 concentration of the ice ages resulted from enhanced storage of CO2 in the ocean interior , largely as a result of changes in the Southern Ocean .
Early in the most recent deglaciation , a reduction in North Atlantic overturning circulation seems to have driven CO2 release from the Southern Ocean , but the mechanism connecting the North Atlantic and the Southern Ocean remains unclear .
Biogenic opal export in the low-latitude ocean relies on silicate from the underlying thermocline , the concentration of which is affected by the circulation of the ocean interior .
Here we report a record of biogenic opal export from a coastal upwelling system off the coast of northwest Africa that shows pronounced opal maxima during each glacial termination over the past 550,000 years .
These opal peaks are consistent with a strong deglacial reduction in the formation of silicate-poor glacial North Atlantic intermediate water ( GNAIW ) .
The loss of GNAIW allowed mixing with underlying silicate-rich deep water to increase the silicate supply to the surface ocean .
An increase in westerly-wind-driven upwelling in the Southern Ocean in response to the North Atlantic change has been proposed to drive the deglacial rise in atmospheric CO2 ( refs 3 , 4 ) .
However , such a circulation change would have accelerated the formation of Antarctic intermediate water and sub-Antarctic mode water , which today have as little silicate as North Atlantic Deep Water and would have thus maintained low silicate concentrations in the Atlantic thermocline .
The deglacial opal maxima reported here suggest an alternative mechanism for the deglacial CO2 release .
Just as the reduction in GNAIW led to upward silicate transport , it should also have allowed the downward mixing of warm , low-density surface water to reach into the deep ocean .
The resulting decrease in the density of the deep Atlantic relative to the Southern Ocean surface promoted Antarctic overturning , which released CO2 to the atmosphere .

[29] Indirect radiative forcing of climate change through ozone effects on the land-carbon sink

The evolution of the Earth 's climate over the twenty-first century depends on the rate at which anthropogenic carbon dioxide emissions are removed from the atmosphere by the ocean and land carbon cycles .
Coupled climate-carbon cycle models suggest that global warming will act to limit the land-carbon sink , but these first generation models neglected the impacts of changing atmospheric chemistry .
Emissions associated with fossil fuel and biomass burning have acted to approximately double the global mean tropospheric ozone concentration , and further increases are expected over the twenty-first century .
Tropospheric ozone is known to damage plants , reducing plant primary productivity and crop yields , yet increasing atmospheric carbon dioxide concentrations are thought to stimulate plant primary productivity .
Increased carbon dioxide and ozone levels can both lead to stomatal closure , which reduces the uptake of either gas , and in turn limits the damaging effect of ozone and the carbon dioxide fertilization of photosynthesis .
Here we estimate the impact of projected changes in ozone levels on the land-carbon sink , using a global land carbon cycle model modified to include the effect of ozone deposition on photosynthesis and to account for interactions between ozone and carbon dioxide through stomatal closure .
For a range of sensitivity parameters based on manipulative field experiments , we find a significant suppression of the global land-carbon sink as increases in ozone concentrations affect plant productivity .
In consequence , more carbon dioxide accumulates in the atmosphere .
We suggest that the resulting indirect radiative forcing by ozone effects on plants could contribute more to global warming than the direct radiative forcing due to tropospheric ozone increases .

[30] Fire as the dominant driver of central Canadian boreal forest carbon balance

Changes in climate , atmospheric carbon dioxide concentration and fire regimes have been occurring for decades in the global boreal forest , with future climate change likely to increase fire frequency -- the primary disturbance agent in most boreal forests .
Previous attempts to assess quantitatively the effect of changing environmental conditions on the net boreal forest carbon balance have not taken into account the competition between different vegetation types on a large scale .
Here we use a process model with three competing vascular and non-vascular vegetation types to examine the effects of climate , carbon dioxide concentrations and fire disturbance on net biome production , net primary production and vegetation dominance in 100 Mha of Canadian boreal forest .
We find that the carbon balance of this region was driven by changes in fire disturbance from 1948 to 2005 .
Climate changes affected the variability , but not the mean , of the landscape carbon balance , with precipitation exerting a more significant effect than temperature .
We show that more frequent and larger fires in the late twentieth century resulted in deciduous trees and mosses increasing production at the expense of coniferous trees .
Our model did not however exhibit the increases in total forest net primary production that have been inferred from satellite data .
We find that poor soil drainage decreased the variability of the landscape carbon balance , which suggests that increased climate and hydrological changes have the potential to affect disproportionately the carbon dynamics of these areas .
Overall , we conclude that direct ecophysiological changes resulting from global climate change have not yet been felt in this large boreal region .
Variations in the landscape carbon balance and vegetation dominance have so far been driven largely by increases in fire frequency .

[31] Physiological plasticity increases resilience of ectothermic animals to climate change

Understanding how climate change affects natural populations remains one of the greatest challenges for ecology and management of natural resources .
Animals can remodel their physiology to compensate for the effects of temperature variation , and this physiological plasticity , or acclimation , can confer resilience to climate change .
The current lack of a comprehensive analysis of the capacity for physiological plasticity across taxonomic groups and geographic regions , however , constrains predictions of the impacts of climate change .
Here , we assembled the largest database to date to establish the current state of knowledge of physiological plasticity in ectothermic animals .
We show that acclimation decreases the sensitivity to temperature and climate change of freshwater and marine animals , but less so in terrestrial animals .
Animals from more stable environments have greater capacity for acclimation , and there is a significant trend showing that the capacity for thermal acclimation increases with decreasing latitude .
Despite the capacity for acclimation , climate change over the past 20 years has already resulted in increased physiological rates of up to 20 % , and we predict further future increases under climate change .
The generality of these predictions is limited , however , because much of the world is drastically undersampled in the literature , and these undersampled regions are the areas of greatest need for future research efforts .

[32] Recent decline in the global land evapotranspiration trend due to limited moisture supply

More than half of the solar energy absorbed by land surfaces is currently used to evaporate water .
Climate change is expected to intensify the hydrological cycle and to alter evapotranspiration , with implications for ecosystem services and feedback to regional and global climate .
Evapotranspiration changes may already be under way , but direct observational constraints are lacking at the global scale .
Until such evidence is available , changes in the water cycle on land -- a key diagnostic criterion of the effects of climate change and variability -- remain uncertain .
Here we provide a data-driven estimate of global land evapotranspiration from 1982 to 2008 , compiled using a global monitoring network , meteorological and remote-sensing observations , and a machine-learning algorithm .
In addition , we have assessed evapotranspiration variations over the same time period using an ensemble of process-based land-surface models .
Our results suggest that global annual evapotranspiration increased on average by 7.1 + / - 1.0 millimetres per year per decade from 1982 to 1997 .
After that , coincident with the last major El Nino event in 1998 , the global evapotranspiration increase seems to have ceased until 2008 .
This change was driven primarily by moisture limitation in the Southern Hemisphere , particularly Africa and Australia .
In these regions , microwave satellite observations indicate that soil moisture decreased from 1998 to 2008 .
Hence , increasing soil-moisture limitations on evapotranspiration largely explain the recent decline of the global land-evapotranspiration trend .
Whether the changing behaviour of evapotranspiration is representative of natural climate variability or reflects a more permanent reorganization of the land water cycle is a key question for earth system science .

[33] Soil-carbon response to warming dependent on microbial physiology

Most ecosystem models predict that climate warming will stimulate microbial decomposition of soil carbon , producing a positive feedback to rising global temperatures .
Although field experiments document an initial increase in the loss of CO2 from soils in response to warming , in line with these predictions , the carbon dioxide loss from soils tends to decline to control levels within a few years .
This attenuation response could result from changes in microbial physiological properties with increasing temperature , such as a decline in the fraction of assimilated carbon that is allocated to growth , termed carbon-use efficiency .
Here we explore these mechanisms using a microbial-enzyme model to simulate the responses of soil carbon to warming by 5 degreesC .
We find that declines in microbial biomass and degradative enzymes can explain the observed attenuation of soil-carbon emissions in response to warming .
Specifically , reduced carbon-use efficiency limits the biomass of microbial decomposers and mitigates the loss of soil carbon .
However , microbial adaptation or a change in microbial communities could lead to an upward adjustment of the efficiency of carbon use , counteracting the decline in microbial biomass and accelerating soil-carbon loss .
We conclude that the soil-carbon response to climate warming depends on the efficiency of soil microbes in using carbon .

[34] Biogeochemical and ecological feedbacks in grassland responses to warming

Plant growth often responds rapidly to experimentally simulated climate change .
Feedbacks can modulate the initial responses , but these feedbacks are difficult to detect when they operate on long timescales .
We transplanted intact plant-soil mesocosms down an elevation gradient to expose them to a warmer climate and used collectors and interceptors to simulate changes in precipitation .
Here , we show that warming initially increased aboveground net primary productivity in four grassland ecosystems , but the response diminished progressively over nine years .
Warming altered the plant community , causing encroachment by species typical of warmer environments and loss of species from the native environment -- trends associated with the declining response of plant productivity .
Warming stimulated soil nitrogen turnover , which dampened but did not reverse the temporal decline in the productivity response .
Warming also enhanced N losses , which may have weakened the expected biogeochemical feedback where warming stimulates N mineralization and plant growth .
Our results , describing the responses of four ecosystems to nearly a decade of simulated climate change , indicate that short-term experiments are insufficient to capture the temporal variability and trend of ecosystem responses to environmental change and their modulation through biogeochemical and ecological feedbacks .

[35] Management of trade-offs in geoengineering through optimal choice of non-uniform radiative forcing

Solar radiation management could be used to offset some or all anthropogenic radiative forcing , with the goal of reducing some of the associated climatic change .
However , the degree of compensation will vary , with residual climate changes larger in some regions than others .
Similarly , the insolation reduction that best compensates climate changes in one region may not be the same as for another , leading to concerns about equity .
Here we show that optimizing the latitudinal and seasonal distribution of solar reduction can improve the fidelity with which solar radiation management offsets anthropogenic climate change .
Using the HadCM3L general circulation model , we explore several trade-offs .
First , residual temperature and precipitation changes in the worst-off region can be reduced by 30 % relative to uniform solar reduction , with only a modest impact on global root-mean-square changes ; this has implications for moderating regional inequalities .
Second , the same root-mean-square residual climate changes can be obtained with up to 30 % less insolation reduction , implying that it may be possible to reduce solar radiation management side-effects and risks ( for example , ozone depletion if stratospheric sulphate aerosols are used ) .
Finally , allowing spatial and temporal variability increases the range of trade-offs to be considered , raising the question of how to weight different objectives .

[36] Global warming and climate forcing by recent albedo changes on Mars

For hundreds of years , scientists have tracked the changing appearance of Mars , first by hand drawings and later by photographs .
Because of this historical record , many classical albedo patterns have long been known to shift in appearance over time .
Decadal variations of the martian surface albedo are generally attributed to removal and deposition of small amounts of relatively bright dust on the surface .
Large swaths of the surface ( up to 56 million km2 ) have been observed to darken or brighten by 10 per cent or more .
It is unknown , however , how these albedo changes affect wind circulation , dust transport and the feedback between these processes and the martian climate .
Here we present predictions from a Mars general circulation model , indicating that the observed interannual albedo alterations strongly influence the martian environment .
Results indicate enhanced wind stress in recently darkened areas and decreased wind stress in brightened areas , producing a positive feedback system in which the albedo changes strengthen the winds that generate the changes .
The simulations also predict a net annual global warming of surface air temperatures by ~ 0.65 K , enhancing dust lifting by increasing the likelihood of dust devil generation .
The increase in global dust lifting by both wind stress and dust devils may affect the mechanisms that trigger large dust storm initiation , a poorly understood phenomenon , unique to Mars .
In addition , predicted increases in summertime air temperatures at high southern latitudes would contribute to the rapid and steady scarp retreat that has been observed in the south polar residual ice for the past four Mars years .
Our results suggest that documented albedo changes affect recent climate change and large-scale weather patterns on Mars , and thus albedo variations are a necessary component of future atmospheric and climate studies .

[37] Rapid responses of British butterflies to opposing forces of climate and habitat change

Habitat degradation and climate change are thought to be altering the distributions and abundances of animals and plants throughout the world , but their combined impacts have not been assessed for any species assemblage .
Here we evaluated changes in the distribution sizes and abundances of 46 species of butterflies that approach their northern climatic range margins in Britain -- where changes in climate and habitat are opposing forces .
These insects might be expected to have responded positively to climate warming over the past 30 years , yet three-quarters of them declined : negative responses to habitat loss have outweighed positive responses to climate warming .
Half of the species that were mobile and habitat generalists increased their distribution sites over this period ( consistent with a climate explanation ) , whereas the other generalists and 89 % of the habitat specialists declined in distribution size ( consistent with habitat limitation ) .
Changes in population abundances closely matched changes in distributions .
The dual forces of habitat modification and climate change are likely to cause specialists to decline , leaving biological communities with reduced numbers of species and dominated by mobile and widespread habitat generalists .

[38] Evolution of increased phenotypic diversity enhances population performance by reducing sexual harassment in damselflies

The effect of evolutionary changes in traits and phenotypic/genetic diversity on ecological dynamics has received much theoretical attention ; however , the mechanisms and ecological consequences are usually unknown .
Female-limited colour polymorphism in damselflies is a counter-adaptation to male mating harassment , and thus , is expected to alter population dynamics through relaxing sexual conflict .
Here we show the side effect of the evolution of female morph diversity on population performance ( for example , population productivity and sustainability ) in damselflies .
Our theoretical model incorporating key features of the sexual interaction predicts that the evolution of increased phenotypic diversity will reduce overall fitness costs to females from sexual conflict , which in turn will increase productivity , density and stability of a population .
Field data and mesocosm experiments support these model predictions .
Our study suggests that increased phenotypic diversity can enhance population performance that can potentially reduce extinction rates and thereby influence macroevolutionary processes .

[39] Intensification of winter transatlantic aviation turbulence in response to climate change

Atmospheric turbulence causes most weather-related aircraft incidents .
Commercial aircraft encounter moderate-or-greater turbulence tens of thousands of times each year worldwide , injuring probably hundreds of passengers ( occasionally fatally ) , costing airlines tens of millions of dollars and causing structural damage to planes .
Clear-air turbulence is especially difficult to avoid , because it can not be seen by pilots or detected by satellites or on-board radar .
Clear-air turbulence is linked to atmospheric jet streams , which are projected to be strengthened by anthropogenic climate change .
However , the response of clear-air turbulence to projected climate change has not previously been studied .
Here we show using climate model simulations that clear-air turbulence changes significantly within the transatlantic flight corridor when the concentration of carbon dioxide in the atmosphere is doubled .
At cruise altitudes within 50-75degrees N and 10-60degrees W in winter , most clear-air turbulence measures show a 10-40 % increase in the median strength of turbulence and a 40-170 % increase in the frequency of occurrence of moderate-or-greater turbulence .
Our results suggest that climate change will lead to bumpier transatlantic flights by the middle of this century .
Journey times may lengthen and fuel consumption and emissions may increase .
Aviation is partly responsible for changing the climate , but our findings show for the first time how climate change could affect aviation .

[40] A two-fold increase of carbon cycle sensitivity to tropical temperature variations

Earth system models project that the tropical land carbon sink will decrease in size in response to an increase in warming and drought during this century , probably causing a positive climate feedback .
But available data are too limited at present to test the predicted changes in the tropical carbon balance in response to climate change .
Long-term atmospheric carbon dioxide data provide a global record that integrates the interannual variability of the global carbon balance .
Multiple lines of evidence demonstrate that most of this variability originates in the terrestrial biosphere .
In particular , the year-to-year variations in the atmospheric carbon dioxide growth rate ( CGR ) are thought to be the result of fluctuations in the carbon fluxes of tropical land areas .
Recently , the response of CGR to tropical climate interannual variability was used to put a constraint on the sensitivity of tropical land carbon to climate change .
Here we use the long-term CGR record from Mauna Loa and the South Pole to show that the sensitivity of CGR to tropical temperature interannual variability has increased by a factor of 1.9 + / - 0.3 in the past five decades .
We find that this sensitivity was greater when tropical land regions experienced drier conditions .
This suggests that the sensitivity of CGR to interannual temperature variations is regulated by moisture conditions , even though the direct correlation between CGR and tropical precipitation is weak .
We also find that present terrestrial carbon cycle models do not capture the observed enhancement in CGR sensitivity in the past five decades .
More realistic model predictions of future carbon cycle and climate feedbacks require a better understanding of the processes driving the response of tropical ecosystems to drought and warming .

[41] Climate warming during Antarctic ice sheet expansion at the Middle Miocene transition

During the Middle Miocene climate transition about 14 million years ago , the Antarctic ice sheet expanded to near-modern volume .
Surprisingly , this ice sheet growth was accompanied by a warming in the surface waters of the Southern Ocean , whereas a slight deep-water temperature increase was delayed by more than 200 thousand years .
Here we use a coupled atmosphere-ocean model to assess the relative effects of changes in atmospheric CO2 concentration and ice sheet growth on regional and global temperatures .
In the simulations , changes in the wind field associated with the growth of the ice sheet induce changes in ocean circulation , deep-water formation and sea-ice cover that result in sea surface warming and deep-water cooling in large swaths of the Atlantic and Indian ocean sectors of the Southern Ocean .
We interpret these changes as the dominant ocean surface response to a 100-thousand-year phase of massive ice growth in Antarctica .
A rise in global annual mean temperatures is also seen in response to increased Antarctic ice surface elevation .
In contrast , the longer-term surface and deep-water temperature trends are dominated by changes in atmospheric CO2 concentration .
We therefore conclude that the climatic and oceanographic impacts of the Miocene expansion of the Antarctic ice sheet are governed by a complex interplay between wind field , ocean circulation and the sea-ice system .

[42] Robust twenty-first-century projections of El Nino and related precipitation variability

The El Nino-Southern Oscillation ( ENSO ) drives substantial variability in rainfall , severe weather , agricultural production , ecosystems and disease in many parts of the world .
Given that further human-forced changes in the Earth 's climate system seem inevitable , the possibility exists that the character of ENSO and its impacts might change over the coming century .
Although this issue has been investigated many times during the past 20 years , there is very little consensus on future changes in ENSO , apart from an expectation that ENSO will continue to be a dominant source of year-to-year variability .
Here we show that there are in fact robust projected changes in the spatial patterns of year-to-year ENSO-driven variability in both surface temperature and precipitation .
These changes are evident in the two most recent generations of climate models , using four different scenarios for CO2 and other radiatively active gases .
By the mid - to late twenty-first century , the projections include an intensification of both El-Nino-driven drying in the western Pacific Ocean and rainfall increases in the central and eastern equatorial Pacific .
Experiments with an Atmospheric General Circulation Model reveal that robust projected changes in precipitation anomalies during El Nino years are primarily determined by a nonlinear response to surface global warming .
Uncertain projected changes in the amplitude of ENSO-driven surface temperature variability have only a secondary role .
Projected changes in key characteristics of ENSO are consequently much clearer than previously realized .

[43] A global synthesis reveals biodiversity loss as a major driver of ecosystem change

Evidence is mounting that extinctions are altering key processes important to the productivity and sustainability of Earth 's ecosystems .
Further species loss will accelerate change in ecosystem processes , but it is unclear how these effects compare to the direct effects of other forms of environmental change that are both driving diversity loss and altering ecosystem function .
Here we use a suite of meta-analyses of published data to show that the effects of species loss on productivity and decomposition -- two processes important in all ecosystems -- are of comparable magnitude to the effects of many other global environmental changes .
In experiments , intermediate levels of species loss ( 21-40 % ) reduced plant production by 5-10 % , comparable to previously documented effects of ultraviolet radiation and climate warming .
Higher levels of extinction ( 41-60 % ) had effects rivalling those of ozone , acidification , elevated CO2 and nutrient pollution .
At intermediate levels , species loss generally had equal or greater effects on decomposition than did elevated CO2 and nitrogen addition .
The identity of species lost also had a large effect on changes in productivity and decomposition , generating a wide range of plausible outcomes for extinction .
Despite the need for more studies on interactive effects of diversity loss and environmental changes , our analyses clearly show that the ecosystem consequences of local species loss are as quantitatively significant as the direct effects of several global change stressors that have mobilized major international concern and remediation efforts .

[44] Changing Arctic Ocean freshwater pathways

Freshening in the Canada basin of the Arctic Ocean began in the 1990s and continued to at least the end of 2008 .
By then , the Arctic Ocean might have gained four times as much fresh water as comprised the Great Salinity Anomalyof the 1970s , raising the spectre of slowing global ocean circulation .
Freshening has been attributed to increased sea ice melting and contributions from runoff , but a leading explanation has been a strengthening of the Beaufort High -- a characteristic peak in sea level atmospheric pressure -- which tends to accelerate an anticyclonic ( clockwise ) wind pattern causing convergence of fresh surface water .
Limited observations have made this explanation difficult to verify , and observations of increasing freshwater content under a weakened Beaufort High suggest that other factors must be affecting freshwater content .
Here we use observations to show that during a time of record reductions in ice extent from 2005 to 2008 , the dominant freshwater content changes were an increase in the Canada basin balanced by a decrease in the Eurasian basin .
Observations are drawn from satellite data ( sea surface height and ocean-bottom pressure ) and in situ data .
The freshwater changes were due to a cyclonic ( anticlockwise ) shift in the ocean pathway of Eurasian runoff forced by strengthening of the west-to-east Northern Hemisphere atmospheric circulation characterized by an increased Arctic Oscillation index .
Our results confirm that runoff is an important influence on the Arctic Ocean and establish that the spatial and temporal manifestations of the runoff pathways are modulated by the Arctic Oscillation , rather than the strength of the wind-driven Beaufort Gyre circulation .

[45] Tolerance limit for fish growth exceeded by warming waters

Climate change can affect organisms both directly , by affecting their physiology , growth , and behaviour , and indirectly , for example through effects on ecosystem structure and function .
For ectotherms , or ` cold-blooded ' animals , warming will directly affect their metabolism , with growth rates in temperate species predicted to increase initially as temperatures rise , but then decline as individuals struggle to maintain cardiac function and respiration in the face of increased metabolic demands .
We provide evidence consistent with this prediction for a marine fish ( Cheilodactylus spectabilis ) in the Tasman Sea ; one of the most rapidly warming regions of the Southern Hemisphere ocean .
We estimated changes in the species ' growth rate over a 90-year period using otoliths -- bony structures that fish use for orientation and detection of movement -- and compared these changes to temperature trends across the species ' distribution .
Increasing temperatures coincide with increased growth for populations in the middle of the species range , but with reduced growth for those at the warm northern edge of the species ' distribution , indicating that temperatures may have already reached levels associated with increased metabolic costs .
If warming continues , the direct metabolic effects of increasing temperatures on this species may lead to declining productivity and range contraction .

[46] Global-scale variations of the ratios of carbon to phosphorus in exported marine organic matter

The ratio of carbon ( C ) to phosphorus ( P ) in marine phytoplankton is thought to be constant throughout the worlds ' oceans .
Known as the Redfield ratio , this relationship describes the links between carbon and phosphorus cycling and marine ecosystems .
However , variations in the stoichiometry of phytoplankton have recently been identified , in particular strong latitudinal variability .
Here we assess the impact of this variability in the C :P ratio of biomass on the C :P ratio of organic matter that is exported to the deep ocean using a biogeochemical inverse-model based on a data-constrained ocean circulation model and a global database of dissolved inorganic carbon and phosphate measurements .
We identify global patterns of variability in the C :P ratios of exported organic matter , with higher values in the nutrient-depleted subtropical gyres , where organic matter export is relatively low , and lower ratios in nutrient-rich upwelling zones and high-latitude regions , where organic matter export is high .
This suggests that total carbon export is relatively constant throughout the oceans , in agreement with recent estimates of carbon fluxes .
We conclude that the latitudinal patterns of C :P in exported organic matter are consistent with the large-scale stoichiometric variations in phytoplankton C :P .
We suggest that a future expansion of nutrient-depleted waters could result in a shift to more efficient C export that compensates for the expected decline in productivity .

[47] Response of salt-marsh carbon accumulation to climate change

About half of annual marine carbon burial takes place in shallow water ecosystems where geomorphic and ecological stability is driven by interactions between the flow of water , vegetation growth and sediment transport .
Although the sensitivity of terrestrial and deep marine carbon pools to climate change has been studied for decades , there is little understanding of how coastal carbon accumulation rates will change and potentially feed back on climate .
Here we develop a numerical model of salt marsh evolution , informed by recent measurements of productivity and decomposition , and demonstrate that competition between mineral sediment deposition and organic-matter accumulation determines the net impact of climate change on carbon accumulation in intertidal wetlands .
We find that the direct impact of warming on soil carbon accumulation rates is more subtle than the impact of warming-driven sea level rise , although the impact of warming increases with increasing rates of sea level rise .
Our simulations suggest that the net impact of climate change will be to increase carbon burial rates in the first half of the twenty-first century , but that carbon-climate feedbacks are likely to diminish over time .

[48] Loss of frugivore seed dispersal services under climate change

The capacity of species to track shifting climates into the future will strongly influence outcomes for biodiversity under a rapidly changing climate .
However , we know remarkably little about the dispersal abilities of most species and how these may be influenced by climate change .
Here we show that climate change is projected to substantially reduce the seed dispersal services provided by frugivorous vertebrates in rainforests across the Australian Wet Tropics .
Our model projections show reductions in both median and long-distance seed dispersal , which may markedly reduce the capacity of many rainforest plant species to track shifts in suitable habitat under climate change .
However , our analyses suggest that active management to maintain the abundances of a small set of important frugivores under climate change could markedly reduce the projected loss of seed dispersal services and facilitate shifting distributions of rainforest plant species .

[49] Detection of human influence on twentieth-century precipitation trends

Human influence on climate has been detected in surface air temperature , sea level pressure , free atmospheric temperature , tropopause height and ocean heat content .
Human-induced changes have not , however , previously been detected in precipitation at the global scale , partly because changes in precipitation in different regions cancel each other out and thereby reduce the strength of the global average signal .
Models suggest that anthropogenic forcing should have caused a small increase in global mean precipitation and a latitudinal redistribution of precipitation , increasing precipitation at high latitudes , decreasing precipitation at sub-tropical latitudes , and possibly changing the distribution of precipitation within the tropics by shifting the position of the Intertropical Convergence Zone .
Here we compare observed changes in land precipitation during the twentieth century averaged over latitudinal bands with changes simulated by fourteen climate models .
We show that anthropogenic forcing has had a detectable influence on observed changes in average precipitation within latitudinal bands , and that these changes can not be explained by internal climate variability or natural forcing .
We estimate that anthropogenic forcing contributed significantly to observed increases in precipitation in the Northern Hemisphere mid-latitudes , drying in the Northern Hemisphere subtropics and tropics , and moistening in the Southern Hemisphere subtropics and deep tropics .
The observed changes , which are larger than estimated from model simulations , may have already had significant effects on ecosystems , agriculture and human health in regions that are sensitive to changes in precipitation , such as the Sahel .

[50] The central role of diminishing sea ice in recent Arctic temperature amplification

The rise in Arctic near-surface air temperatures has been almost twice as large as the global average in recent decades -- a feature known as ` Arctic amplification ' .
Increased concentrations of atmospheric greenhouse gases have driven Arctic and global average warming ; however , the underlying causes of Arctic amplification remain uncertain .
The roles of reductions in snow and sea ice cover and changes in atmospheric and oceanic circulation , cloud cover and water vapour are still matters of debate .
A better understanding of the processes responsible for the recent amplified warming is essential for assessing the likelihood , and impacts , of future rapid Arctic warming and sea ice loss .
Here we show that the Arctic warming is strongest at the surface during most of the year and is primarily consistent with reductions in sea ice cover .
Changes in cloud cover , in contrast , have not contributed strongly to recent warming .
Increases in atmospheric water vapour content , partly in response to reduced sea ice cover , may have enhanced warming in the lower part of the atmosphere during summer and early autumn .
We conclude that diminishing sea ice has had a leading role in recent Arctic temperature amplification .
The findings reinforce suggestions that strong positive ice-temperature feedbacks have emerged in the Arctic , increasing the chances of further rapid warming and sea ice loss , and will probably affect polar ecosystems , ice-sheet mass balance and human activities in the Arctic .

[51] Sensitivity of tropical carbon to climate change constrained by carbon dioxide variability

The release of carbon from tropical forests may exacerbate future climate change , but the magnitude of the effect in climate models remains uncertain .
Coupled climate-carbon-cycle models generally agree that carbon storage on land will increase as a result of the simultaneous enhancement of plant photosynthesis and water use efficiency under higher atmospheric CO2 concentrations , but will decrease owing to higher soil and plant respiration rates associated with warming temperatures .
At present , the balance between these effects varies markedly among coupled climate-carbon-cycle models , leading to a range of 330 gigatonnes in the projected change in the amount of carbon stored on tropical land by 2100 .
Explanations for this large uncertainty include differences in the predicted change in rainfall in Amazonia and variations in the responses of alternative vegetation models to warming .
Here we identify an emergent linear relationship , across an ensemble of models , between the sensitivity of tropical land carbon storage to warming and the sensitivity of the annual growth rate of atmospheric CO2 to tropical temperature anomalies .
Combined with contemporary observations of atmospheric CO2 concentration and tropical temperature , this relationship provides a tight constraint on the sensitivity of tropical land carbon to climate change .
We estimate that over tropical land from latitude 30degrees north to 30degrees south , warming alone will release 53 + / - 17 gigatonnes of carbon per kelvin .
Compared with the unconstrained ensemble of climate-carbon-cycle projections , this indicates a much lower risk of Amazon forest dieback under CO2-induced climate change if CO2 fertilization effects are as large as suggested by current models .
Our study , however , also implies greater certainty that carbon will be lost from tropical land if warming arises from reductions in aerosols or increases in other greenhouse gases .

[52] Increased tree carbon storage in response to nitrogen deposition in the US

Human activities have greatly accelerated emissions of both carbon dioxide and biologically reactive nitrogen to the atmosphere .
As nitrogen availability often limits forest productivity , it has long been expected that anthropogenic nitrogen deposition could stimulate carbon sequestration in forests .
However , spatially extensive evidence for deposition-induced stimulation of forest growth has been lacking , and quantitative estimates from models and plot-level studies are controversial .
Here , we use forest inventory data to examine the impact of nitrogen deposition on tree growth , survival and carbon storage across the northeastern and north-central USA during the 1980s and 1990s .
We show a range of growth and mortality responses to nitrogen deposition among the region 's 24 most common tree species .
Nitrogen deposition ( which ranged from 3 to 11 kg ha-1 yr-1 ) enhanced the growth of 11 species and decreased the growth of 3 species .
Nitrogen deposition enhanced growth of all tree species with arbuscular mycorrhizal fungi associations .
In the absence of disturbances that reduced carbon stocks by more than 50 % , above-ground biomass increment increased by 61 kg of carbon per kg of nitrogen deposited , amounting to a 40 % enhancement over pre-industrial conditions .
Extrapolating to the globe , we estimate that nitrogen deposition could increase tree carbon storage by 0.31 Pg carbon yr-1 .

[53] Increasing subtropical North Pacific Ocean nitrogen fixation since the Little Ice Age

The North Pacific subtropical gyre ( NPSG ) plays a major part in the export of carbon and other nutrients to the deep ocean .
Primary production in the NPSG has increased in recent decades despite a reduction in nutrient supply to surface waters .
It is thought that this apparent paradox can be explained by a shift in plankton community structure from mostly eukaryotes to mostly nitrogen-fixing prokaryotes .
It remains uncertain , however , whether the plankton community domain shift can be linked to cyclical climate variability or a long-term global warming trend .
Here we analyse records of bulk and amino-acid-specific 15N/14N isotopic ratios ( delta15N ) preserved in the skeletons of long-lived deep-sea proteinaceous corals collected from the Hawaiian archipelago ; these isotopic records serve as a proxy for the source of nitrogen-supported export production through time .
We find that the recent increase in nitrogen fixation is the continuation of a much larger , centennial-scale trend .
After a millennium of relatively minor fluctuation , delta15N decreases between 1850 and the present .
The total shift in delta15N of -2 per mil over this period is comparable to the total change in global mean sedimentary delta15N across the Pleistocene-Holocene transition , but it is happening an order of magnitude faster .
We use a steady-state model and find that the isotopic mass balance between nitrate and nitrogen fixation implies a 17 to 27 per cent increase in nitrogen fixation over this time period .
A comparison with independent records suggests that the increase in nitrogen fixation might be linked to Northern Hemisphere climate change since the end of the Little Ice Age .

[54] Effect of climate change relative to ozone depletion on UV exposure in subarctic lakes

The effect of stratospheric ozone depletion on increases in ambient levels of solar ultraviolet ( UV ) radiation in high-latitude regions has raised concerns about the response of northern ecosystems to environmental change .
The concentration of coloured dissolved organic material , which is derived from terrestrial vegetation and acts as a screen for ultraviolet radiation , is low in high-latitude lakes .
The underwater light environment in these lakes is therefore likely to be sensitive to small variations in the supply of this material , in addition to the effects of ozone depletion .
Here we use fossil diatom assemblages in combination with bio-optical models to estimate the magnitude of past variations in the underwater light regime of a lake at the boreal tree line .
We find large shifts in underwater UV-B , UV-A and photosynthetically available radiation associated with changes in the input of coloured dissolved organic material into subarctic lakes during the Holocene .
The inferred changes in biological exposure to UV radiation were at least two orders of magnitude greater than those associated with moderate ( 30 % ) ozone depletion .
Our findings indicate that freshwater ecosystems at present located across vegetation gradients will experience significant shifts in underwater spectral irradiance through the effects of climate change on catchment vegetation and the export of coloured dissolved organic material .

[55] Enhanced poleward moisture transport and amplified northern high-latitude wetting trend

Observations and climate change projections forced by greenhouse gas emissions have indicated a wetting trend in northern high latitudes , evidenced by increasing Eurasian Arctic river discharges .
The increase in river discharge has accelerated in the latest decade and an unprecedented , record high discharge occurred in 2007 along with an extreme loss of Arctic summer sea-ice cover .
Studies have ascribed this increasing discharge to various factors attributable to local global warming effects , including intensifying precipitation minus evaporation , thawing permafrost , increasing greenness and reduced plant transpiration .
However , no agreement has been reached and causal physical processes remain unclear .
Here we show that enhancement of poleward atmospheric moisture transport ( AMT ) decisively contributes to increased Eurasian Arctic river discharges .
Net AMT into the Eurasian Arctic river basins captures 98 % of the gauged climatological river discharges .
The trend of 2.6 % net AMT increase per decade accounts well for the 1.8 % per decade increase in gauged discharges and also suggests an increase in underlying soil moisture .
A radical shift of the atmospheric circulation pattern induced an unusually large AMT and warm surface in 2006-2007 over Eurasia , resulting in the record high discharge .

[56] Resistance and resilience of the forest soil microbiome to logging-associated compaction

Soil compaction is a major disturbance associated with logging , but we lack a fundamental understanding of how this affects the soil microbiome .
We assessed the structural resistance and resilience of the microbiome using a high-throughput pyrosequencing approach in differently compacted soils at two forest sites and correlated these findings with changes in soil physical properties and functions .
Alterations in soil porosity after compaction strongly limited the air and water conductivity .
Compaction significantly reduced abundance , increased diversity , and persistently altered the structure of the microbiota .
Fungi were less resistant and resilient than bacteria ; clayey soils were less resistant and resilient than sandy soils .
The strongest effects were observed in soils with unfavorable moisture conditions , where air and water conductivities dropped well below 10 % of their initial value .
Maximum impact was observed around 6-12 months after compaction , and microbial communities showed resilience in lightly but not in severely compacted soils 4 years post disturbance .
Bacteria capable of anaerobic respiration , including sulfate , sulfur , and metal reducers of the Proteobacteria and Firmicutes , were significantly associated with compacted soils .
Compaction detrimentally affected ectomycorrhizal species , whereas saprobic and parasitic fungi proportionally increased in compacted soils .
Structural shifts in the microbiota were accompanied by significant changes in soil processes , resulting in reduced carbon dioxide , and increased methane and nitrous oxide emissions from compacted soils .
This study demonstrates that physical soil disturbance during logging induces profound and long-lasting changes in the soil microbiome and associated soil functions , raising awareness regarding sustainable management of economically driven logging operations .

[57] Expansion of oxygen minimum zones may reduce available habitat for tropical pelagic fishes

Climate model predictions and observations reveal regional declines in oceanic dissolved oxygen , which are probably influenced by global warming .
Studies indicate ongoing dissolved oxygen depletion and vertical expansion of the oxygen minimum zone ( OMZ ) in the tropical northeast Atlantic Ocean .
OMZ shoaling may restrict the usable habitat of billfishes and tunas to a narrow surface layer .
We report a decrease in the upper ocean layer exceeding 3.5 ml l-1 dissolved oxygen at a rate of < = 1 m yr-1 in the tropical northeast Atlantic ( 0-25degrees N , 12-30degrees W ) , amounting to an annual habitat loss of ~ 5.95 x1013 m3 , or 15 % for the period 1960-2010 .
Habitat compression and associated potential habitat loss was validated using electronic tagging data from 47 blue marlin .
This phenomenon increases vulnerability to surface fishing gear for billfishes and tunas , and may be associated with a 10-50 % worldwide decline of pelagic predator diversity .
Further expansion of the Atlantic OMZ along with overfishing may threaten the sustainability of these valuable pelagic fisheries and marine ecosystems .

[58] Nitrogen limitation of microbial decomposition in a grassland under elevated CO2

Carbon accumulation in the terrestrial biosphere could partially offset the effects of anthropogenic CO2 emissions on atmospheric CO 2 ( refs 1 , 2 ) .
The net impact of increased CO2 on the carbon balance of terrestrial ecosystems is unclear , however , because elevated CO2 effects on carbon input to soils and plant use of water and nutrients often have contrasting effects on microbial processes .
Here we show suppression of microbial decomposition in an annual grassland after continuous exposure to increased CO2 for five growing seasons .
The increased CO 2 enhanced plant nitrogen uptake , microbial biomass carbon , and available carbon for microbes .
But it reduced available soil nitrogen , exacerbated nitrogen constraints on microbes , and reduced microbial respiration per unit biomass .
These results indicate that increased CO2 can alter the interaction between plants and microbes in favour of plant utilization of nitrogen , thereby slowing microbial decomposition and increasing ecosystem carbon accumulation .

[59] Closing yield gaps through nutrient and water management

In the coming decades , a crucial challenge for humanity will be meeting future food demands without undermining further the integrity of the Earth 's environmental systems .
Agricultural systems are already major forces of global environmental degradation , but population growth and increasing consumption of calorie - and meat-intensive diets are expected to roughly double human food demand by 2050 ( ref .
3 ) .
Responding to these pressures , there is increasing focus on ` sustainable intensification ' as a means to increase yields on underperforming landscapes while simultaneously decreasing the environmental impacts of agricultural systems .
However , it is unclear what such efforts might entail for the future of global agricultural landscapes .
Here we present a global-scale assessment of intensification prospects from closing ` yield gaps ' ( differences between observed yields and those attainable in a given region ) , the spatial patterns of agricultural management practices and yield limitation , and the management changes that may be necessary to achieve increased yields .
We find that global yield variability is heavily controlled by fertilizer use , irrigation and climate .
Large production increases ( 45 % to 70 % for most crops ) are possible from closing yield gaps to 100 % of attainable yields , and the changes to management practices that are needed to close yield gaps vary considerably by region and current intensity .
Furthermore , we find that there are large opportunities to reduce the environmental impact of agriculture by eliminating nutrient overuse , while still allowing an approximately 30 % increase in production of major cereals ( maize , wheat and rice ) .
Meeting the food security and sustainability challenges of the coming decades is possible , but will require considerable changes in nutrient and water management .

[60] The role of increasing temperature variability in European summer heatwaves

Instrumental observations and reconstructions of global and hemispheric temperature evolution reveal a pronounced warming during the past ~ 150 years .
One expression of this warming is the observed increase in the occurrence of heatwaves .
Conceptually this increase is understood as a shift of the statistical distribution towards warmer temperatures , while changes in the width of the distribution are often considered small .
Here we show that this framework fails to explain the record-breaking central European summer temperatures in 2003 , although it is consistent with observations from previous years .
We find that an event like that of summer 2003 is statistically extremely unlikely , even when the observed warming is taken into account .
We propose that a regime with an increased variability of temperatures ( in addition to increases in mean temperature ) may be able to account for summer 2003 .
To test this proposal , we simulate possible future European climate with a regional climate model in a scenario with increased atmospheric greenhouse-gas concentrations , and find that temperature variability increases by up to 100 % , with maximum changes in central and eastern Europe .

[61] Little change in global drought over the past 60 years

Drought is expected to increase in frequency and severity in the future as a result of climate change , mainly as a consequence of decreases in regional precipitation but also because of increasing evaporation driven by global warming .
Previous assessments of historic changes in drought over the late twentieth and early twenty-first centuries indicate that this may already be happening globally .
In particular , calculations of the Palmer Drought Severity Index ( PDSI ) show a decrease in moisture globally since the 1970s with a commensurate increase in the area in drought that is attributed , in part , to global warming .
The simplicity of the PDSI , which is calculated from a simple water-balance model forced by monthly precipitation and temperature data , makes it an attractive tool in large-scale drought assessments , but may give biased results in the context of climate change .
Here we show that the previously reported increase in global drought is overestimated because the PDSI uses a simplified model of potential evaporation that responds only to changes in temperature and thus responds incorrectly to global warming in recent decades .
More realistic calculations , based on the underlying physical principles that take into account changes in available energy , humidity and wind speed , suggest that there has been little change in drought over the past 60 years .
The results have implications for how we interpret the impact of global warming on the hydrological cycle and its extremes , and may help to explain why palaeoclimate drought reconstructions based on tree-ring data diverge from the PDSI-based drought record in recent years .

[62] Functional responses of methanogenic archaea to syntrophic growth

Methanococcus maripaludis grown syntrophically with Desulfovibrio vulgaris was compared with M. maripaludis monocultures grown under hydrogen limitation using transcriptional , proteomic and metabolite analyses .
These measurements indicate a decrease in transcript abundance for energy-consuming biosynthetic functions in syntrophically grown M. maripaludis , with an increase in transcript abundance for genes involved in the energy-generating central pathway for methanogenesis .
Compared with growth in monoculture under hydrogen limitation , the response of paralogous genes , such as those coding for hydrogenases , often diverged , with transcripts of one variant increasing in relative abundance , whereas the other was little changed or significantly decreased in abundance .
A common theme was an apparent increase in transcripts for functions using H2 directly as reductant , versus those using the reduced deazaflavin ( coenzyme F420 ) .
The greater importance of direct reduction by H2 was supported by improved syntrophic growth of a deletion mutant in an F420-dependent dehydrogenase of M. maripaludis .
These data suggest that paralogous genes enable the methanogen to adapt to changing substrate availability , sustaining it under environmental conditions that are often near the thermodynamic threshold for growth .
Additionally , the discovery of interspecies alanine transfer adds another metabolic dimension to this environmentally relevant mutualism .

[63] Impact of intensified Indian Ocean winds on mesoscale variability in the Agulhas system

South of Africa , the Agulhas Current retroflects and a portion of its waters flows into the South Atlantic Ocean , typically in the form of Agulhas rings .
This flux of warm and salty water from the Indian to the Atlantic Ocean ( the Agulhas leakage ) is now recognized as a key element in global climate .
An Agulhas leakage shutdown has been associated with extreme glacial periods , whereas a vigorous increase has preceded shifts towards interglacials .
In the absence of a coherent observing system , studies of the Agulhas have relied heavily on ocean models , which have revealed a possible recent increase in Agulhas leakage .
However , owing to the high levels of oceanic turbulence , model solutions of the region are highly sensitive to their numerical choices , stressing the need for observations to confirm these important model results .
Here , using satellite altimetry observations from 1993 to 2009 , we show that the mesoscale variability of the Agulhas system , in particular in the Mozambique Channel and south of Madagascar , has intensified .
This seems to result from an increased South Equatorial Current driven by enhanced trade winds over the tropical Indian Ocean .
Overall , the intensified mesoscale variability of the Agulhas system is reflected in accelerated eddy propagation , in its source regions as well as the retroflection from which eddies propagate into the South Atlantic Ocean .
This suggests that the Agulhas leakage may have increased from 1993 to 2009 , confirming previous modelling studies that have further implied an increased Agulhas leakage may compensate a deceleration of meridional overturning circulation associated with a freshening of the North Atlantic Ocean .

[64] Influence of iron availability on nutrient consumption ratio of diatoms in oceanic waters

The major nutrients ( nitrate , phosphate and silicate ) needed for phytoplankton growth are abundant in the surface waters of the subarctic Pacific , equatorial Pacific and Southern oceans , but this growth is limited by the availability of iron .
Under iron-deficient conditions , phytoplankton exhibit reduced uptake of nitrate and lower cellular levels of carbon , nitrogen and phosphorus .
Here I describe seawater and culture experiments which show that iron limitation can also affect the ratio of consumed silicate to nitrate and phosphate .
In iron-limited waters from all three of the aforementioned environments , addition of iron to phytoplankton assemblages in incubation bottles halved the silicate : nitrate and silicate : phosphate consumption ratios , in spite of the preferential growth of diatoms ( silica-shelled phytoplankton ) .
The nutrient consumption ratios of the phytoplankton assemblage from the Southern Ocean were similar to those of an iron-deficient laboratory culture of Antarctic diatoms , which exhibit increased cellular silicon or decreased cellular nitrogen and phosphorus in response to iron limitation .
Iron limitation therefore increases the export of biogenic silicon , relative to nitrogen and phosphorus , from the surface to deeper waters .
These findings suggest how the sedimentary records of carbon and silicon deposition in the glacial Southern Ocean can be consistent with the idea that changes in productivity , and thus in drawdown of atmospheric CO2 , during the last glaciation were stimulated by changes in iron inputs from atmospheric dust .

[65] Rainfall reductions over Southern Hemisphere semi-arid regions : the role of subtropical dry zone expansion

Since the late 1970s , Southern Hemisphere semi-arid regions such as southern-coastal Chile , southern Africa , and southeastern Australia have experienced a drying trend in austral autumn , predominantly during April and May .
The rainfall reduction coincides with a poleward expansion of the tropical belt and subtropical dry zone by around 2degrees-3degrees in the same season .
This has raised questions as to whether the regional rainfall reductions are attributable to this poleward expansion .
Here we show that the impact of the poleward subtropical dry-zone shift is not longitudinally uniform : a clear shift occurs south of Africa and across southern Australia , but there is no evidence of a poleward shift in the southern Chilean sector .
As such , a poleward shift of climatological April-May rainfall can explain most of the southeastern Australia rainfall decline , a small portion of the southern Africa rainfall trend , but not the autumn drying over southern Chile .

[66] Plant growth enhancement by elevated CO2 eliminated by joint water and nitrogen limitation

Rising atmospheric CO2 concentrations can fertilize plant growth .
The resulting increased plant uptake of CO2 could , in turn , slow increases in atmospheric CO2 levels and associated climate warming .
CO2 fertilization effects may be enhanced when water availability is low , because elevated CO2 also leads to improved plant water-use efficiency .
However , CO2 fertilization effects may be weaker when plant growth is limited by nutrient availability .
How variation in soil nutrients and water may act together to influence CO2 fertilization is unresolved .
Here we report plant biomass levels from a five-year , open-air experiment in a perennial grassland under two contrasting levels of atmospheric CO2 , soil nitrogen and summer rainfall , respectively .
We find that the presence of a CO2 fertilization effect depends on the amount of available nitrogen and water .
Specifically , elevated CO2 levels led to an increase in plant biomass of more than 33 % when summer rainfall , nitrogen supply , or both were at the higher levels ( ambient for rainfall and elevated for soil nitrogen ) .
But elevated CO2 concentrations did not increase plant biomass when both rainfall and nitrogen were at their lower level .
We conclude that given widespread , simultaneous limitation by water and nutrients , large stimulation of biomass by rising atmospheric CO2 concentrations may not be ubiquitous .

[67] Plot-scale evidence of tundra vegetation change and links to recent summer warming

Temperature is increasing at unprecedented rates across most of the tundra biome .
Remote-sensing data indicate that contemporary climate warming has already resulted in increased productivity over much of the Arctic , but plot-based evidence for vegetation transformation is not widespread .
We analysed change in tundra vegetation surveyed between 1980 and 2010 in 158 plant communities spread across 46 locations .
We found biome-wide trends of increased height of the plant canopy and maximum observed plant height for most vascular growth forms ; increased abundance of litter ; increased abundance of evergreen , low-growing and tall shrubs ; and decreased abundance of bare ground .
Intersite comparisons indicated an association between the degree of summer warming and change in vascular plant abundance , with shrubs , forbs and rushes increasing with warming .
However , the association was dependent on the climate zone , the moisture regime and the presence of permafrost .
Our data provide plot-scale evidence linking changes in vascular plant abundance to local summer warming in widely dispersed tundra locations across the globe .

[68] Future increases in Arctic precipitation linked to local evaporation and sea-ice retreat

Precipitation changes projected for the end of the twenty-first century show an increase of more than 50 per cent in the Arctic regions .
This marked increase , which is among the highest globally , has previously been attributed primarily to enhanced poleward moisture transport from lower latitudes .
Here we use state-of-the-art global climate models to show that the projected increases in Arctic precipitation over the twenty-first century , which peak in late autumn and winter , are instead due mainly to strongly intensified local surface evaporation ( maximum in winter ) , and only to a lesser degree due to enhanced moisture inflow from lower latitudes ( maximum in late summer and autumn ) .
Moreover , we show that the enhanced surface evaporation results mainly from retreating winter sea ice , signalling an amplified Arctic hydrological cycle .
This demonstrates that increases in Arctic precipitation are firmly linked to Arctic warming and sea-ice decline .
As a result , the Arctic mean precipitation sensitivity ( 4.5 per cent increase per degree of temperature warming ) is much larger than the global value ( 1.6 to 1.9 per cent per kelvin ) .
The associated seasonally varying increase in Arctic precipitation is likely to increase river discharge and snowfall over ice sheets ( thereby affecting global sea level ) , and could even affect global climate through freshening of the Arctic Ocean and subsequent modulations of the Atlantic meridional overturning circulation .

[69] CO2 enrichment and N addition increase nutrient loss from decomposing leaf litter in subtropical model forest ecosystems

As atmospheric CO2 concentration increases , many experiments have been carried out to study effects of CO2 enrichment on litter decomposition and nutrient release .
However , the result is still uncertain .
Meanwhile , the impact of CO2 enrichment on nutrients other than N and P are far less studied .
Using open-top chambers , we examined effects of elevated CO2 and N addition on leaf litter decomposition and nutrient release in subtropical model forest ecosystems .
We found that both elevated CO2 and N addition increased nutrient ( C , N , P , K , Ca , Mg and Zn ) loss from the decomposing litter .
The N , P , Ca and Zn loss was more than tripled in the chambers exposed to both elevated CO2 and N addition than those in the control chambers after 21 months of treatment .
The stimulation of nutrient loss under elevated CO2 was associated with the increased soil moisture , the higher leaf litter quality and the greater soil acidity .
Accelerated nutrient release under N addition was related to the higher leaf litter quality , the increased soil microbial biomass and the greater soil acidity .
Our results imply that elevated CO2 and N addition will increase nutrient cycling in subtropical China under the future global change .

[70] Direct human influence on atmospheric CO2 seasonality from increased cropland productivity

Ground - and aircraft-based measurements show that the seasonal amplitude of Northern Hemisphere atmospheric carbon dioxide ( CO2 ) concentrations has increased by as much as 50 per cent over the past 50 years .
This increase has been linked to changes in temperate , boreal and arctic ecosystem properties and processes such as enhanced photosynthesis , increased heterotrophic respiration , and expansion of woody vegetation .
However , the precise causal mechanisms behind the observed changes in atmospheric CO2 seasonality remain unclear .
Here we use production statistics and a carbon accounting model to show that increases in agricultural productivity , which have been largely overlooked in previous investigations , explain as much as a quarter of the observed changes in atmospheric CO2 seasonality .
Specifically , Northern Hemisphere extratropical maize , wheat , rice , and soybean production grew by 240 per cent between 1961 and 2008 , thereby increasing the amount of net carbon uptake by croplands during the Northern Hemisphere growing season by 0.33 petagrams .
Maize alone accounts for two-thirds of this change , owing mostly to agricultural intensification within concentrated production zones in the midwestern United States and northern China .
Maize , wheat , rice , and soybeans account for about 68 per cent of extratropical dry biomass production , so it is likely that the total impact of increased agricultural production exceeds the amount quantified here .

[71] Recent geographic convergence in diurnal and annual temperature cycling flattens global thermal profiles

Warming mean temperatures over the past century have probably shifted distributions , altered phenologies , increased extinction risks , and impacted agriculture and human health .
However , knowledge of mean temperatures alone does not provide a complete understanding either of changes in the climate itself or of how changing climate will affect organisms .
Temporal temperature variation , primarily driven by daily and annual temperature cycles , has profound effects on organism physiology and ecology , yet changes in temperature cycling over the past 40 years are still poorly understood .
Here we estimate global changes in the magnitudes of diurnal and annual temperature cycles from 1975 to 2013 from an analysis of over 1.4 billion hourly temperature measurements from 7,906 weather stations .
Increases in daily temperature variation since 1975 in polar ( 1.4 degreesC ) , temperate ( 1.0 degreesC ) and tropical ( 0.3 degreesC ) regions parallel increases in mean temperature .
Concurrently , magnitudes of annual temperature cycles decreased by 0.6 degreesC in polar regions , increased by 0.4 degreesC in temperate regions , and remained largely unchanged in tropical regions .
Stronger increases in daily temperature cycling relative to changes in annual temperature cycling in temperate and polar regions mean that , with respect to diurnal and annual cycling , the world is flattening as temperate and polar regions converge on tropical temperature cycling profiles .

[72] Climatic controls on central African hydrology during the past 20,000 years

Past hydrological changes in Africa have been linked to various climatic processes , depending on region and timescale .
Long-term precipitation changes in the regions of northern and southern Africa influenced by the monsoons are thought to have been governed by precessional variations in summer insolation .
Conversely , short-term precipitation changes in the northern African tropics have been linked to North Atlantic sea surface temperature anomalies , affecting the northward extension of the Intertropical Convergence Zone and its associated rainbelt .
Our knowledge of large-scale hydrological changes in equatorial Africa and their forcing factors is , however , limited .
Here we analyse the isotopic composition of terrigenous plant lipids , extracted from a marine sediment core close to the Congo River mouth , in order to reconstruct past central African rainfall variations and compare this record to sea surface temperature changes in the South Atlantic Ocean .
We find that central African precipitation during the past 20,000 years was mainly controlled by the difference in sea surface temperatures between the tropics and subtropics of the South Atlantic Ocean , whereas we find no evidence that changes in the position of the Intertropical Convergence Zone had a significant influence on the overall moisture availability in central Africa .
We conclude that changes in ocean circulation , and hence sea surface temperature patterns , were important in modulating atmospheric moisture transport onto the central African continent .

[73] Ice-sheet acceleration driven by melt supply variability

Increased ice velocities in Greenland are contributing significantly to eustatic sea level rise .
Faster ice flow has been associated with ice-ocean interactions in water-terminating outlet glaciers and with increased surface meltwater supply to the ice-sheet bed inland .
Observed correlations between surface melt and ice acceleration have raised the possibility of a positive feedback in which surface melting and accelerated dynamic thinning reinforce one another , suggesting that overall warming could lead to accelerated mass loss .
Here I show that it is not simply mean surface melt but an increase in water input variability that drives faster ice flow .
Glacier sliding responds to melt indirectly through changes in basal water pressure , with observations showing that water under glaciers drains through channels at low pressure or through interconnected cavities at high pressure .
Using a model that captures the dynamic switching between channel and cavity drainage modes , I show that channelization and glacier deceleration rather than acceleration occur above a critical rate of water flow .
Higher rates of steady water supply can therefore suppress rather than enhance dynamic thinning , indicating that the melt/dynamic thinning feedback is not universally operational .
Short-term increases in water input are , however , accommodated by the drainage system through temporary spikes in water pressure .
It is these spikes that lead to ice acceleration , which is therefore driven by strong diurnal melt cycles and an increase in rain and surface lake drainage events rather than an increase in mean melt supply .

[74] Contribution of anthropogenic and natural sources to atmospheric methane variability

Methane is an important greenhouse gas , and its atmospheric concentration has nearly tripled since pre-industrial times .
The growth rate of atmospheric methane is determined by the balance between surface emissions and photochemical destruction by the hydroxyl radical , the major atmospheric oxidant .
Remarkably , this growth rate has decreased markedly since the early 1990s , and the level of methane has remained relatively constant since 1999 , leading to a downward revision of its projected influence on global temperatures .
Large fluctuations in the growth rate of atmospheric methane are also observed from one year to the next , but their causes remain uncertain .
Here we quantify the processes that controlled variations in methane emissions between 1984 and 2003 using an inversion model of atmospheric transport and chemistry .
Our results indicate that wetland emissions dominated the inter-annual variability of methane sources , whereas fire emissions played a smaller role , except during the 1997-1998 El Nino event .
These top-down estimates of changes in wetland and fire emissions are in good agreement with independent estimates based on remote sensing information and biogeochemical models .
On longer timescales , our results show that the decrease in atmospheric methane growth during the 1990s was caused by a decline in anthropogenic emissions .
Since 1999 , however , they indicate that anthropogenic emissions of methane have risen again .
The effect of this increase on the growth rate of atmospheric methane has been masked by a coincident decrease in wetland emissions , but atmospheric methane levels may increase in the near future if wetland emissions return to their mean 1990s levels .

[75] Demographic compensation and tipping points in climate-induced range shifts

To persist , species are expected to shift their geographical ranges polewards or to higher elevations as the Earth 's climate warms .
However , although many species ' ranges have shifted in historical times , many others have not , or have shifted only at the high-latitude or high-elevation limits , leading to range expansions rather than contractions .
Given these idiosyncratic responses to climate warming , and their varied implications for species ' vulnerability to climate change , a critical task is to understand why some species have not shifted their ranges , particularly at the equatorial or low-elevation limits , and whether such resilience will last as warming continues .
Here we show that compensatory changes in demographic rates are buffering southern populations of two North American tundra plants against the negative effects of a warming climate , slowing their northward range shifts , but that this buffering is unlikely to continue indefinitely .
Southern populations of both species showed lower survival and recruitment but higher growth of individual plants , possibly owing to longer , warmer growing seasons .
Because of these and other compensatory changes , the population growth rates of southern populations are not at present lower than those of northern ones .
However , continued warming may yet prove detrimental , as most demographic rates that improved in moderately warmer years declined in the warmest years , with the potential to drive future population declines .
Our results emphasize the need for long-term , range-wide measurement of all population processes to detect demographic compensation and to identify nonlinear responses that may lead to sudden range shifts as climatic tipping points are exceeded .

[76] Influence of mean climate change on climate variability from a 155-year tropical Pacific coral record

Today , the El Nino/Southern Oscillation ( ENSO ) system is the primary driver of interannual variability in global climate , but its long-term behaviour is poorly understood .
Instrumental observations reveal a shift in 1976 towards warmer and wetter conditions in the tropical Pacific , with widespread climatic and ecological consequences .
This shift , unique over the past century , has prompted debate over the influence of increasing atmospheric concentrations of greenhouse gases on ENSO variability .
Here we present a 155-year ENSO reconstruction from a central tropical Pacific coral that provides new evidence for long-term changes in the regional mean climate and its variability .
A gradual transition in the early twentieth century and the abrupt change in 1976 , both towards warmer and wetter conditions , co-occur with changes in variability .
In the mid-late nineteenth century , cooler and drier background conditions coincided with prominent decadal variability ; in the early twentieth century , shorter-period ( ~ 2.9 years ) variability intensified .
After 1920 , variability weakens and becomes focused at interannual timescales ; with the shift in 1976 , variability with a period of about 4 years becomes prominent .
Our results suggest that variability in the tropical Pacific is linked to the region 's mean climate , and that changes in both have occurred during periods of natural as well as anthropogenic climate forcing .

[77] Caribbean coral growth influenced by anthropogenic aerosol emissions

Coral growth rates are highly dependent on environmental variables such as sea surface temperature and solar irradiance .
Multi-decadal variability in coral growth rates has been documented throughout the Caribbean over the past 150-200 years , and linked to variations in Atlantic sea surface temperatures .
Multi-decadal variability in sea surface temperatures in the North Atlantic , in turn , has been linked to volcanic and anthropogenic aerosol forcing .
Here , we examine the drivers of changes in coral growth rates in the western Caribbean between 1880 and 2000 , using previously published coral growth chronologies from two sites in the region , and a numerical model .
Changes in coral growth rates over this period coincided with variations in sea surface temperature and incoming short-wave radiation .
Our model simulations show that variations in the concentration of anthropogenic aerosols caused variations in sea surface temperature and incoming radiation in the second half of the twentieth century .
Before this , variations in volcanic aerosols may have played a more important role .
With the exception of extreme mass bleaching events , we suggest that neither climate change from greenhouse-gas emissions nor ocean acidification is necessarily the driver of multi-decadal variations in growth rates at some Caribbean locations .
Rather , the cause may be regional climate change due to volcanic and anthropogenic aerosol emissions .

[78] Effects of interannual climate variability on tropical tree cover

Climatic warming is substantially intensifying the global water cycle and is projected to increase rainfall variability .
Using satellite data , we show that higher climatic variability is associated with reduced tree cover in the wet tropics globally .
In contrast , interannual variability in rainfall can have neutral or even positive effects on tree cover in the dry tropics .
In South America , tree cover in dry lands is higher in areas with high year-to-year variability in rainfall .
This is consistent with evidence from case studies suggesting that in these areas rare wet episodes are essential for opening windows of opportunity where massive tree recruitment can overwhelm disturbance effects , allowing the establishment of extensive woodlands .
In Australia , wet extremes have similar effects , but the net effect of rainfall variability is overwhelmed by negative effects of extreme dry years .
In Africa , effects of rainfall variability are neutral for dry lands .
It is most likely that differences in herbivore communities and fire regimes contribute to regulating tree expansion during wet extremes .
Our results illustrate that increasing climatic variability may affect ecosystem services in contrasting , and sometimes surprising , ways .
Expansion of dry tropical tree cover during extreme wet events may decrease grassland productivity but enhance carbon sequestration , soil nutrient retention and biodiversity .

[79] The effects of molecular noise and size control on variability in the budding yeast cell cycle

Molecular noise in gene expression can generate substantial variability in protein concentration .
However , its effect on the precision of a natural eukaryotic circuit such as the control of cell cycle remains unclear .
We use single-cell imaging of fluorescently labelled budding yeast to measure times from division to budding ( G1 ) and from budding to the next division .
The variability in G1 decreases with the square root of the ploidy through a 1N/2N/4N ploidy series , consistent with simple stochastic models for molecular noise .
Also , increasing the gene dosage of G1 cyclins decreases the variability in G1 .
A new single-cell reporter for cell protein content allows us to determine the contribution to temporal G1 variability of deterministic size control ( that is , smaller cells extending G1 ) .
Cell size control contributes significantly to G1 variability in daughter cells but not in mother cells .
However , even in daughters , size-independent noise is the largest quantitative contributor to G1 variability .
Exit of the transcriptional repressor Whi5 from the nucleus partitions G1 into two temporally uncorrelated and functionally distinct steps .
The first step , which depends on the G1 cyclin gene CLN3 , corresponds to noisy size control that extends G1 in small daughters , but is of negligible duration in mothers .
The second step , whose variability decreases with increasing CLN2 gene dosage , is similar in mothers and daughters .
This analysis decomposes the regulatory dynamics of the Start transition into two independent modules , a size sensing module and a timing module , each of which is predominantly controlled by a different G1 cyclin .

[80] Relatedness among arbuscular mycorrhizal fungi drives plant growth and intraspecific fungal coexistence

Arbuscular mycorrhizal fungi ( AMF ) form symbioses with most plant species .
They are ecologically important determinants of plant growth and diversity .
Considerable genetic variation occurs in AMF populations .
Thus , plants are exposed to AMF of varying relatedness to each other .
Very little is known about either the effects of coexisting AMF on plant growth or which factors influence intraspecific AMF coexistence within roots .
No studies have addressed whether the genetics of coexisting AMF , and more specifically their relatedness , influences plant growth and AMF coexistence .
Relatedness is expected to influence coexistence between individuals , and it has been suggested that decreasing ability of symbionts to coexist can have negative effects on the growth of the host .
We tested the effect of a gradient of AMF genetic relatedness on the growth of two plant species .
Increasing relatedness between AMFs lead to markedly greater plant growth ( 27 % biomass increase with closely related compared to distantly related AMF ) .
In one plant species , closely related AMF coexisted in fairly equal proportions but decreasing relatedness lead to a very strong disequilibrium between AMF in roots , indicating much stronger competition .
Given the strength of the effects with such a shallow relatedness gradient and the fact that in the field plants are exposed to a steeper gradient , we consider that AMF relatedness can have a strong role in plant growth and the ability of AMF to coexist .
We conclude that AMF relatedness is a driver of plant growth and that relatedness is also a strong driver of intraspecific coexistence of these ecologically important symbionts .

[81] Climate change selects for heterozygosity in a declining fur seal population

Global environmental change is expected to alter selection pressures in many biological systems , but the long-term molecular and life history data required to quantify changes in selection are rare .
An unusual opportunity is afforded by three decades of individual-based data collected from a declining population of Antarctic fur seals in the South Atlantic .
Here , climate change has reduced prey availability and caused a significant decline in seal birth weight .
However , the mean age and size of females recruiting into the breeding population are increasing .
We show that such females have significantly higher heterozygosity ( a measure of within-individual genetic variation ) than their non-recruiting siblings and their own mothers .
Thus , breeding female heterozygosity has increased by 8.5 % per generation over the last two decades .
Nonetheless , as heterozygosity is not inherited from mothers to daughters , substantial heterozygote advantage is not transmitted from one generation to the next and the decreasing viability of homozygous individuals causes the population to decline .
Our results provide compelling evidence that selection due to climate change is intensifying , with far-reaching consequences for demography as well as phenotypic and genetic variation .

[82] Disease and thermal acclimation in a more variable and unpredictable climate

Global climate change is shifting the distribution of infectious diseases of humans and wildlife with potential adverse consequences for disease control .
As well as increasing mean temperatures , climate change is expected to increase climate variability , making climate less predictable .
However , few empirical or theoretical studies have considered the effects of climate variability or predictability on disease , despite it being likely that hosts and parasites will have differential responses to climatic shifts .
Here we present a theoretical framework for how temperature variation and its predictability influence disease risk by affecting host and parasite acclimation responses .
Laboratory experiments conducted in 80 independent incubators , and field data on disease-associated frog declines in Latin America , support the framework and provide evidence that unpredictable temperature fluctuations , on both monthly and diurnal timescales , decrease frog resistance to the pathogenic chytrid fungus Batrachochytrium dendrobatidis .
Furthermore , the pattern of temperature-dependent growth of the fungus on frogs was opposite to the pattern of growth in culture , emphasizing the importance of accounting for the host-parasite interaction when predicting climate-dependent disease dynamics .
If similar acclimation responses influence other host-parasite systems , as seems likely , then present models , which generally ignore small-scale temporal variability in climate , might provide poor predictions for climate effects on disease .

[83] Large climate-induced changes in ultraviolet index and stratosphere-to-troposphere ozone flux

Now that stratospheric ozone depletion has been controlled by the Montreal Protocol , interest has turned to the effects of climate change on the ozone layer .
Climate models predict an accelerated stratospheric circulation , leading to changes in the spatial distribution of stratospheric ozone and an increased stratosphere-to-troposphere ozone flux .
Here we use an atmospheric chemistry climate model to isolate the effects of climate change from those of ozone depletion and recovery on stratosphere-to-troposphere ozone flux and the clear-sky ultraviolet radiation index -- a measure of potential human exposure to ultraviolet radiation .
We show that under the Intergovernmental Panel on Climate Change moderate emissions scenario , global stratosphere-to-troposphere ozone flux increases by 23 % between 1965 and 2095 as a result of climate change .
During this time , the clear-sky ultraviolet radiation index decreases by 9 % in northern high latitudes -- a much larger effect than that of stratospheric ozone recovery -- and increases by 4 % in the tropics , and by up to 20 % in southern high latitudes in late spring and early summer .
The latter increase in the ultraviolet index is equivalent to nearly half of that generated by the Antarctic ` ozone hole ' that was created by anthropogenic halogens .
Our results suggest that climate change will alter the tropospheric ozone budget and the ultraviolet index , which would have consequences for tropospheric radiative forcing , air quality and human and ecosystem health .

[84] Rapid genotypic change and plasticity in arbuscular mycorrhizal fungi is caused by a host shift and enhanced by segregation

Arbuscular mycorrhizal fungi ( AMF ) are among the most abundant symbionts of plants , improving plant productivity and diversity .
They are thought to mostly grow vegetatively , a trait assumed to limit adaptability .
However , AMF can also harbor genetically different nuclei ( nucleotypes ) .
It has been shown that one AMF can produce genotypically novel offspring with proportions of different nucleotypes .
We hypothesized that ( 1 ) AMF respond rapidly to a change of environment ( plant host ) through changes in the frequency of nucleotypes ; ( 2 ) genotypically novel offspring exhibit different genetic responses to environmental change than the parent ; and ( 3 ) genotypically novel offspring exhibit a wide range of phenotypic plasticity to a change of environment .
We subjected AMF parents and offspring to a host shift .
We observed rapid and large genotypic changes in all AMF lines that were not random .
Genotypic and phenotypic responses were different among offspring and their parents .
Even though growing vegetatively , AMF offspring display a broad range of genotypic and phenotypic changes in response to host shift .
We conclude that AMF have the ability to rapidly produce variable progeny , increasing their probability to produce offspring with different fitness than their parents and , consequently , their potential adaptability to new environmental conditions .
Such genotypic and phenotypic flexibility could be a fast alternative to sexual reproduction and is likely to be a key to the ecological success of AMF .

[85] The impact of humidity above stratiform clouds on indirect aerosol climate forcing

Some of the global warming from anthropogenic greenhouse gases is offset by increased reflection of solar radiation by clouds with smaller droplets that form in air polluted with aerosol particles that serve as cloud condensation nuclei .
The resulting cooling tendency , termed the indirect aerosol forcing , is thought to be comparable in magnitude to the forcing by anthropogenic CO2 , but it is difficult to estimate because the physical processes that determine global aerosol and cloud populations are poorly understood .
Smaller cloud droplets not only reflect sunlight more effectively , but also inhibit precipitation , which is expected to result in increased cloud water .
Such an increase in cloud water would result in even more reflective clouds , further increasing the indirect forcing .
Marine boundary-layer clouds polluted by aerosol particles , however , are not generally observed to hold more water .
Here we simulate stratocumulus clouds with a fluid dynamics model that includes detailed treatments of cloud microphysics and radiative transfer .
Our simulations show that the response of cloud water to suppression of precipitation from increased droplet concentrations is determined by a competition between moistening from decreased surface precipitation and drying from increased entrainment of overlying air .
Only when the overlying air is humid or droplet concentrations are very low does sufficient precipitation reach the surface to allow cloud water to increase with droplet concentrations .
Otherwise , the response of cloud water to aerosol-induced suppression of precipitation is dominated by enhanced entrainment of overlying dry air .
In this scenario , cloud water is reduced as droplet concentrations increase , which diminishes the indirect climate forcing .

[86] Deforestation driven by urban population growth and agricultural trade in the twenty-first century

Reducing atmospheric carbon emissions from tropical deforestation is at present considered a cost-effective option for mitigating climate change .
However , the forces associated with tropical forest loss are uncertain .
Here we use satellite-based estimates of forest loss for 2000 to 2005 ( ref .
2 ) to assess economic , agricultural and demographic correlates across 41 countries in the humid tropics .
Two methods of analysis -- linear regression and regression tree -- show that forest loss is positively correlated with urban population growth and exports of agricultural products for this time period .
Rural population growth is not associated with forest loss , indicating the importance of urban-based and international demands for agricultural products as drivers of deforestation .
The strong trend in movement of people to cities in the tropics is , counter-intuitively , likely to be associated with greater pressures for clearing tropical forests .
We therefore suggest that policies to reduce deforestation among local , rural populations will not address the main cause of deforestation in the future .
Rather , efforts need to focus on reducing deforestation for industrial-scale , export-oriented agricultural production , concomitant with efforts to increase yields in non-forested lands to satisfy demands for agricultural products .

[87] Woody plant encroachment facilitated by increased precipitation intensity

Global circulation models and empirical evidence suggest that precipitation events are likely to become more extreme across much of the globe .
As most plant roots are in shallow soils , small but pervasive changes in precipitation intensity could be expected to cause large-scale shifts in plant growth , yet experimental tests of the effects of precipitation intensity are lacking .
Here we show that , without changing the total amount of precipitation , small experimental increases in precipitation intensity can push soil water deeper into the soil , increase aboveground woody plant growth and decrease aboveground grass growth in a savannah system .
These responses seemed to reflect the ability of woody plants to increase their rooting depths and competitively suppress grass growth .
In many parts of the world , woody plant abundance has multiplied in the past 50-100 years , causing changes in fire , forage value , biodiversity and carbon cycling .
Factors such as fire , grazing and atmospheric CO2 concentrations have become dominant explanations for this woody encroachment and semi-arid structure in general .
Our results suggest that niche partitioning is also an important factor in tree-grass coexistence and that the woody plant encroachment observed over the past century may continue in the future should precipitation intensity increase .

[88] Coastal eutrophication as a driver of salt marsh loss

Salt marshes are highly productive coastal wetlands that provide important ecosystem services such as storm protection for coastal cities , nutrient removal and carbon sequestration .
Despite protective measures , however , worldwide losses of these ecosystems have accelerated in recent decades .
Here we present data from a nine-year whole-ecosystem nutrient-enrichment experiment .
Our study demonstrates that nutrient enrichment , a global problem for coastal ecosystems , can be a driver of salt marsh loss .
We show that nutrient levels commonly associated with coastal eutrophication increased above-ground leaf biomass , decreased the dense , below-ground biomass of bank-stabilizing roots , and increased microbial decomposition of organic matter .
Alterations in these key ecosystem properties reduced geomorphic stability , resulting in creek-bank collapse with significant areas of creek-bank marsh converted to unvegetated mud .
This pattern of marsh loss parallels observations for anthropogenically nutrient-enriched marshes worldwide , with creek-edge and bay-edge marsh evolving into mudflats and wider creeks .
Our work suggests that current nutrient loading rates to many coastal ecosystems have overwhelmed the capacity of marshes to remove nitrogen without deleterious effects .
Projected increases in nitrogen flux to the coast , related to increased fertilizer use required to feed an expanding human population , may rapidly result in a coastal landscape with less marsh , which would reduce the capacity of coastal regions to provide important ecological and economic services .

[89] Atmospheric phosphorus deposition may cause lakes to revert from phosphorus limitation back to nitrogen limitation

Recent findings indicate that increased atmospheric deposition of nitrogen of human origin has caused changes in the pattern of ecological nutrient limitation in lakes in the northern hemisphere .
An increase in the nitrogen to phosphorus ratio , and hence a shift from pristine nitrogen limitation to human-induced phosphorus limitation of phytoplankton growth , seems to have been driven by deposition of atmospheric nitrogen .
These findings challenge the classical paradigm of lake phytoplankton productivity being naturally limited by phosphorus availability .
However , atmospheric phosphorus deposition may also be highly relevant .
Here we show how dissolved inorganic nitrogen concentration has decreased in the Pyrenean lake district over recent decades , despite there being an increase in deposition of atmospheric nitrogen .
This is related to an increased atmospheric phosphorus load in the lake water , as a result of higher atmospheric inputs .
These changes are causing phytoplankton to revert from being phosphorus-limited to being nitrogen-limited .

[90] Impact of regional climate change on human health

The World Health Organisation estimates that the warming and precipitation trends due to anthropogenic climate change of the past 30 years already claim over 150,000 lives annually .
Many prevalent human diseases are linked to climate fluctuations , from cardiovascular mortality and respiratory illnesses due to heatwaves , to altered transmission of infectious diseases and malnutrition from crop failures .
Uncertainty remains in attributing the expansion or resurgence of diseases to climate change , owing to lack of long-term , high-quality data sets as well as the large influence of socio-economic factors and changes in immunity and drug resistance .
Here we review the growing evidence that climate-health relationships pose increasing health risks under future projections of climate change and that the warming trend over recent decades has already contributed to increased morbidity and mortality in many regions of the world .
Potentially vulnerable regions include the temperate latitudes , which are projected to warm disproportionately , the regions around the Pacific and Indian oceans that are currently subjected to large rainfall variability due to the El Nino/Southern Oscillation sub-Saharan Africa and sprawling cities where the urban heat island effect could intensify extreme climatic events .

[91] Long-term stability of global erosion rates and weathering during late-Cenozoic cooling

Over geologic timescales , CO2 is emitted from the Earth 's interior and is removed from the atmosphere by silicate rock weathering and organic carbon burial .
This balance is thought to have stabilized greenhouse conditions within a range that ensured habitable conditions .
Changes in this balance have been attributed to changes in topographic relief , where varying rates of continental rock weathering and erosion are superimposed on fluctuations in organic carbon burial .
Geological strata provide an indirect yet imperfectly preserved record of this change through changing rates of sedimentation .
Widespread observations of a recent ( 0-5-Myr ) fourfold increase in global sedimentation rates require a global mechanism to explain them .
Accelerated uplift and global cooling have been given as possible causes , but because of the links between rates of erosion and the correlated rate of weathering , an increase in the drawdown of CO2 that is predicted to follow may be the cause of global climate change instead .
However , globally , rates of uplift can not increase everywhere in the way that apparent sedimentation rates do .
Moreover , proxy records of past atmospheric CO2 provide no evidence for this large reduction in recent CO2 concentrations .
Here we question whether this increase in global weathering and erosion actually occurred and whether the apparent increase in the sedimentation rate is due to observational biases in the sedimentary record .
As evidence , we recast the ocean dissolved 10Be/9Be isotope system as a weathering proxy spanning the past ~ 12 Myr ( ref .
14 ) .
This proxy indicates stable weathering fluxes during the late-Cenozoic era .
The sum of these observations shows neither clear evidence for increased erosion nor clear evidence for a pulse in weathered material to the ocean .
We conclude that processes different from an increase in denudation caused Cenozoic global cooling , and that global cooling had no profound effect on spatially and temporally averaged weathering rates .

[92] Rate of tree carbon accumulation increases continuously with tree size

Forests are major components of the global carbon cycle , providing substantial feedback to atmospheric greenhouse gas concentrations .
Our ability to understand and predict changes in the forest carbon cycle -- particularly net primary productivity and carbon storage -- increasingly relies on models that represent biological processes across several scales of biological organization , from tree leaves to forest stands .
Yet , despite advances in our understanding of productivity at the scales of leaves and stands , no consensus exists about the nature of productivity at the scale of the individual tree , in part because we lack a broad empirical assessment of whether rates of absolute tree mass growth ( and thus carbon accumulation ) decrease , remain constant , or increase as trees increase in size and age .
Here we present a global analysis of 403 tropical and temperate tree species , showing that for most species mass growth rate increases continuously with tree size .
Thus , large , old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees ; at the extreme , a single big tree can add the same amount of carbon to the forest within a year as is contained in an entire mid-sized tree .
The apparent paradoxes of individual tree growth increasing with tree size despite declining leaf-level and stand-level productivity can be explained , respectively , by increases in a tree 's total leaf area that outpace declines in productivity per unit of leaf area and , among other factors , age-related reductions in population density .
Our results resolve conflicting assumptions about the nature of tree growth , inform efforts to undertand and model forest carbon dynamics , and have additional implications for theories of resource allocation and plant senescence .

[93] Adapted conservation measures are required to save the Iberian lynx in a changing climate

The Iberian lynx ( Lynx pardinus ) has suffered severe population declines in the twentieth century and is now on the brink of extinction .
Climate change could further threaten the survival of the species , but its forecast effects are being neglected in recovery plans .
Quantitative estimates of extinction risk under climate change have so far mostly relied on inferences from correlative projections of species ' habitat shifts .
Here we use ecological niche models coupled to metapopulation simulations with source-sink dynamics to directly investigate the combined effects of climate change , prey availability and management intervention on the persistence of the Iberian lynx .
Our approach is unique in that it explicitly models dynamic bi-trophic species interactions in a climate change setting .
We show that anticipated climate change will rapidly and severely decrease lynx abundance and probably lead to its extinction in the wild within 50 years , even with strong global efforts to mitigate greenhouse gas emissions .
In stark contrast , we also show that a carefully planned reintroduction programme , accounting for the effects of climate change , prey abundance and habitat connectivity , could avert extinction of the lynx this century .
Our results demonstrate , for the first time , why considering prey availability , climate change and their interaction in models is important when designing policies to prevent future biodiversity loss .

[94] Shifts in the host range of a promiscuous plasmid through parallel evolution of its replication initiation protein

The ability of bacterial plasmids to adapt to novel hosts and thereby shift their host range is key to their long-term persistence in bacterial communities .
Promiscuous plasmids of the incompatibility group P ( IncP ) -1 can colonize a wide range of hosts , but it is not known if and how they can contract , shift or further expand their host range .
To understand the evolutionary mechanisms of host range shifts of IncP-1 plasmids , an IncP-1beta mini-replicon was experimentally evolved in four hosts in which it was initially unstable .
After 1000 generations in serial batch cultures under antibiotic selection for plasmid maintenance ( kanamycin resistance ) , the stability of the mini-plasmid dramatically improved in all coevolved hosts .
However , only plasmids evolved in Shewanella oneidensis showed improved stability in the ancestor , indicating that adaptive mutations had occurred in the plasmid itself .
Complete genome sequence analysis of nine independently evolved plasmids showed seven unique plasmid genotypes that had various kinds of single mutations at one locus , namely , the N-terminal region of the replication initiation protein TrfA .
Such parallel evolution indicates that this region was under strong selection .
In five of the seven evolved plasmids , these trfA mutations resulted in a significantly higher plasmid copy number .
Evolved plasmids were found to be stable in four other naive hosts , but could no longer replicate in Pseudomonas aeruginosa .
This study shows that plasmids can specialize to a novel host through trade-offs between improved stability in the new host and the ability to replicate in a previously permissive host .

[95] Shrinking of fishes exacerbates impacts of global ocean changes on marine ecosystems

Changes in temperature , oxygen content and other ocean biogeochemical properties directly affect the ecophysiology of marine water-breathing organisms .
Previous studies suggest that the most prominent biological responses are changes in distribution , phenology and productivity .
Both theory and empirical observations also support the hypothesis that warming and reduced oxygen will reduce body size of marine fishes .
However , the extent to which such changes would exacerbate the impacts of climate and ocean changes on global marine ecosystems remains unexplored .
Here , we employ a model to examine the integrated biological responses of over 600 species of marine fishes due to changes in distribution , abundance and body size .
The model has an explicit representation of ecophysiology , dispersal , distribution , and population dynamics .
We show that assemblage-averaged maximum body weight is expected to shrink by 14-24 % globally from 2000 to 2050 under a high-emission scenario .
About half of this shrinkage is due to change in distribution and abundance , the remainder to changes in physiology .
The tropical and intermediate latitudinal areas will be heavily impacted , with an average reduction of more than 20 % .
Our results provide a new dimension to understanding the integrated impacts of climate change on marine ecosystems .

[96] Net carbon dioxide losses of northern ecosystems in response to autumn warming

The carbon balance of terrestrial ecosystems is particularly sensitive to climatic changes in autumn and spring , with spring and autumn temperatures over northern latitudes having risen by about 1.1 degreesC and 0.8 degreesC , respectively , over the past two decades .
A simultaneous greening trend has also been observed , characterized by a longer growing season and greater photosynthetic activity .
These observations have led to speculation that spring and autumn warming could enhance carbon sequestration and extend the period of net carbon uptake in the future .
Here we analyse interannual variations in atmospheric carbon dioxide concentration data and ecosystem carbon dioxide fluxes .
We find that atmospheric records from the past 20 years show a trend towards an earlier autumn-to-winter carbon dioxide build-up , suggesting a shorter net carbon uptake period .
This trend can not be explained by changes in atmospheric transport alone and , together with the ecosystem flux data , suggest increasing carbon losses in autumn .
We use a process-based terrestrial biosphere model and satellite vegetation greenness index observations to investigate further the observed seasonal response of northern ecosystems to autumnal warming .
We find that both photosynthesis and respiration increase during autumn warming , but the increase in respiration is greater .
In contrast , warming increases photosynthesis more than respiration in spring .
Our simulations and observations indicate that northern terrestrial ecosystems may currently lose carbon dioxide in response to autumn warming , with a sensitivity of about 0.2 PgC degreesC-1 , offsetting 90 % of the increased carbon dioxide uptake during spring .
If future autumn warming occurs at a faster rate than in spring , the ability of northern ecosystems to sequester carbon may be diminished earlier than previously suggested .

[97] Effects of agricultural intensification on ability of natural enemies to control aphids

Agricultural intensification through increasing fertilization input and cropland expansion has caused rapid loss of semi-natural habitats and the subsequent loss of natural enemies of agricultural pests .
It is however extremely difficult to disentangle the effects of agricultural intensification on arthropod communities at multiple spatial scales .
Based on a two-year study of seventeen 1500 m-radius sites , we analyzed the relative importance of nitrogen input and cropland expansion on cereal aphids and their natural enemies .
Both the input of nitrogen fertilizer and cropland expansion benefited cereal aphids more than primary parasitoids and leaf-dwelling predators , while suppressing ground-dwelling predators , leading to an disturbance of the interspecific relationship .
The responses of natural enemies to cropland expansion were asymmetric and species-specific , with an increase of primary parasitism but a decline of predator/pest ratio with the increasing nitrogen input .
As such , agricultural intensification ( increasing nitrogen fertilizer and cropland expansion ) can destabilize the interspecific relationship and lead to biodiversity loss .
To this end , sustainable pest management needs to balance the benefit and cost of agricultural intensification and restore biocontrol service through proliferating the role of natural enemies at multiple scales .

[98] Enhanced carbon pump inferred from relaxation of nutrient limitation in the glacial ocean

The modern Eastern Equatorial Pacific ( EEP ) Ocean is a large oceanic source of carbon to the atmosphere .
Primary productivity over large areas of the EEP is limited by silicic acid and iron availability , and because of this constraint the organic carbon export to the deep ocean is unable to compensate for the outgassing of carbon dioxide that occurs through upwelling of deep waters .
It has been suggested that the delivery of dust-borne iron to the glacial ocean could have increased primary productivity and enhanced deep-sea carbon export in this region , lowering atmospheric carbon dioxide concentrations during glacial periods .
Such a role for the EEP is supported by higher organic carbon burial rates documented in underlying glacial sediments , but lower opal accumulation rates cast doubts on the importance of the EEP as an oceanic region for significant glacial carbon dioxide drawdown .
Here we present a new silicon isotope record that suggests the paradoxical decline in opal accumulation rate in the glacial EEP results from a decrease in the silicon to carbon uptake ratio of diatoms under conditions of increased iron availability from enhanced dust input .
Consequently , our study supports the idea of an invigorated biological pump in this region during the last glacial period that could have contributed to glacial carbon dioxide drawdown .
Additionally , using evidence from silicon and nitrogen isotope changes , we infer that , in contrast to the modern situation , the biological productivity in this region is not constrained by the availability of iron , silicon and nitrogen during the glacial period .
We hypothesize that an invigorated biological carbon dioxide pump constrained perhaps only by phosphorus limitation was a more common occurrence in low-latitude areas of the glacial ocean .

[99] Acceleration of Greenland ice mass loss in spring 2004

In 2001 the Intergovernmental Panel on Climate Change projected the contribution to sea level rise from the Greenland ice sheet to be between -0.02 and +0.09 m from 1990 to 2100 ( ref .
1 ) .
However , recent work has suggested that the ice sheet responds more quickly to climate perturbations than previously thought , particularly near the coast .
Here we use a satellite gravity survey by the Gravity Recovery and Climate Experiment ( GRACE ) conducted from April 2002 to April 2006 to provide an independent estimate of the contribution of Greenland ice mass loss to sea level change .
We detect an ice mass loss of 248 + / - 36 km3 yr-1 , equivalent to a global sea level rise of 0.5 + / - 0.1 mm yr-1 .
The rate of ice loss increased by 250 per cent between the periods April 2002 to April 2004 and May 2004 to April 2006 , almost entirely due to accelerated rates of ice loss in southern Greenland ; the rate of mass loss in north Greenland was almost constant .
Continued monitoring will be needed to identify any future changes in the rate of ice loss in Greenland .

[100] Species diversity enhances ecosystem functioning through interspecific facilitation

Facilitation between species is thought to be a key mechanism by which biodiversity affects the rates of resource use that govern the efficiency and productivity of ecosystems ; however , there is no direct empirical evidence to support this hypothesis .
Here we show that increasing the species diversity of a functional group of aquatic organisms induces facilitative interactions , leading to non-additive changes in resource consumption .
We increased the richness and evenness of suspension-feeding caddisfly larvae ( Insecta , Trichoptera ) in stream mesocosms and found that the increased topographical complexity of the benthic habitat alters patterns of near-bed flow such that the feeding success of individuals is enhanced .
Species diversity reduces ` current shading ' ( that is , the deceleration of flow from upstream to downstream neighbours ) , allowing diverse assemblages to capture a greater fraction of suspended resources than is caught by any species monoculture .
The fundamental nature of this form of hydrodynamic facilitation suggests that it is broadly applicable to freshwater and marine habitats ; in addition , it has several analogues in terrestrial ecosystems where fluxes of energy and matter can be influenced by biophysical complexity .
Thus , changes in species diversity may alter the probability of positive species interactions , resulting in disproportionately large changes in the functioning of ecosystems .

[101] Stochasticity of metabolism and growth at the single-cell level

Elucidating the role of molecular stochasticity in cellular growth is central to understanding phenotypic heterogeneity and the stability of cellular proliferation .
The inherent stochasticity of metabolic reaction events should have negligible effect , because of averaging over the many reaction events contributing to growth .
Indeed , metabolism and growth are often considered to be constant for fixed conditions .
Stochastic fluctuations in the expression level of metabolic enzymes could produce variations in the reactions they catalyse .
However , whether such molecular fluctuations can affect growth is unclear , given the various stabilizing regulatory mechanisms , the slow adjustment of key cellular components such as ribosomes , and the secretion and buffering of excess metabolites .
Here we use time-lapse microscopy to measure fluctuations in the instantaneous growth rate of single cells of Escherichia coli , and quantify time-resolved cross-correlations with the expression of lac genes and enzymes in central metabolism .
We show that expression fluctuations of catabolically active enzymes can propagate and cause growth fluctuations , with transmission depending on the limitation of the enzyme to growth .
Conversely , growth fluctuations propagate back to perturb expression .
Accordingly , enzymes were found to transmit noise to other unrelated genes via growth .
Homeostasis is promoted by a noise-cancelling mechanism that exploits fluctuations in the dilution of proteins by cell-volume expansion .
The results indicate that molecular noise is propagated not only by regulatory proteins but also by metabolic reactions .
They also suggest that cellular metabolism is inherently stochastic , and a generic source of phenotypic heterogeneity .

[102] Ecosystem response to elevated CO2 levels limited by nitrogen-induced plant species shift

Terrestrial ecosystems gain carbon through photosynthesis and lose it mostly in the form of carbon dioxide ( CO2 ) .
The extent to which the biosphere can act as a buffer against rising atmospheric CO2 concentration in global climate change projections remains uncertain at the present stage .
Biogeochemical theory predicts that soil nitrogen ( N ) scarcity may limit natural ecosystem response to elevated CO2 concentration , diminishing the CO2-fertilization effect on terrestrial plant productivity in unmanaged ecosystems .
Recent models have incorporated such carbon-nitrogen interactions and suggest that anthropogenic N sources could help sustain the future CO2-fertilization effect .
However , conclusive demonstration that added N enhances plant productivity in response to CO2-fertilization in natural ecosystems remains elusive .
Here we manipulated atmospheric CO2 concentration and soil N availability in a herbaceous brackish wetland where plant community composition is dominated by a C3 sedge and C4 grasses , and is capable of responding rapidly to environmental change .
We found that N addition enhanced the CO2-stimulation of plant productivity in the first year of a multi-year experiment , indicating N-limitation of the CO2 response .
But we also found that N addition strongly promotes the encroachment of C4 plant species that respond less strongly to elevated CO2 concentrations .
Overall , we found that the observed shift in the plant community composition ultimately suppresses the CO2-stimulation of plant productivity by the third and fourth years .
Although extensive research has shown that global change factors such as elevated CO2 concentrations and N pollution affect plant species differently and that they may drive plant community changes , we demonstrate that plant community shifts can act as a feedback effect that alters the whole ecosystem response to elevated CO2 concentrations .
Moreover , we suggest that trade-offs between the abilities of plant taxa to respond positively to different perturbations may constrain natural ecosystem response to global change .

[103] Selection for niche differentiation in plant communities increases biodiversity effects

In experimental plant communities , relationships between biodiversity and ecosystem functioning have been found to strengthen over time , a fact often attributed to increased resource complementarity between species in mixtures and negative plant-soil feedbacks in monocultures .
Here we show that selection for niche differentiation between species can drive this increasing biodiversity effect .
Growing 12 grassland species in test monocultures and mixtures , we found character displacement between species and increased biodiversity effects when plants had been selected over 8 years in species mixtures rather than in monocultures .
When grown in mixtures , relative differences in height and specific leaf area between plant species selected in mixtures ( mixture types ) were greater than between species selected in monocultures ( monoculture types ) .
Furthermore , net biodiversity and complementarity effects were greater in mixtures of mixture types than in mixtures of monoculture types .
Our study demonstrates a novel mechanism for the increase in biodiversity effects : selection for increased niche differentiation through character displacement .
Selection in diverse mixtures may therefore increase species coexistence and ecosystem functioning in natural communities and may also allow increased mixture yields in agriculture or forestry .
However , loss of biodiversity and prolonged selection of crops in monoculture may compromise this potential for selection in the longer term .

[104] Quantifying the benefit of early climate change mitigation in avoiding biodiversity loss

Climate change is expected to have significant influences on terrestrial biodiversity at all system levels , including species-level reductions in range size and abundance , especially amongst endemic species .
However , little is known about how mitigation of greenhouse gas emissions could reduce biodiversity impacts , particularly amongst common and widespread species .
Our global analysis of future climatic range change of common and widespread species shows that without mitigation , 57 + / -6 % of plants and 34 + / -7 % of animals are likely to lose > = 50 % of their present climatic range by the 2080s .
With mitigation , however , losses are reduced by 60 % if emissions peak in 2016 or 40 % if emissions peak in 2030 .
Thus , our analyses indicate that without mitigation , large range contractions can be expected even amongst common and widespread species , amounting to a substantial global reduction in biodiversity and ecosystem services by the end of this century .
Prompt and stringent mitigation , on the other hand , could substantially reduce range losses and buy up to four decades for climate change adaptation .

[105] Habitat modification alters the structure of tropical host-parasitoid food webs

Global conversion of natural habitats to agriculture has led to marked changes in species diversity and composition .
However , it is less clear how habitat modification affects interactions among species .
Networks of feeding interactions ( food webs ) describe the underlying structure of ecological communities , and might be crucially linked to their stability and function .
Here , we analyse 48 quantitative food webs for cavity-nesting bees , wasps and their parasitoids across five tropical habitat types .
We found marked changes in food-web structure across the modification gradient , despite little variation in species richness .
The evenness of interaction frequencies declined with habitat modification , with most energy flowing along one or a few pathways in intensively managed agricultural habitats .
In modified habitats there was a higher ratio of parasitoid to host species and increased parasitism rates , with implications for the important ecosystem services , such as pollination and biological control , that are performed by host bees and wasps .
The most abundant parasitoid species was more specialized in modified habitats , with reduced attack rates on alternative hosts .
Conventional community descriptors failed to discriminate adequately among habitats , indicating that perturbation of the structure and function of ecological communities might be overlooked in studies that do not document and quantify species interactions .
Altered interaction structure therefore represents an insidious and functionally important hidden effect of habitat modification by humans .

[106] Centennial-scale changes in the global carbon cycle during the last deglaciation

Global climate and the concentration of atmospheric carbon dioxide ( CO2 ) are correlated over recent glacial cycles .
The combination of processes responsible for a rise in atmospheric CO2 at the last glacial termination ( 23,000 to 9,000 years ago ) , however , remains uncertain .
Establishing the timing and rate of CO2 changes in the past provides critical insight into the mechanisms that influence the carbon cycle and helps put present and future anthropogenic emissions in context .
Here we present CO2 and methane ( CH4 ) records of the last deglaciation from a new high-accumulation West Antarctic ice core with unprecedented temporal resolution and precise chronology .
We show that although low-frequency CO2 variations parallel changes in Antarctic temperature , abrupt CO2 changes occur that have a clear relationship with abrupt climate changes in the Northern Hemisphere .
A significant proportion of the direct radiative forcing associated with the rise in atmospheric CO2 occurred in three sudden steps , each of 10 to 15 parts per million .
Every step took place in less than two centuries and was followed by no notable change in atmospheric CO2 for about 1,000 to 1,500 years .
Slow , millennial-scale ventilation of Southern Ocean CO2-rich , deep-ocean water masses is thought to have been fundamental to the rise in atmospheric CO2 associated with the glacial termination , given the strong covariance of CO2 levels and Antarctic temperatures .
Our data establish a contribution from an abrupt , centennial-scale mode of CO2 variability that is not directly related to Antarctic temperature .
We suggest that processes operating on centennial timescales , probably involving the Atlantic meridional overturning circulation , seem to be influencing global carbon-cycle dynamics and are at present not widely considered in Earth system models .

[107] Increase in forest water-use efficiency as atmospheric carbon dioxide concentrations rise

Terrestrial plants remove CO2 from the atmosphere through photosynthesis , a process that is accompanied by the loss of water vapour from leaves .
The ratio of water loss to carbon gain , or water-use efficiency , is a key characteristic of ecosystem function that is central to the global cycles of water , energy and carbon .
Here we analyse direct , long-term measurements of whole-ecosystem carbon and water exchange .
We find a substantial increase in water-use efficiency in temperate and boreal forests of the Northern Hemisphere over the past two decades .
We systematically assess various competing hypotheses to explain this trend , and find that the observed increase is most consistent with a strong CO2 fertilization effect .
The results suggest a partial closure of stomata -- small pores on the leaf surface that regulate gas exchange -- to maintain a near-constant concentration of CO2 inside the leaf even under continually increasing atmospheric CO2 levels .
The observed increase in forest water-use efficiency is larger than that predicted by existing theory and 13 terrestrial biosphere models .
The increase is associated with trends of increasing ecosystem-level photosynthesis and net carbon uptake , and decreasing evapotranspiration .
Our findings suggest a shift in the carbon - and water-based economics of terrestrial vegetation , which may require a reassessment of the role of stomatal control in regulating interactions between forests and climate change , and a re-evaluation of coupled vegetation-climate models .

[108] Evolution of the Southern Annular Mode during the past millennium

The Southern Annular Mode ( SAM ) is the primary pattern of climate variability in the Southern Hemisphere , influencing latitudinal rainfall distribution and temperatures from the subtropics to Antarctica .
The positive summer trend in the SAM over recent decades is widely attributed to stratospheric ozone depletion ; however , the brevity of observational records from Antarctica -- one of the core zones that defines SAM variability -- limits our understanding of long-term SAM behaviour .
Here we reconstruct annual mean changes in the SAM since AD 1000 using , for the first time , proxy records that encompass the full mid-latitude to polar domain across the Drake Passage sector .
We find that the SAM has undergone a progressive shift towards its positive phase since the fifteenth century , causing cooling of the main Antarctic continent at the same time that the Antarctic Peninsula has warmed .
The positive trend in the SAM since ~ AD 1940 is reproduced by multimodel climate simulations forced with rising greenhouse gas levels and later ozone depletion , and the long-term average SAM index is now at its highest level for at least the past 1,000 years .
Reconstructed SAM trends before the twentieth century are more prominent than those in radiative-forcing climate experiments and may be associated with a teleconnected response to tropical Pacific climate .
Our findings imply that predictions of further greenhouse-driven increases in the SAM over the coming century also need to account for the possibility of opposing effects from tropical Pacific climate changes .

[109] Atmospheric CO2 forces abrupt vegetation shifts locally , but not globally

It is possible that anthropogenic climate change will drive the Earth system into a qualitatively different state .
Although different types of uncertainty limit our capacity to assess this risk , Earth system scientists are particularly concerned about tipping elements , large-scale components of the Earth system that can be switched into qualitatively different states by small perturbations .
Despite growing evidence that tipping elements exist in the climate system , whether large-scale vegetation systems can tip into alternative states is poorly understood .
Here we show that tropical grassland , savanna and forest ecosystems , areas large enough to have powerful impacts on the Earth system , are likely to shift to alternative states .
Specifically , we show that increasing atmospheric CO2 concentration will force transitions to vegetation states characterized by higher biomass and/or woody-plant dominance .
The timing of these critical transitions varies as a result of between-site variance in the rate of temperature increase , as well as a dependence on stochastic variation in fire severity and rainfall .
We further show that the locations of bistable vegetation zones ( zones where alternative vegetation states can exist ) will shift as climate changes .
We conclude that even though large-scale directional regime shifts in terrestrial ecosystems are likely , asynchrony in the timing of these shifts may serve to dampen , but not nullify , the shock that these changes may represent to the Earth system .

[110] Recent Antarctic ice mass loss from radar interferometry and regional climate modelling

Large uncertainties remain in the current and future contribution to sea level rise from Antarctica .
Climate warming may increase snowfall in the continent 's interior , but enhance glacier discharge at the coast where warmer air and ocean temperatures erode the buttressing ice shelves .
Here , we use satellite interferometric synthetic-aperture radar observations from 1992 to 2006 covering 85 % of Antarctica 's coastline to estimate the total mass flux into the ocean .
We compare the mass fluxes from large drainage basin units with interior snow accumulation calculated from a regional atmospheric climate model for 1980 to 2004 .
In East Antarctica , small glacier losses in Wilkes Land and glacier gains at the mouths of the Filchner and Ross ice shelves combine to a near-zero loss of 4 + / -61 Gt yr-1 .
In West Antarctica , widespread losses along the Bellingshausen and Amundsen seas increased the ice sheet loss by 59 % in 10 years to reach 132 + / -60 Gt yr-1 in 2006 .
In the Peninsula , losses increased by 140 % to reach 60 + / -46 Gt yr-1 in 2006 .
Losses are concentrated along narrow channels occupied by outlet glaciers and are caused by ongoing and past glacier acceleration .
Changes in glacier flow therefore have a significant , if not dominant impact on ice sheet mass balance .

[111] The impact of global land-cover change on the terrestrial water cycle

Floods and droughts cause perhaps the most human suffering of all climate-related events ; a major goal is to understand how humans alter the incidence and severity of these events by changing the terrestrial water cycle .
Here we use over 1,500 estimates of annual evapotranspiration and a database of global land-cover change to project alterations of global scale terrestrial evapotranspiration ( TET ) from current anthropogenic land-cover change .
Geographic modelling reveals that land-cover change reduces annual TET by approximately 3,500 km3 yr-1 ( 5 % ) and that the largest changes in evapotranspiration are associated with wetlands and reservoirs .
Land surface model simulations support these evapotranspiration changes , and project increased runoff ( 7.6 % ) as a result of land-cover changes .
Next we create a synthesis of the major anthropogenic impacts on annual runoff and find that the net result is an increase in annual runoff , although this is uncertain .
The results demonstrate that land-cover change alters annual global runoff to a similar or greater extent than other major drivers , affirming the important role of land-cover change in the Earth System .
Last , we identify which major anthropogenic drivers to runoff change have a mean global change statistic that masks large regional increases and decreases : land-cover change , changes in meteorological forcing , and direct CO2 effects on plants .

[112] Robust direct effect of carbon dioxide on tropical circulation and regional precipitation

Predicting the response of tropical rainfall to climate change remains a challenge .
Rising concentrations of carbon dioxide are expected to affect the hydrological cycle through increases in global mean temperature and the water vapour content of the atmosphere .
However , regional precipitation changes also closely depend on the atmospheric circulation , which is expected to weaken in a warmer world .
Here , we assess the effect of a rise in atmospheric carbon dioxide concentrations on tropical circulation and precipitation by analysing results from a suite of simulations from multiple state-of-the-art climate models , and an operational numerical weather prediction model .
In a scenario in which humans continue to use fossil fuels unabated , about half the tropical circulation change projected by the end of the twenty-first century , and consequently a large fraction of the regional precipitation change , is independent of global surface warming .
Instead , these robust circulation and precipitation changes are a consequence of the weaker net radiative cooling of the atmosphere associated with higher atmospheric carbon dioxide levels , which affects the strength of atmospheric vertical motions .
This implies that geo-engineering schemes aimed at reducing global warming without removing carbon dioxide from the atmosphere would fail to fully mitigate precipitation changes in the tropics .
Strategies that may help constrain rainfall projections are suggested .

[113] Europe-wide reduction in primary productivity caused by the heat and drought in 2003

Future climate warming is expected to enhance plant growth in temperate ecosystems and to increase carbon sequestration .
But although severe regional heatwaves may become more frequent in a changing climate , their impact on terrestrial carbon cycling is unclear .
Here we report measurements of ecosystem carbon dioxide fluxes , remotely sensed radiation absorbed by plants , and country-level crop yields taken during the European heatwave in 2003 .
We use a terrestrial biosphere simulation model to assess continental-scale changes in primary productivity during 2003 , and their consequences for the net carbon balance .
We estimate a 30 per cent reduction in gross primary productivity over Europe , which resulted in a strong anomalous net source of carbon dioxide ( 0.5 Pg C yr-1 ) to the atmosphere and reversed the effect of four years of net ecosystem carbon sequestration .
Our results suggest that productivity reduction in eastern and western Europe can be explained by rainfall deficit and extreme summer heat , respectively .
We also find that ecosystem respiration decreased together with gross primary productivity , rather than accelerating with the temperature rise .
Model results , corroborated by historical records of crop yields , suggest that such a reduction in Europe 's primary productivity is unprecedented during the last century .
An increase in future drought events could turn temperate ecosystems into carbon sources , contributing to positive carbon-climate feedbacks already anticipated in the tropics and at high latitudes .

[114] Global perceptions of local temperature change

It is difficult to detect global warming directly because most people experience changes only in local weather patterns , which are highly variable and may not reflect long-term global climate trends .
However , local climate-change experience may play an important role in adaptation and mitigation behaviour and policy support .
Previous research indicates that people can perceive and adapt to aspects of climate variability and change based on personal observations .
Experience with local weather may also influence global warming beliefs .
Here we examine the extent to which respondents in 89 countries detect recent changes in average local temperatures .
We demonstrate that public perceptions correspond with patterns of observed temperature change from climate records : individuals who live in places with rising average temperatures are more likely than others to perceive local warming .
As global climate change intensifies , changes in local temperatures and weather patterns may be increasingly detected by the global public .
These findings also suggest that public opinion of climate change may shift , at least in part , in response to the personal experience of climate change .

[115] Chinese Grain for Green Program led to highly increased soil organic carbon levels : A meta-analysis

The Grain for Green Program ( GGP ) , initiated in 1999 , is the largest ecological restoration project in central and western China .
Here , for the first time , we performed a meta-analysis and found that the GGP largely increased the soil organic carbon ( SOC ) .
The SOC was increased by 48.1 % , 25.4 % , and 25.5 % at soil depths of 0-20 cm , 20-40 cm , and 40-60 cm , respectively .
Moreover , this carbon accumulation has significantly increased over time since GGP implementation .
The carbon accumulation showed a significantly more active response to the GGP in the top 20 cm of soil than in the deeper soil layers .
Conversion of cropland to forest could lead to significantly greater SOC accumulation than would the conversion of cropland to grassland .
Conversion from cropland to woodland could lead to greater SOC accumulation than would the conversion to either shrubland or orchard .
Our results suggest that the GGP implementation caused SOC to accumulate and that there remains a large potential for further accumulation of carbon in the soil , which will help to mitigate climate change in the near future .

[116] Effect of warming and drought on grassland microbial communities

The soil microbiome is responsible for mediating key ecological processes ; however , little is known about its sensitivity to climate change .
Observed increases in global temperatures and alteration to rainfall patterns , due to anthropogenic release of greenhouse gases , will likely have a strong influence on soil microbial communities and ultimately the ecosystem services they provide .
Therefore , it is vital to understand how soil microbial communities will respond to future climate change scenarios .
To this end , we surveyed the abundance , diversity and structure of microbial communities over a 2-year period from a long-term in situ warming experiment that experienced a moderate natural drought .
We found the warming treatment and soil water budgets strongly influence bacterial population size and diversity .
In normal precipitation years , the warming treatment significantly increased microbial population size 40-150 % but decreased diversity and significantly changed the composition of the community when compared with the unwarmed controls .
However during drought conditions , the warming treatment significantly reduced soil moisture thereby creating unfavorable growth conditions that led to a 50-80 % reduction in the microbial population size when compared with the control .
Warmed plots also saw an increase in species richness , diversity and evenness ; however , community composition was unaffected suggesting that few phylotypes may be active under these stressful conditions .
Our results indicate that under warmed conditions , ecosystem water budget regulates the abundance and diversity of microbial populations and that rainfall timing is critical at the onset of drought for sustaining microbial populations .

[117] Tropospheric ozone variations governed by changes in stratospheric circulation

The downward transport of stratospheric ozone is an important natural source of tropospheric ozone , particularly in the upper troposphere , where changes in ozone have their largest radiative effect .
Stratospheric circulation is projected to intensify over the coming century , which could lead to an increase in the flux of ozone from the stratosphere to the troposphere .
However , large uncertainties in the stratospheric contribution to trends and variability in tropospheric ozone levels make it difficult to reliably project future changes in tropospheric ozone .
Here , we use satellite measurements of stratospheric water vapour and tropospheric ozone levels collected between 2005 and 2010 to assess the effect of changes in stratospheric circulation , driven by El Nino/Southern Oscillation and the stratospheric Quasi-Biennial Oscillation , on tropospheric ozone levels .
We find that interannual variations in the strength of the stratospheric circulation of around 40 % -- comparable to the mean change in stratospheric circulation projected this century -- lead to changes in tropospheric ozone levels in the northern mid-latitudes of around 2 % , approximately half of the interannual variability .
Assuming that the observed response of tropospheric ozone levels to interannual variations in circulation is a good predictor of its equilibrium response , we suggest that the projected intensification of the stratospheric circulation over the coming century could lead to small but important increases in tropospheric ozone levels .

[118] Soil-mediated effects of subambient to increased carbon dioxide on grassland productivity

Grasslands are structured by climate and soils , and are increasingly affected by anthropogenic changes , including rising atmospheric CO2 concentrations .
CO2 enrichment can alter grassland ecosystem function both directly and through indirect , soil-specific effects on moisture , nitrogen availability and plant species composition , potentially leading to threshold change in ecosystem properties .
Here we show that the increase in aboveground net primary productivity ( ANPP ) with CO2 enrichment depends strongly on soil type .
We found that the ANPP-CO2 response of grassland was 2.5 x greater on two soils with higher plant-available soil moisture and where direct CO2 effects on ANPP were accompanied by indirect CO2 effects on ANPP mediated through an increase in soil moisture or increased dominance of a productive C4 grass .
Indirect CO2 effects on ANPP were absent on a third soil that was less responsive to CO2 ( 1.6 x ) .
Unexpectedly , soil N availability changed little with CO2 and did not seem to drive responses in ANPP .
On the more responsive soils , the more productive grass C4 was favoured with CO2 enrichment because of greater photosynthetic efficiency .
Our results enhance present models of the controls on ecosystem responses to CO2 ( refs , , ) and demonstrate mechanisms by which soils could cause spatial variation in CO2 effects on ANPP and other ecosystem attributes .

[119] Plant nitrogen uptake drives responses of productivity to nitrogen and water addition in a grassland

Increased atmospheric nitrogen ( N ) deposition and altered precipitation regimes have profound impacts on ecosystem functioning in semiarid grasslands .
The interactions between those two factors remain largely unknown .
A field experiment with N and water additions was conducted in a semiarid grassland in northern China .
We examined the responses of aboveground net primary production ( ANPP ) and plant N use during two contrasting hydrological growing seasons .
Nitrogen addition had no impact on ANPP , which may be accounted for by the offset between enhanced plant N uptake and decreased plant nitrogen use efficiency ( NUE ) .
Water addition significantly enhanced ANPP , which was largely due to enhanced plant aboveground N uptake .
Nitrogen and water additions significantly interacted to affect ANPP , plant N uptake and N concentrations at the community level .
Our observations highlight the important role of plant N uptake and use in mediating the effects of N and water addition on ANPP .

[120] Increased greenhouse-gas intensity of rice production under future atmospheric conditions

Increased atmospheric CO2 and rising temperatures are expected to affect rice yields and greenhouse-gas ( GHG ) emissions from rice paddies .
This is important , because rice cultivation is one of the largest human-induced sources of the potent GHG methane ( CH4 ) and rice is the world 's second-most produced staple crop .
The need for meeting a growing global food demand argues for assessing GHG emissions from croplands on the basis of yield rather than land area , such that efforts to reduce GHG emissions take into consideration the consequences for food production .
However , it is unclear whether or how the GHG intensity ( that is , yield-scaled GHG emissions ) of cropping systems will be affected by future atmospheric conditions .
Here we show , using meta-analysis , that increased atmospheric CO2 ( ranging from 550 to 743 ppmV ) and warming ( ranging from +0.8 degreesC to +6 degreesC ) both increase the GHG intensity of rice cultivation .
Increased atmospheric CO2 increased GHG intensity by 31.4 % , because CH4 emissions are stimulated more than rice yields .
Warming increased GHG intensity by 11.8 % per 1 degreesC , largely owing to a decrease in yield .
This analysis suggests that rising CO2 and warming will approximately double the GHG intensity of rice production by the end of the twenty-first century , stressing the need for management practices that optimize rice production while reducing its GHG intensity as the climate continues to change .

[121] Climate-society feedbacks and the avoidance of dangerous climate change

The growth in anthropogenic CO2 emissions experienced since the onset of the Industrial Revolution is the most important disturbance operating on the Earth 's climate system .
To avoid dangerous climate change , future greenhouse-gas emissions will have to deviate from business-as-usual trajectories .
This implies that feedback links need to exist between climate change and societal actions .
Here , we show that , consciously or otherwise , these feedbacks can be represented by linking global mean temperature change to the growth dynamics of CO2 emissions .
We show that the global growth of new renewable sources of energy post-1990 represents a climate-society feedback of ~ 0.25 % yr-1 per degree increase in global mean temperature .
We also show that to fulfil the outcomes negotiated in Durban in 2011 , society will have to become ~ 50 times more responsive to global mean temperature change than it has been since 1990 .
If global energy use continues to grow as it has done historically then this would result in amplification of the long-term endogenous rate of decarbonization from -0.6 % yr-1 to ~ -13 % yr-1 .
It is apparent that modest levels of feedback sensitivity pay large dividends in avoiding climate change but that the marginal return on this effort diminishes rapidly as the required feedback strength increases .

[122] Adaptation potential of European agriculture in response to climate change

Projecting the impacts of climate change on agriculture requires knowing or assuming how farmers will adapt .
However , empirical estimates of the effectiveness of this private adaptation are scarce and the sensitivity of impact assessments to adaptation assumptions is not well understood .
Here we assess the potential effectiveness of private farmer adaptation in Europe by jointly estimating both short-run and long-run response functions using time-series and cross-sectional variation in subnational yield and profit data .
The difference between the impacts of climate change projected using the short-run ( limited adaptation ) and long-run ( substantial adaptation ) response curves can be interpreted as the private adaptation potential .
We find high adaptation potential for maize to future warming but large negative effects and only limited adaptation potential for wheat and barley .
Overall , agricultural profits could increase slightly under climate change if farmers adapt but could decrease in many areas if there is no adaptation .
Decomposing the variance in 2040 projected yields and farm profits using an ensemble of 13 climate model runs , we find that the rate at which farmers will adapt to rising temperatures is an important source of uncertainty .

[123] Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes

Geochemical data suggest that oxygenation of the Earth 's atmosphere occurred in two broad steps .
The first rise in atmospheric oxygen is thought to have occurred between ~ 2.45 and 2.2 Gyr ago , leading to a significant increase in atmospheric oxygen concentrations and concomitant oxygenation of the shallow surface ocean .
The second increase in atmospheric oxygen appears to have taken place in distinct stages during the late Neoproterozoic era ( ~ 800-542 Myr ago ) , ultimately leading to oxygenation of the deep ocean ~ 580 Myr ago , but details of the evolution of atmospheric oxygenation remain uncertain .
Here we use chromium ( Cr ) stable isotopes from banded iron formations ( BIFs ) to track the presence of Cr ( VI ) in Precambrian oceans , providing a time-resolved picture of the oxygenation history of the Earth 's atmosphere-hydrosphere system .
The geochemical behaviour of Cr is highly sensitive to the redox state of the surface environment because oxidative weathering processes produce the oxidized hexavalent [ Cr ( VI ) ] form .
Oxidation of reduced trivalent [ Cr ( III ) ] chromium on land is accompanied by an isotopic fractionation , leading to enrichment of the mobile hexavalent form in the heavier isotope .
Our fractionated Cr isotope data indicate the accumulation of Cr ( VI ) in ocean surface waters ~ 2.8 to 2.6 Gyr ago and a likely transient elevation in atmospheric and surface ocean oxygenation before the first great rise of oxygen 2.45-2 .2 Gyr ago ( the Great Oxidation Event ) .
In ~ 1.88-Gyr-old BIFs we find that Cr isotopes are not fractionated , indicating a decline in atmospheric oxygen .
Our findings suggest that the Great Oxidation Event did not lead to a unidirectional stepwise increase in atmospheric oxygen .
In the late Neoproterozoic , we observe strong positive fractionations in Cr isotopes ( delta53Cr up to +4.9 / 1000 ) , providing independent support for increased surface oxygenation at that time , which may have stimulated rapid evolution of macroscopic multicellular life .

[124] Projected increase in continental runoff due to plant responses to increasing carbon dioxide

In addition to influencing climatic conditions directly through radiative forcing , increasing carbon dioxide concentration influences the climate system through its effects on plant physiology .
Plant stomata generally open less widely under increased carbon dioxide concentration , which reduces transpiration and thus leaves more water at the land surface .
This driver of change in the climate system , which we term ` physiological forcing ' , has been detected in observational records of increasing average continental runoff over the twentieth century .
Here we use an ensemble of experiments with a global climate model that includes a vegetation component to assess the contribution of physiological forcing to future changes in continental runoff , in the context of uncertainties in future precipitation .
We find that the physiological effect of doubled carbon dioxide concentrations on plant transpiration increases simulated global mean runoff by 6 per cent relative to pre-industrial levels ; an increase that is comparable to that simulated in response to radiatively forced climate change ( 11 + / - 6 per cent ) .
Assessments of the effect of increasing carbon dioxide concentrations on the hydrological cycle that only consider radiative forcing will therefore tend to underestimate future increases in runoff and overestimate decreases .
This suggests that freshwater resources may be less limited than previously assumed under scenarios of future global warming , although there is still an increased risk of drought .
Moreover , our results highlight that the practice of assessing the climate-forcing potential of all greenhouse gases in terms of their radiative forcing potential relative to carbon dioxide does not accurately reflect the relative effects of different greenhouse gases on freshwater resources .

[125] Biochar and Glomus caledonium Influence Cd Accumulation of Upland Kangkong ( Ipomoea aquatica Forsk . )

Intercropped with Alfred Stonecrop ( Sedum alfredii Hance )
Both biochar application and mycorrhizal inoculation have been proposed to improve plant growth and alter bioaccumulation of toxic metals .
A greenhouse pot trial was conducted to investigate growth and Cd accumulation of upland kangkong ( Ipomoea aquatica Forsk . )
intercropped with Alfred stonecrop ( Sedum alfredii Hance ) in a Cd-contaminated soil inoculated with Glomus caledonium and/or applied with biochar .
Compared with the monocultural control , intercropping with stonecrop ( IS ) decreased kangkong Cd acquisition via rhizosphere competition , and also decreased kangkong yield .
Gc inoculation ( + M ) accelerated growth and Cd acquisition of stonecrop , and hence resulted in further decreases in kangkong Cd acquisition .
Regardless of IS and + M , biochar addition ( + B ) increased kangkong yield via elevating soil available P , and decreased soil Cd phytoavailability and kangkong Cd concentration via increasing soil pH. Compared with the control , the treatment of IS + M + B had a substantially higher kangkong yield ( +25.5 % ) with a lower Cd concentration ( -62.7 % ) .
Gc generated additive effects on soil alkalinization and Cd stabilization to biochar , causing lower DTPA-extractable ( phytoavailable ) Cd concentrations and post-harvest transfer risks .

[126] Cryptic biodiversity loss linked to global climate change

Global climate change ( GCC ) significantly affects distributional patterns of organisms , and considerable impacts on biodiversity are predicted for the next decades .
Inferred effects include large-scale range shifts towards higher altitudes and latitudes , facilitation of biological invasions and species extinctions .
Alterations of biotic patterns caused by GCC have usually been predicted on the scale of taxonomically recognized morphospecies .
However , the effects of climate change at the most fundamental level of biodiversity -- intraspecific genetic diversity -- remain elusive .
Here we show that the use of morphospecies-based assessments of GCC effects will result in underestimations of the true scale of biodiversity loss .
Species distribution modelling and assessments of mitochondrial DNA variability in nine montane aquatic insect species in Europe indicate that future range contractions will be accompanied by severe losses of cryptic evolutionary lineages and genetic diversity within these lineages .
These losses greatly exceed those at the scale of morphospecies .
We also document that the extent of range reduction may be a useful proxy when predicting losses of genetic diversity .
Our results demonstrate that intraspecific patterns of genetic diversity should be considered when estimating the effects of climate change on biodiversity .

[127] Vertical structure of recent Arctic warming

Near-surface warming in the Arctic has been almost twice as large as the global average over recent decades -- a phenomenon that is known as the ` Arctic amplification ' .
The underlying causes of this temperature amplification remain uncertain .
The reduction in snow and ice cover that has occurred over recent decades may have played a role .
Climate model experiments indicate that when global temperature rises , Arctic snow and ice cover retreats , causing excessive polar warming .
Reduction of the snow and ice cover causes albedo changes , and increased refreezing of sea ice during the cold season and decreases in sea-ice thickness both increase heat flux from the ocean to the atmosphere .
Changes in oceanic and atmospheric circulation , as well as cloud cover , have also been proposed to cause Arctic temperature amplification .
Here we examine the vertical structure of temperature change in the Arctic during the late twentieth century using reanalysis data .
We find evidence for temperature amplification well above the surface .
Snow and ice feedbacks can not be the main cause of the warming aloft during the greater part of the year , because these feedbacks are expected to primarily affect temperatures in the lowermost part of the atmosphere , resulting in a pattern of warming that we only observe in spring .
A significant proportion of the observed temperature amplification must therefore be explained by mechanisms that induce warming above the lowermost part of the atmosphere .
We regress the Arctic temperature field on the atmospheric energy transport into the Arctic and find that , in the summer half-year , a significant proportion of the vertical structure of warming can be explained by changes in this variable .
We conclude that changes in atmospheric heat transport may be an important cause of the recent Arctic temperature amplification .

[128] Oceanic nickel depletion and a methanogen famine before the Great Oxidation Event

It has been suggested that a decrease in atmospheric methane levels triggered the progressive rise of atmospheric oxygen , the so-called Great Oxidation Event , about 2.4 Gyr ago .
Oxidative weathering of terrestrial sulphides , increased oceanic sulphate , and the ecological success of sulphate-reducing microorganisms over methanogens has been proposed as a possible cause for the methane collapse , but this explanation is difficult to reconcile with the rock record .
Banded iron formations preserve a history of Precambrian oceanic elemental abundance and can provide insights into our understanding of early microbial life and its influence on the evolution of the Earth system .
Here we report a decline in the molar nickel to iron ratio recorded in banded iron formations about 2.7 Gyr ago , which we attribute to a reduced flux of nickel to the oceans , a consequence of cooling upper-mantle temperatures and decreased eruption of nickel-rich ultramafic rocks at the time .
We measured nickel partition coefficients between simulated Precambrian sea water and diverse iron hydroxides , and subsequently determined that dissolved nickel concentrations may have reached ~ 400 nM throughout much of the Archaean eon , but dropped below ~ 200 nM by 2.5 Gyr ago and to modern day values ( ~ 9 nM ) by ~ 550 Myr ago .
Nickel is a key metal cofactor in several enzymes of methanogens and we propose that its decline would have stifled their activity in the ancient oceans and disrupted the supply of biogenic methane .
A decline in biogenic methane production therefore could have occurred before increasing environmental oxygenation and not necessarily be related to it .
The enzymatic reliance of methanogens on a diminishing supply of volcanic nickel links mantle evolution to the redox state of the atmosphere .

[129] Nitrogen oxide emissions after nitrogen additions in tropical forests

Industrial development and agricultural intensification are projected to increase in the humid tropics over the next few decades , increasing the emissions , transport and deposition of nitrogen-containing compounds .
Most studies of the consequences of enhanced nitrogen deposition have been performed in temperate ecosystems in which biological processes are limited by nitrogen supply ; they indicate that added nitrogen is retained up to decades before losses as nitrogen oxides or as nitrate ( NO3 - ) begin .
We measured soil emissions of two gases that are important in the atmosphere , nitrous oxide ( N2O ) and nitric oxide ( NO ) , after experimental additions of nitrogen in two tropical rainforests of Hawai'i .
Growth of one of the forests was limited by nitrogen ; in the other , nitrogen was abundant and growth was limited by phosphorus , as is more characteristic of most tropical forests .
Here we show that the phosphorus-limited forest lost more nitrogen oxides than the nitrogen-limited forest , and it lost equally large amounts after first-time additions of nitrogen as after chronic , long-term nitrogen additions .
This forest seems to be naturally ` nitrogen saturated ' ; it and perhaps other tropical forests may not retain as much anthropogenic nitrogen as do forests in northern latitudes .

[130] Increased CO2 uncouples growth from isoprene emission in an agriforest ecosystem

The emission of isoprene from the leaves of forest trees is a fundamental component of biosphere-atmosphere interactions , controlling many aspects of photochemistry in the lower atmosphere .
As almost all commercial agriforest species emit high levels of isoprene , proliferation of agriforest plantations has significant potential to increase regional ozone pollution and enhance the lifetime of methane , an important determinant of global climate .
Here we show that growth of an intact Populus deltoides plantation under increased CO2 ( 800 micromol mol-1 and 1,200 micromol mol-1 ) reduced ecosystem isoprene production by 21 % and 41 % , while above-ground biomass accumulation was enhanced by 60 % and 82 % , respectively .
Exposure to increased CO2 significantly reduced the cellular content of dimethylallyl diphosphate , the substrate for isoprene synthesis , in both leaves and leaf protoplasts .
We identify intracellular metabolic competition for phosphoenolpyruvate as a possible control point in explaining the suppression of isoprene emission under increased CO2 .
Our results highlight the potential for uncoupling isoprene emission from biomass accumulation in an agriforest species , and show that negative air-quality effects of proliferating agriforests may be offset by increases in CO2 .

[131] The role of fire in Miocene to Pliocene C4 grassland and ecosystem evolution

Modern savannah grasslands were established during the late Miocene and Pliocene ( 8-3 million years ago ) .
In the tropics , grasslands are dominated by grasses that use the C4 photosynthetic pathway , rather than the C3 pathway .
The C4 pathway is better adapted to warm , dry and low-CO2 conditions , leading to suggestions that declining atmospheric CO2 levels , increasing aridity and enhanced rainfall seasonality allowed grasses using this pathway to expand during this interval .
The role of fire in C4 expansion may have been underestimated .
Here we use analyses of pollen , microscopic charcoal and the stable isotopic composition of plant waxes from a marine sediment core off the coast of Namibia to reconstruct the relative timing of changes in plant composition and fire activity for the late Miocene and Pliocene .
We find that in southwestern Africa , the expansion of C4 grasses occurred alongside increasing aridity and enhanced fire activity .
During further aridification in the Pliocene , the proportion of C4 grasses in the grasslands increased , while the grassland contracted and deserts and semi-deserts expanded .
Our results are consistent with the hypothesis that ecological disturbance by fire was an essential feedback mechanism leading to the establishment of C4 grasslands in the Miocene and Pliocene .

[132] Molecular analysis of phosphate limitation in Geobacteraceae during the bioremediation of a uranium-contaminated aquifer

Nutrient limitation is an environmental stress that may reduce the effectiveness of bioremediation strategies , especially when the contaminants are organic compounds or when organic compounds are added to promote microbial activities such as metal reduction .
Genes indicative of phosphate-limitation were identified by microarray analysis of chemostat cultures of Geobacter sulfureducens .
This analysis revealed that genes in the pst-pho operon , which is associated with a high-affinity phosphate uptake system in other microorganisms , had significantly higher transcript abundance under phosphate-limiting conditions , with the genes pstB and phoU upregulated the most .
Quantitative PCR analysis of pstB and phoU transcript levels in G. sulfurreducens grown in chemostats demonstrated that the expression of these genes increased when phosphate was removed from the culture medium .
Transcripts of pstB and phoU within the subsurface Geobacter species predominating during an in situ uranium-bioremediation field experiment were more abundant than in chemostat cultures of G. sulfurreducens that were not limited for phosphate .
Addition of phosphate to incubations of subsurface sediments did not stimulate dissimilatory metal reduction .
The added phosphate was rapidly adsorbed onto the sediments .
The results demonstrate that Geobacter species can effectively reduce U ( VI ) even when experiencing suboptimal phosphate concentrations and that increasing phosphate availability with phosphate additions is difficult to achieve because of the high reactivity of this compound .
This transcript-based approach developed for diagnosing phosphate limitation should be applicable to assessing the potential need for additional phosphate in other bioremediation processes .

[133] Stabilization of the coupled oxygen and phosphorus cycles by the evolution of bioturbation

Animal burrowing and sediment-mixing ( bioturbation ) began during the run up to the Ediacaran/Cambrian boundary , initiating a transition between the stratified Precambrian and more well-mixed Phanerozoic sedimentary records , against the backdrop of a variable global oxygen reservoir probably smaller in size than present .
Phosphorus is the long-term limiting nutrient for oxygen production via burial of organic carbon , and its retention ( relative to carbon ) within organic matter in marine sediments is enhanced by bioturbation .
Here we explore the biogeochemical implications of a bioturbation-induced organic phosphorus sink in a simple model .
We show that increased bioturbation robustly triggers a net decrease in the size of the global oxygen reservoir -- the magnitude of which is contingent upon the prescribed difference in carbon to phosphorus ratios between bioturbated and laminated sediments .
Bioturbation also reduces steady-state marine phosphate levels , but this effect is offset by the decline in iron-adsorbed phosphate burial that results from a decrease in oxygen concentrations .
The introduction of oxygen-sensitive bioturbation to dynamical model runs is sufficient to trigger a negative feedback loop : the intensity of bioturbation is limited by the oxygen decrease it initially causes .
The onset of this feedback is consistent with redox variations observed during the early Cambrian rise of bioturbation , leading us to suggest that bioturbation helped to regulate early oxygen and phosphorus cycles .

[134] Changes in global nitrogen cycling during the Holocene epoch

Human activities have doubled the pre-industrial supply of reactive nitrogen on Earth , and future rates of increase are expected to accelerate .
Yet little is known about the capacity of the biosphere to buffer increased nitrogen influx .
Past changes in global ecosystems following deglaciation at the end of the Pleistocene epoch provide an opportunity to understand better how nitrogen cycling in the terrestrial biosphere responded to changes in carbon cycling .
We analysed published records of stable nitrogen isotopic values ( delta15N ) in sediments from 86 lakes on six continents .
Here we show that the value of sedimentary delta15N declined from 15,000 years before present to 7,056 + / - 597 years before present , a period of increasing atmospheric carbon dioxide concentrations and terrestrial carbon accumulation .
Comparison of the nitrogen isotope record with concomitant carbon accumulation on land and nitrous oxide in the atmosphere suggests millennia of declining nitrogen availability in terrestrial ecosystems during the Pleistocene-Holocene transition around 11,000 years before present .
In contrast , we do not observe a consistent change in global sedimentary delta15N values during the past 500 years , despite the potential effects of changing temperature and nitrogen influx from anthropogenic sources .
We propose that the lack of a single response may indicate that modern increases in atmospheric carbon dioxide and net carbon sequestration in the biosphere have the potential to offset recent increased supplies of reactive nitrogen in some ecosystems .

[135] High frequency of functional extinctions in ecological networks

Intensified exploitation of natural populations and habitats has led to increased mortality rates and decreased abundances of many species .
There is a growing concern that this might cause critical abundance thresholds of species to be crossed , with extinction cascades and state shifts in ecosystems as a consequence .
When increased mortality rate and decreased abundance of a given species lead to extinction of other species , this species can be characterized as functionally extinct even though it still exists .
Although such functional extinctions have been observed in some ecosystems , their frequency is largely unknown .
Here we use a new modelling approach to explore the frequency and pattern of functional extinctions in ecological networks .
Specifically , we analytically derive critical abundance thresholds of species by increasing their mortality rates until an extinction occurs in the network .
Applying this approach on natural and theoretical food webs , we show that the species most likely to go extinct first is not the one whose mortality rate is increased but instead another species .
Indeed , up to 80 % of all first extinctions are of another species , suggesting that a species ' ecological functionality is often lost before its own existence is threatened .
Furthermore , we find that large-bodied species at the top of the food chains can only be exposed to small increases in mortality rate and small decreases in abundance before going functionally extinct compared to small-bodied species lower in the food chains .
These results illustrate the potential importance of functional extinctions in ecological networks and lend strong support to arguments advocating a more community-oriented approach in conservation biology , with target levels for populations based on ecological functionality rather than on mere persistence .

[136] Co-evolution of eukaryotes and ocean oxygenation in the Neoproterozoic era

The Neoproterozoic era ( about 1,000 to 542 million years ago ) was a time of turbulent environmental change .
Large fluctuations in the carbon cycle were associated with at least two severe -- possible Snowball Earth -- glaciations .
There were also massive changes in the redox state of the oceans , culminating in the oxygenation of much of the deep oceans .
Amid this environmental change , increasingly complex life forms evolved .
The traditional view is that a rise in atmospheric oxygen concentrations led to the oxygenation of the ocean , thus triggering the evolution of animals .
We argue instead that the evolution of increasingly complex eukaryotes , including the first animals , could have oxygenated the ocean without requiring an increase in atmospheric oxygen .
We propose that large eukaryotic particles sank quickly through the water column and reduced the consumption of oxygen in the surface waters .
Combined with the advent of benthic filter feeding , this shifted oxygen demand away from the surface to greater depths and into sediments , allowing oxygen to reach deeper waters .
The decline in bottom-water anoxia would hinder the release of phosphorus from sediments , potentially triggering a potent positive feedback : phosphorus removal from the ocean reduced global productivity and ocean-wide oxygen demand , resulting in oxygenation of the deep ocean .
That , in turn , would have further reinforced eukaryote evolution , phosphorus removal and ocean oxygenation .

[137] Tropical cyclones and climate change

Whether the characteristics of tropical cyclones have changed or will change in a warming climate -- and if so , how -- has been the subject of considerable investigation , often with conflicting results .
Large amplitude fluctuations in the frequency and intensity of tropical cyclones greatly complicate both the detection of long-term trends and their attribution to rising levels of atmospheric greenhouse gases .
Trend detection is further impeded by substantial limitations in the availability and quality of global historical records of tropical cyclones .
Therefore , it remains uncertain whether past changes in tropical cyclone activity have exceeded the variability expected from natural causes .
However , future projections based on theory and high-resolution dynamical models consistently indicate that greenhouse warming will cause the globally averaged intensity of tropical cyclones to shift towards stronger storms , with intensity increases of 2-11 % by 2100 .
Existing modelling studies also consistently project decreases in the globally averaged frequency of tropical cyclones , by 6-34 % .
Balanced against this , higher resolution modelling studies typically project substantial increases in the frequency of the most intense cyclones , and increases of the order of 20 % in the precipitation rate within 100 km of the storm centre .
For all cyclone parameters , projected changes for individual basins show large variations between different modelling studies .

[138] Reduction of soil carbon formation by tropospheric ozone under increased carbon dioxide levels

In the Northern Hemisphere , ozone levels in the troposphere have increased by 35 per cent over the past century , with detrimental impacts on forest and agricultural productivity , even when forest productivity has been stimulated by increased carbon dioxide levels .
In addition to reducing productivity , increased tropospheric ozone levels could alter terrestrial carbon cycling by lowering the quantity and quality of carbon inputs to soils .
However , the influence of elevated ozone levels on soil carbon formation and decomposition are unknown .
Here we examine the effects of elevated ozone levels on the formation rates of total and decay-resistant acid-insoluble soil carbon under conditions of elevated carbon dioxide levels in experimental aspen ( Populus tremuloides ) stands and mixed aspen-birch ( Betula papyrifera ) stands .
With ambient concentrations of ozone and carbon dioxide both raised by 50 per cent , we find that the formation rates of total and acid-insoluble soil carbon are reduced by 50 per cent relative to the amounts entering the soil when the forests were exposed to increased carbon dioxide alone .
Our results suggest that , in a world with elevated atmospheric carbon dioxide concentrations , global-scale reductions in plant productivity due to elevated ozone levels will also lower soil carbon formation rates significantly .

[139] Sensitivity of tropical precipitation extremes to climate change

Precipitation extremes increase in intensity over many regions of the globe in simulations of a warming climate .
The rate of increase of precipitation extremes in the extratropics is consistent across global climate models , but the rate of increase in the tropics varies widely , depending on the model used .
The behaviour of tropical precipitation can , however , be constrained by observations of interannual variability in the current climate .
Here I show that , across state-of-the-art climate models , the response of tropical precipitation extremes to interannual climate variability is strongly correlated with their response to longer-term climate change , although these responses are different .
I then use satellite observations to estimate the response of tropical precipitation extremes to the interannual variability .
Applying this observational constraint to the climate simulations and exploiting the relationship between the simulated responses to interannual variability and climate change , I estimate a sensitivity of the 99.9 th percentile of daily tropical precipitation to climate change at 10 % per K of surface warming , with a 90 % confidence interval of 6-14 % K-1 .
This tropical sensitivity is higher than expectations for the extratropics of about 5 % K-1 .
The inferred percentage increase in tropical precipitation extremes is similar when considering only land regions , where the impacts of extreme precipitation can be severe .

[140] Antibiotics in early life alter the murine colonic microbiome and adiposity

Antibiotics administered in low doses have been widely used as growth promoters in the agricultural industry since the 1950s , yet the mechanisms for this effect are unclear .
Because antimicrobial agents of different classes and varying activity are effective across several vertebrate species , we proposed that such subtherapeutic administration alters the population structure of the gut microbiome as well as its metabolic capabilities .
We generated a model of adiposity by giving subtherapeutic antibiotic therapy to young mice and evaluated changes in the composition and capabilities of the gut microbiome .
Administration of subtherapeutic antibiotic therapy increased adiposity in young mice and increased hormone levels related to metabolism .
We observed substantial taxonomic changes in the microbiome , changes in copies of key genes involved in the metabolism of carbohydrates to short-chain fatty acids , increases in colonic short-chain fatty acid levels , and alterations in the regulation of hepatic metabolism of lipids and cholesterol .
In this model , we demonstrate the alteration of early-life murine metabolic homeostasis through antibiotic manipulation .

[141] Dynamic responses of terrestrial ecosystem carbon cycling to global climate change

Terrestrial ecosystems and the climate system are closely coupled , particularly by cycling of carbon between vegetation , soils and the atmosphere .
It has been suggested , that changes in climate and in atmospheric carbon dioxide concentrations have modified the carbon cycle so as to render terrestrial ecosystems as substantial carbon sinks , ; but direct evidence for this is very limited , .
Changes in ecosystem carbon stocks caused by shifts between stable climate states have been evaluated , , but the dynamic responses of ecosystem carbon fluxes to transient climate changes are still poorly understood .
Here we use a terrestrial biogeochemical model , forced by simulations of transient climate change with a general circulation model , to quantify the dynamic variations in ecosystem carbon fluxes induced by transient changes in atmospheric CO2 and climate from 1861 to 2070 .
Wepredict that these changes increase global net ecosystem production significantly , but that this response will decline as the CO2 fertilization effect becomes saturated and is diminished by changes in climatic factors .
Thus terrestrial ecosystem carbon fluxes both respond to and strongly influence the atmospheric CO2 increase and climate change .

[142] Biogeochemical plant-soil microbe feedback in response to climate warming in peatlands

Peatlands act as global sinks of atmospheric carbon ( C ) through the accumulation of organic matter , primarily made up of decay-resistant litter of peat mosses .
However , climate warming has been shown to promote vascular plant growth in peatlands , especially ericaceous shrubs .
A change in vegetation cover is in turn expected to modify above-ground/below-ground interactions , but the biogeochemical mechanisms involved remain unknown .
Here , by selecting peatlands at different altitudes to simulate a natural gradient of soil temperature , we show that the expansion of ericaceous shrubs with warming is associated with an increase of polyphenol content in both plant litter and pore water .
In turn , this retards the release of nitrogen ( N ) from decomposing litter , increases the amount of dissolved organic N and reduces N immobilization by soil microbes .
A decrease of soil water content with increasing temperature promotes the growth of fungi , which feeds back positively on ericaceous shrubs by facilitating the symbiotic acquisition of dissolved organic N .
We also observed a higher release of labile C from vascular plant roots at higher soil temperatures , which promotes the microbial investment in C-degrading enzymes .
Our data suggest that climate-induced changes in plant cover can reduce the productivity of peat mosses and potentially prime the decomposition of organic matter by affecting the stoichiometry of soil enzymatic activity .

[143] Increasing dominance of large lianas in Amazonian forests

Ecological orthodoxy suggests that old-growth forests should be close to dynamic equilibrium , but this view has been challenged by recent findings that neotropical forests are accumulating carbon and biomass , possibly in response to the increasing atmospheric concentrations of carbon dioxide .
However , it is unclear whether the recent increase in tree biomass has been accompanied by a shift in community composition .
Such changes could reduce or enhance the carbon storage potential of old-growth forests in the long term .
Here we show that non-fragmented Amazon forests are experiencing a concerted increase in the density , basal area and mean size of woody climbing plants ( lianas ) .
Over the last two decades of the twentieth century the dominance of large lianas relative to trees has increased by 1.7-4 .6 % a year .
Lianas enhance tree mortality and suppress tree growth , so their rapid increase implies that the tropical terrestrial carbon sink may shut down sooner than current models suggest .
Predictions of future tropical carbon fluxes will need to account for the changing composition and dynamics of supposedly undisturbed forests .

[144] The impact of climate change on global tropical cyclone damage

One potential impact from greenhouse-gas emissions is increasing damage from extreme events .
Here , we quantify how climate change may affect tropical cyclone damage .
We find that future increases in income are likely to double tropical cyclone damage even without climate change .
Climate change is predicted to increase the frequency of high-intensity storms in selected ocean basins depending on the climate model .
Climate change doubles economic damage , but the result depends on the parameters of the damage function .
Almost all of the tropical cyclone damage from climate change tends to be concentrated in North America , East Asia and the Caribbean-Central American region .
This paper provides a framework to combine atmospheric science and economics , but some effects are not yet modelled , including sea-level rise and adaptation .

[145] Perceptions of climate change and willingness to save energy related to flood experience

One of the reasons that people may not take action to mitigate climate change is that they lack first-hand experience of its potential consequences .
From this perspective , individuals who have direct experience of phenomena that may be linked to climate change would be more likely to be concerned by the issue and thus more inclined to undertake sustainable behaviours .
So far , the evidence available to test this hypothesis is limited , and in part contradictory .
Here we use national survey data collected from 1,822 individuals across the UK in 2010 , to examine the links between direct flooding experience , perceptions of climate change and preparedness to reduce energy use .
We show that those who report experience of flooding express more concern over climate change , see it as less uncertain and feel more confident that their actions will have an effect on climate change .
Importantly , these perceptual differences also translate into a greater willingness to save energy to mitigate climate change .
Highlighting links between local weather events and climate change is therefore likely to be a useful strategy for increasing concern and action .

[146] The decline and fate of an iron-induced subarctic phytoplankton bloom

Iron supply has a key role in stimulating phytoplankton blooms in high-nitrate low-chlorophyll oceanic waters .
However , the fate of the carbon fixed by these blooms , and how efficiently it is exported into the ocean 's interior , remains largely unknown .
Here we report on the decline and fate of an iron-stimulated diatom bloom in the Gulf of Alaska .
The bloom terminated on day 18 , following the depletion of iron and then silicic acid , after which mixed-layer particulate organic carbon ( POC ) concentrations declined over six days .
Increased particulate silica export via sinking diatoms was recorded in sediment traps at depths between 50 and 125 m from day 21 , yet increased POC export was not evident until day 24 .
Only a small proportion of the mixed-layer POC was intercepted by the traps , with more than half of the mixed-layer POC deficit attributable to bacterial remineralization and mesozooplankton grazing .
The depletion of silicic acid and the inefficient transfer of iron-increased POC below the permanent thermocline have major implications both for the biogeochemical interpretation of times of greater iron supply in the geological past , and also for proposed geo-engineering schemes to increase oceanic carbon sequestration .

[147] Holocene oscillations in temperature and salinity of the surface subpolar North Atlantic

The Atlantic meridional overturning circulation ( AMOC ) transports warm salty surface waters to high latitudes , where they cool , sink and return southwards at depth .
Through its attendant meridional heat transport , the AMOC helps maintain a warm northwestern European climate , and acts as a control on the global climate .
Past climate fluctuations during the Holocene epoch ( ~ 11,700 years ago to the present ) have been linked with changes in North Atlantic Ocean circulation .
The behaviour of the surface flowing salty water that helped drive overturning during past climatic changes is , however , not well known .
Here we investigate the temperature and salinity changes of a substantial surface inflow to a region of deep-water formation throughout the Holocene .
We find that the inflow has undergone millennial-scale variations in temperature and salinity ( ~ 3.5 degreesC and ~ 1.5 practical salinity units , respectively ) most probably controlled by subpolar gyre dynamics .
The temperature and salinity variations correlate with previously reported periods of rapid climate change .
The inflow becomes more saline during enhanced freshwater flux to the subpolar North Atlantic .
Model studies predict a weakening of AMOC in response to enhanced Arctic freshwater fluxes , although the inflow can compensate on decadal timescales by becoming more saline .
Our data suggest that such a negative feedback mechanism may have operated during past intervals of climate change .

[148] Divergent global precipitation changes induced by natural versus anthropogenic forcing

As a result of global warming , precipitation is likely to increase in high latitudes and the tropics and to decrease in already dry subtropical regions .
The absolute magnitude and regional details of such changes , however , remain intensely debated .
As is well known from El Nino studies , sea-surface-temperature gradients across the tropical Pacific Ocean can strongly influence global rainfall .
Palaeoproxy evidence indicates that the difference between the warm west Pacific and the colder east Pacific increased in past periods when the Earth warmed as a result of increased solar radiation .
In contrast , in most model projections of future greenhouse warming this gradient weakens .
It has not been clear how to reconcile these two findings .
Here we show in climate model simulations that the tropical Pacific sea-surface-temperature gradient increases when the warming is due to increased solar radiation and decreases when it is due to increased greenhouse-gas forcing .
For the same global surface temperature increase the latter pattern produces less rainfall , notably over tropical land , which explains why in the model the late twentieth century is warmer than in the Medieval Warm Period ( around ad 1000-1250 ) but precipitation is less .
This difference is consistent with the global tropospheric energy budget , which requires a balance between the latent heat released in precipitation and radiative cooling .
The tropospheric cooling is less for increased greenhouse gases , which add radiative absorbers to the troposphere , than for increased solar heating , which is concentrated at the Earth 's surface .
Thus warming due to increased greenhouse gases produces a climate signature different from that of warming due to solar radiation changes .

[149] Changes in deep-water formation during the Younger Dryas event inferred from 10Be and 14C records

Variations in atmospheric radiocarbon ( 14C ) concentrations can be attributed either to changes in the carbon cycle -- through the rate of radiocarbon removal from the atmosphere -- or to variations in the production rate of 14C due to changes in solar activity or the Earth 's magnetic field .
The production rates of 10Be and 14C vary in the same way , but whereas atmospheric radiocarbon concentrations are additionally affected by the carbon cycle , 10Be concentrations reflect production rates more directly .
A record of the 10Be production-rate variations can therefore be used to separate the two influences -- production rates and the carbon cycle -- on radiocarbon concentrations .
Here we present such an analysis of the large fluctuations in atmospheric 14C concentrations , of unclear origin , that occurred during the Younger Dryas cold period .
We use the 10Be record from the GISP2 ice core to model past production rates of radionuclides , and find that the largest part of the fluctuations in atmospheric radiocarbon concentrations can be attributed to variations in production rate .
The residual difference between measured 14C concentrations and those modelled using the 10Be record can be explained with an additional change in the carbon cycle , most probably in the amount of deep-water formation .

[150] Global imprint of climate change on marine life

Past meta-analyses of the response of marine organisms to climate change have examined a limited range of locations , taxonomic groups and/or biological responses .
This has precluded a robust overview of the effect of climate change in the global ocean .
Here , we synthesized all available studies of the consistency of marine ecological observations with expectations under climate change .
This yielded a meta-database of 1,735 marine biological responses for which either regional or global climate change was considered as a driver .
Included were instances of marine taxa responding as expected , in a manner inconsistent with expectations , and taxa demonstrating no response .
From this database , 81-83 % of all observations for distribution , phenology , community composition , abundance , demography and calcification across taxa and ocean basins were consistent with the expected impacts of climate change .
Of the species responding to climate change , rates of distribution shifts were , on average , consistent with those required to track ocean surface temperature changes .
Conversely , we did not find a relationship between regional shifts in spring phenology and the seasonality of temperature .
Rates of observed shifts in species ' distributions and phenology are comparable to , or greater , than those for terrestrial systems .

[151] A potential loss of carbon associated with greater plant growth in the European Arctic

Rapid warming is expected to increase plant growth in the Arctic , and result in trees gradually colonizing tundra .
Models predict that enhanced carbon ( C ) storage in plant biomass may help offset atmospheric CO2 increases and reduce rates of climate change .
However , in some Arctic ecosystems , high plant productivity is associated with rapid cycling and low storage of soil C ( refs , , ) ; thus , as plant growth increases , soil C may be lost through enhanced decomposition .
Here we show that , in northern Sweden , total ecosystem C storage is greater in tundra heath ( owing to greater soil C stocks ) than in more productive mountain-birch forest .
Furthermore , we demonstrate that in the forest , high plant activity during the middle of the growing season stimulates the decomposition of older soil organic matter .
Such a response , referred to as positive priming , helps explain the low soil C storage in the forest when compared with the tundra .
We suggest that , as more productive forest communities colonize tundra , the decomposition of the large C stocks in tundra soils could be stimulated .
Thus , counter-intuitively , increased plant growth in the European Arctic could result in C being released to the atmosphere , accelerating climate change .

[152] No increase in global temperature variability despite changing regional patterns

Evidence from Greenland ice cores shows that year-to-year temperature variability was probably higher in some past cold periods , but there is considerable interest in determining whether global warming is increasing climate variability at present .
This interest is motivated by an understanding that increased variability and resulting extreme weather conditions may be more difficult for society to adapt to than altered mean conditions .
So far , however , in spite of suggestions of increased variability , there is considerable uncertainty as to whether it is occurring .
Here we show that although fluctuations in annual temperature have indeed shown substantial geographical variation over the past few decades , the time-evolving standard deviation of globally averaged temperature anomalies has been stable .
A feature of the changes has been a tendency for many regions of low variability to experience increases , which might contribute to the perception of increased climate volatility .
The normalization of temperature anomalies creates the impression of larger relative overall increases , but our use of absolute values , which we argue is a more appropriate approach , reveals little change .
Regionally , greater year-to-year changes recently occurred in much of North America and Europe .
Many climate models predict that total variability will ultimately decrease under high greenhouse gas concentrations , possibly associated with reductions in sea-ice cover .
Our findings contradict the view that a warming world will automatically be one of more overall climatic variation .

[153] Correlation of patterns of denitrification instability in replicated bioreactor communities with shifts in the relative abundance and the denitrification patterns of specific populations

To assess the effects of community structure on the stability of denitrification , six chemostat cultures derived from the same denitrifying community were subjected to step increases in feed nitrate concentration and monitored for evidence that denitrification was either not occurring ( indicated by the presence of nitrate ) or was incomplete ( indicated by the presence of nitrite or nitrous oxide ) .
Functional stability was defined and quantified from the pattern of effluent concentration trends of nitrate and denitrification intermediates .
Microbial community structure and dynamics were analyzed by terminal restriction fragment length polymorphism analysis of the 16S rRNA gene .
Functional stability varied : one chemostat community lost the ability to reduce all of the influent nitrate ; others continued to reduce all of the influent nitrate , but accumulated varying amounts of nitrous oxide .
The microbial community structure in two of the chemostats diverged from the others , and variation of functional response among chemostats corresponded with the divergence of community structure .
The Acidovorax-like terminal restriction fragment ( T-RF ) dominated the chemostat that accumulated nitrate , and an Acidovorax-like isolate reduced nitrate directly to dinitrogen gas in batch nitrate reduction assays .
In the nitrous oxide-accumulating chemostats , the relative abundance of the Pseudomonas-like T-RF was strongly and significantly correlated with the magnitude of nitrous oxide accumulation , and a Pseudomonas-like isolate accumulated nitrous oxide in batch assays .

[154] Variance in ecological consumer-resource interactions

Food-web models use the effect size of trophic interactions to predict consumer-resource dynamics .
These models anticipate that strong effects of consumers increase spatial and temporal variability in abundance of species , whereas weak effects dampen fluctuations .
Empirical evidence indicates that opposite patterns may occur in natural assemblages .
Here I show that spatial variance in the distribution of resource populations is sensitive to changes in the variance of the trophic interaction , in addition to the mean effect of consumers , relative to other causes of spatial variability .
Simulations indicate that both strong and weak direct effects of consumers can promote spatial variability in abundance of resources , but only trophic interactions with a large mean effect size can reduce variation .
Predictions of the model agree with the results of repeated field experiments and are consistent with data from published consumer-resource interactions , proving to be robust across widely varying environmental conditions and species ' life histories .
Thus , food-web models that embody variance in trophic interactions may have increased capacity to explain the wide range of effects of consumers documented in empirical studies .

[155] Characterization of NaCl tolerance in Desulfovibrio vulgaris Hildenborough through experimental evolution

Desulfovibrio vulgaris Hildenborough strains with significantly increased tolerance to NaCl were obtained via experimental evolution .
A NaCl-evolved strain , ES9-11 , isolated from a population cultured for 1200 generations in medium amended with 100 mM NaCl , showed better tolerance to NaCl than a control strain , EC3-10 , cultured for 1200 generations in parallel but without NaCl amendment in medium .
To understand the NaCl adaptation mechanism in ES9-11 , we analyzed the transcriptional , metabolite and phospholipid fatty acid ( PLFA ) profiles of strain ES9-11 with 0 , 100 - or 250 mM-added NaCl in medium compared with the ancestral strain and EC3-10 as controls .
In all the culture conditions , increased expressions of genes involved in amino-acid synthesis and transport , energy production , cation efflux and decreased expression of flagellar assembly genes were detected in ES9-11 .
Consistently , increased abundances of organic solutes and decreased cell motility were observed in ES9-11 .
Glutamate appears to be the most important osmoprotectant in D. vulgaris under NaCl stress , whereas , other organic solutes such as glutamine , glycine and glycine betaine might contribute to NaCl tolerance under low NaCl concentration only .
Unsaturation indices of PLFA significantly increased in ES9-11 .
Branched unsaturated PLFAs i17 :1 omega9c , a17 :1 omega9c and branched saturated i15 :0 might have important roles in maintaining proper membrane fluidity under NaCl stress .
Taken together , these data suggest that the accumulation of osmolytes , increased membrane fluidity , decreased cell motility and possibly an increased exclusion of Na + contribute to increased NaCl tolerance in NaCl-evolved D. vulgaris .

[156] The limits to tree height

Trees grow tall where resources are abundant , stresses are minor , and competition for light places a premium on height growth .
The height to which trees can grow and the biophysical determinants of maximum height are poorly understood .
Some models predict heights of up to 120 m in the absence of mechanical damage , but there are historical accounts of taller trees .
Current hypotheses of height limitation focus on increasing water transport constraints in taller trees and the resulting reductions in leaf photosynthesis .
We studied redwoods ( Sequoia sempervirens ) , including the tallest known tree on Earth ( 112.7 m ) , in wet temperate forests of northern California .
Our regression analyses of height gradients in leaf functional characteristics estimate a maximum tree height of 122-130 m barring mechanical damage , similar to the tallest recorded trees of the past .
As trees grow taller , increasing leaf water stress due to gravity and path length resistance may ultimately limit leaf expansion and photosynthesis for further height growth , even with ample soil moisture .

[157] Human contribution to more-intense precipitation extremes

Extremes of weather and climate can have devastating effects on human society and the environment .
Understanding past changes in the characteristics of such events , including recent increases in the intensity of heavy precipitation events over a large part of the Northern Hemisphere land area , is critical for reliable projections of future changes .
Given that atmospheric water-holding capacity is expected to increase roughly exponentially with temperature -- and that atmospheric water content is increasing in accord with this theoretical expectation -- it has been suggested that human-influenced global warming may be partly responsible for increases in heavy precipitation .
Because of the limited availability of daily observations , however , most previous studies have examined only the potential detectability of changes in extreme precipitation through model-model comparisons .
Here we show that human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land areas .
These results are based on a comparison of observed and multi-model simulated changes in extreme precipitation over the latter half of the twentieth century analysed with an optimal fingerprinting technique .
Changes in extreme precipitation projected by models , and thus the impacts of future changes in extreme precipitation , may be underestimated because models seem to underestimate the observed increase in heavy precipitation with warming .

[158] Committed terrestrial ecosystem changes due to climate change

Targets for stabilizing climate change are often based on considerations of the impacts of different levels of global warming , usually assessing the time of reaching a particular level of warming .
However , some aspects of the Earth system , such as global mean temperatures and sea level rise due to thermal expansion or the melting of large ice sheets , continue to respond long after the stabilization of radiative forcing .
Here we use a coupled climate-vegetation model to show that in turn the terrestrial biosphere shows significant inertia in its response to climate change .
We demonstrate that the global terrestrial biosphere can continue to change for decades after climate stabilization .
We suggest that ecosystems can be committed to long-term change long before any response is observable : for example , we find that the risk of significant loss of forest cover in Amazonia rises rapidly for a global mean temperature rise above 2 degreesC .
We conclude that such committed ecosystem changes must be considered in the definition of dangerous climate change , and subsequent policy development to avoid it .

[159] Projected response of an endangered marine turtle population to climate change

Assessing the potential impacts of climate change on individual species and populations is essential for the stewardship of ecosystems and biodiversity .
Critically endangered leatherback turtles in the eastern Pacific Ocean are excellent candidates for such an assessment because their sensitivity to contemporary climate variability has been substantially studied .
If incidental fisheries mortality is eliminated , this population still faces the challenge of recovery in a rapidly changing climate .
Here we combined an Earth system model , climate model projections assessed by the Intergovernmental Panel on Climate Change and a population dynamics model to estimate a 7 % per decade decline in the Costa Rica nesting population over the twenty-first century .
Whereas changes in ocean conditions had a small effect on the population , the ~ 2.5 degreesC warming of the nesting beach was the primary driver of the decline through reduced hatching success and hatchling emergence rate .
Hatchling sex ratio did not substantially change .
Adjusting nesting phenology or changing nesting sites may not entirely prevent the decline , but could offset the decline rate .
However , if future observations show a long-term decline in hatching success and emergence rate , anthropogenic climate mitigation of nests ( for example , shading , irrigation ) may be able to preserve the nesting population .

[160] Predicted habitat shifts of Pacific top predators in a changing climate

To manage marine ecosystems proactively , it is important to identify species at risk and habitats critical for conservation .
Climate change scenarios have predicted an average sea surface temperature ( SST ) rise of 1-6 degreesC by 2100 ( refs , ) , which could affect the distribution and habitat of many marine species .
Here we examine top predator distribution and diversity in the light of climate change using a database of 4,300 electronic tags deployed on 23 marine species from the Tagging of Pacific Predators project , and output from a global climate model to 2100 .
On the basis of models of observed species distribution as a function of SST , chlorophyll a and bathymetry , we project changes in species-specific core habitat and basin-scale patterns of biodiversity .
We predict up to a 35 % change in core habitat for some species , significant differences in rates and patterns of habitat change across guilds , and a substantial northward displacement of biodiversity across the North Pacific .
For already stressed species , increased migration times and loss of pelagic habitat could exacerbate population declines or inhibit recovery .
The impending effects of climate change stress the urgency of adaptively managing ecosystems facing multiple threats .

[161] Climate and human influences on global biomass burning over the past two millennia

Large , well-documented wildfires have recently generated worldwide attention , and raised concerns about the impacts of humans and climate change on wildfire regimes .
However , comparatively little is known about the patterns and driving forces of global fire activity before the twentieth century .
Here we compile sedimentary charcoal records spanning six continents to document trends in both natural and anthropogenic biomass burning for the past two millennia .
We find that global biomass burning declined from AD 1 to ~ 1750 , before rising sharply between 1750 and 1870 .
Global burning then declined abruptly after 1870 .
The early decline in biomass burning occurred in concert with a global cooling trend and despite a rise in the human population .
We suggest the subsequent rise was linked to increasing human influences , such as population growth and land-use changes .
Our compilation suggests that the final decline occurred despite increasing air temperatures and population .
We attribute this reduction in the amount of biomass burned over the past 150 years to the global expansion of intensive grazing , agriculture and fire management .

[162] Chlamydomonas reinhardtii thermal tolerance enhancement mediated by a mutualistic interaction with vitamin B12-producing bacteria

Temperature is one of the most important environmental factors affecting the growth and survival of microorganisms and in light of current global patterns is of particular interest .
Here , we highlight studies revealing how vitamin B12 ( cobalamin ) - producing bacteria increase the fitness of the unicellular alga Chlamydomonas reinhardtii following an increase in environmental temperature .
Heat stress represses C. reinhardtii cobalamin-independent methionine synthase ( METE ) gene expression coinciding with a reduction in METE-mediated methionine synthase activity , chlorosis and cell death during heat stress .
However , in the presence of cobalamin-producing bacteria or exogenous cobalamin amendments C. reinhardtii cobalamin-dependent methionine synthase METH-mediated methionine biosynthesis is functional at temperatures that result in C. reinhardtii death in the absence of cobalamin .
Artificial microRNA silencing of C. reinhardtii METH expression leads to nearly complete loss of cobalamin-mediated enhancement of thermal tolerance .
This suggests that methionine biosynthesis is an essential cellular mechanism for adaptation by C. reinhardtii to thermal stress .
Increased fitness advantage of METH under environmentally stressful conditions could explain the selective pressure for retaining the METH gene in algae and the apparent independent loss of the METE gene in various algal species .
Our results show that how an organism acclimates to a change in its abiotic environment depends critically on co-occurring species , the nature of that interaction , and how those species interactions evolve .

[163] Climate impacts on bird and plant communities from altered animal-plant interactions

The contribution of climate change to declining populations of organisms remains a question of outstanding concern .
Much attention to declining populations has focused on how changing climate drives phenological mismatches between animals and their food .
Effects of climate on plant communities may provide an alternative , but particularly powerful , influence on animal populations because plants provide their habitats .
Here , we show that abundances of deciduous trees and associated songbirds have declined with decreasing snowfall over 22 years of study in montane Arizona , USA .
We experimentally tested the hypothesis that declining snowfall indirectly influences plants and associated birds by allowing greater over-winter herbivory by elk ( Cervus canadensis ) .
We excluded elk from one of two paired snowmelt drainages ( 10 ha per drainage ) , and replicated this paired experiment across three distant canyons .
Over six years , we reversed multi-decade declines in plant and bird populations by experimentally inhibiting heavy winter herbivory associated with declining snowfall .
Moreover , predation rates on songbird nests decreased in exclosures , despite higher abundances of nest predators , demonstrating the over-riding importance of habitat quality to avian recruitment .
Thus , our results suggest that climate impacts on plant-animal interactions can have forceful ramifying effects on plants , birds , and ecological interactions .

[164] Linking soil bacterial biodiversity and soil carbon stability

Native soil carbon ( C ) can be lost in response to fresh C inputs , a phenomenon observed for decades yet still not understood .
Using dual-stable isotope probing , we show that changes in the diversity and composition of two functional bacterial groups occur with this ` priming ' effect .
A single-substrate pulse suppressed native soil C loss and reduced bacterial diversity , whereas repeated substrate pulses stimulated native soil C loss and increased diversity .
Increased diversity after repeated C amendments contrasts with resource competition theory , and may be explained by increased predation as evidenced by a decrease in bacterial 16S rRNA gene copies .
Our results suggest that biodiversity and composition of the soil microbial community change in concert with its functioning , with consequences for native soil C stability .

[165] Eco-evolutionary responses of biodiversity to climate change

Climate change is predicted to alter global species diversity , the distribution of human pathogens and ecosystem services .
Forecasting these changes and designing adequate management of future ecosystem services will require predictive models encompassing the most fundamental biotic responses .
However , most present models omit important processes such as evolution and competition .
Here we develop a spatially explicit eco-evolutionary model of multi-species responses to climate change .
We demonstrate that both dispersal and evolution differentially mediate extinction risks and biodiversity alterations through time and across climate gradients .
Together , high genetic variance and low dispersal best minimized extinction risks .
Surprisingly , high dispersal did not reduce extinctions , because the shifting ranges of some species hastened the decline of others .
Evolutionary responses dominated during the later stages of climatic changes and in hot regions .
No extinctions occurred without competition , which highlights the importance of including species interactions in global biodiversity models .
Most notably , climate change created extinction and evolutionary debts , with changes in species richness and traits occurring long after climate stabilization .
Therefore , even if we halt anthropogenic climate change today , transient eco-evolutionary dynamics would ensure centuries of additional alterations in global biodiversity .

[166] Long-term ocean oxygen depletion in response to carbon dioxide emissions from fossil fuels

Ongoing global warming could persist far into the future , because natural processes require decades to hundreds of thousands of years to remove carbon dioxide from fossil-fuel burning from the atmosphere .
Future warming may have large global impacts including ocean oxygen depletion and associated adverse effects on marine life , such as more frequent mortality events , but long , comprehensive simulations of these impacts are currently not available .
Here we project global change over the next 100,000 years using a low-resolution Earth system model , and find severe , long-term ocean oxygen depletion , as well as a great expansion of ocean oxygen-minimum zones for scenarios with high emissions or high climate sensitivity .
We find that climate feedbacks within the Earth system amplify the strength and duration of global warming , ocean heating and oxygen depletion .
Decreased oxygen solubility from surface-layer warming accounts for most of the enhanced oxygen depletion in the upper 500 m of the ocean .
Possible weakening of ocean overturning and convection lead to further oxygen depletion , also in the deep ocean .
We conclude that substantial reductions in fossil-fuel use over the next few generations are needed if extensive ocean oxygen depletion for thousands of years is to be avoided .

[167] Mass and volume contributions to twentieth-century global sea level rise

The rate of twentieth-century global sea level rise and its causes are the subjects of intense controversy .
Most direct estimates from tide gauges give 1.5-2 .0 mm yr-1 , whereas indirect estimates based on the two processes responsible for global sea level rise , namely mass and volume change , fall far below this range .
Estimates of the volume increase due to ocean warming give a rate of about 0.5 mm yr-1 ( ref .
8 ) and the rate due to mass increase , primarily from the melting of continental ice , is thought to be even smaller .
Therefore , either the tide gauge estimates are too high , as has been suggested recently , or one ( or both ) of the mass and volume estimates is too low .
Here we present an analysis of sea level measurements at tide gauges combined with observations of temperature and salinity in the Pacific and Atlantic oceans close to the gauges .
We find that gauge-determined rates of sea level rise , which encompass both mass and volume changes , are two to three times higher than the rates due to volume change derived from temperature and salinity data .
Our analysis supports earlier studies that put the twentieth-century rate in the 1.5-2 .0 mm yr-1 range , but more importantly it suggests that mass increase plays a larger role than ocean warming in twentieth-century global sea level rise .

[168] Increased marine production of N2O due to intensifying anoxia on the Indian continental shelf

Eutrophication of surface waters and hypoxia in bottom waters has been increasing in many coastal areas , leading to very large depletions of marine life in the affected regions .
These areas of high surface productivity and low bottom-water oxygen concentration are caused by increasing runoff of nutrients from land .
Although the local ecological and socio-economic effects have received much attention , the potential contribution of increasing hypoxia to global-change phenomena is unknown .
Here we report the intensification of one of the largest low-oxygen zones in the ocean , which develops naturally over the western Indian continental shelf during late summer and autumn .
We also report the highest accumulations yet observed of hydrogen sulphide ( H2S ) and nitrous oxide ( N 2O ) in open coastal waters .
Increased N2O production is probably caused by the addition of anthropogenic nitrate and its subsequent denitrification , which is favoured by hypoxic conditions .
We suggest that a global expansion of hypoxic zones may lead to an increase in marine production and emission of N2O , which , as a potent greenhouse gas , could contribute significantly to the accumulation of radiatively active trace gases in the atmosphere .

[169] Functional responses of prokaryotes and viruses to grazer effects and nutrient additions in freshwater microcosms

For aquatic systems , there is little data on the interactions between viruses , prokaryotes , grazers and the availability of resources .
We conducted a microcosm experiment using a size fractionation approach to manipulate grazers , with a purpose to examine the effects of inorganic and organic nutrients on viral and prokaryotic standing stocks and activities , and on prokaryotic community composition as assessed by fluorescent in situ hybridization ( FISH ) method .
Experiments were performed during periods of severe phosphate ( P ) - limiting conditions in the oligotrophic Sep Reservoir ( Massif Central , France ) .
In the absence of nutrient addition , the presence of grazers in microcosms stimulated prokaryotic growth and viral proliferation , likely through nutrient and substrate enrichment .
Addition of nutrients had a stronger effect on viral infection of prokaryotes than grazing .
Addition of P led to the most pronounced increase in prokaryotic abundance , production and growth efficiency , thus providing direct evidence of P limitation of prokaryotes .
Enhanced prokaryotic activity in P treatments also stimulated viral abundance and viral-induced lyses of prokaryotes .
Changes in prokaryotic community composition due to nutrient additions were evident in the grazer-free samples .
Prokaryotic populations hybridizing for the probes bacteria , beta-Proteobacteria and alpha-Proteobacteria responded to nutrient enrichment with significant increases in their relative abundances , whereas cells hybridizing for Archaea and Cytophaga-Flavobacterium ( now known as Bacteroidetes ) probes failed to show any functional response .
Cells hybridizing for the latter cluster increased towards the end of incubation period in the control samples ( that is , without nutrient additions ) with grazers present , suggesting the development of grazing resistant forms .
From our nutrient enrichment microcosm experiments , we conclude that the presence of grazers is a stimulating factor for prokaryotic growth and viral proliferation in the plankton , probably through nutrient regeneration process .

[170] Low interannual variability in recent oceanic uptake of atmospheric carbon dioxide

An improved understanding of the partitioning of carbon between the atmosphere , terrestrial biosphere , and ocean allows for more accurate predictions of future atmospheric CO2 concentrations under various fossil-fuel CO2-emission scenarios .
One of the more poorly quantified relevant processes is the interannual variability in the uptake of fossil-fuel CO2 from the atmosphere by the terrestrial biosphere and ocean .
Existing estimates , based on atmospheric measurements , indicate that the oceanic variability is large .
Here we estimate the interannual variability in global net air-sea CO2 flux using changes in the observed wind speeds and the partial pressure of CO2 ( p CO2 ) in surface sea water and the overlying air .
Changes in seawater p CO2 are deduced from interannual anomalies in sea surface temperature and the regionally and seasonally varying temperature-dependence of seawater p CO2 , assuming that variations in sea surface temperature reflect seawater p CO2 changes caused by thermodynamics , biological processes and water mixing .
The calculated interannual variability in oceanic CO2 uptake of 0.4 Gt C yr-1 ( 2sigma ) is much less than that inferred from the analysis of atmospheric measurements .
Our results suggest that variable sequestration of carbon by the terrestrial biosphere is the main cause of observed year-to-year variations in the rate of atmospheric CO2 accumulation .

[171] Grassland species loss resulting from reduced niche dimension

Intact ecosystems contain large numbers of competing but coexisting species .
Although numerous alternative theories have provided potential explanations for this high biodiversity , there have been few field experiments testing between these theories .
In particular , theory predicts that higher diversity of coexisting competitors could result from greater niche dimensionality , for example larger numbers of limiting resources or factors .
Alternatively , diversity could be independent of niche dimensionality because large numbers of species can coexist when limited by just one or two factors if species have appropriate trade-offs .
Here we show that plant coexistence and diversity result from the ` niche dimensionality ' of a habitat .
Plant species numbers decreased with increasing numbers of added limiting soil resources ( soil moisture , nitrogen , phosphorus and base cations ) , which is consistent with theoretical predictions that an increased supply of multiple limiting resources can reduce niche dimension .
An observational field study gave similar results .
The niche dimension hypothesis also explained diversity changes in the classic Park Grass Experiment at Rothamsted .
Our results provide an alternative mechanistic explanation for the effects of nutrient eutrophication on the diversity of terrestrial , freshwater and marine ecosystems .

[172] Long-term warming restructures Arctic tundra without changing net soil carbon storage

High latitudes contain nearly half of global soil carbon , prompting interest in understanding how the Arctic terrestrial carbon balance will respond to rising temperatures .
Low temperatures suppress the activity of soil biota , retarding decomposition and nitrogen release , which limits plant and microbial growth .
Warming initially accelerates decomposition , increasing nitrogen availability , productivity and woody-plant dominance .
However , these responses may be transitory , because coupled abiotic-biotic feedback loops that alter soil-temperature dynamics and change the structure and activity of soil communities , can develop .
Here we report the results of a two-decade summer warming experiment in an Alaskan tundra ecosystem .
Warming increased plant biomass and woody dominance , indirectly increased winter soil temperature , homogenized the soil trophic structure across horizons and suppressed surface-soil-decomposer activity , but did not change total soil carbon or nitrogen stocks , thereby increasing net ecosystem carbon storage .
Notably , the strongest effects were in the mineral horizon , where warming increased decomposer activity and carbon stock : a ` biotic awakening ' at depth .

[173] Evolution and forcing mechanisms of El Nino over the past 21,000 years

The El Nino Southern Oscillation ( ENSO ) is Earth 's dominant source of interannual climate variability , but its response to global warming remains highly uncertain .
To improve our understanding of ENSO 's sensitivity to external climate forcing , it is paramount to determine its past behaviour by using palaeoclimate data and model simulations .
Palaeoclimate records show that ENSO has varied considerably since the Last Glacial Maximum ( 21,000 years ago ) , and some data sets suggest a gradual intensification of ENSO over the past ~ 6,000 years .
Previous attempts to simulate the transient evolution of ENSO have relied on simplified models or snapshot experiments .
Here we analyse a series of transient Coupled General Circulation Model simulations forced by changes in greenhouse gasses , orbital forcing , the meltwater discharge and the ice-sheet history throughout the past 21,000 years .
Consistent with most palaeo-ENSO reconstructions , our model simulates an orbitally induced strengthening of ENSO during the Holocene epoch , which is caused by increasing positive ocean-atmosphere feedbacks .
During the early deglaciation , ENSO characteristics change drastically in response to meltwater discharges and the resulting changes in the Atlantic Meridional Overturning Circulation and equatorial annual cycle .
Increasing deglacial atmospheric CO2 concentrations tend to weaken ENSO , whereas retreating glacial ice sheets intensify ENSO .
The complex evolution of forcings and ENSO feedbacks and the uncertainties in the reconstruction further highlight the challenge and opportunity for constraining future ENSO responses .

[174] Methylation of ribosomal RNA by NSUN5 is a conserved mechanism modulating organismal lifespan

Several pathways modulating longevity and stress resistance converge on translation by targeting ribosomal proteins or initiation factors , but whether this involves modifications of ribosomal RNA is unclear .
Here , we show that reduced levels of the conserved RNA methyltransferase NSUN5 increase the lifespan and stress resistance in yeast , worms and flies .
Rcm1 , the yeast homologue of NSUN5 , methylates C2278 within a conserved region of 25S rRNA .
Loss of Rcm1 alters the structural conformation of the ribosome in close proximity to C2278 , as well as translational fidelity , and favours recruitment of a distinct subset of oxidative stress-responsive mRNAs into polysomes .
Thus , rather than merely being a static molecular machine executing translation , the ribosome exhibits functional diversity by modification of just a single rRNA nucleotide , resulting in an alteration of organismal physiological behaviour , and linking rRNA-mediated translational regulation to modulation of lifespan , and differential stress response .

[175] Climate change decreases aquatic ecosystem productivity of Lake Tanganyika , Africa

Although the effects of climate warming on the chemical and physical properties of lakes have been documented , biotic and ecosystem-scale responses to climate change have been only estimated or predicted by manipulations and models .
Here we present evidence that climate warming is diminishing productivity in Lake Tanganyika , East Africa .
This lake has historically supported a highly productive pelagic fishery that currently provides 25-40 % of the animal protein supply for the populations of the surrounding countries .
In parallel with regional warming patterns since the beginning of the twentieth century , a rise in surface-water temperature has increased the stability of the water column .
A regional decrease in wind velocity has contributed to reduced mixing , decreasing deep-water nutrient upwelling and entrainment into surface waters .
Carbon isotope records in sediment cores suggest that primary productivity may have decreased by about 20 % , implying a roughly 30 % decrease in fish yields .
Our study provides evidence that the impact of regional effects of global climate change on aquatic ecosystem functions and services can be larger than that of local anthropogenic activity or overfishing .

[176] Equatorial refuge amid tropical warming

Upwelling across the tropical Pacific Ocean is projected to weaken in accordance with a reduction of the atmospheric overturning circulation , enhancing the increase in sea surface temperature relative to other regions in response to greenhouse-gas forcing .
In the central Pacific , home to one of the largest marine protected areas and fishery regions in the global tropics , sea surface temperatures are projected to increase by 2.8 degreesC by the end of this century .
Of critical concern is that marine protected areas may not provide refuge from the anticipated rate of large-scale warming , which could exceed the evolutionary capacity of coral and their symbionts to adapt .
Combining high-resolution satellite measurements , an ensemble of global climate models and an eddy-resolving regional ocean circulation model , we show that warming and productivity decline around select Pacific islands will be mitigated by enhanced upwelling associated with a strengthening of the equatorial undercurrent .
Enhanced topographic upwelling will act as a negative feedback , locally mitigating the surface warming .
At the Gilbert Islands , the rate of warming will be reduced by 0.7 + / -0.3 degreesC or 25 + / - 9 % per century , or an overall cooling effect comparable to the local anomaly for a typical El Nino , by the end of this century .
As the equatorial undercurrent is dynamically constrained to the Equator , only a handful of coral reefs stand to benefit from this equatorial island effect .
Nevertheless , those that do face a lower rate of warming , conferring a significant advantage over neighbouring reef systems .
If realized , these predictions help to identify potential refuges for coral reef communities from anticipated climate changes of the twenty-first century .

[177] Widespread decline of Congo rainforest greenness in the past decade

Tropical forests are global epicentres of biodiversity and important modulators of climate change , and are mainly constrained by rainfall patterns .
The severe short-term droughts that occurred recently in Amazonia have drawn attention to the vulnerability of tropical forests to climatic disturbances .
The central African rainforests , the second-largest on Earth , have experienced a long-term drying trend whose impacts on vegetation dynamics remain mostly unknown because in situ observations are very limited .
The Congolese forest , with its drier conditions and higher percentage of semi-evergreen trees , may be more tolerant to short-term rainfall reduction than are wetter tropical forests , but for a long-term drought there may be critical thresholds of water availability below which higher-biomass , closed-canopy forests transition to more open , lower-biomass forests .
Here we present observational evidence for a widespread decline in forest greenness over the past decade based on analyses of satellite data ( optical , thermal , microwave and gravity ) from several independent sensors over the Congo basin .
This decline in vegetation greenness , particularly in the northern Congolese forest , is generally consistent with decreases in rainfall , terrestrial water storage , water content in aboveground woody and leaf biomass , and the canopy backscatter anomaly caused by changes in structure and moisture in upper forest layers .
It is also consistent with increases in photosynthetically active radiation and land surface temperature .
These multiple lines of evidence indicate that this large-scale vegetation browning , or loss of photosynthetic capacity , may be partially attributable to the long-term drying trend .
Our results suggest that a continued gradual decline of photosynthetic capacity and moisture content driven by the persistent drying trend could alter the composition and structure of the Congolese forest to favour the spread of drought-tolerant species .

[178] Offset of the potential carbon sink from boreal forestation by decreases in surface albedo

Carbon uptake by forestation is one method proposed to reduce net carbon dioxide emissions to the atmosphere and so limit the radiative forcing of climate change .
But the overall impact of forestation on climate will also depend on other effects associated with the creation of new forests .
In particular , the albedo of a forested landscape is generally lower than that of cultivated land , especially when snow is lying , and decreasing albedo exerts a positive radiative forcing on climate .
Here I simulate the radiative forcings associated with changes in surface albedo as a result of forestation in temperate and boreal forest areas , and translate these forcings into equivalent changes in local carbon stock for comparison with estimated carbon sequestration potentials .
I suggest that in many boreal forest areas , the positive forcing induced by decreases in albedo can offset the negative forcing that is expected from carbon sequestration .
Some high-latitude forestation activities may therefore increase climate change , rather than mitigating it as intended .

[179] Reduced nitrogen fixation in the glacial ocean inferred from changes in marine nitrogen and phosphorus inventories

To explain the lower atmospheric CO2 concentrations during glacial periods , it has been suggested that the productivity of marine phytoplankton was stimulated by an increased flux of iron-bearing dust to the oceans .
One component of this theory is that iron -- an essential element/nutrient for nitrogen-fixing organisms -- will increase the rate of marine nitrogen fixation , fuelling the growth of other marine phytoplankton and increasing CO2 uptake .
Here we present data that questions this hypothesis .
From a sediment core off the northwestern continental margin of Mexico , we show that denitrification and phosphorite formation -- processes that occur in oxygen-deficient upwelling regions , removing respectively nitrogen and phosphorus from the ocean -- declined in glacial periods , thus increasing marine inventories of nitrogen and phosphorus .
But increases in phosphorus were smaller and less rapid , leading to increased N/P ratios in the oceans .
Acknowledging that phytoplankton require nitrogen and phosphorus in constant proportions , the Redfield ratio , and that N/P ratios greater than the Redfield ratio are likely to suppress nitrogen fixation , we suggest therefore that marine productivity did not increase in glacial periods in response to either increased nutrient inventories or greater iron supply .

[180] Small mammal diversity loss in response to late-Pleistocene climatic change

Communities have been shaped in numerous ways by past climatic change ; this process continues today .
At the end of the Pleistocene epoch about 11,700 years ago , North American communities were substantially altered by the interplay of two events .
The climate shifted from the cold , arid Last Glacial Maximum to the warm , mesic Holocene interglacial , causing many mammal species to shift their geographic distributions substantially .
Populations were further stressed as humans arrived on the continent .
The resulting megafaunal extinction event , in which 70 of the roughly 220 largest mammals in North America ( 32 % ) became extinct , has received much attention .
However , responses of small mammals to events at the end of the Pleistocene have been much less studied , despite the sensitivity of these animals to current and future environmental change .
Here we examine community changes in small mammals in northern California during the last ` natural ' global warming event at the Pleistocene-Holocene transition and show that even though no small mammals in the local community became extinct , species losses and gains , combined with changes in abundance , caused declines in both the evenness and richness of communities .
Modern mammalian communities are thus depauperate not only as a result of megafaunal extinctions at the end of the Pleistocene but also because of diversity loss among small mammals .
Our results suggest that across future landscapes there will be some unanticipated effects of global change on diversity : restructuring of small mammal communities , significant loss of richness , and perhaps the rising dominance of native ` weedy ' species .

[181] Adaptation of US maize to temperature variations

High temperatures are associated with reduced crop yields , and predictions for future warming have raised concerns regarding future productivity and food security .
However , the extent to which adaptation can mitigate such heat-related losses remains unclear .
Here we empirically demonstrate how maize is locally adapted to hot temperatures across US counties .
Using this spatial adaptation as a surrogate for future adaptation , we find that losses to average US maize yields from a 2 degreesC warming would be reduced from 14 % to only 6 % and that loss in net production is wholly averted .
This result does not account for possible changes in temperature variability or water resources , nor does it account for all possible forms of adaptation , but it does show that adaptation is of first-order importance for predicting future changes in yield .
Further research should be undertaken regarding the ability to adapt to a changing climate , including analysis of other crops and regions , the application of more sophisticated models of crop development , and field trials employing artificially increased temperature .

[182] The velocity of climate change

The ranges of plants and animals are moving in response to recent changes in climate .
As temperatures rise , ecosystems with ` nowhere to go ' , such as mountains , are considered to be more threatened .
However , species survival may depend as much on keeping pace with moving climates as the climate 's ultimate persistence .
Here we present a new index of the velocity of temperature change ( km yr-1 ) , derived from spatial gradients ( degreesC km-1 ) and multimodel ensemble forecasts of rates of temperature increase ( degreesC yr-1 ) in the twenty-first century .
This index represents the instantaneous local velocity along Earth 's surface needed to maintain constant temperatures , and has a global mean of 0.42 km yr-1 ( A1B emission scenario ) .
Owing to topographic effects , the velocity of temperature change is lowest in mountainous biomes such as tropical and subtropical coniferous forests ( 0.08 km yr-1 ) , temperate coniferous forest , and montane grasslands .
Velocities are highest in flooded grasslands ( 1.26 km yr-1 ) , mangroves and deserts .
High velocities suggest that the climates of only 8 % of global protected areas have residence times exceeding 100 years .
Small protected areas exacerbate the problem in Mediterranean-type and temperate coniferous forest biomes .
Large protected areas may mitigate the problem in desert biomes .
These results indicate management strategies for minimizing biodiversity loss from climate change .
Montane landscapes may effectively shelter many species into the next century .
Elsewhere , reduced emissions , a much expanded network of protected areas , or efforts to increase species movement may be necessary .

[183] Abrupt glacial climate shifts controlled by ice sheet changes

During glacial periods of the Late Pleistocene , an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes , known as Dansgaard-Oeschger ( DO ) events .
This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present ( bp ) in the ice core record , and has drawn broad attention within the science and policy-making communities alike .
Many studies have been dedicated to investigating the underlying causes of these changes , but no coherent mechanism has yet been identified .
Here we show , by using a comprehensive fully coupled model , that gradual changes in the height of the Northern Hemisphere ice sheets ( NHISs ) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events .
The simulated global climate responses -- including abrupt warming in the North Atlantic , a northward shift of the tropical rainbelts , and Southern Hemisphere cooling related to the bipolar seesaw -- are generally consistent with empirical evidence .
As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets , minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic .
Our results , although based on a single model , thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system , as well as their linkages to the volume of the intermediate ice sheets during glacials .

[184] Why fishing magnifies fluctuations in fish abundance

It is now clear that fished populations can fluctuate more than unharvested stocks .
However , it is not clear why .
Here we distinguish among three major competing mechanisms for this phenomenon , by using the 50-year California Cooperative Oceanic Fisheries Investigations ( CalCOFI ) larval fish record .
First , variable fishing pressure directly increases variability in exploited populations .
Second , commercial fishing can decrease the average body size and age of a stock , causing the truncated population to track environmental fluctuations directly .
Third , age-truncated or juvenescent populations have increasingly unstable population dynamics because of changing demographic parameters such as intrinsic growth rates .
We find no evidence for the first hypothesis , limited evidence for the second and strong evidence for the third .
Therefore , in California Current fisheries , increased temporal variability in the population does not arise from variable exploitation , nor does it reflect direct environmental tracking .
More fundamentally , it arises from increased instability in dynamics .
This finding has implications for resource management as an empirical example of how selective harvesting can alter the basic dynamics of exploited populations , and lead to unstable booms and busts that can precede systematic declines in stock levels .

[185] Soil carbon release enhanced by increased tropical forest litterfall

Tropical forests are a critical component of the global carbon cycle and their response to environmental change will play a key role in determining future concentrations of atmospheric carbon dioxide ( CO2 ) .
Increasing primary productivity in tropical forests over recent decades has been attributed to CO2 fertilization , and greater biomass in tropical forests could represent a substantial sink for carbon in the future .
However , the carbon sequestration capacity of tropical forest soils is uncertain and feedbacks between increased plant productivity and soil carbon dynamics remain unexplored .
Here , we show that experimentally increasing litterfall in a lowland tropical forest enhanced carbon release from the soil .
Using a large-scale litter manipulation experiment combined with carbon isotope measurements , we found that the efflux of CO2 derived from soil organic carbon was significantly increased by litter addition .
Furthermore , this effect was sustained over several years .
We predict that a future increase in litterfall of 30 % with an increase in atmospheric CO2 concentrations of 150 ppm could release about 0.6 t C ha-1 yr-1 from the soil , partially offsetting predicted net gains in carbon storage .
Thus , it is essential that plant-soil feedbacks are taken into account in predictions of the carbon sequestration potential of tropical forests .

[186] Tropospheric ozone trends at Mauna Loa Observatory tied to decadal climate variability

A potent greenhouse gas and biological irritant , tropospheric ozone is also the primary source of atmospheric hydroxyl radicals , which remove numerous hazardous trace gases from the atmosphere .
Tropospheric ozone levels have increased in spring at remote sites in the mid-latitudes of the Northern Hemisphere over the past few decades ; this increase has been attributed to a growth in Asian precursor emissions .
In contrast , 40 years of continuous measurements at Mauna Loa Observatory in Hawaii reveal little change in tropospheric ozone levels during spring ( March-April ) , but a rise in autumn ( September-October ) .
Here we examine the contribution of decadal shifts in atmospheric circulation patterns to decadal variability in tropospheric ozone levels at Mauna Loa using a suite of chemistry-climate model simulations .
We show that the flow of ozone-rich air from Eurasia towards Hawaii during spring weakened in the 2000s as a result of La-Nina-like decadal cooling in the eastern equatorial Pacific Ocean .
During autumn , in contrast , the flow of ozone-rich air from Eurasia to Hawaii strengthened in the mid-1990s onwards , coincident with the positive phase of the Pacific-North American pattern .
We suggest that these shifts in atmospheric circulation patterns can reconcile observed trends in tropospheric ozone levels at Mauna Loa and the northern mid-latitudes in recent decades .
We conclude that decadal variability in atmospheric circulation patterns needs to be considered when attributing observed changes in tropospheric ozone levels to human-induced trends in precursor emissions .

[187] Net carbon uptake has increased through warming-induced changes in temperate forest phenology

The timing of phenological events exerts a strong control over ecosystem function and leads to multiple feedbacks to the climate system .
Phenology is inherently sensitive to temperature ( although the exact sensitivity is disputed ) and recent warming is reported to have led to earlier spring , later autumn and increased vegetation activity .
Such greening could be expected to enhance ecosystem carbon uptake , although reports also suggest decreased uptake for boreal forests .
Here we assess changes in phenology of temperate forests over the eastern US during the past two decades , and quantify the resulting changes in forest carbon storage .
We combine long-term ground observations of phenology , satellite indices , and ecosystem-scale carbon dioxide flux measurements , along with 18 terrestrial biosphere models .
We observe a strong trend of earlier spring and later autumn .
In contrast to previous suggestions we show that carbon uptake through photosynthesis increased considerably more than carbon release through respiration for both an earlier spring and later autumn .
The terrestrial biosphere models tested misrepresent the temperature sensitivity of phenology , and thus the effect on carbon uptake .
Our analysis of the temperature-phenology-carbon coupling suggests a current and possible future enhancement of forest carbon uptake due to changes in phenology .
This constitutes a negative feedback to climate change , and is serving to slow the rate of warming .

[188] Increased capture of magma in the crust promoted by ice-cap retreat in Iceland

Climate warming at the end of the last glaciation caused ice caps on Icelandic volcanoes to retreat .
Removal of surface ice load is thought to have decreased pressures in the underlying mantle , triggering decompression melting , enhanced magma generation and increased volcanic activity .
Present-day climate change could have the same effect , although there may be a time lag of hundreds of years between magma generation and eruption .
However , in addition to increased magma generation , pressure changes associated with ice retreat should also alter the capacity for storing magma within the crust .
Here we use a numerical model to evaluate the effect of the current decrease in ice load on magma storage in the crust at the Kverkfjoll volcanic system , located partially beneath Iceland 's largest ice cap .
We compare the model results with radar and global positioning system measurements of surface displacement and changes in crustal stress between 2007 and 2008 , during the intrusion of a deep dyke at Upptyppingar .
We find that although the main component of stress recorded during dyke intrusion relates to plate extension , another component of stress is consistent with the stress field caused by the retreating ice cap .
We conclude that the retreating ice cap led to enhanced capture of magma within the crust .
We suggest that ice-cap retreat can promote magma storage , rather than eruption , at least in the short term .

[189] The late Precambrian greening of the Earth

Many aspects of the carbon cycle can be assessed from temporal changes in the 13C/12C ratio of oceanic bicarbonate .
13C/12C can temporarily rise when large amounts of 13C-depleted photosynthetic organic matter are buried at enhanced rates , and can decrease if phytomass is rapidly oxidized or if low 13C is rapidly released from methane clathrates .
Assuming that variations of the marine 13C/12C ratio are directly recorded in carbonate rocks , thousands of carbon isotope analyses of late Precambrian examples have been published to correlate these otherwise undatable strata and to document perturbations to the carbon cycle just before the great expansion of metazoan life .
Low 13C/12C in some Neoproterozoic carbonates is considered evidence of carbon cycle perturbations unique to the Precambrian .
These include complete oxidation of all organic matter in the ocean and complete productivity collapse such that low-13C / 12C hydrothermal CO2 becomes the main input of carbon .
Here we compile all published oxygen and carbon isotope data for Neoproterozoic marine carbonates , and consider them in terms of processes known to alter the isotopic composition during transformation of the initial precipitate into limestone/dolostone .
We show that the combined oxygen and carbon isotope systematics are identical to those of well-understood Phanerozoic examples that lithified in coastal pore fluids , receiving a large groundwater influx of photosynthetic carbon from terrestrial phytomass .
Rather than being perturbations to the carbon cycle , widely reported decreases in 13C/12C in Neoproterozoic carbonates are more easily interpreted in the same way as is done for Phanerozoic examples .
This influx of terrestrial carbon is not apparent in carbonates older than ~ 850 Myr , so we infer an explosion of photosynthesizing communities on late Precambrian land surfaces .
As a result , biotically enhanced weathering generated carbon-bearing soils on a large scale and their detrital sedimentation sequestered carbon .
This facilitated a rise in O2 necessary for the expansion of multicellular life .

[190] Contribution of light-absorbing impurities in snow to Greenland 's darkening since 2009

The surface energy balance and mass balance of the Greenland ice sheet depends on the albedo of snow , which governs the amount of solar energy that is absorbed .
The observed decline of Greenland 's albedo over the past decade has been attributed to an enhanced growth of snow grains as a result of atmospheric warming .
Satellite observations show that , since 2009 , albedo values even in springtime at high elevations have been lower than the 2003-2008 average .
Here we show , using a numerical snow model , that the decrease in albedo can not be attributed solely to grain growth enhancement .
Instead , our analysis of remote sensing data indicates that the springtime darkening since 2009 stems from a widespread increase in the amount of light-absorbing impurities in snow , as well as in the atmosphere .
We suggest that the transport of dust from snow-free areas in the Arctic that are experiencing earlier melting of seasonal snow cover as the climate warms may be a contributing source of impurities .
In our snow model simulations , a decrease in the albedo of fresh snow by 0.01 leads to a surface mass loss of 27 Gt yr-1 , which could induce an acceleration of Greenland 's mass loss twice as large as over the past two decades .
Future trends in light-absorbing impurities should therefore be considered in projections of Greenland mass loss .

[191] Boreal carbon loss due to poleward shift in low-carbon ecosystems

Climate change can be thought of in terms of geographical shifts in climate properties .
Examples include assessments of shifts in habitat distributions , of the movement needed to maintain constant temperature or precipitation , and of the emergence and disappearance of climate zones .
Here I track the movement of analogue climates within climate models .
From the model simulations , I define a set of vectors that link a historical reference climate for each location to the location in a changed climate whose seasonal temperature and precipitation cycles best match the reference climate .
I use these vectors to calculate the change in vegetation carbon storage with climate change due to ecosystems following climate analogues .
Comparing the derived carbon content change to direct carbon projections by coupled carbon-climate models reveals two regions of divergence .
In the tropical forests , vector projections are fundamentally uncertain because of a lack of close climatic analogues .
In the southern boreal forest , carbon losses are projected in the vector perspective because low-carbon ecosystems shift polewards .
However , the majority of carbon-climate models -- typically without explicit simulation of the disturbance and mortality processes behind such shifts -- instead project vegetation carbon gains throughout the boreal region .
Southern boreal carbon loss as a result of ecosystem shift is likely to offset carbon gains from northern boreal forest expansion .

[192] Response of corn markets to climate volatility under alternative energy futures

Recent price spikes have raised concern that climate change could increase food insecurity by reducing grain yields in the coming decades .
However , commodity price volatility is also influenced by other factors , which may either exacerbate or buffer the effects of climate change .
Here we show that US corn price volatility exhibits higher sensitivity to near-term climate change than to energy policy influences or agriculture-energy market integration , and that the presence of a biofuels mandate enhances the sensitivity to climate change by more than 50 % .
The climate change impact is driven primarily by intensification of severe hot conditions in the primary corn-growing region of the United States , which causes US corn price volatility to increase sharply in response to global warming projected to occur over the next three decades .
Closer integration of agriculture and energy markets moderates the effects of climate change , unless the biofuels mandate becomes binding , in which case corn price volatility is instead exacerbated .
However , in spite of the substantial impact on US corn price volatility , we find relatively small impact on food prices .
Our findings highlight the critical importance of interactions between energy policies , energy-agriculture linkages and climate change .

[193] Eocene/Oligocene ocean de-acidification linked to Antarctic glaciation by sea-level fall

One of the most dramatic perturbations to the Earth system during the past 100 million years was the rapid onset of Antarctic glaciation near the Eocene/Oligocene epoch boundary ( ~ 34 million years ago ) .
This climate transition was accompanied by a deepening of the calcite compensation depth -- the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution .
Changes in the global carbon cycle , rather than changes in continental configuration , have recently been proposed as the most likely root cause of Antarctic glaciation , but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear .
Here we use a global biogeochemical box model to test competing hypotheses put forward to explain the Eocene/Oligocene transition .
We find that , of the candidate hypotheses , only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor .
In our simulations , glacioeustatic sea-level fall associated with the growth of Antarctic ice sheets permanently reduces global calcium carbonate accumulation on the continental shelves , leading to an increase in pelagic burial via permanent deepening of the calcite compensation depth .
At the same time , fresh limestones are exposed to erosion , thus temporarily increasing global river inputs of dissolved carbonate and increasing seawater delta13C .
Our work sheds new light on the mechanisms linking glaciation and ocean acidity change across arguably the most important climate transition of the Cenozoic era .

[194] Delayed phenology and reduced fitness associated with climate change in a wild hibernator

The most commonly reported ecological effects of climate change are shifts in phenologies , in particular of warmer spring temperatures leading to earlier timing of key events .
Among animals , however , these reports have been heavily biased towards avian phenologies , whereas we still know comparatively little about other seasonal adaptations , such as mammalian hibernation .
Here we show a significant delay ( 0.47 days per year , over a 20-year period ) in the hibernation emergence date of adult females in a wild population of Columbian ground squirrels in Alberta , Canada .
This finding was related to the climatic conditions at our study location : owing to within-individual phenotypic plasticity , females emerged later during years of lower spring temperature and delayed snowmelt .
Although there has not been a significant annual trend in spring temperature , the date of snowmelt has become progressively later owing to an increasing prevalence of late-season snowstorms .
Importantly , years of later emergence were also associated with decreased individual fitness .
There has consequently been a decline in mean fitness ( that is , population growth rate ) across the past two decades .
Our results show that plastic responses to climate change may be driven by climatic trends other than increasing temperature , and may be associated with declines in individual fitness and , hence , population viability .

[195] Reduced growth of Alaskan white spruce in the twentieth century from temperature-induced drought stress

The extension of growing season at high northern latitudes seems increasingly clear from satellite observations of vegetation extent and duration .
This extension is also thought to explain the observed increase in amplitude of seasonal variations in atmospheric CO2 concentration .
Increased plant respiration and photosynthesis both correlate well with increases in temperature this century and are therefore the most probable link between the vegetation and CO2 observations .
From these observations , it has been suggested that increases in temperature have stimulated carbon uptake in high latitudes and for the boreal forest system as a whole .
Here we present multi-proxy tree-ring data ( ring width , maximum late-wood density and carbon-isotope composition ) from 20 productive stands of white spruce in the interior of Alaska .
The tree-ring records show a strong and consistent relationship over the past 90 years and indicate that , in contrast with earlier predictions , radial growth has decreased with increasing temperature .
Our data show that temperature-induced drought stress has disproportionately affected the most rapidly growing white spruce , suggesting that , under recent climate warming , drought may have been an important factor limiting carbon uptake in a large portion of the North American boreal forest .
If this limitation in growth due to drought stress is sustained , the future capacity of northern latitudes to sequester carbon may be less than currently expected .

[196] Indo-China Monsoon Indices

Myanmar and Thailand often experience severe droughts and floods that cause irreparable damage to the socio-economy condition of both countries .
In this study , the Southeastern Asian Summer Monsoon variation is found to be the main element of interannual precipitation variation of the region , more than the El Nino/Southern Oscillation ( ENSO ) .
The ENSO influence is evident only during the boreal spring season .
Although the monsoon is the major factor , the existing Indian Monsoon Index ( IMI ) and Western North Pacific Monsoon Index ( WNPMI ) do not correlate well with the precipitation variation in the study regions of Southern Myanmar and Thailand .
Therefore , a new set of indices is developed based on the regional monsoon variations and presented here for the first time .
Precipitation variations in Southern Myanmar and Thailand differ as well as the elements affecting the precipitation variations in different seasons .
So , separate indices are proposed for each season for Southern Myanmar and Thailand .
Four new monsoon indices based on wind anomalies are formulated and are named as the Indochina Monsoon Indices .
These new indices correlate better with the precipitation variations of the study region as compared to the existing IMI and WNPMI .

[197] Late Holocene methane rise caused by orbitally controlled increase in tropical sources

Considerable debate surrounds the source of the apparently ` anomalous ' increase of atmospheric methane concentrations since the mid-Holocene ( 5,000 years ago ) compared to previous interglacial periods as recorded in polar ice core records .
Proposed mechanisms for the rise in methane concentrations relate either to methane emissions from anthropogenic early rice cultivation or an increase in natural wetland emissions from tropical or boreal sources .
Here we show that our climate and wetland simulations of the global methane cycle over the last glacial cycle ( the past 130,000 years ) recreate the ice core record and capture the late Holocene increase in methane concentrations .
Our analyses indicate that the late Holocene increase results from natural changes in the Earth 's orbital configuration , with enhanced emissions in the Southern Hemisphere tropics linked to precession-induced modification of seasonal precipitation .
Critically , our simulations capture the declining trend in methane concentrations at the end of the last interglacial period ( 115,000-130 ,000 years ago ) that was used to diagnose the Holocene methane rise as unique .
The difference between the two time periods results from differences in the size and rate of regional insolation changes and the lack of glacial inception in the Holocene .
Our findings also suggest that no early agricultural sources are required to account for the increase in methane concentrations in the 5,000 years before the industrial era .

[198] Mitigation of short-lived climate pollutants slows sea-level rise

Under present growth rates of greenhouse gas and black carbon aerosol emissions , global mean temperatures can warm by as much as 2 degreesC from pre-industrial temperatures by about 2050 .
Mitigation of the four short-lived climate pollutants ( SLCPs ) , methane , tropospheric ozone , hydrofluorocarbons and black carbon , has been shown to reduce the warming trend by about 50 % ( refs , ) by 2050 .
Here we focus on the potential impact of this SLCP mitigation on global sea-level rise ( SLR ) .
The temperature projections under various SLCP scenarios simulated by an energy-balance climate model are integrated with a semi-empirical SLR model , derived from past trends in temperatures and SLR , to simulate future trends in SLR .
A coupled ocean-atmosphere climate model is also used to estimate SLR trends due to just the ocean thermal expansion .
Our results show that SLCP mitigation can have significant effects on SLR .
It can decrease the SLR rate by 24-50 % and reduce the cumulative SLR by 22-42 % by 2100 .
If the SLCP mitigation is delayed by 25 years , the warming from pre-industrial temperature exceeds 2 degreesC by 2050 and the impact of mitigation actions on SLR is reduced by about a third .

[199] Time of emergence for regional sea-level change

Determining the time when the climate change signal from increasing greenhouse gases exceeds and thus emerges from natural climate variability ( referred to as the time of emergence , ToE ) is an important climate change issue .
Previous ToE studies were mainly focused on atmospheric variables .
Here , based on three regional sea-level projection products available to 2100 , which have increasing complexity in terms of included processes , we estimate the ToE for sea-level changes relative to the reference period 1986-2005 .
The dynamic sea level derived from ocean density and circulation changes alone leads to emergence over only limited regions .
By adding the global-ocean thermal expansion effect , 50 % of the ocean area will show emergence with rising sea level by the early-to-middle 2040s .
Including additional contributions from land ice mass loss , land water storage change and glacial isostatic adjustment generally enhances the signal of regional sea-level rise ( except in some regions with decreasing total sea levels ) , which leads to emergence over more than 50 % of the ocean area by 2020 .
The ToE for total sea level is substantially earlier than that for surface air temperature and exhibits little dependence on the emission scenarios , which means that our society will face detectable sea-level change and its potential impacts earlier than surface air warming .

[200] Global metabolic network reorganization by adaptive mutations allows fast growth of Escherichia coli on glycerol

Comparative whole-genome sequencing enables the identification of specific mutations during adaptation of bacteria to new environments and allelic replacement can establish their causality .
However , the mechanisms of action are hard to decipher and little has been achieved for epistatic mutations , especially at the metabolic level .
Here we show that a strain of Escherichia coli carrying mutations in the rpoC and glpK genes , derived from adaptation in glycerol , uses two distinct metabolic strategies to gain growth advantage .
A 27-bp deletion in the rpoC gene first increases metabolic efficiency .
Then , a point mutation in the glpK gene promotes growth by improving glycerol utilization but results in increased carbon wasting as overflow metabolism .
In a strain carrying both mutations , these contrasting carbon/energy saving and wasting mechanisms work together to give an 89 % increase in growth rate .
This study provides insight into metabolic reprogramming during adaptive laboratory evolution for fast cellular growth .

[201] Regional precipitation variability in East Asia related to climate and environmental factors during 1979-2012

This paper studies the inter-annual precipitation variations in different regions of East Asia from oceans to interior areas in China during 1979 - 2012 .
The results computed by Empirical Orthogonal Functions ( EOF ) demonstrate that the annual precipitation changes are mainly related to the El Nino-Southern Oscillation , East Asian summer monsoon and aerosols .
We also found that the increased Sea surface temperature ( SST ) could explain the precipitation changes over the Northwest Pacific in the dry season ( Oct. - May ) and the East China Sea and the South China Sea in the rainy season ( Jun. - Sep. ) .
The precipitation changes over the ocean unexplained by SST were likely due to the water vapor transport dominated by dynamic factors .
With the increased SST , the moisture transported from oceans to interior land was likely redistributed and caused the complicated regional variability of precipitation .
Moreover , the impacts of aerosols on cloud and precipitation varied with different pollution levels and different seasons .

[202] Increasing drought under global warming in observations and models

Historical records of precipitation , streamflow and drought indices all show increased aridity since 1950 over many land areas .
Analyses of model-simulated soil moisture , drought indices and precipitation-minus-evaporation suggest increased risk of drought in the twenty-first century .
There are , however , large differences in the observed and model-simulated drying patterns .
Reconciling these differences is necessary before the model predictions can be trusted .
Previous studies show that changes in sea surface temperatures have large influences on land precipitation and the inability of the coupled models to reproduce many observed regional precipitation changes is linked to the lack of the observed , largely natural change patterns in sea surface temperatures in coupled model simulations .
Here I show that the models reproduce not only the influence of El Nino-Southern Oscillation on drought over land , but also the observed global mean aridity trend from 1923 to 2010 .
Regional differences in observed and model-simulated aridity changes result mainly from natural variations in tropical sea surface temperatures that are often not captured by the coupled models .
The unforced natural variations vary among model runs owing to different initial conditions and thus are irreproducible .
I conclude that the observed global aridity changes up to 2010 are consistent with model predictions , which suggest severe and widespread droughts in the next 30-90 years over many land areas resulting from either decreased precipitation and/or increased evaporation .

[203] Decline of forest interior conditions in the conterminous United States

Forest fragmentation threatens the sustainability of forest interior environments , thereby endangering subordinate ecological attributes and functions .
We analyzed the spatial patterns of forest loss and gain for the conterminous United States from 2001 to 2006 to determine whether forest interior environments were maintained at five spatial scales .
A 1.1 % net loss of total forest area translated to net losses of 3.2 % to 10.5 % of forest interior area over spatial scales of 4.41 ha to 5,310 ha .
At the 65.6-ha scale , the reduction of forest interior area was 50,000 km2 - almost double the net loss of total forest area .
The pervasive discrepancy between total forest loss and forest interior loss indicates a widespread shift of the extant forest to more fragmented conditions , even in regions exhibiting small net changes in extant forest area .
In the conterminous United States , trends in total forest area underestimate threats to forest from forest fragmentation .

[204] Harmful filamentous cyanobacteria favoured by reduced water turnover with lake warming

Anthropogenic-induced changes in nutrient ratios have increased the susceptibility of large temperate lakes to several effects of rising air temperatures and the resulting heating of water bodies .
First , warming leads to stronger thermal stratification , thus impeding natural complete water turnover ( holomixis ) , which compensates for oxygen deficits in the deep zones .
Second , increased water temperatures and nutrient concentrations can directly favour the growth of harmful algae .
Thus , lake-restoration programmes have focused on reducing nutrients to limit toxic algal blooms .
Here we present evidence that the ubiquitous harmful cyanobacterium Planktothrix rubescens has become the dominant species in a large lake during the past four decades , although the phosphorus content of the ecosystem decreased fivefold .
However , the nitrogen input was not diminished concomitantly , favouring this non-N2-fixing cyanobacterium owing to increased N :P ratios .
P. rubescens contains gas vesicles that allow for buoyancy to accumulate within the depth of optimal irradiance .
As the toxic cyanobacterium has low consumption by predators , water turnover represents the main mechanism of seasonal population control .
Thus , unidirectional lake-restoration measures in parallel with recurrent absence of holomixis owing to lake warming may lead to similar undesired effects that have formerly emerged from fertilization .

[205] Systemic administration of Follistatin288 increases muscle mass and reduces fat accumulation in mice

The present study describes the physiological response associated with daily subcutaneous injection of mice with recombinant follistatin288 .
This systemic administration of follistatin288 increases the follistatin levels in serum , indicating that the protein enters the circulation .
The data suggest that a dose-dependent increase in body lean mass also occurs , together with an increase in muscle mass , possibly as a result of an increase in the size of the muscle fibers .
After thirteen weeks of treatment , metabolic changes were observed ; additionally , the switching of muscle fiber types was also apparent through myosin heavy chain remodeling , implying that changes are occurring at the molecular level .
Furthermore , an increase in the muscle mass was associated with a significant decrease in the body fat mass .
Overall , this study raises the possibility for the use of follistatin288 as an agent to treat muscle wasting diseases and/or to restrict fat accumulation by systemic administration of the protein .

[206] Increased glacial-age ventilation of the Chilean margin by Antarctic Intermediate Water

Antarctic Intermediate Water is , at present , a water mass that brings oxygen to intermediate depths throughout the Southern Hemisphere oceans .
Models have suggested that intermediate waters had higher concentrations of oxygen during the last glacial period , consistent with globally reduced denitrification and increased production of Antarctic Intermediate Water .
However , some palaeoceanographic reconstructions have indicated that production decreased in the southeast Pacific Ocean at this time .
Here we analyse the concentrations of Re and Mn , the sedimentary concentrations of which are controlled by the amount of dissolved oxygen at the sea floor , from three sediment cores located along the Chilean margin for the past 30,000 years .
Our results from the cores , which bracket the present-day water-column extent of Antarctic Intermediate Water , show that the depth range of well-oxygenated Antarctic Intermediate Water increased off Chile during the Last Glacial Maximum .
Dissolved oxygen content began to decrease approximately 17,000 years ago , coincident with rapid Antarctic warming and a poleward shift of the southern westerly winds .
Our estimates of productivity from accumulation rates of organic carbon and opal do not co-vary with the seafloor oxygen variations , ruling out local control of seafloor oxygenation .
We conclude that the data are best explained by a combination of increased oxygenation and increased flux of Antarctic Intermediate Water during the Last Glacial Maximum .

[207] High interannual variability of sea ice thickness in the Arctic region

Possible future changes in Arctic sea ice cover and thickness , and consequent changes in the ice-albedo feedback , represent one of the largest uncertainties in the prediction of future temperature rise .
Knowledge of the natural variability of sea ice thickness is therefore critical for its representation in global climate models .
Numerical simulations suggest that Arctic ice thickness varies primarily on decadal timescales owing to changes in wind and ocean stresses on the ice , but observations have been unable to provide a synoptic view of sea ice thickness , which is required to validate the model results .
Here we use an eight-year time-series of Arctic ice thickness , derived from satellite altimeter measurements of ice freeboard , to determine the mean thickness field and its variability from 65degrees N to 81.5 degrees N .
Our data reveal a high-frequency interannual variability in mean Arctic ice thickness that is dominated by changes in the amount of summer melt , rather than by changes in circulation .
Our results suggest that a continued increase in melt season length would lead to further thinning of Arctic sea ice .

[208] Impacts of the north and tropical Atlantic Ocean on the Antarctic Peninsula and sea ice

In recent decades , Antarctica has experienced pronounced climate changes .
The Antarctic Peninsula exhibited the strongest warming of any region on the planet , causing rapid changes in land ice .
Additionally , in contrast to the sea-ice decline over the Arctic , Antarctic sea ice has not declined , but has instead undergone a perplexing redistribution .
Antarctic climate is influenced by , among other factors , changes in radiative forcing and remote Pacific climate variability , but none explains the observed Antarctic Peninsula warming or the sea-ice redistribution in austral winter .
However , in the north and tropical Atlantic Ocean , the Atlantic Multidecadal Oscillation ( a leading mode of sea surface temperature variability ) has been overlooked in this context .
Here we show that sea surface warming related to the Atlantic Multidecadal Oscillation reduces the surface pressure in the Amundsen Sea and contributes to the observed dipole-like sea-ice redistribution between the Ross and Amundsen-Bellingshausen-Weddell seas and to the Antarctic Peninsula warming .
Support for these findings comes from analysis of observational and reanalysis data , and independently from both comprehensive and idealized atmospheric model simulations .
We suggest that the north and tropical Atlantic is important for projections of future climate change in Antarctica , and has the potential to affect the global thermohaline circulation and sea-level change .

[209] Iron-limited diatom growth and Si : N uptake ratios in a coastal upwelling regime

There is compelling evidence that phytoplankton growth is limited by iron availability in the subarctic Pacific , and equatorial Pacific and Southern oceans .
A lack of iron prevents the complete biological utilization of the ambient nitrate and influences phytoplankton species composition in these open-ocean ` high-nitrate , low-chlorophyll ' ( HNLC ) regimes .
But the effects of iron availability on coastal primary productivity and nutrient biogeochemistry are unknown .
Here we present the results of shipboard seawater incubation experiments which demonstrate that phytoplankton are iron-limited in parts of the California coastal upwelling region .
As in offshore HNLC regimes , the addition of iron to these nearshore HNLC waters promotes blooms of large chain-forming diatoms .
The silicic acid : nitrate ( Si : N ) uptake ratios in control incubations are two to three times higher than those in iron incubations .
Diatoms stressed by a lack of iron should therefore deplete surface waters of silicic acid before nitrate , leading to a secondary silicic acid limitation of the phytoplankton community .
Higher Si : cell , Si : C and Si : pigment ratios in diatoms in the control incubations suggest that iron limitation leads to more silicified , faster-sinking diatom biomass .
These results raise fundamental questions about the nature of nutrient-limitation interactions in marine ecosystems , palaeoproductivity estimates based on the sedimentary accumulation of biogenic opal , and the controls on carbon export from some of the world 's most productive surface waters .

[210] Limited impact on decadal-scale climate change from increased use of natural gas

The most important energy development of the past decade has been the wide deployment of hydraulic fracturing technologies that enable the production of previously uneconomic shale gas resources in North America .
If these advanced gas production technologies were to be deployed globally , the energy market could see a large influx of economically competitive unconventional gas resources .
The climate implications of such abundant natural gas have been hotly debated .
Some researchers have observed that abundant natural gas substituting for coal could reduce carbon dioxide ( CO2 ) emissions .
Others have reported that the non-CO2 greenhouse gas emissions associated with shale gas production make its lifecycle emissions higher than those of coal .
Assessment of the full impact of abundant gas on climate change requires an integrated approach to the global energy-economy-climate systems , but the literature has been limited in either its geographic scope or its coverage of greenhouse gases .
Here we show that market-driven increases in global supplies of unconventional natural gas do not discernibly reduce the trajectory of greenhouse gas emissions or climate forcing .
Our results , based on simulations from five state-of-the-art integrated assessment models of energy-economy-climate systems independently forced by an abundant gas scenario , project large additional natural gas consumption of up to +170 per cent by 2050 .
The impact on CO2 emissions , however , is found to be much smaller ( from -2 per cent to +11 per cent ) , and a majority of the models reported a small increase in climate forcing ( from -0.3 per cent to +7 per cent ) associated with the increased use of abundant gas .
Our results show that although market penetration of globally abundant gas may substantially change the future energy system , it is not necessarily an effective substitute for climate change mitigation policy .

[211] Declining uncertainty in transient climate response as CO2 forcing dominates future climate change

Carbon dioxide has exerted the largest portion of radiative forcing and surface temperature change over the industrial era , but other anthropogenic influences have also contributed .
However , large uncertainties in total forcing make it difficult to derive climate sensitivity from historical observations .
Anthropogenic forcing has increased between the Fourth and Fifth Assessment Reports of the Intergovernmental Panel of Climate Change ( IPCC ; refs , ) , although its relative uncertainty has decreased .
Here we show , based on data from the two reports , that this evolution towards lower uncertainty can be expected to continue into the future .
Because it is easier to reduce air pollution than carbon dioxide emissions and because of the long lifetime of carbon dioxide , the less uncertain carbon dioxide forcing is expected to become increasingly dominant .
Using a statistical model , we estimate that the relative uncertainty in anthropogenic forcing of more than 40 % quoted in the latest IPCC report for 2011 will be almost halved by 2030 , even without better scientific understanding .
Absolute forcing uncertainty will also decline for the first time , provided projected decreases in aerosols occur .
Other factors being equal , this stronger constraint on forcing will bring a significant reduction in the uncertainty of observation-based estimates of the transient climate response , with a 50 % reduction in its uncertainty range expected by 2030 .

[212] Climate change drives microevolution in a wild bird

To ensure long-term persistence , organisms must adapt to climate change , but an evolutionary response to a quantified selection pressure driven by climate change has not been empirically demonstrated in a wild population .
Here , we show that pheomelanin-based plumage colouration in tawny owls is a highly heritable trait , consistent with a simple Mendelian pattern of brown ( dark ) dominance over grey ( pale ) .
We show that strong viability selection against the brown morph occurs , but only under snow-rich winters .
As winter conditions became milder in the last decades , selection against the brown morph diminished .
Concurrent with this reduced selection , the frequency of brown morphs increased rapidly in our study population during the last 28 years and nationwide during the last 48 years .
Hence , we show the first evidence that recent climate change alters natural selection in a wild population leading to a microevolutionary response , which demonstrates the ability of wild populations to evolve in response to climate change .

[213] Northern Hemisphere forcing of climatic cycles in Antarctica over the past 360,000 years

The Milankovitch theory of climate change proposes that glacial-interglacial cycles are driven by changes in summer insolation at high northern latitudes .
The timing of climate change in the Southern Hemisphere at glacial-interglacial transitions ( which are known as terminations ) relative to variations in summer insolation in the Northern Hemisphere is an important test of this hypothesis .
So far , it has only been possible to apply this test to the most recent termination , because the dating uncertainty associated with older terminations is too large to allow phase relationships to be determined .
Here we present a new chronology of Antarctic climate change over the past 360,000 years that is based on the ratio of oxygen to nitrogen molecules in air trapped in the Dome Fuji and Vostok ice cores .
This ratio is a proxy for local summer insolation , and thus allows the chronology to be constructed by orbital tuning without the need to assume a lag between a climate record and an orbital parameter .
The accuracy of the chronology allows us to examine the phase relationships between climate records from the ice cores and changes in insolation .
Our results indicate that orbital-scale Antarctic climate change lags Northern Hemisphere insolation by a few millennia , and that the increases in Antarctic temperature and atmospheric carbon dioxide concentration during the last four terminations occurred within the rising phase of Northern Hemisphere summer insolation .
These results support the Milankovitch theory that Northern Hemisphere summer insolation triggered the last four deglaciations .

[214] Clouds and temperature drive dynamic changes in tropical flower production

Tropical forests are incredibly dynamic , showing rapid and longer-term changes in growth , mortality and net primary productivity .
Tropical species may be highly sensitive to temperature increases associated with climate change because of their narrow thermal tolerances .
However , at the ecosystem scale the competing effects of temperature , light and precipitation on tropical forest productivity have been difficult to assess .
Here we quantify cloudiness over the past several decades to investigate how clouds , together with temperature and precipitation , affect flower production in two contrasting tropical forests .
Our results show that temperature , rather than clouds , is critically important to tropical forest flower production .
Warmer temperatures increased flower production over seasonal , interannual and longer timescales , contrary to recent evidence that some tropical forests are already near their temperature threshold .
Clouds were primarily important seasonally , and limited production in a seasonally dry forest but enhanced production in an ever-wet forest .
A long-term increase in flower production at the seasonally dry forest is not driven by clouds and instead may be tied to increasing temperatures .
These relationships show that tropical forest productivity , which is not widely thought to be controlled by temperature , is indeed sensitive to small temperature changes ( 1-4degreesC ) across multiple timescales .

[215] Trends in the sources and sinks of carbon dioxide

Efforts to control climate change require the stabilization of atmospheric CO2 concentrations .
This can only be achieved through a drastic reduction of global CO2 emissions .
Yet fossil fuel emissions increased by 29 % between 2000 and 2008 , in conjunction with increased contributions from emerging economies , from the production and international trade of goods and services , and from the use of coal as a fuel source .
In contrast , emissions from land-use changes were nearly constant .
Between 1959 and 2008 , 43 % of each year 's CO2 emissions remained in the atmosphere on average ; the rest was absorbed by carbon sinks on land and in the oceans .
In the past 50 years , the fraction of CO2 emissions that remains in the atmosphere each year has likely increased , from about 40 % to 45 % , and models suggest that this trend was caused by a decrease in the uptake of CO2 by the carbon sinks in response to climate change and variability .
Changes in the CO2 sinks are highly uncertain , but they could have a significant influence on future atmospheric CO2 levels .
It is therefore crucial to reduce the uncertainties .

[216] An energetic perspective on the regional response of precipitation to climate change

Understanding and predicting the response of the hydrological cycle to climate change is a major challenge with important societal implications .
Much progress has been made in understanding the response of global average precipitation by considering the energy balances of the atmosphere and the surface .
This energetic perspective reveals that changes in temperature , greenhouse gases , aerosols , solar forcing and cloud feedbacks can all affect the global average rate of precipitation .
Local precipitation changes have conventionally been analysed using the water vapour budget , but here we show that the energetic approach can be extended to local changes in precipitation by including changes in horizontal energy transport .
In simulations of twenty-first century climate change , this energy transport accounts for much of the spatial variability in precipitation change .
We show that changes in radiative and surface sensible heat fluxes are a guide to the local precipitation response over land and at large scales , but not at small scales over the ocean , where cloud and water vapour radiative feedbacks dampen the response .
The energetic approach described here helps bridge the gap between our understanding of global and regional precipitation changes .
It could be applied to better understand the response of regional precipitation to different radiative forcings , including geo-engineering schemes , as well as to understand the differences between the fast and slow responses of regional precipitation to such forcings .

[217] Linking N2O emissions from biochar-amended soil to the structure and function of the N-cycling microbial community

Nitrous oxide ( N2O ) contributes 8 % to global greenhouse gas emissions .
Agricultural sources represent about 60 % of anthropogenic N2O emissions .
Most agricultural N2O emissions are due to increased fertilizer application .
A considerable fraction of nitrogen fertilizers are converted to N2O by microbiological processes ( that is , nitrification and denitrification ) .
Soil amended with biochar ( charcoal created by pyrolysis of biomass ) has been demonstrated to increase crop yield , improve soil quality and affect greenhouse gas emissions , for example , reduce N2O emissions .
Despite several studies on variations in the general microbial community structure due to soil biochar amendment , hitherto the specific role of the nitrogen cycling microbial community in mitigating soil N2O emissions has not been subject of systematic investigation .
We performed a microcosm study with a water-saturated soil amended with different amounts ( 0 % , 2 % and 10 % ( w/w ) ) of high-temperature biochar .
By quantifying the abundance and activity of functional marker genes of microbial nitrogen fixation ( nifH ) , nitrification ( amoA ) and denitrification ( nirK , nirS and nosZ ) using quantitative PCR we found that biochar addition enhanced microbial nitrous oxide reduction and increased the abundance of microorganisms capable of N2-fixation .
Soil biochar amendment increased the relative gene and transcript copy numbers of the nosZ-encoded bacterial N2O reductase , suggesting a mechanistic link to the observed reduction in N2O emissions .
Our findings contribute to a better understanding of the impact of biochar on the nitrogen cycling microbial community and the consequences of soil biochar amendment for microbial nitrogen transformation processes and N2O emissions from soil .

[218] Isotopic constraints on marine and terrestrial N2O emissions during the last deglaciation

Nitrous oxide ( N2O ) is an important greenhouse gas and ozone-depleting substance that has anthropogenic as well as natural marine and terrestrial sources .
The tropospheric N2O concentrations have varied substantially in the past in concert with changing climate on glacial-interglacial and millennial timescales .
It is not well understood , however , how N2O emissions from marine and terrestrial sources change in response to varying environmental conditions .
The distinct isotopic compositions of marine and terrestrial N2O sources can help disentangle the relative changes in marine and terrestrial N2O emissions during past climate variations .
Here we present N2O concentration and isotopic data for the last deglaciation , from 16,000 to 10,000 years before present , retrieved from air bubbles trapped in polar ice at Taylor Glacier , Antarctica .
With the help of our data and a box model of the N2O cycle , we find a 30 per cent increase in total N2O emissions from the late glacial to the interglacial , with terrestrial and marine emissions contributing equally to the overall increase and generally evolving in parallel over the last deglaciation , even though there is no a priori connection between the drivers of the two sources .
However , we find that terrestrial emissions dominated on centennial timescales , consistent with a state-of-the-art dynamic global vegetation and land surface process model that suggests that during the last deglaciation emission changes were strongly influenced by temperature and precipitation patterns over land surfaces .
The results improve our understanding of the drivers of natural N2O emissions and are consistent with the idea that natural N2O emissions will probably increase in response to anthropogenic warming .

[219] Increased cuticular carbon sequestration and lignin oxidation in response to soil warming

Rising temperatures are predicted to accelerate the decomposition of labile soil organic compounds such as proteins and carbohydrates , whereas biochemically resistant compounds , such as lipids from leaf cuticles and roots and lignin from woody tissues , are expected to remain stable on decadal to centennial timescales .
However , the extent to which soil warming changes the molecular composition of soil organic matter is poorly understood .
Here we examine the impact of soil warming in a mixed temperate forest on the molecular make-up of soil organic matter .
We show that the abundance of leaf-cuticle-derived compounds is increased following 14 months of soil warming ; we confirm this with nuclear magnetic resonance spectra of soil organic matter extracts .
In contrast , we find that the abundance of lignin-derived compounds is decreased after the same treatment , while soil fungi , the primary decomposers of lignin in soil , increase in abundance .
We conclude that future warming could alter the composition of soil organic matter at the molecular level , accelerating lignin degradation and increasing leaf-cuticle-derived carbon sequestration .
With annual litterfall predicted to increase in the world 's major forests with a 3 degreesC warming , we suggest that future warming may enhance the sequestration of cuticular carbon in soil .

[220] A large and abrupt fall in atmospheric CO2 concentration during Cretaceous times

Marine carbonates and organic matter show a sharp increase in their 13C/12C isotope ratio at the Cenomanian/Turonian ( C/T ) boundary , in the Cretaceous period .
This isotopic shift resulted from an increase in the rate of sedimentary burial of 13C-depleted organic carbon in response to the C/T ` oceanic anoxic event ' .
Theenhanced burial rate should have led to a significant drop inthe atmospheric CO2 concentration , which could explain the apparent climate cooling of early Turonian times .
Here we present stable carbon isotope data for specific compounds from terrestrial leaves and marine phytoplankton , and quantify the abruptness and magnitude of the atmospheric CO2 concentration change .
Isotope shifts in leaf-wax components extracted from abyssal sediments in the northeastern tropical Atlantic Ocean -- the components are wind-delivered from Africa -- indicate a sudden change in plant communities of the north African continent .
Specifically , the data suggest that plants using the C3-type photosynthetic pathway were succeeded by plants using the C4-type pathway .
If C4plants can outcompete C3 plants only at atmospheric CO2 concentrations below 500 p.p.m.v. ( ref .
5 ) , the observed vegetation change indicates a far larger reduction in C/T CO2 concentration -- some 40-80 % -- than previously suggested .
The isotopic excursion in the marine phytoplankton compounds is consistent with this estimate .
We infer that this dramatic fall in the atmospheric CO2 concentration was abrupt , occurring in just 60,000 years .

[221] Spatial Simulation of Land Use based on Terrestrial Ecosystem Carbon Storage in Coastal Jiangsu , China

This paper optimises projected land-use structure in 2020 with the goal of increasing terrestrial ecosystem carbon storage and simulates its spatial distribution using the CLUE-S model .
We found the following : The total carbon densities of different land use types were woodland > water area > cultivated land > built-up land > grassland > shallows .
Under the optimised land-use structure projected for 2020 , coastal Jiangsu showed the potential to increase carbon storage , and our method was effective even when only considering vegetation carbon storage .
The total area will increase by reclamation and the original shallows will be exploited , which will greatly increase carbon storage .
For built-up land , rural land consolidation caused the second-largest carbon storage increase , which might contribute the most as the rural population will continue to decrease in the future , while the decrease of cultivated land will contribute the most to carbon loss .
The area near the coastline has the greatest possibility for land-use change and is where land management should be especially strengthened .

[222] Shifts in Arctic vegetation and associated feedbacks under climate change

Climate warming has led to changes in the composition , density and distribution of Arctic vegetation in recent decades .
These changes cause multiple opposing feedbacks between the biosphere and atmosphere , the relative magnitudes of which will have globally significant consequences but are unknown at a pan-Arctic scale .
The precise nature of Arctic vegetation change under future warming will strongly influence climate feedbacks , yet Earth system modelling studies have so far assumed arbitrary increases in shrubs ( for example , +20 % ; refs , ) , highlighting the need for predictions of future vegetation distribution shifts .
Here we show , using climate scenarios for the 2050s and models that utilize statistical associations between vegetation and climate , the potential for extremely widespread redistribution of vegetation across the Arctic .
We predict that at least half of vegetated areas will shift to a different physiognomic class , and woody cover will increase by as much as 52 % .
By incorporating observed relationships between vegetation and albedo , evapotranspiration and biomass , we show that vegetation distribution shifts will result in an overall positive feedback to climate that is likely to cause greater warming than has previously been predicted .
Such extensive changes to Arctic vegetation will have implications for climate , wildlife and ecosystem services .

[223] Elevated CO2 increases productivity and invasive species success in an arid ecosystem

Arid ecosystems , which occupy about 20 % of the earth 's terrestrial surface area , have been predicted to be one of the most responsive ecosystem types to elevated atmospheric CO2 and associated global climate change .
Here we show , using free-air CO2 enrichment ( FACE ) technology in an intact Mojave Desert ecosystem , that new shoot production of a dominant perennial shrub is doubled by a 50 % increase in atmospheric CO2 concentration in a high rainfall year .
However , elevated CO 2 does not enhance production in a drought year .
We also found that above-ground production and seed rain of an invasive annual grass increases more at elevated CO2 than in several species of native annuals .
Consequently , elevated CO2 might enhance the long-term success and dominance of exotic annual grasses in the region .
This shift in species composition in favour of exotic annual grasses , driven by global change , has the potential to accelerate the fire cycle , reduce biodiversity and alter ecosystem function in the deserts of western North America .

[224] Evolutionary loss of the rdar morphotype in Salmonella as a result of high mutation rates during laboratory passage

Rapid evolution of microbes under laboratory conditions can lead to domestication of environmental or clinical strains .
In this work , we show that domestication due to laboratory passage in rich medium is extremely rapid .
Passaging of wild-type Salmonella in rich medium led to diversification of genotypes contributing to the loss of a spatial phenotype , called the rdar morphotype , within days .
Gene expression analysis of the rdar regulatory network demonstrated that mutations were primarily within rpoS , indicating that the selection pressure for scavenging during stationary phase had the secondary effect of impairing this highly conserved phenotype .
If stationary phase was omitted from the experiment , radiation of genotypes and loss of the rdar morphotype was also demonstrated , but due to mutations within the cellulose biosynthesis pathway and also in an unknown upstream regulator .
Thus regardless of the selection pressure , rapid regulatory changes can be observed on laboratory timescales .
The speed of accumulation of rpoS mutations during daily passaging could not be explained by measured fitness and mutation rates .
A model of mutation accumulation suggests that to generate the observed accumulation of sigma38 mutations , this locus must experience a mutation rate of approximately 10-4 mutations/gene/generation .
Sequencing and gene expression of population isolates indicated that there were a wide variety of sigma38 phenotypes within each population .
This suggests that the rpoS locus is highly mutable by an unknown pathway , and that these mutations accumulate rapidly under common laboratory conditions .

[225] Plant immune response to pathogens differs with changing temperatures

Temperature fluctuation is a key determinant for microbial invasion and host evasion .
In contrast to mammals that maintain constant body temperature , plant temperature oscillates on a daily basis .
It remains elusive how plants operate inducible defenses in response to temperature fluctuation .
Here we report that ambient temperature changes lead to pronounced shifts of the following two distinct plant immune responses : pattern-triggered immunity ( PTI ) and effector-triggered immunity ( ETI ) .
Plants preferentially activate ETI signaling at relatively low temperatures ( 10-23 degreesC ) , whereas they switch to PTI signaling at moderately elevated temperatures ( 23-32 degreesC ) .
The Arabidopsis arp6 and hta9hta11 mutants , phenocopying plants grown at elevated temperatures , exhibit enhanced PTI and yet reduced ETI responses .
As the secretion of bacterial effectors favours low temperatures , whereas bacteria multiply vigorously at elevated temperatures accompanied with increased microbe-associated molecular pattern production , our findings suggest that temperature oscillation might have driven dynamic co-evolution of distinct plant immune signaling responding to pathogen physiological changes .

[226] Parental environment mediates impacts of increased carbon dioxide on a coral reef fish

Carbon dioxide concentrations in the surface ocean are increasing owing to rising CO2 concentrations in the atmosphere .
Higher CO2 levels are predicted to affect essential physiological processes of many aquatic organisms , leading to widespread impacts on marine diversity and ecosystem function , especially when combined with the effects of global warming .
Yet the ability for marine species to adjust to increasing CO2 levels over many generations is an unresolved issue .
Here we show that ocean conditions projected for the end of the century ( approximately 1,000 muatm CO2 and a temperature rise of 1.5-3 .0 degreesC ) cause an increase in metabolic rate and decreases in length , weight , condition and survival of juvenile fish .
However , these effects are absent or reversed when parents also experience high CO2 concentrations .
Our results show that non-genetic parental effects can dramatically alter the response of marine organisms to increasing CO2 and demonstrate that some species have more capacity to acclimate to ocean acidification than previously thought .

[227] Simulated response of the ocean carbon cycle to anthropogenic climate warming

A 1995 report of the Intergovernmental Panel on Climate Change provides a set of illustrative anthropogenic CO2 emission models leading to stabilization of atmospheric CO2 concentrations ranging from 350 to 1,000 p.p.m. ( refs 1-4 ) .
Ocean carbon-cycle models used in calculating these scenarios assume that oceanic circulation and biology remain unchanged through time .
Here we examine the importance of this assumption by using a coupled atmosphere-ocean model of global warming for the period 1765 to 2065 .
We find a large potential modification to the ocean carbon sink in a vast region of the Southern Ocean where increased rainfall leads to surface freshening and increased stratification .
The increased stratification reduces the downward flux of carbon and the loss of heat to the atmosphere , both of which decrease the oceanic uptake of anthropogenic CO2 relative to a constant-climate control scenario .
Changes in the formation , transport and cycling of biological material may counteract the reduced uptake , but the response of the biological community to the climate change is difficult to predict on present understanding .
Our simulation suggests that such physical and biological changes might already be occurring , and that they could substantially affect the ocean carbon sink over the next few decades .

[228] Independent variations of CH4 emissions and isotopic composition over the past 160,000 years

During the last glacial cycle , greenhouse gas concentrations fluctuated on decadal and longer timescales .
Concentrations of methane , as measured in polar ice cores , show a close connection with Northern Hemisphere temperature variability , but the contribution of the various methane sources and sinks to changes in concentration is still a matter of debate .
Here we assess changes in methane cycling over the past 160,000 years by measurements of the carbon isotopic composition delta13C of methane in Antarctic ice cores from Dronning Maud Land and Vostok .
We find that variations in the delta13C of methane are not generally correlated with changes in atmospheric methane concentration , but instead more closely correlated to atmospheric CO2 concentrations .
We interpret this to reflect a climatic and CO2-related control on the isotopic signature of methane source material , such as ecosystem shifts in the seasonally inundated tropical wetlands that produce methane .
In contrast , relatively stable delta13C values occurred during intervals of large changes in the atmospheric loading of methane .
We suggest that most methane sources -- most notably tropical wetlands -- must have responded simultaneously to climate changes across these periods .

[229] Gene pleiotropy constrains gene expression changes in fish adapted to different thermal conditions

Understanding the factors that shape the evolution of gene expression is a central goal in biology , but the molecular mechanisms behind this remain controversial .
A related major goal is ascertaining how such factors may affect the adaptive potential of a species or population .
Here we demonstrate that temperature-driven gene expression changes in fish adapted to differing thermal environments are constrained by the level of gene pleiotropy estimated by either the number of protein interactions or gene biological processes .
Genes with low pleiotropy levels were the main drivers of both plastic and evolutionary global expression profile changes , while highly pleiotropic genes had limited expression response to temperature treatment .
Our study provides critical insights into the molecular mechanisms by which natural populations can adapt to changing environments .
In addition to having important implications for climate change adaptation , these results suggest that gene pleiotropy should be considered more carefully when interpreting expression profiling data .

[230] Drought impact on forest carbon dynamics and fluxes in Amazonia

In 2005 and 2010 the Amazon basin experienced two strong droughts , driven by shifts in the tropical hydrological regime possibly associated with global climate change , as predicted by some global models .
Tree mortality increased after the 2005 drought , and regional atmospheric inversion modelling showed basin-wide decreases in CO2 uptake in 2010 compared with 2011 ( ref .
5 ) .
But the response of tropical forest carbon cycling to these droughts is not fully understood and there has been no detailed multi-site investigation in situ .
Here we use several years of data from a network of thirteen 1-ha forest plots spread throughout South America , where each component of net primary production ( NPP ) , autotrophic respiration and heterotrophic respiration is measured separately , to develop a better mechanistic understanding of the impact of the 2010 drought on the Amazon forest .
We find that total NPP remained constant throughout the drought .
However , towards the end of the drought , autotrophic respiration , especially in roots and stems , declined significantly compared with measurements in 2009 made in the absence of drought , with extended decreases in autotrophic respiration in the three driest plots .
In the year after the drought , total NPP remained constant but the allocation of carbon shifted towards canopy NPP and away from fine-root NPP .
Both leaf-level and plot-level measurements indicate that severe drought suppresses photosynthesis .
Scaling these measurements to the entire Amazon basin with rainfall data , we estimate that drought suppressed Amazon-wide photosynthesis in 2010 by 0.38 petagrams of carbon ( 0.23-0 .53 petagrams of carbon ) .
Overall , we find that during this drought , instead of reducing total NPP , trees prioritized growth by reducing autotrophic respiration that was unrelated to growth .
This suggests that trees decrease investment in tissue maintenance and defence , in line with eco-evolutionary theories that trees are competitively disadvantaged in the absence of growth .
We propose that weakened maintenance and defence investment may , in turn , cause the increase in post-drought tree mortality observed at our plots .

[231] Patterns of Indian Ocean sea-level change in a warming climate

Global sea level has risen during the past decades as a result of thermal expansion of the warming ocean and freshwater addition from melting continental ice .
However , sea-level rise is not globally uniform .
Regional sea levels can be affected by changes in atmospheric or oceanic circulation .
As long-term observational records are scarce , regional changes in sea level in the Indian Ocean are poorly constrained .
Yet estimates of future sea-level changes are essential for effective risk assessment .
Here we combine in situ and satellite observations of Indian Ocean sea level with climate-model simulations , to identify a distinct spatial pattern of sea-level rise since the 1960s .
We find that sea level has decreased substantially in the south tropical Indian Ocean whereas it has increased elsewhere .
This pattern is driven by changing surface winds associated with a combined invigoration of the Indian Ocean Hadley and Walker cells , patterns of atmospheric overturning circulation in the north-south and east-west direction , respectively , which is partly attributable to rising levels of atmospheric greenhouse gases .
We conclude that -- if ongoing anthropogenic warming dominates natural variability -- the pattern we detected is likely to persist and to increase the environmental stress on some coasts and islands in the Indian Ocean .

[232] Global protected area expansion is compromised by projected land-use and parochialism

Protected areas are one of the main tools for halting the continuing global biodiversity crisis caused by habitat loss , fragmentation and other anthropogenic pressures .
According to the Aichi Biodiversity Target 11 adopted by the Convention on Biological Diversity , the protected area network should be expanded to at least 17 % of the terrestrial world by 2020 ( http://www.cbd.int/sp/targets ) .
To maximize conservation outcomes , it is crucial to identify the best expansion areas .
Here we show that there is a very high potential to increase protection of ecoregions and vertebrate species by expanding the protected area network , but also identify considerable risk of ineffective outcomes due to land-use change and uncoordinated actions between countries .
We use distribution data for 24,757 terrestrial vertebrates assessed under the International Union for the Conservation of Nature ( IUCN ) ` red list of threatened species ' , and terrestrial ecoregions ( 827 ) , modified by land-use models for the present and 2040 , and introduce techniques for global and balanced spatial conservation prioritization .
First , we show that with a coordinated global protected area network expansion to 17 % of terrestrial land , average protection of species ranges and ecoregions could triple .
Second , if projected land-use change by 2040 ( ref .
11 ) takes place , it becomes infeasible to reach the currently possible protection levels , and over 1,000 threatened species would lose more than 50 % of their present effective ranges worldwide .
Third , we demonstrate a major efficiency gap between national and global conservation priorities .
Strong evidence is shown that further biodiversity loss is unavoidable unless international action is quickly taken to balance land-use and biodiversity conservation .
The approach used here can serve as a framework for repeatable and quantitative assessment of efficiency , gaps and expansion of the global protected area network globally , regionally and nationally , considering current and projected land-use pressures .

[233] Soil amoebae rapidly change bacterial community composition in the rhizosphere of Arabidopsis thaliana

We constructed an experimental model system to study the effects of grazing by a common soil amoeba , Acanthamoeba castellanii , on the composition of bacterial communities in the rhizosphere of Arabidopsis thaliana .
Amoebae showed distinct grazing preferences for specific bacterial taxa , which were rapidly replaced by grazing tolerant taxa in a highly reproducible way .
The relative proportion of active bacteria increased although bacterial abundance was strongly decreased by amoebae .
Specific bacterial taxa had disappeared already two days after inoculation of amoebae .
The decrease in numbers was most pronounced in Betaproteobacteria and Firmicutes .
In contrast , Actinobacteria , Nitrospira , Verrucomicrobia and Planctomycetes increased .
Although other groups , such as betaproteobacterial ammonia oxidizers and Gammaproteobacteria did not change in abundance , denaturing gradient gel electrophoresis with specific primers for pseudomonads ( Gammaproteobacteria ) revealed both specific changes in community composition as well as shifts in functional genes ( gacA ) involved in bacterial defence responses .
The resulting positive feedback on plant growth in the amoeba treatment confirms that bacterial grazers play a dominant role in structuring bacteria-plant interactions .
This is the first detailed study documenting how rapidly protozoan grazers induce shifts in rhizosphere bacterial community composition .

[234] Long-term intensive management increased carbon occluded in phytolith ( PhytOC ) in bamboo forest soils

Carbon ( C ) occluded in phytolith ( PhytOC ) is highly stable at millennium scale and its accumulation in soils can help increase long-term C sequestration .
Here , we report that soil PhytOC storage significantly increased with increasing duration under intensive management ( mulching and fertilization ) in Lei bamboo ( Phyllostachys praecox ) plantations .
The PhytOC storage in 0-40 cm soil layer in bamboo plantations increased by 217 Mg C ha-1 , 20 years after being converted from paddy fields .
The PhytOC accumulated at 79 kg C ha-1 yr-1 , a rate far exceeding the global mean long-term soil C accumulation rate of 24 kg C ha-1 yr-1 reported in the literature .
Approximately 86 % of the increased PhytOC came from the large amount of mulch applied .
Our data clearly demonstrate the decadal scale management effect on PhytOC accumulation , suggesting that heavy mulching is a potential method for increasing long-term organic C storage in soils for mitigating global climate change .

[235] Nitrogen cycling driven by organic matter export in the South Pacific oxygen minimum zone

Oxygen minimum zones are expanding globally , and at present account for around 20-40 % of oceanic nitrogen loss .
Heterotrophic denitrification and anammox -- anaerobic ammonium oxidation with nitrite -- are responsible for most nitrogen loss in these low-oxygen waters .
Anammox is particularly significant in the eastern tropical South Pacific , one of the largest oxygen minimum zones globally .
However , the factors that regulate anammox-driven nitrogen loss have remained unclear .
Here , we present a comprehensive nitrogen budget for the eastern tropical South Pacific oxygen minimum zone , using measurements of nutrient concentrations , experimentally determined rates of nitrogen transformation and a numerical model of export production .
Anammox was the dominant mode of nitrogen loss at the time of sampling .
Rates of anammox , and related nitrogen transformations , were greatest in the productive shelf waters , and tailed off with distance from the coast .
Within the shelf region , anammox activity peaked in both upper and bottom waters .
Overall , rates of nitrogen transformation , including anammox , were strongly correlated with the export of organic matter .
We suggest that the sinking of organic matter , and thus the release of ammonium into the water column , together with benthic ammonium release , fuel nitrogen loss from oxygen minimum zones .

[236] Effect of remote sea surface temperature change on tropical cyclone potential intensity

The response of tropical cyclone activity to global warming is widely debated .
It is often assumed that warmer sea surface temperatures provide a more favourable environment for the development and intensification of tropical cyclones , but cyclone genesis and intensity are also affected by the vertical thermodynamic properties of the atmosphere .
Here we use climate models and observational reconstructions to explore the relationship between changes in sea surface temperature and tropical cyclone ` potential intensity ' -- a measure that provides an upper bound on cyclone intensity and can also reflect the likelihood of cyclone development .
We find that changes in local sea surface temperature are inadequate for characterizing even the sign of changes in potential intensity , but that long-term changes in potential intensity are closely related to the regional structure of warming ; regions that warm more than the tropical average are characterized by increased potential intensity , and vice versa .
We use this relationship to reconstruct changes in potential intensity over the twentieth century from observational reconstructions of sea surface temperature .
We find that , even though tropical Atlantic sea surface temperatures are currently at a historical high , Atlantic potential intensity probably peaked in the 1930s and 1950s , and recent values are near the historical average .
Our results indicate that -- per unit local sea surface temperature change -- the response of tropical cyclone activity to natural climate variations , which tend to involve localized changes in sea surface temperature , may be larger than the response to the more uniform patterns of greenhouse-gas-induced warming .

[237] Programming adaptive control to evolve increased metabolite production

The complexity inherent in biological systems challenges efforts to rationally engineer novel phenotypes , especially those not amenable to high-throughput screens and selections .
In nature , increased mutation rates generate diversity in a population that can lead to the evolution of new phenotypes .
Here we construct an adaptive control system that increases the mutation rate in order to generate diversity in the population , and decreases the mutation rate as the concentration of a target metabolite increases .
This system is called feedback-regulated evolution of phenotype ( FREP ) , and is implemented with a sensor to gauge the concentration of a metabolite and an actuator to alter the mutation rate .
To evolve certain novel traits that have no known natural sensors , we develop a framework to assemble synthetic transcription factors using metabolic enzymes and construct four different sensors that recognize isopentenyl diphosphate in bacteria and yeast .
We verify FREP by evolving increased tyrosine and isoprenoid production .

[238] Weakened stratospheric quasibiennial oscillation driven by increased tropical mean upwelling

The zonal wind in the tropical stratosphere switches between prevailing easterlies and westerlies with a period of about 28 months .
In the lowermost stratosphere , the vertical structure of this quasibiennial oscillation ( QBO ) is linked to the mean upwelling , which itself is a key factor in determining stratospheric composition .
Evidence for changes in the QBO have until now been equivocal , raising questions as to the extent of stratospheric circulation changes in a global warming context .
Here we report an analysis of near-equatorial radiosonde observations for 1953-2012 , and reveal a long-term trend of weakening amplitude in the zonal wind QBO in the tropical lower stratosphere .
The trend is particularly notable at the 70-hectopascal pressure level ( an altitude of about 19 kilometres ) , where the QBO amplitudes dropped by roughly one-third over the period .
This trend is also apparent in the global warming simulations of the four models in the Coupled Model Intercomparison Project Phase 5 ( CMIP5 ) that realistically simulate the QBO .
The weakening is most reasonably explained as resulting from a trend of increased mean tropical upwelling in the lower stratosphere .
Almost all comprehensive climate models have projected an intensifying tropical upwelling in global warming scenarios , but attempts to estimate changes in the upwelling by using observational data have yielded ambiguous , inconclusive or contradictory results .
Our discovery of a weakening trend in the lower-stratosphere QBO amplitude provides strong support for the existence of a long-term trend of enhanced upwelling near the tropical tropopause .

[239] An abrupt wind shift in western Europe at the onset of the Younger Dryas cold period

The Younger Dryas cooling 12,700 years ago is one of the most abrupt climate changes observed in Northern Hemisphere palaeoclimate records .
Annually laminated lake sediments are ideally suited to record the dynamics of such abrupt changes , as the seasonal deposition responds immediately to climate , and the varve counts provide an accurate estimate of the timing of the change .
Here , we present sub-annual records of varve microfacies and geochemistry from Lake Meerfelder Maar in western Germany , providing one of the best dated records of this climate transition .
Our data indicate an abrupt increase in storminess during the autumn to spring seasons , occurring from one year to the next at 12,679 yr BP , broadly coincident with other changes in this region .
We suggest that this shift in wind strength represents an abrupt change in the North Atlantic westerlies towards a stronger and more zonal jet .
Changes in meridional overturning circulation alone can not fully explain the changes in European climate ; we suggest the observed wind shift provides the mechanism for the strong temporal link between North Atlantic Ocean overturning circulation and European climate during deglaciation .

[240] Regional rainfall decline in Australia attributed to anthropogenic greenhouse gases and ozone levels

Precipitation in austral autumn and winter has declined over parts of southern and especially southwestern Australia in the past few decades .
According to observations and climate models , at least part of this decline is associated with changes in large-scale atmospheric circulation , including a poleward movement of the westerly winds and increasing atmospheric surface pressure over parts of southern Australia .
Here we use a high-resolution global climate model to analyse the causes of this rainfall decline .
In our simulations , many aspects of the observed regional rainfall decline over southern and southwest Australia are reproduced in response to anthropogenic changes in levels of greenhouse gases and ozone in the atmosphere , whereas anthropogenic aerosols do not contribute to the simulated precipitation decline .
Simulations of future climate with this model suggest amplified winter drying over most parts of southern Australia in the coming decades in response to a high-end scenario of changes in radiative forcing .
The drying is most pronounced over southwest Australia , with total reductions in austral autumn and winter precipitation of approximately 40 % by the late twenty-first century .

[241] Overexpression of beta-carotene hydroxylase enhances stress tolerance in Arabidopsis

Plant stress caused by extreme environmental conditions is already a principal reason for yield reduction in crops .
The threat of global environment change makes it increasingly important to generate crop plants that will withstand such conditions .
Stress , particularly stress caused by increased sunlight , leads to the production of reactive oxygen species that cause photo-oxidative cell damage .
Carotenoids , which are present in the membranes of all photosynthetic organisms , help protect against such light-dependent oxidative damage .
In plants , the xanthophyll cycle ( the reversible interconversion of two carotenoids , violaxanthin and zeaxanthin ) has a key photoprotective role and is therefore a promising target for genetic engineering to enhance stress tolerance .
Here we show that in Arabidopsis thaliana overexpression of the chyB gene that encodes beta-carotene hydroxylase -- an enzyme in the zeaxanthin biosynthetic pathway -- causes a specific twofold increase in the size of the xanthophyll cycle pool .
The plants are more tolerant to conditions of high light and high temperature , as shown by reduced leaf necrosis , reduced production of the stress indicator anthocyanin and reduced lipid peroxidation .
Stress protection is probably due to the function of zeaxanthin in preventing oxidative damage of membranes .

[242] Increase in Agulhas leakage due to poleward shift of Southern Hemisphere westerlies

The transport of warm and salty Indian Ocean waters into the Atlantic Ocean -- the Agulhas leakage -- has a crucial role in the global oceanic circulation and thus the evolution of future climate .
At present these waters provide the main source of heat and salt for the surface branch of the Atlantic meridional overturning circulation ( MOC ) .
There is evidence from past glacial-to-interglacial variations in foraminiferal assemblages and model studies that the amount of Agulhas leakage and its corresponding effect on the MOC has been subject to substantial change , potentially linked to latitudinal shifts in the Southern Hemisphere westerlies .
A progressive poleward migration of the westerlies has been observed during the past two to three decades and linked to anthropogenic forcing , but because of the sparse observational records it has not been possible to determine whether there has been a concomitant response of Agulhas leakage .
Here we present the results of a high-resolution ocean general circulation model to show that the transport of Indian Ocean waters into the South Atlantic via the Agulhas leakage has increased during the past decades in response to the change in wind forcing .
The increased leakage has contributed to the observed salinification of South Atlantic thermocline waters .
Both model and historic measurements off South America suggest that the additional Indian Ocean waters have begun to invade the North Atlantic , with potential implications for the future evolution of the MOC .

[243] High sensitivity of peat decomposition to climate change through water-table feedback

Historically , northern peatlands have functioned as a carbon sink , sequestering large amounts of soil organic carbon , mainly due to low decomposition in cold , largely waterlogged soils .
The water table , an essential determinant of soil-organic-carbon dynamics , interacts with soil organic carbon .
Because of the high water-holding capacity of peat and its low hydraulic conductivity , accumulation of soil organic carbon raises the water table , which lowers decomposition rates of soil organic carbon in a positive feedback loop .
This two-way interaction between hydrology and biogeochemistry has been noted , but is not reproduced in process-based simulations .
Here we present simulations with a coupled physical-biogeochemical soil model with peat depths that are continuously updated from the dynamic balance of soil organic carbon .
Our model reproduces dynamics of shallow and deep peatlands in northern Manitoba , Canada , on both short and longer timescales .
We find that the feedback between the water table and peat depth increases the sensitivity of peat decomposition to temperature , and intensifies the loss of soil organic carbon in a changing climate .
In our long-term simulation , an experimental warming of 4 degreesC causes a 40 % loss of soil organic carbon from the shallow peat and 86 % from the deep peat .
We conclude that peatlands will quickly respond to the expected warming in this century by losing labile soil organic carbon during dry periods .

[244] Changes in pH at the exterior surface of plankton with ocean acidification

Anthropogenically released CO2 is dissolving in the ocean , causing a decrease in bulk-seawater pH ( ocean acidification ) .
Projections indicate that the pH will drop 0.3 units from its present value by 2100 ( ref . )
.
However , it is unclear how the growth of plankton is likely to respond .
Using simulations we demonstrate how pH and carbonate chemistry at the exterior surface of marine organisms deviates increasingly from those of the bulk sea water as organism metabolic activity and size increases .
These deviations will increase in the future as the buffering capacity of sea water decreases with decreased pH and as metabolic activity increases with raised seawater temperatures .
We show that many marine plankton will experience pH conditions completely outside their recent historical range .
However , ocean acidification is likely to have differing impacts on plankton physiology as taxon-specific differences in organism size , metabolic activity and growth rates during blooms result in very different microenvironments around the organism .
This is an important consideration for future studies in ocean acidification as the carbonate chemistry experienced by most planktonic organisms will probably be considerably different from that measured in bulk-seawater samples .
An understanding of these deviations will assist interpretation of the impacts of ocean acidification on plankton of different size and metabolic activity .

[245] Community shifts of actively growing lake bacteria after N-acetyl-glucosamine addition : improving the BrdU-FACS method

In aquatic environments , community dynamics of bacteria , especially actively growing bacteria ( AGB ) , are tightly linked with dissolved organic matter ( DOM ) quantity and quality .
We analyzed the community dynamics of DNA-synthesizing and accordingly AGB by linking an improved bromodeoxyuridine immunocytochemistry approach with fluorescence-activated cell sorting ( BrdU-FACS ) .
FACS-sorted cells of even oligotrophic ecosystems in winter were characterized by 16S rRNA gene analysis .
In incubation experiments , we examined community shifts of AGB in response to the addition of N-acetyl-glucosamine ( NAG ) , one of the most abundant aminosugars in aquatic systems .
Our improved BrdU-FACS analysis revealed that AGB winter communities of oligotrophic Lake Stechlin ( northeastern Germany ) substantially differ from those of total bacteria and consist of Alpha - , Beta - , Gamma - , Deltaproteobacteria , Actinobacteria , Candidatus OP10 and Chloroflexi .
AGB populations with different BrdU-fluorescence intensities and cell sizes represented different phylotypes suggesting that single-cell growth potential varies at the taxon level .
NAG incubation experiments demonstrated that a variety of widespread taxa related to Alpha - , Beta - , Gammaproteobacteria , Bacteroidetes , Actinobacteria , Firmicutes , Planctomycetes , Spirochaetes , Verrucomicrobia and Chloroflexi actively grow in the presence of NAG .
The BrdU-FACS approach enables detailed phylogenetic studies of AGB and , thus , to identify those phylotypes which are potential key players in aquatic DOM cycling .

[246] A meta-analysis of crop yield under climate change and adaptation

Feeding a growing global population in a changing climate presents a significant challenge to society .
The projected yields of crops under a range of agricultural and climatic scenarios are needed to assess food security prospects .
Previous meta-analyses have summarized climate change impacts and adaptive potential as a function of temperature , but have not examined uncertainty , the timing of impacts , or the quantitative effectiveness of adaptation .
Here we develop a new data set of more than 1,700 published simulations to evaluate yield impacts of climate change and adaptation .
Without adaptation , losses in aggregate production are expected for wheat , rice and maize in both temperate and tropical regions by 2 degreesC of local warming .
Crop-level adaptations increase simulated yields by an average of 7-15 % , with adaptations more effective for wheat and rice than maize .
Yield losses are greater in magnitude for the second half of the century than for the first .
Consensus on yield decreases in the second half of the century is stronger in tropical than temperate regions , yet even moderate warming may reduce temperate crop yields in many locations .
Although less is known about interannual variability than mean yields , the available data indicate that increases in yield variability are likely .

[247] Tension between reducing sea-level rise and global warming through solar-radiation management

Geoengineering using solar-radiation management ( SRM ) is gaining interest as a potential strategy to reduce future climate change impacts .
Basic physics and past observations suggest that reducing insolation will , on average , cool the Earth .
It is uncertain , however , whether SRM can reduce climate change stressors such as sea-level rise or rates of surface air temperature change .
Here we use an Earth system model of intermediate complexity to quantify the possible response of sea levels and surface air temperatures to projected climate forcings and SRM strategies .
We find that SRM strategies introduce a potentially strong tension between the objectives to reduce ( 1 ) the rate of temperature change and ( 2 ) sea-level rise .
This tension arises primarily because surface air temperatures respond faster to radiative forcings than sea levels .
Our results show that the forcing required to stop sea-level rise could cause a rapid cooling with a rate similar to the peak business-as-usual warming rate .
Furthermore , termination of SRM was found to produce warming rates up to five times greater than the maximum rates under the business-as-usual CO2 scenario , whereas sea-level rise rates were only 30 % higher .
Reducing these risks requires a slow phase-out of many decades and thus commits future generations .

[248] Ancient DNA reveals that bowhead whale lineages survived Late Pleistocene climate change and habitat shifts

The climatic changes of the glacial cycles are thought to have been a major driver of population declines and species extinctions .
However , studies to date have focused on terrestrial fauna and there is little understanding of how marine species responded to past climate change .
Here we show that a true Arctic species , the bowhead whale ( Balaena mysticetus ) , shifted its range and tracked its core suitable habitat northwards during the rapid climate change of the Pleistocene-Holocene transition .
Late Pleistocene lineages survived into the Holocene and effective female population size increased rapidly , concurrent with a threefold increase in core suitable habitat .
This study highlights that responses to climate change are likely to be species specific and difficult to predict .
We estimate that the core suitable habitat of bowhead whales will be almost halved by the end of this century , potentially influencing future population dynamics .

[249] Indo-Pacific Warm Pool Area Expansion , Modoki Activity , and Tropical Cold-Point Tropopause Temperature Variations

The tropical cold-point tropopause temperature ( CPTT ) , a potentially important indicator of global climate change , is of particular importance for understanding changes in stratospheric water vapor levels .
Since the 1980s , the tropical CPTT has shown not only interannual variations , but also a decreasing trend .
However , the factors controlling the variations in the tropical CPTT since the 1980s remain elusive .
The present study reveals that the continuous expansion of the area of the Indo-Pacific warm pool ( IPWP ) since the 1980s represents an increase in the total heat energy of the IPWP available to heat the tropospheric air , which is likely to expand as a result .
This process lifts the tropical cold-point tropopause height ( CPTH ) and leads to the observed long-term cooling trend of the tropical CPTT .
In addition , our analysis shows that Modoki activity is an important factor in modulating the interannual variations of the tropical CPTT through significant effects on overshooting convection .

[250] Changes in rainfall seasonality in the tropics

Climate change has altered not only the overall magnitude of rainfall but also its seasonal distribution and interannual variability worldwide .
Such changes in the rainfall regimes will be most keenly felt in arid and semiarid regions , where water availability and timing are key factors controlling biogeochemical cycles , primary productivity , and the phenology of growth and reproduction , while also regulating agricultural production .
Nevertheless , a comprehensive framework to understand the complex seasonal rainfall regimes across multiple timescales is still lacking .
Here , we formulate a global measure of seasonality , which captures the effects of both magnitude and concentration of the rainy season , and use it to identify regions across the tropics with highly seasonal rainfall regimes .
By further decomposing rainfall seasonality into its magnitude , timing and duration components , we find increases in the interannual variability of seasonality over many parts of the dry tropics , implying increasing uncertainty in the intensity , arrival and duration of seasonal rainfall over the past century .
We show that such increases in rainfall variability were accompanied by shifts in its seasonal magnitude , timing and duration , thus underscoring the importance of analysing seasonal rainfall regimes in a context that is most relevant to local ecological and social processes .

[251] Different glacier status with atmospheric circulations in Tibetan Plateau and surroundings

The Tibetan Plateau and surroundings contain the largest number of glaciers outside the polar regions .
These glaciers are at the headwaters of many prominent Asian rivers and are largely experiencing shrinkage , which affects the water discharge of large rivers such as the Indus .
The resulting potential geohazards merit a comprehensive study of glacier status in the Tibetan Plateau and surroundings .
Here we report on the glacier status over the past 30 years by investigating the glacial retreat of 82 glaciers , area reduction of 7,090 glaciers and mass-balance change of 15 glaciers .
Systematic differences in glacier status are apparent from region to region , with the most intensive shrinkage in the Himalayas ( excluding the Karakorum ) characterized by the greatest reduction in glacial length and area and the most negative mass balance .
The shrinkage generally decreases from the Himalayas to the continental interior and is the least in the eastern Pamir , characterized by the least glacial retreat , area reduction and positive mass balance .
In addition to rising temperature , decreased precipitation in the Himalayas and increasing precipitation in the eastern Pamir accompanied by different atmospheric circulation patterns is probably driving these systematic differences .

[252] Effectiveness of stratospheric solar-radiation management as a function of climate sensitivity

If implementation of proposals to engineer the climate through solar-radiation management ( SRM ) ever occurs , it is likely to be contingent on climate sensitivity .
However , modelling studies examining the effectiveness of SRM as a strategy to offset anthropogenic climate change have used only the standard parameterizations of atmosphere-ocean general circulation models that yield climate sensitivities close to the Coupled Model Intercomparison Project mean .
Here , we use a perturbed-physics ensemble modelling experiment to examine how the response of the climate to SRM implemented in the stratosphere ( SRM-S ) varies under different greenhouse-gas climate sensitivities .
When SRM-S is used to compensate for rising atmospheric concentrations of greenhouse gases , its effectiveness in stabilizing regional climates diminishes with increasing climate sensitivity .
However , the potential of SRM-S to slow down unmitigated climate change , even regionally , increases with climate sensitivity .
On average , in variants of the model with higher sensitivity , SRM-S reduces regional rates of temperature change by more than 90 % and rates of precipitation change by more than 50 % .

[253] Importance of background climate in determining impact of land-cover change on regional climate

Humans have modified the Earth 's climate through emissions of greenhouse gases and through land-use and land-cover change ( LULCC ) .
Increasing concentrations of greenhouse gases in the atmosphere warm the mid-latitudes more than the tropics , in part owing to a reduced snow-albedo feedback as snow cover decreases .
Higher concentration of carbon dioxide also increases precipitation in many regions , as a result of an intensification of the hydrological cycle .
The biophysical effects of LULCC since pre-industrial times have probably cooled temperate and boreal regions and warmed some tropical regions .
Here we use a climate model to show that how snow and rainfall change under increased greenhouse gases dominates how LULCC affects regional temperature .
Increased greenhouse-gas-driven changes in snow and rainfall affect the snow-albedo feedback and the supply of water , which in turn limits evaporation .
These changes largely control the net impact of LULCC on regional climate .
Our results show that capturing whether future biophysical changes due to LULCC warm or cool a specific region therefore requires an accurate simulation of changes in snow cover and rainfall geographically coincident with regions of LULCC .
This is a challenge to current climate models , but also provides potential for further improving detection and attribution methods .

[254] Observed changes in extreme wet and dry spells during the South Asian summer monsoon season

The South Asian summer monsoon directly affects the lives of more than 1/6th of the world 's population .
There is substantial variability within the monsoon season , including fluctuations between periods of heavy rainfall ( wet spells ) and low rainfall ( dry spells ) .
These fluctuations can cause extreme wet and dry regional conditions that adversely impact agricultural yields , water resources , infrastructure and human systems .
Through a comprehensive statistical analysis of precipitation observations ( 1951-2011 ) , we show that statistically significant decreases in peak-season precipitation over the core-monsoon region have co-occurred with statistically significant increases in daily-scale precipitation variability .
Further , we find statistically significant increases in the frequency of dry spells and intensity of wet spells , and statistically significant decreases in the intensity of dry spells .
These changes in extreme wet and dry spell characteristics are supported by increases in convective available potential energy and low-level moisture convergence , along with changes to the large-scale circulation aloft in the atmosphere .
The observed changes in wet and dry extremes during the monsoon season are relevant for managing climate-related risks , with particular relevance for water resources , agriculture , disaster preparedness and infrastructure planning .

[255] Natural and anthropogenic variations in methane sources during the past two millennia

Methane is an important greenhouse gas that is emitted from multiple natural and anthropogenic sources .
Atmospheric methane concentrations have varied on a number of timescales in the past , but what has caused these variations is not always well understood .
The different sources and sinks of methane have specific isotopic signatures , and the isotopic composition of methane can therefore help to identify the environmental drivers of variations in atmospheric methane concentrations .
Here we present high-resolution carbon isotope data ( delta13C content ) for methane from two ice cores from Greenland for the past two millennia .
We find that the delta13C content underwent pronounced centennial-scale variations between 100 bc and ad 1600 .
With the help of two-box model calculations , we show that the centennial-scale variations in isotope ratios can be attributed to changes in pyrogenic and biogenic sources .
We find correlations between these source changes and both natural climate variability -- such as the Medieval Climate Anomaly and the Little Ice Age -- and changes in human population and land use , such as the decline of the Roman empire and the Han dynasty , and the population expansion during the medieval period .

[256] The effectiveness of coral reefs for coastal hazard risk reduction and adaptation

The world 's coastal zones are experiencing rapid development and an increase in storms and flooding .
These hazards put coastal communities at heightened risk , which may increase with habitat loss .
Here we analyse globally the role and cost effectiveness of coral reefs in risk reduction .
Meta-analyses reveal that coral reefs provide substantial protection against natural hazards by reducing wave energy by an average of 97 % .
Reef crests alone dissipate most of this energy ( 86 % ) .
There are 100 million or more people who may receive risk reduction benefits from reefs or bear hazard mitigation and adaptation costs if reefs are degraded .
We show that coral reefs can provide comparable wave attenuation benefits to artificial defences such as breakwaters , and reef defences can be enhanced cost effectively .
Reefs face growing threats yet there is opportunity to guide adaptation and hazard mitigation investments towards reef restoration to strengthen this first line of coastal defence .

[257] Separating sensitivity from exposure in assessing extinction risk from climate change

Predictive frameworks of climate change extinction risk generally focus on the magnitude of climate change a species is expected to experience and the potential for that species to track suitable climate .
A species ' risk of extinction from climate change will depend , in part , on the magnitude of climate change the species experiences , its exposure .
However , exposure is only one component of risk .
A species ' risk of extinction will also depend on its intrinsic ability to tolerate changing climate , its sensitivity .
We examine exposure and sensitivity individually for two example taxa , terrestrial amphibians and mammals .
We examine how these factors are related among species and across regions and how explicit consideration of each component of risk may affect predictions of climate change impacts .
We find that species ' sensitivities to climate change are not congruent with their exposures .
Many highly sensitive species face low exposure to climate change and many highly exposed species are relatively insensitive .
Separating sensitivity from exposure reveals patterns in the causes and drivers of species ' extinction risk that may not be evident solely from predictions of climate change .
Our findings emphasise the importance of explicitly including sensitivity and exposure to climate change in assessments of species ' extinction risk .

[258] Ecosystem consequences of wolf behavioural response to climate

Because apex predators exert considerable influence on the structure and function of top-down ecosystems , their responses to climate may shape responses at lower trophic levels .
Previous reports of trophic cascades and ecosystem dynamics induced by predators have focused on changes in their abundance , whereas we investigated whether changes in predator behaviour could precipitate cascades of similar ecological scale .
Here we report the ecological consequences of predator behavioural response to global climatic variation using 40 years of data on wolf predation from Isle Royale , USA , where wolves limit abundance of moose , which limit productivity of fir trees .
In response to increases in winter snow related to the North Atlantic Oscillation , wolves hunted in larger packs and , consequently , tripled the number of moose killed per day compared with less snowy years when they hunted in smaller packs .
Following increased predation rates , moose abundance declined , and , following release from heavy browsing , growth of understory fir increased .
Hence , cascading behavioural responses of apex predators may be a substantial link in the pathway from climatic change to ecosystem function .

[259] Increase in hourly precipitation extremes beyond expectations from temperature changes

Changes in precipitation extremes under greenhouse warming are commonly assumed to be constrained by changes in the amounts of precipitable water in the atmosphere .
Global climate models generally predict only marginal changes in relative humidity , implying that the actual amount of atmospheric precipitable water scales with the water vapour content of saturation , which is governed by the Clausius-Clapeyron relation .
Indeed , changes in daily precipitation extremes in global climate models seem to be consistent with the 7 % increase per degree of warming given by the Clausius-Clapeyron relation , but it is uncertain how general this scaling behaviour is across timescales .
Here , we analyse a 99-year record of hourly precipitation observations from De Bilt , the Netherlands , and find that one-hour precipitation extremes increase twice as fast with rising temperatures as expected from the Clausius-Clapeyron relation when daily mean temperatures exceed 12 degreesC .
In addition , simulations with a high-resolution regional climate model show that one-hour precipitation extremes increase at a rate close to 14 % per degree of warming in large parts of Europe .
Our results demonstrate that changes in short-duration precipitation extremes may well exceed expectations from the Clausius-Clapeyron relation .
These short-duration extreme events can have significant impacts , such as local flooding , erosion and water damage .

[260] Warming of the tropical Atlantic Ocean and slowdown of thermohaline circulation during the last deglaciation

Evidence for abrupt climate changes on millennial and shorter timescales is widespread in marine and terrestrial climate records .
Rapid reorganization of ocean circulation is considered to exert some control over these changes , as are shifts in the concentrations of atmospheric greenhouse gases .
The response of the climate system to these two influences is fundamentally different : slowing of thermohaline overturn in the North Atlantic Ocean is expected to decrease northward heat transport by the ocean and to induce warming of the tropical Atlantic , whereas atmospheric greenhouse forcing should cause roughly synchronous global temperature changes .
So these two mechanisms of climate change should be distinguishable by the timing of surface-water temperature variations relative to changes in deep-water circulation .
Here we present a high-temporal-resolution record of sea surface temperatures from the western tropical North Atlantic Ocean which spans the past 29,000 years , derived from measurements of temperature-sensitive alkenone unsaturation in sedimentary organic matter .
We find significant warming is documented for Heinrich event H1 ( 16,900-15 ,400 calendar years bp ) and the Younger Dryas event ( 12,900-11 ,600 cal .
yr bp ) , which were periods of intense cooling in the northern North Atlantic .
Temperature changes in the tropical and high-latitude North Atlantic are out of phase , suggesting that the thermohaline circulation was the important trigger for these rapid climate changes .

[261] African vegetation controlled by tropical sea surface temperatures in the mid-Pleistocene period

The dominant forcing factors for past large-scale changes in vegetation are widely debated .
Changes in the distribution of C4 plants -- adapted to warm , dry conditions and low atmospheric CO2 concentrations -- have been attributed to marked changes in environmental conditions , but the relative impacts of changes in aridity , temperature and CO2 concentration are not well understood .
Here , we present a record of African C4 plant abundance between 1.2 and 0.45 million years ago , derived from compound-specific carbon isotope analyses of wind-transported terrigenous plant waxes .
We find that large-scale changes in African vegetation are linked closely to sea surface temperatures in the tropical Atlantic Ocean .
We conclude that , in the mid-Pleistocene , changes in atmospheric moisture content -- driven by tropical sea surface temperature changes and the strength of the African monsoon -- controlled aridity on the African continent , and hence large-scale vegetation changes .

[262] Accelerated microbial turnover but constant growth efficiency with warming in soil

Rising temperatures are expected to reduce global soil carbon ( C ) stocks , driving a positive feedback to climate change .
However , the mechanisms underlying this prediction are not well understood , including how temperature affects microbial enzyme kinetics , growth efficiency ( MGE ) , and turnover .
Here , in a laboratory study , we show that microbial turnover accelerates with warming and , along with enzyme kinetics , determines the response of microbial respiration to temperature change .
In contrast , MGE , which is generally thought to decline with warming , showed no temperature sensitivity .
A microbial-enzyme model suggests that such temperature sensitive microbial turnover would promote soil C accumulation with warming , in contrast to reduced soil C predicted by traditional biogeochemical models .
Furthermore , the effect of increased microbial turnover differs from the effects of reduced MGE , causing larger increases in soil C stocks .
Our results demonstrate that the response of soil C to warming is affected by changes in microbial turnover .
This control should be included in the next generation of models to improve prediction of soil C feedbacks to warming .

[263] A weak El Nino/Southern Oscillation with delayed seasonal growth around 4,300 years ago

Earth 's interannual climate variability is dominated by El Nino/Southern Oscillation ( ENSO ) .
Palaeoclimate records indicate a lower ENSO variance during the middle Holocene compared with today ; however , model simulations have not reproduced the full magnitude of the changes , and whether external forcing drives large intrinsic ENSO variability is therefore a matter of considerable debate .
Here we present a 175-year-long , monthly resolved oxygen isotope record , obtained from a Porites coral microatoll located on Kiritimati ( Christmas ) Island , in the NINO3 .4 region of the central equatorial Pacific .
Our quantitative record of ENSO variability about 4,300 years ago shows that ENSO variance was persistently reduced by 79 % , compared with today , and it exhibits a dominant annual cycle .
Season-specific analysis shows that El Nino events were damped during their September-November growth phase , and delayed relative to the climatological year .
We suggest that the higher boreal summer insolation at the time strengthened the tropical Pacific zonal winds as well as the gradients in sea surface temperature , and thereby led to an enhanced annual cycle and suppressed ENSO .
As the weak ENSO is subject to interdecadal amplitude modulation , we conclude that amplitude modulation is likely to remain robust under altered climates .
Our findings show that ENSO is capable of responding to external forcing .

[264] Seasonal not annual rainfall determines grassland biomass response to carbon dioxide

The rising atmospheric concentration of carbon dioxide ( CO2 ) should stimulate ecosystem productivity , but to what extent is highly uncertain , particularly when combined with changing temperature and precipitation .
Ecosystem response to CO2 is complicated by biogeochemical feedbacks but must be understood if carbon storage and associated dampening of climate warming are to be predicted .
Feedbacks through the hydrological cycle are particularly important and the physiology is well known ; elevated CO2 reduces stomatal conductance and increases plant water use efficiency ( the amount of water required to produce a unit of plant dry matter ) .
The CO2 response should consequently be strongest when water is limiting ; although this has been shown in some experiments , it is absent from many .
Here we show that large annual variation in the stimulation of above-ground biomass by elevated CO2 in a mixed C3/C4 temperate grassland can be predicted accurately using seasonal rainfall totals ; summer rainfall had a positive effect but autumn and spring rainfall had negative effects on the CO2 response .
Thus , the elevated CO2 effect mainly depended upon the balance between summer and autumn/spring rainfall .
This is partly because high rainfall during cool , moist seasons leads to nitrogen limitation , reducing or even preventing biomass stimulation by elevated CO2 .
Importantly , the prediction held whether plots were warmed by 2 degreesC or left unwarmed , and was similar for C3 plants and total biomass , allowing us to make a powerful generalization about ecosystem responses to elevated CO2 .
This new insight is particularly valuable because climate projections predict large changes in the timing of rainfall , even where annual totals remain static .
Our findings will help resolve apparent differences in the outcomes of CO2 experiments and improve the formulation and interpretation of models that are insensitive to differences in the seasonal effects of rainfall on the CO2 response .

[265] Simulating the effects of climate change on tropical montane cloud forests

Tropical montane cloud forests are unique among terrestrial ecosystems in that they are strongly linked to regular cycles of cloud formation .
We have explored changes in atmospheric parameters from global climate model simulations of the Last Glacial Maximum and for doubled atmospheric carbon dioxide concentration ( 2 x CO2 ) conditions which are associated with the height of this cloud formation , and hence the occurrence of intact cloud forests .
These parameters include vertical profiles of absolute and relative humidity surfaces , as well as the warmth index , an empirical proxy of forest type .
For the glacial simulations , the warmth index and absolute humidity suggest a downslope shift of cloud forests that agrees with the available palaeodata .
For the 2x CO2 scenario , the relative humidity surface is shifted upwards by hundreds of metres during the winter dry season when these forests typically rely most on the moisture from cloud contact .
At the same time , an increase in the warmth index implies increased evapo-transpiration .
This combination of reduced cloud contact and increased evapo-transpiration could have serious conservation implications , given that these ecosystems typically harbour a high proportion of endemic species and are often situated on mountain tops or ridge lines .

[266] Adjustment to climate change is constrained by arrival date in a long-distance migrant bird

Spring temperatures in temperate regions have increased over the past 20 years , and many organisms have responded to this increase by advancing the date of their growth and reproduction .
Here we show that adaptation to climate change in a long-distance migrant is constrained by the timing of its migratory journey .
For long-distance migrants climate change may advance the phenology of their breeding areas , but the timing of some species ' spring migration relies on endogenous rhythms that are not affected by climate change .
Thus , the spring migration of these species will not advance even though they need to arrive earlier on their breeding grounds to breed at the appropriate time .
We show that the migratory pied flycatcher Ficedula hypoleuca has advanced its laying date over the past 20 years .
This temporal shift has been insufficient , however , as indicated by increased selection for earlier breeding over the same period .
The shift is hampered by its spring arrival date , which has not advanced .
Some of the numerous long-distance migrants will suffer from climate change , because either their migration strategy is unaffected by climate change , or the climate in breeding and wintering areas are changing at different speeds , preventing adequate adaptation .

[267] Evolution of fixed-channel alluvial plains in response to Carboniferous vegetation

The establishment of terrestrial plants during the Palaeozoic era was one of the most significant changes to the Earth system during the Phanerozoic eon .
The continuing evolution and expansion of land plants irrevocably altered the alluvial landscape : the broad , unconfined and unconsolidated blankets of coarse sediment found at the start of the Cambrian period were replaced by a diverse array of braided and meandering channel styles and stable floodplains by the end of the Devonian period .
Here we show that the first appearance of a sedimentary facies suite attributed to low-energy , organic-rich river systems with multiple channels and stable alluvial islands , known as anabranching or anastomosing rivers , occurred during the Carboniferous period .
Our field studies and literature review demonstrate that the appearance of these rivers coincides with the continuing evolution of tree-like plants .
We suggest that increased floodplain stability and new triggers for channel avulsion were provided by the increase in complexity and diversity of root assemblages , density of floodplain forests and production of woody debris associated with expansion of arborescence .
We conclude that the expansion of tree habitats led to the crossing of a threshold in vegetative control of floodplain and river morphology during the Carboniferous .

[268] Abrupt rise in atmospheric CO2 overestimates community response in a model plant-soil system

Attempts to understand the ecological effect of increasing atmospheric CO2 concentration , [ CO2 ] , usually involve exposing today 's ecosystems to expected future [ CO2 ] levels .
However , a major assumption of these approaches has not been tested -- that exposing ecosystems to a single-step increase in [ CO2 ] will yield similar responses to those of a gradual increase over several decades .
We tested this assumption on a mycorrhizal fungal community over a period of six years .
[ CO2 ] was either increased abruptly , as is typical of most [ CO2 ] experiments , or more gradually over 21 generations .
The two approaches resulted in different structural and functional community responses to increased [ CO2 ] .
Some fungi were sensitive to the carbon pulse of the abrupt [ CO2 ] treatment .
This resulted in an immediate decline in fungal species richness and a significant change in mycorrhizal functioning .
The magnitude of changes in fungal diversity and functioning in response to gradually increasing [ CO2 ] was smaller , and not significantly different to those with ambient [ CO2 ] .
Our results suggest that studies may overestimate some community responses to increasing [ CO2 ] because biota may be sensitive to ecosystem changes that occur as a result of abrupt increases .

[269] The impact of temperature on years of life lost in Brisbane , Australia

Temperature is an important determinant of health .
A better knowledge of how temperature affects population health is important not only to the scientific community , but also to the decision-makers who develop and implement early warning systems and intervention strategies to mitigate the health effects of extreme temperatures .
The temperature-health relationship is also of growing interest as climate change is projected to shift the overall temperature distribution higher .
Previous studies have examined the relative risks of temperature-related mortality , but the absolute measure of years of life lost is also useful as it combines the number of deaths with life expectancy .
Here we use years of life lost to provide a novel measure of the impact of temperature on mortality in Brisbane , Australia .
We also project the future temperature-related years of life lost attributable to climate change .
We show that the association between temperature and years of life lost is U-shaped , with increased years of life lost for cold and hot temperatures .
The temperature-related years of life lost will worsen greatly if future climate change goes beyond a 2 degreesC increase and without any adaptation to higher temperatures .
This study highlights that public health adaptation to climate change is necessary .

[270] Changes in coral-associated microbial communities during a bleaching event

Environmental stressors such as increased sea surface temperatures are well-known for contributing to coral bleaching ; however , the effect of increased temperatures and subsequent bleaching on coral-associated microbial communities is poorly understood .
Colonies of the hard coral Acropora millepora were tagged on a reef flat off Magnetic Island ( Great Barrier Reef ) and surveyed over 2.5 years , which included a severe bleaching event in January/February 2002 .
Daily average water temperatures exceeded the previous 10-year average by more than 1 degreesC for extended periods with field-based visual surveys recording all tagged colonies displaying signs of bleaching .
During the bleaching period , direct counts of coral zooxanthellae densities decreased by ~ 64 % , before recovery to pre-bleaching levels after the thermal stress event .
A subset of three tagged coral colonies were sampled through the bleaching event and changes in the microbial community elucidated .
Denaturing gradient gel electrophoresis ( DGGE ) analysis demonstrated conserved bacterial banding profiles between the three coral colonies , confirming previous studies highlighting specific microbial associations .
As coral colonies bleached , the microbial community shifted and redundancy analysis ( RDA ) of DGGE banding patterns revealed a correlation of increasing temperature with the appearance of Vibrio-affiliated sequences .
Interestingly , this shift to a Vibrio-dominated community commenced prior to visual signs of bleaching .
Clone libraries hybridized with Vibrio-specific oligonucleotide probes confirmed an increase in the fraction of Vibrio-affiliated clones during the bleaching period .
Post bleaching , the coral microbial associations again shifted , returning to a profile similar to the fingerprints prior to bleaching .
This provided further evidence for corals selecting and shaping their microbial partners .
For non-bleached samples , a close association with Spongiobacter-related sequences were revealed by both clone libraries and DGGE profiling .
Despite Vibrio species being previously implicated in bleaching of specific coral species , it is unsure if the relative increase in retrieved Vibrio sequences is due to bacterial infection or an opportunistic response to compromised health and changing environmental parameters of the coral host .
This study provides the first molecular-based study demonstrating changes in coral-associated bacterial assemblages during a bleaching event on a natural reef system .

[271] Experimental drying intensifies burning and carbon losses in a northern peatland

For millennia , peatlands have served as an important sink for atmospheric CO2 and today represent a large soil carbon reservoir .
While recent land use and wildfires have reduced carbon sequestration in tropical peatlands , the influence of disturbance on boreal peatlands is uncertain , yet it is important for predicting the fate of northern high-latitude carbon reserves .
Here we quantify rates of organic matter storage and combustion losses in a boreal peatland subjected to long-term experimental drainage , a portion of which subsequently burned during a wildfire .
We show that drainage doubled rates of organic matter accumulation in the soils of unburned plots .
However , drainage also increased carbon losses during wildfire ninefold to 16.8 + / -0.2 kg C m-2 , equivalent to a loss of more than 450 years of peat accumulation .
Interactions between peatland drainage and fire are likely to cause long-term carbon emissions to far exceed rates of carbon uptake , diminishing the northern peatland carbon sink .

[272] Stronger winds over a large lake in response to weakening air-to-lake temperature gradient

The impacts of climate change on the world 's large lakes are a cause for concern .
For example , over the past decades , mean surface water temperatures in Lake Superior , North America , have warmed faster than air temperature during the thermally stratified summer season , because decreasing ice cover has led to increased heat input .
However , the effects of this change on large lakes have not been studied extensively .
Here we analyse observations from buoys and satellites as well as model reanalyses for Lake Superior , and find that increasing temperatures in both air and surface water , and a reduction in the temperature gradient between air and water are destabilizing the atmospheric surface layer above the lake .
As a result , surface wind speeds above the lake are increasing by nearly 5 % per decade , exceeding trends in wind speed over land .
A numerical model of the lake circulation suggests that the increasing wind speeds lead to increases in current speeds , and long-term warming causes the surface mixed layer to shoal and the season of stratification to lengthen .
We conclude that climate change will profoundly affect the biogeochemical cycles of large lakes , the mesoscale atmospheric circulation at lake-land boundaries and the transport of airborne pollutants in regions that are rich in lakes .

[273] Delayed build-up of Arctic ice sheets during 400,000-year minima in insolation variability

Knowledge of the past variability of climate at high northern latitudes during astronomical analogues of the present interglacial may help to inform our understanding of future climate change .
Unfortunately , long-term continuous records of ice-sheet variability in the Northern Hemisphere only are scarce because records of benthic 18O content represent an integrated signal of changes in ice volume in both polar regions .
However , variations in Northern Hemisphere ice sheets influence the Siberian High ( an atmospheric pressure system ) , so variations in the East Asian winter monsoon ( EAWM ) -- as recorded in the aeolian dust deposits on the Chinese Loess Plateau -- can serve as a useful proxy of Arctic climate variability before the ice-core record begins .
Here we present an EAWM proxy record using grain-size variations in two parallel loess sections representative of sequences across the whole of the Chinese Loess Plateau over the past 900,000 years .
The results show that during periods of low eccentricity and precessional variability at approximately 400,000-year intervals , the grain-size-inferred intensity of the EAWM remains weak for up to 20,000 years after the end of the interglacial episode of high summer monsoon activity and strong pedogenesis .
In contrast , there is a rapid increase in the EAWM after the end of most other interglacials .
We conclude that , for both the 400,000-year interglacials , the weak EAWM winds maintain a mild , non-glacial climate at high northern latitudes for much longer than expected from the conventional loess and marine oxygen isotope records .
During these times , the less-severe summer insolation minima at 65degrees N ( ref .
4 ) would have suppressed ice and snow accumulation , leading to a weak Siberian High and , consequently , weak EAWM winds .

[274] Intensification and spatial homogenization of coastal upwelling under climate change

The timing and strength of wind-driven coastal upwelling along the eastern margins of major ocean basins regulate the productivity of critical fisheries and marine ecosystems by bringing deep and nutrient-rich waters to the sunlit surface , where photosynthesis can occur .
How coastal upwelling regimes might change in a warming climate is therefore a question of vital importance .
Although enhanced land-ocean differential heating due to greenhouse warming has been proposed to intensify coastal upwelling by strengthening alongshore winds , analyses of observations and previous climate models have provided little consensus on historical and projected trends in coastal upwelling .
Here we show that there are strong and consistent changes in the timing , intensity and spatial heterogeneity of coastal upwelling in response to future warming in most Eastern Boundary Upwelling Systems ( EBUSs ) .
An ensemble of climate models shows that by the end of the twenty-first century the upwelling season will start earlier , end later and become more intense at high but not low latitudes .
This projected increase in upwelling intensity and duration at high latitudes will result in a substantial reduction of the existing latitudinal variation in coastal upwelling .
These patterns are consistent across three of the four EBUSs ( Canary , Benguela and Humboldt , but not California ) .
The lack of upwelling intensification and greater uncertainty associated with the California EBUS may reflect regional controls associated with the atmospheric response to climate change .
Given the strong linkages between upwelling and marine ecosystems , the projected changes in the intensity , timing and spatial structure of coastal upwelling may influence the geographical distribution of marine biodiversity .

[275] Flooding disturbances increase resource availability and productivity but reduce stability in diverse plant communities

The natural world is increasingly defined by change .
Within the next 100 years , rising atmospheric CO2 concentrations will continue to increase the frequency and magnitude of extreme weather events .
Simultaneously , human activities are reducing global biodiversity , with current extinction rates at ~ 1,000 x what they were before human domination of Earth 's ecosystems .
The co-occurrence of these trends may be of particular concern , as greater biological diversity could help ecosystems resist change during large perturbations .
We use data from a 200-year flood event to show that when a disturbance is associated with an increase in resource availability , the opposite may occur .
Flooding was associated with increases in productivity and decreases in stability , particularly in the highest diversity communities .
Our results undermine the utility of the biodiversity-stability hypothesis during a large number of disturbances where resource availability increases .
We propose a conceptual framework that can be widely applied during natural disturbances .

[276] Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion

Changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature .
In contrast to Arctic sea ice , sea ice surrounding Antarctica has expanded , with record extent in 2010 .
This ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling .
Here we show that accelerated basal melting of Antarctic ice shelves is likely to have contributed significantly to sea-ice expansion .
Specifically , we present observations indicating that melt water from Antarctica 's ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves .
Simulating these processes in a coupled climate model we find that cool and fresh surface water from ice-shelf melt indeed leads to expanding sea ice in austral autumn and winter .
This powerful negative feedback counteracts Southern Hemispheric atmospheric warming .
Although changes in atmospheric dynamics most likely govern regional sea-ice trends , our analyses indicate that the overall sea-ice trend is dominated by increased ice-shelf melt .
We suggest that cool sea surface temperatures around Antarctica could offset projected snowfall increases in Antarctica , with implications for estimates of future sea-level rise .

[277] Reduced calcification of marine plankton in response to increased atmospheric CO2

The formation of calcareous skeletons by marine planktonic organisms and their subsequent sinking to depth generates a continuous rain of calcium carbonate to the deep ocean and underlying sediments .
This is important in regulating marine carbon cycling and ocean-atmosphere CO2 exchange .
The present rise in atmospheric CO2 levels causes significant changes in surface ocean pH and carbonate chemistry .
Such changes have been shown to slow down calcification in corals and coralline macroalgae , , but the majority of marine calcification occurs in planktonic organisms .
Here we report reduced calcite production at increased CO2 concentrations in monospecific cultures of two dominant marine calcifying phytoplankton species , the coccolithophorids Emiliania huxleyi and Gephyrocapsa oceanica .
This was accompanied by an increased proportion of malformed coccoliths and incomplete coccospheres .
Diminished calcification led to a reduction in the ratio of calcite precipitation to organic matter production .
Similar results were obtained in incubations of natural plankton assemblages from the north Pacific ocean when exposed to experimentally elevated CO2 levels .
We suggest that the progressive increase in atmospheric CO2 concentrations may therefore slow down the production of calcium carbonate in the surface ocean .
As the process of calcification releases CO2 to the atmosphere , the response observed here could potentially act as a negative feedback on atmospheric CO2 levels .

[278] Winter forest soil respiration controlled by climate and microbial community composition

Most terrestrial carbon sequestration at mid-latitudes in the Northern Hemisphere occurs in seasonal , montane forest ecosystems .
Winter respiratory carbon dioxide losses from these ecosystems are high , and over half of the carbon assimilated by photosynthesis in the summer can be lost the following winter .
The amount of winter carbon dioxide loss is potentially susceptible to changes in the depth of the snowpack ; a shallower snowpack has less insulation potential , causing colder soil temperatures and potentially lower soil respiration rates .
Recent climate analyses have shown widespread declines in the winter snowpack of mountain ecosystems in the western USA and Europe that are coupled to positive temperature anomalies .
Here we study the effect of changes in snow cover on soil carbon cycling within the context of natural climate variation .
We use a six-year record of net ecosystem carbon dioxide exchange in a subalpine forest to show that years with a reduced winter snowpack are accompanied by significantly lower rates of soil respiration .
Furthermore , we show that the cause of the high sensitivity of soil respiration rate to changes in snow depth is a unique soil microbial community that exhibits exponential growth and high rates of substrate utilization at the cold temperatures that exist beneath the snow .
Our observations suggest that a warmer climate may change soil carbon sequestration rates in forest ecosystems owing to changes in the depth of the insulating snow cover .

[279] Sodium channel mutation leading to saxitoxin resistance in clams increases risk of PSP

Bivalve molluscs , the primary vectors of paralytic shellfish poisoning ( PSP ) in humans , show marked inter-species variation in their capacity to accumulate PSP toxins ( PSTs ) which has a neural basis .
PSTs cause human fatalities by blocking sodium conductance in nerve fibres .
Here we identify a molecular basis for inter-population variation in PSP resistance within a species , consistent with genetic adaptation to PSTs .
Softshell clams ( Mya arenaria ) from areas exposed to ` red tides ' are more resistant to PSTs , as demonstrated by whole-nerve assays , and accumulate toxins at greater rates than sensitive clams from unexposed areas .
PSTs lead to selective mortality of sensitive clams .
Resistance is caused by natural mutation of a single amino acid residue , which causes a 1,000-fold decrease in affinity at the saxitoxin-binding site in the sodium channel pore of resistant , but not sensitive , clams .
Thus PSTs might act as potent natural selection agents , leading to greater toxin resistance in clam populations and increased risk of PSP in humans .
Furthermore , global expansion of PSP to previously unaffected coastal areas might result in long-term changes to communities and ecosystems .

[280] Life-cycle modification in open oceans accounts for genome variability in a cosmopolitan phytoplankton

Emiliania huxleyi is the most abundant calcifying plankton in modern oceans with substantial intraspecific genome variability and a biphasic life cycle involving sexual alternation between calcified 2N and flagellated 1N cells .
We show that high genome content variability in Emiliania relates to erosion of 1N-specific genes and loss of the ability to form flagellated cells .
Analysis of 185 E. huxleyi strains isolated from world oceans suggests that loss of flagella occurred independently in lineages inhabiting oligotrophic open oceans over short evolutionary timescales .
This environmentally linked physiogenomic change suggests life cycling is not advantageous in very large/diluted populations experiencing low biotic pressure and low ecological variability .
Gene loss did not appear to reflect pressure for genome streamlining in oligotrophic oceans as previously observed in picoplankton .
Life-cycle modifications might be common in plankton and cause major functional variability to be hidden from traditional taxonomic or molecular markers .
The ISME Journal advance online publication , 2 December 2014 ; doi :10.1038 / ismej .2014.221

[281] Late Miocene threshold response of marine algae to carbon dioxide limitation

Coccolithophores are marine algae that use carbon for calcification and photosynthesis .
The long-term adaptation of these and other marine algae to decreasing carbon dioxide levels during the Cenozoic era has resulted in modern algae capable of actively enhancing carbon dioxide at the site of photosynthesis .
This enhancement occurs through the transport of dissolved bicarbonate ( HCO3 - ) and with the help of enzymes whose expression can be modulated by variable aqueous carbon dioxide concentration , [ CO2 ] , in laboratory cultures .
Coccolithophores preserve the geological history of this adaptation because the stable carbon and oxygen isotopic compositions of their calcite plates ( coccoliths ) , which are preserved in the fossil record , are sensitive to active carbon uptake and transport by the cell .
Here we use a model of cellular carbon fluxes and show that at low [ CO2 ] the increased demand for HCO3 - at the site of photosynthesis results in a diminished allocation of HCO3 - to calcification , which is most pronounced in larger cells .
This results in a large divergence between the carbon isotopic compositions of small versus large coccoliths only at low [ CO2 ] .
Our evaluation of the oxygen and carbon isotope record of size-separated fossil coccoliths reveals that this isotopic divergence first arose during the late Miocene to the earliest Pliocene epoch ( about 7-5 million years ago ) .
We interpret this to be a threshold response of the cells ' carbon acquisition strategies to decreasing [ CO2 ] .
The documented coccolithophore response is synchronous with a global shift in terrestrial vegetation distribution between 8 and 5 Myr ago , which has been interpreted by some studies as a floral response to decreasing partial pressures of carbon dioxide ( ) in the atmosphere .
We infer a global decrease in carbon dioxide levels for this time interval that has not yet been identified in the sparse proxy record but is synchronous with global cooling and progressive glaciations .

[282] Carbon emissions due to deforestation for the production of charcoal used in Brazil 's steel industry

Steel produced using coal generates 7 % of global anthropogenic CO2 emissions annually .
Opportunities exist to substitute this coal with carbon-neutral charcoal sourced from plantation forests to mitigate project-scale emissions and obtain certified emission reduction credits under the Kyoto Protocol 's Clean Development Mechanism .
This mitigation strategy has been implemented in Brazil and is one mechanism among many used globally to reduce anthropogenic CO2 emissions ; however , its potential adverse impacts have been overlooked to date .
Here , we report that total CO2 emitted from Brazilian steel production doubled ( 91 to 182 MtCO2 ) and specific emissions increased ( 3.3 to 5.2 MtCO2 per Mt steel ) between 2000 and 2007 , even though the proportion of coal used declined .
Infrastructure upgrades and a national plantation shortage increased industry reliance on charcoal sourced from native forests , which emits up to nine times more CO2 per tonne of steel than coal .
Preventing use of native forest charcoal could have avoided 79 % of the CO2 emitted from steel production between 2000 and 2007 ; however , doing so by increasing plantation charcoal supply is limited by socio-economic costs and risks further indirect deforestation pressures and emissions .
Effective climate change mitigation in Brazil 's steel industry must therefore minimize all direct and indirect carbon emissions generated from steel manufacture .

[283] Eastern Pacific cooling and Atlantic overturning circulation during the last deglaciation

Surface ocean conditions in the equatorial Pacific Ocean could hold the clue to whether millennial-scale global climate change during glacial times was initiated through tropical ocean-atmosphere feedbacks or by changes in the Atlantic thermohaline circulation .
North Atlantic cold periods during Heinrich events and millennial-scale cold events ( stadials ) have been linked with climatic changes in the tropical Atlantic Ocean and South America , as well as the Indian and East Asian monsoon systems , but not with tropical Pacific sea surface temperatures .
Here we present a high-resolution record of sea surface temperatures in the eastern tropical Pacific derived from alkenone unsaturation measurements .
Our data show a temperature drop of ~ 1 degreesC , synchronous ( within dating uncertainties ) with the shutdown of the Atlantic meridional overturning circulation during Heinrich event 1 , and a smaller temperature drop of ~ 0.5 degreesC synchronous with the smaller reduction in the overturning circulation during the Younger Dryas event .
Both cold events coincide with maxima in surface ocean productivity as inferred from 230Th-normalized carbon burial fluxes , suggesting increased upwelling at the time .
From the concurrence of equatorial Pacific cooling with the two North Atlantic cold periods during deglaciation , we conclude that these millennial-scale climate changes were probably driven by a reorganization of the oceans ' thermohaline circulation , although possibly amplified by tropical ocean-atmosphere interaction as suggested before .

[284] Anthropogenic aerosol forcing of Atlantic tropical storms

The frequency of tropical storms in the North Atlantic region varies markedly on decadal timescales , with profound socio-economic impacts .
Climate models largely reproduce the observed variability when forced by observed sea surface temperatures .
However , the relative importance of natural variability and external influences such as greenhouse gases , dust , sulphate and volcanic aerosols on sea surface temperatures , and hence tropical storms , is highly uncertain .
Here , we assess the effect of individual climate drivers on the frequency of North Atlantic tropical storms between 1860 and 2050 , using simulations from a collection of climate models .
We show that anthropogenic aerosols lowered the frequency of tropical storms over the twentieth century .
However , sharp declines in anthropogenic aerosol levels over the North Atlantic at the end of the twentieth century allowed the frequency of tropical storms to increase .
In simulations with a model that comprehensively incorporates aerosol effects ( HadGEM2-ES ; ref . )
, decadal variability in tropical storm frequency is well reproduced through aerosol-induced north-south shifts in the Hadley circulation .
However , this mechanism changes in future projections .
Our results raise the possibility that external factors , particularly anthropogenic aerosols , could be the dominant cause of historical tropical storm variability , and highlight the potential importance of future changes in aerosol emissions .

[285] Three decades of multi-dimensional change in global leaf phenology

Changes in the phenology of vegetation activity may accelerate or dampen rates of climate change by altering energy exchanges between the land surface and the atmosphere and can threaten species with synchronized life cycles .
Current knowledge of long-term changes in vegetation activity is regional , or restricted to highly integrated measures of change such as net primary productivity , which mask details that are relevant for Earth system dynamics .
Such details can be revealed by measuring changes in the phenology of vegetation activity .
Here we undertake a comprehensive global assessment of changes in vegetation phenology .
We show that the phenology of vegetation activity changed severely ( by more than 2 standard deviations in one or more dimensions of phenological change ) on 54 % of the global land surface between 1981 and 2012 .
Our analysis confirms previously detected changes in the boreal and northern temperate regions .
The adverse consequences of these northern phenological shifts for land-surface-climate feedbacks , ecosystems and species are well known .
Our study reveals equally severe phenological changes in the southern hemisphere , where consequences for the energy budget and the likelihood of phenological mismatches are unknown .
Our analysis provides a sensitive and direct measurement of ecosystem functioning , making it useful both for monitoring change and for testing the reliability of early warning signals of change .

[286] Contrasting responses of mean and extreme snowfall to climate change

Snowfall is an important element of the climate system , and one that is expected to change in a warming climate .
Both mean snowfall and the intensity distribution of snowfall are important , with heavy snowfall events having particularly large economic and human impacts .
Simulations with climate models indicate that annual mean snowfall declines with warming in most regions but increases in regions with very low surface temperatures .
The response of heavy snowfall events to a changing climate , however , is unclear .
Here I show that in simulations with climate models under a scenario of high emissions of greenhouse gases , by the late twenty-first century there are smaller fractional changes in the intensities of daily snowfall extremes than in mean snowfall over many Northern Hemisphere land regions .
For example , for monthly climatological temperatures just below freezing and surface elevations below 1,000 metres , the 99.99 th percentile of daily snowfall decreases by 8 % in the multimodel median , compared to a 65 % reduction in mean snowfall .
Both mean and extreme snowfall must decrease for a sufficiently large warming , but the climatological temperature above which snowfall extremes decrease with warming in the simulations is as high as -9 degreesC , compared to -14 degreesC for mean snowfall .
These results are supported by a physically based theory that is consistent with the observed rain-snow transition .
According to the theory , snowfall extremes occur near an optimal temperature that is insensitive to climate warming , and this results in smaller fractional changes for higher percentiles of daily snowfall .
The simulated changes in snowfall that I find would influence surface snow and its hazards ; these changes also suggest that it may be difficult to detect a regional climate-change signal in snowfall extremes .

[287] The emerging anthropogenic signal in land-atmosphere carbon-cycle coupling

Earth system models simulate prominent terrestrial carbon-cycle responses to anthropogenically forced changes in climate and atmospheric composition over the twenty-first century .
The rate and magnitude of the forced climate change is routinely evaluated relative to unforced , or natural , variability using a multi-member ensemble of simulations .
However , Earth system model carbon-cycle analyses do not account for unforced variability .
To investigate unforced terrestrial carbon-cycle variability , we analyse ensembles from the Coupled Model Intercomparison Project ( CMIP5 ) , focusing on the Community Climate System Model ( CCSM4 ) .
The unforced variability of CCSM4 is comparable to that observed at the Harvard Forest eddy covariance flux tower site .
Over the twenty-first century , unforced variability in land-atmosphere CO2 flux is larger than the forced response at decadal timescales in many areas of the world , precluding detection of the forced carbon-cycle change .
Only after several decades does the forced carbon signal consistently emerge in CCSM4 and other models for the business-as-usual radiative forcing scenario ( RCP8 .5 ) .
Grid-cell variability in time of emergence is large , but decreases at regional scales .
To attribute changes in the terrestrial carbon cycle to anthropogenic forcings , monitoring networks and model projections must consider the timescale at which the forced biogeochemical response emerges from the natural variability .

[288] The cycling and redox state of nitrogen in the Archaean ocean

Organisms that produce oxygen through photosynthesis existed during the late Archaean eon , about 2,500 million years ago , but controversial evidence suggests that they may have evolved several hundred million years earlier .
Oxygen is expected to react with oceanic nitrogen , altering its redox state .
The reaction leaves a signature in the isotopic composition of the nitrogen bound in organic matter .
Here we present a record of the nitrogen isotopic composition of kerogen extracted from minimally altered shales from the Campbellrand-Malmani platform in South Africa .
Between the Palaeo-Archaean and about 2,670 million years ago , the delta15N values of the kerogen rose by about 2/1000 .
We interpret this increase as an indication of the onset of coupled nitrification and denitrification or anammox reactions in the surface oceans , which require the presence of free oxygen .
A second increase in nitrogen isotopic composition around 2,520 million years ago implies instability of the N cycle with loss of fixed N .
This evidence for available oxygen in the oceans occurs at least 200 million years before geochemical indications of the presence of significant levels of atmospheric oxygen .
We suggest that coupled nitrification and denitrification drove the loss of fixed inorganic nitrogen , leading to nitrogen limitation , and conclude that the low levels of biologically available nitrogen limited the growth of oxygen-producing plankton , delaying the accumulation of oxygen in the atmosphere .

[289] Long-term stabilization of deep soil carbon by fire and burial during early Holocene climate change

Buried soils contain large reservoirs of organic carbon at depths that are not typically included in regional and global soil carbon inventories .
One such palaeosol , the Brady soil of southwestern Nebraska , USA , is buried under six metres of loess .
The Brady soil developed at the land surface on the late-Pleistocene-aged Peoria Loess in a period of warmth and wetness during which dunefields and dust sources across the region were stabilized .
Abrupt climate change in the early Holocene led to increased loess deposition that buried the soil .
Here , we used spectroscopic and isotopic analyses to determine the composition and stability of organic carbon in the Brady soil .
We identify high levels of black carbon , indicating extensive biomass burning .
In addition , we found intact vascular plant lipids in soil organic matter with radiocarbon ages ranging from 10,500 to 12,400 cal yr BP , indicating decomposition was slowed by rapid burial at the start of the Holocene .
We conclude that landscape disturbance caused by abrupt climate change , fire and the loss of vegetative cover contributed to deep carbon sequestration as the soil was quickly buried under accumulating loess .
We suggest that terrestrial soil carbon storage in arid and semi-arid environments could undergo landscape-scale shifts in response to rising temperatures , increased fire activity or drought .

[290] Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions

Increasing sea surface temperatures in the tropical Atlantic Ocean and measures of Atlantic hurricane activity have been reported to be strongly correlated since at least 1950 ( refs 1 , 2 , 3 , 4 , 5 ) , raising concerns that future greenhouse-gas-induced warming could lead to pronounced increases in hurricane activity .
Models that explicitly simulate hurricanes are needed to study the influence of warming ocean temperatures on Atlantic hurricane activity , complementing empirical approaches .
Our regional climate model of the Atlantic basin reproduces the observed rise in hurricane counts between 1980 and 2006 , along with much of the interannual variability , when forced with observed sea surface temperatures and atmospheric conditions .
Here we assess , in our model system , the changes in large-scale climate that are projected to occur by the end of the twenty-first century by an ensemble of global climate models , and find that Atlantic hurricane and tropical storm frequencies are reduced .
At the same time , near-storm rainfall rates increase substantially .
Our results do not support the notion of large increasing trends in either tropical storm or hurricane frequency driven by increases in atmospheric greenhouse-gas concentrations .

[291] Loss of plant species after chronic low-level nitrogen deposition to prairie grasslands

Rates of atmospheric deposition of biologically active nitrogen ( N ) are two to seven times the pre-industrial rates in many developed nations because of combustion of fossil fuels and agricultural fertilization .
They are expected to increase similarly over the next 50 years in industrializing nations of Asia and South America .
Although the environmental impacts of high rates of nitrogen addition have been well studied , this is not so for the lower , chronic rates that characterize much of the globe .
Here we present results of the first multi-decadal experiment to examine the impacts of chronic , experimental nitrogen addition as low as 10 kg N ha-1 yr-1 above ambient atmospheric nitrogen deposition ( 6 kg N ha-1 yr-1 at our site ) .
This total input rate is comparable to terrestrial nitrogen deposition in many industrialized nations .
We found that this chronic low-level nitrogen addition rate reduced plant species numbers by 17 % relative to controls receiving ambient N deposition .
Moreover , species numbers were reduced more per unit of added nitrogen at lower addition rates , suggesting that chronic but low-level nitrogen deposition may have a greater impact on diversity than previously thought .
A second experiment showed that a decade after cessation of nitrogen addition , relative plant species number , although not species abundances , had recovered , demonstrating that some effects of nitrogen addition are reversible .

[292] Phenotypic consequences of 1,000 generations of selection at elevated CO2 in a green alga

Estimates of the effect of increasing atmospheric CO2 concentrations on future global plant production rely on the physiological response of individual plants or plant communities when exposed to high CO2 ( refs 1-6 ) .
Plant populations may adapt to the changing atmosphere , however , such that the evolved plant communities of the next century are likely to be genetically different from contemporary communities .
The properties of these future communities are unknown , introducing a bias of unknown sign and magnitude into projections of global carbon pool dynamics .
Here we report a long-term selection experiment to investigate the phenotypic consequences of selection for growth at elevated CO2 concentrations .
After about 1,000 generations , selection lines of the unicellular green alga Chlamydomonas failed to evolve specific adaptation to a CO2 concentration of 1,050 parts per million .
Some lines , however , evolved a syndrome involving high rates of photosynthesis and respiration , combined with higher chlorophyll content and reduced cell size .
These lines also grew poorly at ambient concentrations of CO2 .
We tentatively attribute this outcome to the accumulation of conditionally neutral mutations in genes affecting the carbon concentration mechanism .

[293] Seasonal evolution of subglacial drainage and acceleration in a Greenland outlet glacier

The Greenland ice sheet contains enough water to raise sea levels by 7 m. However , its present mass balance and future contribution to sea level rise is poorly understood .
Accelerated mass loss has been observed near the ice sheet margin , partly as a result of faster ice motion .
Surface melt waters can reach the base of the ice sheet and enhance basal ice motion .
However , the response of ice motion to seasonal variations in meltwater supply is poorly constrained both in space and time .
Here we present ice motion data obtained with global positioning system receivers located along a ~ 35 km transect at the western margin of the Greenland ice sheet throughout a summer melt season .
Our measurements reveal substantial increases in ice velocity during summer , up to 220 % above winter background values .
These speed-up events migrate up the glacier over the course of the summer .
The relationship between melt and ice motion varies both at each site throughout the melt season and between sites .
We suggest that these patterns can be explained by the seasonal evolution of the subglacial drainage system similar to hydraulic forcing mechanisms for ice dynamics that have been observed at smaller glaciers .

[294] Recent intensification of tropical climate variability in the Indian Ocean

The interplay of the El Nino Southern Oscillation , Asian monsoon and Indian Ocean Dipole ( IOD ) drives climatic extremes in and around the Indian Ocean .
Historical and proxy records reveal changes in the behaviour of the El Nino Southern Oscillation and the Asian monsoon over recent decades .
However , reliable instrumental records of the IOD cover only the past 50 years , and there is no consensus on long-term variability of the IOD or its possible response to greenhouse gas forcing .
Here we use a suite of coral oxygen-isotope records to reconstruct a basin-wide index of IOD behaviour since AD 1846 .
Our record reveals an increase in the frequency and strength of IOD events during the twentieth century , which is associated with enhanced seasonal upwelling in the eastern Indian Ocean .
Although the El Nino Southern Oscillation has historically influenced the variability of both the IOD and the Asian monsoon , we find that the recent intensification of the IOD coincides with the development of direct , positive IOD-monsoon feedbacks .
We suggest that projected greenhouse warming may lead to a redistribution of rainfall across the Indian Ocean and a growing interdependence between the IOD and Asian monsoon precipitation variability .

[295] Greenhouse conditions induce mineralogical changes and dolomite accumulation in coralline algae on tropical reefs

Human-induced ocean acidification and warming alter seawater carbonate chemistry reducing the calcification of reef-building crustose coralline algae ( CCA ) , which has implications for reef stability .
However , due to the presence of multiple carbonate minerals with different solubilities in seawater , the algal mineralogical responses to changes in carbonate chemistry are poorly understood .
Here we demonstrate a 200 % increase in dolomite concentration in living CCA under greenhouse conditions of high pCO2 ( 1,225 muatm ) and warming ( 30 degreesC ) .
Aragonite , in contrast , increases with lower pCO2 ( 296 muatm ) and low temperature ( 28 degreesC ) .
Mineral changes in the surface pigmented skeleton are minor and dolomite and aragonite formation largely occurs in the white crust beneath .
Dissolution of high-Mg-calcite and particularly the erosive activities of endolithic algae living inside skeletons play key roles in concentrating dolomite in greenhouse treatments .
As oceans acidify and warm in the future , the relative abundance of dolomite in CCA will increase .

[296] Observations from old forests underestimate climate change effects on tree mortality

Understanding climate change-associated tree mortality is central to linking climate change impacts and forest structure and function .
However , whether temporal increases in tree mortality are attributed to climate change or stand developmental processes remains uncertain .
Furthermore , interpreting the climate change-associated tree mortality estimated from old forests for regional forests rests on an un-tested assumption that the effects of climate change are the same for young and old forests .
Here we disentangle the effects of climate change and stand developmental processes on tree mortality .
We show that both climate change and forest development processes influence temporal mortality increases , climate change-associated increases are significantly higher in young than old forests , and higher increases in younger forests are a result of their higher sensitivity to regional warming and drought .
We anticipate our analysis to be a starting point for more comprehensive examinations of how forest ecosystems might respond to climate change .

[297] Transient nature of late Pleistocene climate variability

Climate in the early Pleistocene varied with a period of 41 kyr and was related to variations in Earth 's obliquity .
About 900 kyr ago , variability increased and oscillated primarily at a period of ~ 100 kyr , suggesting that the link was then with the eccentricity of Earth 's orbit .
This transition has often been attributed to a nonlinear response to small changes in external boundary conditions .
Here we propose that increasing variablility within the past million years may indicate that the climate system was approaching a second climate bifurcation point , after which it would transition again to a new stable state characterized by permanent mid-latitude Northern Hemisphere glaciation .
From this perspective the past million years can be viewed as a transient interval in the evolution of Earth 's climate .
We support our hypothesis using a coupled energy-balance/ice-sheet model , which furthermore predicts that the future transition would involve a large expansion of the Eurasian ice sheet .
The process responsible for the abrupt change seems to be the albedo discontinuity at the snow-ice edge .
The best-fit model run , which explains almost 60 % of the variance in global ice volume during the past 400 kyr , predicts a rapid transition in the geologically near future to the proposed glacial state .
Should it be attained , this state would be more ` symmetric ' than the present climate , with comparable areas of ice/sea-ice cover in each hemisphere , and would represent the culmination of 50 million years of evolution from bipolar nonglacial climates to bipolar glacial climates .

[298] Mid-latitude westerlies as a driver of glacier variability in monsoonal High Asia

Glaciers in High Asia store large amounts of water and are affected by climate change .
Efforts to determine decadal-scale glacier change are therefore increasing , predicated on the concept that glaciers outside the northwest of the mountain system are controlled by the tropical monsoon .
Here we show that the mass balance of Zhadang Glacier on the southern Tibetan Plateau , 2001-2011 , was driven by mid-latitude climate as well , on the basis of high-altitude measurements and combined atmospheric-glacier modelling .
Results reveal that precipitation conditions in May-June largely determine the annual mass-balance , but they are shaped by both the intensity of Indian summer monsoon onset and mid-latitude dynamics .
In particular , large-scale westerly waves control the tropospheric flow strength over the Tibetan Plateau remotely .
This strength alone explains 73 % of interannual mass-balance variability of Zhadang Glacier , and affects May-June precipitation and summer air temperatures in many parts of High Asia 's zone of monsoon influence .
Thus , mid-latitude climate should be considered as a possible driver of past and future glacier changes in this zone .

[299] Early Anthropogenic Transformation of the Danube-Black Sea System

Over the last century humans have altered the export of fluvial materials leading to significant changes in morphology , chemistry , and biology of the coastal ocean .
Here we present sedimentary , paleoenvironmental and paleogenetic evidence to show that the Black Sea , a nearly enclosed marine basin , was affected by land use long before the changes of the Industrial Era .
Although watershed hydroclimate was spatially and temporally variable over the last ~ 3000 years , surface salinity dropped systematically in the Black Sea .
Sediment loads delivered by Danube River , the main tributary of the Black Sea , significantly increased as land use intensified in the last two millennia , which led to a rapid expansion of its delta .
Lastly , proliferation of diatoms and dinoflagellates over the last five to six centuries , when intensive deforestation occurred in Eastern Europe , points to an anthropogenic pulse of river-borne nutrients that radically transformed the food web structure in the Black Sea .

[300] Nutrient enrichment can increase the susceptibility of reef corals to bleaching

Mass coral bleaching , resulting from the breakdown of coral-algal symbiosis has been identified as the most severe threat to coral reef survival on a global scale .
Regionally , nutrient enrichment of reef waters is often associated with a significant loss of coral cover and diversity .
Recently , increased dissolved inorganic nitrogen concentrations have been linked to a reduction of the temperature threshold of coral bleaching , a phenomenon for which no mechanistic explanation is available .
Here we show that increased levels of dissolved inorganic nitrogen in combination with limited phosphate concentrations result in an increased susceptibility of corals to temperature - and light-induced bleaching .
Mass spectrometric analyses of the algal lipidome revealed a marked accumulation of sulpholipids under these conditions .
Together with increased phosphatase activities , this change indicates that the imbalanced supply of dissolved inorganic nitrogen results in phosphate starvation of the symbiotic algae .
Based on these findings we introduce a conceptual model that links unfavourable ratios of dissolved inorganic nutrients in the water column with established mechanisms of coral bleaching .
Notably , this model improves the understanding of the detrimental effects of coastal nutrient enrichment on coral reefs , which is urgently required to support knowledge-based management strategies to mitigate the effects of climate change .

[301] Carbon losses from all soils across England and Wales 1978-2003

More than twice as much carbon is held in soils as in vegetation or the atmosphere , and changes in soil carbon content can have a large effect on the global carbon budget .
The possibility that climate change is being reinforced by increased carbon dioxide emissions from soils owing to rising temperature is the subject of a continuing debate .
But evidence for the suggested feedback mechanism has to date come solely from small-scale laboratory and field experiments and modelling studies .
Here we use data from the National Soil Inventory of England and Wales obtained between 1978 and 2003 to show that carbon was lost from soils across England and Wales over the survey period at a mean rate of 0.6 % yr-1 ( relative to the existing soil carbon content ) .
We find that the relative rate of carbon loss increased with soil carbon content and was more than 2 % yr-1 in soils with carbon contents greater than 100 g kg-1 .
The relationship between rate of carbon loss and carbon content is irrespective of land use , suggesting a link to climate change .
Our findings indicate that losses of soil carbon in England and Wales -- and by inference in other temperate regions -- are likely to have been offsetting absorption of carbon by terrestrial sinks .

[302] Ubiquinone accumulation improves osmotic-stress tolerance in Escherichia coli

Bacteria are thought to cope with fluctuating environmental solute concentrations primarily by adjusting the osmolality of their cytoplasm .
To obtain insights into the underlying metabolic adaptations , we analyzed the global metabolic response of Escherichia coli to sustained hyperosmotic stress using nontargeted mass spectrometry .
We observed that 52 % of 1,071 detected metabolites , including known osmoprotectants , changed abundance with increasing salt challenge .
Unexpectedly , unsupervised data analysis showed a substantial increase of most intermediates in the ubiquinone-8 ( Q8 ) biosynthesis pathway and a 110-fold accumulation of Q8 itself , as confirmed by quantitative lipidomics .
We then demonstrated that Q8 is necessary for acute and sustained osmotic-stress tolerance using Q8 mutants and tolerance rescue through feeding nonrespiratory Q8 analogs .
Finally , in vitro experiments with artificial liposomes showed that mechanical membrane stabilization is a principal mechanism of Q8-mediated osmoprotection .
Thus , we find that besides regulating intracellular osmolality , E. coli enhances its cytoplasmic membrane stability to withstand osmotic stress .

[303] Variable effects of nitrogen additions on the stability and turnover of soil carbon

Soils contain the largest near-surface reservoir of terrestrial carbon and so knowledge of the factors controlling soil carbon storage and turnover is essential for understanding the changing global carbon cycle .
The influence of climate on decomposition of soil carbon has been well documented , but there remains considerable uncertainty in the potential response of soil carbon dynamics to the rapid global increase in reactive nitrogen ( coming largely from agricultural fertilizers and fossil fuel combustion ) .
Here , using 14C , 13C and compound-specific analyses of soil carbon from long-term nitrogen fertilization plots , we show that nitrogen additions significantly accelerate decomposition of light soil carbon fractions ( with decadal turnover times ) while further stabilizing soil carbon compounds in heavier , mineral-associated fractions ( with multidecadal to century lifetimes ) .
Despite these changes in the dynamics of different soil pools , we observed no significant changes in bulk soil carbon , highlighting a limitation inherent to the still widely used single-pool approach to investigating soil carbon responses to changing environmental conditions .
It remains to be seen if the effects observed here -- caused by relatively high , short-term fertilizer additions -- are similar to those arising from lower , long-term additions of nitrogen to natural ecosystems from atmospheric deposition , but our results suggest nonetheless that current models of terrestrial carbon cycling do not contain the mechanisms needed to capture the complex relationship between nitrogen availability and soil carbon storage .

[304] Non-social adaptation defers a tragedy of the commons in Pseudomonas aeruginosa quorum sensing

In a process termed quorum sensing ( QS ) , the opportunistic bacterial pathogen Pseudomonas aeruginosa uses diffusible signaling molecules to regulate the expression of numerous secreted factors or public goods that are shared within the population .
But not all cells respond to QS signals .
These social cheaters typically harbor a mutation in the QS receptor gene lasR and exploit the public goods produced by cooperators .
Here we show that non-social adaptation under growth conditions that require QS-dependent public goods increases tolerance to cheating and defers a tragedy of the commons .
The underlying mutation is in the transcriptional repressor gene psdR .
This mutation has no effect on public goods expression but instead increases individual fitness by derepressing growth-limiting intracellular metabolism .
Even though psdR mutant populations remain susceptible to invasion by isogenic psdR lasR cheaters , they bear a lower cheater load than do wild-type populations , and they are completely resistant to invasion by lasR cheaters with functional psdR .
Mutations in psdR also sustain growth near wild-type levels when paired with certain partial loss-of-function lasR mutations .
Targeted sequencing of multiple evolved isolates revealed that mutations in psdR arise before mutations in lasR , and rapidly sweep through the population .
Our results indicate that a QS-favoring environment can lead to adaptations in non-social , intracellular traits that increase the fitness of cooperating individuals and thereby contribute to population-wide maintenance of QS and associated cooperative behaviors .
The ISME Journal ( 2015 ) 0 , 000-000 .
advance online publication , 23 January 2015 ; doi :10.1038 / ismej .2014.259

[305] Transformation of tectonic and climatic signals from source to sedimentary archive

The Earth 's sedimentary successions are an archive of past tectonic and climate events .
The physical characteristics of the sediment record are controlled by three main factors : the sediment supply from the eroding source region , the grain size distribution of that sediment supply , and the area available for sediment accumulation in the downstream regions .
The interplay of these factors can make the interpretation of a climatic or tectonic signal complex , particularly as these processes are nonlinear .
Here we assess the evolution of a tectonically active landscape undergoing erosional and depositional processes , using a numerical model that incorporates variations in grain size and the volumetric sediment budget .
Our simulations indicate that changes in precipitation and tectonic uplift both generate characteristic patterns of grain size and stratigraphic geometry .
An increase in catchment precipitation results in the deposition of a laterally extensive sheet of coarse gravel .
The responses to a changing tectonic regime are more diverse : a large increase in uplift rate results first in the deposition of sediments of larger grain size at proximal sites , followed by a reduction in grain size at distal locations .
We conclude that the stratigraphic record is strongly controlled by the grain size of sediments released from catchments undergoing tectonic or climatic change .

[306] Large climate-driven changes of oceanic oxygen concentrations during the last deglaciation

During the last glacial termination , the solubility of gases in the ocean decreased as ocean temperatures rose .
However , marine sediments have not unanimously recorded ocean deoxygenation throughout this time .
Some records show increasing oxygenation since the Last Glacial Maximum , particularly in the deep sea , while many document abrupt oxygenation changes , often associated with apparent changes in the formation rate of North Atlantic Deep Water .
Here we present a global compilation of marine sediment proxy records that reveals remarkable coherency between regional oxygenation changes throughout deglaciation .
The upper ocean generally became less oxygenated , but this general trend included pauses and even reversals , reflecting changes in nutrient supply , respiration rates and ventilation .
The most pronounced deoxygenation episode in the upper ocean occurred midway through the deglaciation , associated with a reinvigoration of North Atlantic Deep Water formation .
At this time , the upper Indo-Pacific Ocean was less oxygenated than today .
Meanwhile , the bulk of the deep ocean became more oxygenated over the deglaciation , reflecting a transfer of respired carbon to the atmosphere .
The observed divergence from a simple solubility control emphasizes the degree to which oxygen consumption patterns can be altered by changes in ocean circulation and marine ecosystems .

[307] Global warming amplified by reduced sulphur fluxes as a result of ocean acidification

Climate change and decreasing seawater pH ( ocean acidification ) have widely been considered as uncoupled consequences of the anthropogenic CO2 perturbation .
Recently , experiments in seawater enclosures ( mesocosms ) showed that concentrations of dimethylsulphide ( DMS ) , a biogenic sulphur compound , were markedly lower in a low-pH environment .
Marine DMS emissions are the largest natural source of atmospheric sulphur and changes in their strength have the potential to alter the Earth 's radiation budget .
Here we establish observational-based relationships between pH changes and DMS concentrations to estimate changes in future DMS emissions with Earth system model climate simulations .
Global DMS emissions decrease by about 18 ( + / -3 ) % in 2100 compared with pre-industrial times as a result of the combined effects of ocean acidification and climate change .
The reduced DMS emissions induce a significant additional radiative forcing , of which 83 % is attributed to the impact of ocean acidification , tantamount to an equilibrium temperature response between 0.23 and 0.48 K .
Our results indicate that ocean acidification has the potential to exacerbate anthropogenic warming through a mechanism that is not considered at present in projections of future climate change .

[308] Consequences of changing biodiversity

Human alteration of the global environment has triggered the sixth major extinction event in the history of life and caused widespread changes in the global distribution of organisms .
These changes in biodiversity alter ecosystem processes and change the resilience of ecosystems to environmental change .
This has profound consequences for services that humans derive from ecosystems .
The large ecological and societal consequences of changing biodiversity should be minimized to preserve options for future solutions to global environmental problems .

[309] Climate-smart agriculture for food security

Climate-smart agriculture ( CSA ) is an approach for transforming and reorienting agricultural systems to support food security under the new realities of climate change .
Widespread changes in rainfall and temperature patterns threaten agricultural production and increase the vulnerability of people dependent on agriculture for their livelihoods , which includes most of the world 's poor .
Climate change disrupts food markets , posing population-wide risks to food supply .
Threats can be reduced by increasing the adaptive capacity of farmers as well as increasing resilience and resource use efficiency in agricultural production systems .
CSA promotes coordinated actions by farmers , researchers , private sector , civil society and policymakers towards climate-resilient pathways through four main action areas : ( 1 ) building evidence ; ( 2 ) increasing local institutional effectiveness ; ( 3 ) fostering coherence between climate and agricultural policies ; and ( 4 ) linking climate and agricultural financing .
CSA differs from ` business-as-usual ' approaches by emphasizing the capacity to implement flexible , context-specific solutions , supported by innovative policy and financing actions .

[310] Evidence for a weakening relationship between interannual temperature variability and northern vegetation activity

Satellite-derived Normalized Difference Vegetation Index ( NDVI ) , a proxy of vegetation productivity , is known to be correlated with temperature in northern ecosystems .
This relationship , however , may change over time following alternations in other environmental factors .
Here we show that above 30degreesN , the strength of the relationship between the interannual variability of growing season NDVI and temperature ( partial correlation coefficient RNDVI-GT ) declined substantially between 1982 and 2011 .
This decrease in RNDVI-GT is mainly observed in temperate and arctic ecosystems , and is also partly reproduced by process-based ecosystem model results .
In the temperate ecosystem , the decrease in RNDVI-GT coincides with an increase in drought .
In the arctic ecosystem , it may be related to a nonlinear response of photosynthesis to temperature , increase of hot extreme days and shrub expansion over grass-dominated tundra .
Our results caution the use of results from interannual time scales to constrain the decadal response of plants to ongoing warming .

[311] Shifts in coral-assemblage composition do not ensure persistence of reef functionality

Coral communities are changing rapidly worldwide through loss of coral cover and shifts in species composition .
Although many reef-building corals are likely to decline , some weedy opportunistic species might increase in abundance .
Here we explore whether the reshuffling of species can maintain ecosystem integrity and functioning .
Using four common Caribbean reef-building coral genera we modeled rates of reef construction and complexity .
We show that shifting coral assemblages result in rapid losses in coral-community calcification and reef rugosity that are independent of changes in the total abundance of reef corals .
These losses are considerably higher than those recently attributed to climate change .
Dominance patterns of coral assemblages seem to be the most important driver of the functioning of coral reefs and thus , the future of these ecosystems might depend not only on reductions of local and global stressors , but also on the maintenance of keystone coral species .

[312] Holocene periodicity in North Atlantic climate and deep-ocean flow south of Iceland

Climate fluctuations during the past millennium are relatively well documented .
On a longer timescale , there is growing evidence of millennial-scale variability of Holocene climate , at periodicities of ~ 2,500 and 950 years ( possibly caused by changes in solar flux ) , and ~ 1,500 years ( maybe related to an internal oscillation of the climate system ) , , .
But the involvement of deep water masses in these Holocene climate changes has yet to be established .
Here we use sediment grain-size data from the Iceland basin to reconstruct past changes in the speed of deep-water flow .
The study site is under the influence of Iceland-Scotland Overflow Water ( ISOW ) , the flow of which is an important component of the ` thermohaline ' circulation that modulates European climate .
Flow changes coincide with some known climate events ( the Little Ice Age and the Mediaeval Warm Period ) , and extend over the entire Holocene epoch with aquasi-periodicity of ~ 1,500 years .
The grain-size data indicate afaster ISOW flow when the climate of northern Europe is warmer .
However , a second mode of operation is observed in the early Holocene , when warm climate intervals are associated with slower ISOW flow .
At that time the melting remnant of land-based , glacial-age ice may have provided a sufficient source of fresh water to the ocean to reduce ISOW flow south of Iceland .

[313] Increased sedimentation rates and grain sizes 2-4 Myr ago due to the influence of climate change on erosion rates

Around the globe , and in a variety of settings including active and inactive mountain belts , increases in sedimentation rates as well as in grain sizes of sediments were recorded at ~ 2-4 Myr ago , implying increased erosion rates .
A change in climate represents the only process that is globally synchronous and can potentially account for the widespread increase in erosion and sedimentation , but no single process -- like a lowering of sea levels or expanded glaciation -- can explain increases in sedimentation in all environments , encompassing continental margins and interiors , and tropical as well as higher latitudes .
We suggest that climate affected erosion mainly by the transition from a period of climate stability , in which landscapes had attained equilibrium configurations , to a time of frequent and abrupt changes in temperature , precipitation and vegetation , which prevented fluvial and glacial systems from establishing equilibrium states .

[314] Survival of genetically marked Escherichia coli O157 : H7 in soil as affected by soil microbial community shifts

A loamy sand soil sampled from a species-rich permanent grassland at a long-term experimental site ( Wildekamp , Bennekom , The Netherlands ) was used to construct soil microcosms in which the microbial community compositions had been modified by fumigation at different intensities ( depths ) .
As expected , increasing depth of fumigation was shown to result in progressively increasing effects on the microbiological soil parameters , as determined by cultivation-based as well as cultivation-independent ( PCR-DGGE , PLFA ) methods .
Both at 7 and at 60 days after fumigation , shifts in the bacterial , fungal and protozoan communities were noted , indicating that altered community compositions had emerged following a transition phase .
At the level of bacteria culturable on plates , an increase of the prevalence of bacterial r-strategists was noted at 7 days followed by a decline at 60 days , which also hinted at the effectiveness of the fumigation treatments .
The survival of a non-toxigenic Escherichia coli O157 : H7 derivative , strain T , was then assessed over 60 days in these microcosms , using detection via colony forming units counts as well as via PCR-DGGE .
Both data sets were consistent with each other .
Thus , a clear effect of fumigation depth on the survival of the invading strain T was noted , as a progressive increase of depth coincided with a progressively enhanced inoculant survival rate .
As fumigation depth was presumably inversely related to community complexity , this was consistent with the hypothesis that soil systems with reduced biological complexity offer enhanced opportunities for invading microbial species to establish and persist .
The significance of this finding is discussed in the light of the ongoing discussion about the complexity-invasiveness relationship within microbial communities , in particular regarding the opportunities of pathogens to persist .

[315] Loss in microbial diversity affects nitrogen cycling in soil

Microbial communities have a central role in ecosystem processes by driving the Earth 's biogeochemical cycles .
However , the importance of microbial diversity for ecosystem functioning is still debated .
Here , we experimentally manipulated the soil microbial community using a dilution approach to analyze the functional consequences of diversity loss .
A trait-centered approach was embraced using the denitrifiers as model guild due to their role in nitrogen cycling , a major ecosystem service .
How various diversity metrics related to richness , eveness and phylogenetic diversity of the soil denitrifier community were affected by the removal experiment was assessed by 454 sequencing .
As expected , the diversity metrics indicated a decrease in diversity in the 1/103 and 1/105 dilution treatments compared with the undiluted one .
However , the extent of dilution and the corresponding reduction in diversity were not commensurate , as a dilution of five orders of magnitude resulted in a 75 % decrease in estimated richness .
This reduction in denitrifier diversity resulted in a significantly lower potential denitrification activity in soil of up to 4-5 folds .
Addition of wheat residues significantly increased differences in potential denitrification between diversity levels , indicating that the resource level can influence the shape of the microbial diversity-functioning relationship .
This study shows that microbial diversity loss can alter terrestrial ecosystem processes , which suggests that the importance of functional redundancy in soil microbial communities has been overstated .

[316] Significant decadal-scale impact of volcanic eruptions on sea level and ocean heat content

Ocean thermal expansion contributes significantly to sea-level variability and rise .
However , observed decadal variability in ocean heat content and sea level has not been reproduced well in climate models .
Aerosols injected into the stratosphere during volcanic eruptions scatter incoming solar radiation , and cause a rapid cooling of the atmosphere and a reduction in rainfall , as well as other changes in the climate system .
Here we use observations of ocean heat content and a set of climate simulations to show that large volcanic eruptions result in rapid reductions in ocean heat content and global mean sea level .
For the Mt Pinatubo eruption , we estimate a reduction in ocean heat content of about 3 x 1022 J and a global sea-level fall of about 5 mm .
Over the three years following such an eruption , we estimate a decrease in evaporation of up to 0.1 mm d-1 , comparable to observed changes in mean land precipitation .
The recovery of sea level following the Mt Pinatubo eruption in 1991 explains about half of the difference between the long-term rate of sea-level rise of 1.8 mm yr-1 ( for 1950-2000 ) , and the higher rate estimated for the more recent period where satellite altimeter data are available ( 1993-2000 ) .

[317] Enhanced biological carbon consumption in a high CO2 ocean

The oceans have absorbed nearly half of the fossil-fuel carbon dioxide ( CO2 ) emitted into the atmosphere since pre-industrial times , causing a measurable reduction in seawater pH and carbonate saturation .
If CO2 emissions continue to rise at current rates , upper-ocean pH will decrease to levels lower than have existed for tens of millions of years and , critically , at a rate of change 100 times greater than at any time over this period .
Recent studies have shown effects of ocean acidification on a variety of marine life forms , in particular calcifying organisms .
Consequences at the community to ecosystem level , in contrast , are largely unknown .
Here we show that dissolved inorganic carbon consumption of a natural plankton community maintained in mesocosm enclosures at initial CO2 partial pressures of 350 , 700 and 1,050 muatm increases with rising CO2 .
The community consumed up to 39 % more dissolved inorganic carbon at increased CO2 partial pressures compared to present levels , whereas nutrient uptake remained the same .
The stoichiometry of carbon to nitrogen drawdown increased from 6.0 at low CO2 to 8.0 at high CO2 , thus exceeding the Redfield carbon : nitrogen ratio of 6.6 in today 's ocean .
This excess carbon consumption was associated with higher loss of organic carbon from the upper layer of the stratified mesocosms .
If applicable to the natural environment , the observed responses have implications for a variety of marine biological and biogeochemical processes , and underscore the importance of biologically driven feedbacks in the ocean to global change .

[318] Primary forest cover loss in Indonesia over 2000-2012

Extensive clearing of Indonesian primary forests results in increased greenhouse gas emissions and biodiversity loss .
However , there is no consensus on the areal extent and temporal trends of primary forest clearing in Indonesia .
Here we report a spatially and temporally explicit quantification of Indonesian primary forest loss , which totalled over 6.02 Mha from 2000 to 2012 and increased on average by 47,600 ha per year .
By 2012 , annual primary forest loss in Indonesia was estimated to be higher than in Brazil ( 0.84 Mha and 0.46 Mha , respectively ) .
Proportional loss of primary forests in wetland landforms increased and almost all clearing of primary forests occurred within degraded types , meaning logging preceded conversion processes .
Loss within official forest land uses that restrict or prohibit clearing totalled 40 % of all loss within national forest land .
The increasing loss of Indonesian primary forests has significant implications for climate change mitigation and biodiversity conservation efforts .

[319] Coral resilience to ocean acidification and global warming through pH up-regulation

Rapidly rising levels of atmospheric CO2 are not only causing ocean warming , but also lowering seawater pH hence the carbonate saturation state of the oceans , on which many marine organisms depend to calcify their skeletons .
Using boron isotope systematics , we show how scleractinian corals up-regulate pH at their site of calcification such that internal changes are approximately one-half of those in ambient seawater .
This species-dependent pH-buffering capacity enables aragonitic corals to raise the saturation state of their calcifying medium , thereby increasing calcification rates at little additional energy cost .
Using a model of pH regulation combined with abiotic calcification , we show that the enhanced kinetics of calcification owing to higher temperatures has the potential to counter the effects of ocean acidification .
Up-regulation of pH , however , is not ubiquitous among calcifying organisms ; those lacking this ability are likely to undergo severe declines in calcification as CO2 levels increase .
The capacity to up-regulate pH is thus central to the resilience of calcifiers to ocean acidification , although the fate of zooxanthellate corals ultimately depends on the ability of both the photosymbionts and coral host to adapt to rapidly increasing ocean temperatures .

[320] Lightning-induced reduction of phosphorus oxidation state

Phosphorus is frequently the limiting nutrient in marine and terrestrial ecosystems , largely owing to its poor solubility and slow movement through the rock cycle .
Phosphorus is viewed to exist in geological systems almost exclusively in its fully oxidized state as orthophosphate .
However , many microorganisms use the partially oxidized forms -- phosphite and hypophosphite -- as alternative phosphorus sources , and genomic evidence suggests that this selectivity is ancient .
Elucidating the processes that reduce phosphate is therefore key to understanding the biological cycling of phosphorus .
Here we show that cloud-to-ground lightning reduces phosphate in lightning-derived glass compounds , termed fulgurites .
We analysed the phosphorus chemistry of ten fulgurites retrieved from North America , Africa and Australia , using microprobes and 31P nuclear magnetic resonance .
Half of the fulgurites contained reduced phosphorus , mainly in the form of phosphite .
The amount and type of reduced phosphorus was dependent on the composition of the fulgurite section examined : carbon-rich sections contained around 22 % reduced phosphorus in the form of iron phosphide , whereas other fulgurites contained between 37 and 68 % in the form of phosphite .
We suggest that lightning provides some portion of the reduced phosphorus used by microbes , and that phosphate reduction by lightning can be locally important to phosphorus biogeochemistry .

[321] Evolution of gene network activity by tuning the strength of negative-feedback regulation

Despite the examples of protein evolution via mutations in coding sequences , we have very limited understanding on gene network evolution via changes in cis-regulatory elements .
Using the galactose network as a model , here we show how the regulatory promoters of the network contribute to the evolved network activity between two yeast species .
In Saccharomyces cerevisiae , we combinatorially replace all regulatory network promoters by their counterparts from Saccharomyces paradoxus , measure the resulting network inducibility profiles , and model the results .
Lowering relative strength of GAL80-mediated negative feedback by replacing GAL80 promoter is necessary and sufficient to have high network inducibility levels as in S. paradoxus .
This is achieved by increasing OFF-to-ON phenotypic switching rates .
Competitions performed among strains with or without the GAL80 promoter replacement show strong relationships between network inducibility and fitness .
Our results support the hypothesis that gene network activity can evolve by optimizing the strength of negative-feedback regulation .

[322] Human-induced global ocean warming on multidecadal timescales

Large-scale increases in upper-ocean temperatures are evident in observational records .
Several studies have used well-established detection and attribution methods to demonstrate that the observed basin-scale temperature changes are consistent with model responses to anthropogenic forcing and inconsistent with model-based estimates of natural variability .
These studies relied on a single observational data set and employed results from only one or two models .
Recent identification of systematic instrumental biases in expendable bathythermograph data has led to improved estimates of ocean temperature variability and trends and provide motivation to revisit earlier detection and attribution studies .
We examine the causes of ocean warming using these improved observational estimates , together with results from a large multimodel archive of externally forced and unforced simulations .
The time evolution of upper ocean temperature changes in the newer observational estimates is similar to that of the multimodel average of simulations that include the effects of volcanic eruptions .
Our detection and attribution analysis systematically examines the sensitivity of results to a variety of model and data-processing choices .
When global mean changes are included , we consistently obtain a positive identification ( at the 1 % significance level ) of an anthropogenic fingerprint in observed upper-ocean temperature changes , thereby substantially strengthening existing detection and attribution evidence .

[323] Geographic range predicts photosynthetic and growth response to warming in co-occurring tree species

Populations near the warm edge of species ranges may be particularly sensitive to climate change , but lack of empirical data on responses to warming represents a key gap in understanding future range dynamics .
Herein we document the impacts of experimental warming on the performance of 11 boreal and temperate forest species that co-occur at the ecotone between these biomes in North America .
We measured in situ net photosynthetic carbon gain and growth of > 4,100 juvenile trees from local seed sources exposed to a chamberless warming experiment that used infrared heat lamps and soil heating cables to elevate temperatures by +3.4 degreesC above - and belowground for three growing seasons across 48 plots at two sites .
In these ecologically realistic field settings , species growing nearest their warm range limit exhibited reductions in net photosynthesis and growth , whereas species near their cold range limit responded positively to warming .
Differences among species in their three-year growth responses to warming parallel their photosynthetic responses to warming , suggesting that leaf-level responses may scale to whole-plant performance .
These responses are consistent with the hypothesis , from observational data and models , that warming will reduce the competitive ability of currently dominant southern boreal species compared with locally rarer co-occurring species that dominate warmer neighbouring regions .

[324] Pervasive alteration of tree communities in undisturbed Amazonian forests

Amazonian rainforests are some of the most species-rich tree communities on earth .
Here we show that , over the past two decades , forests in a central Amazonian landscape have experienced highly nonrandom changes in dynamics and composition .
Our analyses are based on a network of 18 permanent plots unaffected by any detectable disturbance .
Within these plots , rates of tree mortality , recruitment and growth have increased over time .
Of 115 relatively abundant tree genera , 27 changed significantly in population density or basal area -- a value nearly 14 times greater than that expected by chance .
An independent , eight-year study in nearby forests corroborates these shifts in composition .
Contrary to recent predictions , we observed no increase in pioneer trees .
However , genera of faster-growing trees , including many canopy and emergent species , are increasing in dominance or density , whereas genera of slower-growing trees , including many subcanopy species , are declining .
Rising atmospheric CO2 concentrations may explain these changes , although the effects of this and other large-scale environmental alterations remain uncertain .
These compositional changes could have important impacts on the carbon storage , dynamics and biota of Amazonian forests .

[325] Late-twentieth-century warming in Lake Tanganyika unprecedented since AD 500

Instrumental observations suggest that Lake Tanganyika , the largest rift lake in East Africa , has become warmer , increasingly stratified and less productive over the past 90 years ( refs 1,2 ) .
These trends have been attributed to anthropogenic climate change .
However , it remains unclear whether the decrease in productivity is linked to the temperature rise , and whether the twentieth-century trends are anomalous within the context of longer-term variability .
Here , we use the TEX86 temperature proxy , the weight per cent of biogenic silica and charcoal abundance from Lake Tanganyika sediment cores to reconstruct lake-surface temperature , productivity and regional wildfire frequency , respectively , for the past 1,500 years .
We detect a negative correlation between lake-surface temperature and primary productivity , and our estimates of fire frequency , and hence humidity , preclude decreased nutrient input through runoff as a cause for observed periods of low productivity .
We suggest that , throughout the past 1,500 years , rising lake-surface temperatures increased the stratification of the lake water column , preventing nutrient recharge from below and limiting primary productivity .
Our records indicate that changes in the temperature of Lake Tanganyika in the past few decades exceed previous natural variability .
We conclude that these unprecedented temperatures and a corresponding decrease in productivity can be attributed to anthropogenic global warming , with potentially important implications for the Lake Tanganyika fishery .

[326] Consequences of tropical land use for multitrophic biodiversity and ecosystem functioning

Our knowledge about land-use impacts on biodiversity and ecosystem functioning is mostly limited to single trophic levels , leaving us uncertain about whole-community biodiversity-ecosystem functioning relationships .
We analyse consequences of the globally important land-use transformation from tropical forests to oil palm plantations .
Species diversity , density and biomass of invertebrate communities suffer at least 45 % decreases from rainforest to oil palm .
Combining metabolic and food-web theory , we calculate annual energy fluxes to model impacts of land-use intensification on multitrophic ecosystem functioning .
We demonstrate a 51 % reduction in energy fluxes from forest to oil palm communities .
Species loss clearly explains variation in energy fluxes ; however , this relationship depends on land-use systems and functional feeding guilds , whereby predators are the most heavily affected .
Biodiversity decline from forest to oil palm is thus accompanied by even stronger reductions in functionality , threatening to severely limit the functional resilience of communities to cope with future global changes .

[327] Recent changes to the Gulf Stream causing widespread gas hydrate destabilization

The Gulf Stream is an ocean current that modulates climate in the Northern Hemisphere by transporting warm waters from the Gulf of Mexico into the North Atlantic and Arctic oceans .
A changing Gulf Stream has the potential to thaw and convert hundreds of gigatonnes of frozen methane hydrate trapped below the sea floor into methane gas , increasing the risk of slope failure and methane release .
How the Gulf Stream changes with time and what effect these changes have on methane hydrate stability is unclear .
Here , using seismic data combined with thermal models , we show that recent changes in intermediate-depth ocean temperature associated with the Gulf Stream are rapidly destabilizing methane hydrate along a broad swathe of the North American margin .
The area of active hydrate destabilization covers at least 10,000 square kilometres of the United States eastern margin , and occurs in a region prone to kilometre-scale slope failures .
Previous hypothetical studies postulated that an increase of five degrees Celsius in intermediate-depth ocean temperatures could release enough methane to explain extreme global warming events like the Palaeocene-Eocene thermal maximum ( PETM ) and trigger widespread ocean acidification .
Our analysis suggests that changes in Gulf Stream flow or temperature within the past 5,000 years or so are warming the western North Atlantic margin by up to eight degrees Celsius and are now triggering the destabilization of 2.5 gigatonnes of methane hydrate ( about 0.2 per cent of that required to cause the PETM ) .
This destabilization extends along hundreds of kilometres of the margin and may continue for centuries .
It is unlikely that the western North Atlantic margin is the only area experiencing changing ocean currents ; our estimate of 2.5 gigatonnes of destabilizing methane hydrate may therefore represent only a fraction of the methane hydrate currently destabilizing globally .
The transport from ocean to atmosphere of any methane released -- and thus its impact on climate -- remains uncertain .

[328] Increasing forest disturbances in Europe and their impact on carbon storage

Disturbances from wind , bark beetles and wildfires have increased in Europe 's forests throughout the twentieth century .
Climatic changes were identified as a key driver behind this increase , yet how the expected continuation of climate change will affect Europe 's forest disturbance regime remains unresolved .
Increasing disturbances could strongly impact the forest carbon budget , and are suggested to contribute to the recently observed carbon sink saturation in Europe 's forests .
Here we show that forest disturbance damage in Europe has continued to increase in the first decade of the twenty-first century .
On the basis of an ensemble of climate change scenarios we find that damage from wind , bark beetles and forest fires is likely to increase further in coming decades , and estimate the rate of increase to be +0.91 x 106 m3 of timber per year until 2030 .
We show that this intensification can offset the effect of management strategies aiming to increase the forest carbon sink , and calculate the disturbance-related reduction of the carbon storage potential in Europe 's forests to be 503.4 Tg C in 2021-2030 .
Our results highlight the considerable carbon cycle feedbacks of changing disturbance regimes , and underline that future forest policy and management will require a stronger focus on disturbance risk and resilience .

[329] Changes in North Atlantic nitrogen fixation controlled by ocean circulation

In the ocean , the chemical forms of nitrogen that are readily available for biological use ( known collectively as ` fixed ' nitrogen ) fuel the global phytoplankton productivity that exports carbon to the deep ocean .
Accordingly , variation in the oceanic fixed nitrogen reservoir has been proposed as a cause of glacial-interglacial changes in atmospheric carbon dioxide concentration .
Marine nitrogen fixation , which produces most of the ocean 's fixed nitrogen , is thought to be affected by multiple factors , including ocean temperature and the availability of iron and phosphorus .
Here we reconstruct changes in North Atlantic nitrogen fixation over the past 160,000 years from the shell-bound nitrogen isotope ratio ( 15N/14N ) of planktonic foraminifera in Caribbean Sea sediments .
The observed changes can not be explained by reconstructed changes in temperature , the supply of ( iron-bearing ) dust or water column denitrification .
We identify a strong , roughly 23,000-year cycle in nitrogen fixation and suggest that it is a response to orbitally driven changes in equatorial Atlantic upwelling , which imports ` excess ' phosphorus ( phosphorus in stoichiometric excess of fixed nitrogen ) into the tropical North Atlantic surface .
In addition , we find that nitrogen fixation was reduced during glacial stages 6 and 4 , when North Atlantic Deep Water had shoaled to become glacial North Atlantic intermediate water , which isolated the Atlantic thermocline from excess phosphorus-rich mid-depth waters that today enter from the Southern Ocean .
Although modern studies have yielded diverse views of the controls on nitrogen fixation , our palaeobiogeochemical data suggest that excess phosphorus is the master variable in the North Atlantic Ocean and indicate that the variations in its supply over the most recent glacial cycle were dominated by the response of regional ocean circulation to the orbital cycles .

[330] Increased terrestrial methane cycling at the Palaeocene-Eocene thermal maximum

The Palaeocene-Eocene thermal maximum ( PETM ) , a period of intense , global warming about 55 million years ago , has been attributed to a rapid rise in greenhouse gas levels , with dissociation of methane hydrates being the most commonly invoked explanation .
It has been suggested previously that high-latitude methane emissions from terrestrial environments could have enhanced the warming effect , but direct evidence for an increased methane flux from wetlands is lacking .
The Cobham Lignite , a recently characterized expanded lacustrine/mire deposit in England , spans the onset of the PETM and therefore provides an opportunity to examine the biogeochemical response of wetland-type ecosystems at that time .
Here we report the occurrence of hopanoids , biomarkers derived from bacteria , in the mire sediments from Cobham .
We measure a decrease in the carbon isotope values of the hopanoids at the onset of the PETM interval , which suggests an increase in the methanotroph population .
We propose that this reflects an increase in methane production potentially driven by changes to a warmer and wetter climate .
Our data suggest that the release of methane from the terrestrial biosphere increased and possibly acted as a positive feedback mechanism to global warming .

[331] Climate change and the resurgence of malaria in the East African highlands

The public health and economic consequences of Plasmodium falciparum malaria are once again regarded as priorities for global development .
There has been much speculation on whether anthropogenic climate change is exacerbating the malaria problem , especially in areas of high altitude where P. falciparum transmission is limited by low temperature .
The International Panel on Climate Change has concluded that there is likely to be a net extension in the distribution of malaria and an increase in incidence within this range .
We investigated long-term meteorological trends in four high-altitude sites in East Africa , where increases in malaria have been reported in the past two decades .
Here we show that temperature , rainfall , vapour pressure and the number of months suitable for P. falciparum transmission have not changed significantly during the past century or during the period of reported malaria resurgence .
A high degree of temporal and spatial variation in the climate of East Africa suggests further that claimed associations between local malaria resurgences and regional changes in climate are overly simplistic .

[332] Interactions between above - and belowground organisms modified in climate change experiments

Climate change has been shown to affect ecosystem process rates and community composition , with direct and indirect effects on belowground food webs .
In particular , altered rates of herbivory under future climate can be expected to influence above-belowground interactions .
Here , we use a multifactor , field-scale climate change experiment and independently manipulate atmospheric CO2 concentration , air and soil temperature and drought in all combinations since 2005 .
We show that changes in these factors modify the interaction between above - and belowground organisms .
We use an insect herbivore to experimentally increase aboveground herbivory in grass phytometers exposed to all eight combinations of climate change factors for three years .
Aboveground herbivory increased the abundance of belowground protozoans , microbial growth and microbial nitrogen availability .
Increased CO2 modified these links through a reduction in herbivory and cascading effects through the soil food web .
Interactions between CO2 , drought and warming can affect belowground protozoan abundance .
Our findings imply that climate change affects aboveground-belowground interactions through changes in nutrient availability .

[333] Ocean acidification causes ecosystem shifts via altered competitive interactions

Ocean acidification represents a pervasive environmental change that is predicted to affect a wide range of species , yet our understanding of the emergent ecosystem impacts is very limited .
Many studies report detrimental effects of acidification on single species in lab studies , especially those with calcareous shells or skeletons .
Observational studies using naturally acidified ecosystems have shown profound shifts away from such calcareous species , and there has been an assumption that direct impacts of acidification on sensitive species drive most ecosystem responses .
We tested an alternative hypothesis that species interactions attenuate or amplify the direct effects of acidification on individual species .
Here , we show that altered competitive dynamics between calcareous species and fleshy seaweeds drive significant ecosystem shifts in acidified conditions .
Although calcareous species recruited and grew at similar rates in ambient and low pH conditions during early successional stages , they were rapidly overgrown by fleshy seaweeds later in succession in low pH conditions .
The altered competitive dynamics between calcareous species and fleshy seaweeds is probably the combined result of decreased growth rates of calcareous species , increased growth rates of fleshy seaweeds , and/or altered grazing rates .
Phase shifts towards ecosystems dominated by fleshy seaweed are common in many marine ecosystems , and our results suggest that changes in the competitive balance between these groups represent a key leverage point through which the physiological responses of individual species to acidification could indirectly lead to profound ecosystem changes in an acidified ocean .

[334] Reduced calcification in modern Southern Ocean planktonic foraminifera

Anthropogenic carbon dioxide has been accumulating in the oceans , lowering both the concentration of carbonate ions and the pH ( ref .
1 ) , resulting in the acidification of sea water .
Previous laboratory experiments have shown that decreased carbonate ion concentrations cause many marine calcareous organisms to show reduced calcification rates .
If these results are widely applicable to ocean settings , ocean acidification could lead to ecosystem shifts .
Planktonic foraminifera are single-celled calcite-secreting organisms that represent between 25 and 50 % of the total open-ocean marine carbonate flux and influence the transport of organic carbon to the ocean interior .
Here we compare the shell weights of the modern foraminifer Globigerina bulloides collected from sediment traps in the Southern Ocean with the weights of shells preserved in the underlying Holocene-aged sediments .
We find that modern shell weights are 30-35 % lower than those from the sediments , consistent with reduced calcification today induced by ocean acidification .
We also find a link between higher atmospheric carbon dioxide and low shell weights in a 50,000-year-long record obtained from a Southern Ocean marine sediment core .
It is unclear whether reduced calcification will affect the survival of this and other species , but a decline in the abundance of foraminifera caused by acidification could affect both marine ecosystems and the oceanic uptake of atmospheric carbon dioxide .

[335] Life history and spatial traits predict extinction risk due to climate change

There is an urgent need to develop effective vulnerability assessments for evaluating the conservation status of species in a changing climate .
Several new assessment approaches have been proposed for evaluating the vulnerability of species to climate change based on the expectation that established assessments such as the IUCN Red List need revising or superseding in light of the threat that climate change brings .
However , although previous studies have identified ecological and life history attributes that characterize declining species or those listed as threatened , no study so far has undertaken a quantitative analysis of the attributes that cause species to be at high risk of extinction specifically due to climate change .
We developed a simulation approach based on generic life history types to show here that extinction risk due to climate change can be predicted using a mixture of spatial and demographic variables that can be measured in the present day without the need for complex forecasting models .
Most of the variables we found to be important for predicting extinction risk , including occupied area and population size , are already used in species conservation assessments , indicating that present systems may be better able to identify species vulnerable to climate change than previously thought .
Therefore , although climate change brings many new conservation challenges , we find that it may not be fundamentally different from other threats in terms of assessing extinction risks .

[336] Rapid changes in the mechanism of ocean convection during the last glacial period

High-amplitude , rapid climate fluctuations are common features of glacial times .
The prominent changes in air temperature recorded in the Greenland ice cores are coherent with shifts in the magnitude of the northward heat flux carried by the North Atlantic surface ocean ; changes in the ocean 's thermohaline circulation are a key component in many explanations of this climate flickering .
Here we use stable-isotope and other sedimentological data to reveal specific oceanic reorganizations during these rapid climate-change events .
Deep water was generated more or less continuously in the Nordic Seas during the latter part of the last glacial period ( 60 to 10 thousand years ago ) , but by two different mechanisms .
The deep-water formation occurred by convection in the open ocean during warmer periods ( interstadials ) .
But during colder phases ( stadials ) , a freshening of the surface ocean reduced or stopped open-ocean convection , and deep-water formation was instead driven by brine-release during sea-ice freezing .
These shifting magnitudes and modes nested within the overall continuity of deep-water formation were probably important for the structuring and rapidity of the prevailing climate changes .

[337] Increasing carbon storage in intact African tropical forests

The response of terrestrial vegetation to a globally changing environment is central to predictions of future levels of atmospheric carbon dioxide .
The role of tropical forests is critical because they are carbon-dense and highly productive .
Inventory plots across Amazonia show that old-growth forests have increased in carbon storage over recent decades , but the response of one-third of the world 's tropical forests in Africa is largely unknown owing to an absence of spatially extensive observation networks .
Here we report data from a ten-country network of long-term monitoring plots in African tropical forests .
We find that across 79 plots ( 163 ha ) above-ground carbon storage in live trees increased by 0.63 Mg C ha-1 yr-1 between 1968 and 2007 ( 95 % confidence interval ( CI ) , 0.22-0 .94 ; mean interval , 1987-96 ) .
Extrapolation to unmeasured forest components ( live roots , small trees , necromass ) and scaling to the continent implies a total increase in carbon storage in African tropical forest trees of 0.34 Pg C yr-1 ( CI , 0.15-0 .43 ) .
These reported changes in carbon storage are similar to those reported for Amazonian forests per unit area , providing evidence that increasing carbon storage in old-growth forests is a pan-tropical phenomenon .
Indeed , combining all standardized inventory data from this study and from tropical America and Asia together yields a comparable figure of 0.49 Mg C ha-1 yr-1 ( n = 156 ; 562 ha ; CI , 0.29-0 .66 ; mean interval , 1987-97 ) .
This indicates a carbon sink of 1.3 Pg C yr-1 ( CI , 0.8-1 .6 ) across all tropical forests during recent decades .
Taxon-specific analyses of African inventory and other data suggest that widespread changes in resource availability , such as increasing atmospheric carbon dioxide concentrations , may be the cause of the increase in carbon stocks , as some theory and models predict .

[338] Increased subaerial volcanism and the rise of atmospheric oxygen 2.5 billion years ago

The hypothesis that the establishment of a permanently oxygenated atmosphere at the Archaean-Proterozoic transition ( ~ 2.5 billion years ago ) occurred when oxygen-producing cyanobacteria evolved is contradicted by biomarker evidence for their presence in rocks 200 million years older .
To sustain vanishingly low oxygen levels despite near-modern rates of oxygen production from ~ 2.7-2 .5 billion years ago thus requires that oxygen sinks must have been much larger than they are now .
Here we propose that the rise of atmospheric oxygen occurred because the predominant sink for oxygen in the Archaean era -- enhanced submarine volcanism -- was abruptly and permanently diminished during the Archaean-Proterozoic transition .
Observations are consistent with the corollary that subaerial volcanism only became widespread after a major tectonic episode of continental stabilization at the beginning of the Proterozoic .
Submarine volcanoes are more reducing than subaerial volcanoes , so a shift from predominantly submarine to a mix of subaerial and submarine volcanism more similar to that observed today would have reduced the overall sink for oxygen and led to the rise of atmospheric oxygen .

[339] Global pattern of soil carbon losses due to the conversion of forests to agricultural land

Several reviews have analyzed the factors that affect the change in soil organic C ( SOC ) when forest is converted to agricultural land ; however , the effects of forest type and cultivation stage on these changes have generally been overlooked .
We collated observations from 453 paired or chronosequential sites where forests have been converted to agricultural land and then assessed the effects of forest type , cultivation stage , climate factors , and soil properties on the change in the SOC stock and the SOC turnover rate constant ( k ) .
The percent decrease in SOC stocks and the turnover rate constants both varied significantly according to forest type and cultivation stage .
The largest decrease in SOC stocks was observed in temperate regions ( 52 % decrease ) , followed by tropical regions ( 41 % decrease ) and boreal regions ( 31 % decrease ) .
Climate and soil factors affected the decrease in SOC stocks .
The SOC turnover rate constant after the conversion of forests to agricultural land increased with the mean annual precipitation and temperature .
To our knowledge , this is the first time that original forest type was considered when evaluating changes in SOC after being converted to agricultural land .
The differences between forest types should be considered when calculating global changes in SOC stocks .

[340] Complex causes of amphibian population declines

Amphibian populations have suffered widespread declines and extinctions in recent decades .
Although climatic changes , increased exposure to ultraviolet-B ( UV-B ) radiation and increased prevalence of disease have all been implicated at particular localities , the importance of global environmental change remains unclear .
Here we report that pathogen outbreaks in amphibian populations in the western USA are linked to climate-induced changes in UV-B exposure .
Using long-term observational data and a field experiment , we examine patterns among interannual variability in precipitation , UV-B exposure and infection by a pathogenic oomycete , Saprolegnia ferax .
Our findings indicate that climate-induced reductions in water depth at oviposition sites have caused high mortality of embryos by increasing their exposure to UV-B radiation and , consequently , their vulnerability to infection .
Precipitation , and thus water depth/UV-B exposure , is strongly linked to El Nino/Southern Oscillation cycles , underscoring the role of large-scale climatic patterns involving the tropical Pacific .
Elevated sea-surface temperatures in this region since the mid-1970s , which have affected the climate over much of the world , could be the precursor for pathogen-mediated amphibian declines in many regions .

[341] Feedback with soil biota contributes to plant rarity and invasiveness in communities

Understanding the relative abundance of species in plant communities is an unsolved problem .
Mechanisms such as competition , resource partitioning , dispersal ability and predation tolerance do not adequately explain relative abundance under field conditions .
Recent work suggests that interactions between plants and soil microbes is important .
Here I show that such interaction explains a significant proportion of the variance in the relative abundance of species in plant communities .
Rare plants exhibited a relative decrease in growth on ` home ' soil in which pathogens had had a chance to accumulate , whereas invasive plants benefited from interactions with mycorrhizal fungi .
Some plant species accumulate pathogens quickly and maintain low densities as a result of the accumulation of species-specific pathogens , whereas others accumulate species-specific pathogens more slowly and do not experience negative feedback until plant densities reach high levels .
These results indicate that plants have different abilities to influence their abundance by changing the structure of their soil communities , and that this is an important regulator of plant community structure .

[342] Climate , health , agricultural and economic impacts of tighter vehicle-emission standards

Non-CO2 air pollutants from motor vehicles have traditionally been controlled to protect air quality and health , but also affect climate .
We use global composition-climate modelling to examine the integrated impacts of adopting stringent European on-road vehicle-emission standards for these pollutants in 2015 in many developing countries .
Relative to no extra controls , the tight standards lead to annual benefits in 2030 and beyond of 120,000-280 ,000 avoided premature air pollution-related deaths , 6.1-19 .7 million metric tons of avoided ozone-related yield losses of major food crops , $ US0.6-2 .4 trillion avoided health damage and $ US1.1-4 .3 billion avoided agricultural damage , and mitigation of 0.20 ( +0.14 / -0.17 ) degreesC of Northern Hemisphere extratropical warming during 2040-2070 .
Tighter vehicle-emission standards are thus extremely likely to mitigate short-term climate change in most cases , in addition to providing large improvements in human health and food security .
These standards will not reduce CO2 emissions , however , which is required to mitigate long-term climate change .

[343] Regional atmospheric circulation shifts induced by a grand solar minimum

Large changes in solar ultraviolet radiation can indirectly affect climate by inducing atmospheric changes .
Specifically , it has been suggested that centennial-scale climate variability during the Holocene epoch was controlled by the Sun .
However , the amplitude of solar forcing is small when compared with the climatic effects and , without reliable data sets , it is unclear which feedback mechanisms could have amplified the forcing .
Here we analyse annually laminated sediments of Lake Meerfelder Maar , Germany , to derive variations in wind strength and the rate of 10Be accumulation , a proxy for solar activity , from 3,300 to 2,000 years before present .
We find a sharp increase in windiness and cosmogenic 10Be deposition 2,759 + / - 39 varve years before present and a reduction in both entities 199 + / - 9 annual layers later .
We infer that the atmospheric circulation reacted abruptly and in phase with the solar minimum .
A shift in atmospheric circulation in response to changes in solar activity is broadly consistent with atmospheric circulation patterns in long-term climate model simulations , and in reanalysis data that assimilate observations from recent solar minima into a climate model .
We conclude that changes in atmospheric circulation amplified the solar signal and caused abrupt climate change about 2,800 years ago , coincident with a grand solar minimum .

[344] In Vitro Expansion of Corneal Endothelial Cells on Biomimetic Substrates

Corneal endothelial ( CE ) cells do not divide in vivo , leading to edema , corneal clouding and vision loss when the density drops below a critical level .
The endothelium can be replaced by transplanting allogeneic tissue ; however , access to donated tissue is limited worldwide resulting in critical need for new sources of corneal grafts .
In vitro expansion of CE cells is a potential solution , but is challenging due to limited proliferation and loss of phenotype in vitro via endothelial to mesenchymal transformation ( EMT ) and senescence .
We hypothesized that a bioengineered substrate recapitulating chemo-mechanical properties of Descemet 's membrane would improve the in vitro expansion of CE cells while maintaining phenotype .
Results show that bovine CE cells cultured on a polydimethylsiloxane surface with elastic modulus of 50 kPa and collagen IV coating achieved > 3000-fold expansion .
Cells grew in higher-density monolayers with polygonal morphology and ZO-1 localization at cell-cell junctions in contrast to control cells on polystyrene that lost these phenotypic markers coupled with increased alpha-smooth muscle actin expression and fibronectin fibril assembly .
In total , these results demonstrate that a biomimetic substrate presenting native basement membrane ECM proteins and mechanical environment may be a key element in bioengineering functional CE layers for potential therapeutic applications .

[345] Anthropogenically enhanced fluxes of water and carbon from the Mississippi River

The water and dissolved inorganic carbon exported by rivers are important net fluxes that connect terrestrial and oceanic water and carbon reservoirs .
For most rivers , the majority of dissolved inorganic carbon is in the form of bicarbonate .
The riverine bicarbonate flux originates mainly from the dissolution of rock minerals by soil water carbon dioxide , a process called chemical weathering , which controls the buffering capacity and mineral content of receiving streams and rivers .
Here we introduce an unprecedented high-temporal-resolution , 100-year data set from the Mississippi River and couple it with sub-watershed and precipitation data to reveal that the large increase in bicarbonate flux that has occurred over the past 50 years ( ref .
3 ) is clearly anthropogenically driven .
We show that the increase in bicarbonate and water fluxes is caused mainly by an increase in discharge from agricultural watersheds that has not been balanced by a rise in precipitation , which is also relevant to nutrient and pesticide fluxes to the Gulf of Mexico .
These findings demonstrate that alterations in chemical weathering are relevant to improving contemporary biogeochemical budgets .
Furthermore , land use change and management were arguably more important than changes in climate and plant CO2 fertilization to increases in riverine water and carbon export from this large region over the past 50 years .

[346] Large contribution of sea surface warming to recent increase in Atlantic hurricane activity

Atlantic hurricane activity has increased significantly since 1995 ( refs 1-4 ) , but the underlying causes of this increase remain uncertain .
It is widely thought that rising Atlantic sea surface temperatures have had a role in this , but the magnitude of this contribution is not known .
Here we quantify this contribution for storms that formed in the tropical North Atlantic , Caribbean Sea and Gulf of Mexico ; these regions together account for most of the hurricanes that make landfall in the United States .
We show that a statistical model based on two environmental variables -- local sea surface temperature and an atmospheric wind field -- can replicate a large proportion of the variance in tropical Atlantic hurricane frequency and activity between 1965 and 2005 .
We then remove the influence of the atmospheric wind field to assess the contribution of sea surface temperature .
Our results indicate that the sensitivity of tropical Atlantic hurricane activity to August-September sea surface temperature over the period we consider is such that a 0.5 degreesC increase in sea surface temperature is associated with a ~ 40 % increase in hurricane frequency and activity .
The results also indicate that local sea surface warming was responsible for ~ 40 % of the increase in hurricane activity relative to the 1950-2000 average between 1996 and 2005 .
Our analysis does not identify whether warming induced by greenhouse gases contributed to the increase in hurricane activity , but the ability of climate models to reproduce the observed relationship between hurricanes and sea surface temperature will serve as a useful means of assessing whether they are likely to provide reliable projections of future changes in Atlantic hurricane activity .

[347] Increasing risk of great floods in a changing climate

Radiative effects of anthropogenic changes in atmospheric composition are expected to cause climate changes , in particular an intensification of the global water cycle with a consequent increase in flood risk .
But the detection of anthropogenically forced changes in flooding is difficult because of the substantial natural variability ; the dependence of streamflow trends on flow regime further complicates the issue .
Here we investigate the changes in risk of great floods -- that is , floods with discharges exceeding 100-year levels from basins larger than 200,000 km2 -- using both streamflow measurements and numerical simulations of the anthropogenic climate change associated with greenhouse gases and direct radiative effects of sulphate aerosols .
We find that the frequency of great floods increased substantially during the twentieth century .
The recent emergence of a statistically significant positive trend in risk of great floods is consistent with results from the climate model , and the model suggests that the trend will continue .

[348] Ecological and evolutionary processes at expanding range margins

Many animals are regarded as relatively sedentary and specialized in marginal parts of their geographical distributions .
They are expected to be slow at colonizing new habitats .
Despite this , the cool margins of many species ' distributions have expanded rapidly in association with recent climate warming .
We examined four insect species that have expanded their geographical ranges in Britain over the past 20 years .
Here we report that two butterfly species have increased the variety of habitat types that they can colonize , and that two bush cricket species show increased fractions of longer-winged ( dispersive ) individuals in recently founded populations .
Both ecological and evolutionary processes are probably responsible for these changes .
Increased habitat breadth and dispersal tendencies have resulted in about 3 - to 15-fold increases in expansion rates , allowing these insects to cross habitat disjunctions that would have represented major or complete barriers to dispersal before the expansions started .
The emergence of dispersive phenotypes will increase the speed at which species invade new environments , and probably underlies the responses of many species to both past and future climate change .

[349] Species-area relationships always overestimate extinction rates from habitat loss

Extinction from habitat loss is the signature conservation problem of the twenty-first century .
Despite its importance , estimating extinction rates is still highly uncertain because no proven direct methods or reliable data exist for verifying extinctions .
The most widely used indirect method is to estimate extinction rates by reversing the species-area accumulation curve , extrapolating backwards to smaller areas to calculate expected species loss .
Estimates of extinction rates based on this method are almost always much higher than those actually observed .
This discrepancy gave rise to the concept of an ` extinction debt ' , referring to species ` committed to extinction ' owing to habitat loss and reduced population size but not yet extinct during a non-equilibrium period .
Here we show that the extinction debt as currently defined is largely a sampling artefact due to an unrecognized difference between the underlying sampling problems when constructing a species-area relationship ( SAR ) and when extrapolating species extinction from habitat loss .
The key mathematical result is that the area required to remove the last individual of a species ( extinction ) is larger , almost always much larger , than the sample area needed to encounter the first individual of a species , irrespective of species distribution and spatial scale .
We illustrate these results with data from a global network of large , mapped forest plots and ranges of passerine bird species in the continental USA ; and we show that overestimation can be greater than 160 % .
Although we conclude that extinctions caused by habitat loss require greater loss of habitat than previously thought , our results must not lead to complacency about extinction due to habitat loss , which is a real and growing threat .

[350] Northern Hemisphere atmospheric stilling partly attributed to an increase in surface roughness

Surface winds have declined in China , the Netherlands , the Czech Republic , the United States and Australia over the past few decades .
The precise cause of the stilling is uncertain .
Here , we analyse the extent and potential cause of changes in surface wind speeds over the northern mid-latitudes between 1979 and 2008 , using data from 822 surface weather stations .
We show that surface wind speeds have declined by 5-15 % over almost all continental areas in the northern mid-latitudes , and that strong winds have slowed faster than weak winds .
In contrast , upper-air winds calculated from sea-level pressure gradients , and winds from weather reanalyses , exhibited no such trend .
Changes in atmospheric circulation that are captured by reanalysis data explain 10-50 % of the surface wind slowdown .
In addition , mesoscale model simulations suggest that an increase in surface roughness -- the magnitude of which is estimated from increases in biomass and land-use change in Eurasia -- could explain between 25 and 60 % of the stilling .
Moreover , regions of pronounced stilling generally coincided with regions where biomass has increased over the past 30 years , supporting the role of vegetation increases in wind slowdown .

[351] Disrupted erythropoietin signalling promotes obesity and alters hypothalamus proopiomelanocortin production

Although erythropoietin ( Epo ) is the cytokine known to regulate erythropoiesis , erythropoietin receptor ( EpoR ) expression and associated activity beyond haematopoietic tissue remain uncertain .
Here we show that mice with EpoR expression restricted to haematopoietic tissues ( Tg ) develop obesity and insulin resistance .
Tg-mice exhibit a decrease in energy expenditure and an increase in white fat mass and adipocyte number .
Conversely , Epo treatment of wild-type ( WT ) - mice increases energy expenditure and reduces food intake and fat mass accumulation but shows no effect in body weight of Tg-mice .
EpoR is expressed at a high level in white adipose tissue and in the proopiomelanocortin ( POMC ) neurons of the hypothalamus .
Although Epo treatment in WT-mice induces the expression of the polypeptide hormone precursor , POMC , mice lacking EpoR show reduced levels of POMC in the hypothalamus .
This study provides the first evidence that mice lacking EpoR in non-haematopoietic tissue become obese and insulin resistant with loss of Epo regulation of energy homeostasis .

[352] Probabilistic reanalysis of twentieth-century sea-level rise

Estimating and accounting for twentieth-century global mean sea-level ( GMSL ) rise is critical to characterizing current and future human-induced sea-level change .
Several previous analyses of tide gauge records -- employing different methods to accommodate the spatial sparsity and temporal incompleteness of the data and to constrain the geometry of long-term sea-level change -- have concluded that GMSL rose over the twentieth century at a mean rate of 1.6 to 1.9 millimetres per year .
Efforts to account for this rate by summing estimates of individual contributions from glacier and ice-sheet mass loss , ocean thermal expansion , and changes in land water storage fall significantly short in the period before 1990 .
The failure to close the budget of GMSL during this period has led to suggestions that several contributions may have been systematically underestimated .
However , the extent to which the limitations of tide gauge analyses have affected estimates of the GMSL rate of change is unclear .
Here we revisit estimates of twentieth-century GMSL rise using probabilistic techniques and find a rate of GMSL rise from 1901 to 1990 of 1.2 + / - 0.2 millimetres per year ( 90 % confidence interval ) .
Based on individual contributions tabulated in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change , this estimate closes the twentieth-century sea-level budget .
Our analysis , which combines tide gauge records with physics-based and model-derived geometries of the various contributing signals , also indicates that GMSL rose at a rate of 3.0 + / - 0.7 millimetres per year between 1993 and 2010 , consistent with prior estimates from tide gauge records .
The increase in rate relative to the 1901-90 trend is accordingly larger than previously thought ; this revision may affect some projections of future sea-level rise .

[353] Linking climate change to lemming cycles

The population cycles of rodents at northern latitudes have puzzled people for centuries , and their impact is manifest throughout the alpine ecosystem .
Climate change is known to be able to drive animal population dynamics between stable and cyclic phases , and has been suggested to cause the recent changes in cyclic dynamics of rodents and their predators .
But although predator-rodent interactions are commonly argued to be the cause of the Fennoscandian rodent cycles , the role of the environment in the modulation of such dynamics is often poorly understood in natural systems .
Hence , quantitative links between climate-driven processes and rodent dynamics have so far been lacking .
Here we show that winter weather and snow conditions , together with density dependence in the net population growth rate , account for the observed population dynamics of the rodent community dominated by lemmings ( Lemmus lemmus ) in an alpine Norwegian core habitat between 1970 and 1997 , and predict the observed absence of rodent peak years after 1994 .
These local rodent dynamics are coherent with alpine bird dynamics both locally and over all of southern Norway , consistent with the influence of large-scale fluctuations in winter conditions .
The relationship between commonly available meteorological data and snow conditions indicates that changes in temperature and humidity , and thus conditions in the subnivean space , seem to markedly affect the dynamics of alpine rodents and their linked groups .
The pattern of less regular rodent peaks , and corresponding changes in the overall dynamics of the alpine ecosystem , thus seems likely to prevail over a growing area under projected climate change .

[354] Continent-wide response of mountain vegetation to climate change

Climate impact studies have indicated ecological fingerprints of recent global warming across a wide range of habitats .
Although these studies have shown responses from various local case studies , a coherent large-scale account on temperature-driven changes of biotic communities has been lacking .
Here we use 867 vegetation samples above the treeline from 60 summit sites in all major European mountain systems to show that ongoing climate change gradually transforms mountain plant communities .
We provide evidence that the more cold-adapted species decline and the more warm-adapted species increase , a process described here as thermophilization .
At the scale of individual mountains this general trend may not be apparent , but at the larger , continental scale we observed a significantly higher abundance of thermophilic species in 2008 , compared with 2001 .
Thermophilization of mountain plant communities mirrors the degree of recent warming and is more pronounced in areas where the temperature increase has been higher .
In view of the projected climate change the observed transformation suggests a progressive decline of cold mountain habitats and their biota .

[355] Springtime atmospheric energy transport and the control of Arctic summer sea-ice extent

The summer sea-ice extent in the Arctic has decreased in recent decades , a feature that has become one of the most distinct signals of the continuing climate change .
However , the inter-annual variability is large -- the ice extent by the end of the summer varies by several million square kilometres from year to year .
The underlying processes driving this year-to-year variability are not well understood .
Here we demonstrate that the greenhouse effect associated with clouds and water vapour in spring is crucial for the development of the sea ice during the subsequent months .
In years where the end-of-summer sea-ice extent is well below normal , a significantly enhanced transport of humid air is evident during spring into the region where the ice retreat is encountered .
This enhanced transport of humid air leads to an anomalous convergence of humidity , and to an increase of the cloudiness .
The increase of the cloudiness and humidity results in an enhancement of the greenhouse effect .
As a result , downward long-wave radiation at the surface is larger than usual in spring , which enhances the ice melt .
In addition , the increase of clouds causes an increase of the reflection of incoming solar radiation .
This leads to the counter-intuitive effect : for years with little sea ice in September , the downwelling short-wave radiation at the surface is smaller than usual .
That is , the downwelling short-wave radiation is not responsible for the initiation of the ice anomaly but acts as an amplifying feedback once the melt is started .

[356] Recent Northern Hemisphere tropical expansion primarily driven by black carbon and tropospheric ozone

Observational analyses have shown the width of the tropical belt increasing in recent decades as the world has warmed .
This expansion is important because it is associated with shifts in large-scale atmospheric circulation and major climate zones .
Although recent studies have attributed tropical expansion in the Southern Hemisphere to ozone depletion , the drivers of Northern Hemisphere expansion are not well known and the expansion has not so far been reproduced by climate models .
Here we use a climate model with detailed aerosol physics to show that increases in heterogeneous warming agents -- including black carbon aerosols and tropospheric ozone -- are noticeably better than greenhouse gases at driving expansion , and can account for the observed summertime maximum in tropical expansion .
Mechanistically , atmospheric heating from black carbon and tropospheric ozone has occurred at the mid-latitudes , generating a poleward shift of the tropospheric jet , thereby relocating the main division between tropical and temperate air masses .
Although we still underestimate tropical expansion , the true aerosol forcing is poorly known and could also be underestimated .
Thus , although the insensitivity of models needs further investigation , black carbon and tropospheric ozone , both of which are strongly influenced by human activities , are the most likely causes of observed Northern Hemisphere tropical expansion .

[357] Metabolic determinants of cancer cell sensitivity to glucose limitation and biguanides

As the concentrations of highly consumed nutrients , particularly glucose , are generally lower in tumours than in normal tissues , cancer cells must adapt their metabolism to the tumour microenvironment .
A better understanding of these adaptations might reveal cancer cell liabilities that can be exploited for therapeutic benefit .
Here we developed a continuous-flow culture apparatus ( Nutrostat ) for maintaining proliferating cells in low-nutrient media for long periods of time , and used it to undertake competitive proliferation assays on a pooled collection of barcoded cancer cell lines cultured in low-glucose conditions .
Sensitivity to low glucose varies amongst cell lines , and an RNA interference ( RNAi ) screen pinpointed mitochondrial oxidative phosphorylation ( OXPHOS ) as the major pathway required for optimal proliferation in low glucose .
We found that cell lines most sensitive to low glucose are defective in the OXPHOS upregulation that is normally caused by glucose limitation as a result of either mitochondrial DNA ( mtDNA ) mutations in complex I genes or impaired glucose utilization .
These defects predict sensitivity to biguanides , antidiabetic drugs that inhibit OXPHOS , when cancer cells are grown in low glucose or as tumour xenografts .
Notably , the biguanide sensitivity of cancer cells with mtDNA mutations was reversed by ectopic expression of yeast NDI1 , a ubiquinone oxidoreductase that allows bypass of complex I function .
Thus , we conclude that mtDNA mutations and impaired glucose utilization are potential biomarkers for identifying tumours with increased sensitivity to OXPHOS inhibitors .

[358] Forest stand growth dynamics in Central Europe have accelerated since 1870

Forest ecosystems have been exposed to climate change for more than 100 years , whereas the consequences on forest growth remain elusive .
Based on the oldest existing experimental forest plots in Central Europe , we show that , currently , the dominant tree species Norway spruce and European beech exhibit significantly faster tree growth ( +32 to 77 % ) , stand volume growth ( +10 to 30 % ) and standing stock accumulation ( +6 to 7 % ) than in 1960 .
Stands still follow similar general allometric rules , but proceed more rapidly through usual trajectories .
As forest stands develop faster , tree numbers are currently 17-20 % lower than in past same-aged stands .
Self-thinning lines remain constant , while growth rates increase indicating the stock of resources have not changed , while growth velocity and turnover have altered .
Statistical analyses of the experimental plots , and application of an ecophysiological model , suggest that mainly the rise in temperature and extended growing seasons contribute to increased growth acceleration , particularly on fertile sites .

[359] Climate change may cause severe loss in the economic value of European forest land

European forests , covering more than 2 million km2 or 32 % of the land surface , are to a large extent intensively managed and support an important timber industry .
Climate change is expected to strongly affect tree species distribution within these forests .
Climate and land use are undergoing rapid changes at present , with initial range shifts already visible .
However , discussions on the consequences of biome shifts have concentrated on ecological issues .
Here we show that forecasted changes in temperature and precipitation may have severe economic consequences .
On the basis of our model results , the expected value of European forest land will decrease owing to the decline of economically valuable species in the absence of effective countermeasures .
We found that by 2100 -- depending on the interest rate and climate scenario applied -- this loss varies between 14 and 50 % ( mean : 28 % for an interest rate of 2 % ) of the present value of forest land in Europe , excluding Russia , and may total several hundred billion Euros .
Our model shows that -- depending on different realizations of three climate scenarios -- by 2100 , between 21 and 60 % ( mean : 34 % ) of European forest lands will be suitable only for a Mediterranean oak forest type with low economic returns for forest owners and the timber industry and reduced carbon sequestration .

[360] Silicon isotopes indicate enhanced carbon export efficiency in the North Atlantic during deglaciation

Today 's Sargasso Sea is nutrient starved , except for episodic upwelling events caused by wind-driven winter mixing and eddies .
Enhanced diatom opal burial in Sargasso Sea sediments indicates that silicic acid , a limiting nutrient today , may have been more available in subsurface waters during Heinrich Stadials , millennial-scale climate perturbations of the last glacial and deglaciation .
Here we use the geochemistry of opal-forming organisms from different water depths to demonstrate changes in silicic acid supply and utilization during the most recent Heinrich Stadial .
We suggest that during the early phase ( 17.5-18 ka ) , wind-driven upwelling replenished silicic acid to the subsurface , resulting in low Si utilization .
By 17 ka , stratification reduced the surface silicic acid supply leading to increased Si utilization efficiency .
This abrupt shift in Si cycling would have contributed to high regional carbon export efficiency during the recent Heinrich Stadial , despite being a period of increasing atmospheric CO2 .

[361] Attributing physical and biological impacts to anthropogenic climate change

Significant changes in physical and biological systems are occurring on all continents and in most oceans , with a concentration of available data in Europe and North America .
Most of these changes are in the direction expected with warming temperature .
Here we show that these changes in natural systems since at least 1970 are occurring in regions of observed temperature increases , and that these temperature increases at continental scales can not be explained by natural climate variations alone .
Given the conclusions from the Intergovernmental Panel on Climate Change ( IPCC ) Fourth Assessment Report that most of the observed increase in global average temperatures since the mid-twentieth century is very likely to be due to the observed increase in anthropogenic greenhouse gas concentrations , and furthermore that it is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent except Antarctica , we conclude that anthropogenic climate change is having a significant impact on physical and biological systems globally and in some continents .

[362] Impact of changes in diffuse radiation on the global land carbon sink

Plant photosynthesis tends to increase with irradiance .
However , recent theoretical and observational studies have demonstrated that photosynthesis is also more efficient under diffuse light conditions .
Changes in cloud cover or atmospheric aerosol loadings , arising from either volcanic or anthropogenic emissions , alter both the total photosynthetically active radiation reaching the surface and the fraction of this radiation that is diffuse , with uncertain overall effects on global plant productivity and the land carbon sink .
Here we estimate the impact of variations in diffuse fraction on the land carbon sink using a global model modified to account for the effects of variations in both direct and diffuse radiation on canopy photosynthesis .
We estimate that variations in diffuse fraction , associated largely with the ` global dimming ' period , enhanced the land carbon sink by approximately one-quarter between 1960 and 1999 .
However , under a climate mitigation scenario for the twenty-first century in which sulphate aerosols decline before atmospheric CO2 is stabilized , this ` diffuse-radiation ' fertilization effect declines rapidly to near zero by the end of the twenty-first century .

[363] Simulated climate-vegetation interaction in semi-arid regions affected by plant diversity

The end of the African Humid Period between 6,000 and 4,000 years ago was associated with large changes in precipitation and vegetation cover .
Sediment records from Lake Yoa , Chad , show a gradual decline in precipitation and fluctuation in vegetation over this interval , and have been suggested to demonstrate a weak interaction between climate and vegetation .
However , interpretation of these data has neglected the potential effects of plant diversity on the stability of the climate-vegetation system .
Here we use a conceptual model that represents plant diversity in terms of moisture requirement .
Some of the plant types simulated are sensitive to changes in precipitation , which alone would lead to an unstable system with the possibility of abrupt changes .
Other plants are more resilient , resulting in a stable system that changes gradually .
We demonstrate that plant diversity tends to attenuate the instability of the interaction between climate and sensitive plant types , whereas it reduces the stability of the interaction between climate and less-sensitive plant types .
Hence , despite large sensitivities of individual plant types to precipitation , a gradual decline in precipitation and shift in mean vegetation cover can occur .
However , we suggest that the system could become unstable if some plant types were removed or introduced , leading to an abrupt regime shift .

[364] The effect of permafrost thaw on old carbon release and net carbon exchange from tundra

Permafrost soils in boreal and Arctic ecosystems store almost twice as much carbon as is currently present in the atmosphere .
Permafrost thaw and the microbial decomposition of previously frozen organic carbon is considered one of the most likely positive climate feedbacks from terrestrial ecosystems to the atmosphere in a warmer world .
The rate of carbon release from permafrost soils is highly uncertain , but it is crucial for predicting the strength and timing of this carbon-cycle feedback effect , and thus how important permafrost thaw will be for climate change this century and beyond .
Sustained transfers of carbon to the atmosphere that could cause a significant positive feedback to climate change must come from old carbon , which forms the bulk of the permafrost carbon pool that accumulated over thousands of years .
Here we measure net ecosystem carbon exchange and the radiocarbon age of ecosystem respiration in a tundra landscape undergoing permafrost thaw to determine the influence of old carbon loss on ecosystem carbon balance .
We find that areas that thawed over the past 15 years had 40 per cent more annual losses of old carbon than minimally thawed areas , but had overall net ecosystem carbon uptake as increased plant growth offset these losses .
In contrast , areas that thawed decades earlier lost even more old carbon , a 78 per cent increase over minimally thawed areas ; this old carbon loss contributed to overall net ecosystem carbon release despite increased plant growth .
Our data document significant losses of soil carbon with permafrost thaw that , over decadal timescales , overwhelms increased plant carbon uptake at rates that could make permafrost a large biospheric carbon source in a warmer world .

[365] Solar forcing of North Atlantic surface temperature and salinity over the past millennium

There were several centennial-scale fluctuations in the climate and oceanography of the North Atlantic region over the past 1,000 years , including a period of relative cooling from about AD 1450 to 1850 known as the Little Ice Age .
These variations may be linked to changes in solar irradiance , amplified through feedbacks including the Atlantic meridional overturning circulation .
Changes in the return limb of the Atlantic meridional overturning circulation are reflected in water properties at the base of the mixed layer south of Iceland .
Here we reconstruct thermocline temperature and salinity in this region from AD 818 to 1780 using paired delta18O and Mg/Ca ratio measurements of foraminifer shells from a subdecadally resolved marine sediment core .
The reconstructed centennial-scale variations in hydrography correlate with variability in total solar irradiance .
We find a similar correlation in a simulation of climate over the past 1,000 years .
We infer that the hydrographic changes probably reflect variability in the strength of the subpolar gyre associated with changes in atmospheric circulation .
Specifically , in the simulation , low solar irradiance promotes the development of frequent and persistent atmospheric blocking events , in which a quasi-stationary high-pressure system in the eastern North Atlantic modifies the flow of the westerly winds .
We conclude that this process could have contributed to the consecutive cold winters documented in Europe during the Little Ice Age .

[366] Detection of solar dimming and brightening effects on Northern Hemisphere river flow

Anthropogenic aerosols in the atmosphere have the potential to affect regional-scale land hydrology through solar dimming .
Increased aerosol loading may have reduced historical surface evaporation over some locations , but the magnitude and extent of this effect is uncertain .
Any reduction in evaporation due to historical solar dimming may have resulted in an increase in river flow .
Here we formally detect and quantify the historical effect of changing aerosol concentrations , via solar radiation , on observed river flow over the heavily industrialized , northern extra-tropics .
We use a state-of-the-art estimate of twentieth century surface meteorology as input data for a detailed land surface model , and show that the simulations capture the observed strong inter-annual variability in runoff in response to climatic fluctuations .
Using statistical techniques , we identify a detectable aerosol signal in the observed river flow both over the combined region , and over individual river basins in Europe and North America .
We estimate that solar dimming due to rising aerosol concentrations in the atmosphere around 1980 led to an increase in river runoff by up to 25 % in the most heavily polluted regions in Europe .
We propose that , conversely , these regions may experience reduced freshwater availability in the future , as air quality improvements are set to lower aerosol loading and solar dimming .

[367] Greater temporal changes of sediment microbial community than its waterborne counterpart in Tengchong hot springs , Yunnan Province , China

Temporal variation in geochemistry can cause changes in microbial community structure and diversity .
Here we studied temporal changes of microbial communities in Tengchong hot springs of Yunnan Province , China in response to geochemical variations by using microbial and geochemical data collected in January , June and August of 2011 .
Greater temporal variations were observed in individual taxa than at the whole community structure level .
Water and sediment communities exhibited different temporal variation patterns .
Water communities were largely stable across three sampling times and dominated by similar microbial lineages : Hydrogenobaculum in moderate-temperature acidic springs , Sulfolobus in high-temperature acidic springs , and Hydrogenobacter in high-temperature circumneutral to alkaline springs .
Sediment communities were more diverse and responsive to changing physicochemical conditions .
Most of the sediment communities in January and June were similar to those in waters .
However , the August sediment community was more diverse and contained more anaerobic heterotrophs than the January and June : Desulfurella and Acidicaldus in moderate-temperature acidic springs , Ignisphaera and Desulfurococcus in high-temperature acidic springs , the candidate division OP1 and Fervidobacterium in alkaline springs , and Thermus and GAL35 in neutral springs .
Temporal variations in physicochemical parameters including temperature , pH , and dissolved organic carbon may have triggered the observed microbial community shifts .

[368] Evolution of Asian monsoons and phased uplift of the Himalaya-Tibetan plateau since Late Miocene times

The climates of Asia are affected significantly by the extent and height of the Himalayan mountains and the Tibetan plateau .
Uplift of this region began about 50 Myr ago , and further significant increases in altitude of the Tibetan plateau are thought to have occurred about 10-8 Myr ago , or more recently .
However , the climatic consequences of this uplift remain unclear .
Here we use records of aeolian sediments from China and marine sediments from the Indian and North Pacific oceans to identify three stages of evolution of Asian climates : first , enhanced aridity in the Asian interior and onset of the Indian and east Asian monsoons , about 9-8 Myr ago ; next , continued intensification of the east Asian summer and winter monsoons , together with increased dust transport to the North Pacific Ocean , about 3.6-2 .6 Myr ago ; and last , increased variability and possible weakening of the Indian and east Asian summer monsoons and continued strengthening of the east Asian winter monsoon since about 2.6 Myr ago .
The results of a numerical climate-model experiment , using idealized stepwise increases of mountain-plateau elevation , support the argument that the stages in evolution of Asian monsoons are linked to phases of Himalaya-Tibetan plateau uplift and to Northern Hemisphere glaciation .

[369] Convergence across biomes to a common rain-use efficiency

Water availability limits plant growth and production in almost all terrestrial ecosystems .
However , biomes differ substantially in sensitivity of aboveground net primary production ( ANPP ) to between-year variation in precipitation .
Average rain-use efficiency ( RUE ; ANPP/precipitation ) also varies between biomes , supposedly because of differences in vegetation structure and/or biogeochemical constraints .
Here we show that RUE decreases across biomes as mean annual precipitation increases .
However , during the driest years at each site , there is convergence to a common maximum RUE ( RUEmax ) that is typical of arid ecosystems .
RUEmax was also identified by experimentally altering the degree of limitation by water and other resources .
Thus , in years when water is most limiting , deserts , grasslands and forests all exhibit the same rate of biomass production per unit rainfall , despite differences in physiognomy and site-level RUE .
Global climate models predict increased between-year variability in precipitation , more frequent extreme drought events , and changes in temperature .
Forecasts of future ecosystem behaviour should take into account this convergent feature of terrestrial biomes .

[370] Aridification of the Sahara desert caused by Tethys Sea shrinkage during the Late Miocene

It is widely believed that the Sahara desert is no more than ~ 2-3 million years ( Myr ) old , with geological evidence showing a remarkable aridification of north Africa at the onset of the Quaternary ice ages .
Before that time , north African aridity was mainly controlled by the African summer monsoon ( ASM ) , which oscillated with Earth 's orbital precession cycles .
Afterwards , the Northern Hemisphere glaciation added an ice volume forcing on the ASM , which additionally oscillated with glacial-interglacial cycles .
These findings led to the idea that the Sahara desert came into existence when the Northern Hemisphere glaciated ~ 2-3 Myr ago .
The later discovery , however , of aeolian dune deposits ~ 7 Myr old suggested a much older age , although this interpretation is hotly challenged and there is no clear mechanism for aridification around this time .
Here we use climate model simulations to identify the Tortonian stage ( ~ 7-11 Myr ago ) of the Late Miocene epoch as the pivotal period for triggering north African aridity and creating the Sahara desert .
Through a set of experiments with the Norwegian Earth System Model and the Community Atmosphere Model , we demonstrate that the African summer monsoon was drastically weakened by the Tethys Sea shrinkage during the Tortonian , allowing arid , desert conditions to expand across north Africa .
Not only did the Tethys shrinkage alter the mean climate of the region , it also enhanced the sensitivity of the African monsoon to orbital forcing , which subsequently became the major driver of Sahara extent fluctuations .
These important climatic changes probably caused the shifts in Asian and African flora and fauna observed during the same period , with possible links to the emergence of early hominins in north Africa .

[371] When the forest dies : the response of forest soil fungi to a bark beetle-induced tree dieback

Coniferous forests cover extensive areas of the boreal and temperate zones .
Owing to their primary production and C storage , they have an important role in the global carbon balance .
Forest disturbances such as forest fires , windthrows or insect pest outbreaks have a substantial effect on the functioning of these ecosystems .
Recent decades have seen an increase in the areas affected by disturbances in both North America and Europe , with indications that this increase is due to both local human activity and global climate change .
Here we examine the structural and functional response of the litter and soil microbial community in a Picea abies forest to tree dieback following an invasion of the bark beetle Ips typographus , with a specific focus on the fungal community .
The insect-induced disturbance rapidly and profoundly changed vegetation and nutrient availability by killing spruce trees so that the readily available root exudates were replaced by more recalcitrant , polymeric plant biomass components .
Owing to the dramatic decrease in photosynthesis , the rate of decomposition processes in the ecosystem decreased as soon as the one-time litter input had been processed .
The fungal community showed profound changes , including a decrease in biomass ( 2.5-fold in the litter and 12-fold in the soil ) together with the disappearance of fungi symbiotic with tree roots and a relative increase in saprotrophic taxa .
Within the latter group , successive changes reflected the changing availability of needle litter and woody debris .
Bacterial biomass appeared to be either unaffected or increased after the disturbance , resulting in a substantial increase in the bacterial/fungal biomass ratio .

[372] Closing of the Indonesian seaway as a precursor to east African aridification around 3-4 million years ago

Global climate change around 3-4 Myr ago is thought to have influenced the evolution of hominids , via the aridification of Africa , and may have been the precursor to Pleistocene glaciation about 2.75 Myr ago .
Most explanations of these climatic events involve changes in circulation of the North Atlantic Ocean due to the closing of the Isthmus of Panama .
Here we suggest , instead , that closure of the Indonesian seaway 3-4 Myr ago could be responsible for these climate changes , in particular the aridification of Africa .
We use simple theory and results from an ocean circulation model to show that the northward displacement of New Guinea , about 5 Myr ago , may have switched the source of flow through Indonesia -- from warm South Pacific to relatively cold North Pacific waters .
This would have decreased sea surface temperatures in the Indian Ocean , leading to reduced rainfall over eastern Africa .
We further suggest that the changes in the equatorial Pacific may have reduced atmospheric heat transport from the tropics to higher latitudes , stimulating global cooling and the eventual growth of ice sheets .

[373] Longitudinal study of murine microbiota activity and interactions with the host during acute inflammation and recovery

Although alterations in gut microbiota composition during acute colitis have been repeatedly observed , associated functional changes and the recovery from dysbiosis received little attention .
In this study , we investigated structure and function of the gut microbiota during acute inflammation and recovery in a dextran sodium sulfate ( DSS ) - colitis mouse model using metatranscriptomics , bacterial 16S rRNA gene amplicon sequencing and monitoring of selected host markers .
Parallel to an increase of host markers of inflammation during acute colitis , we observed relative abundance shifts and alterations in phylotype composition of the dominant bacterial orders Clostridiales and Bacteroidales , and an increase of the low abundant Enterobacteriales , Deferribacterales , Verrucomicrobiales and Erysipelotrichales .
During recovery , the microbiota began to resume , but did not reach its original composition until the end of the experiment .
Microbial gene expression was more resilient to disturbance , with pre-perturbation-type transcript profiles appearing quickly after acute colitis .
The decrease of Clostridiales during inflammation correlated with a reduction of transcripts related to butyrate formation , suggesting a disturbance in host-microbe signalling and mucosal nutrient provision .
The impact of acute inflammation on the Clostridiales was also characterized by a significant downregulation of their flagellin-encoding genes .
In contrast , the abundance of members of the Bacteroidales increased along with an increase in transcripts related to mucin degradation .
We propose that acute inflammation triggered a selective reaction of the immune system against flagella of commensals and temporarily altered murine microbiota composition and functions relevant for the host .
Despite changes in specific interactions , the host-microbiota homeostasis revealed a remarkable ability for recovery .

[374] Internal boundary layer model for the evolution of desert dune fields

Desert dunes often exhibit remarkable changes in their morphology over short distances .
For example , sediment-rich dunes can break up into smaller , isolated features , and then become stabilized by plants , over distances of kilometres .
These pattern transitions often coincide with spatial variations in sediment supply , transport rate , hydrology and vegetation , but these factors have not been linked mechanistically .
Here we hypothesize that the abrupt increase in roughness at the upwind margins of dune fields triggers the development of an internal boundary layer that thickens downwind and causes a spatial decrease in the surface wind stress .
We demonstrate that this mechanism forces a downwind decline in sand flux at White Sands , New Mexico , using a combination of physical theory , repeated airborne altimetry surveys and field observations .
The declining sand flux triggers an abrupt increase in vegetation density , which in turn leads to changes in groundwater depth and salinity -- showing that aerodynamics , sediment transport and ecohydrology are tightly interconnected in this landscape .
We conclude that , despite the documented complex climatic and geologic history of White Sands , internal boundary layer theory explains many of the observed first-order patterns of the dune field .

[375] Polyploidy can drive rapid adaptation in yeast

Polyploidy is observed across the tree of life , yet its influence on evolution remains incompletely understood .
Polyploidy , usually whole-genome duplication , is proposed to alter the rate of evolutionary adaptation .
This could occur through complex effects on the frequency or fitness of beneficial mutations .
For example , in diverse cell types and organisms , immediately after a whole-genome duplication , newly formed polyploids missegregate chromosomes and undergo genetic instability .
The instability following whole-genome duplications is thought to provide adaptive mutations in microorganisms and can promote tumorigenesis in mammalian cells .
Polyploidy may also affect adaptation independently of beneficial mutations through ploidy-specific changes in cell physiology .
Here we perform in vitro evolution experiments to test directly whether polyploidy can accelerate evolutionary adaptation .
Compared with haploids and diploids , tetraploids undergo significantly faster adaptation .
Mathematical modelling suggests that rapid adaptation of tetraploids is driven by higher rates of beneficial mutations with stronger fitness effects , which is supported by whole-genome sequencing and phenotypic analyses of evolved clones .
Chromosome aneuploidy , concerted chromosome loss , and point mutations all provide large fitness gains .
We identify several mutations whose beneficial effects are manifest specifically in the tetraploid strains .
Together , these results provide direct quantitative evidence that in some environments polyploidy can accelerate evolutionary adaptation .

[376] Increased fire activity at the Triassic/Jurassic boundary in Greenland due to climate-driven floral change

One of the largest mass extinctions of the past 600 million years ( Myr ) occurred 200 Myr ago , at the Triassic/Jurassic boundary .
The major floral and faunal turnovers have been linked to a marked increase in atmospheric carbon dioxide levels , probably resulting from massive volcanism in the Central Atlantic Magmatic Province .
Future climate change predictions suggest that fire activity may increase , in part because higher global temperatures are thought to increase storminess .
Here we use palaeontological reconstructions of the fossil flora from East Greenland to assess forest flammability along with records of fossil charcoal preserved in the rocks to show that fire activity increased markedly across the Triassic/Jurassic boundary .
We find a fivefold increase in the abundance of fossil charcoal in the earliest Jurassic , which we attribute to a climate-driven shift from a prevalence of broad-leaved taxa to a predominantly narrow-leaved assemblage .
Our fire calorimetry experiments show that narrow leaf morphologies are more flammable than broad-leaved morphologies .
We suggest that the warming associated with increased atmospheric carbon dioxide levels favoured a dominance of narrow-leaved plants , which , coupled with more frequent lightening strikes , led to an increase in fire activity at the Triassic/Jurassic boundary .

[377] Extinction debt of high-mountain plants under twenty-first-century climate change

Quantitative estimates of the range loss of mountain plants under climate change have so far mostly relied on static geographical projections of species ' habitat shifts .
Here , we use a hybrid model that combines such projections with simulations of demography and seed dispersal to forecast the climate-driven spatio-temporal dynamics of 150 high-mountain plant species across the European Alps .
This model predicts average range size reductions of 44-50 % by the end of the twenty-first century , which is similar to projections from the most ` optimistic ' static model ( 49 % ) .
However , the hybrid model also indicates that population dynamics will lag behind climatic trends and that an average of 40 % of the range still occupied at the end of the twenty-first century will have become climatically unsuitable for the respective species , creating an extinction debt .
Alarmingly , species endemic to the Alps seem to face the highest range losses .
These results caution against optimistic conclusions from moderate range size reductions observed during the twenty-first century as they are likely to belie more severe longer-term effects of climate warming on mountain plants .

[378] Pathogens and insect herbivores drive rainforest plant diversity and composition

Tropical forests are important reservoirs of biodiversity , but the processes that maintain this diversity remain poorly understood .
The Janzen-Connell hypothesis suggests that specialized natural enemies such as insect herbivores and fungal pathogens maintain high diversity by elevating mortality when plant species occur at high density ( negative density dependence ; NDD ) .
NDD has been detected widely in tropical forests , but the prediction that NDD caused by insects and pathogens has a community-wide role in maintaining tropical plant diversity remains untested .
We show experimentally that changes in plant diversity and species composition are caused by fungal pathogens and insect herbivores .
Effective plant species richness increased across the seed-to-seedling transition , corresponding to large changes in species composition .
Treating seeds and young seedlings with fungicides significantly reduced the diversity of the seedling assemblage , consistent with the Janzen-Connell hypothesis .
Although suppressing insect herbivores using insecticides did not alter species diversity , it greatly increased seedling recruitment and caused a marked shift in seedling species composition .
Overall , seedling recruitment was significantly reduced at high conspecific seed densities and this NDD was greatest for the species that were most abundant as seeds .
Suppressing fungi reduced the negative effects of density on recruitment , confirming that the diversity-enhancing effect of fungi is mediated by NDD .
Our study provides an overall test of the Janzen-Connell hypothesis and demonstrates the crucial role that insects and pathogens have both in structuring tropical plant communities and in maintaining their remarkable diversity .

[379] Interaction of Pseudostellaria heterophylla with Fusarium oxysporum f.sp .

heterophylla mediated by its root exudates in a consecutive monoculture system
In this study , quantitative real-time PCR ( qPCR ) was used to determine the amount of Fusarium oxysporum , an important replant disease pathogen in Pseudostellaria heterophylla rhizospheric soil .
Moreover , HPLC was used to identify phenolic acids in root exudates then it was further to explore the effects of the phenolic acid allelochemicals on the growth of F. oxysporum f.sp .
heterophylla .
The amount of F. oxysporum increased significantly in P. heterophylla rhizosphere soil under a consecutive replant system as monitored through qPCR analysis .
Furthermore , the growth of F. oxysporum f.sp .
heterophylla mycelium was enhanced by root exudates with a maximum increase of 23.8 % .
In addition , the number of spores increased to a maximum of 12.5-fold .
Some phenolic acids promoted the growth of F. oxysporum f.sp .
heterophylla mycelium and spore production .
Our study revealed that phenolic acids in the root secretion of P. heterophylla increased long with its development , which was closely related to changes in rhizospheric microorganisms .
The population of pathogenic microorganisms such as F. oxysporum in the rhizosphere soil of P. heterophylla also sharply increased .
Our results on plant-microbe communication will help to better clarify the cause of problems associated with P. heterophylla under consecutive monoculture treatment .

[380] Effects of household dynamics on resource consumption and biodiversity

Human population size and growth rate are often considered important drivers of biodiversity loss , whereas household dynamics are usually neglected .
Aggregate demographic statistics may mask substantial changes in the size and number of households , and their effects on biodiversity .
Household dynamics influence per capita consumption and thus biodiversity through , for example , consumption of wood for fuel , habitat alteration for home building and associated activities , and greenhouse gas emissions .
Here we report that growth in household numbers globally , and particularly in countries with biodiversity hotspots ( areas rich in endemic species and threatened by human activities ) , was more rapid than aggregate population growth between 1985 and 2000 .
Even when population size declined , the number of households increased substantially .
Had the average household size ( that is , the number of occupants ) remained static , there would have been 155 million fewer households in hotspot countries in 2000 .
Reduction in average household size alone will add a projected 233 million additional households to hotspot countries during the period 2000-15 .
Rapid increase in household numbers , often manifested as urban sprawl , and resultant higher per capita resource consumption in smaller households pose serious challenges to biodiversity conservation .

[381] A critical transition in leaf evolution facilitated the Cretaceous angiosperm revolution

The revolutionary rise of broad-leaved ( flowering ) angiosperm plant species during the Cretaceous initiated a global ecological transformation towards modern biodiversity .
Still , the mechanisms involved in this angiosperm radiation remain enigmatic .
Here we show that the period of rapid angiosperm evolution initiated after the leaf interior ( post venous ) transport path length for water was reduced beyond the leaf interior transport path length for CO2 at a critical leaf vein density of 2.5-5 mm mm-2 .
Data and our modelling approaches indicate that surpassing this critical vein density was a pivotal moment in leaf evolution that enabled evolving angiosperms to profit from developing leaves with more and smaller stomata in terms of higher carbon returns from equal water loss .
Surpassing the critical vein density may therefore have facilitated evolving angiosperms to develop leaves with higher gas exchange capacities required to adapt to the Cretaceous CO2 decline and outcompete previously dominant coniferous species in the upper canopy .

[382] The phylogenetic composition and structure of soil microbial communities shifts in response to elevated carbon dioxide

One of the major factors associated with global change is the ever-increasing concentration of atmospheric CO2 .
Although the stimulating effects of elevated CO2 ( eCO2 ) on plant growth and primary productivity have been established , its impacts on the diversity and function of soil microbial communities are poorly understood .
In this study , phylogenetic microarrays ( PhyloChip ) were used to comprehensively survey the richness , composition and structure of soil microbial communities in a grassland experiment subjected to two CO2 conditions ( ambient , 368 p.p.m. , versus elevated , 560 p.p.m. ) for 10 years .
The richness based on the detected number of operational taxonomic units ( OTUs ) significantly decreased under eCO2 .
PhyloChip detected 2269 OTUs derived from 45 phyla ( including two from Archaea ) , 55 classes , 99 orders , 164 families and 190 subfamilies .
Also , the signal intensity of five phyla ( Crenarchaeota , Chloroflexi , OP10 , OP9/JS1 , Verrucomicrobia ) significantly decreased at eCO2 , and such significant effects of eCO2 on microbial composition were also observed at the class or lower taxonomic levels for most abundant phyla , such as Proteobacteria , Firmicutes , Actinobacteria , Bacteroidetes and Acidobacteria , suggesting a shift in microbial community composition at eCO2 .
Additionally , statistical analyses showed that the overall taxonomic structure of soil microbial communities was altered at eCO2 .
Mantel tests indicated that such changes in species richness , composition and structure of soil microbial communities were closely correlated with soil and plant properties .
This study provides insights into our understanding of shifts in the richness , composition and structure of soil microbial communities under eCO2 and environmental factors shaping the microbial community structure .

[383] Role of HIF-1alpha in hypoxia-mediated apoptosis , cell proliferation and tumour angiogenesis

As a result of deprivation of oxygen ( hypoxia ) and nutrients , the growth and viability of cells is reduced .
Hypoxia-inducible factor ( HIF ) -1 alpha helps to restore oxygen homeostasis by inducing glycolysis , erythropoiesis and angiogenesis .
Here we show that hypoxia and hypoglycaemia reduce proliferation and increase apoptosis in wild-type ( HIF-1alpha + / + ) embryonic stem ( ES ) cells , but not in ES cells with inactivated HIF-1alpha genes ( HIF-1alpha - / - ) ; however , a deficiency of HIF-1alpha does not affect apoptosis induced by cytokines .
We find that hypoxia/hypoglycaemia-regulated genes involved in controlling the cell cycle are either HIF-1alpha-dependent ( those encoding the proteins p53 , p21 , Bcl-2 ) or HIF-1alpha-independent ( p27 , GADD153 ) , suggesting that there are at least two different adaptive responses to being deprived of oxygen and nutrients .
Loss of HIF-1alpha reduces hypoxia-induced expression of vascular endothelial growth factor , prevents formation of large vessels in ES-derived tumours , and impairs vascular function , resulting in hypoxic microenvironments within the tumour mass .
However , growth of HIF-1alpha tumours was not retarded but was accelerated , owing to decreased hypoxia-induced apoptosis and increased stress-induced proliferation .
As hypoxic stress contributes to many ( patho ) biological disorders , , this new role for HIF-1alpha in hypoxic control of cell growth and death may be of general pathophysiological importance .

[384] Economic development and coastal ecosystem change in China

Despite their value , coastal ecosystems are globally threatened by anthropogenic impacts , yet how these impacts are driven by economic development is not well understood .
We compiled a multifaceted dataset to quantify coastal trends and examine the role of economic growth in China 's coastal degradation since the 1950s .
Although China 's coastal population growth did not change following the 1978 economic reforms , its coastal economy increased by orders of magnitude .
All 15 coastal human impacts examined increased over time , especially after the reforms .
Econometric analysis revealed positive relationships between most impacts and GDP across temporal and spatial scales , often lacking dropping thresholds .
These relationships generally held when influences of population growth were addressed by analyzing per capita impacts , and when population density was included as explanatory variables .
Historical trends in physical and biotic indicators showed that China 's coastal ecosystems changed little or slowly between the 1950s and 1978 , but have degraded at accelerated rates since 1978 .
Thus economic growth has been the cause of accelerating human damage to China 's coastal ecosystems .
China 's GDP per capita remains very low .
Without strict conservation efforts , continuing economic growth will further degrade China 's coastal ecosystems .

[385] The answer lies in the soil

Understanding Soil Change : Soil Sustainability over Millennia , Centuries , and DecadesDaniel D. RichterCambridge University Press
This marvellous little book tells the story of southeastern US ecosystems from the perspective of soil changes over timescales of decades , centuries and millennia .
I was delighted with the author 's organizing of processes into timescales .
This is a natural way of thinking about soil and ecosystem processes , but is more often given lip-service than actually used as an organizing principle .
In this case , it works , both because the soil processes -- from weathering and geomorphic evolution , through leaching and decomposition -- fall into this framework , and because human impacts also change on these timescales .
The first part of the book provides a clear and conceptual overview of the elements of soil science , and their links to human management of soils .
The authors demonstrate clearly that sustaining soil `` health '' is essential to sustaining human societies , and that soil change is linked to historical change in human economy .
They then introduce the system that is the focus of their study , the Calhoun Experimental Forest , a property in South Carolina procured during the regional collapse of unsustainable agricultural practices of the southern United States in the first part of the twentieth century .
In the second section , which addresses millennial processes , they review pedogenesis ( soil formation ) globally and in the old soils of their target region .
Here we begin to see the fruit of the sustained research effort at the Calhoun site , as the processes leading to the acid soils of the region are carefully documented in terms of geomorphic , geochemical and biological dynamics .
Key findings include the role of biologically generated acidity in attacking the soil 's primary minerals .
The third section addresses the centennial timescale .
It includes a history of the agricultural development of the South , drawing attention to the little-known intensive maize cultivation system of the indigenous Americans before the arrival of Europeans .
The authors provide a detailed analysis of the sustainability of this system , and the human and landscape conditions that allowed its success .
They then provide a unique perspective on the ` Old South 's ' cotton economy in terms of agricultural management and the biogeochemistry of the cotton economy .
The discussion on the legacy of cotton growth in today 's soils makes fascinating reading , blending political and economic history with soil chemistry .
The authors conclude that the previous two centuries of agriculture have affected soils to great depth ( two metres ) and will continue to affect ecosystems well into the future .
The authors next describe a period over recent past decades during which agricultural land over huge areas in the southeastern United States has reverted from farmland to forest .
This is the timescale of the Calhoun experiment and describes in detail the recovery of carbon and nitrogen in soils of the regrowing forest .
The rapid and massive response of soil to the re-establishment of forests is astonishing .
The Calhoun soils re-establish soil acidity , carbon content and a functioning nitrogen cycle that can effectively retain inputs .
Likewise , phosphorus chemistry changes as a result of the increase in organic matter and the associated effects of acidity on the inorganic chemistry of this element .
The degree of knowledge of soil processes documented for this site is equalled for only a very small number of other locations .
The final section of the book outlines a research strategy based on a proposed network of long-term soil-research sites and careful experimental design .
This proposal , in which the authors argue for a research paradigm based on replicated manipulative experiments , is founded on experience both at the Calhoun site and in other long-term ecosystem studies .
While the utility , value and rigour of this approach need no comment , the authors themselves have shown the additional value of a perspective that takes into account the dynamics and legacies of millennial and centennial landscape processes .
Decades-long experiments , using conventional manipulation and replicated plots , can not address the role of slow pedogenic and landscape-scaled processes .
For this , the analytical paradigms of the geophysical sciences could be useful , as they can address entities ( such as ecosystems ) for which replication is a challenging problem , which are difficult to manipulate , and which respond on long timescales .
The dependence on fisherian statistics and classical experimental design in soil science is a legacy from agronomy , not altogether suited to large-scale , long-term processes .
This book fills an important niche in the biogeochemical literature , and not only as a regional case study .
Forest ecosystems play a large part in global processes , affecting the global water , carbon and nutrient cycles .
In global studies , processes must necessarily be captured in models , and in general , today 's global models greatly simplify soil carbon dynamics , sketch out or ignore nitrogen and totally neglect phosphorus , acidity and cations .
This study shows the importance of an integrated appraisal of soil dynamics in ecosystem function , and demonstrates the increasing maturity of soil science .
More from the soil Tales from the Underground : A Natural History of Subterranean Life by David W. Wolfe Perseus , $ 26 , pound18 .99

[386] Insolation-driven changes in atmospheric circulation over the past 116,000 years in subtropical Brazil

During the last glacial period , large millennial-scale temperature oscillations -- the ` Dansgaard/Oeschger ' cycles -- were the primary climate signal in Northern Hemisphere climate archives from the high latitudes to the tropics .
But whether the influence of these abrupt climate changes extended to the tropical and subtropical Southern Hemisphere , where changes in insolation are thought to be the main direct forcing of climate , has remained unclear .
Here we present a high-resolution oxygen isotope record of a U/Th-dated stalagmite from subtropical southern Brazil , covering the past 116,200 years .
The oxygen isotope signature varies with shifts in the source region and amount of rainfall in the area , and hence records changes in atmospheric circulation and convective intensity over South America .
We find that these variations in rainfall source and amount are primarily driven by summer solar radiation , which is controlled by the Earth 's precessional cycle .
The Dansgaard/Oeschger cycles can be detected in our record and therefore we confirm that they also affect the tropical hydrological cycle , but that in southern subtropical Brazil , millennial-scale climate changes are not as dominant as they are in the Northern Hemisphere .

[387] Postprandial remodeling of the gut microbiota in Burmese pythons

The vertebrate gut microbiota evolved in an environment typified by periodic fluctuations in nutrient availability , yet little is known about its responses to host feeding and fasting .
As many model species ( for example , mice ) are adapted to lifestyles of frequent small meals , we turned to the Burmese python , a sit-and-wait foraging snake that consumes large prey at long intervals ( > 1 month ) , to examine the effects of a dynamic nutrient milieu on the gut microbiota .
We used multiplexed 16S rRNA gene pyrosequencing to characterize bacterial communities harvested from the intestines of fasted and digesting snakes , and from their rodent meal .
In this unprecedented survey of a reptilian host , we found that Bacteroidetes and Firmicutes numerically dominated the python gut .
In the large intestine , fasting was associated with increased abundances of the genera Bacteroides , Rikenella , Synergistes and Akkermansia , and with reduced overall diversity .
A marked postprandial shift in bacterial community configuration occurred .
Between 12 h and 3 days after feeding , Firmicutes , including the taxa Clostridium , Lactobacillus and Peptostreptococcaceae , gradually outnumbered the fasting-dominant Bacteroidetes , and overall ` species ' - level diversity increased significantly .
Most lineages seemed to be indigenous to the python rather than ingested with the meal , but a dietary source of Lactobacillus could not be ruled out .
Thus , the observed large-scale alterations of the gut microbiota that accompany the Burmese python 's own dramatic physiological and morphological changes during feeding and fasting emphasize the need to consider both microbial and host cellular responses to nutrient flux .
The Burmese python may provide a unique model for dissecting these interrelationships .

[388] Variation in plastic responses of a globally distributed picoplankton species to ocean acidification

Phytoplankton are the basis of marine food webs , and affect biogeochemical cycles .
As CO2 levels increase , shifts in the frequencies and physiology of ecotypes within phytoplankton groups will affect their nutritional value and biogeochemical function .
However , studies so far are based on a few representative genotypes from key species .
Here , we measure changes in cellular function and growth rate at atmospheric CO2 concentrations predicted for the year 2100 in 16 ecotypes of the marine picoplankton Ostreococcus .
We find that variation in plastic responses among ecotypes is on par with published between-genera variation , so the responses of one or a few ecotypes can not estimate changes to the physiology or composition of a species under CO2 enrichment .
We show that ecotypes best at taking advantage of CO2 enrichment by changing their photosynthesis rates most should increase in relative fitness , and so in frequency in a high-CO2 environment .
Finally , information on sampling location , and not phylogenetic relatedness , is a good predictor of ecotypes likely to increase in frequency in this system .

[389] Chance and necessity in the evolution of minimal metabolic networks

It is possible to infer aspects of an organism 's lifestyle from its gene content .
Can the reverse also be done ?
Here we consider this issue by modelling evolution of the reduced genomes of endosymbiotic bacteria .
The diversity of gene content in these bacteria may reflect both variation in selective forces and contingency-dependent loss of alternative pathways .
Using an in silico representation of the metabolic network of Escherichia coli , we examine the role of contingency by repeatedly simulating the successive loss of genes while controlling for the environment .
The minimal networks that result are variable in both gene content and number .
Partially different metabolisms can thus evolve owing to contingency alone .
The simulation outcomes do preserve a core metabolism , however , which is over-represented in strict intracellular bacteria .
Moreover , differences between minimal networks based on lifestyle are predictable : by simulating their respective environmental conditions , we can model evolution of the gene content in Buchnera aphidicola and Wigglesworthia glossinidia with over 80 % accuracy .
We conclude that , at least for the particular cases considered here , gene content of an organism can be predicted with knowledge of its distant ancestors and its current lifestyle .

[390] Effects of constant immigration on the dynamics and persistence of stable and unstable Drosophila populations

Constant immigration can stabilize population size fluctuations but its effects on extinction remain unexplored .
We show that constant immigration significantly reduced extinction in fruitfly populations with relatively stable or unstable dynamics .
In unstable populations with oscillations of amplitude around 1.5 times the mean population size , persistence and constancy were unrelated .
Low immigration enhanced persistence without affecting constancy whereas high immigration increased constancy without enhancing persistence .
In relatively stable populations with erratic fluctuations of amplitude close to the mean population size , both low and high immigration enhanced persistence .
In these populations , the amplitude of fluctuations relative to mean population size went down due to immigration , and their dynamics were altered to low-period cycles .
The effects of immigration on the population size distribution and intrinsic dynamics of stable versus unstable populations differed considerably , suggesting that the mechanisms by which immigration reduced extinction risk depended on underlying dynamics in complex ways .

[391] Predicting climate-driven regime shifts versus rebound potential in coral reefs

Climate-induced coral bleaching is among the greatest current threats to coral reefs , causing widespread loss of live coral cover .
Conditions under which reefs bounce back from bleaching events or shift from coral to algal dominance are unknown , making it difficult to predict and plan for differing reef responses under climate change .
Here we document and predict long-term reef responses to a major climate-induced coral bleaching event that caused unprecedented region-wide mortality of Indo-Pacific corals .
Following loss of > 90 % live coral cover , 12 of 21 reefs recovered towards pre-disturbance live coral states , while nine reefs underwent regime shifts to fleshy macroalgae .
Functional diversity of associated reef fish communities shifted substantially following bleaching , returning towards pre-disturbance structure on recovering reefs , while becoming progressively altered on regime shifting reefs .
We identified threshold values for a range of factors that accurately predicted ecosystem response to the bleaching event .
Recovery was favoured when reefs were structurally complex and in deeper water , when density of juvenile corals and herbivorous fishes was relatively high and when nutrient loads were low .
Whether reefs were inside no-take marine reserves had no bearing on ecosystem trajectory .
Although conditions governing regime shift or recovery dynamics were diverse , pre-disturbance quantification of simple factors such as structural complexity and water depth accurately predicted ecosystem trajectories .
These findings foreshadow the likely divergent but predictable outcomes for reef ecosystems in response to climate change , thus guiding improved management and adaptation .

[392] Food-web interactions govern the resistance of communities after non-random extinctions

Growing concern about how loss of biodiversity will affect ecosystems has stimulated numerous studies .
Although most studies have assumed that species go extinct randomly , species often go extinct in order of their sensitivity to a stress that intensifies through time ( such as climate change ) .
Here we show that the consequences of random and ordered extinctions differ .
Both depend on food-web interactions that create compensation ; that is , the increase of some species when their competitors and/or predators decrease in density due to environmental stress .
Compensation makes communities as a whole more resistant to stress by reducing changes in combined species densities .
As extinctions progress , the potential for compensation is depleted , and communities become progressively less resistant .
For ordered extinctions , however , this depletion is offset and communities retain their resistance , because the surviving species have greater average resistance to the stress .
Despite extinctions being ordered , changes in the food web with successive extinctions make it difficult to predict which species will show compensation in the future .
This unpredictability argues for ` whole-ecosystem ' approaches to biodiversity conservation , as seemingly insignificant species may become important after other species go extinct .

[393] Moisture transport across Central America as a positive feedback on abrupt climatic changes

Moisture transport from the Atlantic to the Pacific ocean across Central America leads to relatively high salinities in the North Atlantic Ocean and contributes to the formation of North Atlantic Deep Water .
This deep water formation varied strongly between Dansgaard/Oeschger interstadials and Heinrich events -- millennial-scale abrupt warm and cold events , respectively , during the last glacial period .
Increases in the moisture transport across Central America have been proposed to coincide with northerly shifts of the Intertropical Convergence Zone and with Dansgaard/Oeschger interstadials , with opposite changes for Heinrich events .
Here we reconstruct sea surface salinities in the eastern equatorial Pacific Ocean over the past 90,000 years by comparing palaeotemperature estimates from alkenones and Mg/Ca ratios with foraminiferal oxygen isotope ratios that vary with both temperature and salinity .
We detect millennial-scale fluctuations of sea surface salinities in the eastern equatorial Pacific Ocean of up to two to four practical salinity units .
High salinities are associated with the southward migration of the tropical Atlantic Intertropical Convergence Zone , coinciding with Heinrich events and with Greenland stadials .
The amplitudes of these salinity variations are significantly larger on the Pacific side of the Panama isthmus , as inferred from a comparison of our data with a palaeoclimate record from the Caribbean basin .
We conclude that millennial-scale fluctuations of moisture transport constitute an important feedback mechanism for abrupt climate changes , modulating the North Atlantic freshwater budget and hence North Atlantic Deep Water formation .

[394] Photochemical production of molecular bromine in Arctic surface snowpacks

Following the springtime polar sunrise , ozone concentrations in the lower troposphere episodically decline to near-zero levels .
These ozone depletion events are initiated by an increase in reactive bromine levels in the atmosphere .
Under these conditions , the oxidative capacity of the Arctic troposphere is altered , leading to the removal of numerous transported trace gas pollutants , including mercury .
However , the sources and mechanisms leading to increased atmospheric reactive bromine levels have remained uncertain , limiting simulations of Arctic atmospheric chemistry with the rapidly transforming sea-ice landscape .
Here , we examine the potential for molecular bromine production in various samples of saline snow and sea ice , in the presence and absence of sunlight and ozone , in an outdoor snow chamber in Alaska .
Molecular bromine was detected only on exposure of surface snow ( collected above tundra and first-year sea ice ) to sunlight .
This suggests that the oxidation of bromide is facilitated by a photochemical mechanism , which was most efficient for more acidic samples characterized by enhanced bromide to chloride ratios .
Molecular bromine concentrations increased significantly when the snow was exposed to ozone , consistent with an interstitial air amplification mechanism .
Aircraft-based observations confirm that bromine oxide levels were enhanced near the snow surface .
We suggest that the photochemical production of molecular bromine in surface snow serves as a major source of reactive bromine , which leads to the episodic depletion of tropospheric ozone in the Arctic springtime .

[395] Evolutionary triage governs fitness in driver and passenger mutations and suggests targeting never mutations

Genetic and epigenetic changes in cancer cells are typically divided into ` drivers ' and ` passengers ' .
Drug development strategies target driver mutations , but inter - and intratumoral heterogeneity usually results in emergence of resistance .
Here we model intratumoral evolution in the context of a fecundity/survivorship trade-off .
Simulations demonstrate that the fitness value of any genetic change is not fixed but dependent on evolutionary triage governed by initial cell properties , current selection forces and prior genotypic/phenotypic trajectories .
We demonstrate that spatial variations in molecular properties of tumour cells are the result of changes in environmental selection forces such as blood flow .
Simulated therapies targeting fitness-increasing ( driver ) mutations usually decrease the tumour burden but almost inevitably fail due to population heterogeneity .
An alternative strategy targets gene mutations that are never observed .
Because up or downregulation of these genes unconditionally reduces cellular fitness , they are eliminated by evolutionary triage but can be exploited for targeted therapy .

[396] Observed increase in local cooling effect of deforestation at higher latitudes

Deforestation in mid - to high latitudes is hypothesized to have the potential to cool the Earth 's surface by altering biophysical processes .
In climate models of continental-scale land clearing , the cooling is triggered by increases in surface albedo and is reinforced by a land albedo-sea ice feedback .
This feedback is crucial in the model predictions ; without it other biophysical processes may overwhelm the albedo effect to generate warming instead .
Ongoing land-use activities , such as land management for climate mitigation , are occurring at local scales ( hectares ) presumably too small to generate the feedback , and it is not known whether the intrinsic biophysical mechanism on its own can change the surface temperature in a consistent manner .
Nor has the effect of deforestation on climate been demonstrated over large areas from direct observations .
Here we show that surface air temperature is lower in open land than in nearby forested land .
The effect is 0.85 + / - 0.44 K ( mean + / - one standard deviation ) northwards of 45degrees N and 0.21 + / - 0.53 K southwards .
Below 35degrees N there is weak evidence that deforestation leads to warming .
Results are based on comparisons of temperature at forested eddy covariance towers in the USA and Canada and , as a proxy for small areas of cleared land , nearby surface weather stations .
Night-time temperature changes unrelated to changes in surface albedo are an important contributor to the overall cooling effect .
The observed latitudinal dependence is consistent with theoretical expectation of changes in energy loss from convection and radiation across latitudes in both the daytime and night-time phase of the diurnal cycle , the latter of which remains uncertain in climate models .

[397] Delays in reducing waterborne and water-related infectious diseases in China under climate change

Despite China 's rapid progress in improving water , sanitation and hygiene ( WSH ) access , in 2011 , 471 million people lacked access to improved sanitation and 401 million to household piped water .
As certain infectious diseases are sensitive to changes in both climate and WSH conditions , we projected impacts of climate change on WSH-attributable diseases in China in 2020 and 2030 by coupling estimates of the temperature sensitivity of diarrhoeal diseases and three vector-borne diseases , temperature projections from global climate models , WSH-infrastructure development scenarios , and projected demographic changes .
By 2030 , climate change is projected to delay China 's rapid progress towards reducing WSH-attributable infectious disease burden by 8-85 months .
This development delay summarizes the adverse impact of climate change on WSH-attributable infectious diseases in China , and can be used in other settings where a significant health burden may accompany future changes in climate even as the total burden of disease falls owing to non-climate reasons .

[398] Research highlights

Molecular neurobiology : Active resilience Cell 131 , 391 - 404 ( 2007 ) , doi : 10.1016 / j.cell .2007.09.018 A molecule known as BDNF may provide a pivotal distinction between people who succumb to conditions such as depression or post-traumatic stress disorder and the majority who do not .
Eric Nestler of the University of Texas Southwestern Medical Center in Dallas and his colleagues had previously identified mice that avoided social contact with cage-mates after repeated ` social defeat ' -- brought about by forced encounters with more aggressive mice .
The researchers found that resilience to stress in this social-defeat model is an active process in which stress-induced firing in part of the brain 's neuronal circuitry associated with reward and drug addiction is suppressed .
This lowers levels of brain-derived neurotrophic factor ( BDNF ) , and mice with a natural variation in their BDNF gene were resilient to stress .
The researchers also found high levels of BDNF in a region associated with reward in post-mortem brains of people with a history of depression .
Ecology : Smelly fish Proc .
R. Soc .
B doi : 10.1098 / rspb .2007.1283 ( 2007 ) Fish that have been exposed to even very low levels of a common pollutant are shunned by their conspecifics , according to research by Ashley Ward at the University of Sydney and his co-workers .
The effect may put the tainted fish at increased risk of predation .
The research looks at the effect of low levels of 4-nonylphenol , a surfactant sometimes found in shampoos and soaps , on schooling in juvenile banded killifish ( Fundulus diaphanous , pictured ) .
Unexposed fish were unwilling to school with fish that had been exposed for as little as an hour to levels commonly found in sewage outflows .
microbiology : A time to die Science 318 , 652-655 ( 2007 ) , doi :10.1126 / science .1147248 Proc .
Natl Acad .
Sci .
USA doi : 10.1073 / pnas .0704256104 ( 2007 ) Bacteria communicate with each other to a greater extent , and in more ways , than was once thought .
Hanna Engelberg-Kulka of the Hebrew University in Jerusalem and her colleagues report that Escherichia coli can send out messages that encourage their neighbours to kill themselves .
The ` extracellular death factor ' involved turns out to be a chain of five amino acids that seems to be produced by the degradation of a metabolic enzyme , glucose-6-phosphate dehydrogenase .
The authors suggest that the ability to coordinate cell death may allow bacteria to release nutrients from a proportion of individuals when the population is under stress , or to defeat phage attacks by means similar to a ` scorched-earth ' policy .
Meanwhile , Frances Arnold at the California Institue of Technology in Pasadena , Ron Weiss at Princeton University , New Jersey , and their colleagues report engineering a system into populations of E. coli that allows a specific pattern of gene expression only when both populations are present in sufficient numbers .
They suggest that such systems could be used to engineer specific responses in artificial biofilms .
Intriguingly , three years ago these labs engineered a ` neighbour killing ' system into bacteria quite similar to that now being reported ( L .
You et al .
Nature 428 , 868 - 871 ; 2004 ) .
This may be the first example of synthetic biology anticipating a function only later revealed in nature .
Relativistic physics : Hot at any speed Phys .
Rev. Lett .
99 , 170601 ( 2007 ) According to the theory of special relativity , measurements of length and time differ depending on the relative velocity of the observer and the thing being measured .
Einstein and other prominent physicists believed that the measured temperature of a gas would also depend on the speed of the observer .
Work by Peter Hanggi of the University of Augsburg in Germany and his collaborators contradicts those early calculations .
The group 's one-dimensional models of particles in a gas show that the same temperature will be observed regardless of the observer 's speed .
The team admits , however , that this may not be true of two - or three-dimensional gases , and believes that further study is needed .
Climate change : Irreducible sensitivity Science 318 , 629 - 632 ; ( 2007 ) , doi : 10.1126 / science .1144735 ; Science 318 , 582-583 ; ( 2007 ) , doi :10.1126 / science .1149988 ; Decades of intensive work on climate change have done little to narrow the range of uncertainty over Earth 's climate sensitivity -- the amount of global warming to be expected under carbon dioxide levels twice those of the pre-industrial world , which the Intergovernmental Panel on Climate Change puts at between 2 degreesC and 4.5 degreesC .
Nor can a substantially better estimate be expected in the future , according to Gerard Roe and Marcia Baker of the University of Washington in Seattle .
Their mathematical analysis stresses that normally distributed uncertainties in the feedbacks associated with climate processes make ruling out a long tail of high sensitivities unrealistic .
In an accompanying Perspective , Myles Allen and David Frame at the University of Oxford , UK , argue that this is not a problem for setting policy , because the concentrations of carbon dioxide associated with specific warmings can be much better constrained .
Chemistry : Clicking without copper Proc .
Natl Acad .
Sci .
USA 104 , 16793-16797 ( 2007 ) Proteins can be quite easily labelled for studies in living cells , but other types of molecule are trickier to track .
One possibility is to use a two-step technique : first get the cell 's own machinery to add a chemical ` socket ' to the molecule of interest , then add a trackable reagent that fits easily into that socket .
` Click ' chemistry -- so named for the ease of assembly -- might be helpful for this second step , but normally depends on toxic copper compounds .
Now Carolyn Bertozzi and her colleagues at the University of California , Berkeley , report using a cyclooctyne onto which fluorine atoms have been added to carry out the same sort of click reaction without the need of copper .
Their system can be used to track sugar molecules in and on living cells for minutes or for days .
Planetary science : Identical twins Astrophys J. 669 , L89-L92 ( 2007 ) Astronomers have identified a star that is in many ways indistinguishable from the Sun .
Peruvian astronomers Jorge Melendez of the Australian National University , and Ivan Ramirez at the McDonald Observatory of the University of Texas in Austin report that the parameters of HIP 56948 , one of four ` solar twins ' they have been studying , are exactly the same as the Sun 's , within the constraints of observational accuracy .
Unlike previous solar twins , this star -- which resides 200 light years away in the constellation of Draco -- shares the Sun 's low lithium content .
In addition , HIP 56948 , like the Sun , has no accompanying ` hot Jupiter ' in close orbit .
Such solar twins are useful for various calibrations , the authors say ; they are also of potential interest to researchers involved in the search for extraterrestrial intelligence .
Chemical physics : Nano steams ahead Phys .
Rev. Lett .
doi : 10.1103 / PhysRevLett .99.178103 ( 2007 ) Nanoparticles may exhibit chemotaxis -- directed motion along a gradient of chemical concentration previously seen at the microscale only for living cells .
Ayusman Sen , Darrell Velegol and their colleagues at Pennsylvania State University have shown previously that nanorods made with platinum at one end and gold at the other move through a solution of hydrogen peroxide , owing to the catalytic production of oxygen gas .
Now they report that in a peroxide gradient the rods -- 370 nm wide and 2 microm long -- move ` uphill ' towards the fuel source , because the increase in speed at higher peroxide concentrations biases their movement .
This offers a simple way to power and guide nanoscale objects .
Acoustics : Extraordinary sound Nature Phys .
doi : 10.1038 / nphys774 ( 2007 ) Light squeezed through a hole of smaller diameter than its wavelength can emerge in a collimated beam when the hole is set in a periodic array of indentations .
This counter-intuitive phenomenon is known as `` extraordinary optical transmission '' .
Now researchers in Spain have shown that an analogous effect can be achieved with sound waves .
Using their understanding of the role of surface plasmons in the optical case , Francisco Garcia-Vidal at the Autonomous University of Madrid and his colleagues designed systems of holes and grooves in which acoustic surface waves have a similar effect , producing a beam of sound through cunningly contrived interference and reinforcement .
The authors think this effect might be applied in non-destructive materials testing and medical ultrasound .

[399] An abrupt drop in Northern Hemisphere sea surface temperature around 1970

The twentieth-century trend in global-mean surface temperature was not monotonic : temperatures rose from the start of the century to the 1940s , fell slightly during the middle part of the century , and rose rapidly from the mid-1970s onwards .
The warming-cooling-warming pattern of twentieth-century temperatures is typically interpreted as the superposition of long-term warming due to increasing greenhouse gases and either cooling due to a mid-twentieth century increase of sulphate aerosols in the troposphere , or changes in the climate of the world 's oceans that evolve over decades ( oscillatory multidecadal variability ) .
Loadings of sulphate aerosol in the troposphere are thought to have had a particularly important role in the differences in temperature trends between the Northern and Southern hemispheres during the decades following the Second World War .
Here we show that the hemispheric differences in temperature trends in the middle of the twentieth century stem largely from a rapid drop in Northern Hemisphere sea surface temperatures of about 0.3 degreesC between about 1968 and 1972 .
The timescale of the drop is shorter than that associated with either tropospheric aerosol loadings or previous characterizations of oscillatory multidecadal variability .
The drop is evident in all available historical sea surface temperature data sets , is not traceable to changes in the attendant metadata , and is not linked to any known biases in surface temperature measurements .
The drop is not concentrated in any discrete region of the Northern Hemisphere oceans , but its amplitude is largest over the northern North Atlantic .

[400] Central Pacific El Nino and decadal climate change in the North Pacific Ocean

Decadal fluctuations of the ocean and atmosphere over the North Pacific Ocean significantly affect the weather and climate of North America and Eurasia .
They also cause transitions between different states of marine ecosystems across the Pacific Ocean .
An important fraction of North Pacific low-frequency variability is linked to the North Pacific Gyre Oscillation , a climate pattern associated with decadal fluctuations of the ocean circulation .
Decadal variations in the North Pacific Gyre Oscillation are characterized by a pattern of sea surface temperature anomalies that resemble the central Pacific El Nino , a dominant mode of interannual variability with far-reaching effects on global climate patterns .
Here we use an ensemble of simulations with a coupled ocean-atmosphere model to show that the sea surface temperature anomalies associated with central Pacific El Nino force changes in the extra-tropical atmospheric circulation .
These changes in turn drive the decadal fluctuations of the North Pacific Gyre Oscillation .
Given that central Pacific El Nino events could become more frequent with increasing levels of greenhouse gases in the atmosphere , we infer that the North Pacific Gyre Oscillation may play an increasingly important role in shaping Pacific climate and marine ecosystems in the twenty-first century .

[401] Our choice from the recent literature

Water for faults J. Geophys .
Res .
doi :10.1029 / 2010JB007739 ( 2011 ) Some small earthquakes in subduction zones are generated by the dehydration of minerals under high temperature and pressure .
Experimental analyses indicate that seismic activity observed at intermediate depths in the subducting slab could result from the rapid release of fluids from deep minerals .
Isabelle Daniel at the Universite de Lyon , France , and colleagues carried out dehydration experiments on samples of antigorite -- a mineral found in the subducting oceanic mantle .
The release of fluids from antigorite grains was not only much faster than the rate of collapse of the mineral itself , but also faster than the collapse of any other mineral in the subducting slab and surrounding mantle .
Dehydration earthquakes are triggered only when the fluids escape the mineral through an open pore before the mineral collapses under pressure .
The authors conclude that the rapid dehydration of antigorite probably triggers seismicity in subducting plates .
Iceberg influence Deep-Sea Res .
II doi : 10.1016 / j.dsr2 .2010.11.010 ( 2011 ) Ocean surveys suggest that meltwater from free-floating icebergs can affect the chemistry and biology of the surrounding sea water as they pass through the ocean .
John Helly of the University of California , San Diego , and colleagues carried out surveys in the Southern Ocean in March and April 2009 to examine the impacts of a single , free-floating iceberg on the surrounding sea water .
The iceberg broke off from the Ross Ice Shelf in 2002 .
They detected a plume of water with lower temperature and salinity than the surrounding sea water , which stretched up to 19 km away and was mixed to depths of 1,500 m .
The plume persisted for up to ten days following the passage of the iceberg .
In total , the researchers estimate that this single iceberg altered the chemical properties of 3,000 km 3 of water during its 23-day transit .
The researchers also observed variations in the partial pressure of carbon dioxide and seawater chlorophyll , suggesting the meltwater influenced the distribution of phytoplankton .
Moisture decline Earth Planet .
Sci .
Lett .
doi : 10.1016 / j.epsl .2010.12.048 ( 2011 ) Analyses of cave deposits indicate that changes in the North Atlantic meridional overturning circulation during the last glacial period affected the strength of the Australian-Indonesian summer monsoon .
Sophie Lewis of the Australian National University and colleagues reconstructed precipitation patterns over Flores , Indonesia , from 31,500 to 25,600 years ago from a fast-growing stalagmite in the Liang Luar cave .
The evolution of oxygen isotope compositions of the stalagmite calcite suggests that precipitation decreased from 30,800 to 30,200 years ago .
This was followed by a hiatus in deposition , indicative of even dryer conditions .
The team attributes this to a southward shift in the rain belt associated with the intertropical convergence zone during this time .
The period of drying corresponds to a shutdown of meridional overturning in the North Atlantic Ocean and widespread cooling in the Northern Hemisphere .
Model simulations have indicated that such cooling could have driven the southward migration of the intertropical convergence zone , which would have reduced precipitation in the regions affected by both the Australian-Indonesian and Asian summer monsoons .
Stirred mantle Geophys .
Res .
Lett .
doi :10.1029 / 2010GL046056 ( 2011 ) The thick and stable continental crust acts as a thermal lid that insulates the hot mantle and reduces the escape of heat from the Earth 's interior .
Numerical simulations show that continental cover should also facilitate efficient mixing of the mantle .
Henri Samuel of Universitat Bayreuth , Germany , and colleagues assessed the influence of continents of varying size on mantle convection using numerical models .
Beneath the continents , mantle temperatures were significantly warmer than those below the oceanic crust .
As a result , the viscosity of the mantle is lower where covered by continents and causes it to convect more vigorously .
When continents are similar in lateral extent to those on Earth today , they cause a three - to sixfold increase in mixing efficiency of the mantle , compared with an Earth with no continents .
How the large-scale heterogeneities that exist at depth in the Earth 's mantle have survived for so long in such a well-stirred mantle remains unclear .
Black-carbon warming Atmos .
Chem .
Phys .
11 , 799-816 ( 2011 ) Aerosols that contain black carbon both reflect and absorb radiation , hindering estimates of their overall impact on climate .
Model simulations and observational data suggest that black-carbon aerosols caused a significant but minimal warming of global near-surface temperatures in the twentieth century .
Gareth Jones , of the Met Office Hadley Centre , UK , and colleagues assessed the climatic impact of black-carbon aerosols over the past century using temperature records and numerical simulations .
According to their model simulations , black-carbon aerosols from fossil fuel and biofuel sources warmed the Earth 's surface by 0.14 K , compared with a greenhouse-gas-induced warming of 1.06 K .
Their analysis of observational data confirmed that black-carbon aerosols had a detectable but small influence on temperatures in the latter half of the twentieth century .
However , the researchers note that changes in the reflectivity of snow caused by the deposition of black carbon on its surface -- which were not considered in their analysis -- could exacerbate the warming effect , at least on a local level .

[402] The significance of nitrogen cost minimization in proteomes of marine microorganisms

Marine microorganisms thrive under low levels of nitrogen ( N ) .
N cost minimization is a major selective pressure imprinted on open-ocean microorganism genomes .
Here we show that amino-acid sequences from the open ocean are reduced in N , but increased in average mass compared with coastal-ocean microorganisms .
Nutrient limitation exerts significant pressure on organisms supporting the trade-off between N cost minimization and increased average mass of amino acids that is a function of increased A+T codon usage .
N cost minimization , especially of highly expressed proteins , reduces the total cellular N budget by 2.7-10 % ; this minimization in combination with reduction in genome size and cell size is an evolutionary adaptation to nutrient limitation .
The biogeochemical and evolutionary precedent for these findings suggests that N limitation is a stronger selective force in the ocean than biosynthetic costs and is an important evolutionary strategy in resource-limited ecosystems .

[403] Simulation of recent northern winter climate trends by greenhouse-gas forcing

The temperature of air at the Earth 's surface has risen during the past century , but the fraction of the warming that can be attributed to anthropogenic greenhouse gases remains controversial .
The strongest warming trends have been over Northern Hemisphere land masses during winter , and are closely related to changes in atmospheric circulation .
These circulation changes are manifested by a gradual reduction in high-latitude sea-level pressure , and an increase in mid-latitude sea-level pressure associated with one phase of the Arctic Oscillation ( a hemisphere-scale version of the North Atlantic Oscillation ) .
Here we use several different climate-model versions to demonstrate that the observed sea-level-pressure trends , including their magnitude , can be simulated by realistic increases in greenhouse-gas concentrations .
Thus , although the warming appears through a naturally occurring mode of atmospheric variability , it may be anthropogenically induced and may continue to rise .
The Arctic Oscillation trend is captured only in climate models that include a realistic representation of the stratosphere , while changes in ozone concentrations are not necessary to simulate the observed climate trends .
The proper representation of stratospheric dynamics appears to be important to the attribution of climate change , at least on a broad regional scale .

[404] Elevated seawater temperature causes a microbial shift on crustose coralline algae with implications for the recruitment of coral larvae

Crustose coralline algae ( CCA ) are key reef-building primary producers that are known to induce the metamorphosis and recruitment of many species of coral larvae .
Reef biofilms ( particularly microorganisms associated with CCA ) are also important as settlement cues for a variety of marine invertebrates , including corals .
If rising sea surface temperatures ( SSTs ) affect CCA and/or their associated biofilms , this may in turn affect recruitment on coral reefs .
Herein , we report that the CCA Neogoniolithon fosliei , and its associated microbial communities do not tolerate SSTs of 32 degreesC , only 2-4 degreesC above the mean maximum annual SST .
After 7 days at 32 degreesC , the CCA exhibited clear signs of stress , including bleaching , a reduction in maximum quantum yield ( Fv/Fm ) and a large shift in microbial community structure .
This shift at 32 degreesC involved an increase in Bacteroidetes and a reduction in Alphaproteobacteria , including the loss of the primary strain ( with high-sequence similarity to a described coral symbiont ) .
A recovery in Fv/Fm was observed in CCA exposed to 31 degreesC following 7 days of recovery ( at 27 degreesC ) ; however , CCA exposed to 32 degreesC did not recover during this time as evidenced by the rapid growth of endolithic green algae .
A 50 % reduction in the ability of N. fosliei to induce coral larval metamorphosis at 32 degreesC accompanied the changes in microbiology , pigmentation and photophysiology of the CCA .
This is the first experimental evidence to demonstrate how thermal stress influences microbial associations on CCA with subsequent downstream impacts on coral recruitment , which is critical for reef regeneration and recovery from climate-related mortality events .

[405] Plant litter decomposition in a semi-arid ecosystem controlled by photodegradation

The carbon balance in terrestrial ecosystems is determined by the difference between inputs from primary production and the return of carbon to the atmosphere through decomposition of organic matter .
Our understanding of the factors that control carbon turnover in water-limited ecosystems is limited , however , as studies of litter decomposition have shown contradictory results and only a modest correlation with precipitation .
Here we evaluate the influence of solar radiation , soil biotic activity and soil resource availability on litter decomposition in the semi-arid Patagonian steppe using the results of manipulative experiments carried out under ambient conditions of rainfall and temperature .
We show that intercepted solar radiation was the only factor that had a significant effect on the decomposition of organic matter , with attenuation of ultraviolet-B and total radiation causing a 33 and 60 per cent reduction in decomposition , respectively .
We conclude that photodegradation is a dominant control on above-ground litter decomposition in this semi-arid ecosystem .
Losses through photochemical mineralization may represent a short-circuit in the carbon cycle , with a substantial fraction of carbon fixed in plant biomass being lost directly to the atmosphere without cycling through soil organic matter pools .
Furthermore , future changes in radiation interception due to decreased cloudiness , increased stratospheric ozone depletion , or reduced vegetative cover may have a more significant effect on the carbon balance in these water-limited ecosystems than changes in temperature or precipitation .

[406] Benthic coral reef calcium carbonate dissolution in an acidifying ocean

Changes in CaCO3 dissolution due to ocean acidification are potentially more important than changes in calcification to the future accretion and survival of coral reef ecosystems .
As most CaCO3 in coral reefs is stored in old permeable sediments , increasing sediment dissolution due to ocean acidification will result in reef loss even if calcification remains unchanged .
Previous studies indicate that CaCO3 dissolution could be more sensitive to ocean acidification than calcification by reef organisms .
Observed changes in net ecosystem calcification owing to ocean acidification could therefore be due mainly to increased dissolution rather than decreased calcification .
In addition , biologically mediated calcification could potentially adapt , at least partially , to future ocean acidification , while dissolution , which is mostly a geochemical response to changes in seawater chemistry , will not adapt .
Here , we review the current knowledge of shallow-water CaCO3 dissolution and demonstrate that dissolution in the context of ocean acidification has been largely overlooked compared with calcification .

[407] Coherent ecological dynamics induced by large-scale disturbance

Aggregate community-level response to disturbance is a principle concern in ecology because post-disturbance dynamics are integral to the ability of ecosystems to maintain function in an uncertain world .
Community-level responses to disturbance can be arrayed along a spectrum ranging from synchronous oscillations where all species rise and fall together , to compensatory dynamics where total biomass remains relatively constant despite fluctuations in the densities of individual species .
An important recent insight is that patterns of synchrony and compensation can vary with the timescale of analysis and that spectral time series methods can enable detection of coherent dynamics that would otherwise be obscured by opposing patterns occurring at different scales .
Here I show that application of wavelet analysis to experimentally manipulated plankton communities reveals strong synchrony after disturbance .
The result is paradoxical because it is well established that these communities contain both disturbance-sensitive and disturbance-tolerant species leading to compensation within functional groups .
Theory predicts that compensatory substitution of functionally equivalent species should stabilize ecological communities , yet I found at the whole-community level a large increase in seasonal biomass variation .
Resolution of the paradox hinges on patterns of seasonality among species .
The compensatory shift in community composition after disturbance resulted in a loss of cold-season dominants , which before disturbance had served to stabilize biomass throughout the year .
Species dominating the disturbed community peaked coherently during the warm season , explaining the observed synchrony and increase in seasonal biomass variation .
These results suggest that theory relating compensatory dynamics to ecological stability needs to consider not only complementarity in species responses to environmental change , but also seasonal complementarity among disturbance-tolerant and disturbance-sensitive species .

[408] Coral and macroalgal exudates vary in neutral sugar composition and differentially enrich reef bacterioplankton lineages

Increasing algal cover on tropical reefs worldwide may be maintained through feedbacks whereby algae outcompete coral by altering microbial activity .
We hypothesized that algae and coral release compositionally distinct exudates that differentially alter bacterioplankton growth and community structure .
We collected exudates from the dominant hermatypic coral holobiont Porites spp .
and three dominant macroalgae ( one each Ochrophyta , Rhodophyta and Chlorophyta ) from reefs of Mo'orea , French Polynesia .
We characterized exudates by measuring dissolved organic carbon ( DOC ) and fractional dissolved combined neutral sugars ( DCNSs ) and subsequently tracked bacterioplankton responses to each exudate over 48 h , assessing cellular growth , DOC/DCNS utilization and changes in taxonomic composition ( via 16S rRNA amplicon pyrosequencing ) .
Fleshy macroalgal exudates were enriched in the DCNS components fucose ( Ochrophyta ) and galactose ( Rhodophyta ) ; coral and calcareous algal exudates were enriched in total DCNS but in the same component proportions as ambient seawater .
Rates of bacterioplankton growth and DOC utilization were significantly higher in algal exudate treatments than in coral exudate and control incubations with each community selectively removing different DCNS components .
Coral exudates engendered the smallest shift in overall bacterioplankton community structure , maintained high diversity and enriched taxa from Alphaproteobacteria lineages containing cultured representatives with relatively few virulence factors ( VFs ) ( Hyphomonadaceae and Erythrobacteraceae ) .
In contrast , macroalgal exudates selected for less diverse communities heavily enriched in copiotrophic Gammaproteobacteria lineages containing cultured pathogens with increased VFs ( Vibrionaceae and Pseudoalteromonadaceae ) .
Our results demonstrate that algal exudates are enriched in DCNS components , foster rapid growth of bacterioplankton and select for bacterial populations with more potential VFs than coral exudates .

[409] Food-chain length alters community responses to global change in aquatic systems

Synergies between large-scale environmental changes , such as climate change and increased humic content ( brownification ) , will have a considerable impact on future aquatic ecosystems .
On the basis of modelling , monitoring and experimental data , we demonstrate that community responses to global change are determined by food-chain length and that the top trophic level , and every second level below , will benefit from climate change , whereas the levels in between will suffer .
Hence , phytoplankton , and thereby algal blooms , will benefit from climate change in three - , but not in two-trophic-level systems .
Moreover , we show that both phytoplankton ( resource ) and zooplankton ( consumer ) advance their spring peak abundances similarly in response to a 3 degreesC temperature increase ; that is , there is no support for a consumer/resource mismatch in a future climate scenario .
However , in contrast to other taxa , cyanobacteria -- known as toxin-producing nuisance phytoplankton -- benefit from a higher temperature and humic content irrespective of the food-chain composition .
Our results are mirrored in natural ecosystems .
By mechanistically merging present food-chain theory with large-scale environmental and climate changes , we provide a powerful framework for predicting and understanding future aquatic ecosystems and their provision of ecosystem services and water resources .

[410] Molybdenum limitation of asymbiotic nitrogen fixation in tropical forest soils

Nitrogen fixation , the biological conversion of di-nitrogen to plant-available ammonium , is the primary natural input of nitrogen to ecosystems , and influences plant growth and carbon exchange at local to global scales .
The role of this process in tropical forests is of particular concern , as these ecosystems harbour abundant nitrogen-fixing organisms and represent one third of terrestrial primary production .
Here we show that the micronutrient molybdenum , a cofactor in the nitrogen-fixing enzyme nitrogenase , limits nitrogen fixation by free-living heterotrophic bacteria in soils of lowland Panamanian forests .
We measured the fixation response to long-term nutrient manipulations in intact forests , and to short-term manipulations in soil microcosms .
Nitrogen fixation increased sharply in treatments of molybdenum alone , in micronutrient treatments that included molybdenum by design and in treatments with commercial phosphorus fertilizer , in which molybdenum was a ` hidden ' contaminant .
Fixation did not respond to additions of phosphorus that were not contaminated by molybdenum .
Our findings show that molybdenum alone can limit asymbiotic nitrogen fixation in tropical forests and raise new questions about the role of molybdenum and phosphorus in the tropical nitrogen cycle .
We suggest that molybdenum limitation may be common in highly weathered acidic soils , and may constrain the ability of some forests to acquire new nitrogen in response to CO2 fertilization .

[411] Changes in hail and flood risk in high-resolution simulations over Colorado 's mountains

The effect of a warming climate on hailstorm frequency and intensity is largely unknown .
Global climate models have too coarse resolution to simulate hailstorms explicitly ; thus it is unclear if a warmer climate will change hailstorm frequency and intensity , and if so , whether such events will become more likely through intensified thunderstorms or less likely owing to overall warmer conditions .
Here we investigate hail generation and maintenance for warm-season extreme precipitation events in Colorado , USA , for both present-day and projected future climates using high-resolution model simulations capable of resolving hailstorms .
Most simulations indicate a near-elimination of hail at the surface in future simulations for this region , despite more intense future storms and significantly larger amounts of hail generated in-cloud .
An increase in the height of the environmental melting level due to climate warming is found to be the primary reason for the disappearance of surface hail , as the warmer atmosphere increases the melting of frozen precipitation .
A decrease in future surface hail at high-elevation locations may imply potential changes in both hail damage and flood risk .

[412] Reversal of the net dinitrogen gas flux in coastal marine sediments

The flux of nitrogen from land and atmosphere to estuaries and the coastal ocean has increased substantially in recent decades .
The observed increase in nitrogen loading is caused by population growth , urbanization , expanding water and sewer infrastructure , fossil fuel combustion and synthetic fertilizer consumption .
Most of the nitrogen is removed by denitrification in the sediments of estuaries and the continental shelf , leading to a reduction in both cultural eutrophication and nitrogen pollution of the open ocean .
Nitrogen fixation , however , is thought to be a negligible process in sub-tidal heterotrophic marine systems .
Here we report sediment core data from Narragansett Bay , USA , which demonstrate that heterotrophic marine sediments can switch from being a net sink to being a net source of nitrogen .
Mesocosm and core incubation experiments , together with a historic data set of mean annual chlorophyll production , support the idea that a climate-induced decrease in primary production has led to a decrease in organic matter deposition to the benthos and the observed reversal of the net sediment nitrogen flux .
Our results suggest that some estuaries may no longer remove nitrogen from the water column .
Instead , nitrogen could be exported to the continental shelf and the open ocean and could shift the effect of anthropogenic nitrogen loading beyond the immediate coastal zone .

[413] Influence of snowfall and melt timing on tree growth in subarctic Eurasia

The causes of a reduced sensitivity of high-latitude tree growth to variations in summer temperature for recent decades , , compared to earlier this century , are unknown .
This sensitivity change is problematic , in that relationships between tree-ring properties and temperature are widely used for reconstructing past climate .
Here we report an analysis of tree-ring and climate data from the forest-tundra zone , in combination with a mechanistic model of tree-ring growth , to argue that an increasing trend of winter precipitation over the past century in many subarctic regions led to delayed snow melt in these permafrost environments .
As a result , the initiation of cambial activity ( necessary for the formation of wood cells ) has been delayed relative to the pre-1960 period in the Siberian subarctic .
Since the early 1960s , less of the growth season has been during what had previously been the period of maximal growth sensitivity to temperature .
This shift results not only in slower growth , but also in a reduced correlation between growth and temperature .
Our results suggest that changes in winter precipitation should be considered in seeking explanations for observed changes in the timing of the ` spring greening ' of high-latitude forests , and should be taken into account in the study of the role of the Siberian subarctic forest in the global carbon cycle .

[414] Atmospheric circulation as a source of uncertainty in climate change projections

The evidence for anthropogenic climate change continues to strengthen , and concerns about severe weather events are increasing .
As a result , scientific interest is rapidly shifting from detection and attribution of global climate change to prediction of its impacts at the regional scale .
However , nearly everything we have any confidence in when it comes to climate change is related to global patterns of surface temperature , which are primarily controlled by thermodynamics .
In contrast , we have much less confidence in atmospheric circulation aspects of climate change , which are primarily controlled by dynamics and exert a strong control on regional climate .
Model projections of circulation-related fields , including precipitation , show a wide range of possible outcomes , even on centennial timescales .
Sources of uncertainty include low-frequency chaotic variability and the sensitivity to model error of the circulation response to climate forcing .
As the circulation response to external forcing appears to project strongly onto existing patterns of variability , knowledge of errors in the dynamics of variability may provide some constraints on model projections .
Nevertheless , higher scientific confidence in circulation-related aspects of climate change will be difficult to obtain .
For effective decision-making , it is necessary to move to a more explicitly probabilistic , risk-based approach .

[415] Signature of ocean warming in global fisheries catch

Marine fishes and invertebrates respond to ocean warming through distribution shifts , generally to higher latitudes and deeper waters .
Consequently , fisheries should be affected by ` tropicalization ' of catch ( increasing dominance of warm-water species ) .
However , a signature of such climate-change effects on global fisheries catch has so far not been detected .
Here we report such an index , the mean temperature of the catch ( MTC ) , that is calculated from the average inferred temperature preference of exploited species weighted by their annual catch .
Our results show that , after accounting for the effects of fishing and large-scale oceanographic variability , global MTC increased at a rate of 0.19 degrees Celsius per decade between 1970 and 2006 , and non-tropical MTC increased at a rate of 0.23 degrees Celsius per decade .
In tropical areas , MTC increased initially because of the reduction in the proportion of subtropical species catches , but subsequently stabilized as scope for further tropicalization of communities became limited .
Changes in MTC in 52 large marine ecosystems , covering the majority of the world 's coastal and shelf areas , are significantly and positively related to regional changes in sea surface temperature .
This study shows that ocean warming has already affected global fisheries in the past four decades , highlighting the immediate need to develop adaptation plans to minimize the effect of such warming on the economy and food security of coastal communities , particularly in tropical regions .

[416] Palaeoclimate reconstructions reveal a strong link between El Nino-Southern Oscillation and Tropical Pacific mean state

The El Nino-Southern Oscillation ( ENSO ) is one of the most important components of the global climate system , but its potential response to an anthropogenic increase in atmospheric CO2 remains largely unknown .
One of the major limitations in ENSO prediction is our poor understanding of the relationship between ENSO variability and long-term changes in Tropical Pacific oceanography .
Here we investigate this relationship using palaeorecords derived from the geochemistry of planktonic foraminifera .
Our results indicate a strong negative correlation between ENSO variability and zonal gradient of sea-surface temperatures across the Tropical Pacific during the last 22 ky. .
This strong correlation implies a mechanistic link that tightly couples zonal sea-surface temperature gradient and ENSO variability during large climate changes and provides a unique insight into potential ENSO evolution in the future by suggesting enhanced ENSO variability under a global warming scenario .

[417] Reduction in areal extent of high-latitude wetlands in response to permafrost thaw

Wetlands are vegetated regions that are inundated with water on a permanent , seasonal or intermittent basis .
These ecosystems play an important role in the carbon cycle : wetlands take up and store carbon , and release carbon dioxide and methane through the decomposition of organic matter .
More than 50 % of wetlands are located in the high northern latitudes , where permafrost also prevails and exerts a strong control on wetland hydrology .
Permafrost degradation is linked to changes in Arctic lakes : between 1973 and 2004 the abundance of lakes increased in continuous permafrost zones , but decreased in other zones .
Here , we use a global climate model to examine the influence of permafrost thaw on the prevalence of high-latitude northern wetlands , under four emissions scenarios .
We show that as permafrost degrades , the areal extent of wetlands declines ; we found a net loss in wetland extent in the three highest emissions scenarios .
We also note an initial increase in the number of days of the year conducive to wetland formation , owing to an increase in unfrozen surface moisture resulting from a lengthening of the thaw season .
This is followed by a dramatic decline in the number of wetland-conducive days , owing to a deepening of the permafrost surface , and drainage of near-surface moisture to deeper soil layers .
We suggest that a reduction in the areal extent and duration of wetlands will influence high-latitude carbon emissions .

[418] Recent acceleration of biomass burning and carbon losses in Alaskan forests and peatlands

Climate change has increased the area affected by forest fires each year in boreal North America .
Increases in burned area and fire frequency are expected to stimulate boreal carbon losses .
However , the impact of wildfires on carbon emissions is also affected by the severity of burning .
How climate change influences the severity of biomass burning has proved difficult to assess .
Here , we examined the depth of ground-layer combustion in 178 sites dominated by black spruce in Alaska , using data collected from 31 fire events between 1983 and 2005 .
We show that the depth of burning increased as the fire season progressed when the annual area burned was small .
However , deep burning occurred throughout the fire season when the annual area burned was large .
Depth of burning increased late in the fire season in upland forests , but not in peatland and permafrost sites .
Simulations of wildfire-induced carbon losses from Alaskan black spruce stands over the past 60 years suggest that ground-layer combustion has accelerated regional carbon losses over the past decade , owing to increases in burn area and late-season burning .
As a result , soils in these black spruce stands have become a net source of carbon to the atmosphere , with carbon emissions far exceeding decadal uptake .

[419] Anthropogenic influence on multidecadal changes in reconstructed global evapotranspiration

Global warming is expected to intensify the global hydrological cycle , with an increase of both evapotranspiration ( EVT ) and precipitation .
Yet , the magnitude and spatial distribution of this global and annual mean response remains highly uncertain .
Better constraining land EVT in twenty-first-century climate scenarios is critical for predicting changes in surface climate , including heatwaves and droughts , evaluating impacts on ecosystems and water resources , and designing adaptation policies .
Continental scale EVT changes may already be underway , but have never been attributed to anthropogenic emissions of greenhouse gases and sulphate aerosols .
Here we provide global gridded estimates of annual EVT and demonstrate that the latitudinal and decadal differentiation of recent EVT variations can not be understood without invoking the anthropogenic radiative forcings .
In the mid-latitudes , the emerging picture of enhanced EVT confirms the end of the dimming decades and highlights the possible threat posed by increasing drought frequency to managing water resources and achieving food security in a changing climate .

[420] Stable isotope constraints on Holocene carbon cycle changes from an Antarctic ice core

Reconstructions of atmospheric CO2 concentrations based on Antarctic ice cores reveal significant changes during the Holocene epoch , but the processes responsible for these changes in CO2 concentrations have not been unambiguously identified .
Distinct characteristics in the carbon isotope signatures of the major carbon reservoirs ( ocean , biosphere , sediments and atmosphere ) constrain variations in the CO2 fluxes between those reservoirs .
Here we present a highly resolved atmospheric delta13C record for the past 11,000 years from measurements on atmospheric CO2 trapped in an Antarctic ice core .
From mass-balance inverse model calculations performed with a simplified carbon cycle model , we show that the decrease in atmospheric CO2 of about 5 parts per million by volume ( p.p.m.v. ) .
The increase in delta13C of about 0.25 / 1000 during the early Holocene is most probably the result of a combination of carbon uptake of about 290 gigatonnes of carbon by the land biosphere and carbon release from the ocean in response to carbonate compensation of the terrestrial uptake during the termination of the last ice age .
The 20 p.p.m.v. increase of atmospheric CO2 and the small decrease in delta13C of about 0.05 / 1000 during the later Holocene can mostly be explained by contributions from carbonate compensation of earlier land-biosphere uptake and coral reef formation , with only a minor contribution from a small decrease of the land-biosphere carbon inventory .

[421] Unusual Southern Hemisphere tree growth patterns induced by changes in the Southern Annular Mode

Recent changes in the summer climate of the Southern Hemisphere extra-tropics are primarily related to the dominance of the positive phase of the Southern Annular Mode .
This shift in the behaviour of the Southern Annular Mode -- essentially a measure of the pressure gradient between Southern Hemisphere mid and high latitudes -- has been predominantly induced by polar stratospheric ozone depletion .
The concomitant southward expansion of the dry subtropical belts could have consequences for forest growth .
Here , we use tree-ring records from over 3,000 trees in South America , Tasmania and New Zealand to identify dominant patterns of tree growth in recent centuries .
We show that the foremost patterns of growth between 1950 and 2000 differed significantly from those in the previous 250 years .
Specifically , growth was higher than the long-term average in the subalpine forests of Tasmania and New Zealand , but lower in the dry-mesic forests of Patagonia .
We further demonstrate that variations in the Southern Annular Mode can explain 12-48 % of the tree growth anomalies in the latter half of the twentieth century .
Tree-ring-based reconstructions of summer Southern Annular Mode indices suggest that the high frequency of the positive phase since the 1950s is unprecedented in the past 600 years .
We propose that changes in the Southern Annular Mode have significantly altered tree growth patterns in the Southern Hemisphere .

[422] Evidence of Geobacter-associated phage in a uranium-contaminated aquifer

Geobacter species may be important agents in the bioremediation of organic and metal contaminants in the subsurface , but as yet unknown factors limit the in situ growth of subsurface Geobacter well below rates predicted by analysis of gene expression or in silico metabolic modeling .
Analysis of the genomes of five different Geobacter species recovered from contaminated subsurface sites indicated that each of the isolates had been infected with phage .
Geobacter-associated phage sequences were also detected by metagenomic and proteomic analysis of samples from a uranium-contaminated aquifer undergoing in situ bioremediation , and phage particles were detected by microscopic analysis in groundwater collected from sediment enrichment cultures .
Transcript abundance for genes from the Geobacter-associated phage structural proteins , tail tube Gp19 and baseplate J , increased in the groundwater in response to the growth of Geobacter species when acetate was added , and then declined as the number of Geobacter decreased .
Western blot analysis of a Geobacter-associated tail tube protein Gp19 in the groundwater demonstrated that its abundance tracked with the abundance of Geobacter species .
These results suggest that the enhanced growth of Geobacter species in the subsurface associated with in situ uranium bioremediation increased the abundance and activity of Geobacter-associated phage and show that future studies should focus on how these phages might be influencing the ecology of this site .

[423] Prediction of seasonal climate-induced variations in global food production

Consumers , including the poor in many countries , are increasingly dependent on food imports and are thus exposed to variations in yields , production and export prices in the major food-producing regions of the world .
National governments and commercial entities are therefore paying increased attention to the cropping forecasts of important food-exporting countries as well as to their own domestic food production .
Given the increased volatility of food markets and the rising incidence of climatic extremes affecting food production , food price spikes may increase in prevalence in future years .
Here we present a global assessment of the reliability of crop failure hindcasts for major crops at two lead times derived by linking ensemble seasonal climatic forecasts with statistical crop models .
We found that moderate-to-marked yield loss over a substantial percentage ( 26-33 % ) of the harvested area of these crops is reliably predictable if climatic forecasts are near perfect .
However , only rice and wheat production are reliably predictable at three months before the harvest using within-season hindcasts .
The reliabilities of estimates varied substantially by crop -- rice and wheat yields were the most predictable , followed by soybean and maize .
The reasons for variation in the reliability of the estimates included the differences in crop sensitivity to the climate and the technology used by the crop-producing regions .
Our findings reveal that the use of seasonal climatic forecasts to predict crop failures will be useful for monitoring global food production and will encourage the adaptation of food systems toclimatic extremes .

[424] Direct impacts on local climate of sugar-cane expansion in Brazil

The increasing global demand for biofuels will require conversion of conventional agricultural or natural ecosystems .
Expanding biofuel production into areas now used for agriculture reduces the need to clear natural ecosystems , leading to indirect climate benefits through reduced greenhouse-gas emissions and faster payback of carbon debts .
Biofuel expansion may also cause direct , local climate changes by altering surface albedo and evapotranspiration , but these effects have been poorly documented .
Here we quantify the direct climate effects of sugar-cane expansion in the Brazilian Cerrado , on the basis of maps of recent sugar-cane expansion and natural-vegetation clearance combined with remotely sensed temperature , albedo and evapotranspiration over a 1.9 million km2 area .
On a regional basis for clear-sky daytime conditions , conversion of natural vegetation to a crop/pasture mosaic warms the cerrado by an average of 1.55 ( 1.45-1 .65 ) degreesC , but subsequent conversion of that mosaic to sugar cane cools the region by an average of 0.93 ( 0.78-1 .07 ) degreesC , resulting in a mean net increase of 0.6 degreesC .
Our results indicate that expanding sugar cane into existing crop and pasture land has a direct local cooling effect that reinforces the indirect climate benefits of this land-use option .

[425] Silica burial enhanced by iron limitation in oceanic upwelling margins

In large swaths of the ocean , primary production by diatoms may be limited by the availability of silica , which in turn limits the biological uptake of carbon dioxide .
The burial of biogenic silica in the form of opal is the main sink of marine silicon .
Opal burial occurs in equal parts in iron-limited open-ocean provinces and upwelling margins , especially the eastern Pacific upwelling zone .
However , it is unclear why opal burial is so efficient in this margin .
Here we measure fluxes of biogenic material , concentrations of diatom-bound iron and silicon isotope ratios using sediment traps and a sediment core from the Gulf of California upwelling margin .
In the sediment trap material , we find that periods of intense upwelling are associated with transient iron limitation that results in a high export of silica relative to organic carbon .
A similar correlation between enhanced silica burial and iron limitation is evident in the sediment core , which spans the past 26,000 years .
A global compilation also indicates that hotspots of silicon burial in the ocean are all characterized by high silica to organic carbon export ratios , a diagnostic trait for diatoms growing under iron stress .
We therefore propose that prevailing conditions of silica limitation in the ocean are largely caused by iron deficiency imposing an indirect constraint on oceanic carbon uptake .

[426] A four-dimensional X-ray tomographic microscopy study of bubble growth in basaltic foam

Understanding the influence of bubble foams on magma permeability and strength is critical to investigations of volcanic eruption mechanisms .
Increasing foam porosity decreases strength , enhancing the probability of an eruption .
However , higher porosities lead to larger permeabilities , which can lessen the eruption hazard .
Here we measure bubble size and wall thickness distributions , as well as connectivity , and calculate permeabilities and tensile strengths of basaltic foams imaged by synchrotron X-ray tomographic microscopy during bubble growth in hydrated basaltic melts .
Rapid vesiculation produces porous foams whose fragmentation thresholds are only 9-10 MPa and whose permeabilities increase from approximately 1x10-10 to 1x10-9 m2 between 10 and 14 s despite decreasing connectivity between bubbles .
These results indicate that basaltic magmas are most susceptible to failure immediately upon vesiculation and at later times , perhaps only 10 's of seconds later , permeability increases may lessen the hazard of explosive , basaltic , Plinian eruptions .

[427] Extreme summer weather in northern mid-latitudes linked to a vanishing cryosphere

The past decade has seen an exceptional number of unprecedented summer extreme weather events in northern mid-latitudes , along with record declines in both summer Arctic sea ice and snow cover on high-latitude land .
The underlying mechanisms that link the shrinking cryosphere with summer extreme weather , however , remain unclear .
Here , we combine satellite observations of early summer snow cover and summer sea-ice extent with atmospheric reanalysis data to demonstrate associations between summer weather patterns in mid-latitudes and losses of snow and sea ice .
Results suggest that the atmospheric circulation responds differently to changes in the ice and snow extents , with a stronger response to sea-ice loss , even though its reduction is half as large as that for the snow cover .
Atmospheric changes associated with the combined snow/ice reductions reveal widespread upper-level height increases , weaker upper-level zonal winds at high latitudes , a more amplified upper-level pattern , and a general northward shift in the jet stream .
More frequent extreme summer heat events over mid-latitude continents are linked with reduced sea ice and snow through these circulation changes .

[428] Intensified deep Pacific inflow and ventilation in Pleistocene glacial times

The production of cold , deep waters in the Southern Ocean is an important factor in the Earth 's heat budget .
The supply of deep water to the Pacific Ocean is presently dominated by a single source , the deep western boundary current east of New Zealand .
Here we use sediment records deposited under the influence of this deep western boundary current to reconstruct deep-water properties and speed changes during the Pleistocene epoch .
In physical and isotope proxies we find evidence for intensified deep Pacific Ocean inflow and ventilation during the glacial periods of the past 1.2 million years .
The changes in throughflow may be directly related to an increased production of Antarctic Bottom Water during glacial times .
Possible causes for such an increased bottom-water production include increasing wind strengths in the Southern Ocean or an increase in annual sea-ice formation , leaving dense water after brine rejection and thereby enhancing deep convection .
We infer also that the global thermohaline circulation was perturbed significantly during the mid-Pleistocene climate transition between 0.86 and 0.45 million years ago .

[429] Recent climate and ice-sheet changes in West Antarctica compared with the past 2,000 years

Changes in atmospheric circulation over the past five decades have enhanced the wind-driven inflow of warm ocean water onto the Antarctic continental shelf , where it melts ice shelves from below .
Atmospheric circulation changes have also caused rapid warming over the West Antarctic Ice Sheet , and contributed to declining sea-ice cover in the adjacent Amundsen-Bellingshausen seas .
It is unknown whether these changes are part of a longer-term trend .
Here , we use water-isotope ( delta18O ) data from an array of ice-core records to place recent West Antarctic climate changes in the context of the past two millennia .
We find that the delta18O of West Antarctic precipitation has increased significantly in the past 50 years , in parallel with the trend in temperature , and was probably more elevated during the 1990s than at any other time during the past 200 years .
However , delta18O anomalies comparable to those of recent decades occur about 1 % of the time over the past 2,000 years .
General circulation model simulations suggest that recent trends in delta18O and climate in West Antarctica can not be distinguished from decadal variability that originates in the tropics .
We conclude that the uncertain trajectory of tropical climate variability represents a significant source of uncertainty in projections of West Antarctic climate and ice-sheet change .

[430] The environmental impact of climate change adaptation on land use and water quality

Encouraging adaptation is an essential aspect of the policy response to climate change .
Adaptation seeks to reduce the harmful consequences and harness any beneficial opportunities arising from the changing climate .
However , given that human activities are the main cause of environmental transformations worldwide , it follows that adaptation itself also has the potential to generate further pressures , creating new threats for both local and global ecosystems .
From this perspective , policies designed to encourage adaptation may conflict with regulation aimed at preserving or enhancing environmental quality .
This aspect of adaptation has received relatively little consideration in either policy design or academic debate .
To highlight this issue , we analyse the trade-offs between two fundamental ecosystem services that will be impacted by climate change : provisioning services derived from agriculture and regulating services in the form of freshwater quality .
Results indicate that climate adaptation in the farming sector will generate fundamental changes in river water quality .
In some areas , policies that encourage adaptation are expected to be in conflict with existing regulations aimed at improving freshwater ecosystems .
These findings illustrate the importance of anticipating the wider impacts of human adaptation to climate change when designing environmental policies .

[431] The missing aerosol response in twentieth-century mid-latitude precipitation observations

Regional temperature change over the twentieth century has been strongly influenced by aerosol forcing .
The aerosol effect is also expected to be pronounced on regional precipitation change .
Changes in historical precipitation -- for the global mean and land mean of certain regions -- should be more sensitive to spatially heterogeneous aerosol forcing than greenhouse gas forcing .
Here , we investigate whether regional precipitation and temperature respond predictably to a significant strengthening in mid-twentieth-century Northern Hemisphere mid-latitude ( NHML ) aerosol forcing .
Using the latest climate model experiments , we find that observed regional temperature changes and observed Northern Hemisphere tropical land precipitation changes are consistent with the IPCC Fifth Assessment Report aerosol forcing estimate , but observed NHML land precipitation changes show little evidence of an aerosol response .
This may be a result of changes in precipitation measurement practice that increased observed precipitation totals at the same time that aerosol forcing was expected to reduce them .
Investigating this inconsistency , we calculate the required increase in early-twentieth-century observed NHML land precipitation to bring this result in line with aerosol forcing .
Biases greater than this calculated correction have been identified in countries within the NHML region previously , notably the former Soviet Union .
These observations are frequently used as a metric for the quality of model-simulated precipitation .
More homogeneity studies would be of huge benefit .

[432] Diversity and dispersal interactively affect predictability of ecosystem function

Theory and small-scale experiments predict that biodiversity losses can decrease the magnitude and stability of ecosystem services such as production and nutrient cycling .
Most of this research , however , has been isolated from the immigration and emigration ( dispersal ) processes that create and maintain diversity in nature .
As common anthropogenic drivers of biodiversity change -- such as habitat fragmentation , species introductions and climate change -- are mediated by these understudied processes , it is unclear how environmental degradation will affect ecosystem services .
Here we tested the interactive effects of mobile grazer diversity and dispersal on the magnitude and stability of ecosystem properties in experimental seagrass communities that were either isolated or connected by dispersal corridors .
We show that , contrary to theoretical predictions , increasing the number of mobile grazer species in these metacommunities increased the spatial and temporal variability of primary and secondary production .
Moreover , allowing grazers to move among and select patches reduced diversity effects on production .
Finally , effects of diversity on stability differed qualitatively between patch and metacommunity scales .
Our results indicate that declining biodiversity and habitat fragmentation synergistically influence the predictability of ecosystem functioning .

[433] Contrasting response of European forest and grassland energy exchange to heatwaves

Recent European heatwaves have raised interest in the impact of land cover conditions on temperature extremes .
At present , it is believed that such extremes are enhanced by stronger surface heating of the atmosphere , when soil moisture content is below average .
However , the impact of land cover on the exchange of water and energy and the interaction of this exchange with the soil water balance during heatwaves is largely unknown .
Here we analyse observations from an extensive network of flux towers in Europe that reveal a difference between the temporal responses of forest and grassland ecosystems during heatwaves .
We find that initially , surface heating is twice as high over forest than over grassland .
Over grass , heating is suppressed by increased evaporation in response to increased solar radiation and temperature .
Ultimately , however , this process accelerates soil moisture depletion and induces a critical shift in the regional climate system that leads to increased heating .
We propose that this mechanism may explain the extreme temperatures in August 2003 .
We conclude that the conservative water use of forest contributes to increased temperatures in the short term , but mitigates the impact of the most extreme heat and/or long-lasting events .

[434] Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years

Atmospheric methane is an important greenhouse gas and a sensitive indicator of climate change and millennial-scale temperature variability .
Its concentrations over the past 650,000 years have varied between ~ 350 and ~ 800 parts per 109 by volume ( p.p.b.v. ) during glacial and interglacial periods , respectively .
In comparison , present-day methane levels of ~ 1,770 p.p.b.v. have been reported .
Insights into the external forcing factors and internal feedbacks controlling atmospheric methane are essential for predicting the methane budget in a warmer world .
Here we present a detailed atmospheric methane record from the EPICA Dome C ice core that extends the history of this greenhouse gas to 800,000 yr before present .
The average time resolution of the new data is ~ 380 yr and permits the identification of orbital and millennial-scale features .
Spectral analyses indicate that the long-term variability in atmospheric methane levels is dominated by ~ 100,000 yr glacial-interglacial cycles up to ~ 400,000 yr ago with an increasing contribution of the precessional component during the four more recent climatic cycles .
We suggest that changes in the strength of tropical methane sources and sinks ( wetlands , atmospheric oxidation ) , possibly influenced by changes in monsoon systems and the position of the intertropical convergence zone , controlled the atmospheric methane budget , with an additional source input during major terminations as the retreat of the northern ice sheet allowed higher methane emissions from extending periglacial wetlands .
Millennial-scale changes in methane levels identified in our record as being associated with Antarctic isotope maxima events are indicative of ubiquitous millennial-scale temperature variability during the past eight glacial cycles .

[435] Major flood disturbance alters river ecosystem evolution

Floods , major formative drivers of channel and floodplain structure and associated riparian and in-stream communities , are increasing in intensity and magnitude with climate change in many regions of the world .
However , predicting how floods will affect stream channels and their communities as climate changes is limited by a lack of long-term pre-flood baseline data sets across different organismal groups .
Here we show salmon , macroinvertebrate and meiofauna communities , monitored for 30 years in a system evolving owing to glacier retreat , were modified significantly by a major rainfall event that caused substantial geomorphic change to the stream channel .
Pink salmon , reduced to one-tenth of pre-flood spawner densities , recovered within two generations .
Macroinvertebrate community structure was significantly different after the flood as some pioneer taxa , which had become locally extinct , recolonized whereas some later colonizers were eliminated .
The trajectory of the macroinvertebrate succession was reset towards the community structure of 15 years earlier .
Meiofaunal abundance recovered rapidly and richness increased post-flood with some previously unrecorded taxa colonizing .
Biotic recovery was independent of geomorphological recovery .
Markedly different responses according to the organismal group suggest caution is required when applying general aquatic ecosystem theories and concepts to predict flood events .

[436] Processes and patterns of oceanic nutrient limitation

Microbial activity is a fundamental component of oceanic nutrient cycles .
Photosynthetic microbes , collectively termed phytoplankton , are responsible for the vast majority of primary production in marine waters .
The availability of nutrients in the upper ocean frequently limits the activity and abundance of these organisms .
Experimental data have revealed two broad regimes of phytoplankton nutrient limitation in the modern upper ocean .
Nitrogen availability tends to limit productivity throughout much of the surface low-latitude ocean , where the supply of nutrients from the subsurface is relatively slow .
In contrast , iron often limits productivity where subsurface nutrient supply is enhanced , including within the main oceanic upwelling regions of the Southern Ocean and the eastern equatorial Pacific .
Phosphorus , vitamins and micronutrients other than iron may also ( co - ) limit marine phytoplankton .
The spatial patterns and importance of co-limitation , however , remain unclear .
Variability in the stoichiometries of nutrient supply and biological demand are key determinants of oceanic nutrient limitation .
Deciphering the mechanisms that underpin this variability , and the consequences for marine microbes , will be a challenge .
But such knowledge will be crucial for accurately predicting the consequences of ongoing anthropogenic perturbations to oceanic nutrient biogeochemistry .

[437] Evolutionary response of the egg hatching date of a herbivorous insect under climate change

Under changing climatic conditions , species need to adapt to their new environment .
Genetic adaptation is crucial to prevent population extinction but examples where climate change leads to genetic changes in wild populations have been few .
The synchronization between the timing of egg hatching of a herbivorous insect , the winter moth ( Operophtera brumata ) , and the seasonal bud burst of its food plant , oak ( Quercus robur ) , has been disrupted by climate change and a quantitative genetic model predicts that selection will delay the egg hatching date .
Here we show , using both long-term observational data and experiments , that the egg hatching date has changed genetically , resulting in closer synchrony with oak bud burst .
The observed rate of change matches the predicted rate of change of one day per year .
Hence , altered selection pressures , caused by environmental change , result in a rapid adaptive response in insect phenology .
These genetic changes in a key life-history trait in this herbivorous insect therefore seem to be fast enough to match the climate-change-induced advancement of their host phenology .

[438] Interdecadal modulation of El Nino amplitude during the past millennium

The El Nino/Southern Oscillation ( ENSO ) is the dominant mode of interannual climate variability on Earth , alternating between anomalously warm ( El Nino ) and cold ( La Nina ) conditions in the tropical Pacific at intervals of 2-8 years .
The amplitude of ENSO variability affects the occurrence and predictability of climate extremes around the world , but our ability to detect and predict changes in ENSO amplitude is limited by the fact that the instrumental record is too short to characterize its natural variability .
Here we use the North American Drought Atlas -- a database of drought reconstructions based on tree-ring records -- to produce a continuous , annually resolved record of ENSO variability over the past 1,100 years .
Our record is in broad agreement with independent , ENSO-sensitive proxy records in the Pacific and surrounding regions .
Together , these records indicate that ENSO amplitude exhibits a quasi-regular cycle of 50-90 years that is closely coupled to the tropical Pacific mean state .
Anomalously warm conditions in the eastern Pacific are associated with enhanced ENSO variability , consistent with model simulations .
The quasi-periodic ENSO amplitude modulation reported here offers a key observational constraint for improving models and their prediction of ENSO behaviour linked to global warming .

[439] No growth stimulation of tropical trees by 150 years of CO2 fertilization but water-use efficiency increased

The biomass of undisturbed tropical forests has likely increased in the past few decades , probably as a result of accelerated tree growth .
Higher CO2 levels are expected to raise plant photosynthetic rates and enhance water-use efficiency , that is , the ratio of carbon assimilation through photosynthesis to water loss through transpiration .
However , there is no evidence that these physiological responses do indeed stimulate tree growth in tropical forests .
Here we present measurements of stable carbon isotopes and growth rings in the wood of 1,100 trees from Bolivia , Cameroon and Thailand .
Measurements of carbon isotope fractions in the wood indicate that intrinsic water-use efficiency in both understorey and canopy trees increased by 30-35 % over the past 150 years as atmospheric CO2 concentrations increased .
However , we found no evidence for the suggested concurrent acceleration of individual tree growth when analysing the width of growth rings .
We conclude that the widespread assumption of a CO2-induced stimulation of tropical tree growth may not be valid .

[440] Global diversity of drought tolerance and grassland climate-change resilience

Drought reduces plant productivity , induces widespread plant mortality and limits the geographic distribution of plant species .
As climates warm and precipitation patterns shift in the future , understanding the distribution of the diversity of plant drought tolerance is central to predicting future ecosystem function and resilience to climate change .
These questions are especially pressing for the world 's 11,000 grass species , which dominate a large fraction of the terrestrial biosphere , yet are poorly characterized with respect to responses to drought .
Here , we show that physiological drought tolerance , which varied tenfold among 426 grass species , is well distributed both climatically and phylogenetically , suggesting most native grasslands are likely to contain a high diversity of drought tolerance .
Consequently , local species may help maintain ecosystem functioning in response to changing drought regimes without requiring long-distance migrations of grass species .
Furthermore , physiologically drought-tolerant species had higher rates of water and carbon dioxide exchange than intolerant species , indicating that severe droughts may generate legacies for ecosystem functioning .
In all , our findings suggest that diverse grasslands throughout the globe have the potential to be resilient to drought in the face of climate change through the local expansion of drought-tolerant species .

[441] Rapid subtropical North Atlantic salinity oscillations across Dansgaard-Oeschger cycles

Geochemical and sedimentological evidence suggest that the rapid climate warming oscillations of the last ice age , the Dansgaard-Oeschger cycles , were coupled to fluctuations in North Atlantic meridional overturning circulation through its regulation of poleward heat flux .
The balance between cold meltwater from the north and warm , salty subtropical gyre waters from the south influenced the strength and location of North Atlantic overturning circulation during this period of highly variable climate .
Here we investigate how rapid reorganizations of the ocean-atmosphere system across these cycles are linked to salinity changes in the subtropical North Atlantic gyre .
We combine Mg/Ca palaeothermometry and oxygen isotope ratio measurements on planktonic foraminifera across four Dansgaard-Oeschger cycles ( spanning 45.9-59 .2 kyr ago ) to generate a seawater salinity proxy record from a subtropical gyre deep-sea sediment core .
We show that North Atlantic gyre surface salinities oscillated rapidly between saltier stadial conditions and fresher interstadials , covarying with inferred shifts in the Tropical Atlantic hydrologic cycle and North Atlantic overturning circulation .
These salinity oscillations suggest a reduction in precipitation into the North Atlantic and/or reduced export of deep salty thermohaline waters during stadials .
We hypothesize that increased stadial salinities preconditioned the North Atlantic Ocean for a rapid return to deep overturning circulation and high-latitude warming by contributing to increased North Atlantic surface-water density on interstadial transitions .

[442] Long-term experimental warming alters nitrogen-cycling communities but site factors remain the primary drivers of community structure in high arctic tundra soils

Arctic air temperatures are expected to rise significantly over the next century .
Experimental warming of arctic tundra has been shown to increase plant productivity and cause community shifts and may also alter microbial community structure .
Hence , the objective of this study was to determine whether experimental warming caused shifts in soil microbial communities by measuring changes in the frequency , relative abundance and/or richness of nosZ and nifH genotypes .
Five sites at a high arctic coastal lowland were subjected to a 13-year warming experiment using open-top chambers ( OTCs ) .
Sites differed by dominant plant community , soil parent material and/or moisture regimen .
Six soil cores were collected from each of four replicate OTC and ambient plots at each site and subdivided into upper and lower samples .
Differences in frequency and relative abundance of terminal restriction fragments were assessed graphically by two-way cluster analysis and tested statistically with permutational multivariate analysis of variance ( ANOVA ) .
Genotypic richness was compared using factorial ANOVA .
The genotype frequency , relative abundance and genotype richness of both nosZ and nifH communities differed significantly by site , and by OTC treatment and/or depth at some sites .
The site that showed the most pronounced treatment effect was a wet sedge meadow , where community structure and genotype richness of both nosZ and nifH were significantly affected by warming .
Although warming was an important factor affecting these communities at some sites at this high arctic lowland , overall , site factors were the main determinants of community structure .

[443] Climate change and population declines in a long-distance migratory bird

Phenological responses to climate change differ across trophic levels , which may lead to birds failing to breed at the time of maximal food abundance .
Here we investigate the population consequences of such mistiming in the migratory pied flycatcher , Ficedula hypoleuca .
In a comparison of nine Dutch populations , we find that populations have declined by about 90 % over the past two decades in areas where the food for provisioning nestlings peaks early in the season and the birds are currently mistimed .
In areas with a late food peak , early-breeding birds still breed at the right time , and there is , at most , a weak population decline .
If food phenology advances further , we also predict population declines in areas with a late food peak , as in these areas adjustment to an advanced food peak is insufficient .
Mistiming as a result of climate change is probably a widespread phenomenon , and here we provide evidence that it can lead to population declines .

[444] Emperor penguins and climate change

Variations in ocean-atmosphere coupling over time in the Southern Ocean have dominant effects on sea-ice extent and ecosystem structure , but the ultimate consequences of such environmental changes for large marine predators can not be accurately predicted because of the absence of long-term data series on key demographic parameters .
Here , we use the longest time series available on demographic parameters of an Antarctic large predator breeding on fast ice and relying on food resources from the Southern Ocean .
We show that over the past 50 years , the population of emperor penguins ( Aptenodytes forsteri ) in Terre Adelie has declined by 50 % because of a decrease in adult survival during the late 1970s .
At this time there was a prolonged abnormally warm period with reduced sea-ice extent .
Mortality rates increased when warm sea-surface temperatures occurred in the foraging area and when annual sea-ice extent was reduced , and were higher for males than for females .
In contrast with survival , emperor penguins hatched fewer eggs when winter sea-ice was extended .
These results indicate strong and contrasting effects of large-scale oceanographic processes and sea-ice extent on the demography of emperor penguins , and their potential high susceptibility to climate change .

[445] The impact of reduced pH on the microbial community of the coral Acropora eurystoma

Rising concentrations of atmospheric carbon dioxide are acidifying the world 's oceans .
Surface seawater pH is 0.1 units lower than pre-industrial values and is predicted to decrease by up to 0.4 units by the end of the century .
This change in pH may result in changes in the physiology of ocean organisms , in particular , organisms that build their skeletons/shells from calcium carbonate , such as corals .
This physiological change may also affect other members of the coral holobiont , for example , the microbial communities associated with the coral , which in turn may affect the coral physiology and health .
In the present study , we examined changes in bacterial communities in the coral mucus , tissue and skeleton following exposure of the coral Acropora eurystoma to two different pH conditions : 7.3 and 8.2 ( ambient seawater ) .
The microbial community was different at the two pH values , as determined by denaturing gradient gel electrophoresis and 16S rRNA gene sequence analysis .
Further analysis of the community in the corals maintained at the lower pH revealed an increase in bacteria associated with diseased and stressed corals , such as Vibrionaceae and Alteromonadaceae .
In addition , an increase in the number of potential antibacterial activity was recorded among the bacteria isolated from the coral maintained at pH 7.3 .
Taken together , our findings highlight the impact that changes in the pH may have on the coral-associated bacterial community and their potential contribution to the coral host .

[446] Effect of evaporite deposition on Early Cretaceous carbon and sulphur cycling

The global carbon and sulphur cycles are central to our understanding of the Earth 's history , because changes in the partitioning between the reduced and oxidized reservoirs of these elements are the primary control on atmospheric oxygen concentrations .
In modern marine sediments , the burial rates of reduced carbon and sulphur are positively coupled , but high-resolution isotope records indicate that these rates were inversely related during the Early Cretaceous period .
This inverse relationship is difficult to reconcile with our understanding of the processes that control organic matter remineralization and pyrite burial .
Here we show that the inverse correlation can be explained by the deposition of evaporites during the opening of the South Atlantic Ocean basin .
Evaporite deposition can alter the chemical composition of sea water , which can in turn affect the ability of sulphate-reducing bacteria to remineralize organic matter and mediate pyrite burial .
We use a reaction-transport model to quantify these effects , and the resulting changes in the burial rates of carbon and sulphur , during the Early Cretaceous period .
Our results indicate that deposition of the South Atlantic evaporites removed enough sulphate from the ocean temporarily to reduce biologically mediated pyrite burial and organic matter remineralization by up to fifty per cent , thus explaining the inverse relationship between the burial rates of reduced carbon and sulphur during this interval .
Furthermore , our findings suggest that the effect of changing seawater sulphate concentrations on the marine subsurface biosphere may be the key to understanding other large-scale perturbations of the global carbon and sulphur cycles .

[447] Global diets link environmental sustainability and human health

Diets link environmental and human health .
Rising incomes and urbanization are driving a global dietary transition in which traditional diets are replaced by diets higher in refined sugars , refined fats , oils and meats .
By 2050 these dietary trends , if unchecked , would be a major contributor to an estimated 80 per cent increase in global agricultural greenhouse gas emissions from food production and to global land clearing .
Moreover , these dietary shifts are greatly increasing the incidence of type II diabetes , coronary heart disease and other chronic non-communicable diseases that lower global life expectancies .
Alternative diets that offer substantial health benefits could , if widely adopted , reduce global agricultural greenhouse gas emissions , reduce land clearing and resultant species extinctions , and help prevent such diet-related chronic non-communicable diseases .
The implementation of dietary solutions to the tightly linked diet-environment-health trilemma is a global challenge , and opportunity , of great environmental and public health importance .

[448] El Nino in a changing climate

El Nino events , characterized by anomalous warming in the eastern equatorial Pacific Ocean , have global climatic teleconnections and are the most dominant feature of cyclic climate variability on subdecadal timescales .
Understanding changes in the frequency or characteristics of El Nino events in a changing climate is therefore of broad scientific and socioeconomic interest .
Recent studies show that the canonical El Nino has become less frequent and that a different kind of El Nino has become more common during the late twentieth century , in which warm sea surface temperatures ( SSTs ) in the central Pacific are flanked on the east and west by cooler SSTs .
This type of El Nino , termed the central Pacific El Nino ( CP-El Nino ; also termed the dateline El Nino , El Nino Modoki or warm pool El Nino ) , differs from the canonical eastern Pacific El Nino ( EP-El Nino ) in both the location of maximum SST anomalies and tropical-midlatitude teleconnections .
Here we show changes in the ratio of CP-El Nino to EP-El Nino under projected global warming scenarios from the Coupled Model Intercomparison Project phase 3 multi-model data set .
Using calculations based on historical El Nino indices , we find that projections of anthropogenic climate change are associated with an increased frequency of the CP-El Nino compared to the EP-El Nino .
When restricted to the six climate models with the best representation of the twentieth-century ratio of CP-El Nino to EP-El Nino , the occurrence ratio of CP-El Nino/EP-El Nino is projected to increase as much as five times under global warming .
The change is related to a flattening of the thermocline in the equatorial Pacific .

[449] Evolution of species interactions in a biofilm community

Biofilms are spatially structured communities of microbes whose function is dependent on a complex web of symbiotic interactions .
Localized interactions within these assemblages are predicted to affect the coexistence of the component species , community structure and function , but there have been few explicit empirical analyses of the evolution of interactions .
Here we show , with the use of a two-species community , that selection in a spatially structured environment leads to the evolution of an exploitative interaction .
Simple mutations in the genome of one species caused it to adapt to the presence of the other , forming an intimate and specialized association .
The derived community was more stable and more productive than the ancestral community .
Our results show that evolution in a spatially structured environment can stabilize interactions between species , provoke marked changes in their symbiotic nature and affect community function .

[450] Projected increase in tropical cyclones near Hawaii

Projections of the potential impacts of global warming on regional tropical cyclone activity are challenging owing to multiple sources of uncertainty in model physical schemes and different assumptions for future sea surface temperatures .
A key factor in projecting climate change is to derive robust signals of future changes in tropical cyclone activity across different model physical schemes and different future patterns in sea surface temperature .
A suite of future warming experiments ( 2075-2099 ) , using a state-of-the-art high-resolution global climate model , robustly predicts an increase in tropical cyclone frequency of occurrence around the Hawaiian Islands .
A physically based empirical model analysis reveals that the substantial increase in the likelihood of tropical cyclone frequency is primarily associated with a northwestward shifting of the tropical cyclone track in the open ocean southeast of the islands .
Moreover , significant and robust changes in large-scale environmental conditions strengthen in situ tropical cyclone activity in the subtropical central Pacific .
These results highlight possible future increases in storm-related socio-economic and ecosystem damage for the Hawaiian Islands .

[451] Reduced North Atlantic Deep Water flux to the glacial Southern Ocean inferred from neodymium isotope ratios

The global circulation of the oceans and the atmosphere transports heat around the Earth .
Broecker and Denton suggested that changes in the global ocean circulation might have triggered or enhanced the glacial-interglacial cycles .
But proxy data for past circulation taken from sediment cores in the South Atlantic Ocean have yielded conflicting interpretations of ocean circulation in glacial times -- delta13C variations in benthic foraminifera support the idea of a glacial weakening or shutdown of North Atlantic Deep Water production , whereas other proxies , such as Cd/Ca , Ba/Ca and 231Pa/230Th ratios , show little change from the Last Glacial Maximum to the Holocene epoch .
Here we report neodymium isotope ratios from the dispersed Fe-Mn oxide component of two southeast Atlantic sediment cores .
Both cores show variations that tend towards North Atlantic signatures during the warm marine isotope stages 1 and 3 , whereas for the full glacial stages 2 and 4 they are closer to Pacific Ocean signatures .
We conclude that the export of North Atlantic Deep Water to the Southern Ocean has resembled present-day conditions during the warm climate intervals , but was reduced during the cold stages .
An increase in biological productivity may explain the various proxy data during the times of reduced North Atlantic Deep Water export .

[452] Time - and sediment depth-related variations in bacterial diversity and community structure in subtidal sands

Bacterial community structure and microbial activity were determined together with a large number of contextual environmental parameters over 2 years in subtidal sands of the German Wadden Sea in order to identify the main factors shaping microbial community structure and activity in this habitat .
Seasonal changes in temperature were directly reflected in bacterial activities and total community respiration , but could not explain variations in the community structure .
Strong sediment depth-related patterns were observed for bacterial abundances , carbon production rates and extracellular enzymatic activities .
Bacterial community structure also showed a clear vertical variation with higher operational taxonomic unit ( OTU ) numbers at 10-15 cm depth than in the top 10 cm , probably because of the decreasing disturbance by hydrodynamic forces with sediment depth .
The depth-related variations in bacterial community structure could be attributed to vertical changes in bacterial abundances , chlorophyll a and NO3 - , indicating that spatial patterns of microbes are partially environmentally controlled .
Time was the most important single factor affecting microbial community structure with an OTU replacement of up to 47 % over 2 years and a contribution of 34 % to the total variation .
A large part of this variation was not related to any environmental parameters , suggesting that temporal variations in bacterial community structure are caused by yet unknown environmental drivers and/or by stochastic events in coastal sand habitats .
Principal ecosystem functions such as benthic oxygen consumption and extracellular hydrolysis of organic matter were , however , at a high level at all times , indicating functional redundancy in the microbial communities .

[453] Multiple phases of chondrocyte enlargement underlie differences in skeletal proportions

The wide diversity of skeletal proportions in mammals is evident upon a survey of any natural history museum 's collections and allows us to distinguish between species even when reduced to their calcified components .
Similarly , each individual is comprised of a variety of bones of differing lengths .
The largest contribution to the lengthening of a skeletal element , and to the differential elongation of elements , comes from a dramatic increase in the volume of hypertrophic chondrocytes in the growth plate as they undergo terminal differentiation .
However , the mechanisms of chondrocyte volume enlargement have remained a mystery .
Here we use quantitative phase microscopy to show that mammalian chondrocytes undergo three distinct phases of volume increase , including a phase of massive cell swelling in which the cellular dry mass is significantly diluted .
In light of the tight fluid regulatory mechanisms known to control volume in many cell types , this is a remarkable mechanism for increasing cell size and regulating growth rate .
It is , however , the duration of the final phase of volume enlargement by proportional dry mass increase at low density that varies most between rapidly and slowly elongating growth plates .
Moreover , we find that this third phase is locally regulated through a mechanism dependent on insulin-like growth factor .
This study provides a framework for understanding how skeletal size is regulated and for exploring how cells sense , modify and establish a volume set point .

[454] Population structure determines functional differences among species and ecosystem processes

Linking the structure of communities to ecosystem functioning has been a perennial challenge in ecology .
Studies on ecosystem function are traditionally focused on changes in species composition .
However , this species-centric approach neglects the often dramatic changes in the ecology of organisms during their development , thereby limiting our ability to link the structure of populations and communities to the functioning of natural ecosystems .
Here we experimentally demonstrate that the impact of organisms on community structure and ecosystem processes often differ more among developmental stages within a species than between species , contrary to current assumptions .
Importantly , we show that functional differences between species vary depending on the specific demographic structure of predators .
One important implication is that changes in the demography of populations can strongly alter the functional composition of communities and change ecosystem processes long before any species are extirpated from communities .

[455] Light limitation of nutrient-poor lake ecosystems

Productivity denotes the rate of biomass synthesis in ecosystems and is a fundamental characteristic that frames ecosystem function and management .
Limitation of productivity by nutrient availability is an established paradigm for lake ecosystems .
Here , we assess the relevance of this paradigm for a majority of the world 's small , nutrient-poor lakes , with different concentrations of coloured organic matter .
By comparing small unproductive lakes along a water colour gradient , we show that coloured terrestrial organic matter controls the key process for new biomass synthesis ( the benthic primary production ) through its effects on light attenuation .
We also show that this translates into effects on production and biomass of higher trophic levels ( benthic invertebrates and fish ) .
These results are inconsistent with the idea that nutrient supply primarily controls lake productivity , and we propose that a large share of the world 's unproductive lakes , within natural variations of organic carbon and nutrient input , are limited by light and not by nutrients .
We anticipate that our result will have implications for understanding lake ecosystem function and responses to environmental change .
Catchment export of coloured organic matter is sensitive to short-term natural variability and long-term , large-scale changes , driven by climate and different anthropogenic influences .
Consequently , changes in terrestrial carbon cycling will have pronounced effects on most lake ecosystems by mediating changes in light climate and productivity of lakes .

[456] An ice core record of near-synchronous global climate changes at the Bolling transition

The abrupt warming that initiated the Bolling-Allerod interstadial was the penultimate warming in a series of climate variations known as Dansgaard-Oeschger events .
Despite the clear expression of this transition in numerous palaeoclimate records , the relative timing of climate shifts in different regions of the world and their causes are subject to debate .
Here we explore the phasing of global climate change at the onset of the Bolling-Allerod using air preserved in bubbles in the North Greenland Eemian ice core .
Specifically , we measured methane concentrations , which act as a proxy for low-latitude climate , and the 15N/14N ratio of N2 , which reflects Greenland surface temperature , over the same interval of time .
We use an atmospheric box model and a firn air model to account for potential uncertainties in the data , and find that changes in Greenland temperature and atmospheric methane emissions at the Bolling onset occurred essentially synchronously , with temperature leading by 4.5 years .
We can not exclude the possibility that tropical climate could lag changing methane concentrations by up to several decades , if the initial methane rise came from boreal sources alone .
However , because even boreal methane-producing regions lie far from Greenland , we conclude that the mechanism that drove abrupt change at this time must be capable of rapidly transmitting climate changes across the globe .

[457] Accelerated thermokarst formation in the McMurdo Dry Valleys , Antarctica

Thermokarst is a land surface lowered and disrupted by melting ground ice .
Thermokarst is a major driver of landscape change in the Arctic , but has been considered to be a minor process in Antarctica .
Here , we use ground-based and airborne LiDAR coupled with timelapse imaging and meteorological data to show that 1 ) thermokarst formation has accelerated in Garwood Valley , Antarctica ; 2 ) the rate of thermokarst erosion is presently ~ 10 times the average Holocene rate ; and 3 ) the increased rate of thermokarst formation is driven most strongly by increasing insolation and sediment/albedo feedbacks .
This suggests that sediment enhancement of insolation-driven melting may act similarly to expected increases in Antarctic air temperature ( presently occurring along the Antarctic Peninsula ) , and may serve as a leading indicator of imminent landscape change in Antarctica that will generate thermokarst landforms similar to those in Arctic periglacial terrains .

[458] Bacterial diversity and White Plague Disease-associated community changes in the Caribbean coral Montastraea faveolata

Increasing evidence confirms the crucial role bacteria and archaea play within the coral holobiont , that is , the coral host and its associated microbial community .
The bacterial component constitutes a community of high diversity , which appears to change in structure in response to disease events .
In this study , we highlight the limitation of 16S rRNA gene ( 16S rDNA ) clone library sequencing as the sole method to comprehensively describe coral-associated communities .
This limitation was addressed by combining a high-density 16S rRNA gene microarray with , clone library sequencing as a novel approach to study bacterial communities in healthy versus diseased corals .
We determined an increase in diversity as well as a significant shift in community structure in Montastraea faveolata colonies displaying phenotypic signs of White Plague Disease type II ( WPD-II ) .
An accumulation of species that belong to families that include known coral pathogens ( Alteromonadaceae , Vibrionaceae ) , bacteria previously isolated from diseased , stressed or injured marine invertebrates ( for example , Rhodobacteraceae ) , and other species ( for example , Campylobacteraceae ) was observed .
Some of these species were also present in healthy tissue samples , but the putative primary pathogen , Aurantimonas corallicida , was not detected in any sample by either method .
Although an ecological succession of bacteria during disease progression after causation by a primary agent represents a possible explanation for our observations , we also discuss the possibility that a disease of yet to be determined etiology may have affected M. faveolata colonies and resulted in ( or be a result of ) an increase in opportunistic pathogens .

[459] The contribution of manure and fertilizer nitrogen to atmospheric nitrous oxide since 1860

Atmospheric nitrous oxide concentrations have been increasing since the industrial revolution and currently account for 6 % of total anthropogenic radiative forcing .
Microbial production in soils is the dominant nitrous oxide source ; this has increased with increasing use of nitrogen fertilizers .
However , fertilizer use alone can not account for the historical trends of atmospheric concentrations of nitrous oxide .
Here , I analyse atmospheric concentrations , industrial sources of nitrous oxide , and fertilizer and manure production since 1860 .
Before 1960 , agricultural expansion , including livestock production , may have caused globally significant mining of soil nitrogen , fuelling a steady increase in atmospheric nitrous oxide .
After 1960 , the rate of the increase rose , due to accelerating use of synthetic nitrogen fertilizers .
Using a regression model , I show that 2.0 % of manure nitrogen and 2.5 % of fertilizer nitrogen was converted to nitrous oxide between 1860 and 2005 ; these percentage contributions explain the entire pattern of increasing nitrous oxide concentrations over this period .
Consideration of processes that re-concentrate soil nitrogen , such as manure production by livestock , improved ` hind-casting ' of nitrous oxide emissions .
As animal protein consumption in human diets increases globally , management of manure will be an important component of future efforts to reduce anthropogenic nitrous oxide sources .

[460] Upper-ocean-to-atmosphere radiocarbon offsets imply fast deglacial carbon dioxide release

Radiocarbon in the atmosphere is regulated largely by ocean circulation , which controls the sequestration of carbon dioxide ( CO2 ) in the deep sea through atmosphere-ocean carbon exchange .
During the last glaciation , lower atmospheric CO2 levels were accompanied by increased atmospheric radiocarbon concentrations that have been attributed to greater storage of CO2 in a poorly ventilated abyssal ocean .
The end of the ice age was marked by a rapid increase in atmospheric CO2 concentrations that coincided with reduced 14C/12C ratios ( Delta14C ) in the atmosphere , suggesting the release of very ` old ' ( 14C-depleted ) CO2 from the deep ocean to the atmosphere .
Here we present radiocarbon records of surface and intermediate-depth waters from two sediment cores in the southwest Pacific and Southern oceans .
We find a steady 170 per mil decrease in Delta14C that precedes and roughly equals in magnitude the decrease in the atmospheric radiocarbon signal during the early stages of the glacial-interglacial climatic transition .
The atmospheric decrease in the radiocarbon signal coincides with regionally intensified upwelling and marine biological productivity , suggesting that CO2 released by means of deep water upwelling in the Southern Ocean lost most of its original depleted-14C imprint as a result of exchange and isotopic equilibration with the atmosphere .
Our data imply that the deglacial 14C depletion previously identified in the eastern tropical North Pacific must have involved contributions from sources other than the previously suggested carbon release by way of a deep Southern Ocean pathway , and may reflect the expanded influence of the 14C-depleted North Pacific carbon reservoir across this interval .
Accordingly , shallow water masses advecting north across the South Pacific in the early deglaciation had little or no residual 14C-depleted signals owing to degassing of CO2 and biological uptake in the Southern Ocean .

[461] Attribution of observed surface humidity changes to human influence

Water vapour is the most important contributor to the natural greenhouse effect , and the amount of water vapour in the atmosphere is expected to increase under conditions of greenhouse-gas-induced warming , leading to a significant feedback on anthropogenic climate change .
Theoretical and modelling studies predict that relative humidity will remain approximately constant at the global scale as the climate warms , leading to an increase in specific humidity .
Although significant increases in surface specific humidity have been identified in several regions , and on the global scale in non-homogenized data , it has not been shown whether these changes are due to natural or human influences on climate .
Here we use a new quality-controlled and homogenized gridded observational data set of surface humidity , with output from a coupled climate model , to identify and explore the causes of changes in surface specific humidity over the late twentieth century .
We identify a significant global-scale increase in surface specific humidity that is attributable mainly to human influence .
Specific humidity is found to have increased in response to rising temperatures , with relative humidity remaining approximately constant .
These changes may have important implications , because atmospheric humidity is a key variable in determining the geographical distribution and maximum intensity of precipitation , the potential maximum intensity of tropical cyclones , and human heat stress , and has important effects on the biosphere and surface hydrology .

[462] Ecosystem regime change inferred from the distribution of trace metals in Lake Erie sediments

Many freshwater and coastal marine ecosystems across the world may have undergone an ecosystem regime change due to a combination of rising anthropogenic disturbances and regional climate change .
Such a change in aquatic ecosystems is commonly seen as shifts in algal species .
But considerably less detail is known about the eutrophication history in terms of changes in algal productivity , particularly for a large lake with a great deal of spatial variability .
Here we present an analysis of trace metals ( Cu , Ni , Cd , and Pb ) on a sediment core recovered from Lake Erie , off the Vermilion coast of northern Ohio , USA , to reconstruct the eutrophication history of the lake over the past 210 years .
Following a slow eutrophication during European settlement , Lake Erie experienced a period of accelerated eutrophication , leading to an ecosystem regime transition into a eutrophic lake state in 1950 .
Our results suggested that the lake 's biological productivity has ever since maintained fairly high even though a significant input reduction was realized from rigorous nutrient abatements that began as early as in 1969 .
This work underscored the role of in-lake biogeochemical cycling in nutrient dynamics of this already eutrophic lake .

[463] Vulnerability of cloud forest reserves in Mexico to climate change

Tropical montane cloud forests are among the most vulnerable terrestrial ecosystems to climate change owing to their restricted climatic requirements and their narrow and fragmented distribution .
Although 12 % of Mexican cloud forest is protected , it is not known whether reserves will ensure the persistence of the ecosystem and its endemic species under climate change .
Here , we show that 68 % of Mexico 's cloud forest could vanish by 2080 because of climate change and more than 90 % of cloud forest that is protected at present will not be climatically suitable for that ecosystem in 2080 .
Moreover , if we assume unprotected forests are cleared , 99 % of the entire ecosystem could be lost through a combination of climate change and habitat loss , resulting in the extinction of about 70 % of endemic cloud forest vertebrate species .
Immediate action is required to minimize this loss -- expansion of the protected-area estate in areas of low climate vulnerability is an urgent priority .
Our analysis indicates that one key area for immediate protection is the Sierra de Juarez in Oaxaca .
This area supports many endemic species and is expected to retain relatively large fragments of cloud forest despite rapid climate change .

[464] A global strategy for road building

The number and extent of roads will expand dramatically this century .
Globally , at least 25 million kilometres of new roads are anticipated by 2050 ; a 60 % increase in the total length of roads over that in 2010 .
Nine-tenths of all road construction is expected to occur in developing nations , including many regions that sustain exceptional biodiversity and vital ecosystem services .
Roads penetrating into wilderness or frontier areas are a major proximate driver of habitat loss and fragmentation , wildfires , overhunting and other environmental degradation , often with irreversible impacts on ecosystems .
Unfortunately , much road proliferation is chaotic or poorly planned , and the rate of expansion is so great that it often overwhelms the capacity of environmental planners and managers .
Here we present a global scheme for prioritizing road building .
This large-scale zoning plan seeks to limit the environmental costs of road expansion while maximizing its benefits for human development , by helping to increase agricultural production , which is an urgent priority given that global food demand could double by mid-century .
Our analysis identifies areas with high environmental values where future road building should be avoided if possible , areas where strategic road improvements could promote agricultural development with relatively modest environmental costs , and ` conflict areas ' where road building could have sizeable benefits for agriculture but with serious environmental damage .
Our plan provides a template for proactively zoning and prioritizing roads during the most explosive era of road expansion in human history .

[465] Multiple mechanisms sustain a plant-animal facilitation on a coastal ecotone

Theory suggests that species distributions are expanded by positive species interactions , but the importance of facilitation in expanding species distributions at physiological range limits has not been widely recognized .
We investigated the effects of the nurse shrub Tamarix chinensis on the crab Helice tientsinensis on the terrestrial borders of salt marshes , a typical coastal ecotone , where Tamarix and Helice were on their lower and upper elevational distribution edges , respectively .
Crab burrows were abundant under Tamarix , but were absent in open areas between Tamarix .
Removing Tamarix decreased associated crab burrows with time , while simulating Tamarix in open areas by shading , excluding predators , and adding Tamarix branches as crab food , increased crab burrows .
Measurements of soil and microclimate factors showed that removing Tamarix increased abiotic stress , while simulating Tamarix by shading decreased abiotic stress .
Survival of tethered crabs was high only when protected from desiccation and predation .
Thus , by alleviating abiotic and biotic stresses , as well as by food provision , Tamarix expanded the upper intertidal distribution of Helice .
Our study provides clear evidence for the importance of facilitation in expanding species distributions at their range limits , and suggests that facilitation is a crucial biological force maintaining the ecotones between ecosystems .

[466] Boron isotope evidence for oceanic carbon dioxide leakage during the last deglaciation

Atmospheric CO2 fluctuations over glacial-interglacial cycles remain a major challenge to our understanding of the carbon cycle and the climate system .
Leading hypotheses put forward to explain glacial-interglacial atmospheric CO2 variations invoke changes in deep-ocean carbon storage , probably modulated by processes in the Southern Ocean , where much of the deep ocean is ventilated .
A central aspect of such models is that , during deglaciations , an isolated glacial deep-ocean carbon reservoir is reconnected with the atmosphere , driving the atmospheric CO2 rise observed in ice-core records .
However , direct documentation of changes in surface ocean carbon content and the associated transfer of carbon to the atmosphere during deglaciations has been hindered by the lack of proxy reconstructions that unambiguously reflect the oceanic carbonate system .
Radiocarbon activity tracks changes in ocean ventilation , but not in ocean carbon content , whereas proxies that record increased deglacial upwelling do not constrain the proportion of upwelled carbon that is degassed relative to that which is taken up by the biological pump .
Here we apply the boron isotope pH proxy in planktic foraminifera to two sediment cores from the sub-Antarctic Atlantic and the eastern equatorial Pacific as a more direct tracer of oceanic CO2 outgassing .
We show that surface waters at both locations , which partly derive from deep water upwelled in the Southern Ocean , became a significant source of carbon to the atmosphere during the last deglaciation , when the concentration of atmospheric CO2 was increasing .
This oceanic CO2 outgassing supports the view that the ventilation of a deep-ocean carbon reservoir in the Southern Ocean had a key role in the deglacial CO2 rise , although our results allow for the possibility that processes operating in other regions may also have been important for the glacial-interglacial ocean-atmosphere exchange of carbon .

[467] Recent decreases in fossil-fuel emissions of ethane and methane derived from firn air

Methane and ethane are the most abundant hydrocarbons in the atmosphere and they affect both atmospheric chemistry and climate .
Both gases are emitted from fossil fuels and biomass burning , whereas methane ( CH4 ) alone has large sources from wetlands , agriculture , landfills and waste water .
Here we use measurements in firn ( perennial snowpack ) air from Greenland and Antarctica to reconstruct the atmospheric variability of ethane ( C2H6 ) during the twentieth century .
Ethane levels rose from early in the century until the 1980s , when the trend reversed , with a period of decline over the next 20 years .
We find that this variability was primarily driven by changes in ethane emissions from fossil fuels ; these emissions peaked in the 1960s and 1970s at 14-16 teragrams per year ( 1 Tg = 1012 g ) and dropped to 8-10 Tg yr-1 by the turn of the century .
The reduction in fossil-fuel sources is probably related to changes in light hydrocarbon emissions associated with petroleum production and use .
The ethane-based fossil-fuel emission history is strikingly different from bottom-up estimates of methane emissions from fossil-fuel use , and implies that the fossil-fuel source of methane started to decline in the 1980s and probably caused the late twentieth century slow-down in the growth rate of atmospheric methane .

[468] Optimal CO2 mitigation under damage risk valuation

The current generation has to set mitigation policy under uncertainty about the economic consequences of climate change .
This uncertainty governs both the level of damages for a given level of warming , and the steepness of the increase in damage per warming degree .
Our model of climate and the economy is a stochastic version of a model employed in assessing the US Social Cost of Carbon ( DICE ) .
We compute the optimal carbon taxes and CO2 abatement levels that maximize welfare from economic consumption over time under different risk states .
In accordance with recent developments in finance , we separate preferences about time and risk to improve the model 's calibration of welfare to observed market interest .
We show that introducing the modern asset pricing framework doubles optimal abatement and carbon taxation .
Uncertainty over the level of damages at a given temperature increase can result in a slight increase of optimal emissions as compared to using expected damages .
In contrast , uncertainty governing the steepness of the damage increase in temperature results in a substantially higher level of optimal mitigation .

[469] Climate change affects key nitrogen-fixing bacterial populations on coral reefs

Coral reefs are at serious risk due to events associated with global climate change .
Elevated ocean temperatures have unpredictable consequences for the ocean 's biogeochemical cycles .
The nitrogen cycle is driven by complex microbial transformations , including nitrogen fixation .
This study investigated the effects of increased seawater temperature on bacteria able to fix nitrogen ( diazotrophs ) that live in association with the mussid coral Mussismilia harttii .
Consistent increases in diazotroph abundances and diversities were found at increased temperatures .
Moreover , gradual shifts in the dominance of particular diazotroph populations occurred as temperature increased , indicating a potential future scenario of climate change .
The temperature-sensitive diazotrophs may provide useful bioindicators of the effects of thermal stress on coral reef health , allowing the impact of thermal anomalies to be monitored .
In addition , our findings support the development of research on different strategies to improve the fitness of corals during events of thermal stress , such as augmentation with specific diazotrophs .

[470] Three keys to the radiation of angiosperms into freezing environments

Early flowering plants are thought to have been woody species restricted to warm habitats .
This lineage has since radiated into almost every climate , with manifold growth forms .
As angiosperms spread and climate changed , they evolved mechanisms to cope with episodic freezing .
To explore the evolution of traits underpinning the ability to persist in freezing conditions , we assembled a large species-level database of growth habit ( woody or herbaceous ; 49,064 species ) , as well as leaf phenology ( evergreen or deciduous ) , diameter of hydraulic conduits ( that is , xylem vessels and tracheids ) and climate occupancies ( exposure to freezing ) .
To model the evolution of species ' traits and climate occupancies , we combined these data with an unparalleled dated molecular phylogeny ( 32,223 species ) for land plants .
Here we show that woody clades successfully moved into freezing-prone environments by either possessing transport networks of small safe conduits and/or shutting down hydraulic function by dropping leaves during freezing .
Herbaceous species largely avoided freezing periods by senescing cheaply constructed aboveground tissue .
Growth habit has long been considered labile , but we find that growth habit was less labile than climate occupancy .
Additionally , freezing environments were largely filled by lineages that had already become herbs or , when remaining woody , already had small conduits ( that is , the trait evolved before the climate occupancy ) .
By contrast , most deciduous woody lineages had an evolutionary shift to seasonally shedding their leaves only after exposure to freezing ( that is , the climate occupancy evolved before the trait ) .
For angiosperms to inhabit novel cold environments they had to gain new structural and functional trait solutions ; our results suggest that many of these solutions were probably acquired before their foray into the cold .

[471] Effects of agricultural land use on the composition of fluvial dissolved organic matter

Nearly 40 % of the Earth 's ice-free surface area is cropland or pasture .
Agricultural land use can increase the delivery of nutrients such as nitrogen and phosphorus to fluvial ecosystems , but the impact of farming on riverine dissolved organic carbon is still largely unknown , despite increasing recognition that rivers act as important modifiers in the global carbon cycle .
Here , we examine the character of riverine dissolved organic matter in 34 watersheds along a gradient of agricultural land use .
We show that changes in the character of dissolved organic matter are related to agricultural land use , nitrogen loading and wetland loss .
Specifically , we find that the structural complexity of dissolved organic matter decreases as the ratio of continuous croplands to wetlands increases .
At the same time , the amount of microbially derived dissolved organic matter increases with greater agricultural land use .
Furthermore , we find that periods of soil dryness are associated with a decrease in the structural complexity of dissolved organic matter .
We suggest that these effects of land use and climate on the character of riverine dissolved organic matter have important implications for global carbon cycling , owing to their potential to control rates of microbial carbon processing ( for example , uptake , retention and outgassing ) in agricultural systems .

[472] Increase in tropospheric nitrogen dioxide over China observed from space

Emissions from fossil fuel combustion and biomass burning reduce local air quality and affect global tropospheric chemistry .
Nitrogen oxides are emitted by all combustion processes and play a key part in the photochemically induced catalytic production of ozone , which results in summer smog and has increased levels of tropospheric ozone globally .
Release of nitrogen oxide also results in nitric acid deposition , and -- at least locally -- increases radiative forcing effects due to the absorption of downward propagating visible light .
Nitrogen oxide concentrations in many industrialized countries are expected to decrease , but rapid economic development has the potential to increase significantly the emissions of nitrogen oxides in parts of Asia .
Here we present the tropospheric column amounts of nitrogen dioxide retrieved from two satellite instruments GOME and SCIAMACHY over the years 1996-2004 .
We find substantial reductions in nitrogen dioxide concentrations over some areas of Europe and the USA , but a highly significant increase of about 50 per cent -- with an accelerating trend in annual growth rate -- over the industrial areas of China , more than recent bottom-up inventories suggest .

[473] Limited forcing of glacier loss through land-cover change on Kilimanjaro

Global climate change is primarily linked to changes in greenhouse gases , but land-cover change ( LCC ) has increasingly been recognized as another forcing on the regional scale .
The related effects on alpine glaciers are , however , not yet known .
Here we present the first quantification of the contribution of LCC-driven atmospheric change to glacier mass loss , illustrated by the well-studied case of Kilimanjaro in tropical Africa .
We employ a novel multi-scale modelling approach , which links atmospheric dynamics and local glacier mass balance in a fully physical way and is validated by in situ measurements .
Using different model settings , this shows that local LCC since the 1970s has contributed 7 + / -6 % ( 17 + / -12 % ) to mass loss of a southern slope glacier in the dry ( wet ) season , but this effect could reverse in the other mountain sectors and also decrease glacier mass loss .
Thus , for the moment , the hypothesis that local LCC is another forcing of glacier loss on Kilimanjaro can not be corroborated .
More generally , our results indicate that the impact of local LCC on mountain glaciers is constrained by regional circulation ( moisture trajectories ) , altitude ( distance to forest ) , and outside the tropics by precipitation mechanisms ( frontal systems ) .
We therefore argue that attribution of glacier change and variability to large-scale climate dynamics is unlikely to be distorted by local LCC .

[474] Temperature-associated increases in the global soil respiration record

Soil respiration , RS , the flux of microbially and plant-respired carbon dioxide ( CO2 ) from the soil surface to the atmosphere , is the second-largest terrestrial carbon flux .
However , the dynamics of RS are not well understood and the global flux remains poorly constrained .
Ecosystem warming experiments , modelling analyses and fundamental biokinetics all suggest that RS should change with climate .
This has been difficult to confirm observationally because of the high spatial variability of RS , inaccessibility of the soil medium and the inability of remote-sensing instruments to measure RS on large scales .
Despite these constraints , it may be possible to discern climate-driven changes in regional or global RS values in the extant four-decade record of RS chamber measurements .
Here we construct a database of worldwide RS observations matched with high-resolution historical climate data and find a previously unknown temporal trend in the RS record after accounting for mean annual climate , leaf area , nitrogen deposition and changes in CO2 measurement technique .
We find that the air temperature anomaly ( the deviation from the 1961-1990 mean ) is significantly and positively correlated with changes in RS .
We estimate that the global RS in 2008 ( that is , the flux integrated over the Earth 's land surface over 2008 ) was 98 + / - 12 Pg C and that it increased by 0.1 Pg C yr-1 between 1989 and 2008 , implying a global RS response to air temperature ( Q10 ) of 1.5 .
An increasing global RS value does not necessarily constitute a positive feedback to the atmosphere , as it could be driven by higher carbon inputs to soil rather than by mobilization of stored older carbon .
The available data are , however , consistent with an acceleration of the terrestrial carbon cycle in response to global climate change .

[475] Changes in fisheries discard rates and seabird communities

It is clear that discards from commercial fisheries are a key food resource for many seabird species around the world .
But predicting the response of seabird communities to changes in discard rates is problematic and requires historical data to elucidate the confounding effects of other , more ` natural ' ecological processes .
In the North Sea , declining stocks , changes in technical measures , changes in population structure and the establishment of a recovery programme for cod ( Gadus morhua ) will alter the amount of fish discarded .
This region also supports internationally important populations of seabirds , some of which feed extensively , but facultatively , on discards , in particular on undersized haddock ( Melanogrammus aeglefinus ) and whiting ( Merlangius merlangus ) .
Here we use long-term data sets from the northern North Sea to show that there is a direct link between discard availability and discard use by a generalist predator and scavenger -- the great skua ( Stercorarius skua ) .
Reduced rates of discarding , particularly when coupled with reduced availability of small shoaling pelagic fish such as sandeel ( Ammodytes marinus ) , result in an increase in predation by great skuas on other birds .
This switching of prey by a facultative scavenger presents a potentially serious threat to some seabird communities .

[476] Projections of seasonal patterns in temperature - related deaths for Manhattan , New York

Global average temperatures have been rising for the past half-century , and the warming trend has accelerated in recent decades .
Further warming is expected over the next few decades , with significant regional variations .
These warming trends will probably result in more frequent , intense and persistent periods of hot temperatures in summer , and generally higher temperatures in winter .
Daily death counts in cities increase markedly when temperatures reach levels that are very high relative to what is normal in a given location .
Relatively cold temperatures also seem to carry risk .
Rising temperatures may result in more heat-related mortality but may also reduce cold-related mortality , and the net impact on annual mortality remains uncertain .
Here we use 16 downscaled global climate models and two emissions scenarios to estimate present and future seasonal patterns in temperature-related mortality in Manhattan , New York .
All 32 projections yielded warm-season increases and cold-season decreases in temperature-related mortality , with positive net annual temperature-related deaths in all cases .
Monthly analyses showed that the largest percentage increases may occur in May and September .
These results suggest that , over a range of models and scenarios of future greenhouse gas emissions , increases in heat-related mortality could outweigh reductions in cold-related mortality , with shifting seasonal patterns .

[477] The search for signs of recovery of the ozone layer

Evidence of mid-latitude ozone depletion and proof that the Antarctic ozone hole was caused by humans spurred policy makers from the late 1980s onwards to ratify the Montreal Protocol and subsequent treaties , legislating for reduced production of ozone-depleting substances .
The case of anthropogenic ozone loss has often been cited since as a success story of international agreements in the regulation of environmental pollution .
Although recent data suggest that total column ozone abundances have at least not decreased over the past eight years for most of the world , it is still uncertain whether this improvement is actually attributable to the observed decline in the amount of ozone-depleting substances in the Earth 's atmosphere .
The high natural variability in ozone abundances , due in part to the solar cycle as well as changes in transport and temperature , could override the relatively small changes expected from the recent decrease in ozone-depleting substances .
Whatever the benefits of the Montreal agreement , recovery of ozone is likely to occur in a different atmospheric environment , with changes expected in atmospheric transport , temperature and important trace gases .
It is therefore unlikely that ozone will stabilize at levels observed before 1980 , when a decline in ozone concentrations was first observed .

[478] Climate-induced range contraction drives genetic erosion in an alpine mammal

Increasing documentation of changes in the distribution of species provides evidence of climate change impacts , yet surprisingly little empirical work has endeavoured to quantify how such recent and rapid changes impact genetic diversity .
Here we compare modern and historical specimens spanning a century to quantify the population genetic effects of a climate-driven elevational range contraction in the alpine chipmunk , Tamias alpinus , in Yosemite National Park , USA .
Previous work showed that T. alpinus responded to warming in the park by retracting its lower elevational limit upslope by more than 500 m , whereas the closely related chipmunk T. speciosus remained stable .
Consistent with a reduced and more fragmented range , we found a decline in overall genetic diversity and increased genetic subdivision in T. alpinus .
In contrast , there were no significant genetic changes in T. speciosus over the same time period .
This study demonstrates genetic erosion accompanying a climate-induced range reduction and points to decreasing size and increasing fragmentation of montane populations as a result of global warming .

[479] Rapid transgenerational acclimation of a tropical reef fish to climate change

Understanding the capacity of species to acclimate and adapt to expected temperature increases is critical for making predictions about the biological impacts of global warming , yet it is one of the least certain aspects of climate change science .
Tropical species are considered to be especially sensitive to climate change because they live close to their thermal maximum and exhibit limited capacity for acclimation .
Here , we demonstrate that a tropical reef fish is highly sensitive to small increases in water temperature , but can rapidly acclimate over multiple generations .
Acute exposure to elevated temperatures ( +1.5 degreesC and +3.0 degreesC ) predicted to occur this century caused a 15 % and 30 % respective decrease in individual 's maximum ability to perform aerobic activities such as swimming or foraging , known as aerobic scope .
However , complete compensation in aerobic scope occurred when both parents and offspring were reared throughout their lives at elevated temperature .
Such acclimation could reduce the impact of warming temperatures and allow populations to persist across their current range .
This study reveals the importance of transgenerational acclimation as a mechanism for coping with rapid climate change and highlights that single generation studies risk underestimating the potential of species to cope .

[480] Changes in plant community composition lag behind climate warming in lowland forests

Climate change is driving latitudinal and altitudinal shifts in species distribution worldwide , leading to novel species assemblages .
Lags between these biotic responses and contemporary climate changes have been reported for plants and animals .
Theoretically , the magnitude of these lags should be greatest in lowland areas , where the velocity of climate change is expected to be much greater than that in highland areas .
We compared temperature trends to temperatures reconstructed from plant assemblages ( observed in 76,634 surveys ) over a 44-year period in France ( 1965-2008 ) .
Here we report that forest plant communities had responded to 0.54 degreesC of the effective increase of 1.07 degreesC in highland areas ( 500-2 ,600 m above sea level ) , while they had responded to only 0.02 degreesC of the 1.11 degreesC warming trend in lowland areas .
There was a larger temperature lag ( by 3.1 times ) between the climate and plant community composition in lowland forests than in highland forests .
The explanation of such disparity lies in the following properties of lowland , as compared to highland , forests : the higher proportion of species with greater ability for local persistence as the climate warms , the reduced opportunity for short-distance escapes , and the greater habitat fragmentation .
Although mountains are currently considered to be among the ecosystems most threatened by climate change ( owing to mountaintop extinction ) , the current inertia of plant communities in lowland forests should also be noted , as it could lead to lowland biotic attrition .

[481] Climate-driven changes to the atmospheric CO2 sink in the subtropical North Pacific Ocean

The oceans represent a significant sink for atmospheric carbon dioxide .
Variability in the strength of this sink occurs on interannual timescales , as a result of regional and basin-scale changes in the physical and biological parameters that control the flux of this greenhouse gas into and out of the surface mixed layer .
Here we analyse a 13-year time series of oceanic carbon dioxide measurements from station ALOHA in the subtropical North Pacific Ocean near Hawaii , and find a significant decrease in the strength of the carbon dioxide sink over the period 1989-2001 .
We show that much of this reduction in sink strength can be attributed to an increase in the partial pressure of surface ocean carbon dioxide caused by excess evaporation and the accompanying concentration of solutes in the water mass .
Our results suggest that carbon dioxide uptake by ocean waters can be strongly influenced by changes in regional precipitation and evaporation patterns brought on by climate variability .

[482] Effects of biodiversity on the functioning of trophic groups and ecosystems

Over the past decade , accelerating rates of species extinction have prompted an increasing number of studies to reduce species diversity experimentally and examine how this alters the efficiency by which communities capture resources and convert those into biomass .
So far , the generality of patterns and processes observed in individual studies have been the subjects of considerable debate .
Here we present a formal meta-analysis of studies that have experimentally manipulated species diversity to examine how it affects the functioning of numerous trophic groups in multiple types of ecosystem .
We show that the average effect of decreasing species richness is to decrease the abundance or biomass of the focal trophic group , leading to less complete depletion of resources used by that group .
At the same time , analyses reveal that the standing stock of , and resource depletion by , the most species-rich polyculture tends to be no different from that of the single most productive species used in an experiment .
Of the known mechanisms that might explain these trends , results are most consistent with what is called the ` sampling effect ' , which occurs when diverse communities are more likely to contain and become dominated by the most productive species .
Whether this mechanism is widespread in natural communities is currently controversial .
Patterns we report are remarkably consistent for four different trophic groups ( producers , herbivores , detritivores and predators ) and two major ecosystem types ( aquatic and terrestrial ) .
Collectively , our analyses suggest that the average species loss does indeed affect the functioning of a wide variety of organisms and ecosystems , but the magnitude of these effects is ultimately determined by the identity of species that are going extinct .

[483] Allowable carbon emissions lowered by multiple climate targets

Climate targets are designed to inform policies that would limit the magnitude and impacts of climate change caused by anthropogenic emissions of greenhouse gases and other substances .
The target that is currently recognized by most world governments places a limit of two degrees Celsius on the global mean warming since preindustrial times .
This would require large sustained reductions in carbon dioxide emissions during the twenty-first century and beyond .
Such a global temperature target , however , is not sufficient to control many other quantities , such as transient sea level rise , ocean acidification and net primary production on land .
Here , using an Earth system model of intermediate complexity ( EMIC ) in an observation-informed Bayesian approach , we show that allowable carbon emissions are substantially reduced when multiple climate targets are set .
We take into account uncertainties in physical and carbon cycle model parameters , radiative efficiencies , climate sensitivity and carbon cycle feedbacks along with a large set of observational constraints .
Within this framework , we explore a broad range of economically feasible greenhouse gas scenarios from the integrated assessment community to determine the likelihood of meeting a combination of specific global and regional targets under various assumptions .
For any given likelihood of meeting a set of such targets , the allowable cumulative emissions are greatly reduced from those inferred from the temperature target alone .
Therefore , temperature targets alone are unable to comprehensively limit the risks from anthropogenic emissions .

[484] Influence of Atlantic meridional overturning circulation on the East Asian winter monsoon

The last glacial period was characterized by abrupt , millennial-scale climate change .
These climate fluctuations are particularly pronounced in records of the East Asian monsoon system , and seem to be linked to changes in North Atlantic circulation .
Here we present records of grain size variations from the northwestern Chinese Loess Plateau , dated using optically stimulated luminescence .
We reconstruct changes in the strength of the East Asian winter monsoon over the past 60,000 years and find reconstructed millennial-scale variations that are broadly correlated with temperature variations over Greenland , suggesting a common forcing .
We investigate the effect of a slow-down of Atlantic meridional overturning circulation on the monsoon system using a coupled climate model simulation with added freshwater flux into the northern North Atlantic , and find a strengthening winter monsoon circulation over the regions that supply dust to the Loess Plateau and a reduction in summer monsoon precipitation over East Asia .
We conclude that Atlantic meridional overturning circulation is a driver of abrupt change in the East Asian winter and summer monsoon systems , and that the northern westerlies play a role in transmitting this signal from the North Atlantic to the Asian monsoon regions .

[485] Northern Hemisphere forcing of Southern Hemisphere climate during the last deglaciation

According to the Milankovitch theory , changes in summer insolation in the high-latitude Northern Hemisphere caused glacial cycles through their impact on ice-sheet mass balance .
Statistical analyses of long climate records supported this theory , but they also posed a substantial challenge by showing that changes in Southern Hemisphere climate were in phase with or led those in the north .
Although an orbitally forced Northern Hemisphere signal may have been transmitted to the Southern Hemisphere , insolation forcing can also directly influence local Southern Hemisphere climate , potentially intensified by sea-ice feedback , suggesting that the hemispheres may have responded independently to different aspects of orbital forcing .
Signal processing of climate records can not distinguish between these conditions , however , because the proposed insolation forcings share essentially identical variability .
Here we use transient simulations with a coupled atmosphere-ocean general circulation model to identify the impacts of forcing from changes in orbits , atmospheric CO2 concentration , ice sheets and the Atlantic meridional overturning circulation ( AMOC ) on hemispheric temperatures during the first half of the last deglaciation ( 22-14 .3 kyr bp ) .
Although based on a single model , our transient simulation with only orbital changes supports the Milankovitch theory in showing that the last deglaciation was initiated by rising insolation during spring and summer in the mid-latitude to high-latitude Northern Hemisphere and by terrestrial snow-albedo feedback .
The simulation with all forcings best reproduces the timing and magnitude of surface temperature evolution in the Southern Hemisphere in deglacial proxy records .
AMOC changes associated with an orbitally induced retreat of Northern Hemisphere ice sheets is the most plausible explanation for the early Southern Hemisphere deglacial warming and its lead over Northern Hemisphere temperature ; the ensuing rise in atmospheric CO2 concentration provided the critical feedback on global deglaciation .

[486] Geographical limits to species-range shifts are suggested by climate velocity

The reorganization of patterns of species diversity driven by anthropogenic climate change , and the consequences for humans , are not yet fully understood or appreciated .
Nevertheless , changes in climate conditions are useful for predicting shifts in species distributions at global and local scales .
Here we use the velocity of climate change to derive spatial trajectories for climatic niches from 1960 to 2009 ( ref .
7 ) and from 2006 to 2100 , and use the properties of these trajectories to infer changes in species distributions .
Coastlines act as barriers and locally cooler areas act as attractors for trajectories , creating source and sink areas for local climatic conditions .
Climate source areas indicate where locally novel conditions are not connected to areas where similar climates previously occurred , and are thereby inaccessible to climate migrants tracking isotherms : 16 % of global surface area for 1960 to 2009 , and 34 % of ocean for the ` business as usual ' climate scenario ( representative concentration pathway ( RCP ) 8.5 ) representing continued use of fossil fuels without mitigation .
Climate sink areas are where climate conditions locally disappear , potentially blocking the movement of climate migrants .
Sink areas comprise 1.0 % of ocean area and 3.6 % of land and are prevalent on coasts and high ground .
Using this approach to infer shifts in species distributions gives global and regional maps of the expected direction and rate of shifts of climate migrants , and suggests areas of potential loss of species richness .

[487] Present and future trends in the atmospheric burden of ozone-depleting halogens

The burden of ozone-depleting chemicals in the lower atmosphere has been decreasing since 1994 as a result of the Montreal Protocol .
Here we show how individual chemicals have influenced this decline , in order to estimate how the burden could change in the near future .
Our measurements of atmospheric concentrations of the persistent , anthropogenic chemicals that account for most ozone-depleting halogens in today 's stratosphere show that the decline stems predominantly from the decrease in the atmospheric load of trichloroethane ( CH3CCl3 ) , a previously common cleaning solvent .
The influence of this chemical on the decline has now peaked , however , and will become much smaller over the next five to ten years .
As this influence lessens , a decrease in theburden of ozone-depleting halogen will be sustained only if emissions of other halocarbons fall .
Although emissions of most gases regulated by the Montreal Protocol have decreased substantially over the past ten years ( refs 4 ) , emissions of the potent ozone-depleting gas CBrClF2 ( halon-1211 ) have remained fairly constant during this period , despite stringent limits on production in developed countries since 1994 .
The consequent atmospheric accumulation of this halon is retarding the decline of ozone-depleting halogens in the atmosphere more than any other persistent gas .

[488] Increased insolation threshold for runaway greenhouse processes on Earth-like planets

The increase in solar luminosity over geological timescales should warm the Earth 's climate , increasing water evaporation , which will in turn enhance the atmospheric greenhouse effect .
Above a certain critical insolation , this destabilizing greenhouse feedback can ` run away ' until the oceans have completely evaporated .
Through increases in stratospheric humidity , warming may also cause evaporative loss of the oceans to space before the runaway greenhouse state occurs .
The critical insolation thresholds for these processes , however , remain uncertain because they have so far been evaluated using one-dimensional models that can not account for the dynamical and cloud feedback effects that are key stabilizing features of the Earth 's climate .
Here we use a three-dimensional global climate model to show that the insolation threshold for the runaway greenhouse state to occur is about 375 W m-2 , which is significantly higher than previously thought .
Our model is specifically developed to quantify the climate response of Earth-like planets to increased insolation in hot and extremely moist atmospheres .
In contrast with previous studies , we find that clouds have a destabilizing feedback effect on the long-term warming .
However , subsident , unsaturated regions created by the Hadley circulation have a stabilizing effect that is strong enough to shift the runaway greenhouse limit to higher values of insolation than are inferred from one-dimensional models .
Furthermore , because of wavelength-dependent radiative effects , the stratosphere remains sufficiently cold and dry to hamper the escape of atmospheric water , even at large fluxes .
This has strong implications for the possibility of liquid water existing on Venus early in its history , and extends the size of the habitable zone around other stars .

[489] Soil fertility limits carbon sequestration by forest ecosystems in a CO2-enriched atmosphere

Northern mid-latitude forests are a large terrestrial carbon sink .
Ignoring nutrient limitations , large increases in carbon sequestration from carbon dioxide ( CO2 ) fertilization are expected in these forests .
Yet , forests are usually relegated to sites of moderate to poor fertility , where tree growth is often limited by nutrient supply , in particular nitrogen .
Here we present evidence that estimates of increases in carbon sequestration of forests , which is expected to partially compensate for increasing CO2 in the atmosphere , are unduly optimistic .
In two forest experiments on maturing pines exposed to elevated atmospheric CO2 , the CO2-induced biomass carbon increment without added nutrients was undetectable at a nutritionally poor site , and the stimulation at a nutritionally moderate site was transient , stabilizing at a marginal gain after three years .
However , a large synergistic gain from higher CO2 and nutrients was detected with nutrients added .
This gain was even larger at the poor site ( threefold higher than the expected additive effect ) than at the moderate site ( twofold higher ) .
Thus , fertility can restrain the response of wood carbon sequestration to increased atmospheric CO2 .
Assessment of future carbon sequestration should consider the limitations imposed by soil fertility , as well as interactions with nitrogen deposition .

[490] Intense hurricane activity over the past 5,000 years controlled by El Nino and the West African monsoon

The processes that control the formation , intensity and track of hurricanes are poorly understood .
It has been proposed that an increase in sea surface temperatures caused by anthropogenic climate change has led to an increase in the frequency of intense tropical cyclones , but this proposal has been challenged on the basis that the instrumental record is too short and unreliable to reveal trends in intense tropical cyclone activity .
Storm-induced deposits preserved in the sediments of coastal lagoons offer the opportunity to study the links between climatic conditions and hurricane activity on longer timescales , because they provide centennial - to millennial-scale records of past hurricane landfalls .
Here we present a record of intense hurricane activity in the western North Atlantic Ocean over the past 5,000 years based on sediment cores from a Caribbean lagoon that contain coarse-grained deposits associated with intense hurricane landfalls .
The record indicates that the frequency of intense hurricane landfalls has varied on centennial to millennial scales over this interval .
Comparison of the sediment record with palaeo-climate records indicates that this variability was probably modulated by atmospheric dynamics associated with variations in the El Nino/Southern Oscillation and the strength of the West African monsoon , and suggests that sea surface temperatures as high as at present are not necessary to support intervals of frequent intense hurricanes .
To accurately predict changes in intense hurricane activity , it is therefore important to understand how the El Nino/Southern Oscillation and the West African monsoon will respond to future climate change .

[491] Effect of the formation of the Isthmus of Panama on Atlantic Ocean thermohaline circulation

The Late Cenozoic closure of the seaway between the North andSouth American continents is thought to have caused extensive changes in ocean circulation and Northern Hemisphere climate .
But the timing and consequences of the emergence of the Isthmus of Panama , which closed the seaway , remain controversial .
Here we present stable-isotope and carbonate sand-fraction records from Caribbean sediments which , when compared to Atlantic and Pacific palaeoceanographic records , indicate that the closure caused a marked reorganization of ocean circulation starting 4.6 million years ago .
Shallowing of the seaway intensified the Gulf Stream and introduced warm and saline water masses to high northern latitudes .
These changes strengthened deep-water formation in the Labrador Sea over the next million years -- as indicated by an increased deep-water ventilation and carbonate preservation in the Caribbean Sea -- and favoured early Pliocene warming of the Northern Hemisphere .
The evaporative cooling of surface waters during North Atlantic Deep Water formation would have introduced moisture to the Northern Hemisphere .
Although the pronounced intensification of Northern Hemisphere glaciation between 3.1 and 2.5 million years ago substantially lagged the full development of North Atlantic Deep Water formation , we propose that the increased atmospheric moisture content was a necessary precondition for ice-sheet growth , which was then triggered by the incremental changes in the Earth 's orbital obliquity .

[492] Increased productivity in the subantarctic ocean during Heinrich events

Massive iceberg discharges from the Northern Hemisphere ice sheets , ` Heinrich events ' , coincided with the coldest periods of the last ice age .
There is widespread evidence for Heinrich events and their profound impact on the climate and circulation of the North Atlantic Ocean , but their influence beyond that region remains uncertain .
Here we use a combination of molecular fingerprints of algal productivity and radioisotope tracers of sedimentation to document eight periods of increased productivity in the subpolar Southern Ocean during the past 70,000 years that occurred within 1,000-2 ,000 years of a Northern Hemisphere Heinrich event .
We discuss possible causes for such a link , including increased supply of iron from upwelling and increased stratification during the growing season , which imply an alteration of the global ocean circulation during Heinrich events .
The mechanisms linking North Atlantic iceberg discharges with subantarctic productivity remain unclear at this point .
We suggest that understanding how the Southern Ocean was altered during these extreme climate perturbations is critical to understanding the role of the ocean in climate change .

[493] Summer-time climate impacts of projected megapolitan expansion in Arizona

Efforts characterizing the changing climate of southwestern North America by focusing exclusively on the impacts of increasing levels of long-lived greenhouse gases omit fundamental elements with similar order-of-magnitude impacts as those owing to large-scale climate change .
Using a suite of ensemble-based , multiyear simulations , here we show the intensification of observationally based urban-induced phenomena and demonstrate that the direct summer-time climate effects of the most rapidly expanding megapolitan region in the USA -- Arizona 's Sun Corridor -- are considerable .
Although urban-induced warming approaches 4 degreesC locally for the maximum expansion scenario , impacts depend on the particular trajectory of development .
Cool-roof implementation reduces simulated warming by about 50 % , yet decreases in summer-time evapotranspiration remain at least as large as those from urban expansion without this mode of adaptation .
The contribution of urban-induced warming relative to mid - and end-of-century climate change illustrates strong dependence on built environment expansion scenarios and emissions pathways .
Our results highlight the direct climate impacts that result from newly emerging megapolitan regions and their significance for overcoming present challenges concerning sustainable development .

[494] Occurrence and persistence of future atmospheric stagnation events

Poor air quality causes an estimated 2.6-4 .4 million premature deaths per year .
Hazardous conditions form when meteorological components allow the accumulation of pollutants in the near-surface atmosphere .
Global-warming-driven changes to atmospheric circulation and the hydrological cycle are expected to alter the meteorological components that control pollutant build-up and dispersal , but the magnitude , direction , geographic footprint and public health impact of this alteration remain unclear .
We used an air stagnation index and an ensemble of bias-corrected climate model simulations to quantify the response of stagnation occurrence and persistence to global warming .
Our analysis projects increases in stagnation occurrence that cover 55 % of the current global population , with areas of increase affecting ten times more people than areas of decrease .
By the late twenty-first century , robust increases of up to 40 days per year are projected throughout the majority of the tropics and subtropics , as well as within isolated mid-latitude regions .
Potential impacts over India , Mexico and the western US are particularly acute owing to the intersection of large populations and increases in the persistence of stagnation events , including those of extreme duration .
These results indicate that anthropogenic climate change is likely to alter the level of pollutant management required to meet future air quality targets .

[495] Increased soil emissions of potent greenhouse gases under increased atmospheric CO2

Increasing concentrations of atmospheric carbon dioxide ( CO2 ) can affect biotic and abiotic conditions in soil , such as microbial activity and water content .
In turn , these changes might be expected to alter the production and consumption of the important greenhouse gases nitrous oxide ( N2O ) and methane ( CH4 ) ( refs 2 , 3 ) .
However , studies on fluxes of N2O and CH4 from soil under increased atmospheric CO2 have not been quantitatively synthesized .
Here we show , using meta-analysis , that increased CO2 ( ranging from 463 to 780 parts per million by volume ) stimulates both N2O emissions from upland soils and CH4 emissions from rice paddies and natural wetlands .
Because enhanced greenhouse-gas emissions add to the radiative forcing of terrestrial ecosystems , these emissions are expected to negate at least 16.6 per cent of the climate change mitigation potential previously predicted from an increase in the terrestrial carbon sink under increased atmospheric CO2 concentrations .
Our results therefore suggest that the capacity of land ecosystems to slow climate warming has been overestimated .

[496] Patterns of the seasonal response of tropical rainfall to global warming

Tropical convection is an important factor in regional climate variability and change around the globe .
The response of regional precipitation to global warming is spatially variable , and state-of-the-art model projections suffer large uncertainties in the geographic distribution of precipitation changes .
Two views exist regarding tropical rainfall change : one predicts increased rainfall in presently rainy regions ( wet-get-wetter ) , and the other suggests increased rainfall where the rise in sea surface temperature exceeds the mean surface warming in the tropics ( warmer-get-wetter ) .
Here we analyse simulations with 18 models from the Coupled Model Intercomparison Project ( CMIP5 ) , and present a unifying view for seasonal rainfall change .
We find that the pattern of ocean warming induces ascending atmospheric flow at the Equator and subsidence on the flanks , anchoring a band of annual mean rainfall increase near the Equator that reflects the warmer-get-wetter view .
However , this climatological ascending motion marches back and forth across the Equator with the Sun , pumping moisture upwards from the boundary layer and causing seasonal rainfall anomalies to follow a wet-get-wetter pattern .
The seasonal mean rainfall , which is the sum of the annual mean and seasonal anomalies , thus combines the wet-get-wetter and warmer-get-wetter trends .
Given that precipitation climatology is well observed whereas the pattern of ocean surface warming is poorly constrained , our results suggest that projections of tropical seasonal mean rainfall are more reliable than the annual mean .

[497] Human land-use-driven reduction of forest volatiles cools global climate

Human conversion of forest ecosystems to agriculture is a major driver of global change .
Conventionally , the impacts of the historical cropland expansion on Earth 's radiation balance have been quantified through two opposing effects : the release of stored carbon to the atmosphere as CO2 ( warming ) versus the increase in surface albedo ( cooling ) .
Changing forest cover has a third effect on the global radiation balance by altering emissions of biogenic volatile organic compounds ( BVOCs ) that control the loadings of multiple warming and cooling climate pollutants : tropospheric ozone ( O3 ) , methane ( CH4 ) and aerosols .
Although human land cover change has dominated BVOC emission variability over the past century , the net effect on global climate has not been quantified .
Here , I show that the effects of the global cropland expansion between the 1850s and 2000s on BVOC emissions and atmospheric chemistry have imposed an additional net global radiative impact of -0.11 + / - 0.17 W m-2 ( cooling ) .
This magnitude is comparable to that of the surface albedo and land carbon release effects .
I conclude that atmospheric chemistry must be considered in climate impact assessments of anthropogenic land cover change and in forestry for climate protection strategies .

[498] Advancing plant phenology and reduced herbivore production in a terrestrial system associated with sea ice decline

The contribution of declining Arctic sea ice to warming in the region through Arctic amplification suggests that sea ice decline has the potential to influence ecological dynamics in terrestrial Arctic systems .
Empirical evidence for such effects is limited , however , particularly at the local population and community levels .
Here we identify an Arctic sea ice signal in the annual timing of vegetation emergence at an inland tundra system in West Greenland .
According to the time series analyses presented here , an ongoing advance in plant phenology at this site is attributable to the accelerating decline in Arctic sea ice , and contributes to declining large herbivore reproductive performance via trophic mismatch .
Arctic-wide sea ice metrics consistently outperform other regional and local abiotic variables in models characterizing these dynamics , implicating large-scale Arctic sea ice decline as a potentially important , albeit indirect , contributor to local-scale ecological dynamics on land .

[499] Vigorous exchange between the Indian and Atlantic oceans at the end of the past five glacial periods

The magnitude of heat and salt transfer between the Indian and Atlantic oceans through ` Agulhas leakage ' is considered important for balancing the global thermohaline circulation .
Increases or reductions of this leakage lead to strengthening or weakening of the Atlantic meridional overturning and associated variation of North Atlantic Deep Water formation .
Here we show that modern Agulhas waters , which migrate into the south Atlantic Ocean in the form of an Agulhas ring , contain a characteristic assemblage of planktic foraminifera .
We use this assemblage as a modern analogue to investigate the Agulhas leakage history over the past 550,000 years from a sediment record in the Cape basin .
Our reconstruction indicates that Indian-Atlantic water exchange was highly variable : enhanced during present and past interglacials and largely reduced during glacial intervals .
Coherent variability of Agulhas leakage with northern summer insolation suggests a teleconnection to the monsoon system .
The onset of increased Agulhas leakage during late glacial conditions took place when glacial ice volume was maximal , suggesting a crucial role for Agulhas leakage in glacial terminations , timing of interhemispheric climate change and the resulting resumption of the Atlantic meridional overturning circulation .

[500] Increasing eolian dust deposition in the western United States linked to human activity

Mineral aerosols from dust are an important influence on climate and on marine and terrestrial biogeochemical cycles .
These aerosols are generated from wind erosion of surface soils .
The amount of dust emission can therefore be affected by human activities that alter surface sediments .
However , changes in regional - and global-scale dust fluxes following the rapid expansion of human populations and settlements over the past two centuries are not well understood .
Here we determine the accumulation rates and geochemical properties of alpine lake sediments from the western interior United States for the past 5,000 years .
We find that dust load levels increased by 500 % above the late Holocene average following the increased western settlement of the United States during the nineteenth century .
We suggest that the increased dust deposition is caused by the expansion of livestock grazing in the early twentieth century .
The larger dust flux , which persists into the early twenty-first century , results in a more than fivefold increase in inputs of K , Mg , Ca , N and P to the alpine ecosystems , with implications for surface-water alkalinity , aquatic productivity and terrestrial nutrient cycling .

[501] Rapid microbial response to the presence of an ancient relic in the Antarctic Dry Valleys

The extreme cold and aridity of the Antarctic McMurdo Dry Valleys have led to the longstanding belief that metabolic rates of soil microbiota are negligible , and that ecosystem changes take place over millennia .
Here we report the first direct experimental evidence that soil microbial communities undergo rapid and lasting changes in response to contemporary environmental conditions .
Mummified seals , curious natural artifacts found scattered throughout Dry Valleys , alter their underlying soil environment by stabilizing temperatures , elevating relative humidity and reducing ultraviolet exposure .
In a unique , multi-year mummified seal transplantation experiment , we found that endemic Dry Valley microbial communities responded to these changes within 3 years , resulting in a sevenfold increase in CO2 flux and a significant reduction in biodiversity .
These findings challenge prevailing ideas about Antarctic Dry Valley ecosystems and indicate that current and future environmental conditions may strongly influence the ecology of the dominant biota in the Dry Valleys .

[502] Effect of interannual climate variability on carbon storage in Amazonian ecosystems

The Amazon Basin contains almost one-half of the world 's undisturbed tropical evergreen forest as well as large areas of tropical savanna , .
The forests account for about 10 per cent of the world 's terrestrial primary productivity and for a similar fraction of the carbon stored in land ecosystems , , and short-term field measurements suggest that these ecosystems are globally important carbon sinks .
But tropical land ecosystems have experienced substantial interannual climate variability owing to frequent El Nino episodes in recent decades .
Of particular importance to climate change policy is how such climate variations , coupled with increases in atmospheric CO2 concentration , affect terrestrial carbon storage .
Previous model analyses have demonstrated the importance of temperature in controlling carbon storage , .
Here we use a transient process-based biogeochemical model of terrestrial ecosystems , to investigate interannual variations of carbon storage in undisturbed Amazonian ecosystems in response to climate variability and increasing atmospheric CO2 concentration during the period 1980 to 1994 .
In El Nino years , which bring hot , dry weather to much of the Amazon region , the ecosystems act as a source of carbon to the atmosphere ( up to 0.2 petagrams of carbon in 1987 and 1992 ) .
In other years , these ecosystems act as a carbon sink ( up to 0.7 Pg C in 1981 and 1993 ) .
These fluxes are large ; they compare to a 0.3 Pg C per year source to the atmosphere associated with deforestation inthe Amazon Basin in the early 1990s .
Soil moisture , which is affected by both precipitation and temperature , and which affects both plant and soil processes , appears to be an important control on carbon storage .

[503] Modulation of Post-Antibiotic Bacterial Community Reassembly and Host Response by Candida albicans

The introduction of Candida albicans into cefoperazone-treated mice results in changes in bacterial community reassembly .
Our objective was to use high-throughput sequencing to characterize at much greater depth the specific changes in the bacterial microbiome .
The colonization of C. albicans significantly altered bacterial community reassembly that was evident at multiple taxonomic levels of resolution .
There were marked changes in the levels of Bacteriodetes and Lactobacillaceae .
Lachnospiraceae and Ruminococcaceae , the two most abundant bacterial families , did not change in relative proportions after antibiotics , but there were marked genera-level shifts within these two bacterial families .
The microbiome shifts occurred in the absence of overt intestinal inflammation .
Overall , these experiments demonstrate that the introduction of a single new microbe in numerically inferior numbers into the bacterial microbiome during a broad community disturbance has the potential to significantly alter the subsequent reassembly of the bacterial community as it recovers from that disturbance .

[504] Reduction of forest soil respiration in response to nitrogen deposition

The use of fossil fuels and fertilizers has increased the amount of biologically reactive nitrogen in the atmosphere over the past century .
As a consequence , forests in industrialized regions have experienced greater rates of nitrogen deposition in recent decades .
This unintended fertilization has stimulated forest growth , but has also affected soil microbial activity , and thus the recycling of soil carbon and nutrients .
A meta-analysis suggests that nitrogen deposition impedes organic matter decomposition , and thus stimulates carbon sequestration , in temperate forest soils where nitrogen is not limiting microbial growth .
The concomitant reduction in soil carbon emissions is substantial , and equivalent in magnitude to the amount of carbon taken up by trees owing to nitrogen fertilization .
As atmospheric nitrogen levels continue to rise , increased nitrogen deposition could spread to older , more weathered soils , as found in the tropics ; however , soil carbon cycling in tropical forests can not yet be assessed .

[505] Climate change ( Communication arising ) : Terrestrial export of organic carbon

Dissolved organic matter in the oceans represents one of the biosphere 's principal stores of organic carbon .
A large proportion of this matter is drained from the continents -- particularly from northern peatlands , which contain 20 % of the global soil carbon .
Freeman et al. have suggested that rising temperatures may enhance this transport of dissolved organic carbon ( DOC ) from peatlands to the oceans .
We argue here that warming can affect DOC export in different ways , depending on whether it is accompanied by increased or decreased precipitation .
An alteration in the rate of relocation of organic carbon from the continents to the oceans can not therefore be predicted on the basis of temperature change alone .

[506] Self-reinforcing impacts of plant invasions change over time

Returning native species to habitats degraded by biological invasions is a critical conservation goal .
A leading hypothesis poses that exotic plant dominance is self-reinforced by impacts on ecosystem processes , leading to persistent stable states .
Invaders have been documented to modify fire regimes , alter soil nutrients or shift microbial communities in ways that feed back to benefit themselves over competitors .
However , few studies have followed invasions through time to ask whether ecosystem impacts and feedbacks persist .
Here we return to woodland sites in Hawai'i Volcanoes National Park that were invaded by exotic C4 grasses in the 1960s , the ecosystem impacts of which were studied intensively in the 1990s .
We show that positive feedbacks between exotic grasses and soil nitrogen cycling have broken down , but rather than facilitating native vegetation , the weakening feedbacks facilitate new exotic species .
Data from the 1990s showed that exotic grasses increased nitrogen-mineralization rates by two - to fourfold , but were nitrogen-limited .
Thus , the impacts of the invader created a positive feedback early in the invasion .
We now show that annual net soil nitrogen mineralization has since dropped to pre-invasion levels .
In addition , a seedling outplanting experiment that varied soil nitrogen and grass competition demonstrates that the changing impacts of grasses do not favour native species re-establishment .
Instead , decreased nitrogen availability most benefits another aggressive invader , the nitrogen-fixing tree Morella faya .
Long-term studies of invasions may reveal that ecosystem impacts and feedbacks shift over time , but that this may not benefit native species recovery .

[507] Impact of diet and individual variation on intestinal microbiota composition and fermentation products in obese men

There is growing interest in understanding how diet affects the intestinal microbiota , including its possible associations with systemic diseases such as metabolic syndrome .
Here we report a comprehensive and deep microbiota analysis of 14 obese males consuming fully controlled diets supplemented with resistant starch ( RS ) or non-starch polysaccharides ( NSPs ) and a weight-loss ( WL ) diet .
We analyzed the composition , diversity and dynamics of the fecal microbiota on each dietary regime by phylogenetic microarray and quantitative PCR ( qPCR ) analysis .
In addition , we analyzed fecal short chain fatty acids ( SCFAs ) as a proxy of colonic fermentation , and indices of insulin sensitivity from blood samples .
The diet explained around 10 % of the total variance in microbiota composition , which was substantially less than the inter-individual variance .
Yet , each of the study diets induced clear and distinct changes in the microbiota .
Multiple Ruminococcaceae phylotypes increased on the RS diet , whereas mostly Lachnospiraceae phylotypes increased on the NSP diet .
Bifidobacteria decreased significantly on the WL diet .
The RS diet decreased the diversity of the microbiota significantly .
The total 16S ribosomal RNA gene signal estimated by qPCR correlated positively with the three major SCFAs , while the amount of propionate specifically correlated with the Bacteroidetes .
The dietary responsiveness of the individual 's microbiota varied substantially and associated inversely with its diversity , suggesting that individuals can be stratified into responders and non-responders based on the features of their intestinal microbiota .

[508] Lack of uniform trends but increasing spatial variability in observed Indian rainfall extremes

Recent studies disagree on how rainfall extremes over India have changed in space and time over the past half century , as well as on whether the changes observed are due to global warming or regional urbanization .
Although a uniform and consistent decrease in moderate rainfall has been reported , a lack of agreement about trends in heavy rainfall may be due in part to differences in the characterization and spatial averaging of extremes .
Here we use extreme value theory to examine trends in Indian rainfall over the past half century in the context of long-term , low-frequency variability .
We show that when generalized extreme value theory is applied to annual maximum rainfall over India , no statistically significant spatially uniform trends are observed , in agreement with previous studies using different approaches .
Furthermore , our space-time regression analysis of the return levels points to increasing spatial variability of rainfall extremes over India .
Our findings highlight the need for systematic examination of global versus regional drivers of trends in Indian rainfall extremes , and may help to inform flood hazard preparedness and water resource management in the region .

[509] Inter-hemispheric temperature variability over the past millennium

The Earth 's climate system is driven by a complex interplay of internal chaotic dynamics and natural and anthropogenic external forcing .
Recent instrumental data have shown a remarkable degree of asynchronicity between Northern Hemisphere and Southern Hemisphere temperature fluctuations , thereby questioning the relative importance of internal versus external drivers of past as well as future climate variability .
However , large-scale temperature reconstructions for the past millennium have focused on the Northern Hemisphere , limiting empirical assessments of inter-hemispheric variability on multi-decadal to centennial timescales .
Here , we introduce a new millennial ensemble reconstruction of annually resolved temperature variations for the Southern Hemisphere based on an unprecedented network of terrestrial and oceanic palaeoclimate proxy records .
In conjunction with an independent Northern Hemisphere temperature reconstruction ensemble , this record reveals an extended cold period ( 1594-1677 ) in both hemispheres but no globally coherent warm phase during the pre-industrial ( 1000-1850 ) era .
The current ( post-1974 ) warm phase is the only period of the past millennium where both hemispheres are likely to have experienced contemporaneous warm extremes .
Our analysis of inter-hemispheric temperature variability in an ensemble of climate model simulations for the past millennium suggests that models tend to overemphasize Northern Hemisphere-Southern Hemisphere synchronicity by underestimating the role of internal ocean-atmosphere dynamics , particularly in the ocean-dominated Southern Hemisphere .
Our results imply that climate system predictability on decadal to century timescales may be lower than expected based on assessments of external climate forcing and Northern Hemisphere temperature variations alone .

[510] Differences in the climatic debts of birds and butterflies at a continental scale

Climate changes have profound effects on the distribution of numerous plant and animal species .
However , whether and how different taxonomic groups are able to track climate changes at large spatial scales is still unclear .
Here , we measure and compare the climatic debt accumulated by bird and butterfly communities at a European scale over two decades ( 1990-2008 ) .
We quantified the yearly change in community composition in response to climate change for 9,490 bird and 2,130 butterfly communities distributed across Europe .
We show that changes in community composition are rapid but different between birds and butterflies and equivalent to a 37 and 114 km northward shift in bird and butterfly communities , respectively .
We further found that , during the same period , the northward shift in temperature in Europe was even faster , so that the climatic debts of birds and butterflies correspond to a 212 and 135 km lag behind climate .
Our results indicate both that birds and butterflies do not keep up with temperature increase and the accumulation of different climatic debts for these groups at national and continental scales .

[511] Ecological succession in long-term experimentally evolved biofilms produces synergistic communities

Many biofilm populations are known for their exceptional biodiversity , but the relative contributions of the forces that could produce this diversity are poorly understood .
This uncertainty grows in the old , well-established communities found on many natural surfaces and in long-term , chronic infections .
If the prevailing interactions among species within biofilms are positive , productivity should increase with diversity , but if they tend towards competition or antagonism , productivity should decrease .
Here , we describe the parallel evolution of synergistic communities derived from a clone of Burkholderia cenocepacia during ~ 1500 generations of biofilm selection .
This long-term evolution was enabled by a new experimental method that selects for daily cycles of colonization , biofilm assembly and dispersal .
Each of the six replicate biofilm populations underwent a common pattern of adaptive morphological diversification , in which three ecologically distinct morphotypes arose in the same order of succession and persisted .
In two focal populations , mixed communities were more productive than any monoculture and each variant benefited from the mixture .
These gains in output resulted from asymmetrical cross-feeding between ecotypes and the expansion and partitioning of biofilm space that constructed new niches .
Therefore , even in the absence of starting genetic variation , prolonged selection for surface colonization generates a dynamic of ecological succession that enhances productivity .

[512] Southern Ocean deep-water carbon export enhanced by natural iron fertilization

The addition of iron to high-nutrient , low-chlorophyll regions induces phytoplankton blooms that take up carbon .
Carbon export from the surface layer and , in particular , the ability of the ocean and sediments to sequester carbon for many years remains , however , poorly quantified .
Here we report data from the CROZEX experiment in the Southern Ocean , which was conducted to test the hypothesis that the observed north-south gradient in phytoplankton concentrations in the vicinity of the Crozet Islands is induced by natural iron fertilization that results in enhanced organic carbon flux to the deep ocean .
We report annual particulate carbon fluxes out of the surface layer , at three kilometres below the ocean surface and to the ocean floor .
We find that carbon fluxes from a highly productive , naturally iron-fertilized region of the sub-Antarctic Southern Ocean are two to three times larger than the carbon fluxes from an adjacent high-nutrient , low-chlorophyll area not fertilized by iron .
Our findings support the hypothesis that increased iron supply to the glacial sub-Antarctic may have directly enhanced carbon export to the deep ocean .
The CROZEX sequestration efficiency ( the amount of carbon sequestered below the depth of winter mixing for a given iron supply ) of 8,600 mol mol-1 was 18 times greater than that of a phytoplankton bloom induced artificially by adding iron , but 77 times smaller than that of another bloom initiated , like CROZEX , by a natural supply of iron .
Large losses of purposefully added iron can explain the lower efficiency of the induced bloom6 .
The discrepancy between the blooms naturally supplied with iron may result in part from an underestimate of horizontal iron supply .

[513] Changes in the phase of the annual cycle of surface temperature

The annual cycle in the Earth 's surface temperature is extremely large -- comparable in magnitude to the glacial-interglacial cycles over most of the planet .
Trends in the phase and the amplitude of the annual cycle have been observed , but the causes and significance of these changes remain poorly understood -- in part because we lack an understanding of the natural variability .
Here we show that the phase of the annual cycle of surface temperature over extratropical land shifted towards earlier seasons by 1.7 days between 1954 and 2007 ; this change is highly anomalous with respect to earlier variations , which we interpret as being indicative of the natural range .
Significant changes in the amplitude of the annual cycle are also observed between 1954 and 2007 .
These shifts in the annual cycles appear to be related , in part , to changes in the northern annular mode of climate variability , although the land phase shift is significantly larger than that predicted by trends in the northern annular mode alone .
Few of the climate models presented by the Intergovernmental Panel on Climate Change reproduce the observed decrease in amplitude and none reproduce the shift towards earlier seasons .

[514] Twenty-first-century warming of a large Antarctic ice-shelf cavity by a redirected coastal current

The Antarctic ice sheet loses mass at its fringes bordering the Southern Ocean .
At this boundary , warm circumpolar water can override the continental slope front , reaching the grounding line through submarine glacial troughs and causing high rates of melting at the deep ice-shelf bases .
The interplay between ocean currents and continental bathymetry is therefore likely to influence future rates of ice-mass loss .
Here we show that a redirection of the coastal current into the Filchner Trough and underneath the Filchner-Ronne Ice Shelf during the second half of the twenty-first century would lead to increased movement of warm waters into the deep southern ice-shelf cavity .
Water temperatures in the cavity would increase by more than 2 degrees Celsius and boost average basal melting from 0.2 metres , or 82 billion tonnes , per year to almost 4 metres , or 1,600 billion tonnes , per year .
Our results , which are based on the output of a coupled ice-ocean model forced by a range of atmospheric outputs from the HadCM3 climate model , suggest that the changes would be caused primarily by an increase in ocean surface stress in the southeastern Weddell Sea due to thinning of the formerly consolidated sea-ice cover .
The projected ice loss at the base of the Filchner-Ronne Ice Shelf represents 80 per cent of the present Antarctic surface mass balance .
Thus , the quantification of basal mass loss under changing climate conditions is important for projections regarding the dynamics of Antarctic ice streams and ice shelves , and global sea level rise .

[515] Carbonaceous particles reduce marine microgel formation

An increase in ambient carbonaceous particle ( CNP ) levels has been found , potentially leading to significant environmental/health hazards .
These particles will ultimately enter the oceanic environment and interact with dissolved organic carbon .
However , a detailed mechanistic understanding of their behavior , transport , and fate in marine systems is still much needed .
This study , using carbon black ( CB , 14 nm ) nanoparticles as a model , aimed to investigate the impact of CNPs on marine microgel formation , a critical shunt between DOC and particulate organic carbon that potentially represents a ~ 70-Gt organic carbon flux .
We found that CB can enhance the stability of DOC polymers and reduce microgel equilibrium sizes in concentration as low as 1 mugL-1 CB , possibly due to negative surface charges on CB that decrease cross-linking bridges through Ca2 + bonds .
The reduction of marine microgel formation induced by CB could lead to a decrease in the downward transportation of microbial substrates and nutrients , and therefore , could have a significant impact on the carbon cycle and the marine ecosystem .

[516] Little net clear-sky radiative forcing from recent regional redistribution of aerosols

Aerosols both scatter and absorb incoming solar radiation , with consequences for the energy balance of the atmosphere .
Unlike greenhouse gases , atmospheric aerosols are distributed non-uniformly around the Earth .
Therefore , regional shifts in aerosol abundance could alter radiative forcing of the climate .
Here , I use multi-angle imaging spectroradiometer ( MISR ) satellite data and the Atmospheric and Environmental Research radiative transfer model to assess the radiative effect of the spatial redistribution of aerosols over the past decade .
Unexpectedly , the radiative transfer model shows that the movement of aerosols from high latitudes towards the Equator , as might happen if pollution shifts from Europe to southeast Asia , has little effect on clear-sky radiative forcing .
Shorter slant paths and smaller upscatter fractions near the Equator compensate for more total sunlight there .
Overall , there has been an almost exact cancellation in the clear-sky radiative forcing from aerosol increases and decreases in different parts of the world , whereas MISR should have been able to easily detect a change of 0.1 W m-2 per decade due to changing patterns .
Long-term changes in global mean aerosol optical depth or indirect aerosol forcing of clouds are difficult to measure from satellites .
However , the satellite data show that the regional redistribution of aerosols had little direct net effect on global average clear-sky radiative forcing from 2000 to 2012 .

[517] Readily available phosphorous and nitrogen counteract for arsenic uptake and distribution in wheat ( Triticum aestivum L. )

Elevated arsenic content in food crops pose a serious human health risk .
Apart from rice wheat being another main food crop is possibly cultivated on contaminated sites .
But for wheat uptake mechanisms are not entirely understood especially with regard to nutrient fertilization and different moisture regimes taking into account heavy rainfall events due to climate change .
Here we show that especially higher P-fertilization under changing redox conditions may enhance arsenic uptake .
This counteracts with higher N-fertilization reducing arsenic transfer and translocation into aboveground plant parts for both higher P-fertilization and reducing soil conditions .
Arsenic speciation did not change in grain but for leaves P-fertilization together with reducing conditions increased the As ( V ) content compared to other arsenic species .
Our results indicate important dependencies of nutrient fertilization , moisture conditions and substrate type on As accumulation of wheat as one of the most important crop plants worldwide with implications for agricultural practices .

[518] Plant diversity enhances ecosystem responses to elevated CO2 and nitrogen deposition

Human actions are causing declines in plant biodiversity , increases in atmospheric CO2 concentrations and increases in nitrogen deposition ; however , the interactive effects of these factors on ecosystem processes are unknown .
Reduced biodiversity has raised numerous concerns , including the possibility that ecosystem functioning may be affected negatively , which might be particularly important in the face of other global changes .
Here we present results of a grassland field experiment in Minnesota , USA , that tests the hypothesis that plant diversity and composition influence the enhancement of biomass and carbon acquisition in ecosystems subjected to elevated atmospheric CO2 concentrations and nitrogen deposition .
The study experimentally controlled plant diversity ( 1 , 4 , 9 or 16 species ) , soil nitrogen ( unamended versus deposition of 4 g of nitrogen per m2 per yr ) and atmospheric CO2 concentrations using free-air CO2 enrichment ( ambient , 368 micromol mol-1 , versus elevated , 560 micromol mol-1 ) .
We found that the enhanced biomass accumulation in response to elevated levels of CO2 or nitrogen , or their combination , is less in species-poor than in species-rich assemblages .

[519] Quorum sensing enhancement of the stress response promotes resistance to quorum quenching and prevents social cheating

Quorum sensing ( QS ) coordinates the expression of virulence factors and allows bacteria to counteract the immune response , partly by increasing their tolerance to the oxidative stress generated by immune cells .
Despite the recognized role of QS in enhancing the oxidative stress response , the consequences of this relationship for the bacterial ecology remain unexplored .
Here we demonstrate that QS increases resistance also to osmotic , thermal and heavy metal stress .
Furthermore a QS-deficient lasR rhlR mutant is unable to exert a robust response against H2O2 as it has less induction of catalase and NADPH-producing dehydrogenases .
Phenotypic microarrays revealed that the mutant is very sensitive to several toxic compounds .
As the anti-oxidative enzymes are private goods not shared by the population , only the individuals that produce them benefit from their action .
Based on this premise , we show that in mixed populations of wild-type and the mexR mutant ( resistant to the QS inhibitor furanone C-30 ) , treatment with C-30 and H2O2 increases the proportion of mexR mutants ; hence , oxidative stress selects resistance to QS compounds .
In addition , oxidative stress alone strongly selects for strains with active QS systems that are able to exert a robust anti oxidative response and thereby decreases the proportion of QS cheaters in cultures that are otherwise prone to invasion by cheats .
As in natural environments stress is omnipresent , it is likely that this QS enhancement of stress tolerance allows cells to counteract QS inhibition and invasions by social cheaters , therefore having a broad impact in bacterial ecology .

[520] Productivity limits and potentials of the principles of conservation agriculture

One of the primary challenges of our time is to feed a growing and more demanding world population with reduced external inputs and minimal environmental impacts , all under more variable and extreme climate conditions in the future .
Conservation agriculture represents a set of three crop management principles that has received strong international support to help address this challenge , with recent conservation agriculture efforts focusing on smallholder farming systems in sub-Saharan Africa and South Asia .
However , conservation agriculture is highly debated , with respect to both its effects on crop yields and its applicability in different farming contexts .
Here we conduct a global meta-analysis using 5,463 paired yield observations from 610 studies to compare no-till , the original and central concept of conservation agriculture , with conventional tillage practices across 48 crops and 63 countries .
Overall , our results show that no-till reduces yields , yet this response is variable and under certain conditions no-till can produce equivalent or greater yields than conventional tillage .
Importantly , when no-till is combined with the other two conservation agriculture principles of residue retention and crop rotation , its negative impacts are minimized .
Moreover , no-till in combination with the other two principles significantly increases rainfed crop productivity in dry climates , suggesting that it may become an important climate-change adaptation strategy for ever-drier regions of the world .
However , any expansion of conservation agriculture should be done with caution in these areas , as implementation of the other two principles is often challenging in resource-poor and vulnerable smallholder farming systems , thereby increasing the likelihood of yield losses rather than gains .
Although farming systems are multifunctional , and environmental and socio-economic factors need to be considered , our analysis indicates that the potential contribution of no-till to the sustainable intensification of agriculture is more limited than often assumed .

[521] Accelerating Forest Growth Enhancement due to Climate and Atmospheric Changes in British Colombia , Canada over 1956-2001

Changes in climate and atmospheric CO2 and nitrogen ( N ) over the last several decades have induced significant effects on forest carbon ( C ) cycling .
However , contributions of individual factors are largely unknown because of the lack of long observational data and the undifferentiating between intrinsic factors and external forces in current ecosystem models .
Using over four decades ( 1956-2001 ) of forest inventory data at 3432 permanent samples in maritime and boreal regions of British Columbia ( B.C. ) , Canada , growth enhancements were reconstructed and partitioned into contributions of climate , CO2 and N after removal of age effects .
We found that climate change contributed a particularly large amount ( over 70 % ) of the accumulated growth enhancement , while the remaining was attributed to CO2 and N , respectively .
We suggest that climate warming is contributing a widespread growth enhancement in B.C. 's forests , but ecosystem models should consider CO2 and N fertilization effects to fully explain inventory-based observations .

[522] Evidence of the dependence of groundwater resources on extreme rainfall in East Africa

Groundwater recharge sustains the groundwater resources on which there is global dependence for drinking water and irrigated agriculture .
For many communities , groundwater is the only perennial source of water .
Here , we present a newly compiled 55-year record of groundwater-level observations in an aquifer of central Tanzania that reveals the highly episodic occurrence of recharge resulting from anomalously intense seasonal rainfall .
Episodic recharge interrupts multiannual recessions in groundwater levels , maintaining the water security of the groundwater-dependent communities in this region .
This long-term record of groundwater storage changes in the semi-arid tropics demonstrates a nonlinear relationship between rainfall and recharge wherein intense seasonal rainfall associated with the El Nino Southern Oscillation and the Indian Ocean Dipole mode of climate variability contributes disproportionately to recharge .
Analysis of the Intergovernmental Panel on Climate Change AR4 and AR5 multi-model ensembles for the twenty-first century indicates that projected increases in extreme monthly rainfall , responsible for observed recharge , are of much greater magnitude than changes to mean rainfall .
Increased use of groundwater may therefore prove a potentially viable adaptation to enhanced variability in surface-water resources and soil moisture resulting from climate change .
Uncertainty in the projected behaviour of the El Nino Southern Oscillation and associated teleconnections remains , however , high .

[523] Response of snow-dependent hydrologic extremes to continued global warming

Snow accumulation is critical for water availability in the Northern Hemisphere , raising concern that global warming could have important impacts on natural and human systems in snow-dependent regions .
Although regional hydrologic changes have been observed ( for example , refs , , , ) , the time of emergence of extreme changes in snow accumulation and melt remains a key unknown for assessing climate-change impacts .
We find that the CMIP5 global climate model ensemble exhibits an imminent shift towards low snow years in the Northern Hemisphere , with areas of western North America , northeastern Europe and the Greater Himalaya showing the strongest emergence during the near-term decades and at 2 degreesC global warming .
The occurrence of extremely low snow years becomes widespread by the late twenty-first century , as do the occurrences of extremely high early-season snowmelt and runoff ( implying increasing flood risk ) , and extremely low late-season snowmelt and runoff ( implying increasing water stress ) .
Our results suggest that many snow-dependent regions of the Northern Hemisphere are likely to experience increasing stress from low snow years within the next three decades , and from extreme changes in snow-dominated water resources if global warming exceeds 2 degreesC above the pre-industrial baseline .

[524] Appropriate Fe ( II ) Addition Significantly Enhances Anaerobic Ammonium Oxidation ( Anammox ) Activity through Improving the Bacterial Growth Rate

The application of anaerobic ammonium oxidation ( Anammox ) process is often limited by the slow growth rate of Anammox bacteria .
As the essential substrate element that required for culturing Anammox sludge , Fe ( II ) is expected to affect Anammox bacterial growth .
This work systematically studied the effects of Fe ( II ) addition on Anammox activity based on the kinetic analysis of specific growth rate using data from batch tests with an enriched Anammox sludge at different dosing levels .
Results clearly demonstrated that appropriate Fe ( II ) dosing ( i.e. , 0.09 mM ) significantly enhanced the specific Anammox growth rate up to 0.172 d-1 compared to 0.118 d-1 at regular Fe ( II ) level ( 0.03 mM ) .
The relationship between Fe ( II ) concentration and specific Anammox growth rate was found to be well described by typical substrate inhibition kinetics , which was integrated into currently well-established Anammox model to describe the enhanced Anammox growth with Fe ( II ) addition .
The validity of the integrated Anammox model was verified using long-term experimental data from three independent Anammox reactors with different Fe ( II ) dosing levels .
This Fe ( II ) - based approach could be potentially implemented to enhance the process rate for possible mainstream application of Anammox technology , in order for an energy autarchic wastewater treatment .

[525] Impacts of biodiversity on the emergence and transmission of infectious diseases

Current unprecedented declines in biodiversity reduce the ability of ecological communities to provide many fundamental ecosystem services .
Here we evaluate evidence that reduced biodiversity affects the transmission of infectious diseases of humans , other animals and plants .
In principle , loss of biodiversity could either increase or decrease disease transmission .
However , mounting evidence indicates that biodiversity loss frequently increases disease transmission .
In contrast , areas of naturally high biodiversity may serve as a source pool for new pathogens .
Overall , despite many remaining questions , current evidence indicates that preserving intact ecosystems and their endemic biodiversity should generally reduce the prevalence of infectious diseases .

[526] Long-term change in a meso-predator community in response to prolonged and heterogeneous human impact

Sharks and rays ' abundance can decline considerably with fishing .
Community changes , however , are more complex because of species interactions , and variable vulnerability and exposure to fishing .
We evaluated long-term changes in the elasmobranch community of the Adriatic Sea , a heavily exploited Mediterranean basin where top-predators have been strongly depleted historically , and fishing developed unevenly between the western and eastern side .
Combining and standardizing catch data from five trawl surveys from 1948-2005 , we estimated abundance trends and explained community changes using life histories , fish-market and effort data , and historical information .
We identified a highly depleted elasmobranch community .
Since 1948 , catch rates have declined by > 94 % and 11 species ceased to be detected .
The exploitation history and spatial gradients in fishing pressure explained most patterns in abundance and diversity , including the absence of strong compensatory increases .
Ecological corridors and large-scale protected areas emerged as potential management options for elasmobranch conservation .

[527] Temperature and vegetation seasonality diminishment over northern lands

Global temperature is increasing , especially over northern lands ( > 50degrees N ) , owing to positive feedbacks .
As this increase is most pronounced in winter , temperature seasonality ( ST ) -- conventionally defined as the difference between summer and winter temperatures -- is diminishing over time , a phenomenon that is analogous to its equatorward decline at an annual scale .
The initiation , termination and performance of vegetation photosynthetic activity are tied to threshold temperatures .
Trends in the timing of these thresholds and cumulative temperatures above them may alter vegetation productivity , or modify vegetation seasonality ( SV ) , over time .
The relationship between ST and SV is critically examined here with newly improved ground and satellite data sets .
The observed diminishment of ST and SV is equivalent to 4degrees and 7degrees ( 5degrees and 6degrees ) latitudinal shift equatorward during the past 30 years in the Arctic ( boreal ) region .
Analysis of simulations from 17 state-of-the-art climate models indicates an additional STdiminishment equivalent to a 20degrees equatorward shift could occur this century .
How SV will change in response to such large projected ST declines and the impact this will have on ecosystem services are not well understood .
Hence the need for continued monitoring of northern lands as their seasonal temperature profiles evolve to resemble thosefurther south .

[528] Satellite-based estimates of groundwater depletion in India

Groundwater is a primary source of fresh water in many parts of the world .
Some regions are becoming overly dependent on it , consuming groundwater faster than it is naturally replenished and causing water tables to decline unremittingly .
Indirect evidence suggests that this is the case in northwest India , but there has been no regional assessment of the rate of groundwater depletion .
Here we use terrestrial water storage-change observations from the NASA Gravity Recovery and Climate Experiment satellites and simulated soil-water variations from a data-integrating hydrological modelling system to show that groundwater is being depleted at a mean rate of 4.0 + / - 1.0 cm yr-1 equivalent height of water ( 17.7 + / - 4.5 km3 yr-1 ) over the Indian states of Rajasthan , Punjab and Haryana ( including Delhi ) .
During our study period of August 2002 to October 2008 , groundwater depletion was equivalent to a net loss of 109 km3 of water , which is double the capacity of India 's largest surface-water reservoir .
Annual rainfall was close to normal throughout the period and we demonstrate that the other terrestrial water storage components ( soil moisture , surface waters , snow , glaciers and biomass ) did not contribute significantly to the observed decline in total water levels .
Although our observational record is brief , the available evidence suggests that unsustainable consumption of groundwater for irrigation and other anthropogenic uses is likely to be the cause .
If measures are not taken soon to ensure sustainable groundwater usage , the consequences for the 114,000,000 residents of the region may include a reduction of agricultural output and shortages of potable water , leading to extensive socioeconomic stresses .

[529] Cathodic oxygen reduction catalyzed by bacteria in microbial fuel cells

Microbial fuel cells ( MFCs ) have the potential to combine wastewater treatment efficiency with energetic efficiency .
One of the major impediments to MFC implementation is the operation of the cathode compartment , as it employs environmentally unfriendly catalysts such as platinum .
As recently shown , bacteria can facilitate sustainable and cost-effective cathode catalysis for nitrate and also oxygen .
Here we describe a carbon cathode open to the air , on which attached bacteria catalyzed oxygen reduction .
The bacteria present were able to reduce oxygen as the ultimate electron acceptor using electrons provided by the solid-phase cathode .
Current densities of up to 2.2 A m-2 cathode projected surface were obtained ( 0.303 + / -0.017 W m-2 , 15 W m-3 total reactor volume ) .
The cathodic microbial community was dominated by Sphingobacterium , Acinetobacter and Acidovorax sp. , according to 16S rRNA gene clone library analysis .
Isolates of Sphingobacterium sp .
and Acinetobacter sp .
were obtained using H2/O2 mixtures .
Some of the pure culture isolates obtained from the cathode showed an increase in the power output of up to three-fold compared to a non-inoculated control , that is , from 0.015 + / -0.001 to 0.049 + / -0.025 W m-2 cathode projected surface .
The strong decrease in activation losses indicates that bacteria function as true catalysts for oxygen reduction .
Owing to the high overpotential for non-catalyzed reduction , oxygen is only to a limited extent competitive toward the electron donor , that is , the cathode .
Further research to refine the operational parameters and increase the current density by modifying the electrode surface and elucidating the bacterial metabolism is warranted .

[530] Nitrogen limitation constrains sustainability of ecosystem response to CO2

Enhanced plant biomass accumulation in response to elevated atmospheric CO2 concentration could dampen the future rate of increase in CO2 levels and associated climate warming .
However , it is unknown whether CO2-induced stimulation of plant growth and biomass accumulation will be sustained or whether limited nitrogen ( N ) availability constrains greater plant growth in a CO2-enriched world .
Here we show , after a six-year field study of perennial grassland species grown under ambient and elevated levels of CO2 and N , that low availability of N progressively suppresses the positive response of plant biomass to elevated CO2 .
Initially , the stimulation of total plant biomass by elevated CO2 was no greater at enriched than at ambient N supply .
After four to six years , however , elevated CO2 stimulated plant biomass much less under ambient than enriched N supply .
This response was consistent with the temporally divergent effects of elevated CO2 on soil and plant N dynamics at differing levels of N supply .
Our results indicate that variability in availability of soil N and deposition of atmospheric N are both likely to influence the response of plant biomass accumulation to elevated atmospheric CO2 .
Given that limitations to productivity resulting from the insufficient availability of N are widespread in both unmanaged and managed vegetation , soil N supply is probably an important constraint on global terrestrial responses to elevated CO2 .

[531] Frequent floods in the European Alps coincide with cooler periods of the past 2500 years

Severe floods triggered by intense precipitation are among the most destructive natural hazards in Alpine environments , frequently causing large financial and societal damage .
Potential enhanced flood occurrence due to global climate change would thus increase threat to settlements , infrastructure , and human lives in the affected regions .
Yet , projections of intense precipitation exhibit major uncertainties and robust reconstructions of Alpine floods are limited to the instrumental and historical period .
Here we present a 2500-year long flood reconstruction for the European Alps , based on dated sedimentary flood deposits from ten lakes in Switzerland .
We show that periods with high flood frequency coincide with cool summer temperatures .
This wet-cold synchronism suggests enhanced flood occurrence to be triggered by latitudinal shifts of Atlantic and Mediterranean storm tracks .
This paleoclimatic perspective reveals natural analogues for varying climate conditions , and thus can contribute to a better understanding and improved projections of weather extremes under climate change .

[532] Increase in observed net carbon dioxide uptake by land and oceans during the past 50 years

One of the greatest sources of uncertainty for future climate predictions is the response of the global carbon cycle to climate change .
Although approximately one-half of total CO2 emissions is at present taken up by combined land and ocean carbon reservoirs , models predict a decline in future carbon uptake by these reservoirs , resulting in a positive carbon-climate feedback .
Several recent studies suggest that rates of carbon uptake by the land and ocean have remained constant or declined in recent decades .
Other work , however , has called into question the reported decline .
Here we use global-scale atmospheric CO2 measurements , CO2 emission inventories and their full range of uncertainties to calculate changes in global CO2 sources and sinks during the past 50 years .
Our mass balance analysis shows that net global carbon uptake has increased significantly by about 0.05 billion tonnes of carbon per year and that global carbon uptake doubled , from 2.4 + / - 0.8 to 5.0 + / - 0.9 billion tonnes per year , between 1960 and 2010 .
Therefore , it is very unlikely that both land and ocean carbon sinks have decreased on a global scale .
Since 1959 , approximately 350 billion tonnes of carbon have been emitted by humans to the atmosphere , of which about 55 per cent has moved into the land and oceans .
Thus , identifying the mechanisms and locations responsible for increasing global carbon uptake remains a critical challenge in constraining the modern global carbon budget and predicting future carbon-climate interactions .

[533] Increased seasonality through the Eocene to Oligocene transition in northern high latitudes

A profound global climate shift took place at the Eocene-Oligocene transition ( ~ 33.5 million years ago ) when Cretaceous/early Palaeogene greenhouse conditions gave way to icehouse conditions .
During this interval , changes in the Earth 's orbit and a long-term drop in atmospheric carbon dioxide concentrations resulted in both the growth of Antarctic ice sheets to approximately their modern size and the appearance of Northern Hemisphere glacial ice .
However , palaeoclimatic studies of this interval are contradictory : although some analyses indicate no major climatic changes , others imply cooler temperatures , increased seasonality and/or aridity .
Climatic conditions in high northern latitudes over this interval are particularly poorly known .
Here we present northern high-latitude terrestrial climate estimates for the Eocene to Oligocene interval , based on bioclimatic analysis of terrestrially derived spore and pollen assemblages preserved in marine sediments from the Norwegian-Greenland Sea .
Our data indicate a cooling of ~ 5 degreesC in cold-month ( winter ) mean temperatures to 0-2 degreesC , and a concomitant increased seasonality before the Oi-1 glaciation event .
These data indicate that a cooling component is indeed incorporated in the delta18O isotope shift across the Eocene-Oligocene transition .
However , the relatively warm summer temperatures at that time mean that continental ice on East Greenland was probably restricted to alpine outlet glaciers .

[534] Changes in ocean denitrification during Late Carboniferous glacial-interglacial cycles

Denitrification ( the process by which nitrate and nitrite are reduced to nitrogen gas ) in the oxygen-minimum zones of modern oceans is an important part of the global nitrogen cycle .
Variations in rates of denitrification over Quaternary glacial-interglacial timescales may have affected global climate .
Evidence of denitrification has been reported from some older marine systems , but it is unclear whether denitrification rates varied during pre-Quaternary glacial cycles .
Here we present ratios of organic carbon to nitrogen and nitrogen isotope data from the Upper Carboniferous black shales of the North American mid-continent .
In these cyclic deposits , we find evidence of variations in the intensity of denitrification in the eastern tropical Panthalassic Ocean associated with glacially driven sea-level changes .
Sedimentary delta15N increases during the interval of rapid sea-level rise in each cycle , indicative of intensified denitrification , before returning to background levels as sea level stabilized during the interglacial phase .
Nearly identical patterns of denitrification have been observed in the eastern tropical Pacific during the Quaternary period .
We therefore conclude that ice ages have produced similar oceanographic conditions and nitrogen cycle dynamics in these regions over the past 300 million years .

[535] A new model for Proterozoic ocean chemistry

There was a significant oxidation of the Earth 's surface around 2 billion years ago ( 2 Gyr ) .
Direct evidence for this oxidation comes , mostly , from geological records of the redox-sensitive elements Fe and U reflecting the conditions prevailing during weathering .
The oxidation event was probably driven by an increased input of oxygen to the atmosphere arising from an increased sedimentary burial of organic matter between 2.3 and 2.0 Gyr .
This episode was postdated by the final large precipitation of banded iron formations around 1.8 Gyr .
It is generally believed that banded iron formations precipitated from an ocean whose bottom waters contained significant concentrations of dissolved ferrous iron , and that this sedimentation process terminated when aerobic bottom waters developed , oxidizing the iron and thus removing it from solution .
In contrast , I argue here that anoxic bottom waters probably persisted until well after the deposition of banded iron formations ceased ; I also propose that sulphide , rather than oxygen , was responsible for removing iron from deep ocean water .
The sulphur-isotope record supports this hypothesis as it indicates increasing concentrations of oceanic sulphate , starting around 2.3 Gyr , leading to increasing rates of sulphide production by sulphate reduction .
The increase in sulphide production became sufficient , around 1.8 Gyr , to precipitate the total flux of iron into the oceans .
I suggest that aerobic deep-ocean waters did not develop until the Neoproterozoic era ( 1.0 to ~ 0.54 Gyr ) , in association with a second large oxidation of the Earth 's surface .
This new model is consistent with the emerging view of Precambrian sulphur geochemistry and the chemical events leading to the evolution of animals , and it is fully testable by detailed geochemical analyses of preserved deep-water marine sediments .

[536] Climate sensitivity to the carbon cycle modulated by past and future changes in ocean chemistry

The carbon cycle has a central role in climate change .
For example , during glacial-interglacial cycles , atmospheric carbon dioxide has altered radiative forcing and amplified temperature changes .
However , it is unclear how sensitive the climate system has been to changes in carbon cycling in previous geological periods , or how this sensitivity may evolve in the future , following massive anthropogenic emissions .
Here we develop an analytical relationship that links the variation of radiative forcing from changes in carbon dioxide concentrations with changes in air-sea carbon cycling on a millennial timescale .
We find that this relationship is affected by the ocean storage of carbon and its chemical partitioning in sea water .
Our analysis reveals that the radiative forcing of climate is more sensitive to carbon perturbations now than it has been over much of the preceding 400 million years .
This high sensitivity is likely to persist into the future as the oceans become more acidic and the bulk of the fossil-fuels inventory is transferred to the ocean and atmosphere .

[537] Stage-structured cycles promote genetic diversity in a predator-prey system of Daphnia and algae

Competition theory predicts that population fluctuations can promote genetic diversity when combined with density-dependent selection .
However , this stabilizing mechanism has rarely been tested , and was recently rejected as an explanation for maintaining diversity in natural populations of the freshwater herbivore Daphnia pulex .
The primary limitation of competition theory is its failure to account for the alternative types of population cycles that are caused by size - or stage-dependent population vital rates -- even though such structure both explains the fluctuating dynamics of many species and may alter the outcome of competition .
Here we provide the first experimental test of whether alternative types of cycles affect natural selection in predator-prey systems .
Using competing Daphnia genotypes , we show that internally generated , stage-structured cycles substantially reduce the magnitude of selection ( thereby contributing to the maintenance of genetic diversity ) , whereas externally forced cycles show rapid competitive exclusion .
The change in selection is ecologically significant , spanning the observed range in natural populations .
We argue that structured cycles reduce selection through a combination of stalled juvenile development and stage-specific mortality .
This potentially general fitness-equalizing mechanism may reduce the need for strong stabilizing mechanisms to explain the maintenance of genetic diversity in natural systems .

[538] Ion antiport accelerates photosynthetic acclimation in fluctuating light environments

Many photosynthetic organisms globally , including crops , forests and algae , must grow in environments where the availability of light energy fluctuates dramatically .
How photosynthesis maintains high efficiency despite such fluctuations in its energy source remains poorly understood .
Here we show that Arabidopsis thaliana K + efflux antiporter ( KEA3 ) is critical for high photosynthetic efficiency under fluctuating light .
On a shift from dark to low light , or high to low light , kea3 mutants show prolonged dissipation of absorbed light energy as heat .
KEA3 localizes to the thylakoid membrane , and allows proton efflux from the thylakoid lumen by proton/potassium antiport .
KEA3 's activity accelerates the downregulation of pH-dependent energy dissipation after transitions to low light , leading to faster recovery of high photosystem II quantum efficiency and increased CO2 assimilation .
Our results reveal a mechanism that increases the efficiency of photosynthesis under fluctuating light .

[539] A systems approach to evaluating the air quality co-benefits of US carbon policies

Because human activities emit greenhouse gases ( GHGs ) and conventional air pollutants from common sources , policy designed to reduce GHGs can have co-benefits for air quality that may offset some or all of the near-term costs of GHG mitigation .
We present a systems approach to quantify air quality co-benefits of US policies to reduce GHG ( carbon ) emissions .
We assess health-related benefits from reduced ozone and particulate matter ( PM2 .5 ) by linking three advanced models , representing the full pathway from policy to pollutant damages .
We also examine the sensitivity of co-benefits to key policy-relevant sources of uncertainty and variability .
We find that monetized human health benefits associated with air quality improvements can offset 26-1 ,050 % of the cost of US carbon policies .
More flexible policies that minimize costs , such as cap-and-trade standards , have larger net co-benefits than policies that target specific sectors ( electricity and transportation ) .
Although air quality co-benefits can be comparable to policy costs for present-day air quality and near-term US carbon policies , potential co-benefits rapidly diminish as carbon policies become more stringent .

[540] FAAH genetic variation enhances fronto-amygdala function in mouse and human

Cross-species studies enable rapid translational discovery and produce the broadest impact when both mechanism and phenotype are consistent across organisms .
We developed a knock-in mouse that biologically recapitulates a common human mutation in the gene for fatty acid amide hydrolase ( FAAH ) ( C385A ; rs324420 ) , the primary catabolic enzyme for the endocannabinoid anandamide .
This common polymorphism impacts the expression and activity of FAAH , thereby increasing anandamide levels .
Here , we show that the genetic knock-in mouse and human variant allele carriers exhibit parallel alterations in biochemisty , neurocircuitry and behaviour .
Specifically , there is reduced FAAH expression associated with the variant allele that selectively enhances fronto-amygdala connectivity and fear extinction learning , and decreases anxiety-like behaviours .
These results suggest a gain of function in fear regulation and may indicate for whom and for what anxiety symptoms FAAH inhibitors or exposure-based therapies will be most efficacious , bridging an important translational gap between the mouse and human .

[541] Early twentieth-century warming linked to tropical Pacific wind strength

Of the rise in global atmospheric temperature over the past century , nearly 30 % occurred between 1910 and 1940 when anthropogenic forcings were relatively weak .
This early warming has been attributed to internal factors , such as natural climate variability in the Atlantic region , and external factors , such as solar variability and greenhouse gas emissions .
However , the warming is too large to be explained by external factors alone and it precedes Atlantic warming by over a decade .
For the late twentieth century , observations and climate model simulations suggest that Pacific trade winds can modulate global temperatures , but instrumental data are scarce in the early twentieth century .
Here we present a westerly wind reconstruction ( 1894-1982 ) from seasonally resolved measurements of Mn/Ca ratios in a western Pacific coral that tracks interannual to multidecadal Pacific climate variability .
We then reconstruct central Pacific temperatures using Sr/Ca ratios in a coral from Jarvis Island , and find that weak trade winds and warm temperatures coincide with rapid global warming from 1910 to 1940 .
In contrast , winds are stronger and temperatures cooler between 1940 and 1970 , when global temperature rise slowed down .
We suggest that variations in Pacific wind strength at decadal timescales significantly influence the rate of surface air temperature change .

[542] Eocene bipolar glaciation associated with global carbon cycle changes

The transition from the extreme global warmth of the early Eocene ` greenhouse ' climate ~ 55 million years ago to the present glaciated state is one of the most prominent changes in Earth 's climatic evolution .
It is widely accepted that large ice sheets first appeared on Antarctica ~ 34 million years ago , coincident with decreasing atmospheric carbon dioxide concentrations and a deepening of the calcite compensation depth in the world 's oceans , and that glaciation in the Northern Hemisphere began much later , between 10 and 6 million years ago .
Here we present records of sediment and foraminiferal geochemistry covering the greenhouse-icehouse climate transition .
We report evidence for synchronous deepening and subsequent oscillations in the calcite compensation depth in the tropical Pacific and South Atlantic oceans from ~ 42 million years ago , with a permanent deepening 34 million years ago .
The most prominent variations in the calcite compensation depth coincide with changes in seawater oxygen isotope ratios of up to 1.5 per mil , suggesting a lowering of global sea level through significant storage of ice in both hemispheres by at least 100 to 125 metres .
Variations in benthic carbon isotope ratios of up to ~ 1.4 per mil occurred at the same time , indicating large changes in carbon cycling .
We suggest that the greenhouse-icehouse transition was closely coupled to the evolution of atmospheric carbon dioxide , and that negative carbon cycle feedbacks may have prevented the permanent establishment of large ice sheets earlier than 34 million years ago .

[543] Dynamics of North American breeding bird populations

Population biologists have long been interested in the variability of natural populations .
One approach to dealing with ecological complexity is to reduce the system to one or a few species , for which meaningful equations can be solved .
Here we explore an alternative approach , by studying the statistical properties of a data set containing over 600 species , namely the North American breeding bird survey .
The survey has recorded annual species abundances over a 31-year period along more than 3,000 observation routes .
We now analyse the dynamics of population variability using this data set , and find scaling features in common with inanimate systems composed of strongly interacting subunits .
Specifically , we find that the distribution of changes in population abundance over a one-year interval is remarkably symmetrical , with long tails extending over six orders of magnitude .
The variance of the population over a time series increases as a power-law with increasing time lag , indicating long-range correlation in population size fluctuations .
We also find that the distribution of species lifetimes ( the time between colonization and local extinction ) within local patches is a power-law with an exponential cutoff imposed by the finite length of the time series .
Our results provide a quantitative basis for modelling the dynamics of large species assemblages .

[544] Acidification of subsurface coastal waters enhanced by eutrophication

Human inputs of nutrients to coastal waters can lead to the excessive production of algae , a process known as eutrophication .
Microbial consumption of this organic matter lowers oxygen levels in the water .
In addition , the carbon dioxide produced during microbial respiration increases acidity .
The dissolution of atmospheric carbon dioxide in ocean waters also raises acidity , a process known as ocean acidification .
Here , we assess the combined impact of eutrophication and ocean acidification on acidity in the coastal ocean , using data collected in the northern Gulf of Mexico and the East China Sea -- two regions heavily influenced by nutrient-laden rivers .
We show that eutrophication in these waters is associated with the development of hypoxia and the acidification of subsurface waters , as expected .
Model simulations , using data collected from the northern Gulf of Mexico , however , suggest that the drop in pH since pre-industrial times is greater than that expected from eutrophication and ocean acidification alone .
We attribute the additional drop in pH -- of 0.05 units -- to a reduction in the ability of these carbon dioxide-rich waters to buffer changes in pH. We suggest that eutrophication could increase the susceptibility of coastal waters to ocean acidification .

[545] Links between viruses and prokaryotes throughout the water column along a North Atlantic latitudinal transect

Viruses are an abundant , diverse and dynamic component of marine ecosystems and have a key role in the biogeochemical processes of the ocean by controlling prokaryotic and phytoplankton abundance and diversity .
However , most of the studies on virus-prokaryote interactions in marine environments have been performed in nearshore waters .
To assess potential variations in the relation between viruses and prokaryotes in different oceanographic provinces , we determined viral and prokaryotic abundance and production throughout the water column along a latitudinal transect in the North Atlantic .
Depth-related trends in prokaryotic and viral abundance ( both decreasing by one order of magnitude from epi - to abyssopelagic waters ) , and prokaryotic production ( decreasing by three orders of magnitude ) were observed along the latitudinal transect .
The virus-to-prokaryote ratio ( VPR ) increased from ~ 19 in epipelagic to ~ 53 in the bathy - and abyssopelagic waters .
Although the lytic viral production decreased significantly with depth , the lysogenic viral production did not vary with depth .
In bathypelagic waters , pronounced differences in prokaryotic and viral abundance were found among different oceanic provinces with lower leucine incorporation rates and higher VPRs in the North Atlantic Gyre province than in the provinces further north and south .
The percentage of lysogeny increased from subpolar regions toward the more oligotrophic lower latitudes .
Based on the observed trends over this latitudinal transect , we conclude that the viral-host interactions significantly change among different oceanic provinces in response to changes in the biotic and abiotic variables .

[546] Volcanic triggering of a biogeochemical cascade during Oceanic Anoxic Event 2

During the Cretaceous period ( ~ 145-65 million years ago ) , there were several periods of global ocean anoxia , each lasting less than one million years .
These events , known as ocean anoxic events , were marked by significant increases in organic carbon burial , and are generally attributed to increased primary productivity in surface waters .
The details underpinning the initiation , maintenance and termination of these events , however , remain equivocal .
Here we present sulphur isotope data spanning the Ocean Anoxic Event 2 ( about 94.5 million years ago ) from sedimentary rocks in Colorado that were formed in the Western Interior Seaway ; this seaway ran north-south , splitting North America during the Cretaceous .
Sulphate levels increased rapidly from relatively low background levels at the onset of the event , most likely from the release of sulphur by massive volcanism , and fell during the anoxic event .
We infer that the input of sulphate facilitated increased carbon remineralization , which enhanced nutrient recycling and increased global primary productivity , eventually resulting in widespread ocean anoxia .
Our scenario indicates that Ocean Anoxic Event 2 may have persisted until sulphate levels were stabilized by the formation and burial of the sulphur mineral pyrite , which returned primary productivity to background levels .
We suggest that fluctuations in sulphate levels may have regulated the marine carbon cycle during past periods of low oceanic sulphate concentration .

[547] Ocean acidification impacts mussel control on biomineralisation

Ocean acidification is altering the oceanic carbonate saturation state and threatening the survival of marine calcifying organisms .
Production of their calcium carbonate exoskeletons is dependent not only on the environmental seawater carbonate chemistry but also the ability to produce biominerals through proteins .
We present shell growth and structural responses by the economically important marine calcifier Mytilus edulis to ocean acidification scenarios ( 380 , 550 , 750 , 1000 microatm pCO2 ) .
After six months of incubation at 750 microatm pCO2 , reduced carbonic anhydrase protein activity and shell growth occurs in M. edulis .
Beyond that , at 1000 microatm pCO2 , biomineralisation continued but with compensated metabolism of proteins and increased calcite growth .
Mussel growth occurs at a cost to the structural integrity of the shell due to structural disorientation of calcite crystals .
This loss of structural integrity could impact mussel shell strength and reduce protection from predators and changing environments .

[548] Microbial biogeochemistry of coastal upwelling regimes in a changing ocean

Coastal upwelling regimes associated with eastern boundary currents are the most biologically productive ecosystems in the ocean .
As a result , they play a disproportionately important role in the microbially mediated cycling of marine nutrients .
These systems are characterized by strong natural variations in carbon dioxide concentrations , pH , nutrient levels and sea surface temperatures on both seasonal and interannual timescales .
Despite this natural variability , changes resulting from human activities are starting to emerge .
Carbon dioxide derived from fossil fuel combustion is adding to the acidity of upwelled low-pH waters .
Low-oxygen waters associated with coastal upwelling systems are growing in their extent and intensity as a result of a rise in upper ocean temperatures and productivity .
And nutrient inputs to the coastal ocean continue to grow .
Coastal upwelling systems may prove more resilient to changes resulting from human activities than other ocean ecosystems because of their ability to function under extremely variable conditions .
Nevertheless , shifts in primary production , fish yields , nitrogen gain and loss , and the flux of climate-relevant gases could result from the perturbation of these highly productive and dynamic ecosystems .

[549] Climate change patterns in Amazonia and biodiversity

Precise characterization of hydroclimate variability in Amazonia on various timescales is critical to understanding the link between climate change and biodiversity .
Here we present absolute-dated speleothem oxygen isotope records that characterize hydroclimate variation in western and eastern Amazonia over the past 250 and 20 ka , respectively .
Although our records demonstrate the coherent millennial-scale precipitation variability across tropical-subtropical South America , the orbital-scale precipitation variability between western and eastern Amazonia exhibits a quasi-dipole pattern .
During the last glacial period , our records imply a modest increase in precipitation amount in western Amazonia but a significant drying in eastern Amazonia , suggesting that higher biodiversity in western Amazonia , contrary to ` Refugia Hypothesis ' , is maintained under relatively stable climatic conditions .
In contrast , the glacial-interglacial climatic perturbations might have been instances of loss rather than gain in biodiversity in eastern Amazonia , where forests may have been more susceptible to fragmentation in response to larger swings in hydroclimate .

[550] Strong hemispheric coupling of glacial climate through freshwater discharge and ocean circulation

The climate of the last glacial period was extremely variable , characterized by abrupt warming events in the Northern Hemisphere , accompanied by slower temperature changes in Antarctica and variations of global sea level .
It is generally accepted that this millennial-scale climate variability was caused by abrupt changes in the ocean thermohaline circulation .
Here we use a coupled ocean-atmosphere-sea ice model to show that freshwater discharge into the North Atlantic Ocean , in addition to a reduction of the thermohaline circulation , has a direct effect on Southern Ocean temperature .
The related anomalous oceanic southward heat transport arises from a zonal density gradient in the subtropical North Atlantic caused by a fast wave-adjustment process .
We present an extended and quantitative bipolar seesaw concept that explains the timing and amplitude of Greenland and Antarctic temperature changes , the slow changes in Antarctic temperature and its similarity to sea level , as well as a possible time lag of sea level with respect to Antarctic temperature during Marine Isotope Stage 3 .

[551] Projected changes in wave climate from a multi-model ensemble

Future changes in wind-wave climate have broad implications for the operation and design of coastal , near - and off-shore industries and ecosystems , and may further exacerbate the anticipated vulnerabilities of coastal regions to projected sea-level rise .
However , wind waves have received little attention in global assessments of projected future climate change .
We present results from the first community-derived multi-model ensemble of wave-climate projections .
We find an agreed projected decrease in annual mean significant wave height ( HS ) over 25.8 % of the global ocean area .
The area of projected decrease is greater during boreal winter ( January-March , mean ; 38.5 % of the global ocean area ) than austral winter ( July-September , mean ; 8.4 % ) .
A projected increase in annual mean HS is found over 7.1 % of the global ocean , predominantly in the Southern Ocean , which is greater during austral winter ( July-September ; 8.8 % ) .
Increased Southern Ocean wave activity influences a larger proportion of the global ocean as swell propagates northwards into the other ocean basins , observed as an increase in annual mean wave period ( TM ) over 30.2 % of the global ocean and associated rotation of the annual mean wave direction ( thetaM ) .
The multi-model ensemble is too limited to systematically sample total uncertainty associated with wave-climate projections .
However , variance of wave-climate projections associated with study methodology dominates other sources of uncertainty ( for example , climate scenario and model uncertainties ) .

[552] Adaptive evolution of a key phytoplankton species to ocean acidification

Ocean acidification , the drop in seawater pH associated with the ongoing enrichment of marine waters with carbon dioxide from fossil fuel burning , may seriously impair marine calcifying organisms .
Our present understanding of the sensitivity of marine life to ocean acidification is based primarily on short-term experiments , in which organisms are exposed to increased concentrations of CO2 .
However , phytoplankton species with short generation times , in particular , may be able to respond to environmental alterations through adaptive evolution .
Here , we examine the ability of the world 's single most important calcifying organism , the coccolithophore Emiliania huxleyi , to evolve in response to ocean acidification in two 500-generation selection experiments .
Specifically , we exposed E. huxleyi populations founded by single or multiple clones to increased concentrations of CO2 .
Around 500 asexual generations later we assessed their fitness .
Compared with populations kept at ambient CO2 partial pressure , those selected at increased partial pressure exhibited higher growth rates , in both the single - and multiclone experiment , when tested under ocean acidification conditions .
Calcification was partly restored : rates were lower under increased CO2 conditions in all cultures , but were up to 50 % higher in adapted compared with non-adapted cultures .
We suggest that contemporary evolution could help to maintain the functionality of microbial processes at the base of marine food webs in the face of global change .

[553] A new class of plant lipid is essential for protection against phosphorus depletion

Phosphorus supply is a major factor responsible for reduced crop yields .
As a result , plants utilize various adaptive mechanisms against phosphorus depletion , including lipid remodelling .
Here we report the involvement of a novel plant lipid , glucuronosyldiacylglycerol , against phosphorus depletion .
Lipidomic analysis of Arabidopsis plants cultured in phosphorus-depleted conditions revealed inducible accumulation of glucuronosyldiacylglycerol .
Investigation using a series of sulfolipid sulfoquinovosyldiacylglycerol synthesis-deficient mutants of Arabidopsis determined that the biosynthesis of glucuronosyldiacylglycerol shares the pathway of sulfoquinovosyldiacylglycerol synthesis in chloroplasts .
Under phosphorus-depleted conditions , the Arabidopsis sqd2 mutant , which does not accumulate either sulfoquinovosyldiacylglycerol or glucuronosyldiacylglycerol , was the most severely damaged of three sulfoquinovosyldiacylglycerol-deficient mutants .
As glucuronosyldiacylglycerol is still present in the other two mutants , this result indicates that glucuronosyldiacylglycerol has a role in the protection of plants against phosphorus limitation stress .
Glucuronosyldiacylglycerol was also found in rice , and its concentration increased significantly following phosphorus limitation , suggesting a shared physiological significance of this novel lipid against phosphorus depletion in plants .

[554] Global soil carbon projections are improved by modelling microbial processes

Society relies on Earth system models ( ESMs ) to project future climate and carbon ( C ) cycle feedbacks .
However , the soil C response to climate change is highly uncertain in these models and they omit key biogeochemical mechanisms .
Specifically , the traditional approach in ESMs lacks direct microbial control over soil C dynamics .
Thus , we tested a new model that explicitly represents microbial mechanisms of soil C cycling on the global scale .
Compared with traditional models , the microbial model simulates soil C pools that more closely match contemporary observations .
It also projects a much wider range of soil C responses to climate change over the twenty-first century .
Global soils accumulate C if microbial growth efficiency declines with warming in the microbial model .
If growth efficiency adapts to warming , the microbial model projects large soil C losses .
By comparison , traditional models project modest soil C losses with global warming .
Microbes also change the soil response to increased C inputs , as might occur with CO2 or nutrient fertilization .
In the microbial model , microbes consume these additional inputs ; whereas in traditional models , additional inputs lead to C storage .
Our results indicate that ESMs should simulate microbial physiology to more accurately project climate change feedbacks .

[555] Determining indicator taxa across spatial and seasonal gradients in the Columbia River coastal margin

Bacterioplankton communities are deeply diverse and highly variable across space and time , but several recent studies demonstrate repeatable and predictable patterns in this diversity .
We expanded on previous studies by determining patterns of variability in both individual taxa and bacterial communities across coastal environmental gradients .
We surveyed bacterioplankton diversity across the Columbia River coastal margin , USA , using amplicon pyrosequencing of 16S rRNA genes from 596 water samples collected from 2007 to 2010 .
Our results showed seasonal shifts and annual reassembly of bacterioplankton communities in the freshwater-influenced Columbia River , estuary , and plume , and identified indicator taxa , including species from freshwater SAR11 , Oceanospirillales , and Flavobacteria groups , that characterize the changing seasonal conditions in these environments .
In the river and estuary , Actinobacteria and Betaproteobacteria indicator taxa correlated strongly with seasonal fluctuations in particulate organic carbon ( rho = -0.664 ) and residence time ( rho = 0.512 ) , respectively .
In contrast , seasonal change in communities was not detected in the coastal ocean and varied more with the spatial variability of environmental factors including temperature and dissolved oxygen .
Indicator taxa of coastal ocean environments included SAR406 and SUP05 taxa from the deep ocean , and Prochlorococcus and SAR11 taxa from the upper water column .
We found that in the Columbia River coastal margin , freshwater-influenced environments were consistent and predictable , whereas coastal ocean community variability was difficult to interpret due to complex physical conditions .
This study moves beyond beta-diversity patterns to focus on the occurrence of specific taxa and lends insight into the potential ecological roles these taxa have in coastal ocean environments .

[556] Contribution of semi-arid ecosystems to interannual variability of the global carbon cycle

The land and ocean act as a sink for fossil-fuel emissions , thereby slowing the rise of atmospheric carbon dioxide concentrations .
Although the uptake of carbon by oceanic and terrestrial processes has kept pace with accelerating carbon dioxide emissions until now , atmospheric carbon dioxide concentrations exhibit a large variability on interannual timescales , considered to be driven primarily by terrestrial ecosystem processes dominated by tropical rainforests .
We use a terrestrial biogeochemical model , atmospheric carbon dioxide inversion and global carbon budget accounting methods to investigate the evolution of the terrestrial carbon sink over the past 30 years , with a focus on the underlying mechanisms responsible for the exceptionally large land carbon sink reported in 2011 ( ref .
2 ) .
Here we show that our three terrestrial carbon sink estimates are in good agreement and support the finding of a 2011 record land carbon sink .
Surprisingly , we find that the global carbon sink anomaly was driven by growth of semi-arid vegetation in the Southern Hemisphere , with almost 60 per cent of carbon uptake attributed to Australian ecosystems , where prevalent La Nina conditions caused up to six consecutive seasons of increased precipitation .
In addition , since 1981 , a six per cent expansion of vegetation cover over Australia was associated with a fourfold increase in the sensitivity of continental net carbon uptake to precipitation .
Our findings suggest that the higher turnover rates of carbon pools in semi-arid biomes are an increasingly important driver of global carbon cycle inter-annual variability and that tropical rainforests may become less relevant drivers in the future .
More research is needed to identify to what extent the carbon stocks accumulated during wet years are vulnerable to rapid decomposition or loss through fire in subsequent years .

[557] Evaluation of climate models using palaeoclimatic data

There is large uncertainty about the magnitude of warming and how rainfall patterns will change in response to any given scenario of future changes in atmospheric composition and land use .
The models used for future climate projections were developed and calibrated using climate observations from the past 40 years .
The geologic record of environmental responses to climate changes provides a unique opportunity to test model performance outside this limited climate range .
Evaluation of model simulations against palaeodata shows that models reproduce the direction and large-scale patterns of past changes in climate , but tend to underestimate the magnitude of regional changes .
As part of the effort to reduce model-related uncertainty and produce more reliable estimates of twenty-first century climate , the Palaeoclimate Modelling Intercomparison Project is systematically applying palaeoevaluation techniques to simulations of the past run with the models used to make future projections .
This evaluation will provide assessments of model performance , including whether a model is sufficiently sensitive to changes in atmospheric composition , as well as providing estimates of the strength of biosphere and other feedbacks that could amplify the model response to these changes and modify the characteristics of climate variability .

[558] Diversity loss with persistent human disturbance increases vulnerability to ecosystem collapse

Long-term and persistent human disturbances have simultaneously altered the stability and diversity of ecological systems , with disturbances directly reducing functional attributes such as invasion resistance , while eliminating the buffering effects of high species diversity .
Theory predicts that this combination of environmental change and diversity loss increases the risk of abrupt and potentially irreversible ecosystem collapse , but long-term empirical evidence from natural systems is lacking .
Here we demonstrate this relationship in a degraded but species-rich pyrogenic grassland in which the combined effects of fire suppression , invasion and trophic collapse have created a species-poor grassland that is highly productive , resilient to yearly climatic fluctuations , and resistant to invasion , but vulnerable to rapid collapse after the re-introduction of fire .
We initially show how human disturbance has created a negative relationship between diversity and function , contrary to theoretical predictions .
Fire prevention since the mid-nineteenth century is associated with the loss of plant species but it has stabilized high-yield annual production and invasion resistance , comparable to a managed high-yield low-diversity agricultural system .
In managing for fire suppression , however , a hidden vulnerability to sudden environmental change emerges that is explained by the elimination of the buffering effects of high species diversity .
With the re-introduction of fire , grasslands only persist in areas with remnant concentrations of native species , in which a range of rare and mostly functionally redundant plants proliferate after burning and prevent extensive invasion including a rapid conversion towards woodland .
This research shows how biodiversity can be crucial for ecosystem stability despite appearing functionally insignificant beforehand , a relationship probably applicable to many ecosystems given the globally prevalent combination of intensive long-term land management and species loss .

[559] Zonally asymmetric response of the Southern Ocean mixed-layer depth to the Southern Annular Mode

Interactions between the atmosphere and ocean are mediated by the mixed layer at the ocean surface .
The depth of this layer is determined by wind forcing and heating from the atmosphere .
Variations in mixed-layer depth affect the rate of exchange between the atmosphere and deeper ocean , the capacity of the ocean to store heat and carbon and the availability of light and nutrients to support the growth of phytoplankton .
However , the response of the Southern Ocean mixed layer to changes in the atmosphere is not well known .
Here we analyse temperature and salinity data from Argo profiling floats to show that the Southern Annular Mode ( SAM ) , the dominant mode of atmospheric variability in the Southern Hemisphere , leads to large-scale anomalies in mixed-layer depth that are zonally asymmetric .
From a simple heat budget of the mixed layer we conclude that meridional winds associated with departures of the SAM from zonal symmetry cause anomalies in heat flux that can , in turn , explain the observed changes of mixed-layer depth and sea surface temperature .
Our results suggest that changes in the SAM , including recent and projected trends attributed to human activity , drive variations in Southern Ocean mixed-layer depth , with consequences for air-sea exchange , ocean sequestration of heat and carbon , and biological productivity .

[560] Nonlinear grassland responses to past and future atmospheric CO2

Carbon sequestration in soil organic matter may moderate increases in atmospheric CO2 concentrations ( Ca ) as Ca increases to more than 500 micromol mol-1 this century from interglacial levels of less than 200 micromol mol-1 ( refs 1-6 ) .
However , such carbon storage depends on feedbacks between plant responses to Ca and nutrient availability .
Here we present evidence that soil carbon storage and nitrogen cycling in a grassland ecosystem are much more responsive to increases in past Ca than to those forecast for the coming century .
Along a continuous gradient of 200 to 550 micromol mol-1 ( refs 9 , 10 ) , increased Ca promoted higher photosynthetic rates and altered plant tissue chemistry .
Soil carbon was lost at subambient Ca , but was unchanged at elevated Ca where losses of old soil carbon offset increases in new carbon .
Along the experimental gradient in Ca there was a nonlinear , threefold decrease in nitrogen availability .
The differences in sensitivity of carbon storage to historical and future Ca and increased nutrient limitation suggest that the passive sequestration of carbon in soils may have been important historically , but the ability of soils to continue as sinks is limited .

[561] Cold induces acute stress but heat is ultimately more deleterious for the reef-building coral Acropora yongei

Climate change driven increases in intensity and frequency of both hot and cold extreme events contribute to coral reef decline by causing widespread coral bleaching and mortality .
Here , we show that hot and cold temperature changes cause distinct physiological responses on different time scales in reef-building corals .
We exposed the branching coral Acropora yongei in individual aquaria to a + / - 5degreesC temperature change .
Compared to heat-treated corals , cold-treated corals initially show greater declines in growth and increases in photosynthetic pressure .
However , after 2-3 weeks , cold-treated corals acclimate and show improvements in physiological state .
In contrast , heat did not initially harm photochemical efficiency , but after a delay , photosynthetic pressure increased rapidly and corals experienced severe bleaching and cessation of growth .
These results suggest that short-term cold temperature is more damaging for branching corals than short-term warm temperature , whereas long-term elevated temperature is more harmful than long-term depressed temperature .

[562] Decline of forereef corals in response to recent warming linked to history of thermal exposure

Rising ocean temperatures have reduced rates of coral calcification and increased rates of coral mortality , thereby negatively impacting the health of coral reef ecosystems .
Nevertheless , the response of corals to thermal stress seems to vary spatially across the reef environment .
Here , we show that between 1982 and 2008 in the western Caribbean Sea , skeletal extension within forereef colonies of the reef-building coral Siderastrea siderea declined with increasing seawater temperature , whereas extension rates of backreef and nearshore colonies were not impacted .
These results suggest that forereef S. siderea corals are more vulnerable to ocean warming than their backreef and nearshore counterparts .
This may arise from backreef and nearshore coral colonies experiencing greater baseline diurnal and seasonal thermal fluctuations than forereef colonies , which may promote acclimatization and/or adaptation to more recent anthropogenic thermal stress .
These findings reveal how corals have responded to recent anthropogenic warming , offer insights into how they are likely to respond to future warming and highlight the importance of understanding cross-reef differences in coral thermal tolerance for managing coral reef ecosystems in an era of rapid regional and global climate change .

[563] Changes in marine dinoflagellate and diatom abundance under climate change

Marine diatoms and dinoflagellates play a variety of key ecosystem roles as important primary producers ( diatoms and some dinoflagellates ) and grazers ( some dinoflagellates ) .
Additionally some are harmful algal bloom ( HAB ) species and there is widespread concern that HAB species may be increasing accompanied by major negative socio-economic impacts , including threats to human health and marine harvesting .
Using 92,263 samples from the Continuous Plankton Recorder survey , we generated a 50-year ( 1960-2009 ) time series of diatom and dinoflagellate occurrence in the northeast Atlantic and North Sea .
Dinoflagellates , including both HAB taxa ( for example , Prorocentrum spp . )
and non-HAB taxa ( for example , Ceratium furca ) , have declined in abundance , particularly since 2006 .
In contrast , diatom abundance has not shown this decline with some common diatoms , including both HAB ( for example , Pseudo-nitzschia spp . )
and non-HAB ( for example , Thalassiosira spp . )
taxa , increasing in abundance .
Overall these changes have led to a marked increase in the relative abundance of diatoms versus dinoflagellates .
Our analyses , including Granger tests to identify criteria of causality , indicate that this switch is driven by an interaction effect of both increasing sea surface temperatures combined with increasingly windy conditions in summer .

[564] Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation

The covariation of carbon dioxide ( CO2 ) concentration and temperature in Antarctic ice-core records suggests a close link between CO2 and climate during the Pleistocene ice ages .
The role and relative importance of CO2 in producing these climate changes remains unclear , however , in part because the ice-core deuterium record reflects local rather than global temperature .
Here we construct a record of global surface temperature from 80 proxy records and show that temperature is correlated with and generally lags CO2 during the last ( that is , the most recent ) deglaciation .
Differences between the respective temperature changes of the Northern Hemisphere and Southern Hemisphere parallel variations in the strength of the Atlantic meridional overturning circulation recorded in marine sediments .
These observations , together with transient global climate model simulations , support the conclusion that an antiphased hemispheric temperature response to ocean circulation changes superimposed on globally in-phase warming driven by increasing CO2 concentrations is an explanation for much of the temperature change at the end of the most recent ice age .

[565] Antarctic glaciation caused ocean circulation changes at the Eocene-Oligocene transition

Two main hypotheses compete to explain global cooling and the abrupt growth of the Antarctic ice sheet across the Eocene-Oligocene transition about 34 million years ago : thermal isolation of Antarctica due to southern ocean gateway opening , and declining atmospheric CO2 ( refs 5 , 6 ) .
Increases in ocean thermal stratification and circulation in proxies across the Eocene-Oligocene transition have been interpreted as a unique signature of gateway opening , but at present both mechanisms remain possible .
Here , using a coupled ocean-atmosphere model , we show that the rise of Antarctic glaciation , rather than altered palaeogeography , is best able to explain the observed oceanographic changes .
We find that growth of the Antarctic ice sheet caused enhanced northward transport of Antarctic intermediate water and invigorated the formation of Antarctic bottom water , fundamentally reorganizing ocean circulation .
Conversely , gateway openings had much less impact on ocean thermal stratification and circulation .
Our results support available evidence that CO2 drawdown -- not gateway opening -- caused Antarctic ice sheet growth , and further show that these feedbacks in turn altered ocean circulation .
The precise timing and rate of glaciation , and thus its impacts on ocean circulation , reflect the balance between potentially positive feedbacks ( increases in sea ice extent and enhanced primary productivity ) and negative feedbacks ( stronger southward heat transport and localized high-latitude warming ) .
The Antarctic ice sheet had a complex , dynamic role in ocean circulation and heat fluxes during its initiation , and these processes are likely to operate in the future .

[566] Does mechanical disturbance affect the performance and species composition of submerged macrophyte communities ?

Submerged macrophyte communities are frequently subjected to disturbance of various frequency and strength .
However , there is still little experimental evidence on how mechanical disturbance affects the performance and species composition of such plant communities .
In a greenhouse experiment , we constructed wetland communities consisting of five co-occurring clonal submerged macrophyte species ( Hydrilla verticillata , Elodea canadensis , Ceratophyllum demersum , Chara fragilis , and Myriophyllum spicatum ) and subjected these communities to three mechanical disturbance regimes ( no , moderate and strong disturbance ) .
Strong mechanical disturbance greatly decreased overall biomass , number of shoot nodes and total shoot length , and increased species diversity ( evenness ) of the total community .
It also substantially decreased the growth of the most abundant species ( H. verticillata ) , but did not affect growth of the other four species .
Our data reveal that strong disturbance can have different effects on different submerged macrophyte species and thus alters the performance and species composition of submerged macrophyte communities .

[567] Acceleration of Jakobshavn Isbrae triggered by warm subsurface ocean waters

Observations over the past decades show a rapid acceleration of several outlet glaciers in Greenland and Antarctica .
One of the largest changes is a sudden switch of Jakobshavn Isbrae , a large outlet glacier feeding a deep-ocean fjord on Greenland 's west coast , from slow thickening to rapid thinning in 1997 , associated with a doubling in glacier velocity .
Suggested explanations for the speed-up of Jakobshavn Isbrae include increased lubrication of the ice-bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers and weakening and break-up of the floating ice tongue that buttressed the glacier .
Here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of Greenland , suggesting that the changes in Jakobshavn Isbrae were instead triggered by the arrival of relatively warm water originating from the Irminger Sea near Iceland .
We trace these oceanic changes back to changes in the atmospheric circulation in the North Atlantic region .
We conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets .

[568] Morning reduction of photosynthetic capacity before midday depression

Midday depression of photosynthesis has important consequences for ecosystem carbon exchange .
Recent studies of forest trees have demonstrated that latent reduction of photosynthetic capacity can begin in the early morning , preceding the midday depression .
We investigated whether such early morning reduction also occurs in an herbaceous species , Oenothera biennis .
Diurnal changes of the photosynthetic light response curve ( measured using a light-emitting diode ) and incident sunlight intensity were measured under field conditions .
The following results were obtained : ( 1 ) the light-saturated photosynthetic rate decreased beginning at sunrise ; ( 2 ) the incident sunlight intensity on the leaves increased from sunrise ; and ( 3 ) combining ( 1 ) and ( 2 ) , the net photosynthetic rate under natural sunlight intensity increased from sunrise , reached a maximum at mid-morning , and then showed midday depression .
Our results demonstrate that the latent morning reduction of photosynthetic capacity begins at sunrise , preceding the apparent midday depression , in agreement with previous studies of forest trees .

[569] Abrupt changes in Antarctic Intermediate Water circulation over the past 25,000 years

The circulation of Antarctic Intermediate Water is thought to make an important contribution to the global ocean-climate system , but the details of this interaction are not fully understood .
Furthermore , the behaviour of Antarctic Intermediate Water under glacial and interglacial conditions is not well constrained .
Here we present a 25,000-year-long record of neodymium isotopic variations -- a tracer of water-mass mixing -- from the middle depths of the tropical Atlantic Ocean .
Our data reveal abruptly enhanced northward advection of Antarctic Intermediate Water during periods of reduced North Atlantic overturning circulation during the last deglaciation .
These events coincide with an increase in the formation of Antarctic Intermediate Water and warming in the southwest Pacific Ocean , which suggests a tight link with Southern Hemisphere climate .
In contrast , the initial incursion of southern source water into the North Atlantic ~ 19,000 years ago coincided with weak Antarctic Intermediate Water formation in the Pacific and reduced overturning in the North Atlantic .
We conclude that reduced competition at intermediate water depth at this time allowed expansion of Antarctic Intermediate Water into the North Atlantic .
This early incursion of Antarctic Intermediate Water may have contributed to freshening of the North Atlantic , perhaps spurring the subsequent collapse of North Atlantic deep convection .

[570] Physiology and evolution of nitrate acquisition in Prochlorococcus

Prochlorococcus is the numerically dominant phototroph in the oligotrophic subtropical ocean and carries out a significant fraction of marine primary productivity .
Although field studies have provided evidence for nitrate uptake by Prochlorococcus , little is known about this trait because axenic cultures capable of growth on nitrate have not been available .
Additionally , all previously sequenced genomes lacked the genes necessary for nitrate assimilation .
Here we introduce three Prochlorococcus strains capable of growth on nitrate and analyze their physiology and genome architecture .
We show that the growth of high-light ( HL ) adapted strains on nitrate is ~ 17 % slower than their growth on ammonium .
By analyzing 41 Prochlorococcus genomes , we find that genes for nitrate assimilation have been gained multiple times during the evolution of this group , and can be found in at least three lineages .
In low-light adapted strains , nitrate assimilation genes are located in the same genomic context as in marine Synechococcus .
These genes are located elsewhere in HL adapted strains and may often exist as a stable genetic acquisition as suggested by the striking degree of similarity in the order , phylogeny and location of these genes in one HL adapted strain and a consensus assembly of environmental Prochlorococcus metagenome sequences .
In another HL adapted strain , nitrate utilization genes may have been independently acquired as indicated by adjacent phage mobility elements ; these genes are also duplicated with each copy detected in separate genomic islands .
These results provide direct evidence for nitrate utilization by Prochlorococcus and illuminate the complex evolutionary history of this trait .

[571] Decline of fog , mist and haze in Europe over the past 30 years

Surface solar radiation has undergone decadal variations since the middle of the twentieth century , producing global ` dimming ' and ` brightening ' effects .
These variations presumably result from changes in aerosol burden and clouds , but the detailed processes involved have yet to be determined .
Over Europe , the marked solar radiation increase since the 1980s is thought to have contributed to the observed large continental warming , but this contribution has not been quantified .
Here we analyse multidecadal data of horizontal visibility , and find that the frequency of low-visibility conditions such as fog , mist and haze has declined in Europe over the past 30 years , for all seasons and all visibility ranges between distances of 0 and 8 km .
This decline is spatially and temporally correlated with trends in sulphur dioxide emissions , suggesting a significant contribution of air-quality improvements .
Statistically linking local visibility changes with temperature variations , we estimate that the reduction in low-visibility conditions could have contributed on average to about 10-20 % of Europe 's recent daytime warming and to about 50 % of eastern European warming .
Large improvements in air quality and visibility already achieved in Europe over the past decades may mean that future reductions in the frequency of low-visibility events will be limited , possibly leading to less rapid regional warming .

[572] Meiofauna reduces bacterial mineralization of naphthalene in marine sediment

The role of sediment-living meiofauna , benthic invertebrates smaller than 1000 mum such as nematodes and ostracods , on the mineralization of naphthalene , a common polycyclic aromatic hydrocarbon ( PAH ) in marine sediments , was studied in microcosms using radiorespirometry .
A method to extract live meiofauna was developed and used in order to experimentally manipulate meiofauna abundance and group diversity .
Higher abundances of meiofauna were found to significantly decrease naphthalene mineralization .
Furthermore , a change in the bacterial community composition ( studied using terminal restriction fragment length polymorphism ) was also observed in presence of higher meiofauna abundance , as well as a lower number of cultivable naphthalene-degrading bacteria .
The reduced mineralization of naphthalene and the altered bacterial community composition in the presence of increased meiofauna abundance is likely the result of top-down control by meiofauna .
This study shows that higher abundances of meiofauna can significantly decrease the microbial mineralization of PAHs such as naphthalene and also significantly modify the bacterial community composition in natural marine sediments .

[573] Moderate drop in water table increases peatland vulnerability to post-fire regime shift

Northern and tropical peatlands represent a globally significant carbon reserve accumulated over thousands of years of waterlogged conditions .
It is unclear whether moderate drying predicted for northern peatlands will stimulate burning and carbon losses as has occurred in their smaller tropical counterparts where the carbon legacy has been destabilized due to severe drainage and deep peat fires .
Capitalizing on a unique long-term experiment , we quantify the post-wildfire recovery of a northern peatland subjected to decadal drainage .
We show that the moderate drop in water table position predicted for most northern regions triggers a shift in vegetation composition previously observed within only severely disturbed tropical peatlands .
The combined impact of moderate drainage followed by wildfire converted the low productivity , moss-dominated peatland to a non-carbon accumulating shrub-grass ecosystem .
This new ecosystem is likely to experience a low intensity , high frequency wildfire regime , which will further deplete the legacy of stored peat carbon .

[574] Land-use protection for climate change mitigation

Land-use change , mainly the conversion of tropical forests to agricultural land , is a massive source of carbon emissions and contributes substantially to global warming .
Therefore , mechanisms that aim to reduce carbon emissions from deforestation are widely discussed .
A central challenge is the avoidance of international carbon leakage if forest conservation is not implemented globally .
Here , we show that forest conservation schemes , even if implemented globally , could lead to another type of carbon leakage by driving cropland expansion in non-forested areas that are not subject to forest conservation schemes ( non-forest leakage ) .
These areas have a smaller , but still considerable potential to store carbon .
We show that a global forest policy could reduce carbon emissions by 77 Gt CO2 , but would still allow for decreases in carbon stocks of non-forest land by 96 Gt CO2 until 2100 due to non-forest leakage effects .
Furthermore , abandonment of agricultural land and associated carbon uptake through vegetation regrowth is hampered .
Effective mitigation measures thus require financing structures and conservation investments that cover the full range of carbon-rich ecosystems .
However , our analysis indicates that greater agricultural productivity increases would be needed to compensate for such restrictions on agricultural expansion .

[575] Strong coherence between solar variability and the monsoon in Oman between 9 and 6 kyr ago

Variations in the amount of solar radiation reaching the Earth are thought to influence climate , but the extent of this influence on timescales of millennia to decades is unclear .
A number of climate records show correlations between solar cycles and climate , but the absolute changes in solar intensity over the range of decades to millennia are small and the influence of solar flux on climate is not well established .
The formation of stalagmites in northern Oman has recorded past northward shifts of the intertropical convergence zone , whose northward migration stops near the southern shoreline of Arabia in the present climate .
Here we present a high-resolution record of oxygen isotope variations , for the period from 9.6 to 6.1 kyr before present , in a Th-U-dated stalagmite from Oman .
The delta18O record from the stalagmite , which serves as a proxy for variations in the tropical circulation and monsoon rainfall , allows us to make a direct comparison of the delta18O record with the Delta14C record from tree rings , which largely reflects changes in solar activity .
The excellent correlation between the two records suggests that one of the primary controls on centennial - to decadal-scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation .

[576] Contemporary white-band disease in Caribbean corals driven by climate change

Over the past 40 years , two of the dominant reef-building corals in the Caribbean , Acropora palmata and Acropora cervicornis , have experienced unprecedented declines .
That loss has been largely attributed to a syndrome commonly referred to as white-band disease .
Climate change-driven increases in sea surface temperature ( SST ) have been linked to several coral diseases , yet , despite decades of research , the attribution of white-band disease to climate change remains unknown .
Here we hindcasted the potential relationship between recent ocean warming and outbreaks of white-band disease on acroporid corals .
We quantified eight SST metrics , including rates of change in SST and contemporary thermal anomalies , and compared them with records of white-band disease on A. palmata and A. cervicornis from 473 sites across the Caribbean , surveyed from 1997 to 2004 .
The results of our models suggest that decades-long climate-driven changes in SST , increases in thermal minima , and the breach of thermal maxima have all played significant roles in the spread of white-band disease .
We conclude that white-band disease has been strongly coupled with thermal stresses associated with climate change , which has contributed to the regional decline of these once-dominant reef-building corals .

[577] Mycophagous growth of Collimonas bacteria in natural soils , impact on fungal biomass turnover and interactions with mycophagous Trichoderma fungi

Bacteria of the genus Collimonas are widely distributed in soils , although at low densities .
In the laboratory , they were shown to be mycophagous , that is , they are able to grow at the expense of living hyphae .
However , so far the importance of mycophagy for growth and survival of collimonads in natural soil habitats is unknown .
Using a Collimonas-specific real-time PCR assay , we show here that the invasion of field soils by fungal hyphae ( Absidia sp . )
resulted in a short-term , significant increase ( average fourfold ) of indigenous collimonads .
No such responses were observed for other soil bacteria studied ( Pseudomonas , Burkholderia , PCR-denaturing gradient gel electrophoresis patterns of total bacteria and Burkholderia ) .
Hence , it appears that the stimulation of growth of Collimonas bacteria by fungal hyphae is not common among other soil bacteria .
In the same field soils , Trichoderma , a fungal genus known for mycophagous ( mycoparasitic ) growth , increased upon introduction of Absidia hyphae .
Hence , mycophagous growth by Collimonas and Trichoderma can occur in the same soils .
However , in controlled experiments ( sand microcosms ) , collimonads appeared to have a negative effect on mycophagous growth of a Trichoderma strain .
The effect of mycophagous growth of collimonads on fungal biomass dynamics was studied in sand microcosms using the same Absidia sp .
as a test fungus .
The growth of collimonads did not cause a significant reduction in the Absidia biomass .
Overall , the study indicates that mycophagous nutrition may be important for collimonads in natural soils , but the impact on fungal biomass turnover is likely to be minor .

[578] Holocene changes in the position and intensity of the southern westerly wind belt

The position and intensity of the southern westerly wind belt varies seasonally as a consequence of changes in sea surface temperature .
During the austral winter , the belt expands northward and the wind intensity in the core decreases .
Conversely , during the summer , the belt contracts , and the intensity within the core is strengthened .
Reconstructions of the westerly winds since the last glacial maximum , however , have suggested that changes at a single site reflected shifts throughout the entire southern wind belt .
Here we use sedimentological and pollen records to reconstruct precipitation patterns over the past 12,500 yr from sites along the windward side of the Andes .
Precipitation at the sites , located in the present core and northern margin of the westerlies , is driven almost entirely by the wind belt , and can be used to reconstruct its intensity .
Rather than varying coherently throughout the Holocene epoch , we find a distinct anti-phasing of wind strength between the core and northern margin over multi-millennial timescales .
During the early Holocene , the core westerlies were strong whereas the northern margin westerlies were weak .
We observe the opposite pattern in the late Holocene .
As this variation resembles modern seasonal variability , we suggest that our observed changes in westerly wind strength can best be explained by variations in sea surface temperature in the eastern South Pacific Ocean .

[579] The key role of dry days in changing regional climate and precipitation regimes

Future changes in the number of dry days per year can either reinforce or counteract projected increases in daily precipitation intensity as the climate warms .
We analyze climate model projected changes in the number of dry days using 28 coupled global climate models from the Coupled Model Intercomparison Project , version 5 ( CMIP5 ) .
We find that the Mediterranean Sea region , parts of Central and South America , and western Indonesia could experience up to 30 more dry days per year by the end of this century .
We illustrate how changes in the number of dry days and the precipitation intensity on precipitating days combine to produce changes in annual precipitation , and show that over much of the subtropics the change in number of dry days dominates the annual changes in precipitation and accounts for a large part of the change in interannual precipitation variability .

[580] Predictions of avian Plasmodium expansion under climate change

Vector-borne diseases are particularly responsive to changing environmental conditions .
Diurnal temperature variation has been identified as a particularly important factor for the development of malaria parasites within vectors .
Here , we conducted a survey across France , screening populations of the house sparrow ( Passer domesticus ) for malaria ( Plasmodium relictum ) .
We investigated whether variation in remotely-sensed environmental variables accounted for the spatial variation observed in prevalence and parasitemia .
While prevalence was highly correlated to diurnal temperature range and other measures of temperature variation , environmental conditions could not predict spatial variation in parasitemia .
Based on our empirical data , we mapped malaria distribution under climate change scenarios and predicted that Plasmodium occurrence will spread to regions in northern France , and that prevalence levels are likely to increase in locations where transmission already occurs .
Our findings , based on remote sensing tools coupled with empirical data suggest that climatic change will significantly alter transmission of malaria parasites .

[581] Will ocean acidification affect marine microbes ?

The pH of the surface ocean is changing as a result of increases in atmospheric carbon dioxide ( CO2 ) , and there are concerns about potential impacts of lower pH and associated alterations in seawater carbonate chemistry on the biogeochemical processes in the ocean .
However , it is important to place these changes within the context of pH in the present-day ocean , which is not constant ; it varies systematically with season , depth and along productivity gradients .
Yet this natural variability in pH has rarely been considered in assessments of the effect of ocean acidification on marine microbes .
Surface pH can change as a consequence of microbial utilization and production of carbon dioxide , and to a lesser extent other microbially mediated processes such as nitrification .
Useful comparisons can be made with microbes in other aquatic environments that readily accommodate very large and rapid pH change .
For example , in many freshwater lakes , pH changes that are orders of magnitude greater than those projected for the twenty second century oceans can occur over periods of hours .
Marine and freshwater assemblages have always experienced variable pH conditions .
Therefore , an appropriate null hypothesis may be , until evidence is obtained to the contrary , that major biogeochemical processes in the oceans other than calcification will not be fundamentally different under future higher CO2/lower pH conditions .

[582] Abrupt vegetation change after the Late Quaternary megafaunal extinction in southeastern Australia

A substantial extinction of megafauna occurred in Australia between 50 and 45 kyr ago , a period that coincides with human colonization of Australia .
Large shifts in vegetation also occurred around this time , but it is unclear whether the vegetation changes were driven by the human use of fire -- and thus contributed to the extinction event -- or were a consequence of the loss of megafaunal grazers .
Here we reconstruct past vegetation changes in southeastern Australia using the stable carbon isotopic composition of higher plant wax n-alkanes and levels of biomass burning from the accumulation rates of the biomarker levoglucosan from a well-dated sediment core offshore from the Murray-Darling Basin .
We find that from 58 to 44 kyr ago , the abundance of plants with the C4 carbon fixation pathway was generally high -- between 60 and 70 % .
By 43 kyr ago , the abundance of C4 plants dropped to 30 % and biomass burning increased .
This transient shift lasted for about 3,000 years and came after the period of human arrival and directly followed megafauna extinction at 48.9-43 .6 kyr ago .
We conclude that the vegetation shift was not the cause of the megafaunal extinction in this region .
Instead , our data are consistent with the hypothesis that vegetation change was the consequence of the extinction of large browsers and led to the build-up of fire-prone vegetation in the Australian landscape .

[583] Global disparity in the ecological benefits of reducing carbon emissions for coral reefs

Even if carbon emissions are reduced drastically in the next decade the amount of carbon already stored in the atmosphere would lead to the occurrence of extreme thermal events every three to four years between 2040 and 2080 .
This time lag on the effect of reducing emissions suggests that the benefits of carbon emission reduction on the health of coral reefs will be noticeable only in the long term .
Here , we use a spatially explicit ecosystem model to compare the potential ecosystem benefits that Caribbean and Pacific reefs could gain from reductions in carbon emissions , and the timescale of these benefits .
We found that whereas the effect of a reduction in emissions on Caribbean reefs will be modest and realized only in the long term ( more than 60 years ) , Pacific reefs would start to show benefits within the first half of this century .
Moreover , it seems that Pacific reefs have the potential to maintain their ecological integrity and ecosystem state in the mid - to long term if carbon emissions are reduced , but only if plate-like corals are present .

[584] Low Atlantic hurricane activity in the 1970s and 1980s compared to the past 270 years

Hurricane activity in the North Atlantic Ocean has increased significantly since 1995 ( refs 1 , 2 ) .
This trend has been attributed to both anthropogenically induced climate change and natural variability , but the primary cause remains uncertain .
Changes in the frequency and intensity of hurricanes in the past can provide insights into the factors that influence hurricane activity , but reliable observations of hurricane activity in the North Atlantic only cover the past few decades .
Here we construct a record of the frequency of major Atlantic hurricanes over the past 270 years using proxy records of vertical wind shear and sea surface temperature ( the main controls on the formation of major hurricanes in this region ) from corals and a marine sediment core .
The record indicates that the average frequency of major hurricanes decreased gradually from the 1760s until the early 1990s , reaching anomalously low values during the 1970s and 1980s .
Furthermore , the phase of enhanced hurricane activity since 1995 is not unusual compared to other periods of high hurricane activity in the record and thus appears to represent a recovery to normal hurricane activity , rather than a direct response to increasing sea surface temperature .
Comparison of the record with a reconstruction of vertical wind shear indicates that variability in this parameter primarily controlled the frequency of major hurricanes in the Atlantic over the past 270 years , suggesting that changes in the magnitude of vertical wind shear will have a significant influence on future hurricane activity .

[585] Pronounced interannual variability in tropical South Pacific temperatures during Heinrich Stadial 1

The early last glacial termination was characterized by intense North Atlantic cooling and weak overturning circulation .
This interval between ~ 18,000 and 14,600 years ago , known as Heinrich Stadial 1 , was accompanied by a disruption of global climate and has been suggested as a key factor for the termination .
However , the response of interannual climate variability in the tropical Pacific ( El Nino-Southern Oscillation ) to Heinrich Stadial 1 is poorly understood .
Here we use Sr/Ca in a fossil Tahiti coral to reconstruct tropical South Pacific sea surface temperature around 15,000 years ago at monthly resolution .
Unlike today , interannual South Pacific sea surface temperature variability at typical El Nino-Southern Oscillation periods was pronounced at Tahiti .
Our results indicate that the El Nino-Southern Oscillation was active during Heinrich Stadial 1 , consistent with climate model simulations of enhanced El Nino-Southern Oscillation variability at that time .
Furthermore , a greater El Nino-Southern Oscillation influence in the South Pacific during Heinrich Stadial 1 is suggested , resulting from a southward expansion or shift of El Nino-Southern Oscillation sea surface temperature anomalies .

[586] Stream denitrification across biomes and its response to anthropogenic nitrate loading

Anthropogenic addition of bioavailable nitrogen to the biosphere is increasing and terrestrial ecosystems are becoming increasingly nitrogen-saturated , causing more bioavailable nitrogen to enter groundwater and surface waters .
Large-scale nitrogen budgets show that an average of about 20-25 per cent of the nitrogen added to the biosphere is exported from rivers to the ocean or inland basins , indicating that substantial sinks for nitrogen must exist in the landscape .
Streams and rivers may themselves be important sinks for bioavailable nitrogen owing to their hydrological connections with terrestrial systems , high rates of biological activity , and streambed sediment environments that favour microbial denitrification .
Here we present data from nitrogen stable isotope tracer experiments across 72 streams and 8 regions representing several biomes .
We show that total biotic uptake and denitrification of nitrate increase with stream nitrate concentration , but that the efficiency of biotic uptake and denitrification declines as concentration increases , reducing the proportion of in-stream nitrate that is removed from transport .
Our data suggest that the total uptake of nitrate is related to ecosystem photosynthesis and that denitrification is related to ecosystem respiration .
In addition , we use a stream network model to demonstrate that excess nitrate in streams elicits a disproportionate increase in the fraction of nitrate that is exported to receiving waters and reduces the relative role of small versus large streams as nitrate sinks .

[587] Contribution of natural decadal variability to global warming acceleration and hiatus

Reasons for the apparent pause in the rise of global-mean surface air temperature ( SAT ) after the turn of the century has been a mystery , undermining confidence in climate projections .
Recent climate model simulations indicate this warming hiatus originated from eastern equatorial Pacific cooling associated with strengthening of trade winds .
Using a climate model that overrides tropical wind stress anomalies with observations for 1958-2012 , we show that decadal-mean anomalies of global SAT referenced to the period 1961-1990 are changed by 0.11 , 0.13 and -0.11 degreesC in the 1980s , 1990s and 2000s , respectively , without variation in human-induced radiative forcing .
They account for about 47 % , 38 % and 27 % of the respective temperature change .
The dominant wind stress variability consistent with this warming/cooling represents the deceleration/acceleration of the Pacific trade winds , which can be robustly reproduced by atmospheric model simulations forced by observed sea surface temperature excluding anthropogenic warming components .
Results indicate that inherent decadal climate variability contributes considerably to the observed global-mean SAT time series , but that its influence on decadal-mean SAT has gradually decreased relative to the rising anthropogenic warming signal .

[588] Early human use of marine resources and pigment in South Africa during the Middle Pleistocene

Genetic and anatomical evidence suggests that Homo sapiens arose in Africa between 200 and 100 thousand years ( kyr ) ago , and recent evidence indicates symbolic behaviour may have appeared ~ 135-75 kyr ago .
From 195-130 kyr ago , the world was in a fluctuating but predominantly glacial stage ( marine isotope stage MIS6 ) ; much of Africa was cooler and drier , and dated archaeological sites are rare .
Here we show that by ~ 164 kyr ago ( + / -12 kyr ) at Pinnacle Point ( on the south coast of South Africa ) humans expanded their diet to include marine resources , perhaps as a response to these harsh environmental conditions .
The earliest previous evidence for human use of marine resources and coastal habitats was dated to ~ 125 kyr ago .
Coincident with this diet and habitat expansion is an early use and modification of pigment , probably for symbolic behaviour , as well as the production of bladelet stone tool technology , previously dated to post-70 kyr ago .
Shellfish may have been crucial to the survival of these early humans as they expanded their home ranges to include coastlines and followed the shifting position of the coast when sea level fluctuated over the length of MIS6 .

[589] Recent patterns of crop yield growth and stagnation

In the coming decades , continued population growth , rising meat and dairy consumption and expanding biofuel use will dramatically increase the pressure on global agriculture .
Even as we face these future burdens , there have been scattered reports of yield stagnation in the world 's major cereal crops , including maize , rice and wheat .
Here we study data from ~ 2.5 million census observations across the globe extending over the period 1961-2008 .
We examined the trends in crop yields for four key global crops : maize , rice , wheat and soybeans .
Although yields continue to increase in many areas , we find that across 24-39 % of maize - , rice - , wheat - and soybean-growing areas , yields either never improve , stagnate or collapse .
This result underscores the challenge of meeting increasing global agricultural demands .
New investments in underperforming regions , as well as strategies to continue increasing yields in the high-performing areas , are required .

[590] Lagged effects of ocean climate change on fulmar population dynamics

Environmental variation reflected by the North Atlantic Oscillation affects breeding and survival in terrestrial vertebrates , and climate change is predicted to have an impact on population dynamics by influencing food quality or availability .
The North Atlantic Oscillation also affects the abundance of marine fish and zooplankton , but it is unclear whether this filters up trophic levels to long-lived marine top predators .
Here we show by analysis of data from a 50-year study of the fulmar that two different indices of ocean climate variation may have lagged effects on population dynamics in this procellariiform seabird .
Annual variability in breeding performance is influenced by the North Atlantic Oscillation , whereas cohort differences in recruitment are related to temperature changes in the summer growing season in the year of birth .
Because fulmars exhibit delayed reproduction , there is a 5-year lag in the population 's response to these effects of environmental change .
These data show how interactions between different climatic factors result in complex dynamics , and that the effects of climate change may take many years to become apparent in long-lived marine top predators .

[591] Warming-related increases in soil CO2 efflux are explained by increased below-ground carbon flux

The universally observed exponential increase in soil-surface CO2 efflux ( ` soil respiration ' ; FS ) with increasing temperature has led to speculation that global warming will accelerate soil-organic-carbon ( SOC ) decomposition , reduce SOC storage , and drive a positive feedback to future warming .
However , interpreting temperature-FS relationships , and so modelling terrestrial carbon balance in a warmer world , is complicated by the many sources of respired carbon that contribute to FS ( ref . )
and a poor understanding of how temperature influences SOC decomposition rates .
Here we quantified FS , litterfall , bulk SOC and SOC fraction size and turnover , and total below-ground carbon flux ( TBCF ) across a highly constrained 5.2 degreesC mean annual temperature ( MAT ) gradient in tropical montane wet forest .
From these , we determined that : increases in TBCF and litterfall explain > 90 % of the increase in FS with MAT ; bulk SOC and SOC fraction size and turnover rate do not vary with MAT ; and increases in TBCF and litterfall do not influence SOC storage or turnover on century to millennial timescales .
This gradient study shows that for tropical montane wet forest , long-term and whole-ecosystem warming accelerates below-ground carbon processes with no apparent impact on SOC storage .

[592] Impact of delay in reducing carbon dioxide emissions

Recent downward revisions in the climate response to rising CO2 levels , and opportunities for reducing non-CO2 climate warming , have both been cited as evidence that the case for reducing CO2 emissions is less urgent than previously thought .
Evaluating the impact of delay is complicated by the fact that CO2 emissions accumulate over time , so what happens after they peak is as relevant for long-term warming as the size and timing of the peak itself .
Previous discussions have focused on how the rate of reduction required to meet any given temperature target rises asymptotically the later the emissions peak .
Here we focus on a complementary question : how fast is peak CO2-induced warming increasing while mitigation is delayed , assuming no increase in rates of reduction after the emissions peak ?
We show that this peak-committed warming is increasing at the same rate as cumulative CO2 emissions , about 2 % per year , much faster than observed warming , independent of the climate response .

[593] Bioturbators enhance ecosystem function through complex biogeochemical interactions

Predicting the consequences of species loss is critically important , given present threats to biological diversity such as habitat destruction , overharvesting and climate change .
Several empirical studies have reported decreased ecosystem performance ( for example , primary productivity ) coincident with decreased biodiversity , although the relative influence of biotic effects and confounding abiotic factors has been vigorously debated .
Whereas several investigations focused on single trophic levels ( for example , grassland plants ) , studies of whole systems have revealed multiple layers of feedbacks , hidden drivers and emergent properties , making the consequences of species loss more difficult to predict .
Here we report functionally important organisms and considerable biocomplexity in a sedimentary seafloor habitat , one of Earth 's most widespread ecosystems .
Experimental field measurements demonstrate how the abundance of spatangoid urchins -- infaunal ( in seafloor sediment ) grazers / deposit feeders -- is positively related to primary production , as their activities change nutrient fluxes and improve conditions for production by microphytobenthos ( sedimentatry microbes and unicellular algae ) .
Declines of spatangoid urchins after trawling are well documented , and our research linking these bioturbators to important benthic-pelagic fluxes highlights potential ramifications for productivity in coastal oceans .

[594] Relative impacts of human-induced climate change and natural climate variability

Assessments of the regional impacts of human-induced climate change on a wide range of social and environmental systems are fundamental for determining the appropriate policy responses to climate change .
Yet regional-scale impact assessments are fraught with difficulties , such as the uncertainties of regional climate-change prediction , the specification of appropriate environmental-response models , and the interpretation of impact results in the context of future socio-economic and technological change .
The effects of such confounding factors on estimates of climate-change impacts have only been poorly explored .
Here we use results from recent global climate simulations and two environmental response models , to consider systematically the effects of natural climate variability ( 30-year timescales ) and future climate-change uncertainties on river runoff and agricultural potential in Europe .
We find that , for some regions , the impacts of human-induced climate change by 2050 will be undetectable relative to those due to natural multi-decadal climate variability .
If misleading assessments of -- and inappropriate adaptation strategies to -- climate-change impacts are to be avoided , future studies should consider the impacts of natural multi-decadal climate variability alongside those of human-induced climate change .

[595] Efficiency of short-lived halogens at influencing climate through depletion of stratospheric ozone

Halogens released from long-lived anthropogenic substances , such as chlorofluorocarbons , are the principal cause of recent depletion of stratospheric ozone , a greenhouse gas .
Recent observations show that very short-lived substances , with lifetimes generally under six months , are also an important source of stratospheric halogens .
Short-lived bromine substances are produced naturally by seaweed and phytoplankton , whereas short-lived chlorine substances are primarily anthropogenic .
Here we used a chemical transport model to quantify the depletion of ozone in the lower stratosphere from short-lived halogen substances , and a radiative transfer model to quantify the radiative effects of that ozone depletion .
According to our simulations , ozone loss from short-lived substances had a radiative effect nearly half that from long-lived halocarbons in 2011 and , since pre-industrial times , has contributed a total of about -0.02 W m-2 to global radiative forcing .
We find natural short-lived bromine substances exert a 3.6 times larger ozone radiative effect than long-lived halocarbons , normalized by halogen content , and show atmospheric levels of dichloromethane , a short-lived chlorine substance not controlled by the Montreal Protocol , are rapidly increasing .
We conclude that potential further significant increases in the atmospheric abundance of short-lived halogen substances , through changing natural processes or continued anthropogenic emissions , could be important for future climate .

[596] Forecasting Andean rainfall and crop yield from the influence of El Nino on Pleiades visibility

Farmers in drought-prone regions of Andean South America have historically made observations of changes in the apparent brightness of stars in the Pleiades around the time of the southern winter solstice in order to forecast interannual variations in summer rainfall and in autumn harvests .
They moderate the effect of reduced rainfall by adjusting the planting dates of potatoes , their most important crop .
Here we use data on cloud cover and water vapour from satellite imagery , agronomic data from the Andean altiplano and an index of El Nino variability to analyse this forecasting method .
We find that poor visibility of the Pleiades in June -- caused by an increase in subvisual high cirrus clouds -- is indicative of an El Nino year , which is usually linked to reduced rainfall during the growing season several months later .
Our results suggest that this centuries-old method of seasonal rainfall forecasting may be based on a simple indicator of El Nino variability .

[597] Spatial community shift from hard to soft corals in acidified water

Anthropogenic increases in the partial pressure of CO2 ( pCO2 ) cause ocean acidification , declining calcium carbonate saturation states , reduced coral reef calcification and changes in the compositions of marine communities .
Most projected community changes due to ocean acidification describe transitions from hard coral to non-calcifying macroalgal communities ; other organisms have received less attention , despite the biotic diversity of coral reef communities .
We show that the spatial distributions of both hard and soft coral communities in volcanically acidified , semi-enclosed waters off Iwotorishima Island , Japan , are related to pCO2 levels .
Hard corals are restricted to non-acidified low - pCO2 ( 225 muatm ) zones , dense populations of the soft coral Sarcophyton elegans dominate medium - pCO2 ( 831 muatm ) zones , and both hard and soft corals are absent from the highest - pCO2 ( 1,465 muatm ) zone .
In CO2-enriched culture experiments , high - pCO2 conditions benefited Sarcophyton elegans by enhancing photosynthesis rates and did not affect light calcification , but dark decalcification ( negative net calcification ) increased with increasing pCO2 .
These results suggest that reef communities may shift from reef-building hard corals to non-reef-building soft corals under pCO2 levels ( 550-970 muatm ) predicted by the end of this century , and that higher pCO2 levels would challenge the survival of some reef organisms .

[598] Contrasting arbuscular mycorrhizal responses of vascular and non-vascular plants to a simulated Palaeozoic CO2 decline

The arbuscular mycorrhizal ( AM ) fungal symbiosis is widely hypothesized to have promoted the evolution of land plants from rootless gametophytes to rooted sporophytes during the mid-Palaeozoic ( 480-360 Myr , ago ) , at a time coincident with a 90 % fall in the atmospheric CO2 concentration ( [ CO2 ] a ) .
Here we show using standardized dual isotopic tracers ( 14C and 33P ) that AM symbiosis efficiency ( defined as plant P gain per unit of C invested into fungi ) of liverwort gametophytes declines , but increases in the sporophytes of vascular plants ( ferns and angiosperms ) , at 440 p.p.m. compared with 1,500 p.p.m. [ CO2 ] a .
These contrasting responses are associated with larger AM hyphal networks , and structural advances in vascular plant water-conducting systems , promoting P transport that enhances AM efficiency at 440 p.p.m. [ CO2 ] a .
Our results suggest that non-vascular land plants not only faced intense competition for light , as vascular land floras grew taller in the Palaeozoic , but also markedly reduced efficiency and total capture of P as [ CO2 ] a fell .

[599] Arctic-nesting birds find physiological relief in the face of trophic constraints

A climate-induced phenological mismatch between the timing of reproduction and the timing of food resource peaks is one of the key hypothesized effects of climate change on wildlife .
Though supported as a mechanism of population decline in birds , few studies have investigated whether the same temperature increases that drive this mismatch have the potential to decrease energetic costs of growth and compensate for the potential negative effects of reduced food availability .
We generated independent indices of climate and resource availability and quantified their effects on growth of Dunlin ( Calidris alpina ) chicks , in the sub-arctic tundra of Churchill , Manitoba during the summers of 2010-2011 and found that when resource availability was below average , above average growth could be maintained in the presence of increasing temperatures .
These results provide evidence that chicks may find physiological relief from the trophic constraints hypothesized by climate change studies .

[600] Rising river flows throughout the twenty-first century in two Himalayan glacierized watersheds

Greater Himalayan glaciers are retreating and losing mass at rates comparable to glaciers in other regions of the world .
Assessments of future changes and their associated hydrological impacts are scarce , oversimplify glacier dynamics or include a limited number of climate models .
Here , we use results from the latest ensemble of climate models in combination with a high-resolution glacio-hydrological model to assess the hydrological impact of climate change on two climatically contrasting watersheds in the Greater Himalaya , the Baltoro and Langtang watersheds that drain into the Indus and Ganges rivers , respectively .
We show that the largest uncertainty in future runoff is a result of variations in projected precipitation between climate models .
In both watersheds , strong , but highly variable , increases in future runoff are projected and , despite the different characteristics of the watersheds , their responses are surprisingly similar .
In both cases , glaciers will recede but net glacier melt runoff is on a rising limb at least until 2050 .
In combination with a positive change in precipitation , water availability during this century is not likely to decline .
We conclude that river basins that depend on monsoon rains and glacier melt will continue to sustain the increasing water demands expected in these areas .

[601] Drought-induced carbon loss in peatlands

Peatlands store vast amounts of organic carbon , amounting to approximately 455 Pg .
Carbon builds up in these water-saturated environments owing to the presence of phenolic compounds -- which inhibit microbial activity and therefore prevent the breakdown of organic matter .
Anoxic conditions limit the activity of phenol oxidase , the enzyme responsible for the breakdown of phenolic compounds .
Droughts introduce oxygen into these systems , and the frequency of these events is rising .
Here , we combine in vitro manipulations , mesocosm experiments and field observations to examine the impact of drought on peatland carbon loss .
We show that drought stimulates bacterial growth and phenol oxidase activity , resulting in a reduction in the concentration of phenolic compounds in peat .
This further stimulates microbial growth , causing the breakdown of organic matter and the release of carbon dioxide in a biogeochemical cascade .
We further show that re-wetting the peat accelerates carbon losses to the atmosphere and receiving waters , owing to drought-induced increases in nutrient and labile carbon levels , which raise pH and stimulate anaerobic decomposition .
We suggest that severe drought , and subsequent re-wetting , could destabilize peatland carbon stocks ; understanding this process could aid understanding of interactions between peatlands and other environmental trends , and lead to the development of strategies for increasing carbon stocks .

[602] Economic development and the carbon intensity of human well-being

Humans use fossil fuels in various activities tied to economic development , leading to increases in carbon emissions , and economic development is widely recognized as a pathway to improving human well-being .
Strategies for effective sustainability efforts require reducing the carbon intensity of human well-being ( CIWB ) : the level of anthropogenic carbon emissions per unit of human well-being .
Here I examine how the effect of economic development on CIWB has changed since 1970 for 106 countries in multiple regional samples throughout the world .
I find that early in this time period , increased development led to a reduction in CIWB for nations in Africa , but in recent decades the relationship has changed , becoming less sustainable .
For nations in Asia and South and Central America , I find that development increases CIWB , and increasingly so throughout the 40-year period of study .
The effect of development on CIWB for nations in the combined regions of North America , Europe and Oceania has remained positive , relatively larger than in other regions , and stable through time .
Although future economic growth will probably improve human well-being throughout the world , this research suggests that it will also cost an increasing amount of carbon emissions .

[603] Phosphorus limitation of nitrogen fixation by Trichodesmium in the central Atlantic Ocean

Marine fixation of atmospheric nitrogen is believed to be an important source of biologically useful nitrogen to ocean surface waters , stimulating productivity of phytoplankton and so influencing the global carbon cycle .
The majority of nitrogen fixation in tropical waters is carried out by the marine cyanobacterium Trichodesmium , which supplies more than half of the new nitrogen used for primary production .
Although the factors controlling marine nitrogen fixation remain poorly understood , it has been thought that nitrogen fixation is limited by iron availability in the ocean .
This was inferred from the high iron requirement estimated for growth of nitrogen fixing organisms and the higher apparent densities of Trichodesmium where aeolian iron inputs are plentiful .
Here we report that nitrogen fixation rates in the central Atlantic appear to be independent of both dissolved iron levels in sea water and iron content in Trichodesmium colonies .
Nitrogen fixation was , instead , highly correlated to the phosphorus content of Trichodesmium and was enhanced at higher irradiance .
Furthermore , our calculations suggest that the structural iron requirement for the growth of nitrogen-fixing organisms is much lower than previously calculated .
Although iron deficiency could still potentially limit growth of nitrogen-fixing organisms in regions of low iron availability -- for example , in the subtropical North Pacific Ocean -- our observations suggest that marine nitrogen fixation is not solely regulated by iron supply .

[604] Microbial diversity and impact on carbonate geochemistry across a changing geochemical gradient in a karst aquifer

Although microbes are known to influence karst ( carbonate ) aquifer ecosystem-level processes , comparatively little information is available regarding the diversity of microbial activities that could influence water quality and geological modification .
To assess microbial diversity in the context of aquifer geochemistry , we coupled 16S rRNA Sanger sequencing and 454 tag pyrosequencing to in situ microcosm experiments from wells that cross the transition from fresh to saline and sulfidic water in the Edwards Aquifer of central Texas , one of the largest karst aquifers in the United States .
The distribution of microbial groups across the transition zone correlated with dissolved oxygen and sulfide concentration , and significant variations in community composition were explained by local carbonate geochemistry , specifically calcium concentration and alkalinity .
The waters were supersaturated with respect to prevalent aquifer minerals , calcite and dolomite , but in situ microcosm experiments containing these minerals revealed significant mass loss from dissolution when colonized by microbes .
Despite differences in cell density on the experimental surfaces , carbonate loss was greater from freshwater wells than saline , sulfidic wells .
However , as cell density increased , which was correlated to and controlled by local geochemistry , dissolution rates decreased .
Surface colonization by metabolically active cells promotes dissolution by creating local disequilibria between bulk aquifer fluids and mineral surfaces , but this also controls rates of karst aquifer modification .
These results expand our understanding of microbial diversity in karst aquifers and emphasize the importance of evaluating active microbial processes that could affect carbonate weathering in the subsurface .

[605] Forests fuel fish growth in freshwater deltas

Aquatic ecosystems are fuelled by biogeochemical inputs from surrounding lands and within-lake primary production .
Disturbances that change these inputs may affect how aquatic ecosystems function and deliver services vital to humans .
Here we test , using a forest cover gradient across eight separate catchments , whether disturbances that remove terrestrial biomass lower organic matter inputs into freshwater lakes , thereby reducing food web productivity .
We focus on deltas formed at the stream-lake interface where terrestrial-derived particulate material is deposited .
We find that organic matter export increases from more forested catchments , enhancing bacterial biomass .
This transfers energy upwards through communities of heavier zooplankton , leading to a fourfold increase in weights of planktivorous young-of-the-year fish .
At least 34 % of fish biomass is supported by terrestrial primary production , increasing to 66 % with greater forest cover .
Habitat tracers confirm fish were closely associated with individual catchments , demonstrating that watershed protection and restoration increase biomass in critical life-stages of fish .

[606] Crop yields in a geoengineered climate

Crop models predict that recent and future climate change may have adverse effects on crop yields .
Intentional deflection of sunlight away from the Earth could diminish the amount of climate change in a high-CO2 world .
However , it has been suggested that this diminution would come at the cost of threatening the food and water supply for billions of people .
Here , we carry out high-CO2 , geoengineering and control simulations using two climate models to predict the effects on global crop yields .
We find that in our models solar-radiation geoengineering in a high-CO2 climate generally causes crop yields to increase , largely because temperature stresses are diminished while the benefits of CO2 fertilization are retained .
Nevertheless , possible yield losses on the local scale as well as known and unknown side effects and risks associated with geoengineering indicate that the most certain way to reduce climate risks to global food security is to reduce emissions of greenhouse gases .

[607] Climate-driven changes in northeastern US butterfly communities

Climate warming is expected to change the distribution and abundance of many species .
Range shifts have been detected in a number of European taxa for which long-term government-initiated or organized-survey data are available .
In North America , well-organized long-term data needed to document such shifts are much less common .
Opportunistic observations made by citizen scientist groups may be an excellent alternative to systematic surveys .
From 1992 to 2010 , 19,779 butterfly surveys were made by amateur naturalists in Massachusetts , a geographically small state located at the convergence of northern and southern bioclimatic zones in eastern North America .
From these data , we estimated population trends for nearly all butterfly species ( 100 of 116 species present ) using list-length analysis .
Population trajectories indicate increases of many species near their northern range limits and declines in nearly all species ( 17 of 21 ) near their southern range limits .
Certain life-history traits , especially overwintering stage , were strongly associated with declines .
Our results suggest that a major , climate-induced shift of North American butterflies , characterized by northward expansions of warm-adapted and retreat of cold-adapted species , is underway .

[608] Signature of recent climate change in frequencies of natural atmospheric circulation regimes

A crucial question in the global-warming debate concerns the extent to which recent climate change is caused by anthropogenic forcing or is a manifestation of natural climate variability .
It is commonly thought that the climate response to anthropogenic forcing should be distinct from the patterns of natural climate variability .
But , on the basis of studies of nonlinear chaotic models with preferred states or ` regimes ' , it has been argued , that the spatial patterns of the response to anthropogenic forcing may in fact project principally onto modes of natural climate variability .
Here we use atmospheric circulation data from the Northern Hemisphere to show that recent climate change can be interpreted in terms of changes in the frequency of occurrence of natural atmospheric circulation regimes .
We conclude that recent Northern Hemisphere warming may be more directly related to the thermal structure of these circulation regimes than to any anthropogenic forcing pattern itself .
Conversely , the fact that observed climate change projects onto natural patterns can not be used as evidence of no anthropogenic effect on climate .
These results may help explain possible differences between trends in surface temperature and satellite-based temperature in the free atmosphere , , .

[609] Southern Ocean sea-ice extent , productivity and iron flux over the past eight glacial cycles

Sea ice and dust flux increased greatly in the Southern Ocean during the last glacial period .
Palaeorecords provide contradictory evidence about marine productivity in this region , but beyond one glacial cycle , data were sparse .
Here we present continuous chemical proxy data spanning the last eight glacial cycles ( 740,000 years ) from the Dome C Antarctic ice core .
These data constrain winter sea-ice extent in the Indian Ocean , Southern Ocean biogenic productivity and Patagonian climatic conditions .
We found that maximum sea-ice extent is closely tied to Antarctic temperature on multi-millennial timescales , but less so on shorter timescales .
Biological dimethylsulphide emissions south of the polar front seem to have changed little with climate , suggesting that sulphur compounds were not active in climate regulation .
We observe large glacial-interglacial contrasts in iron deposition , which we infer reflects strongly changing Patagonian conditions .
During glacial terminations , changes in Patagonia apparently preceded sea-ice reduction , indicating that multiple mechanisms may be responsible for different phases of CO2 increase during glacial terminations .
We observe no changes in internal climatic feedbacks that could have caused the change in amplitude of Antarctic temperature variations observed 440,000 years ago .

[610] Evolution of species interactions determines microbial community productivity in new environments

Diversity generally increases ecosystem productivity over short timescales .
Over longer timescales , both ecological and evolutionary responses to new environments could alter productivity and diversity-productivity relationships .
In turn , diversity might affect how component species adapt to new conditions .
We tested these ideas by culturing artificial microbial communities containing between 1 and 12 species in three different environments for ~ 60 generations .
The relationship between community yields and diversity became steeper over time in one environment .
This occurred despite a general tendency for the separate yields of isolates of constituent species to be lower at the end if they had evolved in a more diverse community .
Statistical comparisons of community and species yields showed that species interactions had evolved to be less negative over time , especially in more diverse communities .
Diversity and evolution therefore interacted to enhance community productivity in a new environment .

[611] Reduction in carbon uptake during turn of the century drought in western North America

Fossil fuel emissions aside , temperate North America is a net sink of carbon dioxide at present .
Year-to-year variations in this carbon sink are linked to variations in hydroclimate that affect net ecosystem productivity .
The severity and incidence of climatic extremes , including drought , have increased as a result of climate warming .
Here , we examine the effect of the turn of the century drought in western North America on carbon uptake in the region , using reanalysis data , remote sensing observations and data from global monitoring networks .
We show that the area-integrated strength of the western North American carbon sink declined by 30-298 Tg C yr-1 during the 2000-2004 drought .
We further document a pronounced drying of the terrestrial biosphere during this period , together with a reduction in river discharge and a loss of cropland productivity .
We compare our findings with previous palaeoclimate reconstructions and show that the last drought of this magnitude occurred more than 800 years ago .
Based on projected changes in precipitation and drought severity , we estimate that the present mid-latitude carbon sink of 177-623 Tg C yr-1 in western North America could disappear by the end of the century .

[612] Sulphide oxidation and carbonate dissolution as a source of CO2 over geological timescales

The observed stability of Earth 's climate over millions of years is thought to depend on the rate of carbon dioxide ( CO2 ) release from the solid Earth being balanced by the rate of CO2 consumption by silicate weathering .
During the Cenozoic era , spanning approximately the past 66 million years , the concurrent increases in the marine isotopic ratios of strontium , osmium and lithium suggest that extensive uplift of mountain ranges may have stimulated CO2 consumption by silicate weathering , but reconstructions of sea-floor spreading do not indicate a corresponding increase in CO2 inputs from volcanic degassing .
The resulting imbalance would have depleted the atmosphere of all CO2 within a few million years .
As a result , reconciling Cenozoic isotopic records with the need for mass balance in the long-term carbon cycle has been a major and unresolved challenge in geochemistry and Earth history .
Here we show that enhanced sulphide oxidation coupled to carbonate dissolution can provide a transient source of CO2 to Earth 's atmosphere that is relevant over geological timescales .
Like drawdown by means of silicate weathering , this source is probably enhanced by tectonic uplift , and so may have contributed to the relative stability of the partial pressure of atmospheric CO2 during the Cenozoic .
A variety of other hypotheses have been put forward to explain the ` Cenozoic isotope-weathering paradox ' , and the evolution of the carbon cycle probably depended on multiple processes .
However , an important role for sulphide oxidation coupled to carbonate dissolution is consistent with records of radiogenic isotopes , atmospheric CO2 partial pressure and the evolution of the Cenozoic sulphur cycle , and could be accounted for by geologically reasonable changes in the global dioxygen cycle , suggesting that this CO2 source should be considered a potentially important but as yet generally unrecognized component of the long-term carbon cycle .

[613] Slip-stick and the evolution of frictional strength

The evolution of frictional strength has great fundamental and practical importance .
Applications range from earthquake dynamics to hard-drive read/write cycles .
Frictional strength is governed by the resistance to shear of the large ensemble of discrete contacts that forms the interface that separates two sliding bodies .
An interface 's overall strength is determined by both the real contact area and the contacts ' shear strength .
Whereas the average motion of large , slowly sliding bodies is well-described by empirical friction laws , interface strength is a dynamic entity that is inherently related to both fast processes such as detachment/re-attachment and the slow process of contact area rejuvenation .
Here we show how frictional strength evolves from extremely short to long timescales , by continuous measurements of the concurrent local evolution of the real contact area and the corresponding interface motion ( slip ) from the first microseconds when contact detachment occurs to large ( 100-second ) timescales .
We identify four distinct and inter-related phases of evolution .
First , all of the local contact area reduction occurs within a few microseconds , on the passage of a crack-like front .
This is followed by the onset of rapid slip over a characteristic time , the value of which suggests a fracture-induced reduction of contact strength before any slip occurs .
This rapid slip phase culminates with a sharp transition to slip at velocities an order of magnitude slower .
At slip arrest , ` ageing ' immediately commences as contact area increases on a characteristic timescale determined by the system 's local memory of its effective contact time before slip arrest .
We show how the singular logarithmic behaviour generally associated with ageing is cut off at short times .
These results provide a comprehensive picture of how frictional strength evolves from the short times and rapid slip velocities at the onset of motion to ageing at the long times following slip arrest .

[614] Effect of trace metal availability on coccolithophorid calcification

The deposition of atmospheric dust into the ocean has varied considerably over geological time .
Because some of the trace metals contained in dust are essential plant nutrients which can limit phytoplankton growth in parts of the ocean , it has been suggested that variations in dust supply to the surface ocean might influence primary production .
Whereas the role of trace metal availability in photosynthetic carbon fixation has received considerable attention , its effect on biogenic calcification is virtually unknown .
The production of both particulate organic carbon and calcium carbonate ( CaCO3 ) drives the ocean 's biological carbon pump .
The ratio of particulate organic carbon to CaCO3 export , the so-called rain ratio , is one of the factors determining CO2 sequestration in the deep ocean .
Here we investigate the influence of the essential trace metals iron and zinc on the prominent CaCO3-producing microalga Emiliania huxleyi .
We show that whereas at low iron concentrations growth and calcification are equally reduced , low zinc concentrations result in a de-coupling of the two processes .
Despite the reduced growth rate of zinc-limited cells , CaCO3 production rates per cell remain unaffected , thus leading to highly calcified cells .
These results suggest that changes in dust deposition can affect biogenic calcification in oceanic regions characterized by trace metal limitation , with possible consequences for CO2 partitioning between the atmosphere and the ocean .

[615] Biodiversity decreases disease through predictable changes in host community competence

Accelerating rates of species extinctions and disease emergence underscore the importance of understanding how changes in biodiversity affect disease outcomes .
Over the past decade , a growing number of studies have reported negative correlations between host biodiversity and disease risk , prompting suggestions that biodiversity conservation could promote human and wildlife health .
Yet the generality of the diversity-disease linkage remains conjectural , in part because empirical evidence of a relationship between host competence ( the ability to maintain and transmit infections ) and the order in which communities assemble has proven elusive .
Here we integrate high-resolution field data with multi-scale experiments to show that host diversity inhibits transmission of the virulent pathogen Ribeiroia ondatrae and reduces amphibian disease as a result of consistent linkages among species richness , host composition and community competence .
Surveys of 345 wetlands indicated that community composition changed nonrandomly with species richness , such that highly competent hosts dominated in species-poor assemblages whereas more resistant species became progressively more common in diverse assemblages .
As a result , amphibian species richness strongly moderated pathogen transmission and disease pathology among 24,215 examined hosts , with a 78.4 % decline in realized transmission in richer assemblages .
Laboratory and mesocosm manipulations revealed an approximately 50 % decrease in pathogen transmission and host pathology across a realistic diversity gradient while controlling for host density , helping to establish mechanisms underlying the diversity-disease relationship and their consequences for host fitness .
By revealing a consistent link between species richness and community competence , these findings highlight the influence of biodiversity on infection risk and emphasize the benefit of a community-based approach to understanding infectious diseases .

[616] Interdependence of groundwater dynamics and land-energy feedbacks under climate change

Climate change will have a significant impact on the hydrologic cycle , creating changes in freshwater resources , land cover and land-atmosphere feedbacks .
Recent studies have investigated the response of groundwater to climate change but do not account for energy feedbacks across the complete hydrologic cycle .
Although land-surface models have begun to include an operational groundwater-type component , they do not include physically based lateral surface and subsurface flow and allow only for vertical transport processes .
Here we use a variably saturated groundwater flow model with integrated overland flow and land-surface model processes to examine the interplay between water and energy flows in a changing climate for the southern Great Plains , USA , an important agricultural region that is susceptible to drought .
We compare three scenario simulations with modified atmospheric forcing in terms of temperature and precipitation with a simulation of present-day climate .
We find that groundwater depth , which results from lateral water flow at the surface and subsurface , determines the relative susceptibility of regions to changes in temperature and precipitation .
This groundwater control is critical to understand processes of recharge and drought in a changing climate .

[617] Land use alters the resistance and resilience of soil food webs to drought

Soils deliver several ecosystem services including carbon sequestration and nutrient cycling , which are of central importance to climate mitigation and sustainable food production .
Soil biota play an important role in carbon and nitrogen cycling , and , although the effects of land use on soil food webs are well documented , the consequences for their resistance and resilience to climate change are not known .
We compared the resistance and resilience to drought -- which is predicted to increase under climate change -- of soil food webs of two common land-use systems : intensively managed wheat with a bacterial-based soil food web and extensively managed grassland with a fungal-based soil food web .
We found that the fungal-based food web , and the processes of C and N loss it governs , of grassland soil was more resistant , although not resilient , and better able to adapt to drought than the bacterial-based food web of wheat soil .
Structural equation modelling revealed that fungal-based soil food webs and greater microbial evenness mitigated C and N loss .
Our findings show that land use strongly affects the resistance and resilience of soil food webs to climate change , and that extensively managed grassland promotes more resistant , and adaptable , fungal-based soil food webs .

[618] The next generation of scenarios for climate change research and assessment

Advances in the science and observation of climate change are providing a clearer understanding of the inherent variability of Earth 's climate system and its likely response to human and natural influences .
The implications of climate change for the environment and society will depend not only on the response of the Earth system to changes in radiative forcings , but also on how humankind responds through changes in technology , economies , lifestyle and policy .
Extensive uncertainties exist in future forcings of and responses to climate change , necessitating the use of scenarios of the future to explore the potential consequences of different response options .
To date , such scenarios have not adequately examined crucial possibilities , such as climate change mitigation and adaptation , and have relied on research processes that slowed the exchange of information among physical , biological and social scientists .
Here we describe a new process for creating plausible scenarios to investigate some of the most challenging and important questions about climate change confronting the global community .

[619] Herbivores and nutrients control grassland plant diversity via light limitation

Human alterations to nutrient cycles and herbivore communities are affecting global biodiversity dramatically .
Ecological theory predicts these changes should be strongly counteractive : nutrient addition drives plant species loss through intensified competition for light , whereas herbivores prevent competitive exclusion by increasing ground-level light , particularly in productive systems .
Here we use experimental data spanning a globally relevant range of conditions to test the hypothesis that herbaceous plant species losses caused by eutrophication may be offset by increased light availability due to herbivory .
This experiment , replicated in 40 grasslands on 6 continents , demonstrates that nutrients and herbivores can serve as counteracting forces to control local plant diversity through light limitation , independent of site productivity , soil nitrogen , herbivore type and climate .
Nutrient addition consistently reduced local diversity through light limitation , and herbivory rescued diversity at sites where it alleviated light limitation .
Thus , species loss from anthropogenic eutrophication can be ameliorated in grasslands where herbivory increases ground-level light .

[620] Growth rates of Florida corals from 1937 to 1996 and their response to climate change

Ocean acidification causes declines in calcification rates of corals because of decreasing aragonite saturation states ( Omegaarag ) .
Recent evidence also indicates that increasing sea surface temperatures may have already reduced growth and calcification rates because of the stenothermic threshold of localized coral populations .
Density banding in coral skeletons provides a record of growth over the coral 's lifespan .
Here we present coral extension , bulk density and calcification master chronologies from seven subtropical corals ( Montastraea faveolata ) located in the Florida Keys , USA with a 60-year common period , 1937-1996 .
Linear trends indicate that extension increased , density decreased and calcification remained stable while the most recent decade was not significantly different than decadal averages over the preceding 50 years for extension and calcification .
The results suggest that growth rates in this species of subtropical coral have been tolerant to recent climatic changes up to the time of collection ( 1996 ) .

[621] Asian pollution climatically modulates mid-latitude cyclones following hierarchical modelling and observational analysis

Increasing levels of anthropogenic aerosols in Asia have raised considerable concern regarding its potential impact on the global atmosphere , but the magnitude of the associated climate forcing remains to be quantified .
Here , using a novel hierarchical modelling approach and observational analysis , we demonstrate modulated mid-latitude cyclones by Asian pollution over the past three decades .
Regional and seasonal simulations using a cloud-resolving model show that Asian pollution invigorates winter cyclones over the northwest Pacific , increasing precipitation by 7 % and net cloud radiative forcing by 1.0 W m-2 at the top of the atmosphere and by 1.7 W m-2 at the Earth 's surface .
A global climate model incorporating the diabatic heating anomalies from Asian pollution produces a 9 % enhanced transient eddy meridional heat flux and reconciles a decadal variation of mid-latitude cyclones derived from the Reanalysis data .
Our results unambiguously reveal a large impact of the Asian pollutant outflows on the global general circulation and climate .

[622] Abrupt pre-Bolling-Allerod warming and circulation changes in the deep ocean

Several large and rapid changes in atmospheric temperature and the partial pressure of carbon dioxide in the atmosphere -- probably linked to changes in deep ocean circulation -- occurred during the last deglaciation .
The abrupt temperature rise in the Northern Hemisphere and the restart of the Atlantic meridional overturning circulation at the start of the Bolling-Allerod interstadial , 14,700 years ago , are among the most dramatic deglacial events , but their underlying physical causes are not known .
Here we show that the release of heat from warm waters in the deep North Atlantic Ocean probably triggered the Bolling-Allerod warming and reinvigoration of the Atlantic meridional overturning circulation .
Our results are based on coupled radiocarbon and uranium-series dates , along with clumped isotope temperature estimates , from water column profiles of fossil deep-sea corals in a limited area of the western North Atlantic .
We find that during Heinrich stadial 1 ( the cool period immediately before the Bolling-Allerod interstadial ) , the deep ocean was about three degrees Celsius warmer than shallower waters above .
This reversal of the ocean 's usual thermal stratification pre-dates the Bolling-Allerod warming and must have been associated with increased salinity at depth to preserve the static stability of the water column .
The depleted radiocarbon content of the warm and salty water mass implies a long-term disconnect from rapid surface exchanges , and , although uncertainties remain , is most consistent with a Southern Ocean source .
The Heinrich stadial 1 ocean profile is distinct from the modern water column , that for the Last Glacial Maximum and that for the Younger Dryas , suggesting that the patterns we observe are a unique feature of the deglacial climate system .
Our observations indicate that the deep ocean influenced dramatic Northern Hemisphere warming by storing heat at depth that preconditioned the system for a subsequent abrupt overturning event during the Bolling-Allerod interstadial .

[623] Modulation of cadmium uptake in phytoplankton by seawater CO2 concentration

The vertical distribution of cadmium in the ocean is characteristic of an algal nutrient , although an underlying physiological basis remains undiscovered .
The strong correlation between dissolved cadmium and phosphorus concentrations in sea water has nevertheless been exploited for reconstructing past nutrient distributions in the ocean .
In culture experiments , the addition of cadmium accelerates the growth of some marine phytoplankton and increases the activity of carbonic anhydrase , normally a zinc-based metalloenzyme that is involved in inorganic carbon acquisition .
Here we show that the concentration of a Cd-carbonic-anhydrase -- distinct from Zn-carbonic-anhydrases -- in a marine diatom is regulated by the CO2 partial pressure ( pCO2 ) as well as by the zinc concentration .
Field studies in intensely productive coastal waters off central California demonstrate that cadmium content in natural phytoplankton populations similarly increases as surface-water pCO2 decreases .
Incubation experiments confirm that cadmium uptake by natural phytoplankton is inversely related to seawater pCO2 and zinc concentration .
We thus propose that biological removal of cadmium from ocean surface waters is related to its utilization in carbonic anhydrase , and is regulated by dissolved CO2 and zinc concentrations .
The dissolved seawater Cd/P ratio would therefore vary with atmospheric pCO2 , complicating the use of cadmium as a tracer of past nutrient concentrations in the upper ocean .

[624] Observed and predicted effects of climate change on species abundance in protected areas

The dynamic nature and diversity of species ' responses to climate change poses significant difficulties for developing robust , long-term conservation strategies .
One key question is whether existing protected area networks will remain effective in a changing climate .
To test this , we developed statistical models that link climate to the abundance of internationally important bird populations in northwestern Europe .
Spatial climate-abundance models were able to predict 56 % of the variation in recent 30-year population trends .
Using these models , future climate change resulting in 4.0 degreesC global warming was projected to cause declines of at least 25 % for more than half of the internationally important populations considered .
Nonetheless , most EU Special Protection Areas in the UK were projected to retain species in sufficient abundances to maintain their legal status , and generally sites that are important now were projected to be important in the future .
The biological and legal resilience of this network of protected areas is derived from the capacity for turnover in the important species at each site as species ' distributions and abundances alter in response to climate .
Current protected areas are therefore predicted to remain important for future conservation in a changing climate .

[625] Berberine activates thermogenesis in white and brown adipose tissue

Obesity develops when energy intake exceeds energy expenditure .
Promoting brown adipose tissue formation and function increases energy expenditure and hence may counteract obesity .
Berberine ( BBR ) is a compound derived from the Chinese medicinal plant Coptis chinensis .
Here we show that BBR increases energy expenditure , limits weight gain , improves cold tolerance and enhances brown adipose tissue ( BAT ) activity in obese db/db mice .
BBR markedly induces the development of brown-like adipocytes in inguinal , but not epididymal adipose depots .
BBR also increases expression of UCP1 and other thermogenic genes in white and BAT and primary adipocytes via a mechanism involving AMPK and PGC-1alpha .
BBR treatment also inhibits AMPK activity in the hypothalamus , but genetic activation of AMPK in the ventromedial nucleus of the hypothalamus does not prevent BBR-induced weight loss and activation of the thermogenic programme .
Our findings establish a role for BBR in regulating organismal energy balance , which may have potential therapeutic implications for the treatment of obesity .

[626] Caesium accumulation in yeast and plants is selectively repressed by loss of the SNARE Sec22p/SEC22

The non-essential cation caesium ( Cs + ) is assimilated by all organisms .
Thus , anthropogenically released radiocaesium is of concern to agriculture .
Cs + accumulates owing to its chemical similarity to the potassium ion ( K + ) .
The apparent lack of a Cs + - specific uptake mechanism has obstructed attempts to manipulate Cs + accumulation without causing pleiotropic effects .
Here we show that the SNARE protein Sec22p/SEC22 specifically impacts Cs + accumulation in yeast and in plants .
Loss of Saccharomyces cerevisiae Sec22p does not affect K + homeostasis , yet halves Cs + concentration compared with the wild type .
Mathematical modelling of the uptake time course predicts a compromised vacuolar Cs + deposition in sec22Delta .
Biochemical fractionation confirms this and indicates a new feature of Sec22p in enhancing non-selective cation deposition .
A developmentally controlled loss-of-function mutant of the orthologous Arabidopsis thaliana SEC22 phenocopies the reduced Cs + uptake without affecting plant growth .
This finding provides a new strategy to reduce radiocaesium entry into the food chain .

[627] Extracellular electron transfer through microbial reduction of solid-phase humic substances

The decay of soil and sedimentary organic matter yieldsorganic compounds with a high molecular weight , termed humic substances .
Microorganisms can transfer electrons to dissolved humic substances , and reduced humic substances can rapidly reduce iron ( III ) oxides .
Thus , dissolved humic substances can serve as electron shuttles that promote iron ( III ) oxide reduction in sediments .
However , most humic substances in soils and sediments are in particulate , rather than dissolved , form ; the ability of microorganisms to reduce solid-phase humics and their capacity to shuttle electrons is thus far unknown .
Here we show through incubation experiments and electron spin resonance measurements that iron ( III ) - oxide-reducing bacteria can transfer electrons to solid-phase humic substances in sediments sampled from wetlands .
Although the electron-accepting capacity of the solid-phase humics was modest , solid-phase humics significantly accelerated iron ( III ) oxide reduction , by shuttling electrons from bacteria to oxide surfaces .
Microbial solid-phase humics reduction represents a new mechanism for extracellular electron transfer that can facilitate reduction of iron ( III ) oxide and other redox reactions in sediments and soils .

[628] High-resolution summer precipitation variations in the western Chinese Loess Plateau during the last glacial

We present a summer precipitation reconstruction for the last glacial ( LG ) on the western edge of the Chinese Loess Plateau ( CLP ) using a well-dated organic carbon isotopic dataset together with an independent modern process study results .
Our results demonstrate that summer precipitation variations in the CLP during the LG were broadly correlated to the intensity of the Asian summer monsoon ( ASM ) as recorded by stalagmite oxygen isotopes from southern China .
During the last deglaciation , the onset of the increase in temperatures at high latitudes in the Northern Hemisphere and decline in the intensity of the East Asia winter monsoon in mid latitudes was earlier than the increase in ASM intensity and our reconstructed summer precipitation in the western CLP .
Quantitative reconstruction of a single paleoclimatic factor provides new insights and opportunities for further understanding of the paleoclimatic variations in monsoonal East Asia and their relation to the global climatic system .

[629] Co-benefits of mitigating global greenhouse gas emissions for future air quality and human health

Actions to reduce greenhouse gas ( GHG ) emissions often reduce co-emitted air pollutants , bringing co-benefits for air quality and human health .
Past studies typically evaluated near-term and local co-benefits , neglecting the long-range transport of air pollutants , long-term demographic changes , and the influence of climate change on air quality .
Here we simulate the co-benefits of global GHG reductions on air quality and human health using a global atmospheric model and consistent future scenarios , via two mechanisms : reducing co-emitted air pollutants , and slowing climate change and its effect on air quality .
We use new relationships between chronic mortality and exposure to fine particulate matter and ozone , global modelling methods and new future scenarios .
Relative to a reference scenario , global GHG mitigation avoids 0.5 + / -0.2 , 1.3 + / -0.5 and 2.2 + / -0.8 million premature deaths in 2030 , 2050 and 2100 .
Global average marginal co-benefits of avoided mortality are US$ 50-380 per tonne of CO2 , which exceed previous estimates , exceed marginal abatement costs in 2030 and 2050 , and are within the low range of costs in 2100 .
East Asian co-benefits are 10-70 times the marginal cost in 2030 .
Air quality and health co-benefits , especially as they are mainly local and near-term , provide strong additional motivation for transitioning to a low-carbon future .

[630] Large-scale changes in Greenland outlet glacier dynamics triggered at the terminus

The recent marked retreat , thinning and acceleration of most of Greenland 's outlet glaciers south of 70degrees N has increased concerns over Greenland 's contribution to future sea level rise .
These dynamic changes seem to be parallel to the warming trend in Greenland , but the mechanisms that link climate and ice dynamics are poorly understood , and current numerical models of ice sheets do not simulate these changes realistically .
Uncertainties in the predictions of mass loss from the Greenland ice sheet have therefore been highlighted as one of the main limitations in forecasting future sea levels .
Here we present a numerical ice-flow model that reproduces the observed marked changes in Helheim Glacier , one of Greenland 's largest outlet glaciers .
Our simulation shows that the ice acceleration , thinning and retreat begin at the calving terminus and then propagate upstream through dynamic coupling along the glacier .
We find that these changes are unlikely to be caused by basal lubrication through surface melt propagating to the glacier bed .
We conclude that tidewater outlet glaciers adjust extremely rapidly to changing boundary conditions at the calving terminus .
Our results imply that the recent rates of mass loss in Greenland 's outlet glaciers are transient and should not be extrapolated into the future .

[631] Strong increase in convective precipitation in response to higher temperatures

Precipitation changes can affect society more directly than variations in most other meteorological observables , but precipitation is difficult to characterize because of fluctuations on nearly all temporal and spatial scales .
In addition , the intensity of extreme precipitation rises markedly at higher temperature , faster than the rate of increase in the atmosphere 's water-holding capacity , termed the Clausius-Clapeyron rate .
Invigoration of convective precipitation ( such as thunderstorms ) has been favoured over a rise in stratiform precipitation ( such as large-scale frontal precipitation ) as a cause for this increase , but the relative contributions of these two types of precipitation have been difficult to disentangle .
Here we combine large data sets from radar measurements and rain gauges over Germany with corresponding synoptic observations and temperature records , and separate convective and stratiform precipitation events by cloud observations .
We find that for stratiform precipitation , extremes increase with temperature at approximately the Clausius-Clapeyron rate , without characteristic scales .
In contrast , convective precipitation exhibits characteristic spatial and temporal scales , and its intensity in response to warming exceeds the Clausius-Clapeyron rate .
We conclude that convective precipitation responds much more sensitively to temperature increases than stratiform precipitation , and increasingly dominates events of extreme precipitation .

[632] Short-term parasite-infection alters already the biomass , activity and functional diversity of soil microbial communities

Native parasitic plants may be used to infect and control invasive plants .
We established microcosms with invasive Mikania micrantha and native Coix lacryma-jobi growing in mixture on native soils , with M. micrantha being infected by parasitic Cuscuta campestris at four intensity levels for seven weeks to estimate the top-down effects of plant parasitism on the biomass and functional diversity of soil microbial communities .
Parasitism significantly decreased root biomass and altered soil microbial communities .
Soil microbial biomass decreased , but soil respiration increased at the two higher infection levels , indicating a strong stimulation of soil microbial metabolic activity ( +180 % ) .
Moreover , a Biolog assay showed that the infection resulted in a significant change in the functional diversity indices of soil microbial communities .
Pearson correlation analysis indicated that microbial biomass declined significantly with decreasing root biomass , particularly of the invasive M. micrantha .
Also , the functional diversity indices of soil microbial communities were positively correlated with soil microbial biomass .
Therefore , the negative effects on the biomass , activity and functional diversity of soil microbial community by the seven week long plant parasitism was very likely caused by decreased root biomass and root exudation of the invasive M. micrantha .

[633] 135 years of global ocean warming between the Challenger expedition and the Argo Programme

Changing temperature throughout the oceans is a key indicator of climate change .
Since the 1960s about 90 % of the excess heat added to the Earth 's climate system has been stored in the oceans .
The ocean 's dominant role over the atmosphere , land , or cryosphere comes from its high heat capacity and ability to remove heat from the sea surface by currents and mixing .
The longest interval over which instrumental records of subsurface global-scale temperature can be compared is the 135 years between the voyage of HMS Challenger ( 1872-1876 ) and the modern data set of the Argo Programme ( 2004-2010 ) .
Argo 's unprecedented global coverage permits its comparison with any earlier measurements .
This , the first global-scale comparison of Challenger and modern data , shows spatial mean warming at the surface of 0.59 degreesC + / -0.12 , consistent with previous estimates of globally averaged sea surface temperature increase .
Below the surface the mean warming decreases to 0.39 degreesC + / -0.18 at 366 m ( 200 fathoms ) and 0.12 degreesC + / -0.07 at 914 m ( 500 fathoms ) .
The 0.33 degreesC + / -0.14 average temperature difference from 0 to 700 m is twice the value observed globally in that depth range over the past 50 years , implying a centennial timescale for the present rate of global warming .
Warming in the Atlantic Ocean is stronger than in the Pacific .
Systematic errors in the Challenger data mean that these temperature changes are a lower bound on the actual values .
This study underlines the scientific significance of the Challenger expedition and the modern Argo Programme and indicates that globally the oceans have been warming at least since the late-nineteenth or early-twentieth century .

[634] Mussel byssus attachment weakened by ocean acidification

Biomaterials connect organisms to their environments .
Their function depends on biological , chemical and environmental factors , both at the time of creation and throughout the life of the material .
Shifts in the chemistry of the oceans driven by anthropogenic CO2 ( termed ocean acidification ) have profound implications for the function of critical materials formed under these altered conditions .
Most ocean acidification studies have focused on one biomaterial ( secreted calcium carbonate ) , frequently using a single assay ( net rate of calcification ) to quantify whether reductions in environmental pH alter how organisms create biomaterials .
Here , we examine biological structures critical for the success of ecologically and economically important bivalve molluscs .
One non-calcified material , the proteinaceous byssal threads that anchor mytilid mussels to hard substrates , exhibited reduced mechanical performance when secreted under elevated pCO2 conditions , whereas shell and tissue growth were unaffected .
Threads made under high pCO2 ( > 1,200 muatm ) were weaker and less extensible owing to compromised attachment to the substratum .
According to a mathematical model , this reduced byssal fibre performance , decreasing individual tenacity by 40 % .
In the face of ocean acidification , weakened attachment presents a potential challenge for suspension-culture mussel farms and for intertidal communities anchored by mussel beds .

[635] Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning

During the last glacial termination , the upwelling strength of the southern polar limb of the Atlantic Meridional Overturning Circulation varied , changing the ventilation and stratification of the high-latitude Southern Ocean .
During the same period , at least two phases of abrupt global sea-level rise -- meltwater pulses -- took place .
Although the timing and magnitude of these events have become better constrained , a causal link between ocean stratification , the meltwater pulses and accelerated ice loss from Antarctica has not been proven .
Here we simulate Antarctic ice sheet evolution over the last 25 kyr using a data-constrained ice-sheet model forced by changes in Southern Ocean temperature from an Earth system model .
Results reveal several episodes of accelerated ice-sheet recession , the largest being coincident with meltwater pulse 1A .
This resulted from reduced Southern Ocean overturning following Heinrich Event 1 , when warmer subsurface water thermally eroded grounded marine-based ice and instigated a positive feedback that further accelerated ice-sheet retreat .

[636] Modulation of oxygen production in Archaean oceans by episodes of Fe ( II ) toxicity

Oxygen accumulated in the surface waters of the Earth 's oceans and atmosphere several hundred million years before the Great Oxidation Event between 2.4 and 2.3 billion years ago .
Before the Great Oxidation Event , periods of enhanced submarine volcanism associated with mantle plume events supplied Fe ( II ) to sea water .
These periods generally coincide with the disappearance of indicators of the presence of molecular oxygen in Archaean sedimentary records .
The presence of Fe ( II ) in the water column can lead to oxidative stress in some organisms as a result of reactions between Fe ( II ) and oxygen that produce reactive oxygen species .
Here we test the hypothesis that the upwelling of Fe ( II ) - rich , anoxic water into the photic zone during the late Archaean subjected oxygenic phototrophic bacteria to Fe ( II ) toxicity .
In laboratory experiments , we found that supplying Fe ( II ) to the anoxic growth medium housing a common species of planktonic cyanobacteria decreased both the efficiency of oxygenic photosynthesis and their growth rates .
We suggest that this occurs because of increasing intracellular concentrations of reactive oxygen species .
We use geochemical modelling to show that Fe ( II ) toxicity in conditions found in the late Archaean photic zone could have substantially inhibited water column oxygen production , thus decreasing fluxes of oxygen to the atmosphere .
We therefore propose that the timing of atmospheric oxygenation was controlled by the timing of submarine , plume-type volcanism , with Fe ( II ) toxicity as the modulating factor .

[637] Rapid Cenozoic glaciation of Antarctica induced by declining atmospheric CO2

The sudden , widespread glaciation of Antarctica and the associated shift towards colder temperatures at the Eocene/Oligocene boundary ( ~ 34 million years ago ) ( refs 1-4 ) is one of the most fundamental reorganizations of global climate known in the geologic record .
The glaciation of Antarctica has hitherto been thought to result from the tectonic opening of Southern Ocean gateways , which enabled the formation of the Antarctic Circumpolar Current and the subsequent thermal isolation of the Antarctic continent .
Here we simulate the glacial inception and early growth of the East Antarctic Ice Sheet using a general circulation model with coupled components for atmosphere , ocean , ice sheet and sediment , and which incorporates palaeogeography , greenhouse gas , changing orbital parameters , and varying ocean heat transport .
In our model , declining Cenozoic CO2 first leads to the formation of small , highly dynamic ice caps on high Antarctic plateaux .
At a later time , a CO2 threshold is crossed , initiating ice-sheet height/mass-balance feedbacks that cause the ice caps to expand rapidly with large orbital variations , eventually coalescing into a continental-scale East Antarctic Ice Sheet .
According to our simulation the opening of Southern Ocean gateways plays a secondary role in this transition , relative to CO2 concentration .

[638] Response of El Nino sea surface temperature variability to greenhouse warming

The destructive environmental and socio-economic impacts of the El Nino/Southern Oscillation ( ENSO ) demand an improved understanding of how ENSO will change under future greenhouse warming .
Robust projected changes in certain aspects of ENSO have been recently established .
However , there is as yet no consensus on the change in the magnitude of the associated sea surface temperature ( SST ) variability , commonly used to represent ENSO amplitude , despite its strong effects on marine ecosystems and rainfall worldwide .
Here we show that the response of ENSO SST amplitude is time-varying , with an increasing trend in ENSO amplitude before 2040 , followed by a decreasing trend thereafter .
We attribute the previous lack of consensus to an expectation that the trend in ENSO amplitude over the entire twenty-first century is unidirectional , and to unrealistic model dynamics of tropical Pacific SST variability .
We examine these complex processes across 22 models in the Coupled Model Intercomparison Project phase 5 ( CMIP5 ) database , forced under historical and greenhouse warming conditions .
The nine most realistic models identified show a strong consensus on the time-varying response and reveal that the non-unidirectional behaviour is linked to a longitudinal difference in the surface warming rate across the Indo-Pacific basin .
Our results carry important implications for climate projections and climate adaptation pathways .

[639] Phosphate addition enhanced soil inorganic nutrients to a large extent in three tropical forests

Elevated nitrogen ( N ) deposition may constrain soil phosphorus ( P ) and base cation availability in tropical forests , for which limited evidence have yet been available .
In this study , we reported responses of soil inorganic nutrients to full factorial N and P treatments in three tropical forests different in initial soil N status ( N-saturated old-growth forest and two less-N-rich younger forests ) .
Responses of microbial biomass , annual litterfall production and nutrient input were also monitored .
Results showed that N treatments decreased soil inorganic nutrients ( except N ) in all three forests , but the underlying mechanisms varied depending on forests : through inhibition on litter decomposition in the old-growth forest and through Al3 + replacement of Ca2 + in the two younger forests .
In contrast , besides great elevation in soil available P , P treatments induced 60 % , 50 % , 26 % increases in sum of exchangeable ( K + + Ca2 + + Mg2 + ) in the old-growth and the two younger forests , respectively .
These positive effects of P were closely related to P-stimulated microbial biomass and litter nutrient input , implying possible stimulation of nutrient return .
Our results suggest that N deposition may result in decreases in soil inorganic nutrients ( except N ) and that P addition can enhance soil inorganic nutrients to support ecosystem processes in these tropical forests .

[640] Revolatilization of persistent organic pollutants in the Arctic induced by climate change

Persistent organic pollutants ( POPs ) are organic compounds produced by human activities that are resistant to environmental degradation .
They include industrial chemicals , such as polychlorinated biphenyls , and pesticides , such as dichlorodiphenyltrichloroethane .
Owing to their persistence in the environment , POPs are transported long distances in the atmosphere , accumulating in regions such as the Arctic , where low temperatures induce their deposition .
Here the compounds accumulate in wildlife and humans , putting their health at risk .
The concentrations of many POPs have decreased in Arctic air over the past few decades owing to restrictions on their production and use .
As the climate warms , however , POPs deposited in sinks such as water and ice are expected to revolatilize into the atmosphere , and there is evidence that this process may have already begun for volatile compounds .
Here we show that many POPs , including those with lower volatilities , are being remobilized into the air from repositories in the Arctic region as a result of sea-ice retreat and rising temperatures .
We analysed records of the concentrations of POPs in Arctic air since the early 1990s and compared the results with model simulations of the effect of climate change on their atmospheric abundances .
Our results indicate that a wide range of POPs have been remobilized into the Arctic atmosphere over the past two decades as a result of climate change , confirming that Arctic warming could undermine global efforts to reduce environmental and human exposure to these toxic chemicals .

[641] Grazing-induced reduction of natural nitrous oxide release from continental steppe

Atmospheric concentrations of the greenhouse gas nitrous oxide ( N2O ) have increased significantly since pre-industrial times owing to anthropogenic perturbation of the global nitrogen cycle , with animal production being one of the main contributors .
Grasslands cover about 20 per cent of the temperate land surface of the Earth and are widely used as pasture .
It has been suggested that high animal stocking rates and the resulting elevated nitrogen input increase N2O emissions .
Internationally agreed methods to upscale the effect of increased livestock numbers on N2O emissions are based directly on per capita nitrogen inputs .
However , measurements of grassland N2O fluxes are often performed over short time periods , with low time resolution and mostly during the growing season .
In consequence , our understanding of the daily and seasonal dynamics of grassland N2O fluxes remains limited .
Here we report year-round N2O flux measurements with high and low temporal resolution at ten steppe grassland sites in Inner Mongolia , China .
We show that short-lived pulses of N2O emission during spring thaw dominate the annual N2O budget at our study sites .
The N2O emission pulses are highest in ungrazed steppe and decrease with increasing stocking rate , suggesting that grazing decreases rather than increases N2O emissions .
Our results show that the stimulatory effect of higher stocking rates on nitrogen cycling and , hence , on N2O emission is more than offset by the effects of a parallel reduction in microbial biomass , inorganic nitrogen production and wintertime water retention .
By neglecting these freeze-thaw interactions , existing approaches may have systematically overestimated N2O emissions over the last century for semi-arid , cool temperate grasslands by up to 72 per cent .

[642] Climate-driven trends in contemporary ocean productivity

Contributing roughly half of the biosphere 's net primary production ( NPP ) , photosynthesis by oceanic phytoplankton is a vital link in the cycling of carbon between living and inorganic stocks .
Each day , more than a hundred million tons of carbon in the form of CO2 are fixed into organic material by these ubiquitous , microscopic plants of the upper ocean , and each day a similar amount of organic carbon is transferred into marine ecosystems by sinking and grazing .
The distribution of phytoplankton biomass and NPP is defined by the availability of light and nutrients ( nitrogen , phosphate , iron ) .
These growth-limiting factors are in turn regulated by physical processes of ocean circulation , mixed-layer dynamics , upwelling , atmospheric dust deposition , and the solar cycle .
Satellite measurements of ocean colour provide a means of quantifying ocean productivity on a global scale and linking its variability to environmental factors .
Here we describe global ocean NPP changes detected from space over the past decade .
The period is dominated by an initial increase in NPP of 1,930 teragrams of carbon a year ( Tg C yr-1 ) , followed by a prolonged decrease averaging 190 Tg C yr-1 .
These trends are driven by changes occurring in the expansive stratified low-latitude oceans and are tightly coupled to coincident climate variability .
This link between the physical environment and ocean biology functions through changes in upper-ocean temperature and stratification , which influence the availability of nutrients for phytoplankton growth .
The observed reductions in ocean productivity during the recent post-1999 warming period provide insight on how future climate change can alter marine food webs .

[643] Geographically structured host specificity is caused by the range expansions and host shifts of a symbiotic fungus

The inability to associate with local species may constrain the spread of mutualists arriving to new habitats , but the fates of introduced , microbial mutualists are largely unknown .
The deadly poisonous ectomycorrhizal fungus Amanita phalloides ( the death cap ) is native to Europe and introduced to the East and West Coasts of North America .
By cataloging host associations across the two continents , we record dramatic changes in specificity among the three ranges .
On the East Coast , where the fungus is restricted in its distribution , it associates almost exclusively with pines , which are rarely hosts of A. phalloides in its native range .
In California , where the fungus is widespread and locally abundant , it associates almost exclusively with oaks , mirroring the host associations observed in Europe .
The most common host of the death cap in California is the endemic coast live oak ( Quercus agrifolia ) , and the current distribution of A. phalloides appears constrained within the distribution of Q. agrifolia .
In California , host shifts to native plants are also associated with a near doubling in the resources allocated to sexual reproduction and a prolonged fruiting period ; mushrooms are twice as large as they are elsewhere and mushrooms are found throughout the year .
Host and niche shifts are likely to shape the continuing range expansion of A. phalloides and other ectomycorrhizal fungi introduced across the world .

[644] Increase in the range between wet and dry season precipitation

Global temperatures have risen over the past few decades .
The water vapour content of the atmosphere has increased as a result , strengthening the global hydrological cycle .
This , in turn , has led to wet regions getting wetter , and dry regions drier .
Climate model simulations suggest that a similar intensification of existing patterns may also apply to the seasonal cycle of rainfall .
Here , we analyse regional and global trends in seasonal precipitation extremes over the past three decades , using a number of global and land-alone observational data sets .
We show that globally the annual range of precipitation has increased , largely because wet seasons have become wetter .
Although the magnitude of the shift is uncertain , largely owing to limitations inherent in the data sets used , the sign of the tendency is robust .
On a regional scale , the tendency for wet seasons to get wetter occurs over climatologically rainier regions .
Similarly , the tendency for dry season to get drier is seen in drier regions .
Even if the total amount of annual rainfall does not change significantly , the enhancement in the seasonal precipitation cycle could have marked consequences for the frequency of droughts and floods .

[645] Reduction in local ozone levels in urban Sao Paulo due to a shift from ethanol to gasoline use

Ethanol-based vehicles are thought to generate less pollution than gasoline-based vehicles , because ethanol emissions contain lower concentrations of mono-nitrogen oxides than those from gasoline emissions .
However , the predicted effect of various gasoline/ethanol blends on the concentration of atmospheric pollutants such as ozone varies between model and laboratory studies , including those that seek to simulate the same environmental conditions .
Here , we report the consequences of a real-world shift in fuel use in the subtropical megacity of Sao Paulo , Brazil , brought on by large-scale fluctuations in the price of ethanol relative to gasoline between 2009 and 2011 .
We use highly spatially and temporally resolved observations of road traffic levels , meteorology and pollutant concentrations , together with a consumer demand model , to show that ambient ozone concentrations fell by about 20 % as the share of bi-fuel vehicles burning gasoline rose from 14 to 76 % .
In contrast , nitric oxide and carbon monoxide concentrations increased .
We caution that although gasoline use seems to lower ozone levels in the Sao Paulo metropolitan area relative to ethanol use , strategies to reduce ozone pollution require knowledge of the local chemistry and consideration of other pollutants , particularly fine particles .

[646] Orbital forcing of the East Antarctic ice sheet during the Pliocene and Early Pleistocene

The Pliocene and Early Pleistocene , between 5.3 and 0.8 million years ago , span a transition from a global climate state that was 2-3 degreesC warmer than present with limited ice sheets in the Northern Hemisphere to one that was characterized by continental-scale glaciations at both poles .
Growth and decay of these ice sheets was paced by variations in the Earth 's orbit around the Sun .
However , the nature of the influence of orbital forcing on the ice sheets is unclear , particularly in light of the absence of a strong 20,000-year precession signal in geologic records of global ice volume and sea level .
Here we present a record of the rate of accumulation of iceberg-rafted debris offshore from the East Antarctic ice sheet , adjacent to the Wilkes Subglacial Basin , between 4.3 and 2.2 million years ago .
We infer that maximum iceberg debris accumulation is associated with the enhanced calving of icebergs during ice-sheet margin retreat .
In the warmer part of the record , between 4.3 and 3.5 million years ago , spectral analyses show a dominant periodicity of about 40,000 years .
Subsequently , the powers of the 100,000-year and 20,000-year signals strengthen .
We suggest that , as the Southern Ocean cooled between 3.5 and 2.5 million years ago , the development of a perennial sea-ice field limited the oceanic forcing of the ice sheet .
After this threshold was crossed , substantial retreat of the East Antarctic ice sheet occurred only during austral summer insolation maxima , as controlled by the precession cycle .

[647] The role of subglacial water in ice-sheet mass balance

In the coming decades , significant changes in the polar regions will increase the contribution of ice sheets to global sea-level rise .
Under the ice streams and outlet glaciers that deliver ice to the oceans , water and deformable wet sediments lubricate the base , facilitating fast ice flow .
The influence of subglacial water on fast ice flow depends on the geometry and capacity of the subglacial hydrologic system : water moving rapidly through a well-connected system of conduits or channels will have little impact on ice-sheet velocities , but water injected into a spatially dispersed subglacial system may reduce the effective pressure at the base of the ice sheet , and thereby trigger increased ice-sheet velocities .
In Greenland , the form of the subglacial hydrologic system encountered by increasing surface melt water will determine the influence of changing atmospheric conditions on ice-sheet mass balance .
In Antarctica , subglacial lakes have the capacity to both modulate velocities in ice streams and outlet glaciers and provide nucleation points for new fast ice-flow tributaries .
Climate models of ice-sheet responses to global change remain incomplete without a parameterization of subglacial hydrodynamics and ice dynamics .

[648] Calving fluxes and basal melt rates of Antarctic ice shelves

Iceberg calving has been assumed to be the dominant cause of mass loss for the Antarctic ice sheet , with previous estimates of the calving flux exceeding 2,000 gigatonnes per year .
More recently , the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front .
So far , however , no study has reliably quantified the calving flux and the basal mass balance ( the balance between accretion and ablation at the ice-shelf base ) for the whole of Antarctica .
The distribution of fresh water in the Southern Ocean and its partitioning between the liquid and solid phases is therefore poorly constrained .
Here we estimate the mass balance components for all ice shelves in Antarctica , using satellite measurements of calving flux and grounding-line flux , modelled ice-shelf snow accumulation rates and a regional scaling that accounts for unsurveyed areas .
We obtain a total calving flux of 1,321 + / - 144 gigatonnes per year and a total basal mass balance of -1,454 + / - 174 gigatonnes per year .
This means that about half of the ice-sheet surface mass gain is lost through oceanic erosion before reaching the ice front , and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking .
In addition , the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves .
We find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering and enhanced discharge .
We suggest that basal mass loss is a valuable metric for predicting future ice-shelf vulnerability to oceanic forcing .

[649] Effect of iron supply on Southern Ocean CO2 uptake and implications for glacial atmospheric CO2

Photosynthesis by marine phytoplankton in the Southern Ocean , and the associated uptake of carbon , is thought to be currently limited by the availability of iron .
One implication of this limitation is that a larger iron supply to the region in glacial times could have stimulated algal photosynthesis , leading to lower concentrations of atmospheric CO 2 .
Similarly , it has been proposed that artificial iron fertilization of the oceans might increase future carbon sequestration .
Here we report data from a whole-ecosystem test of the iron-limitation hypothesis in the Southern Ocean , which show that surface uptake of atmospheric CO 2 and uptake ratios of silica to carbon by phytoplankton were strongly influenced by nanomolar increases of iron concentration .
We use these results to inform a model of global carbon and ocean nutrients , forced with atmospheric iron fluxes to the region derived from the Vostok ice-core dust record .
During glacial periods , predicted magnitudes and timings of atmospheric CO2 changes match ice-core records well .
At glacial terminations , the model suggests that forcing of Southern Ocean biota by iron caused the initial ~ 40 p.p.m. of glacial-interglacial CO2 change , but other mechanisms must have accounted for the remaining 40 p.p.m. increase .
The experiment also confirms that modest sequestration of atmospheric CO2 by artificial additions of iron to the Southern Ocean is in principle possible , although the period and geographical extent over which sequestration would be effective remain poorly known .

[650] Diatom carbon export enhanced by silicate upwelling in the northeast Atlantic

Diatoms are unicellular or chain-forming phytoplankton that use silicon ( Si ) in cell wall construction .
Their survival during periods of apparent nutrient exhaustion enhances carbon sequestration in frontal regions of the northern North Atlantic .
These regions may therefore have a more important role in the ` biological pump ' than they have previously been attributed , but how this is achieved is unknown .
Diatom growth depends on silicate availability , in addition to nitrate and phosphate , but northern Atlantic waters are richer in nitrate than silicate .
Following the spring stratification , diatoms are the first phytoplankton to bloom .
Once silicate is exhausted , diatom blooms subside in a major export event .
Here we show that , with nitrate still available for new production , the diatom bloom is prolonged where there is a periodic supply of new silicate : specifically , diatoms thrive by ` mining ' deep-water silicate brought to the surface by an unstable ocean front .
The mechanism we present here is not limited to silicate fertilization ; similar mechanisms could support nitrate - , phosphate - or iron-limited frontal regions in oceans elsewhere .

[651] Reduced mixing generates oscillations and chaos in the oceanic deep chlorophyll maximum

Deep chlorophyll maxima ( DCMs ) are widespread in large parts of the world 's oceans .
These deep layers of high chlorophyll concentration reflect a compromise of phytoplankton growth exposed to two opposing resource gradients : light supplied from above and nutrients supplied from below .
It is often argued that DCMs are stable features .
Here we show , however , that reduced vertical mixing can generate oscillations and chaos in phytoplankton biomass and species composition of DCMs .
These fluctuations are caused by a difference in the timescales of two processes : ( 1 ) rapid export of sinking plankton , withdrawing nutrients from the euphotic zone and ( 2 ) a slow upward flux of nutrients fuelling new phytoplankton production .
Climate models predict that global warming will reduce vertical mixing in the oceans .
Our model indicates that reduced mixing will generate more variability in DCMs , thereby enhancing variability in oceanic primary production and in carbon export into the ocean interior .

[652] Microbe-driven turnover offsets mineral-mediated storage of soil carbon under elevated CO2

The sensitivity of soil organic carbon ( SOC ) to changing environmental conditions represents a critical uncertainty in coupled carbon cycle-climate models .
Much of this uncertainty arises from our limited understanding of the extent to which root-microbe interactions induce SOC losses ( through accelerated decomposition or ` priming ' ) or indirectly promote SOC gains ( via ` protection ' through interactions with mineral particles ) .
We developed a new SOC model to examine priming and protection responses to rising atmospheric CO2 .
The model captured disparate SOC responses at two temperate free-air CO2 enrichment ( FACE ) experiments .
We show that stabilization of ` new ' carbon in protected SOC pools may equal or exceed microbial priming of ` old ' SOC in ecosystems with readily decomposable litter and high clay content ( for example , Oak Ridge ) .
In contrast , carbon losses induced through priming dominate the net SOC response in ecosystems with more resistant litters and lower clay content ( for example , Duke ) .
The SOC model was fully integrated into a global terrestrial carbon cycle model to run global simulations of elevated CO2 effects .
Although protected carbon provides an important constraint on priming effects , priming nonetheless reduced SOC storage in the majority of terrestrial areas , partially counterbalancing SOC gains from enhanced ecosystem productivity .

[653] Recent global-warming hiatus tied to equatorial Pacific surface cooling

Despite the continued increase in atmospheric greenhouse gas concentrations , the annual-mean global temperature has not risen in the twenty-first century , challenging the prevailing view that anthropogenic forcing causes climate warming .
Various mechanisms have been proposed for this hiatus in global warming , but their relative importance has not been quantified , hampering observational estimates of climate sensitivity .
Here we show that accounting for recent cooling in the eastern equatorial Pacific reconciles climate simulations and observations .
We present a novel method of uncovering mechanisms for global temperature change by prescribing , in addition to radiative forcing , the observed history of sea surface temperature over the central to eastern tropical Pacific in a climate model .
Although the surface temperature prescription is limited to only 8.2 % of the global surface , our model reproduces the annual-mean global temperature remarkably well with correlation coefficient r = 0.97 for 1970-2012 ( which includes the current hiatus and a period of accelerated global warming ) .
Moreover , our simulation captures major seasonal and regional characteristics of the hiatus , including the intensified Walker circulation , the winter cooling in northwestern North America and the prolonged drought in the southern USA .
Our results show that the current hiatus is part of natural climate variability , tied specifically to a La-Nina-like decadal cooling .
Although similar decadal hiatus events may occur in the future , the multi-decadal warming trend is very likely to continue with greenhouse gas increase .

[654] High sensitivity of the continental-weathering carbon dioxide sink to future climate change

According to future anthropogenic emission scenarios , the atmospheric CO2 concentration may double before the end of the twenty-first century .
This increase is predicted to result in a global warming of more than 6 degreesC in the worst case .
The global temperature increase will promote changes in the hydrologic cycle through redistributions of rainfall patterns and continental vegetation cover .
All of these changes will impact the chemical weathering of continental rocks .
Long considered an inert CO2 consumption flux at the century timescale , recent works have demonstrated its potential high sensitivity to the ongoing climate and land-use changes .
Here we show that the CO2 consumption flux related to weathering processes increases by more than 50 % for an atmospheric CO2 doubling for one of the most important Arctic watersheds : the Mackenzie River Basin .
This result has been obtained using a process-based model of the chemical weathering of continental surfaces forced by models describing the atmospheric general circulation and the dynamic of the vegetation under increased atmospheric CO2 .
Our study stresses the potential role that weathering may play in the evolution of the global carbon cycle over the next centuries .

[655] Policy : The perils of doing nothing

A lack of buy-in by the United States arguably represents the greatest obstacle to tackling climate change .
A major new report urges America to take action to cut emissions and begin adapting to climate change .

[656] Earthworms increase plant production : a meta-analysis

To meet the challenge of feeding a growing world population with minimal environmental impact , we need comprehensive and quantitative knowledge of ecological factors affecting crop production .
Earthworms are among the most important soil dwelling invertebrates .
Their activity affects both biotic and abiotic soil properties , in turn affecting plant growth .
Yet , studies on the effect of earthworm presence on crop yields have not been quantitatively synthesized .
Here we show , using meta-analysis , that on average earthworm presence in agroecosystems leads to a 25 % increase in crop yield and a 23 % increase in aboveground biomass .
The magnitude of these effects depends on presence of crop residue , earthworm density and type and rate of fertilization .
The positive effects of earthworms become larger when more residue is returned to the soil , but disappear when soil nitrogen availability is high .
This suggests that earthworms stimulate plant growth predominantly through releasing nitrogen locked away in residue and soil organic matter .
Our results therefore imply that earthworms are of crucial importance to decrease the yield gap of farmers who ca n't - or wo n't - use nitrogen fertilizer .

[657] Temperature sensitivity of soil respiration rates enhanced by microbial community response

Soils store about four times as much carbon as plant biomass , and soil microbial respiration releases about 60 petagrams of carbon per year to the atmosphere as carbon dioxide .
Short-term experiments have shown that soil microbial respiration increases exponentially with temperature .
This information has been incorporated into soil carbon and Earth-system models , which suggest that warming-induced increases in carbon dioxide release from soils represent an important positive feedback loop that could influence twenty-first-century climate change .
The magnitude of this feedback remains uncertain , however , not least because the response of soil microbial communities to changing temperatures has the potential to either decrease or increase warming-induced carbon losses substantially .
Here we collect soils from different ecosystems along a climate gradient from the Arctic to the Amazon and investigate how microbial community-level responses control the temperature sensitivity of soil respiration .
We find that the microbial community-level response more often enhances than reduces the mid - to long-term ( 90 days ) temperature sensitivity of respiration .
Furthermore , the strongest enhancing responses were observed in soils with high carbon-to-nitrogen ratios and in soils from cold climatic regions .
After 90 days , microbial community responses increased the temperature sensitivity of respiration in high-latitude soils by a factor of 1.4 compared to the instantaneous temperature response .
This suggests that the substantial carbon stores in Arctic and boreal soils could be more vulnerable to climate warming than currently predicted .

[658] Carbon isotope records reveal precise timing of enhanced Southern Ocean upwelling during the last deglaciation

The Southern Ocean plays a prominent role in the Earth 's climate and carbon cycle .
Changes in the Southern Ocean circulation may have regulated the release of CO2 to the atmosphere from a deep-ocean reservoir during the last deglaciation .
However , the path and exact timing of this deglacial CO2 release are still under debate .
Here we present measurements of deglacial surface reservoir 14C age changes in the eastern Pacific sector of the Southern Ocean , obtained by 14C dating of tephra deposited over the marine and terrestrial regions .
These results , along with records of foraminifera benthic-planktic 14C age and delta13C difference , provide evidence for three periods of enhanced upwelling in the Southern Ocean during the last deglaciation , supporting the hypothesis that Southern Ocean upwelling contributed to the deglacial rise in atmospheric CO2 .
These independently dated marine records suggest synchronous changes in the Southern Ocean circulation and Antarctic climate during the last deglaciation .

[659] Irregular tropical glacier retreat over the Holocene epoch driven by progressive warming

The causes and timing of tropical glacier fluctuations during the Holocene epoch ( 10,000 years ago to present ) are poorly understood .
Yet constraining their sensitivity to changes in climate is important , as these glaciers are both sensitive indicators of climate change and serve as water reservoirs for highland regions .
Studies have so far documented extra-tropical glacier fluctuations , but in the tropics , glacier-climate relationships are insufficiently understood .
Here we present a 10Be chronology for the past 11,000 years ( 11 kyr ) , using 57 moraines from the Bolivian Telata glacier ( in the Cordillera Real mountain range ) .
This chronology indicates that Telata glacier retreated irregularly .
A rapid and strong melting from the maximum extent occurred from 10.8 + / - 0.9 to 8.5 + / - 0.4 kyr ago , followed by a slower retreat until the Little Ice Age , about 200 years ago .
A dramatic increase in the rate of retreat occurred over the twentieth century .
A glacier-climate model indicates that , relative to modern climate , annual mean temperature for the Telata glacier region was -3.3 + / - 0.8 degreesC cooler at 11 kyr ago and remained -2.1 + / - 0.8 degreesC cooler until the end of the Little Ice Age .
We suggest that long-term warming of the eastern tropical Pacific and increased atmospheric temperature in response to enhanced austral summer insolation were the main drivers for the long-term Holocene retreat of glaciers in the southern tropics .

[660] Metagenomic insights into evolution of a heavy metal-contaminated groundwater microbial community

Understanding adaptation of biological communities to environmental change is a central issue in ecology and evolution .
Metagenomic analysis of a stressed groundwater microbial community reveals that prolonged exposure to high concentrations of heavy metals , nitric acid and organic solvents ( ~ 50 years ) has resulted in a massive decrease in species and allelic diversity as well as a significant loss of metabolic diversity .
Although the surviving microbial community possesses all metabolic pathways necessary for survival and growth in such an extreme environment , its structure is very simple , primarily composed of clonal denitrifying gamma - and beta-proteobacterial populations .
The resulting community is overabundant in key genes conferring resistance to specific stresses including nitrate , heavy metals and acetone .
Evolutionary analysis indicates that lateral gene transfer could have a key function in rapid response and adaptation to environmental contamination .
The results presented in this study have important implications in understanding , assessing and predicting the impacts of human-induced activities on microbial communities ranging from human health to agriculture to environmental management , and their responses to environmental changes .

[661] Onset of deglacial warming in West Antarctica driven by local orbital forcing

The cause of warming in the Southern Hemisphere during the most recent deglaciation remains a matter of debate .
Hypotheses for a Northern Hemisphere trigger , through oceanic redistributions of heat , are based in part on the abrupt onset of warming seen in East Antarctic ice cores and dated to 18,000 years ago , which is several thousand years after high-latitude Northern Hemisphere summer insolation intensity began increasing from its minimum , approximately 24,000 years ago .
An alternative explanation is that local solar insolation changes cause the Southern Hemisphere to warm independently .
Here we present results from a new , annually resolved ice-core record from West Antarctica that reconciles these two views .
The records show that 18,000 years ago snow accumulation in West Antarctica began increasing , coincident with increasing carbon dioxide concentrations , warming in East Antarctica and cooling in the Northern Hemisphere associated with an abrupt decrease in Atlantic meridional overturning circulation .
However , significant warming in West Antarctica began at least 2,000 years earlier .
Circum-Antarctic sea-ice decline , driven by increasing local insolation , is the likely cause of this warming .
The marine-influenced West Antarctic records suggest a more active role for the Southern Ocean in the onset of deglaciation than is inferred from ice cores in the East Antarctic interior , which are largely isolated from sea-ice changes .

[662] Posttranslational modification and sequence variation of redox-active proteins correlate with biofilm life cycle in natural microbial communities

Characterizing proteins recovered from natural microbial communities affords the opportunity to correlate protein expression and modification with environmental factors , including species composition and successional stage .
Proteogenomic and biochemical studies of pellicle biofilms from subsurface acid mine drainage streams have shown abundant cytochromes from the dominant organism , Leptospirillum Group II .
These cytochromes are proposed to be key proteins in aerobic Fe ( II ) oxidation , the dominant mode of cellular energy generation by the biofilms .
In this study , we determined that posttranslational modification and expression of amino-acid sequence variants change as a function of biofilm maturation .
For Cytochrome579 ( Cyt579 ) , the most abundant cytochrome in the biofilms , late developmental-stage biofilms differed from early-stage biofilms in N-terminal truncations and decreased redox potentials .
Expression of sequence variants of two monoheme c-type cytochromes also depended on biofilm development .
For Cyt572 , an abundant membrane-bound cytochrome , the expression of multiple sequence variants was observed in both early and late developmental-stage biofilms ; however , redox potentials of Cyt572 from these different sources did not vary significantly .
These cytochrome analyses show a complex response of the Leptospirillum Group II electron transport chain to growth within a microbial community and illustrate the power of multiple proteomics techniques to define biochemistry in natural systems .

[663] Divergence across diet , time and populations rules out parallel evolution in the gut microbiomes of Trinidadian guppies

Diverse microbial consortia profoundly influence animal biology , necessitating an understanding of microbiome variation in studies of animal adaptation .
Yet , little is known about such variability among fish , in spite of their importance in aquatic ecosystems .
The Trinidadian guppy , Poecilia reticulata , is an intriguing candidate to test microbiome-related hypotheses on the drivers and consequences of animal adaptation , given the recent parallel origins of a similar ecotype across streams .
To assess the relationships between the microbiome and host adaptation , we used 16S rRNA amplicon sequencing to characterize gut bacteria of two guppy ecotypes with known divergence in diet , life history , physiology and morphology collected from low-predation ( LP ) and high-predation ( HP ) habitats in four Trinidadian streams .
Guts were populated by several recurring , core bacteria that are related to other fish associates and rarely detected in the environment .
Although gut communities of lab-reared guppies differed from those in the wild , microbiome divergence between ecotypes from the same stream was evident under identical rearing conditions , suggesting host genetic divergence can affect associations with gut bacteria .
In the field , gut communities varied over time , across streams and between ecotypes in a stream-specific manner .
This latter finding , along with PICRUSt predictions of metagenome function , argues against strong parallelism of the gut microbiome in association with LP ecotype evolution .
Thus , bacteria can not be invoked in facilitating the heightened reliance of LP guppies on lower-quality diets .
We argue that the macroevolutionary microbiome convergence seen across animals with similar diets may be a signature of secondary microbial shifts arising some time after host-driven adaptation .
The ISME Journal advance online publication , 9 January 2015 ; doi :10.1038 / ismej .2014.231

[664] Uncertainty in predictions of the climate response to rising levels of greenhouse gases

The range of possibilities for future climate evolution needs to be taken into account when planning climate change mitigation and adaptation strategies .
This requires ensembles of multi-decadal simulations to assess both chaotic climate variability and model response uncertainty .
Statistical estimates of model response uncertainty , based on observations of recent climate change , admit climate sensitivities -- defined as the equilibrium response of global mean temperature to doubling levels of atmospheric carbon dioxide -- substantially greater than 5 K .
But such strong responses are not used in ranges for future climate change because they have not been seen in general circulation models .
Here we present results from the ` climateprediction.net ' experiment , the first multi-thousand-member grand ensemble of simulations using a general circulation model and thereby explicitly resolving regional details .
We find model versions as realistic as other state-of-the-art climate models but with climate sensitivities ranging from less than 2 K to more than 11 K. Models with such extreme sensitivities are critical for the study of the full range of possible responses of the climate system to rising greenhouse gas levels , and for assessing the risks associated with specific targets for stabilizing these levels .

[665] Mountain pine beetle and forest carbon feedback to climate change

The mountain pine beetle ( Dendroctonus ponderosae Hopkins , Coleoptera : Curculionidae , Scolytinae ) is a native insect of the pine forests of western North America , and its populations periodically erupt into large-scale outbreaks .
During outbreaks , the resulting widespread tree mortality reduces forest carbon uptake and increases future emissions from the decay of killed trees .
The impacts of insects on forest carbon dynamics , however , are generally ignored in large-scale modelling analyses .
The current outbreak in British Columbia , Canada , is an order of magnitude larger in area and severity than all previous recorded outbreaks .
Here we estimate that the cumulative impact of the beetle outbreak in the affected region during 2000-2020 will be 270 megatonnes ( Mt ) carbon ( or 36 g carbon m-2 yr-1 on average over 374,000 km2 of forest ) .
This impact converted the forest from a small net carbon sink to a large net carbon source both during and immediately after the outbreak .
In the worst year , the impacts resulting from the beetle outbreak in British Columbia were equivalent to ~ 75 % of the average annual direct forest fire emissions from all of Canada during 1959-1999 .
The resulting reduction in net primary production was of similar magnitude to increases observed during the 1980s and 1990s as a result of global change .
Climate change has contributed to the unprecedented extent and severity of this outbreak .
Insect outbreaks such as this represent an important mechanism by which climate change may undermine the ability of northern forests to take up and store atmospheric carbon , and such impacts should be accounted for in large-scale modelling analyses .

[666] Permanent El Nino during the Pliocene warm period not supported by coral evidence

The El Nino/Southern Oscillation ( ENSO ) system during the Pliocene warm period ( PWP ; 3-5 million years ago ) may have existed in a permanent El Nino state with a sharply reduced zonal sea surface temperature ( SST ) gradient in the equatorial Pacific Ocean .
This suggests that during the PWP , when global mean temperatures and atmospheric carbon dioxide concentrations were similar to those projected for near-term climate change , ENSO variability -- and related global climate teleconnections -- could have been radically different from that today .
Yet , owing to a lack of observational evidence on seasonal and interannual SST variability from crucial low-latitude sites , this fundamental climate characteristic of the PWP remains controversial .
Here we show that permanent El Nino conditions did not exist during the PWP .
Our spectral analysis of the delta18O SST and salinity proxy , extracted from two 35-year , monthly resolved PWP Porites corals in the Philippines , reveals variability that is similar to present ENSO variation .
Although our fossil corals can not be directly compared with modern ENSO records , two lines of evidence suggest that Philippine corals are appropriate ENSO proxies .
First , delta18O anomalies from a nearby live Porites coral are correlated with modern records of ENSO variability .
Second , negative-delta18O events in the fossil corals closely resemble the decreases in delta18O seen in the live coral during El Nino events .
Prior research advocating a permanent El Nino state may have been limited by the coarse resolution of many SST proxies , whereas our coral-based analysis identifies climate variability at the temporal scale required to resolve ENSO structure firmly .

[667] Convective forcing of mercury and ozone in the Arctic boundary layer induced by leads in sea ice

The ongoing regime shift of Arctic sea ice from perennial to seasonal ice is associated with more dynamic patterns of opening and closing sea-ice leads ( large transient channels of open water in the ice ) , which may affect atmospheric and biogeochemical cycles in the Arctic .
Mercury and ozone are rapidly removed from the atmospheric boundary layer during depletion events in the Arctic , caused by destruction of ozone along with oxidation of gaseous elemental mercury ( Hg ( 0 ) ) to oxidized mercury ( Hg ( ii ) ) in the atmosphere and its subsequent deposition to snow and ice .
Ozone depletion events can change the oxidative capacity of the air by affecting atmospheric hydroxyl radical chemistry , whereas atmospheric mercury depletion events can increase the deposition of mercury to the Arctic , some of which can enter ecosystems during snowmelt .
Here we present near-surface measurements of atmospheric mercury and ozone from two Arctic field campaigns near Barrow , Alaska .
We find that coastal depletion events are directly linked to sea-ice dynamics .
A consolidated ice cover facilitates the depletion of Hg ( 0 ) and ozone , but these immediately recover to near-background concentrations in the upwind presence of open sea-ice leads .
We attribute the rapid recoveries of Hg ( 0 ) and ozone to lead-initiated shallow convection in the stable Arctic boundary layer , which mixes Hg ( 0 ) and ozone from undepleted air masses aloft .
This convective forcing provides additional Hg ( 0 ) to the surface layer at a time of active depletion chemistry , where it is subject to renewed oxidation .
Future work will need to establish the degree to which large-scale changes in sea-ice dynamics across the Arctic alter ozone chemistry and mercury deposition in fragile Arctic ecosystems .

[668] Patterns in household-level engagement with climate change in Indonesia

Understanding how individuals engage with climate change is critical for developing successful climate adaptation policies .
Indonesia ranks among the world 's top CO2 emitters , affirming its relevance to the global climate change policy arena , yet the dynamics of climate change engagement in Indonesia may differ from developed countries from which much research on this issue derives .
We surveyed 6,310 households in two Indonesian regions to investigate patterns in four steps of engagement : observation , risk perception , reactive action ( in response to present climate change ) and proactive action ( in anticipation of future climate change ) .
We show that 89.5 % of households exhibited a pattern whereby taking each of these steps in sequence implied taking all steps that precede it .
Exceptions occurred in urban areas , where households were more likely to take action without having observed climate change or perceiving risks .
In rural areas , households were more likely to observe climate change without taking action .
These variations suggest a potentially nonlinear relationship between steps of engagement .
We distinguish three types of household requiring adaptation support , and stress that Indonesian climate policy should shift emphasis from raising awareness to identifying broader institutional structures and processes to facilitate household engagement .

[669] Coevolution with phages does not influence the evolution of bacterial mutation rates in soil

Coevolution with phages drive the evolution of high bacterial mutation rates in vitro , but the relevance of this finding to natural populations is unclear .
Here , we investigated how coevolution affects mutation rate evolution in soil , in the presence and absence of the rest of the natural microbial community .
Although mutation rate on average increased threefold , neither coevolving phages nor the rest of natural community significantly affected mutation rates .
Our results suggest that features of the soil over and above directly interacting organisms constrain the evolution of strong mutators , helping to explain their relatively low frequency compared with some laboratory and clinical settings .

[670] Carbon benefits of anthropogenic reactive nitrogen offset by nitrous oxide emissions

Additions of reactive nitrogen to terrestrial ecosystems -- primarily through fertilizer application and atmospheric deposition -- have more than doubled since 1860 owing to human activities .
Nitrogen additions tend to increase the net uptake of carbon by the terrestrial biosphere , but they also stimulate nitrous oxide release from soils .
However , given that the magnitude of these effects is uncertain , and that the carbon and nitrogen cycles are tightly coupled , the net climatic impact of anthropogenic nitrogen inputs is unknown .
Here we use a process-based model of the terrestrial biosphere to evaluate the overall impact of anthropogenic nitrogen inputs on terrestrial ecosystem carbon and nitrous oxide fluxes between 1700 and 2005 .
We show that anthropogenic nitrogen inputs account for about a fifth of the carbon sequestered by terrestrial ecosystems between 1996 and 2005 , and for most of the increase in global nitrous oxide emissions in recent decades ; the latter is largely due to agricultural intensification .
We estimate that carbon sequestration due to nitrogen deposition has reduced current carbon dioxide radiative forcing by 96 + / -14 mW m-2 .
However , this effect has been offset by the increase in radiative forcing resulting from nitrous oxide emissions , which amounts to 125 + / -20 mW m-2 .

[671] Food web expansion and contraction in response to changing environmental conditions

Macroscopic ecosystem properties , such as major material pathways and community biomass structure , underlie the ecosystem services on which humans rely .
While ecologists have long sought to identify the determinants of the trophic height of food webs ( food chain length ) , it is somewhat surprising how little research effort is invested in understanding changes among other food web properties across environmental conditions .
Here we theoretically and empirically show how a suite of fundamental macroscopic food web structures respond , in concert , to changes in habitat accessibility using post-glacial lakes as model ecosystems .
We argue that as resource accessibility increases in coupled food webs , food chain length contracts ( that is , reduced predator trophic position ) , habitat coupling expands ( that is , increasingly coupled macrohabitats ) and biomass pyramid structure becomes more top heavy .
Our results further support an emerging theoretical view of flexible food webs that provides a foundation for generally understanding ecosystem responses to changing environmental conditions .

[672] Water-quality impacts from climate-induced forest die-off

Increased ecosystem susceptibility to pests and other stressors has been attributed to climate change , resulting in unprecedented tree mortality from insect infestations .
In turn , large-scale tree die-off alters physical and biogeochemical processes , such as organic matter decay and hydrologic flow paths , that could enhance leaching of natural organic matter to soil and surface waters and increase potential formation of harmful drinking water disinfection by-products ( DBPs ) .
Whereas previous studies have investigated water-quantity alterations due to climate-induced , forest die-off , impacts on water quality are unclear .
Here , water-quality data sets from water-treatment facilities in Colorado were analysed to determine whether the municipal water supply has been perturbed by tree mortality .
Results demonstrate higher total organic carbon concentrations along with significantly more DBPs at water-treatment facilities using mountain-pine-beetle-infested source waters when contrasted with those using water from control watersheds .
In addition to this differentiation between watersheds , DBP concentrations demonstrated an increase within mountain pine beetle watersheds related to the degree of infestation .
Disproportionate DBP increases and seasonal decoupling of peak DBP and total organic carbon concentrations further suggest that the total organic carbon composition is being altered in these systems .

[673] Negligible glacial-interglacial variation in continental chemical weathering rates

Chemical weathering of the continents is central to the regulation of atmospheric carbon dioxide concentrations , and hence global climate .
On million-year timescales silicate weathering leads to the draw-down of carbon dioxide , and on millennial timescales chemical weathering affects the calcium carbonate saturation state of the oceans and hence their uptake of carbon dioxide .
However , variations in chemical weathering rates over glacial-interglacial cycles remain uncertain .
During glacial periods , cold and dry conditions reduce the rate of chemical weathering , but intense physical weathering and the exposure of carbonates on continental shelves due to low sea levels may increase this rate .
Here we present high-resolution records of the lead isotope composition of ferromanganese crusts from the North Atlantic Ocean that cover the past 550,000 years .
Combining these records with a simple quantitative model of changes in the lead isotope composition of the deep North Atlantic Ocean in response to chemical weathering , we find that chemical weathering rates were two to three times lower in the glaciated interior of the North Atlantic Region during glacial periods than during the intervening interglacial periods .
This decrease roughly balances the increase in chemical weathering caused by the exposure of continental shelves , indicating that chemical weathering rates remained relatively constant on glacial-interglacial timescales .
On timescales of more than a million years , however , we suggest that enhanced weathering of silicate glacial sediments during interglacial periods results in a net draw-down of atmospheric carbon dioxide , creating a positive feedback on global climate that , once initiated , promotes cooling and further glaciation .

[674] A global non-coding RNA system modulates fission yeast protein levels in response to stress

Non-coding RNAs ( ncRNAs ) are frequent and prevalent across the taxa .
Although individual non-coding loci have been assigned a function , most are uncharacterized .
Their global biological significance is unproven and remains controversial .
Here we investigate the role played by ncRNAs in the stress response of Schizosaccharomyces pombe .
We integrate global proteomics and RNA sequencing data to identify a systematic programme in which elevated antisense RNA arising both from ncRNAs and from 3 ' - overlapping convergent gene pairs is directly associated with substantial reductions in protein levels throughout the genome .
We describe an extensive array of ncRNAs with trans associations that have the potential to influence multiple pathways .
Deletion of one such locus reduces levels of atf1 , a transcription factor downstream of the stress-activated mitogen-activated protein kinase ( MAPK ) pathway , and alters sensitivity to oxidative stress .
These non-coding transcripts therefore regulate specific stress responses , adding unanticipated information-processing capacity to the MAPK signalling system .

[675] Improved estimates of upper-ocean warming and multi-decadal sea-level rise

Changes in the climate system 's energy budget are predominantly revealed in ocean temperatures and the associated thermal expansion contribution to sea-level rise .
Climate models , however , do not reproduce the large decadal variability in globally averaged ocean heat content inferred from the sparse observational database , even when volcanic and other variable climate forcings are included .
The sum of the observed contributions has also not adequately explained the overall multi-decadal rise .
Here we report improved estimates of near-global ocean heat content and thermal expansion for the upper 300 m and 700 m of the ocean for 1950-2003 , using statistical techniques that allow for sparse data coverage and applying recent corrections to reduce systematic biases in the most common ocean temperature observations .
Our ocean warming and thermal expansion trends for 1961-2003 are about 50 per cent larger than earlier estimates but about 40 per cent smaller for 1993-2003 , which is consistent with the recognition that previously estimated rates for the 1990s had a positive bias as a result of instrumental errors .
On average , the decadal variability of the climate models with volcanic forcing now agrees approximately with the observations , but the modelled multi-decadal trends are smaller than observed .
We add our observational estimate of upper-ocean thermal expansion to other contributions to sea-level rise and find that the sum of contributions from 1961 to 2003 is about 1.5 + / - 0.4 mm yr-1 , in good agreement with our updated estimate of near-global mean sea-level rise ( using techniques established in earlier studies ) of 1.6 + / - 0.2 mm yr-1 .

[676] Bacterial community succession during in situ uranium bioremediation : spatial similarities along controlled flow paths

Bacterial community succession was investigated in a field-scale subsurface reactor formed by a series of wells that received weekly ethanol additions to re-circulating groundwater .
Ethanol additions stimulated denitrification , metal reduction , sulfate reduction and U ( VI ) reduction to sparingly soluble U ( IV ) .
Clone libraries of SSU rRNA gene sequences from groundwater samples enabled tracking of spatial and temporal changes over a 1.5-year period .
Analyses showed that the communities changed in a manner consistent with geochemical variations that occurred along temporal and spatial scales .
Canonical correspondence analysis revealed that the levels of nitrate , uranium , sulfide , sulfate and ethanol were strongly correlated with particular bacterial populations .
As sulfate and U ( VI ) levels declined , sequences representative of sulfate reducers and metal reducers were detected at high levels .
Ultimately , sequences associated with sulfate-reducing populations predominated , and sulfate levels declined as U ( VI ) remained at low levels .
When engineering controls were compared with the population variation through canonical ordination , changes could be related to dissolved oxygen control and ethanol addition .
The data also indicated that the indigenous populations responded differently to stimulation for bioreduction ; however , the two biostimulated communities became more similar after different transitions in an idiosyncratic manner .
The strong associations between particular environmental variables and certain populations provide insight into the establishment of practical and successful remediation strategies in radionuclide-contaminated environments with respect to engineering controls and microbial ecology .

[677] Magnitude and timing of temperature change in the Indo-Pacific warm pool during deglaciation

Ocean-atmosphere interactions in the tropical Pacific region have a strong influence on global heat and water vapour transport and thus constitute an important component of the climate system .
Changes in sea surface temperatures and convection in the tropical Indo-Pacific region are thought to be responsible for the interannual to decadal climate variability observed in extra-tropical regions , but the role of the tropics in climate changes on millennial and orbital timescales is less clear .
Here we analyse oxygen isotopes and Mg/Ca ratios of foraminiferal shells from the Makassar strait in the heart of the Indo-Pacific warm pool , to obtain synchronous estimates of sea surface temperatures and ice volume .
We find that sea surface temperatures increased by 3.5-4 .0 degreesC during the last two glacial -- interglacial transitions , synchronous with the global increase in atmospheric CO2 and Antarctic warming , but the temperature increase occurred 2,000-3 ,000 years before the Northern Hemisphere ice sheets melted .
Our observations suggest that the tropical Pacific region plays an important role in driving glacial -- interglacial cycles , possibly through a system similar to how El Nino/Southern Oscillation regulates the poleward flux of heat and water vapour .

[678] Oceanic link between abrupt changes in the North Atlantic Ocean and the African monsoon

Abrupt changes in the African monsoon can have pronounced socioeconomic impacts on many West African countries .
Evidence for both prolonged humid periods and monsoon failures have been identified throughout the late Pleistocene and early Holocene epochs .
In particular , drought conditions in West Africa have occurred during periods of reduced North Atlantic thermohaline circulation , such as the Younger Dryas cold event .
Here , we use an ocean-atmosphere general circulation model to examine the link between oceanographic changes in the North Atlantic Ocean and changes in the strength of the African monsoon .
Our simulations show that when North Atlantic thermohaline circulation is substantially weakened , the flow of the subsurface North Brazil Current reverses .
This leads to decreased upper tropical ocean stratification and warmer sea surface temperatures in the equatorial South Atlantic Ocean , and consequently reduces African summer monsoonal winds and rainfall over West Africa .
This mechanism is in agreement with reconstructions of past climate .
We therefore suggest that the interaction between thermohaline circulation in the North Atlantic Ocean and wind-driven currents in the tropical Atlantic Ocean contributes to the rapidity of African monsoon transitions during abrupt climate change events .

[679] Air-sea temperature decoupling in western Europe during the last interglacial-glacial transition

A period of continental ice growth between about 80,000 and 70,000 years ago was controlled by a decrease in summer insolation , and was among the four largest ice expansions of the past 250,000 years .
The moisture source for this ice sheet expansion , known as the Marine Isotope Stage ( MIS ) 5a/4 transition , has been proposed to be the warm subpolar and northern subtropical Atlantic Ocean .
However , the mechanism by which glaciers kept growing through three suborbital cooling events within this period , which were associated with iceberg discharge in the North Atlantic and cooling over Greenland , is unclear .
Here we reconstruct parallel records of sea surface and air temperatures from marine microfossil and pollen data , respectively , from two sediment cores collected within the northern subtropical gyre .
The thermal gradient between the cold air and warmer sea increased throughout the MIS5a/4 transition , and was marked by three intervals of even more pronounced thermal gradients associated with the C20 , C19 and C18 ' cold events .
We argue that the warm ocean surface along the western European margin provided a source of moisture that was transported , through northward-tracking storms , to feed ice sheets in colder Greenland , northern Europe and the Arctic .

[680] Arabian Sea tropical cyclones intensified by emissions of black carbon and other aerosols

Throughout the year , average sea surface temperatures in the Arabian Sea are warm enough to support the development of tropical cyclones , but the atmospheric monsoon circulation and associated strong vertical wind shear limits cyclone development and intensification , only permitting a pre-monsoon and post-monsoon period for cyclogenesis .
Thus a recent increase in the intensity of tropical cyclones over the northern Indian Ocean is thought to be related to the weakening of the climatological vertical wind shear .
At the same time , anthropogenic emissions of aerosols have increased sixfold since the 1930s , leading to a weakening of the southwesterly lower-level and easterly upper-level winds that define the monsoonal circulation over the Arabian Sea .
In principle , this aerosol-driven circulation modification could affect tropical cyclone intensity over the Arabian Sea , but so far no such linkage has been shown .
Here we report an increase in the intensity of pre-monsoon Arabian Sea tropical cyclones during the period 1979-2010 , and show that this change in storm strength is a consequence of a simultaneous upward trend in anthropogenic black carbon and sulphate emissions .
We use a combination of observational , reanalysis and model data to demonstrate that the anomalous circulation , which is radiatively forced by these anthropogenic aerosols , reduces the basin-wide vertical wind shear , creating an environment more favourable for tropical cyclone intensification .
Because most Arabian Sea tropical cyclones make landfall , our results suggest an additional impact on human health from regional air pollution .

[681] Delayed hydrological response to Greenland cooling at the onset of the Younger Dryas in western Europe

The general warming trend of the last deglaciation was interrupted by the Younger Dryas , a period of abrupt cooling and widespread environmental change .
Ice core records suggest the abrupt cooling began 12,846 years ago in Greenland , about 170 years before the significant environmental and vegetation change in western Europe classically defined as the Younger Dryas .
However , this difference in timing falls within age model uncertainties .
Here we use the hydrogen isotope composition of lipid biomarkers from precisely dated varved sediments from Lake Meerfelder Maar to reconstruct hydroclimate over western Europe .
We observe a decrease in the hydrogen isotope values of both aquatic and terrestrial lipids 12,850 years ago , indicating cooling climate in this region synchronous with the abrupt cooling in Greenland .
A second drop occurs 170 years later , mainly in the hydrogen isotope record of aquatic lipids but to a lesser extent in the terrestrial lipids , which we attribute to aridification , as well as a change in moisture source and pathway .
We thus confirm that there was indeed a lag between cooling and substantial hydrologic and environmental change in western Europe .
We suggest the delay is related to the expansion of sea ice in the North Atlantic Ocean and the subsequent southward migration of the westerly wind system .
We further suggest that these hydrological changes amplified environmental change in western Europe at the onset of the Younger Dryas .

[682] Experimental tests of the bacterial distance-decay relationship

Community similarity declines with increasing geographic distance if species tend to be locally adapted or if they are dispersal limited .
The distance-decay of similarity has been shown for bacteria previously , but distinguishing between these competing mechanisms is difficult from observational surveys .
I found little evidence of a relationship between geographic distance and similarity in community composition in an aquatic bacterial community .
When bacterial colonization occurred into initially identical sterile microcosms across a woodland , a strong distance-decay relationship was observed after 28 days , implying that dispersal limitation created a strong pattern in these communities in the absence of environmental differences .
This conclusion was not supported by the results of a reciprocal transplant experiment .
When microcosms at the extremities of the study area were transplanted to the opposite end of the study area , the communities converged on the community composition at the site to which they were transplanted .
This convergence did not depend on whether colonization into the microcosms was prevented , implying a minor role for dispersal limitation over these spatial and temporal scales .
Additional manipulations of colonization rates were consistent with the hypothesis that dispersal limitation structured these communities over short time scales ( a few days ) , but that dispersal limitation had a minor role over longer time scales ( > 7 days ) .

[683] Heavier summer downpours with climate change revealed by weather forecast resolution model

The intensification of precipitation extremes with climate change is of key importance to society as a result of the large impact through flooding .
Observations show that heavy rainfall is increasing on daily timescales in many regions , but how changes will manifest themselves on sub-daily timescales remains highly uncertain .
Here we perform the first climate change experiments with a very high resolution ( 1.5 km grid spacing ) model more typically used for weather forecasting , in this instance for a region of the UK .
The model simulates realistic hourly rainfall characteristics , including extremes , unlike coarser resolution climate models , giving us confidence in its ability to project future changes at this timescale .
We find the 1.5 km model shows increases in hourly rainfall intensities in winter , consistent with projections from a coarser 12 km resolution model and previous studies at the daily timescale .
However , the 1.5 km model also shows a future intensification of short-duration rain in summer , with significantly more events exceeding the high thresholds indicative of serious flash flooding .
We conclude that accurate representation of the local storm dynamics is an essential requirement for predicting changes to convective extremes ; when included we find for the model here that summer downpours intensify with warming .

[684] Origins and estimates of uncertainty in predictions of twenty-first century temperature rise

Predictions of temperature rise over the twenty-first century are necessarily uncertain , both because the sensitivity of the climate system to changing atmospheric greenhouse-gas concentrations , as well as the rate of ocean heat uptake , is poorly quantified and because future influences on climate -- of anthropogenic as well as natural origin -- are difficult to predict .
Past observations have been used to help constrain the range of uncertainties in future warming rates , but under the assumption of a particular scenario of future emissions .
Here we investigate the relative importance of the uncertainty in climate response to a particular emissions scenario versus the uncertainty caused by the differences between future emissions scenarios for our estimates of future change .
We present probabilistic forecasts of global-mean temperatures for four representative scenarios for future emissions , obtained with a comprehensive climate model .
We find that , in the absence of policies to mitigate climate change , global-mean temperature rise is insensitive to the differences in the emissions scenarios over the next four decades .
We also show that in the future , as the signal of climate change emerges further , the predictions will become better constrained .

[685] Solutions for a cultivated planet

Increasing population and consumption are placing unprecedented demands on agriculture and natural resources .
Today , approximately a billion people are chronically malnourished while our agricultural systems are concurrently degrading land , water , biodiversity and climate on a global scale .
To meet the world 's future food security and sustainability needs , food production must grow substantially while , at the same time , agriculture 's environmental footprint must shrink dramatically .
Here we analyse solutions to this dilemma , showing that tremendous progress could be made by halting agricultural expansion , closing ` yield gaps ' on underperforming lands , increasing cropping efficiency , shifting diets and reducing waste .
Together , these strategies could double food production while greatly reducing the environmental impacts of agriculture .

[686] Winter and spring controls on the summer food web of the coastal West Antarctic Peninsula

Understanding the mechanisms by which climate variability affects multiple trophic levels in food webs is essential for determining ecosystem responses to climate change .
Here we use over two decades of data collected by the Palmer Long Term Ecological Research program ( PAL-LTER ) to determine how large-scale climate and local physical forcing affect phytoplankton , zooplankton and an apex predator along the West Antarctic Peninsula ( WAP ) .
We show that positive anomalies in chlorophyll-a ( chl-a ) at Palmer Station , occurring every 4-6 years , are constrained by physical processes in the preceding winter/spring and a negative phase of the Southern Annular Mode ( SAM ) .
Favorable conditions for phytoplankton included increased winter ice extent and duration , reduced spring/summer winds , and increased water column stability via enhanced salinity-driven density gradients .
Years of positive chl-a anomalies are associated with the initiation of a robust krill cohort the following summer , which is evident in Adelie penguin diets , thus demonstrating tight trophic coupling .
Projected climate change in this region may have a significant , negative impact on phytoplankton biomass , krill recruitment and upper trophic level predators in this coastal Antarctic ecosystem .

[687] Coral and mollusc resistance to ocean acidification adversely affected by warming

Increasing atmospheric carbon dioxide ( CO2 ) concentrations are expectedto decrease surface ocean pH by 0.3-0 .5 units by 2100 ( refs , ) , lowering the carbonate ion concentration of surfacewaters .
This rapid acidification is predicted to dramatically decrease calcification in many marine organisms .
Reduced skeletal growth under increased CO2 levels has already been shown for corals , molluscs and many other marine organisms .
The impact of acidification on the ability of individual species to calcify has remained elusive , however , as measuring net calcification fails to disentangle the relative contributions of gross calcification and dissolution rates on growth .
Here , we show that corals and molluscs transplanted along gradients of carbonate saturation state at Mediterranean CO2 vents are able to calcify and grow at even faster than normal rates when exposed to the high CO2 levels projected for the next 300 years .
Calcifiers remain at risk , however , owing to the dissolution of exposed shells and skeletons that occurs as pH levels fall .
Our results show that tissues and external organic layers play a major role in protecting shells and skeletons from corrosive sea water , limiting dissolution and allowing organisms to calcify .
Our combined field and laboratory results demonstrate that the adverse effects of global warming are exacerbated when high temperatures coincide with acidification .

[688] An efficient process for wastewater treatment to mitigate free nitrous acid generation and its inhibition on biological phosphorus removal

Free nitrous acid ( FNA ) , which is the protonated form of nitrite and inevitably produced during biological nitrogen removal , has been demonstrated to strongly inhibit the activity of polyphosphate accumulating organisms ( PAOs ) .
Herein we reported an efficient process for wastewater treatment , i.e. , the oxic/anoxic/oxic / extended-idle process to mitigate the generation of FNA and its inhibition on PAOs .
The results showed that this new process enriched more PAOs which thereby achieved higher phosphorus removal efficiency than the conventional four-step ( i.e. , anaerobic/oxic/anoxic / oxic ) biological nutrient removal process ( 41 + / - 7 % versus 30 + / - 5 % in abundance of PAOs and 97 + / - 0.73 % versus 82 + / - 1.2 % in efficiency of phosphorus removal ) .
It was found that this new process increased pH value but decreased nitrite accumulation , resulting in the decreased FNA generation .
Further experiments showed that the new process could alleviate the inhibition of FNA on the metabolisms of PAOs even under the same FNA concentration .

[689] Distinct soil microbial diversity under long-term organic and conventional farming

Low-input agricultural systems aim at reducing the use of synthetic fertilizers and pesticides in order to improve sustainable production and ecosystem health .
Despite the integral role of the soil microbiome in agricultural production , we still have a limited understanding of the complex response of microbial diversity to organic and conventional farming .
Here we report on the structural response of the soil microbiome to more than two decades of different agricultural management in a long-term field experiment using a high-throughput pyrosequencing approach of bacterial and fungal ribosomal markers .
Organic farming increased richness , decreased evenness , reduced dispersion and shifted the structure of the soil microbiota when compared with conventionally managed soils under exclusively mineral fertilization .
This effect was largely attributed to the use and quality of organic fertilizers , as differences became smaller when conventionally managed soils under an integrated fertilization scheme were examined .
The impact of the plant protection regime , characterized by moderate and targeted application of pesticides , was of subordinate importance .
Systems not receiving manure harboured a dispersed and functionally versatile community characterized by presumably oligotrophic organisms adapted to nutrient-limited environments .
Systems receiving organic fertilizer were characterized by specific microbial guilds known to be involved in degradation of complex organic compounds such as manure and compost .
The throughput and resolution of the sequencing approach permitted to detect specific structural shifts at the level of individual microbial taxa that harbours a novel potential for managing the soil environment by means of promoting beneficial and suppressing detrimental organisms .
The ISME Journal advance online publication , 31 October 2014 ; doi :10.1038 / ismej .2014.210

[690] Origin of upper-ocean warming and El Nino change on decadal scales in the tropical Pacific Ocean

The cause of decadal-scale variability in the tropical Pacific Ocean -- such as that marked by the 1976-77 shift in the El Nino/Southern Oscillation -- is poorly understood .
Unravelling the mechanism of the recent decade-long warming in the tropical upper ocean is a particularly important challenge , given the link to El Nino variability , but establishing the hypothesized interannual/decadal oceanic connections between middle latitudes and tropics has proved elusive .
Here we present observational evidence that Pacific upper-ocean warming and decadal changes in the El Nino/Southern Oscillation after 1976 may originate from decadal mid-latitude variability .
In the middle 1970s the North Pacific Ocean is observed to have undergone a clear phase-transition ; a ` see-saw ' subsurface temperature anomaly pattern that rotates clockwise around the subtropical gyre .
At middle latitudes a subsurface warm anomaly formed in the early 1970s from subducted surface-waters and penetrated through the subtropics and into the tropics , thus perturbing the tropical thermocline and driving the formation of a warm surface-water anomaly that may have influenced El Nino in the 1980s .
The identification of this teleconnection of extratropical thermal anomalies to the tropics , through a subsurface ocean ` bridge ' , may enable improved prediction of decadal-scale climate variability .

[691] Impact of climate change on marine pelagic phenology and trophic mismatch

Phenology , the study of annually recurring life cycle events such as the timing of migrations and flowering , can provide particularly sensitive indicators of climate change .
Changes in phenology may be important to ecosystem function because the level of response to climate change may vary across functional groups and multiple trophic levels .
The decoupling of phenological relationships will have important ramifications for trophic interactions , altering food-web structures and leading to eventual ecosystem-level changes .
Temperate marine environments may be particularly vulnerable to these changes because the recruitment success of higher trophic levels is highly dependent on synchronization with pulsed planktonic production .
Using long-term data of 66 plankton taxa during the period from 1958 to 2002 , we investigated whether climate warming signals are emergent across all trophic levels and functional groups within an ecological community .
Here we show that not only is the marine pelagic community responding to climate changes , but also that the level of response differs throughout the community and the seasonal cycle , leading to a mismatch between trophic levels and functional groups .

[692] Methane dynamics regulated by microbial community response to permafrost thaw

Permafrost contains about 50 % of the global soil carbon .
It is thought that the thawing of permafrost can lead to a loss of soil carbon in the form of methane and carbon dioxide emissions .
The magnitude of the resulting positive climate feedback of such greenhouse gas emissions is still unknown and may to a large extent depend on the poorly understood role of microbial community composition in regulating the metabolic processes that drive such ecosystem-scale greenhouse gas fluxes .
Here we show that changes in vegetation and increasing methane emissions with permafrost thaw are associated with a switch from hydrogenotrophic to partly acetoclastic methanogenesis , resulting in a large shift in the delta13C signature ( 10-15/1000 ) of emitted methane .
We used a natural landscape gradient of permafrost thaw in northern Sweden as a model to investigate the role of microbial communities in regulating methane cycling , and to test whether a knowledge of community dynamics could improve predictions of carbon emissions under loss of permafrost .
Abundance of the methanogen Candidatus ` Methanoflorens stordalenmirensis ' is a key predictor of the shifts in methane isotopes , which in turn predicts the proportions of carbon emitted as methane and as carbon dioxide , an important factor for simulating the climate feedback associated with permafrost thaw in global models .
By showing that the abundance of key microbial lineages can be used to predict atmospherically relevant patterns in methane isotopes and the proportion of carbon metabolized to methane during permafrost thaw , we establish a basis for scaling changing microbial communities to ecosystem isotope dynamics .
Our findings indicate that microbial ecology may be important in ecosystem-scale responses to global change .

[693] Nitrogen deposition makes a minor contribution to carbon sequestration in temperate forests

Humans have altered global nitrogen cycling such that more atmospheric N2 is being converted ( ` fixed ' ) into biologically reactive forms by anthropogenic activities than by all natural processes combined .
In particular , nitrogen oxides emitted during fuel combustion and ammonia volatilized as a result of intensive agriculture have increased atmospheric nitrogen inputs ( mostly NO3 and NH4 ) to temperate forests in the Northern Hemisphere .
Because tree growth in northern temperate regions is typically nitrogen-limited , increased nitrogen deposition could have the effect of attenuating rising atmospheric CO2 by stimulating the accumulation of forest biomass .
Forest inventories indicate that the carbon contents of northern forests have increased concurrently with nitrogen deposition since the 1950s .
In addition , variations in atmospheric CO2 indicate a globally significant carbon sink in northern mid-latitude forest regions .
It is unclear , however , whether elevated nitrogen deposition or other factors are the primary cause of carbon sequestration in northern forests .
Here we use evidence from 15N-tracer studies in nine forests to show that elevated nitrogen deposition is unlikely to be a major contributor to the putative CO2 sink in forested northern temperature regions .

[694] Selection on soil microbiomes reveals reproducible impacts on plant function

Soil microorganisms found in the root zone impact plant growth and development , but the potential to harness these benefits is hampered by the sheer abundance and diversity of the players influencing desirable plant traits .
Here , we report a high level of reproducibility of soil microbiomes in altering plant flowering time and soil functions when partnered within and between plant hosts .
We used a multi-generation experimental system using Arabidopsis thaliana Col to select for soil microbiomes inducing earlier or later flowering times of their hosts .
We then inoculated the selected microbiomes from the tenth generation of plantings into the soils of three additional A. thaliana genotypes ( Ler , Be , RLD ) and a related crucifer ( Brassica rapa ) .
With the exception of Ler , all other plant hosts showed a shift in flowering time corresponding with the inoculation of early - or late-flowering microbiomes .
Analysis of the soil microbial community using 16 S rRNA gene sequencing showed distinct microbiota profiles assembling by flowering time treatment .
Plant hosts grown with the late-flowering-associated microbiomes showed consequent increases in inflorescence biomass for three A. thaliana genotypes and an increase in total biomass for B. rapa .
The increase in biomass was correlated with two - to five-fold enhancement of microbial extracellular enzyme activities associated with nitrogen mineralization in soils .
The reproducibility of the flowering phenotype across plant hosts suggests that microbiomes can be selected to modify plant traits and coordinate changes in soil resource pools .

[695] Constraints on future sea-level rise from past sea-level change

It is difficult to project sea-level rise in response to warming climates by the end of the century , especially because the response of the Greenland and Antarctic ice sheets to warming is not well understood .
However , sea-level fluctuations in response to changing climate have been reconstructed for the past 22,000 years from fossil data , a period that covers the transition from the Last Glacial Maximum to the warm Holocene interglacial period .
Here we present a simple model of the integrated sea-level response to temperature change that implicitly includes contributions from the thermal expansion and the reduction of continental ice .
Our model explains much of the centennial-scale variability observed over the past 22,000 years , and estimates 4-24 cm of sea-level rise during the twentieth century , in agreement with the Fourth Assessment Report of the Intergovernmental Panel on Climate Change ( IPCC ) .
In response to the minimum ( 1.1 degreesC ) and maximum ( 6.4 degreesC ) warming projected for AD 2100 by the IPCC models , our model predicts 7 and 82 cm of sea-level rise by the end of the twenty-first century , respectively .
The range of sea-level rise is slightly larger than the estimates from the IPCC models of 18-76 cm , but is sufficiently similar to increase confidence in the projections .

[696] Thermodynamic targeting of microbial perchlorate reduction by selective electron donors

Here we describe 2,6-anthrahydroquinone disulfonate ( AH2DS ) as a model thermodynamically ` targeting ' electron donor capable of selectively stimulating respiratory processes relevant to the bioremediation of perchlorate .
Pure cultures of Dechloromonas aromatica , Dechloromonas agitata and Azospira suillum , as well as uncharacterized microbial consortia , were capable of stoichiometrically reducing perchlorate to chloride upon oxidation of AH2DS to the corresponding quinone 2,6-anthraquinone disulfonate ( AQDS ) .
No degradation of the anthraquinone structure was observed , and no organism tested grew by this metabolism .
Thermodynamic calculations suggest that AH2DS oxidation should support nitrate and perchlorate reduction , whereas sulfate reduction and methanogenesis are predicted to be unfavorable .
Mixed community microcosms oxidizing AH2DS reduced nitrate and perchlorate , whereas sulfate reduction never occurred .
In contrast , microcosms amended with acetate respired nitrate , perchlorate and sulfate , as would be predicted by thermodynamic calculation .
Our results suggest that the thermodynamic properties of hydroquinones allow for targeted stimulation of only a subset of potential respiratory processes .
This observation could help improve enhanced in situ bioremediation of perchlorate by negating many of the detrimental aspects of biofouling .

[697] Glaciers as a source of ancient and labile organic matter to the marine environment

Riverine organic matter supports of the order of one-fifth of estuarine metabolism .
Coastal ecosystems are therefore sensitive to alteration of both the quantity and lability of terrigenous dissolved organic matter ( DOM ) delivered by rivers .
The lability of DOM is thought to vary with age , with younger , relatively unaltered organic matter being more easily metabolized by aquatic heterotrophs than older , heavily modified material .
This view is developed exclusively from work in watersheds where terrestrial plant and soil sources dominate streamwater DOM .
Here we characterize streamwater DOM from 11 coastal watersheds on the Gulf of Alaska that vary widely in glacier coverage ( 0-64 per cent ) .
In contrast to non-glacial rivers , we find that the bioavailability of DOM to marine microorganisms is significantly correlated with increasing 14C age .
Moreover , the most heavily glaciated watersheds are the source of the oldest ( ~ 4 kyr 14C age ) and most labile ( 66 per cent bioavailable ) DOM .
These glacial watersheds have extreme runoff rates , in part because they are subject to some of the highest rates of glacier volume loss on Earth .
We estimate the cumulative flux of dissolved organic carbon derived from glaciers contributing runoff to the Gulf of Alaska at 0.13 + / - 0.01 Tg yr-1 ( 1 Tg = 1012 g ) , of which ~ 0.10 Tg is highly labile .
This indicates that glacial runoff is a quantitatively important source of labile reduced carbon to marine ecosystems .
Moreover , because glaciers and ice sheets represent the second largest reservoir of water in the global hydrologic system , our findings indicate that climatically driven changes in glacier volume could alter the age , quantity and reactivity of DOM entering coastal oceans .

[698] Low sea level rise projections from mountain glaciers and icecaps under global warming

The mean sea level has been projected to rise in the 21st century as a result of global warming .
Such projections of sea level change depend on estimated future greenhouse emissions and on differing models , but model-average results from a mid-range scenario ( A1B ) suggests a 0.387-m rise by 2100 ( refs 1 , 2 ) .
The largest contributions to sea level rise are estimated to come from thermal expansion ( 0.288 m ) and the melting of mountain glaciers and icecaps ( 0.106 m ) , with smaller inputs from Greenland ( 0.024 m ) and Antarctica ( - 0.074 m ) .
Here we apply a melt model and a geometric volume model to our lower estimate of ice volume and assess the contribution of glaciers to sea level rise , excluding those in Greenland and Antarctica .
We provide the first separate assessment of melt contributions from mountain glaciers and icecaps , as well as an improved treatment of volume shrinkage .
We find that icecaps melt more slowly than mountain glaciers , whose area declines rapidly in the 21st century , making glaciers a limiting source for ice melt .
Using two climate models , we project sea level rise due to melting of mountain glaciers and icecaps to be 0.046 and 0.051 m by 2100 , about half that of previous projections .

[699] Northern Hemisphere ice-sheet responses to past climate warming

During ice-age glacial maxima of the last ~ 2.6 million years , ice sheets covered large portions of the Northern Hemisphere .
Records from the retreat of these ice sheets during deglaciations provide important insights into how ice sheets behave under a warming climate .
During the last two deglaciations , the southernmost margins of land-based Northern Hemisphere ice sheets responded nearly instantaneously to warming caused by increased summertime solar energy reaching the Earth .
Land-based ice sheets subsequently retreated at a rate commensurate with deglacial climate warming .
By contrast , marine-based ice sheets experienced a delayed onset of retreat relative to warming from increased summertime solar energy , with retreat characterized by periods of rapid collapse .
Both observations raise concern over the response of Earth 's remaining ice sheets to carbon-dioxide-induced global warming .
The almost immediate reaction of land-based ice margins to past small increases in summertime energy implies that the Greenland Ice Sheet could be poised to respond to continuing climate change .
Furthermore , the prehistoric precedent of marine-based ice sheets undergoing abrupt collapses raises the potential for a less predictable response of the marine-based West Antarctic Ice Sheet to future climate change .

[700] Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation

Our understanding of the deglacial evolution of the Antarctic Ice Sheet ( AIS ) following the Last Glacial Maximum ( 26,000-19 ,000 years ago ) is based largely on a few well-dated but temporally and geographically restricted terrestrial and shallow-marine sequences .
This sparseness limits our understanding of the dominant feedbacks between the AIS , Southern Hemisphere climate and global sea level .
Marine records of iceberg-rafted debris ( IBRD ) provide a nearly continuous signal of ice-sheet dynamics and variability .
IBRD records from the North Atlantic Ocean have been widely used to reconstruct variability in Northern Hemisphere ice sheets , but comparable records from the Southern Ocean of the AIS are lacking because of the low resolution and large dating uncertainties in existing sediment cores .
Here we present two well-dated , high-resolution IBRD records that capture a spatially integrated signal of AIS variability during the last deglaciation .
We document eight events of increased iceberg flux from various parts of the AIS between 20,000 and 9,000 years ago , in marked contrast to previous scenarios which identified the main AIS retreat as occurring after meltwater pulse 1A and continuing into the late Holocene epoch .
The highest IBRD flux occurred 14,600 years ago , providing the first direct evidence for an Antarctic contribution to meltwater pulse 1A .
Climate model simulations with AIS freshwater forcing identify a positive feedback between poleward transport of Circumpolar Deep Water , subsurface warming and AIS melt , suggesting that small perturbations to the ice sheet can be substantially enhanced , providing a possible mechanism for rapid sea-level rise .

[701] The metabolite alpha-ketoglutarate extends lifespan by inhibiting ATP synthase and TOR

Metabolism and ageing are intimately linked .
Compared with ad libitum feeding , dietary restriction consistently extends lifespan and delays age-related diseases in evolutionarily diverse organisms .
Similar conditions of nutrient limitation and genetic or pharmacological perturbations of nutrient or energy metabolism also have longevity benefits .
Recently , several metabolites have been identified that modulate ageing ; however , the molecular mechanisms underlying this are largely undefined .
Here we show that alpha-ketoglutarate ( alpha-KG ) , a tricarboxylic acid cycle intermediate , extends the lifespan of adult Caenorhabditis elegans .
ATP synthase subunit beta is identified as a novel binding protein of alpha-KG using a small-molecule target identification strategy termed drug affinity responsive target stability ( DARTS ) .
The ATP synthase , also known as complex V of the mitochondrial electron transport chain , is the main cellular energy-generating machinery and is highly conserved throughout evolution .
Although complete loss of mitochondrial function is detrimental , partial suppression of the electron transport chain has been shown to extend C. elegans lifespan .
We show that alpha-KG inhibits ATP synthase and , similar to ATP synthase knockdown , inhibition by alpha-KG leads to reduced ATP content , decreased oxygen consumption , and increased autophagy in both C. elegans and mammalian cells .
We provide evidence that the lifespan increase by alpha-KG requires ATP synthase subunit beta and is dependent on target of rapamycin ( TOR ) downstream .
Endogenous alpha-KG levels are increased on starvation and alpha-KG does not extend the lifespan of dietary-restricted animals , indicating that alpha-KG is a key metabolite that mediates longevity by dietary restriction .
Our analyses uncover new molecular links between a common metabolite , a universal cellular energy generator and dietary restriction in the regulation of organismal lifespan , thus suggesting new strategies for the prevention and treatment of ageing and age-related diseases .

[702] Projections of declining surface-water availability for the southwestern United States

Global warming driven by rising greenhouse-gas concentrations is expected to cause wet regions of the tropics and mid to high latitudes to get wetter and subtropical dry regions to get drier and expand polewards .
Over southwest North America , models project a steady drop in precipitation minus evapotranspiration , P-E , the net flux of water at the land surface , leading to , for example , a decline in Colorado River flow .
This would cause widespread and important social and ecological consequences .
Here , using new simulations from the Coupled Model Intercomparison Project Five , to be assessed in Intergovernmental Panel on Climate Change Assessment Report Five , we extend previous work by examining changes in P , E , runoff and soil moisture by season and for three different water resource regions .
Focusing on the near future , 2021-2040 , the new simulations project declines in surface-water availability across the southwest that translate into reduced soil moisture and runoff in California and Nevada , the Colorado River headwaters and Texas .

[703] How much has the increase in atmospheric CO2 directly affected past soybean production ?

Understanding the effects of climate change is vital for food security .
Among the most important environmental impacts of climate change is the direct effect of increased atmospheric carbon dioxide concentration ( [ CO2 ] ) on crop yields , known as the CO2 fertilization effect .
Although several statistical studies have estimated past impacts of temperature and precipitation on crop yield at regional scales , the impact of past CO2 fertilization is not well known .
We evaluated how soybean yields have been enhanced by historical atmospheric [ CO2 ] increases in three major soybean-producing countries .
The estimated average yields during 2002-2006 in the USA , Brazil , and China were 4.34 % , 7.57 % , and 5.10 % larger , respectively , than the average yields estimated using the atmospheric [ CO2 ] of 1980 .
Our results demonstrate the importance of considering atmospheric [ CO2 ] increases in evaluations of the past effects of climate change on crop yields .

[704] Global metabolic impacts of recent climate warming

Documented shifts in geographical ranges , seasonal phenology , community interactions , genetics and extinctions have been attributed to recent global warming .
Many such biotic shifts have been detected at mid - to high latitudes in the Northern Hemisphere -- a latitudinal pattern that is expected because warming is fastest in these regions .
In contrast , shifts in tropical regions are expected to be less marked because warming is less pronounced there .
However , biotic impacts of warming are mediated through physiology , and metabolic rate , which is a fundamental measure of physiological activity and ecological impact , increases exponentially rather than linearly with temperature in ectotherms .
Therefore , tropical ectotherms ( with warm baseline temperatures ) should experience larger absolute shifts in metabolic rate than the magnitude of tropical temperature change itself would suggest , but the impact of climate warming on metabolic rate has never been quantified on a global scale .
Here we show that estimated changes in terrestrial metabolic rates in the tropics are large , are equivalent in magnitude to those in the north temperate-zone regions , and are in fact far greater than those in the Arctic , even though tropical temperature change has been relatively small .
Because of temperature 's nonlinear effects on metabolism , tropical organisms , which constitute much of Earth 's biodiversity , should be profoundly affected by recent and projected climate warming .

[705] Indonesian vegetation response to changes in rainfall seasonality over the past 25,000 years

The hydrologic response to climate forcing in the Indo-Pacific warm pool region has varied spatially over the past 25,000 years .
For example , drier conditions are inferred on Java and Borneo for the period following the end of the Last Glacial Maximum , whereas wetter conditions are reconstructed for northwest Australia .
The response of vegetation to these past rainfall variations is poorly constrained .
Using a suite of 30 surface marine sediment samples from throughout the Indo-Pacific warm pool , we demonstrate that today the stable isotopic composition of vascular plant fatty acids ( delta13Cfa ) reflects the regional vegetation composition .
This in turn is controlled by the seasonality of rainfall consistent with dry season water stress .
Applying this proxy in a sediment core from offshore northeast Borneo , we show broadly similar vegetation cover during the Last Glacial Maximum and the Holocene , suggesting that , despite generally drier glacial conditions , there was no pronounced dry season .
In contrast , delta13Cfa and pollen data from a core off the coast of Sumba indicate an expansion of C4 herbs during the most recent glaciation , implying enhanced aridity and water stress during the dry season .
Holocene vegetation trends are also consistent with a response to dry season water stress .
We therefore conclude that vegetation in tropical monsoon regions is susceptible to increases in water stress arising from an enhanced seasonality of rainfall , as has occurred in past decades .

[706] Shrinking body size as an ecological response to climate change

Determining how climate change will affect global ecology and ecosystem services is one of the next important frontiers in environmental science .
Many species already exhibit smaller sizes as a result of climate change and many others are likely to shrink in response to continued climate change , following fundamental ecological and metabolic rules .
This could negatively impact both crop plants and protein sources such as fish that are important for human nutrition .
Furthermore , heterogeneity in response is likely to upset ecosystem balances .
We discuss future research directions to better understand the trend and help ameliorate the trophic cascades and loss of biodiversity that will probably result from continued decreases in organism size .

[707] Opposing decadal changes for the North Atlantic meridional overturning circulation

The hydrographic properties of the North Atlantic Ocean changed significantly from 1950 to 2000 : the subtropics warmed and became more saline , whereas the subpolar ocean cooled and freshened .
These changes directly affect the storage of heat and fresh water in the ocean , but their consequences for ocean dynamics are determined by the resultant changes in seawater density .
Here we use historical hydrographic data to show that the overall seawater density in the North Atlantic basin decreased during this 50-year period .
As a result of these density changes , sea-surface heights changed in a spatially varying pattern with typical rates of 2 mm yr-1 , in broad agreement with tide-gauge measurements .
Melding the observed density fields within a numerical model we find a slight weakening in the overturning of the subtropical gyre by -1.5 + / -1 Sv and a slight strengthening in the overturning of the subpolar gyre by +0.8 + / -0.5 Sv .
These gyre-specific changes run counter to the canonical notion of a single , basin-scale overturning cell and probably reflect interannual and decadal trends rather than any long-term climate trend .
We conclude that gyre dynamics strongly affect temperature and salinity changes that translate into changes in the meridional overturning circulation .

[708] Sustainable biochar to mitigate global climate change

Production of biochar ( the carbon ( C ) - rich solid formed by pyrolysis of biomass ) and its storage in soils have been suggested as a means of abating climate change by sequestering carbon , while simultaneously providing energy and increasing crop yields .
Substantial uncertainties exist , however , regarding the impact , capacity and sustainability of biochar at the global level .
In this paper we estimate the maximum sustainable technical potential of biochar to mitigate climate change .
Annual net emissions of carbon dioxide ( CO2 ) , methane and nitrous oxide could be reduced by a maximum of 1.8 Pg CO2-C equivalent ( CO2-Ce ) per year ( 12 % of current anthropogenic CO2-Ce emissions ; 1 Pg = 1 Gt ) , and total net emissions over the course of a century by 130 Pg CO2-Ce , without endangering food security , habitat or soil conservation .
Biochar has a larger climate-change mitigation potential than combustion of the same sustainably procured biomass for bioenergy , except when fertile soils are amended while coal is the fuel being offset .

[709] Combined speeds of climate and land-use change of the conterminous US until 2050

High rates of climate and land-use changes threaten biodiversity and ecosystem function , creating a need for integrated assessments and planning at regional to global scales .
We develop a new approach to measure multivariate estimates of climate and land-use change that builds on recently developed measures of climate velocity , and apply it to assess the combined speeds of climate and land use for the conterminous US from 2001 to 2051 .
The combined speeds of climate and land-use change are highest in a broad north-to-south swath in the central US and in parts of the intermountain west .
Climate speeds are roughly an order of magnitude higher than land-use speeds in most regions , but land-use speed is particularly high in the Appalachians and north-central forests .
Joint speeds are low across much of the intermountain west .
Our results highlight areas expected to be most vulnerable to changes in biodiversity and ecosystem function due to the individual or combined effects of climate and land-use change .
The integration of climate and land-use scenarios suggests different conservation prioritization strategies from climate velocities and species alone .

[710] Historical trends of atmospheric black carbon on Sanjiang Plain as reconstructed from a 150-year peat record

Black carbon ( BC ) , one of the major components of atmosphere aerosol , could be the second dominant driver of climate change .
We reconstructed historical trend of BC fluxes in Sanjiang Plain ( Northeast China ) through peat record to better understand its long-term trend and relationship of this atmosphere aerosol with intensity of human activities .
The BC fluxes in peatland were higher than other sedimentary archives .
Although global biomass burning decreased in last 150 years , regional large scale reclaiming caused BC fluxes of the Sanjiang Plain increased dramatically between 1950s ' and 1980s ' , most likely resulting from using fire to clearing dense pastures and forests for reclaiming .
The BC fluxes have increased since 1900s with increasing of the population and the area of farmland ; the increase trend has been more clearly since 1980s .
Based on Generalized additive models ( GAM ) , the proportional influence of regional anthropogenic impacts have increased and became dominant factors on BC deposition .

[711] Identification and isolation of active N2O reducers in rice paddy soil

Dissolved N2O is occasionally detected in surface and ground water in rice paddy fields , whereas little or no N2O is emitted to the atmosphere above these fields .
This indicates the occurrence of N2O reduction in rice paddy fields ; however , identity of the N2O reducers is largely unknown .
In this study , we employed both culture-dependent and culture-independent approaches to identify N2O reducers in rice paddy soil .
In a soil microcosm , N2O and succinate were added as the electron acceptor and donor , respectively , for N2O reduction .
For the stable isotope probing ( SIP ) experiment , 13C-labeled succinate was used to identify succinate-assimilating microbes under N2O-reducing conditions .
DNA was extracted 24 h after incubation , and heavy and light DNA fractions were separated by density gradient ultracentrifugation .
Denaturing gradient gel electrophoresis and clone library analysis targeting the 16S rRNA and the N2O reductase gene were performed .
For culture-dependent analysis , the microbes that elongated under N2O-reducing conditions in the presence of cell-division inhibitors were individually captured by a micromanipulator and transferred to a low-nutrient medium .
The N2O-reducing ability of these strains was examined by gas chromatography/mass spectrometry .
Results of the SIP analysis suggested that Burkholderiales and Rhodospirillales bacteria dominated the population under N2O-reducing conditions , in contrast to the control sample ( soil incubated with only 13C-succinate ) .
Results of the single-cell isolation technique also indicated that the majority of the N2O-reducing strains belonged to the genera Herbaspirillum ( Burkholderiales ) and Azospirillum ( Rhodospirillales ) .
In addition , Herbaspirillum strains reduced N2O faster than Azospirillum strains .
These results suggest that Herbaspirillum spp .
may have an important role in N2O reduction in rice paddy soils .

[712] Responses of plant nutrient resorption to phosphorus addition in freshwater marsh of Northeast China

Anthropogenic activities have increased phosphorus ( P ) inputs to most aquatic and terrestrial ecosystems .
However , the relationship between plant nutrient resorption and P availability is still unclear , and much less is known about the underlying mechanisms .
Here , we used a multi-level P addition experiment ( 0 , 1.2 , 4.8 , and 9.6 g P m-2 year-1 ) to assess the effect of P enrichment on nutrient resorption at plant organ , species , and community levels in a freshwater marsh of Northeast China .
The response of nutrient resorption to P addition generally did not vary with addition rates .
Moreover , nutrient resorption exhibited similar responses to P addition across the three hierarchical levels .
Specifically , P addition decreased nitrogen ( N ) resorption proficiency , P resorption efficiency and proficiency , but did not impact N resorption efficiency .
In addition , P resorption efficiency and proficiency were linearly related to the ratio of inorganic P to organic P and organic P fraction in mature plant organs , respectively .
Our findings suggest that the allocation pattern of plant P between inorganic and organic P fractions is an underlying mechanism controlling P resorption processes , and that P enrichment could strongly influence plant-mediated biogeochemical cycles through altered nutrient resorption in the freshwater wetlands of Northeast China .

[713] Near-future carbon dioxide levels alter fish behaviour by interfering with neurotransmitter function

Predicted future CO2 levels have been found to alter sensory responses and behaviour of marine fishes .
Changes include increased boldness and activity , loss of behavioural lateralization , altered auditory preferences and impaired olfactory function .
Impaired olfactory function makes larval fish attracted to odours they normally avoid , including ones from predators and unfavourable habitats .
These behavioural alterations have significant effects on mortality that may have far-reaching implications for population replenishment , community structure and ecosystem function .
However , the underlying mechanism linking high CO2 to these diverse responses has been unknown .
Here we show that abnormal olfactory preferences and loss of behavioural lateralization exhibited by two species of larval coral reef fish exposed to high CO2 can be rapidly and effectively reversed by treatment with an antagonist of the GABA-A receptor .
GABA-A is a major neurotransmitter receptor in the vertebrate brain .
Thus , our results indicate that high CO2 interferes with neurotransmitter function , a hitherto unrecognized threat to marine populations and ecosystems .
Given the ubiquity and conserved function of GABA-A receptors , we predict that rising CO2 levels could cause sensory and behavioural impairment in a wide range of marine species , especially those that tightly control their acid-base balance through regulatory changes in HCO3 - and Cl - levels .

[714] Fishing elevates variability in the abundance of exploited species

The separation of the effects of environmental variability from the impacts of fishing has been elusive , but is essential for sound fisheries management .
We distinguish environmental effects from fishing effects by comparing the temporal variability of exploited versus unexploited fish stocks living in the same environments .
Using the unique suite of 50-year-long larval fish surveys from the California Cooperative Oceanic Fisheries Investigations we analyse fishing as a treatment effect in a long-term ecological experiment .
Here we present evidence from the marine environment that exploited species exhibit higher temporal variability in abundance than unexploited species .
This remains true after accounting for life-history effects , abundance , ecological traits and phylogeny .
The increased variability of exploited populations is probably caused by fishery-induced truncation of the age structure , which reduces the capacity of populations to buffer environmental events .
Therefore , to avoid collapse , fisheries must be managed not only to sustain the total viable biomass but also to prevent the significant truncation of age structure .
The double jeopardy of fishing to potentially deplete stock sizes and , more immediately , to amplify the peaks and valleys of population variability , calls for a precautionary management approach .

[715] Ecosystem carbon storage in arctic tundra reduced by long-term nutrient fertilization

Global warming is predicted to be most pronounced at high latitudes , and observational evidence over the past 25 years suggests that this warming is already under way .
One-third of the global soil carbon pool is stored in northern latitudes , so there is considerable interest in understanding how the carbon balance of northern ecosystems will respond to climate warming .
Observations of controls over plant productivity in tundra and boreal ecosystems have been used to build a conceptual model of response to warming , where warmer soils and increased decomposition of plant litter increase nutrient availability , which , in turn , stimulates plant production and increases ecosystem carbon storage .
Here we present the results of a long-term fertilization experiment in Alaskan tundra , in which increased nutrient availability caused a net ecosystem loss of almost 2,000 grams of carbon per square meter over 20 years .
We found that annual aboveground plant production doubled during the experiment .
Losses of carbon and nitrogen from deep soil layers , however , were substantial and more than offset the increased carbon and nitrogen storage in plant biomass and litter .
Our study suggests that projected release of soil nutrients associated with high-latitude warming may further amplify carbon release from soils , causing a net loss of ecosystem carbon and a positive feedback to climate warming .

[716] Hydrological effects of forest transpiration loss in bark beetle-impacted watersheds

The recent climate-exacerbated mountain pine beetle infestation in the Rocky Mountains of North America has resulted in tree death that is unprecedented in recorded history .
The spatial and temporal heterogeneity inherent in insect infestation creates a complex and often unpredictable watershed response , influencing the primary storage and flow components of the hydrologic cycle .
Despite the increased vulnerability of forested ecosystems under changing climate , watershed-scale implications of interception , ground evaporation , and transpiration changes remain relatively unknown , with conflicting reports of streamflow perturbations across regions .
Here , contributions to streamflow are analysed through time and space to investigate the potential for increased groundwater inputs resulting from hydrologic change after infestation .
Results demonstrate that fractional late-summer groundwater contributions from impacted watersheds are 30 + / - 15 % greater after infestation and when compared with a neighbouring watershed that experienced earlier and less-severe attack , albeit uncertainty propagations through time and space are considerable .
Water budget analysis confirms that transpiration loss resulting from beetle kill can account for the relative increase in groundwater contributions to streams , often considered the sustainable flow fraction and critical to mountain water supplies and ecosystems .

[717] Evolutionary rescue from extinction is contingent on a lower rate of environmental change

The extinction rate of populations is predicted to rise under increasing rates of environmental change .
If a population experiencing increasingly stressful conditions lacks appropriate phenotypic plasticity or access to more suitable habitats , then genetic change may be the only way to avoid extinction .
Evolutionary rescue from extinction occurs when natural selection enriches a population for more stress-tolerant genetic variants .
Some experimental studies have shown that lower rates of environmental change lead to more adapted populations or fewer extinctions .
However , there has been little focus on the genetic changes that underlie evolutionary rescue .
Here we demonstrate that some evolutionary trajectories are contingent on a lower rate of environmental change .
We allowed hundreds of populations of Escherichia coli to evolve under variable rates of increase in concentration of the antibiotic rifampicin .
We then genetically engineered all combinations of mutations from isolates evolved under lower rates of environmental change .
By assessing fitness of these engineered strains across a range of drug concentrations , we show that certain genotypes are evolutionarily inaccessible under rapid environmental change .
Rapidly deteriorating environments not only limit mutational opportunities by lowering population size , but they can also eliminate sets of mutations as evolutionary options .
As anthropogenic activities are leading to environmental change at unprecedented rapidity , it is critical to understand how the rate of environmental change affects both demographic and genetic underpinnings of evolutionary rescue .

[718] Pre-treatment for ultrafiltration : effect of pre-chlorination on membrane fouling

Microbial effects are believed to be a major contributor to membrane fouling in drinking water treatment .
Sodium hypochlorite ( NaClO ) is commonly applied in membrane cleaning , but its potential use as a pretreatment for controlling operational fouling has received little attention .
In this study , the effect of adding a continuous low dose of NaClO ( 1 mg/l as active Cl ) in combination with alum , before ultrafiltration , was compared with only alum as pretreatment .
The results showed that the addition of NaClO substantially reduced membrane fouling both in terms of the rate of TMP development and the properties of the membrane cake layer .
Although the size of nano-scale primary coagulant flocs changed little by the addition of NaClO , the cake layer on the membrane had a greater porosity and a substantially reduced thickness .
NaClO was found to inactivate bacteria in the influent flow , which reduced both microbial proliferation and the production of proteins and polysaccharides in the cake layer and contributed significantly to improving the overall ultrafiltration performance .
NaClO dosing had no adverse impact on the formation of currently regulated disinfection by-product compounds ( THMs and HAAs ) .

[719] Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year

Assessments of Antarctic temperature change have emphasized the contrast between strong warming of the Antarctic Peninsula and slight cooling of the Antarctic continental interior in recent decades .
This pattern of temperature change has been attributed to the increased strength of the circumpolar westerlies , largely in response to changes in stratospheric ozone .
This picture , however , is substantially incomplete owing to the sparseness and short duration of the observations .
Here we show that significant warming extends well beyond the Antarctic Peninsula to cover most of West Antarctica , an area of warming much larger than previously reported .
West Antarctic warming exceeds 0.1 degreesC per decade over the past 50 years , and is strongest in winter and spring .
Although this is partly offset by autumn cooling in East Antarctica , the continent-wide average near-surface temperature trend is positive .
Simulations using a general circulation model reproduce the essential features of the spatial pattern and the long-term trend , and we suggest that neither can be attributed directly to increases in the strength of the westerlies .
Instead , regional changes in atmospheric circulation and associated changes in sea surface temperature and sea ice are required to explain the enhanced warming in West Antarctica .

[720] The role of the thermohaline circulation in abrupt climate change

The possibility of a reduced Atlantic thermohaline circulation in response to increases in greenhouse-gas concentrations has been demonstrated in a number of simulations with general circulation models of the coupled ocean-atmosphere system .
But it remains difficult to assess the likelihood of future changes in the thermohaline circulation , mainly owing to poorly constrained model parameterizations and uncertainties in the response of the climate system to greenhouse warming .
Analyses of past abrupt climate changes help to solve these problems .
Data and models both suggest that abrupt climate change during the last glaciation originated through changes in the Atlantic thermohaline circulation in response to small changes in the hydrological cycle .
Atmospheric and oceanic responses to these changes were then transmitted globally through a number of feedbacks .
The palaeoclimate data and the model results also indicate that the stability of the thermohaline circulation depends on the mean climate state .

[721] Reactive nitrogen requirements to feed the world in 2050 and potential to mitigate nitrogen pollution

Reactive nitrogen ( Nr ) is an indispensable nutrient for agricultural production and human alimentation .
Simultaneously , agriculture is the largest contributor to Nr pollution , causing severe damages to human health and ecosystem services .
The trade-off between food availability and Nr pollution can be attenuated by several key mitigation options , including Nr efficiency improvements in crop and animal production systems , food waste reduction in households and lower consumption of Nr-intensive animal products .
However , their quantitative mitigation potential remains unclear , especially under the added pressure of population growth and changes in food consumption .
Here we show by model simulations , that under baseline conditions , Nr pollution in 2050 can be expected to rise to 102-156 % of the 2010 value .
Only under ambitious mitigation , does pollution possibly decrease to 36-76 % of the 2010 value .
Air , water and atmospheric Nr pollution go far beyond critical environmental thresholds without mitigation actions .
Even under ambitious mitigation , the risk remains that thresholds are exceeded .

[722] Temperature-related changes in polar cyanobacterial mat diversity and toxin production

One of the fastest rates of recent climate warming has been reported for the Arctic and the maritime Antarctic ; for example , mean annual temperatures increased by 0.5 degreesC per decade over the Antarctic Peninsula during the past 50 years .
Owing to their comparatively simple and highly sensitive food webs , polar freshwater systems , with cyanobacterial mats representing the dominant benthic primary producers , seem well suited for monitoring environmental perturbation , including climate change .
Prolonged climate change may challenge the resilience , plasticity and adaptability and thus affect the community composition of cyanobacterial mats .
We demonstrate that exposing polar mat samples to raised temperatures for six months results in a change in species predominance .
Mats exposed to a constant temperature of 8 degreesC or 16 degreesC showed high cyanobacterial diversity , commensurate with an increased presence of cyanobacterial toxins .
In contrast , mats held at 4 degreesC and 23 degreesC seemed low in diversity .
Our data thus indicate that a temperature shift to 8-16 degreesC , potentially reached during summer months in polar regions at the present warming rate , could affect cyanobacterial diversity , and in some instances result in a shift to toxin-producing species or to elevated toxin concentrations by pre-existing species that could profoundly alter freshwater polar ecosystems .

[723] Multiple greenhouse-gas feedbacks from the land biosphere under future climate change scenarios

Atmospheric concentrations of the three important greenhouse gases ( GHGs ) CO2 , CH4 and N2O are mediated by processes in the terrestrial biosphere that are sensitive to climate and CO2 .
This leads to feedbacks between climate and land and has contributed to the sharp rise in atmospheric GHG concentrations since pre-industrial times .
Here , we apply a process-based model to reproduce the historical atmospheric N2O and CH4 budgets within their uncertainties and apply future scenarios for climate , land-use change and reactive nitrogen ( Nr ) inputs to investigate future GHG emissions and their feedbacks with climate in a consistent and comprehensive framework .
Results suggest that in a business-as-usual scenario , terrestrial N2O and CH4 emissions increase by 80 and 45 % , respectively , and the land becomes a net source of C by AD 2100 .
N2O and CH4 feedbacks imply an additional warming of 0.4-0 .5 degreesC by AD 2300 ; on top of 0.8-1 .0 degreesC caused by terrestrial carbon cycle and Albedo feedbacks .
The land biosphere represents an increasingly positive feedback to anthropogenic climate change and amplifies equilibrium climate sensitivity by 22-27 % .
Strong mitigation limits the increase of terrestrial GHG emissions and prevents the land biosphere from acting as an increasingly strong amplifier to anthropogenic climate change .

[724] Unabated planetary warming and its ocean structure since 2006

Increasing heat content of the global ocean dominates the energy imbalance in the climate system .
Here we show that ocean heat gain over the 0-2 ,000 m layer continued at a rate of 0.4-0 .6 W m-2 during 2006-2013 .
The depth dependence and spatial structure of temperature changes are described on the basis of the Argo Program 's accurate and spatially homogeneous data set , through comparison of three Argo-only analyses .
Heat gain was divided equally between upper ocean , 0-500 m and 500-2 ,000 m components .
Surface temperature and upper 100 m heat content tracked interannual El Nino/Southern Oscillation fluctuations , but were offset by opposing variability from 100-500 m .
The net 0-500 m global average temperature warmed by 0.005 degreesC yr-1 .
Between 500 and 2,000 m steadier warming averaged 0.002 degreesC yr-1 with a broad intermediate-depth maximum between 700 and 1,400 m. Most of the heat gain ( 67 to 98 % ) occurred in the Southern Hemisphere extratropical ocean .
Although this hemispheric asymmetry is consistent with inhomogeneity of radiative forcing and the greater area of the Southern Hemisphere ocean , ocean dynamics also influence regional patterns of heat gain .

[725] Methylotrophic methanogenic Thermoplasmata implicated in reduced methane emissions from bovine rumen

Rumen methanogens are major sources of anthropogenic methane emissions , and these archaea are targets in strategies aimed at reducing methane emissions .
Here we show that the poorly characterised Thermoplasmata archaea in bovine rumen are methylotrophic methanogens and that they are reduced upon dietary supplementation with rapeseed oil in lactating cows .
In a metatranscriptomic survey , Thermoplasmata 16S rRNA and methyl-coenzyme M reductase ( mcr ) transcripts decreased concomitantly with mRNAs of enzymes involved in methanogenesis from methylamines that were among the most abundant archaeal transcripts , indicating that these Thermoplasmata degrade methylamines .
Their methylotrophic methanogenic lifestyle was corroborated by in vitro incubations , showing enhanced growth of these organisms upon methylamine supplementation paralleled by elevated methane production .
The Thermoplasmata have a high potential as target in future strategies to mitigate methane emissions from ruminant livestock .
Our findings and the findings of others also indicate a wider distribution of methanogens than previously anticipated .

[726] The role of short-lived climate pollutants in meeting temperature goals

Some recent high-profile publications have suggested that immediately reducing emissions of methane , black carbon and other short-lived climate pollutants ( SLCPs ) may contribute substantially towards the goal of limiting global warming to 2 degreesC above pre-industrial levels .
Although this literature acknowledges that action on long-lived climate pollutants ( LLCPs ) such as CO2 is also required , it is not always appreciated that SLCP emissions in any given decade only have a significant impact on peak temperature under circumstances in which CO2 emissions are falling .
Immediate action on SLCPs might potentially ` buy time ' for adaptation by reducing near-term warming ; however early SLCP reductions , compared with reductions in a future decade , do not buy time to delay reductions in CO2 .

[727] Coral thermal tolerance shaped by local adaptation of photosymbionts

Coral thermal tolerance is strongly influenced by the identity of obligate photosymbionts , which encompass numerous types belonging to the dinoflagellate genus Symbiodinium .
Physiological advantages achieved by partnering with functionally diverse symbionts have been assumed to be available only to corals that can form associations with multiple Symbiodinium types .
Functional variation among populations of the same type of Symbiodinium has been overlooked , despite local adaptation being feasible because of large population sizes , genetic isolation and short asexual generation times .
Here we demonstrate divergent thermal tolerance in a generalist Symbiodinium type from two different thermal environments .
Symbiodinium from the warmer reef maintained greater photo-chemical performance and survivorship when exposed to an elevated temperature of 32 degreesC , both in symbiosis and in culture .
Juvenile corals associated with Symbiodinium from the warmer reef grew rapidly when exposed to 32 degreesC , yet underwent bleaching and tissue death when associated with Symbiodinium from the cooler reef .
These results demonstrate that Symbiodinium types can adapt to local differences in thermal climate and that this adaptation shapes the fitness of coral hosts .
If Symbiodinium populations are able to further adapt to increases in temperature at the pace at which ocean climates warm , they may assist corals to increase their thermal tolerance and persist into the future .

[728] Impact of climate change on the Baltic Sea ecosystem over the past 1,000 years

Climate change has a strong impact on ecosystem health , particularly in marginal seas such as the Baltic , for example causing the spreading of anoxic areas ( oxygen-free areas , the so-called dead zones ) through strong feedbacks .
Marked ecosystem changes in the Baltic Sea have been recorded in the sedimentary archive , but the reasons are not fully understood .
Here we report an integrated study of high-resolution sediment records ( past 1,000 years ) in combination with an ecosystem modelling approach , providing new insights into the functioning of the Baltic Sea ecosystem under natural and human-influenced climatic changes .
Between the Little Ice Age and the Modern Warm Period the surface water temperatures reconstructed using TEX86 palaeothermometry increased by ~ 2 degreesC .
Simultaneously , the anoxic areas in the Baltic Sea began to expand significantly as evident from the accumulation of laminated sediments .
Ecosystem model simulations support our findings of widespread oxic areas during the Little Ice Age .
Backed up by the modelling results that take into account anthropogenic-influenced nutrient load scenarios , our results provide evidence that surface temperature changes strongly influence deepwater oxygenation .
This highlights the risk of a continued spreading of anoxic areas during scenarios of continued climate warming in the future .

[729] Carbon sequestration during the Palaeocene-Eocene Thermal Maximum by an efficient biological pump

A perturbation of the carbon cycle and biosphere , linked to globally increased temperatures about 55.9 million years ago , characterized the Palaeocene-Eocene Thermal Maximum .
Its effect on global oceanic productivity is controversial .
Here we present records of marine barite accumulation rates that show distinct peaks during this time interval , suggesting a general increase in export productivity .
We propose that changes in marine ecosystems , resulting from high atmospheric partial pressure of CO2 and ocean acidification , led to enhanced carbon export from the photic zone to depth , thereby increasing the efficiency of the biological pump .
Higher seawater temperatures at that time increased bacterial activity and organic matter regeneration .
Through this process much of the sinking particulate organic matter was probably converted to dissolved inorganic and organic carbon .
We estimate that an annual carbon export flux out of the euphotic zone and into the deep ocean waters could have amounted to about 15 Gt during the Palaeocene-Eocene Thermal Maximum .
About 0.4 % of this carbon is expected to have entered the refractory dissolved organic pool , where it could be sequestered from the atmosphere for tens of thousands of years .
Our estimates are consistent with the amount of carbon redistribution expected for the recovery from the Palaeocene-Eocene Thermal Maximum .

[730] Evolution of leaf-form in land plants linked to atmospheric CO2 decline in the Late Palaeozoic era

The widespread appearance of megaphyll leaves , with their branched veins and planate form , did not occur until the close of the Devonian period at about 360 Myr ago .
This happened about 40 Myr after simple leafless vascular plants first colonized the land in the Late Silurian/Early Devonian , but the reason for the slow emergence of this common feature of present-day plants is presently unresolved .
Here we show , in a series of quantitative analyses using fossil leaf characters and biophysical principles , that the delay was causally linked with a 90 % drop in atmospheric pCO2 during the Late Palaeozoic era .
In contrast to simulations for a typical Early Devonian land plant , possessing few stomata on leafless stems , those for a planate leaf with the same stomatal characteristics indicate that it would have suffered lethal overheating , because of greater interception of solar energy and low transpiration .
When planate leaves first appeared in the Late Devonian and subsequently diversified in the Carboniferous period , they possessed substantially higher stomatal densities .
This observation is consistent with the effects of the pCO2 on stomatal development and suggests that the evolution of planate leaves could only have occurred after an increase in stomatal density , allowing higher transpiration rates that were sufficient to maintain cool and viable leaf temperatures .

[731] Persistent export of 231Pa from the deep central Arctic Ocean over the past 35,000 years

The Arctic Ocean has an important role in Earth 's climate , both through surface processes such as sea-ice formation and transport , and through the production and export of waters at depth that contribute to the global thermohaline circulation .
Deciphering the deep Arctic Ocean 's palaeo-oceanographic history is a crucial part of understanding its role in climatic change .
Here we show that sedimentary ratios of the radionuclides thorium-230 ( 230Th ) and protactinium-231 ( 231Pa ) , which are produced in sea water and removed by particle scavenging on timescales of decades to centuries , respectively , record consistent evidence for the export of 231Pa from the deep Arctic and may indicate continuous deep-water exchange between the Arctic and Atlantic oceans throughout the past 35,000 years .
Seven well-dated box-core records provide a comprehensive overview of 231Pa and 230Th burial in Arctic sediments during glacial , deglacial and interglacial conditions .
Sedimentary 231Pa/230Th ratios decrease nearly linearly with increasing water depth above the core sites , indicating efficient particle scavenging in the upper water column and greater influence of removal by lateral transport at depth .
Although the measured 230Th burial is in balance with its production in Arctic sea water , integrated depth profiles for all time intervals reveal a deficit in 231Pa burial that can be balanced only by lateral export in the water column .
Because no enhanced sink for 231Pa has yet been found in the Arctic , our records suggest that deep-water exchange through the Fram strait may export 231Pa .
Such export may have continued for the past 35,000 years , suggesting a century-scale replacement time for deep waters in the Arctic Ocean since the most recent glaciation and a persistent contribution of Arctic waters to the global ocean circulation .

[732] Abrupt changes in North American climate during early Holocene times

Recent studies of the Greenland ice cores have offered many insights into Holocene climatic dynamics at decadal to century timescales .
Despite the abundance of continental records of Holocene climate , few have sufficient chronological control and sampling resolution to compare with the Greenland findings .
Butannually laminated sediments ( varves ) from lakes can provide high-resolution continental palaeoclimate data with secure chronologies .
Here we present analyses of varved sediments from Deep Lake in Minnesota , USA .
Trends in the stable oxygen-isotope composition of the sedimentary carbonate indicate a pronounced climate cooling from 8.9 to 8.3 kyr before present , probably characterized by increased outbreaks of polar air , decreased precipitation temperatures , and a higher fraction of the annual precipitation falling as snow .
The abrupt onset of this climate reversal , over several decades , was probably caused by a reorganization of atmospheric circulation and cooling of the Arctic airmass in summer that resulted from the final collapse of the Laurentide ice near Hudson Bay and the discharge of icebergs from the Quebec and Keewatin centres into the Tyrell Sea .
The timing and duration of this climate reversal suggest that it is distinct from the prominent widespread cold snap that occurred 8,200 years ago in Greenland and other regions , , .
No shifts in the oxygen-isotope composition of sediment carbonate occurred at 8.2 kyr before present at Deep Lake , but varve thickness increased dramatically , probably as a result of increased deposition of aeolian dust .
Taken together , our data suggest that two separate regional-scale climate reversals occurred between 9,000 and 8,000 years ago , and that they were driven by different mechanisms .

[733] Continuing decline in the growth rate of the atmospheric methane burden

The global atmospheric methane burden has more than doubled since pre-industrial times , , and this increase is responsible for about 20 % of the estimated change in direct radiative forcing due to anthropogenic greenhouse-gas emissions .
Research into future climate change and the development of remedial environmental policies therefore require a reliable assessment of the long-term growth rate in the atmospheric methane load .
Measurements have revealed that although the global atmospheric methane burden continues to increase with significant interannual variability , , the overall rate of increase has slowed , .
Here we present an analysis of methane measurements from a global air sampling network that suggests that , assuming constant OH concentration , global annual methane emissions have remained nearly constant during the period 1984-96 , and that the decreasing growth rate in atmospheric methane reflects the approach to a steady state on a timescale comparable to methane 's atmospheric lifetime .
If the global methane sources and OH concentration continue to remain constant , we expect average methane mixing ratios to increase slowly from today 's 1,730 nmol mol-1 to ~ 1,800 nmol mol-1 , with little change in the contribution of methane to the greenhouse effect .

[734] Large temperature drop across the Eocene-Oligocene transition in central North America

The Eocene-Oligocene transition towards a cool climate ( ~ 33.5 million years ago ) was one of the most pronounced climate events during the Cenozoic era .
The marine record of this transition has been extensively studied .
However , significantly less research has focused on continental climate change at the time , yielding partly inconsistent results on the magnitude and timing of the changes .
Here we use a combination of in vivo stable isotope compositions of fossil tooth enamel with diagenetic stable isotope compositions of fossil bone to derive a high-resolution ( about 40,000 years ) continental temperature record for the Eocene-Oligocene transition .
We find a large drop in mean annual temperature of 8.2 + / - 3.1 degreesC over about 400,000 years , the possibility of a small increase in temperature seasonality , and no resolvable change in aridity across the transition .
The large change in mean annual temperature , exceeding changes in sea surface temperatures at comparable latitudes and possibly delayed in time with respect to marine changes by up to 400,000 years , explains the faunal turnover for gastropods , amphibians and reptiles , whereas most mammals in the region were unaffected .
Our results are in agreement with modelling studies that attribute the climate cooling at the Eocene-Oligocene transition to a significant drop in atmospheric carbon dioxide concentrations .

[735] A new anode material for oxygen evolution in molten oxide electrolysis

Molten oxide electrolysis ( MOE ) is an electrometallurgical technique that enables the direct production of metal in the liquid state from oxide feedstock , and compared with traditional methods of extractive metallurgy offers both a substantial simplification of the process and a significant reduction in energy consumption .
MOE is also considered a promising route for mitigation of CO2 emissions in steelmaking , production of metals free of carbon , and generation of oxygen for extra-terrestrial exploration .
Until now , MOE has been demonstrated using anode materials that are consumable ( graphite for use with ferro-alloys and titanium ) or unaffordable for terrestrial applications ( iridium for use with iron ) .
To enable metal production without process carbon , MOE requires an anode material that resists depletion while sustaining oxygen evolution .
The challenges for iron production are threefold .
First , the process temperature is in excess of 1,538 degrees Celsius ( ref .
10 ) .
Second , under anodic polarization most metals inevitably corrode in such conditions .
Third , iron oxide undergoes spontaneous reduction on contact with most refractory metals and even carbon .
Here we show that anodes comprising chromium-based alloys exhibit limited consumption during iron extraction and oxygen evolution by MOE .
The anode stability is due to the formation of an electronically conductive solid solution of chromium ( iii ) and aluminium oxides in the corundum structure .
These findings make practicable larger-scale evaluation of MOE for the production of steel , and potentially provide a key material component enabling mitigation of greenhouse-gas emissions while producing metal of superior metallurgical quality .

[736] Metabolic efficiency underpins performance trade-offs in growth of Arabidopsis thaliana

Growth often involves a trade-off between the performance of contending tasks ; metabolic plasticity can play an important role .
Here we grow 97 Arabidopsis thaliana accessions in three conditions with a differing supply of carbon and nitrogen and identify a trade-off between two tasks required for rosette growth : increasing the physical size and increasing the protein concentration .
We employ the Pareto performance frontier concept to rank accessions based on their multitask performance ; only a few accessions achieve a good trade-off under all three growth conditions .
We determine metabolic efficiency in each accession and condition by using metabolite levels and activities of enzymes involved in growth and protein synthesis .
We demonstrate that accessions with high metabolic efficiency lie closer to the performance frontier and show increased metabolic plasticity .
We illustrate how public domain data can be used to search for additional contending tasks , which may underlie the sub-optimality in some accessions .

[737] Ionic Polymer-Coated Laccase with High Activity and Enhanced Stability : Application in the Decolourisation of Water Containing AO7

Eliminating dyes in environmental water purification remains a formidable challenge .
Laccase is a unique , environmentally friendly and efficient biocatalyst that can degrade pollutants .
However , the use of laccase for the degradation of pollutants is considerably limited by its susceptibility to environmental changes and its poor reusability .
We fabricated a novel biocatalyst ( LacPG ) by coating polyethylenimine onto the native laccase ( Lac ) followed by crosslinking with glutaraldehyde .
The stability of the resulting LacPG was highly enhanced against pH variations , thermal treatments and provided better long-term storage with a negligible loss in enzymatic activity .
Compared to Lac , LacPG exhibited significantly higher decolourisation efficiency in the degradation of a representative azo dye , acid orange 7 ( AO7 ) , which resulted from the electrostatic attraction between the coating and AO7 .
LacPG was separated from the AO7 solution using an ultrafiltration unit .
The increased size and modified surface chemistry of LacPG facilitated ultrafiltration and reduced membrane fouling .
LacPG exhibited enhanced stability , high catalytic activity and favourable properties for membrane separation ; therefore , LacPG could be continuously reused in an enzymatic membrane reactor with a high efficiency for decolourising water containing AO7 .
The developed strategy appears to be promising for enhancing the applicability of laccase in practical water treatment .

[738] Increased dissolved oxygen in Pacific intermediate waters due to lower rates of carbon oxidation in sediments

Concentrations of dissolved oxygen in the ocean seem to correlate well with climate instabilities over the past 100,000 years .
For example , the concentration of dissolved oxygen in Pacific intermediate waters was considerably higher during Pleistocene glacial periods than it is today .
This has been inferred from the presence of bioturbated sediments , implying that oxygen levels were sufficient for burrowing organisms to live .
Today , basins in the northeastern Pacific Ocean are floored by laminated sediments implying lower oxygen levels , which may be explained by reduced ventilation .
Here we report a recent return to bioturbated sediments in the northeastern Pacific Ocean since the late 1970s .
From the carbon isotope composition of benthic foraminifers living in the sediment , we infer a twofold decrease in the carbon oxidation rate occurring within sediments , equivalent to an increase in dissolved oxygen concentration of 15-20 micromoles per litre .
These changes , at the edges of the Santa Barbara , Santa Monica and Alfonso basins , are coincident with a change in North Pacific climate which has reduced upwelling by 20-30 % and increased sea surface temperatures by 1.5-3 degreesC .
This suggests that climate effects on surface productivity , reducing the supply organic matter to sediments , may have had a greater effect on benthic oxygen levels than changes in ocean circulation patterns .

[739] Eddy-induced reduction of biological production in eastern boundary upwelling systems

Eddies and other mesoscale oceanic processes , such as fronts , can enhance biological production in the ocean , according to several open-ocean studies .
The effect is thought to be particularly pronounced in low-nutrient environments , where mesoscale processes increase the net upward flux of limiting nutrients .
However , eddies have been suggested to suppress production in the highly productive eastern boundary upwelling systems .
Here , we examine the relationship between satellite-derived estimates of net primary production , of upwelling strength , and of eddy-kinetic energy -- a measure of the intensity of mesoscale activity -- in the four most productive eastern boundary upwelling systems .
We show that high levels of eddy activity tend to be associated with low levels of biological production , indicative of a suppressive effect .
Simulations using eddy-resolving models of two of these upwelling systems support the suggestion that eddies suppress production , and show that the downward export of organic matter is also reduced .
According to these simulations , the reduction in production and export results from an eddy-induced transport of nutrients from the nearshore environment to the open ocean .
Eddies might have a similar effect on marine productivity in other oceanic systems that are characterized by intense eddy activity , such as the Southern Ocean .

[740] Resource quality affects carbon cycling in deep-sea sediments

Deep-sea sediments cover ~ 70 % of Earth 's surface and represent the largest interface between the biological and geological cycles of carbon .
Diatoms and zooplankton faecal pellets naturally transport organic material from the upper ocean down to the deep seabed , but how these qualitatively different substrates affect the fate of carbon in this permanently cold environment remains unknown .
We added equal quantities of 13C-labelled diatoms and faecal pellets to a cold water ( -0.7 degreesC ) sediment community retrieved from 1080 m in the Faroe-Shetland Channel , Northeast Atlantic , and quantified carbon mineralization and uptake by the resident bacteria and macrofauna over a 6-day period .
High-quality , diatom-derived carbon was mineralized > 300 % faster than that from low-quality faecal pellets , demonstrating that qualitative differences in organic matter drive major changes in the residence time of carbon at the deep seabed .
Benthic bacteria dominated biological carbon processing in our experiments , yet showed no evidence of resource quality-limited growth ; they displayed lower growth efficiencies when respiring diatoms .
These effects were consistent in contrasting months .
We contend that respiration and growth in the resident sediment microbial communities were substrate and temperature limited , respectively .
Our study has important implications for how future changes in the biochemical makeup of exported organic matter will affect the balance between mineralization and sequestration of organic carbon in the largest ecosystem on Earth .

[741] Rapid interhemispheric climate links via the Australasian monsoon during the last deglaciation

Recent studies have proposed that millennial-scale reorganization of the ocean-atmosphere circulation drives increased upwelling in the Southern Ocean , leading to rising atmospheric carbon dioxide levels and ice age terminations .
Southward migration of the global monsoon is thought to link the hemispheres during deglaciation , but vital evidence from the southern sector of the vast Australasian monsoon system is yet to emerge .
Here we present a 230thorium-dated stalagmite oxygen isotope record of millennial-scale changes in Australian-Indonesian monsoon rainfall over the last 31,000 years .
The record shows that abrupt southward shifts of the Australian-Indonesian monsoon were synchronous with North Atlantic cold intervals 17,600-11 ,500 years ago .
The most prominent southward shift occurred in lock-step with Heinrich Stadial 1 ( 17,600-14 ,600 years ago ) , and rising atmospheric carbon dioxide .
Our findings show that millennial-scale climate change was transmitted rapidly across Australasia and lend support to the idea that the 3,000-year-long Heinrich 1 interval could have been critical in driving the last deglaciation .

[742] Abrupt reversal in ocean overturning during the Palaeocene/Eocene warm period

An exceptional analogue for the study of the causes and consequences of global warming occurs at the Palaeocene/Eocene Thermal Maximum , 55 million years ago .
A rapid rise of global temperatures during this event accompanied turnovers in both marine and terrestrial biota , as well as significant changes in ocean chemistry and circulation .
Here we present evidence for an abrupt shift in deep-ocean circulation using carbon isotope records from fourteen sites .
These records indicate that deep-ocean circulation patterns changed from Southern Hemisphere overturning to Northern Hemisphere overturning at the start of the Palaeocene/Eocene Thermal Maximum .
This shift in the location of deep-water formation persisted for at least 40,000 years , but eventually recovered to original circulation patterns .
These results corroborate climate model inferences that a shift in deep-ocean circulation would deliver relatively warmer waters to the deep sea , thus producing further warming .
Greenhouse conditions can thus initiate abrupt deep-ocean circulation changes in less than a few thousand years , but may have lasting effects ; in this case taking 100,000 years to revert to background conditions .

[743] Importance of food-demand management for climate mitigation

Recent studies show that current trends in yield improvement will not be sufficient to meet projected global food demand in 2050 , and suggest that a further expansion of agricultural area will be required .
However , agriculture is the main driver of losses of biodiversity and a major contributor to climate change and pollution , and so further expansion is undesirable .
The usual proposed alternative -- intensification with increased resource use -- also has negative effects .
It is therefore imperative to find ways to achieve global food security without expanding crop or pastureland and without increasing greenhouse gas emissions .
Some authors have emphasized a role for sustainable intensification in closing global ` yield gaps ' between the currently realized and potentially achievable yields .
However , in this paper we use a transparent , data-driven model , to show that even if yield gaps are closed , the projected demand will drive further agricultural expansion .
There are , however , options for reduction on the demand side that are rarely considered .
In the second part of this paper we quantify the potential for demand-side mitigation options , and show that improved diets and decreases in food waste are essential to deliver emissions reductions , and to provide global food security in 2050 .

[744] Links between iron input and opal deposition in the Pleistocene equatorial Pacific Ocean

Increases in overall marine primary productivity and export production in high-nutrient , low-chlorophyll regions of the ocean have , particularly during dry and dusty glacial periods , been hypothesized to be linked to the enhanced delivery of iron .
In the modern ocean , iron availability limits production in high-nutrient , low-chlorophyll regions , and may be important in lower-nutrient settings as well .
Here , we assess the relationship between productivity and iron in sedimentary records from the high-nutrient , low-chlorophyll region of the equatorial Pacific Ocean over the past million years .
We find strong links between iron input , the export and burial of biogenic silica ( opal ) and total export production .
Our data demonstrate that iron accumulation was more closely tied to the accumulation of opal than any other biogenic component , with high iron input associated with substantially increased opal sedimentation .
The strong links between iron and opal accumulation over the past one million years are in agreement with the modern biogeochemical behaviour of iron and silica , and the response of the diatom community to their mutual availablity .
Our data support earlier suggestions of a biological response to iron delivery over geologic timescales .

[745] Climate response to regional radiative forcing during the twentieth century

Regional climate change can arise from three different effects : regional changes to the amount of radiative heating that reaches the Earth 's surface , an inhomogeneous response to globally uniform changes in radiative heating and variability without a specific forcing .
The relative importance of these effects is not clear , particularly because neither the response to regional forcings nor the regional forcings themselves are well known for the twentieth century .
Here we investigate the sensitivity of regional climate to changes in carbon dioxide , black carbon aerosols , sulphate aerosols and ozone in the tropics , mid-latitudes and polar regions , using a coupled ocean-atmosphere model .
We find that mid - and high-latitude climate is quite sensitive to the location of the forcing .
Using these relationships between forcing and response along with observations of twentieth century climate change , we reconstruct radiative forcing from aerosols in space and time .
Our reconstructions broadly agree with historical emissions estimates , and can explain the differences between observed changes in Arctic temperatures and expectations from non-aerosol forcings plus unforced variability .
We conclude that decreasing concentrations of sulphate aerosols and increasing concentrations of black carbon have substantially contributed to rapid Arctic warming during the past three decades .

[746] Drought survival of tropical tree seedlings enhanced by non-structural carbohydrate levels

Plants in most biomes are thought to be living at their hydraulic limits , and alterations to precipitation patterns consistent with climate change trends are causing die-back in forests across the globe .
However , within - and among-species variation in plant traits that promote persistence and adaptation under these new rainfall regimes may reduce mortality in these changing climates .
Storage of non-structural carbohydrates ( NSCs ) is posited as an important trait for resistance and resilience of forests to climate-change-induced drought , but the underlying mechanisms remain unclear .
Here we demonstrate a positive relationship between NSCs and drought survival by manipulating NSC concentrations within seedlings of ten tropical tree species .
Seedlings experimentally enriched in NSCs showed higher stem water potentials and sustained NSCs during drought .
NSC use for maintenance of osmoregulation and hydraulic function therefore seems to underlie improved drought resistance .
That drought mortality is delayed by higher NSC concentrations has implications for predicting the impacts of climate change on forest die-back and may help focus restoration efforts on species that increase the resistance and resilience of forests to climate change .

[747] Forcing of wet phases in southeast Africa over the past 17,000 years

Intense debate persists about the climatic mechanisms governing hydrologic changes in tropical and subtropical southeast Africa since the Last Glacial Maximum , about 20,000 years ago .
In particular , the relative importance of atmospheric and oceanic processes is not firmly established .
Southward shifts of the intertropical convergence zone ( ITCZ ) driven by high-latitude climate changes have been suggested as a primary forcing , whereas other studies infer a predominant influence of Indian Ocean sea surface temperatures on regional rainfall changes .
To address this question , a continuous record representing an integrated signal of regional climate variability is required , but has until now been missing .
Here we show that remote atmospheric forcing by cold events in the northern high latitudes appears to have been the main driver of hydro-climatology in southeast Africa during rapid climate changes over the past 17,000 years .
Our results are based on a reconstruction of precipitation and river discharge changes , as recorded in a marine sediment core off the mouth of the Zambezi River , near the southern boundary of the modern seasonal ITCZ migration .
Indian Ocean sea surface temperatures did not exert a primary control over southeast African hydrologic variability .
Instead , phases of high precipitation and terrestrial discharge occurred when the ITCZ was forced southwards during Northern Hemisphere cold events , such as Heinrich stadial 1 ( around 16,000 years ago ) and the Younger Dryas ( around 12,000 years ago ) , or when local summer insolation was high in the late Holocene , that is , during the past 4,000 years .

[748] Age of stratospheric air unchanged within uncertainties over the past 30 years

The rising abundances of greenhouse gases in the atmosphere is associated with an increase in radiative forcing that leads to warming of the troposphere , the lower portion of the Earth 's atmosphere , and cooling of the stratosphere above .
A secondary effect of increasing levels of greenhouse gases is a possible change in the stratospheric circulation , which could significantly affect chlorofluorocarbon lifetimes , ozone levels and the climate system more generally .
Model simulations have shown that the mean age of stratospheric air is a good indicator of the strength of the residual circulation , and that this mean age is expected to decrease with rising levels of greenhouse gases in the atmosphere .
Here we use balloon-borne measurements of stratospheric trace gases over the past 30 years to derive the mean age of air from sulphur hexafluoride ( SF6 ) and CO2 mixing ratios .
In contrast to the models , these observations do not show a decrease in mean age with time .
If models are to make valid predictions of future stratospheric ozone levels , and of the coupling between ozone and climate change , a correct description of stratospheric transport and possible changes in the transport pathways are necessary .

[749] Summertime climate response to mountain pine beetle disturbance in British Columbia

The present mountain pine beetle infestation in forests in British Columbia ranks among the largest ecological disturbances recorded in Canada so far .
These recent outbreaks are thought to have been favoured by large-scale climatic shifts , and may foreshadow outbreaks of a similar magnitude in North American forests over the coming decades .
The associated forest dieback could result in substantial shifts in evapotranspiration and albedo , thereby altering the local surface energy balance , and in turn regional temperature and climate .
Here we quantify the impact of the Canadian pine beetle disturbance on the local summertime surface energy budget , using measurements of evapotranspiration , albedo and surface temperature , obtained primarily through remote sensing .
We show that over the 170,000 km2 of affected forest , the typical decrease in summertime evapotranspiration is 19 % .
Changes to the absorbed short-wave flux are negligible , in comparison .
As a result , outgoing sensible and radiative heat fluxes increased by 8 % and 1 % , respectively , corresponding to a typical increase in surface temperature of 1 degreesC .
These changes are comparable to those observed for other types of disturbance , such as wildfire , and may have secondary consequences for climate , including modifications to circulation , cloud cover and precipitation .

[750] Ecosystem stability and compensatory effects in the Inner Mongolia grassland

Numerous studies have suggested that biodiversity reduces variability in ecosystem productivity through compensatory effects ; that is , a species increases in its abundance in response to the reduction of another in a fluctuating environment .
But this view has been challenged on several grounds .
Because most studies have been based on artificially constructed grasslands with short duration , long-term studies of natural ecosystems are needed .
On the basis of a 24-year study of the Inner Mongolia grassland , here we present three key findings .
First , that January-July precipitation is the primary climatic factor causing fluctuations in community biomass production ; second , that ecosystem stability ( conversely related to variability in community biomass production ) increases progressively along the hierarchy of organizational levels ( that is , from species to functional group to whole community ) ; and finally , that the community-level stability seems to arise from compensatory interactions among major components at both species and functional group levels .
From a hierarchical perspective , our results corroborate some previous findings of compensatory effects .
Undisturbed mature steppe ecosystems seem to culminate with high biodiversity , productivity and ecosystem stability concurrently .
Because these relationships are correlational , further studies are necessary to verify the causation among these factors .
Our study provides new insights for better management and restoration of the rapidly degrading Inner Mongolia grassland .

[751] Mediterranean seagrass vulnerable to regional climate warming

The Mediterranean Sea , one of the regions warming fastest under climate change , harbours lush seagrass ( Posidonia oceanica ) meadows that form the basis for a key ecosystem in the region .
Recent field results have shown that increased maximum annual seawater temperature in the Mediterranean has already led to increased seagrass mortality .
Here we project the trajectory of P. oceanica meadows under the warming expected in the western Mediterranean through the twenty-first century to conclude that warming will lead to the functional extinction of P. oceanica meadows by the middle of this century ( year 2049 + / -10 ) even under a relatively mild greenhouse-gas emissions scenario .
Efforts to alleviate local stresses adding to the loss of P. oceanica meadows will have a limited effect in conserving the meadows under climate change .
Efforts to mitigate climate change are urgently needed to preserve this key ecosystem .

[752] Increased multidecadal variability of the North Atlantic Oscillation since 1781

The North Atlantic Oscillation is a meridional oscillation of atmospheric mass measured between Iceland and the Acores , which drives winter climate variability in eastern North America and Europe .
A prolonged period of the positive phase during the 1990s led to the suggestion that anthropogenic warming was affecting the behaviour of the North Atlantic Oscillation .
However , instrumental records are too short to compare observations during periods of extended warm and cold hemispheric temperatures , and existing palaeoclimate reconstructions primarily capture terrestrial variability .
Here we present a record of Sr/Ca , a sea surface temperature proxy , from a Bermuda coral from 1781 to 1999 .
We use this monthly resolved record to reconstruct past variability of the North Atlantic Oscillation at multiple frequencies .
Our record shows enhanced multidecadal scale variability during the late twentieth century compared with the end of the Little Ice Age ( 1800-1850 ) .
We suggest that variability within the North Atlantic Oscillation is linked to the mean temperature of the Northern Hemisphere , which must be considered in any long-term predictions .

[753] Externally forced fluctuations in ocean temperature at Greenland glaciers in non-summer months

Enhanced submarine melting of outlet glaciers has been identified as a plausible trigger for part of the accelerated mass loss from the Greenland ice sheet , which at present accounts for a quarter of global sea level rise .
However , our understanding of what controls the submarine melt rate is limited and largely informed by brief summer surveys in the fjords where glaciers terminate .
Here , we present continuous records of water properties and velocity from September to May in Sermilik Fjord ( 2011-2012 ) and Kangerdlugssuaq Fjord ( 2009-2010 ) , the fjords into which the Helheim and Kangerdlugssuaq glaciers drain .
We show that water properties , including heat content , vary significantly over timescales of three to ten days in both fjords .
This variability results from frequent velocity pulses that originate on the shelf outside the fjord .
The pulses drive rapid water exchange with the shelf and renew warm water in the fjord more effectively than any glacial freshwater-driven circulation .
Our observations suggest that , during non-summer months , the glacier melt rate varies substantially and depends on externally forced ocean flows that rapidly transport changes on the shelf towards the glaciers ' margins .

[754] Deoxygenation alters bacterial diversity and community composition in the ocean 's largest oxygen minimum zone

Oceanic oxygen minimum zones ( OMZs ) have a central role in biogeochemical cycles and are expanding as a consequence of climate change , yet how deoxygenation will affect the microbial communities that control these cycles is unclear .
Here we sample across dissolved oxygen gradients in the oceans ' largest OMZ and show that bacterial richness displays a unimodal pattern with decreasing dissolved oxygen , reaching maximum values on the edge of the OMZ and decreasing within it .
Rare groups on the OMZ margin are abundant at lower dissolved oxygen concentrations , including sulphur-cycling Chromatiales , for which 16S rRNA was amplified from extracted RNA .
Microbial species distribution models accurately replicate community patterns based on multivariate environmental data , demonstrate likely changes in distributions and diversity in the eastern tropical North Pacific Ocean , and highlight the sensitivity of key bacterial groups to deoxygenation .
Through these mechanisms , OMZ expansion may alter microbial composition , competition , diversity and function , all of which have implications for biogeochemical cycling in OMZs .

[755] Volcanic carbon dioxide vents show ecosystem effects of ocean acidification

The atmospheric partial pressure of carbon dioxide ( pCO2 ) will almost certainly be double that of pre-industrial levels by 2100 and will be considerably higher than at any time during the past few million years .
The oceans are a principal sink for anthropogenic CO2 where it is estimated to have caused a 30 % increase in the concentration of H + in ocean surface waters since the early 1900s and may lead to a drop in seawater pH of up to 0.5 units by 2100 ( refs 2 , 3 ) .
Our understanding of how increased ocean acidity may affect marine ecosystems is at present very limited as almost all studies have been in vitro , short-term , rapid perturbation experiments on isolated elements of the ecosystem .
Here we show the effects of acidification on benthic ecosystems at shallow coastal sites where volcanic CO2 vents lower the pH of the water column .
Along gradients of normal pH ( 8.1-8 .2 ) to lowered pH ( mean 7.8-7 .9 , minimum 7.4-7 .5 ) , typical rocky shore communities with abundant calcareous organisms shifted to communities lacking scleractinian corals with significant reductions in sea urchin and coralline algal abundance .
To our knowledge , this is the first ecosystem-scale validation of predictions that these important groups of organisms are susceptible to elevated amounts of pCO2 .
Sea-grass production was highest in an area at mean pH 7.6 ( 1,827 muatm pCO2 ) where coralline algal biomass was significantly reduced and gastropod shells were dissolving due to periods of carbonate sub-saturation .
The species populating the vent sites comprise a suite of organisms that are resilient to naturally high concentrations of pCO2 and indicate that ocean acidification may benefit highly invasive non-native algal species .
Our results provide the first in situ insights into how shallow water marine communities might change when susceptible organisms are removed owing to ocean acidification .

[756] Accumulation of persistent organochlorine compounds in mountains of western Canada

Persistent , semi-volatile organochlorine compounds , including toxic industrial pollutants and agricultural pesticides , are found everywhere on Earth , including in pristine polar and near-polar locations .
Higher than expected occurrences of these compounds in remote regions are the result of long-range transport in the atmosphere , precipitation and ` cold condensation ' -- the progressive volatilization in relatively warm locations and subsequent condensation in cooler environments , which leads to enhanced concentrations at high latitudes .
The upper reaches of high mountains are similar to high-latitude regions in that they too are characterized by relatively low average temperatures , but the accumulation of organochlorine compounds as a function of altitude has not yet been documented .
Here we repororganochlorine deposition in snow from mountain ranges in western Canada that show a 10 - to 100-fold increase between 770 and 3,100 m altitude .
In the case of less-volatile compounds , the observed increase by a factor of 10 is simply due to a 10-fold increase in snowfall over the altitude range of the sampling sites .
In the case of the more-volatile organochlorines , cold-condensation effects further enhance the concentration of these compounds with increasing altitude .
These findings demonstrate that temperate-zone mountain regions , which tend to receive high levels of precipitation while being close to pollutant sources , are particularly susceptible to the accumulation of semivolatile organochlorine compounds .

[757] El Nino-La Nina cycle and recent trends in continental evaporation

The hydrological cycle is expected to intensify in response to global warming .
Yet , little unequivocal evidence of such an acceleration has been found on a global scale .
This holds in particular for terrestrial evaporation , the crucial return flow of water from land to atmosphere .
Here we use satellite observations to reveal that continental evaporation has increased in northern latitudes , at rates consistent with expectations derived from temperature trends .
However , at the global scale , the dynamics of the El Nino/Southern Oscillation ( ENSO ) have dominated the multi-decadal variability .
During El Nino , limitations in terrestrial moisture supply result in vegetation water stress and reduced evaporation in eastern and central Australia , southern Africa and eastern South America .
The opposite situation occurs during La Nina .
Our results suggest that recent multi-year declines in global average continental evaporation reflect transitions to El Nino conditions , and are not the consequence of a persistent reorganization of the terrestrial water cycle .
Future changes in continental evaporation will be determined by the response of ENSO to changes in global radiative forcing , which still remains highly uncertain .

[758] The role of coastal plant communities for climate change mitigation and adaptation

Marine vegetated habitats ( seagrasses , salt-marshes , macroalgae and mangroves ) occupy 0.2 % of the ocean surface , but contribute 50 % of carbon burial in marine sediments .
Their canopies dissipate wave energy and high burial rates raise the seafloor , buffering the impacts of rising sea level and wave action that are associated with climate change .
The loss of a third of the global cover of these ecosystems involves a loss of CO2 sinks and the emission of 1 Pg CO2 annually .
The conservation , restoration and use of vegetated coastal habitats in eco-engineering solutions for coastal protection provide a promising strategy , delivering significant capacity for climate change mitigation and adaption .

[759] Thermodynamic constraints on methanogenic crude oil biodegradation

Methanogenic degradation of crude oil hydrocarbons is an important process in subsurface petroleum reservoirs and anoxic environments contaminated with petroleum .
There are several possible routes whereby hydrocarbons may be converted to methane : ( i ) complete oxidation of alkanes to H2 and CO2 , linked to methanogenesis from CO2 reduction ; ( ii ) oxidation of alkanes to acetate and H2 , linked to acetoclastic methanogenesis and CO2 reduction ; ( iii ) oxidation of alkanes to acetate and H2 , linked to syntrophic acetate oxidation and methanogenesis from CO2 reduction ; ( iv ) oxidation of alkanes to acetate alone , linked to acetoclastic methanogenesis and ( v ) oxidation of alkanes to acetate alone , linked to syntrophic acetate oxidation and methanogenesis from CO2 reduction .
We have developed the concept of a ` window of opportunity ' to evaluate the range of conditions under which each route is thermodynamically feasible .
On this basis the largest window of opportunity is presented by the oxidation of alkanes to acetate alone , linked to acetoclastic methanogenesis .
This contradicts field-based evidence that indicates that in petroleum rich environments acetoclastic methanogenesis is inhibited and that methanogenic CO2 reduction is the predominant methanogenic process .
Our analysis demonstrates that under those biological constraints oxidation of alkanes to acetate and H2 , linked to syntrophic acetate oxidation and methanogenesis from CO2 reduction offers a greater window of opportunity than complete oxidation of alkanes to H2 and CO2 linked to methanogenic CO2 reduction , and hence is the process most likely to occur .

[760] Consequences of climate change on the tree of life in Europe

Many species are projected to become vulnerable to twenty-first-century climate changes , with consequent effects on the tree of life .
If losses were not randomly distributed across the tree of life , climate change could lead to a disproportionate loss of evolutionary history .
Here we estimate the consequences of climate change on the phylogenetic diversities of plant , bird and mammal assemblages across Europe .
Using a consensus across ensembles of forecasts for 2020 , 2050 and 2080 and high-resolution phylogenetic trees , we show that species vulnerability to climate change clusters weakly across phylogenies .
Such phylogenetic signal in species vulnerabilities does not lead to higher loss of evolutionary history than expected with a model of random extinctions .
This is because vulnerable species have neither fewer nor closer relatives than the remaining clades .
Reductions in phylogenetic diversity will be greater in southern Europe , and gains are expected in regions of high latitude or altitude .
However , losses will not be offset by gains and the tree of life faces a trend towards homogenization across the continent .

[761] Strong contributions of local background climate to urban heat islands

The urban heat island ( UHI ) , a common phenomenon in which surface temperatures are higher in urban areas than in surrounding rural areas , represents one of the most significant human-induced changes to Earth 's surface climate .
Even though they are localized hotspots in the landscape , UHIs have a profound impact on the lives of urban residents , who comprise more than half of the world 's population .
A barrier to UHI mitigation is the lack of quantitative attribution of the various contributions to UHI intensity ( expressed as the temperature difference between urban and rural areas , DeltaT ) .
A common perception is that reduction in evaporative cooling in urban land is the dominant driver of DeltaT ( ref .
5 ) .
Here we use a climate model to show that , for cities across North America , geographic variations in daytime DeltaT are largely explained by variations in the efficiency with which urban and rural areas convect heat to the lower atmosphere .
If urban areas are aerodynamically smoother than surrounding rural areas , urban heat dissipation is relatively less efficient and urban warming occurs ( and vice versa ) .
This convection effect depends on the local background climate , increasing daytime DeltaT by 3.0 + / - 0.3 kelvin ( mean and standard error ) in humid climates but decreasing DeltaT by 1.5 + / - 0.2 kelvin in dry climates .
In the humid eastern United States , there is evidence of higher DeltaT in drier years .
These relationships imply that UHIs will exacerbate heatwave stress on human health in wet climates where high temperature effects are already compounded by high air humidity and in drier years when positive temperature anomalies may be reinforced by a precipitation-temperature feedback .
Our results support albedo management as a viable means of reducing DeltaT on large scales .

[762] A Winogradsky-based culture system shows an association between microbial fermentation and cystic fibrosis exacerbation

There is a poor understanding of how the physiology of polymicrobial communities in cystic fibrosis ( CF ) lungs contributes to pulmonary exacerbations and lung function decline .
In this study , a microbial culture system based on the principles of the Winogradsky column ( WinCF system ) was developed to study the physiology of CF microbes .
The system used glass capillary tubes filled with artificial sputum medium to mimic a clogged airway bronchiole .
Chemical indicators were added to observe microbial physiology within the tubes .
Characterization of sputum samples from seven patients showed variation in pH , respiration , biofilm formation and gas production , indicating that the physiology of CF microbial communities varied among patients .
Incubation of homogenized tissues from an explant CF lung mirrored responses of a Pseudomonas aeruginosa pure culture , supporting evidence that end-stage lungs are dominated by this pathogen .
Longitudinal sputum samples taken through two exacerbation events in a single patient showed that a two-unit drop in pH and a 30 % increase in gas production occurred in the tubes prior to exacerbation , which was reversed with antibiotic treatment .
Microbial community profiles obtained through amplification and sequencing of the 16S rRNA gene showed that fermentative anaerobes became more abundant during exacerbation and were then reduced during treatment where P. aeruginosa became the dominant bacterium .
Results from the WinCF experiments support the model where two functionally different CF microbial communities exist , the persistent Climax Community and the acute Attack Community .
Fermentative anaerobes are hypothesized to be the core members of the Attack Community and production of acidic and gaseous products from fermentation may drive developing exacerbations .
Treatment targeting the Attack Community may better resolve exacerbations and resulting lung damage .
The ISME Journal advance online publication , 16 December 2014 ; doi :10.1038 / ismej .2014.234

[763] Symbiotic relationships between soil fungi and plants reduce N2O emissions from soil

N2O is a potent greenhouse gas involved in the destruction of the protective ozone layer in the stratosphere and contributing to global warming .
The ecological processes regulating its emissions from soil are still poorly understood .
Here , we show that the presence of arbuscular mycorrhizal fungi ( AMF ) , a dominant group of soil fungi , which form symbiotic associations with the majority of land plants and which influence a range of important ecosystem functions , can induce a reduction in N2O emissions from soil .
To test for a functional relationship between AMF and N2O emissions , we manipulated the abundance of AMF in two independent greenhouse experiments using two different approaches ( sterilized and re-inoculated soil and non-mycorrhizal tomato mutants ) and two different soils .
N2O emissions were increased by 42 and 33 % in microcosms with reduced AMF abundance compared to microcosms with a well-established AMF community , suggesting that AMF regulate N2O emissions .
This could partly be explained by increased N immobilization into microbial or plant biomass , reduced concentrations of mineral soil N as a substrate for N2O emission and altered water relations .
Moreover , the abundance of key genes responsible for N2O production ( nirK ) was negatively and for N2O consumption ( nosZ ) positively correlated to AMF abundance , indicating that the regulation of N2O emissions is transmitted by AMF-induced changes in the soil microbial community .
Our results suggest that the disruption of the AMF symbiosis through intensification of agricultural practices may further contribute to increased N2O emissions .

[764] Increased ventilation age of the deep northeast Pacific Ocean during the last deglaciation

The rise in atmospheric carbon dioxide during the last deglaciation may have been driven by the release of carbon from the abyssal ocean .
This mechanism would require a poorly ventilated deep Pacific Ocean during the Last Glacial Maximum and enhanced exchange with the atmosphere during deglaciation .
Here we use radiocarbon measurements of planktonic and benthic foraminiferal shells from a core collected at 2.7 km water depth in the northeast Pacific to estimate the ventilation age of deep waters using the projection age method .
In contrast to the above scenario , we show that ventilation ages during the Last Glacial Maximum were similar to today .
This suggests that this part of the Pacific was not an important reservoir of carbon during glacial times .
During deglaciation , ventilation ages increased by ~ 1,000 years , indicating a decrease in the ventilation rate , an increase in the surface water reservoir age in the Southern Ocean , or an influx of old carbon from another source .
Despite the increased ventilation age during deglaciation , the deep northeast Pacific still had a higher 14C/C ratio than intermediate waters near Baja California .
We therefore conclude that the deep northeast Pacific was apparently not old enough to be the source of deglacial radiocarbon anomalies found shallower in the water column .

[765] Effect of aquaculture on world fish supplies

Global production of farmed fish and shellfish has more than doubled in the past 15 years .
Many people believe that such growth relieves pressure on ocean fisheries , but the opposite is true for some types of aquaculture .
Farming carnivorous species requires large inputs of wild fish for feed .
Some aquaculture systems also reduce wild fish supplies through habitat modification , wild seedstock collection and other ecological impacts .
On balance , global aquaculture production still adds to world fish supplies ; however , if the growing aquaculture industry is to sustain its contribution to world fish supplies , it must reduce wild fish inputs in feed and adopt more ecologically sound management practices .

[766] Holocene winter climate variability in mid-latitude western North America

Water resources in western North America depend on winter precipitation , yet our knowledge of its sensitivity to climate change remains limited .
Similarly , understanding the potential for future loss of winter snow pack requires a longer perspective on natural climate variability .
Here we use stable isotopes from a speleothem in southwestern Oregon to reconstruct winter climate change for much of the past 13,000 years .
We find that on millennial time scales there were abrupt transitions between warm-dry and cold-wet regimes .
Temperature and precipitation changes on multi-decadal to century timescales are consistent with ocean-atmosphere interactions that arise from mechanisms similar to the Pacific Decadal Oscillation .
Extreme cold-wet and warm-dry events that punctuated the Holocene appear to be sensitive to solar forcing , possibly through the influence of the equatorial Pacific on the winter storm tracks reaching the US Pacific Northwest region .

[767] Reconstructed changes in Arctic sea ice over the past 1,450 years

Arctic sea ice extent is now more than two million square kilometres less than it was in the late twentieth century , with important consequences for the climate , the ocean and traditional lifestyles in the Arctic .
Although observations show a more or less continuous decline for the past four or five decades , there are few long-term records with which to assess natural sea ice variability .
Until now , the question of whether or not current trends are potentially anomalous has therefore remained unanswerable .
Here we use a network of high-resolution terrestrial proxies from the circum-Arctic region to reconstruct past extents of summer sea ice , and show that -- although extensive uncertainties remain , especially before the sixteenth century -- both the duration and magnitude of the current decline in sea ice seem to be unprecedented for the past 1,450 years .
Enhanced advection of warm Atlantic water to the Arctic seems to be the main factor driving the decline of sea ice extent on multidecadal timescales , and may result from nonlinear feedbacks between sea ice and the Atlantic meridional overturning circulation .
These results reinforce the assertion that sea ice is an active component of Arctic climate variability and that the recent decrease in summer Arctic sea ice is consistent with anthropogenically forced warming .

[768] A general integrative model for scaling plant growth , carbon flux , and functional trait spectra

Linking functional traits to plant growth is critical for scaling attributes of organisms to the dynamics of ecosystems and for understanding how selection shapes integrated botanical phenotypes .
However , a general mechanistic theory showing how traits specifically influence carbon and biomass flux within and across plants is needed .
Building on foundational work on relative growth rate , recent work on functional trait spectra , and metabolic scaling theory , here we derive a generalized trait-based model of plant growth .
In agreement with a wide variety of empirical data , our model uniquely predicts how key functional traits interact to regulate variation in relative growth rate , the allometric growth normalizations for both angiosperms and gymnosperms , and the quantitative form of several functional trait spectra relationships .
The model also provides a general quantitative framework to incorporate additional leaf-level trait scaling relationships and hence to unite functional trait spectra with theories of relative growth rate , and metabolic scaling .
We apply the model to calculate carbon use efficiency .
This often ignored trait , which may influence variation in relative growth rate , appears to vary directionally across geographic gradients .
Together , our results show how both quantitative plant traits and the geometry of vascular transport networks can be merged into a common scaling theory .
Our model provides a framework for predicting not only how traits covary within an integrated allometric phenotype but also how trait variation mechanistically influences plant growth and carbon flux within and across diverse ecosystems .

[769] Statistically derived contributions of diverse human influences to twentieth-century temperature changes

The warming of the climate system is unequivocal as evidenced by an increase in global temperatures by 0.8 degreesC over the past century .
However , the attribution of the observed warming to human activities remains less clear , particularly because of the apparent slow-down in warming since the late 1990s .
Here we analyse radiative forcing and temperature time series with state-of-the-art statistical methods to address this question without climate model simulations .
We show that long-term trends in total radiative forcing and temperatures have largely been determined by atmospheric greenhouse gas concentrations , and modulated by other radiative factors .
We identify a pronounced increase in the growth rates of both temperatures and radiative forcing around 1960 , which marks the onset of sustained global warming .
Our analyses also reveal a contribution of human interventions to two periods when global warming slowed down .
Our statistical analysis suggests that the reduction in the emissions of ozone-depleting substances under the Montreal Protocol , as well as a reduction in methane emissions , contributed to the lower rate of warming since the 1990s .
Furthermore , we identify a contribution from the two world wars and the Great Depression to the documented cooling in the mid-twentieth century , through lower carbon dioxide emissions .
We conclude that reductions in greenhouse gas emissions are effective in slowing the rate of warming in the short term .

[770] Plant spore walls as a record of long-term changes in ultraviolet-B radiation

Stratospheric ozone screens the Earth 's surface from harmful ultraviolet-B radiation .
Concentrations of stratospheric ozone are governed by a variety of natural and anthropogenic factors , including solar cycles , volcanic aerosols , ozone-depleting substances and climate change .
However , assessing this variability before instrumental records has proved difficult owing to the lack of a well-constrained proxy .
Here , we use microspectroscopy to analyse the chemical composition of herbarium samples of clubmoss ( Lycophyta ) spores originating from high - and low-latitude localities , where they were exposed to different ultraviolet-B histories .
We show that the concentration of two ultraviolet-B-absorbing compounds in the walls of high-northern - and southern-latitude spores is strongly regulated by historical variations in ultraviolet-B radiation .
Conversely , we find little change in the concentration of these compounds in spores originating from tropical Ecuador , where ultraviolet levels have remained relatively stable .
Using spores from Greenland , we reconstruct past ( 1907-1993 ) changes in ozone concentration and ultraviolet-B flux ; we reveal strong similarities between spore-wall reconstructions , and independent instrumental records and model results .
Our findings suggest that ultraviolet-B-absorbing compounds in plant spore walls have the potential to act as a proxy for past changes in terrestrial ultraviolet-B radiation and stratospheric ozone .
The chemical signature of plant spore walls in herbaria , and possibly also in sedimentary and ice-core archives , may therefore prove valuable for reconstructing past variations in stratospheric ozone and their connections with changes in solar radiation and climate .

[771] The acceleration of oceanic denitrification during deglacial warming

Over much of the ocean 's surface , productivity and growth are limited by a scarcity of bioavailable nitrogen .
Sedimentary delta15N records spanning the last deglaciation suggest marked shifts in the nitrogen cycle during this time , but the quantification of these changes has been hindered by the complexity of nitrogen isotope cycling .
Here we present a database of delta15N in sediments throughout the world 's oceans , including 2,329 modern seafloor samples , and 76 timeseries spanning the past 30,000 years .
We show that the delta15N values of modern seafloor sediments are consistent with values predicted by our knowledge of nitrogen cycling in the water column .
Despite many local deglacial changes , the globally averaged delta15N values of sinking organic matter were similar during the Last Glacial Maximum and Early Holocene .
Considering the global isotopic mass balance , we explain these observations with the following deglacial history of nitrogen inventory processes .
During the Last Glacial Maximum , the nitrogen cycle was near steady state .
During the deglaciation , denitrification in the pelagic water column accelerated .
The flooding of continental shelves subsequently increased denitrification at the seafloor , and denitrification reached near steady-state conditions again in the Early Holocene .
We use a recent parameterization of seafloor denitrification to estimate a 30-120 % increase in benthic denitrification between 15,000 and 8,000 years ago .
Based on the similarity of globally averaged delta15N values during the Last Glacial Maximum and Early Holocene , we infer that pelagic denitrification must have increased by a similar amount between the two steady states .

[772] Human-induced nitrogen-phosphorus imbalances alter natural and managed ecosystems across the globe

The availability of carbon from rising atmospheric carbon dioxide levels and of nitrogen from various human-induced inputs to ecosystems is continuously increasing ; however , these increases are not paralleled by a similar increase in phosphorus inputs .
The inexorable change in the stoichiometry of carbon and nitrogen relative to phosphorus has no equivalent in Earth 's history .
Here we report the profound and yet uncertain consequences of the human imprint on the phosphorus cycle and nitrogen : phosphorus stoichiometry for the structure , functioning and diversity of terrestrial and aquatic organisms and ecosystems .
A mass balance approach is used to show that limited phosphorus and nitrogen availability are likely to jointly reduce future carbon storage by natural ecosystems during this century .
Further , if phosphorus fertilizers can not be made increasingly accessible , the crop yields projections of the Millennium Ecosystem Assessment imply an increase of the nutrient deficit in developing regions .

[773] Regional trends in aquatic recovery from acidification in North America and Europe

Rates of acidic deposition from the atmosphere ( ` acid rain ' ) have decreased throughout the 1980s and 1990s across large portions of North America and Europe .
Many recent studies have attributed observed reversals in surface-water acidification at national and regional scales to the declining deposition .
To test whether emissions regulations have led to widespread recovery in surface-water chemistry , we analysed regional trends between 1980 and 1995 in indicators of acidification ( sulphate , nitrate and base-cation concentrations , and measured ( Gran ) alkalinity ) for 205 lakes and streams in eight regions of North America and Europe .
Dramatic differences in trend direction and strength for the two decades are apparent .
In concordance with general temporal trends in acidic deposition , lake and stream sulphate concentrations decreased in all regions with the exception of Great Britain ; all but one of these regions exhibited stronger downward trends in the 1990s than in the 1980s .
In contrast , regional declines in lake and stream nitrate concentrations were rare and , when detected , were very small .
Recovery in alkalinity , expected wherever strong regional declines in sulphate concentrations have occurred , was observed in all regions of Europe , especially in the 1990s , but in only one region ( of five ) in North America .
We attribute the lack of recovery in three regions ( south/central Ontario , the Adirondack/Catskill mountains and midwestern North America ) to strong regional declines in base-cation concentrations that exceed the decreases in sulphate concentrations .

[774] Persistent growth of CO2 emissions and implications for reaching climate targets

Efforts to limit climate change below a given temperature level require that global emissions of CO2 cumulated over time remain below a limited quota .
This quota varies depending on the temperature level , the desired probability of staying below this level and the contributions of other gases .
In spite of this restriction , global emissions of CO2 from fossil fuel combustion and cement production have continued to grow by 2.5 % per year on average over the past decade .
Two thirds of the CO2 emission quota consistent with a 2 degreesC temperature limit has already been used , and the total quota will likely be exhausted in a further 30 years at the 2014 emissions rates .
We show that CO2 emissions track the high end of the latest generation of emissions scenarios , due to lower than anticipated carbon intensity improvements of emerging economies and higher global gross domestic product growth .
In the absence of more stringent mitigation , these trends are set to continue and further reduce the remaining quota until the onset of a potential new climate agreement in 2020 .
Breaking current emission trends in the short term is key to retaining credible climate targets within a rapidly diminishing emission quota .

[775] Insolation-induced mid-Brunhes transition in Southern Ocean ventilation and deep-ocean temperature

Glacial-interglacial cycles characterized by long cold periods interrupted by short periods of warmth are the dominant feature of Pleistocene climate , with the relative intensity and duration of past and future interglacials being of particular interest for civilization .
The interglacials after 430,000 years ago were characterized by warmer climates and higher atmospheric concentrations of carbon dioxide than the interglacials before , but the cause of this climatic transition ( the so-called mid-Brunhes event ( MBE ) ) is unknown .
Here I show , on the basis of model simulations , that in response to insolation changes only , feedbacks between sea ice , temperature , evaporation and salinity caused vigorous pre-MBE Antarctic bottom water formation and Southern Ocean ventilation .
My results also show that strong westerlies increased the pre-MBE overturning in the Southern Ocean via an increased latitudinal insolation gradient created by changes in eccentricity during austral winter and by changes in obliquity during austral summer .
The stronger bottom water formation led to a cooler deep ocean during the older interglacials .
These insolation-induced differences in the deep-sea temperature and in the Southern Ocean ventilation between the more recent interglacials and the older ones were not expected , because there is no straightforward systematic difference in the astronomical parameters between the interglacials before and after 430,000 years ago .
Rather than being a real ` event ' , the apparent MBE seems to have resulted from a series of individual interglacial responses -- including notable exceptions to the general pattern -- to various combinations of insolation conditions .
Consequently , assuming no anthropogenic interference , future interglacials may have pre - or post-MBE characteristics without there being a systematic change in forcings .
These findings are a first step towards understanding the magnitude change of the interglacial carbon dioxide concentration around 430,000 years ago .

[776] Effects of young poplar plantations on understory plant diversity in the Dongting Lake wetlands , China

This study evaluated the effects of young poplar plantations on understory plant diversity in the Dongting Lake wetlands , China .
Poplar plantations resulted in a higher species number and Shannon 's diversity .
Species compositions were different between areas with poplar and reed populations : a lower ratio of hygrophytes but a higher ratio of mesophytes , and a higher ratio of heliophytes but a lower ratio of neutrophilous or shade plants in poplar areas compared to reed areas .
Poplar plantations supported a higher ratio of ligneous plants in the entire Dongting Lake area , but there was no difference in the monitored plots .
Unlike reedy areas , poplar plantations had higher light availability but lower soil water content during the growing seasons .
These data suggest that young poplar plantations generally increased species richness and plant diversity , but significantly changed species composition due to the reduced soil water and increased light availability .

[777] Microbial degradation of isosaccharinic acid at high pH

Intermediate-level radioactive waste ( ILW ) , which dominates the radioactive waste inventory in the United Kingdom on a volumetric basis , is proposed to be disposed of via a multibarrier deep geological disposal facility ( GDF ) .
ILW is a heterogeneous wasteform that contains substantial amounts of cellulosic material encased in concrete .
Upon resaturation of the facility with groundwater , alkali conditions will dominate and will lead to the chemical degradation of cellulose , producing a substantial amount of organic co-contaminants , particularly isosaccharinic acid ( ISA ) .
ISA can form soluble complexes with radionuclides , thereby mobilising them and posing a potential threat to the surrounding environment or ` far field ' .
Alkaliphilic microorganisms sampled from a legacy lime working site , which is an analogue for an ILW-GDF , were able to degrade ISA and couple this degradation to the reduction of electron acceptors that will dominate as the GDF progresses from an aerobic ` open phase ' through nitrate - and Fe ( III ) - reducing conditions post closure .
Furthermore , pyrosequencing analyses showed that bacterial diversity declined as the reduction potential of the electron acceptor decreased and that more specialised organisms dominated under anaerobic conditions .
These results imply that the microbial attenuation of ISA and comparable organic complexants , initially present or formed in situ , may play a role in reducing the mobility of radionuclides from an ILW-GDF , facilitating the reduction of undue pessimism in the long-term performance assessment of such facilities .

[778] Methane emissions from permafrost thaw lakes limited by lake drainage

Thaw lakes in permafrost areas are sources of the strong greenhouse gas methane .
They develop mostly in sedimentary lowlands with permafrost and a high excess ground ice volume , resulting in large areas covered with lakes and drained thaw-lake basins ( DTLBs ; refs , ) .
Their expansion is enhanced by climate warming , which boosts methane emission and contributes a positive feedback to future climate change .
Modelling of thaw-lake growth is necessary to quantify this feedback .
Here , we present a two-dimensional landscape-scale model that includes the entire life cycle of thaw lakes ; initiation , expansion , drainage and eventual re-initiation .
Application of our model to past and future lake expansion in northern Siberia shows that lake drainage strongly limits lake expansion , even under conditions of continuous permafrost .
Our results suggest that methane emissions from thaw lakes in Siberia are an order of magnitude less alarming than previously suggested , although predicted lake expansion will still profoundly affect permafrost ecosystems and infrastructure .

[779] Role of sulphuric acid , ammonia and galactic cosmic rays in atmospheric aerosol nucleation

Atmospheric aerosols exert an important influence on climate through their effects on stratiform cloud albedo and lifetime and the invigoration of convective storms .
Model calculations suggest that almost half of the global cloud condensation nuclei in the atmospheric boundary layer may originate from the nucleation of aerosols from trace condensable vapours , although the sensitivity of the number of cloud condensation nuclei to changes of nucleation rate may be small .
Despite extensive research , fundamental questions remain about the nucleation rate of sulphuric acid particles and the mechanisms responsible , including the roles of galactic cosmic rays and other chemical species such as ammonia .
Here we present the first results from the CLOUD experiment at CERN .
We find that atmospherically relevant ammonia mixing ratios of 100 parts per trillion by volume , or less , increase the nucleation rate of sulphuric acid particles more than 100-1 ,000 - fold .
Time-resolved molecular measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia molecules .
Ions increase the nucleation rate by an additional factor of between two and more than ten at ground-level galactic-cosmic-ray intensities , provided that the nucleation rate lies below the limiting ion-pair production rate .
We find that ion-induced binary nucleation of H2SO4-H2O can occur in the mid-troposphere but is negligible in the boundary layer .
However , even with the large enhancements in rate due to ammonia and ions , atmospheric concentrations of ammonia and sulphuric acid are insufficient to account for observed boundary-layer nucleation .

[780] Strain-specific functional and numerical responses are required to evaluate impacts on predator-prey dynamics

We use strains recently collected from the field to establish cultures ; then , through laboratory studies we investigate how among strain variation in protozoan ingestion and growth rates influences population dynamics and intraspecific competition .
We focused on the impact of changing temperature because of its well-established effects on protozoan rates and its ecological relevance , from daily fluctuations to climate change .
We show , first , that there is considerable inter-strain variability in thermal sensitivity of maximum growth rate , revealing distinct differences among multiple strains of our model species Oxyrrhis marina .
We then intensively examined two representative strains that exhibit distinctly different thermal responses and parameterised the influence of temperature on their functional and numerical responses .
Finally , we assessed how these responses alter predator-prey population dynamics .
We do this first considering a standard approach , which assumes that functional and numerical responses are directly coupled , and then compare these results with a novel framework that incorporates both functional and numerical responses in a fully parameterised model .
We conclude that : ( i ) including functional diversity of protozoa at the sub-species level will alter model predictions and ( ii ) including directly measured , independent functional and numerical responses in a model can provide a more realistic account of predator-prey dynamics .

[781] Long-term nitrogen fertilization of paddy soil shifts iron-reducing microbial community revealed by RNA-13C-acetate probing coupled with pyrosequencing

Iron reduction is an important biogeochemical process in paddy soils , yet little is known about the microbial coupling between nitrogen and iron reduction .
Here , we investigated the shift of acetate-metabolizing iron-reducers under long-term nitrogen fertilization using 13C-acetate-based ribosomal RNA ( rRNA ) - stable isotope probing ( SIP ) and pyrosequencing in an incubation experiment , and the shift of putative iron-reducers in original field samples were investigated by 16S rRNA gene-based pyrosequencing .
During SIP incubations , in the presence of iron ( III ) oxyhydroxides , more iron ( II ) formation and less methane production were detected in nitrogen-fertilized ( N ) compared with non-fertilized ( NF ) soil .
In 13C-rRNA from microcosms amended with ferrihydrite ( FER ) , Geobacter spp .
were the important active iron-reducers in both soils , and labeled to a greater extent in N ( 31 % of the bacterial classified sequences ) than NF soils ( 11 % ) .
Pyrosequencing of the total 16S rRNA transcripts from microcosms at the whole community level further revealed hitherto unknown metabolisms of potential FER reduction by microorganisms including Pseudomonas and Solibacillus spp .
in N soil , Dechloromonas , Clostridium , Bacillus and Solibacillus spp .
in NF soil .
Goethite ( GOE ) amendment stimulated Geobacter spp .
to a lesser extent in both soils compared with FER treatment .
Pseudomonas spp .
in the N soil and Clostridium spp .
in the NF soil may also be involved in GOE reduction .
Pyrosequencing results from field samples showed that Geobacter spp .
were the most abundant putative iron-reducers in both soils , and significantly stimulated by long-term nitrogen fertilization .
Overall , for the first time , we demonstrate that long-term nitrogen fertilization promotes iron ( III ) reduction and modulates iron-reducing bacterial community in paddy soils .

[782] Weakening of the equatorial Atlantic cold tongue over the past six decades

Seasonal and interannual variations of the equatorial cold tongue are defining features of the tropical Atlantic Ocean , with significant climatic and biogeochemical effects .
However , its long-term changes are poorly understood owing to biases in observations and climate models .
Here we use a suite of bias-corrected observations , and find that cold-tongue variability has weakened during the past six decades .
We find that sea surface temperature has increased across the basin , with a local enhancement over the eastern equatorial Atlantic .
This warming pattern of the sea surface is most pronounced during boreal summer , reducing the annual cycle through a positive ocean-atmosphere feedback .
Specifically , the eastward-intensified warming leads to enhanced atmospheric convection in the equatorial eastern Atlantic region , as well as to less vigorous trade winds .
These in turn deepen the thermocline in the east , and reinforce the sea surface warming pattern .
The flattened thermocline and reduced thermocline feedback weaken interannual variability of equatorial sea surface temperatures and Guinea coast precipitation associated with the Atlantic Nino .
We suggest that the observed changes could be associated with cooling by anthropogenic aerosols , an effect that is stronger in the Northern than in the Southern Hemisphere .
If the aerosol emissions decrease in the next decades , the tropical Atlantic may experience yet another shift as the greenhouse gas forcing increases .

[783] Increased frequency of extreme La Nina events under greenhouse warming

The El Nino/Southern Oscillation is Earth 's most prominent source of interannual climate variability , alternating irregularly between El Nino and La Nina , and resulting in global disruption of weather patterns , ecosystems , fisheries and agriculture .
The 1998-1999 extreme La Nina event that followed the 1997-1998 extreme El Nino event switched extreme El Nino-induced severe droughts to devastating floods in western Pacific countries , and vice versa in the southwestern United States .
During extreme La Nina events , cold sea surface conditions develop in the central Pacific , creating an enhanced temperature gradient from the Maritime continent to the central Pacific .
Recent studies have revealed robust changes in El Nino characteristics in response to simulated future greenhouse warming , but how La Nina will change remains unclear .
Here we present climate modelling evidence , from simulations conducted for the Coupled Model Intercomparison Project phase 5 ( ref . )
, for a near doubling in the frequency of future extreme La Nina events , from one in every 23 years to one in every 13 years .
This occurs because projected faster mean warming of the Maritime continent than the central Pacific , enhanced upper ocean vertical temperature gradients , and increased frequency of extreme El Nino events are conducive to development of the extreme La Nina events .
Approximately 75 % of the increase occurs in years following extreme El Nino events , thus projecting more frequent swings between opposite extremes from one year to the next .

[784] Indole cell signaling occurs primarily at low temperatures in Escherichia coli

We have shown that the quorum-sensing signals acylhomoserine lactones , autoinducer-2 ( AI-2 ) and indole influence the biofilm formation of Escherichia coli .
Here , we investigate how the environment , that is , temperature , affects indole and AI-2 signaling in E. coli .
We show in biofilms that indole addition leads to more extensive differential gene expression at 30 degreesC ( 186 genes ) than at 37 degreesC ( 59 genes ) , that indole reduces biofilm formation ( without affecting growth ) more significantly at 25 and 30 degreesC than at 37 degreesC and that the effect is associated with the quorum-sensing protein SdiA .
The addition of indole at 30 degreesC compared to 37 degreesC most significantly repressed genes involved in uridine monophosphate ( UMP ) biosynthesis ( carAB , pyrLBI , pyrC , pyrD , pyrF and upp ) and uracil transport ( uraA ) .
These uracil-related genes are also repressed at 30 degreesC by SdiA , which confirms SdiA is involved in indole signaling .
Also , compared to 37 degreesC , indole more significantly decreased flagella-related qseB , flhD and fliA promoter activity , enhanced antibiotic resistance and inhibited cell division at 30 degreesC .
In contrast to indole and SdiA , the addition of ( S ) -4,5 - dihydroxy-2 ,3 - pentanedione ( the AI-2 precursor ) leads to more extensive differential gene expression at 37 degreesC ( 63 genes ) than at 30 degreesC ( 11 genes ) , and , rather than repressing UMP synthesis genes , AI-2 induces them at 37 degreesC ( but not at 30 degreesC ) .
Also , the addition of AI-2 induces the transcription of virulence genes in enterohemorrhagic E. coli O157 : H7 at 37 degreesC but not at 30 degreesC .
Hence , cell signals cause diverse responses at different temperatures , and indole - and AI-2-based signaling are intertwined .

[785] Supraglacial lakes on the Greenland ice sheet advance inland under warming climate

Supraglacial lakes ( SGLs ) form annually on the Greenland ice sheet and , when they drain , their discharge enhances ice-sheet flow by lubricating the base and potentially by warming the ice .
Today , SGLs tend to form within the ablation zone , where enhanced lubrication is offset by efficient subglacial drainage .
However , it is not clear what impact a warming climate will have on this arrangement .
Here , we use an SGL initiation and growth model to show that lakes form at higher altitudes as temperatures rise , consistent with satellite observations .
Our simulations show that in southwest Greenland , SGLs spread 103 and 110 km further inland by the year 2060 under moderate ( RCP 4.5 ) and extreme ( RCP 8.5 ) climate change scenarios , respectively , leading to an estimated 48-53 % increase in the area over which they are distributed across the ice sheet as a whole .
Up to half of these new lakes may be large enough to drain , potentially delivering water and heat to the ice-sheet base in regions where subglacial drainage is inefficient .
In such places , ice flow responds positively to increases in surface water delivered to the bed through enhanced basal lubrication and warming of the ice , and so the inland advance of SGLs should be considered in projections of ice-sheet change .

[786] Limited carbon storage in soil and litter of experimental forest plots under increased atmospheric CO2

The current rise in atmospheric CO2 concentration is thought to be mitigated in part by carbon sequestration within forest ecosystems , where carbon can be stored in vegetation or soils .
The storage of carbon in soils is determined by the fraction that is sequestered in persistent organic materials , such as humus .
In experimental forest plots of loblolly pine ( Pinus taeda ) exposed to high CO2 concentrations , nearly half of the carbon uptake is allocated to short-lived tissues , largely foliage .
These tissues fall to the ground and decompose , normally contributing only a small portion of their carbon content to refractory soil humic materials .
Such findings call into question the role of soils as long-term carbon sinks , and show the need for a better understanding of carbon cycling in forest soils .
Here we report a significant accumulation of carbon in the litter layer of experimental forest plots after three years of growth at increased CO2 concentrations ( 565 microl l-1 ) .
But fast turnover times of organic carbon in the litter layer ( of about three years ) appear to constrain the potential size of this carbon sink .
Given the observation that carbon accumulation in the deeper mineral soil layers was absent , we suggest that significant , long-term net carbon sequestration in forest soils is unlikely .

[787] Stock dynamics and emission pathways of the global aluminium cycle

Climate change mitigation in the materials sector faces a twin challenge : satisfying rapidly rising global demand for materials while significantly curbing greenhouse-gas emissions .
Process efficiency improvement and recycling can contribute to reducing emissions per material output ; however , long-term material demand and scrap availability for recycling depend fundamentally on the dynamics of societies ' stocks of products in use , an issue that has been largely neglected in climate science .
Here , we show that aluminium in-use stock patterns set essential boundary conditions for future emission pathways , which has significant implications for mitigation priority setting .
If developing countries follow industrialized countries in their aluminium stock patterns , a 50 % emission reduction by 2050 below 2000 levels can not be reached even under very optimistic recycling and technology assumptions .
The target can be reached only if future global per-capita aluminium stocks saturate at a level much lower than that in present major industrialized countries .
As long as global in-use stocks are growing rapidly , radical new technologies in primary production ( for example , inert anode and carbon capture and storage ) have the greatest impact in emission reduction ; however , their window of opportunity is closing once the stocks begin to saturate and the largest reduction potential shifts to post-consumer scrap recycling .

[788] Silver hake tracks changes in Northwest Atlantic circulation

Recent studies documenting shifts in spatial distribution of many organisms in response to a warming climate highlight the need to understand the mechanisms underlying species distribution at large spatial scales .
Here we present one noteworthy example of remote oceanographic processes governing the spatial distribution of adult silver hake , Merluccius bilinearis , a commercially important fish in the Northeast US shelf region .
Changes in spatial distribution of silver hake over the last 40 years are highly correlated with the position of the Gulf Stream .
These changes in distribution are in direct response to local changes in bottom temperature on the continental shelf that are responding to the same large scale circulation change affecting the Gulf Stream path , namely changes in the Atlantic meridional overturning circulation ( AMOC ) .
If the AMOC weakens , as is suggested by global climate models , silver hake distribution will remain in a poleward position , the extent to which could be forecast at both decadal and multidecadal scales .

[789] Suppression of Elongation and Growth of Tomato Seedlings by Auxin Biosynthesis Inhibitors and Modeling of the Growth and Environmental Response

To develop a growth inhibitor , the effects of auxin inhibitors were investigated .
Application of 30 muM L-alpha-aminooxy-beta-phenylpropionic acid ( AOPP ) or ( S ) - methyl 2 - ( ( 1,3-dioxoisoindolin-2-yl ) oxy ) -3 - phenylpropanoate ( KOK1101 ) , decreased the endogenous IAA levels in tomato seedlings at 8 days after sowing .
Then , 10-1200 muM AOPP or KOK1101 were sprayed on the leaves and stem of 2-3 leaf stage tomato plants grown under a range of environmental conditions .
We predicted plant growth and environmental response using a model based on the observed suppression of leaf enlargement .
Spraying AOPP or KOK1101 decreased stem length and leaf area .
Concentration-dependent inhibitions and dose response curves were observed .
Although the effects of the inhibitors on dry weight varied according to the environmental conditions , the net assimilation rate was not influenced by the inhibitors .
Accordingly , the observed decrease in dry weight caused by the inhibitors may result from decreased leaf area .
Validation of the model based on observed data independent of the dataset showed good correlations between the observed and predicted values of dry weight and leaf area index .

[790] Increasing Australian-Indonesian monsoon rainfall linked to early Holocene sea-level rise

The Australian-Indonesian summer monsoon affects rainfall variability and hence terrestrial productivity in the densely populated tropical Indo-Pacific region .
It has been proposed that the main control of summer monsoon precipitation on millennial timescales is local insolation , but unravelling the mechanisms that have influenced monsoon variability and teleconnections has proven difficult , owing to the lack of high-resolution records of past monsoon behaviour .
Here we present a precisely dated reconstruction of monsoon rainfall over the past 12,000 years , based on oxygen isotope measurements from two stalagmites collected in southeast Indonesia .
We show that the summer monsoon precipitation increased during the Younger Dryas cooling event , when Atlantic meridional overturning circulation was relatively weak .
Monsoon precipitation intensified even more rapidly from 11,000 to 7,000 years ago , when the Indonesian continental shelf was flooded by global sea-level rise .
We suggest that the intensification during the Younger Dryas cooling was caused by enhanced winter monsoon outflow from Asia and a related southward migration of the intertropical convergence zone .
However , the early Holocene intensification of monsoon precipitation was driven by sea-level rise , which increased the supply of moisture to the Indonesian archipelago .

[791] Sea surface temperature variability in the southwest tropical Pacific since AD 1649

A prime focus of research is differentiating the contributions of natural climate variability from those that are anthropogenically forced , especially as it relates to climate prediction .
The short length of instrumental records , particularly from the South Pacific , hampers this research , specifically for investigations of decadal to centennial scale variability .
Here we present a sea surface temperature ( SST ) reconstruction derived from highly reproducible records of strontium-to-calcium ratios ( Sr/Ca ) in corals from New Caledonia to investigate natural SST variability in the southwest tropical Pacific from AD 1649-1999 .
Our results reveal periods of warmer and colder temperatures of the order of decades during the Little Ice Age that do not correspond to long-term variations in solar irradiance or the 11-year sunspot cycle .
We suggest that solar variability does not explain decadal to centennial scale SST variability in reconstructions from the southwest tropical Pacific .
Our SST reconstruction covaries with the Southern Hemisphere Pacific decadal oscillation and the South Pacific decadal oscillation , from which SST anomalies in the southwest Pacific are linked to precipitation anomalies in the western tropical Pacific .
We find that decadal scale SST variability has changed in strength and periodicity after 1893 , suggesting a shift in natural variability for this location .

[792] Global flood risk under climate change

A warmer climate would increase the risk of floods .
So far , only a few studies have projected changes in floods on a global scale .
None of these studies relied on multiple climate models .
A few global studies have started to estimate the exposure to flooding ( population in potential inundation areas ) as a proxy of risk , but none of them has estimated it in a warmer future climate .
Here we present global flood risk for the end of this century based on the outputs of 11 climate models .
A state-of-the-art global river routing model with an inundation scheme was employed to compute river discharge and inundation area .
An ensemble of projections under a new high-concentration scenario demonstrates a large increase in flood frequency in Southeast Asia , Peninsular India , eastern Africa and the northern half of the Andes , with small uncertainty in the direction of change .
In certain areas of the world , however , flood frequency is projected to decrease .
Another larger ensemble of projections under four new concentration scenarios reveals that the global exposure to floods would increase depending on the degree of warming , but interannual variability of the exposure may imply the necessity of adaptation before significant warming .

[793] Forcing of the cold event of 8,200 years ago by catastrophic drainage of Laurentide lakes

The sensitivity of oceanic thermohaline circulation to freshwater perturbations is a critical issue for understanding abrupt climate change .
Abrupt climate fluctuations that occurred during both Holocene and Late Pleistocene times have been linked to changes in ocean circulation , but their causes remain uncertain .
One of the largest such events in the Holocene occurred between 8,400 and 8,000 calendar years ago , , ( 7,650-7 ,200 14C years ago ) , when the temperature dropped by 4-8 degreesC in central Greenland and 1.5-3 degreesC at marine , and terrestrial , sites around the northeastern North Atlantic Ocean .
The pattern of cooling implies that heat transfer from the ocean to the atmosphere was reduced in the North Atlantic .
Here we argue that this cooling event was forced by a massive outflow of fresh water from the Hudson Strait .
This conclusion is based on our estimates of the marine 14C reservoir for Hudson Bay which , in combination with other regional data , indicate that the glacial lakes Agassiz and Ojibway , ( originally dammed by a remnant of the Laurentide ice sheet ) drained catastrophically ~ 8,470 calendar years ago ; this would have released > 1014 m3 of fresh water into the Labrador Sea .
This finding supports the hypothesis , , that a sudden increase in freshwater flux from the waning Laurentide ice sheet reduced sea surface salinity and altered ocean circulation , thereby initiating the most abrupt and widespread cold event to have occurred in the past 10,000 years .

[794] Nitrogen and water availability to tomato plants triggers bottom-up effects on the leafminer Tuta absoluta

This study examined the effects of various levels of nitrogen inputs ( optimal , insufficient and excessive ) and water inputs ( optimal , low drought and high drought ) to tomato plants ( Solanum lycopersicum ) on survival and development of an invasive tomato leafminer , Tuta absoluta ( Meytick ) ( Lepidoptera : Gelechiidae ) .
Plant growth i.e. plant height and the number of nodes declined under insufficient or excessive nitrogen treatment .
Compared to optimal N , insufficient N treatment decreased leaf N content and increased the carbon/nitrogen ratio ( C/N ) whereas an excess of N had no effect on both leaf N content and leaf C/N ratio .
Sub-optimal nitrogen supplies , water treatments and their interactions , significantly reduced the leafminer survival rate and slowed down its development .
Together with the findings from three recent companion studies , we assumed that a combination of changes in nutritional value and chemical defense could explain these observed effects .
Furthermore , our findings supported both the `` Plant vigor hypothesis '' and the `` Nitrogen limitation hypothesis '' .

[795] Counterintuitive carbon-to-nutrient coupling in an Arctic pelagic ecosystem

Predicting the ocean 's role in the global carbon cycle requires an understanding of the stoichiometric coupling between carbon and growth-limiting elements in biogeochemical processes .
A recent addition to such knowledge is that the carbon/nitrogen ratio of inorganic consumption and release of dissolved organic matter may increase in a high-CO2 world .
This will , however , yield a negative feedback on atmospheric CO2 only if the extra organic material escapes mineralization within the photic zone .
Here we show , in the context of an Arctic pelagic ecosystem , how the fate and effects of added degradable organic carbon depend critically on the state of the microbial food web .
When bacterial growth rate was limited by mineral nutrients , extra organic carbon accumulated in the system .
When bacteria were limited by organic carbon , however , addition of labile dissolved organic carbon reduced phytoplankton biomass and activity and also the rate at which total organic carbon accumulated , explained as the result of stimulated bacterial competition for mineral nutrients .
This counterintuitive ` more organic carbon gives less organic carbon ' effect was particularly pronounced in diatom-dominated systems where the carbon/mineral nutrient ratio in phytoplankton production was high .
Our results highlight how descriptions of present and future states of the oceanic carbon cycle require detailed understanding of the stoichiometric coupling between carbon and growth-limiting mineral nutrients in both autotrophic and heterotrophic processes .

[796] Tropical forcing of the recent rapid Arctic warming in northeastern Canada and Greenland

Rapid Arctic warming and sea-ice reduction in the Arctic Ocean are widely attributed to anthropogenic climate change .
The Arctic warming exceeds the global average warming because of feedbacks that include sea-ice reduction and other dynamical and radiative feedbacks .
We find that the most prominent annual mean surface and tropospheric warming in the Arctic since 1979 has occurred in northeastern Canada and Greenland .
In this region , much of the year-to-year temperature variability is associated with the leading mode of large-scale circulation variability in the North Atlantic , namely , the North Atlantic Oscillation .
Here we show that the recent warming in this region is strongly associated with a negative trend in the North Atlantic Oscillation , which is a response to anomalous Rossby wave-train activity originating in the tropical Pacific .
Atmospheric model experiments forced by prescribed tropical sea surface temperatures simulate the observed circulation changes and associated tropospheric and surface warming over northeastern Canada and Greenland .
Experiments from the Coupled Model Intercomparison Project Phase 5 ( ref .
16 ) models with prescribed anthropogenic forcing show no similar circulation changes related to the North Atlantic Oscillation or associated tropospheric warming .
This suggests that a substantial portion of recent warming in the northeastern Canada and Greenland sector of the Arctic arises from unforced natural variability .

[797] Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997

The evolution of the Earth 's climate has been extensively studied , and a strong link between increases in surface temperatures and greenhouse gases has been established .
But this relationship is complicated by several feedback processes -- most importantly the hydrological cycle -- that are not well understood .
Changes in the Earth 's greenhouse effect can be detected from variations in the spectrum of outgoing longwave radiation , which is a measure of how the Earth cools to space and carries the imprint of the gases that are responsible for the greenhouse effect .
Here we analyse the difference between the spectra of the outgoing longwave radiation of the Earth as measured by orbiting spacecraft in 1970 and 1997 .
We find differences in the spectra that point to long-term changes in atmospheric CH4 , CO2 and O3 as well as CFC-11 and CFC-12 .
Our results provide direct experimental evidence for a significant increase in the Earth 's greenhouse effect that is consistent with concerns over radiative forcing of climate .

[798] Reduced early life growth and survival in a fish in direct response to increased carbon dioxide

Absorption of anthropogenic carbon dioxide by the world 's oceans is causing mankind 's ` other CO2 problem ' , ocean acidification .
Although this process will challenge marine organisms that synthesize calcareous exoskeletons or shells , it is unclear how it will affect internally calcifying organisms , such as marine fish .
Adult fish tolerate short-term exposures to CO2 levels that exceed those predicted for the next 300 years ( ~ 2,000 ppm ; ref . )
, but potential effects of increased CO2 on growth and survival during the early life stages of fish remain poorly understood .
Here we show that the exposure of early life stages of a common estuarine fish ( Menidia beryllina ) to CO2 concentrations expected in the world 's oceans later this century caused severely reduced survival and growth rates .
When compared with present-day CO2 levels ( ~ 400 ppm ) , exposure of M. beryllina embryos to ~ 1,000 ppm until one week post-hatch reduced average survival and length by 74 % and 18 % , respectively .
The egg stage was significantly more vulnerable to high CO2-induced mortality than the post-hatch larval stage .
These findings challenge the belief that ocean acidification will not affect fish populations , because even small changes in early life survival can generate large fluctuations in adult-fish abundance .

[799] A change in the freshwater balance of the Atlantic Ocean over the past four decades

The oceans are a global reservoir and redistribution agent for several important constituents of the Earth 's climate system , among them heat , fresh water and carbon dioxide .
Whereas these constituents are actively exchanged with the atmosphere , salt is a component that is approximately conserved in the ocean .
The distribution of salinity in the ocean is widely measured , and can therefore be used to diagnose rates of surface freshwater fluxes , freshwater transport and local ocean mixing -- important components of climate dynamics .
Here we present a comparison of salinities on a long transect ( 50degrees S to 60degrees N ) through the western basins of the Atlantic Ocean between the 1950s and the 1990s .
We find systematic freshening at both poleward ends contrasted with large increases of salinity pervading the upper water column at low latitudes .
Our results extend a growing body of evidence indicating that shifts in the oceanic distribution of fresh and saline waters are occurring worldwide in ways that suggest links to global warming and possible changes in the hydrologic cycle of the Earth .

[800] Asymmetry of projected increases in extreme temperature distributions

A statistical analysis reveals projections of consistently larger increases in the highest percentiles of summer and winter temperature maxima and minima versus the respective lowest percentiles , resulting in a wider range of temperature extremes in the future .
These asymmetric changes in tail distributions of temperature appear robust when explored through 14 CMIP5 climate models and three reanalysis datasets .
Asymmetry of projected increases in temperature extremes generalizes widely .
Magnitude of the projected asymmetry depends significantly on region , season , land-ocean contrast , and climate model variability as well as whether the extremes of consideration are seasonal minima or maxima events .
An assessment of potential physical mechanisms provides support for asymmetric tail increases and hence wider temperature extremes ranges , especially for northern winter extremes .
These results offer statistically grounded perspectives on projected changes in the IPCC-recommended extremes indices relevant for impacts and adaptation studies .

[801] Ground water and climate change

As the world 's largest distributed store of fresh water , ground water plays a central part in sustaining ecosystems and enabling human adaptation to climate variability and change .
The strategic importance of ground water for global water and food security will probably intensify under climate change as more frequent and intense climate extremes ( droughts and floods ) increase variability in precipitation , soil moisture and surface water .
Here we critically review recent research assessing the impacts of climate on ground water through natural and human-induced processes as well as through groundwater-driven feedbacks on the climate system .
Furthermore , we examine the possible opportunities and challenges of using and sustaining groundwater resources in climate adaptation strategies , and highlight the lack of groundwater observations , which , at present , limits our understanding of the dynamic relationship between ground water and climate .

[802] A novel grass hybrid to reduce flood generation in temperate regions

We report on the evaluation of a novel grass hybrid that provides efficient forage production and could help mitigate flooding .
Perennial ryegrass ( Lolium perenne ) is the grass species of choice for most farmers , but lacks resilience against extremes of climate .
We hybridised L. perenne onto a closely related and more stress-resistant grass species , meadow fescue Festuca pratensis .
We demonstrate that the L. perenne x F. pratensis cultivar can reduce runoff during the events by 51 % compared to a leading UK nationally recommended L. perenne cultivar and by 43 % compared to F. pratensis over a two year field experiment .
We present evidence that the reduced runoff from this Festulolium cultivar was due to intense initial root growth followed by rapid senescence , especially at depth .
Hybrid grasses of this type show potential for reducing the likelihood of flooding , whilst providing food production under conditions of changing climate .

[803] Modelling the effects of sanitary policies on European vulture conservation

Biodiversity losses are increasing as a consequence of negative anthropogenic effects on ecosystem dynamics .
However , the magnitude and complexity of these effects may still be greatly underestimated .
Most Old World vultures have experienced rapid population declines in recent years .
In Europe , their immediate conservation depends on changes in health regulations affecting the availability of food provided by domestic carcasses .
Information is lacking on the effects of a hypothetical food shortage on the population dynamics of vultures , and is necessary to assess the potential impacts of policy decisions on future changes in biodiversity and ecosystem services .
A novel computational model ( P-systems ) was used to model these effects , forecasting a rapid decline in the Eurasian griffon vulture ( Gyps fulvus ) .
By contrast , vulture species with greater plasticity in their dietary range appeared less sensitive to declining food availability .
This study extends our understanding of vulture ecosystem services , which have social and economic implications .

[804] Enrichment of specific protozoan populations during in situ bioremediation of uranium-contaminated groundwater

The importance of bacteria in the anaerobic bioremediation of groundwater polluted with organic and/or metal contaminants is well recognized and in some instances so well understood that modeling of the in situ metabolic activity of the relevant subsurface microorganisms in response to changes in subsurface geochemistry is feasible .
However , a potentially significant factor influencing bacterial growth and activity in the subsurface that has not been adequately addressed is protozoan predation of the microorganisms responsible for bioremediation .
In field experiments at a uranium-contaminated aquifer located in Rifle , CO , USA , acetate amendments initially promoted the growth of metal-reducing Geobacter species , followed by the growth of sulfate reducers , as observed previously .
Analysis of 18S rRNA gene sequences revealed a broad diversity of sequences closely related to known bacteriovorous protozoa in the groundwater before the addition of acetate .
The bloom of Geobacter species was accompanied by a specific enrichment of sequences most closely related to the ameboid flagellate , Breviata anathema , which at their peak accounted for over 80 % of the sequences recovered .
The abundance of Geobacter species declined following the rapid emergence of B. anathema .
The subsequent growth of sulfate-reducing Peptococcaceae was accompanied by another specific enrichment of protozoa , but with sequences most similar to diplomonadid flagellates from the family Hexamitidae , which accounted for up to 100 % of the sequences recovered during this phase of the bioremediation .
These results suggest a prey-predator response with specific protozoa responding to increased availability of preferred prey bacteria .
Thus , quantifying the influence of protozoan predation on the growth , activity and composition of the subsurface bacterial community is essential for predictive modeling of in situ uranium bioremediation strategies .

[805] Effectiveness of US state policies in reducing CO2 emissions from power plants

President Obama 's landmark initiative to reduce the CO2 emissions of existing power plants , the nation 's largest source of greenhouse gas ( GHG ) pollutants , depends heavily on states and their ability to devise policies that meet the goals set by the Environmental Protection Agency ( EPA ) .
Under the EPA 's proposed Clean Power Plan , states will be responsible for cutting power plants ' carbon pollution 30 % from 2005 levels by 2030 .
States have already adopted several policies to reduce the electricity sector 's climate impact .
Some of these policies focus on reducing power plants ' CO2 emissions , and others address this outcome in a more roundabout fashion by encouraging energy efficiency and renewable energy .
However , it remains unclear which , if any , of these direct and indirect strategies actually mitigate plants ' emissions because scholars have yet to test their effects using plant-level emission data .
Here we use a newly released data source to determine whether states ' policies significantly shape individual power plants ' CO2 emissions .
Findings reveal that certain types of direct strategy ( emission caps and GHG targets ) and indirect ones ( public benefit funds and electric decoupling ) lower plants ' emissions and thus are viable building blocks of a federal climate regime .

[806] Antibiotic-induced shifts in the mouse gut microbiome and metabolome increase susceptibility to Clostridium difficile infection

Antibiotics can have significant and long-lasting effects on the gastrointestinal tract microbiota , reducing colonization resistance against pathogens including Clostridium difficile .
Here we show that antibiotic treatment induces substantial changes in the gut microbial community and in the metabolome of mice susceptible to C. difficile infection .
Levels of secondary bile acids , glucose , free fatty acids and dipeptides decrease , whereas those of primary bile acids and sugar alcohols increase , reflecting the modified metabolic activity of the altered gut microbiome .
In vitro and ex vivo analyses demonstrate that C. difficile can exploit specific metabolites that become more abundant in the mouse gut after antibiotics , including the primary bile acid taurocholate for germination , and carbon sources such as mannitol , fructose , sorbitol , raffinose and stachyose for growth .
Our results indicate that antibiotic-mediated alteration of the gut microbiome converts the global metabolic profile to one that favours C. difficile germination and growth .

[807] Resilience and signatures of tropicalization in protected reef fish communities

Habitat reserves can promote ecological resilience to climate variability by supporting intact trophic webs and large-bodied individuals .
Protection may also alter community responses to long-term climate change by offering habitat for range-shifting species .
Here we analyse the species richness , diversity and functional traits of temperate reef fish communities over 20 years in a global warming hotspot and compare patterns in a marine reserve with nearby sites open to fishing .
Species richness and diversity oscillated strongly on the decadal scale .
Long-term warming signatures were also present as increasing functional trait richness and functional diversity , driven in part by a general increase in herbivores .
Nevertheless , reserve sites were distinguished from fished sites by displaying : greater stability in some aspects of biodiversity ; recovery of large-bodied temperate species ; resistance to colonization by subtropical vagrants ; and less pronounced increases in the community-averaged temperature affinity .
We empirically demonstrate that protection from fishing has buffered fluctuations in biodiversity and provided resistance to the initial stages of tropicalization .

[808] Atlantic Ocean CO2 uptake reduced by weakening of the meridional overturning circulation

Uptake of atmospheric carbon dioxide in the subpolar North Atlantic Ocean declined rapidly between 1990 and 2006 .
This reduction in carbon dioxide uptake was related to warming at the sea surface , which -- according to model simulations -- coincided with a reduction in the Atlantic meridional overturning circulation .
The extent to which the slowdown of this circulation system -- which transports warm surface waters to the northern high latitudes , and cool deep waters south -- contributed to the reduction in carbon uptake has remained uncertain .
Here , we use data on the oceanic transport of volume , heat and carbon dioxide to track carbon dioxide uptake in the subtropical and subpolar regions of the North Atlantic Ocean over the past two decades .
We separate anthropogenic carbon from natural carbon by assuming that the latter corresponds to a pre-industrial atmosphere , whereas the remaining is anthropogenic .
We find that the uptake of anthropogenic carbon dioxide -- released by human activities -- occurred almost exclusively in the subtropical gyre .
In contrast , natural carbon dioxide uptake -- which results from natural Earth system processes -- dominated in the subpolar gyre .
We attribute the weakening of contemporary carbon dioxide uptake in the subpolar North Atlantic to a reduction in the natural component .
We show that the slowdown of the meridional overturning circulation was largely responsible for the reduction in carbon uptake , through a reduction of oceanic heat loss to the atmosphere , and for the concomitant decline in anthropogenic CO2 storage in subpolar waters .

[809] Achieving temperature-size changes in a unicellular organism

The temperature-size rule ( TSR ) is an intraspecific phenomenon describing the phenotypic plastic response of an organism size to the temperature : individuals reared at cooler temperatures mature to be larger adults than those reared at warmer temperatures .
The TSR is ubiquitous , affecting > 80 % species including uni - and multicellular groups .
How the TSR is established has received attention in multicellular organisms , but not in unicells .
Further , conceptual models suggest the mechanism of size change to be different in these two groups .
Here , we test these theories using the protist Cyclidium glaucoma .
We measure cell sizes , along with population growth during temperature acclimation , to determine how and when the temperature-size changes are achieved .
We show that mother and daughter sizes become temporarily decoupled from the ratio 2:1 during acclimation , but these return to their coupled state ( where daughter cells are half the size of the mother cell ) once acclimated .
Thermal acclimation is rapid , being completed within approximately a single generation .
Further , we examine the impact of increased temperatures on carrying capacity and total biomass , to investigate potential adaptive strategies of size change .
We demonstrate no temperature effect on carrying capacity , but maximum supported biomass to decrease with increasing temperature .

[810] Influence of environmental changes on degradation of chiral pollutants in soils

Numerous anthropogenic chemicals of environmental concern -- including some phenoxy acid herbicides , organophosphorus insecticides , polychlorinated biphenyls , phthalates , freon substitutes and some DDT derivatives -- are chiral .
Their potential biological effects , such as toxicity , mutagenicity , carcinogenicity , and endocrine disrupter activity , are generally enantiomer-selective , and different enantiomers are preferentially degraded ( transformed ) by micro-organisms in various environments .
Here we use field and laboratory experiments to demonstrate that environmental changes in soils can alter these preferences , and to suggest that the preferences shift owing to different groups of related microbial genotypes being activated by different environmental changes .
In Brazilian soils , almost all pasture samples preferentially transformed the non-herbicidal enantiomer of dichlorprop ( ( RS ) -2 - ( 2,4-dichlorophenoxy ) propionic acid ) , while most forest samples either transformed the herbicidal enantiomer more readily or as rapidly as the non-herbicidal enantiomer .
Organic nutrient enrichments shifted enantioselectivity for methyl dichlorprop ( ( RS ) - methyl 2 - ( 2,4-dichlorophenoxy ) propionic acid ) strongly towards preferentially removing the non-herbicidal enantiomer in soils from Brazil and North America , potentially increasing phytotoxicity of its residues relative to that of the racemate .
Assessments of the risks chemical pollutants pose to public health and the environment need to take into account the chiral selectivity of microbial transformation processes and their alteration by environmental changes , especially for pesticides as up to 25 per cent are chiral .

[811] Herpes simplex virus enhances chemokine function through modulation of receptor trafficking and oligomerization

Glycoprotein G ( gG ) from herpes simplex virus 1 and 2 ( HSV-1 and HSV-2 , important human neurotropic pathogens ) is the first viral chemokine-binding protein found to potentiate chemokine function .
Here we show that gG attaches to cell surface glycosaminoglycans and induces lipid raft clustering , increasing the incorporation of CXCR4 receptors into these microdomains .
gG induces conformational rearrangements in CXCR4 homodimers and changes their intracellular partners , leading to sustained , functional chemokine/receptor complexes at the surface .
This results in increased chemotaxis dependent on the cholesterol content of the plasma membrane and receptor association to Src-kinases and phosphatidylinositol-3-kinase signalling pathways , but independent of clathrin-mediated endocytosis .
Furthermore , using electron microscopy , we show that such enhanced functionality is associated with the accumulation of low-order CXCR4 nanoclusters .
Our results provide insights into basic mechanisms of chemokine receptor function and into a viral strategy of immune modulation .

[812] Chinese stalagmite delta18O controlled by changes in the Indian monsoon during a simulated Heinrich event

Carbonate cave deposits in India and China are assumed to record the intensity of monsoon precipitation , because the delta18O of the carbonate tracks the isotopic signature of precipitation .
These records show spatially coherent variability throughout the last ice age and suggest that monsoon strength was altered during the millennial-scale climate variations known as Dansgaard-Oeschger events and during the Heinrich cooling events .
Here we use a numerical climate model with an embedded oxygen-isotope model to assess what caused the shifts in the oxygen-isotope signature of precipitation during a climate perturbation designed to mimic a Heinrich event .
Our simulations show that a sudden increase in North Atlantic sea-ice extent during the last glacial period leads to cooling in the Northern Hemisphere , reduced precipitation over the Indian basin and weakening of the Indian monsoon .
The precipitation is isotopically heavier over India and the water vapour exported to China is isotopically enriched .
Our model broadly reproduces the enrichment of delta18O over Northern India and East Asia evident in speleothem records during Heinrich events .
We therefore conclude that changes in the delta18O of cave carbonates associated with Heinrich events reflect changes in the intensity of Indian rather than East Asian monsoon precipitation .

[813] Impact of Arctic meltdown on the microbial cycling of sulphur

The Arctic is warming faster than any other region in the world .
Among the changes already witnessed , the loss of seasonal sea ice is by far the most striking .
This large-scale shift in sea-ice cover could affect oceanic emissions of dimethylsulphide -- a climate-relevant trace gas generated by ice algae and phytoplankton .
During the spring melt period , conditions at the margin of Arctic sea ice favour the growth of these organisms .
As a result , high levels of dimethylsulphide can accumulate at the bottom of the ice , in leads , and in the water column at the ice edge during the spring melt season .
Production of dimethylsulphide is not limited to the sea-ice edge , however .
Significant concentrations have also been detected in the seasonal ice-free zone in spring and summer .
Preliminary observations , together with model results , suggest that the production and emission of dimethylsulphide will increase in the Arctic as seasonal sea-ice cover recedes .
If it escapes to the atmosphere , this newly generated dimethylsulphide could potentially cool the Arctic climate .

[814] Agrochemicals increase trematode infections in a declining amphibian species

Global amphibian declines have often been attributed to disease , but ignorance of the relative importance and mode of action of potential drivers of infection has made it difficult to develop effective remediation .
In a field study , here we show that the widely used herbicide , atrazine , was the best predictor ( out of more than 240 plausible candidates ) of the abundance of larval trematodes ( parasitic flatworms ) in the declining northern leopard frog Rana pipiens .
The effects of atrazine were consistent across trematode taxa .
The combination of atrazine and phosphate -- principal agrochemicals in global corn and sorghum production -- accounted for 74 % of the variation in the abundance of these often debilitating larval trematodes ( atrazine alone accounted for 51 % ) .
Analysis of field data supported a causal mechanism whereby both agrochemicals increase exposure and susceptibility to larval trematodes by augmenting snail intermediate hosts and suppressing amphibian immunity .
A mesocosm experiment demonstrated that , relative to control tanks , atrazine tanks had immunosuppressed tadpoles , had significantly more attached algae and snails , and had tadpoles with elevated trematode loads , further supporting a causal relationship between atrazine and elevated trematode infections in amphibians .
These results raise concerns about the role of atrazine and phosphate in amphibian declines , and illustrate the value of quantifying the relative importance of several possible drivers of disease risk while determining the mechanisms by which they facilitate disease emergence .

[815] How shorter black carbon lifetime alters its climate effect

Black carbon ( BC ) , unlike most aerosol types , absorbs solar radiation .
However , the quantification of its climate impact is uncertain and presently under debate .
Recently , attention has been drawn both to a likely underestimation of global BC emissions in climate models , and an overestimation of BC at high altitudes .
Here we show that doubling present day BC emissions in a model simulation , while reducing BC lifetime based on observational evidence , leaves the direct aerosol effect of BC virtually unchanged .
Increased emissions , together with increased wet removal that reduces the lifetime , yields modelled BC vertical profiles that are in strongly improved agreement with recent aircraft observations .
Furthermore , we explore the consequences of an altered BC profile in a global circulation model , and show that both the vertical profile of BC and rapid climate adjustments need to be taken into account in order to assess the total climate impact of BC .

[816] Nitrogen loss from unpolluted South American forests mainly via dissolved organic compounds

Conceptual and numerical models of nitrogen cycling in temperate forests assume that nitrogen is lost from these ecosystems predominantly by way of inorganic forms , such as nitrate and ammonium ions .
Of these , nitrate is thought to be particularly mobile , being responsible for nitrogen loss to deep soil and stream waters .
But human activities -- such as fossil fuel combustion , fertilizer production and land-use change -- have substantially altered the nitrogen cycle over large regions , making it difficult to separate natural aspects of nitrogen cycling from those induced by human perturbations .
Here we report stream chemistry data from 100 unpolluted primary forests in temperate South America .
Although the sites exhibit a broad range of environmental factors that influence ecosystem nutrient cycles ( such as climate , parent material , time of ecosystem development , topography and biotic diversity ) , we observed a remarkably consistent pattern of nitrogen loss across all forests .
In contrast to findings from forests in polluted regions , streamwater nitrate concentrations are exceedingly low , such that nitrate to ammonium ratios were less than unity , and dissolved organic nitrogen is responsible for the majority of nitrogen losses from these forests .
We therefore suggest that organic nitrogen losses should be considered in models of forest nutrient cycling , which could help to explain observations of nutrient limitation in temperate forest ecosystems .

[817] Phanerozoic concentrations of atmospheric oxygen reconstructed from sedimentary charcoal

Variations of the Earth 's atmospheric oxygen concentration ( pO2 ) are thought to be closely tied to the evolution of life , with strong feedbacks between uni - and multicellular life and oxygen .
On the geologic timescale , pO2 is regulated by the burial of organic carbon and sulphur , as well as by weathering .
Reconstructions of atmospheric O2 for the past 400 million years have therefore been based on geochemical models of carbon and sulphur cycling .
However , these reconstructions vary widely , particularly for the Mesozoic and early Cenozoic eras .
Here we show that the abundance of charcoal in mire settings is controlled by pO2 , and use this proxy to reconstruct the concentration of atmospheric oxygen for the past 400 million years .
We estimate that pO2 was continuously above 26 % during the Carboniferous and Permian periods , and that it declined abruptly around the time of the Permian-Triassic mass extinction .
During the Triassic and Jurassic periods , pO2 fluctuated cyclically , with amplitudes up to 10 % and a frequency of 20-30 million years .
Atmospheric oxygen concentrations have declined steadily from the middle of the Cretaceous period to present-day values of about 21 % .
We conclude , however , that variation in pO2 was not the main driver of the loss of faunal diversity during the Permo-Triassic and Triassic-Jurassic mass extinction events .

[818] Plankton effect on cod recruitment in the North Sea

The Atlantic cod ( Gadus morhua L. ) has been overexploited in the North Sea since the late 1960s and great concern has been expressed about the decline in cod biomass and recruitment .
Here we show that , in addition to the effects of overfishing , fluctuations in plankton have resulted in long-term changes in cod recruitment in the North Sea ( bottom-up control ) .
Survival of larval cod is shown to depend on three key biological parameters of their prey : the mean size of prey , seasonal timing and abundance .
We suggest a mechanism , involving the match/mismatch hypothesis , by which variability in temperature affects larval cod survival and conclude that rising temperature since the mid-1980s has modified the plankton ecosystem in a way that reduces the survival of young cod .

[819] Determinants of stagnating carbon intensity in China

China committed itself to reduce the carbon intensity of its economy ( the amount of CO2 emitted per unit of GDP ) by 40-45 % during 2005-2020 .
Yet , between 2002 and 2009 , China experienced a 3 % increase in carbon intensity , though trends differed greatly among its 30 provinces .
Decomposition analysis shows that sectoral efficiency gains in nearly all provinces were offset by movement towards a more carbon-intensive economic structure .
Such a sectoral shift seemed to be heavily affected by the growing role of investments and capital accumulation in China 's growth process which has favoured sectors with high carbon intensity .
Panel data regressions show that changes in carbon intensity were smallest in sectors dominating the regional economy ( so as not to endanger these large sectors , which are the mainstay of the provincial economy ) , whereas scale and convergence effects played a much smaller role .

[820] In situ dynamics of O2 , pH and cyanobacterial transcripts associated with CCM , photosynthesis and detoxification of ROS

The relative abundance of transcripts encoding proteins involved in inorganic carbon concentrating mechanisms ( CCM ) , detoxification of reactive oxygen species ( ROS ) and photosynthesis in the thermophilic cyanobacterium Synechococcus OS-B ' was measured in hot spring microbial mats over two diel cycles , and was coupled with in situ determinations of incoming irradiance and microenvironmental dynamics of O2 and pH. Fluctuations in pH and O2 in the mats were largely driven by the diel cycle of solar irradiance , with a pH variation from ~ 7.0 to ~ 9.5 , and O2 levels ranging from anoxia to supersaturation during night and day , respectively .
Levels of various transcripts from mat cyanobacteria revealed several patterns that correlated with incident irradiance , O2 and pH within the mat matrix .
Transcript abundances for most genes increased during the morning dark-light transition .
Some transcripts remained at a near constant level throughout the light period , whereas others showed an additional increase in abundance as the mat underwent transition from low-to-high light ( potentially reflecting changes in O2 concentration and pH ) , followed by either a decreased abundance in the early afternoon , or a gradual decline during the early afternoon and into the evening .
One specific transcipt , psbA1 , was the lowest during mid-day under high irradiance and increased when the light levels declined .
We discuss these complex in situ transcriptional patterns with respect to environmental and endogenous cues that might impact and regulate transcription over the diel cycle .

[821] Single yeast cells vary in transcription activity not in delay time after a metabolic shift

Individual cells respond very differently to changes in environmental conditions .
Stochasticity causes cells to respond at different times , magnitudes or both .
Here we disentangle and quantify these two sources of heterogeneity .
We track the adaptation dynamics of single Saccharomyces cerevisiae cells exposed to a nutrient shift from methionine to sulphate and back .
Using single-molecule RNA fluorescence in situ hybridization , we count the number of transcripts of a methionine-biosynthesis enzyme in single cells during adaptation .
The variation of response times between cells is small , yet we find a high transient variability in the messenger RNA copy numbers .
Surprisingly , single cells display strongly delayed transcription induction , as we could induce transcription fourfold quicker by direct activation and bypassing the cellular control circuitry .
Transcription repression occurs rapidly within several minutes .
This study indicates that small variability in response timing combined with high , stochastic transcription activity can cause large cell-to-cell variability in dynamic adaptation responses .

[822] Global insights into water resources , climate change and governance

The threats of climate change and the trade-offs between extractions and flows are examined for the Colorado , the Murray , the Orange and the Yellow Rivers .
In all four basins , and over a long period of time , outflows have greatly reduced as a direct result of increased water extractions .
Although climate change will aggravate hydrological impacts on river systems , currently high levels of water extractions remain the principal contributor to reduced system flows .
Changes in governance , including sharing the variability between the environment and consumers , are urgently required if the health of these rivers is to be maintained .

[823] alpha-ketoglutarate coordinates carbon and nitrogen utilization via enzyme I inhibition

Microbes survive in a variety of nutrient environments by modulating their intracellular metabolism .
Balanced growth requires coordinated uptake of carbon and nitrogen , the primary substrates for biomass production .
Yet the mechanisms that balance carbon and nitrogen uptake are poorly understood .
We find in Escherichia coli that a sudden increase in nitrogen availability results in an almost immediate increase in glucose uptake .
The concentrations of glycolytic intermediates and known regulators , however , remain homeostatic .
Instead , we find that alpha-ketoglutarate , which accumulates in nitrogen limitation , directly blocks glucose uptake by inhibiting enzyme I , the first step of the sugar-phosphoenolpyruvate phosphotransferase system ( PTS ) .
This inhibition enables rapid modulation of glycolytic flux without marked changes in the concentrations of glycolytic intermediates by simultaneously altering import of glucose and consumption of the terminal glycolytic intermediate phosphoenolpyruvate .
Quantitative modeling shows that this previously unidentified regulatory connection is , in principle , sufficient to coordinate carbon and nitrogen utilization .

[824] Widening of the tropical belt in a changing climate

Some of the earliest unequivocal signs of climate change have been the warming of the air and ocean , thawing of land and melting of ice in the Arctic .
But recent studies are showing that the tropics are also changing .
Several lines of evidence show that over the past few decades the tropical belt has expanded .
This expansion has potentially important implications for subtropical societies and may lead to profound changes in the global climate system .
Most importantly , poleward movement of large-scale atmospheric circulation systems , such as jet streams and storm tracks , could result in shifts in precipitation patterns affecting natural ecosystems , agriculture , and water resources .
The implications of the expansion for stratospheric circulation and the distribution of ozone in the atmosphere are as yet poorly understood .
The observed recent rate of expansion is greater than climate model projections of expansion over the twenty-first century , which suggests that there is still much to be learned about this aspect of global climate change .

[825] Effects of double cropping on summer climate of the North China Plain and neighbouring regions

The North China Plain ( NCP ) is one of the most important agricultural regions in Asia and produces up to 50 % of the cereal consumed in China each year .
To meet increasing food demands without expanding croplands , annual agricultural practice in much of the NCP has changed from single to double cropping .
The impact of double cropping on the regional climate , through biophysical feedbacks caused by changes in land surface conditions , remains largely unknown .
Here we show that observed surface air temperatures during the inter-cropping season ( June and July ) are 0.40 degreesC higher over double cropping regions ( DCRs ) than over single cropping regions ( SCRs ) , with increases in the daily maximum temperature as large as 1.02 degreesC .
Using regional climate modelling , we attribute the higher temperatures in DCRs to reduced evapotranspiration during the inter-cropping period .
The higher surface temperatures in June and July affect low-level circulation and , in turn , rainfall associated with the East Asian monsoon over the NCP and neighbouring countries .
These findings suggest that double cropping in the NCP can amplify the magnitude of summertime climate changes over East Asia .

[826] Social controversy belongs in the climate science classroom

Scientists , educators and stakeholders are grappling with how to best approach climate change education for diverse audiences , a task made difficult due to persistent social controversy .
This Perspective examines how sociocultural learning theories can inform the design and implementation of climate change education experiences for learners with varied understandings of and attitudes towards climate change .
The literature demonstrates that explicitly addressing learners ' social and community experiences , values and knowledge supports understandings of and increased concern about climate change .
Science learning environments that situate climate change in its social context can support conceptual understandings , shift attitudes and increase the participation of diverse communities in responding to climate change .
Examples are provided of successful programmes that attend to social dimensions and learners ' previous experiences , including experiences of social controversy .

[827] A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization

Changes in iron supply to oceanic plankton are thought to have a significant effect on concentrations of atmospheric carbon dioxide by altering rates of carbon sequestration , a theory known as the ` iron hypothesis ' .
For this reason , it is important to understand the response of pelagic biota to increased iron supply .
Here we report the results of a mesoscale iron fertilization experiment in the polar Southern Ocean , where the potential to sequester iron-elevated algal carbon is probably greatest .
Increased iron supply led to elevated phytoplankton biomass and rates of photosynthesis in surface waters , causing a large drawdown of carbon dioxide and macronutrients , and elevated dimethyl sulphide levels after 13 days .
This drawdown was mostly due to the proliferation of diatom stocks .
But downward export of biogenic carbon was not increased .
Moreover , satellite observations of this massive bloom 30 days later , suggest that a sufficient proportion of the added iron was retained in surface waters .
Our findings demonstrate that iron supply controls phytoplankton growth and community composition during summer in these polar Southern Ocean waters , but the fate of algal carbon remains unknown and depends on the interplay between the processes controlling export , remineralisation and timescales of water mass subduction .

[828] Endangered plants persist under phosphorus limitation

Nitrogen enrichment is widely thought to be responsible for the loss of plant species from temperate terrestrial ecosystems .
This view is based on field surveys and controlled experiments showing that species richness correlates negatively with high productivity and nitrogen enrichment .
However , as the type of nutrient limitation has never been examined on a large geographical scale the causality of these relationships is uncertain .
We investigated species richness in herbaceous terrestrial ecosystems , sampled along a transect through temperate Eurasia that represented a gradient of declining levels of atmospheric nitrogen deposition -- from ~ 50 kg ha-1 yr-1 in western Europe to natural background values of less than 5 kg ha-1 yr-1 in Siberia .
Here we show that many more endangered plant species persist under phosphorus-limited than under nitrogen-limited conditions , and we conclude that enhanced phosphorus is more likely to be the cause of species loss than nitrogen enrichment .
Our results highlight the need for a better understanding of the mechanisms of phosphorus enrichment , and for a stronger focus on conservation management to reduce phosphorus availability .

[829] Millennial-scale storminess variability in the northeastern United States during the Holocene epoch

For the purpose of detecting the effects of human activities on climate change , it is important to document natural change in past climate .
In this context , it has proved particularly difficult to study the variability in the occurrence of extreme climate events , such as storms with exceptional rainfall .
Previous investigations have established storm chronologies using sediment cores from single lakes , but such studies can be susceptible to local environmental bias .
Here we date terrigenous inwash layers in cores from 13 lakes , which show that the frequency of storm-related floods in the northeastern United States has varied in regular cycles during the past 13,000 years ( 13 kyr ) , with a characteristic period of about 3 kyr .
Our data show four peaks in storminess during the past 14 kyr , approximately 2.6 , 5.8 , 9.1 and 11.9 kyr ago .
This pattern is consistent with long-term changes in the average sign of the Arctic Oscillation , suggesting that modulation of this dominant atmospheric mode may account for a significant fraction of Holocene climate variability in North America and Europe .

[830] The effect of millennial-scale changes in Arabian Sea denitrification on atmospheric CO2

Most global biogeochemical processes are known to respond to climate change , some of which have the capacity to produce feedbacks through the regulation of atmospheric greenhouse gases .
Marine denitrification -- the reduction of nitrate to gaseous nitrogen -- is an important process in this regard , affecting greenhouse gas concentrations directly through the incidental production of nitrous oxide , and indirectly through modification of the marine nitrogen inventory and hence the biological pump for CO2 .
Although denitrification has been shown to vary with glacial-interglacial cycles , its response to more rapid climate change has not yet been well characterized .
Here we present nitrogen isotope ratio , nitrogen content and chlorin abundance data from sediment cores with high accumulation rates on the Oman continental margin that reveal substantial millennial-scale variability in Arabian Sea denitrification and productivity during the last glacial period .
The detailed correspondence of these changes with Dansgaard-Oeschger events recorded in Greenland ice cores indicates rapid , century-scale reorganization of the Arabian Sea ecosystem in response to climate excursions , mediated through the intensity of summer monsoonal upwelling .
Considering the several-thousand-year residence time of fixed nitrogen in the ocean , the response of global marine productivity to changes in denitrification would have occurred at lower frequency and appears to be related to climatic and atmospheric CO2 oscillations observed in Antarctic ice cores between 20 and 60 kyr ago .

[831] Short-term variations in the oxidizing power of the atmosphere

The hydroxyl radical is the predominant atmospheric oxidant , responsible for removing a wide range of trace gases , including greenhouse gases , from the atmosphere .
Determination of trends and variability in hydroxyl radical concentrations is critical to understanding whether the ` cleansing ' properties of the atmosphere are changing .
The variability in hydroxyl radical concentrations on annual to monthly timescales , however , is difficult to quantify .
Here we show records of carbon monoxide containing radiocarbon ( 14CO ) , which is oxidized by hydroxyl radicals , from clean-air sites at Baring Head , New Zealand , and Scott Base , Antarctica , spanning 13 years .
Using a model study , we correct for known variations in production of 14CO ( refs 6 , 7 ) , allowing us to exploit this species as a diagnostic for short term changes in hydroxyl radical concentrations .
We find no significant long-term trend in hydroxyl radical concentrations but provide evidence for recurring short-term variations of around ten per cent persisting for a few months .
We also find decreases in hydroxyl radical concentrations of up to 20 per cent , apparently triggered by the eruption of Mt Pinatubo in 1991 and by the occurrence of extensive fires in Indonesia in 1997 .

[832] Interdependency of tropical marine ecosystems in response to climate change

Ecosystems are linked within landscapes by the physical and biological processes they mediate .
In such connected landscapes , the response of one ecosystem to climate change could have profound consequences for neighbouring systems .
Here , we report the first quantitative predictions of interdependencies between ecosystems in response to climate change .
In shallow tropical marine ecosystems , coral reefs shelter lagoons from incoming waves , allowing seagrass meadows to thrive .
Deepening water over coral reefs from sea-level rise results in larger , more energetic waves traversing the reef into the lagoon , potentially generating hostile conditions for seagrass .
However , growth of coral reef such that the relative water depth is maintained could mitigate negative effects of sea-level rise on seagrass .
Parameterizing physical and biological models for Lizard Island , Great Barrier Reef , Australia , we find negative effects of sea-level rise on seagrass before the middle of this century given reasonable rates of reef growth .
Rates of vertical carbonate accretion typical of modern reef flats ( up to 3 mm yr-1 ) will probably be insufficient to maintain suitable conditions for reef lagoon seagrass under moderate to high greenhouse gas emissions scenarios by 2100 .
Accounting for interdependencies in ecosystem responses to climate change is challenging , but failure to do so results in inaccurate predictions of habitat extent in the future .

[833] Impact of urbanization and land-use change on climate

The most important anthropogenic influences on climate are the emission of greenhouse gases and changes in land use , such as urbanization and agriculture .
But it has been difficult to separate these two influences because both tend to increase the daily mean surface temperature .
The impact of urbanization has been estimated by comparing observations in cities with those in surrounding rural areas , but the results differ significantly depending on whether population data or satellite measurements of night light are used to classify urban and rural areas .
Here we use the difference between trends in observed surface temperatures in the continental United States and the corresponding trends in a reconstruction of surface temperatures determined from a reanalysis of global weather over the past 50 years , which is insensitive to surface observations , to estimate the impact of land-use changes on surface warming .
Our results suggest that half of the observed decrease in diurnal temperature range is due to urban and other land-use changes .
Moreover , our estimate of 0.27 degreesC mean surface warming per century due to land-use changes is at least twice as high as previous estimates based on urbanization alone .

[834] The influence of climate on the tectonic evolution of mountain belts

Simple physical arguments , analogue experiments and numerical experiments all suggest that the internal dynamics of actively deforming collisional mountain ranges are influenced by climate .
However , obtaining definitive field evidence of a significant impact of climate on mountain building has proved challenging .
Spatial correlations between intense precipitation or glaciation and zones of rapid rock-uplift have indeed been documented in numerous mountain ranges , and are consistent with model predictions .
More compelling evidence -- such as tectonic changes in response to ( rather than just coincident with ) climate change -- has , however , rarely been documented .
Triggered by a climate-driven increase in erosion rate , friction-dominated mountain ranges are expected to show a number of simultaneous responses : a decrease in the width of the range , a temporary increase in sediment yield , a persistent increase in the rate of rock uplift and a reduction in the subsidence rate of surrounding basins .
The most convincing field evidence for such a coordinated response of a mountain range to climate change comes from the European Alps and the St Elias range of Alaska .

[835] Eurasian Arctic greening reveals teleconnections and the potential for structurally novel ecosystems

Arctic warming has been linked to observed increases in tundra shrub cover and growth in recent decades on the basis of significant relationships between deciduous shrub growth/biomass and temperature .
These vegetation trends have been linked to Arctic sea-ice decline and thus to the sea-ice/albedo feedback known as Arctic amplification .
However , the interactions between climate , sea ice and tundra vegetation remain poorly understood .
Here we reveal a 50-year growth response over a > 100,000 km2 area to a rise in summer temperature for alder ( Alnus ) and willow ( Salix ) , the most abundant shrub genera respectively at and north of the continental treeline .
We demonstrate that whereas plant productivity is related to sea ice in late spring , the growing season peak responds to persistent synoptic-scale air masses over West Siberia associated with Fennoscandian weather systems through the Rossby wave train .
Substrate is important for biomass accumulation , yet a strong correlation between growth and temperature encompasses all observed soil types .
Vegetation is especially responsive to temperature in early summer .
These results have significant implications for modelling present and future Low Arctic vegetation responses to climate change , and emphasize the potential for structurally novel ecosystems to emerge from within the tundra zone .

[836] Decline of the marine ecosystem caused by a reduction in the Atlantic overturning circulation

Reorganizations of the Atlantic meridional overturning circulation were associated with large and abrupt climatic changes in the North Atlantic region during the last glacial period .
Projections with climate models suggest that similar reorganizations may also occur in response to anthropogenic global warming .
Here I use ensemble simulations with a coupled climate-ecosytem model of intermediate complexity to investigate the possible consequences of such disturbances to the marine ecosystem .
In the simulations , a disruption of the Atlantic meridional overturning circulation leads to a collapse of the North Atlantic plankton stocks to less than half of their initial biomass , owing to rapid shoaling of winter mixed layers and their associated separation from the deep ocean nutrient reservoir .
Globally integrated export production declines by more than 20 per cent owing to reduced upwelling of nutrient-rich deep water and gradual depletion of upper ocean nutrient concentrations .
These model results are consistent with the available high-resolution palaeorecord , and suggest that global ocean productivity is sensitive to changes in the Atlantic meridional overturning circulation .

[837] Widespread adoption of Bt cotton and insecticide decrease promotes biocontrol services

Over the past 16 years , vast plantings of transgenic crops producing insecticidal proteins from the bacterium Bacillus thuringiensis ( Bt ) have helped to control several major insect pests and reduce the need for insecticide sprays .
Because broad-spectrum insecticides kill arthropod natural enemies that provide biological control of pests , the decrease in use of insecticide sprays associated with Bt crops could enhance biocontrol services .
However , this hypothesis has not been tested in terms of long-term landscape-level impacts .
On the basis of data from 1990 to 2010 at 36 sites in six provinces of northern China , we show here a marked increase in abundance of three types of generalist arthropod predators ( ladybirds , lacewings and spiders ) and a decreased abundance of aphid pests associated with widespread adoption of Bt cotton and reduced insecticide sprays in this crop .
We also found evidence that the predators might provide additional biocontrol services spilling over from Bt cotton fields onto neighbouring crops ( maize , peanut and soybean ) .
Our work extends results from general studies evaluating ecological effects of Bt crops by demonstrating that such crops can promote biocontrol services in agricultural landscapes .

[838] Transcriptome response of high - and low-light-adapted Prochlorococcus strains to changing iron availability

Prochlorococcus contributes significantly to ocean primary productivity .
The link between primary productivity and iron in specific ocean regions is well established and iron limitation of Prochlorococcus cell division rates in these regions has been shown .
However , the extent of ecotypic variation in iron metabolism among Prochlorococcus and the molecular basis for differences is not understood .
Here , we examine the growth and transcriptional response of Prochlorococcus strains , MED4 and MIT9313 , to changing iron concentrations .
During steady state , MIT9313 sustains growth at an order-of-magnitude lower iron concentration than MED4 .
To explore this difference , we measured the whole-genome transcriptional response of each strain to abrupt iron starvation and rescue .
Only four of the 1159 orthologs of MED4 and MIT9313 were differentially expressed in response to iron in both strains .
However , in each strain , the expression of over a hundred additional genes changed , many of which are in labile genomic regions , suggesting a role for lateral gene transfer in establishing diversity of iron metabolism among Prochlorococcus .
Furthermore , we found that MED4 lacks three genes near the iron-deficiency-induced gene ( idiA ) that are present and induced by iron stress in MIT9313 .
These genes are interesting targets for studying the adaptation of natural Prochlorococcus assemblages to local iron conditions as they show more diversity than other genomic regions in environmental metagenomic databases .

[839] Recent mass balance of polar ice sheets inferred from patterns of global sea-level change

Global sea level is an indicator of climate change , as it is sensitive to both thermal expansion of the oceans and a reduction of land-based glaciers .
Global sea-level rise has been estimated by correcting observations from tide gauges for glacial isostatic adjustment -- the continuing sea-level response due to melting of Late Pleistocene ice -- and by computing the global mean of these residual trends .
In such analyses , spatial patterns of sea-level rise are assumed to be signals that will average out over geographically distributed tide-gauge data .
But a long history of modelling studies has demonstrated that non-uniform -- that is , non-eustatic -- sea-level redistributions can be produced by variations in the volume of the polar ice sheets .
Here we present numerical predictions of gravitationally consistent patterns of sea-level change following variations in either the Antarctic or Greenland ice sheets or the melting of a suite of small mountain glaciers .
These predictions are characterized by geometrically distinct patterns that reconcile spatial variations in previously published sea-level records .
Under the -- albeit coarse -- assumption of a globally uniform thermal expansion of the oceans , our approach suggests melting of the Greenland ice complex over the last century equivalent to ~ 0.6 mm yr-1 of sea-level rise .

[840] Mysterious abrupt carbon-14 increase in coral contributed by a comet

A large and sudden increase in radiocarbon ( 14C ) around AD 773 are documented in coral skeletons from the South China Sea .
The 14C increased by ~ 15/1000 during winter , and remain elevated for more than 4 months , then increased and dropped down within two months , forming a spike of 45/1000 high in late spring , followed by two smaller spikes .
The 14C anomalies coincide with an historic comet collision with the Earth 's atmosphere on 17 January AD 773 .
Comas are known to have percent-levels of nitrogen by weight , and are exposed to cosmic radiation in space .
Hence they may be expected to contain highly elevated 14C/12C ratios , as compared to the Earth 's atmosphere .
The significant input of 14C by comets may have contributed to the fluctuation of 14C in the atmosphere throughout the Earth 's history , which should be considered carefully to better constrain the cosmic ray fluctuation .

[841] Impacts of biofuel cultivation on mortality and crop yields

Ground-level ozone is a priority air pollutant , causing ~ 22,000 excess deaths per year in Europe , significant reductions in crop yields and loss of biodiversity .
It is produced in the troposphere through photochemical reactions involving oxides of nitrogen ( NOx ) and volatile organic compounds ( VOCs ) .
The biosphere is the main source of VOCs , with an estimated 1,150 TgC yr-1 ( ~ 90 % of total VOC emissions ) released from vegetation globally .
Isoprene ( 2-methyl-1 ,3 - butadiene ) is the most significant biogenic VOC in terms of mass ( around 500 TgC yr-1 ) and chemical reactivity and plays an important role in the mediation of ground-level ozone concentrations .
Concerns about climate change and energy security are driving an aggressive expansion of bioenergy crop production and many of these plant species emit more isoprene than the traditional crops they are replacing .
Here we quantify the increases in isoprene emission rates caused by cultivation of 72 Mha of biofuel crops in Europe .
We then estimate the resultant changes in ground-level ozone concentrations and the impacts on human mortality and crop yields that these could cause .
Our study highlights the need to consider more than simple carbon budgets when considering the cultivation of biofuel feedstock crops for greenhouse-gas mitigation .

[842] Simulated future sea-level rise due to glacier melt based on regionally and seasonally resolved temperature changes

Climate change is expected over the next century as a result of anthropogenic emissions of greenhouse gases and aerosols into the atmosphere , and global average sea level will consequently rise .
Estimates indicate that by 2100 sea level will be about 500 mm higher than today as a result of global warming , with thermal expansion of sea water accounting for over half of this rise .
The melting of glaciers and ice sheets will contribute much of the remainder .
We present an improved calculation of glacier melt , which uses the temperature patterns generated by a coupled atmosphere-ocean general circulation model , as inputs to a seasonally and regionally differentiated glacier model , .
Under specified greenhouse-gas and sulphate-aerosol forcings , our model predicts that glacier melt equivalent to 132 mm of sea-level rise will occur over the period 1990-2100 , with a further 76 mm from melting of the Greenland ice sheet .
These figures fall within the range of previous estimates made using simpler models ; the advantage of our approach is that we take into account the effects of regional and seasonal temperature variations .
Our inclusion of these effects increases the calculated glacier melt by 20 % .

[843] Enhancement of faba bean competitive ability by arbuscular mycorrhizal fungi is highly correlated with dynamic nutrient acquisition by competing wheat

The mechanistic understanding of the dynamic processes linking nutrient acquisition and biomass production of competing individuals can be instructive in optimizing intercropping systems .
Here , we examine the effect of inoculation with Funneliformis mosseae on competitive dynamics between wheat and faba bean .
Wheat is less responsive to mycorrhizal inoculation .
Both inoculated and uninoculated wheat attained the maximum instantaneous N and P capture approximately five days before it attained the maximum instantaneous biomass production , indicating that wheat detected the competitor and responded physiologically to resource limitation prior to the biomass response .
By contrast , the instantaneous N and P capture by uninoculated faba bean remained low throughout the growth period , and plant growth was not significantly affected by competing wheat .
However , inoculation substantially enhanced biomass production and N and P acquisition of faba bean .
The exudation of citrate and malate acids and acid phosphatase activity were greater in mycorrhizal than in uninoculated faba bean , and rhizosphere pH tended to decrease .
We conclude that under N and P limiting conditions , temporal separation of N and P acquisition by competing plant species and enhancement of complementary resource use in the presence of AMF might be attributable to the competitive co-existence of faba bean and wheat .

[844] Phylotype-level 16S rRNA analysis reveals new bacterial indicators of health state in acute murine colitis

Human inflammatory bowel disease and experimental colitis models in mice are associated with shifts in intestinal microbiota composition , but it is unclear at what taxonomic/phylogenetic level such microbiota dynamics can be indicative for health or disease .
Here , we report that dextran sodium sulfate ( DSS ) - induced colitis is accompanied by major shifts in the composition and function of the intestinal microbiota of STAT1 - / - and wild-type mice , as determined by 454 pyrosequencing of bacterial 16S rRNA ( gene ) amplicons , metatranscriptomics and quantitative fluorescence in situ hybridization of selected phylotypes .
The bacterial families Ruminococcaceae , Bacteroidaceae , Enterobacteriaceae , Deferribacteraceae and Verrucomicrobiaceae increased in relative abundance in DSS-treated mice .
Comparative 16S rRNA sequence analysis at maximum possible phylogenetic resolution identified several indicator phylotypes for DSS treatment , including the putative mucin degraders Akkermansia and Mucispirillum .
The analysis additionally revealed strongly contrasting abundance changes among phylotypes of the same family , particularly within the Lachnospiraceae .
These extensive phylotype-level dynamics were hidden when reads were grouped at higher taxonomic levels .
Metatranscriptomic analysis provided insights into functional shifts in the murine intestinal microbiota , with increased transcription of genes associated with regulation and cell signaling , carbohydrate metabolism and respiration and decreased transcription of flagellin genes during inflammation .
These findings ( i ) establish the first in-depth inventory of the mouse gut microbiota and its metatranscriptome in the DSS colitis model , ( ii ) reveal that family-level microbial community analyses are insufficient to reveal important colitis-associated microbiota shifts and ( iii ) support a scenario of shifting intra-family structure and function in the phylotype-rich and phylogenetically diverse Lachnospiraceae in DSS-treated mice .

[845] More extreme swings of the South Pacific convergence zone due to greenhouse warming

The South Pacific convergence zone ( SPCZ ) is the Southern Hemisphere 's most expansive and persistent rain band , extending from the equatorial western Pacific Ocean southeastward towards French Polynesia .
Owing to its strong rainfall gradient , a small displacement in the position of the SPCZ causes drastic changes to hydroclimatic conditions and the frequency of extreme weather events -- such as droughts , floods and tropical cyclones -- experienced by vulnerable island countries in the region .
The SPCZ position varies from its climatological mean location with the El Nino/Southern Oscillation ( ENSO ) , moving a few degrees northward during moderate El Nino events and southward during La Nina events .
During strong El Nino events , however , the SPCZ undergoes an extreme swing -- by up to ten degrees of latitude toward the Equator -- and collapses to a more zonally oriented structure with commensurately severe weather impacts .
Understanding changes in the characteristics of the SPCZ in a changing climate is therefore of broad scientific and socioeconomic interest .
Here we present climate modelling evidence for a near doubling in the occurrences of zonal SPCZ events between the periods 1891-1990 and 1991-2090 in response to greenhouse warming , even in the absence of a consensus on how ENSO will change .
We estimate the increase in zonal SPCZ events from an aggregation of the climate models in the Coupled Model Intercomparison Project phases 3 and 5 ( CMIP3 and CMIP5 ) multi-model database that are able to simulate such events .
The change is caused by a projected enhanced equatorial warming in the Pacific and may lead to more frequent occurrences of extreme events across the Pacific island nations most affected by zonal SPCZ events .

[846] The effect of aggressiveness on the population dynamics of a territorial bird

A central issue in ecology lies in identifying the importance of resources , natural enemies and behaviour in the regulation of animal populations .
Much of the debate on this subject has focused on animals that show cyclic fluctuations in abundance .
However , there is still disagreement about the role of extrinsic ( food , parasites or predators ) and intrinsic ( behaviour ) factors in causing cycles .
Recent studies have examined the impact of natural enemies , although spatial patterns resulting from restricted dispersal or recruitment are increasingly recognized as having the potential to influence unstable population dynamics .
We tested the hypothesis that population cycles in a territorial bird , red grouse Lagopus lagopus scoticus , are caused by delayed density-dependent changes in the aggressiveness and spacing behaviour of males .
Here we show that increasing aggressiveness experimentally for a short period in autumn reduced recruitment and subsequent breeding density by 50 % , and changed population trajectories from increasing to declining .
Intrinsic processes can therefore have fundamental effects on population dynamics .

[847] Variable North Pacific influence on drought in southwestern North America since AD 854

Precipitation in southwestern North America has exhibited significant natural variability over the past few thousand years .
This variability has been attributed to sea surface temperature regimes in the Pacific and Atlantic oceans , and to the attendant shifts in atmospheric circulation patterns .
In particular , decadal variability in the North Pacific has influenced precipitation in this region during the twentieth century , but links to earlier droughts and pluvials are unclear .
Here we assess these links using delta18O data from a speleothem from southern California that spans AD 854-2007 .
We show that variations in the oxygen isotopes of the speleothem correlate to sea surface temperatures in the Kuroshio Extension region of the North Pacific , which affect the atmospheric trajectory and isotopic composition of moisture reaching the study site .
Interpreting our speleothem data as a record of sea surface temperatures in the Kuroshio Extension , we find a strong 22-year periodicity , suggesting a persistent solar influence on North Pacific decadal variability .
A comparison with tree-ring records of precipitation during the past millennium shows that some droughts occurred during periods of warmth in the Kuroshio Extension , similar to the instrumental record .
However , other droughts did not and instead must have been influenced by other factors .
Finally , we find a significant increase in sea surface temperature variability over the past 150 years , which may reflect an influence of greenhouse gas concentrations on variability in the North Pacific .

[848] Climate modelling : Northern Hemisphere circulation

Air pressure at sea level during winter has decreased over the Arctic and increased in the Northern Hemisphere subtropics in recent decades , a change that has been associated with 50 % of the Eurasian winter warming observed over the past 30 years , with 60 % of the rainfall increase in Scotland and with 60 % of the rainfall decrease in Spain .
This trend is inconsistent with the simulated response to greenhouse-gas and sulphate-aerosol changes , but it has been proposed that other climate influences -- such as ozone depletion -- could account for the discrepancy .
Here I compare observed Northern Hemisphere sea-level pressure trends with those simulated in response to all the major human and natural climate influences in nine state-of-the-art coupled climate models over the past 50 years .
I find that these models all underestimate the circulation trend .
This inconsistency suggests that we can not yet simulate changes in this important property of the climate system or accurately predict regional climate changes .

[849] The critical role of extreme heat for maize production in the United States

Statistical studies of rainfed maize yields in the United States and elsewhere have indicated two clear features : a strong negative yield response to accumulation of temperatures above 30 degreesC ( or extreme degree days ( EDD ) ) , and a relatively weak response to seasonal rainfall .
Here we show that the process-based Agricultural Production Systems Simulator ( APSIM ) is able to reproduce both of these relationships in the Midwestern United States and provide insight into underlying mechanisms .
The predominant effects of EDD in APSIM are associated with increased vapour pressure deficit , which contributes to water stress in two ways : by increasing demand for soil water to sustain a given rate of carbon assimilation , and by reducing future supply of soil water by raising transpiration rates .
APSIM computes daily water stress as the ratio of water supply to demand , and during the critical month of July this ratio is three times more responsive to 2 degreesC warming than to a 20 % precipitation reduction .
The results suggest a relatively minor role for direct heat stress on reproductive organs at present temperatures in this region .
Effects of elevated CO2 on transpiration efficiency should reduce yield sensitivity to EDD in the coming decades , but at most by 25 % .

[850] Transcriptomic analysis of a marine bacterial community enriched with dimethylsulfoniopropionate

Dimethylsulfoniopropionate ( DMSP ) is an important source of reduced sulfur and carbon for marine microbial communities , as well as the precursor of the climate-active gas dimethylsulfide ( DMS ) .
In this study , we used metatranscriptomic sequencing to analyze gene expression profiles of a bacterial assemblage from surface waters at the Bermuda Atlantic Time-series Study ( BATS ) station with and without a short-term enrichment of DMSP ( 25 nM for 30 min ) .
An average of 303 143 reads were obtained per treatment using 454 pyrosequencing technology , of which 51 % were potential protein-encoding sequences .
Transcripts from Gammaproteobacteria and Bacteroidetes increased in relative abundance on DMSP addition , yet there was little change in the contribution of two bacterioplankton groups whose cultured members harbor known DMSP degradation genes , Roseobacter and SAR11 .
The DMSP addition led to an enrichment of transcripts supporting heterotrophic activity , and a depletion of those encoding light-related energy generation .
Genes for the degradation of C3 compounds were significantly overrepresented after DMSP addition , likely reflecting the metabolism of the C3 component of DMSP .
Mapping these transcripts to known biochemical pathways indicated that both acetyl-CoA and succinyl-CoA may be common entry points of this moiety into the tricarboxylic acid cycle .
In a short time frame ( 30 min ) in the extremely oligotrophic Sargasso Sea , different gene expression patterns suggest the use of DMSP by a diversity of marine bacterioplankton as both carbon and sulfur sources .

[851] Allometric scaling of production and life-history variation in vascular plants

A prominent feature of comparative life histories is the well documented negative correlation between growth rate and life span .
Patterns of resource allocation during growth and reproduction reflect life-history differences between species .
This is particularly striking in tropical forests , where tree species can differ greatly in their rates of growth and ages of maturity but still attain similar canopy sizes .
Here we provide a theoretical framework for relating life-history variables to rates of production , dM/dt , where M is above-ground mass and t is time .
As metabolic rate limits production as an individual grows , dM/dt ~ M3/4 .
Incorporating interspecific variation in resource allocation to wood density , we derive a universal growth law that quantitatively fits data for a large sample of tropical tree species with diverse life histories .
Combined with evolutionary life-history theory , the growth law also predicts several qualitative features of tree demography and reproduction .
This framework also provides a general quantitative answer to why relative growth rate ( 1/M ) ( dM/df ) decreases with increasing plant size ( ~ M-1 / 4 ) and how it varies with differing allocation strategies .

[852] The genome sequence of the psychrophilic archaeon , Methanococcoides burtonii : the role of genome evolution in cold adaptation

Psychrophilic archaea are abundant and perform critical roles throughout the Earth 's expansive cold biosphere .
Here we report the first complete genome sequence for a psychrophilic methanogenic archaeon , Methanococcoides burtonii .
The genome sequence was manually annotated including the use of a five-tiered evidence rating ( ER ) system that ranked annotations from ER1 ( gene product experimentally characterized from the parent organism ) to ER5 ( hypothetical gene product ) to provide a rapid means of assessing the certainty of gene function predictions .
The genome is characterized by a higher level of aberrant sequence composition ( 51 % ) than any other archaeon .
In comparison to hyper/thermophilic archaea , which are subject to selection of synonymous codon usage , M. burtonii has evolved cold adaptation through a genomic capacity to accommodate highly skewed amino-acid content , while retaining codon usage in common with its mesophilic Methanosarcina cousins .
Polysaccharide biosynthesis genes comprise at least 3.3 % of protein coding genes in the genome , and Cell wall , membrane , envelope biogenesis COG genes are overrepresented .
Likewise , signal transduction ( COG category T ) genes are overrepresented and M. burtonii has a high ` IQ ' ( a measure of adaptive potential ) compared to many methanogens .
Numerous genes in these two overrepresented COG categories appear to have been acquired from epsilon - and delta-Proteobacteria , as do specific genes involved in central metabolism such as a novel B form of aconitase .
Transposases also distinguish M. burtonii from other archaea , and their genomic characteristics indicate they have an important role in evolving the M. burtonii genome .
Our study reveals a capacity for this model psychrophile to evolve through genome plasticity ( including nucleotide skew , horizontal gene transfer and transposase activity ) that enables adaptation to the cold , and to the biological and physical changes that have occurred over the last several thousand years as it adapted from a marine to an Antarctic lake environment .

[853] Efficient export of carbon to the deep ocean through dissolved organic matter

Oceanic dissolved organic carbon ( DOC ) constitutes one of the largest pools of reduced carbon in the biosphere .
Estimated DOC export from the surface ocean represents 20 % of total organic carbon flux to the deep ocean , which constitutes a primary control on atmospheric carbon dioxide levels .
DOC is the carbon component of dissolved organic matter ( DOM ) and an accurate quantification of DOM pools , fluxes and their controls is therefore critical to understanding oceanic carbon cycling .
DOC export is directly coupled with dissolved organic nitrogen and phosphorus export .
However , the C : N :P stoichiometry ( by atoms ) of DOM dynamics is poorly understood .
Here we study the stoichiometry of the DOM pool and of DOM decomposition in continental shelf , continental slope and central ocean gyre environments .
We find that DOM is remineralized and produced with a C : N :P stoichiometry of 199:20:1 that is substantially lower than for bulk pools ( typically > 775:54:1 ) , but greater than for particulate organic matter ( 106:16:1 -- the Redfield ratio ) .
Thus for a given mass of new N and P introduced into surface water , more DOC can be exported than would occur at the Redfield ratio .
This may contribute to the excess respiration estimated to occur in the interior ocean .
Our results place an explicit constraint on global carbon export and elemental balance via advective pathways .

[854] Fluvial response to abrupt global warming at the Palaeocene/Eocene boundary

Climate strongly affects the production of sediment from mountain catchments as well as its transport and deposition within adjacent sedimentary basins .
However , identifying climatic influences on basin stratigraphy is complicated by nonlinearities , feedback loops , lag times , buffering and convergence among processes within the sediment routeing system .
The Palaeocene/Eocene thermal maximum ( PETM ) arguably represents the most abrupt and dramatic instance of global warming in the Cenozoic era and has been proposed to be a geologic analogue for anthropogenic climate change .
Here we evaluate the fluvial response in western Colorado to the PETM .
Concomitant with the carbon isotope excursion marking the PETM we document a basin-wide shift to thick , multistoried , sheets of sandstone characterized by variable channel dimensions , dominance of upper flow regime sedimentary structures , and prevalent crevasse splay deposits .
This progradation of coarse-grained lithofacies matches model predictions for rapid increases in sediment flux and discharge , instigated by regional vegetation overturn and enhanced monsoon precipitation .
Yet the change in fluvial deposition persisted long after the approximately 200,000-year-long PETM with its increased carbon dioxide levels in the atmosphere , emphasizing the strong role the protracted transmission of catchment responses to distant depositional systems has in constructing large-scale basin stratigraphy .
Our results , combined with evidence for increased dissolved loads and terrestrial clay export to world oceans , indicate that the transient hyper-greenhouse climate of the PETM may represent a major geomorphic ` system-clearing event ' , involving a global mobilization of dissolved and solid sediment loads on Earth 's surface .

[855] Biomass enables the transition to a carbon-negative power system across western North America

Sustainable biomass can play a transformative role in the transition to a decarbonized economy , with potential applications in electricity , heat , chemicals and transportation fuels .
Deploying bioenergy with carbon capture and sequestration ( BECCS ) results in a net reduction in atmospheric carbon .
BECCS may be one of the few cost-effective carbon-negative opportunities available should anthropogenic climate change be worse than anticipated or emissions reductions in other sectors prove particularly difficult .
Previous work , primarily using integrated assessment models , has identified the critical role of BECCS in long-term ( pre - or post-2100 time frames ) climate change mitigation , but has not investigated the role of BECCS in power systems in detail , or in aggressive time frames , even though commercial-scale facilities are starting to be deployed in the transportation sector .
Here , we explore the economic and deployment implications for BECCS in the electricity system of western North America under aggressive ( pre-2050 ) time frames and carbon emissions limitations , with rich technology representation and physical constraints .
We show that BECCS , combined with aggressive renewable deployment and fossil-fuel emission reductions , can enable a carbon-negative power system in western North America by 2050 with up to 145 % emissions reduction from 1990 levels .
In most scenarios , the offsets produced by BECCS are found to be more valuable to the power system than the electricity it provides .
Advanced biomass power generation employs similar system design to advanced coal technology , enabling a transition strategy to low-carbon energy .

[856] Regional carbon dioxide implications of forest bioenergy production

Strategies for reducing carbon dioxide emissions include substitution of fossil fuel with bioenergy from forests , where carbon emitted is expected to be recaptured in the growth of new biomass to achieve zero net emissions , and forest thinning to reduce wildfire emissions .
Here , we use forest inventory data to show that fire prevention measures and large-scale bioenergy harvest in US West Coast forests lead to 2-14 % ( 46-405 Tg C ) higher emissions compared with current management practices over the next 20 years .
We studied 80 forest types in 19 ecoregions , and found that the current carbon sink in 16 of these ecoregions is sufficiently strong that it can not be matched or exceeded through substitution of fossil fuels by forest bioenergy .
If the sink in these ecoregions weakens below its current level by 30-60 g C m-2 yr-1 owing to insect infestations , increased fire emissions or reduced primary production , management schemes including bioenergy production may succeed in jointly reducing fire risk and carbon emissions .
In the remaining three ecoregions , immediate implementation of fire prevention and biofuel policies may yield net emission savings .
Hence , forest policy should consider current forest carbon balance , local forest conditions and ecosystem sustainability in establishing how to decrease emissions .

[857] Cyclic precipitation variation on the western Loess Plateau of China during the past four centuries

Precipitation variation on the Loess Plateau ( LP ) of China is not only important for rain-fed agriculture in this environmentally sensitive region , but also critical for the water and life securities over the whole Yellow River basin .
Here we reconstruct high resolution precipitation variation on the western LP during the past 370 years by using two replicated , annually-laminated stalagmites .
Spatial analysis suggests that the reconstruction can be also representative for the whole LP region .
The precipitation variations show a significant quasi-50 year periodicity during the last 370 years , and have an important role in determining the runoff of the middle Yellow River .
The main factor controlling the decadal scale variations and long-term trend in precipitation over this region is southerly water vapour transport associated with the Asian summer monsoon .
The Pacific Decadal Oscillation is also an important influence on precipitation variation in this region , as it can affect the East Asian summer monsoon and the West Pacific Subtropical High .

[858] Bacteriophage predation regulates microbial abundance and diversity in a full-scale bioreactor treating industrial wastewater

Changes in the microbial community composition of a full-scale membrane bioreactor treating industrial wastewater were studied over a period of 462 days using a series of 16S rRNA gene clone libraries .
Frequent changes in the relative abundance of specific taxonomic groups were observed , which could not be explained by changes in the reactor 's conditions or wastewater composition .
Phage activity was proposed to drive some of the observed changes .
Bacterial hosts were isolated from a biomass sample obtained towards the end of the study period , and specific phage counts were carried out for some of the isolated hosts using stored frozen biomass samples as the phage inocula .
Plaque-forming unit concentrations were shown to change frequently over the study period , in correlation with changes in the relative abundance of taxonomic groups closely related by 16S rRNA gene sequence to the isolated strains .
Quantitative PCR was used to verify changes in the abundance of a taxonomic group closely related to one of the isolated hosts , showing good agreement with the changes in relative abundance in the clone libraries of that group .
The emerging pattern was consistent with the ` killing the winner ' hypothesis , although alternative interaction mechanisms could not be ruled out .
This is the first time that phage-host interactions in a complex microbial community are demonstrated over an extended period , and possibly the first in situ demonstration of ` killing the winner ' stochastic behavior .

[859] reply Climate variability and crop yields in Europe

Hulme et al. reply -- point out the importance of changes in climate variability on different timescales when assessing the significance of climate-change impacts .
They are correct to assert that changes in inter-daily , inter-annual and multi-decadal climate variability are important , but our study was intended to draw attention to natural multi-decadal climate variability and to indicate how it might obscure the identification of significant effects of anthropogenic climate change .
It was therefore primarily a study of signal-to-noise ratios in impacts indicators , something that has not previously been attempted using low-frequency climate variability .
The effects on crop yields of changes in inter-annual and inter-daily climate variability have been considered previously .

[860] Rapid early Holocene deglaciation of the Laurentide ice sheet

The demise of the Laurentide ice sheet during the early Holocene epoch is the most recent and best constrained disappearance of a large ice sheet in the Northern Hemisphere , and thus allows an assessment of rates of ice-sheet decay as well as attendant contributions to sea level rise .
Here , we use terrestrial and marine records of the deglaciation to identify two periods of rapid melting during the final demise of the Laurentide ice sheet , when melting ice contributed about 1.3 and 0.7 cm of sea level rise per year , respectively .
Our simulations with a fully coupled ocean-atmosphere model suggest that increased ablation due to enhanced early Holocene boreal summer insolation was the predominant cause of Laurentide ice-sheet retreat .
Although the surface radiative forcing in boreal summer during the early Holocene is twice as large as the greenhouse-gas forcing expected by the year 2100 , the associated increase in summer surface air temperatures is very similar .
We conclude that our geologic evidence for a rapid retreat of the Laurentide ice sheet may therefore describe a prehistoric precedent for mass balance changes of the Greenland ice sheet over the coming century .

[861] North American ice-sheet dynamics and the onset of 100,000-year glacial cycles

The onset of major glaciations in the Northern Hemisphere about 2.7 million years ago was most probably induced by climate cooling during the late Pliocene epoch .
These glaciations , during which the Northern Hemisphere ice sheets successively expanded and retreated , are superimposed on this long-term climate trend , and have been linked to variations in the Earth 's orbital parameters .
One intriguing problem associated with orbitally driven glacial cycles is the transition from 41,000-year to 100,000-year climatic cycles that occurred without an apparent change in insolation forcing .
Several hypotheses have been proposed to explain the transition , both including and excluding ice-sheet dynamics .
Difficulties in finding a conclusive answer to this palaeoclimatic problem are related to the lack of sufficiently long records of ice-sheet volume or sea level .
Here we use a comprehensive ice-sheet model and a simple ocean-temperature model to extract three-million-year mutually consistent records of surface air temperature , ice volume and sea level from marine benthic oxygen isotopes .
Although these records and their relative phasings are subject to considerable uncertainty owing to limited availability of palaeoclimate constraints , the results suggest that the gradual emergence of the 100,000-year cycles can be attributed to the increased ability of the merged North American ice sheets to survive insolation maxima and reach continental-scale size .
The oversized , wet-based ice sheet probably responded to the subsequent insolation maximum by rapid thinning through increased basal-sliding , thereby initiating a glacial termination .
Based on our assessment of the temporal changes in air temperature and ice volume during individual glacials , we demonstrate the importance of ice dynamics and ice-climate interactions in establishing the 100,000-year glacial cycles , with enhanced North American ice-sheet growth and the subsequent merging of the ice sheets being key elements .

[862] Producing more grain with lower environmental costs

Agriculture faces great challenges to ensure global food security by increasing yields while reducing environmental costs .
Here we address this challenge by conducting a total of 153 site-year field experiments covering the main agro-ecological areas for rice , wheat and maize production in China .
A set of integrated soil-crop system management practices based on a modern understanding of crop ecophysiology and soil biogeochemistry increases average yields for rice , wheat and maize from 7.2 million grams per hectare ( Mg ha-1 ) , 7.2 Mg ha-1 and 10.5 Mg ha-1 to 8.5 Mg ha-1 , 8.9 Mg ha-1 and 14.2 Mg ha-1 , respectively , without any increase in nitrogen fertilizer .
Model simulation and life-cycle assessment show that reactive nitrogen losses and greenhouse gas emissions are reduced substantially by integrated soil-crop system management .
If farmers in China could achieve average grain yields equivalent to 80 % of this treatment by 2030 , over the same planting area as in 2012 , total production of rice , wheat and maize in China would be more than enough to meet the demand for direct human consumption and a substantially increased demand for animal feed , while decreasing the environmental costs of intensive agriculture .

[863] Millennial and orbital variations of El Nino/Southern Oscillation and high-latitude climate in the last glacial period

The El Nino/Southern Oscillation ( ENSO ) phenomenon is believed to have operated continuously over the last glacial-interglacial cycle .
ENSO variability has been suggested to be linked to millennial-scale oscillations in North Atlantic climate during that time , but the proposals disagree on whether increased frequency of El Nino events , the warm phase of ENSO , was linked to North Atlantic warm or cold periods .
Here we present a high-resolution record of surface moisture , based on the degree of peat humification and the ratio of sedges to grass , from northern Queensland , Australia , covering the past 45,000 yr .
We observe millennial-scale dry periods , indicating periods of frequent El Nino events ( summer precipitation declines in El Nino years in northeastern Australia ) .
We find that these dry periods are correlated to the Dansgaard-Oeschger events -- millennial-scale warm events in the North Atlantic climate record -- although no direct atmospheric connection from the North Atlantic to our site can be invoked .
Additionally , we find climatic cycles at a semiprecessional timescale ( ~ 11,900 yr ) .
We suggest that climate variations in the tropical Pacific Ocean on millennial as well as orbital timescales , which determined precipitation in northeastern Australia , also exerted an influence on North Atlantic climate through atmospheric and oceanic teleconnections .

[864] Microbial biodiversity in glacier-fed streams

While glaciers become increasingly recognised as a habitat for diverse and active microbial communities , effects of their climate change-induced retreat on the microbial ecology of glacier-fed streams remain elusive .
Understanding the effect of climate change on microorganisms in these ecosystems is crucial given that microbial biofilms control numerous stream ecosystem processes with potential implications for downstream biodiversity and biogeochemistry .
Here , using a space-for-time substitution approach across 26 Alpine glaciers , we show how microbial community composition and diversity , based on 454-pyrosequencing of the 16S rRNA gene , in biofilms of glacier-fed streams may change as glaciers recede .
Variations in streamwater geochemistry correlated with biofilm community composition , even at the phylum level .
The most dominant phyla detected in glacial habitats were Proteobacteria , Bacteroidetes , Actinobacteria and Cyanobacteria/chloroplasts .
Microorganisms from ice had the lowest alpha diversity and contributed marginally to biofilm and streamwater community composition .
Rather , streamwater apparently collected microorganisms from various glacial and non-glacial sources forming the upstream metacommunity , thereby achieving the highest alpha diversity .
Biofilms in the glacier-fed streams had intermediate alpha diversity and species sorting by local environmental conditions likely shaped their community composition .
alpha diversity of streamwater and biofilm communities decreased with elevation , possibly reflecting less diverse sources of microorganisms upstream in the catchment .
In contrast , beta diversity of biofilms decreased with increasing streamwater temperature , suggesting that glacier retreat may contribute to the homogenisation of microbial communities among glacier-fed streams .

[865] Reduced survival of Antarctic benthos linked to climate-induced iceberg scouring

The West Antarctic Peninsula ( WAP ) is a hotspot of recent rapid regional warming and ice loss .
The WAP sea surface freezes each winter to form a ` fast-ice ' skin that can reduce iceberg drift and collisions between their keels and the sea bed , in what is termed scouring .
Scouring disturbance is thus inversely correlated with fast-ice duration .
We examined long-term records of fast ice , ice scour and mortality of benthos around Rothera research station ( WAP ) to determine whether there is a biological response from the sea bed coincident with fast-ice changes .
Here we show that the duration of fast ice at Rothera has significantly decreased by > 5 d yr-1 over 25 years and that this is strongly correlated with increased ice scour and mortality of benthos in the shallows .
The number of experimental markers at Rothera crushed by iceberg scouring increased over the past decade .
We found that survival of one of the most common shallow species , the bryozoan Fenestrulina rugula , is linked to ice-scour frequency and has markedly decreased over the past 12 years .
The chance of colonies reaching two years old , the age at which they typically begin to sexually reproduce , has halved since 1997 .
These findings suggest that increased scouring of the sea bed has led to higher benthic mortality , with implications for the region 's biodiversity .

[866] Biodiversity under threat in glacier-fed river systems

Freshwater biodiversity is under threat across the globe , with climate change being a significant contributor .
One impact of climate change is the rapid shrinking of glaciers , resulting in a reduction in glacial meltwater contribution to river flow in many glacierized catchments .
These changes potentially affect the biodiversity of specialized glacier-fed river communities .
Perhaps surprisingly then , although freshwater biodiversity is a major conservation priority , the effects of shrinkage and disappearance of glaciers on river biodiversity have hitherto been poorly quantified .
Here we focus on macroinvertebrates ( mainly insect larvae ) and demonstrate that local ( alpha ) and regional ( gamma ) diversity , as well as turnover among reaches ( beta-diversity ) , will be consistently reduced by the shrinkage of glaciers .
We show that 11-38 % of the regional species pools , including endemics , can be expected to be lost following complete disappearance of glaciers in a catchment , and steady shrinkage is likely to reduce taxon turnover in proglacial river systems and local richness at downstream reaches where glacial cover in the catchment is less than 5-30 % .
Our analysis demonstrates not only the vulnerability of local biodiversity hotspots but also that extinction will probably greatly exceed the few known endemic species in glacier-fed rivers .

[867] Size and frequency of natural forest disturbances and the Amazon forest carbon balance

Forest inventory studies in the Amazon indicate a large terrestrial carbon sink .
However , field plots may fail to represent forest mortality processes at landscape-scales of tropical forests .
Here we characterize the frequency distribution of disturbance events in natural forests from 0.01 ha to 2,651 ha size throughout Amazonia using a novel combination of forest inventory , airborne lidar and satellite remote sensing data .
We find that small-scale mortality events are responsible for aboveground biomass losses of ~ 1.7 Pg C y-1 over the entire Amazon region .
We also find that intermediate-scale disturbances account for losses of ~ 0.2 Pg C y-1 , and that the largest-scale disturbances as a result of blow-downs only account for losses of ~ 0.004 Pg C y-1 .
Simulation of growth and mortality indicates that even when all carbon losses from intermediate and large-scale disturbances are considered , these are outweighed by the net biomass accumulation by tree growth , supporting the inference of an Amazon carbon sink .

[868] Early Palaeogene temperature evolution of the southwest Pacific Ocean

Relative to the present day , meridional temperature gradients in the Early Eocene age ( ~ 56-53 Myr ago ) were unusually low , with slightly warmer equatorial regions but with much warmer subtropical Arctic and mid-latitude climates .
By the end of the Eocene epoch ( ~ 34 Myr ago ) , the first major Antarctic ice sheets had appeared , suggesting that major cooling had taken place .
Yet the global transition into this icehouse climate remains poorly constrained , as only a few temperature records are available portraying the Cenozoic climatic evolution of the high southern latitudes .
Here we present a uniquely continuous and chronostratigraphically well-calibrated TEX86 record of sea surface temperature ( SST ) from an ocean sediment core in the East Tasman Plateau ( palaeolatitude ~ 65degrees S ) .
We show that southwest Pacific SSTs rose above present-day tropical values ( to ~ 34 degreesC ) during the Early Eocene age ( ~ 53 Myr ago ) and had gradually decreased to about 21 degreesC by the early Late Eocene age ( ~ 36 Myr ago ) .
Our results imply that there was almost no latitudinal SST gradient between subequatorial and subpolar regions during the Early Eocene age ( 55-50 Myr ago ) .
Thereafter , the latitudinal gradient markedly increased .
In theory , if Eocene cooling was largely driven by a decrease in atmospheric greenhouse gas concentration , additional processes are required to explain the relative stability of tropical SSTs given that there was more significant cooling at higher latitudes .

[869] Chance and necessity : the evolution of morphological complexity and diversity

The primary foundation for contemplating the possible forms of life elsewhere in the Universe is the evolutionary trends that have marked life on Earth .
For its first three billion years , life on Earth was a world of microscopic forms , rarely achieving a size greater than a millimetre or a complexity beyond two or three cell types .
But in the past 600 million years , the evolution of much larger and more complex organisms has transformed the biosphere .
Despite their disparate forms and physiologies , the evolution and diversification of plants , animals , fungi and other macroforms has followed similar global trends .
One of the most important features underlying evolutionary increases in animal and plant size , complexity and diversity has been their modular construction from reiterated parts .
Although simple filamentous and spherical forms may evolve wherever cellular life exists , the evolution of motile , modular mega-organisms might not be a universal pattern .
`` Drawn out of the realm of pure chance , the accident enters into that of necessity , of the most implacable certainties . ''
J. Monod

[870] A model for orbital pacing of methane hydrate destabilization during the Palaeogene

A series of transient global warming events occurred during the late Palaeocene and early Eocene , about 59 to 50 million years ago .
The events , although variable in magnitude , were apparently paced by orbital cycles and linked to massive perturbations of the global carbon cycle .
However , a causal link between orbital changes in insolation and the carbon cycle has yet to be established for this time period .
Here we present a series of coupled climate model simulations that demonstrate that orbitally induced changes in ocean circulation and intermediate water temperature can trigger the destabilization of methane hydrates .
We then use a simple threshold model to show that progressive global warming over millions of years , in combination with the increasing tendency of the ocean to remain in a more stagnant state , can explain the decreasing magnitude and increasing frequency of hyperthermal events throughout the early Eocene .
Our work shows that nonlinear interactions between climate and the carbon cycle can modulate the effect of orbital variations , in this case producing transient global warming events with varying timing and magnitude .

[871] Nitrogen and phosphorus enrichment alter the composition of ammonia-oxidizing bacteria in salt marsh sediments

Ammonia oxidation is a central process in the nitrogen cycle .
Particularly in marine and estuarine environments , few experiments have been conducted to tease apart the factors influencing their abundance and composition .
To investigate the effect of nitrogen and phosphorus availability on ammonia-oxidizing bacteria ( AOB ) , we conducted a nutrient enrichment experiment in a Maine salt marsh and sampled sediment communities in three seasons over 2 years .
We assessed community composition using terminal restriction fragment length polymorphism analysis and sequencing of cloned fragments of the ammonia monooxygenase ( amoA ) gene .
Almost all of the amoA sequences fell within the marine and estuarine-specific Nitrosospira-like clade .
Applied separately , nitrogen and phosphorus significantly altered AOB composition ; however , together the nutrients had an interactive effect , and composition did not change .
In contrast , nutrient enrichment did not alter AOB abundance .
Furthermore , the response of AOB composition to nutrient enrichment varied over time .
We conclude that closely related taxa within the marine/estuarine-specific Nitrosospira-like clade vary in their preference for nutrient concentrations , and this preference may depend on other temporally variable abiotic factors .
Finally , AOB composition was highly variable within and across years even in untreated plots .
Further studies are needed to test how these different aspects of compositional variability in AOB communities influence nitrogen cycling .

[872] Metagenomic analysis reveals significant changes of microbial compositions and protective functions during drinking water treatment

The metagenomic approach was applied to characterize variations of microbial structure and functions in raw ( RW ) and treated water ( TW ) in a drinking water treatment plant ( DWTP ) at Pearl River Delta , China .
Microbial structure was significantly influenced by the treatment processes , shifting from Gammaproteobacteria and Betaproteobacteria in RW to Alphaproteobacteria in TW .
Further functional analysis indicated the basic metabolic functions of microorganisms in TW did not vary considerably .
However , protective functions , i.e. glutathione synthesis genes in ` oxidative stress ' and ` detoxification ' subsystems , significantly increased , revealing the surviving bacteria may have higher chlorine resistance .
Similar results were also found in glutathione metabolism pathway , which identified the major reaction for glutathione synthesis and supported more genes for glutathione metabolism existed in TW .
This metagenomic study largely enhanced our knowledge about the influences of treatment processes , especially chlorination , on bacterial community structure and protective functions ( e.g. glutathione metabolism ) in ecosystems of DWTPs .

[873] Lithological control on phytolith carbon sequestration in moso bamboo forests

Phytolith-occluded carbon ( PhytOC ) is a stable carbon ( C ) fraction that has effects on long-term global C balance .
Here , we report the phytolith and PhytOC accumulation in moso bamboo leaves developed on four types of parent materials .
The results show that PhytOC content of moso bamboo varies with parent material in the order of granodiorite ( 2.0 g kg-1 ) > granite ( 1.6 g kg-1 ) > basalt ( 1.3 g kg-1 ) > shale ( 0.7 g kg-1 ) .
PhytOC production flux of moso bamboo on four types of parent materials varies significantly from 1.0 to 64.8 kg CO2 ha-1 yr-1 , thus a net 4.7 x 106 -310.8 x 106 kg CO2 yr-1 would be sequestered by moso bamboo phytoliths in China .
The phytolith C sequestration rate in moso bamboo of China will continue to increase in the following decades due to nationwide bamboo afforestation/reforestation , demonstrating the potential of bamboo in regulating terrestrial C balance .
Management practices such as afforestation of bamboo in granodiorite area and granodiorite powder amendment may further enhance phytolith C sequestration through bamboo plants .

[874] Long-term CO2 production following permafrost thaw

Thawing permafrost represents a poorly understood feedback mechanism of climate change in the Arctic , but with a potential impact owing to stored carbon being mobilized .
We have quantified the long-term loss of carbon ( C ) from thawing permafrost in Northeast Greenland from 1996 to 2008 by combining repeated sediment sampling to assess changes in C stock and > 12 years of CO2 production in incubated permafrost samples .
Field observations show that the active-layer thickness has increased by > 1 cm yr-1 but thawing has not resulted in a detectable decline in C stocks .
Laboratory mineralization rates at 5 degreesC resulted in a C loss between 9 and 75 % , depending on drainage , highlighting the potential of fast mobilization of permafrost C under aerobic conditions , but also that C at near-saturated conditions may remain largely immobilized over decades .
This is confirmed by a three-pool C dynamics model that projects a potential C loss between 13 and 77 % for 50 years of incubation at 5 degreesC .

[875] Dynamic microbe and molecule networks in a mouse model of colitis-associated colorectal cancer

Bacterial colonisation of the gut is involved in the development of colitis-associated colorectal cancer .
However , it remains unclear how the gut microbiota dynamically shifts correlating with colorectal carcinogenesis .
Here , we reveal the longitudinal shifts in the microbial community that occur with colitis-associated colorectal cancer .
High-throughput sequencing results for the bacterial 16S rRNA gene ( V3 region ) were compared for azoxymethane/dextran sodium sulphate-treated mice and control mice .
We found that microbial community structure was significantly altered by chronic colitis .
Microbes in the species Streptococcus luteciae , Lactobacillus hamster , Bacteroides uniformis and Bacteroides ovatus were increased during colorectal carcinogenesis .
Histological measurements for a molecular network including six interconnected key factors from inflammation to cancer , namely p65 , p53 , COX-2 , PPARgamma , CCR2 and beta-catenin , indicated that the microbiome modifications were correlated with molecular pathogenesis of colitis-associated colorectal cancer .
Phylotype modifications after each AOM/DSS cycle were identified .
A longitudinal microbial network was then constructed for the gut microbiome and showed that the phylotype shifts during this process were complex and highly dynamic .
This work may provide a deeper understanding of the role of the microbiota and microbe-host interactions in colitis-associated colorectal cancer .

[876] Identification and application of keto acids transporters in Yarrowia lipolytica

Production of organic acids by microorganisms is of great importance for obtaining building-block chemicals from sustainable biomass .
Extracellular accumulation of organic acids involved a series of transporters , which play important roles in the accumulation of specific organic acid while lack of systematic demonstration in eukaryotic microorganisms .
To circumvent accumulation of by-product , efforts have being orchestrated to carboxylate transport mechanism for potential clue in Yarrowia lipolytica WSH-Z06 .
Six endogenous putative transporter genes , YALI0B19470g , YALI0C15488g , YALI0C21406g , YALI0D24607g , YALI0D20108g and YALI0E32901g , were identified .
Transport characteristics and substrate specificities were further investigated using a carboxylate-transport-deficient Saccharomyces cerevisiae strain .
These transporters were expressed in Y. lipolytica WSH-Z06 to assess their roles in regulating extracellular keto acids accumulation .
In a Y. lipolytica T1 line over expressing YALI0B19470g , alpha-ketoglutarate accumulated to 46.7 g.L-1 , whereas the concentration of pyruvate decreased to 12.3 g.L-1 .
Systematic identification of these keto acids transporters would provide clues to further improve the accumulation of specific organic acids with higher efficiency in eukaryotic microorganisms .

[877] Nitrate competition in a coral symbiosis varies with temperature among Symbiodinium clades

Many reef-building corals form symbioses with dinoflagellates from the diverse genus Symbiodinium .
There is increasing evidence of functional significance to Symbiodinium diversity , which affects the coral holobiont 's response to changing environmental conditions .
For example , corals hosting Symbiodinium from the clade D taxon exhibit greater resistance to heat-induced coral bleaching than conspecifics hosting the more common clade C. Yet , the relatively low prevalence of clade D suggests that this trait is not advantageous in non-stressful environments .
Thus , clade D may only be able to out-compete other Symbiodinium types within the host habitat when conditions are chronically stressful .
Previous studies have observed enhanced photosynthesis and fitness by clade C holobionts at non-stressful temperatures , relative to clade D. Yet , carbon-centered metrics can not account for enhanced growth rates and patterns of symbiont succession to other genetic types when nitrogen often limits reef productivity .
To investigate the metabolic costs of hosting thermally tolerant symbionts , we examined the assimilation and translocation of inorganic 15N and 13C in the coral Acropora tenuis experimentally infected with either clade C ( sub-type C1 ) or D Symbiodinium at 28 and 30 degreesC .
We show that at 28 degreesC , C1 holobionts acquired 22 % more 15N than clade D. However , at 30 degreesC , C1 symbionts acquired equivalent nitrogen and 16 % less carbon than D .
We hypothesize that C1 competitively excludes clade D in hospite via enhanced nitrogen acquisition and thus dominates coral populations despite warming oceans .

[878] Warming-induced increase in aerosol number concentration likely to moderate climate change

Atmospheric aerosol particles influence the climate system directly by scattering and absorbing solar radiation , and indirectly by acting as cloud condensation nuclei .
Apart from black carbon aerosol , aerosols cause a negative radiative forcing at the top of the atmosphere and substantially mitigate the warming caused by greenhouse gases .
In the future , tightening of controls on anthropogenic aerosol and precursor vapour emissions to achieve higher air quality may weaken this beneficial effect .
Natural aerosols , too , might affect future warming .
Here we analyse long-term observations of concentrations and compositions of aerosol particles and their biogenic precursor vapours in continental mid - and high-latitude environments .
We use measurements of particle number size distribution together with boundary layer heights derived from reanalysis data to show that the boundary layer burden of cloud condensation nuclei increases exponentially with temperature .
Our results confirm a negative feedback mechanism between the continental biosphere , aerosols and climate : aerosol cooling effects are strengthened by rising biogenic organic vapour emissions in response to warming , which in turn enhance condensation on particles and their growth to the size of cloud condensation nuclei .
This natural growth mechanism produces roughly 50 % of particles at the size of cloud condensation nuclei across Europe .
We conclude that biosphere-atmosphere interactions are crucial for aerosol climate effects and can significantly influence the effects of anthropogenic aerosol emission controls , both on climate and air quality .

[879] Negative impact of nitrogen deposition on soil buffering capacity

Anthropogenic nitrogen deposition over the past half century has had a detrimental impact on temperate ecosystems in Europe and North America , resulting in soil acidification and a reduction in plant biodiversity .
During the acidification process , soils release base cations , such as calcium and magnesium , neutralizing the increase in acidity .
Once these base cations have been depleted , aluminium is released from the soils , often reaching toxic levels .
Here , we present results from a nitrogen deposition experiment that suggests that a long legacy of acid deposition in the Western Tatra Mountains of Slovakia has pushed soils to a new threshold of acidification usually associated with acid mine drainage soils .
We show that increases in nitrogen deposition in the region result in a depletion of both base cations and soluble aluminium , and an increase in extractable iron concentrations .
In conjunction with this , we observe a nitrogen-deposition-induced reduction in the biomass of vascular plants , associated with a decrease in shoot calcium and magnesium concentrations .
We suggest that this site , and potentially others in central Europe , have reached a new and potentially more toxic level of soil acidification in which aluminium release is superseded by iron release into soil water .

[880] The impact of global warming on the tropical Pacific Ocean and El Nino

The El Nino-Southern Oscillation ( ENSO ) is a naturally occurring fluctuation that originates in the tropical Pacific region and affects ecosystems , agriculture , freshwater supplies , hurricanes and other severe weather events worldwide .
Under the influence of global warming , the mean climate of the Pacific region will probably undergo significant changes .
The tropical easterly trade winds are expected to weaken ; surface ocean temperatures are expected to warm fastest near the equator and more slowly farther away ; the equatorial thermocline that marks the transition between the wind-mixed upper ocean and deeper layers is expected to shoal ; and the temperature gradients across the thermocline are expected to become steeper .
Year-to-year ENSO variability is controlled by a delicate balance of amplifying and damping feedbacks , and one or more of the physical processes that are responsible for determining the characteristics of ENSO will probably be modified by climate change .
Therefore , despite considerable progress in our understanding of the impact of climate change on many of the processes that contribute to El Nino variability , it is not yet possible to say whether ENSO activity will be enhanced or damped , or if the frequency of events will change .

[881] The social cost of CO2 in a low-growth world

Action on mitigating climate change seems to be grinding to a halt within the global political arena .
Major emitters seem unwilling to accept binding emissions reductions targets as their economies have stagnated .
The talks at the United Nations Framework Convention on Climate Change conference in Copenhagen in 2009 were meant to represent a watershed moment for global cooperation on climate change but produced little more than a symbolic accord .
Fast forward another three years and the outcomes of the Doha negotiations deferred the key decisions on climate change mitigation to 2015 , as the Durban Platform did before .
Is this neglect justified ?
Here we use the PAGE09 integrated assessment model to estimate the mean social cost of CO2 for a wide range of economic growth scenarios .
The social cost of CO2 measures the net present value of the extra damage caused by the emission of one more tonne of CO2 today .
The results show that in a world with sustained lower economic growth the mean social cost of CO2 increases because the climate impacts occur in a relatively poor world , suggesting that , if anything , mitigating climate change should be a higher priority for policymakers in a low-growth world .

[882] Thresholds for Cenozoic bipolar glaciation

The long-standing view of Earth 's Cenozoic glacial history calls for the first continental-scale glaciation of Antarctica in the earliest Oligocene epoch ( ~ 33.6 million years ago ) , followed by the onset of northern-hemispheric glacial cycles in the late Pliocene epoch , about 31 million years later .
The pivotal early Oligocene event is characterized by a rapid shift of 1.5 parts per thousand in deep-sea benthic oxygen-isotope values ( Oi-1 ) within a few hundred thousand years , reflecting a combination of terrestrial ice growth and deep-sea cooling .
The apparent absence of contemporaneous cooling in deep-sea Mg/Ca records , however , has been argued to reflect the growth of more ice than can be accommodated on Antarctica ; this , combined with new evidence of continental cooling and ice-rafted debris in the Northern Hemisphere during this period , raises the possibility that Oi-1 represents a precursory bipolar glaciation .
Here we test this hypothesis using an isotope-capable global climate/ice-sheet model that accommodates both the long-term decline of Cenozoic atmospheric CO2 levels and the effects of orbital forcing .
We show that the CO2 threshold below which glaciation occurs in the Northern Hemisphere ( ~ 280 p.p.m.v. ) is much lower than that for Antarctica ( ~ 750 p.p.m.v. ) .
Therefore , the growth of ice sheets in the Northern Hemisphere immediately following Antarctic glaciation would have required rapid CO2 drawdown within the Oi-1 timeframe , to levels lower than those estimated by geochemical proxies and carbon-cycle models .
Instead of bipolar glaciation , we find that Oi-1 is best explained by Antarctic glaciation alone , combined with deep-sea cooling of up to 4 degreesC and Antarctic ice that is less isotopically depleted ( -30 to -35 / 1000 ) than previously suggested .
Proxy CO2 estimates remain above our model 's northern-hemispheric glaciation threshold of ~ 280 p.p.m.v. until ~ 25 Myr ago , but have been near or below that level ever since .
This implies that episodic northern-hemispheric ice sheets have been possible some 20 million years earlier than currently assumed ( although still much later than Oi-1 ) and could explain some of the variability in Miocene sea-level records .

[883] Increasing stress on disaster-risk finance due to large floods

Recent major flood disasters have shown that single extreme events can affect multiple countries simultaneously , which puts high pressure on trans-national risk reduction and risk transfer mechanisms .
So far , little is known about such flood hazard interdependencies across regions and the corresponding joint risks at regional to continental scales .
Reliable information on correlated loss probabilities is crucial for developing robust insurance schemes and public adaptation funds , and for enhancing our understanding of climate change impacts .
Here we show that extreme discharges are strongly correlated across European river basins .
We present probabilistic trends in continental flood risk , and demonstrate that observed extreme flood losses could more than double in frequency by 2050 under future climate change and socio-economic development .
We suggest that risk management for these increasing losses is largely feasible , and we demonstrate that risk can be shared by expanding risk transfer financing , reduced by investing in flood protection , or absorbed by enhanced solidarity between countries .
We conclude that these measures have vastly different efficiency , equity and acceptability implications , which need to be taken into account in broader consultation , for which our analysis provides a basis .

[884] Experimental evolution of an alternating uni - and multicellular life cycle in Chlamydomonas reinhardtii

The transition to multicellularity enabled the evolution of large , complex organisms , but early steps in this transition remain poorly understood .
Here we show that multicellular complexity , including development from a single cell , can evolve rapidly in a unicellular organism that has never had a multicellular ancestor .
We subject the alga Chlamydomonas reinhardtii to conditions that favour multicellularity , resulting in the evolution of a multicellular life cycle in which clusters reproduce via motile unicellular propagules .
While a single-cell genetic bottleneck during ontogeny is widely regarded as an adaptation to limit among-cell conflict , its appearance very early in this transition suggests that it did not evolve for this purpose .
Instead , we find that unicellular propagules are adaptive even in the absence of intercellular conflict , maximizing cluster-level fecundity .
These results demonstrate that the unicellular bottleneck , a trait essential for evolving multicellular complexity , can arise rapidly via co-option of the ancestral unicellular form .

[885] Ecological-economic optimization of biodiversity conservation under climate change

Substantial investment in climate change research has led to dire predictions of the impacts and risks to biodiversity .
The Intergovernmental Panel on Climate Change fourth assessment report cites 28,586 studies demonstrating significant biological changes in terrestrial systems .
Already high extinction rates , driven primarily by habitat loss , are predicted to increase under climate change .
Yet there is little specific advice or precedent in the literature to guide climate adaptation investment for conserving biodiversity within realistic economic constraints .
Here we present a systematic ecological and economic analysis of a climate adaptation problem in one of the world 's most species-rich and threatened ecosystems : the South African fynbos .
We discover a counterintuitive optimal investment strategy that switches twice between options as the available adaptation budget increases .
We demonstrate that optimal investment is nonlinearly dependent on available resources , making the choice of how much to invest as important as determining where to invest and what actions to take .
Our study emphasizes the importance of a sound analytical framework for prioritizing adaptation investments .
Integrating ecological predictions in an economic decision framework will help support complex choices between adaptation options under severe uncertainty .
Our prioritization method can be applied at any scale to minimize species loss and to evaluate the robustness of decisions to uncertainty about key assumptions .

[886] Competition favours reduced cost of plasmids to host bacteria

Conjugative plasmids of Gram-negative bacteria have both vertical and horizontal modes of transmission : they are segregated to daughter cells during division , and transferred between hosts by plasmid-encoded conjugative machinery .
Despite maintaining horizontal mobility , many plasmids carry fertility inhibition ( fin ) systems that repress their own conjugative transfer .
To assess the ecological basis of self-transfer repression , we compared the invasion of bacterial populations by fin + and fin - variants of the plasmid R1 using a computational model and co-culture competitions .
We observed that the fin + variant had a modest cost to the host ( measured by reduction in growth rate ) , while the fin - variant incurred a larger cost .
In simulations and empirical competitions the fin - plasmid invaded cultures quickly , but was subsequently displaced by the fin + plasmid .
This indicated a competitive advantage to reducing horizontal transmission and allowing increased host replication .
Computational simulations predicted that the advantage associated with reduced cost to the host would be maintained over a wide range of environmental conditions and plasmid costs .
We infer that vertical transmission in concert with competitive exclusion favour decreased horizontal mobility of plasmids .
Similar dynamics may exert evolutionary pressure on parasites , such as temperate bacteriophages and vertically transmitted animal viruses , to limit their rates of horizontal transfer .

[887] Extended megadroughts in the southwestern United States during Pleistocene interglacials

The potential for increased drought frequency and severity linked to anthropogenic climate change in the semi-arid regions of the southwestern United States ( US ) is a serious concern .
Multi-year droughts during the instrumental period and decadal-length droughts of the past two millennia were shorter and climatically different from the future permanent , ` dust-bowl-like ' megadrought conditions , lasting decades to a century , that are predicted as a consequence of warming .
So far , it has been unclear whether or not such megadroughts occurred in the southwestern US , and , if so , with what regularity and intensity .
Here we show that periods of aridity lasting centuries to millennia occurred in the southwestern US during mid-Pleistocene interglacials .
Using molecular palaeotemperature proxies to reconstruct the mean annual temperature ( MAT ) in mid-Pleistocene lacustrine sediment from the Valles Caldera , New Mexico , we found that the driest conditions occurred during the warmest phases of interglacials , when the MAT was comparable to or higher than the modern MAT .
A collapse of drought-tolerant C4 plant communities during these warm , dry intervals indicates a significant reduction in summer precipitation , possibly in response to a poleward migration of the subtropical dry zone .
Three MAT cycles ~ 2 degreesC in amplitude occurred within Marine Isotope Stage ( MIS ) 11 and seem to correspond to the muted precessional cycles within this interglacial .
In comparison with MIS 11 , MIS 13 experienced higher precessional-cycle amplitudes , larger variations in MAT ( 4-6 degreesC ) and a longer period of extended warmth , suggesting that local insolation variations were important to interglacial climatic variability in the southwestern US .
Comparison of the early MIS 11 climate record with the Holocene record shows many similarities and implies that , in the absence of anthropogenic forcing , the region should be entering a cooler and wetter phase .

[888] Modelling predicts that heat stress , not drought , will increase vulnerability of wheat in Europe

New crop cultivars will be required for a changing climate characterised by increased summer drought and heat stress in Europe .
However , the uncertainty in climate predictions poses a challenge to crop scientists and breeders who have limited time and resources and must select the most appropriate traits for improvement .
Modelling is a powerful tool to quantify future threats to crops and hence identify targets for improvement .
We have used a wheat simulation model combined with local-scale climate scenarios to predict impacts of heat stress and drought on winter wheat in Europe .
Despite the lower summer precipitation projected for 2050s across Europe , relative yield losses from drought is predicted to be smaller in the future , because wheat will mature earlier avoiding severe drought .
By contrast , the risk of heat stress around flowering will increase , potentially resulting in substantial yield losses for heat sensitive cultivars commonly grown in northern Europe .

[889] Recent multidecadal strengthening of the Walker circulation across the tropical Pacific

The Pacific Walker circulation is a large overturning cell that spans the tropical Pacific Ocean , characterized by rising motion ( lower sea-level pressure ) over Indonesia and sinking motion ( higher sea level-pressure ) over the eastern Pacific .
Fluctuations in the Walker circulation reflect changes in the location and strength of tropical heating , so related circulation anomalies have global impacts .
On interannual timescales , the El Nino/Southern Oscillation accounts for much of the variability in the Walker circulation , but there is considerable interest in longer-term trends and their drivers , including anthropogenic climate change .
Here , we examine sea-level pressure trends in ten different data sets drawn from reanalysis , reconstructions and in situ measurements for 1900-2011 .
We show that periods with fewer in situ measurements result in lower signal-to-noise ratios , making assessments of sea-level pressure trends largely unsuitable before about the 1950s .
Multidecadal trends evaluated since 1950 reveal statistically significant , negative values over the Indonesian region , with weaker , positive trends over the eastern Pacific .
The overall trend towards a stronger , La Nina-like Walker circulation is nearly concurrent with the observed increase in global average temperatures , thereby justifying closer scrutiny of how the Pacific climate system has changed in the historical record .

[890] Model projections of rapid sea-level rise on the northeast coast of the United States

Human-induced climate change could cause global sea-level rise .
Through the dynamic adjustment of the sea surface in response to a possible slowdown of the Atlantic meridional overturning circulation , a warming climate could also affect regional sea levels , especially in the North Atlantic region , leading to high vulnerability for low-lying Florida and western Europe .
Here we analyse climate projections from a set of state-of-the-art climate models for such regional changes , and find a rapid dynamical rise in sea level on the northeast coast of the United States during the twenty-first century .
For New York City , the rise due to ocean circulation changes amounts to 15 , 20 and 21 cm for scenarios with low , medium and high rates of emissions respectively , at a similar magnitude to expected global thermal expansion .
Analysing one of the climate models in detail , we find that a dynamic , regional rise in sea level is induced by a weakening meridional overturning circulation in the Atlantic Ocean , and superimposed on the global mean sea-level rise .
We conclude that together , future changes in sea level and ocean circulation will have a greater effect on the heavily populated northeastern United States than estimated previously .

[891] Multielement stoichiometry in Quercus variabilis under natural phosphorus variation in subtropical China

Plant stoichiometry in relation to environmental factors has recently received increasing attention .
However , regulations and variations of plant elements in different environments are not well understood .
We investigated homeostasis and variation of macroelements ( C , N , P , K , Ca , Mg , and S ) , essential microelements ( Fe , Mn , and Zn ) and non-essential elements ( Al ) in Quercus variabilis leaves at a range of natural P concentration from P-rich to P-deficient ( typical subtropical conditions ) soils .
The results showed that element ratios were more stable ( except for C :P and Mn :P ) than individual element concentrations .
Of the individual elements , protein-related elements ( e.g. N , S , and Fe ) were correlated with leaf P while non-protein elements ( e.g. C , K , and Ca ) were not .
The degree of homeostasis indicated that macroelements ( N , P , and Ca ) concentrations were more variable than microelements ( Mn , Zn , and Al ) under a varying element concentration in soils .
These results suggest that local P-rich geochemistry alters leaf element concentrations , but not element ratios , and that plants are capable of meeting their needs for elements in certain proportions to achieve optimal performance under varying elemental conditions .

[892] Aridity threshold in controlling ecosystem nitrogen cycling in arid and semi-arid grasslands

Higher aridity and more extreme rainfall events in drylands are predicted due to climate change .
Yet , it is unclear how changing precipitation regimes may affect nitrogen ( N ) cycling , especially in areas with extremely high aridity .
Here we investigate soil N isotopic values ( delta15N ) along a 3,200 km aridity gradient and reveal a hump-shaped relationship between soil delta15N and aridity index ( AI ) with a threshold at AI = 0.32 .
Variations of foliar delta15N , the abundance of nitrification and denitrification genes , and metabolic quotient along the gradient provide further evidence for the existence of this threshold .
Data support the hypothesis that the increase of gaseous N loss is higher than the increase of net plant N accumulation with increasing AI below AI = 0.32 , while the opposite is favoured above this threshold .
Our results highlight the importance of N-cycling microbes in extremely dry areas and suggest different controlling factors of N-cycling on either side of the threshold .

[893] Microseismological evidence for a changing wave climate in the northeast Atlantic Ocean

One possible consequence of a change in climate over the past several decades is an increase in wave heights , potentially threatening coastal areas as well as the marine industry .
But the difficulties in observing wave heights exacerbates a general problem of climate-change detection : inhomogeneities in long-term observational records owing to changes in the instruments or techniques used , which may cause artificial trends .
Ground movements with periods of 4-16 seconds , known as microseisms , are associated with ocean waves and coastal surf , and have been recorded continuously since the early days of seismology .
Here we use such a 40-year record of wintertime microseisms from Hamburg , Germany , to reconstruct the wave climate in the northeast Atlantic Ocean .
For the period 1954-77 , we detect an average of seven days per month with strong microseismic activity , without a significant trend .
This number increases significantly in the second half of the record , reaching approximately 14 days of strong microseisms per month .
The implied increase in northeast Atlantic wave height over the past 20 years parallels increased surface air temperatures and storminess in this region , suggesting a common forcing .

[894] Losers and winners in coral reefs acclimatized to elevated carbon dioxide concentrations

Experiments have shown that ocean acidification due to rising atmospheric carbon dioxide concentrations has deleterious effects on the performance of many marine organisms .
However , few empirical or modelling studies have addressed the long-term consequences of ocean acidification for marine ecosystems .
Here we show that as pH declines from 8.1 to 7.8 ( the change expected if atmospheric carbon dioxide concentrations increase from 390 to 750 ppm , consistent with some scenarios for the end of this century ) some organisms benefit , but many more lose out .
We investigated coral reefs , seagrasses and sediments that are acclimatized to low pH at three cool and shallow volcanic carbon dioxide seeps in Papua New Guinea .
At reduced pH , we observed reductions in coral diversity , recruitment and abundances of structurally complex framework builders , and shifts in competitive interactions between taxa .
However , coral cover remained constant between pH 8.1 and ~ 7.8 , because massive Porites corals established dominance over structural corals , despite low rates of calcification .
Reef development ceased below pH 7.7 .
Our empirical data from this unique field setting confirm model predictions that ocean acidification , together with temperature stress , will probably lead to severely reduced diversity , structural complexity and resilience of Indo-Pacific coral reefs within this century .

[895] Future distribution of tundra refugia in northern Alaska

Climate change in the Arctic is a growing concern for natural resource conservation and management as a result of accelerated warming and associated shifts in the distribution and abundance of northern species .
We introduce a predictive framework for assessing the future extent of Arctic tundra and boreal biomes in northern Alaska .
We use geo-referenced museum specimens to predict the velocity of distributional change into the next century and compare predicted tundra refugial areas with current land-use .
The reliability of predicted distributions , including differences between fundamental and realized niches , for two groups of species is strengthened by fossils and genetic signatures of demographic shifts .
Evolutionary responses to environmental change through the late Quaternary are generally consistent with past distribution models .
Predicted future refugia overlap managed areas and indicate potential hotspots for tundra diversity .
To effectively assess future refugia , variable responses among closely related species to climate change warrants careful consideration of both evolutionary and ecological histories .

[896] Connecting thermal physiology and latitudinal niche partitioning in marine Synechococcus

Marine Synechococcus cyanobacteria constitute a monophyletic group that displays a wide latitudinal distribution , ranging from the equator to the polar fronts .
Whether these organisms are all physiologically adapted to stand a large temperature gradient or stenotherms with narrow growth temperature ranges has so far remained unexplored .
We submitted a panel of six strains , isolated along a gradient of latitude in the North Atlantic Ocean , to long - and short-term variations of temperature .
Upon a downward shift of temperature , the strains showed strikingly distinct resistance , seemingly related to their latitude of isolation , with tropical strains collapsing while northern strains were capable of growing .
This behaviour was associated to differential photosynthetic performances .
In the tropical strains , the rapid photosystem II inactivation and the decrease of the antioxydant beta-carotene relative to chl a suggested a strong induction of oxidative stress .
These different responses were related to the thermal preferenda of the strains .
The northern strains could grow at 10 degreesC while the other strains preferred higher temperatures .
In addition , we pointed out a correspondence between strain isolation temperature and phylogeny .
In particular , clades I and IV laboratory strains were all collected in the coldest waters of the distribution area of marine Synechococus .
We , however , show that clade I Synechococcus exhibit different levels of adaptation , which apparently reflect their location on the latitudinal temperature gradient .
This study reveals the existence of lineages of marine Synechococcus physiologically specialised in different thermal niches , therefore suggesting the existence of temperature ecotypes within the marine Synechococcus radiation .

[897] Successful range-expanding plants experience less above-ground and below-ground enemy impact

Many species are currently moving to higher latitudes and altitudes .
However , little is known about the factors that influence the future performance of range-expanding species in their new habitats .
Here we show that range-expanding plant species from a riverine area were better defended against shoot and root enemies than were related native plant species growing in the same area .
We grew fifteen plant species with and without non-coevolved polyphagous locusts and cosmopolitan , polyphagous aphids .
Contrary to our expectations , the locusts performed more poorly on the range-expanding plant species than on the congeneric native plant species , whereas the aphids showed no difference .
The shoot herbivores reduced the biomass of the native plants more than they did that of the congeneric range expanders .
Also , the range-expanding plants developed fewer pathogenic effects in their root-zone soil than did the related native species .
Current predictions forecast biodiversity loss due to limitations in the ability of species to adjust to climate warming conditions in their range .
Our results strongly suggest that the plants that shift ranges towards higher latitudes and altitudes may include potential invaders , as the successful range expanders may experience less control by above-ground or below-ground enemies than the natives .

[898] Climate change in the North Pacific region over the past three centuries

The relatively short length of most instrumental climate records restricts the study of climate variability , and it is therefore essential to extend the record into the past with the help of proxy data .
Only since the late 1940s have atmospheric data been available that are sufficient in quality and spatial resolution to identify the dominant patterns of climate variability , such as the Pacific North America pattern and the Pacific Decadal Oscillation .
Here we present a 301-year snow accumulation record from an ice core at a height of 5,340 m above sea level -- from Mount Logan , in northwestern North America .
This record shows features that are closely linked with the Pacific North America pattern for the period of instrumental data availability .
Our record extends back in time to cover the period from the closing stages of the Little Ice Age to the warmest decade in the past millennium .
We find a positive , accelerating trend in snow accumulation after the middle of the nineteenth century .
This trend is paralleled by a warming over northwestern North America which has been associated with secular changes in both the Pacific North America pattern and the Pacific Decadal Oscillation .

[899] Carbonate counter pump stimulated by natural iron fertilization in the Polar Frontal Zone

The production of organic carbon in the ocean 's surface and its subsequent downward export transfers carbon dioxide to the deep ocean .
This CO2 drawdown is countered by the biological precipitation of carbonate , followed by sinking of particulate inorganic carbon , which is a source of carbon dioxide to the surface ocean , and hence the atmosphere over 100-1 ,000 year timescales .
The net transfer of CO2 to the deep ocean is therefore dependent on the relative amount of organic and inorganic carbon in sinking particles .
In the Southern Ocean , iron fertilization has been shown to increase the export of organic carbon , but it is unclear to what degree this effect is compensated by the export of inorganic carbon .
Here we assess the composition of sinking particles collected from sediment traps located in the Polar Frontal Zone of the Southern Ocean .
We find that in high-nutrient , low-chlorophyll regions that are characterized by naturally high iron concentrations , fluxes of both organic and inorganic carbon are higher than in regions with no iron fertilization .
However , the excess flux of inorganic carbon is greater than that of organic carbon .
We estimate that the production and flux of carbonate in naturally iron-fertilized waters reduces the overall amount of CO2 transferred to the deep ocean by 6-32 % , compared to 1-4 % at the non-fertilized site .
We suggest that an increased export of organic carbon , stimulated by iron availability in the glacial sub-Antarctic oceans , may have been accompanied by a strengthened carbonate counter pump .

[900] Continued global warming after CO2 emissions stoppage

Recent studies have suggested that global mean surface temperature would remain approximately constant on multi-century timescales after CO2 emissions are stopped .
Here we use Earth system model simulations of such a stoppage to demonstrate that in some models , surface temperature may actually increase on multi-century timescales after an initial century-long decrease .
This occurs in spite of a decline in radiative forcing that exceeds the decline in ocean heat uptake -- a circumstance that would otherwise be expected to lead to a decline in global temperature .
The reason is that the warming effect of decreasing ocean heat uptake together with feedback effects arising in response to the geographic structure of ocean heat uptake overcompensates the cooling effect of decreasing atmospheric CO2 on multi-century timescales .
Our study also reveals that equilibrium climate sensitivity estimates based on a widely used method of regressing the Earth 's energy imbalance against surface temperature change are biased .
Uncertainty in the magnitude of the feedback effects associated with the magnitude and geographic distribution of ocean heat uptake therefore contributes substantially to the uncertainty in allowable carbon emissions for a given multi-century warming target .

[901] One-to-one coupling of glacial climate variability in Greenland and Antarctica

Precise knowledge of the phase relationship between climate changes in the two hemispheres is a key for understanding the Earth 's climate dynamics .
For the last glacial period , ice core studies have revealed strong coupling of the largest millennial-scale warm events in Antarctica with the longest Dansgaard-Oeschger events in Greenland through the Atlantic meridional overturning circulation .
It has been unclear , however , whether the shorter Dansgaard-Oeschger events have counterparts in the shorter and less prominent Antarctic temperature variations , and whether these events are linked by the same mechanism .
Here we present a glacial climate record derived from an ice core from Dronning Maud Land , Antarctica , which represents South Atlantic climate at a resolution comparable with the Greenland ice core records .
After methane synchronization with an ice core from North Greenland , the oxygen isotope record from the Dronning Maud Land ice core shows a one-to-one coupling between all Antarctic warm events and Greenland Dansgaard-Oeschger events by the bipolar seesaw6 .
The amplitude of the Antarctic warm events is found to be linearly dependent on the duration of the concurrent stadial in the North , suggesting that they all result from a similar reduction in the meridional overturning circulation .

[902] Species traits and phylogenetic conservatism of climate-induced range shifts in stream fishes

Understanding climate-induced range shifts is crucial for biodiversity conservation .
However , no general consensus has so far emerged about the mechanisms involved and the role of phylogeny in shaping species responses has been poorly explored .
Here , we investigate whether species traits and their underlying phylogenetic constraints explain altitudinal shifts at the trailing and leading edges of stream fish species ranges .
We demonstrate that these shifts are related to dissimilar mechanisms : whereas range retractions show some support for phylogenetic clustering due to a high level of conservatism in thermal safety margins , range expansions are underpinned by both evolutionarily conserved and labile traits , notably trophic position and life-history strategy , hence decreasing the strength of phylogenetic signal .
Therefore , while climate change brings many difficulties in establishing a general understanding of species vulnerability , these findings emphasize how combining trait-based approaches in light of the species evolutionary history may offer new opportunities in facing conservation challenges .

[903] Strong and deep Atlantic meridional overturning circulation during the last glacial cycle

Extreme , abrupt Northern Hemisphere climate oscillations during the last glacial cycle ( 140,000 years ago to present ) were modulated by changes in ocean circulation and atmospheric forcing .
However , the variability of the Atlantic meridional overturning circulation ( AMOC ) , which has a role in controlling heat transport from low to high latitudes and in ocean CO2 storage , is still poorly constrained beyond the Last Glacial Maximum .
Here we show that a deep and vigorous overturning circulation mode has persisted for most of the last glacial cycle , dominating ocean circulation in the Atlantic , whereas a shallower glacial mode with southern-sourced waters filling the deep western North Atlantic prevailed during glacial maxima .
Our results are based on a reconstruction of both the strength and the direction of the AMOC during the last glacial cycle from a highly resolved marine sedimentary record in the deep western North Atlantic .
Parallel measurements of two independent chemical water tracers ( the isotope ratios of 231Pa/230Th and 143Nd/144Nd ) , which are not directly affected by changes in the global cycle , reveal consistent responses of the AMOC during the last two glacial terminations .
Any significant deviations from this configuration , resulting in slowdowns of the AMOC , were restricted to centennial-scale excursions during catastrophic iceberg discharges of the Heinrich stadials .
Severe and multicentennial weakening of North Atlantic Deep Water formation occurred only during Heinrich stadials close to glacial maxima with increased ice coverage , probably as a result of increased fresh-water input .
In contrast , the AMOC was relatively insensitive to submillennial meltwater pulses during warmer climate states , and an active AMOC prevailed during Dansgaard-Oeschger interstadials ( Greenland warm periods ) .

[904] Phase variation has a role in Burkholderia ambifaria niche adaptation

Members of the Burkholderia cepacia complex ( Bcc ) , such as B. ambifaria , are effective biocontrol strains , for instance , as plant growth-promoting bacteria ; however , Bcc isolates can also cause severe respiratory infections in people suffering from cystic fibrosis ( CF ) .
No distinction is known between isolates from environmental and human origins , suggesting that the natural environment is a potential source of infectious Bcc species .
While investigating the presence and role of phase variation in B. ambifaria HSJ1 , an isolate recovered from a CF patient , we identified stable variants that arose spontaneously irrespective of the culture conditions .
Phenotypic and proteomic approaches revealed that the transition from wild-type to variant types affects the expression of several putative virulence factors .
By using four different infection models ( Drosophila melanogaster , Galleria mellonella , macrophages and Dictyostelium discoideum ) , we showed that the wild-type was more virulent than the variant .
It may be noted that the variant showed reduced replication in a human monocyte cell line when compared with the wild-type .
On the other hand , the variant of isolate HSJ1 was more competitive in colonizing plant roots than the wild-type .
Furthermore , we observed that only clinical B. ambifaria isolates generated phase variants , and that these variants showed the same phenotypes as observed with the HSJ1 variant .
Finally , we determined that environmental B. ambifaria isolates showed traits that were characteristic of variants derived from clinical isolates .
Our study therefore suggest that B. ambifaria uses phase variation to adapt to drastically different environments : the lung of patients with CF or the rhizosphere .

[905] Solar ultraviolet radiation in a changing climate

The projected large increases in damaging ultraviolet radiation as a result of global emissions of ozone-depleting substances have been forestalled by the success of the Montreal Protocol .
New challenges are now arising in relation to climate change .
We highlight the complex interactions between the drivers of climate change and those of stratospheric ozone depletion , and the positive and negative feedbacks among climate , ozone and ultraviolet radiation .
These will result in both risks and benefits of exposure to ultraviolet radiation for the environment and human welfare .
This Review synthesizes these new insights and their relevance in a world where changes in climate as well as in stratospheric ozone are altering exposure to ultraviolet radiation with largely unknown consequences for the biosphere .

[906] Low temperature delays timing and enhances the cost of nitrogen fixation in the unicellular cyanobacterium Cyanothece

Marine nitrogen-fixing cyanobacteria are largely confined to the tropical and subtropical ocean .
It has been argued that their global biogeographical distribution reflects the physiologically feasible temperature range at which they can perform nitrogen fixation .
In this study we refine this line of argumentation for the globally important group of unicellular diazotrophic cyanobacteria , and pose the following two hypotheses : ( i ) nitrogen fixation is limited by nitrogenase activity at low temperature and by oxygen diffusion at high temperature , which is manifested by a shift from strong to weak temperature dependence of nitrogenase activity , and ( ii ) high respiration rates are required to maintain very low levels of oxygen for nitrogenase , which results in enhanced respiratory cost per molecule of fixed nitrogen at low temperature .
We tested these hypotheses in laboratory experiments with the unicellular cyanobacterium Cyanothece sp .
BG043511 .
In line with the first hypothesis , the specific growth rate increased strongly with temperature from 18 to 30 degreesC , but leveled off at higher temperature under nitrogen-fixing conditions .
As predicted by the second hypothesis , the respiratory cost of nitrogen fixation and also the cellular C : N ratio rose sharply at temperatures below 21 degreesC .
In addition , we found that low temperature caused a strong delay in the onset of the nocturnal nitrogenase activity , which shortened the remaining nighttime available for nitrogen fixation .
Together , these results point at a lower temperature limit for unicellular nitrogen-fixing cyanobacteria , which offers an explanation for their ( sub ) tropical distribution and suggests expansion of their biogeographical range by global warming .

[907] Crop pests and pathogens move polewards in a warming world

Global food security is threatened by the emergence and spread of crop pests and pathogens .
Spread is facilitated primarily by human transportation , but there is increasing concern that climate change allows establishment in hitherto unsuitable regions .
However , interactions between climate change , crops and pests are complex , and the extent to which crop pests and pathogens have altered their latitudinal ranges in response to global warming is largely unknown .
Here , we demonstrate an average poleward shift of 2.7 + / -0.8 km yr-1 since 1960 , in observations of hundreds of pests and pathogens , but with significant variation in trends among taxonomic groups .
Observational bias , where developed countries at high latitudes detect pests earlier than developing countries at low latitudes , would result in an apparent shift towards the Equator .
The observed positive latitudinal trends in many taxa support the hypothesis of global warming-driven pest movement .

[908] Air pollution and forest water use

Arising from T. F. Keenan et al. .
Nature 499 , 324-327 ( 2013 )
Forests in North America and northern Europe increased their water-use efficiency ( WUE ) -- the ratio of photosynthetic CO2 uptake to water loss through evapotranspiration -- over the last two decades , according to a recent Letter .
Keenan et al. attribute the rising WUE to fertilization by increasing levels of atmospheric CO2 ( ref .
1 ) , although biosphere models predict this effect to be much smaller than the observed trend .
Here , I show that falling concentrations of ozone and other phytotoxic air pollutants , which were not considered in ref .
1 , may explain part of the WUE trend .
Future efforts to reconcile biosphere models with field data should , therefore , use integrated modelling approaches that include both air quality and CO2 effects on forest growth and water use .
There is a Reply to this Brief Communication Arising by Keenan , T. F. et al. .
Nature 507 , http://dx.doi.org/10.1038/nature13114 ( 2014 ) .

[909] Nitrification of archaeal ammonia oxidizers in acid soils is supported by hydrolysis of urea

The hydrolysis of urea as a source of ammonia has been proposed as a mechanism for the nitrification of ammonia-oxidizing bacteria ( AOB ) in acidic soil .
The growth of Nitrososphaera viennensis on urea suggests that the ureolysis of ammonia-oxidizing archaea ( AOA ) might occur in natural environments .
In this study , 15N isotope tracing indicates that ammonia oxidation occurred upon the addition of urea at a concentration similar to the in situ ammonium content of tea orchard soil ( pH 3.75 ) and forest soil ( pH 5.4 ) and was inhibited by acetylene .
Nitrification activity was significantly stimulated by urea fertilization and coupled well with abundance changes in archaeal amoA genes in acidic soils .
Pyrosequencing of 16S rRNA genes at whole microbial community level demonstrates the active growth of AOA in urea-amended soils .
Molecular fingerprinting further shows that changes in denaturing gradient gel electrophoresis fingerprint patterns of archaeal amoA genes are paralleled by nitrification activity changes .
However , bacterial amoA and 16S rRNA genes of AOB were not detected .
The results strongly suggest that archaeal ammonia oxidation is supported by hydrolysis of urea and that AOA , from the marine Group 1.1a-associated lineage , dominate nitrification in two acidic soils tested .

[910] Response and resilience of soil biocrust bacterial communities to chronic physical disturbance in arid shrublands

The impact of 10 years of annual foot trampling on soil biocrusts was examined in replicated field experiments at three cold desert sites of the Colorado Plateau , USA .
Trampling detrimentally impacted lichens and mosses , and the keystone cyanobacterium , Microcoleus vaginatus , resulting in increased soil erosion and reduced C and N concentrations in surface soils .
Trampled biocrusts contained approximately half as much extractable DNA and 20-52 % less chlorophyll a when compared with intact biocrusts at each site .
Two of the three sites also showed a decline in scytonemin-containing , diazotrophic cyanobacteria in trampled biocrusts .
16S rRNA gene sequence and terminal restriction fragment length polymorphism ( T-RFLP ) analyses of soil bacteria from untrampled and trampled biocrusts demonstrated a reduced proportion ( 23-65 % reduction ) of M. vaginatus and other Cyanobacteria in trampled plots .
In parallel , other soil bacterial species that are natural residents of biocrusts , specifically members of the Actinobacteria , Chloroflexi and Bacteroidetes , became more readily detected in trampled than in untrampled biocrusts .
Replicate 16S rRNA T-RFLP profiles from trampled biocrusts at all three sites contained significantly more fragments ( n = 17 ) than those of untrampled biocrusts ( n6 ) and exhibited much higher variability among field replicates , indicating transition to an unstable disturbed state .
Despite the dramatic negative impacts of trampling on biocrust physical structure and composition , M. vaginatus could still be detected in surface soils after 10 years of annual trampling , suggesting the potential for biocrust re-formation over time .
Physical damage of biocrusts , in concert with changing temperature and precipitation patterns , has potential to alter performance of dryland ecosystems for decades .

[911] Greater efficiency of photosynthetic carbon fixation due to single amino-acid substitution

The C4-photosynthetic carbon cycle is an elaborated addition to the classical C3-photosynthetic pathway , which improves solar conversion efficiency .
The key enzyme in this pathway , phosphoenolpyruvate carboxylase , has evolved from an ancestral non-photosynthetic C3 phosphoenolpyruvate carboxylase .
During evolution , C4 phosphoenolpyruvate carboxylase has increased its kinetic efficiency and reduced its sensitivity towards the feedback inhibitors malate and aspartate .
An open question is the molecular basis of the shift in inhibitor tolerance .
Here we show that a single-point mutation is sufficient to account for the drastic differences between the inhibitor tolerances of C3 and C4 phosphoenolpyruvate carboxylases .
We solved high-resolution X-ray crystal structures of a C3 phosphoenolpyruvate carboxylase and a closely related C4 phosphoenolpyruvate carboxylase .
The comparison of both structures revealed that Arg884 supports tight inhibitor binding in the C3-type enzyme .
In the C4 phosphoenolpyruvate carboxylase isoform , this arginine is replaced by glycine .
The substitution reduces inhibitor affinity and enables the enzyme to participate in the C4 photosynthesis pathway .

[912] Emission pathways consistent with a 2 degreesC global temperature limit

In recent years , international climate policy has increasingly focused on limiting temperature rise , as opposed to achieving greenhouse-gas-concentration-related objectives .
The agreements reached at the United Nations Framework Convention on Climate Change conference in Cancun in 2010 recognize that countries should take urgent action to limit the increase in global average temperature to less than 2 degreesC relative to pre-industrial levels .
If this is to be achieved , policymakers need robust information about the amounts of future greenhouse-gas emissions that are consistent with such temperature limits .
This , in turn , requires an understanding of both the technical and economic implications of reducing emissions and the processes that link emissions to temperature .
Here we consider both of these aspects by reanalysing a large set of published emission scenarios from integrated assessment models in a risk-based climate modelling framework .
We find that in the set of scenarios with a ` likely ' ( greater than 66 % ) chance of staying below 2 degreesC , emissions peak between 2010 and 2020 and fall to a median level of 44 Gt of CO2 equivalent in 2020 ( compared with estimated median emissions across the scenario set of 48 Gt of CO2 equivalent in 2010 ) .
Our analysis confirms that if the mechanisms needed to enable an early peak in global emissions followed by steep reductions are not put in place , there is a significant risk that the 2 degreesC target will not be achieved .

[913] Long-term carbon loss in fragmented Neotropical forests

Tropical forests play an important role in the global carbon cycle , as they store a large amount of carbon ( C ) .
Tropical forest deforestation has been identified as a major source of CO2 emissions , though biomass loss due to fragmentation -- the creation of additional forest edges -- has been largely overlooked as an additional CO2 source .
Here , through the combination of remote sensing and knowledge on ecological processes , we present long-term carbon loss estimates due to fragmentation of Neotropical forests : within 10 years the Brazilian Atlantic Forest has lost 69 ( + / -14 ) Tg C , and the Amazon 599 ( + / -120 ) Tg C due to fragmentation alone .
For all tropical forests , we estimate emissions up to 0.2 Pg C y-1 or 9 to 24 % of the annual global C loss due to deforestation .
In conclusion , tropical forest fragmentation increases carbon loss and should be accounted for when attempting to understand the role of vegetation in the global carbon balance .

[914] Microbial endemism : does phosphorus limitation enhance speciation ?

There is increasing evidence for the existence of unique ecosystems that are dominated by locally adapted microbiota which harbour distinct lineages and biological capabilities , much like the macrobiota of Darwin 's Galapagos Islands .
As a primary example of such a system , we highlight key discoveries from the Cuatro Cienegas basin in Mexico .
We argue that high microbial endemism requires a combination of geographical isolation , long-term continuity and mechanisms for reducing the intensity of horizontal gene transfer ( HGT ) .
We also propose that strong phosphorus limitation has an important role in microbial diversification by reducing the intensity of HGT .

[915] Increases in terrestrially derived carbon stimulate organic carbon processing and CO2 emissions in boreal aquatic ecosystems

The concentrations of terrestrially derived dissolved organic carbon have been increasing throughout northern aquatic ecosystems in recent decades , but whether these shifts have an impact on aquatic carbon emissions at the continental scale depends on the potential for this terrestrial carbon to be converted into carbon dioxide .
Here , via the analysis of hundreds of boreal lakes , rivers and wetlands in Canada , we show that , contrary to conventional assumptions , the proportion of biologically degradable dissolved organic carbon remains constant and the photochemical degradability increases with terrestrial influence .
Thus , degradation potential increases with increasing amounts of terrestrial carbon .
Our results provide empirical evidence of a strong causal link between dissolved organic carbon concentrations and aquatic fluxes of carbon dioxide , mediated by the degradation of land-derived organic carbon in aquatic ecosystems .
Future shifts in the patterns of terrestrial dissolved organic carbon in inland waters thus have the potential to significantly increase aquatic carbon emissions across northern landscapes .

[916] Temperature regulation of virulence factors in the pathogen Vibrio coralliilyticus

Sea surface temperatures ( SST ) are rising because of global climate change .
As a result , pathogenic Vibrio species that infect humans and marine organisms during warmer summer months are of growing concern .
Coral reefs , in particular , are already experiencing unprecedented degradation worldwide due in part to infectious disease outbreaks and bleaching episodes that are exacerbated by increasing SST .
For example , Vibrio coralliilyticus , a globally distributed bacterium associated with multiple coral diseases , infects corals at temperatures above 27 degreesC .
The mechanisms underlying this temperature-dependent pathogenicity , however , are unknown .
In this study , we identify potential virulence mechanisms using whole genome sequencing of V. coralliilyticus ATCC ( American Type Culture Collection ) BAA-450 .
Furthermore , we demonstrate direct temperature regulation of numerous virulence factors using proteomic analysis and bioassays .
Virulence factors involved in motility , host degradation , secretion , antimicrobial resistance and transcriptional regulation are upregulated at the higher virulent temperature of 27 degreesC , concurrent with phenotypic changes in motility , antibiotic resistance , hemolysis , cytotoxicity and bioluminescence .
These results provide evidence that temperature regulates multiple virulence mechanisms in V. coralliilyticus , independent of abundance .
The ecological and biological significance of this temperature-dependent virulence response is reinforced by climate change models that predict tropical SST to consistently exceed 27 degreesC during the spring , summer and fall seasons .
We propose V. coralliilyticus as a model Gram-negative bacterium to study temperature-dependent pathogenicity in Vibrio-related diseases .

[917] Temperature thresholds for bacterial symbiosis with a sponge

The impact of elevated seawater temperature on bacterial communities within the marine sponge Rhopaloeides odorabile was assessed .
Sponges were exposed to temperatures ranging between 27 and 33 degreesC .
No differences in bacterial community composition or sponge health were detected in treatments between 27 and 31 degreesC .
In contrast , sponges exposed to 33 degreesC exhibited a complete loss of the primary cultivated symbiont within 24 h and cellular necrosis after 3 days .
Furthermore , denaturing gradient gel electrophoresis ( DGGE ) and clone sequence analysis detected a dramatic shift in bacterial community composition between 31 and 33 degreesC .
Within the first 24 h most of the DGGE bands detected in samples from 27 to 31 degreesC were absent from the 33 degreesC sponges whereas eight bands were detected exclusively in the 33 degreesC sponges .
The 16S rRNA sequencing revealed that most of the microbes from sponges exposed to 27-31 degreesC had highest homology to known sponge-associated bacteria .
In contrast , many of the microbes from sponges exposed to 33 degreesC were similar to sequences previously retrieved from diseased and bleached corals .
The 16S rRNA clone library analysis also detected a significant shift in bacterial community structure .
The 27 degreesC library was composed of Proteobacteria , Actinobacteria , Nitrospira , Acidobacteria and Chloroflexi whereas the 33 degreesC library contained sequences from the Proteobacteria , Bacteroidetes and Firmicutes .
The clear shifts in community composition at elevated temperatures can be attributed to the loss of symbionts and to the establishment of alien microbial populations including potential pathogens .
Breakdown of symbioses and stress in the sponge occurred at temperatures identical to those reported for coral bleaching , indicating that sponges may be similarly threatened by climate change .

[918] Physiology and behaviour of marine Thioploca

Among prokaryotes , the large vacuolated marine sulphur bacteria are unique in their ability to store , transport and metabolize significant quantities of sulphur , nitrogen , phosphorus and carbon compounds .
In this study , unresolved questions of metabolism , storage management and behaviour were addressed in laboratory experiments with Thioploca species collected on the continental shelf off Chile .
The Thioploca cells had an aerobic metabolism with a potential oxygen uptake rate of 1760 mumol O2 per dm3 biovolume per h , equivalent to 4.4 nmol O2 per min per mg protein .
When high ambient sulphide concentrations ( ~ 200 muM ) were present , a sulphide uptake of 6220 + / -2230 mumol H2S per dm3 per h , ( mean + / - s.e.m. , n = 4 ) was measured .
This sulphide uptake rate was six times higher than the oxidation rate of elemental sulphur by oxygen or nitrate , thus indicating a rapid sulphur accumulation by Thioploca .
Thioploca reduce nitrate to ammonium and we found that dinitrogen was not produced , neither through denitrification nor through anammox activity .
Unexpectedly , polyphosphate storage was not detectable by microautoradiography in physiological assays or by staining and microscopy .
Carbon dioxide fixation increased when nitrate and nitrite were externally available and when organic carbon was added to incubations .
Sulphide addition did not increase carbon dioxide fixation , indicating that Thioploca use excess of sulphide to rapidly accumulate sulphur rather than to accelerate growth .
This is interpreted as an adaptation to infrequent high sulphate reduction rates in the seabed .
The physiology and behaviour of Thioploca are summarized and the adaptations to an environment , dominated by infrequent oxygen availability and periods of high sulphide abundance , are discussed .

[919] Cenozoic climate change as a possible cause for the rise of the Andes

Causal links between the rise of a large mountain range and climate have often been considered to work in one direction , with significant uplift provoking climate change .
Here we propose a mechanism by which Cenozoic climate change could have caused the rise of the Andes .
Based on considerations of the force balance in the South American lithosphere , we suggest that the height of , and tectonics in , the Andes are strongly controlled both by shear stresses along the plate interface in the subduction zone and by buoyancy stress contrasts between the trench and highlands , and shear stresses in the subduction zone depend on the amount of subducted sediments .
We propose that the dynamics of subduction and mountain-building in this region are controlled by the processes of erosion and sediment deposition , and ultimately climate .
In central South America , climate-controlled sediment starvation would then cause high shear stress , focusing the plate boundary stresses that support the high Andes .

[920] Reconciliation of marine and terrestrial carbon isotope excursions based on changing atmospheric CO2 levels

Negative carbon isotope excursions measured in marine and terrestrial substrates indicate large-scale changes in the global carbon cycle , yet terrestrial substrates characteristically record a larger-amplitude carbon isotope excursion than marine substrates for a single event .
Here we reconcile this difference by accounting for the fundamental increase in carbon isotope fractionation by land plants in response to increasing atmospheric CO2 concentration ( pCO2 ) .
We show that for any change in pCO2 concentration ( DeltapCO2 ) , terrestrial and marine records can be used together to reconstruct background and maximum pCO2 levels across the carbon isotope excursion .
When applied to the carbon isotope excursion at the Palaeocene-Eocene boundary , we calculate pCO2 = 674-1 ,034 p.p.m.v. during the Late Palaeocene and 1,384-3 ,342 p.p.m.v. during the height of the carbon isotope excursion across all sources postulated for the carbon release .
This analysis demonstrates the need to account for changing pCO2 concentration when analysing large-scale changes in the carbon isotope composition of terrestrial substrates .

[921] Anthropogenic impact on Earth 's hydrological cycle

The global hydrological cycle is a key component of Earth 's climate system .
A significant amount of the energy the Earth receives from the Sun is redistributed around the world by the hydrological cycle in the form of latent heat flux .
Changes in the hydrological cycle have a direct impact on droughts , floods , water resources and ecosystem services .
Observed land precipitation and global river discharges do not show an increasing trend as might be expected in a warming world .
Here we show that this apparent discrepancy can be resolved when the effects of tropospheric aerosols are considered .
Analysing state-of-the-art climate model simulations , we find for the first time that there was a detectable weakening of the hydrological cycle between the 1950s and the 1980s , attributable to increased anthropogenic aerosols , after which the hydrological cycle recovered as a result of increasing greenhouse gas concentrations .
The net result of these two counter-acting effects is an insignificant trend in the global hydrological cycle , but the individual influence of each is substantial .
Reductions in air pollution have already shown an intensification in the past two decades and a further rapid increase in precipitation could be expected if the current trend continues .

[922] The effects of carbon dioxide and temperature on microRNA expression in Arabidopsis development

Elevated levels of CO2 and temperature can both affect plant growth and development , but the signalling pathways regulating these processes are still obscure .
MicroRNAs function to silence gene expression , and environmental stresses can alter their expressions .
Here we identify , using the small RNA-sequencing method , microRNAs that change significantly in expression by either doubling the atmospheric CO2 concentration or by increasing temperature 3-6 degreesC .
Notably , nearly all CO2-influenced microRNAs are affected inversely by elevated temperature .
Using the RNA-sequencing method , we determine strongly correlated expression changes between miR156/157 and miR172 , and their target transcription factors under elevated CO2 concentration .
Similar correlations are also found for microRNAs acting in auxin-signalling , stress responses and potential cell wall carbohydrate synthesis .
Our results demonstrate that both CO2 and temperature alter microRNA expression to affect Arabidopsis growth and development , and miR156/157 - and miR172-regulated transcriptional network might underlie the onset of early flowering induced by increasing CO2 .

[923] Variations in solar luminosity and their effect on the Earth 's climate

Variations in the Sun 's total energy output ( luminosity ) are caused by changing dark ( sunspot ) and bright structures on the solar disk during the 11-year sunspot cycle .
The variations measured from spacecraft since 1978 are too small to have contributed appreciably to accelerated global warming over the past 30 years .
In this Review , we show that detailed analysis of these small output variations has greatly advanced our understanding of solar luminosity change , and this new understanding indicates that brightening of the Sun is unlikely to have had a significant influence on global warming since the seventeenth century .
Additional climate forcing by changes in the Sun 's output of ultraviolet light , and of magnetized plasmas , can not be ruled out .
The suggested mechanisms are , however , too complex to evaluate meaningfully at present .

[924] Carbon availability triggers the decomposition of plant litter and assimilation of nitrogen by an ectomycorrhizal fungus

The majority of nitrogen in forest soils is found in organic matter-protein complexes .
Ectomycorrhizal fungi ( EMF ) are thought to have a key role in decomposing and mobilizing nitrogen from such complexes .
However , little is known about the mechanisms governing these processes , how they are regulated by the carbon in the host plant and the availability of more easily available forms of nitrogen sources .
Here we used spectroscopic analyses and transcriptome profiling to examine how the presence or absence of glucose and/or ammonium regulates decomposition of litter material and nitrogen mobilization by the ectomycorrhizal fungus Paxillus involutus .
We found that the assimilation of nitrogen and the decomposition of the litter material are triggered by the addition of glucose .
Glucose addition also resulted in upregulation of the expression of genes encoding enzymes involved in oxidative degradation of polysaccharides and polyphenols , peptidases , nitrogen transporters and enzymes in pathways of the nitrogen and carbon metabolism .
In contrast , the addition of ammonium to organic matter had relatively minor effects on the expression of transcripts and the decomposition of litter material , occurring only when glucose was present .
On the basis of spectroscopic analyses , three major types of chemical modifications of the litter material were observed , each correlated with the expression of specific sets of genes encoding extracellular enzymes .
Our data suggest that the expression of the decomposition and nitrogen assimilation processes of EMF can be tightly regulated by the host carbon supply and that the availability of inorganic nitrogen as such has limited effects on saprotrophic activities .

[925] High Arctic wetting reduces permafrost carbon feedbacks to climate warming

The carbon ( C ) balance of permafrost regions is predicted to be extremely sensitive to climatic changes .
Major uncertainties exist in the rate of permafrost thaw and associated C emissions ( 33-508 Pg C or 0.04-1 .69 degreesC by 2100 ; refs , ) and plant C uptake .
In the High Arctic , semi-deserts retain unique soil-plant-permafrost interactions and heterogeneous soil C pools ( > 12 Pg C ; ref . )
.
Owing to its coastal proximity , marked changes are expected for High Arctic tundra .
With declining summer sea-ice cover , these systems are simultaneously exposed to rising temperatures , increases in precipitation and permafrost degradation .
Here we show , using measurements of tundra-atmosphere C fluxes and soil C sources ( 14C ) at a long-term climate change experiment in northwest Greenland , that warming decreased the summer CO2 sink strength of semi-deserts by up to 55 % .
In contrast , warming combined with wetting increased the CO2 sink strength by an order of magnitude .
Further , wetting while relocating recently assimilated plant C into the deep soil decreased old C loss compared with the warming-only treatment .
Consequently , the High Arctic has the potential to remain a strong C sink even as the rest of the permafrost region transitions to a net C source as a result of future global warming .

[926] The effect of sea level on glacial Indo-Pacific climate

The Indo-Pacific warm pool -- the main source of heat and moisture to the global atmosphere -- plays a prominent role in tropical and global climate variability .
During the Last Glacial Maximum , temperatures within the warm pool were cooler than today and precipitation patterns were altered , but the mechanism responsible for these shifts remains unclear .
Here we use a synthesis of proxy reconstructions of warm pool hydrology and a multi-model ensemble of climate simulations to assess the drivers of these changes .
The proxy data suggest drier conditions throughout the centre of the warm pool and wetter conditions in the western Indian and Pacific oceans .
Only one model out of twelve simulates a pattern of hydroclimate change similar to our reconstructions , as measured by the Cohen 's kappa statistic .
Exposure of the Sunda Shelf by lower glacial sea level plays a key role in the hydrologic pattern simulated by this model , which results from changes in the Walker circulation driven by weakened convection over the warm pool .
We therefore conclude that on glacial-interglacial timescales , the growth and decay of ice sheets exert a first-order influence on tropical climate through the associated changes in global sea level .

[927] Global pattern of trends in streamflow and water availability in a changing climate

Water availability on the continents is important for human health , economic activity , ecosystem function and geophysical processes .
Because the saturation vapour pressure of water in air is highly sensitive to temperature , perturbations in the global water cycle are expected to accompany climate warming .
Regional patterns of warming-induced changes in surface hydroclimate are complex and less certain than those in temperature , however , with both regional increases and decreases expected in precipitation and runoff .
Here we show that an ensemble of 12 climate models exhibits qualitative and statistically significant skill in simulating observed regional patterns of twentieth-century multidecadal changes in streamflow .
These models project 10-40 % increases in runoff in eastern equatorial Africa , the La Plata basin and high-latitude North America and Eurasia , and 10-30 % decreases in runoff in southern Africa , southern Europe , the Middle East and mid-latitude western North America by the year 2050 .
Such changes in sustainable water availability would have considerable regional-scale consequences for economies as well as ecosystems .

[928] Enhanced warming over the global subtropical western boundary currents

Subtropical western boundary currents are warm , fast-flowing currents that form on the western side of ocean basins .
They carry warm tropical water to the mid-latitudes and vent large amounts of heat and moisture to the atmosphere along their paths , affecting atmospheric jet streams and mid-latitude storms , as well as ocean carbon uptake .
The possibility that these highly energetic currents might change under greenhouse-gas forcing has raised significant concerns , but detecting such changes is challenging owing to limited observations .
Here , using reconstructed sea surface temperature datasets and century-long ocean and atmosphere reanalysis products , we find that the post-1900 surface ocean warming rate over the path of these currents is two to three times faster than the global mean surface ocean warming rate .
The accelerated warming is associated with a synchronous poleward shift and/or intensification of global subtropical western boundary currents in conjunction with a systematic change in winds over both hemispheres .
This enhanced warming may reduce the ability of the oceans to absorb anthropogenic carbon dioxide over these regions .
However , uncertainties in detection and attribution of these warming trends remain , pointing to a need for a long-term monitoring network of the global western boundary currents and their extensions .

[929] Harnessing nature to help people adapt to climate change

Adapting to climate change is among the biggest challenges humanity faces in the next century .
An overwhelming focus of adaptation strategies to reduce climate change-related hazards has been on hard-engineering structures such as sea walls , irrigation infrastructure and dams .
Closer attention to a broader spectrum of adaptation options is urgently needed .
In particular , ecosystem-based adaptation approaches provide flexible , cost-effective and broadly applicable alternatives for buffering the impacts of climate change , while overcoming many drawbacks of hard infrastructure .
As such , they are a critical tool at adaptation planners ' disposal for tackling the threats that climate change poses to peoples ' lives and livelihoods .

[930] Relative outcomes of climate change mitigation related to global temperature versus sea-level rise

There is a common perception that , if human societies make the significant adjustments necessary to substantively cut emissions of greenhouse gases , global temperature increases could be stabilized , and the most dangerous consequences of climate change could be avoided .
Here we show results from global coupled climate model simulations with the new representative concentration pathway mitigation scenarios to 2300 to illustrate that , with aggressive mitigation in two of the scenarios , globally averaged temperature increase indeed could be stabilized either below 2 degreesC or near 3 degreesC above pre-industrial values .
However , even as temperatures stabilize , sea level would continue to rise .
With little mitigation , future sea-level rise would be large and continue unabated for centuries .
Though sea-level rise can not be stopped for at least the next several hundred years , with aggressive mitigation it can be slowed down , and this would buy time for adaptation measures to be adopted .

[931] Inhibition of the positive snow-albedo feedback by precipitation in interior Antarctica

The high albedo of snow largely determines the climate of polar regions by controlling energy absorption at the surface .
In Antarctica , where light-absorbing impurities are few , snow albedo is mostly determined by the size of snow grains .
Snow metamorphism , the process of grain coarsening , occurs at a rate that increases with temperature , so that snow albedo generally decreases as temperature increases .
This increases energy absorption at the surface and atmospheric warming ensues , leading to a positive snow-albedo feedback .
Here we use passive microwave satellite data and model outputs to show that this feedback is inhibited by small increases in precipitation .
This is explained by the fact that grain coarsening in Antarctica is more sensitive to the deposition of small grains on the surface than previously assumed .
We deduce that projected future increases in precipitation can increase snow albedo by 0.4 % on average during the twenty-first century and hence overcompensate the expected albedo decrease owing to warming ( 0.3 % for 3 degreesC ) .
Albedo-change projections in the Coupled Model Intercomparison Projects 3 and 5 do not reach a consensus on the sign and amplitude of this compensation , showing the need for a finer representation of the impact of precipitation on albedo in Antarctica .

[932] Urbanization effects on tree growth in the vicinity of New York City

Plants in urban ecosystems are exposed to many pollutants and higher temperatures , CO2 and nitrogen deposition than plants in rural areas .
Although each factor has a detrimental or beneficial influence on plant growth , the net effect of all factors and the key driving variables are unknown .
We grew the same cottonwood clone in urban and rural sites and found that urban plant biomass was double that of rural sites .
Using soil transplants , nutrient budgets , chamber experiments and multiple regression analyses , we show that soils , temperature , CO2 , nutrient deposition , urban air pollutants and microclimatic variables could not account for increased growth in the city .
Rather , higher rural ozone ( O3 ) exposures reduced growth at rural sites .
Urban precursors fuel the reactions of O3 formation , but NOx scavenging reactions resulted in lower cumulative urban O3 exposures compared to agricultural and forested sites throughout the northeastern USA .
Our study shows the overriding effect of O3 despite a diversity of altered environmental factors , reveals ` footprints ' of lower cumulative urban O3 exposures amidst a background of higher regional exposures , and shows a greater adverse effect of urban pollutant emissions beyond the urban core .

[933] Extended leaf phenology and the autumn niche in deciduous forest invasions

The phenology of growth in temperate deciduous forests , including the timing of leaf emergence and senescence , has strong control over ecosystem properties such as productivity and nutrient cycling , and has an important role in the carbon economy of understory plants .
Extended leaf phenology , whereby understory species assimilate carbon in early spring before canopy closure or in late autumn after canopy fall , has been identified as a key feature of many forest species invasions , but it remains unclear whether there are systematic differences in the growth phenology of native and invasive forest species or whether invaders are more responsive to warming trends that have lengthened the duration of spring or autumn growth .
Here , in a 3-year monitoring study of 43 native and 30 non-native shrub and liana species common to deciduous forests in the eastern United States , I show that extended autumn leaf phenology is a common attribute of eastern US forest invasions , where non-native species are extending the autumn growing season by an average of 4 weeks compared with natives .
In contrast , there was no consistent evidence that non-natives as a group show earlier spring growth phenology , and non-natives were not better able to track interannual variation in spring temperatures .
Seasonal leaf production and photosynthetic data suggest that most non-native species capture a significant proportion of their annual carbon assimilate after canopy leaf fall , a behaviour that was virtually absent in natives and consistent across five phylogenetic groups .
Pronounced differences in how native and non-native understory species use pre - and post-canopy environments suggest eastern US invaders are driving a seasonal redistribution of forest productivity that may rival climate change in its impact on forest processes .

[934] Wetter then drier in some tropical areas

To the Editor -- Projected changes in precipitation are generally assumed to be monotonic with respect to global temperature changes : rainfall will either increase or decrease as the climate warms .
However , using an example in South America , we demonstrate that , under a high emissions scenario , rainfall changes in some regions can actually be non-monotonic , which has important implications for biodiversity , the carbon cycle and long-term climate policy .

[935] ` Candidatus Accumulibacter ' gene expression in response to dynamic EBPR conditions

Enhanced biological phosphorus removal ( EBPR ) activated sludge communities enriched in ` Candidatus Accumulibacter ' relatives are widely used in wastewater treatment , but much remains to be learned about molecular-level controls on the EBPR process .
The expression of genes found in the carbon and polyphosphate metabolic pathways in Accumulibacter was investigated using reverse transcription quantitative PCR .
During a normal anaerobic/aerobic EBPR cycle , gene expression exhibited a dynamic change in response to external acetate , oxygen , phosphate concentrations and probably internal chemical pools .
Anaerobic acetate addition induced expression of genes associated with the methylmalonyl-CoA pathway enabling the split mode of the tricarboxylic acid ( TCA ) cycle .
Components of the full TCA cycle were induced after the switch to aerobic conditions .
The induction of a key gene in the glyoxylate shunt pathway was observed under both anaerobic and aerobic conditions , with a higher induction by aeration .
Polyphosphate kinase 1 from Accumulibacter was expressed , but did not appear to be regulated by phosphate limitation .
To understand how Accumulibacter responds to disturbed electron donor and acceptor conditions , we perturbed the process by adding acetate aerobically .
When high concentrations of oxygen were present simultaneously with acetate , phosphate-release was almost completely inhibited , and polyphosphate kinase 1 transcript abundance decreased .
Genes associated with the methylmalonyl-CoA pathway were repressed and genes associated with the aerobic TCA cycle exhibited higher expression under this perturbation , suggesting that more acetyl-CoA was metabolized through the TCA cycle .
These findings suggest that several genes involved in EBPR are tightly regulated at the transcriptional level .

[936] Snowfall increase in coastal East Antarctica linked with southwest Western Australian drought

The southwest corner of Western Australia has been subject to a serious drought in recent decades .
A range of factors , such as natural variability and changes in land use , ocean temperatures and atmospheric circulation , have been implicated in this drought , but the ultimate cause and the relative importance of the various factors remain unclear .
Here we report a significant inverse correlation between the records of precipitation at Law Dome , East Antarctica and southwest Western Australia over the instrumental period , including the most recent decades .
This relationship accounts for up to 40 % of the variability on interannual to decadal timescales , and seems to be driven by the meridional circulation south of Australia that simultaneously produces a northward flow of relatively cool , dry air to southwest Western Australia and a southward flow of warm , moist air to East Antarctica .
This pattern of meridional flow is consistent with some projections of circulation changes arising from anthropogenic climate change .
The precipitation anomaly of the past few decades in Law Dome is the largest in 750 years , and lies outside the range of variability for the record as a whole , suggesting that the drought in Western Australia may be similarly unusual .

[937] Seabird diets provide early warning of sardine fishery declines in the Gulf of California

Small pelagic fisheries show wide fluctuations , generally attributed to oceanographic anomalies .
Most data on these fisheries come from landings , often reporting sustained catches-per-unit-effort ( CPUEs ) until a decline occurs .
Fishery-independent data are important as management tools .
In this study we show that the proportions of Pacific Sardine and Northern Anchovy in the diet of three seabird species ( California Brown Pelicans , Heermann 's Gulls , and Elegant Terns ) nesting in spring in the Gulf of California show significant relationships with CPUEs during the following season in gulls and terns , or during the same season in pelicans .
As sardine availability for seabirds declines , CPUEs remain high until the fishery falls , one or two seasons later .
A declining proportion of sardines in the seabirds ' diet , combined with the status of the Pacific warm-phase anomaly ( El Nino ) , give a reliable forecast of diminishing CPUEs and signals the need to reduce fishing efforts in the ensuing season .

[938] Dynamic changes in saliva after acute mental stress

Stress-related variations of fluoride concentration in supernatant saliva and salivary sediment , salivary cortisol , total protein and pH after acute mental stress were assessed .
The hypothesis was that stress reactions have no influence on these parameters .
Thirty-four male students were distributed into two groups : first received the stress exposure followed by the same protocol two weeks later but without stress exposure , second underwent the protocol without stress exposure followed by the stress exposure two weeks later .
The stressor was a public speech followed by tooth brushing .
Saliva was collected before , immediately after stress induction and immediately , at 10 , 30 and 120 min .
after tooth brushing .
Cortisol concentrations , total protein , intraoral pH , and fluoride content in saliva were measured .
The data were analyzed statistically .
Salivary sediment was ca 4.33 % by weight of whole unstimulated saliva .
Fluoride bioavailability was higher in salivary sediment than in supernatant saliva .
The weight and fluoride concentration was not altered during 2 hours after stress exposure .
After a public speech , the salivary cortisol concentration significantly increased after 20 minutes compared to the baseline .
The salivary protein concentration and pH also increased .
Public speaking influences protein concentration and salivary pH but does not alter the fluoride concentration of saliva .

[939] Alternating Si and Fe deposition caused by temperature fluctuations in Precambrian oceans

Precambrian banded iron formations provide an extensive archive of pivotal environmental changes and the evolution of biological processes on early Earth .
The formations are characterized by bands ranging from micrometre - to metre-scale layers of alternating iron - and silica-rich minerals .
However , the nature of the mechanisms of layer formation is unknown .
To properly evaluate this archive , the physical , chemical and/or biological triggers for the deposition of both the iron - and silica-rich layers , and crucially their alternate banding , must be identified .
Here we use laboratory experiments and geochemical modelling to study the potential for a microbial mechanism in the formation of alternating iron-silica bands .
We find that the rate of biogenic iron ( III ) mineral formation by iron-oxidizing microbes reaches a maximum between 20 and 25 degreesC .
Decreasing or increasing water temperatures slow microbial iron mineral formation while promoting abiotic silica precipitation .
We suggest that natural fluctuations in the temperature of the ocean photic zone during the period when banded iron formations were deposited could have led to the primary layering observed in these formations by successive cycles of microbially catalysed iron ( III ) mineral deposition and abiotic silica precipitation .

[940] Reversal in competitive dominance of a toxic versus non-toxic cyanobacterium in response to rising CO2

Climate change scenarios predict a doubling of the atmospheric CO2 concentration by the end of this century .
Yet , how rising CO2 will affect the species composition of aquatic microbial communities is still largely an open question .
In this study , we develop a resource competition model to investigate competition for dissolved inorganic carbon in dense algal blooms .
The model predicts how dynamic changes in carbon chemistry , pH and light conditions during bloom development feed back on competing phytoplankton species .
We test the model predictions in chemostat experiments with monocultures and mixtures of a toxic and non-toxic strain of the freshwater cyanobacterium Microcystis aeruginosa .
The toxic strain was able to reduce dissolved CO2 to lower concentrations than the non-toxic strain , and became dominant in competition at low CO2 levels .
Conversely , the non-toxic strain could grow at lower light levels , and became dominant in competition at high CO2 levels but low light availability .
The model captured the observed reversal in competitive dominance , and was quantitatively in good agreement with the results of the competition experiments .
To assess whether microcystins might have a role in this reversal of competitive dominance , we performed further competition experiments with the wild-type strain M. aeruginosa PCC 7806 and its mcyB mutant impaired in microcystin production .
The microcystin-producing wild type had a strong selective advantage at low CO2 levels but not at high CO2 levels .
Our results thus demonstrate both in theory and experiment that rising CO2 levels can alter the community composition and toxicity of harmful algal blooms .

[941] Biofuels from crop residue can reduce soil carbon and increase CO2 emissions

Removal of corn residue for biofuels can decrease soil organic carbon ( SOC ; refs , ) and increase CO2 emissions because residue C in biofuels is oxidized to CO2 at a faster rate than when added to soil .
Net CO2 emissions from residue removal are not adequately characterized in biofuel life cycle assessment ( LCA ; refs , , ) .
Here we used a model to estimate CO2 emissions from corn residue removal across the US Corn Belt at 580 million geospatial cells .
To test the SOC model , we compared estimated daily CO2 emissions from corn residue and soil with CO2 emissions measured using eddy covariance , with 12 % average error over nine years .
The model estimated residue removal of 6 Mg per ha-1 yr-1 over five to ten years could decrease regional net SOC by an average of 0.47-0 .66 Mg C ha-1 yr-1 .
These emissions add an average of 50-70 g CO2 per megajoule of biofuel ( range 30-90 ) and are insensitive to the fraction of residue removed .
Unless lost C is replaced , life cycle emissions will probably exceed the US legislative mandate of 60 % reduction in greenhouse gas ( GHG ) emissions compared with gasoline .

[942] Caenorhabditis elegans dauers need LKB1/AMPK to ration lipid reserves and ensure long-term survival

Many organisms can enter a dormant state or diapause to survive harsh environmental conditions for extended durations .
When Caenorhabditis elegans larvae enter dauer they arrest feeding but remain active and motile , yet become stress-resistant , extremely long-lived and non-ageing .
Entry into dauer is associated with a reduction in insulin-like signalling , the accumulation of nutritive resources and a concomitant global change in metabolism , yet the precise molecular and physiological processes that enable long-term survival in the absence of caloric intake remain largely unknown .
We show here that C. elegans larvae that lack LKB1/AMPK ( AMP-activated protein kinase ) signalling enter dauer normally , but then rapidly consume their stored energy and prematurely expire following vital organ failure .
We found that this signalling pathway acts in adipose-like tissues to downregulate triglyceride hydrolysis so that these lipid reserves are rationed to last the entire duration of the arrest .
Indeed , the downregulation of adipose triglyceride lipase ( ATGL-1 ) activity suppresses both the rapid depletion of stored lipids and reduced life span of AMPK mutant dauers , while AMPK directly phosphorylates ATGL-1 .
Finally , we show that the slow release of energy during dauer is critical for appropriate long-term osmoregulation , which fails as triglyceride resources become depleted .
These mechanisms may be essential for survival through diapause , hibernation , or long-term fasting in diverse organisms and may also underlie AMPK-dependent life span extension .

[943] The impacts of climate change on water resources and agriculture in China

China is the world 's most populous country and a major emitter of greenhouse gases .
Consequently , much research has focused on China 's influence on climate change but somewhat less has been written about the impact of climate change on China .
China experienced explosive economic growth in recent decades , but with only 7 % of the world 's arable land available to feed 22 % of the world 's population , China 's economy may be vulnerable to climate change itself .
We find , however , that notwithstanding the clear warming that has occurred in China in recent decades , current understanding does not allow a clear assessment of the impact of anthropogenic climate change on China 's water resources and agriculture and therefore China 's ability to feed its people .
To reach a more definitive conclusion , future work must improve regional climate simulations -- especially of precipitation -- and develop a better understanding of the managed and unmanaged responses of crops to changes in climate , diseases , pests and atmospheric constituents .

[944] C4 grasses prosper as carbon dioxide eliminates desiccation in warmed semi-arid grassland

Global warming is predicted to induce desiccation in many world regions through increases in evaporative demand .
Rising CO2 may counter that trend by improving plant water-use efficiency .
However , it is not clear how important this CO2-enhanced water use efficiency might be in offsetting warming-induced desiccation because higher CO2 also leads to higher plant biomass , and therefore greater transpirational surface .
Furthermore , although warming is predicted to favour warm-season , C4 grasses , rising CO2 should favour C3 , or cool-season plants .
Here we show in a semi-arid grassland that elevated CO2 can completely reverse the desiccating effects of moderate warming .
Although enrichment of air to 600 p.p.m.v. CO2 increased soil water content ( SWC ) , 1.5 / 3.0 degreesC day/night warming resulted in desiccation , such that combined CO2 enrichment and warming had no effect on SWC relative to control plots .
As predicted , elevated CO2 favoured C3 grasses and enhanced stand productivity , whereas warming favoured C4 grasses .
Combined warming and CO2 enrichment stimulated above-ground growth of C4 grasses in 2 of 3 years when soil moisture most limited plant productivity .
The results indicate that in a warmer , CO2-enriched world , both SWC and productivity in semi-arid grasslands may be higher than previously expected .

[945] Limits in detecting acceleration of ice sheet mass loss due to climate variability

The Greenland and Antarctic ice sheets have been reported to be losing mass at accelerating rates .
If sustained , this accelerating mass loss will result in a global mean sea-level rise by the year 2100 that is approximately 43 cm greater than if a linear trend is assumed .
However , at present there is no scientific consensus on whether these reported accelerations result from variability inherent to the ice-sheet-climate system , or reflect long-term changes and thus permit extrapolation to the future .
Here we compare mass loss trends and accelerations in satellite data collected between January 2003 and September 2012 from the Gravity Recovery and Climate Experiment to long-term mass balance time series from a regional surface mass balance model forced by re-analysis data .
We find that the record length of spaceborne gravity observations is too short at present to meaningfully separate long-term accelerations from short-term ice sheet variability .
We also find that the detection threshold of mass loss acceleration depends on record length : to detect an acceleration at an accuracy within + / -10 Gt yr-2 , a period of 10 years or more of observations is required for Antarctica and about 20 years for Greenland .
Therefore , climate variability adds uncertainty to extrapolations of future mass loss and sea-level rise , underscoring the need for continuous long-term satellite monitoring .

[946] Atmospheric carbon dioxide linked with Mesozoic and early Cenozoic climate change

The relationship between atmospheric carbon dioxide ( CO2 ) and climate in the Quaternary period has been extensively investigated , but the role of CO2 in temperature changes during the rest of Earth 's history is less clear .
The range of geological evidence for cool periods during the high CO2 Mesozoic ` greenhouse world ' of high atmospheric CO2 concentrations , indicated by models and fossil soils , has been particularly difficult to interpret .
Here , we present high-resolution records of Mesozoic and early Cenozoic atmospheric CO2 concentrations from a combination of carbon-isotope analyses of non-vascular plant ( bryophyte ) fossils and theoretical modelling .
These records indicate that atmospheric CO2 rose from ~ 420 p.p.m.v. in the Triassic period ( about 200 million years ago ) to a peak of ~ 1,130 p.p.m.v. in the Middle Cretaceous ( about 100 million years ago ) .
Atmospheric CO2 levels then declined to ~ 680 p.p.m.v. by 60 million years ago .
Time-series comparisons show that these variations coincide with large Mesozoic climate shifts , in contrast to earlier suggestions of climate-CO2 decoupling during this interval .
These reconstructed atmospheric CO2 concentrations drop below the simulated threshold for the initiation of glaciations on several occasions and therefore help explain the occurrence of cold intervals in a ` greenhouse world ' .

[947] Effects of macrophyte species richness on wetland ecosystem functioning and services

Wetlands provide many important ecosystem services to human society , which may depend on how plant diversity influences biomass production and nutrient retention .
Vascular aquatic plant diversity may not necessarily enhance wetland ecosystem functioning , however , because competition among these plant species can be strong , often resulting in the local dominance of a single species .
Here we have manipulated the species richness of rooted , submerged aquatic plant ( macrophyte ) communities in experimental wetland mesocosms .
We found higher algal and total plant ( algal plus macrophyte ) biomass , as well as lower loss of total phosphorus , in mesocosms with a greater richness of macrophyte species .
Greater plant biomass resulted from a sampling effect ; that is , the increased chance in species mixtures that algal production would be facilitated by the presence of a less competitive species -- in this case , crisped pondweed .
Lower losses of total phosphorus resulted from the greater chance in species mixtures of a high algal biomass and the presence of sago pondweed , which physically filter particulate phosphorus from the water .
These indirect and direct effects of macrophyte species richness on algal production , total plant biomass and phosphorus loss suggest that management practices that maintain macrophyte diversity may enhance the functioning and associated services of wetland ecosystems .

[948] Metabolic activity of subterranean microbial communities in deep granitic groundwater supplemented with methane and H2

It was previously concluded that opposing gradients of sulphate and methane , observations of 16S ribosomal DNA sequences displaying great similarity to those of anaerobic methane-oxidizing Archaea and a peak in sulphide concentration in groundwater from a depth of 250-350 m in Olkiluoto , Finland , indicated proper conditions for methane oxidation with sulphate .
In the present research , pressure-resistant , gas-tight circulating systems were constructed to enable the investigation of attached and unattached anaerobic microbial populations from a depth of 327 m in Olkiluoto under in situ pressure ( 2.4 MPa ) , diversity , dissolved gas and chemistry conditions .
Three parallel flow cell cabinets were configured to allow observation of the influence on microbial metabolic activity of 11 mM methane , 11 mM methane plus 10 mM H2 or 2.1 mM O2 plus 7.9 mM N2 ( that is , air ) .
The concentrations of these gases and of organic acids and carbon , sulphur chemistry , pH and Eh , ATP , numbers of cultivable micro-organisms , and total numbers of cells and bacteriophages were subsequently recorded under batch conditions for 105 days .
The system containing H2 and methane displayed microbial reduction of 0.7 mM sulphate to sulphide , whereas the system containing only methane resulted in 0.2 mM reduced sulphate .
The system containing added air became inhibited and displayed no signs of microbial activity .
Added H2 and methane induced increasing numbers of lysogenic bacteriophages per cell .
It appears likely that a microbial anaerobic methane-oxidizing process coupled to acetate formation and sulphate reduction may be ongoing in aquifers at a depth of 250-350 m in Olkiluoto .

[949] Cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode

Oceanic anoxic events ( OAEs ) were episodes of widespread marine anoxia during which large amounts of organic carbon were buried on the ocean floor under oxygen-deficient bottom waters .
OAE2 , occurring at the Cenomanian/Turonian boundary ( about 93.5 Myr ago ) , is the most widespread and best defined OAE of the mid-Cretaceous .
Although the enhanced burial of organic matter can be explained either through increased primary productivity or enhanced preservation scenarios , the actual trigger mechanism , corresponding closely to the onset of these episodes of increased carbon sequestration , has not been clearly identified .
It has been postulated that large-scale magmatic activity initially triggered OAE2 ( refs 4 , 5 ) , but a direct proxy of magmatism preserved in the sedimentary record coinciding closely with the onset of OAE2 has not yet been found .
Here we report seawater osmium isotope ratios in organic-rich sediments from two distant sites .
We find that at both study sites the marine osmium isotope record changes abruptly just at or before the onset of OAE2 .
Using a simple two-component mixing equation , we calculate that over 97 per cent of the total osmium content in contemporaneous seawater at both sites is magmatic in origin , a ~ 30-50-fold increase relative to pre-OAE conditions .
Furthermore , the magmatic osmium isotope signal appears slightly before the OAE2 -- as indicated by carbon isotope ratios -- suggesting a time-lag of up to ~ 23 kyr between magmatism and the onset of significant organic carbon burial , which may reflect the reaction time of the global ocean system .
Our marine osmium isotope data are indicative of a widespread magmatic pulse at the onset of OAE2 , which may have triggered the subsequent deposition of large amounts of organic matter .

[950] Twenty-first-century projections of North Atlantic tropical storms from CMIP5 models

Assessing potential changes in North Atlantic ( NA ) tropical storm ( TS ) activity this century is of paramount societal and economic significance , and the topic of intense scientific research .
We explore projections of NA TS changes over the twenty-first century by applying a statistical downscaling methodology to a suite of experiments with the latest state-of-the-art global coupled climate models .
We also apply a methodology to partition the dominant sources of uncertainty in the TS projections .
We find that over the first half of the twenty-first century radiative forcing changes act to increase NA TS frequency ; this increase arises from radiative forcings other than increasing CO2 ( probably aerosols ) .
However , NA TS trends over the entire twenty-first century are of ambiguous sign .
We find that for NA TS frequency , in contrast to sea surface temperature ( SST ) , the largest uncertainties are driven by the chaotic nature of the climate system and by the climate response to radiative forcing .
These results highlight the need to better understand the processes controlling patterns of SST change in response to radiative forcing and internal climate variability to constrain estimates of future NA TS activity .
Coordinated experiments isolating forcing agents in projections should improve our understanding , and would enable better assessment of future TS activity .

[951] Changing spatial structure of the thermohaline circulation in response to atmospheric CO2 forcing in a climate model

The heat transported northwards by the North Atlantic thermohaline circulation warms the climate of western Europe .
Previous model studies have suggested that the circulation is sensitive to increases in atmospheric greenhouse-gas concentrations , but such models have been criticised for the use of unphysical ` flux adjustments ' ( artificial corrections that keep the model from drifting to unrealistic states ) , and for their inability to simulate deep-water formation both north and south of the Greenland-Iceland-Scotland ridge , as seen in observations , .
Here we present simulations of today 's thermohaline circulation using a coupled ocean-atmosphere general circulation model without flux adjustments .
These simulations compare well with the observed thermohaline circulation , including the formation of deep water on each side of the Greenland-Iceland-Scotland ridge .
The model responds to forcing with increasing atmospheric greenhouse-gas concentrations by a collapse of the circulation and convection in the Labrador Sea , while the deep-water formation north of the ridge remains stable .
These changes are similar intwo simulations with different rates of increase of CO2 concentrations .
The effects of increasing atmospheric greenhouse-gas concentrations that we simulate are potentially observable , suggesting that it is possible to set up an oceanic monitoring system for the detection of anthropogenic influence on ocean circulation .

[952] Graphene oxide amplifies the phytotoxicity of arsenic in wheat

Graphene oxide ( GO ) is widely used in various fields and is considered to be relatively biocompatible .
Herein , `` indirect '' nanotoxicity is first defined as toxic amplification of toxicants or pollutants by nanomaterials .
This work revealed that GO greatly amplifies the phytotoxicity of arsenic ( As ) , a widespread contaminant , in wheat , for example , causing a decrease in biomass and root numbers and increasing oxidative stress , which are thought to be regulated by its metabolisms .
Compared with As or GO alone , GO combined with As inhibited the metabolism of carbohydrates , enhanced amino acid and secondary metabolism and disrupted fatty acid metabolism and the urea cycle .
GO also triggered damage to cellular structures and electrolyte leakage and enhanced the uptake of GO and As .
Co-transport of GO-loading As and transformation of As ( V ) to high-toxicity As ( III ) by GO were observed .
The generation of dimethylarsinate , produced from the detoxification of inorganic As , was inhibited by GO in plants .
GO also regulated phosphate transporter gene expression and arsenate reductase activity to influence the uptake and transformation of As , respectively .
Moreover , the above effects of GO were concentration dependent .
Given the widespread exposure to As in agriculture , the indirect nanotoxicity of GO should be carefully considered in food safety .

[953] Simulated resilience of tropical rainforests to CO2-induced climate change

How tropical forest carbon stocks might alter in response to changes in climate and atmospheric composition is uncertain .
However , assessing potential future carbon loss from tropical forests is important for evaluating the efficacy of programmes for reducing emissions from deforestation and degradation .
Uncertainties are associated with different carbon stock responses in models with different representations of vegetation processes on the one hand , and differences in projected changes in temperature and precipitation patterns on the other hand .
Here we present a systematic exploration of these sources of uncertainty , along with uncertainty arising from different emissions scenarios for all three main tropical forest regions : the Americas ( that is , Amazonia and Central America ) , Africa and Asia .
Using simulations with 22 climate models and the MOSES-TRIFFID land surface scheme , we find that only in one of the simulations are tropical forests projected to lose biomass by the end of the twenty-first century -- and then only for the Americas .
When comparing with alternative models of plant physiological processes , we find that the largest uncertainties are associated with plant physiological responses , and then with future emissions scenarios .
Uncertainties from differences in the climate projections are significantly smaller .
Despite the considerable uncertainties , we conclude that there is evidence of forest resilience for all three regions .

[954] Decoupling of soil nutrient cycles as a function of aridity in global drylands

The biogeochemical cycles of carbon ( C ) , nitrogen ( N ) and phosphorus ( P ) are interlinked by primary production , respiration and decomposition in terrestrial ecosystems .
It has been suggested that the C , N and P cycles could become uncoupled under rapid climate change because of the different degrees of control exerted on the supply of these elements by biological and geochemical processes .
Climatic controls on biogeochemical cycles are particularly relevant in arid , semi-arid and dry sub-humid ecosystems ( drylands ) because their biological activity is mainly driven by water availability .
The increase in aridity predicted for the twenty-first century in many drylands worldwide may therefore threaten the balance between these cycles , differentially affecting the availability of essential nutrients .
Here we evaluate how aridity affects the balance between C , N and P in soils collected from 224 dryland sites from all continents except Antarctica .
We find a negative effect of aridity on the concentration of soil organic C and total N , but a positive effect on the concentration of inorganic P. Aridity is negatively related to plant cover , which may favour the dominance of physical processes such as rock weathering , a major source of P to ecosystems , over biological processes that provide more C and N , such as litter decomposition .
Our findings suggest that any predicted increase in aridity with climate change will probably reduce the concentrations of N and C in global drylands , but increase that of P .
These changes would uncouple the C , N and P cycles in drylands and could negatively affect the provision of key services provided by these ecosystems .

[955] Ras , PI ( 3 ) K and mTOR signalling controls tumour cell growth

All eukaryotic cells coordinate cell growth with the availability of nutrients in their environment .
The mTOR protein kinase has emerged as a critical growth-control node , receiving stimulatory signals from Ras and phosphatidylinositol-3-OH kinase ( PI ( 3 ) K ) downstream from growth factors , as well as nutrient inputs in the form of amino-acid , glucose and oxygen availability .
Notably , components of the Ras and PI ( 3 ) K signalling pathways are mutated in most human cancers .
The preponderance of mutations in these interconnected pathways suggests that the loss of growth-control checkpoints and promotion of cell survival in nutrient-limited conditions may be an obligate event in tumorigenesis .

[956] Limited potential of no-till agriculture for climate change mitigation

The Emissions Gap Report 2013 from the United Nations Environment Programme restates the claim that changing to no-till practices in agriculture , as an alternative to conventional tillage , causes an accumulation of organic carbon in soil , thus mitigating climate change through carbon sequestration .
But these claims ignore a large body of experimental evidence showing that the quantity of additional organic carbon in soil under no-till is relatively small : in large part apparent increases result from an altered depth distribution .
The larger concentration near the surface in no-till is generally beneficial for soil properties that often , though not always , translate into improved crop growth .
In many regions where no-till is practised it is common for soil to be cultivated conventionally every few years for a range of agronomic reasons , so any soil carbon benefit is then lost .
We argue that no-till is beneficial for soil quality and adaptation of agriculture to climate change , but its role in mitigation is widely overstated .

[957] A universal transition in the robustness of evolving open systems

Can the structure of a system that consists of many elements interacting with each other grow in complexity when new elements are added to it ?
This is an essential question for understanding various real , open , complex systems , such as living organisms , ecosystems , and social systems .
Using a very simple model , this study demonstrates that such systems can grow only when the elements have a moderate number of interactions on average .
This behaviour comes from a balance between two opposing effects : although an increase in the number of interactions makes each individual element more robust against disturbances , it also increases the net impact of the loss of any element on the system .

[958] Link between Antarctic ozone depletion and summer warming over southern Africa

The notable rise in surface air temperatures over southern Africa over the past two decades is thought to largely result from the human-induced increase in atmospheric greenhouse gas concentrations .
In addition , the loss of stratospheric ozone over Antarctica is thought to have had a significant impact on tropospheric circulation , and hence climate , in the Southern Hemisphere summer , by favouring the positive phase of the Southern Annular Mode .
Here , we use reanalysis data to compare the climate of southern Africa before and after the development of the large ozone hole , and investigate possible links between the development of the Antarctic ozone hole and summer warming in the region , defining 1970-1993 as the pre-ozone hole era , and 1993-2011 as the large ozone hole era .
We find that the ozone-induced shift in the polarity of the Southern Annular Mode after 1993 coincided with an intensification of the Angola Low , a continental low pressure system that normally develops in austral summer and is mostly located over Angola .
We show that the deepening of this low pressure system , in turn , was associated with an increase in the flux of warm surface air from the lower latitudes to southern Africa .
We suggest that the recent summer warming over southern Africa is linked to these shifts in atmospheric circulation that are probably induced by Antarctic ozone loss .

[959] Increasing trends of soil greenhouse gas fluxes in Japanese forests from 1980 to 2009

Forest soils are a source/sink of greenhouse gases , and have significant impacts on the budget of these terrestrial greenhouse gases .
Here , we show climate-driven changes in soil GHG fluxes ( CO2 emission , CH4 uptake , and N2O emission ) in Japanese forests from 1980 to 2009 , which were estimated using a regional soil GHG model that is data-oriented .
Our study reveals that the soil GHG fluxes in Japanese forests have been increasing over the past 30 years at the rate of 0.31 Tg C yr-2 for CO2 ( 0.23 % yr-1 , relative to the average from 1980 to 2009 ) , 0.40 Gg C yr-2 for CH4 ( 0.44 % yr-1 ) , and 0.0052 Gg N yr-2 for N2O ( 0.27 % yr-1 ) .
Our estimates also show large interannual variations in soil GHG fluxes .
The increasing trends and large interannual variations in soil GHG fluxes seem to substantially affect Japan 's Kyoto accounting and future GHG mitigation strategies .

[960] Optimal timing for managed relocation of species faced with climate change

Managed relocation is a controversial climate-adaptation strategy to combat negative climate change impacts on biodiversity .
While the scientific community debates the merits of managed relocation , species are already being moved to new areas predicted to be more suitable under climate change .
To inform these moves , we construct a quantitative decision framework to evaluate the timing of relocation in the face of climate change .
We find that the optimal timing depends on many factors , including the size of the population , the demographic costs of translocation and the expected carrying capacities over time in the source and destination habitats .
In some settings , such as when a small population would benefit from time to grow before risking translocation losses , haste is ill advised .
We also find that active adaptive management is valuable when the effect of climate change on source habitat is uncertain , and leads to delayed movement .

[961] The effect of experimental warming on the root-associated fungal community of Salix arctica

The effect of experimental warming on the root-associated fungal community of arctic willow ( Salix arctica ) was studied in three distinct habitats at a tundra site in the Canadian High Arctic .
Plots were passively warmed for 5-7 years using open-top chambers and compared to control plots at ambient temperature .
Fungal communities were assessed using terminal restriction fragment length polymorphisms .
We found the following : ( 1 ) the root-associated fungal community in these high arctic tundra habitats is highly diverse ; ( 2 ) site and soil characteristics are the most important drivers of community structure and ( 3 ) warming increased the density of different genotypes on individual root sections but has not ( yet ) affected the composition , richness or evenness of the community .
The change in genotype density in the warmed plots was associated with an increase in PCR amplification efficiency , suggesting that increased C allocation belowground is increasing the overall biomass of the fungal community .

[962] Aerosol forcing of the position of the intertropical convergence zone since ad 1550

The position of the intertropical convergence zone is an important control on the distribution of low-latitude precipitation .
Its position is largely controlled by hemisphere temperature contrasts .
The release of aerosols by human activities may have resulted in a southward shift of the intertropical convergence zone since the early 1900s ( refs , , , , ) by muting the warming of the Northern Hemisphere relative to the Southern Hemisphere over this interval , but this proposed shift remains equivocal .
Here we reconstruct monthly rainfall over Belize for the past 456 years from variations in the carbon isotope composition of a well-dated , monthly resolved speleothem .
We identify an unprecedented drying trend since ad 1850 that indicates a southward displacement of the intertropical convergence zone .
This drying coincides with increasing aerosol emissions in the Northern Hemisphere and also marks a breakdown in the relationship between Northern Hemisphere temperatures and the position of the intertropical convergence zone observed earlier in the record .
We also identify nine short-lived drying events since ad 1550 each following a large volcanic eruption in the Northern Hemisphere .
We conclude that anthropogenic aerosol emissions have led to a reduction of rainfall in the northern tropics during the twentieth century , and suggest that geographic changes in aerosol emissions should be considered when assessing potential future rainfall shifts in the tropics .

[963] Ecophysiology of uncultivated marine euryarchaea is linked to particulate organic matter

Particles in aquatic environments host distinct communities of microbes , yet the evolution of particle-specialized taxa and the extent to which specialized microbial metabolism is associated with particles is largely unexplored .
Here , we investigate the hypothesis that a widely distributed and uncultivated microbial group -- the marine group II euryarchaea ( MGII ) -- interacts with living and detrital particulate organic matter ( POM ) in the euphotic zone of the central California Current System .
Using fluorescent in situ hybridization , we verified the association of euryarchaea with POM .
We further quantified the abundance and distribution of MGII 16 S ribosomal RNA genes in size-fractionated seawater samples and compared MGII functional capacity in metagenomes from the same fractions .
The abundance of MGII in free-living and > 3 mum fractions decreased with increasing distance from the coast , whereas MGII abundance in the 0.8-3 mum fraction remained constant .
At several offshore sites , MGII abundance was highest in particle fractions , indicating that particle-attached MGII can outnumber free-living MGII under oligotrophic conditions .
Compared with free-living MGII , the genome content of MGII in particle-associated fractions exhibits an increased capacity for surface adhesion , transcriptional regulation and catabolism of high molecular weight substrates .
Moreover , MGII populations in POM fractions are phylogenetically distinct from and more diverse than free-living MGII .
Eukaryotic phytoplankton additions stimulated MGII growth in bottle incubations , providing the first MGII net growth rate measurements .
These ranged from 0.47 to 0.54 d-1 .
However , MGII were not recovered in whole-genome amplifications of flow-sorted picoeukaryotic phytoplankton and heterotrophic nanoflagellates , suggesting that MGII in particle fractions are not physically attached to living POM .
Collectively , our results support a linkage between MGII ecophysiology and POM , implying that marine archaea have a role in elemental cycling through interactions with particles .
The ISME Journal advance online publication , 23 January 2015 ; doi :10.1038 / ismej .2014.260

[964] Hotspot of accelerated sea-level rise on the Atlantic coast of North America

Climate warming does not force sea-level rise ( SLR ) at the same rate everywhere .
Rather , there are spatial variations of SLR superimposed on a global average rise .
These variations are forced by dynamic processes , arising from circulation and variations in temperature and/or salinity , and by static equilibrium processes , arising from mass redistributions changing gravity and the Earth 's rotation and shape .
These sea-level variations form unique spatial patterns , yet there are very few observations verifying predicted patterns or fingerprints .
Here , we present evidence of recently accelerated SLR in a unique 1,000-km-long hotspot on the highly populated North American Atlantic coast north of Cape Hatteras and show that it is consistent with a modelled fingerprint of dynamic SLR .
Between 1950-1979 and 1980-2009 , SLR rate increases in this northeast hotspot were ~ 3-4 times higher than the global average .
Modelled dynamic plus steric SLR by 2100 at New York City ranges with Intergovernmental Panel on Climate Change scenario from 36 to 51 cm ( ref . )
; lower emission scenarios project 24-36 cm ( ref . )
.
Extrapolations from data herein range from 20 to 29 cm .
SLR superimposed on storm surge , wave run-up and set-up will increase the vulnerability of coastal cities to flooding , and beaches and wetlands to deterioration .

[965] Post-synthetic Ti Exchanged UiO-66 Metal-Organic Frameworks that Deliver Exceptional Gas Permeability in Mixed Matrix Membranes

Gas separation membranes are one of the lowest energy technologies available for the separation of carbon dioxide from flue gas .
Key to handling the immense scale of this separation is maximised membrane permeability at sufficient selectivity for CO2 over N2 .
For the first time it is revealed that metals can be post-synthetically exchanged in MOFs to drastically enhance gas transport performance in membranes .
Ti-exchanged UiO-66 MOFs have been found to triple the gas permeability without a loss in selectivity due to several effects that include increased affinity for CO2 and stronger interactions between the polymer matrix and the Ti-MOFs .
As a result , it is also shown that MOFs optimized in previous works for batch-wise adsorption applications can be applied to membranes , which have lower demands on material quantities .
These membranes exhibit exceptional CO2 permeability enhancement of as much as 153 % when compared to the non-exchanged UiO-66 mixed-matrix controls , which places them well above the Robeson upper bound at just a 5 wt .
% loading .
The fact that maximum permeability enhancement occurs at such low loadings , significantly less than the optimum for other MMMs , is a major advantage in large-scale application due to the more attainable quantities of MOF needed .

[966] Coralline algal Barium as indicator for 20th century northwestern North Atlantic surface ocean freshwater variability

During the past decades climate and freshwater dynamics in the northwestern North Atlantic have undergone major changes .
Large-scale freshening episodes , related to polar freshwater pulses , have had a strong influence on ocean variability in this climatically important region .
However , little is known about variability before 1950 , mainly due to the lack of long-term high-resolution marine proxy archives .
Here we present the first multidecadal-length records of annually resolved Ba/Ca variations from Northwest Atlantic coralline algae .
We observe positive relationships between algal Ba/Ca ratios from two Newfoundland sites and salinity observations back to 1950 .
Both records capture episodical multi-year freshening events during the 20th century .
Variability in algal Ba/Ca is sensitive to freshwater-induced changes in upper ocean stratification , which affect the transport of cold , Ba-enriched deep waters onto the shelf ( highly stratified equals less Ba/Ca ) .
Algal Ba/Ca ratios therefore may serve as a new resource for reconstructing past surface ocean freshwater changes .

[967] Microbial genomic analysis reveals the essential role of inflammation in bacteria-induced colorectal cancer

Enterobacteria , especially Escherichia coli , are abundant in patients with inflammatory bowel disease or colorectal cancer ( CRC ) .
However , it is unclear whether cancer is promoted by inflammation-induced expansion of E. coli and/or changes in expression of specific microbial genes .
Here we use longitudinal ( 2 , 12 and 20 weeks ) 16S rRNA sequencing of luminal microbiota from ex-germ-free mice to show that inflamed Il10 - / - mice maintain a higher abundance of Enterobacteriaceae than healthy wild-type mice .
Experiments with mono-colonized Il10 - / - mice reveal that host inflammation is necessary for E. coli cancer-promoting activity .
RNA-sequence analysis indicates significant changes in E. coli gene catalogue in Il10 - / - mice , with changes mostly driven by adaptation to the intestinal environment .
Expression of specific genes present in the tumour-promoting E. coli pks island are modulated by inflammation/CRC development .
Thus , progression of inflammation in Il10 - / - mice supports Enterobacteriaceae and alters a small subset of microbial genes important for tumour development .

[968] Similar meltwater contributions to glacial sea level changes from Antarctic and northern ice sheets

The period between 75,000 and 20,000 years ago was characterized by high variability in climate and sea level .
Southern Ocean records of ice-rafted debris suggest a significant contribution to the sea level changes from melt water of Antarctic origin , in addition to likely contributions from northern ice sheets , but the relative volumes of melt water from northern and southern sources have yet to be established .
Here we simulate the first-order impact of a range of relative meltwater releases from the two polar regions on the distribution of marine oxygen isotopes , using an intermediate complexity model .
By comparing our simulations with oxygen isotope data from sediment cores , we infer that the contributions from Antarctica and the northern ice sheets to the documented sea level rises between 65,000 and 35,000 years ago were approximately equal , each accounting for a rise of about 15 m .
The reductions in Antarctic ice volume implied by our analysis are comparable to that inferred previously for the Antarctic contribution to meltwater pulse 1A ( refs 16 , 17 ) , which occurred about 14,200 years ago , during the last deglaciation .

[969] Spatiotemporal modulation of biodiversity in a synthetic chemical-mediated ecosystem

Biodiversity , or the relative abundance of species , measures the persistence of an ecosystem .
To better understand its modulation , we analyzed the spatial and temporal dynamics of a synthetic , chemical-mediated ecosystem that consisted of two engineered Escherichia coli populations .
Depending on the specific experimental conditions implemented , the dominant interaction between the two populations could be competition for nutrients or predation due to engineered communication .
While the two types of interactions resulted in different spatial patterns , they demonstrated a common trend in terms of the modulation of biodiversity .
Specifically , biodiversity decreased with increasing cellular motility if the segregation distance between the two populations was comparable to the length scale of the chemical-mediated interaction .
Otherwise , biodiversity was insensitive to cellular motility .
Our results suggested a simple criterion for predicting the modulation of biodiversity by habitat partitioning and cellular motility in chemical-mediated ecosystems .

[970] Human deforestation outweighs future climate change impacts of sedimentation on coral reefs

Near-shore coral reef systems are experiencing increased sediment supply due to conversion of forests to other land uses .
Counteracting increased sediment loads requires an understanding of the relationship between forest cover and sediment supply , and how this relationship might change in the future .
Here we study this relationship by simulating river flow and sediment supply in four watersheds that are adjacent to Madagascar 's major coral reef ecosystems for a range of future climate change projections and land-use change scenarios .
We show that by 2090 , all four watersheds are predicted to experience temperature increases and/or precipitation declines that , when combined , result in decreases in river flow and sediment load .
However , these climate change-driven declines are outweighed by the impact of deforestation .
Consequently , our analyses suggest that regional land-use management is more important than mediating climate change for influencing sedimentation of Malagasy coral reefs .

[971] Ecosystem carbon loss with woody plant invasion of grasslands

The invasion of woody vegetation into deserts , grasslands and savannas is generally thought to lead to an increase in the amount of carbon stored in those ecosystems .
For this reason , shrub and forest expansion ( for example , into grasslands ) is also suggested to be a substantial , if uncertain , component of the terrestrial carbon sink .
Here we investigate woody plant invasion along a precipitation gradient ( 200 to 1,100 mm yr-1 ) by comparing carbon and nitrogen budgets and soil delta13C profiles between six pairs of adjacent grasslands , in which one of each pair was invaded by woody species 30 to 100 years ago .
We found a clear negative relationship between precipitation and changes in soil organic carbon and nitrogen content when grasslands were invaded by woody vegetation , with drier sites gaining , and wetter sites losing , soil organic carbon .
Losses of soil organic carbon at the wetter sites were substantial enough to offset increases in plant biomass carbon , suggesting that current land-based assessments may overestimate carbon sinks .
Assessments relying on carbon stored from woody plant invasions to balance emissions may therefore be incorrect .

[972] The architecture of mutualistic networks minimizes competition and increases biodiversity

The main theories of biodiversity either neglect species interactions or assume that species interact randomly with each other .
However , recent empirical work has revealed that ecological networks are highly structured , and the lack of a theory that takes into account the structure of interactions precludes further assessment of the implications of such network patterns for biodiversity .
Here we use a combination of analytical and empirical approaches to quantify the influence of network architecture on the number of coexisting species .
As a case study we consider mutualistic networks between plants and their animal pollinators or seed dispersers .
These networks have been found to be highly nested , with the more specialist species interacting only with proper subsets of the species that interact with the more generalist .
We show that nestedness reduces effective interspecific competition and enhances the number of coexisting species .
Furthermore , we show that a nested network will naturally emerge if new species are more likely to enter the community where they have minimal competitive load .
Nested networks seem to occur in many biological and social contexts , suggesting that our results are relevant in a wide range of fields .

[973] A constructive scheme unravelled ?

The Collapse of the Kyoto Protocol is a serious , detailed , but ultimately paradoxical book .
Apart from the introductory chapter -- which contains some misleading caricatures about the Kyoto Protocol , the international agreement that set targets for greenhouse-gas emissions -- it is written with an authority and detail that few can muster .
It is also an absolutely independent assessment , beholden to no one .
Yet the core conclusion reveals a fundamental inconsistency in the analysis .
David Victor gives short shrift to many of the sacred cows of US opposition to the protocol .
Whereas most US criticisms centre on the lack of quantified commitments for developing countries , Victor argues the opposite , that the commitments should have focused only on the rich countries of the OECD .
It would then have avoided the institutional difficulties raised particularly by including Russia and Ukraine .
Most US economists argue that Kyoto 's targets are too close , but Victor says they should have been closer , to minimize the uncertainties .
Kyoto 's targets cover many different gases ; whereas opponents want the effort to focus more on gases other than carbon dioxide , Victor says the targets should have been restricted to carbon dioxide only , because it is hard to monitor the others properly .
The core of Victor 's analysis is thus an institutional critique , particularly with respect to emissions trading -- the option for countries to trade their emissions allowances .
Trading , he rightly asserts , is an inevitable consequence of adopting emissions targets .
Yet he believes that bringing money into emissions control will create incentives to cheat the system that will exacerbate the already difficult problems of monitoring and enforcement .
He also claims that , although Kyoto 's flexibilities would allow the United States to meet its commitment through investing in emission reduction projects or systems abroad , the foreign institutions concerned may not be able to guarantee that this will really reduce emissions elsewhere .
Victor 's book is built on years of experience and commentary on the climate-change regime .
He has always been a critic of the targets-and-trading approach , and sees the collapse of the recent talks in The Hague as vindicating his stance .
But his final chapter marks an important evolution in his thinking .
Previously , he argued for a soft-law approach based on national reporting and review -- a climate equivalent of the OECD 's economic review process .
Here he acknowledges that something stronger is needed .
The answer ?
A mix of targets-and-trading with a tax system that sets a limit on the market price of emission permits .
Putting a cap on permit prices and restricting the system to carbon dioxide in the OECD countries , he argues , would overcome the institutional difficulties he has identified .
But one senses an air of desperation .
By the end of the book Victor has argued himself into supporting many of the Kyoto Protocol 's fundamental principles .
The problems he identifies are not unmanageable , and the changes he seeks are relatively minor compared with the prospect of negotiating an entirely new system .
But as a long-standing critic , he can not bear to recognize that .
He would rather tear down the house and start again according to his own specifications .
Despite all its important insights , its ultimate negativity -- and political naivete -- makes this a depressing book .
For example , the difficulty of monitoring methane emissions does not preclude keeping the Kyoto basket of gases for national targets , while domestic policies target carbon dioxide and other gases separately .
Monitoring need not involve unacceptably intrusive international inspection ; a reasonable degree of democracy and transparency could minimize the scope for abuse .
Victor complains that no one compared the benefits of including methane against the costs of ( imperfect ) monitoring , but he makes no attempt to compare such costs with his own alternative of abandoning the protocol along with the whole idea of cost-effectiveness across the different gases .
Victor 's analytical strength and peculiar negativity are nowhere more striking than in his treatment of liability .
He knows that emissions trading can do much to solve the thorny problem of compliance , provided that the validity of acquired emission allowances is made dependent on the selling country complying with its commitments ( ` buyer liability ' ) .
The alternative of seller liability `` invites disaster ... it will fail because it is a fiction in international law '' .
With buyer liability , however , selling countries would not get a good price unless they could convince the countries interested in buying that they have both the systems and the intent to comply .
Indeed , the case Victor presents for such buyer liability is unanswerable and unsurpassed in the whole of the literature .
Yet he then meekly notes that the `` international debate '' ( actually the US position ) at The Hague conference supported seller liability .
He could have castigated the previous US administration for its cowardice and lack of imagination on the issue , and argued passionately that the rescheduling of the suspended Hague talks offers the world a chance to get this cornerstone of international emissions trading on the right footing .
Instead , he simply concludes that the protocol is hopeless , but that if the world starts again with his own scheme , it will get the liability rules right .
There are too many such inconsistencies between Victor 's critique of trading in the protocol and his endorsement of trading according to his scheme .
This is coupled with the casual assumption that the Kyoto deal can be completely rewritten .
Victor vastly underestimates Kyoto 's achievement in obtaining agreement and the centrality of the strong US target in return for extensive flexibilities .
Indeed , despite its analytical depth , the book is marred -- and perhaps the negativity explained -- by viewing everything through a US lens .
This results in scepticism about US implementation and cynicism about the rest of the world .
For example , it is grossly misleading to assert that `` no major government has a viable plan for compliance '' .
Ten years in advance of the Kyoto target period ( 2008-12 ) , the United Kingdom is on track , and , like many other European governments , if its current plans prove inadequate , they will be strengthened and/or supplemented by using Kyoto 's mechanisms to achieve compliance .
There are other peculiar inconsistencies .
At the core of his attack on emissions trading is the assertion that negotiating allocations is the equivalent of agreeing on how to distribute money , and is hence impossible , or too weak .
Yet Kyoto did reach agreement -- Victor 's claim that all this was an accident born of governmental ignorance is arrogant and does not hold water .
And his complaint about Kyoto is that the targets are too strong .
Indeed , in the United Nations , the European Union , and even in individual governments , negotiations regularly distribute budgets .
All that is needed is the common understanding that there is a collective interest in agreeing , and that simply printing more money only leads to inflation.Victor has not factored in the politics of pressure in the hothouse of negotiating allocations .
It is the achievement of having agreed in Kyoto that Victor wants to unravel .
Ultimately , Victor 's book reminds me of Tolkien 's Lord Denethor in The Lord of the Rings , who was given a crystal ball to see events around the world -- but only negative ones .
Overwhelmed with despair , he led his family to the pyre , decrying the ignorant fools who fought on .
He burnt to death just as his allies were mustering for their final victory .
David Victor 's analysis is that of a fine mind overwhelmed by the problems he sees and led to a destructive conclusion .
Nevertheless , the book should be read by all policy-makers attempting to find international solutions to the climate problem .
It identifies the important questions to be answered , and the big problems to be solved .
There are answers , and ironically , some may be easier to find while the present US administration is withdrawn from the Kyoto negotiations .
Do not follow Victor onto the pyre .

[974] Contributions of microbial biofilms to ecosystem processes in stream mesocosms

In many aquatic ecosystems , most microbes live in matrix-enclosed biofilms and contribute substantially to energy flow and nutrient cycling .
Little is known , however , about the coupling of structure and dynamics of these biofilms to ecosystem function .
Here we show that microbial biofilms changed the physical and chemical microhabitat and contributed to ecosystem processes in 30-m-long stream mesocosms .
Biofilm growth increased hydrodynamic transient storage -- streamwater detained in quiescent zones , which is a major physical template for ecological processes in streams -- by 300 % and the retention of suspended particles by 120 % .
In addition , by enhancing the relative uptake of organic molecules of lower bioavailability , the interplay of biofilm microarchitecture and mass transfer changed their downstream linkage .
As living zones of transient storage , biofilms bring hydrodynamic retention and biochemical processing into close spatial proximity and influence biogeochemical processes and patterns in streams .
Thus , biofilms are highly efficient and successful ecological communities that may also contribute to the influence that headwater streams have on rivers , estuaries and even oceans through longitudinal linkages of local biogeochemical and hydrodynamic processes .

[975] One hundred years of Arctic surface temperature variation due to anthropogenic influence

Observations show that Arctic-average surface temperature increased from 1900 to 1940 , decreased from 1940 to 1970 , and increased from 1970 to present .
Here , using new observational data and improved climate models employing observed natural and anthropogenic forcings , we demonstrate that contributions from greenhouse gas and aerosol emissions , along with explosive volcanic eruptions , explain most of this observed variation in Arctic surface temperature since 1900 .
In addition , climate model simulations without natural and anthropogenic forcings indicate very low probabilities that the observed trends in each of these periods were due to internal climate variability alone .
Arctic climate change has important environmental and economic impacts and these results improve our understanding of past Arctic climate change and our confidence in future projections .

[976] Slowdown of the meridional overturning circulation in the upper Pacific Ocean

Decadal temperature fluctuations in the Pacific Ocean have a significant effect on marine ecosystems and the climate of North America .
The physical mechanisms responsible for these fluctuations are poorly understood .
Some theories ascribe a central role to the wind-driven meridional overturning circulation between the tropical and subtropical oceans .
Here we show , from observations over the past 50 years , that this overturning circulation has been slowing down since the 1970s , causing a decrease in upwelling of about 25 % in an equatorial strip between 9degrees N and 9degrees S .
This reduction in equatorial upwelling of relatively cool water , from 47 x 106 to 35 x 106 m3 s-1 , is associated with a rise in equatorial sea surface temperatures of about 0.8 degreesC .
Another effect of the slowing circulation is a reduction in the outgassing of CO2 from the equatorial Pacific Ocean-at present the largest oceanic source of carbon dioxide to the atmosphere .

[977] Glacial to Holocene swings of the Australian-Indonesian monsoon

The Australian-Indonesian monsoon is an important component of the climate system in the tropical Indo-Pacific region .
However , its past variability , relation with northern and southern high-latitude climate and connection to the other Asian monsoon systems are poorly understood .
Here we present high-resolution records of monsoon-controlled austral winter upwelling during the past 22,000 years , based on planktic foraminiferal oxygen isotopes and faunal composition in a sedimentary archive collected offshore southern Java .
We show that glacial-interglacial variations in the Australian-Indonesian winter monsoon were in phase with the Indian summer monsoon system , consistent with their modern linkage through cross-equatorial surface winds .
Likewise , millennial-scale variability of upwelling shares similar sign and timing with upwelling variability in the Arabian Sea .
On the basis of element composition and grain-size distribution as precipitation-sensitive proxies in the same archive , we infer that ( austral ) summer monsoon rainfall was highest during the Bolling-Allerod period and the past 2,500 years .
Our results indicate drier conditions during Heinrich Stadial 1 due to a southward shift of summer rainfall and a relatively weak Hadley cell south of the Equator .
We suggest that the Australian-Indonesian summer and winter monsoon variability were closely linked to summer insolation and abrupt climate changes in the northern hemisphere .

[978] Signatures of the Antarctic ozone hole in Southern Hemisphere surface climate change

Anthropogenic emissions of carbon dioxide and other greenhouse gases have driven and will continue to drive widespread climate change at the Earth 's surface .
But surface climate change is not limited to the effects of increasing atmospheric greenhouse gas concentrations .
Anthropogenic emissions of ozone-depleting gases also lead to marked changes in surface climate , through the radiative and dynamical effects of the Antarctic ozone hole .
The influence of the Antarctic ozone hole on surface climate is most pronounced during the austral summer season and strongly resembles the most prominent pattern of large-scale Southern Hemisphere climate variability , the Southern Annular Mode .
The influence of the ozone hole on the Southern Annular Mode has led to a range of significant summertime surface climate changes not only over Antarctica and the Southern Ocean , but also over New Zealand , Patagonia and southern regions of Australia .
Surface climate change as far equatorward as the subtropical Southern Hemisphere may have also been affected by the ozone hole .
Over the next few decades , recovery of the ozone hole and increases in greenhouse gases are expected to have significant but opposing effects on the Southern Annular Mode and its attendant climate impacts during summer .

[979] Formate-driven growth coupled with H2 production

Although a common reaction in anaerobic environments , the conversion of formate and water to bicarbonate and H2 ( with a change in Gibbs free energy of DeltaGdegrees = +1.3 kJ mol-1 ) has not been considered energetic enough to support growth of microorganisms .
Recently , experimental evidence for growth on formate was reported for syntrophic communities of Moorella sp .
strain AMP and a hydrogen-consuming Methanothermobacter species and of Desulfovibrio sp .
strain G11 and Methanobrevibacter arboriphilus strain AZ. .
The basis of the sustainable growth of the formate-users is explained by H2 consumption by the methanogens , which lowers the H2 partial pressure , thus making the pathway exergonic .
However , it has not been shown that a single strain can grow on formate by catalysing its conversion to bicarbonate and H2 .
Here we report that several hyperthermophilic archaea belonging to the Thermococcus genus are capable of formate-oxidizing , H2-producing growth .
The actual DeltaG values for the formate metabolism are calculated to range between -8 and -20 kJ mol-1 under the physiological conditions where Thermococcus onnurineus strain NA1 are grown .
Furthermore , we detected ATP synthesis in the presence of formate as a sole energy source .
Gene expression profiling and disruption identified the gene cluster encoding formate hydrogen lyase , cation/proton antiporter and formate transporter , which were responsible for the growth of T. onnurineus NA1 on formate .
This work shows formate-driven growth by a single microorganism with protons as the electron acceptor , and reports the biochemical basis of this ability .

[980] Synechococcus elongatus UTEX 2973 , a fast growing cyanobacterial chassis for biosynthesis using light and CO2

Photosynthetic microbes are of emerging interest as production organisms in biotechnology because they can grow autotrophically using sunlight , an abundant energy source , and CO2 , a greenhouse gas .
Important traits for such microbes are fast growth and amenability to genetic manipulation .
Here we describe Synechococcus elongatus UTEX 2973 , a unicellular cyanobacterium capable of rapid autotrophic growth , comparable to heterotrophic industrial hosts such as yeast .
Synechococcus UTEX 2973 can be readily transformed for facile generation of desired knockout and knock-in mutations .
Genome sequencing coupled with global proteomics studies revealed that Synechococcus UTEX 2973 is a close relative of the widely studied cyanobacterium Synechococcus elongatus PCC 7942 , an organism that grows more than two times slower .
A small number of nucleotide changes are the only significant differences between the genomes of these two cyanobacterial strains .
Thus , our study has unraveled genetic determinants necessary for rapid growth of cyanobacterial strains of significant industrial potential .

[981] Bioelectrochemical enhancement of anaerobic methanogenesis for high organic load rate wastewater treatment in a up-flow anaerobic sludge blanket ( UASB ) reactor

A coupling process of anaerobic methanogenesis and electromethanogenesis was proposed to treat high organic load rate ( OLR ) wastewater .
During the start-up stage , acetate removal efficiency of the electric-biological reactor ( R1 ) reached the maximization about 19 percentage points higher than that of the control anaerobic reactor without electrodes ( R2 ) , and CH4 production rate of R1 also increased about 24.9 % at the same time , while additional electric input was 1/1 .17 of the extra obtained energy from methane .
Coulombic efficiency and current recorded showed that anodic oxidation contributed a dominant part in degrading acetate when the metabolism of methanogens was low during the start-up stage .
Along with prolonging operating time , aceticlastic methanogenesis gradually replaced anodic oxidation to become the main pathway of degrading acetate .
When the methanogens were inhibited under the acidic conditions , anodic oxidation began to become the main pathway of acetate decomposition again , which ensured the reactor to maintain a stable performance .
FISH analysis confirmed that the electric field imposed could enrich the H2/H + - utilizing methanogens around the cathode to help for reducing the acidity .
This study demonstrated that an anaerobic digester with a pair of electrodes inserted to form a coupling system could enhance methanogenesis and reduce adverse impacts .

[982] 500-year climate cycles stacking of recent centennial warming documented in an East Asian pollen record

Here we presented a high-resolution 5350-year pollen record from a maar annually laminated lake in East Asia ( EA ) .
Pollen record reflected the dynamics of vertical vegetation zones and temperature change .
Spectral analysis on pollen percentages/concentrations of Pinus and Quercus , and a temperature proxy , revealed ~ 500-year quasi-periodic cold-warm fluctuations during the past 5350 years .
This ~ 500-year cyclic climate change occurred in EA during the mid-late Holocene and even the last 150 years dominated by anthropogenic forcing .
It was almost in phase with a ~ 500-year periodic change in solar activity and Greenland temperature change , suggesting that ~ 500-year small variations in solar output played a prominent role in the mid-late Holocene climate dynamics in EA , linked to high latitude climate system .
Its last warm phase might terminate in the next several decades to enter another ~ 250-year cool phase , and thus this future centennial cyclic temperature minimum could partially slow down man-made global warming .

[983] Cultivation and quantitative proteomic analyses of acidophilic microbial communities

Acid mine drainage ( AMD ) , an extreme environment characterized by low pH and high metal concentrations , can support dense acidophilic microbial biofilm communities that rely on chemoautotrophic production based on iron oxidation .
Field determined production rates indicate that , despite the extreme conditions , these communities are sufficiently well adapted to their habitats to achieve primary production rates comparable to those of microbial communities occurring in some non-extreme environments .
To enable laboratory studies of growth , production and ecology of AMD microbial communities , a culturing system was designed to reproduce natural biofilms , including organisms recalcitrant to cultivation .
A comprehensive metabolic labeling-based quantitative proteomic analysis was used to verify that natural and laboratory communities were comparable at the functional level .
Results confirmed that the composition and core metabolic activities of laboratory-grown communities were similar to a natural community , including the presence of active , low abundance bacteria and archaea that have not yet been isolated .
However , laboratory growth rates were slow compared with natural communities , and this correlated with increased abundance of stress response proteins for the dominant bacteria in laboratory communities .
Modification of cultivation conditions reduced the abundance of stress response proteins and increased laboratory community growth rates .
The research presented here represents the first description of the application of a metabolic labeling-based quantitative proteomic analysis at the community level and resulted in a model microbial community system ideal for testing physiological and ecological hypotheses .

[984] A possible nitrogen crisis for Archaean life due to reduced nitrogen fixation by lightning

Nitrogen is an essential element for life and is often the limiting nutrient for terrestrial ecosystems .
As most nitrogen is locked in the kinetically stable form , N2 , in the Earth 's atmosphere , processes that can fix N2 into biologically available forms -- such as nitrate and ammonia -- control the supply of nitrogen for organisms .
On the early Earth , nitrogen is thought to have been fixed abiotically , as nitric oxide formed during lightning discharge .
The advent of biological nitrogen fixation suggests that at some point the demand for fixed nitrogen exceeded the supply from abiotic sources , but the timing and causes of the onset of biological nitrogen fixation remain unclear .
Here we report an experimental simulation of nitrogen fixation by lightning over a range of Hadean ( 4.5-3 .8 Gyr ago ) and Archaean ( 3.8-2 .5 Gyr ago ) atmospheric compositions , from predominantly carbon dioxide to predominantly dinitrogen ( but always without oxygen ) .
We infer that , as atmospheric CO2 decreased over the Archaean period , the production of nitric oxide from lightning discharge decreased by two orders of magnitude until about 2.2 Gyr .
After this time , the rise in oxygen ( or methane ) concentrations probably initiated other abiotic sources of nitrogen .
Although the temporary reduction in nitric oxide production may have lasted for only 100 Myr or less , this was potentially long enough to cause an ecological crisis that triggered the development of biological nitrogen fixation .

[985] Dysregulation of transition metal ion homeostasis is the molecular basis for cadmium toxicity in Streptococcus pneumoniae

Cadmium is a transition metal ion that is highly toxic in biological systems .
Although relatively rare in the Earth 's crust , anthropogenic release of cadmium since industrialization has increased biogeochemical cycling and the abundance of the ion in the biosphere .
Despite this , the molecular basis of its toxicity remains unclear .
Here we combine metal-accumulation assays , high-resolution structural data and biochemical analyses to show that cadmium toxicity , in Streptococcus pneumoniae , occurs via perturbation of first row transition metal ion homeostasis .
We show that cadmium uptake reduces the millimolar cellular accumulation of manganese and zinc , and thereby increases sensitivity to oxidative stress .
Despite this , high cellular concentrations of cadmium ( ~ 17 mM ) are tolerated , with negligible impact on growth or sensitivity to oxidative stress , when manganese and glutathione are abundant .
Collectively , this work provides insight into the molecular basis of cadmium toxicity in prokaryotes , and the connection between cadmium accumulation and oxidative stress .

[986] Increasing destructiveness of tropical cyclones over the past 30 years

Theory and modelling predict that hurricane intensity should increase with increasing global mean temperatures , but work on the detection of trends in hurricane activity has focused mostly on their frequency and shows no trend .
Here I define an index of the potential destructiveness of hurricanes based on the total dissipation of power , integrated over the lifetime of the cyclone , and show that this index has increased markedly since the mid-1970s .
This trend is due to both longer storm lifetimes and greater storm intensities .
I find that the record of net hurricane power dissipation is highly correlated with tropical sea surface temperature , reflecting well-documented climate signals , including multi-decadal oscillations in the North Atlantic and North Pacific , and global warming .
My results suggest that future warming may lead to an upward trend in tropical cyclone destructive potential , and -- taking into account an increasing coastal population -- a substantial increase in hurricane-related losses in the twenty-first century .

[987] Episodic reductions in bottom-water currents since the last ice age

Past changes in the freshwater balance of the surface North Atlantic Ocean are thought to have influenced the rate of deep-water formation , and consequently climate .
Although water-mass proxies are generally consistent with an impact of freshwater input on meridional overturning circulation , there has been little dynamic evidence to support this linkage .
Here we present a 25,000 year record of variations in sediment grain size from south of Iceland , which indicates vigorous bottom-water currents during both the last glacial maximum and the Holocene period .
Together with reconstructions of North Atlantic water-mass distribution , vigorous bottom currents suggest a shorter residence time of northern-source waters during the last glacial maximum , relative to the Holocene period .
The most significant reductions in flow strength occur during periods that have been associated with freshening of the surface North Atlantic .
The short-term deglacial oscillations in bottom current strength are closely coupled to changes in Greenland air temperature , with a minimum during the Younger Dryas cold reversal and a maximum at the time of rapid warming at the onset of the Holocene .
Our results support a strong connection between ocean circulation and rapid climate change .

[988] Obliquity-paced Pliocene West Antarctic ice sheet oscillations

Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth 's orbital geometry control the ice ages , fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles .
Furthermore , an understanding of the behaviour of the marine-based West Antarctic ice sheet ( WAIS ) during the ` warmer-than-present ' early-Pliocene epoch ( ~ 5-3 Myr ago ) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming .
Here we present a marine glacial record from the upper 600 m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated , ~ 40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth 's axial tilt ( obliquity ) during the Pliocene .
Our data provide direct evidence for orbitally induced oscillations in the WAIS , which periodically collapsed , resulting in a switch from grounded ice , or ice shelves , to open waters in the Ross embayment when planetary temperatures were up to ~ 3 degreesC warmer than today and atmospheric CO2 concentration was as high as ~ 400 p.p.m.v. ( refs 5 , 6 ) .
The evidence is consistent with a new ice-sheet/ice-shelf model that simulates fluctuations in Antarctic ice volume of up to +7 m in equivalent sea level associated with the loss of the WAIS and up to +3 m in equivalent sea level from the East Antarctic ice sheet , in response to ocean-induced melting paced by obliquity .
During interglacial times , diatomaceous sediments indicate high surface-water productivity , minimal summer sea ice and air temperatures above freezing , suggesting an additional influence of surface melt under conditions of elevated CO2 .

[989] Acceleration of snow melt in an Antarctic Peninsula ice core during the twentieth century

Over the past 50 years , warming of the Antarctic Peninsula has been accompanied by accelerating glacier mass loss and the retreat and collapse of ice shelves .
A key driver of ice loss is summer melting ; however , it is not usually possible to specifically reconstruct the summer conditions that are critical for determining ice melt in Antarctic .
Here we reconstruct changes in ice-melt intensity and mean temperature on the northern Antarctic Peninsula since AD 1000 based on the identification of visible melt layers in the James Ross Island ice core and local mean annual temperature estimates from the deuterium content of the ice .
During the past millennium , the coolest conditions and lowest melt occurred from about AD 1410 to 1460 , when mean temperature was 1.6 degreesC lower than that of 1981-2000 .
Since the late 1400s , there has been a nearly tenfold increase in melt intensity from 0.5 to 4.9 % .
The warming has occurred in progressive phases since about AD 1460 , but intensification of melt is nonlinear , and has largely occurred since the mid-twentieth century .
Summer melting is now at a level that is unprecedented over the past 1,000 years .
We conclude that ice on the Antarctic Peninsula is now particularly susceptible to rapid increases in melting and loss in response to relatively small increases in mean temperature .

[990] Src tyrosine kinase signaling antagonizes nuclear localization of FOXO and inhibits its transcription factor activity

Biochemical experiments in mammalian cells have linked Src family kinase activity to the insulin signaling pathway .
To explore the physiological link between Src and a central insulin pathway effector , we investigated the effect of different Src signaling levels on the Drosophila transcription factor dFOXO in vivo .
Ectopic activation of Src42A in the starved larval fatbody was sufficient to drive dFOXO out of the nucleus .
When Src signaling levels were lowered by means of loss-of-function mutations or pharmacological inhibition , dFOXO localization was shifted to the nucleus in growing animals , and transcription of the dFOXO target genes d4E-BP and dInR was induced .
dFOXO loss-of-function mutations rescued the induction of dFOXO target gene expression and the body size reduction of Src42A mutant larvae , establishing dFOXO as a critical downstream effector of Src signaling .
Furthermore , we provide evidence that the regulation of FOXO transcription factors by Src is evolutionarily conserved in mammalian cells .

[991] The twentieth century was the wettest period in northern Pakistan over the past millennium

Twentieth-century warming could lead to increases in the moisture-holding capacity of the atmosphere , altering the hydrological cycle and the characteristics of precipitation .
Such changes in the global rate and distribution of precipitation may have a greater direct effect on human well-being and ecosystem dynamics than changes in temperature itself .
Despite the co-variability of both of these climate variables , attention in long-term climate reconstruction has mainly concentrated on temperature changes .
Here we present an annually resolved oxygen isotope record from tree-rings , providing a millennial-scale reconstruction of precipitation variability in the high mountains of northern Pakistan .
The climatic signal originates mainly from winter precipitation , and is robust over ecologically different sites .
Centennial-scale variations reveal dry conditions at the beginning of the past millennium and through the eighteenth and early nineteenth centuries , with precipitation increasing during the late nineteenth and the twentieth centuries to yield the wettest conditions of the past 1,000 years .
Comparison with other long-term precipitation reconstructions indicates a large-scale intensification of the hydrological cycle coincident with the onset of industrialization and global warming , and the unprecedented amplitude argues for a human role .

[992] Timescales for detecting a significant acceleration in sea level rise

There is observational evidence that global sea level is rising and there is concern that the rate of rise will increase , significantly threatening coastal communities .
However , considerable debate remains as to whether the rate of sea level rise is currently increasing and , if so , by how much .
Here we provide new insights into sea level accelerations by applying the main methods that have been used previously to search for accelerations in historical data , to identify the timings ( with uncertainties ) at which accelerations might first be recognized in a statistically significant manner ( if not apparent already ) in sea level records that we have artificially extended to 2100 .
We find that the most important approach to earliest possible detection of a significant sea level acceleration lies in improved understanding ( and subsequent removal ) of interannual to multidecadal variability in sea level records .

[993] September sea-ice cover in the Arctic Ocean projected to vanish by 2100

The Arctic climate is changing rapidly .
From 1979 to 2006 , September sea-ice extent decreased by almost 25 % or about 100,000 km2 per year ( ref .
2 ) .
In September 2007 , Arctic sea-ice extent reached its lowest level since satellite observations began and in September 2008 , sea-ice cover was still low .
This development has raised concerns that the Arctic Ocean could be ice-free in late summer in only a few decades , with important economic and geopolitical implications .
Unfortunately , most current climate models underestimate significantly the observed trend in Arctic sea-ice decline , leading to doubts regarding their projections for the timing of ice-free conditions .
Here we analyse the simulated trends in past sea-ice cover in 18 state-of-art-climate models and find a direct relationship between the simulated evolution of September sea-ice cover over the twenty-first century and the magnitude of past trends in sea-ice cover .
Using this relationship together with observed trends , we project the evolution of September sea-ice cover over the twenty-first century .
We find that under a scenario with medium future greenhouse-gas emissions , the Arctic Ocean will probably be ice-free in September before the end of the twenty-first century .

[994] Mg2 + as an indicator of nutritional status in marine bacteria

Cells maintain an osmotic pressure essential for growth and division , using organic compatible solutes and inorganic ions .
Mg2 + , which is the most abundant divalent cation in living cells , has not been considered an osmotically important solute .
Here we show that under carbon limitation or dormancy native marine bacterial communities have a high cellular concentration of Mg2 + ( 370-940 mM ) and a low cellular concentration of Na + ( 50-170 mM ) .
With input of organic carbon , the average cellular concentration of Mg2 + decreased 6-12-fold , whereas that of Na + increased ca 3-4-fold .
The concentration of chlorine , which was in the range of 330-1200 mM , and was the only inorganic counterion of quantitative significance , balanced and followed changes in the concentration of Mg2 + + Na + .
In an osmotically stable environment , like seawater , any major shift in bacterial osmolyte composition should be related to shifts in growth conditions , and replacing organic compatible solutes with inorganic solutes is presumably a favorable strategy when growing in carbon-limited condition .
A high concentration of Mg2 + in cells may also serve to protect and stabilize macromolecules during periods of non-growth and dormancy .
Our results suggest that Mg2 + has a major role as osmolyte in marine bacteria , and that the [ Mg2 + ] / [ Na + ] ratio is related to its physiological condition and nutritional status .
Bacterial degradation is a main sink for dissolved organic carbon in the ocean , and understanding the mechanisms limiting bacterial activity is therefore essential for understanding the oceanic C-cycle .
The [ Mg2 + ] / [ Na + ] - ratio in cells may provide a physiological proxy for the transitions between C-limited and mineral nutrient-limited bacterial growth in the ocean 's surface layer .

[995] Permafrost collapse after shrub removal shifts tundra ecosystem to a methane source

Arctic tundra ecosystems are warming almost twice as fast as the global average .
Permafrost thaw and the resulting release of greenhouse gases from decomposing soil organic carbon have the potential to accelerate climate warming .
In recent decades , Arctic tundra ecosystems have changed rapidly , including expansion of woody vegetation , in response to changing climate conditions .
How such vegetation changes contribute to stabilization or destabilization of the permafrost is unknown .
Here we present six years of field observations in a shrub removal experiment at a Siberian tundra site .
Removing the shrub part of the vegetation initiated thawing of ice-rich permafrost , resulting in collapse of the originally elevated shrub patches into waterlogged depressions within five years .
This thaw pond development shifted the plots from a methane sink into a methane source .
The results of our field experiment demonstrate the importance of the vegetation cover for protection of the massive carbon reservoirs stored in the permafrost and illustrate the strong vulnerability of these tundra ecosystems to perturbations .
If permafrost thawing can more frequently trigger such local permafrost collapse , methane-emitting wet depressions could become more abundant in the lowland tundra landscape , at the cost of permafrost-stabilizing low shrub vegetation .

[996] Palaeozoic landscapes shaped by plant evolution

Fluvial landscapes diversified markedly over the 250 million years between the Cambrian and Pennsylvanian periods .
The diversification occurred in tandem with the evolution of vascular plants and expanding vegetation cover .
In the absence of widespread vegetation , landscapes during the Cambrian and Ordovican periods were dominated by rivers with wide sand-beds and aeolian tracts .
During the late Silurian and Devonian periods , the appearance of vascular plants with root systems was associated with the development of channelled sand-bed rivers , meandering rivers and muddy floodplains .
The widespread expansion of trees by the Early Pennsylvanian marks the appearance of narrow fixed channels , some representing anabranching systems , and braided rivers with vegetated islands .
We conclude that the development of roots stabilized the banks of rivers and streams .
The subsequent appearance of woody debris led to log jams that promoted the rapid formation of new river channels .
Our contention is supported by studies of modern fluvial systems and laboratory experiments .
In turn , fluvial styles influenced plant evolution as new ecological settings developed along the fluvial systems .
We suggest that terrestrial plant and landscape evolution allowed colonization by an increasingly diverse array of organisms .

[997] Atlantic overturning responses to Late Pleistocene climate forcings

The factors driving glacial changes in ocean overturning circulation are not well understood .
On the basis of a comparison of 20 climate variables over the past four glacial cycles , the SPECMAP project proposed that summer insolation at high northern latitudes ( that is , Milankovitch forcing ) drives the same sequence of ocean circulation and other climate responses over 100-kyr eccentricity cycles , 41-kyr obliquity cycles and 23-kyr precession cycles .
SPECMAP analysed the circulation response at only a few sites in the Atlantic Ocean , however , and the phase of circulation response has been shown to vary by site and orbital band .
Here we test the SPECMAP hypothesis by measuring the phase of orbital responses in benthic delta13C ( a proxy indicator of ocean nutrient content ) at 24 sites throughout the Atlantic over the past 425 kyr .
On the basis of delta13C responses at 3,000-4 ,010 m water depth , we find that maxima in Milankovitch forcing are associated with greater mid-depth overturning in the obliquity band but less overturning in the precession band .
This suggests that Atlantic overturning is strongly sensitive to factors beyond ice volume and summer insolation at high northern latitudes .
A better understanding of these processes could lead to improvements in model estimates of overturning rates , which range from a 40 per cent increase to a 40 per cent decrease at the Last Glacial Maximum and a 10-50 per cent decrease over the next 140 yr in response to projected increases in atmospheric CO2 ( ref .
4 ) .

[998] Terrestrial carbon cycle affected by non-uniform climate warming

Feedbacks between the terrestrial carbon cycle and climate change could affect many ecosystem functions and services , such as food production , carbon sequestration and climate regulation .
The rate of climate warming varies on diurnal and seasonal timescales .
A synthesis of global air temperature data reveals a greater rate of warming in winter than in summer in northern mid and high latitudes , and the inverse pattern in some tropical regions .
The data also reveal a decline in the diurnal temperature range over 51 % of the global land area and an increase over only 13 % , because night-time temperatures in most locations have risen faster than daytime temperatures .
Analyses of satellite data , model simulations and in situ observations suggest that the impact of seasonal warming varies between regions .
For example , spring warming has largely stimulated ecosystem productivity at latitudes between 30degrees and 90degrees N , but suppressed productivity in other regions .
Contrasting impacts of day - and night-time warming on plant carbon gain and loss are apparent in many regions .
We argue that ascertaining the effects of non-uniform climate warming on terrestrial ecosystems is a key challenge in carbon cycle research .

[999] Southern Ocean dust-climate coupling over the past four million years

Dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean .
Indeed , dust supply to the Southern Ocean increases during ice ages , and ` iron fertilization ' of the subantarctic zone may have contributed up to 40 parts per million by volume ( p.p.m.v. ) of the decrease ( 80-100 p.p.m.v. ) in atmospheric carbon dioxide observed during late Pleistocene glacial cycles .
So far , however , the magnitude of Southern Ocean dust deposition in earlier times and its role in the development and evolution of Pleistocene glacial cycles have remained unclear .
Here we report a high-resolution record of dust and iron supply to the Southern Ocean over the past four million years , derived from the analysis of marine sediments from ODP Site 1090 , located in the Atlantic sector of the subantarctic zone .
The close correspondence of our dust and iron deposition records with Antarctic ice core reconstructions of dust flux covering the past 800,000 years ( refs 8 , 9 ) indicates that both of these archives record large-scale deposition changes that should apply to most of the Southern Ocean , validating previous interpretations of the ice core data .
The extension of the record beyond the interval covered by the Antarctic ice cores reveals that , in contrast to the relatively gradual intensification of glacial cycles over the past three million years , Southern Ocean dust and iron flux rose sharply at the Mid-Pleistocene climatic transition around 1.25 million years ago .
This finding complements previous observations over late Pleistocene glacial cycles , providing new evidence of a tight connection between high dust input to the Southern Ocean and the emergence of the deep glaciations that characterize the past one million years of Earth history .

[1000] Diversity of protists and bacteria determines predation performance and stability

Predation influences prey diversity and productivity while it effectuates the flux and reallocation of organic nutrients into biomass at higher trophic levels .
However , it is unknown how bacterivorous protists are influenced by the diversity of their bacterial prey .
Using 456 microcosms , in which different bacterial mixtures with equal initial cell numbers were exposed to single or multiple predators ( Tetrahymena sp. , Poterioochromonas sp .
and Acanthamoeba sp . )
, we showed that increasing prey richness enhanced production of single predators .
The extent of the response depended , however , on predator identity .
Bacterial prey richness had a stabilizing effect on predator performance in that it reduced variability in predator production .
Further , prey richness tended to enhance predator evenness in the predation experiment including all three protists predators ( multiple predation experiment ) .
However , we also observed a negative relationship between prey richness and predator production in multiple predation experiments .
Mathematical analysis of potential ecological mechanisms of positive predator diversity -- functioning relationships revealed predator complementarity as a factor responsible for both enhanced predator production and prey reduction .
We suggest that the diversity at both trophic levels interactively determines protistan performance and might have implications in microbial ecosystem processes and services .

[1001] Genome-wide analysis of lysine catabolism in bacteria reveals new connections with osmotic stress resistance

Lysine is catabolized via the saccharopine pathway in plants and mammals .
In this pathway , lysine is converted to alpha-aminoadipic-delta-semialdehyde ( AASA ) by lysine-ketoglutarate reductase/saccharopine dehydrogenase ( LKR/SDH ) ; thereafter , AASA is converted to aminoadipic acid ( AAA ) by alpha-aminoadipic-delta-semialdehyde dehydrogenase ( AASADH ) .
Here , we investigate the occurrence , genomic organization and functional role of lysine catabolic pathways among prokaryotes .
Surprisingly , only 27 species of the 1478 analyzed contain the lkr and sdh genes , whereas 323 species contain aasadh orthologs .
A sdh-related gene , identified in 159 organisms , was frequently found contiguously to an aasadh gene .
This gene , annotated as lysine dehydrogenase ( lysdh ) , encodes LYSDH an enzyme that directly converts lysine to AASA .
Pipecolate oxidase ( PIPOX ) and lysine-6-aminotransferase ( LAT ) , that converts lysine to AASA , were also found associated with aasadh .
Interestingly , many lysdh-aasadh-containing organisms live under hyperosmotic stress .
To test the role of the lysine-to-AASA pathways in the bacterial stress response , we subjected Silicibacter pomeroyi to salt stress .
All but lkr , sdh , lysdh and aasadh were upregulated under salt stress conditions .
In addition , lysine-supplemented culture medium increased the growth rate of S. pomeroyi under high-salt conditions and induced high-level expression of the lysdh-aasadh operon .
Finally , transformation of Escherichia coli with the S. pomeroyi lysdh-aasadh operon resulted in increased salt tolerance .
The transformed E. coli accumulated high levels of the compatible solute pipecolate , which may account for the salt resistance .
These findings suggest that the lysine-to-AASA pathways identified in this work may have a broad evolutionary importance in osmotic stress resistance .

[1002] Millennial-scale trends in west Pacific warm pool hydrology since the Last Glacial Maximum

Models and palaeoclimate data suggest that the tropical Pacific climate system plays a key part in the mechanisms underlying orbital-scale and abrupt climate change .
Atmospheric convection over the western tropical Pacific is a major source of heat and moisture to extratropical regions , and may therefore influence the global climate response to a variety of forcing factors .
The response of tropical Pacific convection to changes in global climate boundary conditions , abrupt climate changes and radiative forcing remains uncertain , however .
Here we present three absolutely dated oxygen isotope records from stalagmites in northern Borneo that reflect changes in west Pacific warm pool hydrology over the past 27,000 years .
Our results suggest that convection over the western tropical Pacific weakened 18,000-20 ,000 years ago , as tropical Pacific and Antarctic temperatures began to rise during the early stages of deglaciation .
Convective activity , as inferred from oxygen isotopes , reached a minimum during Heinrich event 1 ( ref .
10 ) , when the Atlantic meridional overturning circulation was weak , pointing to feedbacks between the strength of the overturning circulation and tropical Pacific hydrology .
There is no evidence of the Younger Dryas event in the stalagmite records , however , suggesting that different mechanisms operated during these two abrupt deglacial climate events .
During the Holocene epoch , convective activity appears to track changes in spring and autumn insolation , highlighting the sensitivity of tropical Pacific convection to external radiative forcing .
Together , these findings demonstrate that the tropical Pacific hydrological cycle is sensitive to high-latitude climate processes in both hemispheres , as well as to external radiative forcing , and that it may have a central role in abrupt climate change events .

[1003] Eutrophication weakens stabilizing effects of diversity in natural grasslands

Studies of experimental grassland communities have demonstrated that plant diversity can stabilize productivity through species asynchrony , in which decreases in the biomass of some species are compensated for by increases in others .
However , it remains unknown whether these findings are relevant to natural ecosystems , especially those for which species diversity is threatened by anthropogenic global change .
Here we analyse diversity-stability relationships from 41 grasslands on five continents and examine how these relationships are affected by chronic fertilization , one of the strongest drivers of species loss globally .
Unmanipulated communities with more species had greater species asynchrony , resulting in more stable biomass production , generalizing a result from biodiversity experiments to real-world grasslands .
However , fertilization weakened the positive effect of diversity on stability .
Contrary to expectations , this was not due to species loss after eutrophication but rather to an increase in the temporal variation of productivity in combination with a decrease in species asynchrony in diverse communities .
Our results demonstrate separate and synergistic effects of diversity and eutrophication on stability , emphasizing the need to understand how drivers of global change interactively affect the reliable provisioning of ecosystem services in real-world systems .

[1004] Early maximum extent of paleoglaciers from Mediterranean mountains during the last glaciation

Mountain glaciers respond directly to changes in precipitation and temperature , thus their margin extent is a high-sensitivity climate proxy .
Here , we present a robust 10Be chronology for the glacier maximum areal extent of central Spain paleoglaciers dated at 26.1 + / - 1.3 ka BP .
These glaciers reached their maximum extent several thousand years earlier than those from central Europe due to the increased precipitation within a cold period between 25 to 29 ka BP , as confirmed by a local speleothem record .
These paleoclimate conditions impacted the maximum extent of mountain glaciers along the western and central Mediterranean region .
The cause and timing of the enhanced precipitation implies a southward shift of the North Atlantic Polar Front followed by storm tracks in response to changes in insolation via orbital parameters modulation .
Thus , these mountain paleoglaciers from the Mediterranean region record an ocean-continent climate interaction triggered by external forcing .

[1005] North Atlantic warming and the retreat of Greenland 's outlet glaciers

Mass loss from the Greenland ice sheet quadrupled over the past two decades , contributing a quarter of the observed global sea-level rise .
Increased submarine melting is thought to have triggered the retreat of Greenland 's outlet glaciers , which is partly responsible for the ice loss .
However , the chain of events and physical processes remain elusive .
Recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes , multidecadal natural ocean variability and a long-term increase in the North Atlantic 's upper ocean heat content since the 1950s all contributed to a warming of the subpolar North Atlantic .
This led , in conjunction with increased runoff , to enhanced submarine glacier melting .
Future climate projections raise the potential for continued increases in warming and ice-mass loss , with implications for sea level and climate .

[1006] Skilful multi-year predictions of Atlantic hurricane frequency

North Atlantic hurricane activity has increased substantially since the 1970s ( refs 1 , 2 ) , but whether this is attributable to natural internal variability or external forcing has not been resolved .
Either way , hurricane frequency is potentially predictable , because climate models can directly simulate year-to-year variations in Atlantic tropical storm frequency , if forced by observed sea surface temperatures .
However , skilful predictions have been limited to lead times of one season , and evidence for external forcing of hurricane frequency has been indirect , relying on statistical relationships or external influences on related environmental factors .
Here we extend skilful climate model predictions of hurricane frequency to lead times of several years , using decadal predictions with nine variants of a general circulation model .
In our experiments , the recent increase in tropical storm numbers was not caused by internal variability alone .
This provides physically based model evidence of externally forced changes in hurricane frequency , albeit from a single modelling system .
Initialization of the model with the observed state of the climate improves forecast skill , mainly through better predictions of tropical Pacific and North Atlantic ocean conditions , in line with previously documented teleconnections .
Our results show that predictions of hurricane frequency are viable beyond the seasonal scale , and further elucidate causes of hurricane variability .

[1007] Minimal change in Antarctic Circumpolar Current flow speed between the last glacial and Holocene

The Antarctic Circumpolar Current is key to the mixing and ventilation of the world 's oceans .
This current flows from west to east between about 45degrees and 70degrees S ( refs , , ) connecting the Atlantic , Pacific and Indian oceans , and is driven by westerly winds and buoyancy forcing .
High levels of productivity in the current regulate atmospheric CO2 concentrations .
Reconstructions of the current during the last glacial period suggest that flow speeds were faster or similar to present , and it is uncertain whether the strength and position of the westerly winds changed .
Here we reconstruct Antarctic Circumpolar Current bottom speeds through the constricting Drake Passage and Scotia Sea during the Last Glacial Maximum and Holocene based on the mean grain size of sortable silt from a suite of sediment cores .
We find essentially no change in bottom flow speeds through the region , and , given that the momentum imparted by winds , and modulated by sea-ice cover , is balanced by the interaction of these flows with the seabed , this argues against substantial changes in wind stress .
However , glacial flow speeds in the sea-ice zone south of 56degrees S were significantly slower than present , whereas flow in the north was faster , but not significantly so .
We suggest that slower flow over the rough topography south of 56degrees S may have reduced diapycnal mixing in this region during the last glacial period , possibly reducing the diapycnal contribution to the Southern Ocean overturning circulation .

[1008] Ploughing the deep sea floor

Bottom trawling is a non-selective commercial fishing technique whereby heavy nets and gear are pulled along the sea floor .
The direct impact of this technique on fish populations and benthic communities has received much attention , but trawling can also modify the physical properties of seafloor sediments , water-sediment chemical exchanges and sediment fluxes .
Most of the studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments , however , where the capacity of trawling to modify the seafloor morphology coexists with high-energy natural processes driving sediment erosion , transport and deposition .
Here we show that on upper continental slopes , the reworking of the deep sea floor by trawling gradually modifies the shape of the submarine landscape over large spatial scales .
We found that trawling-induced sediment displacement and removal from fishing grounds causes the morphology of the deep sea floor to become smoother over time , reducing its original complexity as shown by high-resolution seafloor relief maps .
Our results suggest that in recent decades , following the industrialization of fishing fleets , bottom trawling has become an important driver of deep seascape evolution .
Given the global dimension of this type of fishery , we anticipate that the morphology of the upper continental slope in many parts of the world 's oceans could be altered by intensive bottom trawling , producing comparable effects on the deep sea floor to those generated by agricultural ploughing on land .

[1009] Serine starvation induces stress and p53-dependent metabolic remodelling in cancer cells

Cancer cells acquire distinct metabolic adaptations to survive stress associated with tumour growth and to satisfy the anabolic demands of proliferation .
The tumour suppressor protein p53 ( also known as TP53 ) influences a range of cellular metabolic processes , including glycolysis , oxidative phosphorylation , glutaminolysis and anti-oxidant response .
In contrast to its role in promoting apoptosis during DNA-damaging stress , p53 can promote cell survival during metabolic stress , a function that may contribute not only to tumour suppression but also to non-cancer-associated functions of p53 .
Here we show that human cancer cells rapidly use exogenous serine and that serine deprivation triggered activation of the serine synthesis pathway and rapidly suppressed aerobic glycolysis , resulting in an increased flux to the tricarboxylic acid cycle .
Transient p53-p21 ( also known as CDKN1A ) activation and cell-cycle arrest promoted cell survival by efficiently channelling depleted serine stores to glutathione synthesis , thus preserving cellular anti-oxidant capacity .
Cells lacking p53 failed to complete the response to serine depletion , resulting in oxidative stress , reduced viability and severely impaired proliferation .
The role of p53 in supporting cancer cell proliferation under serine starvation was translated to an in vivo model , indicating that serine depletion has a potential role in the treatment of p53-deficient tumours .

[1010] Biological response to climate change on a tropical mountain

Recent warming has caused changes in species distribution and abundance , but the extent of the effects is unclear .
Here we investigate whether such changes in highland forests at Monteverde , Costa Rica , are related to the increase in air temperatures that followed a step-like warming of tropical oceans in 1976 ( refs4 , 5 ) .
Twenty of 50 species of anurans ( frogs and toads ) in a 30-km2 study area , including the locally endemic golden toad ( Bufo periglenes ) , disappeared following synchronous population crashes in 1987 ( refs 6-8 ) .
Our results indicate that these crashes probably belong to a constellation of demographic changes that have altered communities of birds , reptiles and amphibians in the area and are linked to recent warming .
The changes are all associated with patterns of dry-season mist frequency , which is negatively correlated with sea surface temperatures in the equatorial Pacific and has declined dramatically since the mid-1970s .
The biological and climatic patterns suggest that atmospheric warming has raised the average altitude at the base of the orographic cloud bank , as predicted by the lifting-cloud-base hypothesis , .

[1011] Diet rapidly and reproducibly alters the human gut microbiome

Long-term dietary intake influences the structure and activity of the trillions of microorganisms residing in the human gut , but it remains unclear how rapidly and reproducibly the human gut microbiome responds to short-term macronutrient change .
Here we show that the short-term consumption of diets composed entirely of animal or plant products alters microbial community structure and overwhelms inter-individual differences in microbial gene expression .
The animal-based diet increased the abundance of bile-tolerant microorganisms ( Alistipes , Bilophila and Bacteroides ) and decreased the levels of Firmicutes that metabolize dietary plant polysaccharides ( Roseburia , Eubacterium rectale and Ruminococcus bromii ) .
Microbial activity mirrored differences between herbivorous and carnivorous mammals , reflecting trade-offs between carbohydrate and protein fermentation .
Foodborne microbes from both diets transiently colonized the gut , including bacteria , fungi and even viruses .
Finally , increases in the abundance and activity of Bilophila wadsworthia on the animal-based diet support a link between dietary fat , bile acids and the outgrowth of microorganisms capable of triggering inflammatory bowel disease .
In concert , these results demonstrate that the gut microbiome can rapidly respond to altered diet , potentially facilitating the diversity of human dietary lifestyles .

[1012] Constraints on radiative forcing and future climate change from observations and climate model ensembles

The assessment of uncertainties in global warming projections is often based on expert judgement , because a number of key variables in climate change are poorly quantified .
In particular , the sensitivity of climate to changing greenhouse-gas concentrations in the atmosphere and the radiative forcing effects by aerosols are not well constrained , leading to large uncertainties in global warming simulations .
Here we present a Monte Carlo approach to produce probabilistic climate projections , using a climate model of reduced complexity .
The uncertainties in the input parameters and in the model itself are taken into account , and past observations of oceanic and atmospheric warming are used to constrain the range of realistic model responses .
We obtain a probability density function for the present-day total radiative forcing , giving 1.4 to 2.4 W m-2 for the 5-95 per cent confidence range , narrowing the global-mean indirect aerosol effect to the range of 0 to -1.2 W m-2 .
Ensemble simulations for two illustrative emission scenarios suggest a 40 per cent probability that global-mean surface temperature increase will exceed the range predicted by the Intergovernmental Panel on Climate Change ( IPCC ) , but only a 5 per cent probability that warming will fall below that range .

[1013] The microbial gene diversity along an elevation gradient of the Tibetan grassland

Tibet is one of the most threatened regions by climate warming , thus understanding how its microbial communities function may be of high importance for predicting microbial responses to climate changes .
Here , we report a study to profile soil microbial structural genes , which infers functional roles of microbial communities , along four sites/elevations of a Tibetan mountainous grassland , aiming to explore the potential microbial responses to climate changes via a strategy of space-for-time substitution .
Using a microarray-based metagenomics tool named GeoChip 4.0 , we showed that microbial communities were distinct for most but not all of the sites .
Substantial variations were apparent in stress , N and C-cycling genes , but they were in line with the functional roles of these genes .
Cold shock genes were more abundant at higher elevations .
Also , gdh converting ammonium into urea was more abundant at higher elevations , whereas ureC converting urea into ammonium was less abundant , which was consistent with soil ammonium contents .
Significant correlations were observed between N-cycling genes ( ureC , gdh and amoA ) and nitrous oxide flux , suggesting that they contributed to community metabolism .
Lastly , we found by Canonical correspondence analysis , Mantel tests and the similarity tests that soil pH , temperature , NH4 + - N and vegetation diversity accounted for the majority ( 81.4 % ) of microbial community variations , suggesting that these four attributes were major factors affecting soil microbial communities .
On the basis of these observations , we predict that climate changes in the Tibetan grasslands are very likely to change soil microbial community functional structure , with particular impacts on microbial N-cycling genes and consequently microbe-mediated soil N dynamics .

[1014] Dual modes of the carbon cycle since the Last Glacial Maximum

The most conspicuous feature of the record of past climate contained in polar ice is the rapid warming which occurs after long intervals of gradual cooling .
During the last four transitions from glacial to interglacial conditions , over which such abrupt warmings occur , ice records indicate that the CO2 concentration of the atmosphere increased by roughly 80 to 100 parts per million by volume ( refs 1-4 ) .
But the causes of the atmospheric CO2 concentration increases are unclear .
Here we present the stable-carbon-isotope composition ( delta13CO2 ) of CO2 extracted from air trapped in ice at Taylor Dome , Antarctica , from the Last Glacial Maximum to the onset of Holocene times .
The global carbon cycle is shown to have operated in two distinct primary modes on the timescale of thousands of years , one when climate was changing relatively slowly and another when warming was rapid , each with a characteristic average stable-carbon-isotope composition of the net CO2 exchanged by the atmosphere with the land and oceans .
delta13CO2 increased between 16.5 and 9 thousand years ago by slightly more than would be estimated to be caused by the physical effects of a 5 degreesC rise in global average sea surface temperature driving a CO2 efflux from the ocean , but our data do not allow specific causes to be constrained .

[1015] Evolution of complex life cycles in helminth parasites

The fundamental question of how complex life cycles -- where there is typically more than one host -- evolve in host-parasite systems remains largely unexplored .
We suggest that complex cycles in helminths without penetrative infective stages evolve by two essentially different processes , depending on where in the cycle a new host is inserted .
In ` upward incorporation ' , a new definitive host , typically higher up a food web and which preys on the original definitive host , is added .
Advantages to the parasite are avoidance of mortality due to the predator , greater body size at maturity and higher fecundity .
The original host typically becomes an intermediate host , in which reproduction is suppressed .
In ` downward incorporation ' , a new intermediate host is added at a lower trophic level ; this reduces mortality and facilitates transmission to the original definitive host .
These two processes should also apply in helminths with penetrative infective stages , although the mathematical conditions differ .

[1016] Sequence variability of the pattern recognition receptor Mermaid mediates specificity of marine nematode symbioses

Selection of a specific microbial partner by the host is an all-important process .
It guarantees the persistence of highly specific symbioses throughout host generations .
The cuticle of the marine nematode Laxus oneistus is covered by a single phylotype of sulfur-oxidizing bacteria .
They are embedded in a layer of host-secreted mucus containing the mannose-binding protein Mermaid .
This Ca2 + - dependent lectin mediates symbiont aggregation and attachment to the nematode .
Here , we show that Stilbonema majum -- a symbiotic nematode co-occurring with L. oneistus in shallow water sediment -- is covered by bacteria phylogenetically distinct to those covering L. oneistus .
Mermaid cDNA analysis revealed extensive protein sequence variability in both the nematode species .
We expressed three recombinant Mermaid isoforms , which based on the structural predictions display the most different carbohydrate recognition domains ( CRDs ) .
We show that the three CRDs ( DNT , DDA and GDA types ) possess different affinities for L. oneistus and S. majum symbionts .
In particular , the GDA type , exclusively expressed by S. majum , displays highest agglutination activity towards its symbionts and lowest towards its L. oneistus symbionts .
Moreover , incubation of L. oneistus in the GDA type does not result in complete symbiont detachment , whereas incubation in the other types does .
This indicates that the presence of particular Mermaid isoforms on the nematode surface has a role in the attachment of specific symbionts .
This is the first report of the functional role of sequence variability in a microbe-associated molecular patterns receptor in a beneficial association .

[1017] Arctic microorganisms respond more to elevated UV-B radiation than CO2

Surface ultraviolet-B radiation and atmospheric CO2 concentrations have increased as a result of ozone depletion and burning of fossil fuels .
The effects are likely to be most apparent in polar regions where ozone holes have developed and ecosystems are particularly sensitive to disturbance .
Polar plant communities are dependent on nutrient cycling by soil microorganisms , which represent a significant and highly labile portion of soil carbon ( C ) and nitrogen ( N ) .
It was thought that the soil microbial biomass was unlikely to be affected by exposure of their associated plant communities to increased UV-B .
In contrast , increasing atmospheric CO2 concentrations were thought to have a strong effect as a result of greater below-ground C allocation .
In addition , there is a growing belief that ozone depletion is of only minor environmental concern because the impacts of UV-B radiation on plant communities are often very subtle .
Here we show that 5 years of exposure of a subarctic heath to enhanced UV-B radiation both alone and in combination with elevated CO2 resulted in significant changes in the C : N ratio and in the bacterial community structure of the soil microbial biomass .

[1018] Shorter flowering seasons and declining abundance of flower visitors in a warmer Arctic

Advancing phenology in response to global warming has been reported across biomes , raising concerns about the temporal uncoupling of trophic interactions .
Concurrently , widely reported flower visitor declines have been linked to resource limitations .
Phenological responses in the Arctic have been shown to outpace responses from lower latitudes and recent studies suggest that differences between such responses for plants and their flower visitors could be particularly pronounced in the Arctic .
The evidence for phenological uncoupling is scant because relevant data sets are lacking or not available at a relevant spatial scale .
Here , we present evidence of a climate-associated shortening of the flowering season and a concomitant decline in flower visitor abundance based on a long-term , spatially replicated ( 1996-2009 ) data set from high-Arctic Greenland .
A unique feature of the data set is the spatial and temporal overlap of independent observations of plant and insect phenology .
The shortening of the flowering season arose through spatial variation in phenological responses to warming .
The shorter flowering seasons may have played a role in the observed decline in flower visitor abundance .
Our results demonstrate that the dramatic climatic changes currently taking place in the Arctic are strongly affecting individual species and ecological communities , with implications for trophic interactions .

[1019] Tracking the Atlantic Multidecadal Oscillation through the last 8,000 years

Understanding the internal ocean variability and its influence on climate is imperative for society .
A key aspect concerns the enigmatic Atlantic Multidecadal Oscillation ( AMO ) , a feature defined by a 60 - to 90-year variability in North Atlantic sea-surface temperatures .
The nature and origin of the AMO is uncertain , and it remains unknown whether it represents a persistent periodic driver in the climate system , or merely a transient feature .
Here , we show that distinct , ~ 55 - to 70-year oscillations characterized the North Atlantic ocean-atmosphere variability over the past 8,000 years .
We test and reject the hypothesis that this climate oscillation was directly forced by periodic changes in solar activity .
We therefore conjecture that a quasi-persistent ~ 55 - to 70-year AMO , linked to internal ocean-atmosphere variability , existed during large parts of the Holocene .
Our analyses further suggest that the coupling from the AMO to regional climate conditions was modulated by orbitally induced shifts in large-scale ocean-atmosphere circulation .

[1020] Potential influences on the United Kingdom 's floods of winter 2013/14

During the winter of 2013/14 , much of the UK experienced repeated intense rainfall events and flooding .
This had a considerable impact on property and transport infrastructure .
A key question is whether the burning of fossil fuels is changing the frequency of extremes , and if so to what extent .
We assess the scale of the winter flooding before reviewing a broad range of Earth system drivers affecting UK rainfall .
Some drivers can be potentially disregarded for these specific storms whereas others are likely to have increased their risk of occurrence .
We discuss the requirements of hydrological models to transform rainfall into river flows and flooding .
To determine any general changing flood risk , we argue that accurate modelling needs to capture evolving understanding of UK rainfall interactions with a broad set of factors .
This includes changes to multiscale atmospheric , oceanic , solar and sea-ice features , and land-use and demographics .
Ensembles of such model simulations may be needed to build probability distributions of extremes for both pre-industrial and contemporary concentration levels of atmospheric greenhouse gases .

[1021] Synthesis and characterization of ZnS with controlled amount of S vacancies for photocatalytic H2 production under visible light

Controlling amount of intrinsic S vacancies was achieved in ZnS spheres which were synthesized by a hydrothermal method using Zn and S powders in concentrated NaOH solution with NaBH4 added as reducing agent .
These S vacancies efficiently extend absorption spectra of ZnS to visible region .
Their photocatalytic activities for H2 production under visible light were evaluated by gas chromatograph , and the midgap states of ZnS introduced by S vacancies were examined by density functional calculations .
Our study reveals that the concentration of S vacancies in the ZnS samples can be controlled by varying the amount of the reducing agent NaBH4 in the synthesis , and the prepared ZnS samples exhibit photocatalytic activity for H2 production under visible-light irradiation without loading noble metal .
This photocatalytic activity of ZnS increases steadily with increasing the concentration of S vacancies until the latter reaches an optimum value .
Our density functional calculations show that S vacancies generate midgap defect states in ZnS , which lead to visible-light absorption and responded .

[1022] Microbial nitrate-dependent cyclohexane degradation coupled with anaerobic ammonium oxidation

An anaerobic nitrate-reducing enrichment culture was established with a cyclic saturated petroleum hydrocarbon , cyclohexane , the fate of which in anoxic environments has been scarcely investigated .
GC-MS showed cyclohexylsuccinate as a metabolite , in accordance with an anaerobic enzymatic activation of cyclohexane by carbon-carbon addition to fumarate .
Furthermore , long-chain cyclohexyl-substituted cell fatty acids apparently derived from cyclohexane were detected .
Nitrate reduction was not only associated with cyclohexane utilization but also with striking depletion of added ammonium ions .
Significantly more ammonium was consumed than could be accounted for by assimilation .
This indicated the occurrence of anaerobic ammonium oxidation ( anammox ) with nitrite from cyclohexane-dependent nitrate reduction .
Indeed , nitrite depletion was stimulated upon further addition of ammonium .
Analysis of 16S rRNA genes and subsequent cell hybridization with specific probes showed that approximately 75 % of the bacterial cells affiliated with the Geobacteraceae and approximately 18 % with Candidatus ` Brocadia anammoxidans ' ( member of the Planctomycetales ) , an anaerobic ammonium oxidizer .
These results and additional quantitative growth experiments indicated that the member of the Geobacteraceae reduced nitrate with cyclohexane to nitrite and some ammonium ; the latter two and ammonium added to the medium were scavenged by anammox bacteria to yield dinitrogen .
A model was established to quantify the partition of each microorganism in the overall process .
Such hydrocarbon oxidation by an alleged ` denitrification ' ( ` pseudo-denitrification ' ) , which in reality is a dissimilatory loop through anammox , can in principle also occur in other microbial systems with nitrate-dependent hydrocarbon attenuation .

[1023] Advancing decadal-scale climate prediction in the North Atlantic sector

The climate of the North Atlantic region exhibits fluctuations on decadal timescales that have large societal consequences .
Prominent examples include hurricane activity in the Atlantic , and surface-temperature and rainfall variations over North America , Europe and northern Africa .
Although these multidecadal variations are potentially predictable if the current state of the ocean is known , the lack of subsurface ocean observations that constrain this state has been a limiting factor for realizing the full skill potential of such predictions .
Here we apply a simple approach -- that uses only sea surface temperature ( SST ) observations -- to partly overcome this difficulty and perform retrospective decadal predictions with a climate model .
Skill is improved significantly relative to predictions made with incomplete knowledge of the ocean state , particularly in the North Atlantic and tropical Pacific oceans .
Thus these results point towards the possibility of routine decadal climate predictions .
Using this method , and by considering both internal natural climate variations and projected future anthropogenic forcing , we make the following forecast : over the next decade , the current Atlantic meridional overturning circulation will weaken to its long-term mean ; moreover , North Atlantic SST and European and North American surface temperatures will cool slightly , whereas tropical Pacific SST will remain almost unchanged .
Our results suggest that global surface temperature may not increase over the next decade , as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming .

[1024] Uncertainty in simulating wheat yields under climate change

Projections of climate change impacts on crop yields are inherently uncertain .
Uncertainty is often quantified when projecting future greenhouse gas emissions and their influence on climate .
However , multi-model uncertainty analysis of crop responses to climate change is rare because systematic and objective comparisons among process-based crop simulation models are difficult .
Here we present the largest standardized model intercomparison for climate change impacts so far .
We found that individual crop models are able to simulate measured wheat grain yields accurately under a range of environments , particularly if the input information is sufficient .
However , simulated climate change impacts vary across models owing to differences in model structures and parameter values .
A greater proportion of the uncertainty in climate change impact projections was due to variations among crop models than to variations among downscaled general circulation models .
Uncertainties in simulated impacts increased with CO2 concentrations and associated warming .
These impact uncertainties can be reduced by improving temperature and CO2 relationships in models and better quantified through use of multi-model ensembles .
Less uncertainty in describing how climate change may affect agricultural productivity will aid adaptation strategy development andpolicymaking .

[1025] Observed changes in top-of-the-atmosphere radiation and upper-ocean heating consistent within uncertainty

Global climate change results from a small yet persistent imbalance between the amount of sunlight absorbed by Earth and the thermal radiation emitted back to space .
An apparent inconsistency has been diagnosed between interannual variations in the net radiation imbalance inferred from satellite measurements and upper-ocean heating rate from in situ measurements , and this inconsistency has been interpreted as ` missing energy ' in the system .
Here we present a revised analysis of net radiation at the top of the atmosphere from satellite data , and we estimate ocean heat content , based on three independent sources .
We find that the difference between the heat balance at the top of the atmosphere and upper-ocean heat content change is not statistically significant when accounting for observational uncertainties in ocean measurements , given transitions in instrumentation and sampling .
Furthermore , variability in Earth 's energy imbalance relating to El Nino-Southern Oscillation is found to be consistent within observational uncertainties among the satellite measurements , a reanalysis model simulation and one of the ocean heat content records .
We combine satellite data with ocean measurements to depths of 1,800 m , and show that between January 2001 and December 2010 , Earth has been steadily accumulating energy at a rate of 0.50 + / -0.43 Wm-2 ( uncertainties at the 90 % confidence level ) .
We conclude that energy storage is continuing to increase in the sub-surface ocean .

[1026] Water balance altered in cucumber plants infected with Fusarium oxysporum f. sp .

cucumerinum
Fusarium wilt is caused by the infection and growth of the fungus Fusarium oxysporum in the xylem of host plants .
The physiological responses of cucumbers that are infected with Fusarium oxysporum f. sp .
cucumerinum ( FOC ) was studied in pot and hydroponic experiments in a greenhouse .
The results showed that although water absorption and stem hydraulic conductance decreased markedly in infected plants , large amounts of red ink accumulated in the leaves of infected cucumber plants .
The transpiration rate ( E ) and stomatal conductance ( gs ) of the infected plants were significantly reduced , but the E/gs was higher than healthy plants .
We further found that there was a positive correlation between leaf membrane injury and E/gs , indicating that the leaf cell membrane injury increased the non-stomatal water loss from infected plants .
The fusaric acid ( FA ) , which was detected in the infected plant , resulted in damage to the leaf cell membranes and an increase in E/gs , suggesting that FA plays an important role in non-stomatal water loss .
In conclusion , leaf cell membrane injury in the soil-borne Fusarium wilt of cucumber plants induced uncontrolled water loss from damaged cells .
FA plays a critical role in accelerating the development of Fusarium wilt in cucumber plants .

[1027] Stimulated Leaf Dark Respiration in Tomato in an Elevated Carbon Dioxide Atmosphere

It is widely accepted that leaf dark respiration is a determining factor for the growth and maintenance of plant tissues and the carbon cycle .
However , the underlying effect and mechanism of elevated CO2 concentrations ( [ CO2 ] ) on dark respiration remain unclear .
In this study , tomato plants grown at elevated [ CO2 ] showed consistently higher leaf dark respiratory rate , as compared with ambient control plants .
The increased respiratory capacity was driven by a greater abundance of proteins , carbohydrates , and transcripts involved in pathways of glycolysis carbohydrate metabolism , the tricarboxylic acid cycle , and mitochondrial electron transport energy metabolism .
This study provides substantial evidence in support of the concept that leaf dark respiration is increased by elevated [ CO2 ] in tomato plants and suggests that the increased availability of carbohydrates and the increased energy status are involved in the increased rate of dark respiration in response to elevated [ CO2 ] .

[1028] Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus

Despite ongoing increases in atmospheric greenhouse gases , the Earth 's global average surface air temperature has remained more or less steady since 2001 .
A variety of mechanisms have been proposed to account for this slowdown in surface warming .
A key component of the global hiatus that has been identified is cool eastern Pacific sea surface temperature , but it is unclear how the ocean has remained relatively cool there in spite of ongoing increases in radiative forcing .
Here we show that a pronounced strengthening in Pacific trade winds over the past two decades -- unprecedented in observations/reanalysis data and not captured by climate models -- is sufficient to account for the cooling of the tropical Pacific and a substantial slowdown in surface warming through increased subsurface ocean heat uptake .
The extra uptake has come about through increased subduction in the Pacific shallow overturning cells , enhancing heat convergence in the equatorial thermocline .
At the same time , the accelerated trade winds have increased equatorial upwelling in the central and eastern Pacific , lowering sea surface temperature there , which drives further cooling in other regions .
The net effect of these anomalous winds is a cooling in the 2012 global average surface air temperature of 0.1-0 .2 degreesC , which can account for much of the hiatus in surface warming observed since 2001 .
This hiatus could persist for much of the present decade if the trade wind trends continue , however rapid warming is expected to resume once the anomalous wind trends abate .

[1029] Carbonic anhydrases , EPF2 and a novel protease mediate CO2 control of stomatal development

Environmental stimuli , including elevated carbon dioxide levels , regulate stomatal development ; however , the key mechanisms mediating the perception and relay of the CO2 signal to the stomatal development machinery remain elusive .
To adapt CO2 intake to water loss , plants regulate the development of stomatal gas exchange pores in the aerial epidermis .
A diverse range of plant species show a decrease in stomatal density in response to the continuing rise in atmospheric CO2 ( ref .
4 ) .
To date , one mutant that exhibits deregulation of this CO2-controlled stomatal development response , hic ( which is defective in cell-wall wax biosynthesis , ref .
5 ) , has been identified .
Here we show that recently isolated Arabidopsis thaliana beta-carbonic anhydrase double mutants ( ca1 ca4 ) exhibit an inversion in their response to elevated CO2 , showing increased stomatal development at elevated CO2 levels .
We characterized the mechanisms mediating this response and identified an extracellular signalling pathway involved in the regulation of CO2-controlled stomatal development by carbonic anhydrases .
RNA-seq analyses of transcripts show that the extracellular pro-peptide-encoding gene EPIDERMAL PATTERNING FACTOR 2 ( EPF2 ) , but not EPF1 ( ref .
9 ) , is induced in wild-type leaves but not in ca1 ca4 mutant leaves at elevated CO2 levels .
Moreover , EPF2 is essential for CO2 control of stomatal development .
Using cell-wall proteomic analyses and CO2-dependent transcriptomic analyses , we identified a novel CO2-induced extracellular protease , CRSP ( CO2 RESPONSE SECRETED PROTEASE ) , as a mediator of CO2-controlled stomatal development .
Our results identify mechanisms and genes that function in the repression of stomatal development in leaves during atmospheric CO2 elevation , including the carbonic-anhydrase-encoding genes CA1 and CA4 and the secreted protease CRSP , which cleaves the pro-peptide EPF2 , in turn repressing stomatal development .
Elucidation of these mechanisms advances the understanding of how plants perceive and relay the elevated CO2 signal and provides a framework to guide future research into how environmental challenges can modulate gas exchange in plants .

[1030] Deep ocean carbonate ion increase during mid Miocene CO2 decline

Characterised by long term cooling and abrupt ice sheet expansion on Antarctica ~ 14 Ma ago , the mid Miocene marked the beginning of the modern ice-house world , yet there is still little consensus on its causes , in part because carbon cycle dynamics are not well constrained .
In particular , changes in carbonate ion concentration ( [ CO32 - ] ) in the ocean , the largest carbon reservoir of the ocean-land-atmosphere system , are poorly resolved .
We use benthic foraminiferal B/Ca ratios to reconstruct relative changes in [ CO32 - ] from the South Atlantic , East Pacific , and Southern Oceans .
Our results suggest an increase of perhaps ~ 40 mumol/kg may have occurred between ~ 15 and 14 Ma in intermediate to deep waters in each basin .
This long-term increase suggests elevated alkalinity input , perhaps from the Himalaya , rather than other shorter-term mechanisms such as ocean circulation or ecological changes , and may account for some of the proposed atmospheric CO2 decline before ~ 14 Ma .

[1031] Observations of increasing carbon dioxide concentration in Earth 's thermosphere

Carbon dioxide occurs naturally throughout Earth ` satmosphere .
In the thermosphere , CO2 is the primary radiative cooling agent and fundamentally affects the energy balance and temperature of this high-altitude atmospheric layer .
Anthropogenic CO2 increases are expected to propagate upward throughout the entire atmosphere , which should result in a cooler , more contracted thermosphere .
This contraction , in turn , will reduce atmospheric drag on satellites and may have adverse consequences for the orbital debris environment that is already unstable .
However , observed thermospheric mass density trends derived from satellite orbits are generally stronger than model predictions , indicating that our quantitative understanding of these changes is incomplete .
So far , CO2 trends have been measured only up to 35 km altitude .
Here , we present direct evidence that CO2 concentrations in the upper atmosphere -- probably the primary driver of long-term thermospheric trends -- are increasing .
We analyse eight years of CO2 and carbon monoxide mixing ratios derived from satellite-based solar occultation spectra .
After correcting for seasonal-latitudinal and solar influences , we obtain an estimated global increase in COx ( CO2 and CO , combined ) concentrations of 23.5 + / -6.3 ppm per decade at an altitude of 101 km , about 10 ppm per decade faster than predicted by an upper atmospheric model .
We suggest that this discrepancy may explain why the thermospheric density decrease is stronger than expected .

[1032] Drought alters the structure and functioning of complex food webs

Climate change is expected to make many regions of the world much drier over coming decades .
More intense drought would transform rivers with potentially severe but largely unknown consequences at higher ( multispecies ) levels of organization .
Here we show experimentally how the intensification of drought may alter the underlying structure and functioning ( biomass flux dynamics ) of freshwater food webs -- networks of species and their interactions .
Drought triggered substantial losses of species and links , especially among predators , leading to the partial collapse of the food webs .
Total resource-consumer biomass flux was also strongly suppressed by disturbance , yet several network-level properties ( such as connectance and interaction diversity ) were conserved , driven by consumer resource fidelity and a substantial reconfiguration of fluxes within the webs as production shifted down the size spectrum from large to small species .
Our research demonstrates that drier climates could have far-reaching impacts on the functioning of freshwater ecosystems .

[1033] Distinguishing random environmental fluctuations from ecological catastrophes for the North Pacific Ocean

The prospect of rapid dynamic changes in the environment is a pressing concern that has profound management and public policy implications .
Worries over sudden climate change and irreversible changes in ecosystems are rooted in the potential that nonlinear systems have for complex and ` pathological ' behaviours .
Nonlinear behaviours have been shown in model systems and in some natural systems , but their occurrence in large-scale marine environments remains controversial .
Here we show that time series observations of key physical variables for the North Pacific Ocean that seem to show these behaviours are not deterministically nonlinear , and are best described as linear stochastic .
In contrast , we find that time series for biological variables having similar properties exhibit a low-dimensional nonlinear signature .
To our knowledge , this is the first direct test for nonlinearity in large-scale physical and biological data for the marine environment .
These results address a continuing debate over the origin of rapid shifts in certain key marine observations as coming from essentially stochastic processes or from dominant nonlinear mechanisms .
Our measurements suggest that large-scale marine ecosystems are dynamically nonlinear , and as such have the capacity for dramatic change in response to stochastic fluctuations in basin-scale physical states .

[1034] Long-term projections and acclimatization scenarios of temperature-related mortality in Europe

The steady increase in greenhouse gas concentrations is inducing a detectable rise in global temperatures .
The sensitivity of human societies to warming temperatures is , however , a transcendental question not comprehensively addressed to date .
Here we show the link between temperature , humidity and daily numbers of deaths in nearly 200 European regions , which are subsequently used to infer transient projections of mortality under state-of-the-art high-resolution greenhouse gas scenario simulations .
Our analyses point to a change in the seasonality of mortality , with maximum monthly incidence progressively shifting from winter to summer .
The results also show that the rise in heat-related mortality will start to completely compensate the reduction of deaths from cold during the second half of the century , amounting to an average drop in human lifespan of up 3-4 months in 2070-2100 .
Nevertheless , projections suggest that human lifespan might indeed increase if a substantial degree of adaptation to warm temperatures takes place .

[1035] Rapid response of Helheim Glacier in Greenland to climate variability over the past century

During the early 2000s the Greenland Ice Sheet experienced the largest ice-mass loss of the instrumental record , largely as a result of the acceleration , thinning and retreat of large outlet glaciers in West and southeast Greenland .
The quasi-simultaneous change in the glaciers suggests a common climate forcing .
Increasing air and ocean temperatures have been indicated as potential triggers .
Here , we present a record of calving activity of Helheim Glacier , East Greenland , that extends back to about AD 1890 , based on an analysis of sedimentary deposits from Sermilik Fjord , where Helheim Glacier terminates .
Specifically , we use the annual deposition of sand grains as a proxy for iceberg discharge .
Our record reveals large fluctuations in calving rates , but the present high rate was reproduced only in the 1930s .
A comparison with climate indices indicates that high calving activity coincides with a relatively strong influence of Atlantic water and a lower influence of polar water on the shelf off Greenland , as well as with warm summers and the negative phase of the North Atlantic Oscillation .
Our analysis provides evidence that Helheim Glacier responds to short-term fluctuations of large-scale oceanic and atmospheric conditions , on timescales of 3-10 years .

[1036] Origin and evolution of a splay fault in the Nankai accretionary wedge

Subduction zones are often characterized by wedge-shaped sedimentary complexes -- called accretionary prisms -- that form when sediments are scraped off the subducting plate and added to the overriding plate .
Large , landward-dipping thrust faults can cut through such a prism : these faults , known as ` megasplay faults ' , originate near the top of the subducting plate and terminate at the shallow , landward edge of the prism .
Megasplay faults have been the subject of numerous geological and geophysical studies , but their initiation and evolution through time remains poorly constrained .
Here we combine seismic reflection data from the Nankai accretionary wedge with geological data collected by the Integrated Ocean Drilling Program ( IODP ) and find that the splay fault cutting this wedge initiated ~ 1.95 Million years ( Myr ) ago in the lower part of the prism as an out-of-sequence thrust ( OOST ) .
After an initial phase of high activity , the movement along the fault slowed down , but uplift and reactivation of the fault resumed about 1.55 Myr ago .
The alternating periods of high and low activity along the splay fault that we document hint at episodic changes in the mechanical stability of accretionary prisms .

[1037] Increased ventilation of Antarctic deep water during the warm mid-Pliocene

The mid-Pliocene warm period is a recent warm geological period that shares similarities with predictions of future climate .
It is generally held the mid-Pliocene Atlantic Meridional Overturning Circulation must have been stronger , to explain a weak Atlantic meridional delta13C gradient and large northern high-latitude warming .
However , climate models do not simulate such stronger Atlantic Meridional Overturning Circulation , when forced with mid-Pliocene boundary conditions .
Proxy reconstructions allow for an alternative scenario that the weak delta13C gradient can be explained by increased ventilation and reduced stratification in the Southern Ocean .
Here this alternative scenario is supported by simulations with the Norwegian Earth System Model ( NorESM-L ) , which simulate an intensified and slightly poleward shifted wind field off Antarctica , giving enhanced ventilation and reduced stratification in the Southern Ocean .
Our findings challenge the prevailing theory and show how increased Southern Ocean ventilation can reconcile existing model-data discrepancies about Atlantic Meridional Overturning Circulation while explaining fundamental ocean features .

[1038] The origin of malaria : mixed messages from genetic diversity

Over the past 35 years , the incidence of malaria has increased 2-3-fold .
At present , it affects 300-500 million people and causes about 1 million deaths , primarily in Africa .
The continuing upsurge has come from a coincidence of drug-resistant parasites , insecticide-resistant mosquitoes , global climate change and continuing poverty and political instability .
An analogous rapid increase in malaria might have taken place about 10,000 years ago .
Patterns of genetic variation in mitochondrial DNA support this model , but variation in nuclear genes gives an ambiguous message .
Resolving these discrepancies has implications for the evolution of drug resistance and vaccine evasion .

[1039] Influence of NOx emissions from ships on tropospheric photochemistry and climate

Emissions of nitrogen oxides ( NOx , the sum of NO and NO2 ) from fossil-fuel burning dominate the NOx burden of the lower troposphere in many regions .
These emissions increase tropospheric ozone and hydroxyl-radical concentrations over their natural ` background ' levels , thereby increasing the oxidizing power of the atmosphere .
Fossil-fuel emissions of NOx ( refs 3 , 4 ) account for about half of the global NOx source to the atmosphere ; other significant sources are from biomass burning , soil emissions , aircraft exhausts and lightning , all primarily continental .
However , ocean-going ships burning fossil fuels may also contribute a significant fraction ( > 10 % ) to global NOx production .
Here we use NOx emission data and a high-resolution chemistry-transport model to estimate that ship NOx emissions result in a more than 100-fold increase in surface NOx concentrations in heavily traversed ocean regions .
This enhancement has a notable effect on modelled surface ozone and hydroxyl-radical concentrations .
In particular , a predicted fivefold increase in the July hydroxyl-radical burden over the northern Atlantic and Pacific oceans would be expected to reduce the atmospheric lifetimes of reactive greenhouse gases -- such as methane -- as well as to increase aerosol production rates and cloud reflectivities , therefore exerting a cooling influence on the climate .

[1040] Channelized fluid flow in oceanic crust reconciles heat-flow and permeability data

Hydrothermal fluid circulation within the sea floor profoundly influences the physical , chemical and biological state of the crust and the oceans .
Circulation within ridge flanks ( in crust more than 1 Myr old ) results in greater heat loss and fluid flux than that at ridge crests and persists for millions of years , thereby altering the composition of the crust and overlying ocean .
Fluid flow in oceanic crust is , however , limited by the extent and nature of the rock 's permeability .
Here we demonstrate that the global data set of borehole permeability measurements in uppermost oceanic crust defines a trend with age that is consistent with changes in seismic velocity .
This trend -- which indicates that fluid flow should be greatly reduced in crust older than a few million years -- would appear to be inconsistent with heat-flow observations , which on average indicate significant advective heat loss in crust up to 65 Myr old .
But our calculations , based on a lateral flow model , suggest that regional-scale permeabilities are much higher than have been measured in boreholes .
These results can be reconciled if most of the fluid flow in the upper crust is channelized through a small volume of rock , influencing the geometry of convection and the nature of fluid-rock interaction .

[1041] Specific rhizosphere bacterial and fungal groups respond differently to elevated atmospheric CO2

Soil community responses to increased atmospheric CO2 concentrations are expected to occur mostly through interactions with changing vegetation patterns and plant physiology .
To gain insight into the effects of elevated atmospheric CO2 on the composition and functioning of microbial communities in the rhizosphere , Carex arenaria ( a non-mycorrhizal plant species ) and Festuca rubra ( a mycorrhizal plant species ) were grown under defined atmospheric conditions with either ambient ( 350 p.p.m. ) or elevated ( 700 p.p.m. ) CO2 concentrations .
PCR-DGGE ( PCR-denaturing gradient gel electrophoresis ) and quantitative-PCR were carried out to analyze , respectively , the structure and abundance of the communities of actinomycetes , Fusarium spp. , Trichoderma spp. , Pseudomonas spp. , Burkholderia spp .
and Bacillus spp .
Responses of specific functional groups , such as phloroglucinol , phenazine and pyrrolnitrin producers , were also examined by quantitative-PCR , and HPLC ( high performance liquid chromatography ) was employed to assess changes in exuded sugars in the rhizosphere .
Multivariate analysis of group-specific community profiles showed disparate responses to elevated CO2 for the different bacterial and fungal groups examined , and these responses were dependent on plant type and soil nutrient availability .
Within the bacterial community , the genera Burkholderia and Pseudomonas , typically known as successful rhizosphere colonizers , were significantly influenced by elevated CO2 , whereas the genus Bacillus and actinomycetes , typically more dominant in bulk soil , were not .
Total sugar concentrations in the rhizosphere also increased in both plants in response to elevated CO2 .
The abundances of phloroglucinol - , phenazine - and pyrrolnitrin-producing bacterial communities were also influenced by elevated CO2 , as was the abundance of the fungal genera Fusarium and Trichoderma .

[1042] Chemical and biological trends during lake evolution in recently deglaciated terrain

As newly formed landscapes evolve , physical and biological changes occur that are collectively known as primary succession .
Although succession is a fundamental concept in ecology , it is poorly understood in the context of aquatic environments .
The prevailing view is that lakes become more enriched in nutrients as they age , leading to increased biological production .
Here we report the opposite pattern of lake development , observed from the water chemistry of lakes that formed at various times within the past 10,000 years during glacial retreat at Glacier Bay , Alaska .
The lakes have grown more dilute and acidic with time , accumulated dissolved organic carbon and undergone a transient rise in nitrogen concentration , all as a result of successional changes in surrounding vegetation and soils .
Similar trends are evident from fossil diatom stratigraphy of lake sediment cores .
These results demonstrate a tight hydrologic coupling between terrestrial and aquatic environments during the colonization of newly deglaciated landscapes , and provide a conceptual basis for mechanisms of primary succession in boreal lake ecosystems .

[1043] Improving farming practices reduces the carbon footprint of spring wheat production

Wheat is one of the world 's most favoured food sources , reaching millions of people on a daily basis .
However , its production has climatic consequences .
Fuel , inorganic fertilizers and pesticides used in wheat production emit greenhouse gases that can contribute negatively to climate change .
It is unknown whether adopting alternative farming practices will increase crop yield while reducing carbon emissions .
Here we quantify the carbon footprint of alternative wheat production systems suited to semiarid environments .
We find that integrating improved farming practices ( that is , fertilizing crops based on soil tests , reducing summerfallow frequencies and rotating cereals with grain legumes ) lowers wheat carbon footprint effectively , averaging -256 kg CO2 eq ha-1 per year .
For each kg of wheat grain produced , a net 0.027-0 .377 kg CO2 eq is sequestered into the soil .
With the suite of improved farming practices , wheat takes up more CO2 from the atmosphere than is actually emitted during its production .

[1044] Coupled dynamics of body mass and population growth in response to environmental change

Environmental change has altered the phenology , morphological traits and population dynamics of many species .
However , the links underlying these joint responses remain largely unknown owing to a paucity of long-term data and the lack of an appropriate analytical framework .
Here we investigate the link between phenotypic and demographic responses to environmental change using a new methodology and a long-term ( 1976-2008 ) data set from a hibernating mammal ( the yellow-bellied marmot ) inhabiting a dynamic subalpine habitat .
We demonstrate how earlier emergence from hibernation and earlier weaning of young has led to a longer growing season and larger body masses before hibernation .
The resulting shift in both the phenotype and the relationship between phenotype and fitness components led to a decline in adult mortality , which in turn triggered an abrupt increase in population size in recent years .
Direct and trait-mediated effects of environmental change made comparable contributions to the observed marked increase in population growth .
Our results help explain how a shift in phenology can cause simultaneous phenotypic and demographic changes , and highlight the need for a theory integrating ecological and evolutionary dynamics in stochastic environments .

[1045] Microbial mediation of carbon-cycle feedbacks to climate warming

Understanding the mechanisms of biospheric feedbacks to climate change is critical to project future climate warming .
Although microorganisms catalyse most biosphere processes related to fluxes of greenhouse gases , little is known about the microbial role in regulating future climate change .
Integrated metagenomic and functional analyses of a long-term warming experiment in a grassland ecosystem showed that microorganisms play crucial roles in regulating soil carbon dynamics through three primary feedback mechanisms : shifting microbial community composition , which most likely led to the reduced temperature sensitivity of heterotrophic soil respiration ; differentially stimulating genes for degrading labile but not recalcitrant carbon so as to maintain long-term soil carbon stability and storage ; and enhancing nutrient-cycling processes to promote plant nutrient-use efficiency and hence plant growth .
Elucidating microbially mediated feedbacks is fundamental to understanding ecosystem responses to climate warming and provides a mechanistic basis for carbon-climate modelling .

[1046] Responses of soil microbial activity to cadmium pollution and elevated CO2

To address the combined effects of cadmium ( Cd ) and elevated CO2 on soil microbial communities , DGGE ( denaturing gradient gel electrophoresis ) profiles , respiration , carbon ( C ) and nitrogen ( N ) concentrations , loessial soils were exposed to four levels of Cd , i.e. , 0 ( Cd0 ) , 1.5 ( Cd1 .5 ) , 3.0 ( Cd3 .0 ) and 6.0 ( Cd6 .0 ) mg Cd kg-1 soil , and two levels of CO2 , i.e. , 360 ( aCO2 ) and 480 ( eCO2 ) ppm .
Compared to Cd0 , Cd1 .5 increased fungal abundance but decreased bacterial abundance under both CO2 levels , whilst Cd3 .0 and Cd6 .0 decreased both fungal and bacterial abundance .
Profiles of DGGE revealed alteration of soil microbial communities under eCO2 .
Soil respiration decreased with Cd concentrations and was greater under eCO2 than under aCO2 .
Soil total C and N were greater under higher Cd .
These results suggest eCO2 could stimulate , while Cd pollution could restrain microbial reproduction and C decomposition with the restraint effect alleviated by eCO2 .

[1047] Pasture damage by an Amazonian earthworm

Almost all cultivated soils undergo some reduction in the porosity of the surface layers , and nowhere is this more evident than in tropical rainforests that have been converted to pastures .
Following deforestation in an area of Costa Rica , soil bulk density has been shown to increase rapidly after conversion to pasture , leading to poor drainage and a reduced rate of gaseous diffusion .
These factors limit methane consumption and promote the anaerobic production of methane .
A similar effect on methane flux has been found in upland soils in the Brazilian Amazonian basin after conversion from forest to pasture , .
Increases in atmospheric methane are therefore not limited to emissions from flooded soils , as forest-to-pasture conversion promotes the anaerobic mineralization of organic matter by changing the physical properties of soil .

[1048] Onset of permanent stratification in the subarctic Pacific Ocean

The surface waters of the modern subarctic Pacific Ocean are isolated from the nutrient-rich waters below by a steep vertical gradient in salinity ( halocline ) , a feature which is a dominant control on upper-ocean stratification in polar environments .
The physical processes which maintain the halocline and , in turn , its physical , biological , and geochemical effects have long been subjects of intense inquiry .
The stratification of polar surface waters influences the exchange of CO2 between ocean and atmosphere , so the history of the subarctic Pacific halocline may have played a role in past changes in atmospheric CO2 concentration .
Here we report opal accumulation rates and nitrogen-isotope data from sediments in this region which indicate that the subarctic Pacific halocline developed abruptly 2.73 million years ago , coincident with the onset of extensive Northern Hemisphere glaciation .
The halocline would have reduced the transport of nutrient-rich deep water into the euphotic zone , leading to a decrease in biological production but an increase in the fraction of nutrient stocks utilized .
This increase in the efficiency of the ` biological pump ' would have lowered the rate of CO2 evasion from ocean to atmosphere , potentially reducing atmospheric CO2 concentrations from the suggested higher level of the preceding mid-Pliocene warm interval .

[1049] Variability of the North Atlantic Oscillation over the past 5,200 years

Climate in the Arctic region and northwestern Europe is strongly affected by the North Atlantic Oscillation ( NAO ) , the dominant mode of atmospheric variability at mid-latitudes in the North Atlantic region .
The NAO index is an indicator of atmospheric circulation and weather patterns : when the index is positive , Europe and the eastern US are mild and wet , whereas Greenland and northern Canada are cold and dry .
A negative index is associated with the reverse pattern .
Reconstructions of the NAO have so far been limited to the past 900 years .
Here we analyse a 5,200-year-long , high-resolution lake sediment record from southwestern Greenland to reconstruct lake hypolimnic anoxia , and link the results to an existing reconstruction of the NAO index from tree rings and speleothems .
Using the relationship between the two records , we find that around 4,500 and 650 years ago -- around the end of the Holocene Thermal Maximum and the beginning of the Little Ice Age , respectively -- the NAO changed from generally positive to variable , intermittently negative conditions .
We suggest that variability in the dominant state of the NAO tend to coincide with large-scale changes in Northern Hemisphere climate .
However , the onset of the Medieval Climate Anomaly was not associated with any notable changes in the NAO .

[1050] Projected continent-wide declines of the emperor penguin under climate change

Climate change has been projected to affect species distribution and future trends of local populations , but projections of global population trends are rare .
We analyse global population trends of the emperor penguin ( Aptenodytes forsteri ) , an iconic Antarctic top predator , under the influence of sea ice conditions projected by coupled climate models assessed in the Intergovernmental Panel on Climate Change ( IPCC ) effort .
We project the dynamics of all 45 known emperor penguin colonies by forcing a sea-ice-dependent demographic model with local , colony-specific , sea ice conditions projected through to the end of the twenty-first century .
Dynamics differ among colonies , but by 2100 all populations are projected to be declining .
At least two-thirds are projected to have declined by > 50 % from their current size .
The global population is projected to have declined by at least 19 % .
Because criteria to classify species by their extinction risk are based on the global population dynamics , global analyses are critical for conservation .
We discuss uncertainties arising in such global projections and the problems of defining conservation criteria for species endangered by future climate change .

[1051] Diversity-dependent production can decrease the stability of ecosystem functioning

There is concern that species loss may adversely affect ecosystem functioning and stability .
But although there is evidence that biodiversity loss can lead to reductions in biomass production , there is no direct evidence that biodiversity loss affects ecosystem resistance ( ability to withstand perturbation ) or resilience ( recovery from perturbation ) .
Yet theory , laboratory experiments and indirect experimental evidence strongly suggest that diversity and stability are related .
Here we report results from a field experiment with factorially crossed perturbation and diversity manipulations .
We simulated drought perturbation on constructed grassland ecosystems containing 1 , 2 , 4 , 8 or 32 plant species .
Under unperturbed conditions , the species-poor systems achieved lower biomass production than the species-rich systems .
However , the species-poor systems were more resistant to perturbation than the species-rich systems .
The species-poor systems also showed a larger initial resilience following perturbation , although the original relationship between diversity and productivity was fully restored after 1 year .
Our results confirm that biodiversity increases biomass production , but they also point to the fact that such diversity-production associations may lead to an inverse relationship between biodiversity and the stability of ecosystem functioning .

[1052] Graphite formation by carbonate reduction during subduction

Carbon is transported from Earth 's surface into its interior at subduction zones .
Carbonates in sediments overlying hydrothermally altered rocks ( including serpentinites ) within the subducted slab are the main carriers of this carbon .
Part of the carbon is recycled back to the surface by volcanism , but some is transferred to the deep Earth .
Redox transformations during shallow subduction control the transfer and long-term fate of carbon , but are poorly explored .
Here we use carbon stable isotopes and Raman spectroscopy to analyse the reduction of carbonate in an exhumed serpentinite-sediment contact in Alpine Corsica , France .
We find that highly crystalline graphite was formed during subduction metamorphism and was concentrated in the sediment , within a reaction zone in direct contact with the serpentinite .
The graphite in this reaction zone has a carbon isotopic signature ( delta13C ) of up to 0.8 + / -0.1 / 1000 , similar to that of the original calcite that composed the sediments , and is texturally associated with the calcium-bearing mineral wollastonite that is also formed in the process .
We use mass-balance calculations to show that about 9 % of the total carbonaceous matter in the sedimentary unit results from complete calcite reduction in the reaction zone .
We conclude that graphite formation , under reducing and low-temperature conditions , provides a mechanism to retain carbon in a subducting slab , aiding transport of carbon into the deeper Earth .

[1053] Water-CO2 trade-offs in electricity generation planning

In 2011 , the state of Texas experienced the lowest annual rainfall on record , with similar droughts affecting East Africa , China and Australia .
Climate change is expected to further increase the likelihood and severity of future droughts .
Simultaneously , population and industrial growth increases demand for drought-stressed water resources and energy , including electricity .
In the US , nearly half of water withdrawals are for electricity generation , much of which comes from greenhouse gas emitting fossil fuel combustion .
The result is a three-way tension among efforts to meet growing energy demands while reducing greenhouse gas emissions and water withdrawals , a critical issue within the so-called water-energy nexus .
We focus on this interaction within the electric sector by using a generation expansion planning model to explore the trade-offs .
We show that large reductions in CO2 emissions would probably increase water withdrawals for electricity generation in the absence of limits on water usage , and that simultaneous restriction of CO2 emissions and water withdrawals requires a different mix of energy technologies and higher costs than one would plan to reduce either CO2 or water alone .

[1054] Decreased frequency of North Atlantic polar lows associated with future climate warming

Every winter , the high-latitude oceans are struck by severe storms that are considerably smaller than the weather-dominating synoptic depressions .
Accompanied by strong winds and heavy precipitation , these often explosively developing mesoscale cyclones -- termed polar lows -- constitute a threat to offshore activities such as shipping or oil and gas exploitation .
Yet owing to their small scale , polar lows are poorly represented in the observational and global reanalysis data often used for climatological investigations of atmospheric features and can not be assessed in coarse-resolution global simulations of possible future climates .
Here we show that in a future anthropogenically warmed climate , the frequency of polar lows is projected to decline .
We used a series of regional climate model simulations to downscale a set of global climate change scenarios from the Intergovernmental Panel of Climate Change .
In this process , we first simulated the formation of polar low systems in the North Atlantic and then counted the individual cases .
A previous study using NCEP/NCAR re-analysis data revealed that polar low frequency from 1948 to 2005 did not systematically change .
Now , in projections for the end of the twenty-first century , we found a significantly lower number of polar lows and a northward shift of their mean genesis region in response to elevated atmospheric greenhouse gas concentration .
This change can be related to changes in the North Atlantic sea surface temperature and mid-troposphere temperature ; the latter is found to rise faster than the former so that the resulting stability is increased , hindering the formation or intensification of polar lows .
Our results provide a rare example of a climate change effect in which a type of extreme weather is likely to decrease , rather than increase .

[1055] Toward a mechanistic understanding of how natural bacterial communities respond to changes in temperature in aquatic ecosystems

We examine how heterotrophic bacterioplankton communities respond to temperature by mathematically defining two thermally adapted species and showing how changes in environmental temperature affect competitive outcome in a two-resource environment .
We did this by adding temperature dependence to both the respiration and uptake terms of a two species , two-resource model rooted in Droop kinetics .
We used published literature values and results of our own work with experimental microcosms to parameterize the model and to quantitatively and qualitatively define relationships between temperature and bacterioplankton physiology .
Using a graphical resource competition framework , we show how physiological adaptation to temperature can allow organisms to be more , or less , competitive for limiting resources across a thermal gradient ( 2-34 degreesC ) .
Our results suggest that the effect of temperature on bacterial community composition , and therefore bacterially mediated biogeochemical processes , depends on the available resource pool in a given system .
In addition , our results suggest that the often unclear relationship between temperature and bacterial metabolism , as reported in the literature , can be understood by allowing for changes in the relative contribution of thermally adapted populations to community metabolism .

[1056] Reliability of flipper-banded penguins as indicators of climate change

In 2007 , the Intergovernmental Panel on Climate Change highlighted an urgent need to assess the responses of marine ecosystems to climate change .
Because they lie in a high-latitude region , the Southern Ocean ecosystems are expected to be strongly affected by global warming .
Using top predators of this highly productive ocean ( such as penguins ) as integrative indicators may help us assess the impacts of climate change on marine ecosystems .
Yet most available information on penguin population dynamics is based on the controversial use of flipper banding .
Although some reports have found the effects of flipper bands to be deleterious , some short-term ( one-year ) studies have concluded otherwise , resulting in the continuation of extensive banding schemes and the use of data sets thus collected to predict climate impact on natural populations .
Here we show that banding of free-ranging king penguins ( Aptenodytes patagonicus ) impairs both survival and reproduction , ultimately affecting population growth rate .
Over the course of a 10-year longitudinal study , banded birds produced 39 % fewer chicks and had a survival rate 16 % lower than non-banded birds , demonstrating a massive long-term impact of banding and thus refuting the assumption that birds will ultimately adapt to being banded .
Indeed , banded birds still arrived later for breeding at the study site and had longer foraging trips even after 10 years .
One of our major findings is that responses of flipper-banded penguins to climate variability ( that is , changes in sea surface temperature and in the Southern Oscillation index ) differ from those of non-banded birds .
We show that only long-term investigations may allow an evaluation of the impact of flipper bands and that every major life-history trait can be affected , calling into question the banding schemes still going on .
In addition , our understanding of the effects of climate change on marine ecosystems based on flipper-band data should be reconsidered .

[1057] Reduced plant nutrition under elevated CO2 depresses the immunocompetence of cotton bollworm against its endoparasite

Estimating the immunocompetence of herbivore insects under elevated CO2 is an important step in understanding the effects of elevated CO2 on crop-herbivore-natural enemy interactions .
Current study determined the effect of elevated CO2 on the immune response of Helicoverpa armigera against its parasitoid Microplitis mediator .
H. armigera were reared in growth chambers with ambient or elevated CO2 , and fed wheat grown in the concentration of CO2 corresponding to their treatment levels .
Our results showed that elevated CO2 decreases the nutritional quality of wheat , and reduces the total hemocyte counts and impairs the capacity of hemocyte spreading of hemolymph of cotton bollworm larvae , fed wheat grown in the elevated CO2 , against its parasitoid ; however , this effect was insufficient to change the development and parasitism traits of M. mediator .
Our results suggested that lower plant nutritional quality under elevated CO2 could decrease the immune response of herbivorous insects against their parasitoid natural enemies .

[1058] The isotopic effects of deuteration on optoelectronic properties of conducting polymers

The attractive optoelectronic properties of conducting polymers depend sensitively upon intra - and inter-polymer chain interactions , and therefore new methods to manipulate these interactions are continually being pursued .
Here , we report a study of the isotopic effects of deuterium substitution on the structure , morphology and optoelectronic properties of regioregular poly ( 3-hexylthiophene ) s with an approach that combines the synthesis of deuterated materials , optoelectronic properties measurements , theoretical simulation and neutron scattering .
Selective substitutions of deuterium on the backbone or side-chains of poly ( 3-hexylthiophene ) s result in distinct optoelectronic responses in poly ( 3-hexylthiophene ) / [ 6,6 ] - phenyl-C61-butyric acid methyl ester ( PCBM ) photovoltaics .
Specifically , the weak non-covalent intermolecular interactions induced by the main-chain deuteration are shown to change the film crystallinity and morphology of the active layer , consequently reducing the short-circuit current .
However , side-chain deuteration does not significantly modify the film morphology but causes a decreased electronic coupling , the formation of a charge transfer state , and increased electron-phonon coupling , leading to a remarkable reduction in the open circuit voltage .

[1059] Effects of freeze-thaw cycles on anaerobic microbial processes in an Arctic intertidal mud flat

Insight into the effects of repeated freezing and thawing on microbial processes in sediments and soils is important for understanding sediment carbon cycling at high latitudes acutely affected by global warming .
Microbial responses to repeated freeze-thaw conditions were studied in three complementary experiments using arctic sediment collected from an intertidal flat that is exposed to seasonal freeze-thaw conditions ( Ymerbukta , Svalbard , Arctic Ocean ) .
The sediment was subjected to oscillating freeze-thaw incubations , either gradual , from -5 to 4 degreesC , or abrupt , from -20 to 10 degreesC .
Concentrations of low-molecular weight carboxylic acids ( volatile fatty acids ) were measured and sulfate reduction was assessed by measuring 35S sulfate reduction rates ( SRRs ) .
Gradual freeze-thaw incubation decreased microbial activity in the frozen state to 0.25 % of initial levels at 4 degreesC , but activity resumed rapidly reaching > 60 % of initial activity in the thawed state .
Exposure of sediments to successive large temperature changes ( -20 versus 10 degreesC ) decreased SRR by 80 % of the initial activity , suggesting that a fraction of the bacterial community recovered rapidly from extreme temperature fluctuations .
This is supported by 16S rRNA gene-based denaturing gradient gel electrophoresis profiles that revealed persistence of the dominant microbial taxa under repeated freeze-thaw cycles .
The fast recovery of the SRRs suggests that carbon mineralization in thawing arctic sediment can resume without delay or substantial growth of microbial populations .

[1060] Model estimates of sea-level change due to anthropogenic impacts on terrestrial water storage

Global sea level has been rising over the past half century , according to tide-gauge data .
Thermal expansion of oceans , melting of glaciers and loss of the ice masses in Greenland and Antarctica are commonly considered as the largest contributors , but these contributions do not entirely explain the observed sea-level rise .
Changes in terrestrial water storage are also likely to affect sea level , but comprehensive and reliable estimates of this contribution , particularly through human water use , are scarce .
Here , we estimate sea-level change in response to human impacts on terrestrial water storage by using an integrated model that simulates global terrestrial water stocks and flows ( exclusive to Greenland and Antarctica ) and especially accounts for human activities such as reservoir operation and irrigation .
We find that , together , unsustainable groundwater use , artificial reservoir water impoundment , climate-driven changes in terrestrial water storage and the loss of water from closed basins have contributed a sea-level rise of about 0.77 mm yr-1 between 1961 and 2003 , about 42 % of the observed sea-level rise .
We note that , of these components , the unsustainable use of groundwater represents the largest contribution .

[1061] Changes in land use alter the structure of bacterial communities in Western Amazon soils

Here we show how agricultural practices by indigenous peoples as well as forest recovery relate to the structure and composition of Amazon soil bacterial communities .
Soil samples were collected in different land use systems and bacterial community composition and diversity were explored by T-RFLP , cloning and sequencing , and data were analyzed with multivariate techniques .
The main differences in bacterial community structure were related to changes in the soil attributes that , in turn , were correlated to land use .
Community structure changed significantly along gradients of base saturation , [ Al3 + ] and pH. The relationship with soil attributes accounted for about 31 % of the variation of the studied communities .
Clear differences were observed in community composition as shown by the differential distribution of Proteobacteria , Bacteroidetes , Firmicutes , Acidobacteria and Actinobacteria .
Similarity between primary and secondary forest communities indicates the recovery of bacterial community structure during succession .
Pasture and crop soil communities were among the most diverse , showing that these land use types did not deplete bacterial diversity under the conditions found in our sites .

[1062] Increased mobilization of aged carbon to rivers by human disturbance

Approximately 8 % of anthropogenic carbon dioxide emissions are estimated to come from land-use change , but this estimate excludes fluxes of terrestrial carbon to aquatic ecosystems from human disturbance .
Carbon fluxes from land to rivers have probably increased by 0.1 to 0.2 petagrams of carbon per year as a result of disturbances such as deforestation , agricultural intensification and the injection of human wastewater .
Most dissolved organic carbon in rivers originates from young organic carbon from soils and vegetation , but aged carbon removed from the modern carbon cycle is also exported in many systems .
Here we analyse a global data set of radiocarbon ages of riverine dissolved organic carbon and spatial data on land cover , population and environmental variables .
We find that the age of dissolved organic carbon in rivers increases with population density and the proportion of human-dominated landscapes within a watershed , and decreases with annual precipitation .
We reason that disturbance reintroduces aged soil organic matter into the modern carbon cycle , although fossil carbon in fertilizer or petroleum products may also be a source of aged carbon in disturbed watersheds .
The total export from the terrestrial environment to freshwater systems remains unknown ; nevertheless , our results suggest that 3-9 % of dissolved organic carbon in rivers is aged carbon mobilized by human disturbance .

[1063] Atlantic Ocean influence on a shift in European climate in the 1990s

European climate exhibits variability on a wide range of timescales .
Understanding the nature and drivers of this variability is an essential step in developing robust climate predictions and risk assessments .
The Atlantic Ocean has been suggested as an important driver of variability in European climate on decadal timescales , but the importance of this influence in recent decades has been unclear , partly because of difficulties in separating the influence of the Atlantic Ocean from other contributions , for example , from the tropical Pacific Ocean and the stratosphere .
Here we analyse four data sets derived from observations to show that , during the 1990s , there was a substantial shift in European climate towards a pattern characterized by anomalously wet summers in northern Europe , and hot , dry , summers in southern Europe , with related shifts in spring and autumn .
These changes in climate coincided with a substantial warming of the North Atlantic Ocean , towards a state last seen in the 1950s .
The patterns of European climate change in the 1990s are consistent with earlier changes attributed to the influence of the North Atlantic Ocean and provide compelling evidence that the Atlantic Ocean was the key driver .
Our results suggest that the recent pattern of anomalies in European climate will persist as long as the North Atlantic Ocean remains anomalously warm .

[1064] Reconstruction of the South Atlantic Subtropical Dipole index for the past 12,000 years from surface temperature proxy

Climate indices based on sea surface temperature ( SST ) can synthesize information related to physical processes that describe change and variability in continental precipitation from floods to droughts .
The South Atlantic Subtropical Dipole index ( SASD ) is based on the distribution of SST in the South Atlantic and fits these criteria .
It represents the dominant mode of variability of SST in the South Atlantic , which is modulated by changes in the position and intensity of the South Atlantic Subtropical High .
Here we reconstructed an index of the South Atlantic Ocean SST ( SASD-like ) for the past twelve thousand years ( the Holocene period ) based on proxy-data .
This has great scientific implications and important socio-economic ramifications because of its ability to infer variability of precipitation and moisture over South America where past climate data is limited .
For the first time a reconstructed index based on proxy data on opposite sides of the SASD-like mode is able to capture , in the South Atlantic , the significant cold events in the Northern Hemisphere at 12.9-11 .6 kyr BP and 8.6-8 .0 ky BP .
These events are related , using a transient model simulation , to precipitation changes over South America .

[1065] How ecological restoration alters ecosystem services : an analysis of carbon sequestration in China 's Loess Plateau

Restoring disturbed and over-exploited ecosystems is important to mitigate human pressures on natural ecosystems .
China has launched an ambitious national ecosystem restoration program called Grain to Green Program ( GTGP ) over the last decade .
By using remote sensing techniques and ecosystem modelling , we quantitatively evaluated the changes in ecosystem carbon sequestration since China 's GTGP program during period of 2000-2008 .
It was found the NPP and NEP in this region had steadily increased after the initiative of the GTGP program , and a total of 96.1 Tg of additional carbon had been sequestered during that period .
Changes in soil carbon storage were lagged behind and thus insignificant over the period , but was expected to follow in the coming decades .
As a result , the Loess Plateau ecosystem had shifted from a net carbon source in 2000 to a net carbon sink in 2008 .
The carbon sequestration efficiency was constrained by precipitation , and appropriate choices of restoration types ( trees , shrubs , and grasses ) in accordance to local climate are critical for achieving the best benefit/cost efficiency .

[1066] Effects of temperature on the diversity and community structure of known methanogenic groups and other archaea in high Arctic peat

Archaeal populations are abundant in cold and temperate environments , but little is known about their potential response to climate change-induced temperature changes .
The effects of temperature on archaeal communities in unamended slurries of weakly acidic peat from Spitsbergen were studied using a combination of fluorescent in situ hybridization ( FISH ) , 16S rRNA gene clone libraries and denaturing gradient gel electrophoresis ( DGGE ) .
A high relative abundance of active archaeal cells ( 11-12 % of total count ) was seen at low temperatures ( 1 and 5 degreesC ) , and this community was dominated by Group 1.3 b Crenarchaeota and the euryarchaeal clusters rice cluster V ( RC-V ) , and Lake Dagow sediment ( LDS ) .
Increasing temperature reduced the diversity and relative abundance of these clusters .
The methanogenic community in the slurries was diverse and included representatives of Methanomicrobiales , Methanobacterium , Methanosarcina and Methanosaeta .
The overall relative abundance and diversity of the methanogenic archaea increased with increasing temperature , in accordance with a strong stimulation of methane production rates .
However , DGGE profiling showed that the structure of this community changed with temperature and time .
While the relative abundance of some populations was affected directly by temperature , the relative abundance of other populations was controlled by indirect effects or did not respond to temperature .

[1067] The impact of remineralization depth on the air-sea carbon balance

As particulate organic carbon rains down from the surface ocean it is respired back to carbon dioxide and released into the ocean 's interior .
The depth at which this sinking carbon is converted back to carbon dioxide -- known as the remineralization depth -- depends on the balance between particle sinking speeds and their rate of decay .
A host of climate-sensitive factors can affect this balance , including temperature , oxygen concentration , stratification , community composition and the mineral content of the sinking particles .
Here we use a three-dimensional global ocean biogeochemistry model to show that a modest change in remineralization depth can have a substantial impact on atmospheric carbon dioxide concentrations .
For example , when the depth at which 63 % of sinking carbon is respired increases by 24 m globally , atmospheric carbon dioxide concentrations fall by 10-27 ppm .
This reduction in atmospheric carbon dioxide concentration results from the redistribution of remineralized carbon from intermediate waters to bottom waters .
As a consequence of the reduced concentration of respired carbon in upper ocean waters , atmospheric carbon dioxide is preferentially stored in newly formed North Atlantic Deep Water .
We suggest that atmospheric carbon dioxide concentrations are highly sensitive to the potential changes in remineralization depth that may be caused by climate change .

[1068] Insolation-driven 100,000-year glacial cycles and hysteresis of ice-sheet volume

The growth and reduction of Northern Hemisphere ice sheets over the past million years is dominated by an approximately 100,000-year periodicity and a sawtooth pattern ( gradual growth and fast termination ) .
Milankovitch theory proposes that summer insolation at high northern latitudes drives the glacial cycles , and statistical tests have demonstrated that the glacial cycles are indeed linked to eccentricity , obliquity and precession cycles .
Yet insolation alone can not explain the strong 100,000-year cycle , suggesting that internal climatic feedbacks may also be at work .
Earlier conceptual models , for example , showed that glacial terminations are associated with the build-up of Northern Hemisphere ` excess ice ' , but the physical mechanisms underpinning the 100,000-year cycle remain unclear .
Here we show , using comprehensive climate and ice-sheet models , that insolation and internal feedbacks between the climate , the ice sheets and the lithosphere-asthenosphere system explain the 100,000-year periodicity .
The responses of equilibrium states of ice sheets to summer insolation show hysteresis , with the shape and position of the hysteresis loop playing a key part in determining the periodicities of glacial cycles .
The hysteresis loop of the North American ice sheet is such that after inception of the ice sheet , its mass balance remains mostly positive through several precession cycles , whose amplitudes decrease towards an eccentricity minimum .
The larger the ice sheet grows and extends towards lower latitudes , the smaller is the insolation required to make the mass balance negative .
Therefore , once a large ice sheet is established , a moderate increase in insolation is sufficient to trigger a negative mass balance , leading to an almost complete retreat of the ice sheet within several thousand years .
This fast retreat is governed mainly by rapid ablation due to the lowered surface elevation resulting from delayed isostatic rebound , which is the lithosphere-asthenosphere response .
Carbon dioxide is involved , but is not determinative , in the evolution of the 100,000-year glacial cycles .

[1069] Extreme deepening of the Atlantic overturning circulation during deglaciation

Glacial terminations during the late Pleistocene epoch are associated with changes in insolation .
They are also punctuated by millennial-scale climate shifts , characterized by a weakening and subsequent strengthening of the Atlantic meridional overturning circulation .
This ubiquitous association suggests that these oscillations may be a necessary component of deglaciation .
Model simulations have suggested that the period of weakened circulation during these terminal oscillations would be followed by an overshoot of the circulation on its resumption , but this phenomenon has not yet been observed .
Here we use radiocarbon measurements of benthic foraminifera and carbonate preservation indices to reconstruct ventilation changes in the deep South Atlantic Ocean over the past 40,000 years .
We find evidence for a particularly deep expansion of the Atlantic overturning cell directly following the weak mode associated with Heinrich Stadial 1 .
Our analysis of an ocean general circulation model simulation suggests that North Atlantic Deep Water export during the expansion was greater than that of interglacial conditions .
We find a similar deep expansion during Dansgaard-Oeschger Interstadial Event 8 , 38,000 years ago , which followed Heinrich Stadial 4 .
We conclude that the rise in atmospheric CO2 concentrations and resultant warming associated with an especially weak overturning circulation are sufficient to trigger a switch to a vigorous circulation , but a full transition to interglacial conditions requires additional forcing at an orbital scale .

[1070] Anthropogenic greenhouse gas contribution to flood risk in England and Wales in autumn 2000

Interest in attributing the risk of damaging weather-related events to anthropogenic climate change is increasing .
Yet climate models used to study the attribution problem typically do not resolve the weather systems associated with damaging events such as the UK floods of October and November 2000 .
Occurring during the wettest autumn in England and Wales since records began in 1766 , these floods damaged nearly 10,000 properties across that region , disrupted services severely , and caused insured losses estimated at pound1 .3 billion ( refs 5 , 6 ) .
Although the flooding was deemed a ` wake-up call ' to the impacts of climate change at the time , such claims are typically supported only by general thermodynamic arguments that suggest increased extreme precipitation under global warming , but fail to account fully for the complex hydrometeorology associated with flooding .
Here we present a multi-step , physically based ` probabilistic event attribution ' framework showing that it is very likely that global anthropogenic greenhouse gas emissions substantially increased the risk of flood occurrence in England and Wales in autumn 2000 .
Using publicly volunteered distributed computing , we generate several thousand seasonal-forecast-resolution climate model simulations of autumn 2000 weather , both under realistic conditions , and under conditions as they might have been had these greenhouse gas emissions and the resulting large-scale warming never occurred .
Results are fed into a precipitation-runoff model that is used to simulate severe daily river runoff events in England and Wales ( proxy indicators of flood events ) .
The precise magnitude of the anthropogenic contribution remains uncertain , but in nine out of ten cases our model results indicate that twentieth-century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20 % , and in two out of three cases by more than 90 % .

[1071] Key role of symbiotic dinitrogen fixation in tropical forest secondary succession

Forests contribute a significant portion of the land carbon sink , but their ability to sequester CO2 may be constrained by nitrogen , a major plant-limiting nutrient .
Many tropical forests possess tree species capable of fixing atmospheric dinitrogen ( N2 ) , but it is unclear whether this functional group can supply the nitrogen needed as forests recover from disturbance or previous land use , or expand in response to rising CO2 ( refs 6 , 8 ) .
Here we identify a powerful feedback mechanism in which N2 fixation can overcome ecosystem-scale deficiencies in nitrogen that emerge during periods of rapid biomass accumulation in tropical forests .
Over a 300-year chronosequence in Panama , N2-fixing tree species accumulated carbon up to nine times faster per individual than their non-fixing neighbours ( greatest difference in youngest forests ) , and showed species-specific differences in the amount and timing of fixation .
As a result of fast growth and high fixation , fixers provided a large fraction of the nitrogen needed to support net forest growth ( 50,000 kg carbon per hectare ) in the first 12 years .
A key element of ecosystem functional diversity was ensured by the presence of different N2-fixing tree species across the entire forest age sequence .
These findings show that symbiotic N2 fixation can have a central role in nitrogen cycling during tropical forest stand development , with potentially important implications for the ability of tropical forests to sequester CO2 .

[1072] Lithium isotope evidence for enhanced weathering during Oceanic Anoxic Event 2

The Ocean Anoxic Event 2 ( OAE2 ) about 93.5 million years ago was marked by high atmospheric CO2 concentration , rapid global warming and marine anoxia and euxinia .
The event lasted for about 440,000 years and led to habitat loss and mass extinction .
The marine anoxia is thought to be linked to enhanced biological productivity , but it is unclear what triggered the increased production and what allowed the subsequent rapid climate recovery .
Here we use lithium isotope measurements from carbonates spanning the interval including OAE2 to assess the role of silicate weathering .
We find the lightest values of the Li isotope ratio ( delta7Li ) during OAE2 , indicating high levels of weathering -- and therefore atmospheric CO2 removal -- which we attribute to an enhanced hydrological cycle .
We use a geochemical model to simulate the evolution of delta7Li and the Ca , Sr and Os isotope tracers .
Our simulations suggest a scenario in which the eruption of a large igneous province led to high atmospheric CO2 concentrations and rapid global warming , which initiated OAE2 .
The simulated warming was accompanied by a roughly 200,000 year pulse of accelerated weathering of mafic silicate rocks , which removed CO2 from the atmosphere .
The weathering also delivered nutrients to the oceans that stimulated primary productivity .
We suggest that this process , together with the burial of organic carbon , allowed the rapid recovery and stabilization from the greenhouse state .

[1073] Insolation driven biomagnetic response to the Holocene Warm Period in semi-arid East Asia

The Holocene Warm Period ( HWP ) provides valuable insights into the climate system and biotic responses to environmental variability and thus serves as an excellent analogue for future global climate changes .
Here we document , for the first time , that warm and wet HWP conditions were highly favourable for magnetofossil proliferation in the semi-arid Asian interior .
The pronounced increase of magnetofossil concentrations at ~ 9.8 ka and decrease at ~ 5.9 ka in Dali Lake coincided respectively with the onset and termination of the HWP , and are respectively linked to increased nutrient supply due to postglacial warming and poor nutrition due to drying at ~ 6 ka in the Asian interior .
The two-stage transition at ~ 7.7 ka correlates well with increased organic carbon in middle HWP and suggests that improved climate conditions , leading to high quality nutrient influx , fostered magnetofossil proliferation .
Our findings represent an excellent lake record in which magnetofossil abundance is , through nutrient availability , controlled by insolation driven climate changes .

[1074] Spectral biases in tree-ring climate proxies

External forcing and internal dynamics result in climate system variability ranging from sub-daily weather to multi-centennial trends and beyond .
State-of-the-art palaeoclimatic methods routinely use hydroclimatic proxies to reconstruct temperature ( for example , refs , ) , possibly blurring differences in the variability continuum of temperature and precipitation before the instrumental period .
Here , we assess the spectral characteristics of temperature and precipitation fluctuations in observations , model simulations and proxy records across the globe .
We find that whereas an ensemble of different general circulation models represents patterns captured in instrumental measurements , such as land-ocean contrasts and enhanced low-frequency tropical variability , the tree-ring-dominated proxy collection does not .
The observed dominance of inter-annual precipitation fluctuations is not reflected in the annually resolved hydroclimatic proxy records .
Likewise , temperature-sensitive proxies overestimate , on average , the ratio of low - to high-frequency variability .
These spectral biases in the proxy records seem to propagate into multi-proxy climate reconstructions for which we observe an overestimation of low-frequency signals .
Thus , a proper representation of the high - to low-frequency spectrum in proxy records is needed to reduce uncertainties in climate reconstruction efforts .

[1075] Methylmercury photodegradation influenced by sea-ice cover in Arctic marine ecosystems

Atmospheric deposition of mercury to remote areas has increased threefold since pre-industrial times .
Mercury deposition is particularly pronounced in the Arctic .
Following deposition to surface oceans and sea ice , mercury can be converted into methylmercury , a biologically accessible form of the toxin , which biomagnifies along the marine food chain .
Mass-independent fractionation of mercury isotopes accompanies the photochemical breakdown of methylmercury to less bioavailable forms in surface waters .
Here we examine the isotopic composition of mercury in seabird eggs collected from colonies in the North Pacific Ocean , the Bering Sea and the western Arctic Ocean , to determine geographical variations in methylmercury breakdown at northern latitudes .
We find evidence for mass-independent fractionation of mercury isotopes .
The degree of mass-independent fractionation declines with latitude .
Foraging behaviour and geographic variations in mercury sources and solar radiation fluxes were unable to explain the latitudinal gradient .
However , mass-independent fractionation was negatively correlated with sea-ice cover .
We conclude that sea-ice cover impedes the photochemical breakdown of methylmercury in surface waters , and suggest that further loss of Arctic sea ice this century will accelerate sunlight-induced breakdown of methylmercury in northern surface waters .

[1076] Botany : Constraints to growth of boreal forests

Understanding how the growth of trees at high latitudes in boreal forest is controlled is important for projections of global carbon sequestration and timber production in relation to climate change .
Is stem growth of boreal forest trees constrained by the length of the growing season when stem cambial cells divide , or by the length of the period when resources can be captured ?
In both cases , the timing of the thaw in the spring is critical : neither cambial cell division nor uptake of nutrients and carbon dioxide can occur while the soil is frozen .
Here we argue , on the basis of long-term observations made in northern Saskatchewan and Sweden , that the time between the spring thaw and the autumn freeze determines the amount of annual tree growth , mainly through temperature effects on carbon-dioxide uptake in spring and on nutrient availability and uptake during summer , rather than on cambial cell division .

[1077] High frequency of ` super-cyclones ' along the Great Barrier Reef over the past 5,000 years

Understanding long-term variability in the occurrence of tropical cyclones that are of extreme intensity is important for determining their role in ecological disturbances , for predicting present and future community vulnerability and economic loss and for assessing whether changes in the variability of such cyclones are induced by climate change .
Our ability to accurately make these assessments has been limited by the short ( less than 100 years ) instrumented record of cyclone intensity .
Here we determine the intensity of prehistoric tropical cyclones over the past 5,000 years from ridges of detrital coral and shell deposited above highest tide and terraces that have been eroded into coarse-grained alluvial fan deposits .
These features occur along 1,500 km of the Great Barrier Reef and also the Gulf of Carpentaria , Australia .
We infer that the deposits were formed by storms with recurrence intervals of two to three centuries , and we show that the cyclones responsible must have been of extreme intensity ( central pressures less than 920 hPa ) .
Our estimate of the frequency of such ` super-cyclones ' is an order of magnitude higher than that previously estimated ( which was once every several millennia ) , and is sufficiently high to suggest that the character of rainforests and coral reef communities were probably shaped by these events .

[1078] Nonstationary Precipitation Intensity-Duration-Frequency Curves for Infrastructure Design in a Changing Climate

Extreme climatic events are growing more severe and frequent , calling into question how prepared our infrastructure is to deal with these changes .
Current infrastructure design is primarily based on precipitation Intensity-Duration-Frequency ( IDF ) curves with the so-called stationary assumption , meaning extremes will not vary significantly over time .
However , climate change is expected to alter climatic extremes , a concept termed nonstationarity .
Here we show that given nonstationarity , current IDF curves can substantially underestimate precipitation extremes and thus , they may not be suitable for infrastructure design in a changing climate .
We show that a stationary climate assumption may lead to underestimation of extreme precipitation by as much as 60 % , which increases the flood risk and failure risk in infrastructure systems .
We then present a generalized framework for estimating nonstationary IDF curves and their uncertainties using Bayesian inference .
The methodology can potentially be integrated in future design concepts .

[1079] A natural variant of NAL1 , selected in high-yield rice breeding programs , pleiotropically increases photosynthesis rate

Improvement of leaf photosynthesis is an important strategy for greater crop productivity .
Here we show that the quantitative trait locus GPS ( GREEN FOR PHOTOSYNTHESIS ) in rice ( Oryza sativa L. ) controls photosynthesis rate by regulating carboxylation efficiency .
Map-based cloning revealed that GPS is identical to NAL1 ( NARROW LEAF1 ) , a gene previously reported to control lateral leaf growth .
The high-photosynthesis allele of GPS was found to be a partial loss-of-function allele of NAL1 .
This allele increased mesophyll cell number between vascular bundles , which led to thickened leaves , and it pleiotropically enhanced photosynthesis rate without the detrimental side effects observed in previously identified nal1 mutants , such as dwarf plant stature .
Furthermore , pedigree analysis suggested that rice breeders have repeatedly selected the high-photosynthesis allele in high-yield breeding programs .
The identification and utilization of NAL1 ( GPS ) can enhance future high-yield breeding and provides a new strategy for increasing rice productivity .

[1080] The impact of ocean deoxygenation on iron release from continental margin sediments

In the oceans ' high-nitrate-low-chlorophyll regions , such as the Peru/Humboldt Current system and the adjacent eastern equatorial Pacific , primary productivity is limited by the micronutrient iron .
Within the Peruvian upwelling area , bioavailable iron is released from the reducing continental margin sediments .
The magnitude of this seafloor source could change with fluctuations in the extension or intensity of the oxygen minimum zones .
Here we show that measurements of molybdenum , uranium and iron concentrations can be used as a proxy for sedimentary iron release , and use this proxy to assess iron release from the sea floor beneath the Peru upwelling system during the past 140,000 years .
We observe a coupling between levels of denitrification , as indicated by nitrogen isotopes , trace metal proxies for oxygenation , and sedimentary iron concentrations .
Specifically , periods with poor upper ocean oxygenation are characterized by more efficient iron retention in the sediment and a diminished iron supply to the water column .
We attribute efficient iron retention under more reducing conditions to widespread sulphidic conditions in the surface sediment and concomitant precipitation of iron sulphides .
We argue that iron release from continental margin sediments is most effective in a narrow redox window where neither oxygen nor sulphide is present .
We therefore suggest that future deoxygenation in the Peru upwelling area would be unlikely to result in increased iron availability , whereas in weaker oxygen minimum zones partial deoxygenation may enhance the iron supply .

[1081] Electricity-driven metabolic shift through direct electron uptake by electroactive heterotroph Clostridiumpasteurianum

Although microbes directly accepting electrons from a cathode have been applied for CO2 reduction to produce multicarbon-compounds , a high electron demand and low product concentration are critical limitations .
Alternatively , the utilization of electrons as a co-reducing power during fermentation has been attempted , but there must be exogenous mediators due to the lack of an electroactive heterotroph .
Here , we show that Clostridium pasteurianum DSM 525 simultaneously utilizes both cathode and substrate as electron donors through direct electron transfer .
In a cathode compartment poised at +0.045 V vs. SHE , a metabolic shift in C. pasteurianum occurs toward NADH-consuming metabolite production such as butanol from glucose ( 20 % shift in terms of NADH consumption ) and 1,3-propandiol from glycerol ( 21 % shift in terms of NADH consumption ) .
Notably , a small amount of electron uptake significantly induces NADH-consuming pathways over the stoichiometric contribution of the electrons as reducing equivalents .
Our results demonstrate a previously unknown electroactivity and metabolic shift in the biochemical-producing heterotroph , opening up the possibility of efficient and enhanced production of electron-dense metabolites using electricity .

[1082] Seasonal bone growth and physiology in endotherms shed light on dinosaur physiology

Cyclical growth leaves marks in bone tissue that are in the forefront of discussions about physiologies of extinct vertebrates .
Ectotherms show pronounced annual cycles of growth arrest that correlate with a decrease in body temperature and metabolic rate ; endotherms are assumed to grow continuously until they attain maturity because of their constant high body temperature and sustained metabolic rate .
This apparent dichotomy has driven the argument that zonal bone denotes ectotherm-like physiologies , thus fuelling the controversy on dinosaur thermophysiology and the evolution of endothermy in birds and mammal-like reptiles .
Here we show , from a comprehensive global study of wild ruminants from tropical to polar environments , that cyclical growth is a universal trait of homoeothermic endotherms .
Growth is arrested during the unfavourable season concurrently with decreases in body temperature , metabolic rate and bone-growth-mediating plasma insulin-like growth factor-1 levels , forming part of a plesiomorphic thermometabolic strategy for energy conservation .
Conversely , bouts of intense tissue growth coincide with peak metabolic rates and correlated hormonal changes at the beginning of the favourable season , indicating an increased efficiency in acquiring and using seasonal resources .
Our study supplies the strongest evidence so far that homeothermic endotherms arrest growth seasonally , which precludes the use of lines of arrested growth as an argument in support of ectothermy .
However , high growth rates are a distinctive trait of mammals , suggesting the capacity for endogenous heat generation .
The ruminant annual cycle provides an extant model on which to base inferences regarding the thermophysiology of dinosaurs and other extinct taxa .

[1083] Recent trends in African fires driven by cropland expansion and El Nino to La Nina transition

Landscape fires are key in African ecosystems and the continent is responsible for ~ 70 % of global burned area and ~ 50 % of fire-related carbon emissions .
Fires are mostly human ignited , but precipitation patterns govern when and where fires can occur .
The relative role of humans and precipitation in driving the spatio-temporal variability in burned area is not fully disentangled but is required to predict future burned area .
Over 2001-2012 , observations indicate strong but opposing trends in the African hemispheres .
Here we use satellite data and statistical modelling and show that changes in precipitation , driven by the El Nino/Southern Oscillation ( ENSO ) , which changed from El Nino to La Nina dominance over our study period , contributed substantially ( 51 % ) to the upward trend over southern Africa .
This also contributed to the downward trend over northern Africa ( 24 % ) , but here rapid demographic and socio-economic changes were almost as important ( 20 % ) , mainly due to conversion of savannah into cropland , muting burned area .
Given the economic perspective of Africa and the oscillative nature of ENSO , future African savannah burned area will probably decline .
Combined with increasing global forest fire activity due to climate change , our results indicate a potential shift in global pyrogeography from being savannah dominated to being forest dominated .

[1084] Cloud albedo enhancement by surface-active organic solutes in growing droplets

Understanding the properties of clouds in the Earth 's atmosphere is currently limited by difficulties at the fundamental level of adequately describing the processes of cloud droplet nucleation and growth .
Small changes in droplet population may significantly influence cloud albedo as well as formation of precipitation .
Models of cloud formation based on laboratory studies with idealized composition of nuclei suggest that organic solutes significantly lower surface tension -- one of the parameters determining droplet population -- but the lack of data on composition and properties of the organic material in the atmosphere precludes realistic laboratory or model studies .
Here , we report measurements on vacuum-evaporated samples of cloud water from the Po Valley , Italy , that show a large decrease in surface tension , by up to about one-third relative to pure water , for realistic concentrations of organic solutes expected to exist in growing droplets .
Such large surface-tension changes , if they occur in cloud droplets near the critical size for nucleation , lead to an increase in droplet population and hence in cloud albedo .
The error produced in ignoring this effect is estimated to be comparable to other calculated direct and indirect influences of aerosols on scattering and absorption of solar radiation .

[1085] Changes in the taste and textural attributes of apples in response to climate change

The effects of climate change on the taste and textural attributes of foods remain largely unknown , despite much public interest .
On the basis of 30-40 years of records , we provide evidence that the taste and textural attributes of apples have changed as a result of recent global warming .
Decreases in both acid concentration , fruit firmness and watercore development were observed regardless of the maturity index used for harvest date ( e.g. , calendar date , number of days after full bloom , peel colour and starch concentration ) , whereas in some cases the soluble-solids concentration increased ; all such changes may have resulted from earlier blooming and higher temperatures during the maturation period .
These results suggest that the qualities of apples in the market are undergoing long-term changes .

[1086] Shifts in bacterial communities of two caribbean reef-building coral species affected by white plague disease

Coral reefs are deteriorating at an alarming rate mainly as a consequence of the emergence of coral diseases .
The white plague disease ( WPD ) is the most prevalent coral disease in the southwestern Caribbean , affecting dozens of coral species .
However , the identification of a single causal agent has proved problematic .
This suggests more complex etiological scenarios involving alterations in the dynamic interaction between environmental factors , the coral immune system and the symbiotic microbial communities .
Here we compare the microbiome of healthy and WPD-affected corals from the two reef-building species Diploria strigosa and Siderastrea siderea collected at the Tayrona National Park in the Caribbean of Colombia .
Microbiomes were analyzed by combining culture-dependent methods and pyrosequencing of 16S ribosomal DNA ( rDNA ) V5-V6 hypervariable regions .
A total of 20 410 classifiable 16S rDNA sequences reads were obtained including all samples .
No significant differences in operational taxonomic unit diversity were found between healthy and affected tissues ; however , a significant increase of Alphaproteobacteria and a concomitant decrease in the Beta - and Gammaproteobacteria was observed in WPD-affected corals of both species .
Significant shifts were also observed in the orders Rhizobiales , Caulobacteriales , Burkholderiales , Rhodobacterales , Aleteromonadales and Xanthomonadales , although they were not consistent between the two coral species .
These shifts in the microbiome structure of WPD-affected corals suggest a loss of community-mediated growth control mechanisms on bacterial populations specific for each holobiont system .

[1087] Demography of the endangered North Atlantic right whale

Northern right whales ( Eubalaena glacialis ) were formerly abundant in the northwestern Atlantic , but by 1900 they had been hunted to near extinction .
After the end of commercial whaling the population was thought to be recovering slowly ; however , evidence indicates that it has been declining since about 1990 ( ref .
1 ) .
There are now fewer than 300 individuals , and the species may already be functionally extinct owing to demographic stochasticity or the difficulty of females locating mates in the vast Atlantic Ocean ( Allee effect ) .
Using a data set containing over 10,000 sightings of photographically identified individuals we estimated trends in right whale demographic parameters since 1980 .
Here we construct , using these estimates , matrix population models allowing us to analyse the causes of right whale imperilment .
Mortality has increased , especially among mother whales , causing declines in population growth rate , life expectancy and the mean lifetime number of reproductive events between the period 1980-1995 .
Increased mortality of mother whales can explain the declining population size , suggesting that the population is not doomed to extinction as a result of the Allee effect .
An analysis of extinction time shows that demographic stochasticity has only a small effect , but preventing the deaths of only two female right whales per year would increase the population growth rate to replacement level .

[1088] Riverine organic matter and nutrients in southeast Alaska affected by glacial coverage

The delivery of fresh water , carbon , nitrogen and phosphorous from high-latitude regional watersheds is important to the ecology and nutrient balance of coastal marine ecosystems in the Northern and Southern hemispheres .
Bioavailable dissolved organic matter from rivers can support microbes in near-shore environments , and may also stimulate primary production .
Recent studies suggest that impacts of climate change , such as thawing permafrost , may affect nutrient yields in large northern rivers .
Here we analyse riverine dissolved organic matter and nutrient loads in three adjacent coastal watersheds along the Gulf of Alaska .
We find that different levels of glacial coverage can alter the timing and magnitude of fresh water , dissolved organic matter and nutrient yields .
Our results suggest that a lower extent of glacial coverage within a watershed can lead to higher amounts of dissolved organic matter , but decreased phosphorous yields .
Moreover , an abundance of early successional plant species following deglaciation can increase riverine nitrogen levels .
We conclude that changes in riverine yields of dissolved organic matter and nutrients due to reductions in glacier extent in coastal watersheds may affect the productivity and function of near-shore coastal ecosystems .

[1089] The response of the Antarctic Circumpolar Current to recent climate change

Observations show a significant intensification of the Southern Hemisphere westerlies , the prevailing winds between the latitudes of 30degrees and 60degrees S , over the past decades .
A continuation of this intensification trend is projected by climate scenarios for the twenty-first century .
The response of the Antarctic Circumpolar Current and the carbon sink in the Southern Ocean to changes in wind stress and surface buoyancy fluxes is under debate .
Here we analyse the Argo network of profiling floats and historical oceanographic data to detect coherent hemispheric-scale warming and freshening trends that extend to depths of more than 1,000 m .
The warming and freshening is partly related to changes in the properties of the water masses that make up the Antarctic Circumpolar Current , which are consistent with the anthropogenic changes in heat and freshwater fluxes suggested by climate models .
However , we detect no increase in the tilt of the surfaces of equal density across the Antarctic Circumpolar Current , in contrast to coarse-resolution model studies .
Our results imply that the transport in the Antarctic Circumpolar Current and meridional overturning in the Southern Ocean are insensitive to decadal changes in wind stress .

[1090] Dramatically increasing chance of extremely hot summers since the 2003 European heatwave

Socio-economic stress from the unequivocal warming of the global climate system could be mostly felt by societies through weather and climate extremes .
The vulnerability of European citizens was made evident during the summer heatwave of 2003 ( refs , ) when the heat-related death toll ran into tens of thousands .
Human influence at least doubled the chances of the event according to the first formal event attribution study , which also made the ominous forecast that severe heatwaves could become commonplace by the 2040s .
Here we investigate how the likelihood of having another extremely hot summer in one of the worst affected parts of Europe has changed ten years after the original study was published , given an observed summer temperature increase of 0.81 K since then .
Our analysis benefits from the availability of new observations and data from several new models .
Using a previously employed temperature threshold to define extremely hot summers , we find that events that would occur twice a century in the early 2000s are now expected to occur twice a decade .
For the more extreme threshold observed in 2003 , the return time reduces from thousands of years in the late twentieth century to about a hundred years in little over a decade .

[1091] Controls on tropical Pacific Ocean productivity revealed through nutrient stress diagnostics

In situ enrichment experiments have shown that the growth of bloom-forming diatoms in the major high-nitrate low-chlorophyll ( HNLC ) regions of the world 's oceans is limited by the availability of iron .
Yet even the largest of these manipulative experiments represents only a small fraction of an ocean basin , and the responses observed are strongly influenced by the proliferation of rare species rather than the growth of naturally dominant populations .
Here we link unique fluorescence attributes of phytoplankton to specific physiological responses to nutrient stress , and use these relationships to evaluate the factors that constrain phytoplankton growth in the tropical Pacific Ocean on an unprecedented spatial scale .
On the basis of fluorescence measurements taken over 12 years , we delineate three major ecophysiological regimes in this region .
We find that iron has a key function in regulating phytoplankton growth in both HNLC and oligotrophic waters near the Equator and further south , whereas nitrogen and zooplankton grazing are the primary factors that regulate biomass production in the north .
Application of our findings to the interpretation of satellite chlorophyll fields shows that productivity in the tropical Pacific basin may be 1.2-2 .5 Pg C yr-1 lower than previous estimates have suggested , a difference that is comparable to the global change in ocean production that accompanied the largest El Nino to La Nina transition on record .

[1092] Environmental variability and biodiversity of megabenthos on the Hebrides Terrace Seamount ( Northeast Atlantic )

We present the first remotely operated vehicle investigation of megabenthic communities ( 1004-1695 m water depth ) on the Hebrides Terrace Seamount ( Northeast Atlantic ) .
Conductivity-temperature-depth casts showed rapid light attenuation below the summit and an oceanographic regime on the flanks consistent with an internal tide , and high short-term variability in water temperature , salinity , light attenuation , aragonite and oxygen down to 1500 m deep .
Minor changes in species composition ( 3-14 % ) were explained by changes in depth , substratum and oceanographic stability , whereas environmental variability explained substantially more variation in species richness ( 40-56 % ) .
Two peaks in species richness occurred , the first at 1300-1400 m where cooler Wyville Thomson Overflow Water ( WTOW ) mixes with subtropical gyre waters and the second at 1500-1600 m where WTOW mixes with subpolar mode waters .
Our results suggest that internal tides , substrate heterogeneity and oceanographic interfaces may enhance biological diversity on this and adjacent seamounts in the Rockall Trough .

[1093] Rapid and early export of Phaeocystis antarctica blooms in the Ross Sea , Antarctica

The Southern Ocean is very important for the potential sequestration of carbon dioxide in the oceans and is expected to be vulnerable to changes in carbon export forced by anthropogenic climate warming .
Annual phytoplankton blooms in seasonal ice zones are highly productive and are thought to contribute significantly to pCO2 drawdown in the Southern Ocean .
Diatoms are assumed to be the most important phytoplankton class with respect to export production in the Southern Ocean ; however , the colonial prymnesiophyte Phaeocystis antarctica regularly forms huge blooms in seasonal ice zones and coastal Antarctic waters .
There is little evidence regarding the fate of carbon produced by P. antarctica in the Southern Ocean , although remineralization in the upper water column has been proposed to be the main pathway in polar waters .
Here we present evidence for early and rapid carbon export from P. antarctica blooms to deep water and sediments in the Ross Sea .
Carbon sequestration from P. antarctica blooms may influence the carbon cycle in the Southern Ocean , especially if projected climatic changes lead to an alteration in the structure of the phytoplankton community .

[1094] Distinct microbial communities associated with buried soils in the Siberian tundra

Cryoturbation , the burial of topsoil material into deeper soil horizons by repeated freeze-thaw events , is an important storage mechanism for soil organic matter ( SOM ) in permafrost-affected soils .
Besides abiotic conditions , microbial community structure and the accessibility of SOM to the decomposer community are hypothesized to control SOM decomposition and thus have a crucial role in SOM accumulation in buried soils .
We surveyed the microbial community structure in cryoturbated soils from nine soil profiles in the northeastern Siberian tundra using high-throughput sequencing and quantification of bacterial , archaeal and fungal marker genes .
We found that bacterial abundances in buried topsoils were as high as in unburied topsoils .
In contrast , fungal abundances decreased with depth and were significantly lower in buried than in unburied topsoils resulting in remarkably low fungal to bacterial ratios in buried topsoils .
Fungal community profiling revealed an associated decrease in presumably ectomycorrhizal ( ECM ) fungi .
The abiotic conditions ( low to subzero temperatures , anoxia ) and the reduced abundance of fungi likely provide a niche for bacterial , facultative anaerobic decomposers of SOM such as members of the Actinobacteria , which were found in significantly higher relative abundances in buried than in unburied topsoils .
Our study expands the knowledge on the microbial community structure in soils of Northern latitude permafrost regions , and attributes the delayed decomposition of SOM in buried soils to specific microbial taxa , and particularly to a decrease in abundance and activity of ECM fungi , and to the extent to which bacterial decomposers are able to act as their functional substitutes .

[1095] Environmental variability promotes plant invasion

Global environmental change not only entails changes in mean environmental conditions but also in their variability .
Changes in climate variability are often associated with altered disturbance regimes and temporal patterns of resource availability .
Here we show that increased variability of soil nutrients strongly promotes another key process of global change , plant invasion .
In experimental plant communities , the success of one of the world 's most invasive plants , Japanese knotweed , is two - to four-fold increased if extra nutrients are not supplied uniformly , but in a single large pulse , or in multiple pulses of different magnitudes .
The superior ability to take advantage of variable environments may be a key mechanism of knotweed dominance , and possibly many other plant invaders .
Our study demonstrates that increased nutrient variability can promote plant invasion , and that changes in environmental variability may interact with other global change processes and thereby substantially accelerate ecological change .

[1096] Microbead-based biomimetic synthetic neighbors enhance survival and function of rat pancreatic beta-cells

Diabetes is caused by the loss or dysfunction of insulin-secreting beta-cells in the pancreas .
beta-cells reduce their mass and lose insulin-producing ability in vitro , likely due to insufficient cell-cell and cell-extracellular matrix ( ECM ) interactions as beta-cells lose their native microenvironment .
Herein , we built an ex-vivo cell microenvironment by culturing primary beta-cells in direct contact with ` synthetic neighbors ' , cell-sized soft polymer microbeads that were modified with cell-cell signaling factors as well as components from pancreatic-tissue-specific ECMs .
This biomimetic 3D microenvironment was able to promote native cell-cell and cell-ECM interactions .
We obtained sustained maintenance of beta-cell function in vitro enhanced cell viability from the few days usually observed in 2D culture to periods exceeding three weeks , with enhanced beta-cell stability and insulin production .
Our approach can be extended to create a general 3D culture platform for other cell types .

[1097] Mesopredator release and avifaunal extinctions in a fragmented system

Mammalian carnivores are particularly vulnerable to extinction in fragmented landscapes , and their disappearance may lead to increased numbers of smaller carnivores that are principle predators of birds and other small vertebrates .
Such ` mesopredator release ' has been implicated in the decline and extinction of prey species .
Because experimental manipulation of carnivores is logistically , financially and ethically problematic , , however , few studies have evaluated how trophic cascades generated by the decline of dominant predators combine with other fragmentation effects to influence species diversity in terrestrial systems .
Although the mesopredator release hypothesis has received only limited critical evaluation and remains controversial , it has become the basis for conservation programmes justifying the protection of carnivores .
Here we describe a study that exploits spatial and temporal variation in the distribution and abundance of an apex predator , the coyote , in a landscape fragmented by development .
It appears that the decline and disappearance of the coyote , in conjunction with the effects of habitat fragmentation , affect the distribution and abundance of smaller carnivores and the persistence of their avian prey .

[1098] Potential regime shift in decreased sea ice production after the Mertz Glacier calving

Variability in dense shelf water formation can potentially impact Antarctic Bottom Water ( AABW ) production , a vital component of the global climate system .
In East Antarctica , the George V Land polynya system ( 142-150degreesE ) is structured by the local ` icescape ' , promoting sea ice formation that is driven by the offshore wind regime .
Here we present the first observations of this region after the repositioning of a large iceberg ( B9B ) precipitated the calving of the Mertz Glacier Tongue in 2010 .
Using satellite data , we find that the total sea ice production for the region in 2010 and 2011 was 144 and 134 km3 , respectively , representing a 14-20 % decrease from a value of 168 km3 averaged from 2000-2009 .
This abrupt change to the regional icescape could result in decreased polynya activity , sea ice production , and ultimately the dense shelf water export and AABW production from this region for the coming decades .

[1099] Temperature as a potent driver of regional forest drought stress and tree mortality

As the climate changes , drought may reduce tree productivity and survival across many forest ecosystems ; however , the relative influence of specific climate parameters on forest decline is poorly understood .
We derive a forest drought-stress index ( FDSI ) for the southwestern United States using a comprehensive tree-ring data set representing AD 1000-2007 .
The FDSI is approximately equally influenced by the warm-season vapour-pressure deficit ( largely controlled by temperature ) and cold-season precipitation , together explaining 82 % of the FDSI variability .
Correspondence between the FDSI and measures of forest productivity , mortality , bark-beetle outbreak and wildfire validate the FDSI as a holistic forest-vigour indicator .
If the vapour-pressure deficit continues increasing as projected by climate models , the mean forest drought-stress by the 2050s will exceed that of the most severe droughts in the past 1,000 years .
Collectively , the results foreshadow twenty-first-century changes in forest structures and compositions , with transition of forests in the southwestern United States , and perhaps water-limited forests globally , towards distributions unfamiliar to modern civilization .

[1100] Glucocerebrosidase depletion enhances cell-to-cell transmission of alpha-synuclein

Deposition of alpha-synuclein aggregates occurs widely in the central and peripheral nervous systems in Parkinson 's disease ( PD ) .
Although recent evidence has suggested that cell-to-cell transmission of alpha-synuclein aggregates is associated with the progression of PD , the mechanism by which alpha-synuclein aggregates spread remains undefined .
Here , we show that alpha-synuclein aggregates are transmitted from cell to cell through a cycle involving uptake of external aggregates , co-aggregation with endogenous alpha-synuclein and exocytosis of the co-aggregates .
Moreover , we find that glucocerebrosidase depletion , which has previously been strongly associated with PD and increased cognitive impairment , promotes propagation of alpha-synuclein aggregates .
These studies define how alpha-synuclein aggregates spread among neuronal cells and may provide an explanation for how glucocerebrosidase mutations increase the risk of developing PD and other synucleinopathies .

[1101] A middle Eocene carbon cycle conundrum

The Middle Eocene Climatic Optimum ( MECO ) was an approximately 500,000-year-long episode of widespread ocean-atmosphere warming about 40 million years ago , superimposed on a long-term middle Eocene cooling trend .
It was marked by a rise in atmospheric CO2 concentrations , biotic changes and prolonged carbonate dissolution in the deep ocean .
However , based on carbon cycle theory , a rise in atmospheric CO2 and warming should have enhanced continental weathering on timescales of the MECO .
This should have in turn increased ocean carbonate mineral saturation state and carbonate burial in deep-sea sediments , rather than the recorded dissolution .
We explore several scenarios using a carbon cycle model in an attempt to reconcile the data with theory , but these simulations confirm the problem .
The model only produces critical MECO features when we invoke a sea-level rise , which redistributes carbonate burial from deep oceans to continental shelves and decreases shelf sediment weathering .
Sufficient field data to assess this scenario is currently lacking .
We call for an integrated approach to unravel Earth system dynamics during carbon cycle variations that are of intermediate timescales ( several hundreds of thousands of years ) , such as the MECO .

[1102] A major advance of tropical Andean glaciers during the Antarctic cold reversal

The Younger Dryas stadial , a cold event spanning 12,800 to 11,500 years ago , during the last deglaciation , is thought to coincide with the last major glacial re-advance in the tropical Andes .
This interpretation relies mainly on cosmic-ray exposure dating of glacial deposits .
Recent studies , however , have established new production rates for cosmogenic 10Be and 3He , which make it necessary to update all chronologies in this region and revise our understanding of cryospheric responses to climate variability .
Here we present a new 10Be moraine chronology in Colombia showing that glaciers in the northern tropical Andes expanded to a larger extent during the Antarctic cold reversal ( 14,500 to 12,900 years ago ) than during the Younger Dryas .
On the basis of a homogenized chronology of all 10Be and 3He moraine ages across the tropical Andes , we show that this behaviour was common to the northern and southern tropical Andes .
Transient simulations with a coupled global climate model suggest that the common glacier behaviour was the result of Atlantic meridional overturning circulation variability superimposed on a deglacial increase in the atmospheric carbon dioxide concentration .
During the Antarctic cold reversal , glaciers advanced primarily in response to cold sea surface temperatures over much of the Southern Hemisphere .
During the Younger Dryas , however , northern tropical Andes glaciers retreated owing to abrupt regional warming in response to reduced precipitation and land-surface feedbacks triggered by a weakened Atlantic meridional overturning circulation .
Conversely , glacier retreat during the Younger Dryas in the southern tropical Andes occurred as a result of progressive warming , probably influenced by an increase in atmospheric carbon dioxide .
Considered with evidence from mid-latitude Andean glaciers , our results argue for a common glacier response to cold conditions in the Antarctic cold reversal exceeding that of the Younger Dryas .

[1103] Evidence that decomposition rates of organic carbon in mineral soil do not vary with temperature

It has been suggested that increases in temperature can accelerate the decomposition of organic carbon contained in forest mineral soil ( Cs ) , and , therefore , that global warming should increase the release of soil organic carbon to the atmosphere .
These predictions assume , however , that decay constants can be accurately derived from short-term laboratory incubations of soil or that in situ incubations of fresh litter accurately represent the temperature sensitivity of C s decomposition .
But our limited understanding of the biophysical factors that control Cs decomposition rates , and observations of only minor increases in Cs decomposition rate with temperature in longer-term forest soil heating experiments and in latitudinal comparisons of Cs decomposition rates bring these predictions into question .
Here we have compiled Cs decomposition data from 82 sites on five continents .
We found that Cs decomposition rates were remarkably constant across a global-scale gradient in mean annual temperature .
These data suggest that Cs decomposition rates for forest soils are not controlled by temperature limitations to microbial activity , and that increased temperature alone will not stimulate the decomposition of forest-derived carbon in mineral soil .

[1104] Increased water storage in North America and Scandinavia from GRACE gravity data

Space-borne gravity data from the Gravity Recovery and Climate Experiment ( GRACE ) have revealed trends in present-day continental water storage in many parts of the world .
In North America and northern Europe , it has been difficult to provide reliable estimates because of the strong background signals of glacial isostatic adjustment .
Attempts to separate the hydrologic signal from the background with numerical models are affected by uncertainties in our understanding of the precise glacial history and mantle viscosity .
Here we use a combination of GRACE data and measurements from the global positioning system to separate the hydrological signals without any model assumptions .
According to our estimates , water storage in central North America increased by 43.0 + / -5.0 Gt yr-1 over the past decade .
We attribute this increase to a recovery in terrestrial water storage after the extreme Canadian Prairies drought between 1999 and 2005 .
We find a smaller rise in water storage in southern Scandinavia , by 2.3 + / -0.8 Gt yr-1 .
In both North America and Scandinavia , our computed increases in water storage are consistent with long-term observations of terrestrial water level .
We suggest that the detected mass gains in terrestrial water storage need to be taken into account in studies on global sea-level rise .

[1105] An in vitro culture model to study the dynamics of colonic microbiota in Syrian golden hamsters and their susceptibility to infection with Clostridium difficile

Clostridium difficile infections ( CDI ) are caused by colonization and growth of toxigenic strains of C. difficile in individuals whose intestinal microbiota has been perturbed , in most cases following antimicrobial therapy .
Determination of the protective commensal gut community members could inform the development of treatments for CDI .
Here , we utilized the lethal enterocolitis model in Syrian golden hamsters to analyze the microbiota disruption and recovery along a 20-day period following a single dose of clindamycin on day 0 , inducing in vivo susceptibility to C. difficile infection .
To determine susceptibility in vitro , spores of strain VPI 10463 were cultured with and without soluble hamster fecal filtrates and growth was quantified by quantitative PCR and toxin immunoassay .
Fecal microbial population changes over time were tracked by 16S ribosomal RNA gene analysis via V4 sequencing and the PhyloChip assay .
C. difficile culture growth and toxin production were inhibited by the presence of fecal extracts from untreated hamsters but not extracts collected 5 days post-administration of clindamycin .
In vitro inhibition was re-established by day 15 , which correlated with resistance of animals to lethal challenge .
A substantial fecal microbiota shift in hamsters treated with antibiotics was observed , marked by significant changes across multiple phyla including Bacteroidetes and Proteobacteria .
An incomplete return towards the baseline microbiome occurred by day 15 correlating with the inhibition of C. difficile growth in vitro and in vivo .
These data suggest that soluble factors produced by the gut microbiota may be responsible for the suppression of C. difficile growth and toxin production .

[1106] Identifying the causes of sea-level change

Global mean sea-level change has increased from a few centimetres per century over recent millennia to a few tens of centimetres per century in recent decades .
This tenfold increase in the rate of rise can be attributed to climate change through the melting of land ice and the thermal expansion of ocean water .
As the present warming trend is expected to continue , global mean sea level will continue to rise .
Here we review recent insights into past sea-level changes on decadal to millennial timescales and how they may help constrain future changes .
We find that most studies constrain global mean sea-level rise to less than one metre over the twenty-first century , but departures from this global mean could reach several decimetres in many areas .
We conclude that improving estimates of the spatial variability in future sea-level change is an important research target in coming years .

[1107] How to Decrease the Viscosity of Suspension with the Second Fluid and Nanoparticles ?

According to recent research reports , addition of small amounts of a secondary fluid to a suspension could dramatically increase viscosity of suspension .
Results of this study indicate another interesting behavior that the secondary fluid could form a thin hydrophobic membrane around particle surface and significantly decrease the viscosity and yield stress of the suspension .
To enhance the surface hydrophobicity , hydrophobic nanoparticles ( nano-CaCO3 ) were added to the hydrophobic membrane of particles to improve the surface roughness , and to generate composite particles having a hierarchical structure similar to the micromorphology of lotus leaf .
This composite particle has a higher contact angle , and the suspension of composite particles has a lower viscosity and a lower yield stress .

[1108] Variability of sea-ice conditions in the Fram Strait over the past 30,000 years

Sea ice is a critical component of the climate system : variations in sea-ice cover affect the albedo of polar regions , and also the rate of deepwater formation .
Changes in the sea-ice cover of the North Atlantic Ocean are thought to have been related to abrupt climate changes throughout the last glacial termination , but reconstructions of sea-ice conditions are rare .
Here we use the sedimentary abundance of the IP25 and brassicasterol biomarkers , produced by sea-ice-associated diatoms and open-water phytoplankton , respectively , to generate a record of sea-ice conditions in the northernmost Atlantic Ocean for the past 30,000 years .
Our reconstruction shows that a stationary margin between sea-ice cover and the open ocean existed during the Last Glacial , although perennial sea-ice cover prevailed for most of the Last Glacial Maximum .
An early warming about 14,000 years ago was associated with ice-free conditions ; however , seasonal sea ice was present throughout the Holocene .
We find temporal links between our record of sea ice and reconstructions of the amount of relatively warm Atlantic water advected into the Nordic Seas .
We therefore conclude that changes in sea-ice conditions are linked to regional and global climate anomalies and oceanographic circulation in the North Atlantic .

[1109] Warming shifts ` worming ' : effects of experimental warming on invasive earthworms in northern North America

Climate change causes species range shifts and potentially alters biological invasions .
The invasion of European earthworm species across northern North America has severe impacts on native ecosystems .
Given the long and cold winters in that region that to date supposedly have slowed earthworm invasion , future warming is hypothesized to accelerate earthworm invasions into yet non-invaded regions .
Alternatively , warming-induced reductions in soil water content ( SWC ) can also decrease earthworm performance .
We tested these hypotheses in a field warming experiment at two sites in Minnesota , USA by sampling earthworms in closed and open canopy in three temperature treatments in 2010 and 2012 .
Structural equation modeling revealed that detrimental warming effects on earthworm densities and biomass could indeed be partly explained by warming-induced reductions in SWC .
The direction of warming effects depended on the current average SWC : warming had neutral to positive effects at high SWC , whereas the opposite was true at low SWC .
Our results suggest that warming limits the invasion of earthworms in northern North America by causing less favorable soil abiotic conditions , unless warming is accompanied by increased and temporally even distributions of rainfall sufficient to offset greater water losses from higher evapotranspiration .

[1110] Climate change-driven species ' range shifts filtered by photoperiodism

Forecasts of species range shifts as a result of climate change are essential , because invasions by exotic species shape biodiversity and therefore ecosystem functions and services .
Ecologists have focused on propagule pressure ( for example , the number of individuals and invasion events ) , the characteristics of an invading species , and its new abiotic and biotic environment to predict the likelihood of range expansion and invasion .
Here , we emphasize the role of photoperiodic response on the range expansion of species .
Unlike temperature , the latitudinal gradient of seasonal changes in day length is a stable , abiotic environmental factor that does not change with local or global climate .
Predicting range expansions across latitudes and the subsequent consequences for native communities requires a more comprehensive understanding of how species use day length to coordinate seasonal growth , reproduction , physiology and synchronization of life cycles with interacting individuals and species .

[1111] The microbe-mediated mechanisms affecting topsoil carbon stock in Tibetan grasslands

Warming has been shown to cause soil carbon ( C ) loss in northern grasslands owing to accelerated microbial decomposition that offsets increased grass productivity .
Yet , a multi-decadal survey indicated that the surface soil C stock in Tibetan alpine grasslands remained relatively stable .
To investigate this inconsistency , we analyzed the feedback responses of soil microbial communities to simulated warming by soil transplant in Tibetan grasslands .
Whereas microbial functional diversity decreased in response to warming , microbial community structure did not correlate with changes in temperature .
The relative abundance of catabolic genes associated with nitrogen ( N ) and C cycling decreased with warming , most notably in genes encoding enzymes associated with more recalcitrant C substrates .
By contrast , genes associated with C fixation increased in relative abundance .
The relative abundance of genes associated with urease , glutamate dehydrogenase and ammonia monoxygenase ( ureC , gdh and amoA ) were significantly correlated with N2O efflux .
These results suggest that unlike arid/semiarid grasslands , Tibetan grasslands maintain negative feedback mechanisms that preserve terrestrial C and N pools .
To examine whether these trends were applicable to the whole plateau , we included these measurements in a model and verified that topsoil C stocks remained relatively stable .
Thus , by establishing linkages between microbial metabolic potential and soil biogeochemical processes , we conclude that long-term C loss in Tibetan grasslands is ameliorated by a reduction in microbial decomposition of recalcitrant C substrates .

[1112] High water level impedes the adaptation of Polygonum hydropiper to deep burial : Responses of biomass allocation and root morphology

Many studies have investigated the individual effects of sedimentation or inundation on the performance of wetland plants , but few have examined the combined influence of these processes .
Wetland plants might show greater morphological plasticity in response to inundation than to sedimentation when these processes occur simultaneously since inundation can negate the negative effects of burial on plant growth .
Here , we evaluate this hypothesis by assessing growth of the emergent macrophyte Polygonum hydropiper under flooding ( 0 and 40 cm ) and sedimentation ( 0 , 5 , and 10 cm ) , separately and in combination .
Deep burial and high water level each led to low oxidation-reduction potential , biomass ( except for 5-cm burial ) , and growth of thick , short roots .
These characteristics were generally more significant under high water level than under deep burial conditions .
More biomass was allocated to stems in the deep burial treatments , but more to leaves in the high water level treatments .
Additionally , biomass accumulation was lower and leaf mass ratio was higher in the 40-cm water level + 10-cm burial depth treatment than both separate effects .
Our data indicate that inundation plays a more important role than sedimentation in determining plant morphology , suggesting hierarchical effects of environmental stressors on plant growth .

[1113] Increased forest ecosystem carbon and nitrogen storage from nitrogen rich bedrock

Nitrogen ( N ) limits the productivity of many ecosystems worldwide , thereby restricting the ability of terrestrial ecosystems to offset the effects of rising atmospheric CO2 emissions naturally .
Understanding input pathways of bioavailable N is therefore paramount for predicting carbon ( C ) storage on land , particularly in temperate and boreal forests .
Paradigms of nutrient cycling and limitation posit that new N enters terrestrial ecosystems solely from the atmosphere .
Here we show that bedrock comprises a hitherto overlooked source of ecologically available N to forests .
We report that the N content of soils and forest foliage on N-rich metasedimentary rocks ( 350-950 mg N kg-1 ) is elevated by more than 50 % compared with similar temperate forest sites underlain by N-poor igneous parent material ( 30-70 mg N kg-1 ) .
Natural abundance N isotopes attribute this difference to rock-derived N : 15N/14N values for rock , soils and plants are indistinguishable in sites underlain by N-rich lithology , in marked contrast to sites on N-poor substrates .
Furthermore , forests associated with N-rich parent material contain on average 42 % more carbon in above-ground tree biomass and 60 % more carbon in the upper 30 cm of the soil than similar sites underlain by N-poor rocks .
Our results raise the possibility that bedrock N input may represent an important and overlooked component of ecosystem N and C cycling elsewhere .

[1114] Recuperation of nitrogen cycling in Amazonian forests following agricultural abandonment

Phosphorus ( P ) is generally considered the most common limiting nutrient for productivity of mature tropical lowland forests growing on highly weathered soils .
It is often assumed that P limitation also applies to young tropical forests , but nitrogen ( N ) losses during land-use change may alter the stoichiometric balance of nutrient cycling processes .
In the Amazon basin , about 16 % of the original forest area has been cleared , and about 30-50 % of cleared land is estimated now to be in some stage of secondary forest succession following agricultural abandonment .
Here we use forest age chronosequences to demonstrate that young successional forests growing after agricultural abandonment on highly weathered lowland tropical soils exhibit conservative N-cycling properties much like those of N-limited forests on younger soils in temperate latitudes .
As secondary succession progresses , N-cycling properties recover and the dominance of a conservative P cycle typical of mature lowland tropical forests re-emerges .
These successional shifts in N :P cycling ratios with forest age provide a mechanistic explanation for initially lower and then gradually increasing soil emissions of the greenhouse gas nitrous oxide ( N2O ) .
The patterns of N and P cycling during secondary forest succession , demonstrated here over decadal timescales , are similar to N - and P-cycling patterns during primary succession as soils age over thousands and millions of years , thus revealing that N availability in terrestrial ecosystems is ephemeral and can be disrupted by either natural or anthropogenic disturbances at several timescales .

[1115] Comparative metagenomic , phylogenetic and physiological analyses of soil microbial communities across nitrogen gradients

Terrestrial ecosystems are receiving elevated inputs of nitrogen ( N ) from anthropogenic sources and understanding how these increases in N availability affect soil microbial communities is critical for predicting the associated effects on belowground ecosystems .
We used a suite of approaches to analyze the structure and functional characteristics of soil microbial communities from replicated plots in two long-term N fertilization experiments located in contrasting systems .
Pyrosequencing-based analyses of 16S rRNA genes revealed no significant effects of N fertilization on bacterial diversity , but significant effects on community composition at both sites ; copiotrophic taxa ( including members of the Proteobacteria and Bacteroidetes phyla ) typically increased in relative abundance in the high N plots , with oligotrophic taxa ( mainly Acidobacteria ) exhibiting the opposite pattern .
Consistent with the phylogenetic shifts under N fertilization , shotgun metagenomic sequencing revealed increases in the relative abundances of genes associated with DNA/RNA replication , electron transport and protein metabolism , increases that could be resolved even with the shallow shotgun metagenomic sequencing conducted here ( average of 75 000 reads per sample ) .
We also observed shifts in the catabolic capabilities of the communities across the N gradients that were significantly correlated with the phylogenetic and metagenomic responses , indicating possible linkages between the structure and functioning of soil microbial communities .
Overall , our results suggest that N fertilization may , directly or indirectly , induce a shift in the predominant microbial life-history strategies , favoring a more active , copiotrophic microbial community , a pattern that parallels the often observed replacement of K-selected with r-selected plant species with elevated N.

[1116] Temporal variation of beta-diversity and assembly mechanisms in a bacterial metacommunity

The turnover of community composition across space , beta-diversity , is influenced by different assembly mechanisms , which place varying weight on local habitat factors , such as environmental conditions and species interactions , and regional factors such as dispersal and history .
Several assembly mechanisms may function simultaneously ; however , little is known about how their importance changes over time and why .
Here , we implemented a field survey where we sampled a bacterial metacommunity consisting of 17 rock pools located at the Swedish Baltic Sea coast at 11 occasions during 1 year .
We determined to which extent communities were structured by different assembly mechanisms using variation partitioning and studied changes in beta-diversity across environmental gradients over time .
beta-Diversity was highest at times of high overall productivity and environmental heterogeneity in the metacommunity , at least partly due to species sorting , that is , selection of taxa by the prevailing environmental conditions .
In contrast , dispersal-driven assembly mechanisms were primarily detected at times when beta-diversity was relatively low .
There were no indications for strong and persistent differences in community composition or beta-diversity between permanent and temporary pools , indicating that the physical disturbance regime is of relatively minor importance .
In summary , our study clearly suggests that there are temporal differences in the relative importance of different assembly mechanisms related to abiotic factors and shows that the temporal variability of those factors is important for a more complete understanding of bacterial metacommunity dynamics .

[1117] Stable isotope evidence for the food web consequences of species invasions in lakes

Species invasions pose a serious threat to biodiversity and native ecosystems ; however , predicting and quantifying the impacts of invasive species has proven problematic .
Here we use stable isotope ratios to document the food-web consequences of the invasion of two non-native predators , smallmouth bass and rock bass , into Canadian lakes .
Invaded lakes had lower littoral prey-fish diversity and abundance than uninvaded reference lakes .
Consistent with this difference , lake trout from invaded lakes had more negative delta13C values ( -29.2 / 1000 versus -27.4 / 1000 ) and reduced trophic positions ( 3.3 versus 3.9 ) than those from reference lakes , indicating differences in food-web structure .
Furthermore , a comparison of the pre - and post-invasion food webs of two recently invaded lakes showed that invasion was followed by substantial declines in littoral prey-fish abundance and the trophic position of lake trout , reflecting a shift in the diet of lake trout towards zooplankton and reduced dependence on littoral fish .
This study demonstrates the use of stable isotope techniques to detect changes in food-web structure following perturbations ; in this instance , bass-induced food-web shifts may have severe consequences for native species and ecosystems .

[1118] Human Tra2 proteins jointly control a CHEK1 splicing switch among alternative and constitutive target exons

Alternative splicing -- the production of multiple messenger RNA isoforms from a single gene -- is regulated in part by RNA binding proteins .
While the RBPs transformer2 alpha ( Tra2alpha ) and Tra2beta have both been implicated in the regulation of alternative splicing , their relative contributions to this process are not well understood .
Here we find simultaneous -- but not individual -- depletion of Tra2alpha and Tra2beta induces substantial shifts in splicing of endogenous Tra2beta target exons , and that both constitutive and alternative target exons are under dual Tra2alpha-Tra2beta control .
Target exons are enriched in genes associated with chromosome biology including CHEK1 , which encodes a key DNA damage response protein .
Dual Tra2 protein depletion reduces expression of full-length CHK1 protein , results in the accumulation of the DNA damage marker gammaH2AX and decreased cell viability .
We conclude Tra2 proteins jointly control constitutive and alternative splicing patterns via paralog compensation to control pathways essential to the maintenance of cell viability .

[1119] Attribution of polar warming to human influence

The polar regions have long been expected to warm strongly as a result of anthropogenic climate change , because of the positive feedbacks associated with melting ice and snow .
Several studies have noted a rise in Arctic temperatures over recent decades , but have not formally attributed the changes to human influence , owing to sparse observations and large natural variability .
Both warming and cooling trends have been observed in Antarctica , which the Intergovernmental Panel on Climate Change Fourth Assessment Report concludes is the only continent where anthropogenic temperature changes have not been detected so far , possibly as a result of insufficient observational coverage .
Here we use an up-to-date gridded data set of land surface temperatures and simulations from four coupled climate models to assess the causes of the observed polar temperature changes .
We find that the observed changes in Arctic and Antarctic temperatures are not consistent with internal climate variability or natural climate drivers alone , and are directly attributable to human influence .
Our results demonstrate that human activities have already caused significant warming in both polar regions , with likely impacts on polar biology , indigenous communities , ice-sheet mass balance and global sea level .

[1120] Iron deficiency increases growth and nitrogen-fixation rates of phosphorus-deficient marine cyanobacteria

Marine dinitrogen ( N2 ) - fixing cyanobacteria have large impacts on global biogeochemistry as they fix carbon dioxide ( CO2 ) and fertilize oligotrophic ocean waters with new nitrogen .
Iron ( Fe ) and phosphorus ( P ) are the two most important limiting nutrients for marine biological N2 fixation , and their availabilities vary between major ocean basins and regions .
A long-standing question concerns the ability of two globally dominant N2-fixing cyanobacteria , unicellular Crocosphaera and filamentous Trichodesmium , to maintain relatively high N2-fixation rates in these regimes where both Fe and P are typically scarce .
We show that under P-deficient conditions , cultures of these two cyanobacteria are able to grow and fix N2 faster when Fe deficient than when Fe replete .
In addition , growth affinities relative to P increase while minimum concentrations of P that support growth decrease at low Fe concentrations .
In Crocosphaera , this effect is accompanied by a reduction in cell sizes and elemental quotas .
Relatively high growth rates of these two biogeochemically critical cyanobacteria in low-P , low-Fe environments such as those that characterize much of the oligotrophic ocean challenge the common assumption that low Fe levels can have only negative effects on marine primary producers .
The closely interdependent influence of Fe and P on N2-fixing cyanobacteria suggests that even subtle shifts in their supply ratio in the past , present and future oceans could have large consequences for global carbon and nitrogen cycles .

[1121] Observed variations of methane on Mars unexplained by known atmospheric chemistry and physics

The detection of methane on Mars has revived the possibility of past or extant life on this planet , despite the fact that an abiogenic origin is thought to be equally plausible .
An intriguing aspect of the recent observations of methane on Mars is that methane concentrations appear to be locally enhanced and change with the seasons .
However , methane has a photochemical lifetime of several centuries , and is therefore expected to have a spatially uniform distribution on the planet .
Here we use a global climate model of Mars with coupled chemistry to examine the implications of the recently observed variations of Martian methane for our understanding of the chemistry of methane .
We find that photochemistry as currently understood does not produce measurable variations in methane concentrations , even in the case of a current , local and episodic methane release .
In contrast , we find that the condensation-sublimation cycle of Mars ' carbon dioxide atmosphere can generate large-scale methane variations differing from those observed .
In order to reproduce local methane enhancements similar to those recently reported , we show that an atmospheric lifetime of less than 200 days is necessary , even if a local source of methane is only active around the time of the observation itself .
This implies an unidentified methane loss process that is 600 times faster than predicted by standard photochemistry .
The existence of such a fast loss in the Martian atmosphere is difficult to reconcile with the observed distribution of other trace gas species .
In the case of a destruction mechanism only active at the surface of Mars , destruction of methane must occur with an even shorter timescale of the order of ~ 1 hour to explain the observations .
If recent observations of spatial and temporal variations of methane are confirmed , this would suggest an extraordinarily harsh environment for the survival of organics on the planet .

[1122] Rising temperatures are likely to reduce crop yields

Sir Your News story about the Royal Society meeting on climate change and food production ( `` Hikes in surface ozone could suffocate crops '' Nature 435 , 7 ; 2005 ) noted that rising CO 2 levels will generally benefit crop growth , as this stimulates photosynthesis in most crop plants .
However , the links between climate change and food production are even more complex than your story suggests .

[1123] Expansion of host cellular niche can drive adaptation of a zoonotic malaria parasite to humans

The macaque malaria parasite Plasmodium knowlesi has recently emerged as an important zoonosis in Southeast Asia .
Infections are typically mild but can cause severe disease , achieving parasite densities similar to fatal Plasmodium falciparum infections .
Here we show that a primate-adapted P. knowlesi parasite proliferates poorly in human blood due to a strong preference for young red blood cells ( RBCs ) .
We establish a continuous in vitro culture system by using human blood enriched for young cells .
Mathematical modelling predicts that parasite adaptation for invasion of older RBCs is a likely mechanism leading to high parasite densities in clinical infections .
Consistent with this model , we find that P. knowlesi can adapt to invade a wider age range of RBCs , resulting in proliferation in normal human blood .
Such cellular niche expansion may increase pathogenesis in humans and will be a key feature to monitor as P. knowlesi emerges in human populations .

[1124] Predators increase the risk of catastrophic extinction of prey populations

There has been considerable research on both top-down effects and on disturbances in ecological communities ; however , the interaction between the two , when the disturbance is catastrophic , has rarely been examined .
Predators may increase the probability of prey extinction resulting from a catastrophic disturbance both by reducing prey population size and by changing ecological traits of prey individuals such as habitat characteristics in a way that increases the vulnerability of prey species to extinction .
We show that a major hurricane in the Bahamas led to the extinction of lizard populations on most islands onto which a predator had been experimentally introduced , whereas no populations became extinct on control islands .
Before the hurricane , the predator had reduced prey populations to about half of those on control islands .
Two months after the hurricane , we found only recently hatched individuals -- apparently lizards survived the inundating storm surge only as eggs .
On predator-introduction islands , those hatchling populations were a smaller fraction of pre-hurricane populations than on control islands .
Egg survival allowed rapid recovery of prey populations to pre-hurricane levels on all control islands but on only a third of predator-introduction islands -- the other two-thirds lost their prey populations .
Thus climatic disturbance compounded by predation brought prey populations to extinction .

[1125] Agulhas leakage dynamics affects decadal variability in Atlantic overturning circulation

Predicting the evolution of climate over decadal timescales requires a quantitative understanding of the dynamics that govern the meridional overturning circulation ( MOC ) .
Comprehensive ocean measurement programmes aiming to monitor MOC variations have been established in the subtropical North Atlantic ( RAPID , at latitude 26.5 degrees N , and MOVE , at latitude 16degrees N ) and show strong variability on intraseasonal to interannual timescales .
Observational evidence of longer-term changes in MOC transport remains scarce , owing to infrequent sampling of transoceanic sections over past decades .
Inferences based on long-term sea surface temperature records , however , supported by model simulations , suggest a variability with an amplitude of + / -1.5 -3 Sv ( 1 Sv = 106 m3 s-1 ) on decadal timescales in the subtropics .
Such variability has been attributed to variations of deep water formation in the sub-arctic Atlantic , particularly the renewal rate of Labrador Sea Water .
Here we present results from a model simulation that suggest an additional influence on decadal MOC variability having a Southern Hemisphere origin : dynamic signals originating in the Agulhas leakage region at the southern tip of Africa .
These contribute a MOC signal in the tropical and subtropical North Atlantic that is of the same order of magnitude as the northern source .
A complete rationalization of observed MOC changes therefore also requires consideration of signals arriving from the south .

[1126] Observed thinning of Totten Glacier is linked to coastal polynya variability

Analysis of ICESat-1 data ( 2003-2008 ) shows significant surface lowering of Totten Glacier , the glacier discharging the largest volume of ice in East Antarctica , and less change on nearby Moscow University Glacier .
After accounting for firn compaction anomalies , the thinning appears to coincide with fast-flowing ice indicating a dynamical origin .
Here , to elucidate these observations , we apply high-resolution ice-ocean modelling .
Totten Ice Shelf is simulated to have higher , more variable basal melting rates .
We link this variability to the volume of cold water , originating in polynyas upon sea ice formation , reaching the sub-ice-shelf cavity .
Hence , we propose that the observed increased thinning of Totten Glacier is due to enhanced basal melting caused by a decrease in cold polynya water reaching its cavity .
We support this hypothesis with passive microwave data of polynya extent variability .
Considering the widespread changes in sea ice conditions , this mechanism could be contributing extensively to ice-shelf instability .

[1127] Integration of TiO2 into the diatom Thalassiosira weissflogii during frustule synthesis

Nature has inspired the design of complex hierarchical structures in the field of material science .
Diatoms , unicellular algae with a hallmark intricate siliceous cell wall , have provided such a stimulus .
Altering the chemistry of the diatom frustule has been explored to expand on the potential application of diatoms .
The ability to modify the diatom in vivo opens the possibility to tailor the diatom to the end application .
Herein , we report the chemical modification of the living diatom T. weissflogii using a titania precursor , titanium ( IV ) bis - ( ammonium lactato ) - dihydroxide ( TiBALDH ) .
Incorporation of Ti into the diatom is achieved via repeated treatment of cultures with non-toxic concentrations of TiBALDH .
The characteristic architectural features of the diatom are unaltered following chemical modification .
Transformation of the living diatom provides opportunity to confer novel structural , chemical or functional properties upon the diatom .
We report on a photocatalytic ability imparted upon the TiBALDH-modified diatom .

[1128] The evolution of the marine phosphate reservoir

Phosphorus is a biolimiting nutrient that has an important role in regulating the burial of organic matter and the redox state of the ocean-atmosphere system .
The ratio of phosphorus to iron in iron-oxide-rich sedimentary rocks can be used to track dissolved phosphate concentrations if the dissolved silica concentration of sea water is estimated .
Here we present iron and phosphorus concentration ratios from distal hydrothermal sediments and iron formations through time to study the evolution of the marine phosphate reservoir .
The data suggest that phosphate concentrations have been relatively constant over the Phanerozoic eon , the past 542 million years ( Myr ) of Earth 's history .
In contrast , phosphate concentrations seem to have been elevated in Precambrian oceans .
Specifically , there is a peak in phosphorus-to-iron ratios in Neoproterozoic iron formations dating from ~ 750 to ~ 635 Myr ago , indicating unusually high dissolved phosphate concentrations in the aftermath of widespread , low-latitude ` snowball Earth ' glaciations .
An enhanced postglacial phosphate flux would have caused high rates of primary productivity and organic carbon burial and a transition to more oxidizing conditions in the ocean and atmosphere .
The snowball Earth glaciations and Neoproterozoic oxidation are both suggested as triggers for the evolution and radiation of metazoans .
We propose that these two factors are intimately linked ; a glacially induced nutrient surplus could have led to an increase in atmospheric oxygen , paving the way for the rise of metazoan life .

[1129] Stable sea surface temperatures in the western Pacific warm pool over the past 1.75 million years

About 850,000 years ago , the period of the glacial cycles changed from 41,000 to 100,000 years .
This mid-Pleistocene climate transition has been attributed to global cooling , possibly caused by a decrease in atmospheric carbon dioxide concentrations .
However , evidence for such cooling is currently restricted to the cool upwelling regions in the eastern equatorial oceans , although the tropical warm pools on the western side of the ocean basins are particularly sensitive to changes in radiative forcing .
Here we present high-resolution records of sea surface temperatures spanning the past 1.75 million years , obtained from oxygen isotopes and Mg/Ca ratios in planktonic foraminifera from the western Pacific warm pool .
In contrast with the eastern equatorial regions , sea surface temperatures in the western Pacific warm pool are relatively stable throughout the Pleistocene epoch , implying little long-term change in the tropical net radiation budget .
Our results challenge the hypothesis of a gradual decrease in atmospheric carbon dioxide concentrations as a dominant trigger of the longer glacial cycles since 850,000 years ago .
Instead , we infer that the temperature contrast across the equatorial Pacific Ocean increased , which might have had a significant influence on the mid-Pleistocene climate transition .

[1130] Enhanced Bio-hydrogen Production from Protein Wastewater by Altering Protein Structure and Amino Acids Acidification Type

Enhanced bio-hydrogen production from protein wastewater by altering protein structure and amino acids acidification type via pH control was investigated .
The hydrogen production reached 205.2 mL/g-protein when protein wastewater was pretreated at pH 12 and then fermented at pH 10 .
The mechanism studies showed that pH 12 pretreatment significantly enhanced protein bio-hydrolysis during the subsequent fermentation stage as it caused the unfolding of protein , damaged the protein hydrogen bonding networks , and destroyed the disulfide bridges , which increased the susceptibility of protein to protease .
Moreover , pH 10 fermentation produced more acetic but less propionic acid during the anaerobic fermentation of amino acids , which was consistent with the theory of fermentation type affecting hydrogen production .
Further analyses of the critical enzymes , genes , and microorganisms indicated that the activity and abundance of hydrogen producing bacteria in the pH 10 fermentation reactor were greater than those in the control .

[1131] Cooperative secretions facilitate host range expansion in bacteria

The majority of emergent human pathogens are zoonotic in origin , that is , they can transmit to humans from other animals .
Understanding the factors underlying the evolution of pathogen host range is therefore of critical importance in protecting human health .
There are two main evolutionary routes to generalism : organisms can tolerate multiple environments or they can modify their environments to forms to which they are adapted .
Here we use a combination of theory and a phylogenetic comparative analysis of 191 pathogenic bacterial species to show that bacteria use cooperative secretions that modify their environment to extend their host range and infect multiple host species .
Our results suggest that cooperative secretions are key determinants of host range in bacteria , and that monitoring for the acquisition of secreted proteins by horizontal gene transfer can help predict emerging zoonoses .

[1132] Characterizing the nonlinear growth of large-scale structure in the Universe

The local Universe displays a rich hierarchical pattern of galaxy clusters and superclusters .
The early Universe , however , was almost smooth , with only slight ` ripples ' , as seen in the cosmic microwave background radiation .
Models of the evolution of cosmic structure link these observations through the effect of gravity , because the small initially overdense fluctuations are predicted to attract additional mass as the Universe expands .
During the early stages of this expansion , the ripples evolve independently , like linear waves on the surface of deep water .
As the structures grow in mass , they interact with each other in nonlinear ways , more like waves breaking in shallow water .
We have recently shown how cosmic structure can be characterized by phase correlations associated with these nonlinear interactions , but it was not clear how to use that information to obtain quantitative insights into the growth of structures .
Here we report a method of revealing phase information , and show quantitatively how this relates to the formation of filaments , sheets and clusters of galaxies by nonlinear collapse .
We develop a statistical method based on information entropy to separate linear from nonlinear effects , and thereby are able to disentangle those aspects of galaxy clustering that arise from initial conditions ( the ripples ) from the subsequent dynamical evolution .

[1133] More-frequent extreme northward shifts of eastern Indian Ocean tropical convergence under greenhouse warming

The Intertropical Convergence Zone ( ITCZ ) in the tropical eastern Indian Ocean exhibits strong interannual variability , often co-occurring with positive Indian Ocean Dipole ( pIOD ) events .
During what we identify as an extreme ITCZ event , a drastic northward shift of atmospheric convection coincides with an anomalously strong north-minus-south sea surface temperature ( SST ) gradient over the eastern equatorial Indian Ocean .
Such shifts lead to severe droughts over the maritime continent and surrounding islands but also devastating floods in southern parts of the Indian subcontinent .
Understanding future changes of the ITCZ is therefore of major scientific and socioeconomic interest .
Here we find a more-than-doubling in the frequency of extreme ITCZ events under greenhouse warming , estimated from climate models participating in the Coupled Model Intercomparison Project phase 5 that are able to simulate such events .
The increase is due to a mean state change with an enhanced north-minus-south SST gradient and a weakened Walker Circulation , facilitating smaller perturbations to shift the ITCZ northwards .

[1134] The evolution of sensory divergence in the context of limited gene flow in the bumblebee bat

The sensory drive theory of speciation predicts that populations of the same species inhabiting different environments can differ in sensory traits , and that this sensory difference can ultimately drive speciation .
However , even in the best-known examples of sensory ecology driven speciation , it is uncertain whether the variation in sensory traits is the cause or the consequence of a reduction in levels of gene flow .
Here we show strong genetic differentiation , no gene flow and large echolocation differences between the allopatric Myanmar and Thai populations of the world 's smallest mammal , Craseonycteris thonglongyai , and suggest that geographic isolation most likely preceded sensory divergence .
Within the geographically continuous Thai population , we show that geographic distance has a primary role in limiting gene flow rather than echolocation divergence .
In line with sensory-driven speciation models , we suggest that in C. thonglongyai , limited gene flow creates the suitable conditions that favour the evolution of sensory divergence via local adaptation .

[1135] D-Glucosamine supplementation extends life span of nematodes and of ageing mice

D-Glucosamine ( GlcN ) is a freely available and commonly used dietary supplement potentially promoting cartilage health in humans , which also acts as an inhibitor of glycolysis .
Here we show that GlcN , independent of the hexosamine pathway , extends Caenorhabditis elegans life span by impairing glucose metabolism that activates AMP-activated protein kinase ( AMPK/AAK -2 ) and increases mitochondrial biogenesis .
Consistent with the concept of mitohormesis , GlcN promotes increased formation of mitochondrial reactive oxygen species ( ROS ) culminating in increased expression of the nematodal amino acid-transporter 1 ( aat-1 ) gene .
Ameliorating mitochondrial ROS formation or impairment of aat-1-expression abolishes GlcN-mediated life span extension in an NRF2/SKN -1 - dependent fashion .
Unlike other calorie restriction mimetics , such as 2-deoxyglucose , GlcN extends life span of ageing C57BL/6 mice , which show an induction of mitochondrial biogenesis , lowered blood glucose levels , enhanced expression of several murine amino-acid transporters , as well as increased amino-acid catabolism .
Taken together , we provide evidence that GlcN extends life span in evolutionary distinct species by mimicking a low-carbohydrate diet .

[1136] Response of glacier basal motion to transient water storage

Basal motion of glaciers is responsible for short-term variations in glacier velocity .
At the calving fronts of marine-terminating outlet glaciers , accelerated basal motion has led to increased ice discharge and thus is tightly connected to sea level rise .
Subglacial water passes through dynamic conduits that are fed by distributed linked cavities at the bed , and plays a critical role in setting basal motion .
However , neither measured subglacial water pressure nor the volume of water in storage can fully explain basal motion .
Here , we use global positioning system observations to document basal motion during highly variable inputs of water from diurnal and seasonal melt , and from an outburst flood at Kennicott Glacier , Alaska .
We find that glacier velocity increases when englacial and subglacial water storage is increasing .
We suggest that whenever water inputs exceed the ability of the existing conduits to transmit water , the conduits pressurize and drive water back into the areally extensive linked cavity system .
This in turn promotes basal motion .
Sustained high melt rates do not imply continued rapid basal motion , however , because the subglacial conduit system evolves to greater efficiency .
Large pulses of water to the bed can overwhelm the subglacial hydrologic network and incite basal motion , potentially explaining recent accelerations of the Greenland Ice Sheet , where rapid drainage of large surficial melt ponds delivers water through cold ice .

[1137] Convergent evolution in locomotory patterns of flying and swimming animals

Locomotion is one of the major energetic costs faced by animals and various strategies have evolved to reduce its cost .
Birds use interspersed periods of flapping and gliding to reduce the mechanical requirements of level flight while undergoing cyclical changes in flight altitude , known as undulating flight .
Here we equipped free-ranging marine vertebrates with accelerometers and demonstrate that gait patterns resembling undulating flight occur in four marine vertebrate species comprising sharks and pinnipeds .
Both sharks and pinnipeds display intermittent gliding interspersed with powered locomotion .
We suggest , that the convergent use of similar gait patterns by distinct groups of animals points to universal physical and physiological principles that operate beyond taxonomic limits and shape common solutions to increase energetic efficiency .
Energetically expensive large-scale migrations performed by many vertebrates provide common selection pressure for efficient locomotion , with potential for the convergence of locomotory strategies by a wide variety of species .

[1138] Photosynthetic architecture differs in coastal and oceanic diatoms

Diatoms are a key taxon of eukaryotic phytoplankton and a major contributor to global carbon fixation .
They are ubiquitous in the marine ecosystem despite marked gradients in environmental properties , such as dissolved iron concentrations , between coastal and oceanic waters .
Previous studies have shown that offshore species of diatoms and other eukaryotic algae have evolved lower iron requirements to subsist in iron-poor oceanic waters , but the biochemical mechanisms responsible for their decreased iron demand are unknown .
Here we show , using laboratory-cultured model species , a fundamental difference between a coastal and an oceanic diatom in their photosynthetic architecture .
Specifically , the oceanic diatom had up to fivefold lower photosystem I and up to sevenfold lower cytochrome b6f complex concentrations than a coastal diatom .
These changes to the photosynthetic apparatus markedly decrease the cellular iron requirements of the oceanic diatom but not its photosynthetic rates .
However , oceanic diatoms might have also sacrificed their ability to acclimate to rapid fluctuations in light intensity -- a characteristic of dynamic and turbid coastal waters .
We suggest that diatoms , and probably other eukaryotic algal taxa , exploited this difference in the underwater light climate between oceanic and coastal waters , enabling them to decrease their iron requirements without compromising photosynthetic capacity .
This adaptation probably facilitated the colonization of the open ocean by diatoms , and contributes to their persistence in this iron-impoverished environment .

[1139] Arsenic sequestration by organic sulphur in peat

Wetlands cover more than 6 % of the global ice-free land area , and have been recognized as important sinks for arsenic .
Wetland soils and sediments are subject to frequent changes in redox conditions , driven by fluctuations in the water table and shifts in biological activity .
Under oxic conditions , natural organic matter promotes arsenic release from metal - ( hydr ) oxides , thereby enhancing arsenic mobility .
Under strongly reducing conditions , however , organic matter triggers the formation of arsenic-sequestering sulphides , leading to a reduction in arsenic mobility .
Furthermore , the sorption of arsenic to natural organic matter is increasingly thought to suppress arsenic mobility , but the binding mechanisms have remained elusive .
Here we use X-ray absorption spectroscopy to analyse the speciation of solid-phase arsenic in peat samples collected from a naturally arsenic-enriched peatland in Switzerland .
We show that natural organic matter can completely sequester arsenic through the formation of covalent bonds between trivalent arsenic and organic sulphur groups , which have an average arsenic-sulphur bond distance of 2.26 A .
We suggest that by binding arsenic in this way , natural organic matter plays an active role in arsenic immobilization in sulphur-enriched , anoxic wetlands .

[1140] Severe plant invasions can increase mycorrhizal fungal abundance and diversity

Invasions by non-native plants can alter ecosystem functions and reduce native plant diversity , but relatively little is known about their effect on belowground microbial communities .
We show that invasions by knapweed ( Centaurea stoebe ) and leafy spurge ( Euphorbia esula , hereafter spurge ) -- but not cheatgrass ( Bromus tectorum ) -- support a higher abundance and diversity of symbiotic arbuscular mycorrhizal fungi ( AMF ) than multi-species native plant communities .
The higher AMF richness associated with knapweed and spurge is unlikely due to a co-invasion by AMF , because a separate sampling showed that individual native forbs hosted a similar AMF abundance and richness as exotic forbs .
Native grasses associated with fewer AMF taxa , which could explain the reduced AMF richness in native , grass-dominated communities .
The three invasive plant species harbored distinct AMF communities , and analyses of co-occurring native and invasive plants indicate that differences were partly driven by the invasive plants and were not the result of pre-invasion conditions .
Our results suggest that invasions by mycotrophic plants that replace poorer hosts can increase AMF abundance and richness .
The high AMF richness in monodominant plant invasions also indicates that the proposed positive relationship between above and belowground diversity is not always strong .
Finally , the disparate responses among exotic plants and consistent results between grasses and forbs suggest that AMF respond more to plant functional group than plant provenance .

[1141] Variations of Younger Dryas atmospheric radiocarbon explicable without ocean circulation changes

The concentration of radiocarbon , 14C , in the atmosphere depends on its production rate by cosmic rays , and on the intensity of carbon exchange between the atmosphere and other reservoirs , for example the deep oceans .
For the Holocene ( the past ~ 11,500 years ) , it has been shown that fluctuations in atmospheric radiocarbon concentrations have been caused mostly by variations in the solar magnetic field .
Recent progress in extending the radiocarbon record backwards in time has indicated especially high atmospheric radiocarbon concentrations in the Younger Dryas cold period , between 12,700 and 11,500 years before the present .
These high concentrations have been interpreted as a result of a reduced exchange with the deep-ocean reservoir , caused by a drastic weakening of the deep-ocean ventilation .
Here we present a high-resolution reconstruction of atmospheric radiocarbon concentrations , derived from annually laminated sediments of two Polish lakes , Lake Gosciz and Lake Perespilno .
These records indicate that the maximum in atmospheric radiocarbon concentrations in the early Younger Dryas was smaller than previously believed , and might have been caused by variations in solar activity .
If so , there is no indication that the deep-ocean ventilation in the Younger Dryas was significantly different from today 's .

[1142] Ecosystem consequences of species richness and composition in pond food webs

Resolving current concerns about the role of biodiversity on ecosystems calls for understanding the separate roles of changes in species numbers and of composition .
Recent work shows that primary productivity often , but not always , saturates with species richness within single trophic levels .
However , any interpretation of such patterns must consider that variation in biodiversity is necessarily associated with changes in species composition ( identity ) , and that changes in biodiversity often occur across multiple trophic levels .
Here we present results from a mesocosm experiment in which we independently manipulated species richness and species composition across multiple trophic levels in pond food webs .
In contrast to previous studies that focused on single trophic levels , we found that productivity is either idiosyncratic or increases with respect to species richness , and that richness influences trophic structure .
However , the composition of species within richness levels can have equally or more marked effects on ecosystems than average effects of richness per se .
Indirect evidence suggests that richness and associated changes in species composition affect ecosystem attributes through indirect effects and trophic interactions among species , features that are highly characteristic of natural , complex ecosystems .

[1143] The Southern Ocean biogeochemical divide

Modelling studies have demonstrated that the nutrient and carbon cycles in the Southern Ocean play a central role in setting the air-sea balance of CO2 and global biological production .
Box model studies first pointed out that an increase in nutrient utilization in the high latitudes results in a strong decrease in the atmospheric carbon dioxide partial pressure ( pCO2 ) .
This early research led to two important ideas : high latitude regions are more important in determining atmospheric pCO2 than low latitudes , despite their much smaller area , and nutrient utilization and atmospheric pCO2 are tightly linked .
Subsequent general circulation model simulations show that the Southern Ocean is the most important high latitude region in controlling pre-industrial atmospheric CO2 because it serves as a lid to a larger volume of the deep ocean .
Other studies point out the crucial role of the Southern Ocean in the uptake and storage of anthropogenic carbon dioxide and in controlling global biological production .
Here we probe the system to determine whether certain regions of the Southern Ocean are more critical than others for air-sea CO2 balance and the biological export production , by increasing surface nutrient drawdown in an ocean general circulation model .
We demonstrate that atmospheric CO2 and global biological export production are controlled by different regions of the Southern Ocean .
The air-sea balance of carbon dioxide is controlled mainly by the biological pump and circulation in the Antarctic deep-water formation region , whereas global export production is controlled mainly by the biological pump and circulation in the Subantarctic intermediate and mode water formation region .
The existence of this biogeochemical divide separating the Antarctic from the Subantarctic suggests that it may be possible for climate change or human intervention to modify one of these without greatly altering the other .

[1144] Robustness and uncertainties in the new CMIP5 climate model projections

Estimates of impacts from anthropogenic climate change rely on projections from climate models .
Uncertainties in those have often been a limiting factor , in particular on local scales .
A new generation of more complex models running scenarios for the upcoming Intergovernmental Panel on Climate Change Fifth Assessment Report ( IPCC AR5 ) is widely , and perhaps naively , expected to provide more detailed and more certain projections .
Here we show that projected global temperature change from the new models is remarkably similar to that from those used in IPCC AR4 after accounting for the different underlying scenarios .
The spatial patterns of temperature and precipitation change are also very consistent .
Interestingly , the local model spread has not changed much despite substantial model development and a massive increase in computational capacity .
Part of this model spread is irreducible owing to internal variability in the climate system , yet there is also uncertainty from model differences that can potentially be eliminated .
We argue that defining progress in climate modelling in terms of narrowing uncertainties is too limited .
Models improve , representing more processes in greater detail .
This implies greater confidence in their projections , but convergence may remain slow .
The uncertainties should not stop decisions being made .

[1145] Decomposition of Phragmites australis litter retarded by invasive Solidago canadensis in mixtures : an antagonistic non-additive effect

Solidago canadensis is an aggressive invader in China .
Solidago invasion success is partially attributed to allelopathic compounds release and more benefits from AM fungi , which potentially makes the properties of Solidago litter different from co-occurring natives .
These properties may comprehensively affect litter decomposition of co-occurring natives .
We conducted a field experiment to examine litter mixing effects in a Phragmites australis dominated community invaded by Solidago in southeast China .
Solidago had more rapid mass and N loss rate than Phragmites when they decomposed separately .
Litter mixing decreased N loss rate in Phragmites litter and increased that of Solidago .
Large decreases in Phragmites mass loss and smaller increases in Solidago mass loss caused negative non-additive effect .
Solidago litter extracts reduced soil C decomposition and N processes , suggested an inhibitory effect of Solidago secondary compounds .
These results are consistent with the idea that nutrient transfer and secondary compounds both affected litter mixtures decomposition .

[1146] The role of terrestrial plants in limiting atmospheric CO2 decline over the past 24 million years

Environmental conditions during the past 24 million years are thought to have been favourable for enhanced rates of atmospheric carbon dioxide drawdown by silicate chemical weathering .
Proxy records indicate , however , that the Earth 's atmospheric carbon dioxide concentrations did not fall below about 200-250 parts per million during this period .
The stabilization of atmospheric carbon dioxide concentrations near this minimum value suggests that strong negative feedback mechanisms inhibited further drawdown of atmospheric carbon dioxide by high rates of global silicate rock weathering .
Here we investigate one possible negative feedback mechanism , occurring under relatively low carbon dioxide concentrations and in warm climates , that is related to terrestrial plant productivity and its role in the decomposition of silicate minerals .
We use simulations of terrestrial and geochemical carbon cycles and available experimental evidence to show that vegetation activity in upland regions of active orogens was severely limited by near-starvation of carbon dioxide in combination with global warmth over this period .
These conditions diminished biotic-driven silicate rock weathering and thereby attenuated an important long-term carbon dioxide sink .
Although our modelling results are semi-quantitative and do not capture the full range of biogeochemical feedbacks that could influence the climate , our analysis indicates that the dynamic equilibrium between plants , climate and the geosphere probably buffered the minimum atmospheric carbon dioxide concentrations over the past 24 million years .

[1147] Laboratory evolution of Geobacter sulfurreducens for enhanced growth on lactate via a single-base-pair substitution in a transcriptional regulator

The addition of organic compounds to groundwater in order to promote bioremediation may represent a new selective pressure on subsurface microorganisms .
The ability of Geobacter sulfurreducens , which serves as a model for the Geobacter species that are important in various types of anaerobic groundwater bioremediation , to adapt for rapid metabolism of lactate , a common bioremediation amendment , was evaluated .
Serial transfer of five parallel cultures in a medium with lactate as the sole electron donor yielded five strains that could metabolize lactate faster than the wild-type strain .
Genome sequencing revealed that all five strains had non-synonymous single-nucleotide polymorphisms in the same gene , GSU0514 , a putative transcriptional regulator .
Introducing the single-base-pair mutation from one of the five strains into the wild-type strain conferred rapid growth on lactate .
This strain and the five adaptively evolved strains had four to eight-fold higher transcript abundance than wild-type cells for genes for the two subunits of succinyl-CoA synthase , an enzyme required for growth on lactate .
DNA-binding assays demonstrated that the protein encoded by GSU0514 bound to the putative promoter of the succinyl-CoA synthase operon .
The binding sequence was not apparent elsewhere in the genome .
These results demonstrate that a single-base-pair mutation in a transcriptional regulator can have a significant impact on the capacity for substrate utilization and suggest that adaptive evolution should be considered as a potential response of microorganisms to environmental change ( s ) imposed during bioremediation .

[1148] Disturbance and temporal partitioning of the activated sludge metacommunity

The resilience of microbial communities to press disturbances and whether ecosystem function is governed by microbial composition or by the environment have not been empirically tested .
To address these issues , a whole-ecosystem manipulation was performed in a full-scale activated sludge wastewater treatment plant .
The parameter solids retention time ( SRT ) was used to manipulate microbial composition , which started at 30 days , then decreased to 12 and 3 days , before operation was restored to starting conditions ( 30-day SRT ) .
Activated sludge samples were collected throughout the 313-day time series in parallel with bioreactor performance ( ` ecosystem function ' ) .
Bacterial small subunit ( SSU ) rRNA genes were surveyed from sludge samples resulting in a sequence library of > 417 000 SSU rRNA genes .
A shift in community composition was observed for 12 - and 3-day SRTs .
The composition was altered such that r-strategists were enriched in the system during the 3-day SRT , whereas K-strategists were only present at SRTs < = 12 days .
This shift corresponded to loss of ecosystem functions ( nitrification , denitrification and biological phosphorus removal ) for SRTs > = 12 days .
Upon return to a 30-day SRT , complete recovery of the bioreactor performance was observed after 54 days despite an incomplete recovery of bacterial diversity .
In addition , a different , yet phylogenetically related , community with fewer of its original rare members displaced the pre-disturbance community .
Our results support the hypothesis that microbial ecosystems harbor functionally redundant phylotypes with regard to general ecosystem functions ( carbon oxidation , nitrification , denitrification and phosphorus accumulation ) .
However , the impacts of decreased rare phylotype membership on ecosystem stability and micropollutant removal remain unknown .

[1149] Phages can constrain protist predation-driven attenuation of Pseudomonas aeruginosa virulence in multienemy communities

The coincidental theory of virulence predicts that bacterial pathogenicity could be a by-product of selection by natural enemies in environmental reservoirs .
However , current results are ambiguous and the simultaneous impact of multiple ubiquitous enemies , protists and phages on virulence evolution has not been investigated previously .
Here we tested experimentally how Tetrahymena thermophila protist predation and PNM phage parasitism ( bacteria-specific virus ) alone and together affect the evolution of Pseudomonas aeruginosa PAO1 virulence , measured in wax moth larvae .
Protist predation selected for small colony types , both in the absence and presence of phage , which showed decreased edibility to protists , reduced growth in the absence of enemies and attenuated virulence .
Although phage selection alone did not affect the bacterial phenotype , it weakened protist-driven antipredatory defence ( biofilm formation ) , its associated pleiotropic growth cost and the correlated reduction in virulence .
These results suggest that protist selection can be a strong coincidental driver of attenuated bacterial virulence , and that phages can constrain this effect owing to effects on population dynamics and conflicting selection pressures .
Attempting to define causal links such as these might help us to predict the cold and hot spots of coincidental virulence evolution on the basis of microbial community composition of environmental reservoirs .

[1150] Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability

Systematic climate shifts have been linked to multidecadal variability in observed sea surface temperatures in the North Atlantic Ocean .
These links are extensive , influencing a range of climate processes such as hurricane activity and African Sahel and Amazonian droughts .
The variability is distinct from historical global-mean temperature changes and is commonly attributed to natural ocean oscillations .
A number of studies have provided evidence that aerosols can influence long-term changes in sea surface temperatures , but climate models have so far failed to reproduce these interactions and the role of aerosols in decadal variability remains unclear .
Here we use a state-of-the-art Earth system climate model to show that aerosol emissions and periods of volcanic activity explain 76 per cent of the simulated multidecadal variance in detrended 1860-2005 North Atlantic sea surface temperatures .
After 1950 , simulated variability is within observational estimates ; our estimates for 1910-1940 capture twice the warming of previous generation models but do not explain the entire observed trend .
Other processes , such as ocean circulation , may also have contributed to variability in the early twentieth century .
Mechanistically , we find that inclusion of aerosol-cloud microphysical effects , which were included in few previous multimodel ensembles , dominates the magnitude ( 80 per cent ) and the spatial pattern of the total surface aerosol forcing in the North Atlantic .
Our findings suggest that anthropogenic aerosol emissions influenced a range of societally important historical climate events such as peaks in hurricane activity and Sahel drought .
Decadal-scale model predictions of regional Atlantic climate will probably be improved by incorporating aerosol-cloud microphysical interactions and estimates of future concentrations of aerosols , emissions of which are directly addressable by policy actions .

[1151] Biochar and denitrification in soils : when , how much and why does biochar reduce N2O emissions ?

Agricultural soils represent the main source of anthropogenic N2O emissions .
Recently , interactions of black carbon with the nitrogen cycle have been recognized and the use of biochar is being investigated as a means to reduce N2O emissions .
However , the mechanisms of reduction remain unclear .
Here we demonstrate the significant impact of biochar on denitrification , with a consistent decrease in N2O emissions by 10-90 % in 14 different agricultural soils .
Using the 15N gas-flux method we observed a consistent reduction of the N2O / ( N2 + N2O ) ratio , which demonstrates that biochar facilitates the last step of denitrification .
Biochar acid buffer capacity was identified as an important aspect for mitigation that was not primarily caused by a pH shift in soil .
We propose the function of biochar as an `` electron shuttle '' that facilitates the transfer of electrons to soil denitrifying microorganisms , which together with its liming effect would promote the reduction of N2O to N2 .

[1152] A new biofilm-associated colicin with increased efficiency against biofilm bacteria

Formation of bacterial biofilm communities leads to profound physiological modifications and increased physical and metabolic exchanges between bacteria .
It was previously shown that bioactive molecules produced within the biofilm environment contribute to bacterial interactions .
Here we describe new pore-forming colicin R , specifically produced in biofilms formed by the natural isolate Escherichia coli ROAR029 but that can not be detected under planktonic culture conditions .
We demonstrate that an increased SOS stress response within mature biofilms induces SOS-dependent colicin R expression .
We provide evidence that colicin R displays increased activity against E. coli strains that have a reduced lipopolysaccharide length , such as the pathogenic enteroaggregative E. coli LF82 clinical isolate , therefore pointing to lipopolysaccharide size as an important determinant for resistance to colicins .
We show that colicin R toxicity toward E. coli LF82 is increased under biofilm conditions compared with planktonic susceptibility and that release of colicin R confers a strong competitive advantage in mixed biofilms by rapidly outcompeting sensitive neighboring bacteria .
This work identifies the first biofilm-associated colicin that preferentially targets biofilm bacteria .
Furthermore , it indicates that the study of antagonistic molecules produced in biofilm and multispecies contexts could reveal unsuspected , ecologically relevant bacterial interactions influencing population dynamics in natural environments .

[1153] Hydrogen sulphide poisoning of shallow seas following the end-Triassic extinction

The evolution of complex life over the past 600 million years was disrupted by at least five mass extinctions , one of which occurred at the close of the Triassic period .
The end-Triassic extinction corresponds to a period of high atmospheric-CO2 concentrations caused by massive volcanism and biomass burning ; most extinction scenarios invoke the resulting environmental perturbations in accounting for the loss of marine and terrestrial biodiversity .
Here we reconstruct changes in Tethyan shallow marine ecosystems and ocean redox chemistry from earliest Jurassic ( Hettangian ) - aged black shales from Germany and Luxemburg .
The shales contain increased concentrations of the biomarker isorenieratane , a fossilized pigment from green sulphur bacteria .
The abundance of green sulphur bacteria suggests that the photic zone underwent prolonged periods of high concentrations of hydrogen sulphide .
This interval is also marked by the proliferation of green algae , an indicator of anoxia .
We conclude that the redox changes in the entire water column reflect sluggish circulation in marginal regions of the Tethys Ocean .
We suggest that the resultant repeated poisoning of shallow epicontinental seas -- hotspots of Mesozoic biodiversity -- with hydrogen sulphide may have slowed the recovery of marine ecosystems during the Early Jurassic .

[1154] Coordination of bacterial proteome with metabolism by cyclic AMP signalling

The cyclic AMP ( cAMP ) - dependent catabolite repression effect in Escherichia coli is among the most intensely studied regulatory processes in biology .
However , the physiological function ( s ) of cAMP signalling and its molecular triggers remain elusive .
Here we use a quantitative physiological approach to show that cAMP signalling tightly coordinates the expression of catabolic proteins with biosynthetic and ribosomal proteins , in accordance with the cellular metabolic needs during exponential growth .
The expression of carbon catabolic genes increased linearly with decreasing growth rates upon limitation of carbon influx , but decreased linearly with decreasing growth rate upon limitation of nitrogen or sulphur influx .
In contrast , the expression of biosynthetic genes showed the opposite linear growth-rate dependence as the catabolic genes .
A coarse-grained mathematical model provides a quantitative framework for understanding and predicting gene expression responses to catabolic and anabolic limitations .
A scheme of integral feedback control featuring the inhibition of cAMP signalling by metabolic precursors is proposed and validated .
These results reveal a key physiological role of cAMP-dependent catabolite repression : to ensure that proteomic resources are spent on distinct metabolic sectors as needed in different nutrient environments .
Our findings underscore the power of quantitative physiology in unravelling the underlying functions of complex molecular signalling networks .

[1155] An aerial view of 80 years of climate-related glacier fluctuations in southeast Greenland

Widespread retreat of glaciers has been observed along the southeastern margin of Greenland .
This retreat has been associated with increased air and ocean temperatures .
However , most observations are from the satellite era ; presatellite observations of Greenlandic glaciers are rare .
Here we present a unique record that documents the frontal positions for 132 southeast Greenlandic glaciers from rediscovered historical aerial imagery beginning in the early 1930s .
We combine the historical aerial images with both early and modern satellite imagery to extract frontal variations of marine - and land-terminating outlet glaciers , as well as local glaciers and ice caps , over the past 80 years .
The images reveal a regional response to external forcing regardless of glacier type , terminal environment and size .
Furthermore , the recent retreat was matched in its vigour during a period of warming in the 1930s with comparable increases in air temperature .
We show that many land-terminating glaciers underwent a more rapid retreat in the 1930s than in the 2000s , whereas marine-terminating glaciers retreated more rapidly during the recent warming .

[1156] Anthropogenic perturbation of the carbon fluxes from land to ocean

A substantial amount of the atmospheric carbon taken up on land through photosynthesis and chemical weathering is transported laterally along the aquatic continuum from upland terrestrial ecosystems to the ocean .
So far , global carbon budget estimates have implicitly assumed that the transformation and lateral transport of carbon along this aquatic continuum has remained unchanged since pre-industrial times .
A synthesis of published work reveals the magnitude of present-day lateral carbon fluxes from land to ocean , and the extent to which human activities have altered these fluxes .
We show that anthropogenic perturbation may have increased the flux of carbon to inland waters by as much as 1.0 Pg C yr-1 since pre-industrial times , mainly owing to enhanced carbon export from soils .
Most of this additional carbon input to upstream rivers is either emitted back to the atmosphere as carbon dioxide ( ~ 0.4 Pg C yr-1 ) or sequestered in sediments ( ~ 0.5 Pg C yr-1 ) along the continuum of freshwater bodies , estuaries and coastal waters , leaving only a perturbation carbon input of ~ 0.1 Pg C yr-1 to the open ocean .
According to our analysis , terrestrial ecosystems store ~ 0.9 Pg C yr-1 at present , which is in agreement with results from forest inventories but significantly differs from the figure of 1.5 Pg C yr-1 previously estimated when ignoring changes in lateral carbon fluxes .
We suggest that carbon fluxes along the land-ocean aquatic continuum need to be included in global carbon dioxide budgets .

[1157] On-line monitoring of methane in sewer air

Methane is a highly potent greenhouse gas and contributes significantly to climate change .
Recent studies have shown significant methane production in sewers .
The studies conducted so far have relied on manual sampling followed by off-line laboratory-based chromatography analysis .
These methods are labor-intensive when measuring methane emissions from a large number of sewers , and do not capture the dynamic variations in methane production .
In this study , we investigated the suitability of infrared spectroscopy-based on-line methane sensors for measuring methane in humid and condensing sewer air .
Two such sensors were comprehensively tested in the laboratory .
Both sensors displayed high linearity ( R2 > 0.999 ) , with a detection limit of 0.023 % and 0.110 % by volume , respectively .
Both sensors were robust against ambient temperature variations in the range of 5 to 35degreesC .
While one sensor was robust against humidity variations , the other was found to be significantly affected by humidity .
However , the problem was solved by equipping the sensor with a heating unit to increase the sensor surface temperature to 35degreesC .
Field studies at three sites confirmed the performance and accuracy of the sensors when applied to actual sewer conditions , and revealed substantial and highly dynamic methane concentrations in sewer air .

[1158] High rates of sea-level rise during the last interglacial period

The last interglacial period , Marine Isotope Stage ( MIS ) 5e , was characterized by global mean surface temperatures that were at least 2 oC warmer than present .
Mean sea level stood 4-6 m higher than modern sea level , with an important contribution from a reduction of the Greenland ice sheet .
Although some fossil reef data indicate sea-level fluctuations of up to 10 m around the mean , so far it has not been possible to constrain the duration and rates of change of these shorter-term variations .
Here , we use a combination of a continuous high-resolution sea-level record , based on the stable oxygen isotopes of planktonic foraminifera from the central Red Sea , and age constraints from coral data to estimate rates of sea-level change during MIS-5e .
We find average rates of sea-level rise of 1.6 m per century .
As global mean temperatures during MIS-5e were comparable to projections for future climate change under the influence of anthropogenic greenhouse-gas emissions , these observed rates of sea-level change inform the ongoing debate about high versus low rates of sea-level rise in the coming century .

[1159] Climate change impacts on the biophysics and economics of world fisheries

Global marine fisheries are underperforming economically because of overfishing , pollution and habitat degradation .
Added to these threats is the looming challenge of climate change .
Observations , experiments and simulation models show that climate change would result in changes in primary productivity , shifts in distribution and changes in the potential yield of exploited marine species , resulting in impacts on the economics of fisheries worldwide .
Despite the gaps in understanding climate change effects on fisheries , there is sufficient scientific information that highlights the need to implement climate change mitigation and adaptation policies to minimize impacts on fisheries .

[1160] Skeletal trade-offs in coralline algae in response to ocean acidification

Ocean acidification is changing the marine environment , with potentially serious consequences for many organisms .
Much of our understanding of ocean acidification effects comes from laboratory experiments , which demonstrate physiological responses over relatively short timescales .
Observational studies and , more recently , experimental studies in natural systems suggest that ocean acidification will alter the structure of seaweed communities .
Here , we provide a mechanistic understanding of altered competitive dynamics among a group of seaweeds , the crustose coralline algae ( CCA ) .
We compare CCA from historical experiments ( 1981-1997 ) with specimens from recent , identical experiments ( 2012 ) to describe morphological changes over this time period , which coincides with acidification of seawater in the Northeastern Pacific .
Traditionally thick species decreased in thickness by a factor of 2.0-2 .3 , but did not experience a change in internal skeletal metrics .
In contrast , traditionally thin species remained approximately the same thickness but reduced their total carbonate tissue by making thinner inter-filament cell walls .
These changes represent alternative mechanisms for the reduction of calcium carbonate production in CCA and suggest energetic trade-offs related to the cost of building and maintaining a calcium carbonate skeleton as pH declines .
Our classification of stress response by morphological type may be generalizable to CCA at other sites , as well as to other calcifying organisms with species-specific differences in morphological types .

[1161] Combined effects of the Pacific Decadal Oscillation and El Nino-Southern Oscillation on Global Land Dry-Wet Changes

The effects of natural variability , especially El Nino-Southern Oscillation ( ENSO ) effects , have been the focus of several recent studies on the change of drought patterns with climate change .
The interannual relationship between ENSO and the global climate is not stationary and can be modulated by the Pacific Decadal Oscillation ( PDO ) .
However , the global land distribution of the dry-wet changes associated with the combination of ENSO and the PDO remains unclear .
In the present study , this is investigated using a revised Palmer Drought Severity Index dataset ( sc_PDSI_pm ) .
We find that the effect of ENSO on dry-wet changes varies with the PDO phase .
When in phase with the PDO , ENSO-induced dry-wet changes are magnified with respect to the canonical pattern .
When out of phase , these dry-wet variations weaken or even disappear .
This remarkable contrast in ENSO 's influence between the two phases of the PDO highlights exciting new avenues for obtaining improved global climate predictions .
In recent decades , the PDO has turned negative with more La Nina events , implying more rain and flooding over land .
La Nina-induced wet areas become wetter and the dry areas become drier and smaller due to the effects of the cold PDO phase .

[1162] Stronger ocean circulation and increased melting under Pine Island Glacier ice shelf

In 1994 , ocean measurements near Antarctica 's Pine Island Glacier showed that the ice shelf buttressing the glacier was melting rapidly .
This melting was attributed to the presence of relatively warm , deep water on the Amundsen Sea continental shelf .
Heat , salt and ice budgets along with ocean modelling provided steady-state calving and melting rates .
Subsequent satellite observations and modelling have indicated large system imbalances , including ice-shelf thinning and more intense melting , glacier acceleration and drainage basin drawdown .
Here we combine our earlier data with measurements taken in 2009 to show that the temperature and volume of deep water in Pine Island Bay have increased .
Ocean transport and tracer calculations near the ice shelf reveal a rise in meltwater production by about 50 % since 1994 .
The faster melting seems to result mainly from stronger sub-ice-shelf circulation , as thinning ice has increased the gap above an underlying submarine bank on which the glacier was formerly grounded .
We conclude that the basal melting has exceeded the increase in ice inflow , leading to the formation and enlargement of an inner cavity under the ice shelf within which sea water nearly 4 degreesC above freezing can now more readily access the grounding zone .

[1163] A short-term sink for atmospheric CO2 in subtropical mode water of the North Atlantic Ocean

Large-scale features of ocean circulation , such as deep water formation in the northern North Atlantic Ocean , are known to regulate the long-term physical uptake of CO2 from the atmosphere by moving CO2-laden surface waters into the deep ocean .
But the importance of CO2 uptake into water masses that ventilate shallower ocean depths , such as subtropical mode waters of the subtropical gyres , are poorly quantified .
Here we report that , between 1988 and 2001 , dissolved CO2 concentrations in subtropical mode waters of the North Atlantic have increased at a rate twice that expected from these waters keeping in equilibrium with increasing atmospheric CO2 .
This accounts for an extra ~ 0.4-2 .8 Pg C ( 1 Pg = 1015 g ) over this period ( that is , about 0.03-0 .24 Pg C yr-1 ) , equivalent to ~ 3-10 % of the current net annual ocean uptake of CO2 ( ref .
3 ) .
We suggest that the lack of strong winter mixing events , to greater than 300 m in depth , in recent decades is responsible for this accumulation , which would otherwise disturb the mode water layer and liberate accumulated CO2 back to the atmosphere .
However , future climate variability ( which influences subtropical mode water formation ) and changes in the North Atlantic Oscillation ( leading to a return of deep winter mixing events ) may reduce CO2 accumulation in subtropical mode waters .
We therefore conclude that , although CO2 uptake by subtropical mode waters in the North Atlantic -- and possibly elsewhere -- does not always represent a long-term CO2 sink , the phenomenon is likely to contribute substantially to interannual variability in oceanic CO2 uptake .

[1164] Isotopic evidence for microbial sulphate reduction in the early Archaean era

Sulphate-reducing microbes affect the modern sulphur cycle , and may be quite ancient , though when they evolved is uncertain .
These organisms produce sulphide while oxidizing organic matter or hydrogen with sulphate .
At sulphate concentrations greater than 1 mM , the sulphides are isotopically fractionated ( depleted in 34S ) by 10-40/1000 compared to the sulphate , with fractionations decreasing to near 0/1000 at lower concentrations .
The isotope record of sedimentary sulphides shows large fractionations relative to seawater sulphate by 2.7 Gyr ago , indicating microbial sulphate reduction .
In older rocks , however , much smaller fractionations are of equivocal origin , possibly biogenic but also possibly volcanogenic .
Here we report microscopic sulphides in ~ 3.47-Gyr-old barites from North Pole , Australia , with maximum fractionations of 21.1 / 1000 , about a mean of 11.6 / 1000 , clearly indicating microbial sulphate reduction .
Our results extend the geological record of microbial sulphate reduction back more than 750 million years , and represent direct evidence of an early specific metabolic pathway -- allowing time calibration of a deep node on the tree of life .

[1165] Drought impacts on children 's respiratory health in the Brazilian Amazon

Drought conditions in Amazonia are associated with increased fire incidence , enhancing aerosol emissions with degradation in air quality .
Quantifying the synergic influence of climate and human-driven environmental changes on human health is , therefore , critical for identifying climate change adaptation pathways for this vulnerable region .
Here we show a significant increase ( 1.2 % -267 % ) in hospitalisations for respiratory diseases in children under-five in municipalities highly exposed to drought .
Aerosol was the primary driver of hospitalisations in drought affected municipalities during 2005 , while human development conditions mitigated the impacts in 2010 .
Our results demonstrated that drought events deteriorated children 's respiratory health particularly during 2005 when the drought was more geographically concentrated .
This indicates that if governments act on curbing fire usage and effectively plan public health provision , as a climate change adaptation procedure , health quality would improve and public expenditure for treatment would decrease in the region during future drought events .

[1166] A reversal of fortunes : climate change ` winners ' and ` losers ' in Antarctic Peninsula penguins

Climate change is a major threat to global biodiversity .
Antarctic ecosystems are no exception .
Investigating past species responses to climatic events can distinguish natural from anthropogenic impacts .
Climate change produces ` winners ' , species that benefit from these events and ` losers ' , species that decline or become extinct .
Using molecular techniques , we assess the demographic history and population structure of Pygoscelis penguins in the Scotia Arc related to climate warming after the Last Glacial Maximum ( LGM ) .
All three pygoscelid penguins responded positively to post-LGM warming by expanding from glacial refugia , with those breeding at higher latitudes expanding most .
Northern ( Pygoscelis papua papua ) and Southern ( Pygoscelis papua ellsworthii ) gentoo sub-species likely diverged during the LGM .
Comparing historical responses with the literature on current trends , we see Southern gentoo penguins are responding to current warming as they did during post-LGM warming , expanding their range southwards .
Conversely , Adelie and chinstrap penguins are experiencing a ` reversal of fortunes ' as they are now declining in the Antarctic Peninsula , the opposite of their response to post-LGM warming .
This suggests current climate warming has decoupled historic population responses in the Antarctic Peninsula , favoring generalist gentoo penguins as climate change ` winners ' , while Adelie and chinstrap penguins have become climate change ` losers ' .

[1167] A ` rare biosphere ' microorganism contributes to sulfate reduction in a peatland

Methane emission from peatlands contributes substantially to global warming but is significantly reduced by sulfate reduction , which is fuelled by globally increasing aerial sulfur pollution .
However , the biology behind sulfate reduction in terrestrial ecosystems is not well understood and the key players for this process as well as their abundance remained unidentified .
Comparative 16S rRNA gene stable isotope probing ( SIP ) in the presence and absence of sulfate indicated that a Desulfosporosinus species , which constitutes only 0.006 % of the total microbial community 16S rRNA genes , is an important sulfate reducer in a long-term experimental peatland field site .
Parallel SIP using dsrAB ( encoding subunit A and B of the dissimilatory ( bi ) sulfite reductase ) identified no additional sulfate reducers under the conditions tested .
For the identified Desulfosporosinus species a high cell-specific sulfate reduction rate of up to 341 fmol SO42 - cell-1 day-1 was estimated .
Thus , the small Desulfosporosinus population has the potential to reduce sulfate in situ at a rate of 4.0-36 .8 nmol ( g soil w. wt . )
-1 day-1 , sufficient to account for a considerable part of sulfate reduction in the peat soil .
Modeling of sulfate diffusion to such highly active cells identified no limitation in sulfate supply even at bulk concentrations as low as 10 muM .
Collectively , these data show that the identified Desulfosporosinus species , despite being a member of the ` rare biosphere ' , contributes to an important biogeochemical process that diverts the carbon flow in peatlands from methane to CO2 and , thus , alters their contribution to global warming .

[1168] Soil production limits and the transition to bedrock-dominated landscapes

The extent and persistence of the Earth 's soil cover depends on the long-term balance between soil production and erosion .
Higher soil production rates under thinner soils provide a critical stabilizing feedback mechanism , and climate - and lithology-controlled soil production is thought to set the upper limit for steady-state hillslope erosion .
In this framework , erosion rates exceeding the maximum soil production rate can be due only to bedrock mass wasting .
However , observation of pervasive , if patchy , soil cover in areas of rugged topography and rapid erosion indicates additional stabilizing mechanisms .
Here we present 10Be-derived estimates of soil-production and detrital erosion rates that show that soil production rates increase with increasing catchment-averaged erosion rates , a feedback that enhances soil-cover persistence .
We show that a process transition to landslide-dominated erosion in steeper , more rapidly eroding catchments results in thinner , patchier soils and rockier topography , but find that there is no sudden transition to bedrock landscapes .
Instead , using our global data compilation , we suggest that soil production may increase in frequency and magnitude to keep up with increasing erosion rates .
We therefore conclude that existing models greatly exaggerate changes in critical-zone processes in response to tectonic uplift .

[1169] Topographic heterogeneity effect on the accumulation of Fukushima-derived radiocesium on forest floor driven by biologically mediated processes

The accident at the Fukushima Daiichi nuclear power plant caused serious radiocesium ( 137Cs ) contamination of forest ecosystems located in mountainous and hilly regions with steep terrain .
To understand topographic effects on the redistribution and accumulation of 137Cs on forest floor , we investigated the distribution of Fukushima-derived 137Cs in forest-floor litter layers on a steep hillslope in a Japanese deciduous forest in August 2013 ( 29 months after the accident ) .
Both leaf-litter materials and litter-associated 137Cs were accumulated in large amounts at the bottom of the hillslope .
At the bottom , a significant fraction ( 65 % ) of the 137Cs inventory was observed to be associated with newly shed and less degraded leaf-litter materials , with estimated mean ages of 0.5-1 .5 years , added via litterfall after the accident .
Newly emerged leaves were contaminated with Fukushima-derived 137Cs in May 2011 ( two months after the accident ) and 137Cs concentration in them decreased with time .
However , the concentrations were still two orders of magnitude higher than the pre-accident level in 2013 and 2014 .
These observations are the first to show that 137Cs redistribution on a forested hillslope is strongly controlled by biologically mediated processes and continues to supply 137Cs to the bottom via litterfall at a reduced rate .

[1170] Taxon-specific response of marine nitrogen fixers to elevated carbon dioxide concentrations

Much of the bioavailable nitrogen that supports open ocean food webs and biogeochemical cycles is fixed from the atmosphere by marine cyanobacteria of the genera Trichodesmium and Crocosphaera .
In previous experiments carried out with a limited set of cyanobacterial isolates , rates of cyanobacterial nitrogen fixation were shown to increase with carbon dioxide concentrations .
Here , we report results from a series of laboratory experiments in which we grew seven strains of Trichodesmium and Crocosphaera from the Atlantic and Pacific oceans under a wide range of carbon dioxide concentrations , and monitored rates of nitrogen fixation and growth .
We document large , strain-specific differences in the relationship between nitrogen fixation and carbon dioxide concentration , suggesting that individual strains within each genus are adapted to grow and fix nitrogen at different concentrations of carbon dioxide .
We apply kinetic constants from the individual carbon dioxide response curves to an illustrative biogeochemical model of the ocean in 2100 , which suggests that strains adapted to high carbon dioxide concentrations could potentially be favoured in a future acidified ocean .
We suggest that surface ocean carbon dioxide concentrations could constitute a previously unrecognized selective force that shapes the community composition and diversity of nitrogen-fixing cyanobacteria .

[1171] Mycobacterium hassiacum recovers from nitrogen starvation with up-regulation of a novel glucosylglycerate hydrolase and depletion of the accumulated glucosylglycerate

Some microorganisms accumulate glucosylglycerate ( GG ) during growth under nitrogen deprivation .
However , the molecular mechanisms underlying the role of GG and the regulation of its levels in the nitrogen stress response are elusive .
Since GG is required for biosynthesis of mycobacterial methylglucose lipopolysaccharides ( MGLP ) we examined the molecular mechanisms linking replenishment of assimilable nitrogen to nitrogen-starved M. hassiacum with depletion of GG accumulated during nitrogen deficiency .
To probe the involvement of a newly identified glycoside hydrolase in GG depletion , we produced the mycobacterial enzyme recombinantly and confirmed the specific hydrolysis of GG ( GG hydrolase , GgH ) in vitro .
We have also observed a pronounced up-regulation of GgH mRNA in response to the nitrogen shock , which positively correlates with GG depletion in vivo and growth stimulation , implicating GgH in the recovery process .
Since GgH orthologs seem to be absent from most slowly-growing mycobacteria including M. tuberculosis , the disclosure of the GgH function allows reconfiguration of the MGLP pathway in rapidly-growing species and accommodation of this possible regulatory step .
This new link between GG metabolism , MGLP biosynthesis and recovery from nitrogen stress furthers our knowledge on the mycobacterial strategies to endure a frequent stress faced in some environments and during long-term infection .

[1172] The legacy of the Pleistocene megafauna extinctions on nutrient availability in Amazonia

In the late Pleistocene , 97 genera of large animals went extinct , concentrated in the Americas and Australia .
These extinctions had significant effects on ecosystem structure , seed dispersal and land surface albedo .
However , the impact of this dramatic extinction on ecosystem nutrient biogeochemistry , through the lateral transport of dung and bodies , has never been explored .
Here we analyse this process using a novel mathematical framework that analyses this lateral transport as a diffusion-like process , and we demonstrate that large animals play a disproportionately large role in the horizontal transfer of nutrients across landscapes .
For example , we estimate that the extinction of the Amazonian megafauna decreased the lateral flux of the limiting nutrient phosphorus by more than 98 % , with similar , though less extreme , decreases in all continents outside of Africa .
This resulted in strong decreases in phosphorus availability in eastern Amazonia away from fertile floodplains , a decline which may still be ongoing .
The current P limitation in the Amazon basin may be partially a relic of an ecosystem without the functional connectivity it once had .
We argue that the Pleistocene megafauna extinctions resulted in large and ongoing disruptions to terrestrial biogeochemical cycling at continental scales and increased nutrient heterogeneity globally .

[1173] Reduction of carbon dioxide to oxalate by a binuclear copper complex

Reduction of carbon dioxide to products such as oxalate ( C2O42 - ) is an active area of research , as the process converts an environmental pollutant into more useful organic compounds .
However , carbon dioxide reduction remains a major challenge .
Here we demonstrate a three-step reaction sequence in which a copper complex converts carbon dioxide to oxalate under mild conditions .
The copper ( II ) complex is reduced to copper ( I ) in solution , either electrochemically or using sodium ascorbate .
The reduced complex selectively reacts with carbon dioxide from air and fixes it into oxalate , with the oxalate ion bridging between two copper atoms .
The bound oxalate ion is released as oxalic acid on treatment with mineral acids , regenerating the original copper ( II ) complex .
This completes the process for conversion of carbon dioxide into oxalate using a binuclear copper complex and a mild reducing agent .

[1174] Non-CO2 greenhouse gases and climate change

Earth 's climate is warming as a result of anthropogenic emissions of greenhouse gases , particularly carbon dioxide ( CO2 ) from fossil fuel combustion .
Anthropogenic emissions of non-CO2 greenhouse gases , such as methane , nitrous oxide and ozone-depleting substances ( largely from sources other than fossil fuels ) , also contribute significantly to warming .
Some non-CO2 greenhouse gases have much shorter lifetimes than CO2 , so reducing their emissions offers an additional opportunity to lessen future climate change .
Although it is clear that sustainably reducing the warming influence of greenhouse gases will be possible only with substantial cuts in emissions of CO2 , reducing non-CO2 greenhouse gas emissions would be a relatively quick way of contributing to this goal .

[1175] A global assessment of the effects of climate policy on the impacts of climate change

This study presents the first global-scale multi-sectoral regional assessment of the magnitude and uncertainty in the impacts of climate change avoided by emissions policies .
The analysis suggests that the most stringent emissions policy considered here -- which gives a 50 % chance of remaining below a 2 degreesC temperature rise target -- reduces impacts by 20-65 % by 2100 relative to a ` business-as-usual ' pathway which reaches 4 degreesC , and can delay impacts by several decades .
The effects of mitigation policies vary between sectors and regions , and only a few are noticeable by 2030 .
The impacts avoided by 2100 are more strongly influenced by the date and level at which emissions peak than the rate of decline of emissions , with an earlier and lower emissions peak avoiding more impacts .
The estimated proportion of impacts avoided at the global scale is relatively robust despite uncertainty in the spatial pattern of climate change , but the absolute amount of avoided impacts is considerably more variable and therefore uncertain .

[1176] Blanket peat biome endangered by climate change

Blanket bog is a highly distinctive biome restricted to disjunct hyperoceanic regions .
It is characterized by a landscape covering of peat broken only by the steepest slopes .
Plant and microbial life are adapted to anoxia , low pH and low nutrient availability .
Plant productivity exceeds soil organic matter decomposition , so carbon is sequestered over time .
Unique climatic requirements , including high year-round rainfall and low summer temperatures , make this biome amenable to bioclimatic modelling .
However , projections of the fate of peatlands in general , and blanket bogs in particular , under climate change have been contradictory .
Here we use a simple , well-founded global bioclimatic model , with climate-change projections from seven climate models , to indicate this biome 's fate .
We show marked shrinkage of its present bioclimatic space with only a few , restricted areas of persistence .
Many blanket bog regions are thus at risk of progressive peat erosion and vegetation changes as a direct consequence of climate change .
New areas suitable for blanket bog are also projected , but these are often disjunct from present areas and their location is inconsistently predicted by different climate models .

[1177] The effect of nutrients on carbon and nitrogen fixation by the UCYN-A-haptophyte symbiosis

Symbiotic relationships between phytoplankton and N2-fixing microorganisms play a crucial role in marine ecosystems .
The abundant and widespread unicellular cyanobacteria group A ( UCYN-A ) has recently been found to live symbiotically with a haptophyte .
Here , we investigated the effect of nitrogen ( N ) , phosphorus ( P ) , iron ( Fe ) and Saharan dust additions on nitrogen ( N2 ) fixation and primary production by the UCYN-A-haptophyte association in the subtropical eastern North Atlantic Ocean using nifH expression analysis and stable isotope incubations combined with single-cell measurements .
N2 fixation by UCYN-A was stimulated by the addition of Fe and Saharan dust , although this was not reflected in the nifH expression .
CO2 fixation by the haptophyte was stimulated by the addition of ammonium nitrate as well as Fe and Saharan dust .
Intriguingly , the single-cell analysis using nanometer scale secondary ion mass spectrometry indicates that the increased CO2 fixation by the haptophyte in treatments without added fixed N is likely an indirect result of the positive effect of Fe and/or P on UCYN-A N2 fixation and the transfer of N2-derived N to the haptophyte .
Our results reveal a direct linkage between the marine carbon and nitrogen cycles that is fuelled by the atmospheric deposition of dust .
The comparison of single-cell rates suggests a tight coupling of nitrogen and carbon transfer that stays balanced even under changing nutrient regimes .
However , it appears that the transfer of carbon from the haptophyte to UCYN-A requires a transfer of nitrogen from UCYN-A .
This tight coupling indicates an obligate symbiosis of this globally important diazotrophic association .
The ISME Journal advance online publication , 23 December 2014 ; doi :10.1038 / ismej .2014.253

[1178] Surface-temperature trends and variability in the low-latitude North Atlantic since 1552

Sea surface temperature variability in the North Atlantic Ocean recorded since about 1850 has been ascribed to a natural multidecadal oscillation superimposed on a background warming trend .
It has been suggested that the multidecadal variability may be a persistent feature , raising the possibility that the associated climate impacts may be predictable .
However , our understanding of the multidecadal ocean variability before the instrumental record is based on interpretations of high-latitude terrestrial proxy records .
Here we present an absolutely dated and annually resolved record of sea surface temperature from the Bahamas , based on a 440-year time series of coral growth rates .
The reconstruction indicates that temperatures were as warm as today from about 1552 to 1570 , then cooled by about 1 degreesC from 1650 to 1730 before warming until the present .
Our estimates of background variability suggest that much of the warming since 1900 was driven by anthropogenic forcing .
Interdecadal variability with a period of 15-25 years is superimposed on most of the record , but multidecadal variability becomes significant only after 1730 .
We conclude that the multidecadal variability in sea surface temperatures in the low-latitude western Atlantic Ocean may not be persistent , potentially making accurate decadal climate forecasts more difficult to achieve .

[1179] Regional climate control of glaciers in New Zealand and Europe during the pre-industrial Holocene

Mountain glaciers worldwide have undergone net recession over the past century in response to atmospheric warming , but the extent to which this warming reflects natural versus anthropogenic climate change remains uncertain .
Between about 11,500 years ago and the nineteenth century , progressive atmospheric cooling over the European Alps induced glacier expansion , culminating with several large-scale advances during the seventeen to nineteenth centuries .
However , it is unclear whether this glacier behaviour reflects global or a more regional forcing .
Here we reconstruct glacier fluctuations in the Southern Alps of New Zealand for the past 11,000 years using 10Be exposure ages .
We use those fluctuations to estimate the associated temperature variations .
On orbital to submillennial timescales , changes in glacier snowlines in New Zealand were linked to regional climate and oceanographic variability and were asynchronous with snowline variations in European glaciers .
We attribute this asynchrony to the migration of the intertropical convergence zone .
In light of this persistent asynchrony , we suggest that the net glacier recession and atmospheric warming in both regions over the past century is anomalous in the context of earlier Holocene variability and corresponds with anthropogenic emissions of greenhouse gases .

[1180] Long-term decline in krill stock and increase in salps within the Southern Ocean

Antarctic krill ( Euphausia superba ) and salps ( mainly Salpa thompsoni ) are major grazers in the Southern Ocean , and krill support commercial fisheries .
Their density distributions have been described in the period 1926-51 , while recent localized studies suggest short-term changes .
To examine spatial and temporal changes over larger scales , we have combined all available scientific net sampling data from 1926 to 2003 .
This database shows that the productive southwest Atlantic sector contains > 50 % of Southern Ocean krill stocks , but here their density has declined since the 1970s .
Spatially , within their habitat , summer krill density correlates positively with chlorophyll concentrations .
Temporally , within the southwest Atlantic , summer krill densities correlate positively with sea-ice extent the previous winter .
Summer food and the extent of winter sea ice are thus key factors in the high krill densities observed in the southwest Atlantic Ocean .
Krill need the summer phytoplankton blooms of this sector , where winters of extensive sea ice mean plentiful winter food from ice algae , promoting larval recruitment and replenishing the stock .
Salps , by contrast , occupy the extensive lower-productivity regions of the Southern Ocean and tolerate warmer water than krill .
As krill densities decreased last century , salps appear to have increased in the southern part of their range .
These changes have had profound effects within the Southern Ocean food web .

[1181] Interannual variability in the oxygen isotopes of atmospheric CO2 driven by El Nino

The stable isotope ratios of atmospheric CO2 ( 18O/16O and 13C/12C ) have been monitored since 1977 to improve our understanding of the global carbon cycle , because biosphere-atmosphere exchange fluxes affect the different atomic masses in a measurable way .
Interpreting the 18O/16O variability has proved difficult , however , because oxygen isotopes in CO2 are influenced by both the carbon cycle and the water cycle .
Previous attention focused on the decreasing 18O/16O ratio in the 1990s , observed by the global Cooperative Air Sampling Network of the US National Oceanic and Atmospheric Administration Earth System Research Laboratory .
This decrease was attributed variously to a number of processes including an increase in Northern Hemisphere soil respiration ; a global increase in C4 crops at the expense of C3 forests ; and environmental conditions , such as atmospheric turbulence and solar radiation , that affect CO2 exchange between leaves and the atmosphere .
Here we present 30 years ' worth of data on 18O/16O in CO2 from the Scripps Institution of Oceanography global flask network and show that the interannual variability is strongly related to the El Nino/Southern Oscillation .
We suggest that the redistribution of moisture and rainfall in the tropics during an El Nino increases the 18O/16O ratio of precipitation and plant water , and that this signal is then passed on to atmospheric CO2 by biosphere-atmosphere gas exchange .
We show how the decay time of the El Nino anomaly in this data set can be useful in constraining global gross primary production .
Our analysis shows a rapid recovery from El Nino events , implying a shorter cycling time of CO2 with respect to the terrestrial biosphere and oceans than previously estimated .
Our analysis suggests that current estimates of global gross primary production , of 120 petagrams of carbon per year , may be too low , and that a best guess of 150-175 petagrams of carbon per year better reflects the observed rapid cycling of CO2 .
Although still tentative , such a revision would present a new benchmark by which to evaluate global biospheric carbon cycling models .

[1182] Comparing the yields of organic and conventional agriculture

Numerous reports have emphasized the need for major changes in the global food system : agriculture must meet the twin challenge of feeding a growing population , with rising demand for meat and high-calorie diets , while simultaneously minimizing its global environmental impacts .
Organic farming -- a system aimed at producing food with minimal harm to ecosystems , animals or humans -- is often proposed as a solution .
However , critics argue that organic agriculture may have lower yields and would therefore need more land to produce the same amount of food as conventional farms , resulting in more widespread deforestation and biodiversity loss , and thus undermining the environmental benefits of organic practices .
Here we use a comprehensive meta-analysis to examine the relative yield performance of organic and conventional farming systems globally .
Our analysis of available data shows that , overall , organic yields are typically lower than conventional yields .
But these yield differences are highly contextual , depending on system and site characteristics , and range from 5 % lower organic yields ( rain-fed legumes and perennials on weak-acidic to weak-alkaline soils ) , 13 % lower yields ( when best organic practices are used ) , to 34 % lower yields ( when the conventional and organic systems are most comparable ) .
Under certain conditions -- that is , with good management practices , particular crop types and growing conditions -- organic systems can thus nearly match conventional yields , whereas under others it at present can not .
To establish organic agriculture as an important tool in sustainable food production , the factors limiting organic yields need to be more fully understood , alongside assessments of the many social , environmental and economic benefits of organic farming systems .

[1183] A large ozone-circulation feedback and its implications for global warming assessments

State-of-the-art climate models now include more climate processes simulated at higher spatial resolution than ever .
Nevertheless , some processes , such as atmospheric chemical feedbacks , are still computationally expensive and are often ignored in climate simulations .
Here we present evidence that the representation of stratospheric ozone in climate models can have a first-order impact on estimates of effective climate sensitivity .
Using a comprehensive atmosphere-ocean chemistry-climate model , we find an increase in global mean surface warming of around 1 degreesC ( ~ 20 % ) after 75 years when ozone is prescribed at pre-industrial levels compared with when it is allowed to evolve self-consistently in response to an abrupt 4xCO2 forcing .
The difference is primarily attributed to changes in long-wave radiative feedbacks associated with circulation-driven decreases in tropical lower stratospheric ozone and related stratospheric water vapour and cirrus cloud changes .
This has important implications for global model intercomparison studies in which participating models often use simplified treatments of atmospheric composition changes that are consistent with neither the specified greenhouse gas forcing scenario nor the associated atmospheric circulation feedbacks .

[1184] Ammonia concentration determines differential growth of ammonia-oxidising archaea and bacteria in soil microcosms

The first step of nitrification , oxidation of ammonia to nitrite , is performed by both ammonia-oxidising archaea ( AOA ) and ammonia-oxidising bacteria ( AOB ) in soil , but their relative contributions to ammonia oxidation and existence in distinct ecological niches remain to be determined .
To determine whether available ammonia concentration has a differential effect on AOA and AOB growth , soil microcosms were incubated for 28 days with ammonium at three concentrations : native ( control ) , intermediate ( 20 mug NH4 + - N per gram of soil ) and high ( 200 mug NH4 + - N per gram of soil ) .
Quantitative PCR demonstrated growth of AOA at all concentrations , whereas AOB growth was prominent only at the highest concentration .
Similarly , denaturing gradient gel electrophoresis ( DGGE ) analysis revealed changes in AOA communities at all ammonium concentrations , whereas AOB communities changed significantly only at the highest ammonium concentration .
These results provide evidence that ammonia concentration contributes to the definition of distinct ecological niches of AOA and AOB in soil .

[1185] Variable winter moisture in the southwestern United States linked to rapid glacial climate shifts

During the last glacial period , the climate of the Northern Hemisphere was characterized by rapid , large-amplitude temperature fluctuations through cycles lasting a few thousand years .
These fluctuations are apparent in Greenland temperature reconstructions , and corresponding temperature and hydrological variations have been documented throughout the Northern Hemisphere .
Here we present a record of precipitation in the southwestern United States from 56,000 to 11,000 yr ago , on the basis of delta18O measurements of speleothem calcite from New Mexico .
Our record shows that increased winter precipitation in the southwestern United States is associated with Northern Hemisphere cooling , which we attribute to a southward shift in the polar jet stream , which modulated the position of the winter storm track over North America .
On the western side of the Pacific Ocean basin , decreases in summer monsoon precipitation are associated with Northern Hemisphere cooling , due to southward displacement of the intertropical convergence zone .
We conclude that cooling and warming excursions in the Northern Hemisphere lead to concurrent latitudinal displacement of both the intertropical convergence zone and the polar jet stream over the Pacific Ocean .
Our data are consistent with modern evidence for a northward shift of the polar jet stream in response to global warming , which could lead to increasingly arid conditions in southwestern North America in the future .

[1186] The Amazon basin in transition

Agricultural expansion and climate variability have become important agents of disturbance in the Amazon basin .
Recent studies have demonstrated considerable resilience of Amazonian forests to moderate annual drought , but they also show that interactions between deforestation , fire and drought potentially lead to losses of carbon storage and changes in regional precipitation patterns and river discharge .
Although the basin-wide impacts of land use and drought may not yet surpass the magnitude of natural variability of hydrologic and biogeochemical cycles , there are some signs of a transition to a disturbance-dominated regime .
These signs include changing energy and water cycles in the southern and eastern portions of the Amazon basin .

[1187] Evolution of a new enzyme for carbon disulphide conversion by an acidothermophilic archaeon

Extremophilic organisms require specialized enzymes for their exotic metabolisms .
Acid-loving thermophilic Archaea that live in the mudpots of volcanic solfataras obtain their energy from reduced sulphur compounds such as hydrogen sulphide ( H2S ) and carbon disulphide ( CS2 ) .
The oxidation of these compounds into sulphuric acid creates the extremely acidic environment that characterizes solfataras .
The hyperthermophilic Acidianus strain A1-3 , which was isolated from the fumarolic , ancient sauna building at the Solfatara volcano ( Naples , Italy ) , was shown to rapidly convert CS2 into H2S and carbon dioxide ( CO2 ) , but nothing has been known about the modes of action and the evolution of the enzyme ( s ) involved .
Here we describe the structure , the proposed mechanism and evolution of a CS2 hydrolase from Acidianus A1-3 .
The enzyme monomer displays a typical beta-carbonic anhydrase fold and active site , yet CO2 is not one of its substrates .
Owing to large carboxy - and amino-terminal arms , an unusual hexadecameric catenane oligomer has evolved .
This structure results in the blocking of the entrance to the active site that is found in canonical beta-carbonic anhydrases and the formation of a single 15-A-long , highly hydrophobic tunnel that functions as a specificity filter .
The tunnel determines the enzyme 's substrate specificity for CS2 , which is hydrophobic .
The transposon sequences that surround the gene encoding this CS2 hydrolase point to horizontal gene transfer as a mechanism for its acquisition during evolution .
Our results show how the ancient beta-carbonic anhydrase , which is central to global carbon metabolism , was transformed by divergent evolution into a crucial enzyme in CS2 metabolism .

[1188] How is water-use efficiency of terrestrial ecosystems distributed and changing on Earth ?

A better understanding of ecosystem water-use efficiency ( WUE ) will help us improve ecosystem management for mitigation as well as adaption to global hydrological change .
Here , long-term flux tower observations of productivity and evapotranspiration allow us to detect a consistent latitudinal trend in WUE , rising from the subtropics to the northern high-latitudes .
The trend peaks at approximately 51degreesN , and then declines toward higher latitudes .
These ground-based observations are consistent with global-scale estimates of WUE .
Global analysis of WUE reveals existence of strong regional variations that correspond to global climate patterns .
The latitudinal trends of global WUE for Earth 's major plant functional types reveal two peaks in the Northern Hemisphere not detected by ground-based measurements .
One peak is located at 20degrees ~ 30degreesN and the other extends a little farther north than 51degreesN .
Finally , long-term spatiotemporal trend analysis using satellite-based remote sensing data reveals that land-cover and land-use change in recent years has led to a decline in global WUE .
Our study provides a new framework for global research on the interactions between carbon and water cycles as well as responses to natural and human impacts .

[1189] High-fat diet alters gut microbiota physiology in mice

The intestinal microbiota is known to regulate host energy homeostasis and can be influenced by high-calorie diets .
However , changes affecting the ecosystem at the functional level are still not well characterized .
We measured shifts in cecal bacterial communities in mice fed a carbohydrate or high-fat ( HF ) diet for 12 weeks at the level of the following : ( i ) diversity and taxa distribution by high-throughput 16S ribosomal RNA gene sequencing ; ( ii ) bulk and single-cell chemical composition by Fourier-transform infrared - ( FT-IR ) and Raman micro-spectroscopy and ( iii ) metaproteome and metabolome via high-resolution mass spectrometry .
High-fat diet caused shifts in the diversity of dominant gut bacteria and altered the proportion of Ruminococcaceae ( decrease ) and Rikenellaceae ( increase ) .
FT-IR spectroscopy revealed that the impact of the diet on cecal chemical fingerprints is greater than the impact of microbiota composition .
Diet-driven changes in biochemical fingerprints of members of the Bacteroidales and Lachnospiraceae were also observed at the level of single cells , indicating that there were distinct differences in cellular composition of dominant phylotypes under different diets .
Metaproteome and metabolome analyses based on the occurrence of 1760 bacterial proteins and 86 annotated metabolites revealed distinct HF diet-specific profiles .
Alteration of hormonal and anti-microbial networks , bile acid and bilirubin metabolism and shifts towards amino acid and simple sugars metabolism were observed .
We conclude that a HF diet markedly affects the gut bacterial ecosystem at the functional level .

[1190] Decline in Mesozoic reef-building sponges explained by silicon limitation

Several unrelated clades of siliceous sponges proliferated on the shelves of the Jurassic Tethys Sea , becoming prominent builders in reefs and near-shore mounds .
Many of these builders are characterized by massive , rock-like skeletons made of spicules with a characteristic terminal hypersilicification .
Such hypertrophied spicules are generically known as desmas , irrespective of their phylogenetic origin .
Desma-bearing sponges virtually disappeared from reefs and other neritic environments during the Cretaceous and the Early Tertiary , but have subsisted in relict populations in deeper , bathyal waters .
The causes of the decline and bathymetric shift of these sponges remain obscure .
Here we show experimentally that the concentration of silicic acid in seawater modulates the phenotypic expression of the various spicule types genetically available in a sponge species .
We also show that the concentration of this nutrient in Recent surface waters is insufficient for this species to secrete its desmas .
These findings indicate that silicon limitation , probably aggravated in shallow waters by the diatom burst around the Cretaceous-Tertiary boundary , may have forced neritic sponges with desmas to either lighten their skeletons or move to deeper , silicon-rich environments .

[1191] Reduced sensitivity of recent tree-growth to temperature at high northern latitudes

Tree-ring chronologies that represent annual changes in the density of wood formed during the late summer can provide a proxy for local summertime air temperature .
Here we undertake an examination of large-regional-scale wood-density/air-temperature relationships using measurements from hundreds of sites at high latitudes in the Northern Hemisphere .
When averaged over large areas of northern America and Eurasia , tree-ring density series display a strong coherence with summer temperature measurements averaged over the same areas , demonstrating the ability of this proxy to portray mean temperature changes over sub-continents and even the whole Northern Hemisphere .
During the second half of the twentieth century , the decadal-scale trends in wood density and summer temperatures have increasingly diverged as wood density has progressively fallen .
The cause of this increasing insensitivity of wood density to temperature changes is not known , but if it is not taken into account in dendroclimatic reconstructions , past temperatures could be overestimated .
Moreover , the recent reduction in the response of trees to air-temperature changes would mean that estimates of future atmospheric CO2 concentrations , based on carbon-cycle models that are uniformly sensitive to high-latitude warming , could be too low .

[1192] Australian tropical cyclone activity lower than at any time over the past 550-1 ,500 years

The assessment of changes in tropical cyclone activity within the context of anthropogenically influenced climate change has been limited by the short temporal resolution of the instrumental tropical cyclone record ( less than 50 years ) .
Furthermore , controversy exists regarding the robustness of the observational record , especially before 1990 .
Here we show , on the basis of a new tropical cyclone activity index ( CAI ) , that the present low levels of storm activity on the mid west and northeast coasts of Australia are unprecedented over the past 550 to 1,500 years .
The CAI allows for a direct comparison between the modern instrumental record and long-term palaeotempest ( prehistoric tropical cyclone ) records derived from the 18O/16O ratio of seasonally accreting carbonate layers of actively growing stalagmites .
Our results reveal a repeated multicentennial cycle of tropical cyclone activity , the most recent of which commenced around ad 1700 .
The present cycle includes a sharp decrease in activity after 1960 in Western Australia .
This is in contrast to the increasing frequency and destructiveness of Northern Hemisphere tropical cyclones since 1970 in the Atlantic Ocean and the western North Pacific Ocean .
Other studies project a decrease in the frequency of tropical cyclones towards the end of the twenty-first century in the southwest Pacific , southern Indian and Australian regions .
Our results , although based on a limited record , suggest that this may be occurring much earlier than expected .

[1193] Global nitrogen deposition and carbon sinks

Land and ocean uptake of carbon dioxide plays a critical role in determining atmospheric carbon dioxide levels .
Future increases in nitrogen deposition have been predicted to increase the size of these terrestrial and marine carbon sinks , but although higher rates of nitrogen deposition might enhance carbon uptake in northern and tropical forests , they will probably have less of an impact on ocean sink strength .
Combined , the land and ocean sinks may sequester an additional 10 % of anthropogenic cabon emissions by 2030 owing to increased nitrogen inputs , but a more conservative estimate of 1 to 2 % is more likely .
Thus nitrogen-induced increases in the strength of land and ocean sinks are unlikely to keep pace with future increases in carbon dioxide .

[1194] Increased local retention of reef coral larvae as a result of ocean warming

Climate change will alter many aspects of the ecology of organisms , including dispersal patterns and population connectivity .
Understanding these changes is essential to predict future species distributions , estimate potential for adaptation , and design effective networks of protected areas .
In marine environments , dispersal is often accomplished by larvae .
At higher temperatures , larvae develop faster , but suffer higher mortality , making the effect of temperature on dispersal difficult to predict .
Here , we experimentally calibrate the effect of temperature on larval survival and settlement in a dynamic model of coral dispersal .
Our findings imply that most reefs globally will experience several-fold increases in local retention of larvae due to ocean warming .
This increase will be particularly pronounced for reefs with mean water residence times comparable to the time required for species to become competent to settle .
Higher local retention rates strengthen the link between abundance and recruitment at the reef scale , suggesting that populations will be more responsive to local conservation actions .
Higher rates of local retention and mortality will weaken connectivity between populations , and thus potentially retard recovery following severe disturbances that substantially deplete local populations .
Conversely , on isolated reefs that are dependent on replenishment from local broodstock , increases in local retention may hasten recovery .

[1195] Phylogenetic variation of phytolith carbon sequestration in bamboos

Phytoliths , the amorphous silica deposited in plant tissues , can occlude organic carbon ( phytolith-occluded carbon , PhytOC ) during their formation and play a significant role in the global carbon balance .
This study explored phylogenetic variation of phytolith carbon sequestration in bamboos .
The phytolith content in bamboo varied substantially from 4.28 % to 16.42 % , with the highest content in Sasa and the lowest in Chimonobambusa , Indocalamus and Acidosasa .
The mean PhytOC production flux and rate in China 's bamboo forests were 62.83 kg CO2 ha-1 y-1 and 4.5 x 108 kg CO2 y-1 , respectively .
This implies that 1.4 x 109 kg CO2 would be sequestered in world 's bamboo phytoliths because the global bamboo distribution area is about three to four times higher than China 's bamboo .
Therefore , both increasing the bamboo area and selecting high phytolith-content bamboo species would increase the sequestration of atmospheric CO2 within bamboo phytoliths .

[1196] Clay minerals and metal oxides strongly influence the structure of alkane-degrading microbial communities during soil maturation

Clay minerals , charcoal and metal oxides are essential parts of the soil matrix and strongly influence the formation of biogeochemical interfaces in soil .
We investigated the role of these parental materials for the development of functional microbial guilds using the example of alkane-degrading bacteria harbouring the alkane monooxygenase gene ( alkB ) in artificial mixtures composed of different minerals and charcoal , sterile manure and a microbial inoculum extracted from an agricultural soil .
We followed changes in abundance and community structure of alkane-degrading microbial communities after 3 and 12 months of soil maturation and in response to a subsequent 2-week plant litter addition .
During maturation we observed an overall increasing divergence in community composition .
The impact of metal oxides on alkane-degrading community structure increased during soil maturation , whereas the charcoal impact decreased from 3 to 12 months .
Among the clay minerals illite influenced the community structure of alkB-harbouring bacteria significantly , but not montmorillonite .
The litter application induced strong community shifts in soils , maturated for 12 months , towards functional guilds typical for younger maturation stages pointing to a resilience of the alkane-degradation function potentially fostered by an extant ` seed bank ' .
The ISME Journal advance online publication , 23 December 2014 ; doi :10.1038 / ismej .2014.243

[1197] Characterization and transcription of arsenic respiration and resistance genes during in situ uranium bioremediation

The possibility of arsenic release and the potential role of Geobacter in arsenic biogeochemistry during in situ uranium bioremediation was investigated because increased availability of organic matter has been associated with substantial releases of arsenic in other subsurface environments .
In a field experiment conducted at the Rifle , CO study site , groundwater arsenic concentrations increased when acetate was added .
The number of transcripts from arrA , which codes for the alpha-subunit of dissimilatory As ( V ) reductase , and acr3 , which codes for the arsenic pump protein Acr3 , were determined with quantitative reverse transcription-PCR .
Most of the arrA ( > 60 % ) and acr3-1 ( > 90 % ) sequences that were recovered were most similar to Geobacter species , while the majority of acr3-2 ( > 50 % ) sequences were most closely related to Rhodoferax ferrireducens .
Analysis of transcript abundance demonstrated that transcription of acr3-1 by the subsurface Geobacter community was correlated with arsenic concentrations in the groundwater .
In contrast , Geobacter arrA transcript numbers lagged behind the major arsenic release and remained high even after arsenic concentrations declined .
This suggested that factors other than As ( V ) availability regulated the transcription of arrA in situ , even though the presence of As ( V ) increased the transcription of arrA in cultures of Geobacter lovleyi , which was capable of As ( V ) reduction .
These results demonstrate that subsurface Geobacter species can tightly regulate their physiological response to changes in groundwater arsenic concentrations .
The transcriptomic approach developed here should be useful for the study of a diversity of other environments in which Geobacter species are considered to have an important influence on arsenic biogeochemistry .

[1198] Attribution of Arctic temperature change to greenhouse-gas and aerosol influences

The Arctic has warmed significantly more than global mean surface air temperature over recent decades , as expected from amplification mechanisms .
Previous studies have attributed the observed Arctic warming to the combined effect of greenhouse gases and other anthropogenic influences .
However , given the sensitivity of the Arctic to external forcing and the intense interest in the effects of aerosols on its climate , it is important to examine and quantify the effects of individual groups of anthropogenic forcing agents .
Here we quantify the separate contributions to observed Arctic land temperature change from greenhouse gases , other anthropogenic forcing agents ( which are dominated by aerosols ) and natural forcing agents .
We show that although increases in greenhouse-gas concentrations have driven the observed warming over the past century , approximately 60 % of the greenhouse-gas-induced warming has been offset by the combined response to other anthropogenic forcings , which is substantially greater than the fraction of global greenhouse-gas-induced warming that has been offset by these forcings .
The climate models considered on average simulate the amplitude of response to anthropogenic forcings well , increasing confidence in their projections of profound future Arctic climate change .

[1199] Observed changes in the albedo of the Arctic sea-ice zone for the period 1982-2009

The surface albedo of the Arctic sea-ice zone is a crucial component in the energy budget of the Arctic region .
The treatment of sea-ice albedo has been identified as an important source of variability in the future sea-ice mass loss forecasts in coupled climate models .
There is a clear need to establish data sets of Arctic sea-ice albedo to study the changes based on observational data and to aid future modelling efforts .
Here we present an analysis of observed changes in the mean albedo of the Arctic sea-ice zone using a data set consisting of 28 years of homogenized satellite data .
Along with the albedo reduction resulting from the well-known loss of late-summer sea-ice cover , we show that the mean albedo of the remaining Arctic sea-ice zone is decreasing .
The change per decade in the mean August sea-ice zone albedo is -0.029 + / -0.011 .
All albedo trends , except for the sea-ice zone in May , are significant with a 99 % confidence interval .
Variations in mean sea-ice albedo can be explained using sea-ice concentration , surface air temperature and elapsed time from onset of melt as drivers .

[1200] Nonlinear regional warming with increasing CO2 concentrations

When considering adaptation measures and global climate mitigation goals , stakeholders need regional-scale climate projections , including the range of plausible warming rates .
To assist these stakeholders , it is important to understand whether some locations may see disproportionately high or low warming from additional forcing above targets such as 2 K ( ref . )
.
There is a need to narrow uncertainty in this nonlinear warming , which requires understanding how climate changes as forcings increase from medium to high levels .
However , quantifying and understanding regional nonlinear processes is challenging .
Here we show that regional-scale warming can be strongly superlinear to successive CO2 doublings , using five different climate models .
Ensemble-mean warming is superlinear over most land locations .
Further , the inter-model spread tends to be amplified at higher forcing levels , as nonlinearities grow -- especially when considering changes per kelvin of global warming .
Regional nonlinearities in surface warming arise from nonlinearities in global-mean radiative balance , the Atlantic meridional overturning circulation , surface snow/ice cover and evapotranspiration .
For robust adaptation and mitigation advice , therefore , potentially avoidable climate change ( the difference between business-as-usual and mitigation scenarios ) and unavoidable climate change ( change under strong mitigation scenarios ) may need different analysis methods .

[1201] The Endoparasitoid , Cotesia vestalis , Regulates Host Physiology by Reprogramming the Neuropeptide Transcriptional Network

Endoparasitoids develop inside another insect by regulating host immunity and development via maternal factors injected into hosts during oviposition .
Prior results have provided insights into parasitism-induced immunosuppression , including the neuropeptide accumulation in parasitized insects .
Nonetheless , our understanding of neuropeptide influence on host development and behavior is not yet complete .
We posed the hypothesis that parasitization alters expression of genes encoding pro-neuropeptides and used larvae of Plutella xylostella and its endoparasitoid , Cotesia vestalis to test our hypothesis .
We prepared transcriptomes from the larval P. xylostella brain-CC-CA complex and identified transcripts encoding 19 neuropeptides .
All corresponding cDNAs were confirmed by RACE .
Our results demonstrate that parasitism significantly down-regulated , or delayed , expression of genes encoding pro-neuropeptides within 48 h post-parasitization .
Changing expression of these genes may account for the previously reported decreased feeding behavior , reduced growth rates and aborted development in the host larvae .
In effect , parasitization may operate at the molecular level within the CNS to create global changes in larval host biology .
The significance of our finding is that , in addition to the known effects on immunity , parasitoids influence host pro-neuropeptide gene transcription .
This finding reveals a new mechanism operating in host-parasitoid relationships to the advantage of the parasitoid .

[1202] Disruption of root carbon transport into forest humus stimulates fungal opportunists at the expense of mycorrhizal fungi

Ectomycorrhizal fungi dominate the humus layers of boreal forests .
They depend on carbohydrates that are translocated through roots , via fungal mycelium to microsites in the soil , wherein they forage for nutrients .
Mycorrhizal fungi are therefore sensitive to disruptive disturbances that may restrict their carbon supply .
By disrupting root connections , we induced a sudden decline in mycorrhizal mycelial abundance and studied the consequent effects on growth and activity of free living , saprotrophic fungi and bacteria in pine forest humus , using molecular community analyses in combination with enzyme activity measurements .
Ectomycorrhizal fungi had decreased in abundance 14 days after root severing , but the abundance of certain free-living ascomycetes was three times higher within 5 days of the disturbance compared with undisturbed controls .
Root disruption also increased laccase production by an order of magnitude and cellulase production by a factor of 5 .
In contrast , bacterial populations seemed little affected .
The results indicate that access to an external carbon source enables mycorrhizal fungi to monopolise the humus , but disturbances may induce rapid growth of opportunistic saprotrophic fungi that presumably use the dying mycorrhizal mycelium .
Studies of such functional shifts in fungal communities , induced by disturbance , may shed light on mechanisms behind nutrient retention and release in boreal forests .
The results also highlight the fundamental problems associated with methods that study microbial processes in soil samples that have been isolated from living roots .

[1203] Extensive halogen-mediated ozone destruction over the tropical Atlantic Ocean

Increasing tropospheric ozone levels over the past 150 years have led to a significant climate perturbation ; the prediction of future trends in tropospheric ozone will require a full understanding of both its precursor emissions and its destruction processes .
A large proportion of tropospheric ozone loss occurs in the tropical marine boundary layer and is thought to be driven primarily by high ozone photolysis rates in the presence of high concentrations of water vapour .
A further reduction in the tropospheric ozone burden through bromine and iodine emitted from open-ocean marine sources has been postulated by numerical models , but thus far has not been verified by observations .
Here we report eight months of spectroscopic measurements at the Cape Verde Observatory indicative of the ubiquitous daytime presence of bromine monoxide and iodine monoxide in the tropical marine boundary layer .
A year-round data set of co-located in situ surface trace gas measurements made in conjunction with low-level aircraft observations shows that the mean daily observed ozone loss is ~ 50 per cent greater than that simulated by a global chemistry model using a classical photochemistry scheme that excludes halogen chemistry .
We perform box model calculations that indicate that the observed halogen concentrations induce the extra ozone loss required for the models to match observations .
Our results show that halogen chemistry has a significant and extensive influence on photochemical ozone loss in the tropical Atlantic Ocean boundary layer .
The omission of halogen sources and their chemistry in atmospheric models may lead to significant errors in calculations of global ozone budgets , tropospheric oxidizing capacity and methane oxidation rates , both historically and in the future .

[1204] Climate change impacts on glaciers and runoff in Tien Shan ( Central Asia )

Climate-driven changes in glacier-fed streamflow regimes have direct implications on freshwater supply , irrigation and hydropower potential .
Reliable information about current and future glaciation and runoff is crucial for water allocation , a complex task in Central Asia , where the collapse of the Soviet Union has transformed previously interdependent republics into autonomous upstream and downstream countries .
Although the impacts of climate change on glaciation and runoff have been addressed in previous work undertaken in the Tien Shan ( known as the ` water tower of Central Asia ' ) , a coherent , regional perspective of these findings has not been presented until now .
Here we show that glacier shrinkage is most pronounced in peripheral , lower-elevation ranges near the densely populated forelands , where summers are dry and where snow and glacial meltwater is essential for water availability .
Shifts of seasonal runoff maxima have already been observed in some rivers , and it is suggested that summer runoff will further decrease in these rivers if precipitation and discharge from thawing permafrost bodies do not compensate sufficiently for water shortfalls .

[1205] Telomere dysfunction induces metabolic and mitochondrial compromise

Telomere dysfunction activates p53-mediated cellular growth arrest , senescence and apoptosis to drive progressive atrophy and functional decline in high-turnover tissues .
The broader adverse impact of telomere dysfunction across many tissues including more quiescent systems prompted transcriptomic network analyses to identify common mechanisms operative in haematopoietic stem cells , heart and liver .
These unbiased studies revealed profound repression of peroxisome proliferator-activated receptor gamma , coactivator 1 alpha and beta ( PGC-1alpha and PGC-1beta , also known as Ppargc1a and Ppargc1b , respectively ) and the downstream network in mice null for either telomerase reverse transcriptase ( Tert ) or telomerase RNA component ( Terc ) genes .
Consistent with PGCs as master regulators of mitochondrial physiology and metabolism , telomere dysfunction is associated with impaired mitochondrial biogenesis and function , decreased gluconeogenesis , cardiomyopathy , and increased reactive oxygen species .
In the setting of telomere dysfunction , enforced Tert or PGC-1alpha expression or germline deletion of p53 ( also known as Trp53 ) substantially restores PGC network expression , mitochondrial respiration , cardiac function and gluconeogenesis .
We demonstrate that telomere dysfunction activates p53 which in turn binds and represses PGC-1alpha and PGC-1beta promoters , thereby forging a direct link between telomere and mitochondrial biology .
We propose that this telomere-p53-PGC axis contributes to organ and metabolic failure and to diminishing organismal fitness in the setting of telomere dysfunction .

[1206] Biodiversity inventories , indicator taxa and effects of habitat modification in tropical forest

Despite concern about the effects of tropical forest disturbance and clearance on biodiversity , , data on impacts , particularly on invertebrates , remain scarce .
Here we report a taxonomically diverse inventory on the impacts of tropical forest modification at one locality .
We examined a gradient from near-primary , through old-growth secondary and plantation forests to complete clearance , for eight animal groups ( birds , butterflies , flying beetles , canopy beetles , canopy ants , leaf-litter ants , termites and soil nematodes ) in the Mbalmayo Forest Reserve , south-central Cameroon .
Although species richness generally declined with increasing disturbance , no one group serves as a good indicator taxon for changes in the species richness of other groups .
Species replacement from site to site ( turnover ) along the gradient also differs between taxonomic groups .
The proportion of ` morphospecies ' that can not be assigned to named species and the number of ` scientist-hours ' required to process samples both increase dramatically for smaller-bodied taxa .
Data from these eight groups indicate the huge scale of the biological effort required to provide inventories of tropical diversity , and to measure the impacts of tropical forest modification and clearance .

[1207] Density of founder cells affects spatial pattern formation and cooperation in Bacillus subtilis biofilms

In nature , most bacteria live in surface-attached sedentary communities known as biofilms .
Biofilms are often studied with respect to bacterial interactions .
Many cells inhabiting biofilms are assumed to express ` cooperative traits ' , like the secretion of extracellular polysaccharides ( EPS ) .
These traits can enhance biofilm-related properties , such as stress resilience or colony expansion , while being costly to the cells that express them .
In well-mixed populations cooperation is difficult to achieve , because non-cooperative individuals can reap the benefits of cooperation without having to pay the costs .
The physical process of biofilm growth can , however , result in the spatial segregation of cooperative from non-cooperative individuals .
This segregation can prevent non-cooperative cells from exploiting cooperative neighbors .
Here we examine the interaction between spatial pattern formation and cooperation in Bacillus subtilis biofilms .
We show , experimentally and by mathematical modeling , that the density of cells at the onset of biofilm growth affects pattern formation during biofilm growth .
At low initial cell densities , co-cultured strains strongly segregate in space , whereas spatial segregation does not occur at high initial cell densities .
As a consequence , EPS-producing cells have a competitive advantage over non-cooperative mutants when biofilms are initiated at a low density of founder cells , whereas EPS-deficient cells have an advantage at high cell densities .
These results underline the importance of spatial pattern formation for competition among bacterial strains and the evolution of microbial cooperation .

[1208] Early onset and tropical forcing of 100,000-year Pleistocene glacial cycles

Between 1.5 and 0.6 Myr ago , the period of the Earth 's glacial cycles changed from 41 kyr , the period of the Earth 's obliquity cycles , to 100 kyr , the period of the Earth 's orbital eccentricity , which has a much smaller effect on global insolation .
The timing of this transition and its causes pose one of the most perplexing problems in palaeoclimate research .
Here we use complex demodulation to examine the phase evolution of precession and semiprecession cycles -- the latter of which are phase-coupled to both precession and eccentricity -- in the tropical and extra-tropical Atlantic Ocean .
We find that about 1.5 Myr ago , tropical semiprecession cycles ( with periods of about 11.5 kyr ) started to propagate to higher latitudes , coincident with a growing amplitude envelope of the 100-kyr cycles .
Evidence from numerical models suggests that cycles of about 10 kyr in length may be required to explain the high amplitude of the 100-kyr cycles .
Combining our results with consideration of a modern analogue , we conclude that increased heat flow across the equator or from the tropics to higher latitudes around 1.5 Myr ago strengthened the semiprecession cycle in the Northern Hemisphere , and triggered the transition to sustained 100-kyr glacial cycles .

[1209] Storm-induced sea-ice breakup and the implications for ice extent

The propagation of large , storm-generated waves through sea ice has so far not been measured , limiting our understanding of how ocean waves break sea ice .
Without improved knowledge of ice breakup , we are unable to understand recent changes , or predict future changes , in Arctic and Antarctic sea ice .
Here we show that storm-generated ocean waves propagating through Antarctic sea ice are able to transport enough energy to break sea ice hundreds of kilometres from the ice edge .
Our results , which are based on concurrent observations at multiple locations , establish that large waves break sea ice much farther from the ice edge than would be predicted by the commonly assumed exponential decay .
We observed the wave height decay to be almost linear for large waves -- those with a significant wave height greater than three metres -- and to be exponential only for small waves .
This implies a more prominent role for large ocean waves in sea-ice breakup and retreat than previously thought .
We examine the wider relevance of this by comparing observed Antarctic sea-ice edge positions with changes in modelled significant wave heights for the Southern Ocean between 1997 and 2009 , and find that the retreat and expansion of the sea-ice edge correlate with mean significant wave height increases and decreases , respectively .
This includes capturing the spatial variability in sea-ice trends found in the Ross and Amundsen-Bellingshausen seas .
Climate models fail to capture recent changes in sea ice in both polar regions .
Our results suggest that the incorporation of explicit or parameterized interactions between ocean waves and sea ice may resolve this problem .

[1210] Response of the North Atlantic storm track to climate change shaped by ocean-atmosphere coupling

A poleward shift of the mid-latitude storm tracks in response to anthropogenic greenhouse-gas forcing has been diagnosed in climate model simulations .
Explanations of this effect have focused on atmospheric dynamics .
However , in contrast to storm tracks in other regions , the North Atlantic storm track responds by strengthening and extending farther east , in particular on its southern flank .
These adjustments are associated with an intensification and extension of the eddy-driven jet towards western Europe and are expected to have considerable societal impacts related to a rise in storminess in Europe .
Here , we apply a regression analysis to an ensemble of coupled climate model simulations to show that the coupling between ocean and atmosphere shapes the distinct storm-track response to greenhouse-gas forcing in the North Atlantic region .
In the ensemble of simulations we analyse , at least half of the differences between the storm-track responses of different models are associated with uncertainties in ocean circulation changes .
We compare the fully coupled simulations with both the associated slab model simulations and an ocean-forced experiment with one climate model to establish causality .
We conclude that uncertainties in the response of the North Atlantic storm track to anthropogenic emissions could be reduced through tighter constraints on the future ocean circulation .

[1211] Effects of ecological engineered oxygenation on the bacterial community structure in an anoxic fjord in western Sweden

Oxygen-depleted bodies of water are becoming increasingly common in marine ecosystems .
Solutions to reverse this trend are needed and under development , for example , by the Baltic deep-water OXygenation ( BOX ) project .
In the framework of this project , the Swedish Byfjord was chosen for a pilot study , investigating the effects of an engineered oxygenation on long-term anoxic bottom waters .
The strong stratification of the water column of the Byfjord was broken up by pumping surface water into the deeper layers , triggering several inflows of oxygen-rich water and increasing oxygen levels in the lower water column and the benthic zone up to 110 mumol l-1 .
We used molecular ecologic methods to study changes in bacterial community structure in response to the oxygenation in the Byfjord .
Water column samples from before , during and after the oxygenation as well as from two nearby control fjords were analyzed .
Our results showed a strong shift in bacterial community composition when the bottom water in the Byfjord became oxic .
Initially dominant indicator species for oxygen minimum zones such as members of the SUP05 clade declined in abundance during the oxygenation event and nearly vanished after the oxygenation was accomplished .
In contrast , aerobic species like SAR11 that initially were restricted to surface waters could later be detected deep into the water column .
Overall , the bacterial community in the formerly anoxic bottom waters changed to a community structure similar to those found in oxic waters , showing that an engineered oxygenation of a large body of anoxic marine water is possible and emulates that of a natural oxygenation event .

[1212] Ecosystem remodelling among vertebrates at the Permian-Triassic boundary in Russia

The mass extinction at the Permian-Triassic boundary , 251 million years ( Myr ) ago , is accepted as the most profound loss of life on record .
Global data compilations indicate a loss of 50 % of families or more , both in the sea and on land , and these figures scale to a loss of 80-96 % of species , based on rarefaction analyses .
This level of loss is confirmed by local and regional-scale studies of marine sections , but the terrestrial record has been harder to analyse in such close detail .
Here we document the nature of the event in Russia in a comprehensive survey of 675 specimens of amphibians and reptiles from 289 localities spanning 13 successive geological time zones in the South Urals basin .
These changes in diversity and turnover can not be explained simply by sampling effects .
There was a profound loss of genera and families , and simplification of ecosystems , with the loss of small fish-eaters and insect-eaters , medium and large herbivores and large carnivores .
Faunal dynamics also changed , from high rates of turnover through the Late Permian period to greater stability at low diversity through the Early Triassic period .
Even after 15 Myr of ecosystem rebuilding , some guilds were apparently still absent -- small fish-eaters , small insect-eaters , large herbivores and top carnivores .

[1213] Response of Prochlorococcus ecotypes to co-culture with diverse marine bacteria

Interactions between microorganisms shape microbial ecosystems .
Systematic studies of mixed microbes in co-culture have revealed widespread potential for growth inhibition among marine heterotrophic bacteria , but similar synoptic studies have not been done with autotroph/heterotroph pairs , nor have precise descriptions of the temporal evolution of interactions been attempted in a high-throughput system .
Here , we describe patterns in the outcome of pair-wise co-cultures between two ecologically distinct , yet closely related , strains of the marine cyanobacterium Prochlorococcus and hundreds of heterotrophic marine bacteria .
Co-culture with the collection of heterotrophic strains influenced the growth of Prochlorococcus strain MIT9313 much more than that of strain MED4 , reflected both in the number of different types of interactions and in the magnitude of the effect of co-culture on various culture parameters .
Enhancing interactions , where the presence of heterotrophic bacteria caused Prochlorococcus to grow faster and reach a higher final culture chlorophyll fluorescence , were much more common than antagonistic ones , and for a selected number of cases were shown to be mediated by diffusible compounds .
In contrast , for one case at least , temporary inhibition of Prochlorococcus MIT9313 appeared to require close cellular proximity .
Bacterial strains whose 16S gene sequences differed by 1-2 % tended to have similar effects on MIT9313 , suggesting that the patterns of inhibition and enhancement in co-culture observed here are due to phylogenetically cohesive traits of these heterotrophs .

[1214] Australian climate-carbon cycle feedback reduced by soil black carbon

Annual emissions of carbon dioxide from soil organic carbon are an order of magnitude greater than all anthropogenic carbon dioxide emissions taken together .
Global warming is likely to increase the decomposition of soil organic carbon , and thus the release of carbon dioxide from soils , creating a positive feedback .
Current models of global climate change that recognize this soil carbon feedback are inaccurate if a larger fraction of soil organic carbon than postulated has a very slow decomposition rate .
Here we show that by including realistic stocks of black carbon in prediction models , carbon dioxide emissions are reduced by 18.3 and 24.4 % in two Australian savannah regions in response to a warming of 3 degreesC over 100 years .
This reduction in temperature sensitivity , and thus the magnitude of the positive feedback , results from the long mean residence time of black carbon , which we estimate to be approximately 1,300 and 2,600 years , respectively .
The inclusion of black carbon in climate models is likely to require spatially explicit information about its distribution , given that the black carbon content of soils ranged from 0 to 82 % of soil organic carbon in a continental-scale analysis of Australia .
We conclude that accurate information about the distribution of black carbon in soils is important for projections of future climate change .

[1215] A climatologically significant aerosol longwave indirect effect in the Arctic

The warming of Arctic climate and decreases in sea ice thickness and extent observed over recent decades are believed to result from increased direct greenhouse gas forcing , changes in atmospheric dynamics having anthropogenic origin , and important positive reinforcements including ice-albedo and cloud-radiation feedbacks .
The importance of cloud-radiation interactions is being investigated through advanced instrumentation deployed in the high Arctic since 1997 ( refs 7 , 8 ) .
These studies have established that clouds , via the dominance of longwave radiation , exert a net warming on the Arctic climate system throughout most of the year , except briefly during the summer .
The Arctic region also experiences significant periodic influxes of anthropogenic aerosols , which originate from the industrial regions in lower latitudes .
Here we use multisensor radiometric data to show that enhanced aerosol concentrations alter the microphysical properties of Arctic clouds , in a process known as the ` first indirect ' effect .
Under frequently occurring cloud types we find that this leads to an increase of an average 3.4 watts per square metre in the surface longwave fluxes .
This is comparable to a warming effect from established greenhouse gases and implies that the observed longwave enhancement is climatologically significant .

[1216] Pyrosequencing reveals contrasting seasonal dynamics of taxa within Baltic Sea bacterioplankton communities

Variation in traits causes bacterial populations to respond in contrasting ways to environmental drivers .
Learning about this will help us understand the ecology of individual populations in complex ecosystems .
We used 454 pyrosequencing of the hypervariable region V6 of the 16S rRNA gene to study seasonal dynamics in Baltic Sea bacterioplankton communities , and link community and population changes to biological and chemical factors .
Surface samples were collected from May to October 2003 and in May 2004 at the Landsort Deep in the central Baltic Sea Proper .
The analysis rendered , on average , 20 200 sequence reads for each of the eight samples analyzed , providing the first detailed description of Baltic Sea bacterial communities .
Community composition varied dramatically over time , supporting the idea of strong temporal shifts in bacterioplankton assemblages , and clustered according to season ( including two May samples from consecutive years ) , suggesting repeatable seasonal succession .
Overall , community change was most highly correlated with change in phosphorus concentration and temperature .
Individual bacterial populations were also identified that tightly co-varied with different Cyanobacteria populations .
Comparing the abundance profiles of operational taxonomic units at different phylogenetic distances revealed a weak but significant negative correlation between abundance profile similarity and genetic distance , potentially reflecting habitat filtering of evolutionarily conserved functional traits in the studied bacterioplankton .

[1217] Climate change : Increasing shrub abundance in the Arctic

The warming of the Alaskan Arctic during the past 150 years has accelerated over the last three decades and is expected to increase vegetation productivity in tundra if shrubs become more abundant ; indeed , this transition may already be under way according to local plot studies and remote sensing .
Here we present evidence for a widespread increase in shrub abundance over more than 320 km of Arctic landscape during the past 50 years , based on a comparison of historic and modern aerial photographs .
This expansion will alter the partitioning of energy in summer and the trapping and distribution of snow in winter , as well as increasing the amount of carbon stored in a region that is believed to be a net source of carbon dioxide .

[1218] The short-chain fatty acid acetate reduces appetite via a central homeostatic mechanism

Increased intake of dietary carbohydrate that is fermented in the colon by the microbiota has been reported to decrease body weight , although the mechanism remains unclear .
Here we use in vivo11C-acetate and PET-CT scanning to show that colonic acetate crosses the blood-brain barrier and is taken up by the brain .
Intraperitoneal acetate results in appetite suppression and hypothalamic neuronal activation patterning .
We also show that acetate administration is associated with activation of acetyl-CoA carboxylase and changes in the expression profiles of regulatory neuropeptides that favour appetite suppression .
Furthermore , we demonstrate through 13C high-resolution magic-angle-spinning that 13C acetate from fermentation of 13C-labelled carbohydrate in the colon increases hypothalamic 13C acetate above baseline levels .
Hypothalamic 13C acetate regionally increases the 13C labelling of the glutamate-glutamine and GABA neuroglial cycles , with hypothalamic 13C lactate reaching higher levels than the ` remaining brain ' .
These observations suggest that acetate has a direct role in central appetite regulation .

[1219] Role of biogenic silica in the removal of iron from the Antarctic seas

Iron has a key role in controlling biological production in the Southern Ocean , yet the mechanisms regulating iron availability in this and other ocean regions are not completely understood .
Here , based on analysis of living phytoplankton in the coastal seas of West Antarctica , we present a new pathway for iron removal from marine systems involving structural incorporation of reduced , organic iron into biogenic silica .
Export of iron incorporated into biogenic silica may represent a substantial unaccounted loss of iron from marine systems .
For example , in the Ross Sea , burial of iron incorporated into biogenic silica is conservatively estimated as 11 mumol m-2 per year , which is in the same range as the major bioavailable iron inputs to this region .
As a major sink of bioavailable iron , incorporation of iron into biogenic silica may shift microbial population structure towards taxa with relatively lower iron requirements , and may reduce ecosystem productivity and associated carbon sequestration .

[1220] Increasing frequency of extreme El Nino events due to greenhouse warming

El Nino events are a prominent feature of climate variability with global climatic impacts .
The 1997/98 episode , often referred to as ` the climate event of the twentieth century ' , and the 1982/83 extreme El Nino , featured a pronounced eastward extension of the west Pacific warm pool and development of atmospheric convection , and hence a huge rainfall increase , in the usually cold and dry equatorial eastern Pacific .
Such a massive reorganization of atmospheric convection , which we define as an extreme El Nino , severely disrupted global weather patterns , affecting ecosystems , agriculture , tropical cyclones , drought , bushfires , floods and other extreme weather events worldwide .
Potential future changes in such extreme El Nino occurrences could have profound socio-economic consequences .
Here we present climate modelling evidence for a doubling in the occurrences in the future in response to greenhouse warming .
We estimate the change by aggregating results from climate models in the Coupled Model Intercomparison Project phases 3 ( CMIP3 ; ref . )
and 5 ( CMIP5 ; ref . )
multi-model databases , and a perturbed physics ensemble .
The increased frequency arises from a projected surface warming over the eastern equatorial Pacific that occurs faster than in the surrounding ocean waters , facilitating more occurrences of atmospheric convection in the eastern equatorial region .

[1221] Global phytoplankton decline over the past century

In the oceans , ubiquitous microscopic phototrophs ( phytoplankton ) account for approximately half the production of organic matter on Earth .
Analyses of satellite-derived phytoplankton concentration ( available since 1979 ) have suggested decadal-scale fluctuations linked to climate forcing , but the length of this record is insufficient to resolve longer-term trends .
Here we combine available ocean transparency measurements and in situ chlorophyll observations to estimate the time dependence of phytoplankton biomass at local , regional and global scales since 1899 .
We observe declines in eight out of ten ocean regions , and estimate a global rate of decline of ~ 1 % of the global median per year .
Our analyses further reveal interannual to decadal phytoplankton fluctuations superimposed on long-term trends .
These fluctuations are strongly correlated with basin-scale climate indices , whereas long-term declining trends are related to increasing sea surface temperatures .
We conclude that global phytoplankton concentration has declined over the past century ; this decline will need to be considered in future studies of marine ecosystems , geochemical cycling , ocean circulation and fisheries .

[1222] Precision phenotyping of biomass accumulation in triticale reveals temporal genetic patterns of regulation

To extend agricultural productivity by knowledge-based breeding and tailor varieties adapted to specific environmental conditions , it is imperative to improve our ability to assess the dynamic changes of the phenome of crops under field conditions .
To this end , we have developed a precision phenotyping platform that combines various sensors for a non-invasive , high-throughput and high-dimensional phenotyping of small grain cereals .
This platform yielded high prediction accuracies and heritabilities for biomass of triticale .
Genetic variation for biomass accumulation was dissected with 647 doubled haploid lines derived from four families .
Employing a genome-wide association mapping approach , two major quantitative trait loci ( QTL ) for biomass were identified and the genetic architecture of biomass accumulation was found to be characterized by dynamic temporal patterns .
Our findings highlight the potential of precision phenotyping to assess the dynamic genetics of complex traits , especially those not amenable to traditional phenotyping .

[1223] Coherent high - and low-latitude control of the northwest African hydrological balance

The evolution of the northwest African hydrological balance throughout the Pleistocene epoch influenced the migration of prehistoric humans .
The hydrological balance is also thought to be important to global teleconnection mechanisms during Dansgaard-Oeschger and Heinrich events .
However , most high-resolution African climate records do not span the millennial-scale climate changes of the last glacial-interglacial cycle , or lack an accurate chronology .
Here , we use grain-size analyses of siliciclastic marine sediments from off the coast of Mauritania to reconstruct changes in northwest African humidity over the past 120,000 years .
We compare this reconstruction to simulations of palaeo-humidity from a coupled atmosphere-ocean-vegetation model .
These records are in good agreement , and indicate the reoccurrence of precession-forced humid periods during the last interglacial period similar to the Holocene African Humid Period .
We suggest that millennial-scale arid events are associated with a reduction of the North Atlantic meridional overturning circulation and that millennial-scale humid events are linked to a regional increase of winter rainfall over the coastal regions of northwest Africa .

[1224] Research highlights

Optoelectronics : Speedy silicon Optics Express 15 , 660-668 ( 2007 ) Silicon is the material of choice for computer chips , but has traditionally lagged behind in optics , unable to compete with other materials for speed .
That could soon change .
Ansheng Liu and his colleagues at Intel in Santa Clara , California , and in Jerusalem , Israel , have developed an optical device ( pictured ) that can write up to 30 gigabits of data per second to a laser beam -- three times faster than any previous silicon device .
The optical modulator 's speed stems in part from a design that transmits the electrical signal carrying the data and the light through a single channel , or ` waveguide ' .
The researchers claim they can tweak their device to reach data transfer speeds of up to 40 gigabits per second , which rivals the speeds of optical modulators made from more exotic materials .
Neurobiology : Prion symptoms reversed Neuron 53 , 325-335 ( 2007 ) Early symptoms of the neurodegeneration caused by prion disease can be reversed in genetically engineered mice , report Giovanna Mallucci , of the Medical Research Council 's Institute of Neurology in London , and her colleagues .
The researchers monitored the behaviour of mice infected with a prion protein to look for early indicators of the disease .
Changes in the way the mice responded to their environment occurred before the onset of obvious signs of neurodegeneration , such as reduced grooming .
The mice recovered their normal brain function if production of the naturally occurring protein that propagates the disease was switched off at this stage .
But the implications for treatment of the human prion disease , Creutzfeldt-Jakob disease , are uncertain .
It 's not clear whether human brains could recover , nor how levels of the prion protein could be lowered .
Immunology : The right kind of help J. Exp .
Med .
doi :10.1084 / jem .20061839 ( 2007 ) So far they have only tested their hypothesis in mice , but researchers think they have identified a mechanism that could help to explain why men are less prone than women to developing certain types of autoimmune disease , such as mutliple sclerosis .
Lawrence Steinman of Stanford University Medical Center , California , and his colleagues studied a receptor known as peroxisome proliferator-activated receptor-alpha , which has been implicated in gender differences in lipid metabolism .
The receptor is also expressed in the immune system 's CD4 + T cells .
The researchers showed that the receptor gene is sensitive to testosterone , and is expressed at higher levels in the T cells of male mice than in those of females .
CD4 + T cells differentiate into different types of ` T-helper ' cell .
Expression of the receptor seems to direct differentiation away from the type that is associated with certain autoimmune diseases .
Knocking out the gene in males made the symptoms of a mouse model of multiple sclerosis more severe .
Palaeontology : Could the ` hobbit ' hunt ?
HOMO -- J. Comp .
Hum .
Biol .
doi :10.1016 / j.jchb .2006.11.001 ( 2007 ) Debate over the diminutive Homo floresiensis -- believed to be a hobbit-sized species of hominid -- has inspired a team at Washington University in St Louis , Missouri , to develop a method to estimate the size of hominid brain components from fossil skulls .
Researchers have questioned whether the small-brained H. floresiensis , which lived on an isolated Indonesian island until at least 12,000 years ago , would have been capable of creating tools , using fire and hunting , as some studies have suggested .
Glenn Conroy and Richard Smith looked at the volumes of 11 different brain components in 45 primate species to set limits on the size of each component as a fraction of overall brain size .
The predicted bounds for the brain of H. floresiensis are not consistent with the suggested behaviour , they conclude , unless the brain of H. floresiensis was functionally different from that of modern humans or chimpanzees .
That possibility would force biologists to rethink how hominid brains evolved .
Metagenomics : Invisible communities Science doi :10.1126 / science .1133420 ( 2007 ) Thousands of different microorganisms can share the same habitat , but these populations are hard to study because few individual species survive in cell culture .
One way around this is to perform shotgun sequencing of the whole communitiy -- an approach known as metagenomics .
Peer Bork from the European Molecular Biology Laboratory in Heidelberg , Germany , and his colleagues present a new bioinformatics approach to digging out biologically relevant details from such data .
They examined 31 ` marker genes ' -- genes that are present in all microbes , but show variation between species -- to probe the composition of four communities , including microbes from ocean water and from soil .
This allowed them to show , for example , that some communities evolve faster than others and that some microbes have clear and persistent preferences for particular environments .
Materials Science : Stiffer than diamond Science 315 , 620-622 ( 2007 ) For hardness and stiffness , it 's long been thought that nothing beats diamond .
But Roderic Lakes of the University of Wisconsin - Madison and his colleagues have made a material that is almost ten times stiffer , by embedding small particles of barium titanate in a matrix of tin .
Barium titanate can adopt different crystal structures .
In the composite , it is trapped in a high-temperature form at temperatures below the usual transition point .
This gives the inclusions the strange property of negative stiffness , meaning that they bend in the opposite direction to an applied force .
Warming the composite changes the balance between the mechanical properties of the inclusions and those of the matrix , which responds more conventionally to an applied force .
At a particular temperature , these tendencies cancel each other almost exactly , and the material then scarcely deforms at all .
This extreme stiffness is remarkable , given that neither of the materials involved are especially stiff on their own .
The composite isn ` t , however , expected to be particularly hard or strong .
Astronomy : Super-Earth model Astrophys .
J. 656 , 545-551 ( 2007 ) Recently discovered planets in solar systems beyond our own have masses just a few times that of Earth .
What might these ` super-Earths ' actually look like ?

[1225] Making mistakes when predicting shifts in species range in response to global warming

Many attempts to predict the biotic responses to climate change rely on the ` climate envelope ' approach , in which the current distribution of a species is mapped in climate-space and then , if the position of that climate-space changes , the distribution of the species is predicted to shift accordingly .
The flaw in this approach is that distributions of species also reflect the influence of interactions with other species , so predictions based on climate envelopes may be very misleading if the interactions between species are altered by climate change .
An additional problem is that current distributions may be the result of sources and sinks , in which species appear to thrive in places where they really persist only because individuals disperse into them from elsewhere , .
Here we use microcosm experiments on simple but realistic assemblages to show how misleading the climate envelope approach can be .
We show that dispersal and interactions , which are important elements of population dynamics , must be included in predictions of biotic responses to climate change .

[1226] Influence of anthropogenic aerosols and the Pacific Decadal Oscillation on tropical belt width

The tropical belt has widened by several degrees latitude since 1979 , as evidenced by shifts in atmospheric circulation and climate zones .
Global climate models also simulate tropical belt widening , but less so than observed .
Reasons for this discrepancy and the mechanisms driving the expansion are uncertain .
Here we analyse multidecadal variability in tropical belt width since 1950 using the Coupled Model Intercomparison Project Phase 5 climate model runs and find that simulated rates of tropical expansion over the past 30 years -- particularly in the Northern Hemisphere -- are in better agreement with observations than previous models .
We find that models driven by observed sea surface temperatures over this interval yield the largest rate of tropical expansion .
We link the tropical expansion in the Northern Hemisphere to the leading pattern of sea surface temperature variability in the North Pacific , the Pacific Decadal Oscillation .
We also find , both from models and observations , that the tropical belt contracted in the Northern Hemisphere from 1950 to 1979 , coincident with the reversal of the Pacific Decadal Oscillation trend .
In both time periods , anthropogenic aerosols act to modify the Pacific Decadal Oscillation and therefore contribute to the width of the tropical belt .
We conclude that tropical expansion and contraction are influenced by multidecadal sea surface temperature variability associated with both the Pacific Decadal Oscillation and anthropogenic aerosols .

[1227] Strong effects of weak interactions in ecological communities

The loss or removal of individual species can cause dramatic changes in communities .
Experiments indicate that in many communities only a few species will have such strong effects , whereas most will have weak effects owing to small per capita effects and/or low abundance , , .
But extinction of these ` weak ' interactors could significantly alter natural communities because they play important stabilizing or ` noise-dampening ' roles , , .
I demonstrate here that some ` weak ' interactors may also be important by magnifying spatiotemporal variation in community structure .
An analysis of published interaction strength data shows that the greatest variation in species effect occurred for the weakest interactions .
A field experiment corroborates this and shows how indirect interactions can generate an inverse relationship between the mean and variance of a consumer 's impact on its prey .
When a species ' effects are highly variable in sign and magnitude , they may average to seem weak over broad scales but be strong in local contexts .
Thus , what is frequently considered to be ` noise ' in species interaction data may be a critical part of the signal .

[1228] Long-term impacts of aerosols on the vertical development of clouds and precipitation

Aerosols alter cloud density and the radiative balance of the atmosphere .
This leads to changes in cloud microphysics and atmospheric stability , which can either suppress or foster the development of clouds and precipitation .
The net effect is largely unknown , but depends on meteorological conditions and aerosol properties .
Here , we examine the long-term impact of aerosols on the vertical development of clouds and rainfall frequencies , using a 10-year dataset of aerosol , cloud and meteorological variables collected in the Southern Great Plains in the United States .
We show that cloud-top height and thickness increase with aerosol concentration measured near the ground in mixed-phase clouds -- which contain both liquid water and ice -- that have a warm , low base .
We attribute the effect , which is most significant in summer , to an aerosol-induced invigoration of upward winds .
In contrast , we find no change in cloud-top height and precipitation with aerosol concentration in clouds with no ice or cool bases .
We further show that precipitation frequency and rain rate are altered by aerosols .
Rain increases with aerosol concentration in deep clouds that have a high liquid-water content , but declines in clouds that have a low liquid-water content .
Simulations using a cloud-resolving model confirm these observations .
Our findings provide unprecedented insights of the long-term net impacts of aerosols on clouds and precipitation .

[1229] Microbial contributions to climate change through carbon cycle feedbacks

There is considerable interest in understanding the biological mechanisms that regulate carbon exchanges between the land and atmosphere , and how these exchanges respond to climate change .
An understanding of soil microbial ecology is central to our ability to assess terrestrial carbon cycle-climate feedbacks , but the complexity of the soil microbial community and the many ways that it can be affected by climate and other global changes hampers our ability to draw firm conclusions on this topic .
In this paper , we argue that to understand the potential negative and positive contributions of soil microbes to land-atmosphere carbon exchange and global warming requires explicit consideration of both direct and indirect impacts of climate change on microorganisms .
Moreover , we argue that this requires consideration of complex interactions and feedbacks that occur between microbes , plants and their physical environment in the context of climate change , and the influence of other global changes which have the capacity to amplify climate-driven effects on soil microbes .
Overall , we emphasize the urgent need for greater understanding of how soil microbial ecology contributes to land-atmosphere carbon exchange in the context of climate change , and identify some challenges for the future .
In particular , we highlight the need for a multifactor experimental approach to understand how soil microbes and their activities respond to climate change and consequences for carbon cycle feedbacks .

[1230] Man made deltas

The review of geochronological and historical data documents that the largest southern European deltas formed almost synchronously during two short intervals of enhanced anthropic pressure on landscapes , respectively during the Roman Empire and the Little Ice Age .
These growth phases , that occurred under contrasting climatic regimes , were both followed by generalized delta retreat , driven by two markedly different reasons : after the Romans , the fall of the population and new afforestation let soil erosion in river catchments return to natural background levels ; since the industrial revolution , instead , flow regulation through river dams overkill a still increasing sediment production in catchment basins .
In this second case , furthermore , the effect of a reduced sediment flux to the coasts is amplified by the sinking of modern deltas , due to land subsidence and sea level rise , that hampers delta outbuilding and increases the vulnerability of coastal zone to marine erosion and flooding .

[1231] Enhanced Adaptive Management : Integrating Decision Analysis , Scenario Analysis and Environmental Modeling for the Everglades

We propose to enhance existing adaptive management efforts with a decision-analytical approach that can guide the initial selection of robust restoration alternative plans and inform the need to adjust these alternatives in the course of action based on continuously acquired monitoring information and changing stakeholder values .
We demonstrate an application of enhanced adaptive management for a wetland restoration case study inspired by the Florida Everglades restoration effort .
We find that alternatives designed to reconstruct the pre-drainage flow may have a positive ecological impact , but may also have high operational costs and only marginally contribute to meeting other objectives such as reduction of flooding .
Enhanced adaptive management allows managers to guide investment in ecosystem modeling and monitoring efforts through scenario and value of information analyses to support optimal restoration strategies in the face of uncertain and changing information .

[1232] Amazon forests maintain consistent canopy structure and greenness during the dry season

The seasonality of sunlight and rainfall regulates net primary production in tropical forests .
Previous studies have suggested that light is more limiting than water for tropical forest productivity , consistent with greening of Amazon forests during the dry season in satellite data .
We evaluated four potential mechanisms for the seasonal green-up phenomenon , including increases in leaf area or leaf reflectance , using a sophisticated radiative transfer model and independent satellite observations from lidar and optical sensors .
Here we show that the apparent green up of Amazon forests in optical remote sensing data resulted from seasonal changes in near-infrared reflectance , an artefact of variations in sun-sensor geometry .
Correcting this bidirectional reflectance effect eliminated seasonal changes in surface reflectance , consistent with independent lidar observations and model simulations with unchanging canopy properties .
The stability of Amazon forest structure and reflectance over seasonal timescales challenges the paradigm of light-limited net primary production in Amazon forests and enhanced forest growth during drought conditions .
Correcting optical remote sensing data for artefacts of sun-sensor geometry is essential to isolate the response of global vegetation to seasonal and interannual climate variability .

[1233] Pathways of human development and carbon emissions embodied in trade

It has long been assumed that human development depends on economic growth , that national economic expansion in turn requires greater energy use and , therefore , increased greenhouse-gas emissions .
These interdependences are the topic of current research .
Scarcely explored , however , is the impact of international trade : although some nations develop socio-economically and import high-embodied-carbon products , it is likely that carbon-exporting countries gain significantly fewer benefits .
Here , we use new consumption-based measures of national carbon emissions to explore how the relationship between human development and carbon changes when we adjust national emission rates for trade .
Without such adjustment of emissions , some nations seem to be getting far better development ` bang ' for the carbon ` buck ' than others , who are showing scant gains for disproportionate shares of global emissions .
Adjusting for the transfer of emissions through trade explains many of these outliers , but shows that further socio-economic benefits are accruing to carbon-importing rather than carbon-exporting countries .
We also find that high life expectancies are compatible with low carbon emissions but high incomes are not .
Finally , we see that , despite strong international trends , there is no deterministic industrial development trajectory : there is great diversity in pathways , and national histories do not necessarily follow the global trends .

[1234] Persistent non-solar forcing of Holocene storm dynamics in coastal sedimentary archives

Considerable climatic variability on decadal to millennial timescales has been documented for the past 11,500 years of interglacial climate .
This variability has been particularly pronounced at a frequency of about 1,500 years , with repeated cold intervals in the North Atlantic .
However , there is growing evidence that these oscillations originate from a cluster of different spectral signatures , ranging from a 2,500-year cycle throughout the period to a 1,000-year cycle during the earliest millennia .
Here we present a reappraisal of high-energy estuarine and coastal sedimentary records from the southern coast of the English Channel , and report evidence for five distinct periods during the Holocene when storminess was enhanced during the past 6,500 years .
We find that high storm activity occurred periodically with a frequency of about 1,500 years , closely related to cold and windy periods diagnosed earlier .
We show that millennial-scale storm extremes in northern Europe are phase-locked with the period of internal ocean variability in the North Atlantic of about 1,500 years .
However , no consistent correlation emerges between spectral maxima in records of storminess and solar irradiation .
We conclude that solar activity changes are unlikely to be a primary forcing mechanism of millennial-scale variability in storminess .

[1235] Timing of abrupt climate change at the end of the Younger Dryas interval from thermally fractionated gases in polar ice

Rapid temperature change fractionates gas isotopes in unconsolidated snow , producing a signal that is preserved in trapped air bubbles as the snow forms ice .
The fractionation of nitrogen and argon isotopes at the end of the Younger Dryas cold interval , recorded in Greenland ice , demonstrates that warming at this time was abrupt .
This warming coincides with the onset of a prominent rise in atmospheric methane concentration , indicating that the climate change was synchronous ( within a few decades ) over a region of at least hemispheric extent , and providing constraints on previously proposed mechanisms of climate change at this time .
The depth of the nitrogen-isotope signal relative to the depth of the climate change recorded in the ice matrix indicates that , during the Younger Dryas , the summit of Greenland was 15 + / - 3 degreesC colder than today .

[1236] Environmental modification and niche construction : developing O2 gradients drive the evolution of the Wrinkly Spreader

The evolutionary success of the novel Wrinkly Spreader ( WS ) genotypes in diversifying Pseudomonas fluorescens SBW25 populations in static liquid microcosms has been attributed to the greater availability of O2 at the air-liquid ( A-L ) interface where the WS produces a physically cohesive-class biofilm .
However , the importance of O2 gradients in SBW25 adaptation has never been examined .
We have explicitly tested the role of O2 in evolving populations using microsensor profiling and experiments conducted under high and low O2 conditions .
Initial colonists of static microcosms were found to establish O2 gradients before significant population growth had occurred , converting a previously homogenous environment into one containing a resource continuum with high and low O2 regions .
These gradients were found to persist for long periods by which time significant numbers of WS had appeared colonising the high O2 niches .
Growth was O2 limited in static microcosms , but high O2 conditions like those found near the A-L interface supported greater growth and favoured the emergence of WS-like genotypes .
A fitness advantage to biofilm formation was seen under high but not low O2 conditions , suggesting that the cost of biofilm production could only be offset when O2 levels above the A-L interface were high .
Profiling of mature WS biofilms showed that they also contained high and low O2 regions .
Niches within these may support further diversification and succession of the developing biofilm population .
O2 availability has been found to be a major factor underlying the evolutionary success of the WS genotype in static microcosms and illustrates the importance of this resource continuum in microbial diversification and adaptation .

[1237] Climate-change impact on the 20th-century relationship between the Southern Annular Mode and global mean temperature

The positive phase of the El Nino-Southern Oscillation ( ENSO ) increases global mean temperature , and contributes to a negative phase of the Southern Annular Mode ( SAM ) , the dominant mode of climate variability in the Southern Hemisphere .
This interannual relationship of a high global mean temperature associated with a negative SAM , however , is opposite to the relationship between their trends under greenhouse warming .
We show that over much of the 20th century this relationship undergoes multidecadal fluctuations depending on the intensity of ENSO .
During the period 1925-1955 , subdued ENSO activities weakened the relationship .
However , a similar weakening has occurred since the late 1970s despite the strong ENSO .
We demonstrate that this recent weakening is induced by climate change in the Southern Hemisphere .
Our result highlights a rare situation in which climate change signals emerge against an opposing property of interannual variability , underscoring the robustness of the recent climate change .

[1238] Seasonal and interannual variability of the marine bacterioplankton community throughout the water column over ten years

Microbial activities that affect global oceanographic and atmospheric processes happen throughout the water column , yet the long-term ecological dynamics of microbes have been studied largely in the euphotic zone and adjacent seasonally mixed depths .
We investigated temporal patterns in the community structure of free-living bacteria , by sampling approximately monthly from 5 m , the deep chlorophyll maximum ( ~ 15-40 m ) , 150 , 500 and 890 m , in San Pedro Channel ( maximum depth 900 m , hypoxic below ~ 500 m ) , off the coast of Southern California .
Community structure and biodiversity ( inverse Simpson index ) showed seasonal patterns near the surface and bottom of the water column , but not at intermediate depths .
Inverse Simpson 's index was highest in the winter in surface waters and in the spring at 890 m , and varied interannually at all depths .
Biodiversity appeared to be driven partially by exchange of microbes between depths and was highest when communities were changing slowly over time .
Meanwhile , communities from the surface through 500 m varied interannually .
After accounting for seasonality , several environmental parameters co-varied with community structure at the surface and 890 m , but not at the intermediate depths .
Abundant and seasonally variable groups included , at 890 m , Nitrospina , Flavobacteria and Marine Group A. Seasonality at 890 m is likely driven by variability in sinking particles , which originate in surface waters , pass transiently through the middle water column and accumulate on the seafloor where they alter the chemical environment .
Seasonal subeuphotic groups are likely those whose ecology is strongly influenced by these particles .
This surface-to-bottom , decade-long , study identifies seasonality and interannual variability not only of overall community structure , but also of numerous taxonomic groups and near-species level operational taxonomic units .

[1239] Can marine bacteria be recruited from freshwater sources and the air ?

There is now clear evidence that microorganisms present biogeographic patterns , yet the processes that create and maintain them are still not well understood .
In particular , the contribution of dispersal and its exact impact on local community composition is still unclear .
For example , dispersing cells may not thrive in recipient environments , but may still remain part of the local species pool .
Here , we experimentally tested if marine bacteria can be retrieved from freshwater communities ( pelagic and sediment ) and the atmosphere by exposing bacteria from three lakes , that differ in their proximity to the Norwegian Sea , to marine conditions .
We found that the percentage of freshwater taxa decreased with increasing salinities , whereas marine taxa increased along the same gradient .
Our results further showed that this increase was stronger for lake and sediment compared with air communities .
Further , significant increases in the average niche breadth of taxa were found for all sources , and in particular lake water and sediment communities , at higher salinities .
Our results therefore suggests that marine taxa can readily grow from freshwater sources , but that the response was likely driven by the growth of habitat generalists that are typically found in marine systems .
Finally , there was a greater proportion of marine taxa found in communities originating from the lake closest to the Norwegian Sea .
In summary , this study shows that the interplay between bacterial dispersal limitation and dispersal from internal and external sources may have an important role for community recovery in response to environmental change .

[1240] Heterologous viral expression systems in fosmid vectors increase the functional analysis potential of metagenomic libraries

The extraordinary potential of metagenomic functional analyses to identify activities of interest present in uncultured microorganisms has been limited by reduced gene expression in surrogate hosts .
We have developed vectors and specialized E. coli strains as improved metagenomic DNA heterologous expression systems , taking advantage of viral components that prevent transcription termination at metagenomic terminators .
One of the systems uses the phage T7 RNA-polymerase to drive metagenomic gene expression , while the other approach uses the lambda phage transcription anti-termination protein N to limit transcription termination .
A metagenomic library was constructed and functionally screened to identify genes conferring carbenicillin resistance to E. coli .
The use of these enhanced expression systems resulted in a 6-fold increase in the frequency of carbenicillin resistant clones .
Subcloning and sequence analysis showed that , besides beta-lactamases , efflux pumps are not only able contribute to carbenicillin resistance but may in fact be sufficient by themselves to convey carbenicillin resistance .

[1241] Diversifying evolution of competitiveness

In many species , individuals express phenotypic characteristics that enhance their competitiveness , that is , the ability to acquire resources in competition with others .
Moreover , the degree of competitiveness varies considerably across individuals and in time .
By means of an evolutionary model , we provide an explanation for this finding .
We make the assumption that investment into competitiveness enhances the probability to acquire a high-quality resource , but at the same time reduces the ability of exploiting acquired resources with maximal efficiency .
The model reveals that under a broad range of conditions competitiveness either converges to a polymorphic state , where individuals differing in competitive ability stably coexist , or is subject to perpetual transitions between periods of high and low competitiveness .
The dynamics becomes even more complex if females can evolve preferences for ( or against ) competitive males .
In extreme cases , such preferences can even drive the population to extinction .

[1242] Distinguishing between yield advances and yield plateaus in historical crop production trends

Food security and land required for food production largely depend on rate of yield gain of major cereal crops .
Previous projections of food security are often more optimistic than what historical yield trends would support .
Many econometric projections of future food production assume compound rates of yield gain , which are not consistent with historical yield trends .
Here we provide a framework to characterize past yield trends and show that linear trajectories adequately describe past yield trends , which means the relative rate of gain decreases over time .
Furthermore , there is evidence of yield plateaus or abrupt decreases in rate of yield gain , including rice in eastern Asia and wheat in northwest Europe , which account for 31 % of total global rice , wheat and maize production .
Estimating future food production capacity would benefit from an analysis of past crop yield trends based on a robust statistical analysis framework that evaluates historical yield trajectories and plateaus .

[1243] Reassessment of ice-age cooling of the tropical ocean and atmosphere

The CLIMAP project 's reconstruction of past sea surface temperature inferred limited ice-age cooling in the tropical oceans .
This conclusion has been controversial , however , because of the greater cooling indicated by other terrestrial and ocean proxy data .
A new faunal sea surface temperature reconstruction , calibrated using the variation of foraminiferal species through time , better represents ice-age faunal assemblages and so reveals greater cooling than CLIMAP in the equatorial current systems of the eastern Pacific and tropical Atlantic oceans .
Here we explore the climatic implications of this revised sea surface temperature field for the Last Glacial Maximum using an atmospheric general circulation model .
Relative to model results obtained using CLIMAP sea surface temperatures , the cooler equatorial oceans modify seasonal air temperatures by 1-2 degreesC or more across parts of South America , Africa and southeast Asia and cause attendant changes in regional moisture patterns .
In our simulation of the Last Glacial Maximum , the Amazon lowlands , for example , are cooler and drier , whereas the Andean highlands are cooler and wetter than the control simulation .
Our results may help to resolve some of the apparent disagreements between oceanic and continental proxy climate data .
Moreover , they suggest a wind-related mechanism for enhancing the export of water vapour from the Atlantic to the Indo-Pacific oceans , which may link variations in deep-water production and high-latitude climate changes to equatorial sea surface temperatures .

[1244] Seasonal sea surface cooling in the equatorial Pacific cold tongue controlled by ocean mixing

Sea surface temperature ( SST ) is a critical control on the atmosphere , and numerical models of atmosphere-ocean circulation emphasize its accurate prediction .
Yet many models demonstrate large , systematic biases in simulated SST in the equatorial ` cold tongues ' ( expansive regions of net heat uptake from the atmosphere ) of the Atlantic and Pacific oceans , particularly with regard to a central but little-understood feature of tropical oceans : a strong seasonal cycle .
The biases may be related to the inability of models to constrain turbulent mixing realistically , given that turbulent mixing , combined with seasonal variations in atmospheric heating , determines SST .
In temperate oceans , the seasonal SST cycle is clearly related to varying solar heating ; in the tropics , however , SSTs vary seasonally in the absence of similar variations in solar inputs .
Turbulent mixing has long been a likely explanation , but firm , long-term observational evidence has been absent .
Here we show the existence of a distinctive seasonal cycle of subsurface cooling via mixing in the equatorial Pacific cold tongue , using multi-year measurements of turbulence in the ocean .
In boreal spring , SST rises by 2 kelvin when heating of the upper ocean by the atmosphere exceeds cooling by mixing from below .
In boreal summer , SST decreases because cooling from below exceeds heating from above .
When the effects of lateral advection are considered , the magnitude of summer cooling via mixing ( 4 kelvin per month ) is equivalent to that required to counter the heating terms .
These results provide quantitative assessment of how mixing varies on timescales longer than a few weeks , clearly showing its controlling influence on seasonal cooling of SST in a critical oceanic regime .

[1245] Ongoing climate change following a complete cessation of carbon dioxide emissions

A threat of irreversible damage should prompt action to mitigate climate change , according to the United Nations Framework Convention on Climate Change , which serves as a basis for international climate policy .
CO2-induced climate change is known to be largely irreversible on timescales of many centuries , as simulated global mean temperature remains approximately constant for such periods following a complete cessation of carbon dioxide emissions while thermosteric sea level continues to rise .
Here we use simulations with the Canadian Earth System Model to show that ongoing regional changes in temperature and precipitation are significant , following a complete cessation of carbon dioxide emissions in 2100 , despite almost constant global mean temperatures .
Moreover , our projections show warming at intermediate depths in the Southern Ocean that is many times larger by the year 3000 than that realized in 2100 .
We suggest that a warming of the intermediate-depth ocean around Antarctica at the scale simulated for the year 3000 could lead to the collapse of the West Antarctic Ice Sheet , which would be associated with a rise in sea level of several metres .

[1246] Inference of interactions in cyanobacterial-heterotrophic co-cultures via transcriptome sequencing

We used deep sequencing technology to identify transcriptional adaptation of the euryhaline unicellular cyanobacterium Synechococcus sp .
PCC 7002 and the marine facultative aerobe Shewanella putrefaciens W3-18-1 to growth in a co-culture and infer the effect of carbon flux distributions on photoautotroph-heterotroph interactions .
The overall transcriptome response of both organisms to co-cultivation was shaped by their respective physiologies and growth constraints .
Carbon limitation resulted in the expansion of metabolic capacities , which was manifested through the transcriptional upregulation of transport and catabolic pathways .
Although growth coupling occurred via lactate oxidation or secretion of photosynthetically fixed carbon , there was evidence of specific metabolic interactions between the two organisms .
These hypothesized interactions were inferred from the excretion of specific amino acids ( for example , alanine and methionine ) by the cyanobacterium , which correlated with the downregulation of the corresponding biosynthetic machinery in Shewanella W3-18-1 .
In addition , the broad and consistent decrease of mRNA levels for many Fe-regulated Synechococcus 7002 genes during co-cultivation may indicate increased Fe availability as well as more facile and energy-efficient mechanisms for Fe acquisition by the cyanobacterium .
Furthermore , evidence pointed at potentially novel interactions between oxygenic photoautotrophs and heterotrophs related to the oxidative stress response as transcriptional patterns suggested that Synechococcus 7002 rather than Shewanella W3-18-1 provided scavenging functions for reactive oxygen species under co-culture conditions .
This study provides an initial insight into the complexity of photoautotrophic-heterotrophic interactions and brings new perspectives of their role in the robustness and stability of the association .

[1247] Temporal evolution of methane cycling and phylogenetic diversity of archaea in sediments from a deep-sea whale-fall in Monterey Canyon , California

Whale-falls represent localized areas of extreme organic enrichment in an otherwise oligotrophic deep-sea environment .
Anaerobic remineralization within these habitats is typically portrayed as sulfidogenic ; however , we demonstrate that these systems are also favorable for diverse methane-producing archaeal assemblages , representing up to 40 % of total cell counts .
Chemical analyses revealed elevated methane and depleted sulfate concentrations in sediments under the whale-fall , as compared to surrounding sediments .
Carbon was enriched ( up to 3.5 % ) in whale-fall sediments , as well as the surrounding sea floor to at least 10 m , forming a ` bulls eye ' of elevated carbon .
The diversity of sedimentary archaea associated with the 2893 m whale-fall in Monterey Canyon ( California ) varied both spatially and temporally .
16S rRNA diversity , determined by both sequencing and terminal restriction fragment length polymorphism analysis , as well as quantitative PCR of the methyl-coenzyme M reductase gene , revealed that methanogens , including members of the Methanomicrobiales and Methanosarcinales , were the dominant archaea ( up to 98 % ) in sediments immediately beneath the whale-fall .
Temporal changes in this archaeal community included the early establishment of methylotrophic methanogens followed by development of methanogens thought to be hydrogenotrophic , as well as members related to the newly described methanotrophic lineage , ANME-3 .
In comparison , archaeal assemblages in ` reference ' sediments collected 10 m from the whale-fall primarily consisted of Crenarchaeota affiliated with marine group I and marine benthic group B. Overall , these results indicate that whale-falls can favor the establishment of metabolically and phylogenetically diverse methanogen assemblages , resulting in an active near-seafloor methane cycle in the deep sea .

[1248] Ice plug prevents irreversible discharge from East Antarctica

Changes in ice discharge from Antarctica constitute the largest uncertainty in future sea-level projections , mainly because of the unknown response of its marine basins .
Most of West Antarctica 's marine ice sheet lies on an inland-sloping bed and is thereby prone to a marine ice sheet instability .
A similar topographic configuration is found in large parts of East Antarctica , which holds marine ice equivalent to 19 m of global sea-level rise , that is , more than five times that of West Antarctica .
Within East Antarctica , the Wilkes Basin holds the largest volume of marine ice that is fully connected by subglacial troughs .
This ice body was significantly reduced during the Pliocene epoch .
Strong melting underneath adjacent ice shelves with similar bathymetry indicates the ice sheet 's sensitivity to climatic perturbations .
The stability of the Wilkes marine ice sheet has not been the subject of any comprehensive assessment of future sea level .
Using recently improved topographic data in combination with ice-dynamic simulations , we show here that the removal of a specific coastal ice volume equivalent to less than 80 mm of global sea-level rise at the margin of the Wilkes Basin destabilizes the regional ice flow and leads to a self-sustained discharge of the entire basin and a global sea-level rise of 3-4 m .
Our results are robust with respect to variation in ice parameters , forcing details and model resolution as well as increased surface mass balance , indicating that East Antarctica may become a large contributor to future sea-level rise on timescales beyond a century .

[1249] Stoichiometric control of organic carbon-nitrate relationships from soils to the sea

The production of artificial fertilizers , fossil fuel use and leguminous agriculture worldwide has increased the amount of reactive nitrogen in the natural environment by an order of magnitude since the Industrial Revolution .
This reorganization of the nitrogen cycle has led to an increase in food production , but increasingly causes a number of environmental problems .
One such problem is the accumulation of nitrate in both freshwater and coastal marine ecosystems .
Here we establish that ecosystem nitrate accrual exhibits consistent and negative nonlinear correlations with organic carbon availability along a hydrologic continuum from soils , through freshwater systems and coastal margins , to the open ocean .
The trend also prevails in ecosystems subject to substantial human alteration .
Across this diversity of environments , we find evidence that resource stoichiometry ( organic carbon : nitrate ) strongly influences nitrate accumulation by regulating a suite of microbial processes that couple dissolved organic carbon and nitrate cycling .
With the help of a meta-analysis we show that heterotrophic microbes maintain low nitrate concentrations when organic carbon : nitrate ratios match the stoichiometric demands of microbial anabolism .
When resource ratios drop below the minimum carbon : nitrogen ratio of microbial biomass , however , the onset of carbon limitation appears to drive rapid nitrate accrual , which may then be further enhanced by nitrification .
At low organic carbon : nitrate ratios , denitrification appears to constrain the extent of nitrate accretion , once organic carbon and nitrate availability approach the 1:1 stoichiometry of this catabolic process .
Collectively , these microbial processes express themselves on local to global scales by restricting the threshold ratios underlying nitrate accrual to a constrained stoichiometric window .
Our findings indicate that ecological stoichiometry can help explain the fate of nitrate across disparate environments and in the face of human disturbance .

[1250] Microbial diversity of biofilm communities in microniches associated with the didemnid ascidian Lissoclinum patella

We assessed the microbial diversity and microenvironmental niche characteristics in the didemnid ascidian Lissoclinum patella using 16S rRNA gene sequencing , microsensor and imaging techniques .
L. patella harbors three distinct microbial communities spatially separated by few millimeters of tunic tissue : ( i ) a biofilm on its upper surface exposed to high irradiance and O2 levels , ( ii ) a cloacal cavity dominated by the prochlorophyte Prochloron spp .
characterized by strong depletion of visible light and a dynamic chemical microenvironment ranging from hyperoxia in light to anoxia in darkness and ( iii ) a biofilm covering the underside of the animal , where light is depleted of visible wavelengths and enriched in near-infrared radiation ( NIR ) .
Variable chlorophyll fluorescence imaging demonstrated photosynthetic activity , and hyperspectral imaging revealed a diversity of photopigments in all microhabitats .
Amplicon sequencing revealed the dominance of cyanobacteria in all three layers .
Sequences representing the chlorophyll d containing cyanobacterium Acaryochloris marina and anoxygenic phototrophs were abundant on the underside of the ascidian in shallow waters but declined in deeper waters .
This depth dependency was supported by a negative correlation between A. marina abundance and collection depth , explained by the increased attenuation of NIR as a function of water depth .
The combination of microenvironmental analysis and fine-scale sampling techniques used in this investigation gives valuable first insights into the distribution , abundance and diversity of bacterial communities associated with tropical ascidians .
In particular , we show that microenvironments and microbial diversity can vary significantly over scales of a few millimeters in such habitats ; which is information easily lost by bulk sampling .

[1251] Relationship between bacterial diversity and function under biotic control : the soil pesticide degraders as a case study

In soil , the way biotic parameters impact the relationship between bacterial diversity and function is still unknown .
To understand these interactions better , we used RNA-based stable-isotope probing to study the diversity of active atrazine-degrading bacteria in relation to atrazine degradation and to explore the impact of earthworm-soil engineering with respect to this relationship .
Bulk soil , burrow linings and earthworm casts were incubated with 13C-atrazine .
The pollutant degradation was quantified by liquid chromatography-mass spectrometry for 8 days , whereas active atrazine degraders were identified at 2 and 8 days by sequencing the 16S ribosomal RNA in the 13C-RNA fractions from the three soil microsites .
An original diversity of atrazine degraders was found .
Earthworm soil engineering greatly modified the taxonomic composition of atrazine degraders with dominance of alpha - , beta - and gamma-proteobacteria in burrow linings and of Actinobacteria in casts .
Earthworm soil bioturbation increased the gamma-diversity of atrazine degraders over the soil microsites generated .
Atrazine degradation was enhanced in burrow linings in which primary atrazine degraders , closely related to Pelomonas aquatica , were detected only 2 days after atrazine addition .
Atrazine degradation efficiency was not linearly related to the species richness of degraders but likely relied on keystone species .
By enhancing soil heterogeneity , earthworms sustained high phylogenetic bacterial diversity and exerted a biotic control on the bacterial diversity-function relationships .
Our findings call for future investigations to assess the ecological significance of biotic controls on the relationships between diversity and function on ecosystem properties and services ( for example , soil detoxification ) at larger scales .

[1252] Made-to-order metal-organic frameworks for trace carbon dioxide removal and air capture

Direct air capture is regarded as a plausible alternate approach that , if economically practical , can mitigate the increasing carbon dioxide emissions associated with two of the main carbon polluting sources , namely stationary power plants and transportation .
Here we show that metal-organic framework crystal chemistry permits the construction of an isostructural metal-organic framework ( SIFSIX-3-Cu ) based on pyrazine/copper ( II ) two-dimensional periodic 44 square grids pillared by silicon hexafluoride anions and thus allows further contraction of the pore system to 3.5 versus 3.84 A for the parent zinc ( II ) derivative .
This enhances the adsorption energetics and subsequently displays carbon dioxide uptake and selectivity at very low partial pressures relevant to air capture and trace carbon dioxide removal .
The resultant SIFSIX-3-Cu exhibits uniformly distributed adsorption energetics and offers enhanced carbon dioxide physical adsorption properties , uptake and selectivity in highly diluted gas streams , a performance , to the best of our knowledge , unachievable with other classes of porous materials .

[1253] Iron-reducing bacteria accumulate ferric oxyhydroxide nanoparticle aggregates that may support planktonic growth

Iron-reducing bacteria ( FeRB ) play key roles in anaerobic metal and carbon cycling and carry out biogeochemical transformations that can be harnessed for environmental bioremediation .
A subset of FeRB require direct contact with Fe ( III ) - bearing minerals for dissimilatory growth , yet these bacteria must move between mineral particles .
Furthermore , they proliferate in planktonic consortia during biostimulation experiments .
Thus , a key question is how such organisms can sustain growth under these conditions .
Here we characterized planktonic microbial communities sampled from an aquifer in Rifle , Colorado , USA , close to the peak of iron reduction following in situ acetate amendment .
Samples were cryo-plunged on site and subsequently examined using correlated two - and three-dimensional cryogenic transmission electron microscopy ( cryo-TEM ) and scanning transmission X-ray microscopy ( STXM ) .
The outer membranes of most cells were decorated with aggregates up to 150 nm in diameter composed of ~ 3 nm wide amorphous , Fe-rich nanoparticles .
Fluorescent in situ hybridization of lineage-specific probes applied to rRNA of cells subsequently imaged via cryo-TEM identified Geobacter spp. , a well-studied group of FeRB .
STXM results at the Fe L2 ,3 absorption edges indicate that nanoparticle aggregates contain a variable mixture of Fe ( II ) - Fe ( III ) , and are generally enriched in Fe ( III ) .
Geobacter bemidjiensis cultivated anaerobically in the laboratory on acetate and hydrous ferric oxyhydroxides also accumulated mixed-valence nanoparticle aggregates .
In field-collected samples , FeRB with a wide variety of morphologies were associated with nano-aggregates , indicating that cell surface Fe ( III ) accumulation may be a general mechanism by which FeRB can grow while in planktonic suspension .

[1254] Transitions in bacterial communities along the 2000 km salinity gradient of the Baltic Sea

Salinity is a major factor controlling the distribution of biota in aquatic systems , and most aquatic multicellular organisms are either adapted to life in saltwater or freshwater conditions .
Consequently , the saltwater-freshwater mixing zones in coastal or estuarine areas are characterized by limited faunal and floral diversity .
Although changes in diversity and decline in species richness in brackish waters is well documented in aquatic ecology , it is unknown to what extent this applies to bacterial communities .
Here , we report a first detailed bacterial inventory from vertical profiles of 60 sampling stations distributed along the salinity gradient of the Baltic Sea , one of world 's largest brackish water environments , generated using 454 pyrosequencing of partial ( 400 bp ) 16S rRNA genes .
Within the salinity gradient , bacterial community composition altered at broad and finer-scale phylogenetic levels .
Analogous to faunal communities within brackish conditions , we identified a bacterial brackish water community comprising a diverse combination of freshwater and marine groups , along with populations unique to this environment .
As water residence times in the Baltic Sea exceed 3 years , the observed bacterial community can not be the result of mixing of fresh water and saltwater , but our study represents the first detailed description of an autochthonous brackish microbiome .
In contrast to the decline in the diversity of multicellular organisms , reduced bacterial diversity at brackish conditions could not be established .
It is possible that the rapid adaptation rate of bacteria has enabled a variety of lineages to fill what for higher organisms remains a challenging and relatively unoccupied ecological niche .

[1255] Artificial Weathering as a Function of CO2 Injection in Pahang Sandstone Malaysia : Investigation of Dissolution Rate in Surficial Condition

Formation of carbonate minerals by CO2 sequestration is a potential means to reduce atmospheric CO2 emissions .
Vast amount of alkaline and alkali earth metals exist in silicate minerals that may be carbonated .
Laboratory experiments carried out to study the dissolution rate in Pahang Sandstone , Malaysia , by CO2 injection at different flow rate in surficial condition .
X-ray Powder Diffraction ( XRD ) , Scanning Electron Microscope ( SEM ) with Energy Dispersive X-ray Spectroscopy ( EDX ) , Atomic Absorption Spectroscopy ( AAS ) and weight losses measurement were performed to analyze the solid and liquid phase before and after the reaction process .
The weight changes and mineral dissolution caused by CO2 injection for two hours CO2 bubbling and one week ' aging were 0.28 % and 18.74 % , respectively .
The average variation of concentrations of alkaline earth metals in solution varied from 22.62 % for Ca2 + to 17.42 % for Mg2 + , with in between 16.18 % observed for the alkali earth metal , potassium .
Analysis of variance ( ANOVA ) test is performed to determine significant differences of the element concentration , including Ca , Mg , and K , before and after the reaction experiment .
Such changes show that the deposition of alkali and alkaline earth metals and the dissolution of required elements in sandstone samples are enhanced by CO2 injection .

[1256] Vulnerability to the mortality effects of warm temperature in the districts of England and Wales

Warm temperatures adversely affect disease occurrence and death , in extreme conditions as well as when the temperature changes are more modest .
Therefore climate change , which is expected to affect both average temperatures and temperature variability , is likely to impact health even in temperate climates .
Climate change risk assessment is enriched if there is information on vulnerability and resilience to effects of temperature .
Some studies have analysed socio-demographic characteristics that make individuals vulnerable to adverse effects of temperature .
Less is known about community-level vulnerability .
We used geo-coded mortality and environmental data and Bayesian spatial methods to conduct a national small-area analysis of the mortality effects of warm temperature for all 376 districts in England and Wales .
In the most vulnerable districts , those in London and south/southeast England , odds of dying from cardiorespiratory causes increased by more than 10 % for 1 degreesC warmer temperature , compared with virtually no effect in the most resilient districts , which were in the far north .
A 2 degreesC warmer summer may result in 1,552 ( 95 % credible interval 1,307-1 ,762 ) additional deaths , about one-half of which would occur in 95 districts .
The findings enable risk and adaptation analyses to incorporate local vulnerability to warm temperature and to quantify inequality in its effects .

[1257] Spatial vegetation patterns and imminent desertification in Mediterranean arid ecosystems

Humans and climate affect ecosystems and their services , which may involve continuous and discontinuous transitions from one stable state to another .
Discontinuous transitions are abrupt , irreversible and among the most catastrophic changes of ecosystems identified .
For terrestrial ecosystems , it has been hypothesized that vegetation patchiness could be used as a signature of imminent transitions .
Here , we analyse how vegetation patchiness changes in arid ecosystems with different grazing pressures , using both field data and a modelling approach .
In the modelling approach , we extrapolated our analysis to even higher grazing pressures to investigate the vegetation patchiness when desertification is imminent .
In three arid Mediterranean ecosystems in Spain , Greece and Morocco , we found that the patch-size distribution of the vegetation follows a power law .
Using a stochastic cellular automaton model , we show that local positive interactions among plants can explain such power-law distributions .
Furthermore , with increasing grazing pressure , the field data revealed consistent deviations from power laws .
Increased grazing pressure leads to similar deviations in the model .
When grazing was further increased in the model , we found that these deviations always and only occurred close to transition to desert , independent of the type of transition , and regardless of the vegetation cover .
Therefore , we propose that patch-size distributions may be a warning signal for the onset of desertification .

[1258] Groundwater reorganization in the Floridan aquifer following Holocene sea-level rise

Sea-level fluctuations , particularly those associated with glacial-interglacial cycles , can have profound impacts on the flow and circulation of coastal groundwater : the water found at present in many coastal aquifers may have been recharged during the last glacial period , when sea level was over 100 m lower than present , and thus is not in equilibrium with present recharge conditions .
Here we show that the geochemistry of the groundwater found in the Floridan Aquifer System in south Florida is best explained by a reorganization of groundwater flow following the sea-level rise at the end of the Last Glacial Maximum approximately 18,000 years ago .
We find that the geochemistry of the fresh water found in the upper aquifers at present is consistent with recharge from meteoric water during the last glacial period .
The lower aquifer , however , consists of post-sea-level-rise salt water that is most similar to that of the Straits of Florida , though with some dilution from the residual fresh water from the last glacial period circulation .
We therefore suggest that during the last glacial period , the entire Floridan Aquifer System was recharged with meteoric waters .
After sea level rose , the increased hydraulic head reduced the velocity of the groundwater flow .
This velocity reduction trapped the fresh water in the upper aquifers and initiated saltwater circulation in the lower aquifer .

[1259] Natural variability , radiative forcing and climate response in the recent hiatus reconciled

Global mean surface warming over the past 15 years or so has been less than in earlier decades and than simulated by most climate models .
Natural variability , a reduced radiative forcing , a smaller warming response to atmospheric carbon dioxide concentrations and coverage bias in the observations have been identified as potential causes .
However , the explanations of the so-called ` warming hiatus ' remain fragmented and the implications for long-term temperature projections are unclear .
Here we estimate the contribution of internal variability associated with the El Nino/Southern Oscillation ( ENSO ) using segments of unforced climate model control simulations that match the observed climate variability .
We find that ENSO variability analogous to that between 1997 or 1998 and 2012 leads to a cooling trend of about -0.06 degreesC .
In addition , updated solar and stratospheric aerosol forcings from observations explain a cooling trend of similar magnitude ( -0.07 degreesC ) .
Accounting for these adjusted trends we show that a climate model of reduced complexity with a transient climate response of about 1.8 degreesC is consistent with the temperature record of the past 15 years , as is the ensemble mean of the models in the Coupled Model Intercomparison Project Phase 5 ( CMIP5 ) .
We conclude that there is little evidence for a systematic overestimation of the temperature response to increasing atmospheric CO2 concentrations in the CMIP5 ensemble .

[1260] Coccolithophore calcification response to past ocean acidification and climate change

Anthropogenic carbon dioxide emissions are forcing rapid ocean chemistry changes and causing ocean acidification ( OA ) , which is of particular significance for calcifying organisms , including planktonic coccolithophores .
Detailed analysis of coccolithophore skeletons enables comparison of calcite production in modern and fossil cells in order to investigate biomineralization response of ancient coccolithophores to climate change .
Here we show that the two dominant coccolithophore taxa across the Paleocene-Eocene Thermal Maximum ( PETM ) OA global warming event ( ~ 56 million years ago ) exhibited morphological response to environmental change and both showed reduced calcification rates .
However , only Coccolithus pelagicus exhibits a transient thinning of coccoliths , immediately before the PETM , that may have been OA-induced .
Changing coccolith thickness may affect calcite production more significantly in the dominant modern species Emiliania huxleyi , but , overall , these PETM records indicate that the environmental factors that govern taxonomic composition and growth rate will most strongly influence coccolithophore calcification response to anthropogenic change .

[1261] Climate change as an unexpected co-factor promoting coral eating seastar ( Acanthaster planci ) outbreaks

Coral reefs face a crisis due to local and global anthropogenic stressors .
A large proportion of the ~ 50 % coral loss on the Great Barrier Reef has been attributed to outbreaks of the crown-of-thorns-seastar ( COTS ) .
A widely assumed cause of primary COTS outbreaks is increased larval survivorship due to higher food availability , linked with anthropogenic runoff .
Our experiment using a range of algal food concentrations at three temperatures representing present day average and predicted future increases , demonstrated a strong influence of food concentration on development is modulated by temperature .
A 2degreesC increase in temperature led to a 4.2-4 .9 times ( at Day 10 ) or 1.2-1 .8 times ( Day 17 ) increase in late development larvae .
A model indicated that food was the main driver , but that temperature was an important modulator of development .
For instance , at 5000 cells ml-1 food , a 2degreesC increase may shorten developmental time by 30 % and may increase the probability of survival by 240 % .
The main contribution of temperature is to ` push ' well-fed larvae faster to settlement .
We conclude that warmer sea temperature is an important co-factor promoting COTS outbreaks .

[1262] Climatic and biotic thresholds of coral-reef shutdown

Climate change is now the leading cause of coral-reef degradation and is altering the adaptive landscape of coral populations .
Increasing sea temperatures and declining carbonate saturation states are inhibiting short-term rates of coral calcification , carbonate precipitation and submarine cementation .
A critical challenge to coral-reef conservation is understanding the mechanisms by which environmental perturbations scale up to influence long-term rates of reef-framework construction and ecosystem function .
Here we reconstruct climatic and oceanographic variability using corals sampled from a 6,750-year core from Pacific Panama .
Simultaneous reconstructions of coral palaeophysiology and reef accretion allowed us to identify the climatic and biotic thresholds associated with a 2,500-year hiatus in vertical accretion beginning ~ 4,100 years ago .
Stronger upwelling , cooler sea temperatures and greater precipitation -- indicators of La Nina-like conditions -- were closely associated with abrupt reef shutdown .
The physiological condition of the corals deteriorated at the onset of the hiatus , corroborating theoretical predictions that the tipping points of radical ecosystem transitions should be manifested sublethally in the biotic constituents .
Future climate change could cause similar threshold behaviours , leading to another shutdown in reef development in the tropical eastern Pacific .

[1263] Phylogenetic constraints on ecosystem functioning

There is consensus that biodiversity losses will result in declining ecosystem functioning if species have different functional traits .
Phylogenetic diversity has recently been suggested as a predictor of ecosystem functioning because it could approximate the functional complementarity among species .
Here we describe an experiment that takes advantage of the rapid evolutionary response of bacteria to disentangle the role of phylogenetic and species diversity .
We impose a strong selection regime on marine bacterial lineages and assemble the ancestral and evolved lines in microcosms of varying lineage and phylogenetic diversity .
We find that the relationship between phylogenetic diversity and productivity is strong for the ancestral lineages but brakes down for the evolved lineages .
Our results not only emphasize the potential of using phylogeny to evaluate ecosystem functioning , but also they warn against using phylogenetics as a proxy for functional diversity without good information on species evolutionary history .

[1264] Non-random decay of chordate characters causes bias in fossil interpretation

Exceptional preservation of soft-bodied Cambrian chordates provides our only direct information on the origin of vertebrates .
Fossil chordates from this interval offer crucial insights into how the distinctive body plan of vertebrates evolved , but reading this pre-biomineralization fossil record is fraught with difficulties , leading to controversial and contradictory interpretations .
The cause of these difficulties is taphonomic : we lack data on when and how important characters change as they decompose , resulting in a lack of constraint on anatomical interpretation and a failure to distinguish phylogenetic absence of characters from loss through decay .
Here we show , from experimental decay of amphioxus and ammocoetes , that loss of chordate characters during decay is non-random : the more phylogenetically informative are the most labile , whereas plesiomorphic characters are decay resistant .
The taphonomic loss of synapomorphies and relatively higher preservation potential of chordate plesiomorphies will thus result in bias towards wrongly placing fossils on the chordate stem .
Application of these data to Cathaymyrus ( Cambrian period of China ) and Metaspriggina ( Cambrian period of Canada ) highlights the difficulties : these fossils can not be placed reliably in the chordate or vertebrate stem because they could represent the decayed remains of any non-biomineralized , total-group chordate .
Preliminary data suggest that this decay filter also affects other groups of organisms and that ` stem-ward slippage ' may be a widespread but currently unrecognized bias in our understanding of the early evolution of a number of phyla .

[1265] Influence of high-latitude vegetation feedbacks on late Palaeozoic glacial cycles

Glaciation during the late Palaeozoic era ( 340-250 Myr ago ) is thought to have been episodic , with multiple , often regional , ice-age intervals , each lasting less than 10 million years .
Sedimentary deposits from these ice-age intervals exhibit cyclical depositional patterns , which have been attributed to orbitally driven glacial-interglacial cycles and resultant fluctuations in global sea level .
Here we use a coupled general-circulation/biome/ice-sheet model to assess the conditions necessary for glacial-interglacial fluctuations .
In our simulations , ice sheets appear at atmospheric pCO2 concentrations between 420 and 840 ppmv .
However , we are able to simulate ice-sheet fluctuations consistent with eustasy estimates and the distribution of glacial deposits only when we include vegetation feedbacks from high-latitude ecosystem changes .
We find that ice-sheet advances follow the expansion of high-latitude tundra during insolation minima , whereas ice retreat is associated with the expansion of barren land close to the edge of the ice sheets during periods of high insolation .
We are unable to simulate glacial-interglacial cycles in the absence of a dynamic vegetation component .
We therefore suggest that vegetation feedbacks driven by orbital insolation variations are a crucial element of glacial-interglacial cyclicity .

[1266] Physical processes in the tropical tropopause layer and their roles in a changing climate

Tropical climate and the composition of the global upper atmosphere are affected by the tropical tropopause layer -- the atmospheric transition zone between the well-mixed , convective troposphere ( up to altitudes of 12-14 km ) and the highly stratified stratosphere ( above about 18 km ) .
Featuring chemical and dynamical properties that are midway between those of the troposphere and stratosphere , the tropopause layer is maintained by a complex interplay between large - and small-scale circulation patterns , deep convection , clouds and radiation .
Tropospheric air enters the stratosphere primarily in the tropics .
Ozone - and aerosol-related constituents of the global stratosphere , as well as water vapour content , are therefore largely determined by the composition of the air near the tropical tropopause .
Over the past years , it has emerged that both slow ascent and rapid deep convection contribute to the composition and thermal structure of the tropical tropopause layer .
Ice formation processes at low temperatures affect the efficacy of freeze drying as air passes through the cold tropopause region .
Transport and mixing in the tropopause region has been found to be closely linked with the Asian monsoon and other tropical circulation systems .
Given these connections , climate change is expected to influence the tropopause layer , for example through enhanced large-scale upwelling of air and potential changes in tropical convection , air temperature , chemical composition and cirrus .

[1267] Rapid carbon sequestration at the termination of the Palaeocene-Eocene Thermal Maximum

The Palaeocene-Eocene Thermal Maximum ( PETM ) , an approximately 170,000-year-long period of global warming about 56 million years ago , has been attributed to the release of thousands of petagrams of reduced carbon into the ocean , atmosphere and biosphere .
However , the fate of this excess carbon at the end of the event is poorly constrained : drawdown of atmospheric carbon dioxide has been attributed to an increase in the weathering of silicates or to increased rates of organic carbon burial .
Here we develop constraints on the rate of carbon drawdown based on rates of carbon isotope change in well-dated marine and terrestrial sediments spanning the event .
We find that the rate of recovery is an order of magnitude more rapid than that expected for carbon drawdown by silicate weathering alone .
Unless existing estimates of carbon stocks and cycling during this time are widely inaccurate , our results imply that more than 2,000 Pg of carbon were sequestered as organic carbon over 30,000-40 ,000 years at the end of the PETM .
We suggest that the accelerated sequestration of organic carbon could reflect the regrowth of carbon stocks in the biosphere or shallow lithosphere that were released at the onset of the event .

[1268] Epistasis and balanced polymorphism influencing complex trait variation

Complex traits such as human disease , growth rate , or crop yield are polygenic , or determined by the contributions from numerous genes in a quantitative manner .
Although progress has been made in identifying major quantitative trait loci ( QTL ) , experimental constraints have limited our knowledge of small-effect QTL , which may be responsible for a large proportion of trait variation .
Here , we identified and dissected a one-centimorgan chromosome interval in Arabidopsis thaliana without regard to its effect on growth rate , and examined the signature of historical sequence polymorphism among Arabidopsis accessions .
We found that the interval contained two growth rate QTL within 210 kilobases .
Both QTL showed epistasis ; that is , their phenotypic effects depended on the genetic background .
This amount of complexity in such a small area suggests a highly polygenic architecture of quantitative variation , much more than previously documented .
One QTL was limited to a single gene .
The gene in question displayed a nucleotide signature indicative of balancing selection , and its phenotypic effects are reversed depending on genetic background .
If this region typifies many complex trait loci , then non-neutral epistatic polymorphism may be an important contributor to genetic variation in complex traits .

[1269] The Indonesian seas and their role in the coupled ocean-climate system

The Indonesian seas represent the only pathway that connects different ocean basins in the tropics , and therefore play a pivotal role in the coupled ocean and climate system .
Here , water flows from the Pacific to the Indian Ocean through a series of narrow straits .
The throughflow is characterized by strong velocities at water depths of about 100 m , with more minor contributions from surface flow than previously thought .
A synthesis of observational data and model simulations indicates that the temperature , salinity and velocity depth profiles of the Indonesian throughflow are determined by intense vertical mixing within the Indonesian seas .
This mixing results in the net upwelling of thermocline water in the Indonesian seas , which in turn lowers sea surface temperatures in this region by about 0.5 degreesC , with implications for precipitation and air-sea heat flux .
Moreover , the depth and velocity of the core of the Indonesian throughflow has varied with the El Nino/Southern Oscillation and Indian Ocean Dipole on interannual to decadal timescales .
Specifically , the throughflow slows and shoals during El Nino events .
Changes in the Indonesian throughflow alter surface and subsurface heat content and sea level in the Indian Ocean between 10 and 15degrees S .
We conclude that inter-ocean exchange through the Indonesian seas serves as a feedback modulating the regional precipitation and wind patterns .

[1270] Acclimation of ecosystem CO2 exchange in the Alaskan Arctic in response to decadal climate warming

Long-term sequestration of carbon in Alaskan Arctic tundra ecosystems was reversed by warming and drying of the climate in the early 1980s , resulting in substantial losses of terrestrial carbon .
But recent measurements suggest that continued warming and drying has resulted in diminished CO2 efflux , and in some cases , summer CO2 sink activity .
Here we compile summer CO2 flux data for two Arctic ecosystems from 1960 to the end of 1998 .
The results show that a return to summer sink activity has come during the warmest and driest period observed over the past four decades , and indicates a previously undemonstrated capacity for ecosystems to metabolically adjust to long-term ( decadal or longer ) changes in climate .
The mechanisms involved are likely to include changes in nutrient cycling , physiological acclimation , and population and community reorganization .
Nevertheless , despite the observed acclimation , the Arctic ecosystems studied are still annual net sources of CO2 to the atmosphere of at least 40 g C m-2 yr-1 , due to winter release of CO2 , implying that further climate change may still exacerbate CO2 emissions from Arctic ecosystems .

[1271] Scaling metabolism from organisms to ecosystems

Understanding energy and material fluxes through ecosystems is central to many questions in global change biology and ecology .
Ecosystem respiration is a critical component of the carbon cycle and might be important in regulating biosphere response to global climate change .
Here we derive a general model of ecosystem respiration based on the kinetics of metabolic reactions and the scaling of resource use by individual organisms .
The model predicts that fluxes of CO2 and energy are invariant of ecosystem biomass , but are strongly influenced by temperature , variation in cellular metabolism and rates of supply of limiting resources ( water and/or nutrients ) .
Variation in ecosystem respiration within sites , as calculated from a network of CO2 flux towers , provides robust support for the model 's predictions .
However , data indicate that variation in annual flux between sites is not strongly dependent on average site temperature or latitude .
This presents an interesting paradox with regard to the expected temperature dependence .
Nevertheless , our model provides a basis for quantitatively understanding energy and material flux between the atmosphere and biosphere .

[1272] Microbiota-liberated host sugars facilitate post-antibiotic expansion of enteric pathogens

The human intestine , colonized by a dense community of resident microbes , is a frequent target of bacterial pathogens .
Undisturbed , this intestinal microbiota provides protection from bacterial infections .
Conversely , disruption of the microbiota with oral antibiotics often precedes the emergence of several enteric pathogens .
How pathogens capitalize upon the failure of microbiota-afforded protection is largely unknown .
Here we show that two antibiotic-associated pathogens , Salmonella enterica serovar Typhimurium ( S. typhimurium ) and Clostridium difficile , use a common strategy of catabolizing microbiota-liberated mucosal carbohydrates during their expansion within the gut .
S. typhimurium accesses fucose and sialic acid within the lumen of the gut in a microbiota-dependent manner , and genetic ablation of the respective catabolic pathways reduces its competitiveness in vivo .
Similarly , C. difficile expansion is aided by microbiota-induced elevation of sialic acid levels in vivo .
Colonization of gnotobiotic mice with a sialidase-deficient mutant of Bacteroides thetaiotaomicron , a model gut symbiont , reduces free sialic acid levels resulting in C. difficile downregulating its sialic acid catabolic pathway and exhibiting impaired expansion .
These effects are reversed by exogenous dietary administration of free sialic acid .
Furthermore , antibiotic treatment of conventional mice induces a spike in free sialic acid and mutants of both Salmonella and C. difficile that are unable to catabolize sialic acid exhibit impaired expansion .
These data show that antibiotic-induced disruption of the resident microbiota and subsequent alteration in mucosal carbohydrate availability are exploited by these two distantly related enteric pathogens in a similar manner .
This insight suggests new therapeutic approaches for preventing diseases caused by antibiotic-associated pathogens .

[1273] Evidence for the functional significance of diazotroph community structure in soil

Microbial ecologists continue to seek a greater understanding of the factors that govern the ecological significance of microbial community structure .
Changes in community structure have been shown to have functional significance for processes that are mediated by a narrow spectrum of organisms , such as nitrification and denitrification , but in some cases , functional redundancy in the community seems to buffer microbial ecosystem processes .
The functional significance of microbial community structure is frequently obscured by environmental variation and is hard to detect in short-term experiments .
We examine the functional significance of free-living diazotrophs in a replicated long-term tillage experiment in which extraneous variation is minimized and N-fixation rates can be related to soil characteristics and diazotroph community structure .
Soil characteristics were found to be primarily impacted by tillage management , whereas N-fixation rates and diazotroph community structure were impacted by both biomass management practices and interactions between tillage and biomass management .
The data suggest that the variation in diazotroph community structure has a greater impact on N-fixation rates than do soil characteristics at the site .
N-fixation rates displayed a saturating response to increases in diazotroph community diversity .
These results show that the changes in the community structure of free-living diazotrophs in soils can have ecological significance and suggest that this response is related to a change in community diversity .

[1274] Mixed responses of tropical Pacific fisheries and aquaculture to climate change

Pacific Island countries have an extraordinary dependence on fisheries and aquaculture .
Maintaining the benefits from the sector is a difficult task , now made more complex by climate change .
Here we report how changes to the atmosphere-ocean are likely to affect the food webs , habitats and stocks underpinning fisheries and aquaculture across the region .
We found winners and losers -- tuna are expected to be more abundant in the east and freshwater aquaculture and fisheries are likely to be more productive .
Conversely , coral reef fisheries could decrease by 20 % by 2050 and coastal aquaculture may be less efficient .
We demonstrate how the economic and social implications can be addressed within the sector -- tuna and freshwater aquaculture can help support growing populations as coral reefs , coastal fisheries and mariculture decline .

[1275] Chronology , causes and progression of the Messinian salinity crisis

The Messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years ( refs 1-3 ) .
Earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated Mediterranean basin that had been repeatedly isolated from the Atlantic Ocean , , but elucidation of the causes of the isolation -- whether driven largely by glacio-eustatic or tectonic processes -- have been hampered by the absence of an accurate time frame .
Here we present an astronomically calibrated chronology for the Mediterranean Messinian age based on an integrated high-resolution stratigraphy and ` tuning ' of sedimentary cycle patterns to variations in the Earth 's orbital parameters .
We show that the onset of the Messinian salinity crisis is synchronous over the entire Mediterranean basin , dated at 5.96 + / - 0.02 million years ago .
Isolation from the Atlantic Ocean was established between 5.59 and 5.33 million years ago , causing a large fall in Mediterranean water level followed by erosion ( 5.59-5 .50 million years ago ) and deposition ( 5.50-5 .33 million years ago ) of non-marine sediments in a large ` Lago Mare ' ( Lake Sea ) basin .
Cyclic evaporite deposition is almost entirely related to circum-Mediterranean climate changes driven by changes in the Earth 's precession , and not to obliquity-induced glacio-eustatic sea-level changes .
We argue in favour of a dominantly tectonic origin for the Messinian salinity crisis , although its exact timing may well have been controlled by the ~ 400-kyr component of the Earth 's eccentricity cycle .

[1276] Probabilistic cost estimates for climate change mitigation

For more than a decade , the target of keeping global warming below 2 degreesC has been a key focus of the international climate debate .
In response , the scientific community has published a number of scenario studies that estimate the costs of achieving such a target .
Producing these estimates remains a challenge , particularly because of relatively well known , but poorly quantified , uncertainties , and owing to limited integration of scientific knowledge across disciplines .
The integrated assessment community , on the one hand , has extensively assessed the influence of technological and socio-economic uncertainties on low-carbon scenarios and associated costs .
The climate modelling community , on the other hand , has spent years improving its understanding of the geophysical response of the Earth system to emissions of greenhouse gases .
This geophysical response remains a key uncertainty in the cost of mitigation scenarios but has been integrated with assessments of other uncertainties in only a rudimentary manner , that is , for equilibrium conditions .
Here we bridge this gap between the two research communities by generating distributions of the costs associated with limiting transient global temperature increase to below specific values , taking into account uncertainties in four factors : geophysical , technological , social and political .
We find that political choices that delay mitigation have the largest effect on the cost-risk distribution , followed by geophysical uncertainties , social factors influencing future energy demand and , lastly , technological uncertainties surrounding the availability of greenhouse gas mitigation options .
Our information on temperature risk and mitigation costs provides crucial information for policy-making , because it clarifies the relative importance of mitigation costs , energy demand and the timing of global action in reducing the risk of exceeding a global temperature increase of 2 degreesC , or other limits such as 3 degreesC or 1.5 degreesC , across a wide range of scenarios .

[1277] Major viral impact on the functioning of benthic deep-sea ecosystems

Viruses are the most abundant biological organisms of the world 's oceans .
Viral infections are a substantial source of mortality in a range of organisms -- including autotrophic and heterotrophic plankton -- but their impact on the deep ocean and benthic biosphere is completely unknown .
Here we report that viral production in deep-sea benthic ecosystems worldwide is extremely high , and that viral infections are responsible for the abatement of 80 % of prokaryotic heterotrophic production .
Virus-induced prokaryotic mortality increases with increasing water depth , and beneath a depth of 1,000 m nearly all of the prokaryotic heterotrophic production is transformed into organic detritus .
The viral shunt , releasing on a global scale ~ 0.37-0 .63 gigatonnes of carbon per year , is an essential source of labile organic detritus in the deep-sea ecosystems .
This process sustains a high prokaryotic biomass and provides an important contribution to prokaryotic metabolism , allowing the system to cope with the severe organic resource limitation of deep-sea ecosystems .
Our results indicate that viruses have an important role in global biogeochemical cycles , in deep-sea metabolism and the overall functioning of the largest ecosystem of our biosphere .

[1278] Spatially variable response of Himalayan glaciers to climate change affected by debris cover

Controversy about the current state and future evolution of Himalayan glaciers has been stirred up by erroneous statements in the fourth report by the Intergovernmental Panel on Climate Change .
Variable retreat rates and a paucity of glacial mass-balance data make it difficult to develop a coherent picture of regional climate-change impacts in the region .
Here , we report remotely-sensed frontal changes and surface velocities from glaciers in the greater Himalaya between 2000 and 2008 that provide evidence for strong spatial variations in glacier behaviour which are linked to topography and climate .
More than 65 % of the monsoon-influenced glaciers that we observed are retreating , but heavily debris-covered glaciers with stagnant low-gradient terminus regions typically have stable fronts .
Debris-covered glaciers are common in the rugged central Himalaya , but they are almost absent in subdued landscapes on the Tibetan Plateau , where retreat rates are higher .
In contrast , more than 50 % of observed glaciers in the westerlies-influenced Karakoram region in the northwestern Himalaya are advancing or stable .
Our study shows that there is no uniform response of Himalayan glaciers to climate change and highlights the importance of debris cover for understanding glacier retreat , an effect that has so far been neglected in predictions of future water availability or global sea level .

[1279] Tide-mediated warming of Arctic halocline by Atlantic heat fluxes over rough topography

The largest oceanic heat input to the Arctic Ocean results from inflowing Atlantic water .
This inflowing water is warmer than it has been in the past 2,000 years .
Yet the fate of this heat remains uncertain , partly because the water is relatively saline , and thus dense : it therefore enters the Arctic Ocean at intermediate depths and is separated from surface waters by stratification .
Vertical mixing is generally weak within the Arctic Ocean basins , with very modest heat fluxes ( 0.05-0 .3 W m-2 ) arising largely from double diffusion .
However , geographically limited observations have indicated substantially enhanced turbulent mixing rates over rough topography .
Here we present pan-Arctic microstructure measurements of turbulent kinetic energy dissipation .
Our measurements further demonstrate that the enhanced continental slope dissipation rate , and by implication vertical mixing , varies significantly with both topographic steepness and longitude .
Furthermore , our observations show that dissipation is insensitive to sea-ice conditions .
We identify tides as the main energy source that supports the enhanced dissipation , which generates vertical heat fluxes of more than 50 W m-2 .
We suggest that the increased transfer of momentum from the atmosphere to the ocean as Arctic sea ice declines is likely to lead to an expansion of mixing hotspots in the future Arctic Ocean .

[1280] Distinct temperature sensitivity of soil carbon decomposition in forest organic layer and mineral soil

The roles of substrate availability and quality in determining temperature sensitivity ( Q10 ) of soil carbon ( C ) decomposition are still unclear , which limits our ability to predict how soil C storage and cycling would respond to climate change .
Here we determined Q10 in surface organic layer and subsurface mineral soil along an elevation gradient in a temperate forest ecosystem .
Q10 was calculated by comparing the times required to respire a given amount of soil C at 15 and 25degreesC in a 350-day incubation .
Results indicated that Q10 of the organic layer was 0.22-0 .71 ( absolute difference ) higher than Q10 of the mineral soil .
Q10 in both the organic layer ( 2.5-3 .4 ) and the mineral soil ( 2.1-2 .8 ) increased with decreasing substrate quality during the incubation .
This enhancement of Q10 over incubation time in both layers suggested that Q10 of more labile C was lower than that of more recalcitrant C , consistent with the Arrhenius kinetics .
No clear trend of Q10 was found along the elevation gradient .
Because the soil organic C pool of the organic layer in temperate forests is large , its higher temperature sensitivity highlights its importance in C cycling under global warming .

[1281] Probabilistic evaluation of shallow groundwater resources at a hypothetical carbon sequestration site

Carbon sequestration in geologic reservoirs is an important approach for mitigating greenhouse gases emissions to the atmosphere .
This study first develops an integrated Monte Carlo method for simulating CO2 and brine leakage from carbon sequestration and subsequent geochemical interactions in shallow aquifers .
Then , we estimate probability distributions of five risk proxies related to the likelihood and volume of changes in pH , total dissolved solids , and trace concentrations of lead , arsenic , and cadmium for two possible consequence thresholds .
The results indicate that shallow groundwater resources may degrade locally around leakage points by reduced pH and increased total dissolved solids ( TDS ) .
The volumes of pH and TDS plumes are most sensitive to aquifer porosity , permeability , and CO2 and brine leakage rates .
The estimated plume size of pH change is the largest , while that of cadmium is the smallest among the risk proxies .
Plume volume distributions of arsenic and lead are similar to those of TDS .
The scientific results from this study provide substantial insight for understanding risks of deep fluids leaking into shallow aquifers , determining the area of review , and designing monitoring networks at carbon sequestration sites .

[1282] Identification of Photosynthetic Plankton Communities Using Sedimentary Ancient DNA and Their Response to late-Holocene Climate Change on the Tibetan Plateau

Sediments from Tibetan lakes in NW China are potentially sensitive recorders of climate change and its impact on ecosystem function .
However , the important plankton members in many Tibetan Lakes do not make and leave microscopically diagnostic features in the sedimentary record .
Here we established a taxon-specific molecular approach to specifically identify and quantify sedimentary ancient DNA ( sedaDNA ) of non-fossilized planktonic organisms preserved in a 5-m sediment core from Kusai Lake spanning the last 3100 years .
The reliability of the approach was validated with multiple independent genetic markers .
Parallel analyses of the geochemistry of the core and paleo-climate proxies revealed that Monsoon strength-driven changes in nutrient availability , temperature , and salinity as well as orbitally-driven changes in light intensity were all responsible for the observed temporal changes in the abundance of two dominant phytoplankton groups in the lake , Synechococcus ( cyanobacteria ) and Isochrysis ( haptophyte algae ) .
Collectively our data show that global and regional climatic events exhibited a strong influence on the paleoecology of phototrophic plankton in Kusai Lake .

[1283] Chemical and natural stressors combined : from cryptic effects to population extinction

In addition to natural stressors , populations are increasingly exposed to chemical pollutants released into the environment .
We experimentally demonstrate the loss of resilience for Daphnia magna populations that are exposed to a combination of natural and chemical stressors even though effects on population size of a single stressor were cryptic , i.e. hard to detect statistically .
Data on Daphnia population demography and along with model-based exploration of our predator-prey system revealed that direct trophic interactions changed the population size-structure and thereby increased population vulnerability to the toxicant which acts in a size selective manner .
Moreover , population vulnerability to the toxicant increases with predator size and predation intensity whereas indirect trait-mediated interactions via predator kairomones may buffer chemical effects to a certain extent .
Our study demonstrates that population size can be a poor endpoint for risk assessments of chemicals and that ignoring disturbance interactions can lead to severe underestimation of extinction risk .

[1284] Reductive genome evolution at both ends of the bacterial population size spectrum

Bacterial genomes show substantial variations in size .
The smallest bacterial genomes are those of endocellular symbionts of eukaryotic hosts , which have undergone massive genome reduction and show patterns that are consistent with the degenerative processes that are predicted to occur in species with small effective population sizes .
However , similar genome reduction is found in some free-living marine cyanobacteria that are characterized by extremely large populations .
In this Opinion article , we discuss the different hypotheses that have been proposed to account for this reductive genome evolution at both ends of the bacterial population size spectrum .

[1285] Increased thermohaline stratification as a possible cause for an ocean anoxic event in the Cretaceous period

Ocean anoxic events were periods of high carbon burial that led to drawdown of atmospheric carbon dioxide , lowering of bottom-water oxygen concentrations and , in many cases , significant biological extinction .
Most ocean anoxic events are thought to be caused by high productivity and export of carbon from surface waters which is then preserved in organic-rich sediments , known as black shales .
But the factors that triggered some of these events remain uncertain .
Here we present stable isotope data from a mid-Cretaceous ocean anoxic event that occurred 112 Myr ago , and that point to increased thermohaline stratification as the probable cause .
Ocean anoxic event 1b is associated with an increase in surface-water temperatures and runoff that led to decreased bottom-water formation and elevated carbon burial in the restricted basins of the western Tethys and North Atlantic .
This event is in many ways similar to that which led to the more recent Plio-Pleistocene Mediterranean sapropels , but the greater geographical extent and longer duration ( ~ 46 kyr ) of ocean anoxic event 1b suggest that processes leading to such ocean anoxic events in the North Atlantic and western Tethys were able to act over a much larger region , and sequester far more carbon , than any of the Quaternary sapropels .

[1286] Glacial discharge along the west Antarctic Peninsula during the Holocene

The causes for rising temperatures along the Antarctic Peninsula during the late Holocene have been debated , particularly in light of instrumental records of warming over the past decades .
Suggested mechanisms range from upwelling of warm deep waters onto the continental shelf in response to variations in the westerly winds , to an influence of El Nino-Southern Oscillation on sea surface temperatures .
Here , we present a record of Holocene glacial ice discharge , derived from the oxygen isotope composition of marine diatoms from Palmer Deep along the west Antarctic Peninsula continental margin .
We assess atmospheric versus oceanic influences on glacial discharge at this location , using analyses of diatom geochemistry to reconstruct atmospherically forced glacial ice discharge and diatom assemblage ecology to investigate the oceanic environment .
We show that two processes of atmospheric forcing -- an increasing occurrence of La Nina events and rising levels of summer insolation -- had a stronger influence during the late Holocene than oceanic processes driven by southern westerly winds and upwelling of upper Circumpolar Deepwater .
Given that the evolution of El Nino-Southern Oscillation under global warming is uncertain , its future impacts on the climatically sensitive system of the Antarctic Peninsula Ice Sheet remain to be established .

[1287] Constraining the atmospheric N2O budget from intramolecular site preference in N2O isotopomers

Nitrous oxide ( N2O ) is an important trace gas in the atmosphere .
It is an active greenhouse gas in the troposphere and it also controls ozone concentration in the stratosphere through nitric oxide production .
One way to trace the geochemical cycle of N2O is by measuring the natural abundance of stable isotopes , namely 15N and 18O ( refs 2,3,4,5,6,7,8,9,10,11 , 12,13,14,15 ) .
Here we report the intramolecular distribution of 15N within the linear NNO molecule , determined by measuring molecular and fragment ions of N2O on a modified mass spectrometer .
This revealed a preference for 15N at the central N position , or alpha-site , within N2O isotopomers ( isotope-containing molecules ) .
Moreover , this preference varied significantly throughout the atmosphere .
In the troposphere , low alpha-site preference indicates local emission of N2O from soils and fossil-fuel combustion , each with distinct isotopomer signatures , which then mixes with background N2O .
In the stratosphere , on the other hand , loss of N2O is observed as enhanced alpha-site preference for 15N , due to fractionation during ultraviolet photolysis of N2O .
We have constructed an atmospheric mass balance of N 2O , incorporating isotopomer abundance , which shows that the intramolecular distribution of 15N is a parameter that has the potential to increase significantly the resolution with which sources and sinks of N 2O can be identified and quantified in the atmosphere .

[1288] Direct synthesis of formic acid from carbon dioxide by hydrogenation in acidic media

The chemical transformation of carbon dioxide into useful products becomes increasingly important as CO2 levels in the atmosphere continue to rise as a consequence of human activities .
In this article we describe the direct hydrogenation of CO2 into formic acid using a homogeneous ruthenium catalyst , in aqueous solution and in dimethyl sulphoxide ( DMSO ) , without any additives .
In water , at 40 degreesC , 0.2 M formic acid can be obtained under 200 bar , however , in DMSO the same catalyst affords 1.9 M formic acid .
In both solvents the catalysts can be reused multiple times without a decrease in activity .
Worldwide demand for formic acid continues to grow , especially in the context of a renewable energy hydrogen carrier , and its production from CO2 without base , via the direct catalytic carbon dioxide hydrogenation , is considerably more sustainable than the existing routes .

[1289] Decreased abundance of crustose coralline algae due to ocean acidification

Owing to anthropogenic emissions , atmospheric concentrations of carbon dioxide could almost double between 2006 and 2100 according to business-as-usual carbon dioxide emission scenarios .
Because the ocean absorbs carbon dioxide from the atmosphere , increasing atmospheric carbon dioxide concentrations will lead to increasing dissolved inorganic carbon and carbon dioxide in surface ocean waters , and hence acidification and lower carbonate saturation states .
As a consequence , it has been suggested that marine calcifying organisms , for example corals , coralline algae , molluscs and foraminifera , will have difficulties producing their skeletons and shells at current rates , with potentially severe implications for marine ecosystems , including coral reefs .
Here we report a seven-week experiment exploring the effects of ocean acidification on crustose coralline algae , a cosmopolitan group of calcifying algae that is ecologically important in most shallow-water habitats .
Six outdoor mesocosms were continuously supplied with sea water from the adjacent reef and manipulated to simulate conditions of either ambient or elevated seawater carbon dioxide concentrations .
The recruitment rate and growth of crustose coralline algae were severely inhibited in the elevated carbon dioxide mesocosms .
Our findings suggest that ocean acidification due to human activities could cause significant change to benthic community structure in shallow-warm-water carbonate ecosystems .

[1290] North Atlantic forcing of Amazonian precipitation during the last ice age

The last glacial period was marked by multiple , abrupt reorganizations of ocean and atmosphere circulation .
On thousand-year timescales , slowing of the Atlantic meridional overturning circulation was associated with cooling in the high northern latitudes , whereas strengthened circulation was linked to northern warming .
In the tropics , these millennial-scale events were primarily reflected in altered patterns of precipitation .
These hydrologic fluctuations induced ecological changes in the Atlantic seaboard and the high Andes , but less is known about the Amazon Basin .
Here we reconstruct precipitation over Amazonian Ecuador over the past 94,000 years using a delta18O record from speleothems collected in Santiago Cave in western Amazonia .
We interpret the variability of the delta18O record as changes in the source and amount of precipitation .
With the exception of the period between 40,000 and 17,000 years ago , abrupt , high-frequency changes coincide with shifts in North Atlantic circulation , indicating a high-latitude influence on Amazonian precipitation over millennial timescales .
On longer timescales , the record shows a relationship to precessional changes in the Earth 's orbit .
In light of the lack of extreme aridity in our records , we conclude that ecosystems in western Amazonia have not experienced prolonged drying over the past 94,000 years .

[1291] Microbial ecology of the equine hindgut during oligofructose-induced laminitis

Alimentary carbohydrate overload is a significant cause of laminitis in horses and is correlated with drastic shifts in the composition of hindgut microbiota .
Equine hindgut streptococcal species ( EHSS ) , predominantly Streptococcus lutetiensis , have been shown to be the most common microorganisms culturable from the equine caecum prior to the onset of laminitis .
However , the inherent biases of culture-based methods are estimated to preclude up to 70 % of the normal caecal microbiota .
The objective of this study was to evaluate bacterial population shifts occurring in the equine caecum throughout the course of oligofructose-induced laminitis using several culture-independent techniques and to correlate these with caecal lactate , volatile fatty acid and degrees of polymerization 3-7 fructo-oligosaccharide concentrations .
Our data conclusively show that of the total microbiota present in the equine hindgut , the EHSS S. lutetiensis is the predominant microorganism that proliferates prior to the onset of laminitis , utilizing oligofructose to produce large quantities of lactate .
Population shifts in lactobacilli and Escherichia coli subpopulations occur secondarily to the EHSS population shifts , thus confirming that lactobacilli and coliforms have no role in laminitis .
A large , curved , Gram-negative rod previously observed during the early phases of laminitis induction was most closely related to the Anaerovibrio genus and most likely represents a new , yet to be cultured , genus and species .
Correlation of fluorescence in situ hybridization and quantitative real-time PCR results provide evidence supporting the hypothesis that laminitis is associated with the death en masse and rapid cell lysis of EHSS .
If EHSS are lysed , liberated cellular components may initiate laminitis .

[1292] Similar spatial patterns of climate responses to aerosol and greenhouse gas changes

Spatial variations in ocean warming have been linked to regional changes in tropical cyclones , precipitation and monsoons .
But development of reliable regional climate projections for climate change mitigation and adaptation remains challenging .
The presence of anthropogenic aerosols , which are highly variable in space and time , is thought to induce spatial patterns of climate response that are distinct from those of well-mixed greenhouse gases .
Using CMIP5 climate simulations that consider aerosols and greenhouse gases separately , we show that regional responses to changes in greenhouse gases and aerosols are similar over the ocean , as reflected in similar spatial patterns of ocean temperature and precipitation .
This similarity suggests that the climate response to radiative changes is relatively insensitive to the spatial distribution of these changes .
Although anthropogenic aerosols are largely confined to the Northern Hemisphere , simulations that include aerosol forcing predict decreases in temperature and westerly wind speed that reach the pristine Southern Hemisphere oceans .
Over land , the climate response to aerosol forcing is more localized , but larger scale spatial patterns are also evident .
We suggest that the climate responses induced by greenhouse gases and aerosols share key ocean-atmosphere feedbacks , leading to a qualitative resemblance in spatial distribution .

[1293] Cloud droplet number enhanced by co-condensation of organic vapours

Clouds profoundly influence weather and climate .
The brightness and lifetime of clouds is determined by cloud droplet number concentration , in turn dictated by the number of available seed particles .
The formation of cloud droplets on non-volatile atmospheric particles is well understood .
However , fine particulate matter in the atmosphere ranges widely in volatility .
Co-condensation of semi-volatile compounds with water increases a particle 's propensity for cloud droplet formation , with potential consequences for feedbacks between the terrestrial biosphere and climate .
Here we systematically study cloud droplet formation , using a cloud parcel model extended to include co-condensation of semi-volatile organic compounds under a broad variety of realistic conditions .
As an air parcel rises and cools , the concentration of organic vapour that it can hold declines .
Thus , the simulated organic vapours become increasingly saturated as they ascend , and so condense on growing particles as they swell into cloud droplets .
We show that condensation of increasingly volatile material adds to the soluble mass of these droplets and facilitates the uptake of additional water , which leads , in turn , to a substantial increase in the number of viable cloud droplets .
We suggest that the co-condensation of semi-volatile organic compounds with water vapour has a substantial impact on the radiative properties of clouds .

[1294] Significant contribution of the 18.6 year tidal cycle to regional coastal changes

Although rising global sea levels will affect the shape of coastlines over the coming decades , the most severe and catastrophic shoreline changes occur as a consequence of local and regional-scale processes .
Changes in sediment supply and deltaic subsidence , both natural or anthropogenic , and the occurrences of tropical cyclones and tsunamis have been shown to be the leading controls on coastal erosion .
Here , we use satellite images of South American mangrove-colonized mud banks collected over the past twenty years to reconstruct changes in the extent of the shoreline between the Amazon and Orinoco rivers .
The observed timing of the redistribution of sediment and migration of the mud banks along the 1,500 km muddy coast suggests the dominant control of ocean forcing by the 18.6 year nodal tidal cycle .
Other factors affecting sea level such as global warming or El Nino and La Nina events show only secondary influences on the recorded changes .
In the coming decade , the 18.6 year cycle will result in an increase of mean high water levels of 6 cm along the coast of French Guiana , which will lead to a 90 m shoreline retreat .

[1295] Evidence for a link between global lightning activity and upper tropospheric water vapour

Tropospheric water vapour is a key element of the Earth 's climate , which has direct effects as a greenhouse gas , as well as indirect effects through interaction with clouds , aerosols and tropospheric chemistry .
Small changes in upper-tropospheric water vapour have a much larger impact on the greenhouse effect than small changes in water vapour in the lower atmosphere , but whether this impact is a positive or negative feedback remains uncertain .
The main challenge in addressing this question is the difficulty in monitoring upper-tropospheric water vapour globally over long timescales .
Here I show that upper-tropospheric water-vapour variability and global lightning activity are closely linked , suggesting that upper-tropospheric water-vapour changes can be inferred from records of global lightning activity , readily obtained from observations at a single location on the Earth 's surface .
This correlation reflects the fact that continental deep-convective thunderstorms transport large amounts of water vapour into the upper troposphere and thereby dominate the variations of global upper-tropospheric water vapour while producing most of the lightning on Earth .
As global lightning induces Schumann resonances , an electromagnetic phenomenon in the atmosphere that can be observed easily at low cost , monitoring of these resonances might provide a convenient method for tracking upper-tropospheric water-vapour variability and hence contribute to a better understanding of the processes affecting climate change .

[1296] Counting whales in a challenging , changing environment

Estimating abundance of Antarctic minke whales is central to the International Whaling Commission 's conservation and management work and understanding impacts of climate change on polar marine ecosystems .
Detecting abundance trends is problematic , in part because minke whales are frequently sighted within Antarctic sea ice where navigational safety concerns prevent ships from surveying .
Using icebreaker-supported helicopters , we conducted aerial surveys across a gradient of ice conditions to estimate minke whale density in the Weddell Sea .
The surveys revealed substantial numbers of whales inside the sea ice .
The Antarctic summer sea ice is undergoing rapid regional change in annual extent , distribution , and length of ice-covered season .
These trends , along with substantial interannual variability in ice conditions , affect the proportion of whales available to be counted by traditional shipboard surveys .
The strong association between whales and the dynamic , changing sea ice requires reexamination of the power to detect trends in whale abundance or predict ecosystem responses to climate change .

[1297] Effects of Fe oxide on N transformations in subtropical acid soils

Subtropical ecosystems are often characterized by high N cycling rates , but net nitrification rates are often low in subtropical acid soils .
NO3 -- N immobilization into organic N may be a contributing factor to understand the observed low net nitrification rates in these acid soils .
The effects of Fe oxide and organic matter on soil N transformations were evaluated using a 15N tracing study .
Soil net nitrification was low for highly acidic yellow soil ( Ferralsols ) , but gross ammonia oxidation was 7 times higher than net nitrification .
In weakly acidic purple soil ( Cambisols ) , net nitrification was 8 times higher than in Ferralsols .
The addition of 5 % Fe oxide to Cambisols , reduced the net nitrification rate to a negative rate , while NO3 -- N immobilization rate increased 8 fold .
NO3 -- N immobilization was also observed in Ferralsols which contained high Fe oxides levels .
A possible mechanism for these reactions could be stimulation of NO3 -- N immobilization by Fe oxide which promoted the abiotic formation of nitrogenous polymers , suggesting that the absence of net nitrification in some highly acid soils may be due to high rates of NO3 -- N immobilization caused by high Fe oxide content rather than a low pH.

[1298] Enhanced sea-ice export from the Arctic during the Younger Dryas

The Younger Dryas cold spell of the last deglaciation and related slowing of the Atlantic meridional overturning circulation have been linked to a large array of processes , notably an influx of fresh water into the North Atlantic related to partial drainage of glacial Lake Agassiz .
Here we observe a major drainage event , in marine sediment cores raised from the Lomonosov Ridge , in the central Arctic Ocean marked by a pulse in detrital dolomitic-limestones .
This points to an Arctic-Canadian sediment source area with about fivefold higher Younger Dryas ice-rafting deposition rate , in comparison with the Holocene .
Our findings thus support the hypothesis of a glacial drainage event in the Canadian Arctic area , at the onset of the Younger Dryas , enhancing sea-ice production and drifting through the Arctic , then export through Fram Strait , towards Atlantic meridional overturning circulation sites of the northern North Atlantic .

[1299] Atmospheric nanoparticles formed from heterogeneous reactions of organics

Atmospheric aerosols directly and indirectly affect the radiative balance of the Earth 's atmosphere .
Nanoparticles are a key component of atmospheric aerosols , growing rapidly under ambient conditions .
Organic species are thought to lead to the growth of nanoparticles smaller than 20 nm ( refs 5 , 6 ) , but the identity of these species and the underlying chemical mechanisms remain elusive .
Here we exposed nanoparticles to a range of organic vapours -- 2,4-hexadienal , glyoxal and trimethylamine -- and monitored particle size to determine the contribution of organic vapours to nanoparticle growth .
We show that organic species enhance the growth of nanoparticles , producing non-volatile oligomers , polymers and alkylaminium sulphates in the particle phase .
Nanoparticle growth increased with relative humidity in the presence of glyoxal and trimethylamine , but decreased at higher relative humidities in the presence of 2,4-hexadienal , dependent on the reaction mechanism of the organic species involved .
Oligomerization and polymerization were largely suppressed in particles smaller than 4 nm and nanoparticle growth increased with particle size .
Our findings help to explain the presence of previously measured , but unidentified non-volatile compounds in atmospheric nanoparticles and to improve model simulations of new particle formation .

[1300] Post-Mesozoic Rapid Increase of Seawater Mg/Ca due to Enhanced Mantle-Seawater Interaction

The seawater Mg/Ca ratio increased significantly from ~ 80 Ma to present , as suggested by studies of carbonate veins in oceanic basalts and of fluid inclusions in halite .
We show here that reactions of mantle-derived peridotites with seawater along slow spreading mid-ocean ridges contributed to the post-Cretaceous Mg/Ca increase .
These reactions can release to modern seawater up to 20 % of the yearly Mg river input .
However , no significant peridotite-seawater interaction and Mg-release to the ocean occur in fast spreading , East Pacific Rise-type ridges .
The Mesozoic Pangean superocean implies a hot fast spreading ridge system .
This prevented peridotite-seawater interaction and Mg release to the Mesozoic ocean , but favored hydrothermal Mg capture and Ca release by the basaltic crust , resulting in a low seawater Mg/Ca ratio .
Continent dispersal and development of slow spreading ridges allowed Mg release to the ocean by peridotite-seawater reactions , contributing to the increase of the Mg/Ca ratio of post-Mesozoic seawater .

[1301] The potential for carbon sequestration in Australian agricultural soils is technically and economically limited

Concerns about increasing concentrations of greenhouse gases in the atmosphere , primarily carbon dioxide ( CO2 ) , have raised worldwide interest in the potential of agricultural soils to be carbon ( C ) sinks .
In Australia , studies that have quantified the effects of improved management practices in croplands on soil C have generally been inconclusive and contradictory for different soil depths and durations of the management changes .
We therefore quantitatively synthesised the results of Australian studies using meta-analytic techniques to assess the technical and economic feasibility of increasing the soil C stock by improved management practices .
Our results indicate that the potential of these improved practices to store C is limited to the surface 0-10 cm of soil and diminishes with time .
None of these widely adopted practices is currently financially attractive under Australia 's new legislation known as the Carbon Farming Initiative .

[1302] Isotopic evidence for long term warmth in the Mesozoic

Atmospheric CO2 concentrations appear to have been considerably higher than modern levels during much of the Phanerozoic and it has hence been proposed that surface temperatures were also higher .
Some studies have , however , suggested that Earth 's temperature ( estimated from the isotopic composition of fossil shells ) may have been independent of variations in atmospheric CO2 ( e.g. in the Jurassic and Cretaceous ) .
If large changes in atmospheric CO2 did not produce the expected climate responses in the past , predictions of future climate and the case for reducing current fossil-fuel emissions are potentially undermined .
Here we evaluate the dataset upon which the Jurassic and Cretaceous assertions are based and present new temperature data , derived from the isotopic composition of fossil brachiopods .
Our results are consistent with a warm climate mode for the Jurassic and Cretaceous and hence support the view that changes in atmospheric CO2 concentrations are linked with changes in global temperatures .

[1303] Early warning of climate tipping points

A climate ` tipping point ' occurs when a small change in forcing triggers a strongly nonlinear response in the internal dynamics of part of the climate system , qualitatively changing its future state .
Human-induced climate change could push several large-scale ` tipping elements ' past a tipping point .
Candidates include irreversible melt of the Greenland ice sheet , dieback of the Amazon rainforest and shift of the West African monsoon .
Recent assessments give an increased probability of future tipping events , and the corresponding impacts are estimated to be large , making them significant risks .
Recent work shows that early warning of an approaching climate tipping point is possible in principle , and could have considerable value in reducing the risk that they pose .

[1304] Interspecific competition and siderophore-mediated cooperation in Pseudomonas aeruginosa

Both intra - and interspecific interactions between microbes are likely to play an important role in determining the severity of microbial infections .
Here , we study the impact of interactions between coinfecting opportunistic pathogens Staphylococcus aureus and Pseudomonas aeruginosa on both phenotypic and genetic changes in a P. aeruginosa social trait , the production of iron-scavenging siderophores .
Siderophores are facultatively upregulated in response to iron limitation and play a key role in determining the virulence of microbial infections .
Siderophore production is metabolically expensive to individual producers but benefits the group as a whole because siderophores can be used by all cells in the vicinity with siderophore receptors .
Hence , populations of siderophore producers can be invaded by nonproducing cheats .
Previous work has shown that P. aeruginosa can lyse S. aureus , supplying a source of free iron .
We therefore hypothesized that the presence of S. aureus might result in facultative downregulation of siderophore production , and in turn , reduced selection for siderophore cheats .
We tested this hypothesis by evolving P. aeruginosa in the presence and absence of free iron and S. aureus , in a fully factorial design .
Iron had the expected effect : siderophore production was downregulated and cheats evolved less readily , but the presence of S. aureus instead increased facultative siderophore production and selection for cheats .
This is probably because the S. aureus had the net effect of competing for iron , rather than acting as an iron source .
This study demonstrates that interspecific competition can have a marked effect on intraspecific social interactions .

[1305] Variability of El Nino/Southern Oscillation activity at millennial timescales during the Holocene epoch

The variability of El Nino/Southern Oscillation ( ENSO ) during the Holocene epoch , in particular on millennial timescales , is poorly understood .
Palaeoclimate studies have documented ENSO variability for selected intervals in the Holocene , but most records are either too short or insufficiently resolved to investigate variability on millennial scales .
Here we present a record of sedimentation in Laguna Pallcacocha , southern Ecuador , which is strongly influenced by ENSO variability , and covers the past 12,000 years continuously .
We find that changes on a timescale of 2-8 years , which we attribute to warm ENSO events , become more frequent over the Holocene until about 1,200 years ago , and then decline towards the present .
Periods of relatively high and low ENSO activity , alternating at a timescale of about 2,000 years , are superimposed on this long-term trend .
We attribute the long-term trend to orbitally induced changes in insolation , and suggest internal ENSO dynamics as a possible cause of the millennial variability .
However , the millennial oscillation will need to be confirmed in other ENSO proxy records .

[1306] Signatures of aestivation and migration in Sahelian malaria mosquito populations

During the long Sahelian dry season , mosquito vectors of malaria are expected to perish when no larval sites are available ; yet , days after the first rains , mosquitoes reappear in large numbers .
How these vectors persist over the 3-6-month long dry season has not been resolved , despite extensive research for over a century .
Hypotheses for vector persistence include dry-season diapause ( aestivation ) and long-distance migration ( LDM ) ; both are facets of vector biology that have been highly controversial owing to lack of concrete evidence .
Here we show that certain species persist by a form of aestivation , while others engage in LDM .
Using time-series analyses , the seasonal cycles of Anopheles coluzzii , Anopheles gambiae sensu stricto ( s.s. ) , and Anopheles arabiensis were estimated , and their effects were found to be significant , stable and highly species-specific .
Contrary to all expectations , the most complex dynamics occurred during the dry season , when the density of A. coluzzii fluctuated markedly , peaking when migration would seem highly unlikely , whereas A. gambiae s.s. was undetected .
The population growth of A. coluzzii followed the first rains closely , consistent with aestivation , whereas the growth phase of both A. gambiae s.s. and A. arabiensis lagged by two months .
Such a delay is incompatible with local persistence , but fits LDM .
Surviving the long dry season in situ allows A. coluzzii to predominate and form the primary force of malaria transmission .
Our results reveal profound ecological divergence between A. coluzzii and A. gambiae s.s. , whose standing as distinct species has been challenged , and suggest that climate is one of the selective pressures that led to their speciation .
Incorporating vector dormancy and LDM is key to predicting shifts in the range of malaria due to global climate change , and to the elimination of malaria from Africa .

[1307] A Cenozoic record of the equatorial Pacific carbonate compensation depth

Atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks ; these feedbacks involve the erosion of silicate rocks and organic-carbon-bearing rocks .
The integrated effect of these processes is reflected in the calcium carbonate compensation depth , which is the oceanic depth at which calcium carbonate is dissolved .
Here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial Pacific Ocean .
The carbonate compensation depth tracks long-term ocean cooling , deepening from 3.0-3 .5 kilometres during the early Cenozoic ( approximately 55 million years ago ) to 4.6 kilometres at present , consistent with an overall Cenozoic increase in weathering .
We find large superimposed fluctuations in carbonate compensation depth during the middle and late Eocene .
Using Earth system models , we identify changes in weathering and the mode of organic-carbon delivery as two key processes to explain these large-scale Eocene fluctuations of the carbonate compensation depth .

[1308] Citizen Science : linking the recent rapid advances of plant flowering in Canada with climate variability

The timing of crucial events in plant life cycles is shifting in response to climate change .
We use phenology records from PlantWatch Canada ` Citizen Science ' networks to study recent rapid shifts of flowering phenology and its relationship with climate .
The average first flower bloom day of 19 Canadian plant species has advanced by about 9 days during 2001-2012 .
73 % of the rapid and unprecedented first bloom day advances are explained by changes in mean annual national temperature , allowing the reconstruction of historic flower phenology records starting from 1948 .
The overall trends show that plant flowering in Canada is advancing by about 9 days per degreesC .
This analysis reveals the strongest biological signal yet of climate warming in Canada .
This finding has broad implications for niche differentiation among coexisting species , competitive interactions between species , and the asynchrony between plants and the organisms they interact with .

[1309] Links between annual , Milankovitch and continuum temperature variability

Climate variability exists at all timescales -- and climatic processes are intimately coupled , so that understanding variability at any one timescale requires some understanding of the whole .
Records of the Earth 's surface temperature illustrate this interdependence , having a continuum of variability following a power-law scaling .
But although specific modes of interannual variability are relatively well understood , the general controls on continuum variability are uncertain and usually described as purely stochastic processes .
Here we show that power-law relationships of surface temperature variability scale with annual and Milankovitch-period ( 23,000 - and 41,000-year ) cycles .
The annual cycle corresponds to scaling at monthly to decadal periods , while millennial and longer periods are tied to the Milankovitch cycles .
Thus the annual , Milankovitch and continuum temperature variability together represent the response to deterministic insolation forcing .
The identification of a deterministic control on the continuum provides insight into the mechanisms governing interannual and longer-period climate variability .

[1310] Effects of species and functional group loss on island ecosystem properties

Considerable recent attention has focused on predicting how the losses of species and functional groups influence ecosystem properties , but the extent to which these effects vary among ecosystems remains poorly understood .
Island systems have considerable scope for studying how biotic and abiotic factors influence processes in different ecosystems , because they enable the simultaneous study of large numbers of independent replicate systems at ecologically meaningful spatial scales .
We studied a group of 30 islands in northern Sweden , for which island size determined disturbance history , and therefore vegetation successional stage and biotic and abiotic ecosystem properties .
On each island we conducted a seven-year study that involved experimental removals of combinations of both plant functional groups and plant species .
We show that although losses of functional groups and species often impaired key ecosystem processes , these effects were highly context-dependent and strongly influenced by island size .
Our study provides evidence that the consequences of biotic loss for ecosystem functioning vary greatly among ecosystems and depend on the specific abiotic and biotic attributes of the system .

[1311] Robust Arctic sea-ice influence on the frequent Eurasian cold winters in past decades

Over the past decade , severe winters occurred frequently in mid-latitude Eurasia , despite increasing global - and annual-mean surface air temperatures .
Observations suggest that these cold Eurasian winters could have been instigated by Arctic sea-ice decline , through excitation of circulation anomalies similar to the Arctic Oscillation .
In climate simulations , however , a robust atmospheric response to sea-ice decline has not been found , perhaps owing to energetic internal fluctuations in the atmospheric circulation .
Here we use a 100-member ensemble of simulations with an atmospheric general circulation model driven by observation-based sea-ice concentration anomalies to show that as a result of sea-ice reduction in the Barents-Kara Sea , the probability of severe winters has more than doubled in central Eurasia .
In our simulations , the atmospheric response to sea-ice decline is approximately independent of the Arctic Oscillation .
Both reanalysis data and our simulations suggest that sea-ice decline leads to more frequent Eurasian blocking situations , which in turn favour cold-air advection to Eurasia and hence severe winters .
Based on a further analysis of simulations from 22 climate models we conclude that the sea-ice-driven cold winters are unlikely to dominate in a warming future climate , although uncertainty remains , due in part to an insufficient ensemble size .

[1312] Development of an ecophysiological model for Diplosphaera colotermitum TAV2 , a termite hindgut Verrucomicrobium

Termite hindguts are populated by a dense and diverse community of microbial symbionts working in concert to transform lignocellulosic plant material and derived residues into acetate , to recycle and fix nitrogen , and to remove oxygen .
Although much has been learned about the breadth of microbial diversity in the hindgut , the ecophysiological roles of its members is less understood .
In this study , we present new information about the ecophysiology of microorganism Diplosphaera colotermitum strain TAV2 , an autochthonous member of the Reticulitermes flavipes gut community .
An integrated high-throughput approach was used to determine the transcriptomic and proteomic profiles of cells grown under hypoxia ( 2 % O2 ) or atmospheric ( 20 % O2 ) concentrations of oxygen .
Our results revealed that genes and proteins associated with energy production and utilization , carbohydrate transport and metabolism , nitrogen fixation , and replication and recombination were upregulated under 2 % O2 .
The metabolic map developed for TAV2 indicates that this microorganism may be involved in biological nitrogen fixation , amino-acid production , hemicellulose degradation and consumption of O2 in the termite hindgut .
Variation of O2 concentration explained 55.9 % of the variance in proteomic profiles , suggesting an adaptive evolution of TAV2 to the hypoxic periphery of the hindgut .
Our findings advance the current understanding of microaerophilic microorganisms in the termite gut and expand our understanding of the ecological roles for members of the phylum Verrucomicrobia .

[1313] Taming hurricanes with arrays of offshore wind turbines

Hurricanes are causing increasing damage to many coastal regions worldwide .
Offshore wind turbines can provide substantial clean electricity year-round , but can they also mitigate hurricane damage while avoiding damage to themselves ?
This study uses an advanced climate-weather computer model that correctly treats the energy extraction of wind turbines to examine this question .
It finds that large turbine arrays ( 300 + GW installed capacity ) may diminish peak near-surface hurricane wind speeds by 25-41 m s-1 ( 56-92 mph ) and storm surge by 6-79 % .
Benefits occur whether turbine arrays are placed immediately upstream of a city or along an expanse of coastline .
The reduction in wind speed due to large arrays increases the probability of survival of even present turbine designs .
The net cost of turbine arrays ( capital plus operation cost less cost reduction from electricity generation and from health , climate , and hurricane damage avoidance ) is estimated to be less than today 's fossil fuel electricity generation net cost in these regions and less than the net cost of sea walls used solely to avoid storm surge damage .

[1314] Large-scale variations in the stoichiometry of marine organic matter respiration

The elemental composition of marine organic matter governs resource competition among plankton , and couples the global cycles of carbon , nutrients and oxygen .
Observations have revealed systematic large-scale variation in the ratios of these essential elements removed from surface waters by phytoplankton .
However , an impact of this variability on deep ocean properties has not been detected .
Here we use a data-constrained ocean circulation model and observed long-term mean distributions of dissolved oxygen and the nutrient phosphate to show that there is a threefold variation across latitudes in the amount of dissolved oxygen consumed per unit of phosphate released during organic matter respiration .
This pattern of remineralization ratios is shown to significantly modify the extent and distribution of low-oxygen water masses in the interior ocean .
We also find that ocean biomes with distinct light and nutrient availability are characterized by different regional stoichiometries .
These findings suggest that in a more stratified ocean , an increase in light exposure and decrease in nutrient concentration could raise the C :P ratio of phytoplankton , and the associated carbon storage by the ocean 's biological pump .

[1315] Dietary emulsifiers impact the mouse gut microbiota promoting colitis and metabolic syndrome

The intestinal tract is inhabited by a large and diverse community of microbes collectively referred to as the gut microbiota .
While the gut microbiota provides important benefits to its host , especially in metabolism and immune development , disturbance of the microbiota-host relationship is associated with numerous chronic inflammatory diseases , including inflammatory bowel disease and the group of obesity-associated diseases collectively referred to as metabolic syndrome .
A primary means by which the intestine is protected from its microbiota is via multi-layered mucus structures that cover the intestinal surface , thereby allowing the vast majority of gut bacteria to be kept at a safe distance from epithelial cells that line the intestine .
Thus , agents that disrupt mucus-bacterial interactions might have the potential to promote diseases associated with gut inflammation .
Consequently , it has been hypothesized that emulsifiers , detergent-like molecules that are a ubiquitous component of processed foods and that can increase bacterial translocation across epithelia in vitro , might be promoting the increase in inflammatory bowel disease observed since the mid-twentieth century .
Here we report that , in mice , relatively low concentrations of two commonly used emulsifiers , namely carboxymethylcellulose and polysorbate-80 , induced low-grade inflammation and obesity/metabolic syndrome in wild-type hosts and promoted robust colitis in mice predisposed to this disorder .
Emulsifier-induced metabolic syndrome was associated with microbiota encroachment , altered species composition and increased pro-inflammatory potential .
Use of germ-free mice and faecal transplants indicated that such changes in microbiota were necessary and sufficient for both low-grade inflammation and metabolic syndrome .
These results support the emerging concept that perturbed host-microbiota interactions resulting in low-grade inflammation can promote adiposity and its associated metabolic effects .
Moreover , they suggest that the broad use of emulsifying agents might be contributing to an increased societal incidence of obesity/metabolic syndrome and other chronic inflammatory diseases .

[1316] Diversity and dynamics of rare and of resident bacterial populations in coastal sands

Coastal sands filter and accumulate organic and inorganic materials from the terrestrial and marine environment , and thus provide a high diversity of microbial niches .
Sands of temperate climate zones represent a temporally and spatially highly dynamic marine environment characterized by strong physical mixing and seasonal variation .
Yet little is known about the temporal fluctuations of resident and rare members of bacterial communities in this environment .
By combining community fingerprinting via pyrosequencing of ribosomal genes with the characterization of multiple environmental parameters , we disentangled the effects of seasonality , environmental heterogeneity , sediment depth and biogeochemical gradients on the fluctuations of bacterial communities of marine sands .
Surprisingly , only 3-5 % of all bacterial types of a given depth zone were present at all times , but 50-80 % of them belonged to the most abundant types in the data set .
About 60-70 % of the bacterial types consisted of tag sequences occurring only once over a period of 1 year .
Most members of the rare biosphere did not become abundant at any time or at any sediment depth , but varied significantly with environmental parameters associated with nutritional stress .
Despite the large proportion and turnover of rare organisms , the overall community patterns were driven by deterministic relationships associated with seasonal fluctuations in key biogeochemical parameters related to primary productivity .
The maintenance of major biogeochemical functions throughout the observation period suggests that the small proportion of resident bacterial types in sands perform the key biogeochemical processes , with minimal effects from the rare fraction of the communities .

[1317] Mycorrhizal fungal diversity determines plant biodiversity , ecosystem variability and productivity

The functioning and stability of terrestrial ecosystems are determined by plant biodiversity and species composition .
However , the ecological mechanisms by which plant biodiversity and species composition are regulated and maintained are not well understood .
These mechanisms need to be identified to ensure successful management for conservation and restoration of diverse natural ecosystems .
Here we show , by using two independent , but complementary , ecological experiments , that below-ground diversity of arbuscular mycorrhizal fungi ( AMF ) is a major factor contributing to the maintenance of plant biodiversity and to ecosystem functioning .
At low AMF diversity , the plant species composition and overall structure of microcosms that simulate European calcareous grassland fluctuate greatly when the AMF taxa that are present are changed .
Plant biodiversity , nutrient capture and productivity in macrocosms that simulate North American old-fields increase significantly with increasing AMF-species richness .
These results emphasize the need to protect AMF and to consider these fungi in future management practices in order to maintain diverse ecosystems .
Our results also show that microbial interactions can drive ecosystem functions such as plant biodiversity , productivity and variability .

[1318] Changes in South Pacific rainfall bands in a warming climate

The South Pacific Convergence Zone ( SPCZ ) is the largest rainband in the Southern Hemisphere and provides most of the rainfall to southwest Pacific island nations .
In spite of various modelling efforts , it remains uncertain how the SPCZ will respond to greenhouse warming .
Using a hierarchy of climate models we show that the uncertainty of SPCZ rainfall projections in present-generation climate models can be explained as a result of two competing mechanisms .
Higher tropical sea surface temperatures lead to an overall increase of atmospheric moisture and rainfall whereas weaker sea surface temperature gradients dynamically shift the SPCZ northeastward and promote summer drying in areas of the southwest Pacific .
On the basis of a multi-model ensemble of 76 greenhouse warming experiments and for moderate tropical warming of 1-2 degreesC we estimate a 6 % decrease of SPCZ rainfall with a multi-model uncertainty exceeding + / -20 % .
For stronger tropical warming exceeding 3 degreesC , a tendency for a wetter SPCZ region is identified .

[1319] Old-growth forests as global carbon sinks

Old-growth forests remove carbon dioxide from the atmosphere at rates that vary with climate and nitrogen deposition .
The sequestered carbon dioxide is stored in live woody tissues and slowly decomposing organic matter in litter and soil .
Old-growth forests therefore serve as a global carbon dioxide sink , but they are not protected by international treaties , because it is generally thought that ageing forests cease to accumulate carbon .
Here we report a search of literature and databases for forest carbon-flux estimates .
We find that in forests between 15 and 800 years of age , net ecosystem productivity ( the net carbon balance of the forest including soils ) is usually positive .
Our results demonstrate that old-growth forests can continue to accumulate carbon , contrary to the long-standing view that they are carbon neutral .
Over 30 per cent of the global forest area is unmanaged primary forest , and this area contains the remaining old-growth forests .
Half of the primary forests ( 6 x 108 hectares ) are located in the boreal and temperate regions of the Northern Hemisphere .
On the basis of our analysis , these forests alone sequester about 1.3 + / - 0.5 gigatonnes of carbon per year .
Thus , our findings suggest that 15 per cent of the global forest area , which is currently not considered when offsetting increasing atmospheric carbon dioxide concentrations , provides at least 10 per cent of the global net ecosystem productivity .
Old-growth forests accumulate carbon for centuries and contain large quantities of it .
We expect , however , that much of this carbon , even soil carbon , will move back to the atmosphere if these forests are disturbed .

[1320] Uplift and seismicity driven by groundwater depletion in central California

Groundwater use in California 's San Joaquin Valley exceeds replenishment of the aquifer , leading to substantial diminution of this resource and rapid subsidence of the valley floor .
The volume of groundwater lost over the past century and a half also represents a substantial reduction in mass and a large-scale unburdening of the lithosphere , with significant but unexplored potential impacts on crustal deformation and seismicity .
Here we use vertical global positioning system measurements to show that a broad zone of rock uplift of up to 1-3 mm per year surrounds the southern San Joaquin Valley .
The observed uplift matches well with predicted flexure from a simple elastic model of current rates of water-storage loss , most of which is caused by groundwater depletion .
The height of the adjacent central Coast Ranges and the Sierra Nevada is strongly seasonal and peaks during the dry late summer and autumn , out of phase with uplift of the valley floor during wetter months .
Our results suggest that long-term and late-summer flexural uplift of the Coast Ranges reduce the effective normal stress resolved on the San Andreas Fault .
This process brings the fault closer to failure , thereby providing a viable mechanism for observed seasonality in microseismicity at Parkfield and potentially affecting long-term seismicity rates for fault systems adjacent to the valley .
We also infer that the observed contemporary uplift of the southern Sierra Nevada previously attributed to tectonic or mantle-derived forces is partly a consequence of human-caused groundwater depletion .

[1321] Genomic islands in pathogenic and environmental microorganisms

Horizontal gene transfer is an important mechanism for the evolution of microbial genomes .
Pathogenicity islands -- mobile genetic elements that contribute to rapid changes in virulence potential -- are known to have contributed to genome evolution by horizontal gene transfer in many bacterial pathogens .
Increasing evidence indicates that equivalent elements in non-pathogenic species -- genomic islands -- are important in the evolution of these bacteria , influencing traits such as antibiotic resistance , symbiosis and fitness , and adaptation in general .
This review discusses the recent lessons that have been learned from pathogenicity islands in pathogenic microorganisms and how they apply to the role of genomic islands in commensal , symbiotic and environmental bacteria .

[1322] Rapid worldwide depletion of predatory fish communities

Serious concerns have been raised about the ecological effects of industrialized fishing , spurring a United Nations resolution on restoring fisheries and marine ecosystems to healthy levels .
However , a prerequisite for restoration is a general understanding of the composition and abundance of unexploited fish communities , relative to contemporary ones .
We constructed trajectories of community biomass and composition of large predatory fishes in four continental shelf and nine oceanic systems , using all available data from the beginning of exploitation .
Industrialized fisheries typically reduced community biomass by 80 % within 15 years of exploitation .
Compensatory increases in fast-growing species were observed , but often reversed within a decade .
Using a meta-analytic approach , we estimate that large predatory fish biomass today is only about 10 % of pre-industrial levels .
We conclude that declines of large predators in coastal regions have extended throughout the global ocean , with potentially serious consequences for ecosystems .
Our analysis suggests that management based on recent data alone may be misleading , and provides minimum estimates for unexploited communities , which could serve as the ` missing baseline ' needed for future restoration efforts .

[1323] Diversity peaks at intermediate productivity in a laboratory microcosm

The species diversity of natural communities is often strongly related to their productivity .
The pattern of this relationship seems to vary : diversity is known to increase monotonically with productivity , to decrease monotonically with productivity , and to be unimodally related to productivity , with maximum diversity occurring at intermediate levels of productivity .
The mechanism underlying these patterns remains obscure , although many possibilities have been suggested .
Here we outline a simple mechanism -- involving selection in a heterogeneous environment -- to explain these patterns , and test it using laboratory cultures of the bacterium Pseudomonas fluorescens .
We grew diverse cultures over a wide range of nutrient concentrations , and found a strongly unimodal relationship between diversity and productivity in heterogeneous , but not in homogeneous , environments .
Our result provides experimental evidence that the unimodal relationship often observed in natural communities can be caused by selection for specialized types in a heterogeneous environment .

[1324] Habitat stress initiates changes in composition , CO2 gas exchange and C-allocation as life traits in biological soil crusts

Biological soil crusts ( BSC ) are the dominant functional vegetation unit in some of the harshest habitats in the world .
We assessed BSC response to stress through changes in biotic composition , CO2 gas exchange and carbon allocation in three lichen-dominated BSC from habitats with different stress levels , two more extreme sites in Antarctica and one moderate site in Germany .
Maximal net photosynthesis ( NP ) was identical , whereas the water content to achieve maximal NP was substantially lower in the Antarctic sites , this apparently being achieved by changes in biomass allocation .
Optimal NP temperatures reflected local climate .
The Antarctic BSC allocated fixed carbon ( tracked using 14CO2 ) mostly to the alcohol soluble pool ( low-molecular weight sugars , sugar alcohols ) , which has an important role in desiccation and freezing resistance and antioxidant protection .
In contrast , BSC at the moderate site showed greater carbon allocation into the polysaccharide pool , indicating a tendency towards growth .
The results indicate that the BSC of the more stressed Antarctic sites emphasise survival rather than growth .
Changes in BSC are adaptive and at multiple levels and we identify benefits and risks attached to changing life traits , as well as describing the ecophysiological mechanisms that underlie them .

[1325] Reconstruction of the history of anthropogenic CO2 concentrations in the ocean

The release of fossil fuel CO2 to the atmosphere by human activity has been implicated as the predominant cause of recent global climate change .
The ocean plays a crucial role in mitigating the effects of this perturbation to the climate system , sequestering 20 to 35 per cent of anthropogenic CO2 emissions .
Although much progress has been made in recent years in understanding and quantifying this sink , considerable uncertainties remain as to the distribution of anthropogenic CO2 in the ocean , its rate of uptake over the industrial era , and the relative roles of the ocean and terrestrial biosphere in anthropogenic CO2 sequestration .
Here we address these questions by presenting an observationally based reconstruction of the spatially resolved , time-dependent history of anthropogenic carbon in the ocean over the industrial era .
Our approach is based on the recognition that the transport of tracers in the ocean can be described by a Green 's function , which we estimate from tracer data using a maximum entropy deconvolution technique .
Our results indicate that ocean uptake of anthropogenic CO2 has increased sharply since the 1950s , with a small decline in the rate of increase in the last few decades .
We estimate the inventory and uptake rate of anthropogenic CO2 in 2008 at 140 + / - 25 Pg C and 2.3 + / - 0.6 Pg C yr-1 , respectively .
We find that the Southern Ocean is the primary conduit by which this CO2 enters the ocean ( contributing over 40 per cent of the anthropogenic CO2 inventory in the ocean in 2008 ) .
Our results also suggest that the terrestrial biosphere was a source of CO2 until the 1940s , subsequently turning into a sink .
Taken over the entire industrial period , and accounting for uncertainties , we estimate that the terrestrial biosphere has been anywhere from neutral to a net source of CO2 , contributing up to half as much CO2 as has been taken up by the ocean over the same period .

[1326] Parasitic plants indirectly regulate below-ground properties in grassland ecosystems

Parasitic plants are one of the most ubiquitous groups of generalist parasites in both natural and managed ecosystems , with over 3,000 known species worldwide .
Although much is known about how parasitic plants influence host peformance , their role as drivers of community - and ecosystem-level properties remains largely unexplored .
Parasitic plants have the potential to influence directly the productivity and structure of plant communities because they cause harm to particular host plants , indirectly increasing the competitive status of non-host species .
Such parasite-driven above-ground effects might also have important indirect consequences through altering the quantity and quality of resources that enter soil , thereby affecting the activity of decomposer organisms .
Here we show in model grassland communities that the parasitic plant Rhinanthus minor , which occurs widely throughout Europe and North America , has strong direct effects on above-ground community properties , increasing plant diversity and reducing productivity .
We also show that these direct effects of R. minor on the plant community have marked indirect effects on below-ground properties , ultimately increasing rates of nitrogen cycling .
Our study provides evidence that parasitic plants act as a major driver of both above-ground and below-ground properties of grassland ecosystems .

[1327] Micromonospora from nitrogen fixing nodules of alfalfa ( Medicago sativa L. ) .

A new promising Plant Probiotic Bacteria .
Biotic interactions can improve agricultural productivity without costly and environmentally challenging inputs .
Micromonospora strains have recently been reported as natural endophytes of legume nodules but their significance for plant development and productivity has not yet been established .
The aim of this study was to determine the diversity and function of Micromonospora isolated from Medicago sativa root nodules .
Micromonospora-like strains from field alfalfa nodules were characterized by BOX-PCR fingerprinting and 16S rRNA gene sequencing .
The ecological role of the interaction of the 15 selected representative Micromonospora strains was tested in M. sativa .
Nodulation , plant growth and nutrition parameters were analyzed .
Alfalfa nodules naturally contain abundant and highly diverse populations of Micromonospora , both at the intra - and at interspecific level .
Selected Micromonospora isolates significantly increase the nodulation of alfalfa by Ensifer meliloti 1021 and also the efficiency of the plant for nitrogen nutrition .
Moreover , they promote aerial growth , the shoot-to-root ratio , and raise the level of essential nutrients .
Our results indicate that Micromonospora acts as a Rhizobia Helper Bacteria ( RHB ) agent and has probiotic effects , promoting plant growth and increasing nutrition efficiency .
Its ecological role , biotechnological potential and advantages as a plant probiotic bacterium ( PPB ) are also discussed .

[1328] Pervasive transition of the Brazilian land-use system

Agriculture , deforestation , greenhouse gas emissions and local/regional climate change have been closely intertwined in Brazil .
Recent studies show that this relationship has been changing since the mid 2000s , with the burgeoning intensification and commoditization of Brazilian agriculture .
On one hand , this accrues considerable environmental dividends including a pronounced reduction in deforestation ( which is becoming decoupled from agricultural production ) , resulting in a decrease of ~ 40 % in nationwide greenhouse gas emissions since 2005 , and a potential cooling of the climate at the local scale .
On the other hand , these changes in the land-use system further reinforce the long-established inequality in land ownership , contributing to rural-urban migration that ultimately fuels haphazard expansion of urban areas .
We argue that strong enforcement of sector-oriented policies and solving long-standing land tenure problems , rather than simply waiting for market self-regulation , are key steps to buffer the detrimental effects of agricultural intensification at the forefront of a sustainable pathway for land use in Brazil .

[1329] Despite strong seasonal responses , soil microbial consortia are more resilient to long-term changes in rainfall than overlying grassland

Climate change impacts on soil microbial communities could alter the structure of terrestrial ecosystems and biogeochemical cycles of the Earth .
We used 16S rRNA gene microarrays to evaluate changes in the composition of grassland soil microbial communities under rainfall amendments simulating alternative climate change scenarios , and to compare these to responses of overlying plants and invertebrates .
Following 5 years of rainfall manipulation , soil bacteria and archaea in plots where natural rain was supplemented differed little from ambient controls , despite profound treatment-related changes in the overlying grassland .
During the sixth and seventh year , seasonal differences in bacterial and archaeal assemblages emerged among treatments , but only when watering exacerbated or alleviated periods of particularly aberrant conditions in the ambient climate .
In contrast to effects on plants and invertebrates , effects on bacteria and archaea did not compound across seasons or years , indicating that soil microbial communities may be more robust than associated aboveground macroorganisms to certain alterations in climate .

[1330] IS5 inserts upstream of the master motility operon flhDC in a quasi-Lamarckian way

Mutation rates may be influenced by the environment .
Here , we demonstrate that insertion sequence IS5 in Escherichia coli inserts into the upstream region of the flhDC operon in a manner that depends on whether the environment permits motility ; this operon encodes the master regulator of cell motility , FlhDC , and the IS5 insertion increases motility .
IS5 inserts upstream of flhD + when cells are grown on soft-agar plates that permit swimming motility , but does not insert upstream of this locus on hard-agar plates that do not permit swimming motility or in planktonic cultures .
Furthermore , there was only one IS5 insertion event on soft-agar plates , indicating insertion of IS5 into flhDC is not due to general elevated IS5 transposition throughout the whole genome .
We also show that the highly motile cells with IS5 upstream of flhD + have greater biofilm formation , although there is a growth cost due to the energetic burden of the enhanced motility as these highly motile cells have a lower yield in rich medium and reduced growth rate .
Functional flagella are required for IS5 insertion upstream of flhD + as there was no IS5 insertion upstream of flhD + for flhD , flgK and motA mutants , and the mutation is stable .
Additionally , the IS5 mutation occurs during biofilm formation , which creates genetic and phenotypic diversity .
Hence , the cells appear to ` sense ' whether motility is feasible before a sub-population undergoes a mutation to become hypermotile ; this sensing appears related to the master transcription regulator , FlhDC .

[1331] Changes in coral microbial communities in response to a natural pH gradient

Surface seawater pH is currently 0.1 units lower than pre-industrial values and is projected to decrease by up to 0.4 units by the end of the century .
This acidification has the potential to cause significant perturbations to the physiology of ocean organisms , particularly those such as corals that build their skeletons/shells from calcium carbonate .
Reduced ocean pH could also have an impact on the coral microbial community , and thus may affect coral physiology and health .
Most of the studies to date have examined the impact of ocean acidification on corals and/or associated microbiota under controlled laboratory conditions .
Here we report the first study that examines the changes in coral microbial communities in response to a natural pH gradient ( mean pHT 7.3-8 .1 ) caused by volcanic CO2 vents off Ischia , Gulf of Naples , Italy .
Two Mediterranean coral species , Balanophyllia europaea and Cladocora caespitosa , were examined .
The microbial community diversity and the physiological parameters of the endosymbiotic dinoflagellates ( Symbiodinium spp . )
were monitored .
We found that pH did not have a significant impact on the composition of associated microbial communities in both coral species .
In contrast to some earlier studies , we found that corals present at the lower pH sites exhibited only minor physiological changes and no microbial pathogens were detected .
Together , these results provide new insights into the impact of ocean acidification on the coral holobiont .

[1332] Community shifts of soybean stem-associated bacteria responding to different nodulation phenotypes and N levels

The diversity of stem-associated bacteria of non-nodulated ( Nod - ) , wild-type nodulated ( Nod + ) and hypernodulated ( Nod + + ) soybeans were evaluated by clone library analyses of the 16S ribosomal RNA gene .
Soybeans were dressed with standard nitrogen ( SN ) fertilization ( 15 kg N ha-1 ) and heavy nitrogen ( HN ) fertilization ( 615 kg N ha-1 ) .
The relative abundance of Alphaproteobacteria in Nod + soybeans ( 66 % ) was smaller than that in Nod - and Nod + + soybeans ( 75-76 % ) under SN fertilization , whereas that of Gammaproteobacteria showed the opposite pattern ( 23 % in Nod + and 12-16 % in Nod - and Nod + + soybeans ) .
Principal coordinate analysis showed that the bacterial communities of Nod - and Nod + + soybeans were more similar to each other than to that of Nod + soybeans under SN fertilization .
HN fertilization increased the relative abundance of Gammaproteobacteria in all nodulation phenotypes ( 33-57 % ) and caused drastic shifts of the bacterial community .
The clustering analyses identified a subset of operational taxonomic units ( OTUs ) at the species level in Alpha - and Gammaproteobacteria responding to both the nodulation phenotypes and nitrogen fertilization levels .
Meanwhile , the abundance of Betaproteobacteria was relatively constant in all libraries constructed under these environmental conditions .
The relative abundances of two OTUs in Alphaproteobacteria ( Aurantimonas sp .
and Methylobacterium sp . )
were especially sensitive to nodulation phenotype and were drastically decreased under HN fertilization .
These results suggested that a subpopulation of proteobacteria in soybeans is controlled in a similar manner through both the regulation systems of plant-rhizobia symbiosis and the nitrogen signaling pathway in plants .

[1333] Moisture variability in the southwestern United States linked to abrupt glacial climate change

Many regions of the world experienced abrupt climate variability during the last glacial period ( 75-15 thousand years ago ) .
These changes probably arose from interactions between Northern Hemisphere ice sheets and circulation in the North Atlantic Ocean , but the rapid and widespread propagation of these changes requires a large-scale atmospheric response whose details remain unclear .
Here we use an oxygen isotope record from a speleothem collected from the Cave of the Bells , Arizona , USA , to reconstruct aridity in the southwestern United States during the last glacial period and deglaciation .
We find that , during this period , aridity in the southwestern United States and climate in the North Atlantic region show similar patterns of variability .
Periods of warmth in the North Atlantic Ocean , such as interstadials and the Bolling-Allerod warming , correspond to drier conditions in the southwestern United States .
Conversely , cooler temperatures in the high latitudes are associated with increased regional moisture .
We propose that interstadial warming of the North Atlantic Ocean diverted the westerly storm track northward , perhaps through weakening of the Aleutian Low , and thereby reduced moisture delivery to southwestern North America .
A similar response to future warming would exacerbate aridity in this already very dry region .

[1334] Climatic control of denudation in the deglaciated landscape of the Washington Cascades

Since the Last Glacial Maximum , the extent of glaciers in many mountainous regions has declined , and erosion driven by glacial processes has been supplanted by fluvial incision and mass wasting processes .
This shift in the drivers of erosion is thought to have altered the rate and pattern of denudation of these landscapes .
The Washington Cascades Mountains in the northwestern USA still bear the topographic imprint of Pleistocene glaciations , and are affected by large variations in precipitation , making them an ideal setting to assess the relative controls of denudation .
Here we show that denudation rates over the past millennia , as determined by 10Be exposure ages , range from 0.08 to 0.57 mm yr-1 , about four times higher than the rates inferred for million-year timescales .
We find that the millennial timescale denudation rates increase linearly with modern precipitation rates .
Based on our landscape analyses , we suggest that this relationship arises because intense precipitation triggers landslides , particularly on slopes that have been steepened by glacial erosion before or during the Last Glacial Maximum .
We conclude that the high modern interglacial denudation rates we observe in the Washington Cascades are driven by a disequilibrium between the inherited topography and the current spatial distribution of erosional processes that makes this range particularly sensitive to spatial variations in climate .

[1335] Reductions in labour capacity from heat stress under climate warming

A fundamental aspect of greenhouse-gas-induced warming is a global-scale increase in absolute humidity .
Under continued warming , this response has been shown to pose increasingly severe limitations on human activity in tropical and mid-latitudes during peak months of heat stress .
One heat-stress metric with broad occupational health applications is wet-bulb globe temperature .
We combine wet-bulb globe temperatures from global climate historical reanalysis and Earth System Model ( ESM2M ) projections with industrial and military guidelines for an acclimated individual 's occupational capacity to safely perform sustained labour under environmental heat stress ( labour capacity ) -- here defined as a global population-weighted metric temporally fixed at the 2010 distribution .
We estimate that environmental heat stress has reduced labour capacity to 90 % in peak months over the past few decades .
ESM2M projects labour capacity reduction to 80 % in peak months by 2050 .
Under the highest scenario considered ( Representative Concentration Pathway 8.5 ) , ESM2M projects labour capacity reduction to less than 40 % by 2200 in peak months , with most tropical and mid-latitudes experiencing extreme climatological heat stress .
Uncertainties and caveats associated with these projections include climate sensitivity , climate warming patterns , CO2 emissions , future population distributions , and technological and societal change .

[1336] Metabolic rate links density to demography in Tetrahymena pyriformis

Many populations show density-dependent growth rates .
We suggest that population growth rate may be connected to density through the density dependence of metabolic rate .
If metabolic rate is an index of the total biochemical work being done by an organism , then as populations grow and density suppresses metabolic rate , the rate of reproduction should slow and the ability to avoid death should diminish .
To test this idea , we grew axenic populations of a single-celled protist , Tetrahymena pyriformis , in laboratory microcosms , and measured metabolic rate and density .
We also estimated division ( birth ) and death rates .
The proposed connection was supported by two observations .
First , increasing population density suppressed per-capita metabolic rate in accordance with the predictions of a resource-division model .
The same pattern was shown with experimentally altered densities .
Second , per-capita metabolic rate was positively related to per-capita division rate and negatively related to per-capita death rate .
Thus , the particular pattern of population growth and regulation depends on exactly how individuals respond energetically to the density of conspecifics , and how they allocate metabolism to maintenance and production .
The physiological basis of population regulation in this system is based on the constraints imposed on the total metabolic work that individual cells can perform .

[1337] Climate change ( Communication arising ) : Regional warming and malaria resurgence

Disease outbreaks are known to be often influenced by local weather , but how changes in disease trends might be affected by long-term global warming is more difficult to establish .
In a study of malaria in the African highlands , Hay et al. found no significant change in long-term climate at four locations where malaria incidence has been increasing since 1976 .
We contend , however , that their conclusions are likely to be flawed by their inappropriate use of a global climate data set .
Moreover , the absence of a historical climate signal allows no inference to be drawn about the impact of future climate change on malaria in the region .

[1338] Low abundance of the matrix arm of complex I in mitochondria predicts longevity in mice

Mitochondrial function is an important determinant of the ageing process ; however , the mitochondrial properties that enable longevity are not well understood .
Here we show that optimal assembly of mitochondrial complex I predicts longevity in mice .
Using an unbiased high-coverage high-confidence approach , we demonstrate that electron transport chain proteins , especially the matrix arm subunits of complex I , are decreased in young long-living mice , which is associated with improved complex I assembly , higher complex I-linked state 3 oxygen consumption rates and decreased superoxide production , whereas the opposite is seen in old mice .
Disruption of complex I assembly reduces oxidative metabolism with concomitant increase in mitochondrial superoxide production .
This is rescued by knockdown of the mitochondrial chaperone , prohibitin .
Disrupted complex I assembly causes premature senescence in primary cells .
We propose that lower abundance of free catalytic complex I components supports complex I assembly , efficacy of substrate utilization and minimal ROS production , enabling enhanced longevity .

[1339] Controlling nitrogen migration through micro-nano networks

Nitrogen fertilizer unabsorbed by crops eventually discharges into the environment through runoff , leaching and volatilization , resulting in three-dimensional ( 3D ) pollution spanning from underground into space .
Here we describe an approach for controlling nitrogen loss , developed using loss control fertilizer ( LCF ) prepared by adding modified natural nanoclay ( attapulgite ) to traditional fertilizer .
In the aqueous phase , LCF self-assembles to form 3D micro/nano networks via hydrogen bonds and other weak interactions , obtaining a higher nitrogen spatial scale so that it is retained by a soil filtering layer .
Thus nitrogen loss is reduced and sufficient nutrition for crops is supplied , while the pollution risk of the fertilizer is substantially lowered .
As such , self-fabrication of nano-material was used to manipulate the nitrogen spatial scale , which provides a novel and promising approach for the research and control of the migration of other micro-scaled pollutants in environmental medium .

[1340] Short-term impacts of energy wood harvesting on ectomycorrhizal fungal communities of Norway spruce saplings

The increased demand for harvesting energy wood raises questions about its effects on the functioning of the forest ecosystems , soil processes and biodiversity .
Impacts of tree stump removal on ectomycorrhizal fungal ( EMF ) communities of Norway spruce saplings were studied with 454-pyrosequencing in a 3-year field experiment replicated in 3 geographical areas .
This is possibly the most thorough investigation of EMF communities associated with saplings grown on sites subjected to energy wood harvesting .
To separate impacts of tree stump and logging residue removal on EMF and plant variables , we used three harvesting treatments with increasing complexity from patch mounding alone ( P ) to patch mounding combined with logging residue removal ( RP ) , and patch mounding combined with both logging residue and stump removal ( SRP ) .
Saplings grown in uncut forests ( F ) served as references for harvesting treatments .
A majority of sequences ( > 92 % ) and operational taxonomic units ( OTUs , 55 % ) were assigned as EMF .
EMF OTU richness , fungal community composition or sapling growth did not differ between harvesting treatments ( P , RP and SRP ) , while EMF OTU richness , diversity and evenness were highest and sapling growth lowest in the undisturbed reference forests ( F ) .
The short study period may partially explain the similarities in fungal and sapling variables in different harvesting treatments .
In conclusion , our results indicate that neither stump removal nor logging residue removal have significant additional negative impacts on EMF communities or growth of Norway spruce saplings in the short-term compared with the impacts of more conventional harvesting methods , including clear cutting and patch mounding .

[1341] Dynamic scaling of morphogen gradients on growing domains

Developmental mechanisms are highly conserved , yet act in embryos of very different sizes .
How scaling is achieved has remained elusive .
Here we identify a generally applicable mechanism for dynamic scaling on growing domains and show that it quantitatively agrees with data from the Drosophila wing imaginal disc .
We show that for the measured parameter ranges , the Dpp gradient does not reach steady state during Drosophila wing development .
We further show that both , pre-steady-state dynamics and advection of cell-bound ligand in a growing tissue can , in principle , enable scaling , even for non-uniform tissue growth .
For the parameter values that have been established for the Dpp morphogen in the Drosophila wing imaginal disc , we show that scaling is mainly a result of the pre-steady-state dynamics .
Pre-steady-state dynamics are pervasive in morphogen-controlled systems , thus making this a probable general mechanism for dynamic scaling of morphogen gradients in growing developmental systems .

[1342] Stratospheric aerosol particles and solar-radiation management

The deliberate injection of particles into the stratosphere has been suggested as a possible geoengineering scheme to mitigate the global warming aspect of climate change .
Injected particles scatter solar radiation back to space and thus reduce the radiative balance of Earth .
Previous studies investigating this scheme have focused primarily on sulphuric acid particles to mimic volcanic injections of stratospheric aerosol .
However , the composition and size of volcanic sulphuric acid particles are far from optimal for scattering solar radiation .
We show that aerosols with other compositions , such as minerals , could be used to dramatically increase the amount of light scatter achieved on a per mass basis , thereby reducing the particle mass required for injection .
The chemical consequences of injecting such particles into the stratosphere are discussed with regard to the fate of the ozone layer .
Research questions are identified with which to assess the feasibility of such geoengineering schemes .

[1343] High predictability of the winter Euro-Atlantic climate from cryospheric variability

Seasonal prediction skill for surface winter climate in the Euro-Atlantic sector has been limited so far .
In particular , the predictability of the winter North Atlantic Oscillation , the mode that largely dominates regional atmospheric and climate variability , remains a hurdle for present dynamical prediction systems .
Statistical forecasts have also been largely elusive , but October Eurasian snow cover has been shown to be a robust source of regional predictability .
Here we use maximum covariance analysis to show that Arctic sea-ice variability represents another good predictor of the winter Euro-Atlantic climate at lead times of as much as three months .
Cross-validated hindcasts of the winter North Atlantic Oscillation index using September sea-ice anomalies yield a correlation skill of 0.59 for the period 1979/1980 -2012 / 2013 , suggesting that 35 % of its variance could be predicted three months in advance .
This skill can be further enhanced , at the expense of a shorter lead time , by using October Eurasian snow cover as an additional predictor .
Skilful predictions of winter European surface air temperature and precipitation are also obtained with September sea ice as the only predictor .
We conclude that it is important to incorporate Arctic sea-ice variability in seasonal prediction systems .

[1344] Greenhouse gas production in low-latitude lake sediments responds strongly to warming

Inland water sediments receive large quantities of terrestrial organic matter and are globally important sites for organic carbon preservation .
Sediment organic matter mineralization is positively related to temperature across a wide range of high-latitude ecosystems , but the situation in the tropics remains unclear .
Here we assessed temperature effects on the biological production of CO2 and CH4 in anaerobic sediments of tropical lakes in the Amazon and boreal lakes in Sweden .
On the basis of conservative regional warming projections until 2100 ( ref . )
, we estimate that sediment CO2 and CH4 production will increase 9-61 % above present rates .
Combining the CO2 and CH4 as CO2 equivalents ( CO2eq ; ref . )
, the predicted increase is 2.4-4 .5 times higher in tropical than boreal sediments .
Although the estimated lake area in low latitudes is 3.2 times smaller than that of the boreal zone , we estimate that the increase in gas production from tropical lake sediments would be on average 2.4 times higher for CO2 and 2.8 times higher for CH4 .
The exponential temperature response of organic matter mineralization , coupled with higher increases in the proportion of CH4 relative to CO2 on warming , suggests that the production of greenhouse gases in tropical sediments will increase substantially .
This represents a potential large-scale positive feedback to climate change .

[1345] All flavours of El Nino have similar early subsurface origins

The El Nino/Southern Oscillation phenomenon , characterized by anomalous sea surface temperatures and winds in the tropical Pacific , affects climate across the globe .
El Ninos occur every 2-7 years , whereas the El Nino/Southern Oscillation itself varies on decadal timescales in frequency and amplitude , with a different spatial pattern of surface anomalies each time the tropical Pacific undergoes a regime shift .
Recent work has shown that Bjerknes feedback ( coupling of the atmosphere and the ocean through changes in equatorial winds driven by changes in sea surface temperature owing to suppression of equatorial upwelling in the east Pacific ) is not necessary for the development of an El Nino .
Thus it is unclear what remains constant through regimes and is crucial for producing the anomalies recognized as El Nino .
Here we show that the subsurface process of discharging warm waters always begins in the boreal summer/autumn of the year before the event ( up to 18 months before the peak ) independent of regimes , identifying the discharge process as fundamental to the El Nino onset .
It is therefore imperative that models capture this process accurately to further our theoretical understanding , improve forecasts and predict how the El Nino/Southern Oscillation may respond to climate change .

[1346] A temporary , moderate and responsive scenario for solar geoengineering

The risks and benefits of solar geoengineering , or solar radiation management ( SRM ) , depend on assumptions about its implementation .
Claims that SRM will reduce precipitation , increase ocean acidification or deplete stratospheric ozone , or that it must be continued forever once started , are not inherent features of SRM ; rather , they are features of common scenarios for its implementation .
Most analyses assume , for example , that SRM would be used to stop the increase in global temperature or restore temperature to pre-industrial values .
We argue that these are poor scenario choices on which to base policy-relevant judgements about SRM .
As a basis for further analysis , we provide a scenario that is temporary in that its end point is zero SRM , is moderate in that it offsets only half of the growth in anthropogenic climate forcing and is responsive in that it recognizes that the amount of SRM will be adjusted in light of new information .

[1347] Upper bounds on twenty-first-century Antarctic ice loss assessed using a probabilistic framework

Climate adaptation and flood risk assessments have incorporated sea-level rise ( SLR ) projections developed using semi-empirical methods ( SEMs ) and expert-informed mass-balance scenarios .
These techniques , which do not explicitly model ice dynamics , generate upper bounds on twenty-first century SLR that are up to three times higher than Intergovernmental Panel on Climate Change estimates .
However , the physical basis underlying these projections , and their likelihood of occurrence , remain unclear .
Here , we develop mass-balance projections for the Antarctic ice sheet within a Bayesian probabilistic framework , integrating numerical model output and updating projections with an observational synthesis .
Without abrupt , sustained , changes in ice discharge ( collapse ) , we project a 95th percentile mass loss equivalent to ~ 13 cm SLR by 2100 , lower than previous upper-bound projections .
Substantially higher mass loss requires regional collapse , invoking dynamics that are likely to be inconsistent with the underlying assumptions of SEMs .
In this probabilistic framework , the pronounced sensitivity of upper-bound SLR projections to the poorly known likelihood of collapse is lessened with constraints on the persistence and magnitude of subsequent discharge .
More realistic , fully probabilistic , estimates of the ice-sheet contribution to SLR may thus be obtained by assimilating additional observations and numerical models .

[1348] High secondary aerosol contribution to particulate pollution during haze events in China

Rapid industrialization and urbanization in developing countries has led to an increase in air pollution , along a similar trajectory to that previously experienced by the developed nations .
In China , particulate pollution is a serious environmental problem that is influencing air quality , regional and global climates , and human health .
In response to the extremely severe and persistent haze pollution experienced by about 800 million people during the first quarter of 2013 ( refs 4 , 5 ) , the Chinese State Council announced its aim to reduce concentrations of PM2 .5 ( particulate matter with an aerodynamic diameter less than 2.5 micrometres ) by up to 25 per cent relative to 2012 levels by 2017 ( ref .
6 ) .
Such efforts however require elucidation of the factors governing the abundance and composition of PM2 .5 , which remain poorly constrained in China .
Here we combine a comprehensive set of novel and state-of-the-art offline analytical approaches and statistical techniques to investigate the chemical nature and sources of particulate matter at urban locations in Beijing , Shanghai , Guangzhou and Xi'an during January 2013 .
We find that the severe haze pollution event was driven to a large extent by secondary aerosol formation , which contributed 30-77 per cent and 44-71 per cent ( average for all four cities ) of PM2 .5 and of organic aerosol , respectively .
On average , the contribution of secondary organic aerosol ( SOA ) and secondary inorganic aerosol ( SIA ) are found to be of similar importance ( SOA/SIA ratios range from 0.6 to 1.4 ) .
Our results suggest that , in addition to mitigating primary particulate emissions , reducing the emissions of secondary aerosol precursors from , for example , fossil fuel combustion and biomass burning is likely to be important for controlling China 's PM2 .5 levels and for reducing the environmental , economic and health impacts resulting from particulate pollution .

[1349] Sinking deltas due to human activities

Many of the world 's largest deltas are densely populated and heavily farmed .
Yet many of their inhabitants are becoming increasingly vulnerable to flooding and conversions of their land to open ocean .
The vulnerability is a result of sediment compaction from the removal of oil , gas and water from the delta 's underlying sediments , the trapping of sediment in reservoirs upstream and floodplain engineering in combination with rising global sea level .
Here we present an assessment of 33 deltas chosen to represent the world 's deltas .
We find that in the past decade , 85 % of the deltas experienced severe flooding , resulting in the temporary submergence of 260,000 km2 .
We conservatively estimate that the delta surface area vulnerable to flooding could increase by 50 % under the current projected values for sea-level rise in the twenty-first century .
This figure could increase if the capture of sediment upstream persists and continues to prevent the growth and buffering of the deltas .

[1350] Synchronicity of Antarctic temperatures and local solar insolation on orbital timescales

The Milankovitch theory states that global climate variability on orbital timescales from tens to hundreds of thousands of years is dominated by the summer insolation at high northern latitudes .
The supporting evidence includes reconstructed air temperatures in Antarctica that are nearly in phase with boreal summer insolation and out of phase with local summer insolation .
Antarctic climate is therefore thought to be driven by northern summer insolation .
A clear mechanism that links the two hemispheres on orbital timescales is , however , missing .
We propose that key Antarctic temperature records derived from ice cores are biased towards austral winter because of a seasonal cycle in snow accumulation .
Using present-day estimates of this bias in the ` recorder ' system , here we show that the local insolation can explain the orbital component of the temperature record without having to invoke a link to the Northern Hemisphere .
Therefore , the Antarctic ice-core-derived temperature record , one of the best-dated records of the late Pleistocene temperature evolution , can not be used to support or contradict the Milankovitch hypothesis that global climate changes are driven by Northern Hemisphere summer insolation variations .

[1351] Early warning signals of Atlantic Meridional Overturning Circulation collapse in a fully coupled climate model

The Atlantic Meridional Overturning Circulation ( AMOC ) exhibits two stable states in models of varying complexity .
Shifts between alternative AMOC states are thought to have played a role in past abrupt climate changes , but the proximity of the climate system to a threshold for future AMOC collapse is unknown .
Generic early warning signals of critical slowing down before AMOC collapse have been found in climate models of low and intermediate complexity .
Here we show that early warning signals of AMOC collapse are present in a fully coupled atmosphere-ocean general circulation model , subject to a freshwater hosing experiment .
The statistical significance of signals of increasing lag-1 autocorrelation and variance vary with latitude .
They give up to 250 years warning before AMOC collapse , after ~ 550 years of monitoring .
Future work is needed to clarify suggested dynamical mechanisms driving critical slowing down as the AMOC collapse is approached .

[1352] Termini of calving glaciers as self-organized critical systems

Over the next century , one of the largest contributions to sea level rise will come from ice sheets and glaciers calving ice into the ocean .
Factors controlling the rapid and nonlinear variations in calving fluxes are poorly understood , and therefore difficult to include in prognostic climate-forced land-ice models .
Here we analyse globally distributed calving data sets from Svalbard , Alaska ( USA ) , Greenland and Antarctica in combination with simulations from a first-principles , particle-based numerical calving model to investigate the size and inter-event time of calving events .
We find that calving events triggered by the brittle fracture of glacier ice are governed by the same power-law distributions as avalanches in the canonical Abelian sandpile model .
This similarity suggests that calving termini behave as self-organized critical systems that readily flip between states of sub-critical advance and super-critical retreat in response to changes in climate and geometric conditions .
Observations of sudden ice-shelf collapse and tidewater glacier retreat in response to gradual warming of their environment are consistent with a system fluctuating around its critical point in response to changing external forcing .
We propose that self-organized criticality provides a yet unexplored framework for investigations into calving and projections of sea level rise .

[1353] Rapid sea-level rise along the Antarctic margins in response to increased glacial discharge

The Antarctic shelf seas are a climatically and ecologically important region , and are at present receiving increasing amounts of freshwater from the melting of the Antarctic Ice Sheet and its fringing ice shelves , primarily around the Antarctic Peninsula and the Amudsen Sea .
In response , the surface ocean salinity in this region has declined in past decades .
Here , we assess the effects of the freshwater input on regional sea level using satellite measurements of sea surface height ( for months with no sea-ice cover ) and a global ocean circulation model .
We find that from 1992 to 2011 , sea-level rise along the Antarctic coast is at least 2 + / - 0.8 mm yr-1 greater than the regional mean for the Southern Ocean south of 50degrees S. On the basis of the model simulations , we conclude that this sea-level rise is almost entirely related to steric adjustment , rather than changes in local ocean mass , with a halosteric rise in the upper ocean and thermosteric contributions at depth .
We estimate that an excess freshwater input of 430 + / - 230 Gt yr-1 is required to explain the observed sea-level rise .
We conclude that accelerating discharge from the Antarctic Ice Sheet has had a pronounced and widespread impact on the adjacent subpolar seas over the past two decades .

[1354] Attributing the increase in atmospheric CO2 to emitters and absorbers

Climate change policies need to consider the contribution of each emitting region to the increase in atmospheric carbon dioxide .
We calculate regional attributions of increased atmospheric CO2 using two different assumptions about land sinks .
In the first approach , each absorber region is attributed ` domestic sinks ' that occur within its boundaries .
In the second , alternative approach , each emitter region is attributed ` foreign sinks ' that it created indirectly through its contribution to increasing CO2 .
We unambiguously attribute the largest share of the historical increase in CO2 between pre-industrial times and the present-day period to developed countries .
However , the excess CO2 in the atmosphere since pre-industrial times attributed to developing countries is greater than their share of cumulative CO2 emissions .
This is because a greater fraction of their emissions occurred more recently .
If emissions remain high over the coming decades , the share of excess CO2 attributable to developing countries will grow , and the sink service provided by forested regions -- in particular those with tropical forest -- to other regions will depend critically on future tropical land-use change .

[1355] In situ formation of oxygen vacancy in perovskite Sr0 .95 Ti0 .8 Nb0 .1 M0 .1 O3 ( M = Mn , Cr ) toward efficient carbon dioxide electrolysis

In this work , redox-active Mn or Cr is introduced to the B site of redox stable perovskite Sr0 .95 Ti0 .9 Nb0 .1 O3 .00 to create oxygen vacancies in situ after reduction for high-temperature CO2 electrolysis .
Combined analysis using X-ray diffraction , X-ray photoelectron spectroscopy , transmission electron microscopy and thermogravimetric analysis confirms the change of the chemical formula from oxidized Sr0 .95 Ti0 .9 Nb0 .1 O3 .00 to reduced Sr0 .95 Ti0 .9 Nb0 .1 O2 .90 for the bare sample .
By contrast , a significant concentration of oxygen vacancy is additionally formed in situ for Mn - or Cr-doped samples by reducing the oxidized Sr0 .95 Ti0 .8 Nb0 .1 M0 .1 O3 .00 ( M = Mn , Cr ) to Sr0 .95 Ti0 .8 Nb0 .1 M0 .1 O2 .85 .
The ionic conductivities of the Mn - and Cr-doped titanate improve by approximately 2 times higher than bare titanate in an oxidizing atmosphere and 3-6 times higher in a reducing atmosphere at intermediate temperatures .
A remarkable chemical accommodation of CO2 molecules is achieved on the surface of the reduced and doped titanate , and the chemical desorption temperature reaches a common carbonate decomposition temperature .
The electrical properties of the cathode materials are investigated and correlated with the electrochemical performance of the composite electrodes .
Direct CO2 electrolysis at composite cathodes is investigated in solid-oxide electrolyzers .
The electrode polarizations and current efficiencies are observed to be significantly improved with the Mn - or Cr-doped titanate cathodes .

[1356] Deep instability of deforested tropical peatlands revealed by fluvial organic carbon fluxes

Tropical peatlands contain one of the largest pools of terrestrial organic carbon , amounting to about 89,000 teragrams ( 1 Tg is a billion kilograms ) .
Approximately 65 per cent of this carbon store is in Indonesia , where extensive anthropogenic degradation in the form of deforestation , drainage and fire are converting it into a globally significant source of atmospheric carbon dioxide .
Here we quantify the annual export of fluvial organic carbon from both intact peat swamp forest and peat swamp forest subject to past anthropogenic disturbance .
We find that the total fluvial organic carbon flux from disturbed peat swamp forest is about 50 per cent larger than that from intact peat swamp forest .
By carbon-14 dating of dissolved organic carbon ( which makes up over 91 per cent of total organic carbon ) , we find that leaching of dissolved organic carbon from intact peat swamp forest is derived mainly from recent primary production ( plant growth ) .
In contrast , dissolved organic carbon from disturbed peat swamp forest consists mostly of much older ( centuries to millennia ) carbon from deep within the peat column .
When we include the fluvial carbon loss term , which is often ignored , in the peatland carbon budget , we find that it increases the estimate of total carbon lost from the disturbed peatlands in our study by 22 per cent .
We further estimate that since 1990 peatland disturbance has resulted in a 32 per cent increase in fluvial organic carbon flux from southeast Asia -- an increase that is more than half of the entire annual fluvial organic carbon flux from all European peatlands .
Our findings emphasize the need to quantify fluvial carbon losses in order to improve estimates of the impact of deforestation and drainage on tropical peatland carbon balances .

[1357] Members of native coral microbiota inhibit glycosidases and thwart colonization of coral mucus by an opportunistic pathogen

The outcome of the interactions between native commensal microorganisms and opportunistic pathogens is crucial to the health of the coral holobiont .
During the establishment within the coral surface mucus layer , opportunistic pathogens , including a white pox pathogen Serratia marcescens PDL100 , compete with native bacteria for available nutrients .
Both commensals and pathogens employ glycosidases and N-acetyl-glucosaminidase to utilize components of coral mucus .
This study tested the hypothesis that specific glycosidases were critical for the growth of S. marcescens on mucus and that their inhibition by native coral microbiota reduces fitness of the pathogen .
Consistent with this hypothesis , a S. marcescens transposon mutant with reduced glycosidase and N-acetyl-glucosaminidase activities was unable to compete with the wild type on the mucus of the host coral Acropora palmata , although it was at least as competitive as the wild type on a minimal medium with glycerol and casamino acids .
Virulence of the mutant was modestly reduced in the Aiptasia model .
A survey revealed that ~ 8 % of culturable coral commensal bacteria have the ability to inhibit glycosidases in the pathogen .
A small molecular weight , ethanol-soluble substance ( s ) produced by the coral commensal Exiguobacterium sp .
was capable of the inhibition of the induction of catabolic enzymes in S. marcescens .
This inhibition was in part responsible for the 10-100-fold reduction in the ability of the pathogen to grow on coral mucus .
These results provide insight into potential mechanisms of commensal interference with early colonization and infection behaviors in opportunistic pathogens and highlight an important function for the native microbiota in coral health .

[1358] Quantifying the risk of extreme seasonal precipitation events in a changing climate

Increasing concentrations of atmospheric carbon dioxide will almost certainly lead to changes in global mean climate .
But because -- by definition -- extreme events are rare , it is significantly more difficult to quantify the risk of extremes .
Ensemble-based probabilistic predictions , as used in short - and medium-term forecasts of weather and climate , are more useful than deterministic forecasts using a ` best guess ' scenario to address this sort of problem .
Here we present a probabilistic analysis of 19 global climate model simulations with a generic binary decision model .
We estimate that the probability of total boreal winter precipitation exceeding two standard deviations above normal will increase by a factor of five over parts of the UK over the next 100 years .
We find similar increases in probability for the Asian monsoon region in boreal summer , with implications for flooding in Bangladesh .
Further practical applications of our techniques would be helped by the use of larger ensembles ( for a more complete sampling of model uncertainty ) and a wider range of scenarios at a resolution adequate to analyse average-size river basins .

[1359] Effect of nutrient availability on marine origination rates throughout the Phanerozoic eon

Throughout the Phanerozoic eon ( ~ 542 Myr ago to the present ) , the diversity of marine organisms has varied .
These changes are fairly well resolved , but the controls on origination and diversification are less well understood .
Changes in origination rates are thought to arise from a complex interplay between biological forces such as competition and predation , phytoplankton stoichiometry and bioturbation and abiotic controls such as environmental setting , temperature , sea level and nutrient availability .
Here we statistically assess relationships between records of environmental conditions and global marine origination rates during the Phanerozoic .
We find significant positive correlations between changes in origination rates and variations in indicators of continental weathering ( 87Sr/86Sr ) and phosphorus recycling ( delta34S ) , as well as a significant negative correlation between variability in origination rates and eustatic sea level .
We suggest that continental weathering , phosphorus recycling and sea level -- through the exposure of the continental shelf area to erosion -- are all controls on the availability of marine nutrients .
We therefore propose that over secular timescales , nutrient availability , as controlled by continental weathering and phosphorus recycling , is an important regulator of genus-level origination in the marine realm , with periods of increased nutrient availability associated with higher origination rates .

[1360] Influence of Patagonian glaciers on Antarctic dust deposition during the last glacial period

Ice cores provide a record of changes in dust flux to Antarctica , which is thought to reflect changes in atmospheric circulation and environmental conditions in dust source areas .
Isotopic tracers suggest that South America is the dominant source of the dust , but it is unclear what led to the variable deposition of dust at concentrations 20-50 times higher than present in glacial-aged ice .
Here we characterize the age and composition of Patagonian glacial outwash sediments , to assess the relationship between the Antarctic dust record from Dome C ( refs 9 , 13 ) and Patagonian glacial fluctuations for the past 80,000 years .
We show that dust peaks in Antarctica coincide with periods in Patagonia when rivers of glacial meltwater deposited sediment directly onto easily mobilized outwash plains .
No dust peaks were noted when the glaciers instead terminated directly into pro-glacial lakes .
We thus propose that the variable sediment supply resulting from Patagonian glacial fluctuations may have acted as an on/off switch for Antarctic dust deposition .
At the last glacial termination , Patagonian glaciers quickly retreated into lakes , which may help explain why the deglacial decline in Antarctic dust concentrations preceded the main phase of warming , sea-level rise and reduction in Southern Hemisphere sea-ice extent .

[1361] Increased frequency of extreme Indian Ocean Dipole events due to greenhouse warming

The Indian Ocean dipole is a prominent mode of coupled ocean-atmosphere variability , affecting the lives of millions of people in Indian Ocean rim countries .
In its positive phase , sea surface temperatures are lower than normal off the Sumatra-Java coast , but higher in the western tropical Indian Ocean .
During the extreme positive-IOD ( pIOD ) events of 1961 , 1994 and 1997 , the eastern cooling strengthened and extended westward along the equatorial Indian Ocean through strong reversal of both the mean westerly winds and the associated eastward-flowing upper ocean currents .
This created anomalously dry conditions from the eastern to the central Indian Ocean along the Equator and atmospheric convergence farther west , leading to catastrophic floods in eastern tropical African countries but devastating droughts in eastern Indian Ocean rim countries .
Despite these serious consequences , the response of pIOD events to greenhouse warming is unknown .
Here , using an ensemble of climate models forced by a scenario of high greenhouse gas emissions ( Representative Concentration Pathway 8.5 ) , we project that the frequency of extreme pIOD events will increase by almost a factor of three , from one event every 17.3 years over the twentieth century to one event every 6.3 years over the twenty-first century .
We find that a mean state change -- with weakening of both equatorial westerly winds and eastward oceanic currents in association with a faster warming in the western than the eastern equatorial Indian Ocean -- facilitates more frequent occurrences of wind and oceanic current reversal .
This leads to more frequent extreme pIOD events , suggesting an increasing frequency of extreme climate and weather events in regions affected by the pIOD .

[1362] Effect of natural iron fertilization on carbon sequestration in the Southern Ocean

The availability of iron limits primary productivity and the associated uptake of carbon over large areas of the ocean .
Iron thus plays an important role in the carbon cycle , and changes in its supply to the surface ocean may have had a significant effect on atmospheric carbon dioxide concentrations over glacial-interglacial cycles .
To date , the role of iron in carbon cycling has largely been assessed using short-term iron-addition experiments .
It is difficult , however , to reliably assess the magnitude of carbon export to the ocean interior using such methods , and the short observational periods preclude extrapolation of the results to longer timescales .
Here we report observations of a phytoplankton bloom induced by natural iron fertilization -- an approach that offers the opportunity to overcome some of the limitations of short-term experiments .
We found that a large phytoplankton bloom over the Kerguelen plateau in the Southern Ocean was sustained by the supply of iron and major nutrients to surface waters from iron-rich deep water below .
The efficiency of fertilization , defined as the ratio of the carbon export to the amount of iron supplied , was at least ten times higher than previous estimates from short-term blooms induced by iron-addition experiments .
This result sheds new light on the effect of long-term fertilization by iron and macronutrients on carbon sequestration , suggesting that changes in iron supply from below -- as invoked in some palaeoclimatic and future climate change scenarios -- may have a more significant effect on atmospheric carbon dioxide concentrations than previously thought .

[1363] Microbial mediation of biogeochemical cycles revealed by simulation of global changes with soil transplant and cropping

Despite microbes ' key roles in driving biogeochemical cycles , the mechanism of microbe-mediated feedbacks to global changes remains elusive .
Recently , soil transplant has been successfully established as a proxy to simulate climate changes , as the current trend of global warming coherently causes range shifts toward higher latitudes .
Four years after southward soil transplant over large transects in China , we found that microbial functional diversity was increased , in addition to concurrent changes in microbial biomass , soil nutrient content and functional processes involved in the nitrogen cycle .
However , soil transplant effects could be overridden by maize cropping , which was attributed to a negative interaction .
Strikingly , abundances of nitrogen and carbon cycle genes were increased by these field experiments simulating global change , coinciding with higher soil nitrification potential and carbon dioxide ( CO2 ) efflux .
Further investigation revealed strong correlations between carbon cycle genes and CO2 efflux in bare soil but not cropped soil , and between nitrogen cycle genes and nitrification .
These findings suggest that changes of soil carbon and nitrogen cycles by soil transplant and cropping were predictable by measuring microbial functional potentials , contributing to a better mechanistic understanding of these soil functional processes and suggesting a potential to incorporate microbial communities in greenhouse gas emission modeling .

[1364] The rise and fall of methanotrophy following a deepwater oil-well blowout

The blowout of the Macondo oil well in the Gulf of Mexico in April 2010 injected up to 500,000 tonnes of natural gas , mainly methane , into the deep sea .
Most of the methane released was thought to have been consumed by marine microbes between July and August 2010 .
Here , we report spatially extensive measurements of methane concentrations and oxidation rates in the nine months following the spill .
We show that although gas-rich deepwater plumes were a short-lived feature , water column concentrations of methane remained above background levels throughout the rest of the year .
Rates of microbial methane oxidation peaked in the deepwater plumes in May and early June , coincident with a rapid rise in the abundance of known and new methane-oxidizing microbes .
At this time , rates of methane oxidation reached up to 5,900 nmol l-1 d-1 -- the highest rates documented in the global pelagic ocean before the blowout .
Rates of methane oxidation fell to less than 50 nmol l-1 d-1 in late June , and continued to decline throughout the remainder of the year .
We suggest the precipitous drop in methane consumption in late June , despite the persistence of methane in the water column , underscores the important role that physiological and environmental factors play in constraining the activity of methane-oxidizing bacteria in the Gulf of Mexico .

[1365] Productivity controls food-chain properties in microbial communities

Food webs provide a framework for integrating population dynamics , community structure and ecosystem processes , but the causes of many food-web patterns remain controversial .
An unresolved issue concerns the factors that limit food-chain length in natural ecosystems , although theory predicts that length could be limited by inefficient energy transfer between trophic levels orby the instability of longer food chains .
Experiments provide qualitative support for the instability of longer food chains , but , according to theory , this relationship may depend on the assumptions used to model food chains .
Here we show that experimental manipulations of productivity determine the length of microbial food chains in laboratory microcosms .
Food-chain length is also predicted to determine how productivity influences population densities within trophic levels .
If trophic levels consist entirely ofedible prey , and if consumers feed only on the next-lower trophic level , population densities should alternate between increasing and constant values as food-chain length increases ( Fig. 1 ) .
We find that food-chain length determines population-level responses to productivity , which is consistent with predictions from models .
These results indicate that the impacts of human alterations of productivity will depend crucially on the structure of the affected food chains .

[1366] Invasive hybridization in a threatened species is accelerated by climate change

Climate change will decrease worldwide biodiversity through a number of potential pathways , including invasive hybridization ( cross-breeding between invasive and native species ) .
How climate warming influences the spread of hybridization and loss of native genomes poses difficult ecological and evolutionary questions with little empirical information to guide conservation management decisions .
Here we combine long-term genetic monitoring data with high-resolution climate and stream temperature predictions to evaluate how recent climate warming has influenced the spatio-temporal spread of human-mediated hybridization between threatened native westslope cutthroat trout ( Oncorhynchus clarkii lewisi ) and non-native rainbow trout ( Oncorhynchus mykiss ) , the world 's most widely introduced invasive fish .
Despite widespread release of millions of rainbow trout over the past century within the Flathead River system , a large relatively pristine watershed in western North America , historical samples revealed that hybridization was prevalent only in one ( source ) population .
During a subsequent 30-year period of accelerated warming , hybridization spread rapidly and was strongly linked to interactions between climatic drivers -- precipitation and temperature -- and distance to the source population .
Specifically , decreases in spring precipitation and increases in summer stream temperature probably promoted upstream expansion of hybridization throughout the system .
This study shows that rapid climate warming can exacerbate interactions between native and non-native species through invasive hybridization , which could spell genomic extinction for many species .

[1367] A satellite view of aerosols in the climate system

Anthropogenic aerosols are intricately linked to the climate system and to the hydrologic cycle .
The net effect of aerosols is to cool the climate system by reflecting sunlight .
Depending on their composition , aerosols can also absorb sunlight in the atmosphere , further cooling the surface but warming the atmosphere in the process .
These effects of aerosols on the temperature profile , along with the role of aerosols as cloud condensation nuclei , impact the hydrologic cycle , through changes in cloud cover , cloud properties and precipitation .
Unravelling these feedbacks is particularly difficult because aerosols take a multitude of shapes and forms , ranging from desert dust to urban pollution , and because aerosol concentrations vary strongly over time and space .
To accurately study aerosol distribution and composition therefore requires continuous observations from satellites , networks of ground-based instruments and dedicated field experiments .
Increases in aerosol concentration and changes in their composition , driven by industrialization and an expanding population , may adversely affect the Earth 's climate and water supply .

[1368] Microbial sequestration of phosphorus in anoxic upwelling sediments

Phosphorus is an essential nutrient for life .
In the ocean , phosphorus burial regulates marine primary production .
Phosphorus is removed from the ocean by sedimentation of organic matter , and the subsequent conversion of organic phosphorus to phosphate minerals such as apatite , and ultimately phosphorite deposits .
Bacteria are thought to mediate these processes , but the mechanism of sequestration has remained unclear .
Here , we present results from laboratory incubations in which we labelled organic-rich sediments from the Benguela upwelling system , Namibia , with a 33P-radiotracer , and tracked the fate of the phosphorus .
We show that under both anoxic and oxic conditions , large sulphide-oxidizing bacteria accumulate 33P in their cells , and catalyse the nearly instantaneous conversion of phosphate to apatite .
Apatite formation was greatest under anoxic conditions .
Nutrient analyses of Namibian upwelling waters and sediments suggest that the rate of phosphate-to-apatite conversion beneath anoxic bottom waters exceeds the rate of phosphorus release during organic matter mineralization in the upper sediment layers .
We suggest that bacterial apatite formation is a significant phosphorus sink under anoxic bottom-water conditions .
Expanding oxygen minimum zones are projected in simulations of future climate change , potentially increasing sequestration of marine phosphate , and restricting marine productivity .

[1369] Antarctic ice-sheet loss driven by basal melting of ice shelves

Accurate prediction of global sea-level rise requires that we understand the cause of recent , widespread and intensifying glacier acceleration along Antarctic ice-sheet coastal margins .
Atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves , potentially limiting their ability to buttress the flow of grounded tributary glaciers .
Indeed , recent ice-shelf collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula .
But the extent and magnitude of ice-shelf thickness change , the underlying causes of such change , and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets can not yet be predicted .
Here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum-Antarctic pattern of ice-shelf thinning through increased basal melt .
We deduce that this increased melt is the primary control of Antarctic ice-sheet loss , through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow .
The highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf .
Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic ice shelves , through ocean upwelling in the Amundsen and Bellingshausen seas , and atmospheric warming on the Antarctic Peninsula .
This implies that climate forcing through changing winds influences Antarctic ice-sheet mass balance , and hence global sea level , on annual to decadal timescales .

[1370] Two centuries of limited variability in subtropical North Atlantic thermocline ventilation

Ventilation and mixing of oceanic gyres is important to ocean-atmosphere heat and gas transfer , and to mid-latitude nutrient supply .
The rates of mode water formation are believed to impact climate and carbon exchange between the surface and mid-depth water over decadal periods .
Here , a record of 14C/12C ( 1780-1940 ) , which is a proxy for vertical ocean mixing , from an annually banded coral from Bermuda , shows limited inter-annual variability and a substantial Suess Effect ( the decrease in 14C/12C since 1900 ) .
The Sargasso Sea mixing rates between the surface and thermocline varied minimally over the past two centuries , despite changes to mean-hemispheric climate , including the Little Ice Age and variability in the North Atlantic Oscillation .
This result indicates that regional formation rates of sub-tropical mode water are stable over decades , and that anthropogenic carbon absorbed by the ocean does not return to the surface at a variable rate .

[1371] The case against climate regulation via oceanic phytoplankton sulphur emissions

More than twenty years ago , a biological regulation of climate was proposed whereby emissions of dimethyl sulphide from oceanic phytoplankton resulted in the formation of aerosol particles that acted as cloud condensation nuclei in the marine boundary layer .
In this hypothesis -- referred to as CLAW -- the increase in cloud condensation nuclei led to an increase in cloud albedo with the resulting changes in temperature and radiation initiating a climate feedback altering dimethyl sulphide emissions from phytoplankton .
Over the past two decades , observations in the marine boundary layer , laboratory studies and modelling efforts have been conducted seeking evidence for the CLAW hypothesis .
The results indicate that a dimethyl sulphide biological control over cloud condensation nuclei probably does not exist and that sources of these nuclei to the marine boundary layer and the response of clouds to changes in aerosol are much more complex than was recognized twenty years ago .
These results indicate that it is time to retire the CLAW hypothesis .

[1372] Enhanced ice sheet growth in Eurasia owing to adjacent ice-dammed lakes

Large proglacial lakes cool regional summer climate because of their large heat capacity , and have been shown to modify precipitation through mesoscale atmospheric feedbacks , as in the case of Lake Agassiz .
Several large ice-dammed lakes , with a combined area twice that of the Caspian Sea , were formed in northern Eurasia about 90,000 years ago , during the last glacial period when an ice sheet centred over the Barents and Kara seas blocked the large northbound Russian rivers .
Here we present high-resolution simulations with an atmospheric general circulation model that explicitly simulates the surface mass balance of the ice sheet .
We show that the main influence of the Eurasian proglacial lakes was a significant reduction of ice sheet melting at the southern margin of the Barents-Kara ice sheet through strong regional summer cooling over large parts of Russia .
In our simulations , the summer melt reduction clearly outweighs lake-induced decreases in moisture and hence snowfall , such as has been reported earlier for Lake Agassiz .
We conclude that the summer cooling mechanism from proglacial lakes accelerated ice sheet growth and delayed ice sheet decay in Eurasia and probably also in North America .

[1373] Persistent link between solar activity and Greenland climate during the Last Glacial Maximum

Changes in solar activity have previously been proposed to cause decadal - to millennial-scale fluctuations in both the modern and Holocene climates .
Direct observational records of solar activity , such as sunspot numbers , exist for only the past few hundred years , so solar variability for earlier periods is typically reconstructed from measurements of cosmogenic radionuclides such as 10Be and 14C from ice cores and tree rings .
Here we present a high-resolution 10Be record from the ice core collected from central Greenland by the Greenland Ice Core Project ( GRIP ) .
The record spans from 22,500 to 10,000 years ago , and is based on new and compiled data .
Using 14C records to control for climate-related influences on 10Be deposition , we reconstruct centennial changes in solar activity .
We find that during the Last Glacial Maximum , solar minima correlate with more negative delta18O values of ice and are accompanied by increased snow accumulation and sea-salt input over central Greenland .
We suggest that solar minima could have induced changes in the stratosphere that favour the development of high-pressure blocking systems located to the south of Greenland , as has been found in observations and model simulations for recent climate .
We conclude that the mechanism behind solar forcing of regional climate change may have been similar under both modern and Last Glacial Maximum climate conditions .

[1374] Regional insight into savanna hydrogeomorphology from termite mounds

Global vegetation models predict the spread of woody vegetation in African savannas and grasslands under future climate scenarios , but they operate too broadly to consider hillslope-scale variations in tree-grass distribution .
Topographically linked hydrology-soil-vegetation sequences , or catenas , underpin a variety of ecological processes in savannas , including responses to climate change .
In this study , we explore the three-dimensional structure of hillslopes and vegetation , using high-resolution airborne LiDAR ( Light Detection And Ranging ) , to understand the long-term effects of mean annual precipitation ( MAP ) on catena pattern .
Our results reveal that the presence and position of hillslope hydrological boundaries , or seeplines , vary as a function of MAP through its long-term influence on clay redistribution .
We suggest that changes in climate will differentially alter the structure of savannas through hydrological changes to the seasonally saturated grasslands downslope of seeplines .
The mechanisms underlying future woody encroachment are not simply physiological responses to elevated temperatures and CO2 levels but also involve hydrogeomorphological processes at the hillslope scale .

[1375] Hypoxia regulates CD9-mediated keratinocyte migration via the P38/MAPK pathway

Keratinocyte migration is an early event in the wound healing process .
Although we previously found that CD9 downregulation is required for the keratinocyte migration during wound repair , the mechanism of how CD9 expression is regulated remains unclear .
Here , we observed the effect of hypoxia ( 2 % O2 ) on CD9 expression and keratinocyte migration .
CD9 expression was downregulated and keratinocyte migration was increased under hypoxic conditions .
In addition , CD9 overexpression reversed hypoxia-induced cell migration .
We also found that hypoxia activated the p38/MAPK pathway .
SB203580 , a p38/MAPK inhibitor , increased CD9 expression and inhibited keratinocyte migration under hypoxia , while MKK6 ( Glu ) overexpression decreased CD9 expression and promoted hypoxic keratinocyte migration .
Our results demonstrate that hypoxia regulates CD9 expression and CD9-mediated keratinocyte migration via the p38/MAPK pathway .

[1376] Turion morphological responses to water nutrient concentrations and plant density in the submerged macrophyte Potamogeton crispus

Asexual propagules are the dominant means of propagation in most submerged macrophytes .
To improve the understanding of how water nutrient concentrations and population density influence the turion production of Potamogeton crispus L. , the turions were planted in mesocosms with three water nutrient conditions ( ambient lake water , high P and high N ) and two plant density levels ( 4 and 15 turions m-2 ) .
After a 9-month experiment , the + P in the water column significantly increased the total turion number per plant under both of the plant density treatments .
However , the + N in the water column did not affect the turion number per plant under low plant density .
The + P in the water and high plant density significantly reduced the turion individual biomass .
An examination of 3210 turion individuals from all treatments revealed that the increased water nutrient concentrations and plant density impacted the turion size by producing different stem diameters of individual turions .
Most of the scale leaf morphological traits of the turions were significantly increased under higher water nutrients , but these traits were similar between the different plant density treatments .
These results demonstrate that the water P concentration interacts with plant density , affecting both the production and traits of turions .

[1377] Contribution of Alaskan glaciers to sea-level rise derived from satellite imagery

Over the past 50 years , retreating glaciers and ice caps contributed 0.5 mm yr-1 to sea-level rise , and one third of this contribution is believed to come from ice masses bordering the Gulf of Alaska .
However , these estimates of ice loss in Alaska are based on measurements of a limited number of glaciers that are extrapolated to constrain ice wastage in the many thousands of others .
Uncertainties in these estimates arise , for example , from the complex pattern of decadal elevation changes at the scale of individual glaciers and mountain ranges .
Here we combine a comprehensive glacier inventory with elevation changes derived from sequential digital elevation models .
We find that between 1962 and 2006 , Alaskan glaciers lost 41.9 + / -8.6 km3 yr-1 of water , and contributed 0.12 + / -0.02 mm yr-1 to sea-level rise , 34 % less than estimated earlier .
Reasons for our lower values include the higher spatial resolution of our glacier inventory as well as the reduction of ice thinning underneath debris and at the glacier margins , which were not resolved in earlier work .
We suggest that estimates of mass loss from glaciers and ice caps in other mountain regions could be subject to similar revisions .

[1378] Biodiversity : Climate change and the ecologist

The evidence for rapid climate change now seems overwhelming .
Global temperatures are predicted to rise by up to 4 degreesC by 2100 , with associated alterations in precipitation patterns .
Assessing the consequences for biodiversity , and how they might be mitigated , is a Grand Challenge in ecology .

[1379] Producer-decomposer co-dependency influences biodiversity effects

Producers , such as plants and algae , acquire nutrients from inorganic sources that are supplied primarily by decomposers whereas decomposers , mostly fungi and bacteria , acquire carbon from organic sources that are supplied primarily by producers .
This producer-decomposer co-dependency is important in governing ecosystem processes , which implies that the impacts of declining biodiversity on ecosystem functioning should be strongly infuenced by this process .
Here we show , by simultaneously manipulating producer ( green algal ) and decomposer ( heterotrophic bacterial ) diversity in freshwater microcosms , that algal biomass production varies considerably among microcosms ( 0.0-0 .67 mg ml-1 ) , but that neither algal nor bacterial diversity by itself can explain this variation .
Instead , production is a joint function of both algal and bacterial diversity .
Furthermore , the range in algal production in microscosms in which bacterial diversity was manipulated was nearly double ( 1.82 times ) that of microcosms in which bacterial diversity was not manipulated .
Measures of organic carbon use by bacteria in these microcosms indicate that carbon usage is the mechanism responsible for these results .
Because both producer and microbial diversity respond to disturbance and habitat modification , the main causes of biodiversity loss , these results suggest that ecosystem response to changing biodiversity is likely to be more complex than other studies have shown .

[1380] Persistent summer expansion of the Atlantic Warm Pool during glacial abrupt cold events

Palaeoclimate records and numerical model simulations indicate that changes in tropical and subtropical sea surface temperatures and in the annual average position of the intertropical convergence zone are linked to high-latitude climate changes on millennial to glacial-interglacial timescales .
It has recently been suggested that cooling in the high latitudes associated with abrupt climate-change events is evident primarily during the northern hemisphere winter , implying increased seasonality at these times .
However , it is unclear whether such a seasonal bias also exists for the low latitudes .
Here we analyse the Mg/Ca ratios of surface-dwelling foraminifera to reconstruct sea surface temperatures in the northeastern Gulf of Mexico for the past 300,000 years .
We suggest that sea surface temperatures are controlled by the migration of the northern boundary of the Atlantic Warm Pool , and hence the position of the intertropical convergence zone during boreal summer , and are relatively insensitive to winter conditions .
Our results suggest that summer Atlantic Warm Pool expansion is primarily affected by glacial-interglacial variability and low-latitude summer insolation .
Because a clear signature of rapid climate-change events , such as the Younger Dryas cold event , is lacking in our record , we conclude that high-latitude events seem to influence only the winter Caribbean climate conditions , consistent with the hypothesis of extreme northern-hemisphere seasonality during abrupt cooling events .

[1381] The trophic fingerprint of marine fisheries

Biodiversity indicators provide a vital window on the state of the planet , guiding policy development and management .
The most widely adopted marine indicator is mean trophic level ( MTL ) from catches , intended to detect shifts from high-trophic-level predators to low-trophic-level invertebrates and plankton-feeders .
This indicator underpins reported trends in human impacts , declining when predators collapse ( `` fishing down marine food webs '' ) and when low-trophic-level fisheries expand ( `` fishing through marine food webs '' ) .
The assumption is that catch MTL measures changes in ecosystem MTL and biodiversity .
Here we combine model predictions with global assessments of MTL from catches , trawl surveys and fisheries stock assessments and find that catch MTL does not reliably predict changes in marine ecosystems .
Instead , catch MTL trends often diverge from ecosystem MTL trends obtained from surveys and assessments .
In contrast to previous findings of rapid declines in catch MTL , we observe recent increases in catch , survey and assessment MTL .
However , catches from most trophic levels are rising , which can intensify fishery collapses even when MTL trends are stable or increasing .
To detect fishing impacts on marine biodiversity , we recommend greater efforts to measure true abundance trends for marine species , especially those most vulnerable to fishing .

[1382] Cyclin D control of growth rate in plants

The mechanisms by which plants modulate their growth rate in response to environmental and developmental conditions are unknown , but are presumed to involve specialized regions called meristems where cell division is concentrated .
The possible role of cell division in influencing meristem activity and overall plant growth rate is controversial , with a prevailing view that cell division is secondary to higher order meristem controls .
Here we show that a reduction in the length of the cell-cycle G1 phase and faster cell cycling occur when the rate of cell division in transgenic tobacco plants is increased by the plant D-type cyclin CycD2 ( ref .
8 ) .
The plants have normal cell and meristem sizes , but elevated overall growth rates , an increased rate of leaf initiation and accelerated development in all stages from seedling to maturity .
We conclude that cell division is a principal determinant of meristem activity and overall growth rate , and propose that modulation of plant growth rate is achieved through regulation of G1 .

[1383] Global environmental controls of diversity in large herbivores

Large mammalian herbivores occupy half of the earth 's land surface and are important both ecologically and economically , but their diversity is threatened by human activities .
We investigated how the diversity of large herbivores changes across gradients of global precipitation and soil fertility .
Here we show that more plant-available moisture reduces the nutrient content of plants but increases productivity , whereas more plant-available nutrients increase both of these factors .
Because larger herbivore species tolerate lower plant nutrient content but require greater plant abundance , the highest potential herbivore diversity should occur in locations with intermediate moisture and high nutrients .
These areas are dry enough to yield high quality plants and support smaller herbivores , but productive enough to support larger herbivores .
These predictions fit with observed patterns of body size and diversity for large mammalian herbivores in North America , Africa and Australia , and yield a global map of regions with potentially high herbivore diversity .
Thus , gradients of precipitation , temperature and soil fertility might explain the global distribution of large herbivore diversity and help to identify crucial areas for conservation and restoration .

[1384] Predator richness increases the effect of prey diversity on prey yield

Positive biodiversity-ecosystem functioning relationships are generally attributed to two mechanisms : complementarity and selection .
These mechanisms have been primarily examined using plant communities , whereas bacterial communities remain largely unexplored .
Moreover , it remains uncertain how predation by single or multiple predators affects these mechanisms .
Here using 465 bacterial microcosms , we show that multiple predation by protists results in positive bacterial diversity effects on bacterial yields ( colony-forming units ) possibly due to an increased complementarity and evenness among bacterial species .
By mathematically partitioning the biodiversity effects , we demonstrate that competitive interactions in diverse communities are reduced and the growth of subdominant species is enhanced .
We envisage that , including diversity gradients at other trophic levels , in biodiversity-ecosystem functioning research is a key to understanding and managing ecosystem processes .
Such level of manipulation can be achieved best in microbial model systems , which are powerful tools for fundamental hypothesis-driven experiments and the investigation of general ecological theories .

[1385] The unexpected discovery of a novel low-oxygen-activated locus for the anoxic persistence of Burkholderia cenocepacia

Burkholderia cenocepacia is a Gram-negative aerobic bacterium that belongs to a group of opportunistic pathogens displaying diverse environmental and pathogenic lifestyles .
B. cenocepacia is known for its ability to cause lung infections in people with cystic fibrosis and it possesses a large 8 Mb multireplicon genome encoding a wide array of pathogenicity and fitness genes .
Transcriptomic profiling across nine growth conditions was performed to identify the global gene expression changes made when B. cenocepacia changes niches from an environmental lifestyle to infection .
In comparison to exponential growth , the results demonstrated that B. cenocepacia changes expression of over one-quarter of its genome during conditions of growth arrest , stationary phase and surprisingly , under reduced oxygen concentrations ( 6 % instead of 20.9 % normal atmospheric conditions ) .
Multiple virulence factors are upregulated during these growth arrest conditions .
A unique discovery from the comparative expression analysis was the identification of a distinct , co-regulated 50-gene cluster that was significantly upregulated during growth under low oxygen conditions .
This gene cluster was designated the low-oxygen-activated ( lxa ) locus and encodes six universal stress proteins and proteins predicted to be involved in metabolism , transport , electron transfer and regulation .
Deletion of the lxa locus resulted in B. cenocepacia mutants with aerobic growth deficiencies in minimal medium and compromised viability after prolonged incubation in the absence of oxygen .
In summary , transcriptomic profiling of B. cenocepacia revealed an unexpected ability of aerobic Burkholderia to persist in the absence of oxygen and identified the novel lxa locus as key determinant of this important ecophysiological trait .

[1386] Altered performance of forest pests under atmospheres enriched by CO2 and O3

Human activity causes increasing background concentrations of the greenhouse gases CO2 and O3 .
Increased levels of CO2 can be found in all terrestrial ecosystems .
Damaging O3 concentrations currently occur over 29 % of the world 's temperate and subpolar forests but are predicted to affect fully 60 % by 2100 ( ref .
3 ) .
Although individual effects of CO2 and O3 on vegetation have been widely investigated , very little is known about their interaction , and long-term studies on mature trees and higher trophic levels are extremely rare .
Here we present evidence from the most widely distributed North American tree species , Populus tremuloides , showing that CO2 and O3 , singly and in combination , affected productivity , physical and chemical leaf defences and , because of changes in plant quality , insect and disease populations .
Our data show that feedbacks to plant growth from changes induced by CO2 and O3 in plant quality and pest performance are likely .
Assessments of global change effects on forest ecosystems must therefore consider the interacting effects of CO2 and O3 on plant performance , as well as the implications of increased pest activity .

[1387] Sustained losses of bioavailable nitrogen from montane tropical forests

Tropical forests account for one third of terrestrial primary production and contribute significantly to the land carbon sink .
The future of this sink relies critically on forest interactions with nutrient cycles .
Humid montane tropical forests are often thought to be rich in phosphorus , but to contain low levels of bioavailable nitrogen .
Here , we examine the concentration of dissolved nitrogen compounds and the isotopic composition of nitrate in streams in six well-characterized and phosphorus-rich montane forests in Costa Rica , and in 55 montane forests across Central America and the Caribbean , using data collected between 1990 and 2008 .
We found high levels of nitrate in these streams , indicative of large losses of bioavailable nitrogen from these forests .
We detected no trend in the concentration and isotopic signature of nitrate over the measurement period , implying that high levels of export are neither recent nor episodic .
An analysis of the oxygen isotopic signature of stream nitrate showed that exports are sourced from the plant-soil system , rather than from atmospheric deposition that bypasses forest biota .
Our findings indicate that nitrogen-rich conditions can develop irrespective of phosphorus availability at the ecosystem scale .
We suggest that nitrogen availability may not limit plant growth , or its response to increasing atmospheric carbon dioxide levels , in many montane tropical forests .

[1388] Long-term nitrogen deposition depletes grassland seed banks

Nitrogen ( N ) pollution is a global threat to the biodiversity of many plant communities , but its impacts on grassland soil seed banks are unknown .
Here we show that size and richness of an acid grassland seed bank is strongly reduced after 13 years of simulated N deposition .
Soils receiving 140 kg N ha-1 per year show a decline in total seed abundance , seed species richness , and the abundance of forbs , sedges and grasses .
These results reveal larger effects of N pollution on seed banks than on aboveground vegetation as cover and flowering is not significantly altered for most species .
Further , the seed bank shows no recovery 4 years after the cessation of N deposition .
These results provide insights into the severe negative effects of N pollution on plant communities that threaten the stability of populations , community persistence and the potential for ecosystems to recover following anthropogenic disturbance or climate change .

[1389] Non-cell-autonomous driving of tumour growth supports sub-clonal heterogeneity

Cancers arise through a process of somatic evolution that can result in substantial sub-clonal heterogeneity within tumours .
The mechanisms responsible for the coexistence of distinct sub-clones and the biological consequences of this coexistence remain poorly understood .
Here we used a mouse xenograft model to investigate the impact of sub-clonal heterogeneity on tumour phenotypes and the competitive expansion of individual clones .
We found that tumour growth can be driven by a minor cell subpopulation , which enhances the proliferation of all cells within a tumour by overcoming environmental constraints and yet can be outcompeted by faster proliferating competitors , resulting in tumour collapse .
We developed a mathematical modelling framework to identify the rules underlying the generation of intra-tumour clonal heterogeneity .
We found that non-cell-autonomous driving of tumour growth , together with clonal interference , stabilizes sub-clonal heterogeneity , thereby enabling inter-clonal interactions that can lead to new phenotypic traits .

[1390] Storage and release of organic carbon from glaciers and ice sheets

Polar ice sheets and mountain glaciers , which cover roughly 11 % of the Earth 's land surface , store organic carbon from local and distant sources and then release it to downstream environments .
Climate-driven changes to glacier runoff are expected to be larger than climate impacts on other components of the hydrological cycle , and may represent an important flux of organic carbon .
A compilation of published data on dissolved organic carbon from glaciers across five continents reveals that mountain and polar glaciers represent a quantitatively important store of organic carbon .
The Antarctic Ice Sheet is the repository of most of the roughly 6 petagrams ( Pg ) of organic carbon stored in glacier ice , but the annual release of glacier organic carbon is dominated by mountain glaciers in the case of dissolved organic carbon and the Greenland Ice Sheet in the case of particulate organic carbon .
Climate change contributes to these fluxes : approximately 13 % of the annual flux of glacier dissolved organic carbon is a result of glacier mass loss .
These losses are expected to accelerate , leading to a cumulative loss of roughly 15 teragrams ( Tg ) of glacial dissolved organic carbon by 2050 due to climate change -- equivalent to about half of the annual flux of dissolved organic carbon from the Amazon River .
Thus , glaciers constitute a key link between terrestrial and aquatic carbon fluxes , and will be of increasing importance in land-to-ocean fluxes of organic carbon in glacierized regions .

[1391] Multidecadal variability in East African hydroclimate controlled by the Indian Ocean

The recent decades-long decline in East African rainfall suggests that multidecadal variability is an important component of the climate of this vulnerable region .
Prior work based on analysing the instrumental record implicates both Indian and Pacific ocean sea surface temperatures ( SSTs ) as possible drivers of East African multidecadal climate variability , but the short length of the instrumental record precludes a full elucidation of the underlying physical mechanisms .
Here we show that on timescales beyond the decadal , the Indian Ocean drives East African rainfall variability by altering the local Walker circulation , whereas the influence of the Pacific Ocean is minimal .
Our results , based on proxy indicators of relative moisture balance for the past millennium paired with long control simulations from coupled climate models , reveal that moist conditions in coastal East Africa are associated with cool SSTs ( and related descending circulation ) in the eastern Indian Ocean and ascending circulation over East Africa .
The most prominent event identified in the proxy record -- a coastal pluvial from 1680 to 1765 -- occurred when Indo-Pacific warm pool SSTs reached their minimum values of the past millennium .
Taken together , the proxy and model evidence suggests that Indian Ocean SSTs are the primary influence on East African rainfall over multidecadal and perhaps longer timescales .

[1392] Coordinated regulation of photosynthesis in rice increases yield and tolerance to environmental stress

Plants capture solar energy and atmospheric carbon dioxide ( CO2 ) through photosynthesis , which is the primary component of crop yield , and needs to be increased considerably to meet the growing global demand for food .
Environmental stresses , which are increasing with climate change , adversely affect photosynthetic carbon metabolism ( PCM ) and limit yield of cereals such as rice ( Oryza sativa ) that feeds half the world .
To study the regulation of photosynthesis , we developed a rice gene regulatory network and identified a transcription factor HYR ( HIGHER YIELD RICE ) associated with PCM , which on expression in rice enhances photosynthesis under multiple environmental conditions , determining a morpho-physiological programme leading to higher grain yield under normal , drought and high-temperature stress conditions .
We show HYR is a master regulator , directly activating photosynthesis genes , cascades of transcription factors and other downstream genes involved in PCM and yield stability under drought and high-temperature environmental stress conditions .

[1393] A drought-induced pervasive increase in tree mortality across Canada 's boreal forests

Drought-induced tree mortality is expected to increase worldwide under projected future climate changes .
The Canadian boreal forests , which occupy about 30 % of the boreal forests worldwide and 77 % of Canada 's total forested land , play a critical role in the albedo of Earth 's surface and in its global carbon budget .
Many of the previously reported regional-scale impacts of drought on tree mortality have affected low - and middle-latitude tropical regions and the temperate forests of the western United States , but no study has examined high-latitude boreal regions with multiple species at a regional scale using long-term forest permanent sampling plots .
Here , we estimated tree mortality in natural stands throughout Canada 's boreal forests using data from the permanent sampling plots and statistical models .
We found that tree mortality rates increased by an overall average of 4.7 % yr-1 from 1963 to 2008 , with higher mortality rate increases in western regions than in eastern regions ( about 4.9 and 1.9 % yr-1 , respectively ) .
The water stress created by regional drought may be the dominant contributor to these widespread increases in tree mortality rates across tree species , sizes , elevations , longitudes and latitudes .
Western Canada seems to have been more sensitive to drought than eastern Canada .

[1394] Three decades of global methane sources and sinks

Methane is an important greenhouse gas , responsible for about 20 % of the warming induced by long-lived greenhouse gases since pre-industrial times .
By reacting with hydroxyl radicals , methane reduces the oxidizing capacity of the atmosphere and generates ozone in the troposphere .
Although most sources and sinks of methane have been identified , their relative contributions to atmospheric methane levels are highly uncertain .
As such , the factors responsible for the observed stabilization of atmospheric methane levels in the early 2000s , and the renewed rise after 2006 , remain unclear .
Here , we construct decadal budgets for methane sources and sinks between 1980 and 2010 , using a combination of atmospheric measurements and results from chemical transport models , ecosystem models , climate chemistry models and inventories of anthropogenic emissions .
The resultant budgets suggest that data-driven approaches and ecosystem models overestimate total natural emissions .
We build three contrasting emission scenarios -- which differ in fossil fuel and microbial emissions -- to explain the decadal variability in atmospheric methane levels detected , here and in previous studies , since 1985 .
Although uncertainties in emission trends do not allow definitive conclusions to be drawn , we show that the observed stabilization of methane levels between 1999 and 2006 can potentially be explained by decreasing-to-stable fossil fuel emissions , combined with stable-to-increasing microbial emissions .
We show that a rise in natural wetland emissions and fossil fuel emissions probably accounts for the renewed increase in global methane levels after 2006 , although the relative contribution of these two sources remains uncertain .

[1395] Degradation of cyanobacterial biomass in anoxic tidal-flat sediments : a microcosm study of metabolic processes and community changes

To follow the anaerobic degradation of organic matter in tidal-flat sediments , a stimulation experiment with 13C-labeled Spirulina biomass ( 130 mg per 21 g sediment slurry ) was conducted over a period of 24 days .
A combination of microcalorimetry to record process kinetics , chemical analyses of fermentation products and RNA-based stable-isotope probing ( SIP ) to follow community changes was applied .
Different degradation phases could be identified by microcalorimetry : Within 2 days , heat output reached its maximum ( 55 muW ) , while primary fermentation products were formed ( in mumol ) as follows : acetate 440 , ethanol 195 , butyrate 128 , propionate 112 , H2 127 and smaller amounts of valerate , propanol and butanol .
Sulfate was depleted within 7 days .
Thereafter , methanogenesis was observed and secondary fermentation proceeded .
H2 and alcohols disappeared completely , whereas fatty acids decreased in concentration .
Three main degraders were identified by RNA-based SIP and denaturant gradient gel electrophoresis .
After 12 h , two phylotypes clearly enriched in 13C : ( i ) Psychrilyobacter atlanticus , a fermenter known to produce hydrogen and acetate and ( ii ) bacteria distantly related to Propionigenium .
A Cytophaga-related bacterium was highly abundant after day 3 .
Sulfate reduction appeared to be performed by incompletely oxidizing species , as only sulfate-reducing bacteria related to Desulfovibrio were labeled as long as sulfate was available .

[1396] Elevated CO2 further lengthens growing season under warming conditions

Observations of a longer growing season through earlier plant growth in temperate to polar regions have been thought to be a response to climate warming .
However , data from experimental warming studies indicate that many species that initiate leaf growth and flowering earlier also reach seed maturation and senesce earlier , shortening their active and reproductive periods .
A conceptual model to explain this apparent contradiction , and an analysis of the effect of elevated CO2 -- which can delay annual life cycle events -- on changing season length , have not been tested .
Here we show that experimental warming in a temperate grassland led to a longer growing season through earlier leaf emergence by the first species to leaf , often a grass , and constant or delayed senescence by other species that were the last to senesce , supporting the conceptual model .
Elevated CO2 further extended growing , but not reproductive , season length in the warmed grassland by conserving water , which enabled most species to remain active longer .
Our results suggest that a longer growing season , especially in years or biomes where water is a limiting factor , is not due to warming alone , but also to higher atmospheric CO2 concentrations that extend the active period of plant annual life cycles .

[1397] Oceanic transport of subpolar climate signals to mid-depth subtropical waters

The spatial distributions of certain sea-surface properties , such as temperature , fluctuate on timescales from months to decades and in synchrony with the main regional atmospheric patterns comprising the global climate system .
Although it has long been assumed that the ocean is submissive to the dictates of the atmosphere , recent studies raise the possibility of an assertive , not merely passive , oceanic role in which water-mass circulation controls the timescales of climate fluctuations .
Previously held notions of the immutability of the physical and chemical characteristics of deep water masses are changing as longer time series of ocean measurements indicate that the signatures of varying sea-surface conditions are translated to deep waters , .
Here we use such time-series measurements to track signals ` imprinted ' at the sea surface in the North Atlantic Ocean 's subpolar Labrador Basin into the deep water of the subtropical basins near Bermuda , and infer an approximately 6-year transit time .
We establish a geographic and temporal context for a portion of the long-term warming trend reported for mid-depth subtropical waters over the past 40 or so years , , and we predict that waters at these depths will continue to cool well into the next decade .

[1398] Polar ocean stratification in a cold climate

The low-latitude ocean is strongly stratified by the warmth of its surface water .
As a result , the great volume of the deep ocean has easiest access to the atmosphere through the polar surface ocean .
In the modern polar ocean during the winter , the vertical distribution of temperature promotes overturning , with colder water over warmer , while the salinity distribution typically promotes stratification , with fresher water over saltier .
However , the sensitivity of seawater density to temperature is reduced as temperature approaches the freezing point , with potential consequences for global ocean circulation under cold climates .
Here we present deep-sea records of biogenic opal accumulation and sedimentary nitrogen isotopic composition from the Subarctic North Pacific Ocean and the Southern Ocean .
These records indicate that vertical stratification increased in both northern and southern high latitudes 2.7 million years ago , when Northern Hemisphere glaciation intensified in association with global cooling during the late Pliocene epoch .
We propose that the cooling caused this increased stratification by weakening the role of temperature in polar ocean density structure so as to reduce its opposition to the stratifying effect of the vertical salinity distribution .
The shift towards stratification in the polar ocean 2.7 million years ago may have increased the quantity of carbon dioxide trapped in the abyss , amplifying the global cooling .

[1399] Timing of Neoproterozoic glaciations linked to transport-limited global weathering

The Earth underwent several snowball glaciations between 1,000 and 542 million years ago .
The termination of these glaciations is thought to have been triggered by the accumulation of volcanic CO2 in the atmosphere over millions of years .
Subsequent high temperatures and loss of continental ice would increase silicate weathering and in turn draw down atmospheric CO2 ( ref . )
.
Estimates of the post-snowball weathering rate indicate that equilibrium between CO2 input and removal would be restored within several million years , potentially triggering a new glaciation .
However the transition between deglaciation and the onset a new glaciation was on the order of 107 years .
Over long timescales , the availability of fresh rock can become a limiting factor for silicate weathering rates .
Here we show that when this transport-determined limitation is incorporated into the COPSE biogeochemical model , the stabilization time is substantially longer , > 107 years .
When we include a simple ice-albedo feedback , the model produces greenhouse-icehouse oscillations on this timescale that are compatible with observations .
Our simulations also indicate positive carbon isotope excursions and an increased flux of oxygen to the atmosphere during interglacials , both of which are consistent with the geological record .
We conclude that the long gaps between snowball glaciations can be explained by limitations on silicate weathering rates .

[1400] Temporal variability in soil microbial communities across land-use types

Although numerous studies have investigated changes in soil microbial communities across space , questions about the temporal variability in these communities and how this variability compares across soils have received far less attention .
We collected soils on a monthly basis ( May to November ) from replicated plots representing three land-use types ( conventional and reduced-input row crop agricultural plots and early successional grasslands ) maintained at a research site in Michigan , USA .
Using barcoded pyrosequencing of the 16S rRNA gene , we found that the agricultural and early successional land uses harbored unique soil bacterial communities that exhibited distinct temporal patterns .
alpha-Diversity , the numbers of taxa or lineages , was significantly influenced by the sampling month with the temporal variability in alpha-diversity exceeding the variability between land-use types .
In contrast , differences in community composition across land-use types were reasonably constant across the 7-month period , suggesting that the time of sampling is less important when assessing beta-diversity patterns .
Communities in the agricultural soils were most variable over time and the changes were significantly correlated with soil moisture and temperature .
Temporal shifts in bacterial community composition within the successional grassland plots were less predictable and are likely a product of complex interactions between the soil environment and the more diverse plant community .
Temporal variability needs to be carefully assessed when comparing microbial diversity across soil types and the temporal patterns in microbial community structure can not necessarily be generalized across land uses , even if those soils are exposed to the same climatic conditions .

[1401] Ecological constraints on diversification in a model adaptive radiation

Taxonomic diversification commonly occurs through adaptive radiation , the rapid evolution of a single lineage into a range of genotypes or species each adapted to a different ecological niche .
Radiation size ( measured as the number of new types ) varies widely between phylogenetically distinct taxa and between replicate radiations within a single taxon where the ecological opportunities available seem to be identical .
Here we show how variation in energy input ( productivity ) and environmental disturbance combine to determine the extent of diversification in a single radiating lineage of Pseudomonas fluorescens adapting to laboratory conditions .
Diversity peaked at intermediate rates of both productivity and disturbance and declined towards the extremes in a manner reminiscent of well-known ecological patterns .
The mechanism responsible for the decrease in diversity arises from pleiotropic fitness costs associated with niche specialization , the effects of which are modulated by gradients of productivity and disturbance .
Our results indicate that ecological gradients may constrain the size of adaptive radiations , even in the presence of the strong diversifying selection associated with ecological opportunity , by decoupling evolutionary diversification from ecological coexistence .

[1402] c-Myc regulates mammalian body size by controlling cell number but not cell size

Overexpression of the proto-oncogene c-myc has been implicated in the genesis of diverse human tumours .
c-Myc seems to regulate diverse biological processes , but its role in tumorigenesis and normal physiology remains enigmatic .
Here we report the generation of an allelic series of mice in which c-myc expression is incrementally reduced to zero .
Fibroblasts from these mice show reduced proliferation and after complete loss of c-Myc function they exit the cell cycle .
We show that Myc activity is not needed for cellular growth but does determine the percentage of activated T cells that re-enter the cell cycle .
In vivo , reduction of c-Myc levels results in reduced body mass owing to multiorgan hypoplasia , in contrast to Drosophila dmyc mutants , which are smaller as a result of hypotrophy .
We find that dmyc substitutes for c-myc in fibroblasts , indicating they have similar biological activities .
This suggests there may be fundamental differences in the mechanisms by which mammals and insects control body size .
We propose that in mammals c-Myc controls the decision to divide or not to divide and thereby functions as a crucial mediator of signals that determine organ and body size .

[1403] Constructed wetlands as biofuel production systems

Clean biofuel production is an effective way to mitigate global climate change and energy crisis .
Progress has been made in reducing greenhouse-gas ( GHG ) emissions and nitrogen fertilizer consumption through biofuel production .
Here we advocate an alternative approach that efficiently produces cellulosic biofuel and greatly reduces GHG emissions using waste nitrogen through wastewater treatment with constructed wetlands in China .
Our combined experimental and literature data demonstrate that the net life-cycle energy output of constructed wetlands is higher than that of corn , soybean , switchgrass , low-input high-diversity grassland and algae systems .
Energy output from existing constructed wetlands is ~ 237 % of the input for biofuel production and can be enhanced through optimizing the nitrogen supply , hydrologic flow patterns and plant species selection .
Assuming that all waste nitrogen in China could be used by constructed wetlands , biofuel production can account for 6.7 % of national gasoline consumption .
We also find that constructed wetlands have a greater GHG reduction than the existing biofuel production systems in a full life-cycle analysis .
This alternative approach is worth pursuing because of its great potential for straightforward operation , its economic competitiveness and many ecological benefits .

[1404] The effect of advection on the nutrient reservoir in the North Atlantic subtropical gyre

Though critically important in sustaining the ocean 's biological pump , the cycling of nutrients in the subtropical gyres is poorly understood .
The supply of nutrients to the sunlit surface layer of the ocean has traditionally been attributed solely to vertical processes .
However , horizontal advection may also be important in establishing the availability of nutrients .
Here we show that the production and advection of North Atlantic Subtropical Mode Water introduces spatial and temporal variability in the subsurface nutrient reservoir beneath the North Atlantic subtropical gyre .
As the mode water is formed , its nutrients are depleted by biological utilization .
When the depleted water mass is exported to the gyre , it injects a wedge of low-nutrient water into the upper layers of the ocean .
Contrary to intuition , cold winters that promote deep convective mixing and vigorous mode water formation may diminish downstream primary productivity by altering the subsurface delivery of nutrients .

[1405] Growing season extended in Europe

Changes in phenology ( seasonal plant and animal activity driven by environmental factors ) from year to year may be a sensitive and easily observable indicator of changes in the biosphere .
We have analysed data from more than 30 years of observation in Europe , and found that spring events , such as leaf unfolding , have advanced by 6 days , whereas autumn events , such as leaf colouring , have been delayed by 4.8 days .
This means that the average annual growing season has lengthened by 10.8 days since the early 1960s .
These shifts can be attributed to changes in air temperature .

[1406] Quantifying the likelihood of a continued hiatus in global warming

Since the end of the twentieth century , global mean surface temperature has not risen as rapidly as predicted by global climate models ( GCMs ) .
This discrepancy has become known as the global warming ` hiatus ' and a variety of mechanisms have been proposed to explain the observed slowdown in warming .
Focusing on internally generated variability , we use pre-industrial control simulations from an observationally constrained ensemble of GCMs and a statistical approach to evaluate the expected frequency and characteristics of variability-driven hiatus periods and their likelihood of future continuation .
Given an expected forced warming trend of ~ 0.2 K per decade , our constrained ensemble of GCMs implies that the probability of a variability-driven 10-year hiatus is ~ 10 % , but less than 1 % for a 20-year hiatus .
Although the absolute probability of a 20-year hiatus is small , the probability that an existing 15-year hiatus will continue another five years is much higher ( up to 25 % ) .
Therefore , given the recognized contribution of internal climate variability to the reduced rate of global warming during the past 15 years , we should not be surprised if the current hiatus continues until the end of the decade .
Following the termination of a variability-driven hiatus , we also show that there is an increased likelihood of accelerated global warming associated with release of heat from the sub-surface ocean and a reversal of the phase of decadal variability in the Pacific Ocean .

[1407] Expression of the bipolar see-saw in Antarctic climate records during the last deglaciation

Ice-core records of climate from Greenland and Antarctica show asynchronous temperature variations on millennial timescales during the last glacial period .
The warming during the transition from glacial to interglacial conditions was markedly different between the hemispheres , a pattern attributed to the thermal bipolar see-saw .
However , a record from the Ross Sea sector of East Antarctica has been suggested to be synchronous with Northern Hemisphere climate change .
Here we present a temperature record from the Talos Dome ice core , also located in the Ross Sea sector .
We compare our record with ice-core analyses from Greenland , based on methane synchronization , and find clearly asynchronous temperature changes during the deglaciation .
We also find distinct differences in Antarctic records , pointing to differences in the climate evolution of the Indo-Pacific and Atlantic sectors of Antarctica .
In the Atlantic sector , we find that the rate of warming slowed between 16,000 and 14,500 years ago , parallel with the deceleration of the rise in atmospheric carbon dioxide concentrations and with a slight cooling over Greenland .
In addition , our chronology supports the hypothesis that the cooling of the Antarctic Cold Reversal is synchronous with the Bolling-Allerod warming in the northern hemisphere 14,700 years ago .

[1408] Rapid increase in the risk of extreme summer heat in Eastern China

The summer of 2013 was the hottest on record in Eastern China .
Severe extended heatwaves affected the most populous and economically developed part of China and caused substantial economic and societal impacts .
The estimated direct economic losses from the accompanying drought alone total 59 billion RMB ( ref . )
.
Summer ( June-August ) mean temperature in the region has increased by 0.82 degreesC since reliable observations were established in the 1950s , with the five hottest summers all occurring in the twenty-first century .
It is challenging to attribute extreme events to causes .
Nevertheless , quantifying the causes of such extreme summer heat and projecting its future likelihood is necessary to develop climate adaptation strategies .
We estimate that anthropogenic influence has caused a more than 60-fold increase in the likelihood of the extreme warm 2013 summer since the early 1950s , and project that similarly hot summers will become even more frequent in the future , with fully 50 % of summers being hotter than the 2013 summer in two decades even under the moderate RCP4 .5 emissions scenario .
Without adaptation to reduce vulnerability to the effects of extreme heat , this would imply a rapid increase in risks from extreme summer heat to Eastern China .

[1409] Increasing summer rainfall in arid eastern-Central Asia over the past 8500 years

A detailed and well-dated proxy record of summer rainfall variation in arid Central Asia is lacking .
Here , we report a long-term , high resolution record of summer rainfall extracted from a peat bog in arid eastern-Central Asia ( AECA ) .
The record indicates a slowly but steadily increasing trend of summer rainfall in the AECA over the past 8500 years .
On this long-term trend are superimposed several abrupt increases in rainfall on millennial timescales that correspond to rapid cooling events in the North Atlantic .
During the last millennium , the hydrological climate pattern of the AECA underwent a major change .
The rainfall in the past century has reached its highest level over the 8500-year history , highlighting the significant impact of the human-induced greenhouse effect on the hydrological climate in the AECA .
Our results demonstrate that even in very dry eastern-Central Asia , the climate can become wetter under global warming .

[1410] Additive threats from pathogens , climate and land-use change for global amphibian diversity

Amphibian population declines far exceed those of other vertebrate groups , with 30 % of all species listed as threatened by the International Union for Conservation of Nature .
The causes of these declines are a matter of continued research , but probably include climate change , land-use change and spread of the pathogenic fungal disease chytridiomycosis .
Here we assess the spatial distribution and interactions of these primary threats in relation to the global distribution of amphibian species .
We show that the greatest proportions of species negatively affected by climate change are projected to be found in Africa , parts of northern South America and the Andes .
Regions with the highest projected impact of land-use and climate change coincide , but there is little spatial overlap with regions highly threatened by the fungal disease .
Overall , the areas harbouring the richest amphibian faunas are disproportionately more affected by one or multiple threat factors than areas with low richness .
Amphibian declines are likely to accelerate in the twenty-first century , because multiple drivers of extinction could jeopardize their populations more than previous , mono-causal , assessments have suggested .

[1411] The ELF4-ELF3-LUX complex links the circadian clock to diurnal control of hypocotyl growth

The circadian clock is required for adaptive responses to daily and seasonal changes in environmental conditions .
Light and the circadian clock interact to consolidate the phase of hypocotyl cell elongation to peak at dawn under diurnal cycles in Arabidopsis thaliana .
Here we identify a protein complex ( called the evening complex ) -- composed of the proteins encoded by EARLY FLOWERING 3 ( ELF3 ) , ELF4 and the transcription-factor-encoding gene LUX ARRHYTHMO ( LUX ; also known as PHYTOCLOCK 1 ) -- that directly regulates plant growth .
ELF3 is both necessary and sufficient to form a complex between ELF4 and LUX , and the complex is diurnally regulated , peaking at dusk .
ELF3 , ELF4 and LUX are required for the proper expression of the growth-promoting transcription factors encoded by PHYTOCHROME INTERACTING FACTOR 4 ( PIF4 ) and PIF5 ( also known as PHYTOCHROME INTERACTING FACTOR 3-LIKE 6 ) under diurnal conditions .
LUX targets the complex to the promoters of PIF4 and PIF5 in vivo .
Mutations in PIF4 and/or PIF5 are epistatic to the loss of the ELF4-ELF3-LUX complex , suggesting that regulation of PIF4 and PIF5 is a crucial function of the complex .
Therefore , the evening complex underlies the molecular basis for circadian gating of hypocotyl growth in the early evening .

[1412] Quantifying future climate change

Quantitative projections of future climate are in increasing demand from the scientific community , policymakers and other stakeholders .
Climate models of varying complexity are used to make projections , but approximations and inadequacies or ` errors ' in models mean that those projections are uncertain , sometimes exploring a very wide range of possible futures .
Techniques for quantifying the uncertainties are described here in terms of a common framework whereby models are used to explore relationships between past climate and climate change and future projections .
Model parameters may be varied to produce a range of different simulations of past climate that are then compared with observations using ` metrics ' .
If the model parameters can be constrained to a tighter range as a result of observational comparisons , projections can also be constrained to a tighter range .
The strengths and weaknesses of different implementations are discussed .

[1413] Sex increases the efficacy of natural selection in experimental yeast populations

Why sex evolved and persists is a problem for evolutionary biology , because sex disrupts favourable gene combinations and requires an expenditure of time and energy .
Further , in organisms with unequal-sized gametes , the female transmits her genes at only half the rate of an asexual equivalent ( the twofold cost of sex ) .
Many modern theories that provide an explanation for the advantage of sex incorporate an idea originally proposed by Weismann more than 100 years ago : sex allows natural selection to proceed more effectively because it increases genetic variation .
Here we test this hypothesis , which still lacks robust empirical support , with the use of experiments on yeast populations .
Capitalizing on recent advances in the molecular biology of recombination in yeast , we produced by genetic manipulation strains that differed only in their capacity for sexual reproduction .
We show that , as predicted by the theory , sex increases the rate of adaptation to a new harsh environment but has no measurable effect on fitness in a new benign environment where there is little selection .

[1414] Negative regulation of bacterial quorum sensing tunes public goods cooperation

Bacterial quorum sensing ( QS ) often coordinates the expression of other , generally more costly public goods involved in virulence and nutrient acquisition .
In many Proteobacteria , the basic QS circuitry consists of a synthase that produces a diffusible acyl-homoserine lactone and a cognate receptor that activates public goods expression .
In some species , the circuitry also contains negative regulators that have the potential to modulate the timing and magnitude of activation .
In this study , we experimentally investigated the contribution of this regulatory function to the evolutionary stability of public goods cooperation in the opportunistic pathogen Pseudomonas aeruginosa .
We compared fitness and public goods expression rates of strains lacking either qteE or qscR , each encoding a distinct negative regulator , with those of the wild-type parent and a signal-blind receptor mutant under defined growth conditions .
We found that ( 1 ) qteE and qscR mutations behave virtually identically and have a stronger effect on the magnitude than on the timing of expression , ( 2 ) high expression in qteE and qscR mutants imposes a metabolic burden under nutrient conditions that advance induction and ( 3 ) high expression in qteE and qscR mutants increases population growth when QS is required , but also permits invasion by both wild-type and receptor mutant strains .
Our data indicate that negative regulation of QS balances the costs and benefits of public goods by attenuating expression after transition to the induced state .
As the cells can not accurately assess the amount of cooperation needed , such bet-hedging would be advantageous in changing parasitic and nonparasitic environments .

[1415] Metabolism , cell growth and the bacterial cell cycle

Adaptation to fluctuations in nutrient availability is a fact of life for single-celled organisms in the ` wild ' .
A decade ago our understanding of how bacteria adjust cell cycle parameters to accommodate changes in nutrient availability stemmed almost entirely from elegant physiological studies completed in the 1960s .
In this Opinion article we summarize recent groundbreaking work in this area and discuss potential mechanisms by which nutrient availability and metabolic status are coordinated with cell growth , chromosome replication and cell division .

[1416] Density-dependent mortality in an oceanic copepod population

Planktonic copepods are primary consumers in the ocean and are perhaps the most numerous metazoans on earth .
Secondary production by these zooplankton supports most food webs of the open sea , directly affecting pelagic fish populations and the biological pump of carbon into the deep ocean .
Models of marine ecosystems are quite sensitive to the formulation of the term for zooplankton mortality , although there are few data available to constrain mortality rates in such models .
Here we present the first evidence for nonlinear , density-dependent mortality rates of open-ocean zooplankton .
A high-frequency time series reveals that per capita mortality rates of eggs of Calanus finmarchicus Gunnerus are a function of the abundance of adult females and juveniles .
The temporal dynamics of zooplankton populations can be influenced as much by time-dependent mortality rates as by variations in ` bottom up ' forcing .
The functional form and rates chosen for zooplankton mortality in ecosystem models can alter the balance of pelagic ecosystems , modify elemental fluxes into the ocean 's interior , and modulate interannual variability in pelagic ecosystems .

[1417] Rapid environmental changes in southern Europe during the last glacial period

Oxygen-isotope records from Greenland ice cores , indicate numerous rapid climate fluctuations during the last glacial period .
North Atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice-rafted debris .
In contrast , very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents .
Here we present high-resolution geochemical , physical and pollen data from lake sediments in Italy and from a Mediterranean sediment core , linked by a common tephrochronology .
Our lacustrine sequence extends to the past 102,000 years .
Many of its features correlate well with the Greenland ice-core records , demonstrating that the closely coupled ocean-atmosphere system of the Northern Hemisphere during the last glacial extended its influence at least as far as the central Mediterranean region .
Numerous vegetation changes were rapid , frequently occurring in less than 200 years , showing that the terrestrial biosphere participated fully in last-glacial climate variability .
Earlier than 65,000 years ago , our record shows more climate fluctuations than are apparent in the Greenland ice cores .
Together , the multi-proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials , and provide a step towards determining the underlying mechanisms of the centennial-millennial-scale variability .

[1418] Selective fishing induces density-dependent growth

Over the last decades , views on fisheries management have oscillated between alarm and trust in management progress .
The predominant policy for remedying the world fishing crisis aims at maximum sustainable yield ( MSY ) by adjusting gear selectivity and fishing effort .
Here we report a case study on how striving for higher yields from the Eastern Baltic cod stock by increasing selectivity has become exceedingly detrimental for its productivity .
Although there is a successive increase in numbers of undersized fish , growth potential is severely reduced , and fishing mortality in fishable size has increased .
Once density-dependent growth is introduced , the process is self-enforcing as long as the recruitment remains stable .
Our findings suggest that policies focusing on maximum yield while targeting greater sizes are risky and should instead prioritize catch rates over yield .
Disregarding the underlying population structure may jeopardize stock productivity , with dire consequences for the fishing industry and ecosystem structure and function .

[1419] Gut microbiome composition is linked to whole grain-induced immunological improvements

The involvement of the gut microbiota in metabolic disorders , and the ability of whole grains to affect both host metabolism and gut microbial ecology , suggest that some benefits of whole grains are mediated through their effects on the gut microbiome .
Nutritional studies that assess the effect of whole grains on both the gut microbiome and human physiology are needed .
We conducted a randomized cross-over trial with four-week treatments in which 28 healthy humans consumed a daily dose of 60 g of whole-grain barley ( WGB ) , brown rice ( BR ) , or an equal mixture of the two ( BR+WGB ) , and characterized their impact on fecal microbial ecology and blood markers of inflammation , glucose and lipid metabolism .
All treatments increased microbial diversity , the Firmicutes/Bacteroidetes ratio , and the abundance of the genus Blautia in fecal samples .
The inclusion of WGB enriched the genera Roseburia , Bifidobacterium and Dialister , and the species Eubacterium rectale , Roseburia faecis and Roseburia intestinalis .
Whole grains , and especially the BR+WGB treatment , reduced plasma interleukin-6 ( IL-6 ) and peak postprandial glucose .
Shifts in the abundance of Eubacterium rectale were associated with changes in the glucose and insulin postprandial response .
Interestingly , subjects with greater improvements in IL-6 levels harbored significantly higher proportions of Dialister and lower abundance of Coriobacteriaceae .
In conclusion , this study revealed that a short-term intake of whole grains induced compositional alterations of the gut microbiota that coincided with improvements in host physiological measures related to metabolic dysfunctions in humans .

[1420] Temporal constraints on future accumulation-area loss of a major Arctic ice cap due to climate change ( Vestfonna , Svalbard )

Arctic glaciers and ice caps are major contributors to past , present and future sea-level fluctuations .
Continued global warming may eventually lead to the equilibrium line altitudes of these ice masses rising above their highest points , triggering unstoppable downwasting .
This may feed future sea-level rise considerably .
We here present projections for the timing of equilibrium-line loss at the major Arctic ice cap Vestfonna , Svalbard .
The projections are based on spatially distributed climatic mass balance modelling driven by the outputs of multiple climate models from the Coupled Model Intercomparison Project Phase 5 ( CMIP5 ) forced by the Representative Concentration Pathways ( RCPs ) 2.6 , 4.5 , 6.0 and 8.5 .
Results indicate strongly decreasing climatic mass balances over the 21st century for all RCPs considered .
Glacier-wide mass-balance rates will drop down to -4 m a-1 w.e. ( water equivalent ) at a maximum .
The date at which the equilibrium line rises above the summit of Vestfonna ( 630 m above sea level ) is calculated to range between 2040 and 2150 , depending on scenario .

[1421] Projected response of the Indian Ocean Dipole to greenhouse warming

Natural modes of variability centred in the tropics , such as the El Nino/Southern Oscillation and the Indian Ocean Dipole , are a significant source of interannual climate variability across the globe .
Future climate warming could alter these modes of variability .
For example , with the warming projected for the end of the twenty-first century , the mean climate of the tropical Indian Ocean is expected to change considerably .
These changes have the potential to affect the Indian Ocean Dipole , currently characterized by an alternation of anomalous cooling in the eastern tropical Indian Ocean and warming in the west in a positive dipole event , and the reverse pattern for negative events .
The amplitude of positive events is generally greater than that of negative events .
Mean climate warming in austral spring is expected to lead to stronger easterly winds just south of the Equator , faster warming of sea surface temperatures in the western Indian Ocean compared with the eastern basin , and a shoaling equatorial thermocline .
The mean climate conditions that result from these changes more closely resemble a positive dipole state .
However , defined relative to the mean state at any given time , the overall frequency of events is not projected to change -- but we expect a reduction in the difference in amplitude between positive and negative dipole events .

[1422] Reading the signs

When it comes to clarifying the causes of climate change it appears that the situation might not be , as some lobby groups would have us believe , hopeless .
At least this is what Simon Tett from the Meteorological Office Bracknell , UK and colleagues report in the 10 June issue of Nature They assume that each of a whole host of influences - natural climate variability , changes in solar activity , volcanic emissions and changes in amounts of human-induced greenhouse gases and sulphate aerosols ( particles that result from the burning of fossil fuels ) - might play a part in causing this century 's erratic temperature rise .

[1423] Sustainable syntrophic growth of Dehalococcoides ethenogenes strain 195 with Desulfovibrio vulgaris Hildenborough and Methanobacterium congolense : global transcriptomic and proteomic analyses

Dehalococcoides ethenogenes strain 195 ( DE195 ) was grown in a sustainable syntrophic association with Desulfovibrio vulgaris Hildenborough ( DVH ) as a co-culture , as well as with DVH and the hydrogenotrophic methanogen Methanobacterium congolense ( MC ) as a tri-culture using lactate as the sole energy and carbon source .
In the co - and tri-cultures , maximum dechlorination rates of DE195 were enhanced by approximately three times ( 11.0 + / -0.01 mumol per day for the co-culture and 10.1 + / -0.3 mumol per day for the tri-culture ) compared with DE195 grown alone ( 3.8 + / -0.1 mumol per day ) .
Cell yield of DE195 was enhanced in the co-culture ( 9.0 + / -0.5 x 107 cells per mumol Cl - released , compared with 6.8 + / -0.9 x 107 cells per mumol Cl - released for the pure culture ) , whereas no further enhancement was observed in the tri-culture ( 7.3 + / -1.8 x 107 cells per mumol Cl - released ) .
The transcriptome of DE195 grown in the co-culture was analyzed using a whole-genome microarray targeting DE195 , which detected 102 significantly up - or down-regulated genes compared with DE195 grown in isolation , whereas no significant transcriptomic difference was observed between co - and tri-cultures .
Proteomic analysis showed that 120 proteins were differentially expressed in the co-culture compared with DE195 grown in isolation .
Physiological , transcriptomic and proteomic results indicate that the robust growth of DE195 in co - and tri-cultures is because of the advantages associated with the capabilities of DVH to ferment lactate to provide H2 and acetate for growth , along with potential benefits from proton translocation , cobalamin-salvaging and amino acid biosynthesis , whereas MC in the tri-culture provided no significant additional benefits beyond those of DVH .

[1424] Broad range of 2050 warming from an observationally constrained large climate model ensemble

Incomplete understanding of three aspects of the climate system -- equilibrium climate sensitivity , rate of ocean heat uptake and historical aerosol forcing -- and the physical processes underlying them lead to uncertainties in our assessment of the global-mean temperature evolution in the twenty-first century .
Explorations of these uncertainties have so far relied on scaling approaches , large ensembles of simplified climate models , or small ensembles of complex coupled atmosphere-ocean general circulation models which under-represent uncertainties in key climate system properties derived from independent sources .
Here we present results from a multi-thousand-member perturbed-physics ensemble of transient coupled atmosphere-ocean general circulation model simulations .
We find that model versions that reproduce observed surface temperature changes over the past 50 years show global-mean temperature increases of 1.4-3 K by 2050 , relative to 1961-1990 , under a mid-range forcing scenario .
This range of warming is broadly consistent with the expert assessment provided by the Intergovernmental Panel on Climate Change Fourth Assessment Report , but extends towards larger warming than observed in ensembles-of-opportunity typically used for climate impact assessments .
From our simulations , we conclude that warming by the middle of the twenty-first century that is stronger than earlier estimates is consistent with recent observed temperature changes and a mid-range ` no mitigation ' scenario for greenhouse-gas emissions .

[1425] The emergence of modern sea ice cover in the Arctic Ocean

Arctic sea ice coverage is shrinking in response to global climate change and summer ice-free conditions in the Arctic Ocean are predicted by the end of the century .
The validity of this prediction could potentially be tested through the reconstruction of the climate of the Pliocene epoch ( 5.33-2 .58 million years ago ) , an analogue of a future warmer Earth .
Here we show that , in the Eurasian sector of the Arctic Ocean , ice-free conditions prevailed in the early Pliocene until sea ice expanded from the central Arctic Ocean for the first time ca. 4 million years ago .
Amplified by a rise in topography in several regions of the Arctic and enhanced freshening of the Arctic Ocean , sea ice expanded progressively in response to positive ice-albedo feedback mechanisms .
Sea ice reached its modern winter maximum extension for the first time during the culmination of the Northern Hemisphere glaciation , ca. 2.6 million years ago .

[1426] Spatial variability in oceanic redox structure 1.8 billion years ago

The evolution of ocean chemistry during the Proterozoic eon ( 2.5-0 .542 billion years ago ) is thought to have played a central role in both the timing and rate of eukaryote evolution .
The timing of the deposition of iron formations implies that , early in the Earth 's history , oceans were predominantly anoxic and rich in dissolved iron .
However , global deposition of iron formations ceased about 1.84 billion years ago .
This termination indicates a major upheaval in ocean chemistry , but the precise nature of this change remains debated .
Here we use iron and sulphur systematics to reconstruct oceanic redox conditions from the 1.88 - to 1.83-billion-year-old Animikie group from the Superior region , North America .
We find that surface waters were oxygenated , whereas at mid-depths , anoxic and sulphidic ( euxinic ) conditions extended over 100 km from the palaeoshoreline .
The spatial extent of euxinia varied through time , but deep ocean waters remained rich in dissolved iron .
Widespread euxinia along continental margins would have removed dissolved iron from the water column through the precipitation of pyrite , which would have reduced the supply of dissolved iron and resulted in the global cessation of the deposition of ` Superior-type ' iron formations .
We suggest that incursions of sulphide from the mid-depths into overlying oxygenated surface waters may have placed severe constraints on eukaryotic evolution .

[1427] Holocene variations in peatland methane cycling associated with the Asian summer monsoon system

Atmospheric methane concentrations decreased during the early to middle Holocene ; however , the governing mechanisms remain controversial .
Although it has been suggested that the mid-Holocene minimum methane emissions are associated with hydrological change , direct evidence is lacking .
Here we report a new independent approach , linking hydrological change in peat sediments from the Tibetan Plateau to changes in archaeal diether concentrations and diploptene delta13C values as tracers for methanogenesis and methanotrophy , respectively .
A minimum in inferred methanogenesis occurred during the mid-Holocene , which , locally , corresponds with the driest conditions of the Holocene , reflecting a minimum in Asian monsoon precipitation .
The close coupling between precipitation and methanogenesis is validated by climate simulations , which also suggest a regionally widespread impact .
Importantly , the minimum in methanogenesis is associated with a maximum in methanotrophy .
Therefore , methane emissions in the Tibetan Plateau region were apparently lower during the mid-Holocene and partially controlled by interactions of large-scale atmospheric circulation .

[1428] Politics is biggest factor in climate uncertainty

Delaying action on emissions will increase costs and reduce chances of limiting temperature increase .

[1429] The phasevarion : phase variation of type III DNA methyltransferases controls coordinated switching in multiple genes

In several host-adapted pathogens , phase variation has been found to occur in genes that encode methyltransferases associated with type III restriction-modification systems .
It was recently shown that in the human pathogens Haemophilus influenzae , Neisseria gonorrhoeae and Neisseria meningitidis phase variation of a type III DNA methyltransferase , encoded by members of the mod gene family , regulates the expression of multiple genes .
This novel genetic system has been termed the ` phasevarion ' ( phase-variable regulon ) .
The wide distribution of phase-variable mod family genes indicates that this may be a common strategy used by host-adapted bacterial pathogens to randomly switch between distinct cell types .

[1430] Oral multispecies biofilm development and the key role of cell-cell distance

Growth of oral bacteria in situ requires adhesion to a surface because the constant flow of host secretions thwarts the ability of planktonic cells to grow before they are swallowed .
Therefore , oral bacteria evolved to form biofilms on hard tooth surfaces and on soft epithelial tissues , which often contain multiple bacterial species .
Because these biofilms are easy to study , they have become the paradigm of multispecies biofilms .
In this Review we describe the factors involved in the formation of these biofilms , including the initial adherence to the oral tissues and teeth , cooperation between bacterial species in the biofilm , signalling between the bacteria and its role in pathogenesis , and the transfer of DNA between bacteria .
In all these aspects distance between cells of different species is integral for oral biofilm growth .

[1431] Significant increase in relief of the European Alps during mid-Pleistocene glaciations

Some of Earth 's greatest relief occurs where glacial processes act on mountain topography .
This dramatic landscape is thought to be an imprint of Pleistocene glaciations .
However , whether the net effect of glacial erosion on mountains is to increase or decrease relief remains disputed .
It has been suggested that in the European Alps , the onset of widespread glaciation since the mid-Pleistocene climate transition led to the growth of large , long-lived and strongly erosive alpine glaciers that profoundly influenced topography .
Here we use 4He/3He thermochronometry and thermal-kinematic models to show that the Rhone Valley in Switzerland deepened by about 1-1 .5 km over the past one million years .
Our results indicate that while the valley was incised and back-cut , high-altitude areas were preserved from erosion .
We find an approximately two-fold increase in both local topographic relief and valley concavity , which occurred around the time of the mid-Pleistocene transition .
Our results support the proposed link between the onset of efficient glacial erosion in the European Alps and the transition to longer , colder glacial periods at the middle of the Pleistocene epoch .

[1432] Facets of diazotrophy in the oxygen minimum zone waters off Peru

Nitrogen fixation , the biological reduction of dinitrogen gas ( N2 ) to ammonium ( NH4 + ) , is quantitatively the most important external source of new nitrogen ( N ) to the open ocean .
Classically , the ecological niche of oceanic N2 fixers ( diazotrophs ) is ascribed to tropical oligotrophic surface waters , often depleted in fixed N , with a diazotrophic community dominated by cyanobacteria .
Although this applies for large areas of the ocean , biogeochemical models and phylogenetic studies suggest that the oceanic diazotrophic niche may be much broader than previously considered , resulting in major implications for the global N-budget .
Here , we report on the composition , distribution and abundance of nifH , the functional gene marker for N2 fixation .
Our results show the presence of eight clades of diazotrophs in the oxygen minimum zone ( OMZ ) off Peru .
Although proteobacterial clades dominated overall , two clusters affiliated to spirochaeta and archaea were identified .
N2 fixation was detected within OMZ waters and was stimulated by the addition of organic carbon sources supporting the view that non-phototrophic diazotrophs were actively fixing dinitrogen .
The observed co-occurrence of key functional genes for N2 fixation , nitrification , anammox and denitrification suggests that a close spatial coupling of N-input and N-loss processes exists in the OMZ off Peru .
The wide distribution of diazotrophs throughout the water column adds to the emerging view that the habitat of marine diazotrophs can be extended to low oxygen/high nitrate areas .
Furthermore , our statistical analysis suggests that NO2 - and PO43 - are the major factors affecting diazotrophic distribution throughout the OMZ .
In view of the predicted increase in ocean deoxygenation resulting from global warming , our findings indicate that the importance of OMZs as niches for N2 fixation may increase in the future .

[1433] Quantitative flux analysis reveals folate-dependent NADPH production

ATP is the dominant energy source in animals for mechanical and electrical work ( for example , muscle contraction or neuronal firing ) .
For chemical work , there is an equally important role for NADPH , which powers redox defence and reductive biosynthesis .
The most direct route to produce NADPH from glucose is the oxidative pentose phosphate pathway , with malic enzyme sometimes also important .
Although the relative contribution of glycolysis and oxidative phosphorylation to ATP production has been extensively analysed , similar analysis of NADPH metabolism has been lacking .
Here we demonstrate the ability to directly track , by liquid chromatography-mass spectrometry , the passage of deuterium from labelled substrates into NADPH , and combine this approach with carbon labelling and mathematical modelling to measure NADPH fluxes .
In proliferating cells , the largest contributor to cytosolic NADPH is the oxidative pentose phosphate pathway .
Surprisingly , a nearly comparable contribution comes from serine-driven one-carbon metabolism , in which oxidation of methylene tetrahydrofolate to 10-formyl-tetrahydrofolate is coupled to reduction of NADP + to NADPH .
Moreover , tracing of mitochondrial one-carbon metabolism revealed complete oxidation of 10-formyl-tetrahydrofolate to make NADPH .
As folate metabolism has not previously been considered an NADPH producer , confirmation of its functional significance was undertaken through knockdown of methylenetetrahydrofolate dehydrogenase ( MTHFD ) genes .
Depletion of either the cytosolic or mitochondrial MTHFD isozyme resulted in decreased cellular NADPH/NADP + and reduced/oxidized glutathione ratios ( GSH/GSSG ) and increased cell sensitivity to oxidative stress .
Thus , although the importance of folate metabolism for proliferating cells has been long recognized and attributed to its function of producing one-carbon units for nucleic acid synthesis , another crucial function of this pathway is generating reducing power .

[1434] Going back to the roots : the microbial ecology of the rhizosphere

The rhizosphere is the interface between plant roots and soil where interactions among a myriad of microorganisms and invertebrates affect biogeochemical cycling , plant growth and tolerance to biotic and abiotic stress .
The rhizosphere is intriguingly complex and dynamic , and understanding its ecology and evolution is key to enhancing plant productivity and ecosystem functioning .
Novel insights into key factors and evolutionary processes shaping the rhizosphere microbiome will greatly benefit from integrating reductionist and systems-based approaches in both agricultural and natural ecosystems .
Here , we discuss recent developments in rhizosphere research in relation to assessing the contribution of the micro - and macroflora to sustainable agriculture , nature conservation , the development of bio-energy crops and the mitigation of climate change .

[1435] Decreasing overflow from the Nordic seas into the Atlantic Ocean through the Faroe Bank channel since 1950

The overflow of cold , dense water from the Nordic seas , across the Greenland-Scotland ridge and into the Atlantic Ocean is the main source for the deep water of the North Atlantic Ocean .
This flow also helps drive the inflow of warm , saline surface water into the Nordic seas .
The Faroe Bank channel is the deepest path across the ridge , and the deep flow through this channel accounts for about one-third of the total overflow .
Previous work has demonstrated that the overflow has become warmer and less saline over time .
Here we show , using direct measurements and historical hydrographic data , that the volume flux of the Faroe Bank channel overflow has also decreased .
Estimating the volume flux conservatively , we find a decrease by at least 20 per cent relative to 1950 .
If this reduction in deep flow from the Nordic seas is not compensated by increased flow from other sources , it implies a weakened global thermohaline circulation and reduced inflow of Atlantic water to the Nordic seas .

[1436] The carbon footprint of traditional woodfuels

Over half of all wood harvested worldwide is used as fuel , supplying ~ 9 % of global primary energy .
By depleting stocks of woody biomass , unsustainable harvesting can contribute to forest degradation , deforestation and climate change .
However , past efforts to quantify woodfuel sustainability failed to provide credible results .
We present a spatially explicit assessment of pan-tropical woodfuel supply and demand , calculate the degree to which woodfuel demand exceeds regrowth , and estimate woodfuel-related greenhouse-gas emissions for the year 2009 .
We estimate 27-34 % of woodfuel harvested was unsustainable , with large geographic variations .
Our estimates are lower than estimates from carbon offset projects , which are probably overstating the climate benefits of improved stoves .
Approximately 275 million people live in woodfuel depletion ` hotspots ' -- concentrated in South Asia and East Africa -- where most demand is unsustainable .
Emissions from woodfuels are 1.0-1 .2 Gt CO2e yr-1 ( 1.9-2 .3 % of global emissions ) .
Successful deployment and utilization of 100 million improved stoves could reduce this by 11-17 % .
At US$ 11 per tCO2e , these reductions would be worth over US$ 1 billion yr-1 in avoided greenhouse-gas emissions if black carbon were integrated into carbon markets .
By identifying potential areas of woodfuel-driven degradation or deforestation , we inform the ongoing discussion about REDD-based approaches to climate change mitigation .

[1437] Hydrology : Arctic wetting

Nature 509 , 479 - 482 ( 2014 ) Global warming will lead to an increase in atmospheric moisture due to increases in evaporation and the holding capacity of the atmosphere .
The Arctic is expected to have one of the highest global increases in precipitation under climate change and enhanced poleward moisture transport is typically reported as the cause .

[1438] Phase-locking and environmental fluctuations generate synchrony in a predator-prey community

Spatially synchronized fluctuations in system state are common in physical and biological systems ranging from individual atoms to species as diverse as viruses , insects and mammals .
Although the causal factors are well known for many synchronized phenomena , several processes concurrently have an impact on spatial synchrony of species , making their separate effects and interactions difficult to quantify .
Here we develop a general stochastic model of predator-prey spatial dynamics to predict the outcome of a laboratory microcosm experiment testing for interactions among all known synchronizing factors : ( 1 ) dispersal of individuals between populations ; ( 2 ) spatially synchronous fluctuations in exogenous environmental factors ( the Moran effect ) ; and ( 3 ) interactions with other species ( for example , predators ) that are themselves spatially synchronized .
The Moran effect synchronized populations of the ciliate protist Tetrahymena pyriformis ; however , dispersal only synchronized prey populations in the presence of the predator Euplotes patella .
Both model and data indicate that synchrony depends on cyclic dynamics generated by the predator .
Dispersal , but not the Moran effect , ` phase-locks ' cycles , which otherwise become ` decoherent ' and drift out of phase .
In the absence of cycles , phase-locking is not possible and the synchronizing effect of dispersal is negligible .
Interspecific interactions determine population synchrony , not by providing an additional source of synchronized fluctuations , but by altering population dynamics and thereby enhancing the action of dispersal .
Our results are robust to wide variation in model parameters representative of many natural predator-prey or host-pathogen systems .
This explains why cyclic systems provide many of the most dramatic examples of spatial synchrony in nature .

[1439] Genetic mechanisms and evolutionary significance of natural variation in Arabidopsis

Genomic studies of natural variation in model organisms provide a bridge between molecular analyses of gene function and evolutionary investigations of adaptation and natural selection .
In the model plant species Arabidopsis thaliana , recent studies of natural variation have led to the identification of genes underlying ecologically important complex traits , and provided new insights about the processes of genome evolution , geographic population structure , and the selective mechanisms shaping complex trait variation in natural populations .
These advances illustrate the potential for a new synthesis to elucidate mechanisms for the adaptive evolution of complex traits from nucleotide sequences to real-world environments .

[1440] High-latitude influence on the eastern equatorial Pacific climate in the early Pleistocene epoch

Many records of tropical sea surface temperature and marine productivity exhibit cycles of 23 kyr ( orbital precession ) and 100 kyr during the past 0.5 Myr ( refs 1-5 ) , whereas high-latitude sea surface temperature records display much more pronounced obliquity cycles at a period of about 41 kyr ( ref .
6 ) .
Little is known , however , about tropical climate variability before the mid-Pleistocene transition about 900 kyr ago , which marks the change from a climate dominated by 41-kyr cycles ( when ice-age cycles and high-latitude sea surface temperature variations were dictated by changes in the Earth 's obliquity ) to the more recent 100-kyr cycles of ice ages .
Here we analyse alkenones from marine sediments in the eastern equatorial Pacific Ocean to reconstruct sea surface temperatures and marine productivity over the past 1.8 Myr .
We find that both records are dominated by the 41-kyr obliquity cycles between 1.8 and 1.2 Myr ago , with a relatively small contribution from orbital precession , and that early Pleistocene sea surface temperatures varied in the opposite sense to local annual insolation in the eastern equatorial Pacific Ocean .
We conclude that during the early Pleistocene epoch , climate variability at our study site must have been determined by high-latitude processes that were driven by orbital obliquity forcing .

[1441] Climate-change impact assessment for inlet-interrupted coastlines

Climate-change ( CC ) - driven sea-level rise ( SLR ) will result in coastline retreat due to landward movement of the coastal profile ( that is , the Bruun effect ) .
Coastline change adjacent to commonly found tidal inlets will be influenced not only by the Bruun effect , but also by SLR-driven basin infilling and CC-driven variations in rainfall/runoff .
However , as a model that accounts for all of the above-mentioned processes has been lacking so far , most coastal CC impact studies until now have considered only the Bruun effect .
Here , we present a scale-aggregated model capable of providing rapid assessments of coastline change adjacent to small inlet-estuary/lagoon systems due to the combined effect of CC-driven SLR and variations in rainfall/runoff .
Model applications to four representative systems show that the Bruun effect represents only 25-50 % of total potential coastline change , and underline the significance of coastline change due to SLR-driven basin infilling and CC-driven variations in rainfall/runoff .

[1442] Ecogenomics and genome landscapes of marine Pseudoalteromonas phage H105/1

Marine phages have an astounding global abundance and ecological impact .
However , little knowledge is derived from phage genomes , as most of the open reading frames in their small genomes are unknown , novel proteins .
To infer potential functional and ecological relevance of sequenced marine Pseudoalteromonas phage H105/1 , two strategies were used .
First , similarity searches were extended to include six viral and bacterial metagenomes paired with their respective environmental contextual data .
This approach revealed ` ecogenomic ' patterns of Pseudoalteromonas phage H105/1 , such as its estuarine origin .
Second , intrinsic genome signatures ( phylogenetic , codon adaptation and tetranucleotide ( tetra ) frequencies ) were evaluated on a resolved intra-genomic level to shed light on the evolution of phage functional modules .
On the basis of differential codon adaptation of Phage H105/1 proteins to the sequenced Pseudoalteromonas spp. , regions of the phage genome with the most ` host ' - adapted proteins also have the strongest bacterial tetra signature , whereas the least ` host ' - adapted proteins have the strongest phage tetra signature .
Such a pattern may reflect the evolutionary history of the respective phage proteins and functional modules .
Finally , analysis of the structural proteome identified seven proteins that make up the mature virion , four of which were previously unknown .
This integrated approach combines both novel and classical strategies and serves as a model to elucidate ecological inferences and evolutionary relationships from phage genomes that typically abound with unknown gene content .

[1443] Glyphosate herbicide affects belowground interactions between earthworms and symbiotic mycorrhizal fungi in a model ecosystem

Herbicides containing glyphosate are widely used in agriculture and private gardens , however , surprisingly little is known on potential side effects on non-target soil organisms .
In a greenhouse experiment with white clover we investigated , to what extent a globally-used glyphosate herbicide affects interactions between essential soil organisms such as earthworms and arbuscular mycorrhizal fungi ( AMF ) .
We found that herbicides significantly decreased root mycorrhization , soil AMF spore biomass , vesicles and propagules .
Herbicide application and earthworms increased soil hyphal biomass and tended to reduce soil water infiltration after a simulated heavy rainfall .
Herbicide application in interaction with AMF led to slightly heavier but less active earthworms .
Leaching of glyphosate after a simulated rainfall was substantial and altered by earthworms and AMF .
These sizeable changes provide impetus for more general attention to side-effects of glyphosate-based herbicides on key soil organisms and their associated ecosystem services .

[1444] Ice-sheet mass balance and climate change

Since the 2007 Intergovernmental Panel on Climate Change Fourth Assessment Report , new observations of ice-sheet mass balance and improved computer simulations of ice-sheet response to continuing climate change have been published .
Whereas Greenland is losing ice mass at an increasing pace , current Antarctic ice loss is likely to be less than some recently published estimates .
It remains unclear whether East Antarctica has been gaining or losing ice mass over the past 20 years , and uncertainties in ice-mass change for West Antarctica and the Antarctic Peninsula remain large .
We discuss the past six years of progress and examine the key problems that remain .

[1445] The more , the merrier : heterotroph richness stimulates methanotrophic activity

Although microorganisms coexist in the same environment , it is still unclear how their interaction regulates ecosystem functioning .
Using a methanotroph as a model microorganism , we determined how methane oxidation responds to heterotroph diversity .
Artificial communities comprising of a methanotroph and increasing heterotroph richness , while holding equal starting cell numbers were assembled .
We considered methane oxidation rate as a functional response variable .
Our results showed a significant increase of methane oxidation with increasing heterotroph richness , suggesting a complex interaction in the cocultures leading to a stimulation of methanotrophic activity .
Therefore , not only is the methanotroph diversity directly correlated to methanotrophic activity for some methanotroph groups as shown before , but also the richness of heterotroph interacting partners is relevant to enhance methane oxidation too .
In this unprecedented study , we provide direct evidence showing how heterotroph richness exerts a response in methanotroph-heterotroph interaction , resulting in increased methanotrophic activity .
Our study has broad implications in how methanotroph and heterotroph interact to regulate methane oxidation , and is particularly relevant in methane-driven ecosystems .

[1446] Millennial-scale changes in atmospheric CO2 levels linked to the Southern Ocean carbon isotope gradient and dust flux

The rise in atmospheric CO2 concentrations observed at the end of glacial periods has , at least in part , been attributed to the upwelling of carbon-rich deep water in the Southern Ocean .
The magnitude of outgassing of dissolved CO2 , however , is influenced by the biological fixation of upwelled inorganic carbon and its transfer back to the deep sea as organic carbon .
The efficiency of this biological pump is controlled by the extent of nutrient utilization , which can be stimulated by the delivery of iron by atmospheric dust particles .
Changes in nutrient utilization should be reflected in the delta13C gradient between intermediate and deep waters .
Here we use the delta13C values of intermediate - and bottom-dwelling foraminifera to reconstruct the carbon isotope gradient between thermocline and abyssal water in the subantarctic zone of the South Atlantic Ocean over the past 360,000 years .
We find millennial-scale oscillations of the carbon isotope gradient that correspond to changes in dust flux and atmospheric CO2 concentrations as reported from Antarctic ice cores .
We interpret this correlation as a relationship between the efficiency of the biological pump and fertilization by dust-borne iron .
As the correlation is exponential , we suggest that the sensitivity of the biological pump to dust-borne iron fertilization may be increased when the background dust flux is low .

[1447] Holocene evolution of the Indonesian throughflow and the western Pacific warm pool

High sea surface temperatures in the western Pacific warm pool fuel atmospheric convection and influence tropical climate .
This region also hosts the Indonesian throughflow , the network of currents through which surface and thermocline waters are transported from the western equatorial Pacific Ocean into the Indian Ocean .
Here we show , using records of the delta18O and Mg/Ca of planktonic foraminifera from eight sediment cores , that from about 10,000 to 7,000 years ago , sea surface temperatures in the western sector of the western Pacific warm pool were about 0.5 degreesC higher than during pre-industrial times .
We also find that about 9,500 years ago , when the South China and Indonesian seas were connected by rising sea level , surface waters in the Makassar Strait became relatively fresher .
We suggest that the permanent reduction of surface salinity initiated the enhanced flow at lower , thermocline depths seen in the modern Indonesian throughflow .
However , the uniformly warm sea surface temperatures found upstream and downstream of the Indonesian throughflow indicate that the early Holocene warmth in this region was not directly related to reduced heat transport by the throughflow that may have resulted from surface freshening of the Makassar Strait .
Instead , we propose that the elevated temperatures were the result of a westward shift or expansion of the boundaries of the western Pacific warm pool .

[1448] Eastern Pacific tropical cyclones intensified by El Nino delivery of subsurface ocean heat

The El Nino Southern Oscillation ( ENSO ) creates strong variations in sea surface temperature in the eastern equatorial Pacific , leading to major climatic and societal impacts .
In particular , ENSO influences the yearly variations of tropical cyclone ( TC ) activities in both the Pacific and Atlantic basins through atmospheric dynamical factors such as vertical wind shear and stability .
Until recently , however , the direct ocean thermal control of ENSO on TCs has not been taken into consideration because of an apparent mismatch in both timing and location : ENSO peaks in winter and its surface warming occurs mostly along the Equator , a region without TC activity .
Here we show that El Nino -- the warm phase of an ENSO cycle -- effectively discharges heat into the eastern North Pacific basin two to three seasons after its wintertime peak , leading to intensified TCs .
This basin is characterized by abundant TC activity and is the second most active TC region in the world .
As a result of the time involved in ocean transport , El Nino 's equatorial subsurface ` heat reservoir ' , built up in boreal winter , appears in the eastern North Pacific several months later during peak TC season ( boreal summer and autumn ) .
By means of this delayed ocean transport mechanism , ENSO provides an additional heat supply favourable for the formation of strong hurricanes .
This thermal control on intense TC variability has significant implications for seasonal predictions and long-term projections of TC activity over the eastern North Pacific .

[1449] Shape and evolution of the fundamental niche in marine Vibrio

Hutchinson 's fundamental niche , defined by the physical and biological environments in which an organism can thrive in the absence of inter-species interactions , is an important theoretical concept in ecology .
However , little is known about the overlap between the fundamental niche and the set of conditions species inhabit in nature , and about natural variation in fundamental niche shape and its change as species adapt to their environment .
Here , we develop a custom-made dual gradient apparatus to map a cross-section of the fundamental niche for several marine bacterial species within the genus Vibrio based on their temperature and salinity tolerance , and compare tolerance limits to the environment where these species commonly occur .
We interpret these niche shapes in light of a conceptual model comprising five basic niche shapes .
We find that the fundamental niche encompasses a much wider set of conditions than those strains typically inhabit , especially for salinity .
Moreover , though the conditions that strains typically inhabit agree well with the strains ' temperature tolerance , they are negatively correlated with the strains ' salinity tolerance .
Such relationships can arise when the physiological response to different stressors is coupled , and we present evidence for such a coupling between temperature and salinity tolerance .
Finally , comparison with well-documented ecological range in V. vulnificus suggests that biotic interactions limit the occurrence of this species at low-temperature -- high-salinity conditions .
Our findings highlight the complex interplay between the ecological , physiological and evolutionary determinants of niche morphology , and caution against making inferences based on a single ecological factor .

[1450] Abrupt changes in the Asian southwest monsoon during the Holocene and their links to the North Atlantic Ocean

During the last ice age , the Indian Ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial-scale climate events in the North Atlantic region , suggesting a mechanistic link .
In the Holocene epoch , which had a more stable climate , the amplitude of abrupt changes in North Atlantic climate was much smaller , and it has been unclear whether these changes are related to monsoon variability .
Here we present a continuous record of centennial-scale monsoon variability throughout the Holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic Arabian Sea .
Our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the North Atlantic region -- including the most recent climate changes from the Medieval Warm Period to the Little Ice Age and then to the present .
We therefore suggest that the link between North Atlantic climate and the Asian monsoon is a persistent aspect of global climate .

[1451] Modulating the frequency and bias of stochastic switching to control phenotypic variation

Mechanisms that control cell-to-cell variation in gene expression ( ` phenotypic variation ' ) can determine a population 's growth rate , robustness , adaptability and capacity for complex behaviours .
Here we describe a general strategy ( termed FABMOS ) for tuning the phenotypic variation and mean expression of cell populations by modulating the frequency and bias of stochastic transitions between ` OFF ' and ` ON ' expression states of a genetic switch .
We validated the strategy experimentally using a synthetic fim switch in Escherichia coli .
Modulating the frequency of switching can generate a bimodal ( low frequency ) or a unimodal ( high frequency ) population distribution with the same mean expression .
Modulating the bias as well as the frequency of switching can generate a spectrum of bimodal and unimodal distributions with the same mean expression .
This remarkable control over phenotypic variation , which can not be easily achieved with standard gene regulatory mechanisms , has many potential applications for synthetic biology , engineered microbial ecosystems and experimental evolution .

[1452] Links between salinity variation in the Caribbean and North Atlantic thermohaline circulation

Variations in the strength of the North Atlantic Ocean thermohaline circulation have been linked to rapid climate changes during the last glacial cycle through oscillations in North Atlantic Deep Water formation and northward oceanic heat flux .
The strength of the thermohaline circulation depends on the supply of warm , salty water to the North Atlantic , which , after losing heat to the atmosphere , produces the dense water masses that sink to great depths and circulate back south .
Here we analyse two Caribbean Sea sediment cores , combining Mg/Ca palaeothermometry with measurements of oxygen isotopes in foraminiferal calcite in order to reconstruct tropical Atlantic surface salinity during the last glacial cycle .
We find that Caribbean salinity oscillated between saltier conditions during the cold oxygen isotope stages 2 , 4 and 6 , and lower salinities during the warm stages 3 and 5 , covarying with the strength of North Atlantic Deep Water formation .
At the initiation of the Bolling/Allerod warm interval , Caribbean surface salinity decreased abruptly , suggesting that the advection of salty tropical waters into the North Atlantic amplified thermohaline circulation and contributed to high-latitude warming .

[1453] Unoxidized Graphene/Alumina Nanocomposite : Fracture - and Wear-Resistance Effects of Graphene on Alumina Matrix

It is of critical importance to improve toughness , strength , and wear-resistance together for the development of advanced structural materials .
Herein , we report on the synthesis of unoxidized graphene/alumina composite materials having enhanced toughness , strength , and wear-resistance by a low-cost and environmentally benign pressure-less-sintering process .
The wear resistance of the composites was increased by one order of magnitude even under high normal load condition ( 25 N ) as a result of a tribological effect of graphene along with enhanced fracture toughness ( KIC ) and flexural strength ( sigmaf ) of the composites by ~ 75 % ( 5.60 MPa.m1 / 2 ) and ~ 25 % ( 430 MPa ) , respectively , compared with those of pure Al2O3 .
Furthermore , we found that only a small fraction of ultra-thin graphene ( 0.25-0 .5 vol % , platelet thickness of 2-5 nm ) was enough to reinforce the composite .
In contrast to unoxidized graphene , graphene oxide ( G-O ) and reduced graphene oxide ( rG-O ) showed little or less enhancement of fracture toughness due to the degraded mechanical strength of rG-O and the structural defects of the G-O composites .

[1454] A large discontinuity in the mid-twentieth century in observed global-mean surface temperature

Data sets used to monitor the Earth 's climate indicate that the surface of the Earth warmed from ~ 1910 to 1940 , cooled slightly from ~ 1940 to 1970 , and then warmed markedly from ~ 1970 onward .
The weak cooling apparent in the middle part of the century has been interpreted in the context of a variety of physical factors , such as atmosphere-ocean interactions and anthropogenic emissions of sulphate aerosols .
Here we call attention to a previously overlooked discontinuity in the record at 1945 , which is a prominent feature of the cooling trend in the mid-twentieth century .
The discontinuity is evident in published versions of the global-mean temperature time series , but stands out more clearly after the data are filtered for the effects of internal climate variability .
We argue that the abrupt temperature drop of ~ 0.3 degreesC in 1945 is the apparent result of uncorrected instrumental biases in the sea surface temperature record .
Corrections for the discontinuity are expected to alter the character of mid-twentieth century temperature variability but not estimates of the century-long trend in global-mean temperatures .

[1455] A less or more dusty future in the Northern Qinghai-Tibetan Plateau ?

Dust plays an important role in climate changes as it can alter atmospheric circulation , and global biogeochemical and hydrologic cycling .
Many studies have investigated the relationship between dust and temperature in an attempt to predict whether global warming in coming decades to centuries can result in a less or more dusty future .
However , dust and temperature changes have rarely been simultaneously reconstructed in the same record .
Here we present a 1600-yr-long quantitative record of temperature and dust activity inferred simultaneously from varved Kusai Lake sediments in the northern Qinghai-Tibetan Plateau , NW China .
At decadal time scale , our temperature reconstructions are generally in agreement with tree-ring records from Karakorum of Pakistan , and temperature reconstructions of China and North Hemisphere based on compilations of proxy records .
A less or more dusty future depends on temperature variations in the Northern Qinghai-Tibetan Plateau , i.e. weak and strong dust activities at centennial time scales are well correlated with low and high June-July-August temperature ( average JJA temperature ) , respectively .
This correlation means that stronger summer and winter monsoon should occur at the same times in the northern Qinghai-Tibetan Plateau .

[1456] Individual improvements and selective mortality shape lifelong migratory performance

Billions of organisms , from bacteria to humans , migrate each year and research on their migration biology is expanding rapidly through ever more sophisticated remote sensing technologies .
However , little is known about how migratory performance develops through life for any organism .
To date , age variation has been almost systematically simplified into a dichotomous comparison between recently born juveniles at their first migration versus adults of unknown age .
These comparisons have regularly highlighted better migratory performance by adults compared with juveniles , but it is unknown whether such variation is gradual or abrupt and whether it is driven by improvements within the individual , by selective mortality of poor performers , or both .
Here we exploit the opportunity offered by long-term monitoring of individuals through Global Positioning System ( GPS ) satellite tracking to combine within-individual and cross-sectional data on 364 migration episodes from 92 individuals of a raptorial bird , aged 1-27 years old .
We show that the development of migratory behaviour follows a consistent trajectory , more gradual and prolonged than previously appreciated , and that this is promoted by both individual improvements and selective mortality , mainly operating in early life and during the pre-breeding migration .
Individuals of different age used different travelling tactics and varied in their ability to exploit tailwinds or to cope with wind drift .
All individuals seemed aligned along a race with their contemporary peers , whose outcome was largely determined by the ability to depart early , affecting their subsequent recruitment , reproduction and survival .
Understanding how climate change and human action can affect the migration of younger animals may be the key to managing and forecasting the declines of many threatened migrants .

[1457] Sea-ice decline due to more than warming alone

Sir The dramatic loss of sea-ice cover over the Arctic this summer was widely reported , for example in your News story ` Arctic melt opens Northwest passage ' ( Nature 449 , 267 ; doi : 10.1038 / 449267b 2007 ) , and frequently attributed to global warming .
Although the gradual decline in sea-ice extent during the past four decades is in line with that expected from global warming , it is very unlikely that the loss of sea-ice cover this year is explicable solely in terms of temperature change .

[1458] Extreme heat effects on wheat senescence in India

An important source of uncertainty in anticipating the effects of climate change on agriculture is limited understanding of crop responses to extremely high temperatures .
This uncertainty partly reflects the relative lack of observations of crop behaviour in farmers ' fields under extreme heat .
We used nine years of satellite measurements of wheat growth in northern India to monitor rates of wheat senescence following exposure to temperatures greater than 34 degreesC .
We detect a statistically significant acceleration of senescence from extreme heat , above and beyond the effects of increased average temperatures .
Simulations with two commonly used process-based crop models indicate that existing models underestimate the effects of heat on senescence .
As the onset of senescence is an important limit to grain filling , and therefore grain yields , crop models probably underestimate yield losses for +2 degreesC by as much as 50 % for some sowing dates .
These results imply that warming presents an even greater challenge to wheat than implied by previous modelling studies , and that the effectiveness of adaptations will depend on how well they reduce crop sensitivity to very hot days .

[1459] Soil bacterial and fungal communities across a pH gradient in an arable soil

Soils collected across a long-term liming experiment ( pH 4.0-8 .3 ) , in which variation in factors other than pH have been minimized , were used to investigate the direct influence of pH on the abundance and composition of the two major soil microbial taxa , fungi and bacteria .
We hypothesized that bacterial communities would be more strongly influenced by pH than fungal communities .
To determine the relative abundance of bacteria and fungi , we used quantitative PCR ( qPCR ) , and to analyze the composition and diversity of the bacterial and fungal communities , we used a bar-coded pyrosequencing technique .
Both the relative abundance and diversity of bacteria were positively related to pH , the latter nearly doubling between pH 4 and 8 .
In contrast , the relative abundance of fungi was unaffected by pH and fungal diversity was only weakly related with pH. The composition of the bacterial communities was closely defined by soil pH ; there was as much variability in bacterial community composition across the 180-m distance of this liming experiment as across soils collected from a wide range of biomes in North and South America , emphasizing the dominance of pH in structuring bacterial communities .
The apparent direct influence of pH on bacterial community composition is probably due to the narrow pH ranges for optimal growth of bacteria .
Fungal community composition was less strongly affected by pH , which is consistent with pure culture studies , demonstrating that fungi generally exhibit wider pH ranges for optimal growth .

[1460] Diverse protist grazers select for virulence-related traits in Legionella

It is generally accepted that selection for resistance to grazing by protists has contributed to the evolution of Legionella pneumophila as a pathogen .
Grazing resistance is becoming more generally recognized as having an important role in the ecology and evolution of bacterial pathogenesis .
However , selection for grazing resistance presupposes the existence of protist grazers that provide the selective pressure .
To determine whether there are protists that graze on pathogenic Legionella species , we investigated the existence of such organisms in a variety of environmental samples .
We isolated and characterized diverse protists that graze on L. pneumophila and determined the effects of adding L. pneumophila on the protist community structures in microcosms made from these environmental samples .
Several unrelated organisms were able to graze efficiently on L. pneumophila .
The community structures of all samples were markedly altered by the addition of L. pneumophila .
Surprisingly , some of the Legionella grazers were closely related to species that are known hosts for L. pneumophila , indicating the presence of unknown specificity determinants for this interaction .
These results provide the first direct support for the hypothesis that protist grazers exert selective pressure on Legionella to acquire and retain adaptations that contribute to survival , and that these properties are relevant to the ability of the bacteria to cause disease in people .
We also report a novel mechanism of killing of amoebae by one Legionella species that requires an intact Type IV secretion system but does not involve intracellular replication .
We refer to this phenomenon as ` food poisoning ' .
The ISME Journal advance online publication , 9 January 2015 ; doi :10.1038 / ismej .2014.248

[1461] Removal of chlorofluorocarbons by increased mass exchange between the stratosphere and troposphere in a changing climate

Chlorofluorocarbons ( CFCs ) , along with bromine compounds , have been unequivocally identified as being responsible for most of the anthropogenic destruction of stratospheric ozone .
With curbs on emissions of these substances , the recovery of the ozone layer will depend on their removal from the atmosphere .
As CFCs have no significant tropospheric removal process , but are rapidly photolysed above the lower stratosphere , the timescale for their removal is set mainly by the rate at which air is transported from the troposphere into the stratosphere .
Using a global climate model we predict that , in response to the projected changes in greenhouse-gas concentrations during the first half of the twenty-first century , this rate of mass exchange will increase by 3 % per decade .
This increase is due to more vigorous extra-tropical planetary waves emanating from the troposphere .
We estimate that this increase in mass exchange will accelerate the removal of CFCs to an extent that recovery to levels currently predicted for 2050 and 2080 will occur 5 and 10 years earlier , respectively .

[1462] Half-precessional dynamics of monsoon rainfall near the East African Equator

External climate forcings -- such as long-term changes in solar insolation -- generate different climate responses in tropical and high latitude regions .
Documenting the spatial and temporal variability of past climates is therefore critical for understanding how such forcings are translated into regional climate variability .
In contrast to the data-rich middle and high latitudes , high-quality climate-proxy records from equatorial regions are relatively few , especially from regions experiencing the bimodal seasonal rainfall distribution associated with twice-annual passage of the Intertropical Convergence Zone .
Here we present a continuous and well-resolved climate-proxy record of hydrological variability during the past 25,000 years from equatorial East Africa .
Our results , based on complementary evidence from seismic-reflection stratigraphy and organic biomarker molecules in the sediment record of Lake Challa near Mount Kilimanjaro , reveal that monsoon rainfall in this region varied at half-precessional ( ~ 11,500-year ) intervals in phase with orbitally controlled insolation forcing .
The southeasterly and northeasterly monsoons that advect moisture from the western Indian Ocean were strengthened in alternation when the inter-hemispheric insolation gradient was at a maximum ; dry conditions prevailed when neither monsoon was intensified and modest local March or September insolation weakened the rain season that followed .
On sub-millennial timescales , the temporal pattern of hydrological change on the East African Equator bears clear high-northern-latitude signatures , but on the orbital timescale it mainly responded to low-latitude insolation forcing .
Predominance of low-latitude climate processes in this monsoon region can be attributed to the low-latitude position of its continental regions of surface air flow convergence , and its relative isolation from the Atlantic Ocean , where prominent meridional overturning circulation more tightly couples low-latitude climate regimes to high-latitude boundary conditions .

[1463] Central West Antarctica among the most rapidly warming regions on Earth

There is clear evidence that the West Antarctic Ice Sheet is contributing to sea-level rise .
In contrast , West Antarctic temperature changes in recent decades remain uncertain .
West Antarctica has probably warmed since the 1950s , but there is disagreement regarding the magnitude , seasonality and spatial extent of this warming .
This is primarily because long-term near-surface temperature observations are restricted to Byrd Station in central West Antarctica , a data set with substantial gaps .
Here , we present a complete temperature record for Byrd Station , in which observations have been corrected , and gaps have been filled using global reanalysis data and spatial interpolation .
The record reveals a linear increase in annual temperature between 1958 and 2010 by 2.4 + / -1.2 degreesC , establishing central West Antarctica as one of the fastest-warming regions globally .
We confirm previous reports of West Antarctic warming , in annual average and in austral spring and winter , but find substantially larger temperature increases .
In contrast to previous studies , we report statistically significant warming during austral summer , particularly in December-January , the peak of the melting season .
A continued rise in summer temperatures could lead to more frequent and extensive episodes of surface melting of the West Antarctic Ice Sheet .
These results argue for a robust long-term meteorological observation network in the region .

[1464] Correlates of virulence in a frog-killing fungal pathogen : evidence from a California amphibian decline

The fungal pathogen Batrachochytrium dendrobatidis ( Bd ) has caused declines and extinctions in amphibians worldwide , and there is increasing evidence that some strains of this pathogen are more virulent than others .
While a number of putative virulence factors have been identified , few studies link these factors to specific epizootic events .
We documented a dramatic decline in juvenile frogs in a Bd-infected population of Cascades frogs ( Rana cascadae ) in the mountains of northern California and used a laboratory experiment to show that Bd isolated in the midst of this decline induced higher mortality than Bd isolated from a more stable population of the same species of frog .
This highly virulent Bd isolate was more toxic to immune cells and attained higher density in liquid culture than comparable isolates .
Genomic analyses revealed that this isolate is nested within the global panzootic lineage and exhibited unusual genomic patterns , including increased copy numbers of many chromosomal segments .
This study integrates data from multiple sources to suggest specific phenotypic and genomic characteristics of the pathogen that may be linked to disease-related declines .

[1465] Large fluctuations in speed on Greenland 's Jakobshavn Isbrae glacier

It is important to understand recent changes in the velocity of Greenland glaciers because the mass balance of the Greenland Ice Sheet is partly determined by the flow rates of these outlets .
Jakobshavn Isbrae is Greenland 's largest outlet glacier , draining about 6.5 per cent of the ice-sheet area , and it has been surveyed repeatedly since 1991 ( ref .
2 ) .
Here we use remote sensing data to measure the velocity of Jakobshavn Isbrae between 1992 and 2003 .
We detect large variability of the velocity over time , including a slowing down from 6,700 m yr-1 in 1985 to 5,700 m yr-1 in 1992 , and a subsequent speeding up to 9,400 m yr-1 by 2000 and 12,600 m yr-1 in 2003 .
These changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter .
Our observations indicate that fast-flowing glaciers can significantly alter ice discharge at sub-decadal timescales , with at least a potential to respond rapidly to a changing climate .

[1466] Carbon dioxide concentration dictates alternative methanogenic pathways in oil reservoirs

Deep subsurface formations ( for example , high-temperature oil reservoirs ) are candidate sites for carbon capture and storage technology .
However , very little is known about how the subsurface microbial community would respond to an increase in CO2 pressure resulting from carbon capture and storage .
Here we construct microcosms mimicking reservoir conditions ( 55 degreesC , 5 MPa ) using high-temperature oil reservoir samples .
Methanogenesis occurs under both high and low CO2 conditions in the microcosms .
However , the increase in CO2 pressure accelerates the rate of methanogenesis to more than twice than that under low CO2 conditions .
Isotope tracer and molecular analyses show that high CO2 conditions invoke acetoclastic methanogenesis in place of syntrophic acetate oxidation coupled with hydrogenotrophic methanogenesis that typically occurs in this environment ( low CO2 conditions ) .
Our results present a possibility of carbon capture and storage for enhanced microbial energy production in deep subsurface environments that can mitigate global warming and energy depletion .

[1467] External forcing as a metronome for Atlantic multidecadal variability

Instrumental records , proxy data and climate modelling show that multidecadal variability is a dominant feature of North Atlantic sea-surface temperature variations , with potential impacts on regional climate .
To understand the observed variability and to gauge any potential for climate predictions it is essential to identify the physical mechanisms that lead to this variability , and to explore the spatial and temporal characteristics of multidecadal variability modes .
Here we use a coupled ocean-atmosphere general circulation model to show that the phasing of the multidecadal fluctuations in the North Atlantic during the past 600 years is , to a large degree , governed by changes in the external solar and volcanic forcings .
We find that volcanoes play a particularly important part in the phasing of the multidecadal variability through their direct influence on tropical sea-surface temperatures , on the leading mode of northern-hemisphere atmosphere circulation and on the Atlantic thermohaline circulation .
We suggest that the implications of our findings for decadal climate prediction are twofold : because volcanic eruptions can not be predicted a decade in advance , longer-term climate predictability may prove challenging , whereas the systematic post-eruption changes in ocean and atmosphere may hold promise for shorter-term climate prediction .

[1468] Postglacial Fringing-Reef to Barrier-Reef conversion on Tahiti links Darwin 's reef types

In 1842 Charles Darwin claimed that vertical growth on a subsiding foundation caused fringing reefs to transform into barrier reefs then atolls .
Yet historically no transition between reef types has been discovered and they are widely considered to develop independently from antecedent foundations during glacio-eustatic sea-level rise .
Here we reconstruct reef development from cores recovered by IODP Expedition 310 to Tahiti , and show that a fringing reef retreated upslope during postglacial sea-level rise and transformed into a barrier reef when it encountered a Pleistocene reef-flat platform .
The reef became stranded on the platform edge , creating a lagoon that isolated it from coastal sediment and facilitated a switch to a faster-growing coral assemblage dominated by acroporids .
The switch increased the reef 's accretion rate , allowing it to keep pace with rising sea level , and transform into a barrier reef .
This retreat mechanism not only links Darwin 's reef types , but explains the re-occupation of reefs during Pleistocene glacio-eustacy .

[1469] The energy-diversity relationship of complex bacterial communities in Arctic deep-sea sediments

The availability of nutrients and energy is a main driver of biodiversity for plant and animal communities in terrestrial and marine ecosystems , but we are only beginning to understand whether and how energy-diversity relationships may be extended to complex natural bacterial communities .
Here , we analyzed the link between phytodetritus input , diversity and activity of bacterial communities of the Siberian continental margin ( 37-3427 m water depth ) .
Community structure and functions , such as enzymatic activity , oxygen consumption and carbon remineralization rates , were highly related to each other , and with energy availability .
Bacterial richness substantially increased with increasing sediment pigment content , suggesting a positive energy-diversity relationship in oligotrophic regions .
Richness leveled off , forming a plateau , when mesotrophic sites were included , suggesting that bacterial communities and other benthic fauna may be structured by similar mechanisms .
Dominant bacterial taxa showed strong positive or negative relationships with phytodetritus input and allowed us to identify candidate bioindicator taxa .
Contrasting responses of individual taxa to changes in phytodetritus input also suggest varying ecological strategies among bacterial groups along the energy gradient .
Our results imply that environmental changes affecting primary productivity and particle export from the surface ocean will not only affect bacterial community structure but also bacterial functions in Arctic deep-sea sediment , and that sediment bacterial communities can record shifts in the whole ocean ecosystem functioning .

[1470] Observed sources and variability of Nordic seas overflow

The overflows from the Nordic seas maintain the deep branch of the North Atlantic Ocean 's thermohaline circulation , an important part of the global climate system .
However , the source of these overflows , and of overflow variability , is debated : proposals include open-ocean convection , dense-water production on the Arctic shelves and the gradual transformation of Atlantic water as it circulates the periphery of the Nordic seas and the Arctic Ocean .
Here we analyse time series of observed ocean temperature and salinity between 1950 and 2005 .
We find that the progression of thermohaline anomalies on interannual to decadal timescales does not support a systematic response of the overflow properties to convective mixing in the Greenland Sea as has been suggested .
Instead , anomalies in temperature and salinity that leave the northern seas at the Denmark Strait have travelled along the rim of the Nordic seas from inflow to overflow .
Furthermore , the Faroe-Shetland Channel reflects the variability of an overturning loop within the Norwegian Sea that has not been observed previously .
We thus conclude that the Atlantic water circulating in the Nordic seas is the main source for change in the overflow waters .

[1471] Interhemispheric Atlantic seesaw response during the last deglaciation

The asynchronous relationship between millennial-scale temperature changes over Greenland and Antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to redistribute heat depending on the state of meridional overturning circulation within the Atlantic Ocean .
Here we present new records from the South Atlantic that show rapid changes during the last deglaciation that were instantaneous ( within dating uncertainty ) and of opposite sign to those observed in the North Atlantic .
Our results demonstrate a direct link between the abrupt changes associated with variations in the Atlantic meridional overturning circulation and the more gradual adjustments characteristic of the Southern Ocean .
These results emphasize the importance of the Southern Ocean for the development and transmission of millennial-scale climate variability and highlight its role in deglacial climate change and the associated rise in atmospheric carbon dioxide .

[1472] The curved shape of Caulobacter crescentus enhances surface colonization in flow

Each bacterial species has a characteristic shape , but the benefits of specific morphologies remain largely unknown .
To understand potential functions for cell shape , we focused on the curved bacterium Caulobacter crescentus .
Paradoxically , C. crescentus curvature is robustly maintained in the wild but straight mutants have no known disadvantage in standard laboratory conditions .
Here we demonstrate that cell curvature enhances C. crescentus surface colonization in flow .
Imaging the formation of microcolonies at high spatial and temporal resolution indicates that flow causes curved cells to orient such that they arc over the surface , thereby decreasing the distance between the surface and polar adhesive pili , and orienting pili to face the surface .
C. crescentus thus repurposes pilus retraction , typically used for surface motility , for surface attachment .
The benefit provided by curvature is eliminated at high flow intensity , raising the possibility that diversity in curvature adapts related species for life in different flow environments .

[1473] Contribution of hurricanes to local and global estimates of air-sea exchange of CO2

The effect of hurricanes on the thermal and physical structure of the upper ocean has been described but their influence on the ocean carbon cycle and the exchange of carbon between ocean and atmosphere is not well understood .
Here we present observations from the Sargasso Sea , before and after hurricane Felix in summer 1995 , that show a short-lived ( 2-3 weeks ) surface seawater cooling of about 4 degreesC , and a decrease in seawater partial pressure of CO2 by about 60 microatm .
Despite the localized decrease in seawater partial pressure of CO2 , strong winds during the passage of hurricane Felix increased the efflux of CO2 from ocean to atmosphere .
We estimate that hurricane Felix and two other hurricanes increased the summertime efflux of CO2 into the atmosphere over this part of the Sargasso Sea by nearly 55 % .
We estimate that hurricanes contribute to the global ocean-to-atmosphere flux of CO2 by between +0.04 to +0.51 Pg C ( 1015 g C ) per year .
Such hurricane-forced effluxes are quantitatively significant compared to regional ( 14degrees to 50degrees N zone ) and global effluxes , .
Hurricanes therefore exert an important influence on ocean-atmosphere CO2 exchange and the inferred year-to-year variability of CO2 fluxes over the subtropical oceans .

[1474] Rapid , climate-driven changes in outlet glaciers on the Pacific coast of East Antarctica

Observations of ocean-terminating outlet glaciers in Greenland and West Antarctica indicate that their contribution to sea level is accelerating as a result of increased velocity , thinning and retreat .
Thinning has also been reported along the margin of the much larger East Antarctic ice sheet , but whether glaciers are advancing or retreating there is largely unknown , and there has been no attempt to place such changes in the context of localized mass loss or climatic or oceanic forcing .
Here we present multidecadal trends in the terminus position of 175 ocean-terminating outlet glaciers along 5,400 kilometres of the margin of the East Antarctic ice sheet , and reveal widespread and synchronous changes .
Despite large fluctuations between glaciers -- linked to their size -- three epochal patterns emerged : 63 per cent of glaciers retreated from 1974 to 1990 , 72 per cent advanced from 1990 to 2000 , and 58 per cent advanced from 2000 to 2010 .
These trends were most pronounced along the warmer western South Pacific coast , whereas glaciers along the cooler Ross Sea coast experienced no significant changes .
We find that glacier change along the Pacific coast is consistent with a rapid and coherent response to air temperature and sea-ice trends , linked through the dominant mode of atmospheric variability ( the Southern Annular Mode ) .
We conclude that parts of the world 's largest ice sheet may be more vulnerable to external forcing than recognized previously .

[1475] Life-history traits of voles in a fluctuating population respond to the immediate environment

Life-history traits relating to growth and reproduction vary greatly among species and populations and among individuals within populations .
In vole populations , body size and age at maturation may vary considerably among locations and among years within the same location .
Individuals in increasing populations are typically larger and start reproduction earlier in the spring than those in declining populations .
The cause of such life-history variation within populations has been subject of much discussion .
Much of the controversy concerns whether the memory of past conditions , leading to delayed effects on life-history traits , resides in the environment ( for example , predators , pathogens or food ) or intrinsically within populations or individuals ( age distribution , physiological state , genetic or maternal effects ) .
Here we report from an extensive field transplant experiment in which voles were moved before the breeding season between sites that differed in average overwintering body mass .
Transplanted voles did not retain the characteristics of their source population , and we demonstrate an over-riding role of the immediate environment in shaping life-history traits of small rodents .

[1476] An antioxidant function for DMSP and DMS in marine algae

The algal osmolyte dimethylsulphoniopropionate ( DMSP ) and its enzymatic cleavage product dimethylsulphide ( DMS ) contribute significantly to the global sulphur cycle , yet their physiological functions are uncertain .
Here we report results that , together with those in the literature , show that DMSP and its breakdown products ( DMS , acrylate , dimethylsulphoxide , and methane sulphinic acid ) readily scavenge hydroxyl radicals and other reactive oxygen species , and thus may serve as an antioxidant system , regulated in part by enzymatic cleavage of DMSP .
In support of this hypothesis , we found that oxidative stressors , solar ultraviolet radiation , CO2 limitation , Fe limitation , high Cu2 + ( ref .
9 ) and H2O2 substantially increased cellular DMSP and/or its lysis to DMS in marine algal cultures .
Our results indicate direct links between such stressors and the dynamics of DMSP and DMS in marine phytoplankton , which probably influence the production of DMS and its release to the atmosphere .
As oxidation of DMS to sulphuric acid in the atmosphere provides a major source of sulphate aerosols and cloud condensation nuclei , oxidative stressors -- including solar radiation and Fe limitation -- may be involved in complex ocean-atmosphere feedback loops that influence global climate and hydrological cycles .

[1477] Global warming and changes in drought

Several recently published studies have produced apparently conflicting results of how drought is changing under climate change .
The reason is thought to lie in the formulation of the Palmer Drought Severity Index ( PDSI ) and the data sets used to determine the evapotranspiration component .
Here , we make an assessment of the issues with the PDSI in which several other sources of discrepancy emerge , not least how precipitation has changed and is analysed .
As well as an improvement in the precipitation data available , accurate attribution of the causes of drought requires accounting for natural variability , especially El Nino/Southern Oscillation effects , owing to the predilection for wetter land during La Nina events .
Increased heating from global warming may not cause droughts but it is expected that when droughts occur they are likely to set in quicker and be more intense .

[1478] Robust assessment of the expansion and retreat of Mediterranean climate in the 21st century

The warm-temperate regions of the globe characterized by dry summers and wet winters ( Mediterranean climate ; MED ) are especially vulnerable to climate change .
The potential impact on water resources , ecosystems and human livelihood requires a detailed picture of the future changes in this unique climate zone .
Here we apply a probabilistic approach to quantitatively address how and why the geographic distribution of MED will change based on the latest-available climate projections for the 21st century .
Our analysis provides , for the first time , a robust assessment of significant northward and eastward future expansions of MED over both the Euro-Mediterranean and western North America .
Concurrently , we show a significant 21st century replacement of the equatorward MED margins by the arid climate type .
Moreover , future winters will become wetter and summers drier in both the old and newly established MED zones .
Should these projections be realized , living conditions in some of the most densely populated regions in the world will be seriously jeopardized .

[1479] Veil architecture in a sulphide-oxidizing bacterium enhances countercurrent flux

Solute uptake by microorganisms is limited by molecular diffusion through a boundary layer surrounding the cells , and the uptake is not enhanced ( or only insignificantly ) by convective water transport or by swimming .
It is generally assumed that sediment uptake of oxygen is diffusion-limited , so the steepness ofthe concentration gradient within the 0.5-1-mm-thick diffusive boundary layer is a measure of diffusional flux into thesediment , .
Here we show that veils , which are formed onsediments by the marine sulphide-oxidizing bacterium Thiovulum majus , generate convective oxygen transport through the 0.5-mm-thick water layers above the veil at rates that are about 40 times higher than molecular diffusion .
Chemosensory behaviour of the cells , combined with their generation of water currents , leads to characteristic , aggregated distribution patterns : areas with high cell densities draw oxygenated water downwards through the veil , whereas areas without cells serve for the upward-directed return flow of deoxygenated water .
The microbial community structure thus overcomes the limitations of diffusion and thereby enhances the rates of respiration and sulphide oxidation .

[1480] Securing natural capital and expanding equity to rescale civilization

In biophysical terms , humanity has never been moving faster nor further from sustainability than it is now .
Our increasing population size and per capita impacts are severely testing the ability of Earth to provide for peoples ' most basic needs .
Awareness of these circumstances has grown tremendously , as has the sophistication of efforts to address them .
But the complexity of the challenge remains daunting .
We explore prospects for transformative change in three critical areas of sustainable development : achieving a sustainable population size and securing vital natural capital , both in part through reducing inequity , and strengthening the societal leadership of academia .

[1481] A methyl transferase links the circadian clock to the regulation of alternative splicing

Circadian rhythms allow organisms to time biological processes to the most appropriate phases of the day-night cycle .
Post-transcriptional regulation is emerging as an important component of circadian networks , but the molecular mechanisms linking the circadian clock to the control of RNA processing are largely unknown .
Here we show that PROTEIN ARGININE METHYL TRANSFERASE 5 ( PRMT5 ) , which transfers methyl groups to arginine residues present in histones and Sm spliceosomal proteins , links the circadian clock to the control of alternative splicing in plants .
Mutations in PRMT5 impair several circadian rhythms in Arabidopsis thaliana and this phenotype is caused , at least in part , by a strong alteration in alternative splicing of the core-clock gene PSEUDO RESPONSE REGULATOR 9 ( PRR9 ) .
Furthermore , genome-wide studies show that PRMT5 contributes to the regulation of many pre-messenger-RNA splicing events , probably by modulating 5 ' - splice-site recognition .
PRMT5 expression shows daily and circadian oscillations , and this contributes to the mediation of the circadian regulation of expression and alternative splicing of a subset of genes .
Circadian rhythms in locomotor activity are also disrupted in dart5-1 , a mutant affected in the Drosophila melanogaster PRMT5 homologue , and this is associated with alterations in splicing of the core-clock gene period and several clock-associated genes .
Our results demonstrate a key role for PRMT5 in the regulation of alternative splicing and indicate that the interplay between the circadian clock and the regulation of alternative splicing by PRMT5 constitutes a common mechanism that helps organisms to synchronize physiological processes with daily changes in environmental conditions .

[1482] Genome-wide analysis captures the determinants of the antibiotic cross-resistance interaction network

Understanding how evolution of antimicrobial resistance increases resistance to other drugs is a challenge of profound importance .
By combining experimental evolution and genome sequencing of 63 laboratory-evolved lines , we charted a map of cross-resistance interactions between antibiotics in Escherichia coli , and explored the driving evolutionary principles .
Here , we show that ( 1 ) convergent molecular evolution is prevalent across antibiotic treatments , ( 2 ) resistance conferring mutations simultaneously enhance sensitivity to many other drugs and ( 3 ) 27 % of the accumulated mutations generate proteins with compromised activities , suggesting that antibiotic adaptation can partly be achieved without gain of novel function .
By using knowledge on antibiotic properties , we examined the determinants of cross-resistance and identified chemogenomic profile similarity between antibiotics as the strongest predictor .
In contrast , cross-resistance between two antibiotics is independent of whether they show synergistic effects in combination .
These results have important implications on the development of novel antimicrobial strategies .

[1483] Soil invertebrate fauna enhances grassland succession and diversity

One of the most important areas in ecology is to elucidate the factors that drive succession in ecosystems and thus influence the diversity of species in natural vegetation .
Significant mechanisms in this process are known to be resource limitation and the effects of aboveground vertebrate herbivores .
More recently , symbiotic and pathogenic soil microbes have been shown to exert a profound effect on the composition of vegetation and changes therein .
However , the influence of invertebrate soil fauna on succession has so far received little attention .
Here we report that invertebrate soil fauna might enhance both secondary succession and local plant species diversity .
Soil fauna from a series of secondary grassland succession stages selectively suppress early successional dominant plant species , thereby enhancing the relative abundance of subordinate species and also that of species from later succession stages .
Soil fauna from the mid-succession stage had the strongest effect .
Our results clearly show that soil fauna strongly affects the composition of natural vegetation and we suggest that this knowledge might improve the restoration and conservation of plant species diversity .

[1484] Continental warming preceding the Palaeocene-Eocene thermal maximum

Marine and continental records show an abrupt negative shift in carbon isotope values at ~ 55.8 Myr ago .
This carbon isotope excursion ( CIE ) is consistent with the release of a massive amount of isotopically light carbon into the atmosphere and was associated with a dramatic rise in global temperatures termed the Palaeocene-Eocene thermal maximum ( PETM ) .
Greenhouse gases released during the CIE , probably including methane , have often been considered the main cause of PETM warming .
However , some evidence from the marine record suggests that warming directly preceded the CIE , raising the possibility that the CIE and PETM may have been linked to earlier warming with different origins .
Yet pre-CIE warming is still uncertain .
Disentangling the sequence of events before and during the CIE and PETM is important for understanding the causes of , and Earth system responses to , abrupt climate change .
Here we show that continental warming of about 5 degreesC preceded the CIE in the Bighorn Basin , Wyoming .
Our evidence , based on oxygen isotopes in mammal teeth ( which reflect temperature-sensitive fractionation processes ) and other proxies , reveals a marked temperature increase directly below the CIE , and again in the CIE. Pre-CIE warming is also supported by a negative amplification of delta13C values in soil carbonates below the CIE. Our results suggest that at least two sources of warming -- the earlier of which is unlikely to have been methane -- contributed to the PETM .

[1485] Natural Green Coating Inhibits Adhesion of Clinically Important Bacteria

Despite many advances , biomaterial-associated infections continue to be a major clinical problem .
In order to minimize bacterial adhesion , material surface modifications are currently being investigated and natural products possess large potential for the design of innovative surface coatings .
We report the bioguided phytochemical investigation of Pityrocarpa moniliformis and the characterization of tannins by mass spectrometry .
It was demonstrated that B-type linked proanthocyanidins-coated surfaces , here termed Green coatings , reduced Gram-positive bacterial adhesion and supported mammalian cell spreading .
The proposed mechanism of bacterial attachment inhibition is based on electrostatic repulsion , high hydrophilicity and the steric hindrance provided by the coating that blocks bacterium-substratum interactions .
This work shows the applicability of a prototype Green-coated surface that aims to promote necessary mammalian tissue compatibility , while reducing bacterial colonization .

[1486] Photochemical cycling of iron in the surface ocean mediated by microbial iron ( iii ) - binding ligands

Iron is a limiting nutrient for primary production in large areas of the oceans .
Dissolved iron ( iii ) in the upper oceans occurs almost entirely in the form of complexes with strong organic ligands presumed to be of biological origin .
Although the importance of organic ligands to aquatic iron cycling is becoming clear , the mechanism by which they are involved in this process remains uncertain .
Here we report observations of photochemical reactions involving Fe ( iii ) bound to siderophores -- high-affinity iron ( iii ) ligands produced by bacteria to facilitate iron acquisition .
We show that photolysis of Fe ( iii ) - siderophore complexes leads to the formation of lower-affinity Fe ( iii ) ligands and the reduction of Fe ( iii ) , increasing the availability of siderophore-bound iron for uptake by planktonic assemblages .
These photochemical reactions are mediated by the alpha-hydroxy acid moiety , a group which has generally been found to be present in the marine siderophores that have been characterized .
We suggest that Fe ( iii ) - binding ligands can enhance the photolytic production of reactive iron species in the euphotic zone and so influence iron availability in aquatic systems .

[1487] Climate change and moral judgement

Converging evidence from the behavioural and brain sciences suggests that the human moral judgement system is not well equipped to identify climate change -- a complex , large-scale and unintentionally caused phenomenon -- as an important moral imperative .
As climate change fails to generate strong moral intuitions , it does not motivate an urgent need for action in the way that other moral imperatives do .
We review six reasons why climate change poses significant challenges to our moral judgement system and describe six strategies that communicators might use to confront these challenges .
Enhancing moral intuitions about climate change may motivate greater support for ameliorative actions and policies .

[1488] Radon emanation and electric potential variations associated with transient deformation near reservoir lakes

Two of the most often cited earthquake precursors are radon emanation and electric potential variations , but these few reported examples have generally been deemed questionable .
If a mechanism relating crustal deformation to radon emanation or electrical signals does indeed exist , it is thought to involve fluids .
Some preliminary insight has been gained into these processes from the study of natural systems under controlled mechanical and hydrological conditions .
Here we report electric potential variations , radon emanation and deformation measurements recorded since 1995 in the French Alps in the vicinity of two artificial lakes which have strong seasonal variations in water level of more than 50 metres .
We observe that electric potential variations and radon emanations are repeatedly associated with transient deformation events induced by variations in lake levels .
These events are characterized by a change in ground tilt which deviates from the expected elastic response , and are associated with periods of accelerating strain , which suggests that accelerated loading can enhance fluid transport properties .
Qualitatively , this behaviour can be accounted for by a model in which straining induces fluid overpressure and dynamic flow in cracks .
These observations mayshed light on the sensitivity of rock transport properties to deformation .

[1489] Modelling conservation in the Amazon basin

Expansion of the cattle and soy industries in the Amazon basin has increased deforestation rates and will soon push all-weather highways into the region 's core .
In the face of this growing pressure , a comprehensive conservation strategy for the Amazon basin should protect its watersheds , the full range of species and ecosystem diversity , and the stability of regional climates .
Here we report that protected areas in the Amazon basin -- the central feature of prevailing conservation approaches -- are an important but insufficient component of this strategy , based on policy-sensitive simulations of future deforestation .
By 2050 , current trends in agricultural expansion will eliminate a total of 40 % of Amazon forests , including at least two-thirds of the forest cover of six major watersheds and 12 ecoregions , releasing 32 + / - 8 Pg of carbon to the atmosphere .
One-quarter of the 382 mammalian species examined will lose more than 40 % of the forest within their Amazon ranges .
Although an expanded and enforced network of protected areas could avoid as much as one-third of this projected forest loss , conservation on private lands is also essential .
Expanding market pressures for sound land management and prevention of forest clearing on lands unsuitable for agriculture are critical ingredients of a strategy for comprehensive conservation .

[1490] Human contribution to the European heatwave of 2003

The summer of 2003 was probably the hottest in Europe since at latest ad 1500 , and unusually large numbers of heat-related deaths were reported in France , Germany and Italy .
It is an ill-posed question whether the 2003 heatwave was caused , in a simple deterministic sense , by a modification of the external influences on climate -- for example , increasing concentrations of greenhouse gases in the atmosphere -- because almost any such weather event might have occurred by chance in an unmodified climate .
However , it is possible to estimate by how much human activities may have increased the risk of the occurrence of such a heatwave .
Here we use this conceptual framework to estimate the contribution of human-induced increases in atmospheric concentrations of greenhouse gases and other pollutants to the risk of the occurrence of unusually high mean summer temperatures throughout a large region of continental Europe .
Using a threshold for mean summer temperature that was exceeded in 2003 , but in no other year since the start of the instrumental record in 1851 , we estimate it is very likely ( confidence level > 90 % ) that human influence has at least doubled the risk of a heatwave exceeding this threshold magnitude .

[1491] Seasonality of rDNA - and rRNA-derived archaeal communities and methanogenic potential in a boreal mire

Methane ( CH4 ) emissions from boreal wetlands show considerable seasonal variation , including small winter emissions .
We addressed the seasonality of CH4-producing microbes by comparing archaeal communities and the rates and temperature response of CH4 production in a boreal fen at three key phases of growing season and in winter .
Archaeal community analysis by terminal restriction fragment length polymorphism and cloning of 16S ribosomal DNA and reverse-transcribed RNA revealed slight community shifts with season .
The main archaeal groups remained the same throughout the year and were Methanosarcinaceae , Rice cluster II and Methanomicrobiales-associated Fen cluster .
These methanogens and the crenarchaeal groups 1.1 c and 1.3 were detected from DNA and RNA , but the family Methanosaetaceae was detected only from RNA .
Differences between DNA - and RNA-based results suggested higher stability of DNA-derived communities and better representation of the active CH4 producers in RNA .
Methane production potential , measured as formation of CH4 in anoxic laboratory incubations , showed prominent seasonality .
The potential was strikingly highest in winter , possibly due to accumulation of methanogenic substrates , and maximal CH4 production was observed at ca. 30 degreesC .
Archaeal community size , determined by quantitative PCR , remained similar from winter to summer .
Low production potential in late summer after a water level draw-down suggested diminished activity due to oxygen exposure .
Our results indicated that archaeal community composition and size in the boreal fen varied only slightly despite the large fluctuations of methanogenic potential .
Detection of mRNA of the methanogenic mcrA gene confirmed activity of methanogens in winter , accounting for previously reported winter CH4 emissions .

[1492] High aromatic ring-cleavage diversity in birch rhizosphere : PAH treatment-specific changes of I.E. 3 group extradiol dioxygenases and 16S rRNA bacterial communities in soil

Genes encoding key enzymes of catabolic pathways can be targeted by DNA fingerprinting to explore genetic degradation potential in pristine and polluted soils .
We performed a greenhouse microcosm experiment to elucidate structural and functional bacterial diversity in polyaromatic hydrocarbon ( PAH ) - polluted soil and to test the suitability of birch ( Betula pendula ) for remediation .
Degradation of PAHs was analysed by high-performance liquid chromatography , DNA isolated from soil amplified and fingerprinted by restriction fragment length polymorphism ( RFLP ) and terminal restriction fragment length polymorphism ( T-RFLP ) .
Bacterial 16S rRNA T-RFLP fingerprinting revealed a high structural bacterial diversity in soil where PAH amendment altered the general community structure as well as the rhizosphere community .
Birch augmented extradiol dioxygenase diversity in rhizosphere showing a rhizosphere effect , and further pyrene was more efficiently degraded in planted pots .
Degraders of aromatic compounds upon PAH amendment were shown by the changed extradiol ring-cleavage community structure in soil .
The RFLP analysis grouped extradiol dioxygenase marker genes into 17 distinct operational taxonomic units displaying novel phylogenetic clusters of ring-cleavage dioxygenases representing putative catabolic pathways , and the peptide sequences contained conserved amino-acid signatures of extradiol dioxygenases .
A branch of major environmental TS cluster was identified as being related to Parvibaculum lavantivorans ring-cleavage dioxygenase .
The described structural and functional diversity demonstrated a complex interplay of bacteria in PAH pollution .
The findings improve our understanding of rhizoremediation and unveil the extent of uncharacterized enzymes and may benefit bioremediation research by facilitating the development of molecular tools to detect and monitor populations involved in degradative processes .

[1493] Larger CO2 source at the equatorial Pacific during the last deglaciation

While biogeochemical and physical processes in the Southern Ocean are thought to be central to atmospheric CO2 rise during the last deglaciation , the role of the equatorial Pacific , where the largest CO2 source exists at present , remains largely unconstrained .
Here we present seawater pH and pCO2 variations from fossil Porites corals in the mid equatorial Pacific offshore Tahiti based on a newly calibrated boron isotope paleo-pH proxy .
Our new data , together with recalibrated existing data , indicate that a significant pCO2 increase ( pH decrease ) , accompanied by anomalously large marine 14C reservoir ages , occurred following not only the Younger Dryas , but also Heinrich Stadial 1 .
These findings indicate an expanded zone of equatorial upwelling and resultant CO2 emission , which may be derived from higher subsurface dissolved inorganic carbon concentration .

[1494] Is there a cost of virus resistance in marine cyanobacteria ?

Owing to their abundance and diversity , it is generally perceived that viruses are important for structuring microbial communities and regulating biogeochemical cycles .
The ecological impact of viruses on microbial food webs , however , may be influenced by evolutionary processes , including the ability of bacteria to evolve resistance to viruses and the theoretical prediction that this resistance should be accompanied by a fitness cost .
We conducted experiments using phylogenetically distinct strains of marine Synechococcus ( Cyanobacteria ) to test for a cost of resistance ( COR ) to viral isolates collected from Mount Hope Bay , Rhode Island .
In addition , we examined whether fitness costs ( 1 ) increased proportionally with ` total resistance ' , the number of viruses for which a strain had evolved resistance , or ( 2 ) were determined more by ` compositional resistance ' , the identity of the viruses to which it evolved resistance .
A COR was only found in half of our experiments , which may be attributed to compensatory mutations or the inability to detect a small COR .
When detected , the COR resulted in a ~ 20 % reduction in relative fitness compared to ancestral strains .
The COR was unaffected by total resistance , suggesting a pleiotropic fitness response .
Under competitive conditions , however , the COR was dependent on compositional resistance , suggesting that fitness costs were associated with the identity of a few particular viruses .
Our study provides the first evidence for a COR in marine bacteria , and suggests that Synechococcus production may be influenced by the composition of co-occurring viruses .

[1495] Ancient harbour infrastructure in the Levant : tracking the birth and rise of new forms of anthropogenic pressure

Beirut , Sidon and Tyre were major centres of maritime trade from the Bronze Age onwards .
This economic prosperity generated increased pressures on the local environment , through urbanization and harbour development .
Until now , however , the impact of expanding seaport infrastructure has largely been neglected and there is a paucity of data concerning the environmental stresses caused by these new forms of anthropogenic impacts .
Sediment archives from Beirut , Sidon and Tyre are key to understanding human impacts in harbour areas because : ( i ) they lie at the heart of ancient trade networks ; ( ii ) they encompass the emergence of early maritime infrastructure ; and ( iii ) they enable human alterations of coastal areas to be characterized over long timescales .
Here we report multivariate analyses of litho - and biostratigraphic data to probe human stressors in the context of their evolving seaport technologies .
The statistical outcomes show a notable break between natural and artificial sedimentation that began during the Iron Age .
Three anchorage phases can be distinguished : ( i ) Bronze Age proto-harbours that correspond to natural anchorages , with minor human impacts ; ( ii ) semi-artificial Iron Age harbours , with stratigraphic evidence for artificial reinforcement of the natural endowments ; and ( iii ) heavy human impacts leading to completely artificial Roman and Byzantine harbours .

[1496] Physically based assessment of hurricane surge threat under climate change

Storm surges are responsible for much of the damage and loss of life associated with landfalling hurricanes .
Understanding how global warming will affect hurricane surges thus holds great interest .
As general circulation models ( GCMs ) can not simulate hurricane surges directly , we couple a GCM-driven hurricane model with hydrodynamic models to simulate large numbers of synthetic surge events under projected climates and assess surge threat , as an example , for New York City ( NYC ) .
Struck by many intense hurricanes in recorded history and prehistory , NYC is highly vulnerable to storm surges .
We show that the change of storm climatology will probably increase the surge risk for NYC ; results based on two GCMs show the distribution of surge levels shifting to higher values by a magnitude comparable to the projected sea-level rise ( SLR ) .
The combined effects of storm climatology change and a 1 m SLR may cause the present NYC 100-yr surge flooding to occur every 3-20 yr and the present 500-yr flooding to occur every 25-240 yr by the end of the century .

[1497] Oceanography : Iron , nitrogen and phosphorus in the ocean

It has been proposed that widespread deficits of nitrate in the ocean , like those observed today , are caused by iron limitation of marine nitrogen fixation .
That is , only when iron is sufficiently abundant to satiate nitrogen fixers will the ratio of nitrate to phosphate in the ocean increase to 16 , the average for phytoplankton .
Tyrrell developed a simple two-box model of oceanic nitrogen and phosphorus cycles to describe the regulation of both nitrate and phosphate concentrations in the global ocean .
His criterion for nitrate deficit in the ocean , a molar ratio of N :P in surface waters ( Rs ) of less than 16 , is satisfied without recourse to iron limitation , calling into question Falkowski 's proposal about the biogeochemical significance of iron limitation as it relates to nitrogen fixation and oceanic levels of nitrogen and phosphorus .
Here I show that small changes in the assumptions of Tyrrell 's model , well within acknowledged uncertainty , can lead to values of Rs greater than 16 .
Consequently , the consistency of the model with the observed distributions of nutrients in the ocean is uncertain , and the influence of iron may still be considered important .

[1498] Isolation of an aerobic sulfur oxidizer from the SUP05/Arctic96BD -19 clade

Bacteria from the uncultured SUP05/Arctic96BD -19 clade of gamma proteobacterial sulfur oxidizers ( GSOs ) have the genetic potential to oxidize reduced sulfur and fix carbon in the tissues of clams and mussels , in oxygen minimum zones and throughout the deep ocean ( > 200 m ) .
Here , we report isolation of the first cultured representative from this GSO clade .
Closely related cultures were obtained from surface waters in Puget Sound and from the deep chlorophyll maximum in the North Pacific gyre .
Pure cultures grow aerobically on natural seawater media , oxidize sulfur , and reach higher final cell densities when glucose and thiosulfate are added to the media .
This suggests that aerobic sulfur oxidation enhances organic carbon utilization in the oceans .
The first isolate from the SUP05/Arctic96BD -19 clade was given the provisional taxonomic assignment ` Candidatus : Thioglobus singularis ' , alluding to the clade 's known role in sulfur oxidation and the isolate 's planktonic lifestyle .

[1499] Zero-valent sulphur is a key intermediate in marine methane oxidation

Emissions of methane , a potent greenhouse gas , from marine sediments are controlled by anaerobic oxidation of methane coupled primarily to sulphate reduction ( AOM ) .
Sulphate-coupled AOM is believed to be mediated by a consortium of methanotrophic archaea ( ANME ) and sulphate-reducing Deltaproteobacteria but the underlying mechanism has not yet been resolved .
Here we show that zero-valent sulphur compounds ( S0 ) are formed during AOM through a new pathway for dissimilatory sulphate reduction performed by the methanotrophic archaea .
Hence , AOM might not be an obligate syntrophic process but may be carried out by the ANME alone .
Furthermore , we show that the produced S0 -- in the form of disulphide -- is disproportionated by the Deltaproteobacteria associated with the ANME .
Our observations expand the diversity of known microbially mediated sulphur transformations and have significant implications for our understanding of the biogeochemical carbon and sulphur cycles .

[1500] Ocean productivity before about 1.9 Gyr ago limited by phosphorus adsorption onto iron oxides

After the evolution of oxygen-producing cyanobacteria at some time before 2.7 billion years ago , oxygen production on Earth is thought to have depended on the availability of nutrients in the oceans , such as phosphorus ( in the form of orthophosphate ) .
In the modern oceans , a significant removal pathway for phosphorus occurs by way of its adsorption onto iron oxide deposits .
Such deposits were thought to be more abundant in the past when , under low sulphate conditions , the formation of large amounts of iron oxides resulted in the deposition of banded iron formations .
Under these circumstances , phosphorus removal by iron oxide adsorption could have been enhanced .
Here we analyse the phosphorus and iron content of banded iron formations to show that ocean orthophosphate concentrations from 3.2 to 1.9 billion years ago ( during the Archaean and early Proterozoic eras ) were probably only ~ 10-25 % of present-day concentrations .
We suggest therefore that low phosphorus availability should have significantly reduced rates of photosynthesis and carbon burial , thereby reducing the long-term oxygen production on the early Earth -- as previously speculated -- and contributing to the low concentrations of atmospheric oxygen during the late Archaean and early Proterozoic .

[1501] Climate sensitivity constrained by temperature reconstructions over the past seven centuries

There is a Brief Communications Arising ( 01 March 2007 ) associated with this document
The magnitude and impact of future global warming depends on the sensitivity of the climate system to changes in greenhouse gas concentrations .
The commonly accepted range for the equilibrium global mean temperature change in response to a doubling of the atmospheric carbon dioxide concentration , termed climate sensitivity , is 1.5-4 .5 K ( ref .
2 ) .
A number of observational studies , however , find a substantial probability of significantly higher sensitivities , yielding upper limits on climate sensitivity of 7.7 K to above 9 K ( refs 3-8 ) .
Here we demonstrate that such observational estimates of climate sensitivity can be tightened if reconstructions of Northern Hemisphere temperature over the past several centuries are considered .
We use large-ensemble energy balance modelling and simulate the temperature response to past solar , volcanic and greenhouse gas forcing to determine which climate sensitivities yield simulations that are in agreement with proxy reconstructions .
After accounting for the uncertainty in reconstructions and estimates of past external forcing , we find an independent estimate of climate sensitivity that is very similar to those from instrumental data .
If the latter are combined with the result from all proxy reconstructions , then the 5-95 per cent range shrinks to 1.5-6 .2 K , thus substantially reducing the probability of very high climate sensitivity .

[1502] Adaptation of a globally important coccolithophore to ocean warming and acidification

Although ocean warming and acidification are recognized as two major anthropogenic perturbations of today 's oceans we know very little about how marine phytoplankton may respond via evolutionary change .
We tested for adaptation to ocean warming in combination with ocean acidification in the globally important phytoplankton species Emiliania huxleyi .
Temperature adaptation occurred independently of ocean acidification levels .
Growth rates were up to 16 % higher in populations adapted for one year to warming when assayed at their upper thermal tolerance limit .
Particulate inorganic ( PIC ) and organic ( POC ) carbon production was restored to values under present-day ocean conditions , owing to adaptive evolution , and were 101 % and 55 % higher under combined warming and acidification , respectively , than in non-adapted controls .
Cells also evolved to a smaller size while they recovered their initial PIC : POC ratio even under elevated CO2 .
The observed changes in coccolithophore growth , calcite and biomass production , cell size and elemental composition demonstrate the importance of evolutionary processes for phytoplankton performance in a future ocean .

[1503] Catchment productivity controls CO2 emissions from lakes

Most lakes are oversaturated with CO2 and are net CO2 sources to the atmosphere , yet their contribution to the global carbon cycle is poorly constrained .
Their CO2 excess is widely attributed to in-lake oxidation of terrestrially produced dissolved organic carbon .
Here we use data collected over 26 years to show that the CO2 in 20 lakes is primarily delivered directly through inflowing streams rather than being produced in situ by degradation of terrestrial carbon .
This implies that high CO2 concentrations and atmospheric emissions are not necessarily symptoms of heterotrophic lake ecosystems .
Instead , the annual mean CO2 concentration increased with lake productivity and was proportional to the estimated net primary productivity of the catchment .
Overall , about 1.6 % of net primary productivity ( range 1.2-2 .2 % ) was lost to the atmosphere .
Extrapolating globally , this is equivalent to CO2 losses of ~ 0.9 Pg C yr-1 ( range 0.7-1 .3 ) , consistent with existing estimates .
These data and our catchment productivity hypothesis re-enforce the high connectivity found between lakes , their catchment and the global C cycle .
They indicate that future concentrations of CO2 in lakes , and losses to the atmosphere , will be highly sensitive to altered catchment management and concomitant effects of climate change that modify catchment productivity .

[1504] Interspecies competition triggers virulence and mutability in Candida albicans-Pseudomonas aeruginosa mixed biofilms

Inter-kingdom and interspecies interactions are ubiquitous in nature and are important for the survival of species and ecological balance .
The investigation of microbe-microbe interactions is essential for understanding the in vivo activities of commensal and pathogenic microorganisms .
Candida albicans , a polymorphic fungus , and Pseudomonas aeruginosa , a Gram-negative bacterium , are two opportunistic pathogens that interact in various polymicrobial infections in humans .
To determine how P. aeruginosa affects the physiology of C. albicans and vice versa , we compared the proteomes of each species in mixed biofilms versus single-species biofilms .
In addition , extracellular proteins were analyzed .
We observed that , in mixed biofilms , both species showed differential expression of virulence proteins , multidrug resistance-associated proteins , proteases and cell defense , stress and iron-regulated proteins .
Furthermore , in mixed biofilms , both species displayed an increase in mutability compared with monospecific biofilms .
This characteristic was correlated with the downregulation of enzymes conferring protection against DNA oxidation .
In mixed biofilms , P. aeruginosa regulates its production of various molecules involved in quorum sensing and induces the production of virulence factors ( pyoverdine , rhamnolipids and pyocyanin ) , which are major contributors to the ability of this bacterium to cause disease .
Overall , our results indicate that interspecies competition between these opportunistic pathogens enhances the production of virulence factors and increases mutability and thus can alter the course of host-pathogen interactions in polymicrobial infections .

[1505] Identifying high-risk areas of bacillary dysentery and associated meteorological factors in Wuhan , China

Spatial distribution of bacillary dysentery incidence was mapped at the district level in Wuhan , China .
And a generalized additive time series model was used to examine the effect of daily weather factors on bacillary dysentery in the high-risk areas , after controlling for potential confounding factors .
Central districts were found to be the high-risk areas .
The time series analysis found an acute effect of meteorological factors on bacillary dysentery occurrence .
A positive association was found for mean temperature ( excess risk ( ER ) for 1degreesC increase being 0.94 % ( 95 % confidence interval ( CI ) : 0.46 % to 1.43 % on the lag day 2 ) , while a negative effect was observed for relative humidity and rainfall , the ER for 1 % increase in relative humidity was -0.21 % ( 95 % CI : -0.34 % to -0.08 % ) , and the ER for 1 mm increase in rainfall was -0.23 % ( 95 % CI : -0.37 % to -0.09 % ) .
This study suggests that bacillary dysentery prevention and control strategy should consider local weather variations .

[1506] Recent Arctic amplification and extreme mid-latitude weather

The Arctic region has warmed more than twice as fast as the global average -- a phenomenon known as Arctic amplification .
The rapid Arctic warming has contributed to dramatic melting of Arctic sea ice and spring snow cover , at a pace greater than that simulated by climate models .
These profound changes to the Arctic system have coincided with a period of ostensibly more frequent extreme weather events across the Northern Hemisphere mid-latitudes , including severe winters .
The possibility of a link between Arctic change and mid-latitude weather has spurred research activities that reveal three potential dynamical pathways linking Arctic amplification to mid-latitude weather : changes in storm tracks , the jet stream , and planetary waves and their associated energy propagation .
Through changes in these key atmospheric features , it is possible , in principle , for sea ice and snow cover to jointly influence mid-latitude weather .
However , because of incomplete knowledge of how high-latitude climate change influences these phenomena , combined with sparse and short data records , and imperfect models , large uncertainties regarding the magnitude of such an influence remain .
We conclude that improved process understanding , sustained and additional Arctic observations , and better coordinated modelling studies will be needed to advance our understanding of the influences on mid-latitude weather and extreme events .

[1507] Evidence of a large cooling between 1690 and 1740 AD in southern Africa

A 350-year-long , well-dated delta18O stalagmite record from the summer rainfall region in South Africa is positively correlated with regional air surface temperatures at interannual time scales .
The coldest period documented in this record occurred between 1690 and 1740 , slightly lagging the Maunder Minimum ( 1645-1710 ) .
A temperature reconstruction , based on the correlation between regional surface temperatures and the stalagmite delta18O variations , indicates that parts of this period could have been as much as 1.4 degreesC colder than today .
Significant cycles of 22 , 11 and 4.8 years demonstrate that the solar magnetic and the El Nino-Southern Oscillation cycle could be important drivers of multidecadal to interannual climate variability in this region .
The observation that the most important driver of stalagmite delta18O on interannual time scales from this subtropical region is regional surface temperature cautions against deterministic interpretations of delta18O variations in low-latitude stalagmites as mainly driven by the amount of precipitation .

[1508] Intensification of Northern Hemisphere subtropical highs in a warming climate

Semi-permanent high-pressure systems over the subtropical oceans , known as subtropical highs , influence atmospheric circulation , as well as global climate .
For instance , subtropical highs largely determine the location of the world 's subtropical deserts , the zones of Mediterranean climate and the tracks of tropical cyclones .
The intensity of two such high-pressure systems , present over the Northern Hemisphere oceans during the summer , has changed in recent years .
However , whether such changes are related to climate warming remains unclear .
Here , we use climate model simulations from the Intergovernmental Panel on Climate Change Fourth Assessment Report , reanalysis data from the 40-year European Centre for Medium-Range Weather Forecasts , and an idealized general circulation model , to assess future changes in the intensity of summertime subtropical highs over the Northern Hemisphere oceans .
The simulations suggest that these summertime highs will intensify in the twenty-first century as a result of an increase in atmospheric greenhouse-gas concentrations .
We further show that the intensification of subtropical highs is predominantly caused by an increase in thermal contrast between the land and ocean .
We suggest that summertime near-surface subtropical highs could play an increasingly important role in regional climate and hydrological extremes in the future .

[1509] A biodiversity intactness index

The nations of the world have set themselves a target of reducing the rate of biodiversity loss by 2010 .
Here , we propose a biodiversity intactness index ( BII ) for assessing progress towards this target that is simple and practical -- but sensitive to important factors that influence biodiversity status -- and which satisfies the criteria for policy relevance set by the Convention on Biological Diversity .
Application of the BII is demonstrated on a large region ( 4 x 106 km2 ) of southern Africa .
The BII score in the year 2000 is about 84 % : in other words , averaged across all plant and vertebrate species in the region , populations have declined to 84 % of their presumed pre-modern levels .
The taxonomic group with the greatest loss is mammals , at 71 % of pre-modern levels , and the ecosystem type with the greatest loss is grassland , with 74 % of its former populations remaining .
During the 1990s , a population decline of 0.8 % is estimated to have occurred .

[1510] Bistability of atmospheric oxygen and the Great Oxidation

The history of the Earth has been characterized by a series of major transitions separated by long periods of relative stability .
The largest chemical transition was the ` Great Oxidation ' , approximately 2.4 billion years ago , when atmospheric oxygen concentrations rose from less than 10-5 of the present atmospheric level ( PAL ) to more than 0.01 PAL , and possibly to more than 0.1 PAL .
This transition took place long after oxygenic photosynthesis is thought to have evolved , but the causes of this delay and of the Great Oxidation itself remain uncertain .
Here we show that the origin of oxygenic photosynthesis gave rise to two simultaneously stable steady states for atmospheric oxygen .
The existence of a low-oxygen ( less than 10-5 PAL ) steady state explains how a reducing atmosphere persisted for at least 300 million years after the onset of oxygenic photosynthesis .
The Great Oxidation can be understood as a switch to the high-oxygen ( more than 5 x 10-3 PAL ) steady state .
The bistability arises because ultraviolet shielding of the troposphere by ozone becomes effective once oxygen levels exceed 10-5 PAL , causing a nonlinear increase in the lifetime of atmospheric oxygen .
Our results indicate that the existence of oxygenic photosynthesis is not a sufficient condition for either an oxygen-rich atmosphere or the presence of an ozone layer , which has implications for detecting life on other planets using atmospheric analysis and for the evolution of multicellular life .

[1511] An improved agar-plate method for studying root growth and response of Arabidopsis thaliana

Arabidopsis thaliana is a widely used model plant for plant biology research .
Under traditional agar-plate culture system ( TPG , traditional plant-growing ) , both plant shoots and roots are exposed to illumination , and roots are grown in sucrose-added medium .
This is not a natural environment for the roots and may cause artifact responses .
We have developed an improved agar-plate culture system ( IPG , improved plant-growing ) where shoots are illuminated but roots are grown in darkness without sucrose addition .
Compared to TPG , IPG produced plants with significantly less total root length , lateral root length and root hair density , although their primary roots were longer .
Root gravitropism , PIN2 ( an auxin efflux carrier ) abundance , H + efflux or Ca2 + influx in root apexes , were weaker in IPG-grown roots than those in TPG-grown roots .
We conclude that IPG offers a more natural way to study the root growth and response of Arabidopsis thaliana .

[1512] Magnitude of oceanic nitrogen fixation influenced by the nutrient uptake ratio of phytoplankton

The elemental stoichiometry of sea water and particulate organic matter is remarkably similar .
This observation led Redfield to hypothesize that the oceanic ratio of nitrate to phosphate is controlled by the remineralization of phytoplankton biomass .
The Redfield ratio is used universally to quantitatively link the marine nitrogen and phosphorus cycles in numerous biogeochemical applications .
Yet , empirical and theoretical studies show that the ratio of nitrogen to phosphorus in phytoplankton varies greatly with taxa and growth conditions .
Here we present a dynamic five-box ecosystem model showing that non-Redfield utilization of dissolved nitrogen and phosphorus by non-nitrogen-fixing phytoplankton controls the magnitude and distribution of nitrogen fixation .
In our simulations , systems dominated by rapidly growing phytoplankton with low nitrogen to phosphorus uptake ratios reduce the phosphorus available for nitrogen fixation .
In contrast , in systems dominated by slow-growing phytoplankton with high nitrogen to phosphorus uptake ratios nitrogen deficits are enhanced , and nitrogen fixation is promoted .
We show that estimates of nitrogen fixation are up to fourfold too high when non-Redfield uptake stoichiometries are ignored .
We suggest that the relative abundance of fast - and slow-growing phytoplankton controls the amount of new nitrogen added to the ocean .

[1513] A topographically forced asymmetry in the martian circulation and climate

Large seasonal and hemispheric asymmetries in the martian climate system are generally ascribed to variations in solar heating associated with orbital eccentricity .
As the orbital elements slowly change ( over a period of > 104 years ) , characteristics of the climate such as dustiness and the vigour of atmospheric circulation are thought to vary , as should asymmetries in the climate ( for example , the deposition of water ice at the northern versus the southern pole ) .
Such orbitally driven climate change might be responsible for the observed layering in Mars ' polar deposits by modulating deposition of dust and water ice .
Most current theories assume that climate asymmetries completely reverse as the angular distance between equinox and perihelion changes by 180degrees .
Here we describe a major climate mechanism that will not precess in this way .
We show that Mars ' global north-south elevation difference forces a dominant southern summer Hadley circulation that is independent of perihelion timing .
The Hadley circulation , a tropical overturning cell responsible for trade winds , largely controls interhemispheric transport of water and the bulk dustiness of the atmosphere .
The topography therefore imprints a strong handedness on climate , with water ice and the active formation of polar layered deposits more likely in the north .

[1514] Quaternary tectonic response to intensified glacial erosion in an orogenic wedge

Active orogens are thought to behave as internally deforming critical-taper wedges that are in rough long-term equilibrium with tectonic influx and erosional outflux .
Spatial and temporal variations in climate are therefore hypothesized to have a significant influence on denudation , topography and deformation of orogens , thereby affecting wedge taper .
However , the impact of the most severe transition in Northern Hemisphere climate during the Cenozoic era -- the onset of glaciation -- has hitherto not been empirically documented .
Here we analyse the spatial patterns of denudation and deformation , and their temporal variations , in the heavily glaciated St Elias orogen in southern Alaska .
Low-temperature thermochronometry , thermokinematic modelling and offshore seismic reflection and borehole data suggest that the global-scale intensification of glaciation in the middle Pleistocene epoch enhanced glacier growth and caused ice streams to advance to the edge of the continental shelf .
This led to focused denudation across the subaerial reaches of the orogen and burial of the actively deforming wedge toe by the eroded sediment .
We propose that this climatically driven mass redistribution forced a structural reorganization of the orogen to maintain critical taper .
Our empirical results thus support decades of numerical model predictions of orogenesis and provide compelling field evidence for the significant impact of climate change on tectonics .

[1515] The impact of agricultural soil erosion on biogeochemical cycling

Soils are the main terrestrial reservoir of nutrients , such as nitrogen and phosphorus , and of organic carbon .
Synthesizing earlier studies , we find that the mobilization and deposition of agricultural soils can significantly alter nutrient and carbon cycling .
Specifically , erosion can result in lateral fluxes of nitrogen and phosphorus that are similar in magnitude to those induced by fertilizer application and crop removal .
Furthermore , the translocation and burial of soil reduces decomposition of soil organic carbon , and could lead to long-term carbon storage .
The cycling of carbon , nitrogen and phosphorus are strongly interrelated .
For example , erosion-induced burial of soils stabilizes soil nutrient and carbon pools , thereby increasing primary productivity and carbon uptake , and potentially reducing erosion .
Our analysis shows soils as dynamic systems in time and space .

[1516] Phytoplankton in the ocean use non-phosphorus lipids in response to phosphorus scarcity

Phosphorus is an obligate requirement for the growth of all organisms ; major biochemical reservoirs of phosphorus in marine plankton include nucleic acids and phospholipids .
However , eukaryotic phytoplankton and cyanobacteria ( that is , ` phytoplankton ' collectively ) have the ability to decrease their cellular phosphorus content when phosphorus in their environment is scarce .
The biochemical mechanisms that allow phytoplankton to limit their phosphorus demand and still maintain growth are largely unknown .
Here we show that phytoplankton , in regions of oligotrophic ocean where phosphate is scarce , reduce their cellular phosphorus requirements by substituting non-phosphorus membrane lipids for phospholipids .
In the Sargasso Sea , where phosphate concentrations were less than 10 nmol l-1 , we found that only 1.3 + / - 0.6 % of phosphate uptake was used for phospholipid synthesis ; in contrast , in the South Pacific subtropical gyre , where phosphate was greater than 100 nmol l-1 , plankton used 17 + / - 6 % ( ref .
6 ) .
Examination of the planktonic membrane lipids at these two locations showed that classes of sulphur - and nitrogen-containing membrane lipids , which are devoid of phosphorus , were more abundant in the Sargasso Sea than in the South Pacific .
Furthermore , these non-phosphorus , ` substitute lipids ' were dominant in phosphorus-limited cultures of all of the phytoplankton species we examined .
In contrast , the marine heterotrophic bacteria we examined contained no substitute lipids and only phospholipids .
Thus heterotrophic bacteria , which compete with phytoplankton for nutrients in oligotrophic regions like the Sargasso Sea , appear to have a biochemical phosphorus requirement that phytoplankton avoid by using substitute lipids .
Our results suggest that phospholipid substitutions are fundamental biochemical mechanisms that allow phytoplankton to maintain growth in the face of phosphorus limitation .

[1517] Black-carbon reduction of snow albedo

Climate models indicate that the reduction of surface albedo caused by black-carbon contamination of snow contributes to global warming and near-worldwide melting of ice .
In this study , we generated and characterized pure and black-carbon-laden snow in the laboratory and verified that black-carbon contamination appreciably reduces snow albedo at levels that have been found in natural settings .
Increasing the size of snow grains in our experiments decreased snow albedo and amplified the radiative perturbation of black carbon , which justifies the aging-related positive feedbacks that are included in climate models .
Moreover , our data provide an extensive verification of the Snow , Ice and Aerosol Radiation model , which will be included in the next assessment of the Intergovernmental Panel on Climate Change .

[1518] Manipulation of the microbiota of mass-reared Mediterranean fruit flies Ceratitis capitata ( Diptera : Tephritidae ) improves sterile male sexual performance

The sterile insect technique ( SIT ) is a method of biological control whereby millions of factory reared sterile male insects are released into the field .
This technique is commonly used to combat the Mediterranean fruit fly ( Ceratitis capitata , Diptera : Tephritidae ) .
Sterile medfly males are less competent in attracting and mating with wild females , a property commonly linked to the irradiation process responsible for the sterilization .
As bacteria are important partners in the fly 's life cycle , we used molecular analytical methods to study the community structure of the gut microbiota in irradiated male medflies .
We find that the sterilizing irradiation procedure affects the gut bacterial community structure of the Mediterranean fruit fly .
Although the Enterobacteriaceae family remains the dominant bacterial group present in the gut , the levels of Klebsiella species decreases significantly in the days after sterilization .
In addition , we detected substantial differences in some bacterial species between the mass rearing strain Vienna 8 and the wild strain .
Most notable among these are the increased levels of the potentially pathogenic species Pseudomonas in the industrial strain .
Testing the hypothesis that regenerating the original microbiota community could result in enhanced competitiveness of the sterile flies , we found that the addition of the bacterial species Klebsiella oxytoca to the postirradiation diet enables colonization of these bacteria in the gut while resulting in decreased levels of the Pseudomonas sp .
Feeding on diets containing bacteria significantly improved sterile male performance in copulatory tests .
Further studies will determine the feasibility of bacterial amelioration in SIT operations .

[1519] Detecting regional anthropogenic trends in ocean acidification against natural variability

Since the beginning of the Industrial Revolution humans have released ~ 500 billion metric tons of carbon to the atmosphere through fossil-fuel burning , cement production and land-use changes .
About 30 % has been taken up by the oceans .
The oceanic uptake of carbon dioxide leads to changes in marine carbonate chemistry resulting in a decrease of seawater pH and carbonate ion concentration , commonly referred to as ocean acidification .
Ocean acidification is considered a major threat to calcifying organisms .
Detecting its magnitude and impacts on regional scales requires accurate knowledge of the level of natural variability of surface ocean carbonate ion concentrations on seasonal to annual timescales and beyond .
Ocean observations are severely limited with respect to providing reliable estimates of the signal-to-noise ratio of human-induced trends in carbonate chemistry against natural factors .
Using three Earth system models we show that the current anthropogenic trend in ocean acidification already exceeds the level of natural variability by up to 30 times on regional scales .
Furthermore , it is demonstrated that the current rates of ocean acidification at monitoring sites in the Atlantic and Pacific oceans exceed those experienced during the last glacial termination by two orders of magnitude .

[1520] Effects of cold stress and heat stress on coral fluorescence in reef-building corals

Widespread temperature stress has caused catastrophic coral bleaching events that have been devastating for coral reefs .
Here , we evaluate whether coral fluorescence could be utilized as a noninvasive assessment for coral health .
We conducted cold and heat stress treatments on the branching coral Acropora yongei , and found that green fluorescent protein ( GFP ) concentration and fluorescence decreased with declining coral health , prior to initiation of bleaching .
Ultimately , cold-treated corals acclimated and GFP concentration and fluorescence recovered .
In contrast , heat-treated corals eventually bleached but showed strong fluorescence despite reduced GFP concentration , likely resulting from the large reduction in shading from decreased dinoflagellate density .
Consequently , GFP concentration and fluorescence showed distinct correlations in non-bleached and bleached corals .
Green fluorescence was positively correlated with dinoflagellate photobiology , but its closest correlation was with coral growth suggesting that green fluorescence could be used as a physiological proxy for health in some corals .

[1521] Carbon dioxide release from the North Pacific abyss during the last deglaciation

Atmospheric carbon dioxide concentrations were significantly lower during glacial periods than during intervening interglacial periods , but the mechanisms responsible for this difference remain uncertain .
Many recent explanations call on greater carbon storage in a poorly ventilated deep ocean during glacial periods , but direct evidence regarding the ventilation and respired carbon content of the glacial deep ocean is sparse and often equivocal .
Here we present sedimentary geochemical records from sites spanning the deep subarctic Pacific that -- together with previously published results -- show that a poorly ventilated water mass containing a high concentration of respired carbon dioxide occupied the North Pacific abyss during the Last Glacial Maximum .
Despite an inferred increase in deep Southern Ocean ventilation during the first step of the deglaciation ( 18,000-15 ,000 years ago ) , we find no evidence for improved ventilation in the abyssal subarctic Pacific until a rapid transition ~ 14,600 years ago : this change was accompanied by an acceleration of export production from the surface waters above but only a small increase in atmospheric carbon dioxide concentration .
We speculate that these changes were mechanistically linked to a roughly coeval increase in deep water formation in the North Atlantic , which flushed respired carbon dioxide from northern abyssal waters , but also increased the supply of nutrients to the upper ocean , leading to greater carbon dioxide sequestration at mid-depths and stalling the rise of atmospheric carbon dioxide concentrations .
Our findings are qualitatively consistent with hypotheses invoking a deglacial flushing of respired carbon dioxide from an isolated , deep ocean reservoir , but suggest that the reservoir may have been released in stages , as vigorous deep water ventilation switched between North Atlantic and Southern Ocean source regions .

[1522] Assessment of groundwater inundation as a consequence of sea-level rise

Strong evidence on climate change underscores the need for actions to reduce the impacts of sea-level rise .
Global mean sea level may rise 0.18-0 .48 m by mid-century and 0.5-1 .4 m by the end of the century .
Besides marine inundation , it is largely unrecognized that low-lying coastal areas may also be vulnerable to groundwater inundation , which is localized coastal-plain flooding due to a rise of the groundwater table with sea level .
Measurements of the coastal groundwater elevation and tidal influence in urban Honolulu , Hawaii , allow estimates of the mean water table , which was used to assess vulnerability to groundwater inundation from sea-level rise .
We find that 0.6 m of potential sea-level rise causes substantial flooding , and 1 m sea-level rise inundates 10 % of a 1-km wide heavily urbanized coastal zone .
The flooded area including groundwater inundation is more than twice the area of marine inundation alone .
This has consequences for decision-makers , resource managers and urban planners , and may be applicable to many low-lying coastal areas , especially where groundwater withdrawal is not substantial .

[1523] Increasing active biomass carbon may lead to a breakdown of mature forest equilibrium

The finding that mature forest ecosystems increase carbon in woody tissues and mineral soils indicates that the original equilibriums are being pushed to a higher state .
The final driving forces will probably be increasing CO2 and nitrogen deposition , global warming , and changes to precipitation patterns .
However , which part of a mature forest bears the direct impacts of environmental changes and reactivates the balanced ecosystem processes remains unclear .
Here , we investigated the living biomass of mature forests in the tropical and subtropical biomes in China and found that active organs and small individuals have accumulated carbon at a rate of 203 kg C ha-1 yr-1 in recent decades , whereas the woody tissues did not display carbon accumulation with statistical significance .
Our findings indicate that the increased labile plant inputs may have shifted mature forests from their previous equilibrium and caused them to enter a new non-equilibrium state .

[1524] The geographical distribution of fossil fuels unused when limiting global warming to 2 degreesC

Policy makers have generally agreed that the average global temperature rise caused by greenhouse gas emissions should not exceed 2 degreesC above the average global temperature of pre-industrial times .
It has been estimated that to have at least a 50 per cent chance of keeping warming below 2 degreesC throughout the twenty-first century , the cumulative carbon emissions between 2011 and 2050 need to be limited to around 1,100 gigatonnes of carbon dioxide ( Gt CO2 ) .
However , the greenhouse gas emissions contained in present estimates of global fossil fuel reserves are around three times higher than this , and so the unabated use of all current fossil fuel reserves is incompatible with a warming limit of 2 degreesC .
Here we use a single integrated assessment model that contains estimates of the quantities , locations and nature of the world 's oil , gas and coal reserves and resources , and which is shown to be consistent with a wide variety of modelling approaches with different assumptions , to explore the implications of this emissions limit for fossil fuel production in different regions .
Our results suggest that , globally , a third of oil reserves , half of gas reserves and over 80 per cent of current coal reserves should remain unused from 2010 to 2050 in order to meet the target of 2 degreesC .
We show that development of resources in the Arctic and any increase in unconventional oil production are incommensurate with efforts to limit average global warming to 2 degreesC .
Our results show that policy makers ' instincts to exploit rapidly and completely their territorial fossil fuels are , in aggregate , inconsistent with their commitments to this temperature limit .
Implementation of this policy commitment would also render unnecessary continued substantial expenditure on fossil fuel exploration , because any new discoveries could not lead to increased aggregate production .

[1525] Consequences of widespread tree mortality triggered by drought and temperature stress

Forests provide innumerable ecological , societal and climatological benefits , yet they are vulnerable to drought and temperature extremes .
Climate-driven forest die-off from drought and heat stress has occurred around the world , is expected to increase with climate change and probably has distinct consequences from those of other forest disturbances .
We examine the consequences of drought - and climate-driven widespread forest loss on ecological communities , ecosystem functions , ecosystem services and land-climate interactions .
Furthermore , we highlight research gaps that warrant study .
As the global climate continues to warm , understanding the implications of forest loss triggered by these events will be of increasing importance .

[1526] Hydrostatic pressure and the actomyosin cortex drive mitotic cell rounding

During mitosis , adherent animal cells undergo a drastic shape change , from essentially flat to round .
Mitotic cell rounding is thought to facilitate organization within the mitotic cell and be necessary for the geometric requirements of division .
However , the forces that drive this shape change remain poorly understood in the presence of external impediments , such as a tissue environment .
Here we use cantilevers to track cell rounding force and volume .
We show that cells have an outward rounding force , which increases as cells enter mitosis .
We find that this mitotic rounding force depends both on the actomyosin cytoskeleton and the cells ' ability to regulate osmolarity .
The rounding force itself is generated by an osmotic pressure .
However , the actomyosin cortex is required to maintain this rounding force against external impediments .
Instantaneous disruption of the actomyosin cortex leads to volume increase , and stimulation of actomyosin contraction leads to volume decrease .
These results show that in cells , osmotic pressure is balanced by inwardly directed actomyosin cortex contraction .
Thus , by locally modulating actomyosin-cortex-dependent surface tension and globally regulating osmotic pressure , cells can control their volume , shape and mechanical properties .

[1527] Convergence of atmospheric and North Atlantic carbon dioxide trends on multidecadal timescales

Oceanic uptake of carbon dioxide substantially reduces the rate at which anthropogenic carbon accumulates in the atmosphere , slowing global climate change .
Some studies suggest that the rate at which the oceans take up carbon has significantly decreased in recent years .
Others suggest that decadal variability confounds the detection of long-term trends .
Here , we examine trends in the partial pressure of carbon dioxide in the surface waters of three large biogeographic regions in the North Atlantic , using observational data collected between 1981 and 2009 .
We compare these oceanic observations with trends in atmospheric carbon dioxide levels , taken from a global observational network .
We show that trends in oceanic carbon dioxide concentrations are variable on a decadal timescale , often diverging from trends in atmospheric carbon dioxide .
However , when the entire 29-year period is considered , oceanic trends converge with atmospheric trends in all three regions ; it takes 25 years for this long-term trend to emerge and overcome the influence of decadal-scale variability .
Furthermore , in the southernmost biome , the data suggest that warming -- driven by a multidecadal climate oscillation and anthropogenic forcing -- has started to reduce oceanic uptake of carbon in recent years .

[1528] Clustering in community structure across replicate ecosystems following a long-term bacterial evolution experiment

Experiments to date probing adaptive evolution have predominantly focused on studying a single species or a pair of species in isolation .
In nature , on the other hand , species evolve within complex communities , interacting and competing with many other species .
It is unclear how reproducible or predictable adaptive evolution is within the context of a multispecies ecosystem .
To explore this problem , we let 96 replicates of a multispecies laboratory bacterial ecosystem evolve in parallel for hundreds of generations .
Here we find that relative abundances of individual species vary greatly across the evolved ecosystems and that the final profile of species frequencies within replicates clusters into several distinct types , as opposed to being randomly dispersed across the frequency space or converging fully .
Our results suggest that community structure evolution has a tendency to follow one of only a few distinct paths .

[1529] SLAC1 is required for plant guard cell S-type anion channel function in stomatal signalling

Stomatal pores , formed by two surrounding guard cells in the epidermis of plant leaves , allow influx of atmospheric carbon dioxide in exchange for transpirational water loss .
Stomata also restrict the entry of ozone -- an important air pollutant that has an increasingly negative impact on crop yields , and thus global carbon fixation and climate change .
The aperture of stomatal pores is regulated by the transport of osmotically active ions and metabolites across guard cell membranes .
Despite the vital role of guard cells in controlling plant water loss , ozone sensitivity and CO2 supply , the genes encoding some of the main regulators of stomatal movements remain unknown .
It has been proposed that guard cell anion channels function as important regulators of stomatal closure and are essential in mediating stomatal responses to physiological and stress stimuli .
However , the genes encoding membrane proteins that mediate guard cell anion efflux have not yet been identified .
Here we report the mapping and characterization of an ozone-sensitive Arabidopsis thaliana mutant , slac1 .
We show that SLAC1 ( SLOW ANION CHANNEL-ASSOCIATED 1 ) is preferentially expressed in guard cells and encodes a distant homologue of fungal and bacterial dicarboxylate/malic acid transport proteins .
The plasma membrane protein SLAC1 is essential for stomatal closure in response to CO2 , abscisic acid , ozone , light/dark transitions , humidity change , calcium ions , hydrogen peroxide and nitric oxide .
Mutations in SLAC1 impair slow ( S-type ) anion channel currents that are activated by cytosolic Ca2 + and abscisic acid , but do not affect rapid ( R-type ) anion channel currents or Ca2 + channel function .
A low homology of SLAC1 to bacterial and fungal organic acid transport proteins , and the permeability of S-type anion channels to malate suggest a vital role for SLAC1 in the function of S-type anion channels .

[1530] Simultaneous estimation of global present-day water transport and glacial isostatic adjustment

Global water transport between oceans and continents during the transition from glacial to interglacial times has been enormous .
The viscoelastic solid Earth has been responding to this unloading of large ice masses with a rise of the land masses , in a process termed glacial isostatic adjustment .
In addition , significant changes in the land/ocean water distribution occur at present .
As both present-day changes in the ice/water thickness and glacial isostatic adjustment affect space geodetic measurements , it is difficult to untangle the relative contributions of these two processes .
Here we combine gravity measurements and geodetic data of surface movement with a data-assimilating model of ocean bottom pressure to simultaneously estimate present-day water transport and glacial isostatic adjustment .
We determine their separate contributions to movements in the geocentre , which occur in response to changes in the Earth 's mass distribution , with uncertainties below 0.1 mm yr-1 .
According to our estimates , mass losses between 2002 and 2008 in Greenland , Alaska/Yukon and West Antarctica are 104 + / -23 , 101 + / -23 and 64 + / -32 Gt yr-1 , respectively .
Our estimates of glacial isostatic adjustment indicate a large geocentre velocity of -0.72 + / -0.06 mm yr-1 in the polar direction .
We conclude that a significant revision of the present estimates of glacial isostatic adjustments and land-ocean water exchange is required .

[1531] Role of climate variability in the heatstroke death rates of Kanto region in Japan

The death toll by heatstroke in Japan , especially in Kanto region , has sharply increased since 1994 together with large interannual variability .
The surface air temperature and humidity observed during boreal summers of 1980-2010 were examined to understand the role of climate in the death toll .
The extremely hot days , when the daily maximum temperature exceeds 35degreesC , are more strongly associated with the death toll than the conventional Wet Bulb Globe Temperature index .
The extremely hot days tend to be associated with El Nino/Southern Oscillation or the Indian Ocean Dipole , suggesting a potential link with tropical climate variability to the heatstroke related deaths .
Also , the influence of these climate modes on the death toll has strengthened since 1994 probably related to global warming .
It is possible to develop early warning systems based on seasonal climate predictions since recent climate models show excellent predictability skills for those climate modes .

[1532] Convergence of terrestrial plant production across global climate gradients

Variation in terrestrial net primary production ( NPP ) with climate is thought to originate from a direct influence of temperature and precipitation on plant metabolism .
However , variation in NPP may also result from an indirect influence of climate by means of plant age , stand biomass , growing season length and local adaptation .
To identify the relative importance of direct and indirect climate effects , we extend metabolic scaling theory to link hypothesized climate influences with NPP , and assess hypothesized relationships using a global compilation of ecosystem woody plant biomass and production data .
Notably , age and biomass explained most of the variation in production whereas temperature and precipitation explained almost none , suggesting that climate indirectly ( not directly ) influences production .
Furthermore , our theory shows that variation in NPP is characterized by a common scaling relationship , suggesting that global change models can incorporate the mechanisms governing this relationship to improve predictions of future ecosystem function .

[1533] Increase in penguin populations during the Little Ice Age in the Ross Sea , Antarctica

Penguins are an important seabird species in Antarctica and are sensitive to climate and environmental changes .
Previous studies indicated that penguin populations increased when the climate became warmer and decreased when it became colder in the maritime Antarctic .
Here we determined organic markers in a sediment profile collected at Cape Bird , Ross Island , high Antarctic , and reconstructed the history of Adelie penguin colonies at this location over the past 700 years .
The region transformed from a seal to a penguin habitat when the Little Ice Age ( LIA ; 1500-1800 AD ) began .
Penguins then became the dominant species .
Penguin populations were the highest during ca. 1490 to 1670 AD , a cold period , which is contrary to previous results in other regions much farther north .
Different responses to climate change may occur at low latitudes and high latitudes in the Antarctic , even if for same species .

[1534] Historical land use change has lowered terrestrial silica mobilization

Continental export of Si to the coastal zone is closely linked to the ocean carbon sink and to the dynamics of phytoplankton blooms in coastal ecosystems .
Presently , however , the impact of human cultivation of the landscape on terrestrial Si fluxes remains unquantified and is not incorporated in models for terrestrial Si mobilization .
In this paper , we show that land use is the most important controlling factor of Si mobilization in temperate European watersheds , with sustained cultivation ( > 250 years ) of formerly forested areas leading to a twofold to threefold decrease in baseflow delivery of Si .
This is a breakthrough in our understanding of the biogeochemical Si cycle : it shows that human cultivation of the landscape should be recognized as an important controlling factor of terrestrial Si fluxes .

[1535] Millennial-scale climate instability during the early Pleistocene epoch

Climate-proxy records of the past 100,000 years show that the Earth 's climate has varied significantly and continuously on timescales as short as a few thousand years ( refs 1-7 ) .
Similar variability has also recently been observed for the interval 340-500 thousand years ago .
These dramatic climate shifts , expressed most strongly in the North Atlantic region , may be linked to -- and possibly amplified by -- alterations in the mode of ocean thermohaline circulation .
Here we use sediment records of past iceberg discharge and deep-water chemistry to show that such millennial-scale oscillations in climate occurred over one million years ago .
This was a time of significantly different climate boundary conditions ; not only was the early Pleistocene epoch generally warmer , but global climate variations were governed largely by changes in Earth 's orbital obliguity .
Our results suggest that such millennial-scale climate instability may be a pervasive and long-term characteristic of Earth 's climate , rather than just a feature of the strong glacial-interglacial cycles of the past 800,000 years .

[1536] In situ liquid-cell electron microscopy of silver-palladium galvanic replacement reactions on silver nanoparticles

Galvanic replacement reactions provide an elegant way of transforming solid nanoparticles into complex hollow morphologies .
Conventionally , galvanic replacement is studied by stopping the reaction at different stages and characterizing the products ex situ .
In situ observations by liquid-cell electron microscopy can provide insight into mechanisms , rates and possible modifications of galvanic replacement reactions in the native solution environment .
Here we use liquid-cell electron microscopy to investigate galvanic replacement reactions between silver nanoparticle templates and aqueous palladium salt solutions .
Our in situ observations follow the transformation of the silver nanoparticles into hollow silver-palladium nanostructures .
While the silver-palladium nanocages have morphologies similar to those obtained in ex situ control experiments the reaction rates are much higher , indicating that the electron beam strongly affects the galvanic-type process in the liquid-cell .
By using scavengers added to the aqueous solution we identify the role of radicals generated via radiolysis by high-energy electrons in modifying galvanic reactions .

[1537] Symbiotic fungal endophytes control insect host-parasite interaction webs

Symbiotic microorganisms that live intimately associated with terrestrial plants affect both the quantity and quality of resources , and thus the energy supply to consumer populations at higher levels in the food chain .
Empirical evidence on resource limitation of food webs points to primary productivity as a major determinant of consumer abundance and trophic structure .
Prey quality plays a critical role in community regulation .
Plants infected by endophytic fungi are known to be chemically protected against herbivore consumption .
However , the influence of this microbe-plant association on multi-trophic interactions remains largely unexplored .
Here we present the effects of fungal endophytes on insect food webs that reflect limited energy transfer to consumers as a result of low plant quality , rather than low productivity .
Herbivore-parasite webs on endophyte-free grasses show enhanced insect abundance at alternate trophic levels , higher rates of parasitism , and increased dominance by a few trophic links .
These results mirror predicted effects of increased productivity on food-web dynamics .
Thus ` hidden ' microbial symbionts can have community-wide impacts on the pattern and strength of resource-consumer interactions .

[1538] Climate sensitivity constrained by CO2 concentrations over the past 420 million years

A firm understanding of the relationship between atmospheric carbon dioxide concentration and temperature is critical for interpreting past climate change and for predicting future climate change .
A recent synthesis suggests that the increase in global-mean surface temperature in response to a doubling of the atmospheric carbon dioxide concentration , termed ` climate sensitivity ' , is between 1.5 and 6.2 degreesC ( 5-95 per cent likelihood range ) , but some evidence is inconsistent with this range .
Moreover , most estimates of climate sensitivity are based on records of climate change over the past few decades to thousands of years , when carbon dioxide concentrations and global temperatures were similar to or lower than today , so such calculations tend to underestimate the magnitude of large climate-change events and may not be applicable to climate change under warmer conditions in the future .
Here we estimate long-term equilibrium climate sensitivity by modelling carbon dioxide concentrations over the past 420 million years and comparing our calculations with a proxy record .
Our estimates are broadly consistent with estimates based on short-term climate records , and indicate that a weak radiative forcing by carbon dioxide is highly unlikely on multi-million-year timescales .
We conclude that a climate sensitivity greater than 1.5 degreesC has probably been a robust feature of the Earth 's climate system over the past 420 million years , regardless of temporal scaling .

[1539] Physicochemical impacts associated with natural gas development on methanogenesis in deep sand aquifers

The Minami-Kanto gas field , where gases are dissolved in formation water , is a potential analogue for a marine gas hydrate area because both areas are characterized by the accumulation of microbial methane in marine turbidite sand layers interbedded with mud layers .
This study examined the physicochemical impacts associated with natural gas production and well drilling on the methanogenic activity and composition in this gas field .
Twenty-four gas-associated formation water samples were collected from confined sand aquifers through production wells .
The stable isotopic compositions of methane in the gases indicated their origin to be biogenic via the carbonate reduction pathway .
Consistent with this classification , methanogenic activity measurements using radiotracers , culturing experiments and molecular analysis of formation water samples indicated the predominance of hydrogenotrophic methanogenesis .
The cultivation of water samples amended only with methanogenic substrates resulted in significant increases in microbial cells along with high-yield methane production , indicating the restricted availability of substrates in the aquifers .
Hydrogenotrophic methanogenic activity increased with increasing natural gas production from the corresponding wells , suggesting that the flux of substrates from organic-rich mudstones to adjacent sand aquifers is enhanced by the decrease in fluid pressure in sand layers associated with natural gas/water production .
The transient predominance of methylotrophic methanogens , observed for a few years after well drilling , also suggested the stimulation of the methanogens by the exposure of unutilized organic matter through well drilling .
These results provide an insight into the physicochemical impacts on the methanogenic activity in biogenic gas deposits including marine gas hydrates .

[1540] Reduced selection and accumulation of deleterious mutations in genes exclusively expressed in men

Sex-limited selection can moderate the elimination of deleterious mutations from the population and contribute to the high prevalence of common human diseases .
Accordingly , deleterious mutations in autosomal genes that are exclusively expressed in only one of the sexes undergo sex-limited selection and can reach higher frequencies than mutations similarly selected in both sexes .
Here we show that the number of deleterious SNPs in genes exclusively expressed in men is twofold higher than in genes that are selected in both sexes .
Additional analyses suggest that the increased number of damaging mutations we found in male-specific genes is due to reduced selection in females .
These results are noteworthy since many of these male-specific genes are known to be crucial for male reproduction , and are thus likely to be under strong purifying selection .
We suggest that inheritance of male-infertility-causative mutations through unaffected female lineages contributes to the high incidence of male infertility .

[1541] Agronomic conditions and crop evolution in ancient Near East agriculture

The appearance of agriculture in the Fertile Crescent propelled the development of Western civilization .
Here we investigate the evolution of agronomic conditions in this region by reconstructing cereal kernel weight and using stable carbon and nitrogen isotope signatures of kernels and charcoal from a set of 11 Upper Mesopotamia archaeological sites , with chronologies spanning from the onset of agriculture to the turn of the era .
We show that water availability for crops , inferred from carbon isotope discrimination ( Delta13C ) , was two - to fourfold higher in the past than at present , with a maximum between 10,000 and 8,000 cal BP .
Nitrogen isotope composition ( delta15N ) decreased over time , which suggests cultivation occurring under gradually less-fertile soil conditions .
Domesticated cereals showed a progressive increase in kernel weight over several millennia following domestication .
Our results provide a first comprehensive view of agricultural evolution in the Near East inferred directly from archaeobotanical remains .

[1542] Climate change : The growth of dying seas

Oxygen-deprived dead zones in coastal waters around the world have expanded exponentially since the 1960s and are likely to increase further in a warming climate .
Markus Meier of the Swedish Meteorological and Hydrological Institute in Norrkoping and his colleagues used a group of physical-biogeochemical models , driven by data from regional climate models , to project the effects of climate change and changes in nutrient cycles on oxygen conditions in the Baltic Sea .

[1543] Nitrogen transfer from sea to land via commercial fisheries

Human activity has dramatically altered global nitrogen fluxes , nearly doubling the nitrogen export from land to coast .
Fertilizer run-off accounts for much of this increase .
The role of commercial fisheries in altering fish stocks has been explored , but their effect on the return of nitrogen from coastal oceans to land is less well known .
Here we quantify the nitrogen return to land via fisheries and compare it with nitrogen fertilizer inputs into the coastal ocean regionally and over time .
We find that both fertilizer run-off into the ocean and fishery removal of nitrogen have increased over the past four decades , but the increase in nitrogen input has been faster .
Although our estimate for the ratio of nitrogen return to nitrogen input has therefore decreased over time from about 60 % in 1960 to about 20 % in 2000 , we conclude that fishery harvest is a significant , and currently underappreciated , aspect of anthropogenic nitrogen flux in many coastal regions .

[1544] Intensified Diapycnal Mixing in the Midlatitude Western Boundary Currents

The wind work on oceanic near-inertial motions is suggested to play an important role in furnishing the diapycnal mixing in the deep ocean which affects the uptake of heat and carbon by the ocean as well as climate changes .
However , it remains a puzzle where and through which route the near-inertial energy penetrates into the deep ocean .
Using the measurements collected in the Kuroshio extension region during January 2005 , we demonstrate that the diapycnal mixing in the thermocline and deep ocean is tightly related to the shear variance of wind-generated near-inertial internal waves with the diapycnal diffusivity 6 x 10-5 m2s-1 almost an order stronger than that observed in the circulation gyre .
It is estimated that 45 % -62 % of the local near-inertial wind work 4.5 x 10-3 Wm-2 radiates into the thermocline and deep ocean and accounts for 42 % -58 % of the energy required to furnish mixing there .
The elevated mixing is suggested to be maintained by the energetic near-inertial wind work and strong eddy activities causing enhanced downward near-inertial energy flux than earlier findings .
The western boundary current turns out to be a key region for the penetration of near-inertial energy into the deep ocean and a hotspot for the diapycnal mixing in winter .

[1545] Genetic indicators of iron limitation in wild populations of Thalassiosira oceanica from the northeast Pacific Ocean

Assessing the iron ( Fe ) nutritional status of natural diatom populations has proven challenging as physiological and molecular responses can differ in diatoms of the same genus .
We evaluated expression of genes encoding flavodoxin ( FLDA1 ) and an Fe-starvation induced protein ( ISIP3 ) as indicators of Fe limitation in the marine diatom Thalassiosira oceanica .
The specificity of the response to Fe limitation was tested in cultures grown under Fe - and macronutrient-deficient conditions , as well as throughout the diurnal light cycle .
Both genes showed a robust and specific response to Fe limitation in laboratory cultures and were detected in small volume samples collected from the northeast Pacific , demonstrating the sensitivity of this method .
Overall , FLDA1 and ISIP3 expression was inversely related to Fe concentrations and offered insight into the Fe nutritional health of T. oceanica in the field .
As T. oceanica is a species tolerant to low Fe , indications of Fe limitation in T. oceanica populations may serve as a proxy for severe Fe stress in the overall diatom community .
At two shallow coastal locations , FLD1A and ISIP3 expression revealed Fe stress in areas where dissolved Fe concentrations were high , demonstrating that this approach may be powerful for identifying regions where Fe supply may not be biologically available .

[1546] Variations of sulphur dioxide at the cloud top of Venus 's dynamic atmosphere

Sulphur dioxide is a million times more abundant in the atmosphere of Venus than that of Earth , possibly as a result of volcanism on Venus within the past billion years .
A tenfold decrease in sulphur dioxide column density above Venus 's clouds measured by the Pioneer Venus spacecraft during the 1970s and 1980s has been interpreted as decline following an episode of volcanogenic upwelling from the lower atmosphere .
Here we report that the sulphur dioxide column density above Venus 's clouds decreased by an order of magnitude between 2007 and 2012 using ultraviolet spectrometer data from the SPICAV instrument onboard the Venus Express spacecraft .
This decline is similar to observations during the 1980s .
We also report strong latitudinal and temporal variability in sulphur dioxide column density that is consistent with supply fluctuations from the lower atmosphere .
We suggest that episodic sulphur dioxide injections to the cloud tops may be caused either by periods of increased buoyancy of volcanic plumes , or , in the absence of active volcanism , by long-period oscillations of the general atmospheric circulation .
The 30-year observational record from Pioneer Venus and Venus Express confirms that episodic injections of sulphur dioxide above the clouds recur on decadal timescales , suggesting a more variable atmosphere than expected .

[1547] Formation of artificial pores in nano-TiO2 photo-electrode films using acetylene-black for high-efficiency , dye-sensitized solar cells

Acetylene-black paste without a light scattering layer was applied to meso-porous TiO2 photo-electrode films with a crystalline framework , a low residual carbon , and a tunable morphological pore size .
The thermal-treated TiO2 photo-electrode films had an increased acetylene-black concentration with an increase in artificial pores and a decrease in residual carbon .
The performance of dye-sensitized solar cells ( DSSCs ) was enhanced by the use of the TiO2 photo-anode pastes at various acetylene-black concentrations .
The photo-conversion efficiency of the DSSCs using TiO2 photo-electrode films with 1.5 wt % acetylene-black was enhanced from 7.98 ( no acetylene-black ) to 9.75 % without the integration of a light - scattering layer .

[1548] Linking phylogenetic and functional diversity to nutrient spiraling in microbial mats from Lower Kane Cave ( USA )

Microbial mats in sulfidic cave streams offer unique opportunities to study redox-based biogeochemical nutrient cycles .
Previous work from Lower Kane Cave , Wyoming , USA , focused on the aerobic portion of microbial mats , dominated by putative chemolithoautotrophic , sulfur-oxidizing groups within the Epsilonproteobacteria and Gammaproteobacteria .
To evaluate nutrient cycling and turnover within the whole mat system , a multidisciplinary strategy was used to characterize the anaerobic portion of the mats , including application of the full-cycle rRNA approach , the most probable number method , and geochemical and isotopic analyses .
Seventeen major taxonomic bacterial groups and one archaeal group were retrieved from the anaerobic portions of the mats , dominated by Deltaproteobacteria and uncultured members of the Chloroflexi phylum .
A nutrient spiraling model was applied to evaluate upstream to downstream changes in microbial diversity based on carbon and sulfur nutrient concentrations .
Variability in dissolved sulfide concentrations was attributed to changes in the abundance of sulfide-oxidizing microbial groups and shifts in the occurrence and abundance of sulfate-reducing microbes .
Gradients in carbon and sulfur isotopic composition indicated that released and recycled byproduct compounds from upstream microbial activities were incorporated by downstream communities .
On the basis of the type of available chemical energy , the variability of nutrient species in a spiraling model may explain observed differences in microbial taxonomic affiliations and metabolic functions , thereby spatially linking microbial diversity to nutrient spiraling in the cave stream ecosystem .

[1549] Bacterial diversity , community structure and potential growth rates along an estuarine salinity gradient

Very little is known about growth rates of individual bacterial taxa and how they respond to environmental flux .
Here , we characterized bacterial community diversity , structure and the relative abundance of 16S rRNA and 16S rRNA genes ( rDNA ) using pyrosequencing along the salinity gradient in the Delaware Bay .
Indices of diversity , evenness , structure and growth rates of the surface bacterial community significantly varied along the transect , reflecting active mixing between the freshwater and marine ends of the estuary .
There was no positive correlation between relative abundances of 16S rRNA and rDNA for the entire bacterial community , suggesting that abundance of bacteria does not necessarily reflect potential growth rate or activity .
However , for almost half of the individual taxa , 16S rRNA positively correlated with rDNA , suggesting that activity did follow abundance in these cases .
The positive relationship between 16S rRNA and rDNA was less in the whole water community than for free-living taxa , indicating that the two communities differed in activity .
The 16S rRNA : rDNA ratios of some typically marine taxa reflected differences in light , nutrient concentrations and other environmental factors along the estuarine gradient .
The ratios of individual freshwater taxa declined as salinity increased , whereas the 16S rRNA : rDNA ratios of only some typical marine bacteria increased as salinity increased .
These data suggest that physical and other bottom-up factors differentially affect growth rates , but not necessarily abundance of individual taxa in this highly variable environment .

[1550] Solar forcing of winter climate variability in the Northern Hemisphere

An influence of solar irradiance variations on Earth 's surface climate has been repeatedly suggested , based on correlations between solar variability and meteorological variables .
Specifically , weaker westerly winds have been observed in winters with a less active sun , for example at the minimum phase of the 11-year sunspot cycle .
With some possible exceptions , it has proved difficult for climate models to consistently reproduce this signal .
Spectral Irradiance Monitor satellite measurements indicate that variations in solar ultraviolet irradiance may be larger than previously thought .
Here we drive an ocean-atmosphere climate model with ultraviolet irradiance variations based on these observations .
We find that the model responds to the solar minimum with patterns in surface pressure and temperature that resemble the negative phase of the North Atlantic or Arctic Oscillation , of similar magnitude to observations .
In our model , the anomalies descend through the depth of the extratropical winter atmosphere .
If the updated measurements of solar ultraviolet irradiance are correct , low solar activity , as observed during recent years , drives cold winters in northern Europe and the United States , and mild winters over southern Europe and Canada , with little direct change in globally averaged temperature .
Given the quasiregularity of the 11-year solar cycle , our findings may help improve decadal climate predictions for highly populated extratropical regions .

[1551] Palaeoceanography : Antarctic stratification and glacial CO2

One way of accounting for lowered atmospheric carbon dioxide concentrations during Pleistocene glacial periods is by invoking the Antarctic stratification hypothesis , which links the reduction in CO2 to greater stratification of ocean surface waters around Antarctica .
As discussed by Sigman and Boyle , this hypothesis assumes that increased stratification in the Antarctic zone ( Fig. 1 ) was associated with reduced upwelling of deep waters around Antarctica , thereby allowing CO2 outgassing to be suppressed by biological production while also allowing biological production to decline , which is consistent with Antarctic sediment records .
We point out here , however , that the response of ocean eddies to increased Antarctic stratification can be expected to increase , rather than reduce , the upwelling rate of deep waters around Antarctica .
The stratification hypothesis may have difficulty in accommodating eddy feedbacks on upwelling within the constraints imposed by reconstructions of winds and Antarctic-zone productivity in glacial periods .

[1552] The impacts of climate change on terrestrial Earth surface systems

National and international policy initiatives have focused on reducing carbon emissions as a means by which to limit future climate warming .
Much less attention has been paid by policymakers to monitoring , modelling and managing the impacts of climate change on the dynamics of Earth surface systems , including glaciers , rivers , mountains and coasts .
This is a critical omission , however , as Earth surface systems provide water and soil resources , sustain ecosystem services and strongly influence biogeochemical climate feedbacks in ways that are as yet uncertain .
We argue that there is a significant policy gap regarding the management of Earth surface systems ' impacts under climate change that needs to be closed to facilitate the sustainability of cross-national Earth surface resource use .
It is also a significant challenge to the scientific community to better understand Earth surface systems ' sensitivity to climate forcing .

[1553] Regional climate model simulations indicate limited climatic impacts by operational and planned European wind farms

The rapid development of wind energy has raised concerns about environmental impacts .
Temperature changes are found in the vicinity of wind farms and previous simulations have suggested that large-scale wind farms could alter regional climate .
However , assessments of the effects of realistic wind power development scenarios at the scale of a continent are missing .
Here we simulate the impacts of current and near-future wind energy production according to European Union energy and climate policies .
We use a regional climate model describing the interactions between turbines and the atmosphere , and find limited impacts .
A statistically significant signal is only found in winter , with changes within + / -0.3 degreesC and within 0-5 % for precipitation .
It results from the combination of local wind farm effects and changes due to a weak , but robust , anticyclonic-induced circulation over Europe .
However , the impacts remain much weaker than the natural climate interannual variability and changes expected from greenhouse gas emissions .

[1554] Mixing and convection in the Greenland Sea from a tracer-release experiment

Convective vertical mixing in restricted areas of the subpolar oceans , such as the Greenland Sea , is thought to be the process responsible for forming much of the dense water of the ocean interior .
Deep-water formation varies substantially on annual and decadal timescales , and responds to regional climate signals such as the North Atlantic Oscillation ; its variations may therefore give early warning of changes in the thermohaline circulation that may accompany climate change .
Here we report direct measurements of vertical mixing , by convection and by turbulence , from a sulphur hexafluoride tracer-release experiment in the central Greenland Sea gyre .
In summer , we found rapid turbulent vertical mixing of about 1.1 cm2 s-1 .
In the following late winter , part of the water column was mixed more vigorously by convection , indicated by the rising and vertical redistribution of the tracer patch in the centre of the gyre .
At the same time , mixing outside the gyre centre was only slightly greater than in summer .
The results suggest that about 10 % of the water in the gyre centre was vertically transported in convective plumes , which reached from the surface to , at their deepest , 1,200-1 ,400 m. Convection was limited to a very restricted area , however , and smaller volumes of water were transported to depth than previously estimated .
Our results imply that it may be the rapid year-round turbulent mixing , rather than convection , that dominates vertical mixing in the region as a whole .

[1555] A precipitation shift from snow towards rain leads to a decrease in streamflow

In a warming climate , precipitation is less likely to occur as snowfall .
A shift from a snow - towards a rain-dominated regime is currently assumed not to influence the mean streamflow significantly .
Contradicting the current paradigm , we argue that mean streamflow is likely to reduce for catchments that experience significant reductions in the fraction of precipitation falling as snow .
With more than one-sixth of the Earth 's population depending on meltwater for their water supply and ecosystems that can be sensitive to streamflow alterations , the socio-economic consequences of a reduction in streamflow can be substantial .
By applying the Budyko water balance framework to catchments located throughout the contiguous United States we demonstrate that a higher fraction of precipitation falling as snow is associated with higher mean streamflow , compared to catchments with marginal or no snowfall .
Furthermore , we show that the fraction of each year 's precipitation falling as snowfall has a significant influence on the annual streamflow within individual catchments .
This study is limited to introducing these observations ; process-based understanding at the catchment scale is not yet provided .
Given the importance of streamflow for society , further studies are required to respond to the consequences of a temperature-induced precipitation shift from snow to rain .

[1556] Fire-induced erosion and millennial-scale climate change in northern ponderosa pine forests

Western US ponderosa pine forests have recently suffered extensive stand-replacing fires followed by hillslope erosion and sedimentation .
These fires are usually attributed to increased stand density as a result of fire suppression , grazing and other land use , and are often considered uncharacteristic or unprecedented .
Tree-ring records from the past 500 years indicate that before Euro-American settlement , frequent , low-severity fires maintained open stands .
However , the pre-settlement period between about ad 1500 and ad 1900 was also generally colder than present , raising the possibility that rapid twentieth-century warming promoted recent catastrophic fires .
Here we date fire-related sediment deposits in alluvial fans in central Idaho to reconstruct Holocene fire history in xeric ponderosa pine forests and examine links to climate .
We find that colder periods experienced frequent low-severity fires , probably fuelled by increased understory growth .
Warmer periods experienced severe droughts , stand-replacing fires and large debris-flow events that comprise a large component of long-term erosion and coincide with similar events in sub-alpine forests of Yellowstone National Park .
Our results suggest that given the powerful influence of climate , restoration of processes typical of pre-settlement times may be difficult in a warmer future that promotes severe fires .

[1557] Resistance and resilience of benthic biofilm communities from a temperate saltmarsh to desiccation and rewetting

Periods of desiccation and rewetting are regular , yet stressful events encountered by saltmarsh microbial communities .
To examine the resistance and resilience of microbial biofilms to such stresses , sediments from saltmarsh creeks were allowed to desiccate for 23 days , followed by rewetting for 4 days , whereas control sediments were maintained under a natural tidal cycle .
In the top 2 mm of the dry sediments , salinity increased steadily from 36 to 231 over 23 days , and returned to seawater salinity on rewetting .
After 3 days , desiccated sediments had a lower chlorophyll a ( Chl a ) fluorescence signal as benthic diatoms ceased to migrate to the surface , with a recovery in cell migration and Chl a fluorescence on rewetting .
Extracellular beta-glucosidase and aminopeptidase activities decreased within the first week of drying , but increased sharply on rewetting .
The bacterial community in the desiccating sediment changed significantly from the controls after 14 days of desiccation ( salinity 144 ) .
Rewetting did not cause a return to the original community composition , but led to a further change .
Pyrosequencing analysis of 16S rRNA genes amplified from the sediment revealed diverse microbial responses , for example desiccation enabled haloversatile Marinobacter species to increase their relative abundance , and thus take advantage of rewetting to grow rapidly and dominate the community .
A temporal sequence of effects of desiccation and rewetting were thus observed , but the most notable feature was the overall resistance and resilience of the microbial community .

[1558] Validation of climate model-inferred regional temperature change for late-glacial Europe

Comparisons of climate model hindcasts with independent proxy data are essential for assessing model performance in non-analogue situations .
However , standardized palaeoclimate data sets for assessing the spatial pattern of past climatic change across continents are lacking for some of the most dynamic episodes of Earth 's recent past .
Here we present a new chironomid-based palaeotemperature dataset designed to assess climate model hindcasts of regional summer temperature change in Europe during the late-glacial and early Holocene .
Latitudinal and longitudinal patterns of inferred temperature change are in excellent agreement with simulations by the ECHAM-4 model , implying that atmospheric general circulation models like ECHAM-4 can successfully predict regionally diverging temperature trends in Europe , even when conditions differ significantly from present .
However , ECHAM-4 infers larger amplitudes of change and higher temperatures during warm phases than our palaeotemperature estimates , suggesting that this and similar models may overestimate past and potentially also future summer temperature changes in Europe .

[1559] Links between ocean temperature and iceberg discharge during Heinrich events

Palaeoclimate records have revealed the presence of millennial-scale climate oscillations throughout the last glacial period .
Six periods of extreme cooling in the Northern Hemisphere -- known as Heinrich events -- were marked by an enhanced discharge of icebergs into the North Atlantic Ocean , increasing the deposition of ice-rafted debris .
Increased sliding at the base of ice sheets as a result of basal warming has been proposed to explain the iceberg pulses , but recent observations suggest that iceberg discharge is related to a strong coupling between ice sheets , ice shelves and ocean conditions .
Here we use a conceptual numerical model to simulate the effect of ocean temperature on ice-shelf width , as well as the impact of the resultant changes in ice-shelf geometry on ice-stream velocities .
Our results demonstrate that ocean temperature oscillations affect the basal melting of the ice shelf and will generate periodic pulses of iceberg discharge in an ice sheet with a fringing shelf .
We also find that the irregular occurrence of Heinrich events seen in the palaeoclimate records can be simulated by periodic ocean forcing combined with varying accumulation rates of the ice sheet .
Our model simulations support a link between millennial-scale ocean temperature variability and Heinrich events during the last glacial period .

[1560] Millennial - and orbital-scale changes in the East Asian monsoon over the past 224,000 years

High-resolution speleothem records from China have provided insights into the factors that control the strength of the East Asian monsoon .
Our understanding of these factors remains incomplete , however , owing to gaps in the record of monsoon history over the past two interglacial-glacial cycles .
In particular , missing sections have hampered our ability to test ideas about orbital-scale controls on the monsoon , the causes of millennial-scale events and relationships between changes in the monsoon and climate in other regions .
Here we present an absolute-dated oxygen isotope record from Sanbao cave , central China , that completes a Chinese-cave-based record of the strength of the East Asian monsoon that covers the past 224,000 years .
The record is dominated by 23,000-year-long cycles that are synchronous within dating errors with summer insolation at 65degrees N ( ref .
10 ) , supporting the idea that tropical/subtropical monsoons respond dominantly and directly to changes in Northern Hemisphere summer insolation on orbital timescales .
The cycles are punctuated by millennial-scale strong-summer-monsoon events ( Chinese interstadials ) , and the new record allows us to identify the complete series of these events over the past two interglacial-glacial cycles .
Their duration decreases and their frequency increases during glacial build-up in both the last and penultimate glacial periods , indicating that ice sheet size affects their character and pacing .
The ages of the events are exceptionally well constrained and may thus serve as benchmarks for correlating and calibrating climate records .

[1561] The ( d ) evolution of methanotrophy in the Beijerinckiaceae -- a comparative genomics analysis

The alphaproteobacterial family Beijerinckiaceae contains generalists that grow on a wide range of substrates , and specialists that grow only on methane and methanol .
We investigated the evolution of this family by comparing the genomes of the generalist organotroph Beijerinckia indica , the facultative methanotroph Methylocella silvestris and the obligate methanotroph Methylocapsa acidiphila .
Highly resolved phylogenetic construction based on universally conserved genes demonstrated that the Beijerinckiaceae forms a monophyletic cluster with the Methylocystaceae , the only other family of alphaproteobacterial methanotrophs .
Phylogenetic analyses also demonstrated a vertical inheritance pattern of methanotrophy and methylotrophy genes within these families .
Conversely , many lateral gene transfer ( LGT ) events were detected for genes encoding carbohydrate transport and metabolism , energy production and conversion , and transcriptional regulation in the genome of B. indica , suggesting that it has recently acquired these genes .
A key difference between the generalist B. indica and its specialist methanotrophic relatives was an abundance of transporter elements , particularly periplasmic-binding proteins and major facilitator transporters .
The most parsimonious scenario for the evolution of methanotrophy in the Alphaproteobacteria is that it occurred only once , when a methylotroph acquired methane monooxygenases ( MMOs ) via LGT .
This was supported by a compositional analysis suggesting that all MMOs in Alphaproteobacteria methanotrophs are foreign in origin .
Some members of the Beijerinckiaceae subsequently lost methanotrophic functions and regained the ability to grow on multicarbon energy substrates .
We conclude that B. indica is a recidivist multitroph , the only known example of a bacterium having completely abandoned an evolved lifestyle of specialized methanotrophy .

[1562] Swapping symbionts in spittlebugs : evolutionary replacement of a reduced genome symbiont

Bacterial symbionts that undergo long-term maternal transmission experience elevated fixation of deleterious mutations , resulting in massive loss of genes and changes in gene sequences that appear to limit efficiency of gene products .
Potentially , this dwindling of symbiont functionality impacts hosts that depend on these bacteria for nutrition .
One evolutionary escape route is the acquisition of a novel symbiont with a robust genome and metabolic capabilities .
Such an acquisition has occurred in an ancestor of Philaenus spumarius , the meadow spittlebug ( Insecta : Cercopoidea ) , which has replaced its ancient association with the tiny genome symbiont Zinderia insecticola ( Betaproteobacteria ) with an association with a symbiont related to Sodalis glossinidius ( Gammaproteobacteria ) .
Spittlebugs feed exclusively on xylem sap , a diet that is low both in essential amino acids and in sugar or other substrates for energy production .
The new symbiont genome has undergone proliferation of mobile elements resulting in many gene inactivations ; nonetheless , it has selectively maintained genes replacing functions of its predecessor for amino-acid biosynthesis .
Whereas ancient symbiont partners typically retain perfectly complementary sets of amino-acid biosynthetic pathways , the novel symbiont introduces some redundancy as it retains some pathways also present in the partner symbionts ( Sulcia muelleri ) .
Strikingly , the newly acquired Sodalis-like symbiont retains genes underlying efficient routes of energy production , including a complete TCA cycle , potentially relaxing the severe energy limitations of the xylem-feeding hosts .
Although evolutionary replacements of ancient symbionts are infrequent , they potentially enable evolutionary and ecological novelty by conferring novel metabolic capabilities to host lineages .

[1563] Changes in carbon dioxide during an oceanic anoxic event linked to intrusion into Gondwana coals

The marine sedimentary record exhibits evidence for episodes of enhanced organic carbon burial known as ` oceanic anoxic events ' ( OAEs ) .
They are characterized by carbon-isotope excursions in marine and terrestrial reservoirs and mass extinction of marine faunas .
Causal mechanisms for the enhancement of organic carbon burial during OAEs are still debated , but it is thought that such events should draw down significant quantities of atmospheric carbon dioxide .
In the case of the Toarcian OAE ( ~ 183 million years ago ) , a short-lived negative carbon-isotope excursion in oceanic and terrestrial reservoirs has been interpreted to indicate raised atmospheric carbon dioxide caused by oxidation of methane catastrophically released from either marine gas hydrates or magma-intruded organic-rich rocks .
Here we test these two leading hypotheses for a negative carbon isotopic excursion marking the initiation of the Toarcian OAE using a high-resolution atmospheric carbon dioxide record obtained from fossil leaf stomatal frequency .
We find that coincident with the negative carbon-isotope excursion carbon dioxide is first drawn down by 350 + / - 100 p.p.m.v. and then abruptly elevated by 1,200 + / - 400 p.p.m.v , and infer a global cooling and greenhouse warming of 2.5 + / - 0.1 degreesC and 6.5 + / - 1 degreesC , respectively .
The pattern and magnitude of carbon dioxide change are difficult to reconcile with catastrophic input of isotopically light methane from hydrates as the cause of the negative isotopic signal .
Our carbon dioxide record better supports a magma-intrusion hypothesis , and suggests that injection of isotopically light carbon from the release of thermogenic methane occurred owing to the intrusion of Gondwana coals by Toarcian-aged Karoo-Ferrar dolerites .

[1564] Long-term sensitivity of soil carbon turnover to warming

The sensitivity of soil carbon to warming is a major uncertainty in projections of carbon dioxide concentration and climate .
Experimental studies overwhelmingly indicate increased soil organic carbon ( SOC ) decomposition at higher temperatures , resulting in increased carbon dioxide emissions from soils .
However , recent findings have been cited as evidence against increased soil carbon emissions in a warmer world .
In soil warming experiments , the initially increased carbon dioxide efflux returns to pre-warming rates within one to three years , and apparent carbon pool turnover times are insensitive to temperature .
It has already been suggested that the apparent lack of temperature dependence could be an artefact due to neglecting the extreme heterogeneity of soil carbon , but no explicit model has yet been presented that can reconcile all the above findings .
Here we present a simple three-pool model that partitions SOC into components with different intrinsic turnover rates .
Using this model , we show that the results of all the soil-warming experiments are compatible with long-term temperature sensitivity of SOC turnover : they can be explained by rapid depletion of labile SOC combined with the negligible response of non-labile SOC on experimental timescales .
Furthermore , we present evidence that non-labile SOC is more sensitive to temperature than labile SOC , implying that the long-term positive feedback of soil decomposition in a warming world may be even stronger than predicted by global models .

[1565] A Munc13-like protein in Arabidopsis mediates H + - ATPase translocation that is essential for stomatal responses

Plants control CO2 uptake and water loss by modulating the aperture of stomata located in the epidermis .
Stomatal opening is initiated by the activation of H + - ATPases in the guard-cell plasma membrane .
In contrast to regulation of H + - ATPase activity , little is known about the translocation of the guard cell H + - ATPase to the plasma membrane .
Here we describe the isolation of an Arabidopsis gene , PATROL1 , that controls the translocation of a major H + - ATPase , AHA1 , to the plasma membrane .
PATROL1 encodes a protein with a MUN domain , known to mediate synaptic priming in neuronal exocytosis in animals .
Environmental stimuli change the localization of plasma membrane-associated PATROL1 to an intracellular compartment .
Plasma membrane localization of AHA1 and stomatal opening require the association of PATROL1 with AHA1 .
Increased stomatal opening responses in plants overexpressing PATROL1 enhance the CO2 assimilation rate , promoting plant growth .

[1566] Hydroclimatic shifts driven by human water use for food and energy production

Hydrological change is a central part of global change .
Its drivers in the past need to be understood and quantified for accurate projection of disruptive future changes .
Here we analyse past hydro-climatic , agricultural and hydropower changes from twentieth century data for nine major Swedish drainage basins , and synthesize and compare these results with other regional and global assessments of hydrological change by irrigation and deforestation .
Cross-regional comparison shows similar increases of evapotranspiration by non-irrigated agriculture and hydropower as for irrigated agriculture .
In the Swedish basins , non-irrigated agriculture has also increased , whereas hydropower has decreased temporal runoff variability .
A global indication of the regional results is a net total increase of evapotranspiration that is larger than a proposed associated planetary boundary .
This emphasizes the need for climate and Earth system models to account for different human uses of water as anthropogenic drivers of hydro-climatic change .
The present study shows how these drivers and their effects can be distinguished and quantified for hydrological basins on different scales and in different world regions .
This should encourage further exploration of greater basin variety for better understanding of anthropogenic hydro-climatic change .

[1567] Mechanisms of transient nitric oxide and nitrous oxide production in a complex biofilm

Nitric oxide ( NO ) and nitrous oxide ( N2O ) are formed during N-cycling in complex microbial communities in response to fluctuating molecular oxygen ( O2 ) and nitrite ( NO2 - ) concentrations .
Until now , the formation of NO and N2O in microbial communities has been measured with low spatial and temporal resolution , which hampered elucidation of the turnover pathways and their regulation .
In this study , we combined microsensor measurements with metabolic modeling to investigate the functional response of a complex biofilm with nitrifying and denitrifying activity to variations in O2 and NO2 - .
In steady state , NO and N2O formation was detected if ammonium ( NH4 + ) was present under oxic conditions and if NO2 - was present under anoxic conditions .
Thus , NO and N2O are produced by ammonia-oxidizing bacteria ( AOB ) under oxic conditions and by heterotrophic denitrifiers under anoxic conditions .
NO and N2O formation by AOB occurred at fully oxic conditions if NO2 - concentrations were high .
Modeling showed that steady-state NO concentrations are controlled by the affinity of NO-consuming processes to NO .
Transient accumulation of NO and N2O occurred upon O2 removal from , or NO2 - addition to , the medium only if NH4 + was present under oxic conditions or if NO2 - was already present under anoxic conditions .
This showed that AOB and heterotrophic denitrifiers need to be metabolically active to respond with instantaneous NO and N2O production upon perturbations .
Transiently accumulated NO and N2O decreased rapidly after their formation , indicating a direct effect of NO on the metabolism .
By fitting model results to measurements , the kinetic relationships in the model were extended with dynamic parameters to predict transient NO release from perturbed ecosystems .

[1568] The 2010 Antarctic ozone hole : Observed reduction in ozone destruction by minor sudden stratospheric warmings

Satellite observations show that the 2010 Antarctic ozone hole is characterized by anomalously small amounts of photochemical ozone destruction ( 40-60 % less than the 2005-2009 average ) .
Observations from the MLS instrument show that this is mainly related to reduced photochemical ozone destruction between 20-25 km altitude .
Lower down between 15-20 km the atmospheric chemical composition and photochemical ozone destruction is unaffected .
The modified chemical composition and chemistry between 20-25 km altitude in 2010 is related to the occurrence of a mid-winter minor Antarctic Sudden Stratospheric Warming ( SSW ) .
The measurements indicate that the changes in chemical composition are related to downward motion of air masses rather than horizontal mixing , and affect stratospheric chemistry for several months .
Since 1979 , years with similar anomalously small amounts of ozone destruction are all characterized by either minor or major SSWs , illustrating that their presence has been a necessary pre-condition for reduced Antarctic stratospheric ozone destruction .

[1569] Mechanisms of direct inhibition of the respiratory sulfate-reduction pathway by ( per ) chlorate and nitrate

We investigated perchlorate ( ClO4 - ) and chlorate ( ClO3 - ) ( collectively ( per ) chlorate ) in comparison with nitrate as potential inhibitors of sulfide ( H2S ) production by mesophilic sulfate-reducing microorganisms ( SRMs ) .
We demonstrate the specificity and potency of ( per ) chlorate as direct SRM inhibitors in both pure cultures and undefined sulfidogenic communities .
We demonstrate that ( per ) chlorate and nitrate are antagonistic inhibitors and resistance is cross-inducible implying that these compounds share at least one common mechanism of resistance .
Using tagged-transposon pools we identified genes responsible for sensitivity and resistance in Desulfovibrio alaskensis G20 .
We found that mutants in Dde_2702 ( Rex ) , a repressor of the central sulfate-reduction pathway were resistant to both ( per ) chlorate and nitrate .
In general , Rex derepresses its regulon in response to increasing intracellular NADH : NAD + ratios .
In cells in which respiratory sulfate reduction is inhibited , NADH : NAD + ratios should increase leading to derepression of the sulfate-reduction pathway .
In support of this , in ( per ) chlorate or nitrate-stressed wild-type G20 we observed higher NADH : NAD + ratios , increased transcripts and increased peptide counts for genes in the core Rex regulon .
We conclude that one mode of ( per ) chlorate and nitrate toxicity is as direct inhibitors of the central sulfate-reduction pathway .
Our results demonstrate that ( per ) chlorate are more potent inhibitors than nitrate in both pure cultures and communities , implying that they represent an attractive alternative for controlling sulfidogenesis in industrial ecosystems .
Of these , perchlorate offers better application logistics because of its inhibitory potency , solubility , relative chemical stability , low affinity for mineral cations and high mobility in environmental systems .
The ISME Journal advance online publication , 18 November 2014 ; doi :10.1038 / ismej .2014.216

[1570] Copper-containing plastocyanin used for electron transport by an oceanic diatom

The supply of some essential metals to pelagic ecosystems is less than the demand , so many phytoplankton have slow rates of photosynthetic production and restricted growth .
The types and amounts of metals required by phytoplankton depends on their evolutionary history and on their adaptations to metal availability , which varies widely among ocean habitats .
Diatoms , for example , need considerably less iron ( Fe ) to grow than chlorophyll-b-containing taxa , and the oceanic species demand roughly one-tenth the amount of coastal strains .
Like Fe , copper ( Cu ) is scarce in the open sea , but notably higher concentrations of it are required for the growth of oceanic than of coastal isolates .
Here we report that the greater Cu requirement in an oceanic diatom , Thalassiosira oceanica , is entirely due to a single Cu-containing protein , plastocyanin , which -- until now -- was only known to exist in organisms with chlorophyll b and cyanobacteria .
Algae containing chlorophyll c , including the closely related coastal species T. weissflogii , are thought to lack plastocyanin and contain a functionally equivalent Fe-containing homologue , cytochrome c6 ( ref .
9 ) .
Copper deficiency in T. oceanica inhibits electron transport regardless of Fe status , implying a constitutive role for plastocyanin in the light reactions of photosynthesis in this species .
The results suggest that selection pressure imposed by Fe limitation has resulted in the use of a Cu protein for photosynthesis in an oceanic diatom .
This biochemical switch reduces the need for Fe and increases the requirement for Cu , which is relatively more abundant in the open sea .

[1571] Responding to rising sea levels in the Mekong Delta

Vietnamese communities in the Mekong Delta are faced with the substantial impacts of rising sea levels and salinity intrusion .
The construction of embankments and dykes has historically been the principal strategy of the Vietnamese government to mitigate the effects of salinity intrusion on agricultural production .
A predicted sea-level rise of 30 cm by the year 2050 is expected to accelerate salinity intrusion .
This study combines hydrologic , agronomic and behavioural assessments to identify effective adaptation strategies reliant on land-use change ( soft options ) and investments in water infrastructure ( hard options ) .
As these strategies are managed within different policy portfolios , the political discussion has polarized between choices of either soft or hard options .
This paper argues that an ensemble of hard and soft policies is likely to provide the most effective results for people 's livelihoods in the Mekong Delta .
The consequences of policy deliberations are likely to be felt beyond the Mekong Delta as levels of rice cultivation there also affect national and global food security .

[1572] Intra - and intergenerational discounting in the climate game

The difficulty of avoiding dangerous climate change arises from a tension between group and self-interest and is exacerbated by climate change 's intergenerational nature .
The present generation bears the costs of cooperation , whereas future generations accrue the benefits if present cooperation succeeds , or suffer if present cooperation fails .
Although temporal discounting has long been known to matter in making individual choices , the extent of temporal discounting is poorly understood in a group setting .
We represent the effect of both intra - and intergenerational discounting through a collective-risk group experiment framed around climate change .
Participants could choose to cooperate or to risk losing an additional endowment with a high probability .
The rewards of defection were immediate , whereas the rewards of cooperation were delayed by one day , delayed by seven weeks ( intragenerational discounting ) , or delayed by several decades and spread over a much larger number of potential beneficiaries ( intergenerational discounting ) .
We find that intergenerational discounting leads to a marked decrease in cooperation ; all groups failed to reach the collective target .
Intragenerational discounting was weaker by comparison .
Our results experimentally confirm that international negotiations to mitigate climate change are unlikely to succeed if individual countries ' short-term gains can arise only from defection .

[1573] Winter warming in West Antarctica caused by central tropical Pacific warming

The Pacific sector of Antarctica , including both the Antarctic Peninsula and continental West Antarctica , has experienced substantial warming in the past 30 years .
An increase in the circumpolar westerlies , owing in part to the decline in stratospheric ozone concentrations since the late 1970s , may account for warming trends in the peninsula region in austral summer and autumn .
The more widespread warming in continental West Antarctica ( Ellsworth Land and Marie Byrd Land ) occurs primarily in austral winter and spring , and remains unexplained .
Here we use observations of Antarctic surface temperature and global sea surface temperature , and atmospheric circulation data to show that recent warming in continental West Antarctica is linked to sea surface temperature changes in the tropical Pacific .
Over the past 30 years , anomalous sea surface temperatures in the central tropical Pacific have generated an atmospheric Rossby wave response that influences atmospheric circulation over the Amundsen Sea , causing increased advection of warm air to the Antarctic continent .
General circulation model experiments show that the central tropical Pacific is a critical region for producing the observed high latitude response .
We conclude that , by affecting the atmospheric circulation at high southern latitudes , increasing tropical sea surface temperatures may account for West Antarctic warming through most of the twentieth century .

[1574] Meridional shifts of the Atlantic intertropical convergence zone since the Last Glacial Maximum

The intertropical convergence zone is a near-equatorial band of intense rainfall and convection .
Over the modern Atlantic Ocean , its annual average position is approximately 5degrees N , and it is associated with low sea surface salinity and high surface temperatures .
This average position has varied since the Last Glacial Maximum , in response to changing climate boundary conditions .
The nature of this variation is less clear , with suggestions that the intertropical convergence zone migrated north-south away from the colder hemisphere or that it contracted and expanded symmetrically around its present position .
Here we use paired Mg/Ca and delta18O measurements of planktonic foraminifera for a transect of ocean sediment cores to reconstruct past changes in tropical surface ocean temperature and salinity in the Atlantic Ocean over the past 25,000 years .
We show that the low-salinity , high-temperature surface waters associated with the intertropical convergence zone migrated southward of their present position during the Last Glacial Maximum , when the Northern Hemisphere cooled , and northward during the warmer early Holocene , by about + / -7 degrees of latitude .
Our evidence suggests that the intertropical convergence zone moved latitudinally over the ocean , rather than expanding or contracting .
We conclude that the marine intertropical convergence zone has migrated significantly away from its present position owing to external climate forcing during the past 25,000 years .

[1575] Solar forcing of the Indian summer monsoon variability during the Allerod period

Rapid climatic shifts across the last glacial to Holocene transition are pervasive feature of the North Atlantic as well as low latitude proxy archives .
Our decadal to centennial scale record of summer monsoon proxy Globigerina bulloides from rapidly accumulating sediments from Hole 723A , Arabian Sea shows two distinct intervals of weak summer monsoon wind coinciding with cold periods within Allerod inerstadial of the North Atlantic named here as IACP-A1 and IACP-A2 and dated ( within dating uncertainties ) at 13.5 and 13.3 calibrated kilo years before the present ( cal kyr BP ) , respectively .
Spectral analysis of the Globigerina bulloides time series for the segment 13.6-13 .1 kyr ( Allerod period ) reveals a strong solar 208-year cycle also known as de Vries or Suess cycle , suggesting that the centennial scale variability in Indian summer monsoon winds during the Allerod inerstadial was driven by changes in the solar irradiance through stratospheric-tropospheric interactions .

[1576] Trends and seasonal cycles in the isotopic composition of nitrous oxide since 1940

The atmospheric nitrous oxide mixing ratio has increased by 20 % since 1750 ( ref . )
.
Given that nitrous oxide is both a long-lived greenhouse gas and a stratospheric ozone-depleting substance , this increase is of global concern .
However , the magnitude and geographic distribution of nitrous oxide sources , and how they have changed over time , is uncertain .
A key unknown is the influence of the stratospheric circulation , which brings air depleted in nitrous oxide to the surface .
Here , we report the oxygen and intramolecular nitrogen isotopic compositions of nitrous oxide in firn air samples from Antarctica and archived air samples from Cape Grim , Tasmania , spanning 1940-2005 .
We detect seasonal cycles in the isotopic composition of nitrous oxide at Cape Grim .
The phases and amplitudes of these seasonal cycles allow us to distinguish between the influence of the stratospheric sink and the oceanic source at this site , demonstrating that isotope measurements can help in the attribution and quantification of surface sources in general .
Large interannual variations and long-term decreasing trends in isotope composition are also apparent .
These long-term trends allow us to distinguish between natural and anthropogenic sources of nitrous oxide , and confirm that the rise in atmospheric nitrous oxide levels is largely the result of an increased reliance on nitrogen-based fertilizers .

[1577] The unaccounted yet abundant nitrous oxide-reducing microbial community : a potential nitrous oxide sink

Nitrous oxide ( N2O ) is a major radiative forcing and stratospheric ozone-depleting gas emitted from terrestrial and aquatic ecosystems .
It can be transformed to nitrogen gas ( N2 ) by bacteria and archaea harboring the N2O reductase ( N2OR ) , which is the only known N2O sink in the biosphere .
Despite its crucial role in mitigating N2O emissions , knowledge of the N2OR in the environment remains limited .
Here , we report a comprehensive phylogenetic analysis of the nosZ gene coding the N2OR in genomes retrieved from public databases .
The resulting phylogeny revealed two distinct clades of nosZ , with one unaccounted for in studies investigating N2O-reducing communities .
Examination of N2OR structural elements not considered in the phylogeny revealed that the two clades differ in their signal peptides , indicating differences in the translocation pathway of the N2OR across the membrane .
Sequencing of environmental clones of the previously undetected nosZ lineage in various environments showed that it is widespread and diverse .
Using quantitative PCR , we demonstrate that this clade was most often at least as abundant as the other , thereby more than doubling the known extent of the overall N2O-reducing community in the environment .
Furthermore , we observed that the relative abundance of nosZ from either clade varied among habitat types and environmental conditions .
Our results indicate a physiological dichotomy in the diversity of N2O-reducing microorganisms , which might be of importance for understanding the relationship between the diversity of N2O-reducing microorganisms and N2O reduction in different ecosystems .

[1578] Mitigation of nitrous oxide emissions from soils by Bradyrhizobium japonicum inoculation

Nitrous oxide ( N2O ) is a greenhouse gas that is also capable of destroying the ozone layer .
Agricultural soil is the largest source of N2O ( ref . )
.
Soybean is a globally important leguminous crop , and hosts symbiotic nitrogen-fixing soil bacteria ( rhizobia ) that can also produce N2O ( ref . )
.
In agricultural soil , N2O is emitted from fertilizer and soil nitrogen .
In soybean ecosystems , N2O is also emitted from the degradation of the root nodules .
Organic nitrogen inside the nodules is mineralized to NH4 + , followed by nitrification and denitrification that produce N2O .
N2O is then emitted into the atmosphere or is further reduced to N2 by N2O reductase ( N2OR ) , which is encoded by the nosZ gene .
Pure culture and vermiculite pot experiments showed lower N2O emission by nosZ + strains and nosZ + + strains ( mutants with increased N2OR activity ) of Bradyrhizobium japonicum than by nosZ - strains .
A pot experiment using soil confirmed these results .
Although enhancing N2OR activity has been suggested as a N2O mitigation option , this has never been tested in the field .
Here , we show that post-harvest N2O emission from soybean ecosystems due to degradation of nodules can be mitigated by inoculation of nosZ + and non-genetically modified organism nosZ + + strains of B. japonicum at a field scale .

[1579] Future projections for Mexican faunas under global climate change scenarios

Global climates are changing rapidly , with unexpected consequences .
Because elements of biodiversity respond intimately to climate as an important driving force of distributional limitation , distributional shifts and biodiversity losses are expected .
Nevertheless , in spite of modelling efforts focused on single species or entire ecosystems , a few preliminary surveys of fauna-wide effects , and evidence of climate change-mediated shifts in several species , the likely effects of climate change on species ' distributions remain little known , and fauna-wide or community-level effects are almost completely unexplored .
Here , using a genetic algorithm and museum specimen occurrence data , we develop ecological niche models for 1,870 species occurring in Mexico and project them onto two climate surfaces modelled for 2055 .
Although extinctions and drastic range reductions are predicted to be relatively few , species turnover in some local communities is predicted to be high ( > 40 % of species ) , suggesting that severe ecological perturbations may result .

[1580] Persistent inflow of warm water onto the central Amundsen shelf

The West Antarctic Ice Sheet contains enough ice to raise global sea level by several metres and , because it is grounded mainly below sea level , it is sensitive to ocean warming .
Accelerated thinning of glaciers that discharge into the Amundsen Sea over the past decades has been proposed to be related to the presence of warmer waters beneath the ice shelves .
Three deep troughs crosscut the continental shelf of the Amundsen Sea , forming passages through which warm ocean waters can access the ice shelves , but oceanographic data has been limited .
Here we present direct measurements from an ocean mooring and ship transect of the temperatures , salinities and velocities from one of these troughs in the central Amundsen Sea during the year 2010 .
The data show persistent inflow towards the ice shelf of relatively warm and salty water at the bottom of the trough throughout the year , and outflow of colder water above .
Superposed on this background flow are barotropic current fluctuations that do not contribute significantly to the overall transport .
In contrast to numerical models , which show seasonal inflow changes in response to regional winds , we find that warm water is supplied to the Central Amundsen Shelf without strong seasonal variability .

[1581] Autophagy induction enhances TDP43 turnover and survival in neuronal ALS models

Amyotrophic lateral sclerosis ( ALS ) and frontotemporal dementia ( FTD ) have distinct clinical features but a common pathology -- cytoplasmic inclusions rich in transactive response element DNA-binding protein of 43 kDa ( TDP43 ) .
Rare TDP43 mutations cause ALS or FTD , but abnormal TDP43 levels and localization may cause disease even if TDP43 lacks a mutation .
Here we show that individual neurons vary in their ability to clear TDP43 and are exquisitely sensitive to TDP43 levels .
To measure TDP43 clearance , we developed and validated a single-cell optical method that overcomes the confounding effects of aggregation and toxicity and discovered that pathogenic mutations shorten TDP43 half-life .
New compounds that stimulate autophagy improved TDP43 clearance and localization and enhanced survival in primary murine neurons and in human stem cell-derived neurons and astrocytes harboring mutant TDP43 .
These findings indicate that the levels and localization of TDP43 critically determine neurotoxicity and show that autophagy induction mitigates neurodegeneration by acting directly on TDP43 clearance .

[1582] Interactive effects of ozone depletion and vertical mixing on photosynthesis of Antarctic phytoplankton

Photosynthesis of Antarctic phytoplankton is inhibited by ambient ultraviolet ( UV ) radiation during incubations , and the inhibition is worse in regions beneath the Antarctic ozone ` hole ' .
But to evaluate such effects , experimental results on , and existing models of , photosynthesis can not be extrapolated directly to the conditions of the open waters of the Antarctic because vertical mixing of phytoplankton alters UV exposure and has significant effects on the integrated inhibition through the water column , , .
Here we present a model of UV-influenced photosynthesis in the presence of vertical mixing , which we constrain with comprehensive measurements from the Weddell-Scotia Confluence during the austral spring of 1993 .
Our calculations of photosynthesis integrated through the water column ( denoted PT ) show that photosynthesis is strongly inhibited by near-surface UV radiation .
This inhibition can be either enhanced or decreased by vertical mixing , depending on the depth of the mixed layer .
Predicted inhibition is most severe when mixing is rapid , extending to the lower part of the photic zone .
Our analysis reveals that an abrupt 50 % reduction in stratospheric ozone could , in the worst case , lower PT by as much as 8.5 % .
However , stronger influences on inhibition can come from realistic changes in vertical mixing ( maximum effect on PT of about + / -37 % ) , measured differences in the sensitivity of phytoplankton to UV radiation ( + / -46 % ) and cloudiness ( + / -15 % ) .

[1583] Highly efficient and autocatalytic H2O dissociation for CO2 reduction into formic acid with zinc

Artificial photosynthesis , specifically H2O dissociation for CO2 reduction with solar energy , is regarded as one of the most promising methods for sustainable energy and utilisation of environmental resources .
However , a highly efficient conversion still remains extremely challenging .
The hydrogenation of CO2 is regarded as the most commercially feasible method , but this method requires either exotic catalysts or high-purity hydrogen and hydrogen storage , which are regarded as an energy-intensive process .
Here we report a highly efficient method of H2O dissociation for reducing CO2 into chemicals with Zn powder that produces formic acid with a high yield of approximately 80 % , and this reaction is revealed for the first time as an autocatalytic process in which an active intermediate , ZnH - complex , serves as the active hydrogen .
The proposed process can assist in developing a new concept for improving artificial photosynthetic efficiency by coupling geochemistry , specifically the metal-based reduction of H2O and CO2 , with solar-driven thermochemistry for reducing metal oxide into metal .

[1584] Cessation of deep convection in the open Southern Ocean under anthropogenic climate change

In 1974 , newly available satellite observations unveiled the presence of a giant ice-free area , or polynya , within the Antarctic ice pack of the Weddell Sea , which persisted during the two following winters .
Subsequent research showed that deep convective overturning had opened a conduit between the surface and the abyssal ocean , and had maintained the polynya through the massive release of heat from the deep sea .
Although the polynya has aroused continued interest , the presence of a fresh surface layer has prevented the recurrence of deep convection there since 1976 , and it is now largely viewed as a naturally rare event .
Here , we present a new analysis of historical observations and model simulations that suggest deep convection in the Weddell Sea was more active in the past , and has been weakened by anthropogenic forcing .
The observations show that surface freshening of the southern polar ocean since the 1950s has considerably enhanced the salinity stratification .
Meanwhile , among the present generation of global climate models , deep convection is common in the Southern Ocean under pre-industrial conditions , but weakens and ceases under a climate change scenario owing to surface freshening .
A decline of open-ocean convection would reduce the production rate of Antarctic Bottom Waters , with important implications for ocean heat and carbon storage , and may have played a role in recent Antarctic climate change .

[1585] Potential impacts of a warming climate on water availability in snow-dominated regions

All currently available climate models predict a near-surface warming trend under the influence of rising levels of greenhouse gases in the atmosphere .
In addition to the direct effects on climate -- for example , on the frequency of heatwaves -- this increase in surface temperatures has important consequences for the hydrological cycle , particularly in regions where water supply is currently dominated by melting snow or ice .
In a warmer world , less winter precipitation falls as snow and the melting of winter snow occurs earlier in spring .
Even without any changes in precipitation intensity , both of these effects lead to a shift in peak river runoff to winter and early spring , away from summer and autumn when demand is highest .
Where storage capacities are not sufficient , much of the winter runoff will immediately be lost to the oceans .
With more than one-sixth of the Earth 's population relying on glaciers and seasonal snow packs for their water supply , the consequences of these hydrological changes for future water availability -- predicted with high confidence and already diagnosed in some regions -- are likely to be severe .

[1586] Global distribution patterns of distinct clades of the photosynthetic picoeukaryote Ostreococcus

Ostreococcus is a marine picophytoeukaryote for which culture studies indicate there are ` high-light ' and ` low-light ' adapted ecotypes .
Representatives of these ecotypes fall within two to three 18S ribosomal DNA ( rDNA ) clades for the former and one for the latter .
However , clade distributions and relationships to this form of niche partitioning are unknown in nature .
We developed two quantitative PCR primer-probe sets and enumerated the proposed ecotypes in the Pacific Ocean as well as the subtropical and tropical North Atlantic .
Statistical differences in factors such as salinity , temperature and NO3 indicated the ecophysiological parameters behind clade distributions are more complex than irradiance alone .
Clade OII , containing the putatively low-light adapted strains , was detected at warm oligotrophic sites .
In contrast , Clade OI , containing high-light adapted strains , was present in cooler mesotrophic and coastal waters .
Maximal OI abundance ( 19 555 + / -37 18S rDNA copies per ml ) was detected in mesotrophic waters at 40 m depth , approaching the nutricline .
OII was often more abundant at the deep chlorophyll maximum , when nutrient concentrations were significantly higher than at the surface ( stratified euphotic zone waters ) .
However , in mixed euphotic-zone water columns , relatively high numbers ( for example , 891 + / -107 18S rDNA copies per ml , Sargasso Sea , springtime ) were detected at the surface .
Both Clades OI and OII were found at multiple euphotic zone depths , but co-occurrence at the same geographical location appeared rare and was detected only in continental slope waters .
In situ growth rate estimates using these primer-probes and better comprehension of physiology will enhance ecological understanding of Ostreococcus Clades OII and OI which appear to be oceanic and coastal clades , respectively .

[1587] Formation of supercontinents linked to increases in atmospheric oxygen

Atmospheric oxygen concentrations in the Earth 's atmosphere rose from negligible levels in the Archaean Era to about 21 % in the present day .
This increase is thought to have occurred in six steps , 2.65 , 2.45 , 1.8 , 0.6 , 0.3 and 0.04 billion years ago , with a possible seventh event identified at 1.2 billion years ago .
Here we show that the timing of these steps correlates with the amalgamation of Earth 's land masses into supercontinents .
We suggest that the continent-continent collisions required to form supercontinents produced supermountains .
In our scenario , these supermountains eroded quickly and released large amounts of nutrients such as iron and phosphorus into the oceans , leading to an explosion of algae and cyanobacteria , and thus a marked increase in photosynthesis , and the photosynthetic production of O2 .
Enhanced sedimentation during these periods promoted the burial of a high fraction of organic carbon and pyrite , thus preventing their reaction with free oxygen , and leading to sustained increases in atmospheric oxygen .

[1588] Biting disrupts integration to spur skull evolution in eels

The demand that anatomical structures work together to perform biological functions is thought to impose strong limits on morphological evolution .
Breakthroughs in diversification can occur , however , when functional integration among structures is relaxed .
Although such transitions are expected to generate variation in morphological diversification across the tree of life , empirical tests of this hypothesis are rare .
Here we show that transitions between suction-based and biting modes of prey capture , which require different degrees of coordination among skull components , are associated with shifts in the pattern of skull diversification in eels ( Anguilliformes ) .
Biting eels have experienced greater independence of the jaws , hyoid and operculum during evolution and exhibit more varied morphologies than closely related suction feeders , and this pattern reflects the weakened functional integration among skull components required for biting .
Our results suggest that behavioural transitions can change the evolutionary potential of the vertebrate skeleton by altering functional relationships among structures .

[1589] Methane fluxes show consistent temperature dependence across microbial to ecosystem scales

Methane ( CH4 ) is an important greenhouse gas because it has 25 times the global warming potential of carbon dioxide ( CO2 ) by mass over a century .
Recent calculations suggest that atmospheric CH4 emissions have been responsible for approximately 20 % of Earth 's warming since pre-industrial times .
Understanding how CH4 emissions from ecosystems will respond to expected increases in global temperature is therefore fundamental to predicting whether the carbon cycle will mitigate or accelerate climate change .
Methanogenesis is the terminal step in the remineralization of organic matter and is carried out by strictly anaerobic Archaea .
Like most other forms of metabolism , methanogenesis is temperature-dependent .
However , it is not yet known how this physiological response combines with other biotic processes ( for example , methanotrophy , substrate supply , microbial community composition ) and abiotic processes ( for example , water-table depth ) to determine the temperature dependence of ecosystem-level CH4 emissions .
It is also not known whether CH4 emissions at the ecosystem level have a fundamentally different temperature dependence than other key fluxes in the carbon cycle , such as photosynthesis and respiration .
Here we use meta-analyses to show that seasonal variations in CH4 emissions from a wide range of ecosystems exhibit an average temperature dependence similar to that of CH4 production derived from pure cultures of methanogens and anaerobic microbial communities .
This average temperature dependence ( 0.96 electron volts ( eV ) ) , which corresponds to a 57-fold increase between 0 and 30degreesC , is considerably higher than previously observed for respiration ( approximately 0.65 eV ) and photosynthesis ( approximately 0.3 eV ) .
As a result , we show that both the emission of CH4 and the ratio of CH4 to CO2 emissions increase markedly with seasonal increases in temperature .
Our findings suggest that global warming may have a large impact on the relative contributions of CO2 and CH4 to total greenhouse gas emissions from aquatic ecosystems , terrestrial wetlands and rice paddies .

[1590] Worldwide acceleration of mountain erosion under a cooling climate

Climate influences the erosion processes acting at the Earth 's surface .
However , the effect of cooling during the Late Cenozoic era , including the onset of Pliocene-Pleistocene Northern Hemisphere glaciation ( about two to three million years ago ) , on global erosion rates remains unclear .
The uncertainty arises mainly from a lack of consensus on the use of the sedimentary record as a proxy for erosion and the difficulty of isolating the respective contributions of tectonics and climate to erosion .
Here we compile 18,000 bedrock thermochronometric ages from around the world and use a formal inversion procedure to estimate temporal and spatial variations in erosion rates .
This allows for the quantification of erosion for the source areas that ultimately produce the sediment record on a timescale of millions of years .
We find that mountain erosion rates have increased since about six million years ago and most rapidly since two million years ago .
The increase of erosion rates is observed at all latitudes , but is most pronounced in glaciated mountain ranges , indicating that glacial processes played an important part .
Because mountains represent a considerable fraction of the global production of sediments , our results imply an increase in sediment flux at a global scale that coincides closely with enhanced cooling during the Pliocene and Pleistocene epochs .

[1591] Biological control of terrestrial silica cycling and export fluxes to watersheds

Silicon has a crucial role in many biogeochemical processes -- for example , as a nutrient for marine and terrestrial biota , in buffering soil acidification and in the regulation of atmospheric carbon dioxide .
Traditionally , silica fluxes to soil solutions and stream waters are thought to be controlled by the weathering and subsequent dissolution of silicate minerals .
Rates of mineral dissolution can be enhanced by biological processes .
But plants also take up considerable quantities of silica from soil solution , which is recycled into the soil from falling litter in a separate soil-plant silica cycle that can be significant in comparison with weathering input and hydrologic output .
Here we analyse soil water in basaltic soils across the Hawaiian islands to assess the relative contributions of weathering and biogenic silica cycling by using the distinct signatures of the two processes in germanium/silicon ratios .
Our data imply that most of the silica released to Hawaiian stream water has passed through the biogenic silica pool , whereas direct mineral-water reactions account for a smaller fraction of the stream silica flux .
We expect that other systems exhibiting strong Si depletion of the mineral soils and/or high Si uptake rates by biomass will also have strong biological control on silica cycling and export .

[1592] Accelerating uplift in the North Atlantic region as an indicator of ice loss

Vertical motions of the rocky margins of Greenland and Antarctica respond to mass changes of their respective ice sheets .
However , these motions can be obscured by episodes of glacial advance or retreat that occurred hundreds to thousands of years ago , which trigger a delayed response because of viscous flow in the underlying mantle .
Here we present high-precision global positioning system ( GPS ) data that describe the vertical motion of the rocky margins of Greenland , Iceland and Svalbard .
We focus on vertical accelerations rather than velocities to avoid the confounding effects of past events .
Our data show an acceleration of uplift over the past decade that represents an essentially instantaneous , elastic response to the recent accelerated melting of ice throughout the North Atlantic region .
Our comparison of the GPS data to models for glacial isostatic adjustment suggests that some parts of western coastal Greenland were experiencing accelerated melting of coastal ice by the late 1990s .
Using a simple elastic model , we estimate that western Greenland 's ice loss is accelerating at an average rate of 8.7 + / -3.5 Gt yr-2 , whereas the rate for southeastern Greenland -- based on limited data -- falls at 12.5 + / -5.5 Gt yr-2 .

[1593] Oxygen content of transmembrane proteins over macroevolutionary time scales

We observe that the time of appearance of cellular compartmentalization correlates with atmospheric oxygen concentration .
To explore this correlation , we predict and characterize the topology of all transmembrane proteins in 19 taxa and correlate differences in topology with historical atmospheric oxygen concentrations .
Here we show that transmembrane proteins , individually and as a group , were probably selectively excluding oxygen in ancient ancestral taxa , and that this constraint decreased over time when atmospheric oxygen levels rose .
As this constraint decreased , the size and number of communication-related transmembrane proteins increased .
We suggest the hypothesis that atmospheric oxygen concentrations affected the timing of the evolution of cellular compartmentalization by constraining the size of domains necessary for communication across membranes .

[1594] Vulnerability of US and European electricity supply to climate change

In the United States and Europe , at present 91 % and 78 % ( ref . )
of the total electricity is produced by thermoelectric ( nuclear and fossil-fuelled ) power plants , which directly depend on the availability and temperature of water resources for cooling .
During recent warm , dry summers several thermoelectric power plants in Europe and the southeastern United States were forced to reduce production owing to cooling-water scarcity .
Here we show that thermoelectric power in Europe and the United States is vulnerable to climate change owing to the combined impacts of lower summer river flows and higher river water temperatures .
Using a physically based hydrological and water temperature modelling framework in combination with an electricity production model , we show a summer average decrease in capacity of power plants of 6.3-19 % in Europe and 4.4-16 % in the United States depending on cooling system type and climate scenario for 2031-2060 .
In addition , probabilities of extreme ( > 90 % ) reductions in thermoelectric power production will on average increase by a factor of three .
Considering the increase in future electricity demand , there is a strong need for improved climate adaptation strategies in the thermoelectric power sector to assure futureenergy security .

[1595] Silicon-isotope composition of diatoms as an indicator of past oceanic change

Silicon is essential for the growth of diatoms , a group of phytoplankton with opal ( amorphous hydrated silica ) shells .
Diatoms largely control the cycling of silicon in the ocean and , conversely , diatom silica production rates can be limited by the availability of silicic acid .
Diatoms are biogeochemically important in that they account for an estimated 75 % of the primary production occurring in coastal and nutrient-replete waters , rising to more than 90 % during ice-edge blooms such as occur in the Ross Sea , off Antarctica .
There are few means by which to reconstruct the history of diatom productivity and marine silicon cycling , and thus to explore the potential contribution of diatoms to past oceanic biogeochemistry or climate .
Indices based on the accumulation of sedimentary opal are often biased by the winnowing and focusing of sediments and by opal dissolution .
Normalization of opal accumulation records using particle-reactive natural radionuclides may correct for sediment redistribution artefacts and the dissolution of opal within sediments , , but not for opal dissolution before it arrives at the sea floor .
Half of the opal produced in the euphotic zone may dissolve before sinking to a depth of 200 m ( ref .
1 ) , constituting a potentially large bias to both normalized and uncorrected records of opal accumulation .
Here we exploit the potential that variations in the ratio of 30Si to 28Si in sedimentary opal may provide information on past silicon cycling that is unbiased by opal dissolution .
Our silicon stable-isotope measurements suggest that the percentage utilization of silicic acid by diatoms in the Southern Ocean during the last glacial period was strongly diminished relative to the present interglacial .

[1596] A multiphasic characterization of the impact of the herbicide acetochlor on freshwater bacterial communities

Acetochlor is the third most frequently detected herbicide in natural waters ; however , it is unknown if exposure to environmentally relevant concentrations of acetochlor will impact bacterial community structure and function .
This study examined the impact of acetochlor on freshwater heterotrophic bacteria number , and community structure and function using direct counting , community level physiological profiling ( CLPP ) and denaturing gradient gel electrophoresis ( DGGE ) analysis .
Acetochlor concentration did not appear to correlate with the number of total ( P = 0.69 ) and viable ( P = 0.80 ) bacteria , even at concentrations up to 500 mug l-1 .
However , CLPP indicated that acetochlor increased functional diversity as shown by ( i ) an increase in the number of carbon sources utilized by the microbial community , relative to nonexposed controls and ( ii ) increased functional evenness within the heterotrophic bacterial community .
Conversely , DGGE fingerprints suggested that exposure to acetochlor generally decreased the community complexity , as the average number of DGGE bands in most treatments was significantly less than in the control treatment .
Cluster analysis of DGGE fingerprints revealed three distinct , dose-dependent clusters ( i ) communities exposed to 0 , 1 and 5 mug l-1 ; ( ii ) 50 and 100 mug l-1 and ( iii ) 500 mug l-1 , indicating a relationship between acetochlor concentration bacterial community changes .
This study indicated that while exposure to environmentally relevant concentrations of acetochlor resulted in no significant impact to the number of freshwater bacteria , impacts to the function and structure of the community were revealed by adopting a multiphasic approach .

[1597] Siple Dome ice reveals two modes of millennial CO2 change during the last ice age

Reconstruction of atmospheric CO2 during times of past abrupt climate change may help us better understand climate-carbon cycle feedbacks .
Previous ice core studies reveal simultaneous increases in atmospheric CO2 and Antarctic temperature during times when Greenland and the northern hemisphere experienced very long , cold stadial conditions during the last ice age .
Whether this relationship extends to all of the numerous stadial events in the Greenland ice core record has not been clear .
Here we present a high-resolution record of atmospheric CO2 from the Siple Dome ice core , Antarctica for part of the last ice age .
We find that CO2 does not significantly change during the short Greenlandic stadial events , implying that the climate system perturbation that produced the short stadials was not strong enough to substantially alter the carbon cycle .

[1598] Changing boreal methane sources and constant biomass burning during the last termination

Past atmospheric methane concentrations show strong fluctuations in parallel to rapid glacial climate changes in the Northern Hemisphere superimposed on a glacial-interglacial doubling of methane concentrations .
The processes driving the observed fluctuations remain uncertain but can be constrained using methane isotopic information from ice cores .
Here we present an ice core record of carbon isotopic ratios in methane over the entire last glacial-interglacial transition .
Our data show that the carbon in atmospheric methane was isotopically much heavier in cold climate periods .
With the help of a box model constrained by the present data and previously published results , we are able to estimate the magnitude of past individual methane emission sources and the atmospheric lifetime of methane .
We find that methane emissions due to biomass burning were about 45 Tg methane per year , and that these remained roughly constant throughout the glacial termination .
The atmospheric lifetime of methane is reduced during cold climate periods .
We also show that boreal wetlands are an important source of methane during warm events , but their methane emissions are essentially shut down during cold climate conditions .

[1599] Slip rate variations on normal faults during glacial-interglacial changes in surface loads

Geologic and palaeoseismological data document a marked increase in the slip rates of the Wasatch fault and three adjacent normal faults in the Basin and Range Province during the Late Pleistocene/Early Holocene epochs .
The cause of this synchronous acceleration of fault slip and the subsequent clustering of earthquakes during the Holocene has remained enigmatic , although it has been suggested that the coincidence between the acceleration of slip and the shrinkage of Lake Bonneville after the Last Glacial Maximum may indicate a causal relationship .
Here we use finite-element models of a discrete normal fault within a rheologically layered lithosphere to evaluate the relative importance of two competing processes that affect fault slip : postglacial unloading ( the removal of mass ) , which decreases the slip rate , and lithospheric rebound , which promotes faster slip .
We show that lithospheric rebound caused by regression of Lake Bonneville and deglaciation of adjacent mountain ranges provides a feasible mechanism for the high Holocene rates of faulting in the Wasatch region .
Our analysis implies that climate-controlled changes in loads applied to Earth 's surface may exert a fundamental control on the slip history of individual normal faults .

[1600] Short-term modulation of Indian summer monsoon rainfall by West Asian dust

The Indian summer monsoon is influenced by numerous factors , including aerosol-induced changes to clouds , surface and atmospheric heating , and atmospheric circulation .
Most previous studies assessing the effect of aerosols on monsoon rainfall have focussed on the local impact of aerosols on precipitation on monthly to seasonal timescales .
Here , we show that desert dust aerosol levels over the Arabian Sea , West Asia and the Arabian Peninsula are positively correlated with the intensity of the Indian summer monsoon , using satellite data and models ; a lead-lag analysis indicates that dust and precipitation vary in concert over timescales of about a week .
Our analysis of global climate model simulations indicates that by heating the atmosphere , dust aerosols induce large-scale convergence over North Africa and the Arabian Peninsula , increasing the flow of moisture over India within a week .
According to these simulations , dust-induced heating of the atmosphere over North Africa and West Asia rapidly modulates monsoon rainfall over central India .

[1601] Loss of flight promotes beetle diversification

The evolution of flight is a key innovation that may enable the extreme diversification of insects .
Nonetheless , many species-rich , winged insect groups contain flightless lineages .
The loss of flight may promote allopatric differentiation due to limited dispersal power and may result in a high speciation rate in the flightless lineage .
Here we show that loss of flight accelerates allopatric speciation using carrion beetles ( Coleoptera : Silphidae ) .
We demonstrate that flightless species retain higher genetic differentiation among populations and comprise a higher number of genetically distinct lineages than flight-capable species , and that the speciation rate with the flightless state is twice that with the flight-capable state .
Moreover , a meta-analysis of 51 beetle species from 15 families reveals higher genetic differentiation among populations in flightless compared with flight-capable species .
In beetles , which represent almost one-fourth of all described species , repeated evolution of flightlessness may have contributed to their steady diversification since the Mesozoic era .

[1602] Ecological niche models reveal the importance of climate variability for the biogeography of protosteloid amoebae

Habitat availability and environmental preferences of species are among the most important factors in determining the success of dispersal processes and therefore in shaping the distribution of protists .
We explored the differences in fundamental niches and potential distributions of an ecological guild of slime moulds -- protosteloid amoebae -- in the Iberian Peninsula .
A large set of samples collected in a north-east to south-west transect of approximately 1000 km along the peninsula was used to test the hypothesis that , together with the existence of suitable microhabitats , climate conditions may determine the probability of survival of species .
Although protosteloid amoebae share similar morphologies and life history strategies , canonical correspondence analyses showed that they have varied ecological optima , and that climate conditions have an important effect in niche differentiation .
Maxent environmental niche models provided consistent predictions of the probability of presence of the species based on climate data , and they were used to generate maps of potential distribution in an ` everything is everywhere ' scenario .
The most important climatic factors were , in both analyses , variables that measure changes in conditions throughout the year , confirming that the alternation of fruiting bodies , cysts and amoeboid stages in the life cycles of protosteloid amoebae constitutes an advantage for surviving in a changing environment .
Microhabitat affinity seems to be influenced by climatic conditions , which suggests that the micro-environment may vary at a local scale and change together with the external climate at a larger scale .

[1603] Long-term decline of global atmospheric ethane concentrations and implications for methane

After methane , ethane is the most abundant hydrocarbon in the remote atmosphere .
It is a precursor to tropospheric ozone and it influences the atmosphere 's oxidative capacity through its reaction with the hydroxyl radical , ethane 's primary atmospheric sink .
Here we present the longest continuous record of global atmospheric ethane levels .
We show that global ethane emission rates decreased from 14.3 to 11.3 teragrams per year , or by 21 per cent , from 1984 to 2010 .
We attribute this to decreasing fugitive emissions from ethane 's fossil fuel source -- most probably decreased venting and flaring of natural gas in oil fields -- rather than a decline in its other major sources , biofuel use and biomass burning .
Ethane 's major emission sources are shared with methane , and recent studies have disagreed on whether reduced fossil fuel or microbial emissions have caused methane 's atmospheric growth rate to slow .
Our findings suggest that reduced fugitive fossil fuel emissions account for at least 10-21 teragrams per year ( 30-70 per cent ) of the decrease in methane 's global emissions , significantly contributing to methane 's slowing atmospheric growth rate since the mid-1980s .

[1604] Evading the strength-ductility trade-off dilemma in steel through gradient hierarchical nanotwins

The strength-ductility trade-off has been a long-standing dilemma in materials science .
This has limited the potential of many structural materials , steels in particular .
Here we report a way of enhancing the strength of twinning-induced plasticity steel at no ductility trade-off .
After applying torsion to cylindrical twinning-induced plasticity steel samples to generate a gradient nanotwinned structure along the radial direction , we find that the yielding strength of the material can be doubled at no reduction in ductility .
It is shown that this evasion of strength-ductility trade-off is due to the formation of a gradient hierarchical nanotwinned structure during pre-torsion and subsequent tensile deformation .
A series of finite element simulations based on crystal plasticity are performed to understand why the gradient twin structure can cause strengthening and ductility retention , and how sequential torsion and tension lead to the observed hierarchical nanotwinned structure through activation of different twinning systems .

[1605] GOLPH3 modulates mTOR signalling and rapamycin sensitivity in cancer

Genome-wide copy number analyses of human cancers identified a frequent 5p13 amplification in several solid tumour types , including lung ( 56 % ) , ovarian ( 38 % ) , breast ( 32 % ) , prostate ( 37 % ) and melanoma ( 32 % ) .
Here , using integrative analysis of a genomic profile of the region , we identify a Golgi protein , GOLPH3 , as a candidate targeted for amplification .
Gain - and loss-of-function studies in vitro and in vivo validated GOLPH3 as a potent oncogene .
Physically , GOLPH3 localizes to the trans-Golgi network and interacts with components of the retromer complex , which in yeast has been linked to target of rapamycin ( TOR ) signalling .
Mechanistically , GOLPH3 regulates cell size , enhances growth-factor-induced mTOR ( also known as FRAP1 ) signalling in human cancer cells , and alters the response to an mTOR inhibitor in vivo .
Thus , genomic and genetic , biological , functional and biochemical data in yeast and humans establishes GOLPH3 as a new oncogene that is commonly targeted for amplification in human cancer , and is capable of modulating the response to rapamycin , a cancer drug in clinical use .

[1606] Coral reefs : Corals ' adaptive response to climate change

The long-term response of coral reefs to climate change depends on the ability of reef-building coral symbioses to adapt or acclimatize to warmer temperatures , but there has been no direct evidence that such a response can occur .
Here we show that corals containing unusual algal symbionts that are thermally tolerant and commonly associated with high-temperature environments are much more abundant on reefs that have been severely affected by recent climate change .
This adaptive shift in symbiont communities indicates that these devastated reefs could be more resistant to future thermal stress , resulting in significantly longer extinction times for surviving corals than had been previously assumed .

[1607] Widespread amphibian extinctions from epidemic disease driven by global warming

As the Earth warms , many species are likely to disappear , often because of changing disease dynamics .
Here we show that a recent mass extinction associated with pathogen outbreaks is tied to global warming .
Seventeen years ago , in the mountains of Costa Rica , the Monteverde harlequin frog ( Atelopus sp . )
vanished along with the golden toad ( Bufo periglenes ) .
An estimated 67 % of the 110 or so species of Atelopus , which are endemic to the American tropics , have met the same fate , and a pathogenic chytrid fungus ( Batrachochytrium dendrobatidis ) is implicated .
Analysing the timing of losses in relation to changes in sea surface and air temperatures , we conclude with ` very high confidence ' ( > 99 % , following the Intergovernmental Panel on Climate Change , IPCC ) that large-scale warming is a key factor in the disappearances .
We propose that temperatures at many highland localities are shifting towards the growth optimum of Batrachochytrium , thus encouraging outbreaks .
With climate change promoting infectious disease and eroding biodiversity , the urgency of reducing greenhouse-gas concentrations is now undeniable .

[1608] Caribbean-wide decline in carbonate production threatens coral reef growth

Global-scale deteriorations in coral reef health have caused major shifts in species composition .
One projected consequence is a lowering of reef carbonate production rates , potentially impairing reef growth , compromising ecosystem functionality and ultimately leading to net reef erosion .
Here , using measures of gross and net carbonate production and erosion from 19 Caribbean reefs , we show that contemporary carbonate production rates are now substantially below historical ( mid - to late-Holocene ) values .
On average , current production rates are reduced by at least 50 % , and 37 % of surveyed sites were net erosional .
Calculated accretion rates ( mm year-1 ) for shallow fore-reef habitats are also close to an order of magnitude lower than Holocene averages .
A live coral cover threshold of ~ 10 % appears critical to maintaining positive production states .
Below this ecological threshold carbonate budgets typically become net negative and threaten reef accretion .
Collectively , these data suggest that recent ecological declines are now suppressing Caribbean reef growth potential .

[1609] Terrestrial biogeochemical feedbacks in the climate system

The terrestrial biosphere is a key regulator of atmospheric chemistry and climate .
During past periods of climate change , vegetation cover and interactions between the terrestrial biosphere and atmosphere changed within decades .
Modern observations show a similar responsiveness of terrestrial biogeochemistry to anthropogenically forced climate change and air pollution .
Although interactions between the carbon cycle and climate have been a central focus , other biogeochemical feedbacks could be as important in modulating future climate change .
Total positive radiative forcings resulting from feedbacks between the terrestrial biosphere and the atmosphere are estimated to reach up to 0.9 or 1.5 W m-2 K-1 towards the end of the twenty-first century , depending on the extent to which interactions with the nitrogen cycle stimulate or limit carbon sequestration .
This substantially reduces and potentially even eliminates the cooling effect owing to carbon dioxide fertilization of the terrestrial biota .
The overall magnitude of the biogeochemical feedbacks could potentially be similar to that of feedbacks in the physical climate system , but there are large uncertainties in the magnitude of individual estimates and in accounting for synergies between these effects .

[1610] Growth landscape formed by perception and import of glucose in yeast

An important challenge in systems biology is to quantitatively describe microbial growth using a few measurable parameters that capture the essence of this complex phenomenon .
Two key events at the cell membrane -- extracellular glucose sensing and uptake -- initiate the budding yeast 's growth on glucose .
However , conventional growth models focus almost exclusively on glucose uptake .
Here we present results from growth-rate experiments that can not be explained by focusing on glucose uptake alone .
By imposing a glucose uptake rate independent of the sensed extracellular glucose level , we show that despite increasing both the sensed glucose concentration and uptake rate , the cell 's growth rate can decrease or even approach zero .
We resolve this puzzle by showing that the interaction between glucose perception and import , not their individual actions , determines the central features of growth , and characterize this interaction using a quantitative model .
Disrupting this interaction by knocking out two key glucose sensors significantly changes the cell 's growth rate , yet uptake rates are unchanged .
This is due to a decrease in burden that glucose perception places on the cells .
Our work shows that glucose perception and import are separate and pivotal modules of yeast growth , the interaction of which can be precisely tuned and measured .

[1611] Strong contributors to network persistence are the most vulnerable to extinction

The architecture of mutualistic networks facilitates coexistence of individual participants by minimizing competition relative to facilitation .
However , it is not known whether this benefit is received by each participant node in proportion to its overall contribution to network persistence .
This issue is critical to understanding the trade-offs faced by individual nodes in a network .
We address this question by applying a suite of structural and dynamic methods to an ensemble of flowering plant/insect pollinator networks .
Here we report two main results .
First , nodes contribute heterogeneously to the overall nested architecture of the network .
From simulations , we confirm that the removal of a strong contributor tends to decrease overall network persistence more than the removal of a weak contributor .
Second , strong contributors to collective persistence do not gain individual survival benefits but are in fact the nodes most vulnerable to extinction .
We explore the generality of these results to other cooperative networks by analysing a 15-year time series of the interactions between designer and contractor firms in the New York City garment industry .
As with the ecological networks , a firm 's survival probability decreases as its individual nestedness contribution increases .
Our results , therefore , introduce a new paradox into the study of the persistence of cooperative networks , and potentially address questions about the impact of invasive species in ecological systems and new competitors in economic systems .

[1612] Assessing species vulnerability to climate change

The effects of climate change on biodiversity are increasingly well documented , and many methods have been developed to assess species ' vulnerability to climatic changes , both ongoing and projected in the coming decades .
To minimize global biodiversity losses , conservationists need to identify those species that are likely to be most vulnerable to the impacts of climate change .
In this Review , we summarize different currencies used for assessing species ' climate change vulnerability .
We describe three main approaches used to derive these currencies ( correlative , mechanistic and trait-based ) , and their associated data requirements , spatial and temporal scales of application and modelling methods .
We identify strengths and weaknesses of the approaches and highlight the sources of uncertainty inherent in each method that limit projection reliability .
Finally , we provide guidance for conservation practitioners in selecting the most appropriate approach ( es ) for their planning needs and highlight priority areas for further assessments .

[1613] Antibiotic resistance and its cost : is it possible to reverse resistance ?

Most antibiotic resistance mechanisms are associated with a fitness cost that is typically observed as a reduced bacterial growth rate .
The magnitude of this cost is the main biological parameter that influences the rate of development of resistance , the stability of the resistance and the rate at which the resistance might decrease if antibiotic use were reduced .
These findings suggest that the fitness costs of resistance will allow susceptible bacteria to outcompete resistant bacteria if the selective pressure from antibiotics is reduced .
Unfortunately , the available data suggest that the rate of reversibility will be slow at the community level .
Here , we review the factors that influence the fitness costs of antibiotic resistance , the ways by which bacteria can reduce these costs and the possibility of exploiting them .

[1614] Excess algal symbionts increase the susceptibility of reef corals to bleaching

Rising ocean temperatures associated with global climate change are causing mass coral bleaching and mortality worldwide .
Understanding the genetic and environmental factors that mitigate coral bleaching susceptibility may aid local management efforts to help coral reefs survive climate change .
Although bleaching susceptibility depends partly on the genetic identity of a coral 's algal symbionts , the effect of symbiont density , and the factors controlling it , remain poorly understood .
By applying a new metric of symbiont density to study the coral Pocillopora damicornis during seasonal warming and acute bleaching , we show that symbiont cell ratio density is a function of both symbiont type and environmental conditions , and that corals with high densities are more susceptible to bleaching .
Higher vulnerability of corals with more symbionts establishes a quantitative mechanistic link between symbiont density and the molecular basis for coral bleaching , and indicates that high densities do not buffer corals from thermal stress , as has been previously suggested .
These results indicate that environmental conditions that increase symbiont densities , such as nutrient pollution , will exacerbate climate-change-induced coral bleaching , providing a mechanistic explanation for why local management to reduce these stressors will help coral reefs survive future warming .

[1615] South China Sea hydrological changes and Pacific Walker Circulation variations over the last millennium

The relative importance of north-south migrations of the intertropical convergence zone ( ITCZ ) versus El Nino-Southern Oscillation and its associated Pacific Walker Circulation ( PWC ) variability for past hydrological change in the western tropical Pacific is unclear .
Here we show that north-south ITCZ migration was not the only mechanism of tropical Pacific hydrologic variability during the last millennium , and that PWC variability profoundly influenced tropical Pacific hydrology .
We present hydrological reconstructions from Cattle Pond , Dongdao Island of the South China Sea , where multi-decadal rainfall and downcore grain size variations are correlated to the Southern Oscillation Index during the instrumental era .
Our downcore grain size reconstructions indicate that this site received less precipitation during relatively warm periods , AD 1000-1400 and AD 1850-2000 , compared with the cool period ( AD 1400-1850 ) .
Including our new reconstructions in a synthesis of tropical Pacific records results in a spatial pattern of hydrologic variability that implicates the PWC .

[1616] The equilibrium sensitivity of the Earth 's temperature to radiation changes

The Earth 's climate is changing rapidly as a result of anthropogenic carbon emissions , and damaging impacts are expected to increase with warming .
To prevent these and limit long-term global surface warming to , for example , 2 degreesC , a level of stabilization or of peak atmospheric CO2 concentrations needs to be set .
Climate sensitivity , the global equilibrium surface warming after a doubling of atmospheric CO2 concentration , can help with the translation of atmospheric CO2 levels to warming .
Various observations favour a climate sensitivity value of about 3 degreesC , with a likely range of about 2-4 .5 degreesC .
However , the physics of the response and uncertainties in forcing lead to fundamental difficulties in ruling out higher values .
The quest to determine climate sensitivity has now been going on for decades , with disturbingly little progress in narrowing the large uncertainty range .
However , in the process , fascinating new insights into the climate system and into policy aspects regarding mitigation have been gained .
The well-constrained lower limit of climate sensitivity and the transient rate of warming already provide useful information for policy makers .
But the upper limit of climate sensitivity will be more difficult to quantify .

[1617] Glucose substitution prolongs maintenance of energy homeostasis and lifespan of telomere dysfunctional mice

DNA damage and telomere dysfunction shorten organismal lifespan .
Here we show that oral glucose administration at advanced age increases health and lifespan of telomere dysfunctional mice .
The study reveals that energy consumption increases in telomere dysfunctional cells resulting in enhanced glucose metabolism both in glycolysis and in the tricarboxylic acid cycle at organismal level .
In ageing telomere dysfunctional mice , normal diet provides insufficient amounts of glucose thus leading to impaired energy homeostasis , catabolism , suppression of IGF-1 / mTOR signalling , suppression of mitochondrial biogenesis and tissue atrophy .
A glucose-enriched diet reverts these defects by activating glycolysis , mitochondrial biogenesis and oxidative glucose metabolism .
The beneficial effects of glucose substitution on mitochondrial function and glucose metabolism are blocked by mTOR inhibition but mimicked by IGF-1 application .
Together , these results provide the first experimental evidence that telomere dysfunction enhances the requirement of glucose substitution for the maintenance of energy homeostasis and IGF-1 / mTOR-dependent mitochondrial biogenesis in ageing tissues .

[1618] Magnani et al. reply

Replying to : A. De Schrijver et al. .
Nature 451 , 10.1038 / nature06578 ; W. de Vries et al. .
Nature 451 , 10.1038 / nature06579 ( 2008 )
Nitrogen ( N ) deposition alters ecosystem function in several ways , with important effects on N leaching and water quality , as well as on interspecific competition and biodiversity .
These changes have been attributed to ecosystem N saturation , defined as the alleviation of N limitations on rates of biological function .
After an initial fertilization effect , N saturation has also been suggested to reduce plant function and growth , eventually leading to forest dieback .
Although our observation of a substantial positive effect of N deposition on forest carbon ( C ) sequestration does not imply the absence of nitrate losses or other negative effects , as rightly stressed by De Schrijver et al. , the sustained response observed demonstrates that the fear of a generalized forest decline in response to N fertilization could be overstated , at least within the rather broad N deposition range explored in our analysis .
The nature of the observed response of forest C sequestration to N deposition , however , has been questioned outright by de Vries et al. , who suggested that it could be an artefact resulting from the covariation between N deposition and other environmental variables .
The arguments proposed against an overwhelming N effect , however , do not seem to stand up to close scrutiny .

[1619] Late Pliocene Greenland glaciation controlled by a decline in atmospheric CO2 levels

It is thought that the Northern Hemisphere experienced only ephemeral glaciations from the Late Eocene to the Early Pliocene epochs ( about 38 to 4 million years ago ) , and that the onset of extensive glaciations did not occur until about 3 million years ago .
Several hypotheses have been proposed to explain this increase in Northern Hemisphere glaciation during the Late Pliocene .
Here we use a fully coupled atmosphere-ocean general circulation model and an ice-sheet model to assess the impact of the proposed driving mechanisms for glaciation and the influence of orbital variations on the development of the Greenland ice sheet in particular .
We find that Greenland glaciation is mainly controlled by a decrease in atmospheric carbon dioxide during the Late Pliocene .
By contrast , our model results suggest that climatic shifts associated with the tectonically driven closure of the Panama seaway , with the termination of a permanent El Nino state or with tectonic uplift are not large enough to contribute significantly to the growth of the Greenland ice sheet ; moreover , we find that none of these processes acted as a priming mechanism for glacial inception triggered by variations in the Earth 's orbit .

[1620] Morphological plasticity as a bacterial survival strategy

Bacteria have evolved complex systems to maintain consistent cell morphologies .
Nevertheless , in certain circumstances , bacteria alter this highly regulated process to transform into filamentous organisms .
Accumulating evidence attributes important biological roles to filamentation in stressful environments , including , but not limited to , sites of interaction between pathogenic bacteria and their hosts .
Filamentation could represent an intended response to specific environmental cues that promote survival amidst the threats of consumption and killing .

[1621] Arctic sea ice : Eroding the coast

The Cryosphere 8 , 1777 - 1799 10.5194 / tc-8-1777-2014 ( 2014 ) Changes in Arctic sea ice will impact on coastal areas of the region .
Sea ice isolates the ocean from the land in the winter , and in warmer months it limits the wind-wave activity and associated land impacts such as erosion and storm surge .

[1622] Untangling the confusion around land carbon science and climate change mitigation policy

Depletion of ecosystem carbon stocks is a significant source of atmospheric CO2 and reducing land-based emissions and maintaining land carbon stocks contributes to climate change mitigation .
We summarize current understanding about human perturbation of the global carbon cycle , examine three scientific issues and consider implications for the interpretation of international climate change policy decisions , concluding that considering carbon storage on land as a means to ` offset ' CO2 emissions from burning fossil fuels ( an idea with wide currency ) is scientifically flawed .
The capacity of terrestrial ecosystems to store carbon is finite and the current sequestration potential primarily reflects depletion due to past land use .
Avoiding emissions from land carbon stocks and refilling depleted stocks reduces atmospheric CO2 concentration , but the maximum amount of this reduction is equivalent to only a small fraction of potential fossil fuel emissions .

[1623] Bacterial structures and ecosystem functions in glaciated floodplains : contemporary states and potential future shifts

Glaciated alpine floodplains are responding quickly to climate change through shrinking ice masses .
Given the expected future changes in their physicochemical environment , we anticipated variable shifts in structure and ecosystem functioning of hyporheic microbial communities in proglacial alpine streams , depending on present community characteristics and landscape structures .
We examined microbial structure and functioning during different hydrologic periods in glacial ( kryal ) streams and , as contrasting systems , groundwater-fed ( krenal ) streams .
Three catchments were chosen to cover an array of landscape features , including interconnected lakes , differences in local geology and degree of deglaciation .
Community structure was assessed by automated ribosomal intergenic spacer analysis and microbial function by potential enzyme activities .
We found each catchment to contain a distinct bacterial community structure and different degrees of separation in structure and functioning that were linked to the physicochemical properties of the waters within each catchment .
Bacterial communities showed high functional plasticity , although achieved by different strategies in each system .
Typical kryal communities showed a strong linkage of structure and function that indicated a major prevalence of specialists , whereas krenal sediments were dominated by generalists .
With the rapid retreat of glaciers and therefore altered ecohydrological characteristics , lotic microbial structure and functioning are likely to change substantially in proglacial floodplains in the future .
The trajectory of these changes will vary depending on contemporary bacterial community characteristics and landscape structures that ultimately determine the sustainability of ecosystem functioning .

[1624] Elementary processes governing the evolution of road networks

Urbanisation is a fundamental phenomenon whose quantitative characterisation is still inadequate .
We report here the empirical analysis of a unique data set regarding almost 200 years of evolution of the road network in a large area located north of Milan ( Italy ) .
We find that urbanisation is characterised by the homogenisation of cell shapes , and by the stability throughout time of high-centrality roads which constitute the backbone of the urban structure , confirming the importance of historical paths .
We show quantitatively that the growth of the network is governed by two elementary processes : ( i ) ` densification ' , corresponding to an increase in the local density of roads around existing urban centres and ( ii ) ` exploration ' , whereby new roads trigger the spatial evolution of the urbanisation front .
The empirical identification of such simple elementary mechanisms suggests the existence of general , simple properties of urbanisation and opens new directions for its modelling and quantitative description .

[1625] Climate change and the recent emergence of bluetongue in Europe

Bluetongue , a devastating disease of ruminants , has historically made only brief , sporadic incursions into the fringes of Europe .
However , since 1998 , six strains of bluetongue virus have spread across 12 countries and 800 km further north in Europe than has previously been reported .
We suggest that this spread has been driven by recent changes in European climate that have allowed increased virus persistence during winter , the northward expansion of Culicoides imicola , the main bluetongue virus vector , and , beyond this vector 's range , transmission by indigenous European Culicoides species -- thereby expanding the risk of transmission over larger geographical regions .
Understanding this sequence of events may help us predict the emergence of other vector-borne pathogens .

[1626] Divergent long-term trajectories of human access to the Arctic

Understanding climate change impacts on transportation systemsis particularly critical in northern latitudes , where subzero temperatures restrict shipping , but enable passage of ground vehicles over frozen soil and water surfaces .
Although the major transport challenges related to climate warming are understood , so far there have been no quantitative projections of Arctic transport system change .
Here we present a new modelling framework to quantify changing access to oceans and landscapes northward of 40degrees N by mid-century .
The analysis integrates climate and sea-ice model scenarios with topography , hydrography , land cover , transportation infrastructure and human settlements .
Declining sea-ice concentration and thickness suggest faster travel and improved access to existing ( +5 to +28 % ) and theoretical ( +11 to +37 % ) offshore exclusive economic zones of Canada , Greenland , Russia and the US .
The Northern Sea Route , Arctic Bridge and North Pole routes are projected to become fully accessible from July-September , averaging ~ 11 , 15 and 16 days to traverse , respectively , whereas the Northwest Passage will not .
All eight Arctic states are projected to suffer steep declines ( -11 to -82 % ) in accessibility inland , driven by lost potential for winter road construction caused by milder winters and deeper snow accumulation .

[1627] Tectonic processes in Papua New Guinea and past productivity in the eastern equatorial Pacific Ocean

Phytoplankton growth in the eastern equatorial Pacific Ocean today accounts for about half of the ` new ' production -- the fraction of primary production fuelled by externally supplied nutrients -- in the global ocean .
The recent demonstration that an inadequate supply of iron limits primary production in this region supports earlier speculation that , in the past , fluctuations in the atmospheric deposition of iron-bearing dust may have driven large changes in productivity .
But we argue here that only small ( ~ 2 nM ) increases in the iron concentration in source waters of the upwelling Equatorial Undercurrent are needed to fuel intense diatom production across the entire eastern equatorial Pacific Ocean .
Episodic increases in iron concentrations of this magnitude or larger were probably frequent in the past because a large component of the undercurrent originates in the convergent island-arc region of Papua New Guinea , which has experienced intensive volcanic , erosional and seismic activity over the past 16 million years .
Cycles of plankton productivity recorded in eastern equatorial Pacific sediments may therefore reflect the influence of tectonic processes in the Papua New Guinea region superimposed on the effects of global climate forcing .

[1628] Microorganisms and climate change : terrestrial feedbacks and mitigation options

Microbial processes have a central role in the global fluxes of the key biogenic greenhouse gases ( carbon dioxide , methane and nitrous oxide ) and are likely to respond rapidly to climate change .
Whether changes in microbial processes lead to a net positive or negative feedback for greenhouse gas emissions is unclear .
To improve the prediction of climate models , it is important to understand the mechanisms by which microorganisms regulate terrestrial greenhouse gas flux .
This involves consideration of the complex interactions that occur between microorganisms and other biotic and abiotic factors .
The potential to mitigate climate change by reducing greenhouse gas emissions through managing terrestrial microbial processes is a tantalizing prospect for the future .

[1629] Effect of earthworms on the community structure of active methanotrophic bacteria in a landfill cover soil

In the United Kingdom , landfills are the primary anthropogenic source of methane emissions .
Methanotrophic bacteria present in landfill biocovers can significantly reduce methane emissions via their capacity to oxidize up to 100 % of the methane produced .
Several biotic and abiotic parameters regulate methane oxidation in soil , such as oxygen , moisture , methane concentration and temperature .
Earthworm-mediated bioturbation has been linked to an increase in methanotrophy in a landfill biocover soil ( AC Singer et al. , unpublished ) , but the mechanism of this trophic interaction remains unclear .
The aims of this study were to determine the composition of the active methanotroph community and to investigate the interactions between earthworms and bacteria in this landfill biocover soil where the methane oxidation activity was significantly increased by the earthworms .
Soil microcosms were incubated with 13C-CH4 and with or without earthworms .
DNA and RNA were extracted to characterize the soil bacterial communities , with a particular emphasis on methanotroph populations , using phylogenetic ( 16S ribosomal RNA ) and functional methane monooxygenase ( pmoA and mmoX ) gene probes , coupled with denaturing gradient-gel electrophoresis , clone libraries and pmoA microarray analyses .
Stable isotope probing ( SIP ) using 13C-CH4 substrate allowed us to link microbial function with identity of bacteria via selective recovery of ` heavy ' 13C-labelled DNA or RNA and to assess the effect of earthworms on the active methanotroph populations .
Both types I and II methanotrophs actively oxidized methane in the landfill soil studied .
Results suggested that the earthworm-mediated increase in methane oxidation rate in the landfill soil was more likely to be due to the stimulation of bacterial growth or activity than to substantial shifts in the methanotroph community structure .
A Bacteroidetes-related bacterium was identified only in the active bacterial community of earthworm-incubated soil but its capacity to actually oxidize methane has to be proven .

[1630] Decline of surface temperature and salinity in the western tropical Pacific Ocean in the Holocene epoch

In the present-day climate , surface water salinities are low in the western tropical Pacific Ocean and increase towards the eastern part of the basin .
The salinity of surface waters in the tropical Pacific Ocean is thought to be controlled by a combination of atmospheric convection , precipitation , evaporation and ocean dynamics , and on interannual timescales significant variability is associated with the El Nino/Southern Oscillation cycles .
However , little is known about the variability of the coupled ocean-atmosphere system on timescales of centuries to millennia .
Here we combine oxygen isotope and Mg/Ca data from foraminifers retrieved from three sediment cores in the western tropical Pacific Ocean to reconstruct Holocene sea surface temperatures and salinities in the region .
We find a decrease in sea surface temperatures of ~ 0.5 degreesC over the past 10,000 yr , whereas sea surface salinities decreased by ~ 1.5 practical salinity units .
Our data imply either that the Pacific basin as a whole has become progressively less salty or that the present salinity gradient along the Equator has developed relatively recently .

[1631] Enhanced Moran effect by spatial variation in environmental autocorrelation

Spatial correlations in environmental stochasticity can synchronize populations over wide areas , a phenomenon known as the Moran effect .
The Moran effect has been confirmed in field , laboratory and theoretical investigations .
Little is known , however , about the Moran effect in a common ecological case , when environmental variation is temporally autocorrelated and this autocorrelation varies spatially .
Here we perform chemostat experiments to investigate the temporal response of independent phytoplankton populations to autocorrelated stochastic forcing .
In contrast to naive expectation , two populations without direct coupling can be more strongly correlated than their environmental forcing ( enhanced Moran effect ) , if the stochastic variations differ in their autocorrelation .
Our experimental findings are in agreement with numerical simulations and analytical calculations .
The enhanced Moran effect is robust to changes in population dynamics , noise spectra and different measures of correlation -- suggesting that noise-induced synchrony may play a larger role for population dynamics than previously thought .

[1632] Unsaturated fatty acid content in seston and tropho-dynamic coupling in lakes

Determining the factors that control food web interactions is a key issue in ecology .
The empirical relationship between nutrient loading ( total phosphorus ) and phytoplankton standing stock ( chlorophyll a ) in lakes was described about 30 years ago and is central for managing surface water quality .
The efficiency with which biomass and energy are transferred through the food web and sustain the production of higher trophic levels ( such as fish ) declines with nutrient loading and system productivity , but the underlying mechanisms are poorly understood .
Here we show that in seston ( fine particles in water ) during summer , specific omega3-polyunsaturated fatty acids ( omega3-PUFAs ) , which are important for zooplankton , are significantly correlated to the trophic status of the lake .
The omega3-PUFAs octadecatetraenoic acid , eicosapentaenoic acid ( EPA ) and docosahexaenoic acid , but not alpha-linolenic acid , decrease on a double-logarithmic scale with increasing total phosphorus .
By combining the empirical relationship between EPA-to-carbon content and total phosphorus with functional models relating EPA-to-carbon content to the growth and egg production of daphnids , we predict secondary production for this key consumer .
Thus , the decreasing efficiency in energy transfer with increasing lake productivity can be explained by differences in omega3-PUFA-associated food quality at the plant-animal interface .

[1633] Salinity anomaly as a trigger for ENSO events

According to the classical theories of ENSO , subsurface anomalies in ocean thermal structure are precursors for ENSO events and their initial specification is essential for skillful ENSO forecast .
Although ocean salinity in the tropical Pacific ( particularly in the western Pacific warm pool ) can vary in response to El Nino events , its effect on ENSO evolution and forecasts of ENSO has been less explored .
Here we present evidence that , in addition to the passive response , salinity variability may also play an active role in ENSO evolution , and thus important in forecasting El Nino events .
By comparing two forecast experiments in which the interannually variability of salinity in the ocean initial states is either included or excluded , the salinity variability is shown to be essential to correctly forecast the 2007/08 La Nina starting from April 2007 .
With realistic salinity initial states , the tendency to decay of the subsurface cold condition during the spring and early summer 2007 was interrupted by positive salinity anomalies in the upper central Pacific , which working together with the Bjerknes positive feedback , contributed to the development of the La Nina event .
Our study suggests that ENSO forecasts will benefit from more accurate salinity observations with large-scale spatial coverage .

[1634] Winter diversity and expression of proteorhodopsin genes in a polar ocean

Mixotrophy is a valuable functional trait used by microbes when environmental conditions vary broadly or resources are limited .
In the sunlit waters of the ocean , photoheterotrophy , a form of mixotrophy , is often mediated by proteorhodopsin ( PR ) , a seven helices transmembrane protein binding the retinal chromophore .
Altogether , they allow bacteria to capture photic energy for sensory and proton gradient formation cell functions .
The seasonal occurrence and diversity of the gene coding for PR in cold oligotrophic polar oceans is not known and PR expression has not yet been reported .
Here we show that PR is widely distributed among bacterial taxa , and that PR expression decreased markedly during the winter months in the Arctic Ocean .
Gammaproteobacteria-like PR sequences were always dominant .
However , within the second most common affiliation , there was a transition from Flavobacteria-like PR in early winter to Alphaproteobacteria-like PR in late winter .
The phylogenetic shifts followed carbon dynamics , where patterns in expression were consistent with community succession , as identified by DNA community fingerprinting .
Although genes for PR were always present , the trend in decreasing transcripts from January to February suggested reduced functional utility of PR during winter .
Under winter darkness , sustained expression suggests that PR may continue to be useful for non-ATP forming functions , such as environmental sensing or small solute transport .
The persistence of PR expression in winter among some bacterial groups may offer a competitive advantage , where its multifunctionality enhances microbial survival under harsh polar conditions .
The ISME Journal advance online publication , 20 February 2015 ; doi :10.1038 / ismej .2015.1

[1635] Bottom water warming in the North Pacific Ocean

Observations of changes in the properties of ocean waters have been restricted to surface or intermediate-depth waters , because the detection of change in bottom water is extremely difficult owing to the small magnitude of the expected signals .
Nevertheless , temporal changes in the properties of such deep waters across an ocean basin are of particular interest , as they can be used to constrain the transport of water at the bottom of the ocean and to detect changes in the global thermohaline circulation .
Here we present a comparison of a trans-Pacific survey completed in 1985 ( refs 4 , 5 ) and its repetition in 1999 ( ref .
6 ) .
We find that the deepest waters of the North Pacific Ocean have warmed significantly across the entire width of the ocean basin .
Our observations imply that changes in water properties are now detectable in water masses that have long been insulated from heat exchange with the atmosphere .

[1636] Tracing the stepwise oxygenation of the Proterozoic ocean

Biogeochemical signatures preserved in ancient sedimentary rocks provide clues to the nature and timing of the oxygenation of the Earth 's atmosphere .
Geochemical data suggest that oxygenation proceeded in two broad steps near the beginning and end of the Proterozoic eon ( 2,500 to 542 million years ago ) .
The oxidation state of the Proterozoic ocean between these two steps and the timing of deep-ocean oxygenation have important implications for the evolutionary course of life on Earth but remain poorly known .
Here we present a new perspective on ocean oxygenation based on the authigenic accumulation of the redox-sensitive transition element molybdenum in sulphidic black shales .
Accumulation of authigenic molybdenum from sea water is already seen in shales by 2,650 Myr ago ; however , the small magnitudes of these enrichments reflect weak or transient sources of dissolved molybdenum before about 2,200 Myr ago , consistent with minimal oxidative weathering of the continents .
Enrichments indicative of persistent and vigorous oxidative weathering appear in shales deposited at roughly 2,150 Myr ago , more than 200 million years after the initial rise in atmospheric oxygen .
Subsequent expansion of sulphidic conditions after about 1,800 Myr ago ( refs 8 , 9 ) maintained a mid-Proterozoic molybdenum reservoir below 20 per cent of the modern inventory , which in turn may have acted as a nutrient feedback limiting the spatiotemporal distribution of euxinic ( sulphidic ) bottom waters and perhaps the evolutionary and ecological expansion of eukaryotic organisms .
By 551 Myr ago , molybdenum contents reflect a greatly expanded oceanic reservoir due to oxygenation of the deep ocean and corresponding decrease in sulphidic conditions in the sediments and water column .

[1637] Ants and termites increase crop yield in a dry climate

Agricultural intensification has increased crop yields , but at high economic and environmental cost .
Harnessing ecosystem services of naturally occurring organisms is a cheaper but under-appreciated approach , because the functional roles of organisms are not linked to crop yields , especially outside the northern temperate zone .
Ecosystem services in soil come from earthworms in these cooler and wetter latitudes ; what may fulfill their functional role in agriculture in warmer and drier habitats , where they are absent , is unproven .
Here we show in a field experiment that ants and termites increase wheat yield by 36 % from increased soil water infiltration due to their tunnels and improved soil nitrogen .
Our results suggest that ants and termites have similar functional roles to earthworms , and that they may provide valuable ecosystem services in dryland agriculture , which may become increasingly important for agricultural sustainability in arid climates .

[1638] Abiotic nitrogen reduction on the early Earth

The production of organic precursors to life depends critically onthe form of the reactants .
In particular , an environment dominated by N2 is far less efficient in synthesizing nitrogen-bearing organics than a reducing environment rich in ammonia ( refs 1 , 2 ) .
Relatively reducing lithospheric conditions on the early Earth have been presumed to favour the generation of an ammonia-rich atmosphere , but this hypothesis has not been studied experimentally .
Here we demonstrate mineral-catalysed reduction of N2 , NO2 - and NO3 - to ammonia at temperatures between 300 and 800 degreesC and pressures of 0.1-0 .4 GPa -- conditions typical of crustal and oceanic hydrothermal systems .
We also show that only N2 is stable above 800 degreesC , thus precluding significant atmospheric ammonia formation during hot accretion .
We conclude that mineral-catalysed N2 reduction might have provided a significant source of ammonia to the Hadean ocean .
These results also suggest that , whereas nitrogen in the Earth 's early atmosphere was present predominantly as N2 , exchange with oceanic , hydrothermally derived ammonia could have provided a significant amount of the atmospheric ammonia necessary to resolve the early-faint-Sun paradox .

[1639] Growth rate controlled synthesis of hierarchical Bi2S3/In2S3 core/shell microspheres with enhanced photocatalytic activity

Core/shell heterostructure composite has great potential applications in photocatalytic field because the introduction of core can remarkably improve charge transport and enhance the electron-hole separation .
Herein , hierarchical Bi2S3/In2S3 core/shell structured microspheres were prepared via a simple one-pot hydrothermal process based on different growth rate of the two kinds of sulphides .
The results showed that , the as-prepared hierarchical Bi2S3/In2S3 core/shell heterostructure exhibits significant visible light photocatalytic activity for degradation of 2 , 4-dichlorophenol .
The introduction of Bi2S3 core can not only improve charge transport and enhance the electron-hole separation , but also broaden the visible light response .
The hierarchical porous folwer-like shell of In2S3 could increase the specific surface area and remarkably enhanced the chemical stability of Bi2S3 against oxidation .

[1640] Reductions in nitrogen oxides over Europe driven by environmental policy and economic recession

Fuel combustion is a significant source of numerous air pollutants , which reduce local air quality , and affect global tropospheric chemistry .
Satellite observations of nitrogen dioxide , emitted by combustion processes , allow for robust monitoring of atmospheric concentrations at high spatial resolution on continental scales .
Here we evaluate changes in tropospheric NO2 concentrations over Europe between 2004 and 2010 .
We isolate long-term ( timescales greater than one year ) variability in the daily NO2 observations from the Ozone Monitoring Instrument ( OMI ) using a spectral analysis .
In 2010 , we find substantial reductions in NO2 concentrations of at least 20 % throughout Europe .
These reductions are as much the result of temporary reductions prompted by the 2008-2009 global economic recession , as of European NOx emission controls .
Our results demonstrate that realistic concentration pathways of NO2 do not follow simple linear trends , but reflect a compilation of environmental policy and economic activity .

[1641] Shifting the balance : antibiotic effects on host-microbiota mutualism

Antibiotics have been used effectively as a means to treat bacterial infections in humans and animals for over half a century .
However , through their use , lasting alterations are being made to a mutualistic relationship that has taken millennia to evolve : the relationship between the host and its microbiota .
Host-microbiota interactions are dynamic ; therefore , changes in the microbiota as a consequence of antibiotic treatment can result in the dysregulation of host immune homeostasis and an increased susceptibility to disease .
A better understanding of both the changes in the microbiota as a result of antibiotic treatment and the consequential changes in host immune homeostasis is imperative , so that these effects can be mitigated .

[1642] Satellite mapping of enhanced BrO concentrations in the troposphere

Reactive bromine species contribute significantly to the destruction of ozone in the polar stratosphere .
Reactive halogen compounds can have a strong effect not only on the chemistry of the stratosphere but also on that of the underlying troposphere .
For example , severe ozone depletion events that are less persistent than those in the stratosphere occur in the Arctic and Antarctic boundary layer during springtime and are also associated with enhanced BrO abundances , .
Observations of BrO ( and ClO , which is less important ) at ground level during these ozone depletion events have revealed halogen oxide mixing ratios of up to 30 parts per trillion -- sufficient to destroy within one to two days the 30-40 parts per billion of ozone typically present in the boundary layer .
The catalytic mechanism leading to so-called ` tropospheric ozone holes ' is well established , , but the origin of the increased BrO concentrations and the spatial and temporal extent of these events remains poorly understood .
Here we present satellite observations showing that tropospheric air masses enriched in BrO are always situated close to sea ice and typically extend over areas of about 300-2 ,000 km .
The BrO abundances remain enhanced forperiods of 1 to 3 days .
These observations support the suggestion , , that autocatalytic release of bromine from sea salt gives rise to significant BrO formation which , in turn , initiates ozone depletion in the polar troposphere .

[1643] Interglacial diversity

Earth 's climate has progressively cooled over the past 3 million years with a concomitant expansion of continental ice volume .
This global trend towards increasingly severe and extended ice ages has nevertheless been repeatedly interrupted by relatively mild/warm interglacial intervals such as the one that has characterized the past 11,000 years .
Past interglacials can be thought of as a series of natural experiments in which climate boundary conditions varied considerably , with consequent effects on the character of climate change .
As such they can provide a more complete view of the range and underlying physics of natural climate variability .
Examination of the palaeoclimate record of the past 800,000 years reveals a large diversity among interglacials in terms of their intensity , duration and internal variability , but a general theory accounting for this diversity remains elusive .
Future work should focus on generating new palaeodata and modelling interglacial diversity , and using this information to inform projections on the future evolution of the current interglacial .

[1644] A new simple concept for ocean colour remote sensing using parallel polarisation radiance

Ocean colour remote sensing has supported research on subjects ranging from marine ecosystems to climate change for almost 35 years .
However , as the framework for ocean colour remote sensing is based on the radiation intensity at the top-of-atmosphere ( TOA ) , the polarisation of the radiation , which contains additional information on atmospheric and water optical properties , has largely been neglected .
In this study , we propose a new simple concept to ocean colour remote sensing that uses parallel polarisation radiance ( PPR ) instead of the traditional radiation intensity .
We use vector radiative transfer simulation and polarimetric satellite sensing data to demonstrate that using PPR has two significant advantages in that it effectively diminishes the sun glint contamination and enhances the ocean colour signal at the TOA .
This concept may open new doors for ocean colour remote sensing .
We suggest that the next generation of ocean colour sensors should measure PPR to enhance observational capability .

[1645] Retrospective prediction of the global warming slowdown in the past decade

Despite a sustained production of anthropogenic greenhouse gases , the Earth 's mean near-surface temperature paused its rise during the 2000-2010 period .
To explain such a pause , an increase in ocean heat uptake below the superficial ocean layer has been proposed to overcompensate for the Earth 's heat storage .
Contributions have also been suggested from the deep prolonged solar minimum , the stratospheric water vapour , the stratospheric and tropospheric aerosols .
However , a robust attribution of this warming slowdown has not been achievable up to now .
Here we show successful retrospective predictions of this warming slowdown up to 5 years ahead , the analysis of which allows us to attribute the onset of this slowdown to an increase in ocean heat uptake .
Sensitivity experiments accounting only for the external radiative forcings do not reproduce the slowdown .
The top-of-atmosphere net energy input remained in the [ 0.5-1 ] W m-2 interval during the past decade , which is successfully captured by our predictions .
Most of this excess energy was absorbed in the top 700 m of the ocean at the onset of the warming pause , 65 % of it in the tropical Pacific and Atlantic oceans .
Our results hence point at the key role of the ocean heat uptake in the recent warming slowdown .
The ability to predict retrospectively this slowdown not only strengthens our confidence in the robustness of our climate models , but also enhances the socio-economic relevance of operational decadal climate predictions .

[1646] Ca2 + / calmodulin is critical for brassinosteroid biosynthesis and plant growth

Brassinosteroids are plant-specific steroid hormones that have an important role in coupling environmental factors , especially light , with plant growth and development .
How the endogenous brassinosteroids change in response to environmental stimuli is largely unknown .
Ca2 + / calmodulin has an essential role in sensing and transducing environmental stimuli .
Arabidopsis DWARF1 ( DWF1 ) is responsible for an early step in brassinosteroid biosynthesis that converts 24-methylenecholesterol to campesterol .
Here we show that DWF1 is a Ca2 + / calmodulin-binding protein and this binding is critical for its function .
Molecular genetic analysis using site-directed and deletion mutants revealed that loss of calmodulin binding completely abolished the function of DWF1 in planta , whereas partial loss of calmodulin binding resulted in a partial dwarf phenotype in complementation studies .
These results provide direct proof that Ca2 + / calmodulin-mediated signalling has a critical role in controlling the function of DWF1 .
Furthermore , we observed that DWF1 orthologues from other plants have a similar Ca2 + / calmodulin-binding domain , implying that Ca2 + / calmodulin regulation of DWF1 and its homologues is common in plants .
These results raise the possibility of producing size-engineered crops by altering the Ca2 + / calmodulin-binding property of their DWF1 orthologues .

[1647] Fluorescent pigments in corals are photoprotective

All reef-forming corals depend on the photosynthesis performed by their algal symbiont , and such corals are therefore restricted to the photic zone .
The intensity of light in this zone declines over several orders of magnitude -- from high and damaging levels at the surface to extreme shade conditions at the lower limit .
The ability of corals to tolerate this range implies effective mechanisms for light acclimation and adaptation .
Here we show that the fluorescent pigments ( FPs ) of corals provide a photobiological system for regulating the light environment of coral host tissue .
Previous studies have suggested that under low light , FPs may enhance light availability .
We now report that in excessive sunlight FPs are photoprotective ; they achieve this by dissipating excess energy at wavelengths of low photosynthetic activity , as well as by reflecting of visible and infrared light by FP-containing chromatophores .
We also show that FPs enhance the resistance to mass bleaching of corals during periods of heat stress , which has implications for the effect of environmental stress on the diversity of reef-building corals , such as enhanced survival of a broad range of corals allowing maintenance of habitat diversity .

[1648] The human footprint in the carbon cycle of temperate and boreal forests

Temperate and boreal forests in the Northern Hemisphere cover an area of about 2 x 107 square kilometres and act as a substantial carbon sink ( 0.6-0 .7 petagrams of carbon per year ) .
Although forest expansion following agricultural abandonment is certainly responsible for an important fraction of this carbon sink activity , the additional effects on the carbon balance of established forests of increased atmospheric carbon dioxide , increasing temperatures , changes in management practices and nitrogen deposition are difficult to disentangle , despite an extensive network of measurement stations .
The relevance of this measurement effort has also been questioned , because spot measurements fail to take into account the role of disturbances , either natural ( fire , pests , windstorms ) or anthropogenic ( forest harvesting ) .
Here we show that the temporal dynamics following stand-replacing disturbances do indeed account for a very large fraction of the overall variability in forest carbon sequestration .
After the confounding effects of disturbance have been factored out , however , forest net carbon sequestration is found to be overwhelmingly driven by nitrogen deposition , largely the result of anthropogenic activities .
The effect is always positive over the range of nitrogen deposition covered by currently available data sets , casting doubts on the risk of widespread ecosystem nitrogen saturation under natural conditions .
The results demonstrate that mankind is ultimately controlling the carbon balance of temperate and boreal forests , either directly ( through forest management ) or indirectly ( through nitrogen deposition ) .

[1649] Detection of the Three Gorges Dam influence on the Changjiang ( Yangtze River ) submerged delta

While most large river-deltas in the world are facing the risk of subsidence and erosion in the Anthropocene , it is suspected that the Changjiang submerged delta ( CSD ) could be subjected to the impacts of the world 's largest dam , the Three Gorges Dam ( TGD ) .
Here we firstly indicate that the CSD went through high accumulation ( 1958-1978 ) ; slight accumulation ( 1978-1997 ) , slight erosion ( 1997-2002 ) ; and high accumulation ( 2002-2009 ) , despite the 70 % reduction of the sediment load from upstream since the operation of the TGD in 2003 .
Meanwhile , at the depocenter of the submerged delta , the accumulation maintained a high rate of 10 cm/yr during 1958-2009 .
This suggests on a longer term , the distal sediment source from the upstream had little effect on the CSD .
Within this time frame the changes in the partition of sediment load among the branching channels of the Changjiang Estuary could likely control the shifting of the depocenter of the CSD on a decadal time scale .
Episodic extreme floods and storm surges also increased the magnitude of deposition and erosion of the CSD on short-term scales .
A re-evaluation of the impacts of TGD on the CSD is urgently needed .

[1650] SAR11 marine bacteria require exogenous reduced sulphur for growth

Sulphur is a universally required cell nutrient found in two amino acids and other small organic molecules .
All aerobic marine bacteria are known to use assimilatory sulphate reduction to supply sulphur for biosynthesis , although many can assimilate sulphur from organic compounds that contain reduced sulphur atoms .
An analysis of three complete ` Candidatus Pelagibacter ubique ' genomes , and public ocean metagenomic data sets , suggested that members of the ubiquitous and abundant SAR11 alphaproteobacterial clade are deficient in assimilatory sulphate reduction genes .
Here we show that SAR11 requires exogenous sources of reduced sulphur , such as methionine or 3-dimethylsulphoniopropionate ( DMSP ) for growth .
Titrations of the algal osmolyte DMSP in seawater medium containing all other macronutrients in excess showed that 1.5 x 108 SAR11 cells are produced per nanomole of DMSP .
Although it has been shown that other marine alphaproteobacteria use sulphur from DMSP in preference to sulphate , our results indicate that ` Cand .
P. ubique ' relies exclusively on reduced sulphur compounds that originate from other plankton .

[1651] Visualizing the uncertainty in the relationship between seasonal average climate and malaria risk

Around $ 1.6 billion per year is spent financing anti-malaria initiatives , and though malaria morbidity is falling , the impact of annual epidemics remains significant .
Whilst malaria risk may increase with climate change , projections are highly uncertain and to sidestep this intractable uncertainty , adaptation efforts should improve societal ability to anticipate and mitigate individual events .
Anticipation of climate-related events is made possible by seasonal climate forecasting , from which warnings of anomalous seasonal average temperature and rainfall , months in advance are possible .
Seasonal climate hindcasts have been used to drive climate-based models for malaria , showing significant skill for observed malaria incidence .
However , the relationship between seasonal average climate and malaria risk remains unquantified .
Here we explore this relationship , using a dynamic weather-driven malaria model .
We also quantify key uncertainty in the malaria model , by introducing variability in one of the first order uncertainties in model formulation .
Results are visualized as location-specific impact surfaces : easily integrated with ensemble seasonal climate forecasts , and intuitively communicating quantified uncertainty .
Methods are demonstrated for two epidemic regions , and are not limited to malaria modeling ; the visualization method could be applied to any climate impact .

[1652] Alternative stable states explain unpredictable biological control of Salvinia molesta in Kakadu

Suppression of the invasive plant Salvinia molesta by the salvinia weevil is an iconic example of successful biological control .
However , in the billabongs ( oxbow lakes ) of Kakadu National Park , Australia , control is fitful and incomplete .
By fitting a process-based nonlinear model to thirteen-year data sets from four billabongs , here we show that incomplete control can be explained by alternative stable states -- one state in which salvinia is suppressed and the other in which salvinia escapes weevil control .
The shifts between states are associated with annual flooding events .
In some years , high water flow reduces weevil populations , allowing the shift from a controlled to an uncontrolled state ; in other years , benign conditions for weevils promote the return shift to the controlled state .
In most described ecological examples , transitions between alternative stable states are relatively rare , facilitated by slow-moving environmental changes , such as accumulated nutrient loading or climate change .
The billabongs of Kakadu give a different manifestation of alternative stable states that generate complex and seemingly unpredictable dynamics .
Because shifts between alternative stable states are stochastic , they present a potential management strategy to maximize effective biological control : when the domain of attraction to the state of salvinia control is approached , augmentation of the weevil population or reduction of the salvinia biomass may allow the lower state to trap the system .

[1653] The ERECTA gene regulates plant transpiration efficiency in Arabidopsis

Assimilation of carbon by plants incurs water costs .
In the many parts of the world where water is in short supply , plant transpiration efficiency , the ratio of carbon fixation to water loss , is critical to plant survival , crop yield and vegetation dynamics .
When challenged by variations in their environment , plants often seem to coordinate photosynthesis and transpiration , but significant genetic variation in transpiration efficiency has been identified both between and within species .
This has allowed plant breeders to develop effective selection programmes for the improved transpiration efficiency of crops , after it was demonstrated that carbon isotopic discrimination , Delta , of plant matter was a reliable and sensitive marker negatively related to variation in transpiration efficiency .
However , little is known of the genetic controls of transpiration efficiency .
Here we report the isolation of a gene that regulates transpiration efficiency , ERECTA .
We show that ERECTA , a putative leucine-rich repeat receptor-like kinase ( LRR-RLK ) known for its effects on inflorescence development , is a major contributor to a locus for Delta on Arabidopsis chromosome 2 .
Mechanisms include , but are not limited to , effects on stomatal density , epidermal cell expansion , mesophyll cell proliferation and cell-cell contact .

[1654] Quantifying underestimates of long-term upper-ocean warming

The global ocean stores more than 90 % of the heat associated with observed greenhouse-gas-attributed global warming .
Using satellite altimetry observations and a large suite of climate models , we conclude that observed estimates of 0-700 dbar global ocean warming since 1970 are likely biased low .
This underestimation is attributed to poor sampling of the Southern Hemisphere , and limitations of the analysis methods that conservatively estimate temperature changes in data-sparse regions .
We find that the partitioning of northern and southern hemispheric simulated sea surface height changes are consistent with precise altimeter observations , whereas the hemispheric partitioning of simulated upper-ocean warming is inconsistent with observed in-situ-based ocean heat content estimates .
Relying on the close correspondence between hemispheric-scale ocean heat content and steric changes , we adjust the poorly constrained Southern Hemisphere observed warming estimates so that hemispheric ratios are consistent with the broad range of modelled results .
These adjustments yield large increases ( 2.2-7 .1 x 1022 J 35 yr-1 ) to current global upper-ocean heat content change estimates , and have important implications for sea level , the planetary energy budget and climate sensitivity assessments .

[1655] Partial offsets in ocean acidification from changing coral reef biogeochemistry

Concerns have been raised about how coral reefs will be affected by ocean acidification , but projections of future seawater CO2 chemistry have focused solely on changes in the pH and aragonite saturation state ( Omegaa ) of open-ocean surface seawater conditions surrounding coral reefs rather than the reef systems themselves .
The seawater CO2 chemistry within heterogeneous reef systems can be significantly different from that of the open ocean depending on the residence time , community composition and the main biogeochemical processes occurring on the reef , that is , net ecosystem production ( NEP = gross primary production - autotrophic and heterotrophic respiration ) and net ecosystem calcification ( NEC = gross calcification - gross CaCO3 dissolution ) , which combined act to modify seawater chemistry .
On the basis of observations from the Bermuda coral reef , we show that a range of projected biogeochemical responses of coral reef communities to ocean acidification by the end of this century could partially offset changes in seawater pH and Omegaa by an average of 12-24 % and 15-31 % , respectively .

[1656] Alnus peptides modify membrane porosity and induce the release of nitrogen-rich metabolites from nitrogen-fixing Frankia

Actinorhizal plant growth in pioneer ecosystems depends on the symbiosis with the nitrogen-fixing actinobacterium Frankia cells that are housed in special root organs called nodules .
Nitrogen fixation occurs in differentiated Frankia cells known as vesicles .
Vesicles lack a pathway for assimilating ammonia beyond the glutamine stage and are supposed to transfer reduced nitrogen to the plant host cells .
However , a mechanism for the transfer of nitrogen-fixation products to the plant cells remains elusive .
Here , new elements for this metabolic exchange are described .
We show that Alnus glutinosa nodules express defensin-like peptides , and one of these , Ag5 , was found to target Frankia vesicles .
In vitro and in vivo analyses showed that Ag5 induces drastic physiological changes in Frankia , including an increased permeability of vesicle membranes .
A significant release of nitrogen-containing metabolites , mainly glutamine and glutamate , was found in N2-fixing cultures treated with Ag5 .
This work demonstrates that the Ag5 peptide is central for Frankia physiology in nodules and uncovers a novel cellular function for this large and widespread defensin peptide family .
The ISME Journal advance online publication , 20 January 2015 ; doi :10.1038 / ismej .2014.257

[1657] Isotopic evidence for Mesoarchaean anoxia and changing atmospheric sulphur chemistry

The evolution of the Earth 's atmosphere is marked by a transition from an early atmosphere with very low oxygen content to one with an oxygen content within a few per cent of the present atmospheric level .
Placing time constraints on this transition is of interest because it identifies the time when oxidative weathering became efficient , when ocean chemistry was transformed by delivery of oxygen and sulphate , and when a large part of Earth 's ecology changed from anaerobic to aerobic .
The observation of non-mass-dependent sulphur isotope ratios in sedimentary rocks more than ~ 2.45 billion years ( 2.45 Gyr ) old and the disappearance of this signal in younger sediments is taken as one of the strongest lines of evidence for the transition from an anoxic to an oxic atmosphere around 2.45 Gyr ago .
Detailed examination of the sulphur isotope record before 2.45 Gyr ago also reveals early and late periods of large amplitude non-mass-dependent signals bracketing an intervening period when the signal was attenuated .
Until recently , this record has been too sparse to allow interpretation , but collection of new data has prompted some workers to argue that the Mesoarchaean interval ( 3.2-2 .8 Gyr ago ) lacks a non-mass-dependent signal , and records the effects of earlier and possibly permanent oxygenation of the Earth 's atmosphere .
Here we focus on the Mesoarchaean interval , and demonstrate preservation of a non-mass-dependent signal that differs from that of preceding and following periods in the Archaean .
Our findings point to the persistence of an anoxic early atmosphere , and identify variability within the isotope record that suggests changes in pre-2 .45 - Gyr-ago atmospheric pathways for non-mass-dependent chemistry and in the ultraviolet transparency of an evolving early atmosphere .

[1658] Soil carbon : Resisting climate change

Increasing temperatures are expected to increase decomposition rates in soils , potentially reducing ecosystem carbon storage .
Research now indicates that -- in a tropical montane forest -- soil carbon stocks are unaffected by higher temperatures despite substantially increased rates of CO2 release from the soil .

[1659] Rapid growth in CO2 emissions after the 2008-2009 global financial crisis

To the Editor Global carbon dioxide emissions from fossil-fuel combustion and cement production grew 5.9 % in 2010 , surpassed 9 Pg of carbon ( Pg C ) for the first time , and more than offset the 1.4 % decrease in 2009 .
The impact of the 2008-2009 global financial crisis ( GFC ) on emissions has been short-lived owing to strong emissions growth in emerging economies , a return to emissions growth in developed economies , and an increase in the fossil-fuel intensity of the world economy .

[1660] The central role of selenium in the biochemistry and ecology of the harmful pelagophyte , Aureococcus anophagefferens

The trace element selenium ( Se ) is required for the biosynthesis of selenocysteine ( Sec ) , the 21st amino acid in the genetic code , but its role in the ecology of harmful algal blooms ( HABs ) is unknown .
Here , we examined the role of Se in the biology and ecology of the harmful pelagophyte , Aureococcus anophagefferens , through cell culture , genomic analyses , and ecosystem studies .
This organism has the largest and the most diverse selenoproteome identified to date that consists of at least 59 selenoproteins , including known eukaryotic selenoproteins , selenoproteins previously only detected in bacteria , and novel selenoproteins .
The A. anophagefferens selenoproteome was dominated by the thioredoxin fold proteins and oxidoreductase functions were assigned to the majority of detected selenoproteins .
Insertion of Sec in these proteins was supported by a unique Sec insertion sequence .
Se was required for the growth of A. anophagefferens as cultures grew maximally at nanomolar Se concentrations .
In a coastal ecosystem , dissolved Se concentrations were elevated before and after A. anophagefferens blooms , but were reduced by > 95 % during the peak of blooms to 0.05 nM .
Consistent with this pattern , enrichment of seawater with selenite before and after a bloom did not affect the growth of A. anophagefferens , but enrichment during the peak of the bloom significantly increased population growth rates .
These findings demonstrate that Se inventories , which can be anthropogenically enriched , can support proliferation of HABs , such as A. anophagefferens through its synthesis of a large arsenal of Se-dependent oxidoreductases that fine-tune cellular redox homeostasis .

[1661] In-flight gas phase growth of metal/multi layer graphene core shell nanoparticles with controllable sizes

In this report , we present a general method for a continuous gas-phase synthesis of size-selected metal/multi layer graphene ( MLG ) core shell nanoparticles having a narrow size distribution of metal core and MLG shell for direct deposition onto any desired substrate kept under clean vacuum conditions .
Evolution of MLG signature is clearly observed as the metal-carbon agglomerates get transformed to well defined metal/MLG core shell nanoparticles during their flight through the sintering zone .
The growth takes place via an intermediate state of alloy nanoparticle ( Pd-carbon ) or composite nanoparticle ( Cu-carbon ) , depending upon the carbon solubility in the metal and relative surface energy values .
It has been also shown that metal/MLG nanoparticles can be converted to graphene shells .
This study will have a large impact on how graphene or graphene based composite nanostructures can be grown and deposited in applications requiring controllable dimensions , varied substrate choice , large area and large scale depositions .

[1662] Stability of the West Antarctic ice sheet in a warming world

Ice sheets are expected to shrink in size as the world warms , which in turn will raise sea level .
The West Antarctic ice sheet is of particular concern , because it was probably much smaller at times during the past million years when temperatures were comparable to levels that might be reached or exceeded within the next few centuries .
Much of the grounded ice in West Antarctica lies on a bed that deepens inland and extends well below sea level .
Oceanic and atmospheric warming threaten to reduce or eliminate the floating ice shelves that buttress the ice sheet at present .
Loss of the ice shelves would accelerate the flow of non-floating ice near the coast .
Because of the slope of the sea bed , the consequent thinning could ultimately float much of the ice sheet 's interior .
In this scenario , global sea level would rise by more than three metres , at an unknown rate .
Simplified analyses suggest that much of the ice sheet will survive beyond this century .
We do not know how likely or inevitable eventual collapse of the West Antarctic ice sheet is at this stage , but the possibility can not be discarded .
For confident projections of the fate of the ice sheet and the rate of any collapse , further work including the development of well-validated physical models will be required .

[1663] Seasonal Synechococcus and Thaumarchaeal population dynamics examined with high resolution with remote in situ instrumentation

Monterey Bay , CA is an Eastern boundary upwelling system that is nitrogen limited much of the year .
In order to resolve population dynamics of microorganisms important for nutrient cycling in this region , we deployed the Environmental Sample Processor with quantitative PCR assays targeting both ribosomal RNA genes and functional genes for subclades of cyanobacteria ( Synechococcus ) and ammonia-oxidizing Archaea ( Thaumarchaeota ) populations .
Results showed a strong correlation between Thaumarchaea abundances and nitrate during the spring upwelling but not the fall sampling period .
In relatively stratified fall waters , the Thaumarchaeota community reached higher numbers than in the spring , and an unexpected positive correlation with chlorophyll concentration was observed .
Further , we detected drops in Synechococcus abundance that occurred on short ( that is , daily ) time scales .
Upwelling intensity and blooms of eukaryotic phytoplankton strongly influenced Synechococcus distributions in the spring and fall , revealing what appear to be the environmental limitations of Synechococcus populations in this region .
Each of these findings has implications for Monterey Bay biogeochemistry .
High-resolution sampling provides a better-resolved framework within which to observe changes in the plankton community .
We conclude that controls on these ecosystems change on smaller scales than are routinely assessed , and that more predictable trends will be uncovered if they are evaluated within seasonal ( monthly ) , rather than on annual or interannual scales .

[1664] Impacts of incentives to reduce emissions from deforestation on global species extinctions

Deforestation is a major source of anthropogenic greenhouse gas emissions , and the greatest single driver of species extinctions .
The reduction of emissions from deforestation and forest degradation ( REDD ) has been formally recognized as a climate change mitigation option .
REDD might have important co-benefits for biodiversity conservation , yet the extent of these benefits will depend on as-yet untested associations between fine-scale spatial patterns of deforestation , species distributions and carbon stocks .
Here we combine a global land-use model and spatial data on species distributions to explore scenarios of future deforestation within REDD-eligible countries , to quantify and map the potential impacts on species extinctions as increased by forest loss and decreased by carbon conservation .
We found that the continuation of historical deforestation rates is likely to result in large numbers of species extinctions , but that an adequately funded REDD programme could substantially reduce these losses .
Under our deforestation scenarios , the projected benefits of REDD were remarkably consistent across the four methods used to estimate extinctions , but spatially variable , and highly dependent on the level of carbon payments .
Our results indicate that , if well designed , adequately funded and broadly implemented , carbon-based forest conservation could play a major role in biodiversity conservation as well as climate change mitigation .

[1665] Human amplification of drought-induced biomass burning in Indonesia since 1960

Much of the interannual variability in global atmospheric carbon dioxide concentrations has been attributed to variability of emissions from biomass burning .
Under drought conditions , burning in Indonesia is a disproportionate contributor to these emissions , as seen in the 1997/98 haze disaster .
Yet our understanding of the frequency , severity and underlying causes of severe biomass burning in Indonesia is limited because of the absence of satellite data that are useful for fire monitoring before the mid-1990s .
Here we present a continuous monthly record of severe burning events from 1960 to 2006 using the visibility reported at airports in the region .
We find that these fires cause extremely poor air quality conditions and that they occur only during years when precipitation falls below a well defined threshold .
Historically , large fire events have occurred in Sumatra at least since the 1960s .
By contrast , the first large fires are recorded in Kalimantan ( Indonesian Borneo ) in the 1980s , despite earlier severe droughts .
We attribute this difference to different patterns of changes in land use and population density .
Fires in Indonesia have often been linked with El Nino , but we find that the Indian Ocean Dipole pattern is as important a contributing factor .

[1666] Rhythmic growth explained by coincidence between internal and external cues

Most organisms use circadian oscillators to coordinate physiological and developmental processes such as growth with predictable daily environmental changes like sunrise and sunset .
The importance of such coordination is highlighted by studies showing that circadian dysfunction causes reduced fitness in bacteria and plants , as well as sleep and psychological disorders in humans .
Plant cell growth requires energy and water -- factors that oscillate owing to diurnal environmental changes .
Indeed , two important factors controlling stem growth are the internal circadian oscillator and external light levels .
However , most circadian studies have been performed in constant conditions , precluding mechanistic study of interactions between the clock and diurnal variation in the environment .
Studies of stem elongation in diurnal conditions have revealed complex growth patterns , but no mechanism has been described .
Here we show that the growth phase of Arabidopsis seedlings in diurnal light conditions is shifted 8-12 h relative to plants in continuous light , and we describe a mechanism underlying this environmental response .
We find that the clock regulates transcript levels of two basic helix-loop-helix genes , phytochrome-interacting factor 4 ( PIF4 ) and PIF5 , whereas light regulates their protein abundance .
These genes function as positive growth regulators ; the coincidence of high transcript levels ( by the clock ) and protein accumulation ( in the dark ) allows them to promote plant growth at the end of the night .
Thus , these two genes integrate clock and light signalling , and their coordinated regulation explains the observed diurnal growth rhythms .
This interaction may serve as a paradigm for understanding how endogenous and environmental signals cooperate to control other processes .

[1667] Effects of patch connectivity and heterogeneity on metacommunity structure of planktonic bacteria and viruses

Dispersal limitation is generally considered to have little influence on the spatial structure of biodiversity in microbial metacommunities .
This notion derives mainly from the analysis of spatial patterns in the field , but experimental tests of dispersal limitation using natural communities are rare for prokaryotes and , to our knowledge , non-existent for viruses .
We studied the effects of dispersal intensity ( three levels ) and patch heterogeneity ( two levels ) on the structure of replicate experimental metacommunities of bacteria and viruses using outdoor mesocosms with plankton communities from natural ponds and lakes .
Low levels of dispersal resulted in a decrease in the compositional differences ( beta diversity ) among the communities of both bacteria and viruses , but we found no effects of patch heterogeneity .
The reductions in beta diversity are unlikely to be a result of mass effects and only partly explained by indirect dispersal-mediated interactions with phytoplankton and zooplankton .
Our results suggest that even a very limited exchange among local communities can alter the trajectory of bacterial and viral communities at small temporal and spatial scales .

[1668] Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming

The Greenland ice sheet has been one of the largest contributors to global sea-level rise over the past 20 years , accounting for 0.5 mm yr-1 of a total of 3.2 mm yr-1 .
A significant portion of this contribution is associated with the speed-up of an increased number of glaciers in southeast and northwest Greenland .
Here , we show that the northeast Greenland ice stream , which extends more than 600 km into the interior of the ice sheet , is now undergoing sustained dynamic thinning , linked to regional warming , after more than a quarter of a century of stability .
This sector of the Greenland ice sheet is of particular interest , because the drainage basin area covers 16 % of the ice sheet ( twice that of Jakobshavn Isbrae ) and numerical model predictions suggest no significant mass loss for this sector , leading to an under-estimation of future global sea-level rise .
The geometry of the bedrock and monotonic trend in glacier speed-up and mass loss suggests that dynamic drawdown of ice in this region will continue in the near future .

[1669] Aerobic nitrous oxide production through N-nitrosating hybrid formation in ammonia-oxidizing archaea

Soil emissions are largely responsible for the increase of the potent greenhouse gas nitrous oxide ( N2O ) in the atmosphere and are generally attributed to the activity of nitrifying and denitrifying bacteria .
However , the contribution of the recently discovered ammonia-oxidizing archaea ( AOA ) to N2O production from soil is unclear as is the mechanism by which they produce it .
Here we investigate the potential of Nitrososphaera viennensis , the first pure culture of AOA from soil , to produce N2O and compare its activity with that of a marine AOA and an ammonia-oxidizing bacterium ( AOB ) from soil .
N. viennensis produced N2O at a maximum yield of 0.09 % N2O per molecule of nitrite under oxic growth conditions .
N2O production rates of 4.6 + / -0.6 amol N2O cell-1 h-1 and nitrification rates of 2.6 + / -0.5 fmol NO2 - cell-1 h-1 were in the same range as those of the AOB Nitrosospira multiformis and the marine AOA Nitrosopumilus maritimus grown under comparable conditions .
In contrast to AOB , however , N2O production of the two archaeal strains did not increase when the oxygen concentration was reduced , suggesting that they are not capable of denitrification .
In 15N-labeling experiments we provide evidence that both ammonium and nitrite contribute equally via hybrid N2O formation to the N2O produced by N. viennensis under all conditions tested .
Our results suggest that archaea may contribute to N2O production in terrestrial ecosystems , however , they are not capable of nitrifier-denitrification and thus do not produce increasing amounts of the greenhouse gas when oxygen becomes limiting .

[1670] Microbial and viral metagenomes of a subtropical freshwater reservoir subject to climatic disturbances

Extreme climatic activities , such as typhoons , are widely known to disrupt our natural environment .
In particular , studies have revealed that typhoon-induced perturbations can result in several long-term effects on various ecosystems .
In this study , we have conducted a 2-year metagenomic survey to investigate the microbial and viral community dynamics associated with environmental changes and seasonal variations in an enclosed freshwater reservoir subject to episodic typhoons .
We found that the microbial community structure and the associated metagenomes continuously changed , where microbial richness increased after typhoon events and decreased during winter .
Among the environmental factors that influenced changes in the microbial community , precipitation was considered to be the most significant .
Similarly , the viral community regularly showed higher relative abundances and diversity during summer in comparison to winter , with major variations happening in several viral families including Siphoviridae , Myoviridae , Podoviridae and Microviridae .
Interestingly , we also found that the precipitation level was associated with the terrestrial viral abundance in the reservoir .
In contrast to the dynamic microbial community ( L-divergence 0.73 + / -0.25 ) , we found that microbial metabolic profiles were relatively less divergent ( L-divergence 0.24 + / -0.04 ) at the finest metabolic resolution .
This study provides for the first time a glimpse at the microbial and viral community dynamics of a subtropical freshwater ecosystem , adding a comprehensive set of new knowledge to aquatic environments .

[1671] Climate change : Acidic oceans shrink plankton

As oceans take up more carbon dioxide , their increasing acidity could be decreasing the weight of one of the most abundant calcium-producing marine phytoplankton .
Low pH is known to interfere with phytoplankton calcification and reduce their weight in the lab , but the impacts of ocean acidification in the wild have not been clear .

[1672] Variability of the path of the Kuroshio ocean current over the past 25,000 years

The Kuroshio current is the strong northwestern component of the subtropical North Pacific Ocean gyre , and advects a large amount of heat from the tropics to northern mid-latitudes .
The Kuroshio has bimodal stationary flow patterns , with small and large meander paths east of central Japan , which switch on annual and decadal timescales , .
These switches seem to be caused by changes in current velocity and volume transport of the North Equatorial Current that are associated with variations in the trade-wind intensity in the eastern equatorial North Pacific Ocean , .
Here we present alkenone-derived sea surface temperature records at multicentennial resolution from sediment cores from the Nishishichitou ridge off central Japan .
These 25,000-year records show that the Kuroshio path has also fluctuated on millennial timescales .
This variability resembles that of the subtropical high pressure of the North Pacific , reconstructed from terrestrial pollen distributions , water levels in North American lakes , and marine micropalaeontological records .
Together , these data indicate that climate variability off central Japan over the past 25,000 years may be part of a circum-Pacific phenomenon , reflecting the rate of subtropical surface circulation in the North Pacific Ocean .

[1673] Rapid evolution drives ecological dynamics in a predator-prey system

Ecological and evolutionary dynamics can occur on similar timescales .
However , theoretical predictions of how rapid evolution can affect ecological dynamics are inconclusive and often depend on untested model assumptions .
Here we report that rapid prey evolution in response to oscillating predator density affects predator-prey ( rotifer-algal ) cycles in laboratory microcosms .
Our experiments tested explicit predictions from a model for our system that allows prey evolution .
We verified the predicted existence of an evolutionary tradeoff between algal competitive ability and defence against consumption , and examined its effects on cycle dynamics by manipulating the evolutionary potential of the prey population .
Single-clone algal cultures ( lacking genetic variability ) produced short cycle periods and typical quarter-period phase lags between prey and predator densities , whereas multi-clonal ( genetically variable ) algal cultures produced long cycles with prey and predator densities nearly out of phase , exactly as predicted .
These results confirm that prey evolution can substantially alter predator-prey dynamics , and therefore that attempts to understand population oscillations in nature can not neglect potential effects from ongoing rapid evolution .

[1674] Effect of stream channel size on the delivery of nitrogen to the Gulf of Mexico

An increase in the flux of nitrogen from the Mississippi river during the latter half of the twentieth century has caused eutrophication and chronic seasonal hypoxia in the shallow waters of the Louisiana shelf in the northern Gulf of Mexico .
This has led to reductions in species diversity , mortality of benthic communities and stress in fishery resources .
There is evidence for a predominantly anthropogenic origin of the increased nitrogen flux , but the location of the most significant sources in the Mississippi basin responsible for the delivery of nitrogen to the Gulf of Mexico have not been clearly identified , because the parameters influencing nitrogen-loss rates in rivers are not well known .
Here we present an analysis of data from 374 US monitoring stations , including 123 along the six largest tributaries to the Mississippi , that shows a rapid decline in the average first-order rate of nitrogen loss with channel size -- from 0.45 day-1 in small streams to 0.005 day-1 in the Mississippi river .
Using stream depth as an explanatory variable , our estimates of nitrogen-loss rates agreed with values from earlier studies .
We conclude that the proximity of sources to large streams and rivers is an important determinant of nitrogen delivery to the estuary in the Mississippi basin , and possibly also in other large river basins .

[1675] Unveiling microbial activities along the halocline of Thetis , a deep-sea hypersaline anoxic basin

Deep-sea hypersaline anoxic basins ( DHABs ) in the Eastern Mediterranean Sea are considered some of the most hostile environments on Earth .
Little is known about the biochemical adaptations of microorganisms living in these habitats .
This first metatranscriptome analysis of DHAB samples provides significant insights into shifts in metabolic activities of microorganisms as physicochemical conditions change from deep Mediterranean sea water to brine .
The analysis of Thetis DHAB interface indicates that sulfate reduction occurs in both the upper ( 7.0-16 .3 % salinity ) and lower ( 21.4-27 .6 % ) halocline , but that expression of dissimilatory sulfate reductase is reduced in the more hypersaline lower halocline .
High dark-carbon assimilation rates in the upper interface coincided with high abundance of transcripts for ribulose 1,5-bisphosphate carboxylase affiliated to sulfur-oxidizing bacteria .
In the lower interface , increased expression of genes associated with methane metabolism and osmoregulation is noted .
In addition , in this layer , nitrogenase transcripts affiliated to uncultivated putative methanotrophic archaea were detected , implying nitrogen fixation in this anoxic habitat , and providing evidence of linked carbon , nitrogen and sulfur cycles .

[1676] The paradox of enrichment in phytoplankton by induced competitive interactions

The biodiversity loss of phytoplankton with eutrophication has been reported in many aquatic ecosystems , e.g. , water pollution and red tides .
This phenomenon seems similar , but different from the paradox of enrichment via trophic interactions , e.g. , predator-prey systems .
We here propose the paradox of enrichment by induced competitive interactions using multiple contact process ( a lattice Lotka-Volterra competition model ) .
Simulation results demonstrate how eutrophication invokes more competitions in a competitive ecosystem resulting in the loss of phytoplankton diversity in ecological time .
The paradox is enhanced under local interactions , indicating that the limited dispersal of phytoplankton reduces interspecific competition greatly .
Thus , the paradox of enrichment appears when eutrophication destroys an ecosystem either by elevated interspecific competition within a trophic level and/or destabilization by trophic interactions .
Unless eutrophication due to human activities is ceased , the world 's aquatic ecosystems will be at risk .

[1677] Genome-wide analysis of Sphingomonas wittichii RW1 behaviour during inoculation and growth in contaminated sand

The efficacy of inoculation of single pure bacterial cultures into complex microbiomes , for example , in order to achieve increased pollutant degradation rates in contaminated material ( that is , bioaugmentation ) , has been frustrated by insufficient knowledge on the behaviour of the inoculated bacteria under the specific abiotic and biotic boundary conditions .
Here we present a comprehensive analysis of genome-wide gene expression of the bacterium Sphingomonas wittichii RW1 in contaminated non-sterile sand , compared with regular suspended batch growth in liquid culture .
RW1 is a well-known bacterium capable of mineralizing dibenzodioxins and dibenzofurans .
We tested the reactions of the cells both during the immediate transition phase from liquid culture to sand with or without dibenzofuran , as well as during growth and stationary phase in sand .
Cells during transition show stationary phase characteristics , evidence for stress and for nutrient scavenging , and adjust their primary metabolism if they were not precultured on the same contaminant as found in the soil .
Cells growing and surviving in sand degrade dibenzofuran but display a very different transcriptome signature as in liquid or in liquid culture exposed to chemicals inducing drought stress , and we obtain evidence for numerous ` soil-specific ' expressed genes .
Studies focusing on inoculation efficacy should test behaviour under conditions as closely as possible mimicking the intended microbiome conditions .

[1678] Predictability of El Nino over the past 148 years

Forecasts of El Nino climate events are routinely provided and distributed , but the limits of El Nino predictability are still the subject of debate .
Some recent studies suggest that the predictability is largely limited by the effects of high-frequency atmospheric ` noise ' , whereas others emphasize limitations arising from the growth of initial errors in model simulations .
Here we present retrospective forecasts of the interannual climate fluctuations in the tropical Pacific Ocean for the period 1857 to 2003 , using a coupled ocean-atmosphere model .
The model successfully predicts all prominent El Nino events within this period at lead times of up to two years .
Our analysis suggests that the evolution of El Nino is controlled to a larger degree by self-sustaining internal dynamics than by stochastic forcing .
Model-based prediction of El Nino therefore depends more on the initial conditions than on unpredictable atmospheric noise .
We conclude that throughout the past century , El Nino has been more predictable than previously envisaged .

[1679] Trends and oscillations in the Indian summer monsoon rainfall over the last two millennia

Observations show that summer rainfall over large parts of South Asia has declined over the past five to six decades .
It remains unclear , however , whether this trend is due to natural variability or increased anthropogenic aerosol loading over South Asia .
Here we use stable oxygen isotopes in speleothems from northern India to reconstruct variations in Indian monsoon rainfall over the last two millennia .
We find that within the long-term context of our record , the current drying trend is not outside the envelope of monsoon 's oscillatory variability , albeit at the lower edge of this variance .
Furthermore , the magnitude of multi-decadal oscillatory variability in monsoon rainfall inferred from our proxy record is comparable to model estimates of anthropogenic-forced trends of mean monsoon rainfall in the 21st century under various emission scenarios .
Our results suggest that anthropogenic-forced changes in monsoon rainfall will remain difficult to detect against a backdrop of large natural variability .

[1680] Worldwide variations in artificial skyglow

Despite constituting a widespread and significant environmental change , understanding of artificial nighttime skyglow is extremely limited .
Until now , published monitoring studies have been local or regional in scope , and typically of short duration .
In this first major international compilation of monitoring data we answer several key questions about skyglow properties .
Skyglow is observed to vary over four orders of magnitude , a range hundreds of times larger than was the case before artificial light .
Nearly all of the study sites were polluted by artificial light .
A non-linear relationship is observed between the sky brightness on clear and overcast nights , with a change in behavior near the rural to urban landuse transition .
Overcast skies ranged from a third darker to almost 18 times brighter than clear .
Clear sky radiances estimated by the World Atlas of Artificial Night Sky Brightness were found to be overestimated by ~ 25 % ; our dataset will play an important role in the calibration and ground truthing of future skyglow models .
Most of the brightly lit sites darkened as the night progressed , typically by ~ 5 % per hour .
The great variation in skyglow radiance observed from site-to-site and with changing meteorological conditions underlines the need for a long-term international monitoring program .

[1681] Similar response of labile and resistant soil organic matter pools to changes in temperature

Our understanding of the relationship between the decomposition of soil organic matter ( SOM ) and soil temperature affects our predictions of the impact of climate change on soil-stored carbon .
One current opinion is that the decomposition of soil labile carbon is sensitive to temperature variation whereas resistant components are insensitive .
The resistant carbon or organic matter in mineral soil is then assumed to be unresponsive to global warming .
But the global pattern and magnitude of the predicted future soil carbon stock will mainly rely on the temperature sensitivity of these resistant carbon pools .
To investigate this sensitivity , we have incubated soils under changing temperature .
Here we report that SOM decomposition or soil basal respiration rate was significantly affected by changes in SOM components associated with soil depth , sampling method and incubation time .
We find , however , that the temperature sensitivity for SOM decomposition was not affected , suggesting that the temperature sensitivity for resistant organic matter pools does not differ significantly from that of labile pools , and that both types of SOM will therefore respond similarly to global warming .

[1682] The impact of surface-adsorbed phosphorus on phytoplankton Redfield stoichiometry

The Redfield ratio of 106 carbon :16 nitrogen :1 phosphorus in marine phytoplankton is one of the foundations of ocean biogeochemistry , with applications in algal physiology , palaeoclimatology and global climate change .
However , this ratio varies substantially in response to changes in algal nutrient status and taxonomic affiliation .
Here we report that Redfield ratios are also strongly affected by partitioning into surface-adsorbed and intracellular phosphorus pools .
The C : N : surface-adsorbed P ( 80-105 C :15 -18 N :1 P ) and total ( 71-80 C :13 -14 N :1 P ) ratios in natural populations and cultures of Trichodesmium were close to Redfield values and not significantly different from each other .
In contrast , intracellular ratios consistently exceeded the Redfield ratio ( 316-434 C :59 -83 N :1 intracellular P ) .
These high intracellular ratios were associated with reduced N2 fixation rates , suggestive of phosphorus deficiency .
Other algal species also have substantial surface-adsorbed phosphorus pools , suggesting that our Trichodesmium results are generally applicable to all phytoplankton .
Measurements of the distinct phytoplankton phosphorus pools may be required to assess nutrient limitation accurately from elemental composition .
Deviations from Redfield stoichiometry may be attributable to surface adsorption of phosphorus rather than to biological processes , and this scavenging could affect the interpretation of marine nutrient inventories and ecosystem models .

[1683] Microbial Oxidation of Fe2 + and Pyrite Exposed to Flux of Micromolar H2O2 in Acidic Media

At an initial pH of 2 , while abiotic oxidation of aqueous Fe2 + was enhanced by a flux of H2O2 at micromolar concentrations , bio-oxidation of aqueous Fe2 + could be impeded due to oxidative stress/damage in Acidithiobacillus ferrooxidans caused by Fenton reaction-derived hydroxyl radical , particularly when the molar ratio of Fe2 + to H2O2 was low .
When pyrite cubes were intermittently exposed to fluxes of micromolar H2O2 , the reduced Fe2 + - Fe3 + conversion rate in the solution ( due to reduced microbial activity ) weakened the Fe3 + - catalyzed oxidation of cubic pyrite and added to relative importance of H2O2-driven oxidation in the corrosion of mineral surfaces for the treatments with high H2O2 doses .
This had effects on reducing the build-up of a passivating coating layer on the mineral surfaces .
Cell attachment to the mineral surfaces was only observed at the later stage of the experiment after the solutions became less favorable for the growth of planktonic bacteria .

[1684] Evolution of NO2 levels in Spain from 1996 to 2012

We report on the evolution of tropospheric nitrogen dioxide ( NO2 ) over Spain , focusing on the densely populated cities of Barcelona , Bilbao , Madrid , Sevilla and Valencia , during 17 years , from 1996 to 2012 .
This data series combines observations from in-situ air quality monitoring networks and the satellite-based instruments GOME and SCIAMACHY .
The results in these five cities show a smooth decrease in the NO2 concentrations of ~ 2 % per year in the period 1996-2008 , due to the implementation of emissions control environmental legislation , and a more abrupt descend of ~ 7 % per year from 2008 to 2012 as a consequence of the economic recession .
In the whole Spanish territory the NO2 levels have decreased by ~ 22 % from 1996 to 2012 .
Statistical analysis of several economic indicators is used to investigate the different factors driving the NO2 concentration trends over Spain during the last two decades .

[1685] Renewable and metal-free carbon nanofibre catalysts for carbon dioxide reduction

The development of an efficient catalyst system for the electrochemical reduction of carbon dioxide into energy-rich products is a major research topic .
Here we report the catalytic ability of polyacrylonitrile-based heteroatomic carbon nanofibres for carbon dioxide reduction into carbon monoxide , via a metal-free , renewable and cost-effective route .
The carbon nanofibre catalyst exhibits negligible overpotential ( 0.17 V ) for carbon dioxide reduction and more than an order of magnitude higher current density compared with the silver catalyst under similar experimental conditions .
The carbon dioxide reduction ability of carbon nanofibres is attributed to the reduced carbons rather than to electronegative nitrogen atoms .
The superior performance is credited to the nanofibrillar structure and high binding energy of key intermediates to the carbon nanofibre surfaces .
The finding may lead to a new generation of metal-free and non-precious catalysts with much greater efficiency than the existing noble metal catalysts .

[1686] High-fat-diet-mediated dysbiosis promotes intestinal carcinogenesis independently of obesity

Several features common to a Western lifestyle , including obesity and low levels of physical activity , are known risk factors for gastrointestinal cancers .
There is substantial evidence suggesting that diet markedly affects the composition of the intestinal microbiota .
Moreover , there is now unequivocal evidence linking dysbiosis to cancer development .
However , the mechanisms by which high-fat diet ( HFD ) - mediated changes in the microbial community affect the severity of tumorigenesis in the gut remain to be determined .
Here we demonstrate that an HFD promotes tumour progression in the small intestine of genetically susceptible , K-rasG12Dint , mice independently of obesity .
HFD consumption , in conjunction with K-ras mutation , mediated a shift in the composition of the gut microbiota , and this shift was associated with a decrease in Paneth-cell-mediated antimicrobial host defence that compromised dendritic cell recruitment and MHC class II molecule presentation in the gut-associated lymphoid tissues .
When butyrate was administered to HFD-fed K-rasG12Dint mice , dendritic cell recruitment in the gut-associated lymphoid tissues was normalized , and tumour progression was attenuated .
Importantly , deficiency in MYD88 , a signalling adaptor for pattern recognition receptors and Toll-like receptors , blocked tumour progression .
The transfer of faecal samples from HFD-fed mice with intestinal tumours to healthy adult K-rasG12Dint mice was sufficient to transmit disease in the absence of an HFD .
Furthermore , treatment with antibiotics completely blocked HFD-induced tumour progression , suggesting that distinct shifts in the microbiota have a pivotal role in aggravating disease .
Collectively , these data underscore the importance of the reciprocal interaction between host and environmental factors in selecting a microbiota that favours carcinogenesis , and they suggest that tumorigenesis is transmissible among genetically predisposed individuals .

[1687] Palaeo-oceanography : Deepwater variability in the Holocene epoch

The conversion of surface water to deep water in the North Atlantic results in the release of heat from the ocean to the atmosphere , which may have amplified millennial-scale climate variability during glacial times and could even have contributed to the past 11,700 years of relatively mild climate ( known as the Holocene epoch ) .
Here we investigate changes in the carbon-isotope composition of benthic foraminifera throughout the Holocene and find that deep-water production varied on a centennial-millennial timescale .
These variations may be linked to surface and atmospheric events that hint at a contribution to climate change over this period .

[1688] Atmospheric carbon dioxide through the Eocene-Oligocene climate transition

Geological and geochemical evidence indicates that the Antarctic ice sheet formed during the Eocene-Oligocene transition , 33.5-34 .0 million years ago .
Modelling studies suggest that such ice-sheet formation might have been triggered when atmospheric carbon dioxide levels ( ) fell below a critical threshold of ~ 750 p.p.m.v. , but the timing and magnitude of relative to the evolution of the ice sheet has remained unclear .
Here we use the boron isotope pH proxy on exceptionally well-preserved carbonate microfossils from a recently discovered geological section in Tanzania to estimate before , during and after the climate transition .
Our data suggest that a reduction in occurred before the main phase of ice growth , followed by a sharp recovery to pre-transition values and then a more gradual decline .
During maximum ice-sheet growth , was between ~ 450 and ~ 1,500 p.p.m.v. , with a central estimate of ~ 760 p.p.m.v. .
The ice cap survived the period of recovery , although possibly with some reduction in its volume , implying ( as models predict ) a nonlinear response to climate forcing during melting .
Overall , our results confirm the central role of declining in the development of the Antarctic ice sheet ( in broad agreement with carbon cycle modelling ) and help to constrain mechanisms and feedbacks associated with the Earth 's biggest climate switch of the past 65 Myr .

[1689] Wave attenuation over coastal salt marshes under storm surge conditions

Coastal communities around the world face an increasing risk from flooding as a result of rising sea level , increasing storminess and land subsidence .
Salt marshes can act as natural buffer zones , providing protection from waves during storms .
However , the effectiveness of marshes in protecting the coastline during extreme events when water levels are at a maximum and waves are highest is poorly understood .
Here we experimentally assess wave dissipation under storm surge conditions in a 300-metre-long wave flume tank that contains a transplanted section of natural salt marsh .
We find that the presence of marsh vegetation causes considerable wave attenuation , even when water levels and waves are highest .
From a comparison with experiments without vegetation , we estimate that up to 60 % of observed wave reduction is attributed to vegetation .
We also find that although waves progressively flatten and break vegetation stems and thereby reduce dissipation , the marsh substrate remained stable and resistant to surface erosion under all conditions .
The effectiveness of storm wave dissipation and the resilience of tidal marshes even at extreme conditions suggest that salt marsh ecosystems can be a valuable component of coastal protection schemes .

[1690] Physiology and genetic traits of reverse osmosis membrane biofilms : a case study with Pseudomonas aeruginosa

Biofilm formation of Pseudomonas aeruginosa on the surface of a reverse osmosis ( RO ) membrane was studied using a synthetic wastewater medium to simulate conditions relevant to reclamation of secondary wastewater effluent .
P. aeruginosa biofilm physiology and spatial activity were analyzed following growth on the membrane using a short-life green fluorescent protein derivative expressed in a growth-dependent manner .
As a consequence of the limiting carbon source prevailing in the suspended culture of the RO unit , a higher distribution of active cells was observed in the biofilm close to the membrane surface , likely due to the higher nutrient levels induced by concentration polarization effects .
The faster growth of the RO-sessile cells compared to the planktonic cells in the RO unit was reflected by the transcriptome of the two cultures analyzed with DNA microarrays .
In contrast to the findings recently reported in gene expression studies of P. aeruginosa biofilms , in the RO system , genes related to stress , adaptation , chemotaxis and resistance to antibacterial agents were induced in the planktonic cells .
In agreement with the findings of previous P. aeruginosa biofilm studies , motility - and attachment-related genes were repressed in the RO P. aeruginosa biofilm .
Supported by the microarray data , an increase in both motility and chemotaxis phenotypes was observed in the suspended cells .
The increase in nutrient concentration in close proximity to the membrane is suggested to enhance biofouling by chemotaxis response of the suspended cells and their swimming toward the membrane surface .

[1691] Greater ecosystem carbon in the Mojave Desert after ten years exposure to elevated CO2

Carbon dioxide is the main greenhouse gas inducing climate change .
Increased global CO2 emissions , estimated at 8.4 Pg C yr-1 at present , have accelerated from 1 % yr-1 during 1990-1999 to 2.5 % yr-1 during 2000-2009 ( ref . )
.
The carbon balance of terrestrial ecosystems is the greatest unknown in the global C budget because the actual magnitude , location and causes of terrestrial sinks are uncertain ; estimates of terrestrial C uptake , therefore , are often based on the residuals between direct measurements of the atmospheric sink and well-constrained models of ocean uptake of CO2 ( ref . )
.
Here we report significant terrestrial C accumulation caused by CO2 enhancement to net ecosystem productivity in an intact , undisturbed arid ecosystem following ten years of exposure to elevated atmospheric CO2 .
Results provide direct evidence that CO2 fertilization substantially increases ecosystem C storage and that arid ecosystems are significant , previously unrecognized , sinks for atmospheric CO2 that must be accounted for in efforts to constrain terrestrial and global C cycles .

[1692] Millennial-scale changes in North Atlantic circulation since the last glaciation

Ocean circulation is closely linked to climate change on glacial-interglacial and shorter timescales .
Extensive reorganizations in the circulation of deep and intermediate-depth waters in the Atlantic Ocean have been hypothesized for both the last glaciation and the subsequent Younger Dryas cold interval , , but there has been little palaeoceanographic study of the subtropical gyres .
These gyres are the dominant oceanic features of wind-driven circulation , and as such they reflect changes in climate and are a significant control on nutrient cycling and , possibly , atmospheric CO2 concentrations .
Here we present Cd/Ca ratios in the shells of benthic foraminifera from the Bahama banks that confirm previous suggestions , that nutrient concentrations in the North Atlantic subtropical gyre were much lower during the Last Glacial Maximum than they are today ( up to 50 % lower according to our data ) .
These contrasting nutrient burdens imply much shorter residence times for waters within the thermocline of the Last Glacial Maximum .
Below the glacial thermocline , nutrient concentrations were reduced owing to the presence of Glacial North Atlantic Intermediate Water .
A high-resolution Cd/Ca record from an intermediate depth indicates decreased nutrient concentrations during the Younger Dryas interval as well , mirroring opposite changes at a nearby deep site , .
Together , these observations suggest that the formation of deep and intermediate waters -- North Atlantic Deep Water and Glacial North Atlantic Intermediate Water , respectively -- wax and wane alternately on both orbital and millennial timescales .

[1693] The rate of sea-level rise

Present-day sea-level rise is a major indicator of climate change .
Since the early 1990s , sea level rose at a mean rate of ~ 3.1 mm yr-1 ( refs , ) .
However , over the last decade a slowdown of this rate , of about 30 % , has been recorded .
It coincides with a plateau in Earth 's mean surface temperature evolution , known as the recent pause in warming .
Here we present an analysis based on sea-level data from the altimetry record of the past ~ 20 years that separates interannual natural variability in sea level from the longer-term change probably related to anthropogenic global warming .
The most prominent signature in the global mean sea level interannual variability is caused by El Nino-Southern Oscillation , through its impact on the global water cycle .
We find that when correcting for interannual variability , the past decade 's slowdown of the global mean sea level disappears , leading to a similar rate of sea-level rise ( of 3.3 + / - 0.4 mm yr-1 ) during the first and second decade of the altimetry era .
Our results confirm the need for quantifying and further removing from the climate records the short-term natural climate variability if one wants to extract the global warming signal .

[1694] Carbon emissions from forest conversion by Kalimantan oil palm plantations

Oil palm supplies > 30 % of world vegetable oil production .
Plantation expansion is occurring throughout the tropics , predominantly in Indonesia , where forests with heterogeneous carbon stocks undergo high conversion rates .
Quantifying oil palm 's contribution to global carbon budgets therefore requires refined spatio-temporal assessments of land cover converted to plantations .
Here , we report oil palm development across Kalimantan ( 538,346 km2 ) from 1990 to 2010 , and project expansion to 2020 within government-allocated leases .
Using Landsat satellite analyses to discern multiple land covers , coupled with above - and below-ground carbon accounting , we develop the first high-resolution carbon flux estimates from Kalimantan plantations .
From 1990 to 2010 , 90 % of lands converted to oil palm were forested ( 47 % intact , 22 % logged , 21 % agroforests ) .
By 2010 , 87 % of total oil palm area ( 31,640 km2 ) occurred on mineral soils , and these plantations contributed 61-73 % of 1990-2010 net oil palm emissions ( 0.020-0 .024 GtC yr-1 ) .
Although oil palm expanded 278 % from 2000 to 2010 , 79 % of allocated leases remained undeveloped .
By 2020 , full lease development would convert 93,844 km2 ( ~ 90 % forested lands , including 41 % intact forests ) .
Oil palm would then occupy 34 % of lowlands outside protected areas .
Plantation expansion in Kalimantan alone is projected to contribute 18-22 % ( 0.12-0 .15 GtC yr-1 ) of Indonesia 's 2020 CO2-equivalent emissions .
Allocated oil palm leases represent a critical yet undocumented source of deforestation and carbon emissions .

[1695] A record of the Southern Oscillation Index for the past 2,000 years from precipitation proxies

The El Nino-Southern Oscillation ( ENSO ) is a coupled ocean-atmosphere climate phenomenon in the tropical Pacific Ocean .
The interannual climate variations have been shown to modify both the Hadley and Walker meridional and zonal atmospheric circulations , with strong impacts on global climate .
Proxy-based reconstructions of the Southern Oscillation Index on a multi-decadal scale have shown that the strength and frequency of El Nino occurrences have varied over the past millennium .
Here we compile reconstructions of precipitation from regions that experience substantial ENSO variability to extend the multidecadal-scale Southern Oscillation Index to include the past 2,000 years .
We find that the Medieval Warm Period ( ~ AD 800-1300 ) was characterized by a negative index , which indicates more El Nino-dominated conditions , whereas during the Little Ice Age ( ~ AD 1400-1850 ) more La Nina-dominated conditions prevailed .
The Southern Oscillation Index we derive is significantly correlated with reconstructions of solar irradiance and mean Northern Hemisphere temperature fluctuations .

[1696] Penguins significantly increased phosphine formation and phosphorus contribution in maritime Antarctic soils

Most studies on phosphorus cycle in the natural environment focused on phosphates , with limited data available for the reduced phosphine ( PH3 ) .
In this paper , matrix-bound phosphine ( MBP ) , gaseous phosphine fluxes and phosphorus fractions in the soils were investigated from a penguin colony , a seal colony and the adjacent animal-lacking tundra and background sites .
The MBP levels ( mean 200.3 ng kg-1 ) in penguin colony soils were much higher than those in seal colony soils , animal-lacking tundra soils and the background soils .
Field PH3 flux observation and laboratory incubation experiments confirmed that penguin colony soils produced much higher PH3 emissions than seal colony soils and animal-lacking tundra soils .
Overall high MBP levels and PH3 emissions were modulated by soil biogeochemical processes associated with penguin activities : sufficient supply of the nutrients phosphorus , nitrogen , and organic carbon from penguin guano , high soil bacterial abundance and phosphatase activity .
It was proposed that organic or inorganic phosphorus compounds from penguin guano or seal excreta could be reduced to PH3 in the Antarctic soils through the bacterial activity .
Our results indicated that penguin activity significantly increased soil phosphine formation and phosphorus contribution , thus played an important role in phosphorus cycle in terrestrial ecosystems of maritime Antarctica .

[1697] Phytoplankton change in the North Atlantic

A marked increase in global temperature over the last century was confirmed by the second Assessment Report of the Intergovernmental Panel on Climate Change .
Here we report significant positive and negative linear trends from 1948 to 1995 in phytoplankton measured by the Continuous Plankton Recorder survey in the northeast Atlantic and North Sea that might reflect a response to changing climate on a timescale of decades .
Spreading of unusually cold waters from the Arctic might have contributed to the decline in phytoplankton north of 59o N. Further south , phytoplankton season length and abundance seem to have increased .

[1698] Characterization of salt-adapted secreted lignocellulolytic enzymes from the mangrove fungus Pestalotiopsis sp .

Fungi are important for biomass degradation processes in mangrove forests .
Given the presence of sea water in these ecosystems , mangrove fungi are adapted to high salinity .
Here we isolate Pestalotiopsis sp .
NCi6 , a halotolerant and lignocellulolytic mangrove fungus of the order Xylariales .
We study its lignocellulolytic enzymes and analyse the effects of salinity on its secretomes .
De novo transcriptome sequencing and assembly indicate that this fungus possesses of over 400 putative lignocellulolytic enzymes , including a large fraction involved in lignin degradation .
Proteomic analyses of the secretomes suggest that the presence of salt modifies lignocellulolytic enzyme composition , with an increase in the secretion of xylanases and cellulases and a decrease in the production of oxidases .
As a result , cellulose and hemicellulose hydrolysis is enhanced but lignin breakdown is reduced .
This study highlights the adaptation to salt of mangrove fungi and their potential for biotechnological applications .

[1699] Stimulation by ammonium-based fertilizers of methane oxidation in soil around rice roots

Methane is involved in a number of chemical and physical processes in the Earth 's atmosphere , including global warming .
Atmospheric methane originates mainly from biogenic sources , such as rice paddies and natural wetlands ; the former account for at least 30 % of the global annual emission of methane to the atmosphere .
As an increase of rice production by 60 % is the most appropriate way to sustain the estimated increase of the human population during the next three decades , intensified global fertilizer application will be necessary : but it is known that an increase of the commonly used ammonium-based fertilizers can enhance methane emission from rice agriculture .
Approximately 10-30 % of the methane produced by methanogens in rice paddies is consumed by methane-oxidizing bacteria associated with the roots of rice ; these bacteria are generally thought to be inhibited by ammonium-based fertilizers , as was demonstrated for soils and sediments .
In contrast , we show here that the activity and growth of such bacteria in the root zone of rice plants are stimulated after fertilization .
Using a combination of radioactive fingerprinting and molecular biology techniques , we identify the bacteria responsible for this effect .
We expect that our results will make necessary a re-evaluation of the link between fertilizer use and methane emissions , with effects on global warming studies .

[1700] Southern Hemisphere control on Australian monsoon variability during the late deglaciation and Holocene

The evolution of the Australian monsoon in relation to high-latitude temperature fluctuations over the last termination remains highly enigmatic .
Here we integrate high-resolution riverine runoff and dust proxy data from X-ray fluorescence scanner measurements in four well-dated sediment cores , forming a NE-SW transect across the Timor Sea .
Our records reveal that the development of the Australian monsoon closely followed the deglacial warming history of Antarctica .
A minimum in riverine runoff documents dry conditions throughout the region during the Antarctic Cold Reversal ( 15-12 .9 ka ) .
Massive intensification of the monsoon coincided with Southern Hemisphere warming and intensified greenhouse forcing over Australia during the atmospheric CO2 rise at 12.9-10 ka .
We relate the earlier onset of the monsoon in the Timor Strait ( 13.4 ka ) to regional changes in landmass exposure during deglacial sea-level rise .
A return to dryer conditions occurred between 8.1 and 7.3 ka following the early Holocene runoff maximum .

[1701] Journal club

An oceanographer sees potential in accelerating rock weathering to soak up carbon dioxide from the air .
With CO 2 emissions increasing by more than 2 % per year , rather than decreasing by the 3 % or so needed to effectively mitigate climate change , I am not surprised that many scientists are seeking alternative solutions to simply cutting greenhouse-gas outputs .

[1702] The role of industrial nitrogen in the global nitrogen biogeochemical cycle

Haber-Bosch nitrogen ( N ) has been increasingly used in industrial products , e.g. , nylon , besides fertilizer .
Massive numbers of species of industrial reactive N ( Nr ) have emerged and produced definite consequences but receive little notice .
Based on a comprehensive inventory , we show that ( 1 ) the industrial N flux has increased globally from 2.5 to 25.4 Tg N yr-1 from 1960 through 2008 , comparable to the NOx emissions from fossil fuel combustion ; ( 2 ) more than 25 % of industrial products ( primarily structural forms , e.g. , nylon ) tend to accumulate in human settlements due to their long service lives ; ( 3 ) emerging Nr species define new N-assimilation and decomposition pathways and change the way that Nr is released to the environment ; and ( 4 ) the loss of these Nr species to the environment has significant negative human and ecosystem impacts .
Incorporating industrial Nr into urban environmental and biogeochemical models could help to advance urban ecology and environmental sciences .

[1703] Wind-driven trends in Antarctic sea-ice drift

The sea-ice cover around Antarctica has experienced a slight expansion in area over the past decades .
This small overall increase is the sum of much larger opposing trends in different sectors that have been proposed to result from changes in atmospheric temperature or wind stress , precipitation , ocean temperature , and atmosphere or ocean feedbacks .
However , climate models have failed to reproduce the overall increase in sea ice .
Here we present a data set of satellite-tracked sea-ice motion for the period of 1992-2010 that reveals large and statistically significant trends in Antarctic ice drift , which , in most sectors , can be linked to local winds .
We quantify dynamic and thermodynamic processes in the internal ice pack and show that wind-driven changes in ice advection are the dominant driver of ice-concentration trends around much of West Antarctica , whereas wind-driven thermodynamic changes dominate elsewhere .
The ice-drift trends also imply large changes in the surface stress that drives the Antarctic ocean gyres , and in the fluxes of heat and salt responsible for the production of Antarctic bottom and intermediate waters .

[1704] Seasonal microbial community dynamics correlate with phytoplankton-derived polysaccharides in surface coastal waters

Phytoplankton produce large amounts of polysaccharide gel material known as transparent exopolymer particles ( TEP ) .
We investigated the potential links between phytoplankton-derived TEP and microbial community structure in the sea surface microlayer and underlying water at the English Channel time-series station L4 during a spring diatom bloom , and in two adjacent estuaries .
Major changes in bacterioneuston and bacterioplankton community structure occurred after the peak of the spring bloom at L4 , and coincided with the significant decline of microlayer and water column TEP .
Increased abundance of Flavobacteriales and Rhodobacterales in bacterioneuston and bacterioplankton communities at L4 was significantly related to the TEP decline , indicating that both taxa could be responsible .
The results suggest that TEP is an important factor in determining microbial diversity in coastal waters , and that TEP utilisation could be a niche occupied by Flavobacteriales and Rhodobacterales .

[1705] Eutrophication : Nitrate flux in the Mississippi River

Increased delivery of biologically available nitrogen to estuaries and coastal oceans in recent decades has been linked to eutrophication and seasonal hypoxia in the northern Gulf of Mexico and elsewhere .
We have developed a model that accounts for 95 % of annual variation in delivery of nitrate to the Gulf of Mexico by the Mississippi River in 1960-98 .
Retrospective analysis indicates that this nitrate flux could have been reduced by 33 % if the use of nitrogen-containing fertilizer in the Mississippi River basin had been cut by 12 % .

[1706] Self-Assembly and Horizontal Orientation Growth of VO2 Nanowires

Single-crystalline vanadium dioxide ( VO2 ) nanostructures have attracted an intense research interest recently because of their unique single-domain metal-insulator phase transition property .
Synthesis of these nanostructures in the past was limited in density , alignment , or single-crystallinity .
The assembly of VO2 nanowires ( NWs ) is desirable for a `` bottom-up '' approach to the engineering of intricate structures using nanoscale building blocks .
Here , we report the successful synthesis of horizontally aligned VO2 NWs with a dense growth mode in the [ 1-100 ] quartz direction of a polished x-cut quartz surface using a simple vapor transport method .
Our strategy of controlled growth of VO2 NWs promisingly paves the way for designing novel metal-insulator transition devices based on VO2 NWs .

[1707] Probability of afternoon precipitation in eastern United States and Mexico enhanced by high evaporation

Moisture and heat fluxes from the land surface to the atmosphere form a critical nexus between surface hydrology and atmospheric processes , particularly those relevant to precipitation .
Although current theory suggests that soil moisture generally has a positive impact on subsequent precipitation , individual studies have shown support both for and against this positive feedback .
Broad assessment of the coupling between soil moisture and evapotranspiration , and evapotranspiration and precipitation , has been limited by a lack of large-scale observations .
Quantification of the influence of evapotranspiration on precipitation remains particularly uncertain .
Here , we develop and apply physically based , objective metrics for quantifying the impacts of surface evaporative and sensible heat fluxes on the frequency and intensity of convective rainfall during summer , using North American reanalysis data .
We show that high evaporation enhances the probability of afternoon rainfall east of the Mississippi and in Mexico .
Indeed , variations in surface fluxes lead to changes in afternoon rainfall probability of between 10 and 25 % in these regions .
The intensity of rainfall , by contrast , is largely insensitive to surface fluxes .
We suggest that local surface fluxes represent an important trigger for convective rainfall in the eastern United States and Mexico during the summer , leading to a positive evaporation-precipitation feedback .

[1708] Synchronous basin-wide formation and redox-controlled preservation of a Mediterranean sapropel

Organic-rich sedimentary units called sapropels have formed repeatedly in the eastern Mediterranean Sea , in response to variations of solar radiation .
Sapropel formation is due to a change either in the flux of organic matter to the sea floor from productivity changes or in preservation by bottom-water oxygen levels .
However , the relative importance of surface-ocean productivity versus deep-water preservation for the formation of these organic-rich shale beds is still being debated , and conflicting interpretations are often invoked .
Here we analyse at high resolution the differences in the composition of the most recent sapropel , S1 , in a suite of cores covering the entire eastern Mediterranean basin .
We demonstrate that during the 4,000 years of sapropel formation , surface-water salinity was reduced and the deep eastern Mediterranean Sea , below 1,800 m depth , was devoid of oxygen .
This resulted in the preferential basin-wide preservation of sapropel S1 with different characteristics above and below 1,800 m depth as a result of different redox conditions .
We conclude that climate-induced stratification of the ocean may therefore contribute to enhanced preservation of organic matter in sapropels and potentially also in black shales .

[1709] End-Permian ozone shield unaffected by oceanic hydrogen sulphide and methane releases

Earth experienced repeated episodes of widespread surface and deep-ocean anoxia with a significant accumulation of sulphide-rich waters over the past two billion years .
The resulting massive releases of hydrogen sulphide from the oceans , together with methane from the geosphere , have been suggested as a cause for mass extinctions through destruction of the ozone shield and a lethal accumulation of hydrogen sulphide at the surface .
Here , we use a two-dimensional atmospheric chemistry-transport model with representative climate and atmospheric composition to simulate the effect of large hydrogen sulphide and methane releases at the time of the end-Permian mass extinction ~ 251 million years ago .
In our simulations , the integrity of the stratospheric ozone shield is maintained for oceanic hydrogen sulphide releases up to 15,000 Tg S yr-1 , a limit far exceeding the threshold for ozone collapse identified previously ( 2,000-4 ,000 Tg S yr-1 ) .
Scenarios of simultaneous hydrogen sulphide and methane injections also failed to significantly deplete the Earth 's ozone shield , and generated non-lethal hydrogen sulphide concentrations ( 1-2 p.p.m. ) at the surface .
In our two-dimensional model simulations , the high photolysis environment in the tropics maintains the oxidizing capacity of the tropical troposphere , with high local hydroxyl radical concentrations , and greatly diminishes hydrogen sulphide entry into the stratosphere .
We suggest that given current constraints on possible hydrogen sulphide and methane releases from anoxic oceans , and the geosphere , over the past 0.5 billion years , these gases seem unlikely to be the cause of coincident terrestrial biotic mass extinctions .

[1710] Systemic risk and spatiotemporal dynamics of the US housing market

Housing markets play a crucial role in economies and the collapse of a real-estate bubble usually destabilizes the financial system and causes economic recessions .
We investigate the systemic risk and spatiotemporal dynamics of the US housing market ( 1975-2011 ) at the state level based on the Random Matrix Theory ( RMT ) .
We identify richer economic information in the largest eigenvalues deviating from RMT predictions for the housing market than for stock markets and find that the component signs of the eigenvectors contain either geographical information or the extent of differences in house price growth rates or both .
By looking at the evolution of different quantities such as eigenvalues and eigenvectors , we find that the US housing market experienced six different regimes , which is consistent with the evolution of state clusters identified by the box clustering algorithm and the consensus clustering algorithm on the partial correlation matrices .
We find that dramatic increases in the systemic risk are usually accompanied by regime shifts , which provide a means of early detection of housing bubbles .

[1711] Changes in assembly processes in soil bacterial communities following a wildfire disturbance

Although recent work has shown that both deterministic and stochastic processes are important in structuring microbial communities , the factors that affect the relative contributions of niche and neutral processes are poorly understood .
The macrobiological literature indicates that ecological disturbances can influence assembly processes .
Thus , we sampled bacterial communities at 4 and 16 weeks following a wildfire and used null deviation analysis to examine the role that time since disturbance has in community assembly .
Fire dramatically altered bacterial community structure and diversity as well as soil chemistry for both time-points .
Community structure shifted between 4 and 16 weeks for both burned and unburned communities .
Community assembly in burned sites 4 weeks after fire was significantly more stochastic than in unburned sites .
After 16 weeks , however , burned communities were significantly less stochastic than unburned communities .
Thus , we propose a three-phase model featuring shifts in the relative importance of niche and neutral processes as a function of time since disturbance .
Because neutral processes are characterized by a decoupling between environmental parameters and community structure , we hypothesize that a better understanding of community assembly may be important in determining where and when detailed studies of community composition are valuable for predicting ecosystem function .

[1712] Climate change : All in the timing

How influential are the various factors involved in curbing global warming ?
A study finds that the timing of emissions reduction has the largest impact on the probability of limiting temperature increases to 2 degreesC .
See Letter p. 79

[1713] Vole and lemming activity observed from space

Predicting the impacts of present global warming requires an understanding of the factors controlling plant biomass and production .
The extent to which they are controlled by bottom-up drivers such as climate , nutrient and water availability , and by top-down drivers such as herbivory and diseases in terrestrial systems is still under debate .
By annually recording plant biomass and community composition in grazed control plots and in herbivore-free exclosures , at 12 sites in a subArctic ecosystem , we were able to show that the regular interannual density fluctuations of voles and lemmings drive synchronous interannual fluctuations in the biomass of field-layer vegetation .
Plant biomass in the field layer was between 12 and 24 % lower the year after a vole peak than the year before , and the combined vole and lemming peaks are visible as a reduced normalized difference vegetation index in satellite images over a 770 km2 area in the following year , despite the wide range of abiotic , biotic and anthropogenic forces that influence the vegetation .
This strongly suggests that the cascading effect of rodents for the function and diversity of tundra plant communities needs to be included in our scenarios of how these ecosystems will respond to environmental changes .

[1714] Air density 2.7 billion years ago limited to less than twice modern levels by fossil raindrop imprints

According to the ` Faint Young Sun ' paradox , during the late Archaean eon a Sun approximately 20 % dimmer warmed the early Earth such that it had liquid water and a clement climate .
Explanations for this phenomenon have invoked a denser atmosphere that provided warmth by nitrogen pressure broadening or enhanced greenhouse gas concentrations .
Such solutions are allowed by geochemical studies and numerical investigations that place approximate concentration limits on Archaean atmospheric gases , including methane , carbon dioxide and oxygen .
But no field data constraining ground-level air density and barometric pressure have been reported , leaving the plausibility of these various hypotheses in doubt .
Here we show that raindrop imprints in tuffs of the Ventersdorp Supergroup , South Africa , constrain surface air density 2.7 billion years ago to less than twice modern levels .
We interpret the raindrop fossils using experiments in which water droplets of known size fall at terminal velocity into fresh and weathered volcanic ash , thus defining a relationship between imprint size and raindrop impact momentum .
Fragmentation following raindrop flattening limits raindrop size to a maximum value independent of air density , whereas raindrop terminal velocity varies as the inverse of the square root of air density .
If the Archaean raindrops reached the modern maximum measured size , air density must have been less than 2.3 kg m-3 , compared to today 's 1.2 kg m-3 , but because such drops rarely occur , air density was more probably below 1.3 kg m-3 .
The upper estimate for air density renders the pressure broadening explanation possible , but it is improbable under the likely lower estimates .
Our results also disallow the extreme CO2 levels required for hot Archaean climates .

[1715] Influence of Bering Strait flow and North Atlantic circulation on glacial sea-level changes

Sea-level fluctuations of about 20-30 m occurred throughout the last glacial period .
These fluctuations seem to have been derived primarily from changes in the volume of Northern Hemisphere ice sheets , and can not be attributed solely to ice melt caused by varying solar radiation .
Here we use a fully coupled climate model to show that the transport of relatively fresh Pacific water into the North Atlantic Ocean was limited when lower sea level restricted or closed the Bering Strait , resulting in saltier North Atlantic surface waters .
This invigorated deep convection in the North Atlantic Ocean , strengthening meridional overturning circulation and northward heat transport in our model , which consequently promoted melting of ice sheets in North America and Europe .
Our simulations show that the associated sea-level rise led to a reopening of the Bering Strait ; the flux of relatively fresh water into the North Atlantic Ocean muted meridional overturning circulation and led to cooling and ice-sheet advance in the Northern Hemisphere .
We conclude that the repetition of this cycle could produce the sea-level changes that have been observed throughout the last glacial cycle .

[1716] Climate change : Natural ups and downs

The effects of global warming over the coming decades will be modified by shorter-term climate variability .
Finding ways to incorporate these variations will give us a better grip on what kind of climate change to expect .

[1717] A bacterial pathogen uses dimethylsulfoniopropionate as a cue to target heat-stressed corals

Diseases are an emerging threat to ocean ecosystems .
Coral reefs , in particular , are experiencing a worldwide decline because of disease and bleaching , which have been exacerbated by rising seawater temperatures .
Yet , the ecological mechanisms behind most coral diseases remain unidentified .
Here , we demonstrate that a coral pathogen , Vibrio coralliilyticus , uses chemotaxis and chemokinesis to target the mucus of its coral host , Pocillopora damicornis .
A primary driver of this response is the host metabolite dimethylsulfoniopropionate ( DMSP ) , a key element in the global sulfur cycle and a potent foraging cue throughout the marine food web .
Coral mucus is rich in DMSP , and we found that DMSP alone elicits chemotactic responses of comparable intensity to whole mucus .
Furthermore , in heat-stressed coral fragments , DMSP concentrations increased fivefold and the pathogen 's chemotactic response was correspondingly enhanced .
Intriguingly , despite being a rich source of carbon and sulfur , DMSP is not metabolized by the pathogen , suggesting that it is used purely as an infochemical for host location .
These results reveal a new role for DMSP in coral disease , demonstrate the importance of chemical signaling and swimming behavior in the recruitment of pathogens to corals and highlight the impact of increased seawater temperatures on disease pathways .

[1718] Radiative forcing and albedo feedback from the Northern Hemisphere cryosphere between 1979 and 2008

The extent of snow cover and sea ice in the Northern Hemispherehas declined since 1979 , coincident with hemispheric warming and indicative of a positive feedback of surface reflectivity on climate .
This albedo feedback of snow on land has been quantified from observations at seasonal timescales , and century-scale feedback has been assessed using climate models .
However , the total impact of the cryosphere on radiative forcing and albedo feedback has yet to be determined from measurements .
Here we assess the influence of the Northern Hemisphere cryosphere on Earth 's radiation budget at the top of the atmosphere -- termed cryosphere radiative forcing -- by synthesizing a variety of remote sensing and field measurements .
We estimate mean Northern Hemisphere forcing at -4.6 to -2.2 W m-2 , with a peak in May of -9.0 + / -2.7 W m-2 .
We find that cyrospheric cooling declined by 0.45 W m-2 from 1979 to 2008 , with nearly equal contributions from changes in land snow cover and sea ice .
On the basis of these observations , we conclude that the albedo feedback from the Northern Hemisphere cryosphere falls between 0.3 and 1.1 W m-2 K-1 , substantially larger than comparable estimates obtained from 18 climate models .

[1719] Uncertainty in thermal tolerances and climatic debt

To the Editor -- As modern climate change causes rapid geographical shifts of environmental conditions , there are great concerns that numerous species could be unable to track suitable environments , thereby incurring a ` climatic debt ' .
Recently , Devictor et al .
reported that the composition of bird and butterfly communities across Europe has changed at a lower rate than could be expected given the observed increase in temperature .

[1720] Weakening of the stratospheric polar vortex by Arctic sea-ice loss

Successive cold winters of severely low temperatures in recent years have had critical social and economic impacts on the mid-latitude continents in the Northern Hemisphere .
Although these cold winters are thought to be partly driven by dramatic losses of Arctic sea-ice , the mechanism that links sea-ice loss to cold winters remains a subject of debate .
Here , by conducting observational analyses and model experiments , we show how Arctic sea-ice loss and cold winters in extra-polar regions are dynamically connected through the polar stratosphere .
We find that decreased sea-ice cover during early winter months ( November-December ) , especially over the Barents-Kara seas , enhances the upward propagation of planetary-scale waves with wavenumbers of 1 and 2 , subsequently weakening the stratospheric polar vortex in mid-winter ( January-February ) .
The weakened polar vortex preferentially induces a negative phase of Arctic Oscillation at the surface , resulting in low temperatures in mid-latitudes .

[1721] Differential freshwater flagellate community response to bacterial food quality with a focus on Limnohabitans bacteria

Different bacterial strains can have different value as food for heterotrophic nanoflagellates ( HNF ) , thus modulating HNF growth and community composition .
We examined the influence of prey food quality using four Limnohabitans strains , one Polynucleobacter strain and one freshwater actinobacterial strain on growth ( growth rate , length of lag phase and growth efficiency ) and community composition of a natural HNF community from a freshwater reservoir .
Pyrosequencing of eukaryotic small subunit rRNA amplicons was used to assess time-course changes in HNF community composition .
All four Limnohabitans strains and the Polynucleobacter strain yielded significant HNF community growth while the actinobacterial strain did not although it was detected in HNF food vacuoles .
Notably , even within the Limnohabitans strains we found significant prey-related differences in HNF growth parameters , which could not be related only to size of the bacterial prey .
Sequence data characterizing the HNF communities showed also that different bacterial prey items induced highly significant differences in community composition of flagellates .
Generally , Stramenopiles dominated the communities and phylotypes closely related to Pedospumella ( Chrysophyceae ) were most abundant bacterivorous flagellates rapidly reacting to addition of the bacterial prey of high food quality .

[1722] Carbon loss from an unprecedented Arctic tundra wildfire

Arctic tundra soils store large amounts of carbon ( C ) in organic soil layers hundreds to thousands of years old that insulate , and in some cases maintain , permafrost soils .
Fire has been largely absent from most of this biome since the early Holocene epoch , but its frequency and extent are increasing , probably in response to climate warming .
The effect of fires on the C balance of tundra landscapes , however , remains largely unknown .
The Anaktuvuk River fire in 2007 burned 1,039 square kilometres of Alaska 's Arctic slope , making it the largest fire on record for the tundra biome and doubling the cumulative area burned since 1950 ( ref .
5 ) .
Here we report that tundra ecosystems lost 2,016 + / - 435 g C m-2 in the fire , an amount two orders of magnitude larger than annual net C exchange in undisturbed tundra .
Sixty per cent of this C loss was from soil organic matter , and radiocarbon dating of residual soil layers revealed that the maximum age of soil C lost was 50 years .
Scaled to the entire burned area , the fire released approximately 2.1 teragrams of C to the atmosphere , an amount similar in magnitude to the annual net C sink for the entire Arctic tundra biome averaged over the last quarter of the twentieth century .
The magnitude of ecosystem C lost by fire , relative to both ecosystem and biome-scale fluxes , demonstrates that a climate-driven increase in tundra fire disturbance may represent a positive feedback , potentially offsetting Arctic greening and influencing the net C balance of the tundra biome .

[1723] Jumonji demethylases moderate precocious flowering at elevated temperature via regulation of FLC in Arabidopsis

As sessile organisms , plants have evolved multiple mechanisms to respond to environmental changes to improve survival .
Arabidopsis plants show accelerated flowering at increased temperatures .
Here we show that Jumonji-C domain-containing protein JMJ30 directly binds to the flowering-repressor FLOWERING LOCUS C ( FLC ) locus and removes the repressive histone modification H3 lysine 27 trimethylation ( H3K27me3 ) .
At elevated temperatures , the JMJ30 RNA and protein are stabilized , and FLC expression is maintained at high levels to prevent extreme precocious flowering .
The double mutant of JMJ30 and its homologue JMJ32 , grown at elevated temperatures , exhibits an early-flowering phenotype similar to the flc mutant , which is associated with increased H3K27me3 levels at the FLC locus and decreased FLC expression .
Furthermore , ectopic expression of JMJ30 causes an FLC-dependent late-flowering phenotype .
Taken together , JMJ30/JMJ32-mediated histone demethylation at the FLC locus constitutes a balancing mechanism in flowering control at warm temperatures to prevent premature early flowering .

[1724] Functional diversity of bacteria in a ferruginous hydrothermal sediment

A microbial community showing diverse respiratory processes was identified within an arsenic-rich , ferruginous shallow marine hydrothermal sediment ( 20-40 degreesC , pH 6.0-6 .3 ) in Santorini , Greece .
Analyses showed that ferric iron reduction with depth was broadly accompanied by manganese and arsenic reduction and FeS accumulation .
Clone library analyses indicated the suboxic-anoxic transition zone sediment contained abundant Fe ( III ) - and sulfate-reducing Deltaproteobacteria , whereas the overlying surface sediment was dominated by clones related to the Fe ( II ) - oxidizing zetaproteobacterium , Mariprofundus ferroxydans .
Cultures obtained from the transition zone were enriched in bacteria that reduced Fe ( III ) , nitrate , sulfate and As ( V ) using acetate or lactate as electron donors .
In the absence of added organic carbon , bacteria were enriched that oxidized Fe ( II ) anaerobically or microaerobically , sulfide microaerobically and aerobically and As ( III ) aerobically .
According to 16S rRNA gene analyses , enriched bacteria represented a phylogenetically wide distribution .
Most probable number counts indicated an abundance of nitrate - , As ( V ) - and Fe ( III ) ( s , aq ) - reducers , and dissolved sulfide-oxidizers over sulfate-reducers , and FeS - , As ( III ) - and nitrate-dependent Fe ( II ) - oxidisers in the transition zone .
It is noteworthy that the combined community and geochemical data imply near-surface microbial iron and arsenic redox cycling were dominant biogeochemical processes .

[1725] Spatiotemporal changes in the genetic diversity of a bloom-forming Microcystis aeruginosa ( cyanobacteria ) population

The variations in microcystin concentrations during cyanobacterial blooms in freshwater ecosystems appear to depend on numerous factors , which have still not been fully identified .
To contribute to clarify the situation , we have developed a spatial sampling approach to determine the dynamics and genetic diversity of a bloom-forming population of Microcystis aeruginosa in a large French reservoir , and the variations in the proportions of microcystin-producing genotypes .
We demonstrated that marked changes occurred in the internal transcribed spacer ( ITS ) genotype composition of the M. aeruginosa population during the development of the bloom .
These changes led progressively to the selection of one dominant ITS genotype throughout the entire reservoir when the cell number reached its maximum .
At the same time , we identified a decrease in the proportion of the mcyB + genotype , and a significant negative correlation between this proportion and that of the dominant ITS genotype during the bloom .
Thus , it appeared that favorable conditions for Microcystis cell growth led to the selection , within the Microcystis population , of a non-microcystin-producing genotype , whereas potentially microcystin-producing genotypes were dominant in this population before and after the bloom , when environmental conditions were less favorable for growth .

[1726] Mechanosensitive physiology of chlamydomonas reinhardtii under direct membrane distortion

Cellular membrane distortion invokes variations in cellular physiology .
However , lack of an appropriate system to control the stress and facilitate molecular analyses has hampered progress of relevant studies .
In this study , a microfluidic system that finely manipulates membrane distortion of Chlamydomonas reinhardtii ( C. reinhardtii ) was developed .
The device facilitated a first-time demonstration that directs membrane distortion invokes variations in deflagellation , cell cycle , and lipid metabolism .
C. reinhardtii showed a prolonged G1 phase with an extended total cell cycle time , and upregulated Mat3 regulated a cell size and cell cycle .
Additionally , increased TAG compensated for the loss of cell mass .
Overall , this study suggest that cell biology that requires direct membrane distortion can be realized using this system , and the implication of cell cycle with Mat3 expression of C. reinhardtii was first demonstrated .
Finally , membrane distortion can be an attractive inducer for biodiesel production since it is reliable and robust .

[1727] Greenland ice-sheet contribution to sea-level rise buffered by meltwater storage in firn

Surface melt on the Greenland ice sheet has shown increasing trends in areal extent and duration since the beginning of the satellite era .
Records for melt were broken in 2005 , 2007 , 2010 and 2012 .
Much of the increased surface melt is occurring in the percolation zone , a region of the accumulation area that is perennially covered by snow and firn ( partly compacted snow ) .
The fate of melt water in the percolation zone is poorly constrained : some may travel away from its point of origin and eventually influence the ice sheet 's flow dynamics and mass balance and the global sea level , whereas some may simply infiltrate into cold snow or firn and refreeze with none of these effects .
Here we quantify the existing water storage capacity of the percolation zone of the Greenland ice sheet and show the potential for hundreds of gigatonnes of meltwater storage .
We collected in situ observations of firn structure and meltwater retention along a roughly 85-kilometre-long transect of the melting accumulation area .
Our data show that repeated infiltration events in which melt water penetrates deeply ( more than 10 metres ) eventually fill all pore space with water .
As future surface melt intensifies under Arctic warming , a fraction of melt water that would otherwise contribute to sea-level rise will fill existing pore space of the percolation zone .
We estimate the lower and upper bounds of this storage sink to be 322 + / - 44 gigatonnes and gigatonnes , respectively .
Furthermore , we find that decades are required to fill this pore space under a range of plausible future climate conditions .
Hence , routing of surface melt water into filling the pore space of the firn column will delay expansion of the area contributing to sea-level rise , although once the pore space is filled it can not quickly be regenerated .

[1728] Adhesion of marine cryptic Escherichia isolates to human intestinal epithelial cells

Five distinct cryptic lineages ( clades I-V ) have recently been recognized in the Escherichia genus .
The five clades encompass strains that are phenotypically and taxonomically indistinguishable from Escherichia coli sensu stricto ; however , scant data are available on their ecology , virulence and pathogenic properties .
In this study 20 cryptic E. coli strains isolated from marine sediments were investigated to gain insights into their virulence characteristics and genetic traits .
The ability to adhere to intestinal cells was highest among clade V strains , which also harbored the genes involved in gut colonization as well as the genes ( pduC and eut operon ) typically found in environmentally adapted E. coli strains .
The pduC gene was significantly associated with clade V. Multilocus sequence typing of three representative clade V isolates revealed new sequence types ( STs ) and showed that the strains shared two allelic loci ( adk 51 and recA 37 ) .
Our findings suggest that cryptic Escherichia lineages are common in coastal marine sediments and that this habitat may be suitable for their growth and persistence outside the host .
On the other hand , detection in clade V strains of a gene repertoire and adhesion properties similar to those of intestinal pathogenic strains could indicate their potential virulence .
It could be argued that there is a dual nature of cryptic clade V strains , where the ability to survive and persist in a secondary habitat does not involve the loss of the host-associated lifestyle .
Clade V could be a group of closely related , environmentally adapted E. coli strains .

[1729] The niche of an invasive marine microbe in a subtropical freshwater impoundment

Growing attention in aquatic ecology is focusing on biogeographic patterns in microorganisms and whether these potential patterns can be explained within the framework of general ecology .
The long-standing microbiologist 's credo ` Everything is everywhere , but , the environment selects ' suggests that dispersal is not limiting for microbes , but that the environment is the primary determining factor in microbial community composition .
Advances in molecular techniques have provided new evidence that biogeographic patterns exist in microbes and that dispersal limitation may actually have an important role , yet more recent study using extremely deep sequencing predicts that indeed everything is everywhere .
Using a long-term field study of the ` invasive ' marine haptophyte Prymnesium parvum , we characterize the environmental niche of P. parvum in a subtropical impoundment in the southern United States .
Our analysis contributes to a growing body of evidence that indicates a primary role for environmental conditions , but not dispersal , in the lake-wide abundances and seasonal bloom patterns in this globally important microbe .

[1730] The impact of polar mesoscale storms on northeast Atlantic Ocean circulation

Atmospheric processes regulate the formation of deep water in the subpolar North Atlantic Ocean and hence influence the large-scale ocean circulation .
Every year thousands of mesoscale storms , termed polar lows , cross this climatically sensitive region of the ocean .
These storms are often either too small or too short-lived to be captured in meteorological reanalyses or numerical models .
Here we present simulations with a global , eddy-permitting ocean/sea-ice circulation model , run with and without a parameterization of polar lows .
The parameterization reproduces the high wind speeds and heat fluxes observed in polar lows as well as their integrated effects , and leads to increases in the simulated depth , frequency and area of deep convection in the Nordic seas , which in turn leads to a larger northward transport of heat into the region , and southward transport of deep water through Denmark Strait .
We conclude that polar lows are important for the large-scale ocean circulation and should be accounted for in short-term climate predictions .
Recent studies predict a decrease in the number of polar lows over the northeast Atlantic in the twenty-first century that would imply a reduction in deep convection and a potential weakening of the Atlantic meridional overturning circulation .

[1731] Future ocean increasingly transparent to low-frequency sound owing to carbon dioxide emissions

Low-frequency sound in the ocean is produced by natural phenomena such as rain , waves and marine life , as well as by human activities , such as the use of sonar systems , shipping and construction .
Sea water absorbs sound mainly owing to the viscosity of the water and the presence of chemical constituents , such as magnesium sulphate , boric acid and carbonate ions .
The concentration of dissolved chemicals absorbing sound near 1 kHz depends on the pH of the ocean , which has declined as a result of increases in acidity due to anthropogenic emissions of carbon dioxide .
Here we use a global ocean model forced with projected carbon dioxide emissions to predict regional changes in pH , and thus sound absorption , in the years 1800-2300 .
According to our projections , ocean pH could fall by up to 0.6 units by 2100 .
Sound absorption -- in the range between ~ 100 Hz and ~ 10 kHz -- could fall by up to 60 % in the high latitudes and in areas of deep-water formation over the same time period .
We predict that over the twenty-first century , chemical absorption of sound in this frequency range will nearly halve in some of the regions that experience significant radiated noise from industrial activity , such as the North Atlantic Ocean .
We suggest that our forecast of reduced sound absorption in acoustic hotspots will help in identifying target regions for future monitoring .

[1732] Solar steam generation by heat localization

Currently , steam generation using solar energy is based on heating bulk liquid to high temperatures .
This approach requires either costly high optical concentrations leading to heat loss by the hot bulk liquid and heated surfaces or vacuum .
New solar receiver concepts such as porous volumetric receivers or nanofluids have been proposed to decrease these losses .
Here we report development of an approach and corresponding material structure for solar steam generation while maintaining low optical concentration and keeping the bulk liquid at low temperature with no vacuum .
We achieve solar thermal efficiency up to 85 % at only 10 kW m-2 .
This high performance results from four structure characteristics : absorbing in the solar spectrum , thermally insulating , hydrophilic and interconnected pores .
The structure concentrates thermal energy and fluid flow where needed for phase change and minimizes dissipated energy .
This new structure provides a novel approach to harvesting solar energy for a broad range of phase-change applications .

[1733] Functional and ecological consequences of saprotrophic fungus-grazer interactions

Saprotrophic fungi are key regulators of nutrient cycling in terrestrial ecosystems .
They are the primary agents of plant litter decomposition and their hyphal networks , which grow throughout the soil-litter interface , represent highly dynamic channels through which nutrients are readily distributed .
By ingesting hyphae and dispersing spores , soil invertebrates , including Arthropoda , Oligochaetae and Nematoda , influence fungal-mediated nutrient distribution within soil .
Fungal physiological responses to grazing include changes to hydrolytic enzyme production and respiration rates .
These directly affect nutrient mineralisation and the flux of CO2 between terrestrial and atmospheric pools .
Preferential grazing may also exert selective pressures on saprotrophic communities , driving shifts in fungal succession and community composition .
These functional and ecological consequences of grazing are intrinsically linked , and influenced by invertebrate grazing intensity .
High-intensity grazing often reduces fungal growth and activity , whereas low-intensity grazing can have stimulatory effects .
Grazing intensity is directly related to invertebrate abundance , and varies dramatically between species and functional groups .
Invertebrate diversity and community composition , therefore , represent key factors determining the functioning of saprotrophic fungal communities and the services they provide .

[1734] Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial drainage

Fluctuations in surface melting are known to affect the speed of glaciers and ice sheets , but their impact on the Greenland ice sheet in a warming climate remains uncertain .
Although some studies suggest that greater melting produces greater ice-sheet acceleration , others have identified a long-term decrease in Greenland 's flow despite increased melting .
Here we use satellite observations of ice motion recorded in a land-terminating sector of southwest Greenland to investigate the manner in which ice flow develops during years of markedly different melting .
Although peak rates of ice speed-up are positively correlated with the degree of melting , mean summer flow rates are not , because glacier slowdown occurs , on average , when a critical run-off threshold of about 1.4 centimetres a day is exceeded .
In contrast to the first half of summer , when flow is similar in all years , speed-up during the latter half is 62 + / - 16 per cent less in warmer years .
Consequently , in warmer years , the period of fast ice flow is three times shorter and , overall , summer ice flow is slower .
This behaviour is at odds with that expected from basal lubrication alone .
Instead , it mirrors that of mountain glaciers , where melt-induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient .
A model of ice-sheet flow that captures switching between cavity and channel drainage modes is consistent with the run-off threshold , fast-flow periods , and later-summer speeds we have observed .
Simulations of the Greenland ice-sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage ; a simple model of basal lubrication alone misses key aspects of the ice sheet 's response to climate warming .

[1735] Auxin transport is sufficient to generate a maximum and gradient guiding root growth

The plant growth regulator auxin controls cell identity , cell division and cell expansion .
Auxin efflux facilitators ( PINs ) are associated with auxin maxima in distal regions of both shoots and roots .
Here we model diffusion and PIN-facilitated auxin transport in and across cells within a structured root layout .
In our model , the stable accumulation of auxin in a distal maximum emerges from the auxin flux pattern .
We have experimentally tested model predictions of robustness and self-organization .
Our model explains pattern formation and morphogenesis at timescales from seconds to weeks , and can be understood by conceptualizing the root as an ` auxin capacitor ' .
A robust auxin gradient associated with the maximum , in combination with separable roles of auxin in cell division and cell expansion , is able to explain the formation , maintenance and growth of sharply bounded meristematic and elongation zones .
Directional permeability and diffusion can fully account for stable auxin maxima and gradients that can instruct morphogenesis .

[1736] Salmonella transcriptional signature in Tetrahymena phagosomes and role of acid tolerance in passage through the protist

Salmonella enterica Typhimurium remains undigested in the food vacuoles of the common protist , Tetrahymena .
Contrary to its interaction with Acanthamoeba spp. , S. Typhimurium is not cytotoxic to Tetrahymena and is egested as viable cells in its fecal pellets .
Through microarray gene expression profiling we investigated the factors in S. Typhimurium that are involved in its resistance to digestion by Tetrahymena .
The transcriptome of S. Typhimurium in Tetrahymena phagosomes showed that 989 and 1282 genes were altered in expression compared with that in water and in LB culture medium , respectively .
A great proportion of the upregulated genes have a role in anaerobic metabolism and the use of alternate electron acceptors .
Many genes required for survival and replication within macrophages and human epithelial cells also had increased expression in Tetrahymena , including mgtC , one of the most highly induced genes in all three cells types .
A DeltamgtC mutant of S. Typhimurium did not show decreased viability in Tetrahymena , but paradoxically , was egested at a higher cell density than the wild type .
The expression of adiA and adiY , which are involved in arginine-dependent acid resistance , also was increased in the protozoan phagosome .
A DeltaadiAY mutant had lower viability after passage through Tetrahymena , and a higher proportion of S. Typhimurium wild-type cells within pellets remained viable after exposure to pH 3.4 as compared with uningested cells .
Our results provide evidence that acid resistance has a role in the resistance of Salmonella to digestion by Tetrahymena and that passage through the protist confers physiological advantages relevant to its contamination cycle .

[1737] Formation of chiral morphologies through selective binding of amino acids to calcite surface steps

Many living organisms contain biominerals and composites with finely tuned properties , reflecting a remarkable level of control over the nucleation , growth and shape of the constituent crystals .
Peptides and proteins play an important role in achieving this control .
But the general view that organic molecules affect mineralization through stereochemical recognition , where geometrical and chemical constraints dictate their binding to a mineral , seems difficult to reconcile with a mechanistic understanding , where crystallization is controlled by thermodynamic and kinetic factors .
Indeed , traditional crystal growth models emphasize the inhibiting effect of so-called ` modifiers ' on surface-step growth , rather than stereochemical matching to newly expressed crystal facets .
Here we report in situ atomic force microscope observations and molecular modelling studies of calcite growth in the presence of chiral amino acids that reconcile these two seemingly divergent views .
We find that enantiomer-specific binding of the amino acids to those surface-step edges that offer the best geometric and chemical fit changes the step-edge free energies , which in turn results in macroscopic crystal shape modifications .
Our results emphasize that the mechanism underlying crystal modification through organic molecules is best understood by considering both stereochemical recognition and the effects of binding on the interfacial energies of the growing crystal .

[1738] Evidence for oxygenic photosynthesis half a billion years before the Great Oxidation Event

The early Earth was characterized by the absence of oxygen in the ocean-atmosphere system , in contrast to the well-oxygenated conditions that prevail today .
Atmospheric concentrations first rose to appreciable levels during the Great Oxidation Event , roughly 2.5-2 .3 Gyr ago .
The evolution of oxygenic photosynthesis is generally accepted to have been the ultimate cause of this rise , but it has proved difficult to constrain the timing of this evolutionary innovation .
The oxidation of manganese in the water column requires substantial free oxygen concentrations , and thus any indication that Mn oxides were present in ancient environments would imply that oxygenic photosynthesis was ongoing .
Mn oxides are not commonly preserved in ancient rocks , but there is a large fractionation of molybdenum isotopes associated with the sorption of Mo onto the Mn oxides that would be retained .
Here we report Mo isotopes from rocks of the Sinqeni Formation , Pongola Supergroup , South Africa .
These rocks formed no less than 2.95 Gyr ago in a nearshore setting .
The Mo isotopic signature is consistent with interaction with Mn oxides .
We therefore infer that oxygen produced through oxygenic photosynthesis began to accumulate in shallow marine settings at least half a billion years before the accumulation of significant levels of atmospheric oxygen .

[1739] Malaria epidemics and the influence of the tropical South Atlantic on the Indian monsoon

The existence of predictability in the climate system beyond the relatively short timescales of synoptic weather has provided significant impetus to investigate climate variability and its consequences for society .
In particular , relationships between the relatively slow changes in sea surface temperature ( SST ) and climate variability at widely removed points across the globe provide a basis for statistical and dynamical efforts to predict numerous phenomena , from rainfall to disease incidence , at seasonal to decadal timescales .
We describe here a remote influence , identified through observational analysis and supported through numerical experiments with a coupled atmosphere-ocean model , of the tropical South Atlantic ( TSA ) on both monsoon rainfall and malaria epidemics in arid northwest India .
Moreover , SST in the TSA is shown to provide the basis for an early warning of anomalous hydrological conditions conducive to malaria epidemics four months later , therefore at longer lead times than those afforded by rainfall .
We find that the TSA is not only significant as a modulator of the relationship between the monsoon and the El Nino/Southern Oscillation , as has been suggested by previous work , but for certain regions and temporal lags is in fact a dominant driver of rainfall variability and hence malaria outbreaks .

[1740] Sulphate-climate coupling over the past 300,000 years in inland Antarctica

Sulphate aerosols , particularly micrometre-sized particles of sulphate salt and sulphate-adhered dust , can act as cloud condensation nuclei , leading to increased solar scattering that cools Earth 's climate .
Evidence for such a coupling may lie in the sulphate record from polar ice cores , but previous analyses of melted ice-core samples have provided only sulphate ion concentrations , which may be due to sulphuric acid .
Here we present profiles of sulphate salt and sulphate-adhered dust fluxes over the past 300,000 years from the Dome Fuji ice core in inland Antarctica .
Our results show a nearly constant flux of sulphate-adhered dust through glacial and interglacial periods despite the large increases in total dust flux during glacial maxima .
The sulphate salt flux , however , correlates inversely with temperature , suggesting a climatic coupling between particulate sulphur and temperature .
For example , the total sulphate salt flux during the Last Glacial Maximum averages 5.78 mg m-2 yr-1 , which is almost twice the Holocene value .
Although it is based on a modern analogue with considerable uncertainties when applied to the ice-core record , this analysis indicates that the glacial-to-interglacial decrease in sulphate would lessen the aerosol indirect effects on cloud lifetime and albedo , leading to an Antarctic warming of 0.1 to 5 kelvin .

[1741] Pattern of extinction of the woolly mammoth in Beringia

Extinction of the woolly mammoth in Beringia has long been subject to research and speculation .
Here we use a new geo-referenced database of radiocarbon-dated evidence to show that mammoths were abundant in the open-habitat of Marine Isotope Stage 3 ( ~ 45-30 ka ) .
During the Last Glacial Maximum ( ~ 25-20 ka ) , northern populations declined while those in interior Siberia increased .
Northern mammoths increased after the glacial maximum , but declined at and after the Younger Dryas ( ~ 12.9-11 .5 ka ) .
Remaining continental mammoths , now concentrated in the north , disappeared in the early Holocene with development of extensive peatlands , wet tundra , birch shrubland and coniferous forest .
Long sympatry in Siberia suggests that humans may be best seen as a synergistic cofactor in that extirpation .
The extinction of island populations occurred at ~ 4 ka .
Mammoth extinction was not due to a single cause , but followed a long trajectory in concert with changes in climate , habitat and human presence .

[1742] High-resolution record of climate stability in France during the last interglacial period

The last interglacial period ( 127-110 kyr ago ) has been considered to be an analogue to the present interglacial period , the Holocene , which may help us to understand present climate evolution .
But whereas Holocene climate has been essentially stable in Europe , variability in climate during the last interglacial period has remained unresolved , because climate reconstructions from ice cores , continental records and marine sediment cores give conflicting results for this period .
Here we present a high-resolution multi-proxy lacustrine record of climate change during the last interglacial period , based on oxygen isotopes in diatom silica , diatom assemblages and pollen-climate transfer functions from the Ribains maar in France .
Contrary to a previous study , our data do not show a cold event interrupting the warm interglacial climate .
Instead , we find an early temperature maximum with a transition to a colder climate about halfway through the sequence .
The end of the interglacial period is clearly marked by an abrupt change in all proxy records .
Our study confirms that in southwestern Europe the last interglacial period was a time of climatic stability and is therefore still likely to represent a useful analogue for the present climate .

[1743] Quantification of decadal anthropogenic CO2 uptake in the ocean based on dissolved inorganic carbon measurements

About half of the ` anthropogenic ' CO2 emitted to the atmosphere is taken up by the oceans and terrestrial biosphere , and the amount sequestered by the ocean is generally estimated using numerical ocean carbon-cycle models .
But these models often differ markedly , resulting in different estimated spatial and temporal patterns and magnitudes of uptake .
Because of its importance climatically , the CO2 flux needs to be verified using field measurements .
Accurate estimates of CO2 uptake have been difficult to obtain , however , as the annual increase of dissolved inorganic carbon ( DIC ) concentration in surface water due to anthropogenic input is ~ 0.05 % of the total DIC , an order of magnitude lower than past measurement precision .
Early measurement-based estimates , of total anthropogenic CO2 inventory in the ocean have recently been improved on , , and new approaches have been proposed for determining changes in ocean DIC concentration over one to two decades , .
Here we use recent improvements in DIC measurement techniques to determine changes in DIC concentrations between 1978 and 1995 in the Indian Ocean .
Our method subtracts decadal-scale natural variability , enabling the ocean anthropogenic CO2 increase in this region over the 17-year period to be determined .
The calculated uncertainties and known measurement capabilities allow us to define the minimum sampling strategies that will be required to quantify the regional and global anthropogenic CO2 oceanic uptake over future decades .

[1744] Sensing of mammalian IL-17A regulates fungal adaptation and virulence

Infections by opportunistic fungi have traditionally been viewed as the gross result of a pathogenic automatism , which makes a weakened host more vulnerable to microbial insults .
However , fungal sensing of a host 's immune environment might render this process more elaborate than previously appreciated .
Here we show that interleukin ( IL ) -17 A binds fungal cells , thus tackling both sides of the host-pathogen interaction in experimental settings of host colonization and/or chronic infection .
Global transcriptional profiling reveals that IL-17A induces artificial nutrient starvation conditions in Candida albicans , resulting in a downregulation of the target of rapamycin signalling pathway and in an increase in autophagic responses and intracellular cAMP .
The augmented adhesion and filamentous growth , also observed with Aspergillus fumigatus , eventually translates into enhanced biofilm formation and resistance to local antifungal defenses .
This might exemplify a mechanism whereby fungi have evolved a means of sensing host immunity to ensure their own persistence in an immunologically dynamic environment .

[1745] Emerging fungal threats to animal , plant and ecosystem health

The past two decades have seen an increasing number of virulent infectious diseases in natural populations and managed landscapes .
In both animals and plants , an unprecedented number of fungal and fungal-like diseases have recently caused some of the most severe die-offs and extinctions ever witnessed in wild species , and are jeopardizing food security .
Human activity is intensifying fungal disease dispersal by modifying natural environments and thus creating new opportunities for evolution .
We argue that nascent fungal infections will cause increasing attrition of biodiversity , with wider implications for human and ecosystem health , unless steps are taken to tighten biosecurity worldwide .

[1746] Nutrients drive transcriptional changes that maintain metabolic homeostasis but alter genome architecture in Microcystis

The cyanobacterium Microcystis aeruginosa is a globally distributed bloom-forming organism that degrades freshwater systems around the world .
Factors that drive its dispersion , diversification and success remain , however , poorly understood .
To develop insight into cellular-level responses to nutrient drivers of eutrophication , RNA sequencing was coupled to a comprehensive metabolomics survey of M. aeruginosa sp .
NIES 843 grown in various nutrient-reduced conditions .
Transcriptomes were generated for cultures grown in nutrient-replete ( with nitrate as the nitrogen ( N ) source ) , nitrogen-reduced ( with nitrate , urea or ammonium acting as the N sources ) and phosphate-reduced conditions .
Extensive expression differences ( up to 696 genes for urea-grown cells ) relative to the control treatment were observed , demonstrating that the chemical variant of nitrogen available to cells affected transcriptional activity .
Of particular note , a high number of transposase genes ( up to 81 ) were significantly and reproducibly up-regulated relative to the control when grown on urea .
Conversely , phosphorus ( P ) reduction resulted in a significant cessation in transcription of transposase genes , indicating that variation in nutrient chemistry may influence transcription of transposases and may impact the highly mosaic genomic architecture of M. aeruginosa .
Corresponding metabolomes showed comparably few differences between treatments , suggesting broad changes to gene transcription are required to maintain metabolic homeostasis under nutrient reduction .
The combined observations provide novel and extensive insight into the complex cellular interactions that take place in this important bloom-forming organism during variable nutrient conditions and highlight a potential unknown molecular mechanism that may drive Microcystis blooms and evolution .

[1747] Agricultural impacts : Europe 's diminishing bread basket

Global demand for wheat is projected to increase significantly with continuing population growth .
Currently , Europe reliably produces about 29 % of global wheat supply .
However , this might be under threat from climate change if adaptive measures are not taken now .

[1748] Phage infection of an environmentally relevant marine bacterium alters host metabolism and lysate composition

Viruses contribute to the mortality of marine microbes , consequentially altering biological species composition and system biogeochemistry .
Although it is well established that host cells provide metabolic resources for virus replication , the extent to which infection reshapes host metabolism at a global level and the effect of this alteration on the cellular material released following viral lysis is less understood .
To address this knowledge gap , the growth dynamics , metabolism and extracellular lysate of roseophage-infected Sulfitobacter sp .
2047 was studied using a variety of techniques , including liquid chromatography-tandem mass spectrometry ( LC-MS/MS ) - based metabolomics .
Quantitative estimates of the total amount of carbon and nitrogen sequestered into particulate biomass indicate that phage infection redirects ~ 75 % of nutrients into virions .
Intracellular concentrations for 82 metabolites were measured at seven time points over the infection cycle .
By the end of this period , 71 % of the detected metabolites were significantly elevated in infected populations , and stable isotope-based flux measurements showed that these cells had elevated metabolic activity .
In contrast to simple hypothetical models that assume that extracellular compounds increase because of lysis , a profile of metabolites from infected cultures showed that > 70 % of the 56 quantified compounds had decreased concentrations in the lysate relative to uninfected controls , suggesting that these small , labile nutrients were being utilized by surviving cells .
These results indicate that virus-infected cells are physiologically distinct from their uninfected counterparts , which has implications for microbial community ecology and biogeochemistry .

[1749] Loops and autonomy promote evolvability of ecosystem networks

The structure of ecological networks , in particular food webs , determines their ability to evolve further , i.e. evolvability .
The knowledge about how food web evolvability is determined by the structures of diverse ecological networks can guide human interventions purposefully to either promote or limit evolvability of ecosystems .
However , the focus of prior food web studies was on stability and robustness ; little is known regarding the impact of ecological network structures on their evolvability .
To correlate ecosystem structure and evolvability , we adopt the NK model originally from evolutionary biology to generate and assess the ruggedness of fitness landscapes of a wide spectrum of model food webs with gradual variation in the amount of feeding loops and link density .
The variation in network structures is controlled by linkage rewiring .
Our results show that more feeding loops and lower trophic link density , i.e. higher autonomy of species , of food webs increase the potential for the ecosystem to generate heritable variations with improved fitness .
Our findings allow the prediction of the evolvability of actual food webs according to their network structures , and provide guidance to enhancing or controlling the evolvability of specific ecosystems .

[1750] Bottom-up effects of plant diversity on multitrophic interactions in a biodiversity experiment

Biodiversity is rapidly declining , and this may negatively affect ecosystem processes , including economically important ecosystem services .
Previous studies have shown that biodiversity has positive effects on organisms and processes across trophic levels .
However , only a few studies have so far incorporated an explicit food-web perspective .
In an eight-year biodiversity experiment , we studied an unprecedented range of above - and below-ground organisms and multitrophic interactions .
A multitrophic data set originating from a single long-term experiment allows mechanistic insights that would not be gained from meta-analysis of different experiments .
Here we show that plant diversity effects dampen with increasing trophic level and degree of omnivory .
This was true both for abundance and species richness of organisms .
Furthermore , we present comprehensive above-ground/below-ground biodiversity food webs .
Both above ground and below ground , herbivores responded more strongly to changes in plant diversity than did carnivores or omnivores .
Density and richness of carnivorous taxa was independent of vegetation structure .
Below-ground responses to plant diversity were consistently weaker than above-ground responses .
Responses to increasing plant diversity were generally positive , but were negative for biological invasion , pathogen infestation and hyperparasitism .
Our results suggest that plant diversity has strong bottom-up effects on multitrophic interaction networks , with particularly strong effects on lower trophic levels .
Effects on higher trophic levels are indirectly mediated through bottom-up trophic cascades .

[1751] European sea bass genome and its variation provide insights into adaptation to euryhalinity and speciation

The European sea bass ( Dicentrarchus labrax ) is a temperate-zone euryhaline teleost of prime importance for aquaculture and fisheries .
This species is subdivided into two naturally hybridizing lineages , one inhabiting the north-eastern Atlantic Ocean and the other the Mediterranean and Black seas .
Here we provide a high-quality chromosome-scale assembly of its genome that shows a high degree of synteny with the more highly derived teleosts .
We find expansions of gene families specifically associated with ion and water regulation , highlighting adaptation to variation in salinity .
We further generate a genome-wide variation map through RAD-sequencing of Atlantic and Mediterranean populations .
We show that variation in local recombination rates strongly influences the genomic landscape of diversity within and differentiation between lineages .
Comparing predictions of alternative demographic models to the joint allele-frequency spectrum indicates that genomic islands of differentiation between sea bass lineages were generated by varying rates of introgression across the genome following a period of geographical isolation .

[1752] Observing storm surges from space : Hurricane Igor off Newfoundland

Coastal communities are becoming increasingly more vulnerable to storm surges under a changing climate .
Tide gauges can be used to monitor alongshore variations of a storm surge , but not cross-shelf features .
In this study we combine Jason-2 satellite measurements with tide-gauge data to study the storm surge caused by Hurricane Igor off Newfoundland .
Satellite observations reveal a storm surge of 1 m in the early morning of September 22 , 2010 ( UTC ) after the passage of the storm , consistent with the tide-gauge measurements .
The post-storm sea level variations at St. John 's and Argentia are associated with free equatorward-propagating continental shelf waves ( with a phase speed of ~ 10 m/s and a cross-shelf decaying scale of ~ 100 km ) .
The study clearly shows the utility of satellite altimetry in observing and understanding storm surges , complementing tide-gauge observations for the analysis of storm surge characteristics and for the validation and improvement of storm surge models .

[1753] Sea surface temperature contributes to marine crocodylomorph evolution

During the Mesozoic and Cenozoic , four distinct crocodylomorph lineages colonized the marine environment .
They were conspicuously absent from high latitudes , which in the Mesozoic were occupied by warm-blooded ichthyosaurs and plesiosaurs .
Despite a relatively well-constrained stratigraphic distribution , the varying diversities of marine crocodylomorphs are poorly understood , because their extinctions neither coincided with any major biological crises nor with the advent of potential competitors .
Here we test the potential link between their evolutionary history in terms of taxic diversity and two abiotic factors , sea level variations and sea surface temperatures ( SST ) .
Excluding Metriorhynchoidea , which may have had a peculiar ecology , significant correlations obtained between generic diversity and estimated Tethyan SST suggest that water temperature was a driver of marine crocodylomorph diversity .
Being most probably ectothermic reptiles , these lineages colonized the marine realm and diversified during warm periods , then declined or became extinct during cold intervals .

[1754] Hypothalamic S1P/S1PR1 axis controls energy homeostasis

Sphingosine 1-phosphate receptor 1 ( S1PR1 ) is a G-protein-coupled receptor for sphingosine-1-phosphate ( S1P ) that has a role in many physiological and pathophysiological processes .
Here we show that the S1P/S1PR1 signalling pathway in hypothalamic neurons regulates energy homeostasis in rodents .
We demonstrate that S1PR1 protein is highly enriched in hypothalamic POMC neurons of rats .
Intracerebroventricular injections of the bioactive lipid , S1P , reduce food consumption and increase rat energy expenditure through persistent activation of STAT3 and the melanocortin system .
Similarly , the selective disruption of hypothalamic S1PR1 increases food intake and reduces the respiratory exchange ratio .
We further show that STAT3 controls S1PR1 expression in neurons via a positive feedback mechanism .
Interestingly , several models of obesity and cancer anorexia display an imbalance of hypothalamic S1P/S1PR1/STAT3 axis , whereas pharmacological intervention ameliorates these phenotypes .
Taken together , our data demonstrate that the neuronal S1P/S1PR1/STAT3 signalling axis plays a critical role in the control of energy homeostasis in rats .

[1755] Natural climate variability and future climate policy

Large ensemble climate modelling experiments demonstrate the large role natural variability plays in local climate on a multi-decadal timescale .
Variability in local weather and climate influences individual beliefs about climate change .
To the extent that support for climate mitigation policies is determined by citizens ' local experiences , natural variability will strongly influence the timescale for implementation of such policies .
Under a number of illustrative threshold criteria for both national and international climate action , we show that variability-driven uncertainty about local change , even in the face of a well-constrained estimate of global change , can potentially delay the time to policy implementation by decades .
Because several decades of greenhouse gas emissions can have a large impact on long-term climate outcomes , there is substantial risk associated with climate policies driven by consensus among individuals who are strongly influenced by local weather conditions .

[1756] Differences in soil bacterial diversity : driven by contemporary disturbances or historical contingencies ?

Contemporary environmental disturbances and historical contingencies are considered to be major factors driving current differences in microbial diversity .
However , little was known about their relative importance .
This study combines culture-independent molecular techniques and advanced statistical analyses to examine quantitatively the relative importance of contemporary disturbances and historical contingencies in influencing large-scale soil bacterial diversity using a large set of manipulated field-based molecular data ( 212 samples ) .
Contemporary disturbances were represented by applications of different fertilizers N , P , K and organic manure ( OM ) and historical contingencies by distinct geographic sampling locations and soil profiles .
Multivariate regression tree ( MRT ) analysis showed that diversity estimates were mainly distinguished by sampling locations , which explained 40.8 % of the variation in bacterial diversity , followed by soil profiles ( 19.5 % ) , sampling time ( 13.1 % ) , OM ( 3.7 % ) and P ( 1.8 % ) .
Aggregated boosted tree ( ABT ) analysis showed that the relative importance of different categorical factors on soil bacterial diversity variation was ranked as sampling locations , soil profiles , sampling time , OM and P. Both MRT and ABT analyses showed that historical contingencies were the dominant factor driving variation in bacterial diversity across a regional scale ( about 1000 km ) , whereas some contemporary disturbances also caused variation in bacterial diversity at a local scale .
This study demonstrated that past events and contemporary disturbances had similar influence on soil bacterial diversity to that documented for macroorganisms , indicating that there might be some common aspects of biogeography to all organisms .

[1757] Origin of avian genome size and structure in non-avian dinosaurs

Avian genomes are small and streamlined compared with those of other amniotes by virtue of having fewer repetitive elements and less non-coding DNA .
This condition has been suggested to represent a key adaptation for flight in birds , by reducing the metabolic costs associated with having large genome and cell sizes .
However , the evolution of genome architecture in birds , or any other lineage , is difficult to study because genomic information is often absent for long-extinct relatives .
Here we use a novel bayesian comparative method to show that bone-cell size correlates well with genome size in extant vertebrates , and hence use this relationship to estimate the genome sizes of 31 species of extinct dinosaur , including several species of extinct birds .
Our results indicate that the small genomes typically associated with avian flight evolved in the saurischian dinosaur lineage between 230 and 250 million years ago , long before this lineage gave rise to the first birds .
By comparison , ornithischian dinosaurs are inferred to have had much larger genomes , which were probably typical for ancestral Dinosauria .
Using comparative genomic data , we estimate that genome-wide interspersed mobile elements , a class of repetitive DNA , comprised 5-12 % of the total genome size in the saurischian dinosaur lineage , but was 7-19 % of total genome size in ornithischian dinosaurs , suggesting that repetitive elements became less active in the saurischian lineage .
These genomic characteristics should be added to the list of attributes previously considered avian but now thought to have arisen in non-avian dinosaurs , such as feathers , pulmonary innovations , and parental care and nesting .

[1758] The genome of Tetranychus urticae reveals herbivorous pest adaptations

The spider mite Tetranychus urticae is a cosmopolitan agricultural pest with an extensive host plant range and an extreme record of pesticide resistance .
Here we present the completely sequenced and annotated spider mite genome , representing the first complete chelicerate genome .
At 90 megabases T. urticae has the smallest sequenced arthropod genome .
Compared with other arthropods , the spider mite genome shows unique changes in the hormonal environment and organization of the Hox complex , and also reveals evolutionary innovation of silk production .
We find strong signatures of polyphagy and detoxification in gene families associated with feeding on different hosts and in new gene families acquired by lateral gene transfer .
Deep transcriptome analysis of mites feeding on different plants shows how this pest responds to a changing host environment .
The T. urticae genome thus offers new insights into arthropod evolution and plant-herbivore interactions , and provides unique opportunities for developing novel plant protection strategies .

[1759] Expression of the blood-group-related glycosyltransferase B4galnt2 influences the intestinal microbiota in mice

Glycans on mucosal surfaces have an important role in host-microbe interactions .
The locus encoding the blood-group-related glycosyltransferase beta-1 ,4 - N-acetylgalactosaminyltransferase 2 ( B4galnt2 ) is subject to strong selective forces in natural house-mouse populations that contain a common allelic variant that confers loss of B4galnt2 gene expression in the gastrointestinal ( GI ) tract .
We reasoned that altered glycan-dependent intestinal host-microbe interactions may underlie these signatures of selection .
To determine whether B4galnt2 influences the intestinal microbial ecology , we profiled the microbiota of wild-type and B4galnt2-deficient siblings throughout the GI tract using 16S rRNA gene pyrosequencing .
This revealed both distinct communities at different anatomic sites and significant changes in composition with respect to genotype , indicating a previously unappreciated role of B4galnt2 in host-microbial homeostasis .
Among the numerous B4galnt2-dependent differences identified in the abundance of specific bacterial taxa , we unexpectedly detected a difference in the pathogenic genus , Helicobacter , suggesting Helicobacter spp .
also interact with B4galnt2 glycans .
In contrast to other glycosyltransferases , we found that the host intestinal B4galnt2 expression is not dependent on presence of the microbiota .
Given the long-term maintenance of alleles influencing B4galnt2 expression by natural selection and the GI phenotypes presented here , we suggest that variation in B4galnt2 GI expression may alter susceptibility to GI diseases such as infectious gastroenteritis .

[1760] A stratospheric connection to Atlantic climate variability

The stratosphere is connected to tropospheric weather and climate .
In particular , extreme stratospheric circulation events are known to exert a dynamical feedback on the troposphere .
However , it is unclear whether the state of the stratosphere also affects the ocean and its circulation .
A co-variability of decadal stratospheric flow variations and conditions in the North Atlantic Ocean has been suggested , but such findings are based on short simulations with only one climate model .
Here we assess ocean reanalysis data and find that , over the previous 30 years , the stratosphere and the Atlantic thermohaline circulation experienced low-frequency variations that were similar to each other .
Using climate models , we demonstrate that this similarity is consistent with the hypothesis that variations in the sequence of stratospheric circulation anomalies , combined with the persistence of individual anomalies , significantly affect the North Atlantic Ocean .
Our analyses identify a previously unknown source for decadal climate variability and suggest that simulations of deep layers of the atmosphere and the ocean are needed for realistic predictions of climate .

[1761] Protein-based stable isotope probing ( Protein-SIP ) reveals active species within anoxic mixed cultures

It is still a challenge to link specific metabolic activities to certain species in a microbial community because of methodological limitations .
We developed a method to analyze the specific metabolic activity of a single bacterial species within a consortium making use of [ 13C7 ] - toluene for metabolic labelling of proteins .
Labelled proteins were subsequently analyzed by 2D gel electrophoresis ( 2-DE ) and mass spectrometry ( MS ) to characterize their identity as well as their 13C content as an indicator for function and activity of the host organism .
To establish this method , we analyzed the metabolic incorporation of 13C carbon atoms into proteins of Aromatoleum aromaticum strain EbN1 .
This strain is capable of metabolizing toluene under nitrate-reducing conditions and was grown in either pure culture or in a mixed consortium with a gluconate-consuming enrichment culture .
First , strain EbN1 was grown with non-labelled toluene or labelled [ 13C7 ] - toluene as carbon sources , respectively , and their proteins were subjected to 2-DE .
In total , 60 unique proteins were identified by MALDI-MS/MS .
From 38 proteins , the levels of 13C incorporation were determined as 92.3 + / -0.8 % .
Subsequently , we mixed strain EbN1 and the enrichment culture UFZ-1 , which does not grow on toluene but on gluconate , and added non-labelled toluene , [ 13C7 ] - toluene and/or non-labelled gluconate as carbon sources .
The isotope labelling of proteins was analyzed after 2-DE by MS as a quantitative indicator for metabolic transformation of isotopic-labelled toluene by the active species of the consortium .
Incorporation of 13C was exclusively found in proteins from strain EbN1 at a content of 82.6 + / -2.3 % , as an average calculated from 19 proteins , demonstrating the suitability of the method used to identify metabolic active species with specific properties within a mixed culture .

[1762] Predicted recurrences of mass coral mortality in the Indian Ocean

In 1998 , more than 90 % of shallow corals were killed on most Indian Ocean reefs .
High sea surface temperature ( SST ) was a primary cause , acting directly or by interacting with other factors .
Mean SSTs have been forecast to rise above the 1998 values in a few decades ; however , forecast SSTs rarely flow seamlessly from historical data , or may show erroneous seasonal oscillations , precluding an accurate prediction of when lethal SSTs will recur .
Differential acclimation by corals in different places complicates this further .
Here I scale forecast SSTs at 33 Indian Ocean sites where most shallow corals died in 1998 ( ref .
1 ) to identify geographical patterns in the timing of probable repeat occurrences .
Reefs located 10-15degrees south will be affected every 5 years by 2010-2025 .
North and south from this , dates recede in a pattern not directly related to present SSTs ; paradoxically , some of the warmest sites may be affected last .
Temperatures lethal to corals vary in this region by 6 degreesC , and acclimation of a modest 2 degreesC by corals could prolong their survival by nearly 100 years .

[1763] Fine-Scale Temporal Dynamics of a Fragmented Lotic Microbial Ecosystem

Microbial ecosystems are often assumed to be relatively stable over short periods of time , but this assumption is seldom tested .
An urban stream influenced by both flow and varying levels of anthropogenic influences is expected to have high temporal variability in microbial composition , and short-term ecological instability .
Thus , we analyzed the bacterioplankton composition of a weir-fragmented urban stream using Automated rRNA Intergenic Spacer Analysis ( ARISA ) .
A total of 46 sequential samples were collected in July 2009 for 7 days , every 7 hours , from both the up-stream side of the weir ( stream water ) and the downstream side of the weir ( estuarine ) water .
Bray-Curtis similarity based analysis showed a clear division between upstream and downstream communities .
A sudden pH drop induced change in both communities , but composition stability partially recovered within less than a day .
Thus , our results show that microbial ecosystems can change rapidly , but re-establish a new equilibrium relatively quickly .

[1764] High levels of atmospheric carbon dioxide necessary for the termination of global glaciation

The possibility that the Earth suffered episodes of global glaciation as recently as the Neoproterozoic period , between about 900 and 543 million years ago , has been widely discussed .
Termination of such ` hard snowball Earth ' climate states has been proposed to proceed from accumulation of carbon dioxide in the atmosphere .
Many salient aspects of the snowball scenario depend critically on the threshold of atmospheric carbon dioxide concentrations needed to trigger deglaciation .
Here I present simulations with a general circulation model , using elevated carbon dioxide levels to estimate this deglaciation threshold .
The model simulates several phenomena that are expected to be significant in a ` snowball Earth ' scenario , but which have not been considered in previous studies with less sophisticated models , such as a reduction of vertical temperature gradients in winter , a reduction in summer tropopause height , the effect of snow cover and a reduction in cloud greenhouse effects .
In my simulations , the system remains far short of deglaciation even at atmospheric carbon dioxide concentrations of 550 times the present levels ( 0.2 bar of CO2 ) .
I find that at much higher carbon dioxide levels , deglaciation is unlikely unless unknown feedback cycles that are not captured in the model come into effect .

[1765] Nitrogen regulates chitinase gene expression in a marine bacterium

Ammonium concentration and nitrogen source regulate promoter activity and use for the transcription of chiA , the major chitinase gene of Pseudoalteromonas sp .
S91 and S91CX , an S91 transposon lacZ fusion mutant .
The activity of chiA was quantified by beta-galactosidase assay of S91CX cultures containing different ammonium concentrations ( NH4 + ; 0 , 9.5 or 191 mM ) and with different nitrogen sources ( N-acetylglucosamine ( GlcNAc ) or glutamate ( glt ) ) .
S91 chiA expression was found to depend on both the NH4 + concentration and source of nitrogen in marine minimal medium ( MMM ) .
Pseudoalteromonas sp .
S91 and S91CX can use either GlcNAc or glt as a sole source of carbon in MMM containing a standard concentration of 9.5 mM NH4 + .
Adding excess NH4 + , 20 times the standard concentration , to MMM significantly reduced chiA activity below that found in the presence of either GlcNAc or glt .
When no NH4 + was added to MMM , S91CX was also able to use either GlcNAc or glt as a source of nitrogen ; under these conditions chiA activity was significantly increased .
Under all conditions tested , GlcNAc induced chiA activity significantly more than glt .
Regulation of bacterial chitinases by nitrogen has not been previously reported .
Transcriptional start point analysis of S91 chiA , using 5 ` RACE ( ligation-anchored PCR ) , showed that during growth in MMM supplemented with ( 1 ) maltose ( solely a carbon source for S91 ) , chiA transcription occurred from only one putative sigma70-dependent promoter ; ( 2 ) the chitin monomer GlcNAc , transcription initiated from two putative sigma54-dependent promoters and ( 3 ) glt , transcription initiated from all three putative promoters .

[1766] Spatial and decadal variations in inorganic nitrogen wet deposition in China induced by human activity

Atmospheric nitrogen ( N ) deposition , an important component in the global N cycle , has increased sharply in recent decades in China .
Here , we constructed national-scale inorganic N wet deposition ( Ndep ) patterns in China based on data from 280 observational sites and analysed the effects of anthropogenic sources and precipitation on Ndep .
Our results showed that the mean Ndep over China increased approximately 25 % , from 11.11 kg ha-1 a-1 in the 1990s to 13.87 in the 2000s .
Ndep was highest over southern China and exhibited a decreasing gradient from southern to western and northern China .
The decadal difference in Ndep between the 1990s and 2000s was primarily caused by increases in energy consumption and N fertiliser use .
Our findings conformed that anthropogenic activities were the main reason for the Ndep increase and provide a scientific background for studies on ecological effects of N deposition in China .

[1767] Paired oxygen isotope records reveal modern North American atmospheric dynamics during the Holocene

The Pacific North American ( PNA ) teleconnection has a strong influence on North American climate .
Instrumental records and century-scale reconstructions indicate an accelerating tendency towards the positive PNA state since the mid-1850s , but much less is known about long-term PNA variability .
Here we reconstruct PNA-like climate variability during the mid - and late Holocene using paired oxygen isotope records from two regions in North America with robust , anticorrelated isotopic response to the modern PNA .
We identify mean states of more negative and positive PNA-like climate during the mid - and late Holocene , respectively .
Superimposed on the secular change between states is a robust , quasi-200-year oscillation , which we associate with the de Vries solar cycle .
These findings suggest the persistence of PNA-like climate variability throughout the mid - and late Holocene , provide evidence for modulation of PNA over multiple timescales and may help researchers de-convolve PNA pattern variation from other factors reflected in palaeorecords .

[1768] Pulses of carbon dioxide emissions from intracrustal faults following climatic warming

Carbon capture and geological storage represents a potential means of managing atmospheric carbon dioxide levels .
Understanding the role of faults , as either barriers or conduits to the flow of carbon dioxide , is crucial for predicting the long-term integrity of geological storage sites .
Of particular concern is the influence of geochemical reactions on the sealing behaviour of faults and the impact of seismicity and stress regime on fault stability .
Here , we examine a 135,000-year palaeorecord of carbon dioxide leakage from a faulted , natural carbon dioxide reservoir in Utah .
We assess the isotope and trace-element composition of U-Th-dated carbonate veins , deposited by carbon-dioxide-rich fluids .
Temporal changes in vein geochemistry reveal pulses of carbon dioxide injection into the reservoir from deeper formations .
Surface leakage rates increase by several orders of magnitude following these pulses .
We show that each pulse occurs around 100-2 ,000 years after the onset of significant local climatic warming , at glacial to interglacial transitions .
We suggest that carbon dioxide leakage rates increase as a result of fracture opening , potentially caused by changes in groundwater hydrology , the intermittent presence of a buoyant gas cap and postglacial crustal unloading of regions surrounding the fault .

[1769] Soil pathogens and spatial patterns of seedling mortality in a temperate tree

The Janzen-Connell hypothesis proposes that host-specific , distance - and/or density-dependent predators and herbivores maintain high tree diversity in tropical forests .
Negative feedback between plant and soil communities could be a more effective mechanism promoting species coexistence because soil pathogens can increase rapidly in the presence of their host , causing conditions unfavourable for local conspecific recruitment .
Here we show that a soil pathogen leads to patterns of seedling mortality in a temperate tree ( Prunus serotina ) as predicted by the Janzen-Connell hypothesis .
In the field , the mean distance to parent of seedling cohorts shifted away from maternal trees over a period of 3 years .
Seedlings were grown in soil collected 0-5 m or 25-30 m from Prunus trees .
Sterilization of soil collected beneath trees improved seedling survival relative to unsterilized soil , whereas sterilization of distant soil did not affect survival .
Pythium spp. , isolated from roots of dying seedlings and used to inoculate healthy seedlings , decreased survival by 65 % relative to controls .
Our results provide the most complete evidence that native pathogens influence tree distributions , as predicted by the Janzen-Connell hypothesis , and suggest that similar ecological mechanisms operate in tropical and temperate forests .

[1770] Enhanced biofuel production through coupled acetic acid and xylose consumption by engineered yeast

The anticipation for substituting conventional fossil fuels with cellulosic biofuels is growing in the face of increasing demand for energy and rising concerns of greenhouse gas emissions .
However , commercial production of cellulosic biofuel has been hampered by inefficient fermentation of xylose and the toxicity of acetic acid , which constitute substantial portions of cellulosic biomass .
Here we use a redox balancing strategy to enable efficient xylose fermentation and simultaneous in situ detoxification of cellulosic feedstocks .
By combining a nicotinamide adenine dinucleotide ( NADH ) - consuming acetate consumption pathway and an NADH-producing xylose utilization pathway , engineered yeast converts cellulosic sugars and toxic levels of acetate together into ethanol under anaerobic conditions .
The results demonstrate a breakthrough in making efficient use of carbon compounds in cellulosic biomass and present an innovative strategy for metabolic engineering whereby an undesirable redox state can be exploited to drive desirable metabolic reactions , even improving productivity and yield .

[1771] Regional insolation forcing of late Quaternary climate change in the Southern Hemisphere

In agreement with the Milankovitch orbital forcing hypothesis it is often assumed that glacial-interglacial climate transitions occurred synchronously in the Northern and Southern hemispheres of the Earth .
It is difficult to test this assumption , because of the paucity of long , continuous climate records from the Southern Hemisphere that have not been dated by tuning them to the presumed Northern Hemisphere signals .
Here we present an independently dated terrestrial pollen record from a peat bog on South Island , New Zealand , to investigate global and local factors in Southern Hemisphere climate changes during the last two glacial-interglacial cycles .
Our record largely corroborates the Milankovitch model of orbital forcing but also exhibits some differences : in particular , an earlier onset and longer duration of the Last Glacial Maximum .
Our results suggest that Southern Hemisphere insolation may have been responsible for these differences in timing .
Our findings question the validity of applying orbital tuning to Southern Hemisphere records and suggest an alternative mechanism to the bipolar seesaw for generating interhemispheric asynchrony in climate change .

[1772] A shift of thermokarst lakes from carbon sources to sinks during the Holocene epoch

Thermokarst lakes formed across vast regions of Siberia and Alaska during the last deglaciation and are thought to be a net source of atmospheric methane and carbon dioxide during the Holocene epoch .
However , the same thermokarst lakes can also sequester carbon , and it remains uncertain whether carbon uptake by thermokarst lakes can offset their greenhouse gas emissions .
Here we use field observations of Siberian permafrost exposures , radiocarbon dating and spatial analyses to quantify Holocene carbon stocks and fluxes in lake sediments overlying thawed Pleistocene-aged permafrost .
We find that carbon accumulation in deep thermokarst-lake sediments since the last deglaciation is about 1.6 times larger than the mass of Pleistocene-aged permafrost carbon released as greenhouse gases when the lakes first formed .
Although methane and carbon dioxide emissions following thaw lead to immediate radiative warming , carbon uptake in peat-rich sediments occurs over millennial timescales .
We assess thermokarst-lake carbon feedbacks to climate with an atmospheric perturbation model and find that thermokarst basins switched from a net radiative warming to a net cooling climate effect about 5,000 years ago .
High rates of Holocene carbon accumulation in 20 lake sediments ( 47 + / - 10 grams of carbon per square metre per year ; mean + / - standard error ) were driven by thermokarst erosion and deposition of terrestrial organic matter , by nutrient release from thawing permafrost that stimulated lake productivity and by slow decomposition in cold , anoxic lake bottoms .
When lakes eventually drained , permafrost formation rapidly sequestered sediment carbon .
Our estimate of about 160 petagrams of Holocene organic carbon in deep lake basins of Siberia and Alaska increases the circumpolar peat carbon pool estimate for permafrost regions by over 50 per cent ( ref .
6 ) .
The carbon in perennially frozen drained lake sediments may become vulnerable to mineralization as permafrost disappears , potentially negating the climate stabilization provided by thermokarst lakes during the late Holocene .

[1773] Global potential of biospheric carbon management for climate mitigation

Elevated concentrations of atmospheric greenhouse gases ( GHGs ) , particularly carbon dioxide ( CO2 ) , have affected the global climate .
Land-based biological carbon mitigation strategies are considered an important and viable pathway towards climate stabilization .
However , to satisfy the growing demands for food , wood products , energy , climate mitigation and biodiversity conservation -- all of which compete for increasingly limited quantities of biomass and land -- the deployment of mitigation strategies must be driven by sustainable and integrated land management .
If executed accordingly , through avoided emissions and carbon sequestration , biological carbon and bioenergy mitigation could save up to 38 billion tonnes of carbon and 3-8 % of estimated energy consumption , respectively , by 2050 .

[1774] The contribution of organics to atmospheric nanoparticle growth

Aerosols have a strong , yet poorly quantified , effect on climate .
The growth of the smallest atmospheric particles from diameters in the nanometre range to sizes at which they may act as seeds for cloud droplets is a key step linking aerosols to clouds and climate .
In many environments , atmospheric nanoparticles grow by taking up organic compounds that are derived from biogenic hydrocarbon emissions .
Several mechanisms may control this uptake .
Condensation of low-volatility vapours and formation of organic salts probably dominate the very first steps of growth in particles close to 1 nm in diameter .
As the particles grow further , formation of organic polymers and effects related to the phase of the particle probably become increasingly important .
We suggest that dependence of particle growth mechanisms on particle size needs to be investigated more systematically .

[1775] Rescuing ecosystems from extinction cascades through compensatory perturbations

Food-web perturbations stemming from climate change , overexploitation , invasive species and habitat degradation often cause an initial loss of species that results in a cascade of secondary extinctions , posing considerable challenges to ecosystem conservation efforts .
Here , we devise a systematic network-based approach to reduce the number of secondary extinctions using a predictive modelling framework .
We show that the extinction of one species can often be compensated by the concurrent removal or population suppression of other specific species , a counterintuitive effect not previously tested in complex food webs .
These compensatory perturbations frequently involve long-range interactions that are not evident from local predator-prey relationships .
In numerous cases , even the early removal of a species that would eventually go extinct is found to significantly reduce the number of cascading extinctions .
These compensatory perturbations only exploit resources available in the system , and illustrate the potential of human intervention combined with predictive modelling for ecosystem management .

[1776] Taller plants have lower rates of molecular evolution

Rates of molecular evolution have a central role in our understanding of many aspects of species ' biology .
However , the causes of variation in rates of molecular evolution remain poorly understood , particularly in plants .
Here we show that height accounts for about one-fifth of the among-lineage rate variation in the chloroplast and nuclear genomes of plants .
This relationship holds across 138 families of flowering plants , and when accounting for variation in species richness , temperature , ultraviolet radiation , latitude and growth form .
Our observations can be explained by a link between height and rates of genome copying in plants , and we propose a mechanistic hypothesis to account for this -- the ` rate of mitosis ' hypothesis .
This hypothesis has the potential to explain many disparate observations about rates of molecular evolution across the tree of life .
Our results have implications for understanding the evolutionary history and future of plant lineages in a changing world .

[1777] Climatology : Threatened loss of the Greenland ice-sheet

The Greenland ice-sheet would melt faster in a warmer climate and is likely to be eliminated -- except for residual glaciers in the mountains -- if the annual average temperature in Greenland increases by more than about 3 degreesC .
This could raise the global average sea-level by 7 metres over a period of 1,000 years or more .
We show here that concentrations of greenhouse gases will probably have reached levels before the year 2100 that are sufficient to raise the temperature past this warming threshold .

[1778] Saliva microbiomes distinguish caries-active from healthy human populations

The etiology of dental caries remains elusive because of our limited understanding of the complex oral microbiomes .
The current methodologies have been limited by insufficient depth and breadth of microbial sampling , paucity of data for diseased hosts particularly at the population level , inconsistency of sampled sites and the inability to distinguish the underlying microbial factors .
By cross-validating 16S rRNA gene amplicon-based and whole-genome-based deep-sequencing technologies , we report the most in-depth , comprehensive and collaborated view to date of the adult saliva microbiomes in pilot populations of 19 caries-active and 26 healthy human hosts .
We found that : first , saliva microbiomes in human population were featured by a vast phylogenetic diversity yet a minimal organismal core ; second , caries microbiomes were significantly more variable in community structure whereas the healthy ones were relatively conserved ; third , abundance changes of certain taxa such as overabundance of Prevotella Genus distinguished caries microbiota from healthy ones , and furthermore , caries-active and normal individuals carried different arrays of Prevotella species ; and finally , no ` caries-specific ' operational taxonomic units ( OTUs ) were detected , yet 147 OTUs were ` caries associated ' , that is , differentially distributed yet present in both healthy and caries-active populations .
These findings underscored the necessity of species - and strain-level resolution for caries prognosis , and were consistent with the ecological hypothesis where the shifts in community structure , instead of the presence or absence of particular groups of microbes , underlie the cariogenesis .

[1779] Evidence for enhanced mixing over rough topography in the abyssal ocean

The overturning circulation of the ocean plays an important role in modulating the Earth 's climate .
But whereas the mechanisms for the vertical transport of water into the deep ocean -- deep water formation at high latitudes -- and horizontal transport in ocean currents have been largely identified , it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished .
Turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise .
However , measurements of the internal wave field , the main source of energy for mixing , and of turbulent dissipation rates , have typically implied diffusivities across surfaces of equal density of only ~ 0.1 cm2 s-1 , too small to account for the return flow .
Here we report measurements of tracer dispersion and turbulent energy dissipation in the Brazil basin that reveal diffusivities of 2-4 cm2 s-1 at a depth of 500 m above abyssal hills on the flank of the Mid-Atlantic Ridge , and approximately 10 cm2 s-1 nearer the bottom .
This amount of mixing , probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry , may be large enough to close the buoyancy budget for the Brazil basin and suggests a mechanism for closing the global overturning circulation .

[1780] Metabolically active microbial communities in marine sediment under high-CO2 and low-pH extremes

Sediment-hosting hydrothermal systems in the Okinawa Trough maintain a large amount of liquid , supercritical and hydrate phases of CO2 in the seabed .
The emission of CO2 may critically impact the geochemical , geophysical and ecological characteristics of the deep-sea sedimentary environment .
So far it remains unclear whether microbial communities that have been detected in such high-CO2 and low-pH habitats are metabolically active , and if so , what the biogeochemical and ecological consequences for the environment are .
In this study , RNA-based molecular approaches and radioactive tracer-based respiration rate assays were combined to study the density , diversity and metabolic activity of microbial communities in CO2-seep sediment at the Yonaguni Knoll IV hydrothermal field of the southern Okinawa Trough .
In general , the number of microbes decreased sharply with increasing sediment depth and CO2 concentration .
Phylogenetic analyses of community structure using reverse-transcribed 16S ribosomal RNA showed that the active microbial community became less diverse with increasing sediment depth and CO2 concentration , indicating that microbial activity and community structure are sensitive to CO2 venting .
Analyses of RNA-based pyrosequences and catalyzed reporter deposition-fluorescence in situ hybridization data revealed that members of the SEEP-SRB2 group within the Deltaproteobacteria and anaerobic methanotrophic archaea ( ANME-2a and -2 c ) were confined to the top seafloor , and active archaea were not detected in deeper sediments ( 13-30 cm in depth ) characterized by high CO2 .
Measurement of the potential sulfate reduction rate at pH conditions of 3-9 with and without methane in the headspace indicated that acidophilic sulfate reduction possibly occurs in the presence of methane , even at very low pH of 3 .
These results suggest that some members of the anaerobic methanotrophs and sulfate reducers can adapt to the CO2-seep sedimentary environment ; however , CO2 and pH in the deep-sea sediment were found to severely impact the activity and structure of the microbial community .

[1781] Regional climate response to solar-radiation management

Concerns about the slow pace of climate mitigation have led to renewed dialogue about solar-radiation management , which could be achieved by adding reflecting aerosols to the stratosphere .
Modelling studies suggest that solar-radiation management could produce stabilized global temperatures and reduced global precipitation .
Here we present an analysis of regional differences in a climate modified by solar-radiation management , using a large-ensemble modelling experiment that examines the impacts of 54 scenarios for global temperature stabilization .
Our results confirm that solar-radiation management would generally lead to less extreme temperature and precipitation anomalies , compared with unmitigated greenhouse gas emissions .
However , they also illustrate that it is physically not feasible to stabilize global precipitation and temperature simultaneously as long as atmospheric greenhouse gas concentrations continue to rise .
Over time , simulated temperature and precipitation in large regions such as China and India vary significantly with different trajectories for solar-radiation management , and they diverge from historical baselines in different directions .
Hence , it may not be possible to stabilize the climate in all regions simultaneously using solar-radiation management .
Regional diversity in the response to different levels of solar-radiation management could make consensus about the optimal level of geoengineering difficult , if not impossible , to achieve .

[1782] Simultaneous impairment of mitochondrial fission and fusion reduces mitophagy and shortens replicative lifespan

Aging of biological systems is accompanied by degeneration of mitochondrial functions .
Different pathways are active to counteract the processes which lead to mitochondrial dysfunction .
Mitochondrial dynamics , the fission and fusion of mitochondria , is one of these quality control pathways .
Mitophagy , the controlled degradation of mitochondria , is another one .
Here we show that these pathways are linked .
A double deletion mutant of Saccharomyces cerevisiae in which two essential components of the fission and fusion machinery , Dnm1 and Mgm1 , are simultaneously ablated , contain wild-type like filamentous mitochondria , but are characterized by impaired respiration , an increased sensitivity to different stressors , increased mitochondrial protein carbonylation , and a decrease in mitophagy and replicative lifespan .
These data show that a balanced mitochondrial dynamics and not a filamentous mitochondrial morphotype per se is the key for a long lifespan and demonstrate a cross-talk between two different mitochondrial quality control pathways .

[1783] Dynamics of ice ages on Mars

Unlike Earth , where astronomical climate forcing is comparatively small , Mars experiences dramatic changes in incident sunlight that are capable of redistributing ice on a global scale .
The geographic extent of the subsurface ice found poleward of approximately + / -60 degrees latitude on both hemispheres of Mars coincides with the areas where ice is stable .
However , the tilt of Mars ' rotation axis ( obliquity ) changed considerably in the past several million years .
Earlier work has shown that regions of ice stability , which are defined by temperature and atmospheric humidity , differed in the recent past from today 's , and subsurface ice is expected to retreat quickly when unstable .
Here I explain how the subsurface ice sheets could have evolved to the state in which we see them today .
Simulations of the retreat and growth of ground ice as a result of sublimation loss and recharge reveal forty major ice ages over the past five million years .
Today , this gives rise to pore ice at mid-latitudes and a three-layered depth distribution in the high latitudes of , from top to bottom , a dry layer , pore ice , and a massive ice sheet .
Combined , these layers provide enough ice to be compatible with existing neutron and gamma-ray measurements .

[1784] Aerobic bacterial pyrite oxidation and acid rock drainage during the Great Oxidation Event

The enrichment of redox-sensitive trace metals in ancient marine sedimentary rocks has been used to determine the timing of the oxidation of the Earth 's land surface .
Chromium ( Cr ) is among the emerging proxies for tracking the effects of atmospheric oxygenation on continental weathering ; this is because its supply to the oceans is dominated by terrestrial processes that can be recorded in the Cr isotope composition of Precambrian iron formations .
However , the factors controlling past and present seawater Cr isotope composition are poorly understood .
Here we provide an independent and complementary record of marine Cr supply , in the form of Cr concentrations and authigenic enrichment in iron-rich sedimentary rocks .
Our data suggest that Cr was largely immobile on land until around 2.48 Gyr ago , but within the 160 Myr that followed -- and synchronous with independent evidence for oxygenation associated with the Great Oxidation Event ( see , for example , refs 4-6 ) -- marked excursions in Cr content and Cr/Ti ratios indicate that Cr was solubilized at a scale unrivalled in history .
As Cr isotope fractionations at that time were muted , Cr must have been mobilized predominantly in reduced , Cr ( iii ) , form .
We demonstrate that only the oxidation of an abundant and previously stable crustal pyrite reservoir by aerobic-respiring , chemolithoautotrophic bacteria could have generated the degree of acidity required to solubilize Cr ( iii ) from ultramafic source rocks and residual soils .
This profound shift in weathering regimes beginning at 2.48 Gyr ago constitutes the earliest known geochemical evidence for acidophilic aerobes and the resulting acid rock drainage , and accounts for independent evidence of an increased supply of dissolved sulphate and sulphide-hosted trace elements to the oceans around that time .
Our model adds to amassing evidence that the Archaean-Palaeoproterozoic boundary was marked by a substantial shift in terrestrial geochemistry and biology .

[1785] Illumina sequencing-based analysis of free-living bacterial community dynamics during an Akashiwo sanguine bloom in Xiamen sea , China

Although phytoplankton are the major source of marine dissolved organic matter ( DOM ) , their blooms are a global problem that can greatly affect marine ecological systems , especially free-living bacteria , which are the primary DOM degraders .
In this study , we analyzed free-living bacterial communities from Xiamen sea during an Akashiwo sanguine bloom using Illumina MiSeq sequencing of 16S rRNA gene amplicons .
The bloom was probably stimulated by low salinity and ended after abatement of eutrophication pollution .
A total of 658,446 sequence reads and 11,807 OTUs were obtained in both bloom and control samples with Alpha-proteobacteria and Gamma-proteobacteria being the predominant classes detected .
The bloom decreased bacterial diversity , increased species evenness , and significantly changed the bacterial community structure .
Bacterial communities within the bloom were more homogeneous than those within the control area .
The bacteria stimulated by this bloom included the SAR86 and SAR116 clades and the AEGEAN-169 marine group , but a few were suppressed .
In addition , many bacteria known to be associated with phytoplankton were detected only in the bloom samples .
This study revealed the great influence of an A. sanguinea bloom on free-living bacterial communities , and provided new insights into the relationship between bacteria and A. sanguinea in marine ecosystems .

[1786] Global models of human decision-making for land-based mitigation and adaptation assessment

Understanding the links between land-use change ( LUC ) and climate change is vital in developing effective land-based climate mitigation policies and adaptation measures .
Although mitigation and adaptation are human-mediated processes , current global-scale modelling tools do not account for societal learning and other human responses to environmental change .
We propose the agent functional type ( AFT ) method to advance the representation of these processes , by combining socio-economics ( agent-based modelling ) with natural sciences ( dynamic global vegetation models ) .
Initial AFT-based simulations show the emergence of realistic LUC patterns that reflect known LUC processes , demonstrating the potential of the method to enhance our understanding of the role of people in the Earth system .

[1787] Enabling Universal Memory by Overcoming the Contradictory Speed and Stability Nature of Phase-Change Materials

The quest for universal memory is driving the rapid development of memories with superior all-round capabilities in non-volatility , high speed , high endurance and low power .
Phase-change materials are highly promising in this respect .
However , their contradictory speed and stability properties present a key challenge towards this ambition .
We reveal that as the device size decreases , the phase-change mechanism changes from the material inherent crystallization mechanism ( either nucleation - or growth-dominated ) , to the hetero-crystallization mechanism , which resulted in a significant increase in PCRAM speeds .
Reducing the grain size can further increase the speed of phase-change .
Such grain size effect on speed becomes increasingly significant at smaller device sizes .
Together with the nano-thermal and electrical effects , fast phase-change , good stability and high endurance can be achieved .
These findings lead to a feasible solution to achieve a universal memory .

[1788] Silicon enhances the growth of Phaeodactylum tricornutum Bohlin under green light and low temperature

Phaeodactylum tricornutum Bohlin is an ideal model diatom ; its complete genome is known , and it is an important economic microalgae .
Although silicon is not required in laboratory and factory culture of this species , previous studies have shown that silicon starvation can lead to differential expression of miRNAs .
The role that silicon plays in P. tricornutum growth in nature is poorly understood .
In this study , we compared the growth rate of silicon starved P. tricornutum with that of normal cultured cells under different culture conditions .
Pigment analysis , photosynthesis measurement , lipid analysis , and proteomic analysis showed that silicon plays an important role in P. tricornutum growth and that its presence allows the organism to grow well under green light and low temperature .

[1789] Determinants of biodiversity regulate compositional stability of communities

The world is witnessing a decline in biodiversity which may be greater in magnitude than even previous mass-extinction events .
This has rekindled interest in the relationships between biodiversity and the stability of community and ecosystem processes that have been reported in some empirical studies .
Diversity has been linked with community and ecosystem processes , but disputes remain over whether it is diversity , environmental factors or the variety of functional groups in a community that drive these patterns .
Furthermore , it remains unclear whether variation in diversity resulting from species loss within communities has similar effects on stability as natural variation in diversity associated with gradients in factors that regulate diversity .
We believe that , across larger ecological scales , extrinsic determinants of biodiversity such as disturbance regimes and site history may be the primary determinants of certain measures of community stability .
Here we use controlled field experiments in savanna grasslands in southern India to demonstrate and explain how low-diversity plant communities can show greater compositional stability when subject to experimental perturbations characteristic of their native environments .
These results are best explained by the ecological history and species characteristics of communities rather than by species diversity in itself .

[1790] Measurement Biases Explain Discrepancies between the Observed and Simulated Decadal Variability of Surface Incident Solar Radiation

Observations have reported a widespread dimming of surface incident solar radiation ( Rs ) from the 1950s to the 1980s and a brightening afterwards .
However , none of the state-of-the-art earth system models , including those from the Coupled Model Intercomparison Project phase 5 ( CMIP5 ) , could successfully reproduce the dimming/brightening rates over China .
We find that the decadal variability of observed Rs may have important errors due to instrument sensitivity drifting and instrument replacement .
While sunshine duration ( SunDu ) , which is a robust measurement related to Rs , is nearly free from these problems .
We estimate Rs from SunDu with a method calibrated by the observed Rs at each station .
SunDu-derived Rs declined over China by -2.8 ( with a 95 % confidence interval of -1.9 to -3.7 ) W m-2 per decade from 1960 to 1989 , while the observed Rs declined by -8.5 ( with a 95 % confidence interval of -7.3 to -9.8 ) W m-2 per decade .
The former trend was duplicated by some high-quality CMIP5 models , but none reproduced the latter trend .

[1791] An amorphous solid state of biogenic secondary organic aerosol particles

Secondary organic aerosol ( SOA ) particles are formed in the atmosphere from condensable oxidation products of anthropogenic and biogenic volatile organic compounds ( VOCs ) .
On a global scale , biogenic VOCs account for about 90 % of VOC emissions and of SOA formation ( 90 billion kilograms of carbon per year ) .
SOA particles can scatter radiation and act as cloud condensation or ice nuclei , and thereby influence the Earth 's radiation balance and climate .
They consist of a myriad of different compounds with varying physicochemical properties , and little information is available on the phase state of SOA particles .
Gas-particle partitioning models usually assume that SOA particles are liquid , but here we present experimental evidence that they can be solid under ambient conditions .
We investigated biogenic SOA particles formed from oxidation products of VOCs in plant chamber experiments and in boreal forests within a few hours after atmospheric nucleation events .
On the basis of observed particle bouncing in an aerosol impactor and of electron microscopy we conclude that biogenic SOA particles can adopt an amorphous solid -- most probably glassy -- state .
This amorphous solid state should provoke a rethinking of SOA processes because it may influence the partitioning of semi-volatile compounds , reduce the rate of heterogeneous chemical reactions , affect the particles ' ability to accommodate water and act as cloud condensation or ice nuclei , and change the atmospheric lifetime of the particles .
Thus , the results of this study challenge traditional views of the kinetics and thermodynamics of SOA formation and transformation in the atmosphere and their implications for air quality and climate .

[1792] Multistability and critical thresholds of the Greenland ice sheet

Recent studies have focused on the short-term contribution of the Greenland ice sheet to sea-level rise , yet little is known about its long-term stability .
The present best estimate of the threshold in global temperature rise leading to complete melting of the ice sheet is 3.1 degreesC ( 1.9-5 .1 degreesC , 95 % confidence interval ) above the preindustrial climate , determined as the temperature for which the modelled surface mass balance of the present-day ice sheet turns negative .
Here , using a fully coupled model , we show that this criterion systematically overestimates the temperature threshold and that the Greenland ice sheet is more sensitive to long-term climate change than previously thought .
We estimate that the warming threshold leading to a monostable , essentially ice-free state is in the range of 0.8-3 .2 degreesC , with a best estimate of 1.6 degreesC .
By testing the ice sheet 's ability to regrow after partial mass loss , we find that at least one intermediate equilibrium state is possible , though for sufficiently high initial temperature anomalies , total loss of the ice sheet becomes irreversible .
Crossing the threshold alone does not imply rapid melting ( for temperatures near the threshold , complete melting takes tens of millennia ) .
However , the timescale of melt depends strongly on the magnitude and duration of the temperature overshoot above this critical threshold .

[1793] Phosphorus cycling in the North and South Atlantic Ocean subtropical gyres

Despite similar physical properties , the Northern and Southern Atlantic subtropical gyres have different biogeochemical regimes .
The Northern subtropical gyre , which is subject to iron deposition from Saharan dust , is depleted in the nutrient phosphate , possibly as a result of iron-enhanced nitrogen fixation .
Although phosphate depleted , rates of carbon fixation in the euphotic zone of the North Atlantic subtropical gyre are comparable to those of the South Atlantic subtropical gyre , which is not phosphate limited .
Here we use the activity of the phosphorus-specific enzyme alkaline phosphatase to show potentially enhanced utilization of dissolved organic phosphorus occurring over much of the North Atlantic subtropical gyre .
We find that during the boreal spring up to 30 % of primary production in the North Atlantic gyre is supported by dissolved organic phosphorus .
Our diagnostics and composite map of the surface distribution of dissolved organic phosphorus in the subtropical Atlantic Ocean reveal shorter residence times in the North Atlantic gyre than the South Atlantic gyre .
We interpret the asymmetry of dissolved organic phosphorus cycling in the two gyres as a consequence of enhanced nitrogen fixation in the North Atlantic Ocean , which forces the system towards phosphorus limitation .
We suggest that dissolved organic phosphorus utilization may contribute to primary production in other phosphorus-limited ocean settings as well .

[1794] Western Arctic Ocean freshwater storage increased by wind-driven spin-up of the Beaufort Gyre

The Arctic Ocean 's freshwater budget comprises contributions from river runoff , precipitation , evaporation , sea-ice and exchanges with the North Pacific and Atlantic .
More than 70,000 km3 of freshwater are stored in the upper layer of the Arctic Ocean , leading to low salinities in upper-layer Arctic sea water , separated by a strong halocline from warm , saline water beneath .
Spatially and temporally limited observations show that the Arctic Ocean 's freshwater content has increased over the past few decades , predominantly in the west .
Models suggest that wind-driven convergence drives freshwater accumulation .
Here we use continuous satellite measurements between 1995 and 2010 to show that the dome in sea surface height associated with the western Arctic Beaufort Gyre has been steepening , indicating spin-up of the gyre .
We find that the trend in wind field curl -- a measure of spatial gradients in the wind that lead to water convergence or divergence -- exhibits a corresponding spatial pattern , suggesting that wind-driven convergence controls freshwater variability .
We estimate an increase in freshwater storage of 8,000 + / -2,000 km3 in the western Arctic Ocean , in line with hydrographic observations , and conclude that a reversal in the wind field could lead to a spin-down of the Beaufort Gyre , and release of this freshwater to the Arctic Ocean .

[1795] Functional diversity of marine ecosystems after the Late Permian mass extinction event

The Late Permian mass extinction event about 252 million years ago was the most severe biotic crisis of the past 500 million years and occurred during an episode of global warming .
The loss of around two-thirds of marine genera is thought to have had substantial ecological effects , but the overall impacts on the functioning of marine ecosystems and the pattern of marine recovery are uncertain .
Here we analyse the fossil occurrences of all known benthic marine invertebrate genera from the Permian and Triassic periods , and assign each to a functional group based on their inferred lifestyle .
We show that despite the selective extinction of 62-74 % of these genera , all but one functional group persisted through the crisis , indicating that there was no significant loss of functional diversity at the global scale .
In addition , only one new mode of life originated in the extinction aftermath .
We suggest that Early Triassic marine ecosystems were not as ecologically depauperate as widely assumed .
Functional diversity was , however , reduced in particular regions and habitats , such as tropical reefs ; at these smaller scales , recovery varied spatially and temporally , probably driven by migration of surviving groups .
We find that marine ecosystems did not return to their pre-extinction state , and by the Middle Triassic greater functional evenness is recorded , resulting from the radiation of previously subordinate groups such as motile , epifaunal grazers .

[1796] Variation in local carrying capacity and the individual fate of bacterial colonizers in the phyllosphere

Using a phyllosphere model system , we demonstrated that the term ` carrying capacity ' , as it is commonly used in microbial ecology , needs to be understood as the sum of many ` local carrying capacities ' in order to better explain and predict the course and outcome of bacterial colonization of an environment .
Using a green fluorescent protein-based bioreporter system for the quantification of reproductive success ( RS ) in individual Erwinia herbicola cells , we were able to reconstruct the contribution of individual immigrants to bacterial population sizes on leaves .
Our analysis revealed that plant foliage represents to bacteria an environment where individual fate is determined by the local carrying capacity of the site where an immigrant cell lands .
With increasing inoculation densities , the RS of most immigrants declined , suggesting that local carrying capacity under the tested conditions was linked to local nutrient availability .
Fitting the observed experimental data to an adapted model of phyllosphere colonization indicated that there might exist three types of sites on leaves , which differ in their frequency of occurrence and local carrying capacity .
Specifically , our data were consistent with a leaf environment that is characterized by few sites where individual immigrants can produce high numbers of offspring , whereas the remainder of the leaf offered an equal number of sites with low and medium RS .
Our findings contribute to a bottom-up understanding of bacterial colonization of leaf surfaces , which includes a quantifiable role of chance in the experience at the individual level and in the outcome at the population level .

[1797] Temperature sensitivity of soil carbon decomposition and feedbacks to climate change

Significantly more carbon is stored in the world 's soils -- including peatlands , wetlands and permafrost -- than is present in the atmosphere .
Disagreement exists , however , regarding the effects of climate change on global soil carbon stocks .
If carbon stored belowground is transferred to the atmosphere by a warming-induced acceleration of its decomposition , a positive feedback to climate change would occur .
Conversely , if increases of plant-derived carbon inputs to soils exceed increases in decomposition , the feedback would be negative .
Despite much research , a consensus has not yet emerged on the temperature sensitivity of soil carbon decomposition .
Unravelling the feedback effect is particularly difficult , because the diverse soil organic compounds exhibit a wide range of kinetic properties , which determine the intrinsic temperature sensitivity of their decomposition .
Moreover , several environmental constraints obscure the intrinsic temperature sensitivity of substrate decomposition , causing lower observed ` apparent ' temperature sensitivity , and these constraints may , themselves , be sensitive to climate .

[1798] Prolonged suppression of ecosystem carbon dioxide uptake after an anomalously warm year

Terrestrial ecosystems control carbon dioxide fluxes to and from the atmosphere through photosynthesis and respiration , a balance between net primary productivity and heterotrophic respiration , that determines whether an ecosystem is sequestering carbon or releasing it to the atmosphere .
Global and site-specific data sets have demonstrated that climate and climate variability influence biogeochemical processes that determine net ecosystem carbon dioxide exchange ( NEE ) at multiple timescales .
Experimental data necessary to quantify impacts of a single climate variable , such as temperature anomalies , on NEE and carbon sequestration of ecosystems at interannual timescales have been lacking .
This derives from an inability of field studies to avoid the confounding effects of natural intra-annual and interannual variability in temperature and precipitation .
Here we present results from a four-year study using replicate 12,000-kg intact tallgrass prairie monoliths located in four 184-m3 enclosed lysimeters .
We exposed 6 of 12 monoliths to an anomalously warm year in the second year of the study and continuously quantified rates of ecosystem processes , including NEE .
We find that warming decreases NEE in both the extreme year and the following year by inducing drought that suppresses net primary productivity in the extreme year and by stimulating heterotrophic respiration of soil biota in the subsequent year .
Our data indicate that two years are required for NEE in the previously warmed experimental ecosystems to recover to levels measured in the control ecosystems .
This time lag caused net ecosystem carbon sequestration in previously warmed ecosystems to be decreased threefold over the study period , compared with control ecosystems .
Our findings suggest that more frequent anomalously warm years , a possible consequence of increasing anthropogenic carbon dioxide levels , may lead to a sustained decrease in carbon dioxide uptake by terrestrial ecosystems .

[1799] An alternative approach to establishing trade-offs among greenhouse gases

The Kyoto Protocol permits countries to meet part of their emission reduction obligations by cutting back on gases other than CO2 ( ref .
1 ) .
This approach requires a definition of trade-offs among the radiatively active gases .
The Intergovernmental Panel on Climate Change has suggested global warming potentials for this purpose , which use the accumulated radiative forcing of each gas by a set time horizon to establish emission equivalence .
But it has been suggested that this approach has serious shortcomings : damages or abatement costs are not considered and the choice of time horizon for calculating cumulative radiative force is critical , but arbitrary .
Here we describe an alternative framework for determining emission equivalence between radiatively active gases that addresses these weaknesses .
We focus on limiting temperature change and rate of temperature change , but our framework is also applicable to other objectives .
For a proposed ceiling , we calculate how much one should be willing to pay for emitting an additional unit of each gas .
The relative prices then determine the trade-off between gases at each point in time , taking into account economical as well as physical considerations .
Our analysis shows that the relative prices are sensitive to the lifetime of the gases , the choice of target and the proximity of the target , making short-lived gases more expensive to emit as we approach the prescribed ceiling .

[1800] Arctic amplification dominated by temperature feedbacks in contemporary climate models

Climate change is amplified in the Arctic region .
Arctic amplification has been found in past warm and glacial periods , as well as in historical observations and climate model experiments .
Feedback effects associated with temperature , water vapour and clouds have been suggested to contribute to amplified warming in the Arctic , but the surface albedo feedback -- the increase in surface absorption of solar radiation when snow and ice retreat -- is often cited as the main contributor .
However , Arctic amplification is also found in models without changes in snow and ice cover .
Here we analyse climate model simulations from the Coupled Model Intercomparison Project Phase 5 archive to quantify the contributions of the various feedbacks .
We find that in the simulations , the largest contribution to Arctic amplification comes from a temperature feedbacks : as the surface warms , more energy is radiated back to space in low latitudes , compared with the Arctic .
This effect can be attributed to both the different vertical structure of the warming in high and low latitudes , and a smaller increase in emitted blackbody radiation per unit warming at colder temperatures .
We find that the surface albedo feedback is the second main contributor to Arctic amplification and that other contributions are substantially smaller or even opposeArctic amplification .

[1801] Observations beneath Pine Island Glacier in West Antarctica and implications for its retreat

Thinning ice in West Antarctica , resulting from acceleration in the flow of outlet glaciers , is at present contributing about 10 % of the observed rise in global sea level .
Pine Island Glacier in particular has shown nearly continuous acceleration and thinning , throughout the short observational record .
The floating ice shelf that forms where the glacier reaches the coast has been thinning rapidly , driven by changes in ocean heat transport beneath it .
As a result , the line that separates grounded and floating ice has retreated inland .
These events have been postulated as the cause for the inland thinning and acceleration .
Here we report evidence gathered by an autonomous underwater vehicle operating beneath the ice shelf that Pine Island Glacier was recently grounded on a transverse ridge in the sea floor .
Warm sea water now flows through a widening gap above the submarine ridge , rapidly melting the thick ice of the newly formed upstream half of the ice shelf .
The present evolution of Pine Island Glacier is thus part of a longer-term trend that has moved the downstream limit of grounded ice inland by 30 km , into water that is 300 m deeper than over the ridge crest .
The pace and ultimate extent of such potentially unstable retreat are central to the debate over the possibility of widespread ice-sheet collapse triggered by climate change .

[1802] Bacterial community structure corresponds to performance during cathodic nitrate reduction

Microbial fuel cells ( MFCs ) have applications other than electricity production , including the capacity to power desirable reactions in the cathode chamber .
However , current knowledge of the microbial ecology and physiology of biocathodes is minimal , and as a result more research dedicated to understanding the microbial communities active in cathode biofilms is required .
Here we characterize the microbiology of denitrifying bacterial communities stimulated by reducing equivalents generated from the anodic oxidation of acetate .
We analyzed biofilms isolated from two types of cathodic denitrification systems : ( 1 ) a loop format where the effluent from the carbon oxidation step in the anode is subjected to a nitrifying reactor which is fed to the cathode chamber and ( 2 ) an alternative non-loop format where anodic and cathodic feed streams are separated .
The results of our study indicate the superior performance of the loop reactor in terms of enhanced current production and nitrate removal rates .
We hypothesized that phylogenetic or structural features of the microbial communities could explain the increased performance of the loop reactor .
We used PhyloChip with 16S rRNA ( cDNA ) and fluorescent in situ hybridization to characterize the active bacterial communities .
Our study results reveal a greater richness , as well as an increased phylogenetic diversity , active in denitrifying biofilms than was previously identified in cathodic systems .
Specifically , we identified Proteobacteria , Firmicutes and Chloroflexi members that were dominant in denitrifying cathodes .
In addition , our study results indicate that it is the structural component , in terms of bacterial richness and evenness , rather than the phylogenetic affiliation of dominant bacteria , that best corresponds to cathode performance .

[1803] Cultural dimensions of climate change impacts and adaptation

Society 's response to every dimension of global climate change is mediated by culture .
We analyse new research across the social sciences to show that climate change threatens cultural dimensions of lives and livelihoods that include the material and lived aspects of culture , identity , community cohesion and sense of place .
We find , furthermore , that there are important cultural dimensions to how societies respond and adapt to climate-related risks .
We demonstrate how culture mediates changes in the environment and changes in societies , and we elucidate shortcomings in contemporary adaptation policy .

[1804] Climate-mediated dance of the plankton

Climate change will unquestionably influence global ocean plankton because it directly impacts both the availability of growth-limiting resources and the ecological processes governing biomass distributions and annual cycles .
Forecasting this change demands recognition of the vital , yet counterintuitive , attributes of the plankton world .
The biomass of photosynthetic phytoplankton , for example , is not proportional to their division rate .
Perhaps more surprising , physical processes ( such as deep vertical mixing ) can actually trigger an accumulation in phytoplankton while simultaneously decreasing their division rates .
These behaviours emerge because changes in phytoplankton division rates are paralleled by proportional changes in grazing , viral attack and other loss rates .
Here I discuss this trophic dance between predators and prey , how it dictates when phytoplankton biomass remains constant or achieves massive blooms , and how it can determine even the sign of change in ocean ecosystems under a warming climate .

[1805] Evolution and metabolic significance of the urea cycle in photosynthetic diatoms

Diatoms dominate the biomass of phytoplankton in nutrient-rich conditions and form the basis of some of the world 's most productive marine food webs .
The diatom nuclear genome contains genes with bacterial and plastid origins as well as genes of the secondary endosymbiotic host ( the exosymbiont ) , yet little is known about the relative contribution of each gene group to diatom metabolism .
Here we show that the exosymbiont-derived ornithine-urea cycle , which is similar to that of metazoans but is absent in green algae and plants , facilitates rapid recovery from prolonged nitrogen limitation .
RNA-interference-mediated knockdown of a mitochondrial carbamoyl phosphate synthase impairs the response of nitrogen-limited diatoms to nitrogen addition .
Metabolomic analyses indicate that intermediates in the ornithine-urea cycle are particularly depleted and that both the tricarboxylic acid cycle and the glutamine synthetase/glutamate synthase cycles are linked directly with the ornithine-urea cycle .
Several other depleted metabolites are generated from ornithine-urea cycle intermediates by the products of genes laterally acquired from bacteria .
This metabolic coupling of bacterial - and exosymbiont-derived proteins seems to be fundamental to diatom physiology because the compounds affected include the major diatom osmolyte proline and the precursors for long-chain polyamines required for silica precipitation during cell wall formation .
So far , the ornithine-urea cycle is only known for its essential role in the removal of fixed nitrogen in metazoans .
In diatoms , this cycle serves as a distribution and repackaging hub for inorganic carbon and nitrogen and contributes significantly to the metabolic response of diatoms to episodic nitrogen availability .
The diatom ornithine-urea cycle therefore represents a key pathway for anaplerotic carbon fixation into nitrogenous compounds that are essential for diatom growth and for the contribution of diatoms to marine productivity .

[1806] Genome architecture is a selectable trait that can be maintained by antagonistic pleiotropy

Chromosomal rearrangements are mutations contributing to both within and between species variation ; however their contribution to fitness is yet to be measured .
Here we show that chromosomal rearrangements are pervasive in natural isolates of Schizosaccharomyces pombe and contribute to reproductive isolation .
To determine the fitness effects of chromosome structure , we constructed two inversions and eight translocations without changing the coding sequence .
We show that chromosomal rearrangements contribute to both reproductive success in meiosis and growth rate in mitosis with a strong genotype by environment interaction .
These changes are accompanied by alterations in gene expression .
Strikingly , we find several examples leading to antagonistic pleiotropy .
Even though chromosomal rearrangements may have a deleterious effect during sexual reproduction , some compensate with a strong growth advantage in mitosis .
Our results constitute the first quantification of fitness effects caused by de novo mutations that result in chromosomal rearrangement variation and suggest a mechanism for their maintenance in natural populations .

[1807] Ferritin is used for iron storage in bloom-forming marine pennate diatoms

Primary productivity in 30-40 % of the world 's oceans is limited by availability of the micronutrient iron .
Regions with chronically low iron concentrations are sporadically pulsed with new iron inputs by way of dust or lateral advection from continental margins .
Addition of iron to surface waters in these areas induces massive phytoplankton blooms dominated primarily by pennate diatoms .
Here we provide evidence that the bloom-forming pennate diatoms Pseudo-nitzschia and Fragilariopsis use the iron-concentrating protein , ferritin , to safely store iron .
Ferritin has not been reported previously in any member of the Stramenopiles , a diverse eukaryotic lineage that includes unicellular algae , macroalgae and plant parasites .
Phylogenetic analyses suggest that ferritin may have arisen in this small subset of diatoms through a lateral gene transfer .
The crystal structure and functional assays of recombinant ferritin derived from Pseudo-nitzschia multiseries reveal a maxi-ferritin that exhibits ferroxidase activity and binds iron .
The protein is predicted to be targeted to the chloroplast to control the distribution and storage of iron for proper functioning of the photosynthetic machinery .
Abundance of Pseudo-nitzschia ferritin transcripts is regulated by iron nutritional status , and is closely tied to the loss and recovery of photosynthetic competence .
Enhanced iron storage with ferritin allows the oceanic diatom Pseudo-nitzschia granii to undergo several more cell divisions in the absence of iron than the comparably sized , oceanic centric diatom Thalassiosira oceanica .
Ferritin in pennate diatoms probably contributes to their success in chronically low-iron regions that receive intermittent iron inputs , and provides an explanation for the importance of these organisms in regulating oceanic CO2 over geological timescales .

[1808] Amplified mid-latitude planetary waves favour particular regional weather extremes

There has been an ostensibly large number of extreme weather events in the Northern Hemisphere mid-latitudes during the past decade .
An open question that is critically important for scientists and policy makers is whether any such increase in weather extremes is natural or anthropogenic in origin .
One mechanism proposed to explain the increased frequency of extreme weather events is the amplification of mid-latitude atmospheric planetary waves .
Disproportionately large warming in the northern polar regions compared with mid-latitudes -- and associated weakening of the north-south temperature gradient -- may favour larger amplitude planetary waves , although observational evidence for this remains inconclusive .
A better understanding of the role of planetary waves in causing mid-latitude weather extremes is essential for assessing the potential environmental and socio-economic impacts of future planetary wave changes .
Here we show that months of extreme weather over mid-latitudes are commonly accompanied by significantly amplified quasi-stationary mid-tropospheric planetary waves .
Conversely , months of near-average weather over mid-latitudes are often accompanied by significantly attenuated waves .
Depending on geographical region , certain types of extreme weather ( for example , hot , cold , wet , dry ) are more strongly related to wave amplitude changes than others .
The findings suggest that amplification of quasi-stationary waves preferentially increases the probabilities of heat waves in western North America and central Asia , cold outbreaks in eastern North America , droughts in central North America , Europe and central Asia , and wet spells in western Asia .

[1809] Long-term influence of biochar on native organic carbon mineralisation in a low-carbon clayey soil

Biochar can influence native soil organic carbon ( SOC ) mineralisation through `` priming effects '' .
However , the long-term direction , persistence and extent of SOC priming by biochar remain uncertain .
Using natural 13C abundance and under controlled laboratory conditions , we show that biochar-stimulated SOC mineralisation ( `` positive priming '' ) caused a loss of 4 to 44 mg C g-1 SOC over 2.3 years in a clayey , unplanted soil ( 0.42 % OC ) .
Positive priming was greater for manure-based or 400degreesC biochars , cf. plant-based or 550degreesC biochars , but was trivial relative to recalcitrant C in biochar .
From 2.3 to 5.0 years , the amount of positively-primed soil CO2-C in the biochar treatments decreased by 4 to 7 mg C g-1 SOC .
We conclude that biochar stimulates native SOC mineralisation in the low-C clayey soil but that this effect decreases with time , possibly due to depletion of labile SOC from initial positive priming , and/or stabilisation of SOC caused by biochar-induced organo-mineral interactions .

[1810] How does a hypha grow ?

The biophysics of pressurized growth in fungi
The mechanisms underlying the growth of fungal hyphae are rooted in the physical property of cell pressure .
Internal hydrostatic pressure ( turgor ) is one of the major forces driving the localized expansion at the hyphal tip which causes the characteristic filamentous shape of the hypha .
Calcium gradients regulate tip growth , and secretory vesicles that contribute to this process are actively transported to the growing tip by molecular motors that move along cytoskeletal structures .
Turgor is controlled by an osmotic mitogen-activated protein kinase cascade that causes de novo synthesis of osmolytes and uptake of ions from the external medium .
However , as discussed in this Review , turgor and pressure have additional roles in hyphal growth , such as causing the mass flow of cytoplasm from the basal mycelial network towards the expanding hyphal tips at the colony edge .

[1811] The European functional tree of bird life in the face of global change

Despite the recognized joint impact of climate and land cover change on facets of biodiversity and their associated functions , risk assessments have primarily evaluated impacts on species ranges and richness .
Here we quantify the sensitivity of the functional structure of European avian assemblages to changes in both regional climate and land cover .
We combine species range forecasts with functional-trait information .
We show that species sensitivity to environmental change is randomly distributed across the functional tree of the European avifauna and that functionally unique species are not disproportionately threatened by 2080 .
However , projected species range changes will modify the mean species richness and functional diversity of bird diets and feeding behaviours .
This will unequally affect the spatial structure of functional diversity , leading to homogenization across Europe .
Therefore , global changes may alter the functional structure of species assemblages in the future in ways that need to be accounted for in conservation planning .

[1812] Land management and land-cover change have impacts of similar magnitude on surface temperature

Anthropogenic changes to land cover ( LCC ) remain common , but continuing land scarcity promotes the widespread intensification of land management changes ( LMC ) to better satisfy societal demand for food , fibre , fuel and shelter .
The biophysical effects of LCC on surface climate are largely understood , particularly for the boreal and tropical zones , but fewer studies have investigated the biophysical consequences of LMC ; that is , anthropogenic modification without a change in land cover type .
Harmonized analysis of ground measurements and remote sensing observations of both LCC and LMC revealed that , in the temperate zone , potential surface cooling from increased albedo is typically offset by warming from decreased sensible heat fluxes , with the net effect being a warming of the surface .
Temperature changes from LMC and LCC were of the same magnitude , and averaged 2 K at the vegetation surface and were estimated at 1.7 K in the planetary boundary layer .
Given the spatial extent of land management ( 42-58 % of the land surface ) this calls for increasing the efforts to integrate land management in Earth System Science to better take into account the human impact on the climate .

[1813] Forcing , feedback and internal variability in global temperature trends

Most present-generation climate models simulate an increase in global-mean surface temperature ( GMST ) since 1998 , whereas observations suggest a warming hiatus .
It is unclear to what extent this mismatch is caused by incorrect model forcing , by incorrect model response to forcing or by random factors .
Here we analyse simulations and observations of GMST from 1900 to 2012 , and show that the distribution of simulated 15-year trends shows no systematic bias against the observations .
Using a multiple regression approach that is physically motivated by surface energy balance , we isolate the impact of radiative forcing , climate feedback and ocean heat uptake on GMST -- with the regression residual interpreted as internal variability -- and assess all possible 15 - and 62-year trends .
The differences between simulated and observed trends are dominated by random internal variability over the shorter timescale and by variations in the radiative forcings used to drive models over the longer timescale .
For either trend length , spread in simulated climate feedback leaves no traceable imprint on GMST trends or , consequently , on the difference between simulations and observations .
The claim that climate models systematically overestimate the response to radiative forcing from increasing greenhouse gas concentrations therefore seems to be unfounded .

[1814] Impact of the Mertz Glacier Tongue calving on dense water formation and export

Antarctic Bottom Water ( AABW ) is a critical component of the global climate system , occupying the abyssal layer of the World Ocean and driving the lower limb of the global meridional overturning circulation .
Around East Antarctica , the dense shelf water ( DSW ) precursor to AABW is predominantly formed by enhanced sea ice formation in coastal polynyas .
The dominant source region of AABW supply to the Australian-Antarctic Basin is the Adelie and George V Land coast , in particular , polynyas formed in the western lee of the Mertz Glacier Tongue ( MGT ) and the grounded iceberg B9b over the Adelie and the Mertz Depressions , respectively .
The calving of the MGT , which occurred on 12-13 February 2010 , dramatically changed the environment for producing DSW .
Here , we assess its impact using a state-of-the-art ice-ocean model .
The model shows that oceanic circulation and sea ice production in the region changes immediately after the calving event , and that the DSW export is reduced by up to 23 % .

[1815] Dynamics of bacterial community succession in a salt marsh chronosequence : evidences for temporal niche partitioning

The mechanisms underlying community assembly and promoting temporal succession are often overlooked in microbial ecology .
Here , we studied an undisturbed salt marsh chronosequence , spanning over a century of ecosystem development , to understand bacterial succession in soil .
We used 16S rRNA gene-based quantitative PCR to determine bacterial abundance and multitag 454 pyrosequencing for community composition and diversity analyses .
Despite 10-fold lower 16S rRNA gene abundances , the initial stages of soil development held higher phylogenetic diversities than the soil at late succession .
Temporal variations in phylogenetic beta-diversity were greater at initial stages of soil development , possibly as a result of the great dynamism imposed by the daily influence of the tide , promoting high immigration rates .
Allogenic succession of bacterial communities was mostly driven by shifts in the soil physical structure , as well as variations in pH and salinity , which collectively explained 84.5 % of the variation concerning community assemblage .
The community assembly data for each successional stage were integrated into a network co-occurrence analysis , revealing higher complexity at initial stages , coinciding with great dynamism in turnover and environmental variability .
Contrary to a spatial niche-based perspective of bacterial community assembly , we suggest temporal niche partitioning as the dominant mechanism of assembly ( promoting more phylotype co-occurrence ) in the initial stages of succession , where continuous environmental change results in the existence of multiple niches over short periods of time .

[1816] Amphibian skin may select for rare environmental microbes

Host-microbe symbioses rely on the successful transmission or acquisition of symbionts in each new generation .
Amphibians host a diverse cutaneous microbiota , and many of these symbionts appear to be mutualistic and may limit infection by the chytrid fungus , Batrachochytrium dendrobatidis , which has caused global amphibian population declines and extinctions in recent decades .
Using bar-coded 454 pyrosequencing of the 16S rRNA gene , we addressed the question of symbiont transmission by examining variation in amphibian skin microbiota across species and sites and in direct relation to environmental microbes .
Although acquisition of environmental microbes occurs in some host-symbiont systems , this has not been extensively examined in free-living vertebrate-microbe symbioses .
Juvenile bullfrogs ( Rana catesbeiana ) , adult red-spotted newts ( Notophthalmus viridescens ) , pond water and pond substrate were sampled at a single pond to examine host-specificity and potential environmental transmission of microbiota .
To assess population level variation in skin microbiota , adult newts from two additional sites were also sampled .
Cohabiting bullfrogs and newts had distinct microbial communities , as did newts across the three sites .
The microbial communities of amphibians and the environment were distinct ; there was very little overlap in the amphibians ' core microbes and the most abundant environmental microbes , and the relative abundances of OTUs that were shared by amphibians and the environment were inversely related .
These results suggest that , in a host species-specific manner , amphibian skin may select for microbes that are generally in low abundance in the environment .

[1817] A multitrophic model to quantify the effects of marine viruses on microbial food webs and ecosystem processes

Viral lysis of microbial hosts releases organic matter that can then be assimilated by nontargeted microorganisms .
Quantitative estimates of virus-mediated recycling of carbon in marine waters , first established in the late 1990s , were originally extrapolated from marine host and virus densities , host carbon content and inferred viral lysis rates .
Yet , these estimates did not explicitly incorporate the cascade of complex feedbacks associated with virus-mediated lysis .
To evaluate the role of viruses in shaping community structure and ecosystem functioning , we extend dynamic multitrophic ecosystem models to include a virus component , specifically parameterized for processes taking place in the ocean euphotic zone .
Crucially , we are able to solve this model analytically , facilitating evaluation of model behavior under many alternative parameterizations .
Analyses reveal that the addition of a virus component promotes the emergence of complex communities .
In addition , biomass partitioning of the emergent multitrophic community is consistent with well-established empirical norms in the surface oceans .
At steady state , ecosystem fluxes can be probed to characterize the effects that viruses have when compared with putative marine surface ecosystems without viruses .
The model suggests that ecosystems with viruses will have ( 1 ) increased organic matter recycling , ( 2 ) reduced transfer to higher trophic levels and ( 3 ) increased net primary productivity .
These model findings support hypotheses that viruses can have significant stimulatory effects across whole-ecosystem scales .
We suggest that existing efforts to predict carbon and nutrient cycling without considering virus effects are likely to miss essential features of marine food webs that regulate global biogeochemical cycles .
The ISME Journal advance online publication , 30 January 2015 ; doi :10.1038 / ismej .2014.220

[1818] Highly variable Northern Hemisphere temperatures reconstructed from low - and high-resolution proxy data

A number of reconstructions of millennial-scale climate variability have been carried out in order to understand patterns of natural climate variability , on decade to century timescales , and the role of anthropogenic forcing .
These reconstructions have mainly used tree-ring data and other data sets of annual to decadal resolution .
Lake and ocean sediments have a lower time resolution , but provide climate information at multicentennial timescales that may not be captured by tree-ring data .
Here we reconstruct Northern Hemisphere temperatures for the past 2,000 years by combining low-resolution proxies with tree-ring data , using a wavelet transform technique to achieve timescale-dependent processing of the data .
Our reconstruction shows larger multicentennial variability than most previous multi-proxy reconstructions , but agrees well with temperatures reconstructed from borehole measurements and with temperatures obtained with a general circulation model .
According to our reconstruction , high temperatures -- similar to those observed in the twentieth century before 1990 -- occurred around ad 1000 to 1100 , and minimum temperatures that are about 0.7 K below the average of 1961-90 occurred around ad 1600 .
This large natural variability in the past suggests an important role of natural multicentennial variability that is likely to continue .

[1819] Methanotrophic archaea possessing diverging methane-oxidizing and electron-transporting pathways

Anaerobic oxidation of methane ( AOM ) is a crucial process limiting the flux of methane from marine environments to the atmosphere .
The process is thought to be mediated by three groups of uncultivated methane-oxidizing archaea ( ANME-1 , 2 and 3 ) .
Although the responsible microbes have been intensively studied for more than a decade , central mechanistic details remain unresolved .
On the basis of an integrated analysis of both environmental metatranscriptome and single-aggregate genome of a highly active AOM enrichment dominated by ANME-2a , we provide evidence for a complete and functioning AOM pathway in ANME-2a .
All genes required for performing the seven steps of methanogenesis from CO2 were found present and actively expressed .
Meanwhile , genes for energy conservation and electron transportation including those encoding F420H2 dehydrogenase ( Fpo ) , the cytoplasmic and membrane-associated Coenzyme B-Coenzyme M heterodisulfide ( CoB-S-SCoM ) reductase ( HdrABC , HdrDE ) , cytochrome C and the Rhodobacter nitrogen fixation ( Rnf ) complex were identified and expressed , whereas genes encoding for hydrogenases were absent .
Thus , ANME-2a is likely performing AOM through a complete reversal of methanogenesis from CO2 reduction without involvement of canonical hydrogenase .
ANME-2a is demonstrated to possess versatile electron transfer pathways that would provide the organism with more flexibility in substrate utilization and capacity for rapid adjustment to fluctuating environments .
This work lays the foundation for understanding the environmental niche differentiation , physiology and evolution of different ANME subgroups .

[1820] Entrepreneurial insects

Four British insect species have increased their geographical range as a result of climate warming .
The underlying mechanisms vary from a change in food to an increase in habitat .
Other species may not be quite so lucky .

[1821] Response of methanotrophic communities to afforestation and reforestation in New Zealand

Methanotrophs use methane ( CH4 ) as a carbon source .
They are particularly active in temperate forest soils .
However , the rate of change of CH4 oxidation in soil with afforestation or reforestation is poorly understood .
Here , soil CH4 oxidation was examined in New Zealand volcanic soils under regenerating native forests following burning , and in a mature native forest .
Results were compared with data for pasture to pine land-use change at nearby sites .
We show that following soil disturbance , as little as 47 years may be needed for development of a stable methanotrophic community similar to that in the undisturbed native forest soil .
Corresponding soil CH4-oxidation rates in the regenerating forest soil have the potential to reach those of the mature forest , but climo-edaphic fators appear limiting .
The observed changes in CH4-oxidation rate were directly linked to a prior shift in methanotrophic communities , which suggests microbial control of the terrestrial CH4 flux and identifies the need to account for this response to afforestation and reforestation in global prediction of CH4 emission .

[1822] Global trends in tropical cyclone risk

The impact of tropical cyclones on humans depends on the number of people exposed and their vulnerability , as well as the frequency and intensity of storms .
How will the cumulative effects of climate change , demography and vulnerability affect risk ?
Conventionally , reports assessing tropical cyclone risk trends are based on reported losses , but these figures are biased by improvements to information access .
Here we present a new methodology based on thousands of physically observed events and related contextual parameters .
We show that mortality risk depends on tropical cyclone intensity , exposure , levels of poverty and governance .
Despite the projected reduction in the frequency of tropical cyclones , projected increases in both demographic pressure and tropical cyclone intensity over the next 20 years can be expected to greatly increase the number of people exposed per year and exacerbate disaster risk , despite potential progression in development and governance .

[1823] Global morphological analysis of marine viruses shows minimal regional variation and dominance of non-tailed viruses

Viruses influence oceanic ecosystems by causing mortality of microorganisms , altering nutrient and organic matter flux via lysis and auxiliary metabolic gene expression and changing the trajectory of microbial evolution through horizontal gene transfer .
Limited host range and differing genetic potential of individual virus types mean that investigations into the types of viruses that exist in the ocean and their spatial distribution throughout the world 's oceans are critical to understanding the global impacts of marine viruses .
Here we evaluate viral morphological characteristics ( morphotype , capsid diameter and tail length ) using a quantitative transmission electron microscopy ( qTEM ) method across six of the world 's oceans and seas sampled through the Tara Oceans Expedition .
Extensive experimental validation of the qTEM method shows that neither sample preservation nor preparation significantly alters natural viral morphological characteristics .
The global sampling analysis demonstrated that morphological characteristics did not vary consistently with depth ( surface versus deep chlorophyll maximum waters ) or oceanic region .
Instead , temperature , salinity and oxygen concentration , but not chlorophyll a concentration , were more explanatory in evaluating differences in viral assemblage morphological characteristics .
Surprisingly , given that the majority of cultivated bacterial viruses are tailed , non-tailed viruses appear to numerically dominate the upper oceans as they comprised 51-92 % of the viral particles observed .
Together , these results document global marine viral morphological characteristics , show that their minimal variability is more explained by environmental conditions than geography and suggest that non-tailed viruses might represent the most ecologically important targets for future research .

[1824] Complementing carbon prices with technology policies to keep climate targets within reach

Economic theory suggests that comprehensive carbon pricing is most efficient to reach ambitious climate targets , and previous studies indicated that the carbon price required for limiting global mean warming to 2 degreesC is between US$ 16 and US$ 73 per tonne of CO2 in 2015 ( ref . )
.
Yet , a global implementation of such high carbon prices is unlikely to be politically feasible in the short term .
Instead , most climate policies enacted so far are technology policies or fragmented and moderate carbon pricing schemes .
This paper shows that ambitious climate targets can be kept within reach until 2030 despite a sub-optimal policy mix .
With a state-of-the-art energy-economy model we quantify the interactions and unique effects of three major policy components : ( 1 ) a carbon price starting at US$ 7 per tonne of CO2 in 2015 to incentivize economy-wide mitigation , flanked by ( 2 ) support for low-carbon energy technologies to pave the way for future decarbonization , and ( 3 ) a moratorium on new coal-fired power plants to limit stranded assets .
We find that such a mix limits the efficiency losses compared with the optimal policy , and at the same time lowers distributional impacts .
Therefore , we argue that this instrument mix might be a politically more feasible alternative to the optimal policy based on a comprehensive carbon price alone .

[1825] Genetics of ecological divergence during speciation

Ecological differences often evolve early in speciation as divergent natural selection drives adaptation to distinct ecological niches , leading ultimately to reproductive isolation .
Although this process is a major generator of biodiversity , its genetic basis is still poorly understood .
Here we investigate the genetic architecture of niche differentiation in a sympatric species pair of threespine stickleback fish by mapping the environment-dependent effects of phenotypic traits on hybrid feeding and performance under semi-natural conditions .
We show that multiple , unlinked loci act largely additively to determine position along the major niche axis separating these recently diverged species .
We also find that functional mismatch between phenotypic traits reduces the growth of some stickleback hybrids beyond that expected from an intermediate phenotype , suggesting a role for epistasis between the underlying genes .
This functional mismatch might lead to hybrid incompatibilities that are analogous to those underlying intrinsic reproductive isolation but depend on the ecological context .

[1826] Arctic winter warming amplified by the thermal inversion and consequent low infrared cooling to space

Pronounced warming in the Arctic region , coined Arctic amplification , is an important feature of observed and modelled climate change .
Arctic amplification is generally attributed to the retreat of sea-ice and snow , and the associated surface-albedo feedback , in conjunction with other processes .
In addition , the predominant thermal surface inversion in winter has been suggested to pose a negative feedback to Arctic warming by enhancing infrared radiative cooling .
Here we use the coupled climate model EC-Earth in idealized climate change experiments to quantify the individual contributions of the surface and the atmosphere to infrared radiative cooling .
We find that the surface inversion in fact intensifies Arctic amplification , because the ability of the Arctic wintertime clear-sky atmosphere to cool to space decreases with inversion strength .
Specifically , we find that the cold layers close to the surface in Arctic winter , where most of the warming takes place , hardly contribute to the infrared radiation that goes out to space .
Instead , the additional radiation that is generated by the warming of these layers is directed downwards , and thus amplifies the warming .
We conclude that the predominant Arctic wintertime temperature inversion damps infrared cooling of the system , and thus constitutes a positive warming feedback .

[1827] Emerging Vibrio risk at high latitudes in response to ocean warming

There is increasing concern regarding the role of climate change in driving bacterial waterborne infectious diseases .
Here we illustrate associations between environmental changes observed in the Baltic area and the recent emergence of Vibrio infections and also forecast future scenarios of the risk of infections in correspondence with predicted warming trends .
Using multidecadal long-term sea surface temperature data sets we found that the Baltic Sea is warming at an unprecedented rate .
Sea surface temperature trends ( 1982-2010 ) indicate a warming pattern of 0.063-0 .078 degreesC yr-1 ( 6.3-7 .8 degreesC per century ; refs , ) , with recent peak temperatures unequalled in the history of instrumented measurements for this region .
These warming patterns have coincided with the unexpected emergence of Vibrio infections in northern Europe , many clustered around the Baltic Sea area .
The number and distribution of cases correspond closely with the temporal and spatial peaks in sea surface temperatures .
This is among the first empirical evidence that anthropogenic climate change is driving the emergence of Vibrio disease in temperate regions through its impact on resident bacterial communities , implying that this process is reshaping the distribution of infectious diseases across global scales .

[1828] Permanent storage of carbon dioxide in geological reservoirs by mineral carbonation

Anthropogenic greenhouse-gas emissions continue to increase rapidly despite efforts aimed at curbing the release of such gases .
One potentially long-term solution for offsetting these emissions is the capture and storage of carbon dioxide .
In principle , fluid or gaseous carbon dioxide can be injected into the Earth 's crust and locked up as carbonate minerals through chemical reactions with calcium and magnesium ions supplied by silicate minerals .
This process can lead to near-permanent and secure sequestration , but its feasibility depends on the ease and vigour of the reactions .
Laboratory studies as well as natural analogues indicate that the rate of carbonate mineral formation is much higher in host rocks that are rich in magnesium - and calcium-bearing minerals .
Such rocks include , for example , basalts and magnesium-rich mantle rocks that have been emplaced on the continents .
Carbonate mineral precipitation could quickly clog up existing voids , presenting a challenge to this approach .
However , field and laboratory observations suggest that the stress induced by rapid precipitation may lead to fracturing and subsequent increase in pore space .
Future work should rigorously test the feasibility of this approach by addressing reaction kinetics , the evolution of permeability and field-scale injection methods .

[1829] The functional potential of high Arctic permafrost revealed by metagenomic sequencing , qPCR and microarray analyses

The fate of the carbon stocked in permafrost following global warming and permafrost thaw is of major concern in view of the potential for increased CH4 and CO2 emissions from these soils .
Complex carbon compound degradation and greenhouse gas emissions are due to soil microbial communities , but no comprehensive study has yet addressed their composition and functional potential in permafrost .
Here , a 2-m deep permafrost sample and its overlying active layer soil were subjected to metagenomic sequencing , quantitative PCR ( qPCR ) and microarray analyses .
The active layer soil and the 2-m permafrost microbial community structures were very similar , with Actinobacteria being the dominant phylum .
The two samples also possessed a highly similar spectrum of functional genes , especially when compared with other already published metagenomes .
Key genes related to methane generation , methane oxidation and organic matter degradation were highly diverse for both samples in the metagenomic libraries and some ( for example , pmoA ) showed relatively high abundance in qPCR assays .
Genes related to nitrogen fixation and ammonia oxidation , which could have important roles following climatic change in these nitrogen-limited environments , showed low diversity but high abundance .
The 2-m permafrost showed lower abundance and diversity for all the assessed genes and taxa .
Experimental biases were also evaluated using qPCR and showed that the whole-community genome amplification technique used caused representational biases in the metagenomic libraries by increasing the abundance of Bacteroidetes and decreasing the abundance of Actinobacteria .
This study describes for the first time the detailed functional potential of permafrost-affected soils .

[1830] Ecological consequences of major hydrodynamic disturbances on coral reefs

A recent tsunami and an apparent increase in the frequency of severe tropical storms underscore the need to understand and predict the ecological consequences of major hydrodynamic disturbances .
Reef corals provide the habitat structure that sustains the high biodiversity of tropical reefs , and thus provide the foundation for the ecosystem goods and services that are critical to many tropical societies .
Here we integrate predictions from oceanographic models with engineering theory , to predict the dislodgement of benthic reef corals during hydrodynamic disturbances .
This generalizes earlier work , by incorporating colonies of any shape and by explicitly examining the effects of hydrodynamic gradients on coral assemblage structure .
A field test shows that this model accurately predicts changes in the mechanical vulnerability of coral colonies , and thus their size and shape , with distance from the reef crest .
This work provides a general framework for understanding and predicting the effects of hydrodynamic disturbances on coral reef communities ; such disturbances have a major role in determining species zonation and coexistence on coral reefs , and are critical determinants of how coral assemblages will respond to changes in the frequency and intensity of tropical storms associated with a changing climate .

[1831] Mid-latitude interhemispheric hydrologic seesaw over the past 550,000 years

An interhemispheric hydrologic seesaw -- in which latitudinal migrations of the Intertropical Convergence Zone ( ITCZ ) produce simultaneous wetting ( increased precipitation ) in one hemisphere and drying in the other -- has been discovered in some tropical and subtropical regions .
For instance , Chinese and Brazilian subtropical speleothem ( cave formations such as stalactites and stalagmites ) records show opposite trends in time series of oxygen isotopes ( a proxy for precipitation variability ) at millennial to orbital timescales , suggesting that hydrologic cycles were antiphased in the northerly versus southerly subtropics .
This tropical to subtropical hydrologic phenomenon is likely to be an initial and important climatic response to orbital forcing .
The impacts of such an interhemispheric hydrologic seesaw on higher-latitude regions and the global climate system , however , are unknown .
Here we show that the antiphasing seen in the tropical records is also present in both hemispheres of the mid-latitude western Pacific Ocean .
Our results are based on a new 550,000-year record of the growth frequency of speleothems from the Korean peninsula , which we compare to Southern Hemisphere equivalents .
The Korean data are discontinuous and derived from 24 separate speleothems , but still allow the identification of periods of peak speleothem growth and , thus , precipitation .
The clear hemispheric antiphasing indicates that the sphere of influence of the interhemispheric hydrologic seesaw over the past 550,000 years extended at least to the mid-latitudes , such as northeast Asia , and that orbital-timescale ITCZ shifts can have serious effects on temperate climate systems .
Furthermore , our result implies that insolation-driven ITCZ dynamics may provoke water vapour and vegetation feedbacks in northern mid-latitude regions and could have regulated global climate conditions throughout the late Quaternary ice age cycles .

[1832] Warming and nitrogen deposition lessen microbial residue contribution to soil carbon pool

Microorganisms have a role as gatekeepers for terrestrial carbon fluxes , either causing its release to the atmosphere through their decomposition activities or preventing its release by stabilizing the carbon in a form that can not be easily decomposed .
Although research has focused on microbial sources of greenhouse gas production , somewhat limited attention has been paid to the microbial role in carbon sequestration .
However , increasing numbers of reports indicate the importance of incorporating microbial-derived carbon into soil stable carbon pools .
Here we investigate microbial residues in a California annual grassland after a continuous 9-year manipulation of three environmental factors ( elevated CO2 , warming and nitrogen deposition ) , singly and in combination .
Our results indicate that warming and nitrogen deposition can both alter the fraction of carbon derived from microbes in soils , though for two very different reasons .
A reduction in microbial carbon contribution to stable carbon pools may have implications for our predictions of global change impacts on soil stored carbon .

[1833] Policy : Palatable forest conservation

Current policies to reduce emissions from forest loss could mean that rising demand for food is not met .
A new approach to forest conservation that reduces emissions while meeting demand for agricultural products may be feasible , but more expensive .

[1834] Adaptation of intertidal biofilm communities is driven by metal ion and oxidative stresses

Marine organisms in intertidal zones are subjected to periodical fluctuations and wave activities .
To understand how microbes in intertidal biofilms adapt to the stresses , the microbial metagenomes of biofilms from intertidal and subtidal zones were compared .
The genes responsible for resistance to metal ion and oxidative stresses were enriched in both 6-day and 12-day intertidal biofilms , including genes associated with secondary metabolism , inorganic ion transport and metabolism , signal transduction and extracellular polymeric substance metabolism .
In addition , these genes were more enriched in 12-day than 6-day intertidal biofilms .
We hypothesize that a complex signaling network is used for stress tolerance and propose a model illustrating the relationships between these functions and environmental metal ion concentrations and oxidative stresses .
These findings show that bacteria use diverse mechanisms to adapt to intertidal zones and indicate that the community structures of intertidal biofilms are modulated by metal ion and oxidative stresses .

[1835] Temporal dynamics of Prochlorococcus ecotypes in the Atlantic and Pacific oceans

To better understand the temporal and spatial dynamics of Prochlorococcus populations , and how these populations co-vary with the physical environment , we followed monthly changes in the abundance of five ecotypes -- two high-light adapted and three low-light adapted -- over a 5-year period in coordination with the Bermuda Atlantic Time Series ( BATS ) and Hawaii Ocean Time-series ( HOT ) programs .
Ecotype abundance displayed weak seasonal fluctuations at HOT and strong seasonal fluctuations at BATS .
Furthermore , stable ` layered ' depth distributions , where different Prochlorococcus ecotypes reached maximum abundance at different depths , were maintained consistently for 5 years at HOT .
Layered distributions were also observed at BATS , although winter deep mixing events disrupted these patterns each year and produced large variations in ecotype abundance .
Interestingly , the layered ecotype distributions were regularly reestablished each year after deep mixing subsided at BATS .
In addition , Prochlorococcus ecotypes each responded differently to the strong seasonal changes in light , temperature and mixing at BATS , resulting in a reproducible annual succession of ecotype blooms .
Patterns of ecotype abundance , in combination with physiological assays of cultured isolates , confirmed that the low-light adapted eNATL could be distinguished from other low-light adapted ecotypes based on its ability to withstand temporary exposure to high-intensity light , a characteristic stress of the surface mixed layer .
Finally , total Prochlorococcus and Synechococcus dynamics were compared with similar time series data collected a decade earlier at each location .
The two data sets were remarkably similar -- testimony to the resilience of these complex dynamic systems on decadal time scales .

[1836] The HIC signalling pathway links CO2 perception to stomatal development

Stomatal pores on the leaf surface control both the uptake of CO2 for photosynthesis and the loss of water during transpiration .
Since the industrial revolution , decreases in stomatal numbers in parallel with increases in atmospheric CO2 concentration have provided evidence of plant responses to changes in CO2 levels caused by human activity .
This inverse correlation between stomatal density and CO2 concentration also holds for fossil material from the past 400 million years and has provided clues to the causes of global extinction events .
Here we report the identification of the Arabidopsis gene HIC ( for high carbon dioxide ) , which encodes a negative regulator of stomatal development that responds to CO2 concentration .
This gene encodes a putative 3-keto acyl coenzyme A synthase -- an enzyme involved in the synthesis of very-long-chain fatty acids .
Mutant hic plants exhibit up to a 42 % increase in stomatal density in response to a doubling of CO2 .
Our results identify a gene involved in the signal transduction pathway responsible for controlling stomatal numbers at elevated CO2 .

[1837] Atmospheric science : High winds over Lake Superior

In a warming climate , large lakes experience increasing water temperatures and ice loss .
Observations from Lake Superior show that regional temperature rise has led to an increase in wind speeds over the lake .

[1838] No evidence of aquatic priming effects in hyporheic zone microcosms

The priming effect refers to quantitative changes in microbial decomposition of recalcitrant organic matter upon addition of labile organic matter and is a phenomenon that mainly has been reported and debated in soil science .
Recently , priming effects have been indicated in aquatic ecosystems and have received attention due to the potential significance for ecosystem carbon budgets .
Headwater stream biofilms , which are important degraders of both allochthonous , presumably recalcitrant , organic matter and labile autochthonous organic matter , may be sites where priming effects are important in aquatic environments .
We have experimentally tested for priming effects in stream biofilms within microcosms mimicking the stream hyporheic zone .
A 13C labeled model allochthonous carbon source was used in combination with different carbon sources simulating autochthonous inputs .
We did not detect changes in respiration , removal or incorporation of allochthonous organic matter in response to autochthonous treatments , thus not supporting the occurrence of priming effects under the experimental conditions .
This study is the first to address priming effects in the hyporheic zone , and one of very few studies quantitatively assessing aquatic priming effects .
The results contrast with existing studies , which highlights the need for quantitative approaches to determine the importance of priming effects in aquatic environments .

[1839] Sensitive response of the Greenland Ice Sheet to surface melt drainage over a soft bed

The dynamic response of the Greenland Ice Sheet ( GrIS ) depends on feedbacks between surface meltwater delivery to the subglacial environment and ice flow .
Recent work has highlighted an important role of hydrological processes in regulating the ice flow , but models have so far overlooked the mechanical effect of soft basal sediment .
Here we use a three-dimensional model to investigate hydrological controls on a GrIS soft-bedded region .
Our results demonstrate that weakening and strengthening of subglacial sediment , associated with the seasonal delivery of surface meltwater to the bed , modulates ice flow consistent with observations .
We propose that sedimentary control on ice flow is a viable alternative to existing models of evolving hydrological systems , and find a strong link between the annual flow stability , and the frequency of high meltwater discharge events .
Consequently , the observed GrIS resilience to enhanced melt could be compromised if runoff variability increases further with future climate warming .

[1840] Dynamics extracted from fixed cells reveal feedback linking cell growth to cell cycle

Biologists have long been concerned about what constrains variation in cell size , but progress in this field has been slow and stymied by experimental limitations .
Here we describe a new method , ergodic rate analysis ( ERA ) , that uses single-cell measurements of fixed steady-state populations to accurately infer the rates of molecular events , including rates of cell growth .
ERA exploits the fact that the number of cells in a particular state is related to the average transit time through that state .
With this method , it is possible to calculate full time trajectories of any feature that can be labelled in fixed cells , for example levels of phosphoproteins or total cellular mass .
Using ERA we find evidence for a size-discriminatory process at the G1/S transition that acts to decrease cell-to-cell size variation .

[1841] Inorganic Nanovehicle Targets Tumor in an Orthotopic Breast Cancer Model

The clinical efficacy of conventional chemotherapeutic agent , methotrexate ( MTX ) , can be limited by its very short plasma half-life , the drug resistance , and the high dosage required for cancer cell suppression .
In this study , a new drug delivery system is proposed to overcome such limitations .
To realize such a system , MTX was intercalated into layered double hydroxides ( LDHs ) , inorganic drug delivery vehicle , through a co-precipitation route to produce a MTX-LDH nanohybrid with an average particle size of approximately 130 nm .
Biodistribution studies in mice bearing orthotopic human breast tumors revealed that the tumor-to-liver ratio of MTX in the MTX-LDH-treated-group was 6-fold higher than that of MTX-treated-one after drug treatment for 2 hr .
Moreover , MTX-LDH exhibited superior targeting effect resulting in high antitumor efficacy inducing a 74.3 % reduction in tumor volume compared to MTX alone , and as a consequence , significant survival benefits .
Annexin-V and propidium iodine dual staining and TUNEL analysis showed that MTX-LDH induced a greater degree of apoptosis than free MTX .
Taken together , our data demonstrate that a new MTX-LDH nanohybrid exhibits a superior efficacy profile and improved distribution compared to MTX alone and has the potential to enhance therapeutic efficacy via inhibition of tumor proliferation and induction of apoptosis .

[1842] The influence of Antarctic sea ice on glacial-interglacial CO 2 variations

Ice-core measurements indicate that atmospheric CO2 concentrations during glacial periods were consistently about 80 parts per million lower than during interglacial periods .
Previous explanations for this observation have typically had difficulty accounting for either the estimated glacial O2 concentrations in the deep sea , 13C/12C ratios in Antarctic surface waters , or the depth of calcite saturation ; also lacking is an explanation for the strong link between atmospheric CO2 and Antarctic air temperature .
There is growing evidence that the amount of deep water upwelling at low latitudes is significantly overestimated in most ocean general circulation models and simpler box models previously used to investigate this problem .
Here we use a box model with deep-water upwelling confined to south of 55 degreesS to investigate the glacial-interglacial linkages between Antarctic air temperature and atmospheric CO2 variations .
We suggest that low glacial atmospheric CO2 levels might result from reduced deep-water ventilation associated with either year-round Antarctic sea-ice coverage , or wintertime coverage combined with ice-induced stratification during the summer .
The model presented here reproduces 67 parts per million of the observed glacial-interglacial CO2 difference , as a result of reduced air-sea gas exchange in the Antarctic region , and is generally consistent with the additional observational constraints .

[1843] Mineral dust and NOx promote the conversion of SO2 to sulfate in heavy pollution days

Haze in China has been increasing in frequency of occurrence as well as the area of the affected region .
Here , we report on a new mechanism of haze formation , in which coexistence with NOx can reduce the environmental capacity for SO2 , leading to rapid conversion of SO2 to sulfate because NO2 and SO2 have a synergistic effect when they react on the surface of mineral dust .
Monitoring data from five severe haze episodes in January of 2013 in the Beijing-Tianjin-Hebei regions agreed very well with the laboratory simulation .
The combined air pollution of motor vehicle exhaust and coal-fired flue gases greatly reduced the atmospheric environmental capacity for SO2 , and the formation of sulfate was found to be a main reason for the growth of fine particles , which led to the occurrence of haze .
These results indicate that the impact of motor vehicle exhaust on the atmospheric environment might be underestimated .

[1844] Slower recovery in space before collapse of connected populations

Slower recovery from perturbations near a tipping point and its indirect signatures in fluctuation patterns have been suggested to foreshadow catastrophes in a wide variety of systems .
Recent studies of populations in the field and in the laboratory have used time-series data to confirm some of the theoretically predicted early warning indicators , such as an increase in recovery time or in the size and timescale of fluctuations .
However , the predictive power of temporal warning signals is limited by the demand for long-term observations .
Large-scale spatial data are more accessible , but the performance of warning signals in spatially extended systems needs to be examined empirically .
Here we use spatially extended yeast populations , an experimental system with a fold bifurcation ( tipping point ) , to evaluate early warning signals based on spatio-temporal fluctuations and to identify a novel spatial warning indicator .
We found that two leading indicators based on fluctuations increased before collapse of connected populations ; however , the magnitudes of the increases were smaller than those observed in isolated populations , possibly because local variation is reduced by dispersal .
Furthermore , we propose a generic indicator based on deterministic spatial patterns , which we call ` recovery length ' .
As the spatial counterpart of recovery time , recovery length is the distance necessary for connected populations to recover from spatial perturbations .
In our experiments , recovery length increased substantially before population collapse , suggesting that the spatial scale of recovery can provide a superior warning signal before tipping points in spatially extended systems .

[1845] Nitrate assimilation is inhibited by elevated CO2 in field-grown wheat

Total protein and nitrogen concentrations in plants generally decline under elevated CO2 atmospheres .
Explanations for this decline include that plants under elevated CO2 grow larger , diluting the protein within their tissues ; that carbohydrates accumulate within leaves , downregulating the amount of the most prevalent protein Rubisco ; that carbon enrichment of the rhizosphere leads to progressively greater limitations of the nitrogen available to plants ; and that elevated CO2 directly inhibits plant nitrogen metabolism , especially the assimilation of nitrate into proteins in leaves of C3 plants .
Recently , several meta-analyses have indicated that CO2 inhibition of nitrate assimilation is the explanation most consistent with observations .
Here , we present the first direct field test of this explanation .
We analysed wheat ( Triticum aestivum L. ) grown under elevated and ambient CO2 concentrations in the free-air CO2 enrichment experiment at Maricopa , Arizona .
In leaf tissue , the ratio of nitrate to total nitrogen concentration and the stable isotope ratios of organic nitrogen and free nitrate showed that nitrate assimilation was slower under elevated than ambient CO2 .
These findings imply that food quality will suffer under the CO2 levels anticipated during this century unless more sophisticated approaches to nitrogen fertilization are employed .

[1846] Development of Middle Stone Age innovation linked to rapid climate change

The development of modernity in early human populations has been linked to pulsed phases of technological and behavioural innovation within the Middle Stone Age of South Africa .
However , the trigger for these intermittent pulses of technological innovation is an enigma .
Here we show that , contrary to some previous studies , the occurrence of innovation was tightly linked to abrupt climate change .
Major innovational pulses occurred at times when South African climate changed rapidly towards more humid conditions , while northern sub-Saharan Africa experienced widespread droughts , as the Northern Hemisphere entered phases of extreme cooling .
These millennial-scale teleconnections resulted from the bipolar seesaw behaviour of the Atlantic Ocean related to changes in the ocean circulation .
These conditions led to humid pulses in South Africa and potentially to the creation of favourable environmental conditions .
This strongly implies that innovational pulses of early modern human behaviour were climatically influenced and linked to the adoption of refugia .

[1847] Southward movement of the Pacific intertropical convergence zone AD 1400-1850

Tropical rainfall patterns control the subsistence lifestyle of more than one billion people .
Seasonal changes in these rainfall patterns are associated with changes in the position of the intertropical convergence zone , which is characterized by deep convection causing heavy rainfall near 10degrees N in boreal summer and 3degrees N in boreal winter .
Dynamic controls on the position of the intertropical convergence zone are debated , but palaeoclimatic evidence from continental Asia , Africa and the Americas suggests that it has shifted substantially during the past millennium , reaching its southernmost position some time during the Little Ice Age ( AD 1400-1850 ) .
However , without records from the meteorological core of the intertropical convergence zone in the Pacific Ocean , quantitative constraints on its position are lacking .
Here we report microbiological , molecular and hydrogen isotopic evidence from lake sediments in the Northern Line Islands , Galapagos and Palau indicating that the Pacific intertropical convergence zone was south of its modern position for most of the past millennium , by as much as 500 km during the Little Ice Age .
A colder Northern Hemisphere at that time , possibly resulting from lower solar irradiance , may have driven the intertropical convergence zone south .
We conclude that small changes in Earth 's radiation budget may profoundly affect tropical rainfall .

[1848] In situ growth of nanoparticles through control of non-stoichiometry

Surfaces decorated with uniformly dispersed catalytically active nanoparticles play a key role in many fields , including renewable energy and catalysis .
Typically , these structures are prepared by deposition techniques , but alternatively they could be made by growing the nanoparticles in situ directly from the ( porous ) backbone support .
Here we demonstrate that growing nano-size phases from perovskites can be controlled through judicious choice of composition , particularly by tuning deviations from the ideal ABO3 stoichiometry .
This non-stoichiometry facilitates a change in equilibrium position to make particle exsolution much more dynamic , enabling the preparation of compositionally diverse nanoparticles ( that is , metallic , oxides or mixtures ) and seems to afford unprecedented control over particle size , distribution and surface anchorage .
The phenomenon is also shown to be influenced strongly by surface reorganization characteristics .
The concept exemplified here may serve in the design and development of more sophisticated oxide materials with advanced functionality across a range of possible domains of application .

[1849] An expert judgement assessment of future sea level rise from the ice sheets

A major gap in predictive capability concerning the future evolution of the ice sheets was identified in the Fourth Assessment Report ( AR4 ) of the Intergovernmental Panel on Climate Change .
As a consequence , it has been suggested that the AR4 estimates of future sea-level rise from this source may have been underestimated .
Various approaches for addressing this problem have been tried , including semi-empirical models and conceptual studies .
Here , we report a formalized pooling of expert views on uncertainties in future ice-sheet contributions using a structured elicitation approach .
We find that the median estimate of such contributions is 29 cm -- substantially larger than in the AR4 -- while the upper 95th percentile value is 84 cm , implying a conceivable risk of a sea-level rise of greater than a metre by 2100 .
On the critical question of whether recent ice-sheet behaviour is due to variability in the ice sheet-climate system or reflects a long-term trend , expert opinion is shown to be both very uncertain and undecided .

[1850] Targeting Mycobacterium tuberculosis nucleoid-associated protein HU with structure-based inhibitors

The nucleoid-associated protein HU plays an important role in maintenance of chromosomal architecture and in global regulation of DNA transactions in bacteria .
Although HU is essential for growth in Mycobacterium tuberculosis ( Mtb ) , there have been no reported attempts to perturb HU function with small molecules .
Here we report the crystal structure of the N-terminal domain of HU from Mtb .
We identify a core region within the HU-DNA interface that can be targeted using stilbene derivatives .
These small molecules specifically inhibit HU-DNA binding , disrupt nucleoid architecture and reduce Mtb growth .
The stilbene inhibitors induce gene expression changes in Mtb that resemble those induced by HU deficiency .
Our results indicate that HU is a potential target for the development of therapies against tuberculosis .

[1851] Simulated influences of Lake Agassiz on the climate of central North America 11,000 years ago

Eleven thousand years ago , large lakes existed in central and eastern North America along the margin of the Laurentide Ice Sheet .
The large-scale North American climate at this time has been simulated with atmospheric general circulation models , but these relatively coarse global models do not resolve potentially important features of the mesoscale circulation that arise from interactions among the atmosphere , ice sheet , and proglacial lakes .
Here we present simulations of the climate of central and eastern North America 11,000 years ago with a high-resolution , regional climate model nested within a general circulation model .
The simulated climate is in general agreement with that inferred from palaeoecological evidence .
Our experiments indicate that through mesoscale atmospheric feedbacks , the annual delivery of moisture to the Laurentide Ice Sheet was diminished at times of a large , cold Lake Agassiz relative to periods of lower lake stands .
The resulting changes in the mass balance of the ice sheet may have contributed to fluctuations of the ice margin , thus affecting the routing of fresh water to the North Atlantic Ocean .
A retreating ice margin during periods of high lake level may have opened an outlet for discharge of Lake Agassiz into the North Atlantic .
A subsequent advance of the ice margin due to greater moisture delivery associated with a low lake level could have dammed the outlet , thereby reducing discharge to the North Atlantic .
These variations may have been decisive in causing the Younger Dryas cold event .

[1852] Long-term responses of North Atlantic calcifying plankton to climate change

The global increase in atmospheric carbon dioxide concentration is potentially threatening marine biodiversity in two ways .
First , carbon dioxide and other greenhouse gases accumulating in the atmosphere are causing global warming .
Second , carbon dioxide is altering sea water chemistry , making the ocean more acidic .
Although temperature has a cardinal influence on all biological processes from the molecular to the ecosystem level , acidification might impair the process of calcification or exacerbate dissolution of calcifying organisms .
Here , we show however that North Atlantic calcifying plankton primarily responded to climate-induced changes in temperatures during the period 1960-2009 , overriding the signal from the effects of ocean acidification .
We provide evidence that foraminifers , coccolithophores , both pteropod and non-pteropod molluscs and echinoderms exhibited an abrupt shift circa 1996 at a time of a substantial increase in temperature and that some taxa exhibited a poleward movement in agreement with expected biogeographical changes under sea temperature warming .
Although acidification may become a serious threat to marine calcifying organisms , our results suggest that over the study period the primary driver of North Atlantic calcifying plankton was oceanic temperature .

[1853] Regime change : Savannah Shift

Nature http://doi.org/h3c ( 2012 ) Climate change will affect all ecosystems , and when they reach tipping points , regime shifts may occur .

[1854] Bacterial genome replication at subzero temperatures in permafrost

Microbial metabolic activity occurs at subzero temperatures in permafrost , an environment representing ~ 25 % of the global soil organic matter .
Although much of the observed subzero microbial activity may be due to basal metabolism or macromolecular repair , there is also ample evidence for cellular growth .
Unfortunately , most metabolic measurements or culture-based laboratory experiments can not elucidate the specific microorganisms responsible for metabolic activities in native permafrost , nor , can bulk approaches determine whether different members of the microbial community modulate their responses as a function of changing subzero temperatures .
Here , we report on the use of stable isotope probing with 13C-acetate to demonstrate bacterial genome replication in Alaskan permafrost at temperatures of 0 to -20 degreesC .
We found that the majority ( 80 % ) of operational taxonomic units detected in permafrost microcosms were active and could synthesize 13C-labeled DNA when supplemented with 13C-acetate at temperatures of 0 to -20 degreesC during a 6-month incubation .
The data indicated that some members of the bacterial community were active across all of the experimental temperatures , whereas many others only synthesized DNA within a narrow subzero temperature range .
Phylogenetic analysis of 13C-labeled 16S rRNA genes revealed that the subzero active bacteria were members of the Acidobacteria , Actinobacteria , Chloroflexi , Gemmatimonadetes and Proteobacteria phyla and were distantly related to currently cultivated psychrophiles .
These results imply that small subzero temperature changes may lead to changes in the active microbial community , which could have consequences for biogeochemical cycling in permanently frozen systems .

[1855] Orbitally driven east-west antiphasing of South American precipitation

The variations of tropical precipitation are antiphased between the hemispheres on orbital timescales .
This antiphasing arises through the alternating strength of incoming solar radiation in the two hemispheres , which affects monsoon intensity and hence the position of the meridional atmospheric circulation of the Hadley cells .
Here we compare an oxygen isotopic record recovered from a speleothem from northeast Brazil for the past 26,000 years with existing reconstructions of precipitation in tropical South America .
During the Holocene , we identify a similar , but zonally oriented , antiphasing of precipitation within the same hemisphere : northeast Brazil experiences humid conditions during low summer insolation and aridity when summer insolation is high , whereas the rest of southern tropical South America shows opposite characteristics .
Simulations with a general circulation model that incorporates isotopic variations support this pattern as well as the link to insolation-driven monsoon activity .
Our results suggest that convective heating over tropical South America and associated adjustments in large-scale subsidence over northeast Brazil lead to a remote forcing of the South American monsoon , which determines most of the precipitation changes in the region on orbital timescales .

[1856] Nutrient requirements for growth of the extreme oligotroph ` Candidatus Pelagibacter ubique ' HTCC1062 on a defined medium

Chemoheterotrophic marine bacteria of the SAR11 clade are Earth 's most abundant organisms .
Following the first cultivation of a SAR11 bacterium , ` Candidatus Pelagibacter ubique ' strain HTCC1062 ( Ca .
P. ubique ) in 2002 , unusual nutritional requirements were identified for reduced sulfur compounds and glycine or serine .
These requirements were linked to genome streamlining resulting from selection for efficient resource utilization in nutrient-limited ocean habitats .
Here we report the first successful cultivation of Ca .
P. ubique on a defined artificial seawater medium ( AMS1 ) , and an additional requirement for pyruvate or pyruvate precursors .
Optimal growth was observed with the collective addition of inorganic macro - and micronutrients , vitamins , methionine , glycine and pyruvate .
Methionine served as the sole sulfur source but methionine and glycine were not sufficient to support growth .
Optimal cell yields were obtained when the stoichiometry between glycine and pyruvate was 1:4 , and incomplete cell division was observed in cultures starved for pyruvate .
Glucose and oxaloacetate could fully replace pyruvate , but not acetate , taurine or a variety of tricarboxylic acid cycle intermediates .
Moreover , both glycine betaine and serine could substitute for glycine .
Interestingly , glycolate partially restored growth in the absence of glycine .
We propose that this is the result of the use of glycolate , a product of phytoplankton metabolism , as both a carbon source for respiration and as a precursor to glycine .
These findings are important because they provide support for the hypothesis that some micro-organisms are challenging to cultivate because of unusual nutrient requirements caused by streamlining selection and gene loss .
Our findings also illustrate unusual metabolic rearrangements that adapt these cells to extreme oligotrophy , and underscore the challenge of reconstructing metabolism from genome sequences in organisms that have non-canonical metabolic pathways .

[1857] Malaria early warnings based on seasonal climate forecasts from multi-model ensembles

The control of epidemic malaria is a priority for the international health community and specific targets for the early detection and effective control of epidemics have been agreed .
Interannual climate variability is an important determinant of epidemics in parts of Africa where climate drives both mosquito vector dynamics and parasite development rates .
Hence , skilful seasonal climate forecasts may provide early warning of changes of risk in epidemic-prone regions .
Here we discuss the development of a system to forecast probabilities of anomalously high and low malaria incidence with dynamically based , seasonal-timescale , multi-model ensemble predictions of climate , using leading global coupled ocean-atmosphere climate models developed in Europe .
This forecast system is successfully applied to the prediction of malaria risk in Botswana , where links between malaria and climate variability are well established , adding up to four months lead time over malaria warnings issued with observed precipitation and having a comparably high level of probabilistic prediction skill .
In years in which the forecast probability distribution is different from that of climatology , malaria decision-makers can use this information for improved resource allocation .

[1858] Variation in gut microbial communities and its association with pathogen infection in wild bumble bees ( Bombus )

Bacterial gut symbiont communities are critical for the health of many insect species .
However , little is known about how microbial communities vary among host species or how they respond to anthropogenic disturbances .
Bacterial communities that differ in richness or composition may vary in their ability to provide nutrients or defenses .
We used deep sequencing to investigate gut microbiota of three species in the genus Bombus ( bumble bees ) .
Bombus are among the most economically and ecologically important non-managed pollinators .
Some species have experienced dramatic declines , probably due to pathogens and land-use change .
We examined variation within and across bee species and between semi-natural and conventional agricultural habitats .
We categorized as ` core bacteria ' any operational taxonomic units ( OTUs ) with closest hits to sequences previously found exclusively or primarily in the guts of honey bees and bumble bees ( genera Apis and Bombus ) .
Microbial community composition differed among bee species .
Richness , defined as number of bacterial OTUs , was highest for B. bimaculatus and B. impatiens .
For B. bimaculatus , this was due to high richness of non-core bacteria .
We found little effect of habitat on microbial communities .
Richness of non-core bacteria was negatively associated with bacterial abundance in individual bees , possibly due to deeper sampling of non-core bacteria in bees with low populations of core bacteria .
Infection by the gut parasite Crithidia was negatively associated with abundance of the core bacterium Gilliamella and positively associated with richness of non-core bacteria .
Our results indicate that Bombus species have distinctive gut communities , and community-level variation is associated with pathogen infection .

[1859] Projected impacts of climate change on farmers ' extraction of groundwater from crystalline aquifers in South India

Local groundwater levels in South India are falling alarmingly .
In the semi-arid crystalline Deccan plateau area , agricultural production relies on groundwater resources .
Downscaled Global Climate Model ( GCM ) data are used to force a spatially distributed agro-hydrological model in order to evaluate Climate Change ( CC ) effects on local groundwater extraction ( GWE ) .
The slight increase of precipitation may alleviate current groundwater depletion on average , despite the increased evaporation due to warming .
Nevertheless , projected climatic extremes create worse GWE shortages than for present climate .
Local conditions may lead to opposing impacts on GWE , from increases to decreases ( + / -20 mm/year ) , for a given spatially homogeneous CC forcing .
Areas vulnerable to CC in terms of irrigation apportionment are thus identified .
Our results emphasize the importance of accounting for local characteristics ( water harvesting systems and maximal aquifer capacity versus GWE ) in developing measures to cope with CC impacts in the South Indian region .

[1860] Interhemispheric symmetry of the tropical African rainbelt over the past 23,000 years

The distribution of rainfall in tropical Africa is controlled by the African rainbelt , which oscillates on a seasonal basis .
The rainbelt has varied on centennial to millennial timescales along with changes in Northern Hemisphere high-latitude climate , the Atlantic meridional overturning circulation and low-latitude insolation over the past glacial-interglacial cycle .
However , the overall dynamics of the African rainbelt remain poorly constrained and are not always consistent with a latitudinal migration , as has been proposed for other regions .
Here we use terrestrially derived organic and sedimentary markers from marine sediment cores to reconstruct the distribution of vegetation , and hence rainfall , in tropical Africa during extreme climate states over the past 23,000 years .
Our data indicate that rather than migrating latitudinally , the rainbelt contracted and expanded symmetrically in both hemispheres in response to changes in climate .
During the Last Glacial Maximum and Heinrich Stadial 1 , the rainbelt contracted relative to the late Holocene , which we attribute to a latitudinal compression of atmospheric circulation associated with lower global mean temperatures .
Conversely , during the mid-Holocene climatic optimum , the rainbelt expanded across tropical Africa .
In light of our findings , it is not clear whether the tropical rainbelt has migrated latitudinally on a global scale , as has been suggested .

[1861] Impact of fire on active layer and permafrost microbial communities and metagenomes in an upland Alaskan boreal forest

Permafrost soils are large reservoirs of potentially labile carbon ( C ) .
Understanding the dynamics of C release from these soils requires us to account for the impact of wildfires , which are increasing in frequency as the climate changes .
Boreal wildfires contribute to global emission of greenhouse gases ( GHG -- CO2 , CH4 and N2O ) and indirectly result in the thawing of near-surface permafrost .
In this study , we aimed to define the impact of fire on soil microbial communities and metabolic potential for GHG fluxes in samples collected up to 1 m depth from an upland black spruce forest near Nome Creek , Alaska .
We measured geochemistry , GHG fluxes , potential soil enzyme activities and microbial community structure via 16SrRNA gene and metagenome sequencing .
We found that soil moisture , C content and the potential for respiration were reduced by fire , as were microbial community diversity and metabolic potential .
There were shifts in dominance of several microbial community members , including a higher abundance of candidate phylum AD3 after fire .
The metagenome data showed that fire had a pervasive impact on genes involved in carbohydrate metabolism , methanogenesis and the nitrogen cycle .
Although fire resulted in an immediate release of CO2 from surface soils , our results suggest that the potential for emission of GHG was ultimately reduced at all soil depths over the longer term .
Because of the size of the permafrost C reservoir , these results are crucial for understanding whether fire produces a positive or negative feedback loop contributing to the global C cycle .

[1862] Snowfall less sensitive to warming in Karakoram than in Himalayas due to a unique seasonal cycle

The high mountains of Asia , including the Karakoram , Himalayas and Tibetan Plateau , combine to form a region of perplexing hydroclimate changes .
Glaciers have exhibited mass stability or even expansion in the Karakoram region , contrasting with glacial mass loss across the nearby Himalayas and Tibetan Plateau , a pattern that has been termed the Karakoram anomaly .
However , the remote location , complex terrain and multi-country fabric of high-mountain Asia have made it difficult to maintain longer-term monitoring systems of the meteorological components that may have influenced glacial change .
Here we compare a set of high-resolution climate model simulations from 1861 to 2100 with the latest available observations to focus on the distinct seasonal cycles and resulting climate change signatures of Asia 's high-mountain ranges .
We find that the Karakoram seasonal cycle is dominated by non-monsoonal winter precipitation , which uniquely protects it from reductions in annual snowfall under climate warming over the twenty-first century .
The simulations show that climate change signals are detectable only with long and continuous records , and at specific elevations .
Our findings suggest a meteorological mechanism for regional differences in the glacier response to climate warming .

[1863] The role of nitrogen oxides in human adaptation to hypoxia

Lowland residents adapt to the reduced oxygen availability at high altitude through a process known as acclimatisation , but the molecular changes underpinning these functional alterations are not well understood .
Using an integrated biochemical/whole-body physiology approach we here show that plasma biomarkers of NO production ( nitrite , nitrate ) and activity ( cGMP ) are elevated on acclimatisation to high altitude while S-nitrosothiols are initially consumed , suggesting multiple nitrogen oxides contribute to improve hypoxia tolerance by enhancing NO availability .
Unexpectedly , oxygen cost of exercise and mechanical efficiency remain unchanged with ascent while microvascular blood flow correlates inversely with nitrite .
Our results suggest that NO is an integral part of the human physiological response to hypoxia .
These findings may be of relevance not only to healthy subjects exposed to high altitude but also to patients in whom oxygen availability is limited through disease affecting the heart , lung or vasculature , and to the field of developmental biology .

[1864] Disentangling the relative influence of bacterioplankton phylogeny and metabolism on lysogeny in reservoirs and lagoons

Previous studies indicate that lysogeny is preponderant when environmental conditions are challenging for the bacterial communities and when their metabolism is reduced .
Furthermore , it appears that lysogeny is more frequent within certain bacterial phylogenetic groups .
In this comparative study from 10 freshwater reservoirs and 10 coastal lagoons , we aim to disentangle the influence of these different factors .
In eight reservoirs and four lagoons , lysogeny was detected by induction assays with mitomycin C , and induction significantly modified the bacterial community composition ( BCC ) , whereas community composition remained constant in ecosystems in which lysogeny was not observed .
Among the phylogenetic groups studied , the most abundant ones were Bacteroidetes and alpha-proteobacteria in lagoons , and beta-proteobacteria and Bacteroidetes in reservoirs .
These dominant groups comprised the highest proportions of inducible lysogens .
In order to unravel the effects of bacterial metabolism from phylogeny on lysogeny , we measured bacterial community physiology and the specific activities of selected phylogenetic groups .
The proportion of inducible lysogens within the alpha - and the beta-proteobacteria decreased with increasing group-specific metabolism in lagoons and reservoirs , respectively .
In contrast , this relationship was not observed for the other lysogen-containing groups .
Hence , both host physiology and phylogeny are critical for the establishment of lysogeny .
This study illustrates the importance of lysogeny among the most abundant phylogenetic groups , and further suggests its strong structuring impact on BCC .

[1865] Ocean circulation and mantle melting controlled by radial flow of hot pulses in the Iceland plume

Convection of the mantle influences elevation at the Earth 's surface .
For example , in the North Atlantic Ocean , V-shaped ridges of thickened oceanic crust that straddle the mid-ocean ridge are thought to arise from variations in the underlying mantle properties .
However , the detailed relationship between these V-shaped ridges and convective circulation is uncertain .
Here we use measurements of residual water depth -- a proxy for crustal thickness -- and basaltic geochemistry to assess factors responsible for ridge formation .
We find a correlation between basalt composition and crustal thickness that is best explained if V-shaped ridges are formed by the passage of unusually hot pulses of mantle away from Iceland .
We also show that ocean circulation patterns over the past 7 million years , recorded by flow of the Northern Component Water from the Norwegian Sea into the Atlantic Ocean and the accumulation of thick drifts of sediment , are controlled by variations in the elevation of sea floor between Greenland and Iceland .
We suggest that pulses of hot mantle also drove periodic uplift of the sea floor , and moderated the export of water and sediment into the North Atlantic Ocean .
Diverse observations can therefore be explained if blobs of mantle , 25 degreesC hotter than the background plume temperature , travelled up the conduit beneath Iceland and spread out radially at velocities of 40 cm yr-1 .

[1866] Partitioning selection and complementarity in biodiversity experiments

The impact of biodiversity loss on the functioning of ecosystems and their ability to provide ecological services has become a central issue in ecology .
Several experiments have provided evidence that reduced species diversity may impair ecosystem processes such as plant biomass production .
The interpretation of these experiments , however , has been controversial because two types of mechanism may operate in combination .
In the ` selection effect ' , dominance by species with particular traits affects ecosystem processes .
In the ` complementarity effect ' , resource partitioning or positive interactions lead to increased total resource use .
Here we present a new approach to separate the two effects on the basis of an additive partitioning analogous to the Price equation in evolutionary genetics .
Applying this method to data from the pan-European BIODEPTH experiment reveals that the selection effect is zero on average and varies from negative to positive in different localities , depending on whether species with lower - or higher-than-average biomass dominate communities .
In contrast , the complementarity effect is positive overall , supporting the hypothesis that plant diversity influences primary production in European grasslands through niche differentiation or facilitation .

[1867] Biomarker evidence for green and purple sulphur bacteria in a stratified Palaeoproterozoic sea

The disappearance of iron formations from the geological record ~ 1.8 billion years ( Gyr ) ago was the consequence of rising oxygen levels in the atmosphere starting 2.45-2 .32 Gyr ago .
It marks the end of a 2.5-Gyr period dominated by anoxic and iron-rich deep oceans .
However , despite rising oxygen levels and a concomitant increase in marine sulphate concentration , related to enhanced sulphide oxidation during continental weathering , the chemistry of the oceans in the following mid-Proterozoic interval ( ~ 1.8-0 .8 Gyr ago ) probably did not yet resemble our oxygen-rich modern oceans .
Recent data indicate that marine oxygen and sulphate concentrations may have remained well below current levels during this period , with one model indicating that anoxic and sulphidic marine basins were widespread , and perhaps even globally distributed .
Here we present hydrocarbon biomarkers ( molecular fossils ) from a 1.64-Gyr-old basin in northern Australia , revealing the ecological structure of mid-Proterozoic marine communities .
The biomarkers signify a marine basin with anoxic , sulphidic , sulphate-poor and permanently stratified deep waters , hostile to eukaryotic algae .
Phototrophic purple sulphur bacteria ( Chromatiaceae ) were detected in the geological record based on the new carotenoid biomarker okenane , and they seem to have co-existed with communities of green sulphur bacteria ( Chlorobiaceae ) .
Collectively , the biomarkers support mounting evidence for a long-lasting Proterozoic world in which oxygen levels remained well below modern levels .

[1868] Building world narratives for climate change impact , adaptation and vulnerability analyses

The impacts of climate change on human systems depend not only on the level of emissions but also on how inherently vulnerable these systems are to the changing climate .
The large uncertainties over future development and structure of societies and economies mean that the assessment of climate change effects is complex .
One way to deal with this complexity is by using scenario analysis that takes account of these socio-economic differences .
The challenge is to identify the dimensions along which societies and economies evolve over time in such a way as to cover sufficiently different vulnerability patterns .
This conceptual effort is critical for the development of informative scenarios .
Here , we identify three dimensions that take into account the most relevant factors that define the vulnerability of human systems to climate change and their ability to adapt to it .

[1869] Microbial ecosystem responses to rapid climate change in the Arctic

Rapid climate change in the Arctic has begun to affect the ecology of plants and animals throughout the region , with impacts on species ranges , population dynamics and food web interactions ( Grebmeier et al. , 2006 ; Post et al. , 2009 ) .
By comparison , little attention has been given to the impacts on Arctic microbial communities , despite the major and often dominant contribution of microbes to total ecosystem biomass , biodiversity , nutrient cycling and energy flow .

[1870] The role of networks in transforming Australian agriculture

It has been argued that major , purposeful action often resulting in significant changes in structure or function , known as transformational adaptation , is required in some areas of the agricultural sector to adapt to climate change and other driving factors .
Yet there is limited understanding of what factors instigate and facilitate this scale of change .
From a social science perspective , one key question remains : to what extent do agribusinesses need social capital to plan and implement large-scale , transformational adaptation options , compared with incremental-scale adaptations ?
Data drawn from Australian primary industries found that those undertaking transformational change had more far-reaching information and knowledge network connections yet less extensive social links to family , friends and colleagues .
These findings demonstrate that strong access to knowledge and weak social ties increases the ability to facilitate action that differs from established social norms , hence empowering transformational adaptors to plan and implement novel strategies and options .

[1871] Epigenetic diversity increases the productivity and stability of plant populations

Biological diversity within species can be an important driver of population and ecosystem functioning .
Until now , such within-species diversity effects have been attributed to underlying variation in DNA sequence .
However , within-species differences , and thus potentially functional biodiversity , can also be created by epigenetic variation .
Here , we show that epigenetic diversity increases the productivity and stability of plant populations .
Epigenetically diverse populations of Arabidopsis thaliana produce up to 40 % more biomass than epigenetically uniform populations .
The positive epigenetic diversity effects are strongest when populations are grown together with competitors and infected with pathogens , and they seem to be partly driven by complementarity among epigenotypes .
Our study has two implications : first , we may need to re-evaluate previous within-species diversity studies where some effects could reflect epigenetic diversity ; second , we need to incorporate epigenetics into basic ecological research , by quantifying natural epigenetic diversity and testing for its ecological consequences across many different species .

[1872] Genomic island variability facilitates Prochlorococcus-virus coexistence

Prochlorococcus cyanobacteria are extremely abundant in the oceans , as are the viruses that infect them .
How hosts and viruses coexist in nature remains unclear , although the presence of both susceptible and resistant cells may allow this coexistence .
Combined whole-genome sequencing and PCR screening technology now enables us to investigate the effect of resistance on genome evolution and the genomic mechanisms behind the long-term coexistence of Prochlorococcus and their viruses .
Here we present a genome analysis of 77 substrains selected for resistance to ten viruses , revealing mutations primarily in non-conserved , horizontally transferred genes that localize to a single hypervariable genomic island .
Mutations affected viral attachment to the cell surface and imposed a fitness cost to the host , manifested by significantly lower growth rates or a previously unknown mechanism of more rapid infection by other viruses .
The mutant genes are generally uncommon in nature yet some carry polymorphisms matching those found experimentally .
These data are empirical evidence indicating that viral-attachment genes are preferentially located in genomic islands and that viruses are a selective pressure enhancing the diversity of both island genes and island gene content .
This diversity emerges as a genomic mechanism that reduces the effective host population size for infection by a given virus , thus facilitating long-term coexistence between viruses and their hosts in nature .

[1873] Avian phenology : Climate change and constraints on breeding

Although climate change apparently affects the breeding patterns of many animals , the wider implications for breeding success are unclear .
Here we describe an energy trade-off between reproduction and maintenance that occurs during cold weather in great tits ( Parus major L. ) , pointing to a thermal constraint on the timing of egg laying .
Our observations indicate that the fine-scale pattern of climate change could be critical to the reproduction of some species and underlies previously unexplained variation in the breeding success of other temperate birds .

[1874] Functional GacS in Pseudomonas DSS73 prevents digestion by Caenorhabditis elegans and protects the nematode from killer flagellates

The success of biocontrol bacteria in soil depends in part on their ability to escape predation .
We explored the interactions between Pseudomonas strain DSS73 and two predators , the nematode Caenorhabditis elegans and the flagellate Cercomonas sp .
Growth of the nematode in liquid culture was arrested when it was feeding on DSS73 or a DSS73 mutant ( DSS73-15C2 ) unable to produce the biosurfactant amphisin , whereas a regulatory gacS mutant ( DSS73-12H8 ) that produces no exoproducts supported fast growth of the nematode .
The flagellate Cercomonas sp .
was able to grow on all three strains .
The biosurfactant-deficient DSS73 mutant caused severe dilation of the nematode gut .
In three-species systems ( DSS73 , Cercomonas and C. elegans ) , the nematodes fed on the flagellates , which in turn grazed the bacteria and the number of C. elegans increased .
The flagellates Cercomonas sp .
usually kill C. elegans .
However , DSS73 protected the nematodes from flagellate killing .
Soil microcosms inoculated with six rhizobacteria and grazed by nematodes were colonized more efficiently by DSS73 than similar systems grazed by flagellates or without grazers .
In conclusion , our results suggest that C. elegans and DSS73 mutually increase the survival of one another in complex multispecies systems and that this interaction depends on the GacS regulator .

[1875] Microbialite resurgence after the Late Ordovician extinction

Microbialites , including biogenic stromatolites , thrombolites and dendrolites , were formed by various microbial mats that trapped and bound sediments or formed the locus of mineral precipitation .
Microbialites were common and diverse during the Proterozoic , but declined in abundance and morphological diversity when multicellular life diversified during the Cambrian Radiation .
A second decline occurred during the Ordovician Radiation of marine animals , and from then until the present microbialites have been confined largely to high-stress environments where multicellular organisms are rare .
The microbialite declines in the Phanerozoic are attributed to disruption of the mats by animals .
A resurgence of stromatolite abundance and size during reduced animal diversity after the Permian extinction has been documented anecdotally .
Here we show , with statistical support , that a microbialite resurgence also occurred after the Late Ordovician extinction event in western North America .
The resurgences were associated with loss of mat-inhibiting animals , providing insights into shallow-water community structures after extinction events .

[1876] North Pacific seasonality and the glaciation of North America 2.7 million years ago

In the context of gradual Cenozoic cooling , the timing of the onset of significant Northern Hemisphere glaciation 2.7 million years ago is consistent with Milankovitch 's orbital theory , which posited that ice sheets grow when polar summertime insolation and temperature are low .
However , the role of moisture supply in the initiation of large Northern Hemisphere ice sheets has remained unclear .
The subarctic Pacific Ocean represents a significant source of water vapour to boreal North America , but it has been largely overlooked in efforts to explain Northern Hemisphere glaciation .
Here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic Pacific Ocean , indicating that 2.7 million years ago late-summer sea surface temperatures in this ocean region rose in response to an increase in stratification .
At the same time , winter sea surface temperatures cooled , winter floating ice became more abundant and global climate descended into glacial conditions .
We suggest that the observed summer warming extended into the autumn , providing water vapour to northern North America , where it precipitated and accumulated as snow , and thus allowed the initiation of Northern Hemisphere glaciation .

[1877] Deep sub-seafloor prokaryotes stimulated at interfaces over geological time

The sub-seafloor biosphere is the largest prokaryotic habitat on Earth but also a habitat with the lowest metabolic rates .
Modelled activity rates are very low , indicating that most prokaryotes may be inactive or have extraordinarily slow metabolism .
Here we present results from two Pacific Ocean sites , margin and open ocean , both of which have deep , subsurface stimulation of prokaryotic processes associated with geochemical and/or sedimentary interfaces .
At 90 m depth in the margin site , stimulation was such that prokaryote numbers were higher ( about 13-fold ) and activity rates higher than or similar to near-surface values .
Analysis of high-molecular-mass DNA confirmed the presence of viable prokaryotes and showed changes in biodiversity with depth that were coupled to geochemistry , including a marked community change at the 90-m interface .
At the open ocean site , increases in numbers of prokaryotes at depth were more restricted but also corresponded to increased activity ; however , this time they were associated with repeating layers of diatom-rich sediments ( about 9 Myr old ) .
These results show that deep sedimentary prokaryotes can have high activity , have changing diversity associated with interfaces and are active over geological timescales .

[1878] Genetic diversity of inorganic carbon uptake systems causes variation in CO2 response of the cyanobacterium Microcystis

Rising CO2 levels may act as an important selective factor on the CO2-concentrating mechanism ( CCM ) of cyanobacteria .
We investigated genetic diversity in the CCM of Microcystis aeruginosa , a species producing harmful cyanobacterial blooms in many lakes worldwide .
All 20 investigated Microcystis strains contained complete genes for two CO2 uptake systems , the ATP-dependent bicarbonate uptake system BCT1 and several carbonic anhydrases ( CAs ) .
However , 12 strains lacked either the high-flux bicarbonate transporter BicA or the high-affinity bicarbonate transporter SbtA .
Both genes , bicA and sbtA , were located on the same operon , and the expression of this operon is most likely regulated by an additional LysR-type transcriptional regulator ( CcmR2 ) .
Strains with only a small bicA fragment clustered together in the phylogenetic tree of sbtAB , and the bicA fragments were similar in strains isolated from different continents .
This indicates that a common ancestor may first have lost most of its bicA gene and subsequently spread over the world .
Growth experiments showed that strains with sbtA performed better at low inorganic carbon ( Ci ) conditions , whereas strains with bicA performed better at high Ci conditions .
This offers an alternative explanation of previous competition experiments , as our results reveal that the competition at low CO2 levels was won by a specialist with only sbtA , whereas a generalist with both bicA and sbtA won at high CO2 levels .
Hence , genetic and phenotypic variation in Ci uptake systems provide Microcystis with the potential for microevolutionary adaptation to changing CO2 conditions , with a selective advantage for bicA-containing strains in a high-CO2 world .

[1879] Dolomite-rich coralline algae in reefs resist dissolution in acidified conditions

Coral reef ecosystems develop best in high-flow environments but their fragile frameworks are also vulnerable to high wave energy .
Wave-resistant algal rims , predominantly made up of the crustose coralline algae ( CCA ) Porolithon onkodes and P. pachydermum , are therefore critical structural elements for the survival of many shallow coral reefs .
Concerns are growing about the susceptibility of CCA to ocean acidification because CCA Mg-calcite skeletons are more susceptible to dissolution under low pH conditions than coral aragonite skeletons .
However , the recent discovery of dolomite ( Mg0 .5 Ca0 .5 ( CO3 ) ) , a stable carbonate , in P. onkodes cells necessitates a reappraisal of the impacts of ocean acidification on these CCA .
Here we show , using a dissolution experiment , that dried dolomite-rich CCA have 6-10 times lower rates of dissolution than predominantly Mg-calcite CCA in both high-CO2 ( ~ 700 ppm ) and control ( ~ 380 ppm ) environments , respectively .
We reveal this stabilizing mechanism to be a combination of reduced porosity due to dolomite infilling and selective dissolution of other carbonate minerals .
Physical break-up proceeds by dissolution of Mg-calcite walls until the dolomitized cell eventually drops out intact .
Dolomite-rich CCA frameworks are common in shallow coral reefs globally and our results suggest that it is likely that they will continue to provide protection and stability for coral reef frameworks as CO2 rises .

[1880] Detection of a direct carbon dioxide effect in continental river runoff records

Continental runoff has increased through the twentieth century despite more intensive human water consumption .
Possible reasons for the increase include : climate change and variability , deforestation , solar dimming , and direct atmospheric carbon dioxide ( CO2 ) effects on plant transpiration .
All of these mechanisms have the potential to affect precipitation and/or evaporation and thereby modify runoff .
Here we use a mechanistic land-surface model and optimal fingerprinting statistical techniques to attribute observational runoff changes into contributions due to these factors .
The model successfully captures the climate-driven inter-annual runoff variability , but twentieth-century climate alone is insufficient to explain the runoff trends .
Instead we find that the trends are consistent with a suppression of plant transpiration due to CO2-induced stomatal closure .
This result will affect projections of freshwater availability , and also represents the detection of a direct CO2 effect on the functioning of the terrestrial biosphere .

[1881] A Dehalococcoides-containing co-culture that dechlorinates tetrachloroethene to trans-1 ,2 - dichloroethene

In the microbial reductive dechlorination of tetrachloroethene ( PCE ) and trichloroethene ( TCE ) , dechlorinators usually produce cis-1 ,2 - dichloroethene ( cis-DCE ) as the predominant product or an intermediate .
This study shows that dechlorination of PCE and TCE can also lead to the generation of trans-1 ,2 - dichloroethene ( trans-DCE ) by a co-culture MB .
During its enrichment process , the ratio of trans - to cis-DCE increased from 1.4 ( + / -0.1 ) :1 -3.7 ( + / -0.4 ) :1 , whereas the TCE reductive dechlorination rate went up from ~ 26.2 to ~ 68.8 mumol l-1 day-1 .
PCR-denaturing gradient gel electrophoresis ( PCR-DGGE ) revealed that the increased ratio of trans - / cis-DCE was well correlated with the increased proportions of Dehalococcoides and the disappearance of Desulfuromonas during the enrichment process .
As shown by PCR-DGGE , similar Dehalococcoides species were consistently present in another three sediment-free cultures with various trans - / cis-DCE ratios .
The 16S rRNA gene sequence of this Dehalococcoides sp .
in co-culture MB is 100 % identical ( over 1489 bp ) to that of Dehalococcoides ethenogenes strain 195 ( CP000027 ) , which belongs to the Cornell subgroup of the Dehalococcoides cluster .
The other bacterium in this co-culture MB was a Sedimentibacter species , which showed no PCE or TCE dechlorination activity .
Results from this study show that microbial dechlorination of chloroethenes by this particular subgroup of Dehalococcoides could result in significant accumulation of trans-DCE in the environment if no trans-DCE dechlorinators coexist in the contaminated sites .

[1882] Retreat of Pine Island Glacier controlled by marine ice-sheet instability

Over the past 40 years Pine Island Glacier in West Antarctica has thinned at an accelerating rate , so that at present it is the largest single contributor to sea-level rise in Antarctica .
In recent years , the grounding line , which separates the grounded ice sheet from the floating ice shelf , has retreated by tens of kilometres .
At present , the grounding line is crossing a retrograde bedrock slope that lies well below sea level , raising the possibility that the glacier is susceptible to the marine ice-sheet instability mechanism .
Here , using three state-of-the-art ice-flow models , we show that Pine Island Glacier 's grounding line is probably engaged in an unstable 40 km retreat .
The associated mass loss increases substantially over the course of our simulations from the average value of 20 Gt yr-1 observed for the 1992-2011 period , up to and above 100 Gt yr-1 , equivalent to 3.5-10 mm eustatic sea-level rise over the following 20 years .
Mass loss remains elevated from then on , ranging from 60 to 120 Gt yr-1 .

[1883] Salt marsh sediment diversity : a test of the variability of the rare biosphere among environmental replicates

Much of the phylogenetic diversity in microbial systems arises from rare taxa that comprise the long tail of taxon rank distribution curves .
This vast diversity presents a challenge to testing hypotheses about the effects of perturbations on microbial community composition because variability of rare taxa among environmental replicates may be sufficiently large that it would require a prohibitive degree of sequencing to discern differences between samples .
In this study we used pyrosequencing of 16S rRNA tags to examine the diversity and within-site variability of salt marsh sediment bacteria .
Our goal was to determine whether pyrosequencing could produce similar patterns in community composition among replicate environmental samples from the same location .
We hypothesized that repeated sampling from the same location would produce different snapshots of the rare community due to incomplete sequencing of the taxonomically rich rare biosphere .
We demonstrate that the salt marsh sediments we sampled contain a remarkably diverse array of bacterial taxa and , in contrast to our hypothesis , repeated sampling from within the same site produces reliably similar patterns in bacterial community composition , even among rare organisms .
These results demonstrate that deep sequencing of 16s tags is well suited to distinguish site-specific similarities and differences among rare taxa and is a valuable tool for hypothesis testing in microbial ecology .

[1884] Stability of organic carbon in deep soil layers controlled by fresh carbon supply

The world 's soils store more carbon than is present in biomass and in the atmosphere .
Little is known , however , about the factors controlling the stability of soil organic carbon stocks and the response of the soil carbon pool to climate change remains uncertain .
We investigated the stability of carbon in deep soil layers in one soil profile by combining physical and chemical characterization of organic carbon , soil incubations and radiocarbon dating .
Here we show that the supply of fresh plant-derived carbon to the subsoil ( 0.6-0 .8 m depth ) stimulated the microbial mineralization of 2,567 + / - 226-year-old carbon .
Our results support the previously suggested idea that in the absence of fresh organic carbon , an essential source of energy for soil microbes , the stability of organic carbon in deep soil layers is maintained .
We propose that a lack of supply of fresh carbon may prevent the decomposition of the organic carbon pool in deep soil layers in response to future changes in temperature .
Any change in land use and agricultural practice that increases the distribution of fresh carbon along the soil profile could however stimulate the loss of ancient buried carbon .

[1885] Intensification of open-ocean oxygen depletion by vertically migrating animals

Throughout the ocean , countless small animals swim to depth in the daytime , presumably to seek refuge from large predators .
These animals return to the surface at night to feed .
This substantial diel vertical migration can result in the transfer of significant amounts of carbon and nutrients from the surface to depth .
However , its consequences on ocean chemistry at the global scale have remained uncertain .
Here , we determine the depths of these diel migrations in the global ocean using a global array of backscatter data from acoustic Doppler current profilers , collected between 1990 and 2011 .
We show that the depth of diel migration follows coherent large-scale patterns .
We find that migration depth is greater where subsurface oxygen concentrations are high , such that seawater oxygen concentration is the best single predictor of migration depth at the global scale .
In oxygen minimum zone areas , migratory animals generally descend as far as the upper margins of the low-oxygen waters .
Using an ocean biogeochemical model coupled to a general circulation model , we show that by focusing oxygen consumption in poorly ventilated regions of the upper ocean , diel vertical migration intensifies oxygen depletion in the upper margin of oxygen minimum zones .
We suggest that future changes in the extent of oxygen minimum zones could alter the migratory depths of marine organisms , with consequences for marine biogeochemistry , food webs and fisheries .

[1886] A late Eemian aridity pulse in central Europe during the last glacial inception

Investigating the processes that led to the end of the last interglacial period is relevant for understanding how our ongoing interglacial will end , which has been a matter of much debate ( see , for example , refs 1 , 2 ) .
A recent ice core from Greenland demonstrates climate cooling from 122,000 years ago driven by orbitally controlled insolation , with glacial inception at 118,000 years ago .
Here we present an annually resolved , layer-counted record of varve thickness , quartz grain size and pollen assemblages from a maar lake in the Eifel ( Germany ) , which documents a late Eemian aridity pulse lasting 468 years with dust storms , aridity , bushfire and a decline of thermophilous trees at the time of glacial inception .
We interpret the decrease in both precipitation and temperature as an indication of a close link of this extreme climate event to a sudden southward shift of the position of the North Atlantic drift , the ocean current that brings warm surface waters to the northern European region .
The late Eemian aridity pulse occurred at a 65degrees N July insolation of 416 W m-2 , close to today 's value of 428 W m-2 ( ref .
9 ) , and may therefore be relevant for the interpretation of present-day climate variability .

[1887] Time of emergence : Moving up early detection

Natural climate variability complicates the detection of anthropogenic climate change in the twenty-first century .
Now , research shows that evidence of human influence first emerges from sea level rather than temperature rise .

[1888] Adverse weather conditions for European wheat production will become more frequent with climate change

Europe is the largest producer of wheat , the second most widely grown cereal crop after rice .
The increased occurrence and magnitude of adverse and extreme agroclimatic events are considered a major threat for wheat production .
We present an analysis that accounts for a range of adverse weather events that might significantly affect wheat yield in Europe .
For this purpose we analysed changes in the frequency of the occurrence of 11 adverse weather events .
Using climate scenarios based on the most recent ensemble of climate models and greenhouse gases emission estimates , we assessed the probability of single and multiple adverse events occurring within one season .
We showed that the occurrence of adverse conditions for 14 sites representing the main European wheat-growing areas might substantially increase by 2060 compared to the present ( 1981-2010 ) .
This is likely to result in more frequent crop failure across Europe .
This study provides essential information for developing adaptation strategies .

[1889] A single locus confers tolerance to continuous light and allows substantial yield increase in tomato

An important constraint for plant biomass production is the natural day length .
Artificial light allows for longer photoperiods , but tomato plants develop a detrimental leaf injury when grown under continuous light -- a still poorly understood phenomenon discovered in the 1920s .
Here , we report a dominant locus on chromosome 7 of wild tomato species that confers continuous light tolerance .
Genetic evidence , RNAseq data , silencing experiments and sequence analysis all point to the type III light harvesting chlorophyll a/b binding protein 13 ( CAB-13 ) gene as a major factor responsible for the tolerance .
In Arabidopsis thaliana , this protein is thought to have a regulatory role balancing light harvesting by photosystems I and II .
Introgressing the tolerance into modern tomato hybrid lines , results in up to 20 % yield increase , showing that limitations for crop productivity , caused by the adaptation of plants to the terrestrial 24-h day/night cycle , can be overcome .

[1890] Surface changes in the North Atlantic meridional overturning circulation during the last millennium

Despite numerous investigations , the dynamical origins of the Medieval Climate Anomaly and the Little Ice Age remain uncertain .
A major unresolved issue relating to internal climate dynamics is the mode and tempo of Atlantic meridional overturning circulation variability , and the significance of decadal-to-centennial scale changes in Atlantic meridional overturning circulation strength in regulating the climate of the last millennium .
Here we use the time-constrained high-resolution local radiocarbon reservoir age offset derived from an absolutely dated annually resolved shell chronology spanning the past 1,350 years , to reconstruct changes in surface ocean circulation and climate .
The water mass tracer data presented here from the North Icelandic shelf , combined with previously published data from the Arctic and subtropical Atlantic , show that surface Atlantic meridional overturning circulation dynamics likely amplified the relatively warm conditions during the Medieval Climate Anomaly and the relatively cool conditions during the Little Ice Age within the North Atlantic sector .

[1891] Decadal variability in the outflow from the Nordic seas to the deep Atlantic Ocean

The global thermohaline circulation is the oceanic overturning mode , which is manifested in the North Atlantic Ocean as northward-flowing surface waters which sink in the Nordic ( Greenland , Iceland and Norwegian ) seas and return southwards -- after overflowing the Greenland-Scotland ridge -- as deep water .
This process has been termed the ` conveyor belt ' , and is believed to keep Europe 5-8 degreesC warmer than it would be if the conveyor were to shut down .
The variability of today 's conveyor belt is therefore an important component of climate regulation .
The Nordic seas are the only Northern Hemisphere source of deep water and a previous study has revealed no long-term variability in the outflow of deep water from the Nordic seas to the Atlantic Ocean .
Here I use flows derived from hydrographic data to show that this outflow has approximately doubled , and then returned to previous values , over the past four decades .
I present evidence which suggests that this variability is forced by variability in polar air temperature , which in turn may be connected to the recently reported Arctic warming .

[1892] Implications of temperature variation for malaria parasite development across Africa

Temperature is an important determinant of malaria transmission .
Recent work has shown that mosquito and parasite biology are influenced not only by average temperature , but also by the extent of the daily temperature variation .
Here we examine how parasite development within the mosquito ( Extrinsic Incubation Period ) is expected to vary over time and space depending on the diurnal temperature range and baseline mean temperature in Kenya and across Africa .
Our results show that under cool conditions , the typical approach of using mean monthly temperatures alone to characterize the transmission environment will underestimate parasite development .
In contrast , under warmer conditions , the use of mean temperatures will overestimate development .
Qualitatively similar patterns hold using both outdoor and indoor temperatures .
These findings have important implications for defining malaria risk .
Furthermore , understanding the influence of daily temperature dynamics could provide new insights into ectotherm ecology both now and in response to future climate change .

[1893] Impacts of reactive nitrogen on climate change in China

China is mobilizing the largest anthropogenic reactive nitrogen ( Nr ) in the world due to agricultural , industrial and urban development .
However , the climate effects related to Nr in China remain largely unclear .
Here we comprehensively estimate that the net climate effects of Nr are -100 + / - 414 and 322 + / - 163 Tg CO2e on a GTP20 and a GTP100 basis , respectively .
Agriculture contributes to warming at 187 + / - 108 and 186 + / - 56 Tg CO2e on a 20-y and 100-y basis , respectively , dominated by long-lived nitrous oxide ( N2O ) from fertilized soils .
On a 20-y basis , industry contributes to cooling at -287 + / - 306 Tg CO2e , largely owing to emissions of nitrogen oxides ( NOx ) altering tropospheric ozone , methane and aerosol concentrations .
However , these effects are short-lived .
The effect of industry converts to warming at 136 + / - 107 Tg CO2e on a 100-y basis , mainly as a result of the reduced carbon ( C ) sink from the NOx-induced ozone effect on plant damage .
On balance , the warming effects of gaseous Nr are partly offset by the cooling effects of N-induced carbon sequestration in terrestrial ecosystems .
The large mitigation potentials through reductions in agricultural N2O and industrial NOx will accompany by a certain mitigation pressure from limited N-induced C sequestration in the future .

[1894] Multiple causes of interannual sea surface temperature variability in the equatorial Atlantic Ocean

The eastern equatorial Atlantic Ocean is subject to interannual fluctuations of sea surface temperatures , with climatic impacts on the surrounding continents .
The dynamic mechanism underlying Atlantic temperature variability is thought to be similar to that of the El Nino/Southern Oscillation ( ENSO ) in the equatorial Pacific , where air-sea coupling leads to a positive feedback between surface winds in the western basin , sea surface temperature in the eastern basin , and equatorial oceanic heat content .
Here we use a suite of observational data , climate reanalysis products , and general circulation model simulations to reassess the factors driving the interannual variability .
We show that some of the warm events can not be explained by previously identified equatorial wind stress forcing and ENSO-like dynamics .
Instead , these events are driven by a mechanism in which surface wind forcing just north of the equator induces warm ocean temperature anomalies that are subsequently advected toward the equator .
We find the surface wind patterns are associated with long-lived subtropical sea surface temperature anomalies and suggest they therefore reflect a link between equatorial and subtropical Atlantic variability .

[1895] Rainfall and drought in equatorial east Africa during the past 1,100 years

Knowledge of natural long-term rainfall variability is essential for water-resource and land-use management in sub-humid regions of the world .
In tropical Africa , data relevant to determining this variability are scarce because of the lack of long instrumental climate records and the limited potential of standard high-resolution proxy records such as tree rings and ice cores .
Here we present a decade-scale reconstruction of rainfall and drought in equatorial east Africa over the past 1,100 years , based on lake-level and salinity fluctuations of Lake Naivasha ( Kenya ) inferred from three different palaeolimnological proxies : sediment stratigraphy and the species compositions of fossil diatom and midge assemblages .
Our data indicate that , over the past millennium , equatorial east Africa has alternated between contrasting climate conditions , with significantly drier climate than today during the ` Medieval Warm Period ' ( ~ ad 1000-1270 ) and a relatively wet climate during the ` Little Ice Age ' ( ~ ad 1270-1850 ) which was interrupted by three prolonged dry episodes .
We also find strong chronological links between the reconstructed history of natural long-term rainfall variation and the pre-colonial cultural history of east Africa , highlighting the importance of a detailed knowledge of natural long-term rainfall fluctuations for sustainable socio-economic development .

[1896] Siberian larch forests and the ion content of thaw lakes form a geochemically functional entity

Siberian larch forests growing on shallow permafrost soils have not , until now , been considered to be controlling the abiotic and biotic characteristics of the vast number of thaw-lake ecosystems .
Here we show , using four independent data sets ( a modern data set from 201 lakes from the tundra to taiga , and three lake-core records ) , that lake-water geochemistry in Yakutia is highly correlated with vegetation .
Alkalinity increases with catchment forest density .
We postulate that in this arid area , higher evapotranspiration in larch forests compared with that in the tundra vegetation leads to local salt accumulation in soils .
Solutes are transported to nearby thaw lakes during rain events and snow melt , but are not fully transported into rivers , because there is no continuous groundwater flow within permafrost soils .
This implies that potentially large shifts in the chemical characteristics of aquatic ecosystems to known warming are absent because of the slow response of catchment forests to climate change .

[1897] Sensitivities of extant animal taxa to ocean acidification

Anthropogenic CO2 emitted to the atmosphere is absorbed by the oceans , causing a progressive increase in ocean inorganic carbon concentrations and resulting in decreased water pH and calcium carbonate saturation .
This phenomenon , called ocean acidification , is in addition to the warming effects of CO2 emissions .
Ocean acidification has been reported to affect ocean biota , but the severity of this threat to ocean ecosystems ( and humans depending on these ecosystems ) is poorly understood .
Here we evaluate the scale of this threat in the context of widely used representative concentration pathways ( RCPs ) by analysing the sensitivities of five animal taxa ( corals , echinoderms , molluscs , crustaceans and fishes ) to a wide range of CO2 concentrations .
Corals , echinoderms and molluscs are more sensitive to RCP8 .5 ( 936 ppm in 2100 ) than are crustaceans .
Larval fishes may be even more sensitive than the lower invertebrates , but taxon sensitivity on evolutionary timescales remains obscure .
The variety of responses within and between taxa , together with observations in mesocosms and palaeo-analogues , suggest that ocean acidification is a driver for substantial change in ocean ecosystems this century , potentially leading to long-term shifts in species composition .

[1898] Quantitative and qualitative impact of hospital effluent on dissemination of the integron pool

There is increasing evidence that human activity , and especially the resulting effluent , has a major role in the dissemination of bacterial antibiotic-resistance determinants in the environment .
Hospitals are the major antibiotic consumers and thus facilitate the spread of antibiotic resistance .
Questions are increasingly being raised about the management of hospital effluents , but their involvement in antibiotic-resistance dissemination has never been assessed .
Integrons are a paradigm of genetic transfer between the environmental resistome and both commensal and pathogenic bacteria .
In order to assess the impact of hospital activities on antibiotic-resistance dissemination in the environment , we monitored integrons and their gene cassettes in hospital effluents , and their release in the environment .
We found that bacterial communities present in a hospital effluent contained a high proportion of integrons .
In terms of both their gene cassette diversity and gene cassette arrays , the urban effluent and municipal wastewater treatment plant ( WWTP ) influent were most similar , whereas the hospital effluent and recirculation sludge exhibited very specific patterns .
We found that anthropogenic activities led to the release of abundant integrons and antibiotic-resistance gene cassettes , but we observed no specific impact of hospital activities on the receiving environment .
Furthermore , although the WWTP did not reduce the normalized integron copy number , it reduced the diversity of gene cassette arrays contained in the raw wastewater , underlining the effect of the biological treatment on the anthropogenic integron pool arriving at the WWTP .

[1899] Circadian rhythms of hydraulic conductance and growth are enhanced by drought and improve plant performance

Circadian rhythms enable plants to anticipate daily environmental variations , resulting in growth oscillations under continuous light .
Because plants daily transpire up to 200 % of their water content , their water status oscillates from favourable during the night to unfavourable during the day .
We show that rhythmic leaf growth under continuous light is observed in plants that experience large alternations of water status during an entrainment period , but is considerably buffered otherwise .
Measurements and computer simulations show that this is due to oscillations of plant hydraulic conductance and plasma membrane aquaporin messenger RNA abundance in roots during continuous light .
A simulation model suggests that circadian oscillations of root hydraulic conductance contribute to acclimation to water stress by increasing root water uptake , thereby favouring growth and photosynthesis .
They have a negative effect in favourable hydraulic conditions .
Climate-driven control of root hydraulic conductance therefore improves plant performances in both stressed and non-stressed conditions .

[1900] Permafrost thawing as a possible source of abrupt carbon release at the onset of the Bolling/Allerod

One of the most abrupt and yet unexplained past rises in atmospheric CO2 ( > 10 p.p.m.v. in two centuries ) occurred in quasi-synchrony with abrupt northern hemispheric warming into the Bolling/Allerod , ~ 14,600 years ago .
Here we use a U/Th-dated record of atmospheric Delta14C from Tahiti corals to provide an independent and precise age control for this CO2 rise .
We also use model simulations to show that the release of old ( nearly 14C-free ) carbon can explain these changes in CO2 and Delta14C .
The Delta14C record provides an independent constraint on the amount of carbon released ( ~ 125 Pg C ) .
We suggest , in line with observations of atmospheric CH4 and terrigenous biomarkers , that thawing permafrost in high northern latitudes could have been the source of carbon , possibly with contribution from flooding of the Siberian continental shelf during meltwater pulse 1A .
Our findings highlight the potential of the permafrost carbon reservoir to modulate abrupt climate changes via greenhouse-gas feedbacks .

[1901] Episodic fresh surface waters in the Eocene Arctic Ocean

It has been suggested , on the basis of modern hydrology and fully coupled palaeoclimate simulations , that the warm greenhouse conditions that characterized the early Palaeogene period ( 55-45 Myr ago ) probably induced an intensified hydrological cycle with precipitation exceeding evaporation at high latitudes .
Little field evidence , however , has been available to constrain oceanic conditions in the Arctic during this period .
Here we analyse Palaeogene sediments obtained during the Arctic Coring Expedition , showing that large quantities of the free-floating fern Azolla grew and reproduced in the Arctic Ocean by the onset of the middle Eocene epoch ( ~ 50 Myr ago ) .
The Azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of Arctic surface waters during an ~ 800,000-year interval .
The abundant remains of Azolla that characterize basal middle Eocene marine deposits of all Nordic seas probably represent transported assemblages resulting from freshwater spills from the Arctic Ocean that reached as far south as the North Sea .
The termination of the Azolla phase in the Arctic coincides with a local sea surface temperature rise from ~ 10 degreesC to 13 degreesC , pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans .
We suggest that onset and termination of the Azolla phase depended on the degree of oceanic exchange between Arctic Ocean and adjacent seas .

[1902] Consequences of a biological invasion reveal the importance of mutualism for plant communities

Seed-dispersal mutualisms have a fundamental role in regenerating natural communities .
Interest in the importance of seed dispersal to plant communities has been heightened by worldwide declines in animal dispersers .
One view , the ` keystone mutualist hypothesis ' , predicts that these human-caused losses will trigger a cascade of linked extinctions throughout the community .
Implicitly , this view holds that mutualisms , such as seed dispersal , are crucial ecological interactions that maintain the structure and diversity of natural communities .
Although many studies suggest the importance of mutualism , empirical evidence for community-level impacts of mutualists has remained anecdotal , and the central role of mutualism , relative to other species interactions , has long been debated in the theoretical literature .
Here I report the community-level consequences of a biological invasion that disrupts important seed-dispersal mutualisms .
I show that invasion of South African shrublands by the Argentine ant ( Linepithema humile ) leads to a shift in composition of the plant community , owing to a disproportionate reduction in the densities of large-seeded plants .
This study suggests that the preservation of mutualistic interactions may be essential for maintaining natural communities .

[1903] Atmospheric carbon dioxide concentrations over the past 60 million years

Knowledge of the evolution of atmospheric carbon dioxide concentrations throughout the Earth 's history is important for a reconstruction of the links between climate and radiative forcing of the Earth 's surface temperatures .
Although atmospheric carbon dioxide concentrations in the early Cenozoic era ( about 60 Myr ago ) are widely believed to have been higher than at present , there is disagreement regarding the exact carbon dioxide levels , the timing of the decline and the mechanisms that are most important for the control of CO2 concentrations over geological timescales .
Here we use the boron-isotope ratios of ancient planktonic foraminifer shells to estimate the pH of surface-layer sea water throughout the past 60 million years , which can be used to reconstruct atmospheric CO2 concentrations .
We estimate CO2 concentrations of more than 2,000 p.p.m. for the late Palaeocene and earliest Eocene periods ( from about 60 to 52 Myr ago ) , and find an erratic decline between 55 and 40 Myr ago that may have been caused by reduced CO2 outgassing from ocean ridges , volcanoes and metamorphic belts and increased carbon burial .
Since the early Miocene ( about 24 Myr ago ) , atmospheric CO2 concentrations appear to have remained below 500 p.p.m. and were more stable than before , although transient intervals of CO2 reduction may have occurred during periods of rapid cooling approximately 15 and 3 Myr ago .

[1904] Strain-level genomic variation in natural populations of Lebetimonas from an erupting deep-sea volcano

Chemolithoautotrophic Epsilonproteobacteria are ubiquitous in sulfidic , oxygen-poor habitats , including hydrothermal vents , marine oxygen minimum zones , marine sediments and sulfidic caves and have a significant role in cycling carbon , hydrogen , nitrogen and sulfur in these environments .
The isolation of diverse strains of Epsilonproteobacteria and the sequencing of their genomes have revealed that this group has the metabolic potential to occupy a wide range of niches , particularly at dynamic deep-sea hydrothermal vents .
We expand on this body of work by examining the population genomics of six strains of Lebetimonas , a vent-endemic , thermophilic , hydrogen-oxidizing Epsilonproteobacterium , from a single seamount in the Mariana Arc .
Using Lebetimonas as a model for anaerobic , moderately thermophilic organisms in the warm , anoxic subseafloor environment , we show that genomic content is highly conserved and that recombination is limited between closely related strains .
The Lebetimonas genomes are shaped by mobile genetic elements and gene loss as well as the acquisition of novel functional genes by horizontal gene transfer , which provide the potential for adaptation and microbial speciation in the deep sea .
In addition , these Lebetimonas genomes contain two operons of nitrogenase genes with different evolutionary origins .
Lebetimonas expressed nifH during growth with nitrogen gas as the sole nitrogen source , thus providing the first evidence of nitrogen fixation in any Epsilonproteobacteria from deep-sea hydrothermal vents .
In this study , we provide a comparative overview of the genomic potential within the Nautiliaceae as well as among more distantly related hydrothermal vent Epsilonproteobacteria to broaden our understanding of microbial adaptation and diversity in the deep sea .

[1905] Black carbon aerosol size in snow

The effect of anthropogenic black carbon ( BC ) aerosol on snow is of enduring interest due to its consequences for climate forcing .
Until now , too little attention has been focused on BC 's size in snow , an important parameter affecting BC light absorption in snow .
Here we present first observations of this parameter , revealing that BC can be shifted to larger sizes in snow than are typically seen in the atmosphere , in part due to the processes associated with BC removal from the atmosphere .
Mie theory analysis indicates a corresponding reduction in BC absorption in snow of 40 % , making BC size in snow the dominant source of uncertainty in BC 's absorption properties for calculations of BC 's snow albedo climate forcing .
The shift reduces estimated BC global mean snow forcing by 30 % , and has scientific implications for our understanding of snow albedo and the processing of atmospheric BC aerosol in snowfall .

[1906] Climate-mediated energetic constraints on the distribution of hibernating mammals

To predict the consequences of human-induced global climate change , we need to understand how climate is linked to biogeography .
Energetic constraints are commonly invoked to explain animal distributions , and physiological parameters are known to vary along distributional gradients .
But the causal nature of the links between climate and animal biogeography remain largely obscure .
Here we develop a bioenergetic model that predicts the feasibility of mammalian hibernation under different climatic conditions .
As an example , we use the well-quantified hibernation energetics of the little brown bat ( Myotis lucifugus ) to parameterize the model .
Our model predicts pronounced effects of ambient temperature on total winter energy requirements , and a relatively narrow combination of hibernaculum temperatures and winter lengths permitting successful hibernation .
Microhabitat and northern distribution limits of M. lucifugus are consistent with model predictions , suggesting that the thermal dependence of hibernation energetics constrains the biogeography of this species .
Integrating projections of climate change into our model predicts a pronounced northward range expansion of hibernating bats within the next 80 years .
Bioenergetics can provide the simple link between climate and biogeography needed to predict the consequences of climate change .

[1907] Consequences of warming on tundra carbon balance determined by reindeer grazing history

Arctic tundra currently stores half of the global soil carbon ( C ) stock .
Climate warming in the Arctic may lead to accelerated CO2 release through enhanced decomposition and turn Arctic ecosystems from a net C sink into a net C source , if warming enhances decomposition more than plant photosynthesis .
A large portion of the circumpolar Arctic is grazed by reindeer/caribou , and grazing causes important vegetation shifts in the long-term .
Using a unique experimental set-up , where areas experiencing more than 50 years of either light ( LG ) or heavy ( HG ) grazing were warmed and/or fertilized , we show that under ambient conditions areas under LG were a 70 % stronger C sink than HG areas .
Although warming decreased the C sink by 38 % under LG , it had no effect under HG .
Grazing history will thus be an important determinant in the response of ecosystem C balance to climate warming , which at present is not taken into account in climate change models .

[1908] A salinity and sulfate manipulation of hypersaline microbial mats reveals stasis in the cyanobacterial community structure

The cyanobacterial community structure and composition of hypersaline mats were characterized in an experiment in which native salinity and sulfate levels were modified .
Over the course of approximately 1 year , microbial mats collected from Guerrero Negro ( Baja , California Sur , Mexico ) were equilibrated to lowered salinity ( to 35 p.p.t. ) and lowered sulfate ( below 1 mM ) conditions .
The structure and composition of the cyanobacterial community in the top 5 mm of these mats were examined using a multifaceted cultivation-independent molecular approach .
Overall , the relative abundance of cyanobacteria -- roughly 20 % of the total bacterial community , as assayed with a PCR-based methodology -- was not significantly affected by these manipulations .
Furthermore , the mat cyanobacterial community was only modestly influenced by the dramatic changes in sulfate and salinity , and the dominant cyanobacteria were unaffected .
Community composition analyses confirmed the dominant presence of the cosmopolitan cyanobacterium Microcoleus chthonoplastes , but also revealed the dominance of another Oscillatorian cyanobacterial group , also detected in other hypersaline microbial mats .
Cyanobacterial populations increasing in relative abundance under the modified salinity and sulfate conditions were found to be most closely related to other hypersaline microbial mat organisms , suggesting that the development of these mats under native conditions precludes the development of organisms better suited to the less restrictive experimental conditions .
These results also indicate that within a significant range of salinity and sulfate concentrations , the cyanobacterial community is remarkably stable .

[1909] Heterogeneity in the nutrient limitation of different bacterioplankton groups in the Eastern Mediterranean Sea

The heterotrophic bacterial community of the Eastern Mediterranean Sea is believed to be limited by phosphorus ( P ) availability .
This observation assumes that all bacterial groups are equally limited , something that has not been hitherto examined .
To test this hypothesis , we performed nutrient addition experiments and investigated the response of probe-identified groups using microautoradiography combined with catalyzed reporter deposition fluorescence in situ hybridization .
Our results show contrasting responses between the bacterial groups , with Gammaproteobacteria being the group more affected by P availability .
The Roseobacter clade was likely colimited by P and nitrogen ( N ) , whereas Bacteroidetes by P , N and organic carbon ( C ) .
In contrast , SAR11 cells were active regardless of the nutrient concentration .
These results indicate that there is high heterogeneity in the nutrient limitation of the different components of the bacterioplankton community .

[1910] Is anyone out there listening ?

Those who study global change are well versed in the sobering statistics of the enormous impact of humans on the Earth -- the dramatic change in the chemistry of the atmosphere , the massive alteration of the surface of the land , the diversion and despoiling of a large fraction of the available fresh water , the depletion of ocean fisheries , the homogenization of the Earth 's biota and the extirpation of large numbers of species .
These scientists share a sense of frustration , however , about the fact that the general public and policy-makers are not grasping the significance of these changes nor acting to alter these trajectories for the well-being of future generations .

[1911] Lake ecosystems : Rapid evolution revealed by dormant eggs

Natural selection can lead to rapid changes in organisms , which can in turn influence ecosystem processes .
A key factor in the functioning of lake ecosystems is the rate at which primary producers are eaten , and major consumers , such as the zooplankton Daphnia , can be subject to strong selection pressures when phytoplankton assemblages change .
Lake Constance in central Europe experienced a period of eutrophication ( the biological effects of an input of plant nutrients ) during the 1960s-70s , which caused an increase in the abundance of nutritionally poor or even toxic cyanobacteria .
By hatching long-dormant eggs of Daphnia galeata found in lake sediments , we show that the mean resistance of Daphnia genotypes to dietary cyanobacteria increased significantly during this eutrophication .
This rapid evolution of resistance has implications for the ways that ecosystems respond to nutrient enrichment through the impact of grazers on primary production .

[1912] The genome of a motile marine Synechococcus

Marine unicellular cyanobacteria are responsible for an estimated 20-40 % of chlorophyll biomass and carbon fixation in the oceans .
Here we have sequenced and analysed the 2.4-megabase genome of Synechococcus sp .
strain WH8102 , revealing some of the ways that these organisms have adapted to their largely oligotrophic environment .
WH8102 uses organic nitrogen and phosphorus sources and more sodium-dependent transporters than a model freshwater cyanobacterium .
Furthermore , it seems to have adopted strategies for conserving limited iron stores by using nickel and cobalt in some enzymes , has reduced its regulatory machinery ( consistent with the fact that the open ocean constitutes a far more constant and buffered environment than fresh water ) , and has evolved a unique type of swimming motility .
The genome of WH8102 seems to have been greatly influenced by horizontal gene transfer , partially through phages .
The genetic material contributed by horizontal gene transfer includes genes involved in the modification of the cell surface and in swimming motility .
On the basis of its genome , WH8102 is more of a generalist than two related marine cyanobacteria .

[1913] Plant biomarkers in aerosols record isotopic discrimination of terrestrial photosynthesis

Carbon uptake by the oceans and by the terrestrial biosphere can be partitioned using changes in the 12C/13C isotopic ratio ( delta13C ) of atmospheric carbon dioxide , because terrestrial photosynthesis strongly discriminates against 13CO2 , whereas ocean uptake does not .
This approach depends on accurate estimates of the carbon isotopic discrimination of terrestrial photosynthesis ( Delta ; ref .
5 ) at large regional scales , yet terrestrial ecosystem heterogeneity makes such estimates problematic .
Here we show that ablated plant wax compounds in continental air masses can be used to estimate Delta over large spatial scales and at less than monthly temporal resolution .
We measured plant waxes in continental air masses advected to Bermuda , which are mainly of North American origin , and used the wax isotopic composition to estimate Delta simply .
Our estimates indicate a large ( 5-6/1000 ) seasonal variation in Delta of the temperate North American biosphere , with maximum discrimination occurring in late spring , coincident with the onset of production .
We suggest that the observed seasonality arises from several factors , including seasonal shifts in the proportions of production by C3 and C4 plants , and environmentally controlled adjustments in the photosynthetic discrimination of C3-plant-dominated ecosystems .

[1914] Global rates of water-column denitrification derived from nitrogen gas measurements

Biologically available nitrogen ( N ) limits phytoplankton growth over much of the ocean .
The rate at which N is removed from the contemporary ocean by denitrifying bacteria is highly uncertain .
Some studies suggest that N losses exceed inputs ; others argue for a balanced budget .
Here , we use a global ocean circulation model to simulate the distribution of N2 gas produced by denitrifying bacteria in the three main suboxic zones in the open ocean .
By fitting the model to measured N2 gas concentrations , we infer a globally integrated rate of water-column denitrification of 66 + / -6 Tg N yr-1 .
Taking into account isotopic constraints on the fraction of denitrification occurring in the water column versus marine sediments , we estimate that the global rate of N loss from marine sediments and the oceanic water column combined amounts to around 230 + / -60 Tg N yr-1 .
Given present estimates of N input rates , our findings imply a net loss of around 20 + / - 70 Tg of N from the global ocean each year , indistinguishable from a balanced budget .
A balanced N budget , in turn , implies that the marine N cycle is governed by strong regulatory feedbacks .

[1915] Food restriction enhances visual cortex plasticity in adulthood

Neural circuits display a heightened sensitivity to external stimuli during well-established windows in early postnatal life .
After the end of these critical periods , brain plasticity dramatically wanes .
The visual system is one of the paradigmatic models for studying experience-dependent plasticity .
Here we show that food restriction can be used as a strategy to restore plasticity in the adult visual cortex of rats .
A short period of food restriction in adulthood is able both to reinstate ocular dominance plasticity and promote recovery from amblyopia .
These effects are accompanied by a reduction of intracortical inhibition without modulation of brain-derived neurotrophic factor expression or extracellular matrix structure .
Our results suggest that food restriction could be investigated as a potential way of modulating plasticity .

[1916] The effects of surfactants on spilling breaking waves

Breaking waves markedly increase the rates of air-sea transfer of momentum , energy and mass .
In light to moderate wind conditions , spilling breakers with short wavelengths are observed frequently .
Theory and laboratory experiments have shown that , as these waves approach breaking in clean water , a ripple pattern that is dominated by surface tension forms at the crest .
Under laboratory conditions and in theory , the transition to turbulent flow is triggered by flow separation under the ripples , typically without leading to overturning of the free surface .
Water surfaces in nature , however , are typically contaminated by surfactant films that alter the surface tension and produce surface elasticity and viscosity .
Here we present the results of laboratory experiments in which spilling breaking waves were generated mechanically in water with a range of surfactant concentrations .
We find significant changes in the breaking process owing to surfactants .
At the highest concentration of surfactants , a small plunging jet issues from the front face of the wave at a point below the wave crest and entraps a pocket of air on impact with the front face of the wave .
The bubbles and turbulence created during this process are likely to increase air-sea transfer .

[1917] Inactivating alternative NADH dehydrogenases : enhancing fungal bioprocesses by improving growth and biomass yield ?

Debate still surrounds the physiological roles of the alternative respiratory enzymes found in many fungi and plants .
It has been proposed that alternative NADH : ubiquinone oxidoreductases ( NADH dehydrogenases ) may protect against oxidative stress , conversely , elevated activity of these enzymes has been linked to senescence .
Here we show that inhibition of these enzymes in a fungal protein expression system ( Aspergillus niger ) leads to significantly enhanced specific growth rate , substrate uptake , carbon dioxide evolution , higher protein content , and more efficient use of substrates .
These findings are consistent with a protective role of the NADH dehydrogenases against oxidative stress , thus , when electron flow via these enzymes is blocked , flux through the main respiratory pathway rises , leading to enhanced ATP generation .
We anticipate that our findings will stimulate further studies in fungal and plant cultures leading to significant improvements in these expression systems , and to deeper insights into the cellular roles of alternative respiration .

[1918] Exploiting diversity and synthetic biology for the production of algal biofuels

Modern life is intimately linked to the availability of fossil fuels , which continue to meet the world 's growing energy needs even though their use drives climate change , exhausts finite reserves and contributes to global political strife .
Biofuels made from renewable resources could be a more sustainable alternative , particularly if sourced from organisms , such as algae , that can be farmed without using valuable arable land .
Strain development and process engineering are needed to make algal biofuels practical and economically viable .

[1919] Effects of externally supplied protein on root morphology and biomass allocation in Arabidopsis

Growth , morphogenesis and function of roots are influenced by the concentration and form of nutrients present in soils , including low molecular mass inorganic N ( IN , ammonium , nitrate ) and organic N ( ON , e.g. amino acids ) .
Proteins , ON of high molecular mass , are prevalent in soils but their possible effects on roots have received little attention .
Here , we investigated how externally supplied protein of a size typical of soluble soil proteins influences root development of axenically grown Arabidopsis .
Addition of low to intermediate concentrations of protein ( bovine serum albumen , BSA ) to IN-replete growth medium increased root dry weight , root length and thickness , and root hair length .
Supply of higher BSA concentrations inhibited root development .
These effects were independent of total N concentrations in the growth medium .
The possible involvement of phytohormones was investigated using Arabidopsis with defective auxin ( tir1-1 and axr2-1 ) and ethylene ( ein2-1 ) responses .
That no phenotype was observed suggests a signalling pathway is operating independent of auxin and ethylene responses .
This study expands the knowledge on N form-explicit responses to demonstrate that ON of high molecular mass elicits specific responses .

[1920] Severe tissue damage in Atlantic cod larvae under increasing ocean acidification

Ocean acidification , caused by increasing atmospheric concentrations of CO2 ( refs , , ) , is one of the most critical anthropogenicthreats to marine life .
Changes in seawater carbonate chemistry have the potential to disturb calcification , acid-base regulation , blood circulation and respiration , as well as the nervous system of marine organisms , leading to long-term effects such as reduced growth rates and reproduction .
In teleost fishes , early life-history stages are particularly vulnerable as they lack specialized internal pH regulatory mechanisms .
So far , impacts of relevant CO2 concentrations on larval fish have been found in behaviour and otolith size , mainly in tropical , non-commercial species .
Here we show detrimental effects of ocean acidification on the development of a mass-spawning fish species of high commercial importance .
We reared Atlantic cod larvae at three levels of CO2 , ( 1 ) present day , ( 2 ) end of next century and ( 3 ) an extreme , coastal upwelling scenario , in a long-term ( months ) mesocosm experiment .
Exposure to CO2 resulted in severe to lethal tissue damage in many internal organs , with the degree of damage increasing with CO2 concentration .
As larval survival is the bottleneck to recruitment , ocean acidification has the potential to act as an additional source of natural mortality , affecting populations of already exploited fish stocks .

[1921] Sea-level fluctuations during the last glacial cycle

The last glacial cycle was characterized by substantial millennial-scale climate fluctuations , but the extent of any associated changes in global sea level ( or , equivalently , ice volume ) remains elusive .
Highstands of sea level can be reconstructed from dated fossil coral reef terraces , and these data are complemented by a compilation of global sea-level estimates based on deep-sea oxygen isotope ratios at millennial-scale resolution or higher .
Records based on oxygen isotopes , however , contain uncertainties in the range of + / -30 m , or + / -1 degreesC in deep sea temperature .
Here we analyse oxygen isotope records from Red Sea sediment cores to reconstruct the history of water residence times in the Red Sea .
We then use a hydraulic model of the water exchange between the Red Sea and the world ocean to derive the sill depth -- and hence global sea level -- over the past 470,000 years ( 470 kyr ) .
Our reconstruction is accurate to within + / -12 m , and gives a centennial-scale resolution from 70 to 25 kyr before present .
We find that sea-level changes of up to 35 m , at rates of up to 2 cm yr-1 , occurred , coincident with abrupt changes in climate .

[1922] Modelled suppression of boundary-layer clouds by plants in a CO2-rich atmosphere

Cumulus clouds in the atmospheric boundary layer play a key role in the hydrologic cycle , in the onset of severe weather by thunderstorms and in modulating Earth 's reflectivity and climate .
How these clouds respond to climate change , in particular over land , and how they interact with the carbon cycle are poorly understood .
It is expected that as a consequence of rising atmospheric CO2 concentrations the plant stomata will close , leading to lower latent heat fluxes and higher sensible heat fluxes .
Here we show that this causes a decline in boundary-layer cloud formation in middle latitudes .
This could be partly counteracted by the greater ability of a warmer atmosphere to take up water and by a growth in biomass due to CO2 fertilization .
Our results are based on a new soil-water-atmosphere-plant model supported by comprehensive observational evidence , from which we identify the dominant atmospheric responses to plant physiological processes .
They emphasize the intricate connection between biological and physical aspects of the climate system and the relevance of short-term and small-scale processes in establishing this connection .

[1923] Arsenic release from paddy soils during monsoon flooding

Bangladesh relies heavily on groundwater for the irrigation of dry-season rice .
However , the groundwater used for irrigation often contains high concentrations of arsenic , potentially jeopardizing the future of rice production in the country .
In seasonally flooded fields , topsoil arsenic concentrations decrease during the monsoon season , suggesting that flooding attenuates arsenic accumulation in the soils .
Here we examine the chemistry of soil porewater and floodwater during the monsoon season in rice paddies in Munshiganj , Bangladesh , to assess whether flooding releases significant quantities of arsenic from the soils .
We estimate that between 51 and 250 mg m-2 of soil arsenic is released into floodwater during the monsoon season .
This corresponds to a loss of 13-62 % of the arsenic added to soils through irrigation each year .
The arsenic was distributed throughout the entire floodwater column by vertical mixing and was laterally removed when the floodwater receded .
We conclude that monsoon floodwater removes a large amount of the arsenic added to paddy soils through irrigation , and suggest that non-flooded soils are particularly at risk of arsenic accumulation .

[1924] Determining the natural length of the current interglacial

No glacial inception is projected to occur at the current atmospheric CO2 concentrations of 390 ppmv ( ref . )
.
Indeed , model experiments suggest that in the current orbital configuration -- which is characterized by a weak minimum in summer insolation -- glacial inception would require CO2 concentrations below preindustrial levels of 280 ppmv ( refs , , ) .
However , the precise CO2 threshold as well as the timing of the hypothetical next glaciation remain unclear .
Past interglacials can be used to draw analogies with the present , provided their duration is known .
Here we propose that the minimum age of a glacial inception is constrained by the onset of bipolar-seesaw climate variability , which requires ice-sheets large enough to produce iceberg discharges that disrupt the ocean circulation .
We identify the bipolar seesaw in ice-core and North Atlantic marine records by the appearance of a distinct phasing of interhemispheric climate and hydrographic changes and ice-rafted debris .
The glacial inception during Marine Isotope sub-Stage 19c , a close analogue for the present interglacial , occurred near the summer insolation minimum , suggesting that the interglacial was not prolonged by subdued radiative forcing .
Assuming that ice growth mainly responds to insolation and CO2 forcing , this analogy suggests that the end of the current interglacial would occur within the next 1500 years , if atmospheric CO2 concentrations did not exceed 240 + / -5 ppmv .

[1925] Response of soil respiration and ecosystem carbon budget to vegetation removal in Eucalyptus plantations with contrasting ages

Reforested plantations have substantial effects on terrestrial carbon cycling due to their large coverage area .
Although understory plants are important components of reforested plantations , their effects on ecosystem carbon dynamics remain unclear .
This study was designed to investigate the effects of vegetation removal/understory removal and tree girdling on soil respiration and ecosystem carbon dynamics in Eucalyptus plantations of South China with contrasting ages ( 2 and 24 years old ) .
We conducted a field manipulation experiment from 2008 to 2009 .
Understory removal reduced soil respiration in both plantations , whereas tree girdling decreased soil respiration only in the 2-year-old plantations .
The net ecosystem production was approximately three times greater in the 2-year-old plantations ( 13.4 t C ha-1 yr-1 ) than in the 24-year-old plantations ( 4.2 t C h-1 yr-1 ) .
The biomass increase of understory plants was 12.6 t ha-1 yr-1 in the 2-year-old plantations and 2.9 t ha-1 yr-1 in the 24-year-old plantations , accounting for 33.9 % and 14.1 % of the net primary production , respectively .
Our findings confirm the ecological importance of understory plants in subtropical plantations based on the 2 years of data .
These results also indicate that Eucalyptus plantations in China may be an important carbon sink due to the large plantation area .

[1926] Earthquake-induced changes in a hydrothermal system on the Juan de Fuca mid-ocean ridge

Hydrothermal vents on mid-ocean ridges of the northeast Pacific Ocean are known to respond to seismic disturbances , with observed changes in vent temperature .
But these disturbances resulted from submarine volcanic activity ; until now , there have been no observations of the response of a vent system to non-magmatic , tectonic events .
Here we report measurements of hydrothermal vent temperature from several vents on the Juan de Fuca ridge in June 1999 , before , during and after an earthquake swarm of apparent tectonic origin .
Vent fluid temperatures began to rise 4-11 days after the first earthquake .
Following this initial increase , the vent temperatures oscillated for about a month before settling down to higher values .
We also observed a tenfold increase in fluid output from the hydrothermal system over a period of at least 80 days , extending along the entire ridge segment .
Such a large , segment-wide thermal response to relatively modest tectonic activity is surprising , and raises questions about the sources of excess heat and fluid , and the possible effect on vent biological communities .

[1927] Pattern formation at multiple spatial scales drives the resilience of mussel bed ecosystems

Self-organized complexity at multiple spatial scales is a distinctive characteristic of biological systems .
Yet , little is known about how different self-organizing processes operating at different spatial scales interact to determine ecosystem functioning .
Here we show that the interplay between self-organizing processes at individual and ecosystem level is a key determinant of the functioning and resilience of mussel beds .
In mussel beds , self-organization generates spatial patterns at two characteristic spatial scales : small-scale net-shaped patterns due to behavioural aggregation of individuals , and large-scale banded patterns due to the interplay of between-mussel facilitation and resource depletion .
Model analysis reveals that the interaction between these behavioural and ecosystem-level mechanisms increases mussel bed resilience , enables persistence under deteriorating conditions and makes them less prone to catastrophic collapse .
Our analysis highlights that interactions between different forms of self-organization at multiple spatial scales may enhance the intrinsic ability of ecosystems to withstand both natural and human-induced disturbances .

[1928] Modelling West Antarctic ice sheet growth and collapse through the past five million years

The West Antarctic ice sheet ( WAIS ) , with ice volume equivalent to ~ 5 m of sea level , has long been considered capable of past and future catastrophic collapse .
Today , the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams .
Grounding lines are several hundred metres below sea level and the bed deepens upstream , raising the prospect of runaway retreat .
Projections of future WAIS behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms .
Its variation since the Last Glacial Maximum is best known , with grounding lines advancing to the continental-shelf edges around ~ 15 kyr ago before retreating to near-modern locations by ~ 3 kyr ago .
Prior collapses during the warmth of the early Pliocene epoch and some Pleistocene interglacials have been suggested indirectly from records of sea level and deep-sea-core isotopes , and by the discovery of open-ocean diatoms in subglacial sediments .
Until now , however , little direct evidence of such behaviour has been available .
Here we use a combined ice sheet/ice shelf model capable of high-resolution nesting with a new treatment of grounding-line dynamics and ice-shelf buttressing to simulate Antarctic ice sheet variations over the past five million years .
Modelled WAIS variations range from full glacial extents with grounding lines near the continental shelf break , intermediate states similar to modern , and brief but dramatic retreats , leaving only small , isolated ice caps on West Antarctic islands .
Transitions between glacial , intermediate and collapsed states are relatively rapid , taking one to several thousand years .
Our simulation is in good agreement with a new sediment record ( ANDRILL AND-1B ) recovered from the western Ross Sea , indicating a long-term trend from more frequently collapsed to more glaciated states , dominant 40-kyr cyclicity in the Pliocene , and major retreats at marine isotope stage 31 ( ~ 1.07 Myr ago ) and other super-interglacials .

[1929] Muted change in Atlantic overturning circulation over some glacial-aged Heinrich events

Heinrich events -- surges of icebergs into the North Atlantic Ocean -- punctuated the last glacial period .
The events are associated with millennial-scale cooling in the Northern Hemisphere .
Fresh water from the melting icebergs is thought to have interrupted the Atlantic meridional overturning circulation , thus minimizing heat transport into the northern North Atlantic .
The northward flow of warm water passes through the Florida Straits and is reflected in the distribution of seawater properties in this region .
Here we investigate the northward flow through this region over the past 40,000 years using oxygen isotope measurements of benthic foraminifera from two cores on either side of the Florida Straits .
These measurements allow us to estimate water density , which is related to flow through the thermal wind balance .
We infer a substantial reduction of flow during Heinrich Event 1 and the Younger Dryas cooling , but little change during Heinrich Events 2 and 3 , which occurred during an especially cold phase of the last glacial period .
We speculate that because glacial circulation was already weakened before the onset of Heinrich Events 2 and 3 , freshwater forcing had little additional effect .
However , low-latitude climate perturbations were observed during all events .
We therefore suggest that these perturbations may not have been directly caused by changes in heat transport associated with Atlantic overturning circulation as commonly assumed .

[1930] Effect of oxygen minimum zone formation on communities of marine protists

Changes in ocean temperature and circulation patterns compounded by human activities are leading to oxygen minimum zone ( OMZ ) expansion with concomitant alteration in nutrient and climate active trace gas cycling .
Here , we report the response of microbial eukaryote populations to seasonal changes in water column oxygen-deficiency using Saanich Inlet , a seasonally anoxic fjord on the coast of Vancouver Island British Columbia , as a model ecosystem .
We combine small subunit ribosomal RNA gene sequencing approaches with multivariate statistical methods to reveal shifts in operational taxonomic units during successive stages of seasonal stratification and renewal .
A meta-analysis is used to identify common and unique patterns of community composition between Saanich Inlet and the anoxic/sulfidic Cariaco Basin ( Venezuela ) and Framvaren Fjord ( Norway ) to show shared and unique responses of microbial eukaryotes to oxygen and sulfide in these three environments .
Our analyses also reveal temporal fluctuations in rare populations of microbial eukaryotes , particularly anaerobic ciliates , that may be of significant importance to the biogeochemical cycling of methane in OMZs .

[1931] Climate change : The carbon equation

What will happen to the increasing amounts of carbon being emitted into the atmosphere in the form of CO2 ?
The question is a pressing one , both politically and economically , given the international endeavour to reduce emissions of CO2and minimize the consequent predicted warming .
Models of the effects of environmental change on carbon balance in the oceans and on land , running into the middle of the next century , provide new estimates of the CO2flux in both cases .
Not only do these modelled fluxes differ from those used as base cases at present , but the approaches used highlight the differences , and respective shortcomings , in models of marine and terrestrial processes .

[1932] Carbon sequestration activated by a volcanic CO2 pulse during Ocean Anoxic Event 2

The Cretaceous Ocean Anoxic Event 2 ( about 94 million years ago ) is thought to be linked to extensive volcanism , which triggered a biogeochemical chain of events that eventually led to widespread marine anoxia and a remarkable increase in carbon burial in marine sediments .
It has been suggested that the event was accompanied by a substantial decrease in atmospheric CO2 concentrations , but the quantification of the drawdown remains controversial .
Here we reconstruct atmospheric CO2 concentrations throughout the ocean anoxic event from counts of the stomata in fossil leaves , and use terrestrial carbon isotopes to link the reconstruction to marine records of the event .
We find that before the onset of ocean anoxia , atmospheric CO2 concentrations increased by 20 % over background levels of 370 +100 / -70 ppm .
This was part of a long-term rise in atmospheric CO2 levels , presumably caused by volcanism , which reached a peak of 500 +400 / -180 ppm .
However , two pulses of extensive carbon burial during the ocean anoxic event , as indicated by positive carbon isotope excursions , are associated with decreased atmospheric CO2 concentrations .
We conclude that the sequestration of marine organic carbon led to a decrease in atmospheric CO2 concentration of up to 26 % during Ocean Anoxic Event 2 .

[1933] Quorum sensing-regulated chitin metabolism provides grazing resistance to Vibrio cholerae biofilms

Association of Vibrio cholerae with chitinous surfaces of zooplankton is important for its persistence in marine environments , as it provides accessibility to nutrients and resistance to stresses .
Predation by heterotrophic protists has a major impact on the survival of V. cholerae .
V. cholerae forms biofilms as its main defensive strategy , and quorum sensing ( QS ) additionally regulates the production of antiprotozoal factors .
The role of chitin and QS regulation in V. cholerae grazing resistance was investigated by exposing V. cholerae wild-type ( WT ) and QS mutant biofilms grown on chitin flakes to the bacteriotrophic , surface-feeding flagellate Rhynchomonas nasuta .
V. cholerae formed more biofilm biomass on chitin flakes compared with nonchitinous surfaces .
The growth of R. nasuta was inhibited by WT biofilms grown on chitin flakes , whereas the inhibition was attenuated in QS mutant biofilms .
The chitin-dependent toxicity was also observed when the V. cholerae biofilms were developed under continuous flow or grown on a natural chitin source , the exoskeleton of Artemia .
In addition , the antiprotozoal activity and ammonium concentration of V. cholerae biofilm supernatants were quantified .
The ammonium levels ( 3.5 mM ) detected in the supernatants of V. cholerae WT biofilms grown on chitin flakes were estimated to reduce the number of R. nasuta by > 80 % in add-back experiments , and the supernatant of QS mutant biofilms was less toxic owing to a decrease in ammonium production .
Transcriptomic analysis revealed that the majority of genes involved in chitin metabolism and chemotaxis were significantly downregulated in QS mutant biofilms when grown on chitin compared with the WT biofilms .
The ISME Journal advance online publication , 23 January 2015 ; doi :10.1038 / ismej .2014.265

[1934] Increased seasonality in Middle East temperatures during the last interglacial period

The last interglacial period ( about 125,000 years ago ) is thought to have been at least as warm as the present climate .
Owing to changes in the Earth 's orbit around the Sun , it is thought that insolation in the Northern Hemisphere varied more strongly than today on seasonal timescales , which would have led to corresponding changes in the seasonal temperature cycle .
Here we present seasonally resolved proxy records using corals from the northernmost Red Sea , which record climate during the last interglacial period , the late Holocene epoch and the present .
We find an increased seasonality in the temperature recorded in the last interglacial coral .
Today , climate in the northern Red Sea is sensitive to the North Atlantic Oscillation , a climate oscillation that strongly influences winter temperatures and precipitation in the North Atlantic region .
From our coral records and simulations with a coupled atmosphere-ocean circulation model , we conclude that a tendency towards the high-index state of the North Atlantic Oscillation during the last interglacial period , which is consistent with European proxy records , contributed to the larger amplitude of the seasonal cycle in the Middle East .

[1935] Systems-wide temporal proteomic profiling in glucose-starved Bacillus subtilis

Functional genomics of the Gram-positive model organism Bacillus subtilis reveals valuable insights into basic concepts of cell physiology .
In this study , we monitor temporal changes in the proteome , transcriptome and extracellular metabolome of B. subtilis caused by glucose starvation .
For proteomic profiling , a combination of in vivo metabolic labelling and shotgun mass spectrometric analysis was carried out for five different proteomic subfractions ( cytosolic , integral membrane , membrane , surface and extracellular proteome fraction ) , leading to the identification of ~ 52 % of the predicted proteome of B. subtilis .
Quantitative proteomic and corresponding transcriptomic data were analysed with Voronoi treemaps linking functional classification and relative expression changes of gene products according to their fate in the stationary phase .
The obtained data comprise the first comprehensive profiling of changes in the membrane subfraction and allow in-depth analysis of major physiological processes , including monitoring of protein degradation .

[1936] Coupling of surface temperatures and atmospheric CO2 concentrations during the Palaeozoic era

Atmospheric carbon dioxide concentrations seem to have been several times modern levels during much of the Palaeozoic era ( 543-248 million years ago ) , but decreased during the Carboniferous period to concentrations similar to that of today .
Given that carbon dioxide is a greenhouse gas , it has been proposed that surface temperatures were significantly higher during the earlier portions of the Palaeozoic era .
A reconstruction of tropical sea surface temperatures based on the delta18O of carbonate fossils indicates , however , that the magnitude of temperature variability throughout this period was small , suggesting that global climate may be independent of variations in atmospheric carbon dioxide concentration .
Here we present estimates of sea surface temperatures that were obtained from fossil brachiopod and mollusc shells using the ` carbonate clumped isotope ' method -- an approach that , unlike the delta18O method , does not require independent estimates of the isotopic composition of the Palaeozoic ocean .
Our results indicate that tropical sea surface temperatures were significantly higher than today during the Early Silurian period ( 443-423 Myr ago ) , when carbon dioxide concentrations are thought to have been relatively high , and were broadly similar to today during the Late Carboniferous period ( 314-300 Myr ago ) , when carbon dioxide concentrations are thought to have been similar to the present-day value .
Our results are consistent with the proposal that increased atmospheric carbon dioxide concentrations drive or amplify increased global temperatures .

[1937] Optogenetic characterization methods overcome key challenges in synthetic and systems biology

Systems biologists aim to understand how organism-level processes , such as differentiation and multicellular development , are encoded in DNA .
Conversely , synthetic biologists aim to program systems-level biological processes , such as engineered tissue growth , by writing artificial DNA sequences .
To achieve their goals , these groups have adapted a hierarchical electrical engineering framework that can be applied in the forward direction to design complex biological systems or in the reverse direction to analyze evolved networks .
Despite much progress , this framework has been limited by an inability to directly and dynamically characterize biological components in the varied contexts of living cells .
Recently , two optogenetic methods for programming custom gene expression and protein localization signals have been developed and used to reveal fundamentally new information about biological components that respond to those signals .
This basic dynamic characterization approach will be a major enabling technology in synthetic and systems biology .

[1938] Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum

The Palaeocene/Eocene thermal maximum , ~ 55 million years ago , was a brief period of widespread , extreme climatic warming , that was associated with massive atmospheric greenhouse gas input .
Although aspects of the resulting environmental changes are well documented at low latitudes , no data were available to quantify simultaneous changes in the Arctic region .
Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition .
We show that sea surface temperatures near the North Pole increased from ~ 18 degreesC to over 23 degreesC during this event .
Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming .
At the same time , sea level rose while anoxic and euxinic conditions developed in the ocean 's bottom waters and photic zone , respectively .
Increasing temperature and sea level match expectations based on palaeoclimate model simulations , but the absolute polar temperatures that we derive before , during and after the event are more than 10 degreesC warmer than those model-predicted .
This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms -- perhaps polar stratospheric clouds or hurricane-induced ocean mixing -- to amplify early Palaeogene polar temperatures .

[1939] Positive interactions among alpine plants increase with stress

Plants can have positive effects on each other .
For example , the accumulation of nutrients , provision of shade , amelioration of disturbance , or protection from herbivores by some species can enhance the performance of neighbouring species .
Thus the notion that the distributions and abundances of plant species are independent of other species may be inadequate as a theoretical underpinning for understanding species coexistence and diversity .
But there have been no large-scale experiments designed to examine the generality of positive interactions in plant communities and their importance relative to competition .
Here we show that the biomass , growth and reproduction of alpine plant species are higher when other plants are nearby .
In an experiment conducted in subalpine and alpine plant communities with 115 species in 11 different mountain ranges , we find that competition generally , but not exclusively , dominates interactions at lower elevations where conditions are less physically stressful .
In contrast , at high elevations where abiotic stress is high the interactions among plants are predominantly positive .
Furthermore , across all high and low sites positive interactions are more important at sites with low temperatures in the early summer , but competition prevails at warmer sites .

[1940] Assessment of the temperature effect on childhood diarrhea using satellite imagery

A quasi-Poisson generalized linear model combined with a distributed lag non-linear model was used to quantify the main effect of temperature on emergency department visits ( EDVs ) for childhood diarrhea in Brisbane from 2001 to 2010 .
Residual of the model was checked to examine whether there was an added effect due to heat waves .
The change over time in temperature-diarrhea relation was also assessed .
Both low and high temperatures had significant impact on childhood diarrhea .
Heat waves had an added effect on childhood diarrhea , and this effect increased with intensity and duration of heat waves .
There was a decreasing trend in the main effect of heat on childhood diarrhea in Brisbane across the study period .
Brisbane children appeared to have gradually adapted to mild heat , but they are still very sensitive to persistent extreme heat .
Development of future heat alert systems should take the change in temperature-diarrhea relation over time into account .

[1941] Diverse and divergent protein post-translational modifications in two growth stages of a natural microbial community

Detailed characterization of post-translational modifications ( PTMs ) of proteins in microbial communities remains a significant challenge .
Here we directly identify and quantify a broad range of PTMs ( hydroxylation , methylation , citrullination , acetylation , phosphorylation , methylthiolation , S-nitrosylation and nitration ) in a natural microbial community from an acid mine drainage site .
Approximately 29 % of the identified proteins of the dominant Leptospirillum group II bacteria are modified , and 43 % of modified proteins carry multiple PTM types .
Most PTM events , except S-nitrosylations , have low fractional occupancy .
Notably , PTM events are detected on Cas proteins involved in antiviral defense , an aspect of Cas biochemistry not considered previously .
Further , Cas PTM profiles from Leptospirillum group II differ in early versus mature biofilms .
PTM patterns are divergent on orthologues of two closely related , but ecologically differentiated , Leptospirillum group II bacteria .
Our results highlight the prevalence and dynamics of PTMs of proteins , with potential significance for ecological adaptation and microbial evolution .

[1942] Reorganization of the western Himalayan river system after five million years ago

Uplift of mountains driven by tectonic forces can influence regional climate as well as regional drainage patterns , which in turn control the discharge of eroded sediment to the ocean .
But the nature of the interactions between tectonic forces , climate and drainage evolution remains contested .
Here we reconstruct the erosional discharge from the Indus river over the past 30 million years using seismic reflection data obtained from drill core samples from the Arabian Sea and neodymium isotope data .
We find that the source of the Indus sediments was dominated by erosion within and north of the Indus suture zone until five million years ago ; after that , the river began to receive more erosional products from Himalayan sources .
We propose that this change in the erosional pattern is caused by a rerouting of the major rivers of the Punjab into the Indus , which flowed east into the Ganges river before that time .
Seismic reflection profiles from the Indus fan suggest high mass accumulation rates during the Pleistocene epoch partly driven by increased drainage to the Indus river after five million years ago and partly by faster erosion linked to a stronger monsoon over the past four million years .
Our isotope stratigraphy for the Indus fan provides strong evidence for a significant change in the geometry of western Himalayan river systems in the recent geologic past .

[1943] Sea-level and deep-sea-temperature variability over the past 5.3 million years

Ice volume ( and hence sea level ) and deep-sea temperature are key measures of global climate change .
Sea level has been documented using several independent methods over the past 0.5 million years ( Myr ) .
Older periods , however , lack such independent validation ; all existing records are related to deep-sea oxygen isotope ( delta18O ) data that are influenced by processes unrelated to sea level .
For deep-sea temperature , only one continuous high-resolution ( Mg/Ca-based ) record exists , with related sea-level estimates , spanning the past 1.5 Myr .
Here we present a novel sea-level reconstruction , with associated estimates of deep-sea temperature , which independently validates the previous 0-1 .5 Myr reconstruction and extends it back to 5.3 Myr ago .
We find that deep-sea temperature and sea level generally decreased through time , but distinctly out of synchrony , which is remarkable given the importance of ice-albedo feedbacks on the radiative forcing of climate .
In particular , we observe a large temporal offset during the onset of Plio-Pleistocene ice ages , between a marked cooling step at 2.73 Myr ago and the first major glaciation at 2.15 Myr ago .
Last , we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep-sea temperature .

[1944] Increase in African dust flux at the onset of commercial agriculture in the Sahel region

The Sahara Desert is the largest source of mineral dust in the world .
Emissions of African dust increased sharply in the early 1970s ( ref .
2 ) , a change that has been attributed mainly to drought in the Sahara/Sahel region caused by changes in the global distribution of sea surface temperature .
The human contribution to land degradation and dust mobilization in this region remains poorly understood , owing to the paucity of data that would allow the identification of long-term trends in desertification .
Direct measurements of airborne African dust concentrations only became available in the mid-1960s from a station on Barbados and subsequently from satellite imagery since the late 1970s : they do not cover the onset of commercial agriculture in the Sahel region ~ 170 years ago .
Here we construct a 3,200-year record of dust deposition off northwest Africa by investigating the chemistry and grain-size distribution of terrigenous sediments deposited at a marine site located directly under the West African dust plume .
With the help of our dust record and a proxy record for West African precipitation we find that , on the century scale , dust deposition is related to precipitation in tropical West Africa until the seventeenth century .
At the beginning of the nineteenth century , a sharp increase in dust deposition parallels the advent of commercial agriculture in the Sahel region .
Our findings suggest that human-induced dust emissions from the Sahel region have contributed to the atmospheric dust load for about 200 years .

[1945] Interplay between the Westerlies and Asian monsoon recorded in Lake Qinghai sediments since 32 ka

Two atmospheric circulation systems , the mid-latitude Westerlies and the Asian summer monsoon ( ASM ) , play key roles in northern-hemisphere climatic changes .
However , the variability of the Westerlies in Asia and their relationship to the ASM remain unclear .
Here , we present the longest and highest-resolution drill core from Lake Qinghai on the northeastern Tibetan Plateau ( TP ) , which uniquely records the variability of both the Westerlies and the ASM since 32 ka , reflecting the interplay of these two systems .
These records document the anti-phase relationship of the Westerlies and the ASM for both glacial-interglacial and glacial millennial timescales .
During the last glaciation , the influence of the Westerlies dominated ; prominent dust-rich intervals , correlated with Heinrich events , reflect intensified Westerlies linked to northern high-latitude climate .
During the Holocene , the dominant ASM circulation , punctuated by weak events , indicates linkages of the ASM to orbital forcing , North Atlantic abrupt events , and perhaps solar activity changes .

[1946] Phosphorus supply drives rapid turnover of membrane phospholipids in the diatom Thalassiosira pseudonana

In low-phosphorus ( P ) marine systems , phytoplankton replace membrane phospholipids with non-phosphorus lipids , but it is not known how rapidly this substitution occurs .
Here , when cells of the model diatom Thalassiosira pseudonana were transferred from P-replete medium to P-free medium , the phospholipid content of the cells rapidly declined within 48 h from 45 + / -0.9 to 21 + / -4.5 % of the total membrane lipids ; the difference was made up by non-phosphorus lipids .
Conversely , when P-limited T. pseudonana were resupplied with P , cells reduced the percentage of their total membrane lipids contributed by a non-phosphorus lipid from 43 + / -1.5 to 7.3 + / -0.9 % within 24 h , whereas the contribution by phospholipids rose from 2.2 + / -0.1 to 44 + / -3 % .
This dynamic phospholipid reservoir contained sufficient P to synthesize multiple haploid genomes , suggesting that phospholipid turnover could be an important P source for cells .
Field observations of phytoplankton lipid content may thus reflect short-term changes in P supply and cellular physiology , rather than simply long-term adjustment to the environment .

[1947] Genomic versatility and functional variation between two dominant heterotrophic symbionts of deep-sea Osedax worms

An unusual symbiosis , first observed at ~ 3000 m depth in the Monterey Submarine Canyon , involves gutless marine polychaetes of the genus Osedax and intracellular endosymbionts belonging to the order Oceanospirillales .
Ecologically , these worms and their microbial symbionts have a substantial role in the cycling of carbon from deep-sea whale fall carcasses .
Microheterogeneity exists among the Osedax symbionts examined so far , and in the present study the genomes of the two dominant symbionts , Rs1 and Rs2 , were sequenced .
The genomes revealed heterotrophic versatility in carbon , phosphate and iron uptake , strategies for intracellular survival , evidence for an independent existence , and numerous potential virulence capabilities .
The presence of specific permeases and peptidases ( of glycine , proline and hydroxyproline ) , and numerous peptide transporters , suggests the use of degraded proteins , likely originating from collagenous bone matter , by the Osedax symbionts .
13C tracer experiments confirmed the assimilation of glycine/proline , as well as monosaccharides , by Osedax .
The Rs1 and Rs2 symbionts are genomically distinct in carbon and sulfur metabolism , respiration , and cell wall composition , among others .
Differences between Rs1 and Rs2 and phylogenetic analysis of chemotaxis-related genes within individuals of symbiont Rs1 revealed the influence of the relative age of the whale fall environment and support possible local niche adaptation of ` free-living ' lifestages .
Future genomic examinations of other horizontally-propogated intracellular symbionts will likely enhance our understanding of the contribution of intraspecific symbiont diversity to the ecological diversification of the intact association , as well as the maintenance of host diversity .

[1948] Hybridization may facilitate in situ survival of endemic species through periods of climate change

Predicting survival and extinction scenarios for climate change requires an understanding of the present day ecological characteristics of species and future available habitats , but also the adaptive potential of species to cope with environmental change .
Hybridization is one mechanism that could facilitate this .
Here we report statistical evidence that the transfer of genetic information through hybridization is a feature of species from the plant genus Pachycladon that survived the Last Glacial Maximum in geographically separated alpine refugia in New Zealand 's South Island .
We show that transferred glucosinolate hydrolysis genes also exhibit evidence of intra-locus recombination .
Such gene exchange and recombination has the potential to alter the chemical defence in the offspring of hybridizing species .
We use a mathematical model to show that when hybridization increases the adaptive potential of species , future biodiversity will be best protected by preserving closely related species that hybridize rather than by conserving distantly related species that are genetically isolated .

[1949] Fossil pollen records reveal a late rise of open-habitat ecosystems in Patagonia

The timing of major turnovers in terrestrial ecosystems of the Cenozoic Era has been largely interpreted from the analysis of the assumed feeding preference of extinct mammals .
For example , the expansion of open-habitat ecosystems ( grasslands or savannas ) is inferred to have occurred earlier in Patagonia than elsewhere because of the early advent of high-crowned teeth ( hypsodont ) mammals ~ 26 Ma ago .
However , the plant fossil record from Patagonia implies another evolutionary scenario .
Here we show that the dominance of key open-habitat species -- amaranths , Ephedra , asters and grasses -- occurred during the last 10 Ma , about 15 Ma later than previously inferred using feeding/habitat ecology of extinct mammals .
This late rise of open-landscapes in southern South America brings into question whether the expansion of open-habitat vegetation could have been the prime factor of high-crowned mammal diversification .

[1950] Yersinia pestis infection and laboratory conditions alter flea-associated bacterial communities

We collected Oropsylla montana from rock squirrels , Spermophilus varigatus , and infected a subset of collected fleas with Yersinia pestis , the etiological agent of plague .
We used bar-tagged DNA pyrosequencing to characterize bacterial communities of wild , uninfected controls and infected fleas .
Bacterial communities within Y. pestis-infected fleas were substantially more similar to one another than communities within wild or control fleas , suggesting that infection alters the bacterial community in a directed manner such that specific bacterial lineages are severely reduced in abundance or entirely eliminated from the community .
Laboratory conditions also significantly altered flea-associated bacterial communities relative to wild communities , but much less so than Y. pestis infection .
The abundance of Firmicutes decreased considerably in infected fleas , and Bacteroidetes were almost completely eliminated from both the control and infected fleas .
Bartonella and Wolbachia were unaffected or responded positively to Y. pestis infection .

[1951] Predator diversity dampens trophic cascades

Food web complexity is thought to weaken the strength of terrestrial trophic cascades in which strong impacts of natural enemies on herbivores cascade to influence primary production indirectly .
Predator diversity can enhance food web complexity because predators may feed on each other and on shared prey .
In such cases , theory suggests that the impact of predation on herbivores relaxes and cascading effects on basal resources are dampened .
Despite this view , no empirical studies have explicitly investigated the role of predator diversity in mediating primary productivity in a natural terrestrial system .
Here we compare , in a coastal marsh community , impacts of arthropod predators on herbivores and plant productivity between a simple food web with a single predator species and a complex food web with a diverse predator assemblage .
We show that enhancing predator diversity dampens enemy effects on herbivores and weakens trophic cascades .
Consequently , changes in diversity at higher trophic levels can significantly alter ecosystem function in natural systems .

[1952] Fisheries : Climate variability and North Sea cod

The stock of North Sea cod is under pressure because of overfishing , and we show here that it is also threatened by a decline in the production of young cod that has paralleled warming of the North Sea over the past ten years .
The combination of a diminished stock and the possible persistence of adverse warm conditions is endangering the long-term sustainability of cod in the North Sea .
To decrease the risk of collapse , fishing pressure must be reduced .

[1953] Island biogeography of the Anthropocene

For centuries , biogeographers have examined the factors that produce patterns of biodiversity across regions .
The study of islands has proved particularly fruitful and has led to the theory that geographic area and isolation influence species colonization , extinction and speciation such that larger islands have more species and isolated islands have fewer species ( that is , positive species-area and negative species-isolation relationships ) .
However , experimental tests of this theory have been limited , owing to the difficulty in experimental manipulation of islands at the scales at which speciation and long-distance colonization are relevant .
Here we have used the human-aided transport of exotic anole lizards among Caribbean islands as such a test at an appropriate scale .
In accord with theory , as anole colonizations have increased , islands impoverished in native species have gained the most exotic species , the past influence of speciation on island biogeography has been obscured , and the species-area relationship has strengthened while the species-isolation relationship has weakened .
Moreover , anole biogeography increasingly reflects anthropogenic rather than geographic processes .
Unlike the island biogeography of the past that was determined by geographic area and isolation , in the Anthropocene -- an epoch proposed for the present time interval -- island biogeography is dominated by the economic isolation of human populations .

[1954] Archaea of the Miscellaneous Crenarchaeotal Group are abundant , diverse and widespread in marine sediments

Members of the highly diverse Miscellaneous Crenarchaeotal Group ( MCG ) are globally distributed in various marine and continental habitats .
In this study , we applied a polyphasic approach ( rRNA slot blot hybridization , quantitative PCR ( qPCR ) and catalyzed reporter deposition FISH ) using newly developed probes and primers for the in situ detection and quantification of MCG crenarchaeota in diverse types of marine sediments and microbial mats .
In general , abundance of MCG ( cocci , 0.4 mum ) relative to other archaea was highest ( 12-100 % ) in anoxic , low-energy environments characterized by deeper sulfate depletion and lower microbial respiration rates ( P = 0.06 for slot blot and P = 0.05 for qPCR ) .
When studied in high depth resolution in the White Oak River estuary and Hydrate Ridge methane seeps , changes in MCG abundance relative to total archaea and MCG phylogenetic composition did not correlate with changes in sulfate reduction or methane oxidation with depth .
In addition , MCG abundance did not vary significantly ( P > 0.1 ) between seep sites ( with high rates of methanotrophy ) and non-seep sites ( with low rates of methanotrophy ) .
This suggests that MCG are likely not methanotrophs .
MCG crenarchaeota are highly diverse and contain 17 subgroups , with a range of intragroup similarity of 82 to 94 % .
This high diversity and widespread distribution in subsurface sediments indicates that this group is globally important in sedimentary processes .

[1955] An arbuscular mycorrhizal fungus accelerates decomposition and acquires nitrogen directly from organic material

Arbuscular mycorrhizal fungi ( order Glomales ) , which form mycorrhizal symbioses with two out of three of all plant species , are believed to be obligate biotrophs that are wholly dependent on the plant partner for their carbon supply .
It is thought that they possess no degradative capability and that they are unable to decompose complex organic molecules , the form in which most soil nutrients occur .
Earlier suggestions that they could exist saprotrophically were based on observation of hyphal proliferation on organic materials .
In contrast , other mycorrhizal types have been shown to acquire nitrogen directly from organic sources .
Here we show that the arbuscular mycorrhizal symbiosis can both enhance decomposition of and increase nitrogen capture from complex organic material ( grass leaves ) in soil .
Hyphal growth of the fungal partner was increased in the presence of the organic material , independently of the host plant .

[1956] Human impacts drive a global topographic signature in tree cover

The Anthropocene is a geological epoch marked by major human influences on processes in the atmosphere , biosphere , hydrosphere and geosphere .
One of the most dramatic features of the Anthropocene is the massive alteration of the Earth 's vegetation , including forests .
Here we investigate the role of topography in shaping human impacts on tree cover from local to global scales .
We show that human impacts have resulted in a global tendency for tree cover to be constrained to sloped terrain and losses to be concentrated on flat terrain .
This effect increases in strength with increasing human pressure and is most pronounced in countries with rapidly growing economies , limited human population stress and highly effective governments .
These patterns likely reflect the relative inaccessibility of sloped topography and have important implications for conservation and modelling of future tree cover .

[1957] Reprograming of gut microbiome energy metabolism by the FUT2 Crohn 's disease risk polymorphism

Fucosyltransferase 2 ( FUT2 ) is an enzyme that is responsible for the synthesis of the H antigen in body fluids and on the intestinal mucosa .
The H antigen is an oligosaccharide moiety that acts as both an attachment site and carbon source for intestinal bacteria .
Non-secretors , who are homozygous for the loss-of-function alleles of FUT2 gene ( sese ) , have increased susceptibility to Crohn 's disease ( CD ) .
To characterize the effect of FUT2 polymorphism on the mucosal ecosystem , we profiled the microbiome , meta-proteome and meta-metabolome of 75 endoscopic lavage samples from the cecum and sigmoid of 39 healthy subjects ( 12 SeSe , 18 Sese and 9 sese ) .
Imputed metagenomic analysis revealed perturbations of energy metabolism in the microbiome of non-secretor and heterozygote individuals , notably the enrichment of carbohydrate and lipid metabolism , cofactor and vitamin metabolism and glycan biosynthesis and metabolism-related pathways , and the depletion of amino-acid biosynthesis and metabolism .
Similar changes were observed in mice bearing the FUT2 - / - genotype .
Metabolomic analysis of human specimens revealed concordant as well as novel changes in the levels of several metabolites .
Human metaproteomic analysis indicated that these functional changes were accompanied by sub-clinical levels of inflammation in the local intestinal mucosa .
Therefore , the colonic microbiota of non-secretors is altered at both the compositional and functional levels , affecting the host mucosal state and potentially explaining the association of FUT2 genotype and CD susceptibility .

[1958] Oceanic nitrogen reservoir regulated by plankton diversity and ocean circulation

The average nitrogen-to-phosphorus ratio of marine phytoplankton ( 16N :1 P ) is closely matched to the nutrient content of mean ocean waters ( 14.3 N :1 P ) .
This condition is thought to arise from biological control over the ocean 's nitrogen budget , in which removal of bioavailable nitrogen by denitrifying bacteria ensures widespread selection for diazotrophic phytoplankton that replenish this essential nutrient when it limits the growth of other species .
Here we show that in the context of a realistic ocean circulation model , and a uniform N :P ratio of plankton biomass , this feedback mechanism yields an oceanic nitrate deficit more than double its observed value .
The critical missing phenomenon is diversity in the metabolic N :P requirement of phytoplankton , which has recently been shown to exhibit large-scale patterns associated with species composition .
When we model these variations , such that diazotrophs compete with high N :P communities in subtropical regions , the ocean nitrogen inventory rises and may even exceed the average N :P ratio of plankton .
The latter condition , previously considered impossible , is prevented in the modern ocean by shallow circulations that communicate stoichiometric signals from remote biomes dominated by diatoms with low N :P ratios .
Large-scale patterns of plankton diversity and the circulation pathways connecting them are thus key factors determining the availability of fixed nitrogen in the ocean .

[1959] Recent ice ages on Mars

A key pacemaker of ice ages on the Earth is climatic forcing due to variations in planetary orbital parameters .
Recent Mars exploration has revealed dusty , water-ice-rich mantling deposits that are layered , metres thick and latitude dependent , occurring in both hemispheres from mid-latitudes to the poles .
Here we show evidence that these deposits formed during a geologically recent ice age that occurred from about 2.1 to 0.4 Myr ago .
The deposits were emplaced symmetrically down to latitudes of ~ 30degrees -- equivalent to Saudi Arabia and the southern United States on the Earth -- in response to the changing stability of water ice and dust during variations in obliquity ( the angle between Mars ' pole of rotation and the ecliptic plane ) reaching 30-35degrees .
Mars is at present in an ` interglacial ' period , and the ice-rich deposits are undergoing reworking , degradation and retreat in response to the current instability of near-surface ice .
Unlike the Earth , martian ice ages are characterized by warmer polar climates and enhanced equatorward transport of atmospheric water and dust to produce widespread smooth deposits down to mid-latitudes .

[1960] Elucidating the role of the TRPM7 alpha-kinase : TRPM7 kinase inactivation leads to magnesium deprivation resistance phenotype in mice

TRPM7 is an unusual bi-functional protein containing an ion channel covalently linked to a protein kinase domain .
TRPM7 is implicated in regulating cellular and systemic magnesium homeostasis .
While the biophysical properties of TRPM7 ion channel and its function are relatively well characterized , the function of the TRPM7 enzymatically active kinase domain is not understood yet .
To investigate the physiological role of TRPM7 kinase activity , we constructed mice carrying an inactive TRPM7 kinase .
We found that these mice were resistant to dietary magnesium deprivation , surviving three times longer than wild type mice ; also they displayed decreased chemically induced allergic reaction .
Interestingly , mutant mice have lower magnesium bone content compared to wild type mice when fed regular diet ; unlike wild type mice , mutant mice placed on magnesium-depleted diet did not alter their bone magnesium content .
Furthermore , mouse embryonic fibroblasts isolated from TRPM7 kinase-dead animals exhibited increased resistance to magnesium deprivation and oxidative stress .
Finally , electrophysiological data revealed that the activity of the kinase-dead TRPM7 channel was not significantly altered .
Together , our results suggest that TRPM7 kinase is a sensor of magnesium status and provides coordination of cellular and systemic responses to magnesium deprivation .

[1961] The next water cycle

Adaptation of water resources management will help communities adjust to changes in the water cycle expected with climate change , but it ca n't be fixed by innovations alone .

[1962] A highly unsaturated fatty acid predicts carbon transfer between primary producers and consumers

The factors that regulate energy transfer between primary producers and consumers in aquatic ecosystems have been investigated for more than 50 years ( refs 1,2,3 ) .
Among all levels of the food web ( plants , herbivores , carnivores ) , the plant-animal interface is the most variable and least predictable link .
In hypereutrophic lakes , for example , biomass and energy transfer is often inhibited at the phytoplankton-zooplankton link , resulting in an accumulation of phytoplankton biomass instead of sustaining production at higher trophic levels , such as fish .
Accumulation of phytoplankton ( especially cyanobacteria ) results in severe deterioration of water quality , with detrimental effects on the health of humans and domestic animals , and diminished recreational value of water bodies .
We show here that low transfer efficiencies between primary producers and consumers during cyanobacteria bloom conditions are related to low relative eicosapentaenoic acid ( 20:5 omega3 ) content of the primary producer community .
Zooplankton growth and egg production were strongly related to the primary producer 20:5 omega3 to carbon ratio .
This indicates that limitation of zooplankton production by this essential fatty acid is of central importance at the pelagic producer-consumer interface .

[1963] First evidence of chitin in calcified coralline algae : new insights into the calcification process of Clathromorphum compactum

Interest in calcifying coralline algae has been increasing over the past years due to the discovery of extensive coralline algal dominated ecosystems in Arctic and Subarctic latitudes , their projected sensitivity to ocean acidification and their utility as palaeoenvironmental proxies .
Thus , it is crucial to obtain a detailed understanding of their calcification process .
We here extracted calcified skeletal organic matrix components including soluble and insoluble fractions from the widely-distributed Subarctic and Arctic coralline alga Clathromorphum compactum .
The lyophilized skeletal organic matrix fractions showed comparatively high concentrations of soluble and insoluble organic matrices comprising 0.9 % and 4.5 % of skeletal weight , respectively .
This is significantly higher than in other skeletal marine calcifiers .
Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy ( ATR-FTIR ) and X-Ray Diffraction ( XRD ) results indicate that chitin is present in the skeletal organic matrices of C. compactum .
This polymer exhibits similar hierarchical structural organizations with collagen present in the matrix and serves as a template for nucleation and controls the location and orientation of mineral phases .
Chitin contributes to significantly increasing skeletal strength , making C. compactum highly adapted for living in a shallow high-latitude benthic environment .
Furthermore , chitin containing polysaccharides can increase resistance of calcifiers to negative effects of ocean acidification .

[1964] The critical size is set at a single-cell level by growth rate to attain homeostasis and adaptation

Budding yeast cells are assumed to trigger Start and enter the cell cycle only after they attain a critical size set by external conditions .
However , arguing against deterministic models of cell size control , cell volume at Start displays great individual variability even under constant conditions .
Here we show that cell size at Start is robustly set at a single-cell level by the volume growth rate in G1 , which explains the observed variability .
We find that this growth-rate-dependent sizer is intimately hardwired into the Start network and the Ydj1 chaperone is key for setting cell size as a function of the individual growth rate .
Mathematical modelling and experimental data indicate that a growth-rate-dependent sizer is sufficient to ensure size homeostasis and , as a remarkable advantage over a rigid sizer mechanism , it reduces noise in G1 length and provides an immediate solution for size adaptation to external conditions at a population level .

[1965] Vulnerability and adaptation of US shellfisheries to ocean acidification

Ocean acidification is a global , long-term problem whose ultimate solution requires carbon dioxide reduction at a scope and scale that will take decades to accomplish successfully .
Until that is achieved , feasible and locally relevant adaptation and mitigation measures are needed .
To help to prioritize societal responses to ocean acidification , we present a spatially explicit , multidisciplinary vulnerability analysis of coastal human communities in the United States .
We focus our analysis on shelled mollusc harvests , which are likely to be harmed by ocean acidification .
Our results highlight US regions most vulnerable to ocean acidification ( and why ) , important knowledge and information gaps , and opportunities to adapt through local actions .
The research illustrates the benefits of integrating natural and social sciences to identify actions and other opportunities while policy , stakeholders and scientists are still in relatively early stages of developing research plans and responses to ocean acidification .

[1966] Oceanography : All change in the Arctic

It is increasingly evident that ocean variability in the Arctic can have global consequences .
During the 1990s , thanks in part to data gathered by US submarines , unprecedented and system-wide changes in the region have been observed , and they were subject to discussion at a meeting late last year .

[1967] Global vulnerability of peatlands to fire and carbon loss

Globally , the amount of carbon stored in peats exceeds that stored in vegetation and is similar in size to the current atmospheric carbon pool .
Fire is a threat to many peat-rich biomes and has the potential to disturb these carbon stocks .
Peat fires are dominated by smouldering combustion , which is ignited more readily than flaming combustion and can persist in wet conditions .
In undisturbed peatlands , most of the peat carbon stock typically is protected from smouldering , and resistance to fire has led to a build-up of peat carbon storage in boreal and tropical regions over long timescales .
But drying as a result of climate change and human activity lowers the water table in peatlands and increases the frequency and extent of peat fires .
The combustion of deep peat affects older soil carbon that has not been part of the active carbon cycle for centuries to millennia , and thus will dictate the importance of peat fire emissions to the carbon cycle and feedbacks to the climate .

[1968] Switch of flow direction in an Antarctic ice stream

Fast-flowing ice streams transport ice from the interior of West Antarctica to the ocean , and fluctuations in their activity control the mass balance of the ice sheet .
The mass balance of the Ross Sea sector of the West Antarctic ice sheet is now positive -- that is , it is growing -- mainly because one of the ice streams ( ice stream C ) slowed down about 150 years ago .
Here we present evidence from both surface measurements and remote sensing that demonstrates the highly dynamic nature of the Ross drainage system .
We show that the flow in an area that once discharged into ice stream C has changed direction , now draining into the Whillans ice stream ( formerly ice stream B ) .
This switch in flow direction is a result of continuing thinning of the Whillans ice stream and recent thickening of ice stream C. Further abrupt reorganization of the activity and configuration of the ice streams over short timescales is to be expected in the future as the surface topography of the ice sheet responds to the combined effects of internal dynamics and long-term climate change .
We suggest that caution is needed when using observations of short-term mass changes to draw conclusions about the large-scale mass balance of the ice sheet .

[1969] El Nino in the frame for Pacific temperature and height increases

london Three forms of data have been used to provide a dramatic three-dimensional visualization of increased sea level height and raised sea temperatures in the eastern Pacific linked to the El Nino event ( above ) .
Data from three separate instruments , including the US National Aeronautics and Space Administration 's ( NASA ) 's Topex radar altimetry satellite , released last week , show a 34-cm rise in the height of the eastern Pacific Ocean between January 1997 and March this year .

[1970] Ecology : Prime time for microbes

As atmospheric CO2 increases , more plant litter is expected to enter the soil , stimulating turnover of organic matter and release of carbon .
New field data show that this will intensify the terrestrial carbon cycle in the long term , and may counterbalance expected gains in carbon storage .

[1971] Large tundra methane burst during onset of freezing

Terrestrial wetland emissions are the largest single source of the greenhouse gas methane .
Northern high-latitude wetlands contribute significantly to the overall methane emissions from wetlands , but the relative source distribution between tropical and high-latitude wetlands remains uncertain .
As a result , not all the observed spatial and seasonal patterns of atmospheric methane concentrations can be satisfactorily explained , particularly for high northern latitudes .
For example , a late-autumn shoulder is consistently observed in the seasonal cycles of atmospheric methane at high-latitude sites , but the sources responsible for these increased methane concentrations remain uncertain .
Here we report a data set that extends hourly methane flux measurements from a high Arctic setting into the late autumn and early winter , during the onset of soil freezing .
We find that emissions fall to a low steady level after the growing season but then increase significantly during the freeze-in period .
The integral of emissions during the freeze-in period is approximately equal to the amount of methane emitted during the entire summer season .
Three-dimensional atmospheric chemistry and transport model simulations of global atmospheric methane concentrations indicate that the observed early winter emission burst improves the agreement between the simulated seasonal cycle and atmospheric data from latitudes north of 60degrees N .
Our findings suggest that permafrost-associated freeze-in bursts of methane emissions from tundra regions could be an important and so far unrecognized component of the seasonal distribution of methane emissions from high latitudes .

[1972] Pan-Arctic distributions of continental runoff in the Arctic Ocean

Continental runoff is a major source of freshwater , nutrients and terrigenous material to the Arctic Ocean .
As such , it influences water column stratification , light attenuation , surface heating , gas exchange , biological productivity and carbon sequestration .
Increasing river discharge and thawing permafrost suggest that the impacts of continental runoff on these processes are changing .
Here , a new optical proxy was developed and implemented with remote sensing to determine the first pan-Arctic distribution of terrigenous dissolved organic matter ( tDOM ) and continental runoff in the surface Arctic Ocean .
Retrospective analyses revealed connections between the routing of North American runoff and the recent freshening of the Canada Basin , and indicated a correspondence between climate-driven changes in river discharge and tDOM inventories in the Kara Sea .
By facilitating the real-time , synoptic monitoring of tDOM and freshwater runoff in surface polar waters , this novel approach will help understand the manifestations of climate change in this remote region .

[1973] Mutation rate plasticity in rifampicin resistance depends on Escherichia coli cell-cell interactions

Variation of mutation rate at a particular site in a particular genotype , in other words mutation rate plasticity ( MRP ) , can be caused by stress or ageing .
However , mutation rate control by other factors is less well characterized .
Here we show that in wild-type Escherichia coli ( K-12 and B strains ) , the mutation rate to rifampicin resistance is plastic and inversely related to population density : lowering density can increase mutation rates at least threefold .
This MRP is genetically switchable , dependent on the quorum-sensing gene luxS -- specifically its role in the activated methyl cycle -- and is socially mediated via cell-cell interactions .
Although we identify an inverse association of mutation rate with fitness under some circumstances , we find no functional link with stress-induced mutagenesis .
Our experimental manipulation of mutation rates via the social environment raises the possibility that such manipulation occurs in nature and could be exploited medically .

[1974] Insights into transport velocity of colloid-associated plutonium relative to tritium in porous media

Although faster transport velocities of colloid-associated actinides , bacteria , and virus than nonreactive solutes have been observed in laboratory and field experiments , some questions still need to be answered .
To accurately determine the relative velocity ( UPu/UT ) of 239Pu and tritium representative of the bulk water , a conceptual model of electrostatic interactions coupled with the parabolic water velocity profile in pore channels is developed .
Based on the expression for UPu/UT derived from this model , we study the effects of water flow rates and ionic strengths on the UPu/UT .
Also , the velocity relationship between Pu , tritium and Sr2 + is explored .
The results show that UPu/UT increased fairly linearly with decreasing water flow rates ; UPu/UT declined approximately exponentially with increasing Na + concentrations ; the charge properties of colloid-associated Pu ( negative ) , tritium ( neutral ) and Sr2 + ( positive ) had a close association with their transport velocities as UPu : UT : USr2 + = 1.41 : 1 : 0.579 .

[1975] Feeding currents facilitate a mixotrophic way of life

Mixotrophy is common , if not dominant , among eukaryotic flagellates , and these organisms have to both acquire inorganic nutrients and capture particulate food .
Diffusion limitation favors small cell size for nutrient acquisition , whereas large cell size facilitates prey interception because of viscosity , and hence intermediately sized mixotrophic dinoflagellates are simultaneously constrained by diffusion and viscosity .
Advection may help relax both constraints .
We use high-speed video microscopy to describe prey interception and capture , and micro particle image velocimetry ( micro-PIV ) to quantify the flow fields produced by free-swimming dinoflagellates .
We provide the first complete flow fields of free-swimming interception feeders , and demonstrate the use of feeding currents .
These are directed toward the prey capture area , the position varying between the seven dinoflagellate species studied , and we argue that this efficiently allows the grazer to approach small-sized prey despite viscosity .
Measured flow fields predict the magnitude of observed clearance rates .
The fluid deformation created by swimming dinoflagellates may be detected by evasive prey , but the magnitude of flow deformation in the feeding current varies widely between species and depends on the position of the transverse flagellum .
We also use the near-cell flow fields to calculate nutrient transport to swimming cells and find that feeding currents may enhance nutrient uptake by = ~ 75 % compared with that by diffusion alone .
We argue that all phagotrophic microorganisms must have developed adaptations to counter viscosity in order to allow prey interception , and conclude that the flow fields created by the beating flagella in dinoflagellates are key to the success of these mixotrophic organisms .
The ISME Journal advance online publication , 17 February 2015 ; doi :10.1038 / ismej .2015.27

[1976] Contrasting trends in light pollution across Europe based on satellite observed night time lights

Since the 1970s nighttime satellite images of the Earth from space have provided a striking illustration of the extent of artificial light .
Meanwhile , growing awareness of adverse impacts of artificial light at night on scientific astronomy , human health , ecological processes and aesthetic enjoyment of the night sky has led to recognition of light pollution as a significant global environmental issue .
Links between economic activity , population growth and artificial light are well documented in rapidly developing regions .
Applying a novel method to analysis of satellite images of European nighttime lights over 15 years , we show that while the continental trend is towards increasing brightness , some economically developed regions show more complex patterns with large areas decreasing in observed brightness over this period .
This highlights that opportunities exist to constrain and even reduce the environmental impact of artificial light pollution while delivering cost and energy-saving benefits .

[1977] Climate change : Microbial mitigation

Increasing temperatures stimulate the decomposition of soil organic matter in the short term .
But a shift in microbial carbon allocation could mitigate this response over longer periods of time .

[1978] The microbial ecology of permafrost

Permafrost constitutes a major portion of the terrestrial cryosphere of the Earth and is a unique ecological niche for cold-adapted microorganisms .
There is a relatively high microbial diversity in permafrost , although there is some variation in community composition across different permafrost features and between sites .
Some microorganisms are even active at subzero temperatures in permafrost .
An emerging concern is the impact of climate change and the possibility of subsequent permafrost thaw promoting microbial activity in permafrost , resulting in increased potential for greenhouse-gas emissions .
This Review describes new data on the microbial ecology of permafrost and provides a platform for understanding microbial life strategies in frozen soil as well as the impact of climate change on permafrost microorganisms and their functional roles .

[1979] Correlating the Ancient Maya and Modern European Calendars with High-Precision AMS 14C Dating

The reasons for the development and collapse of Maya civilization remain controversial and historical events carved on stone monuments throughout this region provide a remarkable source of data about the rise and fall of these complex polities .
Use of these records depends on correlating the Maya and European calendars so that they can be compared with climate and environmental datasets .
Correlation constants can vary up to 1000 years and remain controversial .
We report a series of high-resolution AMS 14C dates on a wooden lintel collected from the Classic Period city of Tikal bearing Maya calendar dates .
The radiocarbon dates were calibrated using a Bayesian statistical model and indicate that the dates were carved on the lintel between AD 658-696 .
This strongly supports the Goodman-Martinez-Thompson ( GMT ) correlation and the hypothesis that climate change played an important role in the development and demise of this complex civilization .

[1980] Atmospheric verification of anthropogenic CO2 emission trends

International efforts to limit global warming and ocean acidification aim to slow the growth of atmospheric CO2 , guided primarily by national and industry estimates of production and consumption of fossil fuels .
Atmospheric verification of emissions is vital but present global inversion methods are inadequate for this purpose .
We demonstrate a clear response in atmospheric CO2 coinciding with a sharp 2010 increase in Asian emissions but show persisting slowing mean CO2 growth from 2002/03 .
Growth and inter-hemispheric concentration difference during the onset and recovery of the Global Financial Crisis support a previous speculation that the reported 2000-2008 emissions surge is an artefact , most simply explained by a cumulative underestimation ( ~ 9 Pg C ) of 1994-2007 emissions ; in this case , post-2000 emissions would track mid-range of Intergovernmental Panel on Climate Change emission scenarios .
An alternative explanation requires changes in the northern terrestrial land sink that offset anthropogenic emission changes .
We suggest atmospheric methods to help resolve this ambiguity .

[1981] Global covariation of carbon turnover times with climate in terrestrial ecosystems

The response of the terrestrial carbon cycle to climate change is among the largest uncertainties affecting future climate change projections .
The feedback between the terrestrial carbon cycle and climate is partly determined by changes in the turnover time of carbon in land ecosystems , which in turn is an ecosystem property that emerges from the interplay between climate , soil and vegetation type .
Here we present a global , spatially explicit and observation-based assessment of whole-ecosystem carbon turnover times that combines new estimates of vegetation and soil organic carbon stocks and fluxes .
We find that the overall mean global carbon turnover time is years ( 95 per cent confidence interval ) .
On average , carbon resides in the vegetation and soil near the Equator for a shorter time than at latitudes north of 75degrees north ( mean turnover times of 15 and 255 years , respectively ) .
We identify a clear dependence of the turnover time on temperature , as expected from our present understanding of temperature controls on ecosystem dynamics .
Surprisingly , our analysis also reveals a similarly strong association between turnover time and precipitation .
Moreover , we find that the ecosystem carbon turnover times simulated by state-of-the-art coupled climate/carbon-cycle models vary widely and that numerical simulations , on average , tend to underestimate the global carbon turnover time by 36 per cent .
The models show stronger spatial relationships with temperature than do observation-based estimates , but generally do not reproduce the strong relationships with precipitation and predict faster carbon turnover in many semi-arid regions .
Our findings suggest that future climate/carbon-cycle feedbacks may depend more strongly on changes in the hydrological cycle than is expected at present and is considered in Earth system models .

[1982] Sulphidic Mediterranean surface waters during Pliocene sapropel formation

Sapropels -- organic-matter rich layers -- are common in Neogene sediments of the eastern Mediterranean Sea .
The formation of these layers has been attributed to climate-related increases in organic-matter production and increased organic-matter preservation due to oxygen depletion in more stagnant bottom waters , .
Here we report that eastern Mediterranean Pliocene sapropels contain molecular fossils of a compound ( isorenieratene ) known to be synthesized by photosynthetic green sulphur bacteria , suggesting that sulphidic ( euxinic ) -- and therefore anoxic -- conditions prevailed in the photic zone of the water column .
These sapropels also have a high trace-metal content , which is probably due to the efficient scavenging of these metals by precipitating sulphides in a euxinic water column .
The abundance and sulphur-isotope composition of pyrite are consistent with iron sulphide formation in the water column .
We conclude that basin-wide water-column euxinia occurred over substantial periods during Pliocene sapropel formation in the eastern Mediterranean Sea , and that the ultimate degradation of the increased organic-matter production was strongly influential in generating and sustaining the euxinic conditions .

[1983] Intensification of the meridional temperature gradient in the Great Barrier Reef following the Last Glacial Maximum

Tropical south-western Pacific temperatures are of vital importance to the Great Barrier Reef ( GBR ) , but the role of sea surface temperatures ( SSTs ) in the growth of the GBR since the Last Glacial Maximum remains largely unknown .
Here we present records of Sr/Ca and delta18O for Last Glacial Maximum and deglacial corals that show a considerably steeper meridional SST gradient than the present day in the central GBR .
We find a 1-2 degreesC larger temperature decrease between 17degrees and 20degreesS about 20,000 to 13,000 years ago .
The result is best explained by the northward expansion of cooler subtropical waters due to a weakening of the South Pacific gyre and East Australian Current .
Our findings indicate that the GBR experienced substantial meridional temperature change during the last deglaciation , and serve to explain anomalous deglacial drying of northeastern Australia .
Overall , the GBR developed through significant SST change and may be more resilient than previously thought .

[1984] Spinning up the polymorphs of calcium carbonate

Controlling the growth of the polymorphs of calcium carbonate is important in understanding the changing environmental conditions in the oceans .
Aragonite is the main polymorph in the inner shells of marine organisms , and can be readily converted to calcite , which is the most stable polymorph of calcium carbonate .
Both of these polymorphs are significantly more stable than vaterite , which is the other naturally occurring polymorph of calcium carbonate , and this is reflected in its limited distribution in nature .
We have investigated the effect of high shear forces on the phase behaviour of calcium carbonate using a vortex fluidic device ( VFD ) , with experimental parameters varied to explore calcium carbonate mineralisation .
Variation of tilt angle , rotation speed and temperature allow for control over the size , shape and phase of the resulting calcium carbonate .

[1985] Seasonal characteristics of the Indian Ocean Dipole during the Holocene epoch

The Indian Ocean Dipole ( IOD ) -- an oscillatory mode of coupled ocean-atmosphere variability -- causes climatic extremes and socio-economic hardship throughout the tropical Indian Ocean region .
There is much debate about how the IOD interacts with the El Nino/Southern Oscillation ( ENSO ) and the Asian monsoon , and recent changes in the historic ENSO-monsoon relationship raise the possibility that the properties of the IOD may also be evolving .
Improving our understanding of IOD events and their climatic impacts thus requires the development of records defining IOD activity in different climatic settings , including prehistoric times when ENSO and the Asian monsoon behaved differently from the present day .
Here we use coral geochemical records from the equatorial eastern Indian Ocean to reconstruct surface-ocean cooling and drought during individual IOD events over the past ~ 6,500 years .
We find that IOD events during the middle Holocene were characterized by a longer duration of strong surface ocean cooling , together with droughts that peaked later than those expected by El Nino forcing alone .
Climate model simulations suggest that this enhanced cooling and drying was the result of strong cross-equatorial winds driven by the strengthened Asian monsoon of the middle Holocene .
These IOD-monsoon connections imply that the socioeconomic impacts of projected future changes in Asian monsoon strength may extend throughout Australasia .

[1986] Genome engineering empowers the diatom Phaeodactylum tricornutum for biotechnology

Diatoms , a major group of photosynthetic microalgae , have a high biotechnological potential that has not been fully exploited because of the paucity of available genetic tools .
Here we demonstrate targeted and stable modifications of the genome of the marine diatom Phaeodactylum tricornutum , using both meganucleases and TALE nucleases .
When nuclease-encoding constructs are co-transformed with a selectable marker , high frequencies of genome modifications are readily attained with 56 and 27 % of the colonies exhibiting targeted mutagenesis or targeted gene insertion , respectively .
The generation of an enhanced lipid-producing strain ( 45-fold increase in triacylglycerol accumulation ) through the disruption of the UDP-glucose pyrophosphorylase gene exemplifies the power of genome engineering to harness diatoms for biofuel production .

[1987] Ecosystem carbon storage : Squeezing the Arctic carbon balloon

The advancement of trees into Arctic tundra can increase total aboveground carbon storage .
A study now shows , however , that greater plant growth also enhances belowground decomposition , resulting in a net loss of carbon from the ecosystem .

[1988] The dynamics of microbial partnerships in the coral Isopora palifera

Both bacteria and algal symbionts ( genus Symbiodinium ) , the two major microbial partners in the coral holobiont , respond to fluctuations in the environment , according to current reports ; however , little evidence yet indicates that both populations have any direct interaction with each other in seasonal fluctuation .
In this study , we present field observations of a compositional change in bacteria and Symbiodinium in the coral Isopora palifera in three separate coral colonies following monthly sampling from February to November in 2008 .
Using massively parallel pyrosequencing , over 200 000 bacterial V6 sequences were classified to build the bacterial community profile ; in addition , the relative composition and quantity of Symbiodinium clades C and D were determined by real-time PCR .
The results showed that coral-associated bacterial and Symbiodinium communities were highly dynamic and dissimilar among the tagged coral colonies , suggesting that the effect of host specificity was insignificant .
The coral-associated bacterial community was more diverse ( Shannon index up to 6.71 ) than previous estimates in other corals and showed rapid seasonal changes .
The population ratios between clade C and D groups of Symbiodinium varied in the tagged coral colonies through the different seasons ; clade D dominated in most of the samples .
Although significant association between bacteria and symbiont was not detected , this study presents a more detailed picture of changes in these two major microbial associates of the coral at the same time , using the latest molecular approaches .

[1989] Observational determination of surface radiative forcing by CO2 from 2000 to 2010

The climatic impact of CO2 and other greenhouse gases is usually quantified in terms of radiative forcing , calculated as the difference between estimates of the Earth 's radiation field from pre-industrial and present-day concentrations of these gases .
Radiative transfer models calculate that the increase in CO2 since 1750 corresponds to a global annual-mean radiative forcing at the tropopause of 1.82 + / - 0.19 W m-2 ( ref .
2 ) .
However , despite widespread scientific discussion and modelling of the climate impacts of well-mixed greenhouse gases , there is little direct observational evidence of the radiative impact of increasing atmospheric CO2 .
Here we present observationally based evidence of clear-sky CO2 surface radiative forcing that is directly attributable to the increase , between 2000 and 2010 , of 22 parts per million atmospheric CO2 .
The time series of this forcing at the two locations -- the Southern Great Plains and the North Slope of Alaska -- are derived from Atmospheric Emitted Radiance Interferometer spectra together with ancillary measurements and thoroughly corroborated radiative transfer calculations .
The time series both show statistically significant trends of 0.2 W m-2 per decade ( with respective uncertainties of + / -0.06 W m-2 per decade and + / -0.07 W m-2 per decade ) and have seasonal ranges of 0.1-0 .2 W m-2 .
This is approximately ten per cent of the trend in downwelling longwave radiation .
These results confirm theoretical predictions of the atmospheric greenhouse effect due to anthropogenic emissions , and provide empirical evidence of how rising CO2 levels , mediated by temporal variations due to photosynthesis and respiration , are affecting the surface energy balance .

[1990] Sediment particle size and initial radiocesium accumulation in ponds following the Fukushima DNPP accident

This study used particle size analysis to investigate the initial accumulation and trap efficiency of radiocesium ( 137Cs ) in four irrigation ponds , ~ 45 months after the Fukushima Daiichi nuclear power plant ( DNPP ) accident .
Trap efficiency , represented by the inventory of 137Cs in pond sediment to the inventory of radiocesium in soil surrounding the pond ( i.e. , total 137Cs inventory ) , was less than 100 % for all but one pond .
Trap efficiency decreased as sediment particle size increased , indicating that sediments with a smaller particle size accumulate more 137Cs .
In ponds showing low trap efficiency , fine sediment containing high concentrations of 137Cs appeared to be removed from the system by hydraulic flushing , leaving behind mostly coarse sediment .
The results of this study suggest that sediment particle size can be used to estimate the initial accumulation and trap efficiency of 137Cs in pond sediment , as well as the amount lost through hydraulic flushing .

[1991] Extinction risk from climate change

Climate change over the past ~ 30 years has produced numerous shifts in the distributions and abundances of species and has been implicated in one species-level extinction .
Using projections of species ' distributions for future climate scenarios , we assess extinction risks for sample regions that cover some 20 % of the Earth 's terrestrial surface .
Exploring three approaches in which the estimated probability of extinction shows a power-law relationship with geographical range size , we predict , on the basis of mid-range climate-warming scenarios for 2050 , that 15-37 % of species in our sample of regions and taxa will be ` committed to extinction ' .
When the average of the three methods and two dispersal scenarios is taken , minimal climate-warming scenarios produce lower projections of species committed to extinction ( ~ 18 % ) than mid-range ( ~ 24 % ) and maximum-change ( ~ 35 % ) scenarios .
These estimates show the importance of rapid implementation of technologies to decrease greenhouse gas emissions and strategies for carbon sequestration .

[1992] Corals record long-term Leeuwin current variability including Ningaloo Nino/Nina since 1795

Variability of the Leeuwin current ( LC ) off Western Australia is a footprint of interannual and decadal climate variations in the tropical Indo-Pacific .
La Nina events often result in a strengthened LC , high coastal sea levels and unusually warm sea surface temperatures ( SSTs ) , termed Ningaloo Nino .
The rarity of such extreme events and the response of the southeastern Indian Ocean to regional and remote climate forcing are poorly understood owing to the lack of long-term records .
Here we use well-replicated coral SST records from within the path of the LC , together with a reconstruction of the El Nino-Southern Oscillation to hindcast historical SST and LC strength from 1795 to 2010 .
We show that interannual and decadal variations in SST and LC strength characterized the past 215 years and that the most extreme sea level and SST anomalies occurred post 1980 .
These recent events were unprecedented in severity and are likely aided by accelerated global ocean warming and sea-level rise .

[1993] Biotic carbon feedbacks in a materially closed soil-vegetation-atmosphere system

The magnitude and direction of the coupled feedbacks between the biotic and abiotic components of the terrestrial carbon cycle is a major source of uncertainty in coupled climate-carbon-cycle models .
Materially closed , energetically open biological systems continuously and simultaneously allow the two-way feedback loop between the biotic and abiotic components to take place , but so far have not been used to their full potential in ecological research , owing to the challenge of achieving sustainable model systems .
We show that using materially closed soil-vegetation-atmosphere systems with pro rata carbon amounts for the main terrestrial carbon pools enables the establishment of conditions that balance plant carbon assimilation , and autotrophic and heterotrophic respiration fluxes over periods suitable to investigate short-term biotic carbon feedbacks .
Using this approach , we tested an alternative way of assessing the impact of increased CO2 and temperature on biotic carbon feedbacks .
The results show that without nutrient and water limitations , the short-term biotic responses could potentially buffer a temperature increase of 2.3 degreesC without significant positive feedbacks to atmospheric CO2 .
We argue that such closed-system research represents an important test-bed platform for model validation and parameterization of plant and soil biotic responses to environmental changes .

[1994] Decade-long soil nitrogen constraint on the CO2 fertilization of plant biomass

The stimulation of plant growth by elevated CO2 concentration has been widely observed .
Such fertilization , and associated carbon storage , could dampen future increases in atmospheric CO2 levels and associated climate warming .
However , the CO2 fertilization of plant biomass may be sensitive to nitrogen supply .
Herein we show that in the latest decade of a long-term perennial grassland experiment , low ambient soil nitrogen availability constrained the positive response of plant biomass to elevated CO2 , a result not seen in the first years ( 1998-2000 ) of the study .
From 2001 to 2010 , elevated CO2 stimulated plant biomass half as much under ambient as under enriched nitrogen supply , an effect mirrored over this period by more positive effects of elevated CO2 on soil nitrogen supply ( net nitrogen mineralization ) and plant nitrogen status under enriched than ambient nitrogen supply .
The results did not strongly support either the progressive nitrogen limitation hypothesis , or the alternative hypothesis of priming of soil nitrogen release by elevated CO2 .
As nitrogen limitation to productivity is widespread , persistent nitrogen constraints on terrestrial responses to rising CO2 are probably pervasive .
Further incorporation of such interactions into Earth system models is recommended to better predict future CO2 fertilization effects and impacts on the global carbon cycle .

[1995] Temperature impacts on economic growth warrant stringent mitigation policy

Integrated assessment models compare the costs of greenhouse gas mitigation with damages from climate change to evaluate the social welfare implications of climate policy proposals and inform optimal emissions reduction trajectories .
However , these models have been criticized for lacking a strong empirical basis for their damage functions , which do little to alter assumptions of sustained gross domestic product ( GDP ) growth , even under extreme temperature scenarios .
We implement empirical estimates of temperature effects on GDP growth rates in the DICE model through two pathways , total factor productivity growth and capital depreciation .
This damage specification , even under optimistic adaptation assumptions , substantially slows GDP growth in poor regions but has more modest effects in rich countries .
Optimal climate policy in this model stabilizes global temperature change below 2 degreesC by eliminating emissions in the near future and implies a social cost of carbon several times larger than previous estimates .
A sensitivity analysis shows that the magnitude of climate change impacts on economic growth , the rate of adaptation , and the dynamic interaction between damages and GDP are three critical uncertainties requiring further research .
In particular , optimal mitigation rates are much lower if countries become less sensitive to climate change impacts as they develop , making this a major source of uncertainty and an important subject for future research .

[1996] A global ocean inventory of anthropogenic mercury based on water column measurements

Mercury is a toxic , bioaccumulating trace metal whose emissions to the environment have increased significantly as a result of anthropogenic activities such as mining and fossil fuel combustion .
Several recent models have estimated that these emissions have increased the oceanic mercury inventory by 36-1 ,313 million moles since the 1500s .
Such predictions have remained largely untested owing to a lack of appropriate historical data and natural archives .
Here we report oceanographic measurements of total dissolved mercury and related parameters from several recent expeditions to the Atlantic , Pacific , Southern and Arctic oceans .
We find that deep North Atlantic waters and most intermediate waters are anomalously enriched in mercury relative to the deep waters of the South Atlantic , Southern and Pacific oceans , probably as a result of the incorporation of anthropogenic mercury .
We estimate the total amount of anthropogenic mercury present in the global ocean to be 290 + / - 80 million moles , with almost two-thirds residing in water shallower than a thousand metres .
Our findings suggest that anthropogenic perturbations to the global mercury cycle have led to an approximately 150 per cent increase in the amount of mercury in thermocline waters and have tripled the mercury content of surface waters compared to pre-anthropogenic conditions .
This information may aid our understanding of the processes and the depths at which inorganic mercury species are converted into toxic methyl mercury and subsequently bioaccumulated in marine food webs .

[1997] In situ Growth of NixCu1-x Alloy Nanocatalysts on Redox-reversible Rutile ( Nb , Ti ) O4 Towards High-Temperature Carbon Dioxide Electrolysis

In this paper , we report the in situ growth of NixCu1-x ( x = 0 , 0.25 , 0.50 , 0.75 and 1.0 ) alloy catalysts to anchor and decorate a redox-reversible Nb1 .33 Ti0 .67 O4 ceramic substrate with the aim of tailoring the electrocatalytic activity of the composite materials through direct exsolution of metal particles from the crystal lattice of a ceramic oxide in a reducing atmosphere at high temperatures .
Combined analysis using XRD , SEM , EDS , TGA , TEM and XPS confirmed the completely reversible exsolution/dissolution of the NixCu1-x alloy particles during the redox cycling treatments .
TEM results revealed that the alloy particles were exsolved to anchor onto the surface of highly electronically conducting Nb1 .33 Ti0 .67 O4 in the form of heterojunctions .
The electrical properties of the nanosized NixCu1-x/Nb1 .33 Ti0 .67 O4 were systematically investigated and correlated to the electrochemical performance of the composite electrodes .
A strong dependence of the improved electrode activity on the alloy compositions was observed in reducing atmospheres at high temperatures .
Direct electrolysis of CO2 at the NixCu1-x/Nb1 .33 Ti0 .67 O4 composite cathodes was investigated in solid-oxide electrolysers .
The CO2 splitting rates were observed to be positively correlated with the Ni composition ; however , the Ni0 .75 Cu0 .25 combined the advantages of metallic nickel and copper and therefore maximised the current efficiencies .

[1998] Responses of soil bacterial and fungal communities to extreme desiccation and rewetting

The microbial response to summer desiccation reflects adaptation strategies , setting the stage for a large rainfall-induced soil CO2 pulse upon rewetting , an important component of the ecosystem carbon budget .
In three California annual grasslands , the present ( DNA-based ) and potentially active ( RNA-based ) soil bacterial and fungal communities were tracked over a summer season and in response to controlled rewetting of intact soil cores .
Phylogenetic marker genes for bacterial ( 16S ) and fungal ( 28S ) RNA and DNA were sequenced , and the abundances of these genes and transcripts were measured .
Although bacterial community composition differed among sites , all sites shared a similar response pattern of the present and potentially active bacterial community to dry-down and wet-up .
In contrast , the fungal community was not detectably different among sites , and was largely unaffected by dry-down , showing marked resistance to dessication .
The potentially active bacterial community changed significantly as summer dry-down progressed , then returned to pre-dry-down composition within several hours of rewetting , displaying spectacular resilience .
Upon rewetting , transcript copies of bacterial rpoB genes increased consistently , reflecting rapid activity resumption .
Acidobacteria and Actinobacteria were the most abundant phyla present and potentially active , and showed the largest changes in relative abundance .
The relative increase ( Actinobacteria ) and decrease ( Acidobacteria ) with dry-down , and the reverse responses to rewetting reflected a differential response , which was conserved at the phylum level and consistent across sites .
These contrasting desiccation-related bacterial life-strategies suggest that predicted changes in precipitation patterns may affect soil nutrient and carbon cycling by differentially impacting activity patterns of microbial communities .

[1999] Increasing risk of Amazonian drought due to decreasing aerosol pollution

The Amazon rainforest plays a crucial role in the climate system , helping to drive atmospheric circulations in the tropics by absorbing energy and recycling about half of the rainfall that falls on it .
This region ( Amazonia ) is also estimated to contain about one-tenth of the total carbon stored in land ecosystems , and to account for one-tenth of global , net primary productivity .
The resilience of the forest to the combined pressures of deforestation and global warming is therefore of great concern , especially as some general circulation models ( GCMs ) predict a severe drying of Amazonia in the twenty-first century .
Here we analyse these climate projections with reference to the 2005 drought in western Amazonia , which was associated with unusually warm North Atlantic sea surface temperatures ( SSTs ) .
We show that reduction of dry-season ( July-October ) rainfall in western Amazonia correlates well with an index of the north-south SST gradient across the equatorial Atlantic ( the ` Atlantic N-S gradient ' ) .
Our climate model is unusual among current GCMs in that it is able to reproduce this relationship and also the observed twentieth-century multidecadal variability in the Atlantic N-S gradient , provided that the effects of aerosols are included in the model .
Simulations for the twenty-first century using the same model show a strong tendency for the SST conditions associated with the 2005 drought to become much more common , owing to continuing reductions in reflective aerosol pollution in the Northern Hemisphere .

[2000] More acid , less iron

Science 10.1126 / science .1183517 ( 2010 ) Rising carbon dioxide in the oceans may hinder , not help , marine phytoplankton blooms -- because increasingly acidic waters could stifle their supply of iron , a crucial nutrient .
Dalin Shi and researchers at Princeton University , New Jersey , recorded a decrease in the uptake of iron by four species of plankton as their laboratory-controlled culture medium was acidified , changing from pH 8.6 to 7.7 .
At the same time , the concentration of bioavailable dissolved iron -- in other words , iron not chemically bound by organic matter -- dropped proportionately , suggesting that the phytoplankton 's enforced diet was due to pH-induced changes in iron chemistry that made the nutrient less available to them , and not because of a physiological reaction to more acidic conditions .

[2001] Diatom-associated bacteria are required for aggregation of Thalassiosira weissflogii

Aggregation of algae , mainly diatoms , is an important process in marine systems leading to the settling of particulate organic carbon predominantly in the form of marine snow .
Exudation products of phytoplankton form transparent exopolymer particles ( TEP ) , which acts as the glue for particle aggregation .
Heterotrophic bacteria interacting with phytoplankton may influence TEP formation and phytoplankton aggregation .
This bacterial impact has not been explored in detail .
We hypothesized that bacteria attaching to Thalassiosira weissflogii might interact in a yet-to-be determined manner , which could impact TEP formation and aggregate abundance .
The role of individual T. weissflogii-attaching and free-living new bacterial isolates for TEP production and diatom aggregation was investigated in vitro .
T. weissflogii did not aggregate in axenic culture , and striking differences in aggregation dynamics and TEP abundance were observed when diatom cultures were inoculated with either diatom-attaching or free-living bacteria .
The data indicated that free-living bacteria might not influence aggregation whereas bacteria attaching to diatom cells may increase aggregate formation .
Interestingly , photosynthetically inactivated T. weissflogii cells did not aggregate regardless of the presence of bacteria .
Comparison of aggregate formation , TEP production , aggregate sinking velocity and solid hydrated density revealed remarkable differences .
Both , photosynthetically active T. weissflogii and specific diatom-attaching bacteria were required for aggregation .
It was concluded that interactions between heterotrophic bacteria and diatoms increased aggregate formation and particle sinking and thus may enhance the efficiency of the biological pump .

[2002] Naturally occurring tumours in the basal metazoan Hydra

The molecular nature of tumours is well studied in vertebrates , although their evolutionary origin remains unknown .
In particular , there is no evidence for naturally occurring tumours in pre-bilaterian animals , such as sponges and cnidarians .
This is somewhat surprising given that recent computational studies have predicted that most metazoans might be prone to develop tumours .
Here we provide first evidence for naturally occurring tumours in two species of Hydra .
Histological , cellular and molecular data reveal that these tumours are transplantable and might originate by differentiation arrest of female gametes .
Growth of tumour cells is independent from the cellular environment .
Tumour-bearing polyps have significantly reduced fitness .
In addition , Hydra tumours show a greatly altered transcriptome that mimics expression shifts in vertebrate cancers .
Therefore , this study shows that spontaneous tumours have deep evolutionary roots and that early branching animals may be informative in revealing the fundamental mechanisms of tumorigenesis .

[2003] Consumer co-evolution as an important component of the eco-evolutionary feedback

Rapid evolution in ecologically relevant traits has recently been recognized to significantly alter the interaction between consumers and their resources , a key interaction in all ecological communities .
While these eco-evolutionary dynamics have been shown to occur when prey populations are evolving , little is known about the role of predator evolution and co-evolution between predator and prey in this context .
Here , we investigate the role of consumer co-evolution for eco-evolutionary feedback in bacteria-ciliate microcosm experiments by manipulating the initial trait variation in the predator populations .
With co-evolved predators , prey evolve anti-predatory defences faster , trait values are more variable , and predator and prey population sizes are larger at the end of the experiment compared with the non-co-evolved predators .
Most importantly , differences in predator traits results in a shift from evolution driving ecology , to ecology driving evolution .
Thus we demonstrate that predator co-evolution has important effects on eco-evolutionary dynamics .

[2004] Siderophore production and biofilm formation as linked social traits

The virulence of pathogenic microbes can depend on individual cells cooperating in the concerted production of molecules that facilitate host colonization or exploitation .
However , cooperating groups can be exploited by social defectors or ` cheats ' .
Understanding the ecology and evolution of cooperation is therefore relevant to clinical microbiology .
We studied two genetically linked cooperative traits involved in host exploitation by the opportunistic human pathogen Pseudomonas aeruginosa .
Clones that defected from cooperative production of iron-scavenging siderophores were deficient in biofilm formation .
The presence of such clones in mixed biofilms with a wild-type clone led to reduced biofilm mass .
The fitness advantage of siderophore-deficient mutants in the presence of wild-type bacteria was no greater in biofilm than in planktonic culture , suggesting that these mutants did not gain an additional advantage by exploiting wild-type biofilm polymer .
Reduced biofilm formation therefore represents a pleiotropic cost of defection from siderophore production .

[2005] Long-term water temperature reconstructions from mountain lakes with different catchment and morphometric features

Long-term water temperature records are necessary for better understanding climate change impacts on freshwaters .
We reconstruct summer water temperatures from three climatically sensitive mountain lakes in Austria using paleolimnological methods aiming to examine long-term thermal dynamics and lakes ' responses to regional climate variability since the Little Ice Age .
Our results indicate divergent trends for the lakes .
In two of the lakes , which are located at the sunny southern slope of mountains , water temperature has increased several degrees concurrent with the observed air temperature increase .
In contrast , no change is observed in the reconstructed water temperatures of a shaded lake , located at the northern slope , where also the ecological and thermal changes are most subtle .
The results indicate the importance of cold water inputs , such as snowmelt and groundwater , on lakes ' thermal conditions and suggest that watershed characteristics and lake stratification play a major role in defining the lake-specific thermal regime .

[2006] Restoration of auditory evoked responses by human ES-cell-derived otic progenitors

Deafness is a condition with a high prevalence worldwide , produced primarily by the loss of the sensory hair cells and their associated spiral ganglion neurons ( SGNs ) .
Of all the forms of deafness , auditory neuropathy is of particular concern .
This condition , defined primarily by damage to the SGNs with relative preservation of the hair cells , is responsible for a substantial proportion of patients with hearing impairment .
Although the loss of hair cells can be circumvented partially by a cochlear implant , no routine treatment is available for sensory neuron loss , as poor innervation limits the prospective performance of an implant .
Using stem cells to recover the damaged sensory circuitry is a potential therapeutic strategy .
Here we present a protocol to induce differentiation from human embryonic stem cells ( hESCs ) using signals involved in the initial specification of the otic placode .
We obtained two types of otic progenitors able to differentiate in vitro into hair-cell-like cells and auditory neurons that display expected electrophysiological properties .
Moreover , when transplanted into an auditory neuropathy model , otic neuroprogenitors engraft , differentiate and significantly improve auditory-evoked response thresholds .
These results should stimulate further research into the development of a cell-based therapy for deafness .

[2007] Convergence of soil nitrogen isotopes across global climate gradients

Quantifying global patterns of terrestrial nitrogen ( N ) cycling is central to predicting future patterns of primary productivity , carbon sequestration , nutrient fluxes to aquatic systems , and climate forcing .
With limited direct measures of soil N cycling at the global scale , syntheses of the 15N :14 N ratio of soil organic matter across climate gradients provide key insights into understanding global patterns of N cycling .
In synthesizing data from over 6000 soil samples , we show strong global relationships among soil N isotopes , mean annual temperature ( MAT ) , mean annual precipitation ( MAP ) , and the concentrations of organic carbon and clay in soil .
In both hot ecosystems and dry ecosystems , soil organic matter was more enriched in 15N than in corresponding cold ecosystems or wet ecosystems .
Below a MAT of 9.8 degreesC , soil delta15N was invariant with MAT .
At the global scale , soil organic C concentrations also declined with increasing MAT and decreasing MAP .
After standardizing for variation among mineral soils in soil C and clay concentrations , soil delta15N showed no consistent trends across global climate and latitudinal gradients .
Our analyses could place new constraints on interpretations of patterns of ecosystem N cycling and global budgets of gaseous N loss .

[2008] Macrofauna regulate heterotrophic bacterial carbon and nitrogen incorporation in low-oxygen sediments

Oxygen minimum zones ( OMZs ) currently impinge upon > 1 million km2 of sea floor and are predicted to expand with climate change .
We investigated how changes in oxygen availability , macrofaunal biomass and retention of labile organic matter ( OM ) regulate heterotrophic bacterial C and N incorporation in the sediments of the OMZ-impacted Indian continental margin ( 540-1100 m ; [ O2 ] = 0.35-15 mumol l-1 ) .
In situ pulse-chase experiments traced 13C :15 N-labelled phytodetritus into bulk sediment OM and hydrolysable amino acids , including the bacterial biomarker D-alanine .
Where oxygen availability was lowest ( [ O2 ] = 0.35 mumol l-1 ) , metazoan macrofauna were absent and bacteria assimilated 30-90 % of the labelled phytodetritus within the sediment .
At higher oxygen levels ( [ O2 ] = 2-15 mumol l-1 ) the macrofaunal presence and lower phytodetritus retention with the sediment occur concomitantly , and bacterial phytodetrital incorporation was reduced and retarded .
Bacterial C and N incorporation exhibited a significant negative relationship with macrofaunal biomass across the OMZ .
We hypothesise that fauna-bacterial interactions significantly influence OM recycling in low-oxygen sediments and need to be considered when assessing the consequences of global change on biogeochemical cycles .

[2009] Denitrification as the dominant nitrogen loss process in the Arabian Sea

Primary production in over half of the world 's oceans is limited by fixed nitrogen availability .
The main loss term from the fixed nitrogen inventory is the production of dinitrogen gas ( N2 ) by heterotrophic denitrification or the more recently discovered autotrophic process , anaerobic ammonia oxidation ( anammox ) .
Oceanic oxygen minimum zones ( OMZ ) are responsible for about 35 % of oceanic N2 production and up to half of that occurs in the Arabian Sea .
Although denitrification was long thought to be the only loss term , it has recently been argued that anammox alone is responsible for fixed nitrogen loss in the OMZs .
Here we measure denitrification and anammox rates and quantify the abundance of denitrifying and anammox bacteria in the OMZ regions of the Eastern Tropical South Pacific and the Arabian Sea .
We find that denitrification rather than anammox dominates the N2 loss term in the Arabian Sea , the largest and most intense OMZ in the world ocean .
In seven of eight experiments in the Arabian Sea denitrification is responsible for 87-99 % of the total N2 production .
The dominance of denitrification is reproducible using two independent isotope incubation methods .
In contrast , anammox is dominant in the Eastern Tropical South Pacific OMZ , as detected using one of the isotope incubation methods , as previously reported .
The abundance of denitrifying bacteria always exceeded that of anammox bacteria by up to 7 - and 19-fold in the Eastern Tropical South Pacific and Arabian Sea , respectively .
Geographic and temporal variability in carbon supply may be responsible for the different contributions of denitrification and anammox in these two OMZs .
The large contribution of denitrification to N2 loss in the Arabian Sea indicates the global significance of denitrification to the oceanic nitrogen budget .

[2010] Greenhouse-gas emission targets for limiting global warming to 2 degreesC

More than 100 countries have adopted a global warming limit of 2 degreesC or below ( relative to pre-industrial levels ) as a guiding principle for mitigation efforts to reduce climate change risks , impacts and damages .
However , the greenhouse gas ( GHG ) emissions corresponding to a specified maximum warming are poorly known owing to uncertainties in the carbon cycle and the climate response .
Here we provide a comprehensive probabilistic analysis aimed at quantifying GHG emission budgets for the 2000-50 period that would limit warming throughout the twenty-first century to below 2 degreesC , based on a combination of published distributions of climate system properties and observational constraints .
We show that , for the chosen class of emission scenarios , both cumulative emissions up to 2050 and emission levels in 2050 are robust indicators of the probability that twenty-first century warming will not exceed 2 degreesC relative to pre-industrial temperatures .
Limiting cumulative CO2 emissions over 2000-50 to 1,000 Gt CO2 yields a 25 % probability of warming exceeding 2 degreesC -- and a limit of 1,440 Gt CO2 yields a 50 % probability -- given a representative estimate of the distribution of climate system properties .
As known 2000-06 CO2 emissions were ~ 234 Gt CO2 , less than half the proven economically recoverable oil , gas and coal reserves can still be emitted up to 2050 to achieve such a goal .
Recent G8 Communiques envisage halved global GHG emissions by 2050 , for which we estimate a 12-45 % probability of exceeding 2 degreesC -- assuming 1990 as emission base year and a range of published climate sensitivity distributions .
Emissions levels in 2020 are a less robust indicator , but for the scenarios considered , the probability of exceeding 2 degreesC rises to 53-87 % if global GHG emissions are still more than 25 % above 2000 levels in 2020 .

[2011] Significance of archaeal nitrification in hypoxic waters of the Baltic Sea

Ammonia-oxidizing archaea ( AOA ) of the phylum Thaumarchaeota are widespread , and their abundance in many terrestrial and aquatic ecosystems suggests a prominent role in nitrification .
AOA also occur in high numbers in oxygen-deficient marine environments , such as the pelagic redox gradients of the central Baltic Sea ; however , data on archaeal nitrification rates are scarce and little is known about the factors , for example sulfide , that regulate nitrification in this system .
In the present work , we assessed the contribution of AOA to ammonia oxidation rates in Baltic deep basins and elucidated the impact of sulfide on this process .
Rate measurements with 15N-labeled ammonium , CO2 dark fixation measurements and quantification of AOA by catalyzed reporter deposition-fluorescence in situ hybridization revealed that among the three investigated sites the highest potential nitrification rates ( 122-884 nmol l-1per day ) were measured within gradients of decreasing oxygen , where thaumarchaeotal abundance was maximal ( 2.5-6 .9 x 105 cells per ml ) and CO2 fixation elevated .
In the presence of the archaeal-specific inhibitor GC7 , nitrification was reduced by 86-100 % , confirming the assumed dominance of AOA in this process .
In samples spiked with sulfide at concentrations similar to those of in situ conditions , nitrification activity was inhibited but persisted at reduced rates .
This result together with the substantial nitrification potential detected in sulfidic waters suggests the tolerance of AOA to periodic mixing of anoxic and sulfidic waters .
It begs the question of whether the globally distributed Thaumarchaeota respond similarly in other stratified water columns or whether the observed robustness against sulfide is a specific feature of the thaumarchaeotal subcluster present in the Baltic Deeps .
The ISME Journal advance online publication , 25 November 2014 ; doi :10.1038 / ismej .2014.218

[2012] A semi-synthetic organism with an expanded genetic alphabet

Organisms are defined by the information encoded in their genomes , and since the origin of life this information has been encoded using a two-base-pair genetic alphabet ( A-T and G-C ) .
In vitro , the alphabet has been expanded to include several unnatural base pairs ( UBPs ) .
We have developed a class of UBPs formed between nucleotides bearing hydrophobic nucleobases , exemplified by the pair formed between d5SICS and dNaM ( d5SICS-dNaM ) , which is efficiently PCR-amplified and transcribed in vitro , and whose unique mechanism of replication has been characterized .
However , expansion of an organism 's genetic alphabet presents new and unprecedented challenges : the unnatural nucleoside triphosphates must be available inside the cell ; endogenous polymerases must be able to use the unnatural triphosphates to faithfully replicate DNA containing the UBP within the complex cellular milieu ; and finally , the UBP must be stable in the presence of pathways that maintain the integrity of DNA .
Here we show that an exogenously expressed algal nucleotide triphosphate transporter efficiently imports the triphosphates of both d5SICS and dNaM ( d5SICSTP and dNaMTP ) into Escherichia coli , and that the endogenous replication machinery uses them to accurately replicate a plasmid containing d5SICS-dNaM .
Neither the presence of the unnatural triphosphates nor the replication of the UBP introduces a notable growth burden .
Lastly , we find that the UBP is not efficiently excised by DNA repair pathways .
Thus , the resulting bacterium is the first organism to propagate stably an expanded genetic alphabet .

[2013] Net regional methane sink in High Arctic soils of northeast Greenland

Arctic tundra soils serve as potentially important but poorly understood sinks of atmospheric methane ( CH4 ) , a powerful greenhouse gas .
Numerical simulations project a net increase in methane consumption in soils in high northern latitudes as a consequence of warming in the past few decades .
Advances have been made in quantifying hotspots of methane emissions in Arctic wetlands , but the drivers , magnitude , timing and location of methane consumption rates in High Arctic ecosystems are unclear .
Here , we present measurements of rates of methane consumption in different vegetation types within the Zackenberg Valley in northeast Greenland over a full growing season .
Field measurements show methane uptake in all non-water-saturated landforms studied , with seasonal averages of - 8.3 + / - 3.7 mumol CH4 m-2 h-1 in dry tundra and - 3.1 + / - 1.6 mumol CH4 m-2 h-1 in moist tundra .
The fluxes were sensitive to temperature , with methane uptake increasing with increasing temperatures .
We extrapolate our measurements and published measurements from wetlands with the help of remote-sensing land-cover classification using nine Landsat scenes .
We conclude that the ice-free area of northeast Greenland acts as a net sink of atmospheric methane , and suggest that this sink will probably be enhanced under future warmer climatic conditions .

[2014] Modern and glacial tropical snowlines controlled by sea surface temperature and atmospheric mixing

During the Last Glacial Maximum , tropical sea surface temperatures were 1 to 3 degreesC cooler than present , but the altitude of the snowlines of tropical glaciers was lower than would be expected in light of these sea surface temperatures .
Indeed , both glacial and twentieth-century snowlines seem to require lapse rates that are steeper than a moist adiabat .
Here we use estimates of Last Glacial Maximum sea surface temperature in the Indo-Pacific warm pool based on the clumped isotope palaeotemperature proxy in planktonic foraminifera and coccoliths , along with radiative-convective calculations of vertical atmospheric thermal structure , to assess the controls on tropical glacier snowlines .
Using extensive new data sets for the region , we demonstrate that mean environmental lapse rates are steeper than moist adiabatic during the recent and glacial .
We reconstruct glacial sea surface temperatures 4 to 5 degreesC cooler than modern .
We include modern and glacial sea surface temperatures in calculations of atmospheric convection that account for mixing between rising air and ambient air , and derive tropical glacier snowlines with altitudes consistent with twentieth-century and Last Glacial Maximum reconstructions .
Sea surface temperature changes < = 3 degreesC are excluded unless glacial relative humidity values were outside the range associated with deep convection in the modern .
We conclude that the entrainment of ambient air into rising air masses significantly alters the vertical temperature structure of the troposphere in modern and ancient regions of deep convection .
Furthermore , if all glacial tropical temperatures were cooler than previously estimated , it would imply a higher equilibrium climate sensitivity than included in present models .

[2015] Ocean carbon uptake and storage influenced by wind bias in global climate models

In global climate model pre-industrial control simulations the Southern Hemisphere westerly winds show a systematic bias in position and strength relative to estimates of their actual position and strength .
These wind-stress biases impact the simulated transport of the Antarctic Circumpolar Current and the nature of Southern Ocean water-mass formation and may affect the rate of meridional overturning of the global ocean .
The effect they have on oceanic carbon uptake and storage is unknown , however .
Here we demonstrate , using a coupled carbon-climate model , that the wind-stress biases reduce equilibrium ocean carbon storage , redistribute carbon within the ocean and increase oceanic carbon uptake in climate change simulations .
The wind-stress biases act directly by influencing Ekman pumping dynamics in the Southern Ocean and also seem to have an indirect effect on the overturning circulation and carbon distribution through the Agulhas leakage and Indo-Atlantic salt flux .
Our results indicate that carbon-climate model simulations with the typical pre-industrial wind-stress bias will over-estimate ocean carbon sequestration , and thereby under-estimate atmospheric carbon dioxide concentrations in the twenty-first century , relative to unbiased simulations .
The new generation of coupled carbon-climate models may be subject to these wind biases , which could alter their carbon-climate response , although it is worth noting that the uncertainty arising from wind biases that we demonstrate here is one of several uncertainties that affect modelled ocean carbon uptake .

[2016] Interhemispheric climate links revealed by a late-glacial cooling episode in southern Chile

Understanding the relative timings of climate events in the Northern and Southern hemispheres is a prerequisite for determining the causes of abrupt climate changes .
But climate records from the Patagonian Andes and New Zealand for the period of transition from glacial to interglacial conditions -- about 14.6-10 kyr before present , as determined by radiocarbon dating -- show varying degrees of correlation with similar records from the Northern Hemisphere .
It is necessary to resolve these apparent discrepancies in order to be able to assess the relative roles of Northern Hemisphere ice sheets and oceanic , atmospheric and astronomical influences in initiating climate change in the late-glacial period .
Here we report pollen records from three sites in the Lake District of southern Chile ( 41degrees S ) from which we infer conditions similar to modern climate between about 13 and 12.2 14C kyr before present ( bp ) , followed by cooling events at about 12.2 and 11.4 14C kyr bp , and then by a warming at about 9.8 14C kyr bp .
These events were nearly synchronous with important palaeoclimate changes recorded in the North Atlantic region , supporting the idea that interhemispheric linkage through the atmosphere was the primary control on climate during the last deglaciation .
In other regions of the Southern Hemisphere , where climate events are not in phase with those in the Northern Hemisphere , local oceanic influences may have counteracted the effects that propagated through the atmosphere .

[2017] Effects of tropical deforestation on climate and agriculture

Tower , ground-based and satellite observations indicate that tropical deforestation results in warmer , drier conditions at the local scale .
Understanding the regional or global impacts of deforestation on climate , and ultimately on agriculture , requires modelling .
General circulation models show that completely deforesting the tropics could result in global warming equivalent to that caused by burning of fossil fuels since 1850 , with more warming and considerable drying in the tropics .
More realistic scenarios of deforestation yield less warming and less drying , suggesting critical thresholds beyond which rainfall is substantially reduced .
In regional , mesoscale models that capture topography and vegetation-based discontinuities , small clearings can actually enhance rainfall .
At this smaller scale as well , a critical deforestation threshold exists , beyond which rainfall declines .
Future agricultural productivity in the tropics is at risk from a deforestation-induced increase in mean temperature and the associated heat extremes and from a decline in mean rainfall or rainfall frequency .
Through teleconnections , negative impacts on agriculture could extend well beyond the tropics .

[2018] Trehalose/2-sulfotrehalose biosynthesis and glycine-betaine uptake are widely spread mechanisms for osmoadaptation in the Halobacteriales

We investigated the mechanisms of osmoadaptation in the order Halobacteriales , with special emphasis on Haladaptatus paucihalophilus , known for its ability to survive in low salinities .
H. paucihalophilus genome contained genes for trehalose synthesis ( trehalose-6-phosphate synthase/trehalose -6 - phosphatase ( OtsAB pathway ) and trehalose glycosyl-transferring synthase pathway ) , as well as for glycine betaine uptake ( BCCT family of secondary transporters and QAT family of ABC transporters ) .
H. paucihalophilus cells synthesized and accumulated ~ 1.97-3 .72 mumol per mg protein of trehalose in a defined medium , with its levels decreasing with increasing salinities .
When exogenously supplied , glycine betaine accumulated intracellularly with its levels increasing at higher salinities .
RT-PCR analysis strongly suggested that H. paucihalophilus utilizes the OtsAB pathway for trehalose synthesis .
Out of 83 Halobacteriales genomes publicly available , genes encoding the OtsAB pathway and glycine betaine BCCT family transporters were identified in 38 and 60 genomes , respectively .
Trehalose ( or its sulfonated derivative ) production and glycine betaine uptake , or lack thereof , were experimentally verified in 17 different Halobacteriales species .
Phylogenetic analysis suggested that trehalose synthesis is an ancestral trait within the Halobacteriales , with its absence in specific lineages reflecting the occurrence of gene loss events during Halobacteriales evolution .
Analysis of multiple culture-independent survey data sets demonstrated the preference of trehalose-producing genera to saline and low salinity habitats , and the dominance of genera lacking trehalose production capabilities in permanently hypersaline habitats .
This study demonstrates that , contrary to current assumptions , compatible solutes production and uptake represent a common mechanism of osmoadaptation within the Halobacteriales .

[2019] Long-term ecological impacts of antibiotic administration on the human intestinal microbiota

Antibiotic administration is known to cause short-term disturbances in the microbiota of the human gastrointestinal tract , but the potential long-term consequences have not been well studied .
The aims of this study were to analyse the long-term impact of a 7-day clindamycin treatment on the faecal microbiota and to simultaneously monitor the ecological stability of the microbiota in a control group as a baseline for reference .
Faecal samples from four clindamycin-exposed and four control subjects were collected at nine different time points over 2 years .
Using a polyphasic approach , we observed highly significant disturbances in the bacterial community that persisted throughout the sampling period .
In particular , a sharp decline in the clonal diversity of Bacteroides isolates , as assessed by repetitive sequence-based PCR ( rep-PCR ) and long-term persistence of highly resistant clones were found as a direct response to the antibiotic exposure .
The Bacteroides community never returned to its original composition during the study period as assessed using the molecular fingerprinting technique , terminal restriction fragment length polymorphism ( T-RFLP ) .
Furthermore , using real-time PCR we found a dramatic and persistent increase in levels of specific resistance genes in DNA extracted from the faeces after clindamycin administration .
The temporal variations in the microbiota of the control group were minor compared to the large and persistent shift seen in the exposed group .
These results demonstrate that long after the selection pressure from a short antibiotic exposure has been removed , there are still persistent long term impacts on the human intestinal microbiota that remain for up to 2 years post-treatment .

[2020] Carbon dioxide forcing alone insufficient to explain Palaeocene-Eocene Thermal Maximum warming

The Palaeocene-Eocene Thermal Maximum ( about 55 Myr ago ) represents a possible analogue for the future and thus may provide insight into climate system sensitivity and feedbacks .
The key feature of this event is the release of a large mass of 13C-depleted carbon into the carbon reservoirs at the Earth 's surface , although the source remains an open issue .
Concurrently , global surface temperatures rose by 5-9 degreesC within a few thousand years .
Here we use published palaeorecords of deep-sea carbonate dissolution and stable carbon isotope composition along with a carbon cycle model to constrain the initial carbon pulse to a magnitude of 3,000 Pg C or less , with an isotopic composition lighter than -50 / 1000 .
As a result , atmospheric carbon dioxide concentrations increased during the main event by less than about 70 % compared with pre-event levels .
At accepted values for the climate sensitivity to a doubling of the atmospheric CO2 concentration , this rise in CO2 can explain only between 1 and 3.5 degreesC of the warming inferred from proxy records .
We conclude that in addition to direct CO2 forcing , other processes and/or feedbacks that are hitherto unknown must have caused a substantial portion of the warming during the Palaeocene-Eocene Thermal Maximum .
Once these processes have been identified , their potential effect on future climate change needs to be taken into account .

[2021] Dust-climate couplings over the past 800,000 years from the EPICA Dome C ice core

Dust can affect the radiative balance of the atmosphere by absorbing or reflecting incoming solar radiation ; it can also be a source of micronutrients , such as iron , to the ocean .
It has been suggested that production , transport and deposition of dust is influenced by climatic changes on glacial-interglacial timescales .
Here we present a high-resolution record of aeolian dust from the EPICA Dome C ice core in East Antarctica , which provides an undisturbed climate sequence over the past eight climatic cycles .
We find that there is a significant correlation between dust flux and temperature records during glacial periods that is absent during interglacial periods .
Our data suggest that dust flux is increasingly correlated with Antarctic temperature as the climate becomes colder .
We interpret this as progressive coupling of the climates of Antarctic and lower latitudes .
Limited changes in glacial-interglacial atmospheric transport time suggest that the sources and lifetime of dust are the main factors controlling the high glacial dust input .
We propose that the observed ~ 25-fold increase in glacial dust flux over all eight glacial periods can be attributed to a strengthening of South American dust sources , together with a longer lifetime for atmospheric dust particles in the upper troposphere resulting from a reduced hydrological cycle during the ice ages .

[2022] Climate change in court

As regulatory efforts to curb greenhouse-gas emissions stall , many are seeking legal routes to achieve justice on climate change .

[2023] Predicting climate change impacts on polar bear litter size

Predicting the ecological impacts of climate warming is critical for species conservation .
Incorporating future warming into population models , however , is challenging because reproduction and survival can not be measured for yet unobserved environmental conditions .
In this study , we use mechanistic energy budget models and data obtainable under current conditions to predict polar bear litter size under future conditions .
In western Hudson Bay , we predict climate warming-induced litter size declines that jeopardize population viability : ~ 28 % of pregnant females failed to reproduce for energetic reasons during the early 1990s , but 40-73 % could fail if spring sea ice break-up occurs 1 month earlier than during the 1990s , and 55-100 % if break-up occurs 2 months earlier .
Simultaneously , mean litter size would decrease by 22-67 % and 44-100 % , respectively .
The expected timeline for these declines varies with climate-model-specific sea ice predictions .
Similar litter size declines may occur in over one-third of the global polar bear population .

[2024] Salt marsh sediment bacteria : their distribution and response to external nutrient inputs

A primary focus among microbial ecologists in recent years has been to understand controls on the distribution of microorganisms in various habitats .
Much less attention has been paid to the way that environmental disturbance interacts with processes that regulate bacterial community composition .
We determined how human disturbance affected the distribution and community structure of salt marsh sediment bacteria by using denaturing gradient gel electrophoresis of 16S rRNA in five different habitats in each of four salt marshes located in northeastern Massachusetts , USA .
Two of the four marsh creeks were experimentally enriched 15 x above background by the addition of nitrogen and phosphorus fertilizers for two or more growing seasons .
Our results indicate that extrinsic factors acting at broad scales do not influence the distribution of salt marsh sediment bacteria .
Intrinsic factors , controlled by local-scale environmental heterogeneity , do play a role in structuring these sediment microbial communities , although nutrient enrichment did not have a consequential effect on the microbial community in most marsh habitats .
Only in one habitat , a region of the marsh creek wall that is heavily colonized by filamentous algae , did we see any effect of fertilization on the microbial community structure .
When similar habitats were compared among marshes , there was considerable convergence in the microbial community composition during the growing season .
Environmental factors that correlated best with microbial community composition varied with habitat , suggesting that habitat-specific intrinsic forces are primarily responsible for maintaining microbial diversity in salt marsh sediments .

[2025] Large-scale freshening of intermediate waters in the Pacific and Indian oceans

Despite the central role of the oceans in the global hydrological cycle , direct observations of precipitation over the oceans are too sparse to infer global patterns of variability .
For the regions of water-mass formation ( the high latitudes ) , however , it is possible to obtain indirect information on changes in the surface salinity budget from salinity measurements elsewhere , as water masses in the ocean carry distinct signatures in temperature and salinity over long distances .
Here we present a comparison of historical hydrographic data collected between 1930 and 1980 , with six more-recent trans-oceanic hydrographic sections ( 1985-94 ) fromthe intermediate waters of the Pacific and Indian oceans , .
North Pacific Intermediate Water and Antarctic Intermediate Water both show coherent basin-wide salinity decreases with time .
The simplest explanation for these changes is a freshening of surface waters , over approximately 22 years , in the high-latitude North Pacific and Southern oceans , suggesting that precipitation ( minus evaporation ) has increased over the polar gyres .
We estimate an increase by about 31 mm yr-1 for the Southern Ocean ( between 55degrees S and 65degrees S ) , which is about three times larger than the values suggested by coupled atmosphere-ocean models with increasing atmospheric greenhouse-gas concentrations for the same period .
The patterns of change are , however , qualitatively consistent between models and observations , and our results provide evidence for an intensification of the global hydrological cycle over the past decades .

[2026] Coral calcifying fluid pH dictates response to ocean acidification

Ocean acidification driven by rising levels of CO2 impairs calcification , threatening coral reef growth .
Predicting how corals respond to CO2 requires a better understanding of how calcification is controlled .
Here we show how spatial variations in the pH of the internal calcifying fluid ( pHcf ) in coral ( Stylophora pistillata ) colonies correlates with differential sensitivity of calcification to acidification .
Coral apexes had the highest pHcf and experienced the smallest changes in pHcf in response to acidification .
Lateral growth was associated with lower pHcf and greater changes with acidification .
Calcification showed a pattern similar to pHcf , with lateral growth being more strongly affected by acidification than apical .
Regulation of pHcf is therefore spatially variable within a coral and critical to determining the sensitivity of calcification to ocean acidification .

[2027] A humid climate state during the Palaeocene/Eocene thermal maximum

An abrupt climate warming of 5 to 10 degreesC during the Palaeocene/Eocene boundary thermal maximum ( PETM ) 55 Myr ago is linked to the catastrophic release of ~ 1,050-2 ,100 Gt of carbon from sea-floor methane hydrate reservoirs .
Although atmospheric methane , and the carbon dioxide derived from its oxidation , probably contributed to PETM warming , neither the magnitude nor the timing of the climate change is consistent with direct greenhouse forcing by the carbon derived from methane hydrate .
Here we demonstrate significant differences between marine and terrestrial carbon isotope records spanning the PETM .
We use models of key carbon cycle processes to identify the cause of these differences .
Our results provide evidence for a previously unrecognized discrete shift in the state of the climate system during the PETM , characterized by large increases in mid-latitude tropospheric humidity and enhanced cycling of carbon through terrestrial ecosystems .
A more humid atmosphere helps to explain PETM temperatures , but the ultimate mechanisms underlying the shift remain unknown .

[2028] Quantitative proteomic analysis of thylakoid from two microalgae ( Haematococcus pluvialis and Dunaliella salina ) reveals two different high light-responsive strategies

Under high light ( HL ) stress , astaxanthin-accumulating Haematococcus pluvialis and beta-carotene-accumulating Dunaliella salina showed different responsive patterns .
To elucidate cellular-regulating strategies photosynthetically and metabolically , thylakoid membrane proteins in H. pluvialis and D. salina were extracted and relatively quantified after 0 h , 24 h and 48 h of HL stress .
Proteomic analysis showed that three subunits of the cytochrome b6/f complex were greatly reduced under HL stress in H. pluvialis , while they were increased in D. salina .
Additionally , the major subunits of both photosystem ( PS ) II and PSI reaction center proteins were first reduced and subsequently recovered in H. pluvialis , while they were gradually reduced in D. salina .
D. salina also showed a greater ability to function using the xanthophyll-cycle and the cyclic photosynthetic electron transfer pathway compared to H. pluvialis .
We propose a reoriented and effective HL-responsive strategy in H. pluvialis , enabling it to acclimate under HL .
The promising metabolic pathway described here contains a reorganized pentose phosphate pathway , Calvin cycle and glycolysis pathway participating in carbon sink formation under HL in H. pluvialis .
Additionally , the efficient carbon reorientation strategy in H. pluvialis was verified by elevated extracellular carbon assimilation and rapid conversion into astaxanthin .

[2029] Enhanced seasonal forecast skill following stratospheric sudden warmings

Advances in seasonal forecasting have brought widespread socio-economic benefits .
However , seasonal forecast skill in the extratropics is relatively modest , prompting the seasonal forecasting community to search for additional sources of predictability .
For over a decade it has been suggested that knowledge of the state of the stratosphere can act as a source of enhanced seasonal predictability ; long-lived circulation anomalies in the lower stratosphere that follow stratospheric sudden warmings are associated with circulation anomalies in the troposphere that can last up to two months .
Here , we show by performing retrospective ensemble model forecasts that such enhanced predictability can be realized in a dynamical seasonal forecast system with a good representation of the stratosphere .
When initialized at the onset date of stratospheric sudden warmings , the model forecasts faithfully reproduce the observed mean tropospheric conditions in the months following the stratospheric sudden warmings .
Compared with an equivalent set of forecasts that are not initialized during stratospheric sudden warmings , we document enhanced forecast skill for atmospheric circulation patterns , surface temperatures over northern Russia and eastern Canada and North Atlantic precipitation .
We suggest that seasonal forecast systems initialized during stratospheric sudden warmings are likely to yield significantly greater forecast skill in some regions .

[2030] Groundwater arsenic concentrations in Vietnam controlled by sediment age

Arsenic contamination of groundwater continues to threaten the health of millions of people in southeast Asia .
The oxidation of organic carbon , coupled to the reductive dissolution of arsenic-bearing iron oxides , is thought to control the release of sediment-bound arsenic into groundwater .
However , the cause of the high spatial variability in groundwater arsenic concentrations -- which can range from 5 to 500 mug l-1 within distances of a few kilometres -- has been uncertain .
Here , we combine measurements of sediment age , organic-matter reactivity and water chemistry at four locations along a cross-section of the arsenic-contaminated Red River floodplain in Vietnam to determine the origin of variations in groundwater arsenic concentrations .
The burial age of the aquifer sediments , determined using optical stimulated luminescence , ranged from 460 years near the course of the present-day river to 5,900 years at the margin of the floodplain .
The groundwater arsenic content and the reactivity of sedimentary organic carbon , determined using radiotracer measurements of the rate of methanogenesis , declined with sediment age .
The sedimentary pools of both iron and arsenic also declined with the burial age of the sediments .
We suggest that the age of aquifer sediments is a key determinant of groundwater arsenic concentrations .

[2031] Ontogenetic asymmetry modulates population biomass production and response to harvest

Patterns in biomass production are determined by resource input ( productivity ) and trophic transfer efficiency .
At fixed resource input , variation in consumer biomass production has been related to food quality , metabolic type and diversity among species .
In contrast , intraspecific variation in individual body size because of ontogenetic development , which characterizes the overwhelming majority of taxa , has been largely neglected .
Here we show experimentally in a long-term multigenerational study that reallocating constant resource input in a two-stage consumer system from an equal resource delivery to juveniles and adults to an adult-biased resource delivery is sufficient to cause more than a doubling of total consumer biomass .
We discuss how such changes in consumer stage-specific resource allocation affect the likelihood for alternative stable states in harvested populations as a consequence of stage-specific overcompensation in consumer biomass and thereby the risk of catastrophic collapses in exploited populations .

[2032] The Western English Channel contains a persistent microbial seed bank

Robust seasonal dynamics in microbial community composition have previously been observed in the English Channel L4 marine observatory .
These could be explained either by seasonal changes in the taxa present at the L4 site , or by the continuous modulation of abundance of taxa within a persistent microbial community .
To test these competing hypotheses , deep sequencing of 16S rRNA from one randomly selected time point to a depth of 927 reads was compared with an existing taxonomic survey data covering 6 years .
When compared against the 6-year survey of 72 shallow sequenced time points , the deep sequenced time point maintained 95.4 % of the combined shallow OTUs .
Additionally , on average , 99.75 % + / -0.06 ( mean + / - s.d. ) of the operational taxonomic units found in each shallow sequenced sample were also found in the single deep sequenced sample .
This suggests that the vast majority of taxa identified in this ecosystem are always present , but just in different proportions that are predictable .
Thus observed changes in community composition are actually variations in the relative abundance of taxa , not , as was previously believed , demonstrating extinction and recolonization of taxa in the ecosystem through time .

[2033] Iron and phosphorus co-limit nitrogen fixation in the eastern tropical North Atlantic

The role of iron in enhancing phytoplankton productivity in high nutrient , low chlorophyll oceanic regions was demonstrated first through iron-addition bioassay experiments and subsequently confirmed by large-scale iron fertilization experiments .
Iron supply has been hypothesized to limit nitrogen fixation and hence oceanic primary productivity on geological timescales , providing an alternative to phosphorus as the ultimate limiting nutrient .
Oceanographic observations have been interpreted both to confirm and refute this hypothesis , but direct experimental evidence is lacking .
We conducted experiments to test this hypothesis during the Meteor 55 cruise to the tropical North Atlantic .
This region is rich in diazotrophs and strongly impacted by Saharan dust input .
Here we show that community primary productivity was nitrogen-limited , and that nitrogen fixation was co-limited by iron and phosphorus .
Saharan dust addition stimulated nitrogen fixation , presumably by supplying both iron and phosphorus .
Our results support the hypothesis that aeolian mineral dust deposition promotes nitrogen fixation in the eastern tropical North Atlantic .

[2034] Falling satellites , rising temperatures ?

Satellite-based estimates of trends in atmospheric temperature have disagreed with estimates derived from other measurements .
By taking into account declines in the orbital height of satellites , re-examination of those satellite data yields results that are in better accord with independent evidence of global warming .

[2035] Dynamics and associations of microbial community types across the human body

A primary goal of the Human Microbiome Project ( HMP ) was to provide a reference collection of 16S ribosomal RNA gene sequences collected from sites across the human body that would allow microbiologists to better associate changes in the microbiome with changes in health .
The HMP Consortium has reported the structure and function of the human microbiome in 300 healthy adults at 18 body sites from a single time point .
Using additional data collected over the course of 12-18 months , we used Dirichlet multinomial mixture models to partition the data into community types for each body site and made three important observations .
First , there were strong associations between whether individuals had been breastfed as an infant , their gender , and their level of education with their community types at several body sites .
Second , although the specific taxonomic compositions of the oral and gut microbiomes were different , the community types observed at these sites were predictive of each other .
Finally , over the course of the sampling period , the community types from sites within the oral cavity were the least stable , whereas those in the vagina and gut were the most stable .
Our results demonstrate that even with the considerable intra - and interpersonal variation in the human microbiome , this variation can be partitioned into community types that are predictive of each other and are probably the result of life-history characteristics .
Understanding the diversity of community types and the mechanisms that result in an individual having a particular type or changing types , will allow us to use their community types to assess disease risk and to personalize therapies .

[2036] Abrupt change in the dip of the subducting plate beneath north Chile

No large tsunamigenic earthquake has occurred in north Chile since 1877 and the region has been largely recognized as a mature seismic gap .
At the southern end of the seismic gap , the 2007 Mw 7.7 Tocopilla earthquake ruptured the deeper seismogenic interface , whereas the coupled upper interface remained unbroken .
Seismological studies onshore show a gently varying dip of 20degrees to 30degrees of the downgoing Nazca plate , which extends from the trench down to depths of 40-50 km .
Here , we study the lithospheric structure of the subduction zone of north Chile at about 22degrees S , using wide-angle seismic refraction and reflection data from land and sea , complemented by hypocentre data recorded during the 2007 Tocopilla aftershocks .
Our data document an abrupt increase in the dip of the subducting plate , from less than 10degrees to about 22degrees , at a depth of approximately 20 km .
The distribution of the 2007 aftershocks indicates that the change in dip acted as a barrier for the propagation of the 2007 earthquake towards the trench , which , in turn , indicates that the subduction megathrust is not only segmented along the trench , but also in the direction of the dip .
We propose that large-magnitude tsunamigenic earthquakes must cross the barrier and rupture the entire seismogenic zone .

[2037] Production of dimethylfuran for liquid fuels from biomass-derived carbohydrates

Diminishing fossil fuel reserves and growing concerns about global warming indicate that sustainable sources of energy are needed in the near future .
For fuels to be useful in the transportation sector , they must have specific physical properties that allow for efficient distribution , storage and combustion ; these properties are currently fulfilled by non-renewable petroleum-derived liquid fuels .
Ethanol , the only renewable liquid fuel currently produced in large quantities , suffers from several limitations , including low energy density , high volatility , and contamination by the absorption of water from the atmosphere .
Here we present a catalytic strategy for the production of 2,5-dimethylfuran from fructose ( a carbohydrate obtained directly from biomass or by the isomerization of glucose ) for use as a liquid transportation fuel .
Compared to ethanol , 2,5-dimethylfuran has a higher energy density ( by 40 per cent ) , a higher boiling point ( by 20 K ) , and is not soluble in water .
This catalytic strategy creates a route for transforming abundant renewable biomass resources into a liquid fuel suitable for the transportation sector , and may diminish our reliance on petroleum .

[2038] Late-twentieth-century emergence of the El Nino propagation asymmetry and future projections

The El Nino/Southern Oscillation ( ENSO ) is the Earth 's most prominent source of interannual climate variability , exerting profound worldwide effects .
Despite decades of research , its behaviour continues to challenge scientists .
In the eastern equatorial Pacific Ocean , the anomalously cool sea surface temperatures ( SSTs ) found during La Nina events and the warm waters of modest El Nino events both propagate westwards , as in the seasonal cycle .
In contrast , SST anomalies propagate eastwards during extreme El Nino events , prominently in the post-1976 period , spurring unusual weather events worldwide with costly consequences .
The cause of this propagation asymmetry is currently unknown .
Here we trace the cause of the asymmetry to the variations in upper ocean currents in the equatorial Pacific , whereby the westward-flowing currents are enhanced during La Nina events but reversed during extreme El Nino events .
Our results highlight that propagation asymmetry is favoured when the westward mean equatorial currents weaken , as is projected to be the case under global warming .
By analysing past and future climate simulations of an ensemble of models with more realistic propagation , we find a doubling in the occurrences of El Nino events that feature prominent eastward propagation characteristics in a warmer world .
Our analysis thus suggests that more frequent emergence of propagation asymmetry will be an indication of the Earth 's warming climate .

[2039] Coastal flooding by tropical cyclones and sea-level rise

The future impacts of climate change on landfalling tropical cyclones are unclear .
Regardless of this uncertainty , flooding by tropical cyclones will increase as a result of accelerated sea-level rise .
Under similar rates of rapid sea-level rise during the early Holocene epoch most low-lying sedimentary coastlines were generally much less resilient to storm impacts .
Society must learn to live with a rapidly evolving shoreline that is increasingly prone to flooding from tropical cyclones .
These impacts can be mitigated partly with adaptive strategies , which include careful stewardship of sediments and reductions in human-induced land subsidence .

[2040] Ocean nutrient ratios governed by plankton biogeography

The major nutrients nitrate and phosphate have one of the strongest correlations in the sea , with a slope similar to the average nitrogen ( N ) to phosphorus ( P ) content of plankton biomass ( N/P = 16:1 ) .
The processes through which this global relationship emerges despite the wide range of N/P ratios at the organism level are not known .
Here we use an ocean circulation model and observed nutrient distributions to show that the N/P ratio of biological nutrient removal varies across latitude in Southern Ocean surface waters , from 12:1 in the polar ocean to 20:1 in the sub-Antarctic zone .
These variations are governed by regional differences in the species composition of the plankton community .
The covariation of dissolved nitrate and phosphate is maintained by ocean circulation , which mixes the shallow subsurface nutrients between distinct biogeographic provinces .
Climate-driven shifts in these marine biomes may alter the mean N/P ratio and the associated carbon export by Southern Ocean ecosystems .

[2041] Excess digestive capacity in predators reflects a life of feast and famine

A central challenge for predators is achieving positive energy balance when prey are spatially and temporally heterogeneous .
Ecological heterogeneity produces evolutionary trade-offs in the physiological design of predators ; this is because the ability to capitalize on pulses of food abundance requires high capacity for food-processing , yet maintaining such capacity imposes energetic costs that are taxing during periods of food scarcity .
Recent advances in physiology show that when variation in foraging opportunities is predictable , animals may adjust energetic trade-offs by rapidly modulating their digestive system to track variation in foraging opportunities .
However , it is increasingly recognized that foraging opportunities for animals are unpredictable , which should favour animals that maintain a capacity for food-processing that exceeds average levels of consumption ( loads ) .
Despite this basic principle of quantitative evolutionary design , estimates of digestive load : capacity ratios in wild animals are virtually non-existent .
Here we provide an extensive assessment of load : capacity ratios for the digestive systems of predators in the wild , compiling 639 estimates across 38 species of fish .
We found that piscine predators typically maintain the physiological capacity to feed at daily rates 2-3 times higher than what they experience on average .
A numerical simulation of the trade-off between food-processing capacity and metabolic cost suggests that the observed level of physiological opportunism is profitable only if predator-prey encounters , and thus predator energy budgets , are far more variable in nature than currently assumed .

[2042] Asynchrony of Antarctic and Greenland climate change during the last glacial period

A central issue in climate dynamics is to understand how the Northern and Southern hemispheres are coupled during climate events .
The strongest of the fast temperature changes observed in Greenland ( so-called Dansgaard-Oeschger events ) during the last glaciation have an analogue in the temperature record from Antarctica .
A comparison of the global atmospheric concentration of methane as recorded in ice cores from Antarctica and Greenland permits a determination of the phase relationship ( in leads or lags ) of these temperature variations .
Greenland warming events around 36 and 45 kyr before present lag their Antarctic counterpart by more than 1 kyr .
On average , Antarctic climate change leads that of Greenland by 1-2 .5 kyr over the period 47-23 kyr before present .

[2043] Forecasting flowering phenology under climate warming by modelling the regulatory dynamics of flowering-time genes

Understanding how climate warming has an impact on the life cycle schedule of terrestrial organisms is critical to evaluate ecosystem vulnerability to environmental change .
Despite recent advances identifying the molecular basis of temperature responses , few studies have incorporated this knowledge into predictive models .
Here we develop a method to forecast flowering phenology by modelling regulatory dynamics of key flowering-time genes in perennial life cycles .
The model , parameterized by controlled laboratory experiments , accurately reproduces the seasonal changes in gene expression , the corresponding timing of floral initiation and return to vegetative growth after a period of flowering in complex natural environments .
A striking scenario forecast by the model under climate warming is that the shift in the return time to vegetative growth is greater than that in floral initiation , which results in a significant reduction of the flowering period .
Our study demonstrates the usefulness of gene expression assessment to predict unexplored risks of climate change .

[2044] Observational constraints indicate risk of drying in the Amazon basin

Climate warming due to human activities will be accompanied by hydrological cycle changes .
Economies , societies and ecosystems in South America are vulnerable to such water resource changes .
Hence , water resource impact assessments for South America , and corresponding adaptation and mitigation policies , have attracted increased attention .
However , substantial uncertainties remain in the current water resource assessments that are based on multiple coupled Atmosphere Ocean General Circulation models .
This uncertainty varies from significant wetting to catastrophic drying .
By applying a statistical method , we characterized the uncertainty and identified global-scale metrics for measuring the reliability of water resource assessments in South America .
Here , we show that , although the ensemble mean assessment suggested wetting across most of South America , the observational constraints indicate a higher probability of drying in the Amazon basin .
Thus , over-reliance on the consensus of models can lead to inappropriate decision making .

[2045] Strong correlation between levels of tropospheric hydroxyl radicals and solar ultraviolet radiation

The most important chemical cleaning agent of the atmosphere is the hydroxyl radical , OH .
It determines the oxidizing power of the atmosphere , and thereby controls the removal of nearly all gaseous atmospheric pollutants .
The atmospheric supply of OH is limited , however , and could be overcome by consumption due to increasing pollution and climate change , with detrimental feedback effects .
To date , the high variability of OH concentrations has prevented the use of local observations to monitor possible trends in the concentration of this species .
Here we present and analyse long-term measurements of atmospheric OH concentrations , which were taken between 1999 and 2003 at the Meteorological Observatory Hohenpeissenberg in southern Germany .
We find that the concentration of OH can be described by a surprisingly linear dependence on solar ultraviolet radiation throughout the measurement period , despite the fact that OH concentrations are influenced by thousands of reactants .
A detailed numerical model of atmospheric reactions and measured trace gas concentrations indicates that the observed correlation results from compensations between individual processes affecting OH , but that a full understanding of these interactions may not be possible on the basis of our current knowledge of atmospheric chemistry .
As a consequence of the stable relationship between OH concentrations and ultraviolet radiation that we observe , we infer that there is no long-term trend in the level of OH in the Hohenpeissenberg data set .

[2046] Emergence of structural and dynamical properties of ecological mutualistic networks

Mutualistic networks are formed when the interactions between two classes of species are mutually beneficial .
They are important examples of cooperation shaped by evolution .
Mutualism between animals and plants has a key role in the organization of ecological communities .
Such networks in ecology have generally evolved a nested architecture independent of species composition and latitude ; specialist species , with only few mutualistic links , tend to interact with a proper subset of the many mutualistic partners of any of the generalist species .
Despite sustained efforts to explain observed network structure on the basis of community-level stability or persistence , such correlative studies have reached minimal consensus .
Here we show that nested interaction networks could emerge as a consequence of an optimization principle aimed at maximizing the species abundance in mutualistic communities .
Using analytical and numerical approaches , we show that because of the mutualistic interactions , an increase in abundance of a given species results in a corresponding increase in the total number of individuals in the community , and also an increase in the nestedness of the interaction matrix .
Indeed , the species abundances and the nestedness of the interaction matrix are correlated by a factor that depends on the strength of the mutualistic interactions .
Nestedness and the observed spontaneous emergence of generalist and specialist species occur for several dynamical implementations of the variational principle under stationary conditions .
Optimized networks , although remaining stable , tend to be less resilient than their counterparts with randomly assigned interactions .
In particular , we show analytically that the abundance of the rarest species is linked directly to the resilience of the community .
Our work provides a unifying framework for studying the emergent structural and dynamical properties of ecological mutualistic networks .

[2047] The natural ocean acidification and fertilization event caused by the submarine eruption of El Hierro

The shallow submarine eruption which took place in October 10th 2011 , 1.8 km south of the island of El Hierro ( Canary Islands ) allowed the study of the abrupt changes in the physical-chemical properties of seawater caused by volcanic discharges .
In order to monitor the evolution of these changes , seven oceanographic surveys were carried out over six months ( November 2011-April 2012 ) from the beginning of the eruptive stage to the post-eruptive phase .
Here , we present dramatic changes in the water column chemistry including large decreases in pH , striking effects on the carbonate system , decreases in the oxygen concentrations and enrichment of Fe ( II ) and nutrients .
Our findings highlight that the same volcano which was responsible for the creation of a highly corrosive environment , affecting marine biota , has also provided the nutrients required for the rapid recuperation of the marine ecosystem .

[2048] You are what you talk : quorum sensing induces individual morphologies and cell division modes in Dinoroseobacter shibae

Dinoroseobacter shibae , a member of the Roseobacter clade abundant in marine environments , is characterized by a pronounced pleomorphism .
Cell shapes range from variable-sized ovoid rods to long filaments with a high copy number of chromosomes .
Time-lapse microscopy shows cells dividing either by binary fission or by budding from the cell poles .
Here we demonstrate that this morphological heterogeneity is induced by quorum sensing ( QS ) .
D. shibae utilizes three acylated homoserine lactone ( AHL ) synthases ( luxI1-3 ) to produce AHLs with unsaturated C18 side chains .
A DeltaluxI1-knockout strain completely lacking AHL biosynthesis was uniform in morphology and divided by binary fission only .
Transcriptome analysis revealed that expression of genes responsible for control of cell division was reduced in this strain , providing the link between QS and the observed phenotype .
In addition , flagellar biosynthesis and type IV secretion system ( T4SS ) were downregulated .
The wild-type phenotype and gene expression could be restored through addition of synthetic C18-AHLs .
Their effectiveness was dependent on the number of double bonds in the acyl side chain and the regulated trait .
The wild-type expression level of T4SS genes was fully restored even by an AHL with a saturated C18 side chain that has not been detected in D. shibae .
QS induces phenotypic individualization of D. shibae cells rather than coordinating the population .
This strategy might be beneficial in unpredictably changing environments , for example , during algal blooms when resource competition and grazing exert fluctuating selective pressures .
A specific response towards non-native AHLs might provide D. shibae with the capacity for complex interspecies communication .

[2049] Nutrient availability as the key regulator of global forest carbon balance

Forests strongly affect climate through the exchange of large amounts of atmospheric CO2 ( ref . )
.
The main drivers of spatial variability in net ecosystem production ( NEP ) on a global scale are , however , poorly known .
As increasing nutrient availability increases the production of biomass per unit of photosynthesis and reduces heterotrophic respiration in forests , we expected nutrients to determine carbon sequestration in forests .
Our synthesis study of 92 forests in different climate zones revealed that nutrient availability indeed plays a crucial role in determining NEP and ecosystem carbon-use efficiency ( CUEe ; that is , the ratio of NEP to gross primary production ( GPP ) ) .
Forests with high GPP exhibited high NEP only in nutrient-rich forests ( CUEe = 33 + / - 4 % ; mean + / - s.e.m. ) .
In nutrient-poor forests , a much larger proportion of GPP was released through ecosystem respiration , resulting in lower CUEe ( 6 + / - 4 % ) .
Our finding that nutrient availability exerts a stronger control on NEP than on carbon input ( GPP ) conflicts with assumptions of nearly all global coupled carbon cycle-climate models , which assume that carbon inputs through photosynthesis drive biomass production and carbon sequestration .
An improved global understanding of nutrient availability would therefore greatly improve carbon cycle modelling and should become a critical focus for future research .

[2050] Simulating the amplification of orbital forcing by ocean feedbacks in the last glaciation

According to Milankovitch theory , the lower summer insolation at high latitudes about 115,000 years ago allowed winter snow to persist throughout summer , leading to ice-sheet build-up and glaciation .
But attempts to simulate the last glaciation using global atmospheric models have failed to produce this outcome when forced by insolation changes only .
These results point towards the importance of feedback effects -- for example , through changes in vegetation or the ocean circulation -- for the amplification of solar forcing .
Here we present a fully coupled ocean-atmosphere model of the last glaciation that produces a build-up of perennial snow cover at known locations of ice sheets during this period .
We show that ocean feedbacks lead to a cooling of the high northern latitudes , along with an increase in atmospheric moisture transport from the Equator to the poles .
These changes agree with available geological data and , together , they lead to an increased delivery of snow to high northern latitudes .
The mechanism we present explains the onset of glaciation -- which would be amplified by changes in vegetation -- in response to weak orbital forcing .

[2051] Evidence of intra-specific competition for food in a pelagic seabird

The factors affecting the population dynamics of seabirds have long intrigued biologists .
Current data suggest that density-dependent depletion of prey during the breeding season may regulate population size .
However , much of the evidence for this has been circumstantial , and the underlying mechanisms are unclear .
Here , we show that the per capita population growth rates of northern gannet Morus bassanus at colonies in Britain and Ireland have declined with increasing population size .
Furthermore , direct observations reveal that the mean foraging trip duration of breeding gannets is positively correlated with colony size , both among colonies of different sizes in the same year , and within colonies as they change in size .
To understand this phenomenon , we have developed a model which demonstrates that disturbance of fish alone can readily generate conditions under which gannets at larger colonies have to travel further to obtain food .

[2052] Gut microbiome composition and function in experimental colitis during active disease and treatment-induced remission

Dysregulated immune responses to gut microbes are central to inflammatory bowel disease ( IBD ) , and gut microbial activity can fuel chronic inflammation .
Examining how IBD-directed therapies influence gut microbiomes may identify microbial community features integral to mitigating disease and maintaining health .
However , IBD patients often receive multiple treatments during disease flares , confounding such analyses .
Preclinical models of IBD with well-defined disease courses and opportunities for controlled treatment exposures provide a valuable solution .
Here , we surveyed the gut microbiome of the T-bet - / - Rag2 - / - mouse model of colitis during active disease and treatment-induced remission .
Microbial features modified among these conditions included altered potential for carbohydrate and energy metabolism and bacterial pathogenesis , specifically cell motility and signal transduction pathways .
We also observed an increased capacity for xenobiotics metabolism , including benzoate degradation , a pathway linking host adrenergic stress with enhanced bacterial virulence , and found decreased levels of fecal dopamine in active colitis .
When transferred to gnotobiotic mice , gut microbiomes from mice with active disease versus treatment-induced remission elicited varying degrees of colitis .
Thus , our study provides insight into specific microbial clades and pathways associated with health , active disease and treatment interventions in a mouse model of colitis .

[2053] Implications of streamlining theory for microbial ecology

Whether a small cell , a small genome or a minimal set of chemical reactions with self-replicating properties , simplicity is beguiling .
As Leonardo da Vinci reportedly said , ` simplicity is the ultimate sophistication ' .
Two diverging views of simplicity have emerged in accounts of symbiotic and commensal bacteria and cosmopolitan free-living bacteria with small genomes .
The small genomes of obligate insect endosymbionts have been attributed to genetic drift caused by small effective population sizes ( Ne ) .
In contrast , streamlining theory attributes small cells and genomes to selection for efficient use of nutrients in populations where Ne is large and nutrients limit growth .
Regardless of the cause of genome reduction , lost coding potential eventually dictates loss of function .
Consequences of reductive evolution in streamlined organisms include atypical patterns of prototrophy and the absence of common regulatory systems , which have been linked to difficulty in culturing these cells .
Recent evidence from metagenomics suggests that streamlining is commonplace , may broadly explain the phenomenon of the uncultured microbial majority , and might also explain the highly interdependent ( connected ) behavior of many microbial ecosystems .
Streamlining theory is belied by the observation that many successful bacteria are large cells with complex genomes .
To fully appreciate streamlining , we must look to the life histories and adaptive strategies of cells , which impose minimum requirements for complexity that vary with niche .

[2054] Oxidation of the Ediacaran Ocean

Oxygenation of the Earth 's surface is increasingly thought to have occurred in two steps .
The first step , which occurred ~ 2,300 million years ( Myr ) ago , involved a significant increase in atmospheric oxygen concentrations and oxygenation of the surface ocean .
A further increase in atmospheric oxygen appears to have taken place during the late Neoproterozoic period ( ~ 800-542 Myr ago ) .
This increase may have stimulated the evolution of macroscopic multicellular animals and the subsequent radiation of calcified invertebrates , and may have led to oxygenation of the deep ocean .
However , the nature and timing of Neoproterozoic oxidation remain uncertain .
Here we present high-resolution carbon isotope and sulphur isotope records from the Huqf Supergroup , Sultanate of Oman , that cover most of the Ediacaran period ( ~ 635 to ~ 548 Myr ago ) .
These records indicate that the ocean became increasingly oxygenated after the end of the Marinoan glaciation , and they allow us to identify three distinct stages of oxidation .
When considered in the context of other records from this period , our data indicate that certain groups of eukaryotic organisms appeared and diversified during the second and third stages of oxygenation .
The second stage corresponds with the Shuram excursion in the carbon isotope record and seems to have involved the oxidation of a large reservoir of organic carbon suspended in the deep ocean , indicating that this event may have had a key role in the evolution of eukaryotic organisms .
Our data thus provide new insights into the oxygenation of the Ediacaran ocean and the stepwise restructuring of the carbon and sulphur cycles that occurred during this significant period of Earth 's history .

[2055] Climate change and evolutionary adaptation

Evolutionary adaptation can be rapid and potentially help species counter stressful conditions or realize ecological opportunities arising from climate change .
The challenges are to understand when evolution will occur and to identify potential evolutionary winners as well as losers , such as species lacking adaptive capacity living near physiological limits .
Evolutionary processes also need to be incorporated into management programmes designed to minimize biodiversity loss under rapid climate change .
These challenges can be met through realistic models of evolutionary change linked to experimental data across a range of taxa .

[2056] Onset of Asian desertification by 22 Myr ago inferred from loess deposits in China

The initial desertification in the Asian interior is thought to be one of the most prominent climate changes in the Northern Hemisphere during the Cenozoic era .
But the dating of this transition is uncertain , partly because desert sediments are usually scattered , discontinuous and difficult to date .
Here we report nearly continuous aeolian deposits covering the interval from 22 to 6.2 million years ago , on the basis of palaeomagnetic measurements and fossil evidence .
A total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils .
This new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of Asia by the early Miocene epoch , at least 14 million years earlier than previously thought .
Regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in Asia .

[2057] Earthworms facilitate carbon sequestration through unequal amplification of carbon stabilization compared with mineralization

A recent review concluded that earthworm presence increases CO2 emissions by 33 % but does not affect soil organic carbon stocks .
However , the findings are controversial and raise new questions .
Here we hypothesize that neither an increase in CO2 emission nor in stabilized carbon would entirely reflect the earthworms ' contribution to net carbon sequestration .
We show how two widespread earthworm invaders affect net carbon sequestration through impacts on the balance of carbon mineralization and carbon stabilization .
Earthworms accelerate carbon activation and induce unequal amplification of carbon stabilization compared with carbon mineralization , which generates an earthworm-mediated ` carbon trap ' .
We introduce the new concept of sequestration quotient to quantify the unequal processes .
The patterns of CO2 emission and net carbon sequestration are predictable by comparing sequestration quotient values between treatments with and without earthworms .
This study clarifies an ecological mechanism by which earthworms may regulate the terrestrial carbon sink .

[2058] Quantifying the uncertainty in forecasts of anthropogenic climate change

Forecasts of climate change are inevitably uncertain .
It is therefore essential to quantify the risk of significant departures from the predicted response to a given emission scenario .
Previous analyses of this risk have been based either on expert opinion , perturbation analysis of simplified climate models or the comparison of predictions from general circulation models .
Recent observed changes that appear to be attributable to human influence provide a powerful constraint on the uncertainties in multi-decadal forecasts .
Here we assess the range of warming rates over the coming 50 years that are consistent with the observed near-surface temperature record as well as with the overall patterns of response predicted by several general circulation models .
We expect global mean temperatures in the decade 2036-46 to be 1-2 .5 K warmer than in pre-industrial times under a ` business as usual ' emission scenario .
This range is relatively robust to errors in the models ' climate sensitivity , rate of oceanic heat uptake or global response to sulphate aerosols as long as these errors are persistent over time .
Substantial changes in the current balance of greenhouse warming and sulphate aerosol cooling would , however , increase the uncertainty .
Unlike 50-year warming rates , the final equilibrium warming after the atmospheric composition stabilizes remains very uncertain , despite the evidence provided by the emerging signal .

[2059] Vulnerability of Polar Oceans to Anthropogenic Acidification : Comparison of Arctic and Antarctic Seasonal Cycles

Polar oceans are chemically sensitive to anthropogenic acidification due to their relatively low alkalinity and correspondingly weak carbonate buffering capacity .
Here , we compare unique CO2 system observations covering complete annual cycles at an Arctic ( Amundsen Gulf ) and Antarctic site ( Prydz Bay ) .
The Arctic site experiences greater seasonal warming ( 10 vs 3degreesC ) , and freshening ( 3 vs 2 ) , has lower alkalinity ( 2220 vs 2320 mumol/kg ) , and lower summer pH ( 8.15 vs 8.5 ) , than the Antarctic site .
Despite a larger uptake of inorganic carbon by summer photosynthesis , the Arctic carbon system exhibits smaller seasonal changes than the more alkaline Antarctic system .
In addition , the excess surface nutrients in the Antarctic may allow mitigation of acidification , via CO2 removal by enhanced summer production driven by iron inputs from glacial and sea-ice melting .
These differences suggest that the Arctic system is more vulnerable to anthropogenic change due to lower alkalinity , enhanced warming , and nutrient limitation .

[2060] Departures from eustasy in Pliocene sea-level records

Proxy data suggest that atmospheric CO2 levels during the middle of the Pliocene epoch ( about 3 Myr ago ) were similar to today , leading to the use of this interval as a potential analogue for future climate change .
Estimates for mid-Pliocene sea levels range from 10 to 40 m above present , and a value of +25 m is often adopted in numerical climate model simulations .
A eustatic change of such magnitude implies the complete deglaciation of the West Antarctic and Greenland ice sheets , and significant loss of mass in the East Antarctic ice sheet .
However , the effects of glacial isostatic adjustments have not been accounted for in Pliocene sea-level reconstructions .
Here we numerically model these effects on Pliocene shoreline features using a gravitationally self-consistent treatment of post-glacial sea-level change .
We find that the predicted modern elevation of Pliocene shoreline features can deviate significantly from the eustatic signal , even in the absence of subsequent tectonically-driven movements of the Earth 's surface .
In our simulations , this non-eustatic sea-level change , at individual locations , is caused primarily by residual isostatic adjustments associated with late Pleistocene glaciation .
We conclude that a combination of model results and field observations can help to better constrain sea level in the past , and hence lend insight into the stability of ice sheets under varying climate conditions .

[2061] Natural strategies for photosynthetic light harvesting

Photosynthetic organisms are crucial for life on Earth as they provide food and oxygen and are at the basis of most energy resources .
They have a large variety of light-harvesting strategies that allow them to live nearly everywhere where sunlight can penetrate .
They have adapted their pigmentation to the spectral composition of light in their habitat , they acclimate to slowly varying light intensities and they rapidly respond to fast changes in light quality and quantity .
This is particularly important for oxygen-producing organisms because an overdose of light in combination with oxygen can be lethal .
Rapid progress is being made in understanding how different organisms maximize light harvesting and minimize deleterious effects .
Here we summarize the latest findings and explain the main design principles used in nature .
The available knowledge can be used for optimizing light harvesting in both natural and artificial photosynthesis to improve light-driven production processes .

[2062] Long-term climate implications of twenty-first century options for carbon dioxide emission mitigation

Long-term future warming is primarily constrained by cumulative emissions of carbon dioxide .
Previous studies have estimated that humankind has already emitted about 50 % of the total amount allowed if warming , relative to pre-industrial , is to stay below 2 degreesC ( refs , ) .
Carbon dioxide emissions will thus need to decrease substantially in the future if this target is to be met .
Here we show how links between near-term decisions , long-term behaviour and climate sensitivity uncertainties constrain options for emissions mitigation .
Using a model of intermediate complexity , we explore the implications of non-zero long-term global emissions , combined with various near-term mitigation rates or delays in action .
For a median climate sensitivity , a long-term 90 % emission reduction relative to the present-day level is incompatible with a 2 degreesC target within the coming millennium .
Zero or negative emissions can be compatible with the target if medium to high emission-reduction rates begin within the next two decades .
For a high climate sensitivity , however , even negative emissions would require a global mitigation rate at least as great as the highest rate considered feasible by economic models to be implemented within the coming decade .
Only a low climate sensitivity would allow for a longer delay in mitigation action and a more conservative mitigation rate , and would still require at least 90 % phase-out of emissions thereafter .

[2063] Dispersal and niche evolution jointly shape the geographic turnover of phylogenetic clades across continents

The turnover of phylogenetic clades across space is a fundamental biodiversity pattern that may depend on long-term evolutionary processes , and that has downstream effects on other aspects of diversity including species richness and community structure .
Limited niche evolution and limited dispersal are two major processes causing spatial restriction , and thus turnover , of clades .
We studied the determinants of clade turnover within the World 's richest floristic kingdom , the Neotropics , using the palm family ( Arecaceae ) as a model .
We show that continental-scale clade turnover is driven by a combination of limited niche evolution -- with respect to temperature and soil tolerances -- and limited dispersal .
These findings are consistent with strong dispersal barriers within the Neotropics , and the observation that some palm lineages are most diverse in certain biomes or climates .
The importance of such deep-time effects suggest that palms might be slow to adapt or disperse in response to anthropogenic climate change .

[2064] Global-scale latitudinal patterns of plant fine-root nitrogen and phosphorus

Most water and essential soil nutrient uptake is carried out by fine roots in plants .
It is therefore important to understand the global geographic patterns of fine-root nitrogen and phosphorus cycling .
Here , by compiling plant root data from 211 studies in 51 countries , we show that live fine roots have low nitrogen ( N ) and phosphorus ( P ) , but similar N :P ratios when compared with green leaves .
The fine-root N :P ratio differs between biomes and declines exponentially with latitude in roots of all diameter classes .
This is in contrast to previous reports of a linear latitudinal decline in green leaf N :P , but consistent with nonlinear declines in leaf litter N :P .
Whereas the latitudinal N :P decline in both roots and leaves reflects collective influences of climate , soil age and weathering , differences in the shape of the response function may be a result of their different N and P use strategies .

[2065] Genetic diversity in caribou linked to past and future climate change

Climate-driven range fluctuations during the Pleistocene have continuously reshaped species distribution leading to populations of contrasting genetic diversity .
Contemporary climate change is similarly influencing species distribution and population structure , with important consequences for patterns of genetic diversity and species ' evolutionary potential .
Yet few studies assess the impacts of global climatic changes on intraspecific genetic variation .
Here , combining analyses of molecular data with time series of predicted species distributions and a model of diffusion through time over the past 21 kyr , we unravel caribou response to past and future climate changes across its entire Holarctic distribution .
We found that genetic diversity is geographically structured with two main caribou lineages , one originating from and confined to Northeastern America , the other originating from Euro-Beringia but also currently distributed in western North America .
Regions that remained climatically stable over the past 21 kyr maintained a high genetic diversity and are also predicted to experience higher climatic stability under future climate change scenarios .
Our interdisciplinary approach , combining genetic data and spatial analyses of climatic stability ( applicable to virtually any taxon ) , represents a significant advance in inferring how climate shapes genetic diversity and impacts genetic structure .

[2066] Ice-sheet variability around the North Atlantic Ocean during the last deglaciation

Millennial-scale variability in the flux of ice-rafted detritus to North Atlantic sediments during the last glacial period has been interpreted to reflect a climate-forced increase in the discharge of icebergs from ice-sheet margins surrounding the northern North Atlantic Ocean .
But the relationship between ice-sheet variability and climate change is not clear , as both the sources of ice-rafted detritus and the ice-marginal processes are varied and complex .
Terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice-sheet oscillations , and whether the ice sheet ( or sector ) was advancing or retreating with respect to climate change .
Here we constrain the age and anatomy of a prominent readvance of the British Ice Sheet in the northern Irish Sea region at ~ 14 14C kyr BP ( ~ 16.4 calendar kyr BP ) .
The analysis indicates that the British Ice Sheet participated in an iceberg discharge episode known as Heinrich event 1 .
Comparison with other terrestrial and marine ice-sheet records suggests that the dynamic collapse of the Laurentide Ice Sheet beginning at 14.6-15 .0 14C kyr BP , ( ~ 17.2-17 .6 calendar kyr BP ) initiated varied responses from other ice-sheet margins around the northern North Atlantic region .
These observations support the argument that the release of icebergs and meltwater during Heinrich event 1 disrupted the North Atlantic thermohaline circulation , leading to a delay or reversal of deglaciation of the Northern Hemisphere and at least as far south as 40degrees S for two to three thousand years , , , suggesting a climate forcing and response similar to that of the ensuing Younger Dryas ` cold snap ' , .

[2067] Glacier retreat in New Zealand during the Younger Dryas stadial

Millennial-scale cold reversals in the high latitudes of both hemispheres interrupted the last transition from full glacial to interglacial climate conditions .
The presence of the Younger Dryas stadial ( ~ 12.9 to ~ 11.7 kyr ago ) is established throughout much of the Northern Hemisphere , but the global timing , nature and extent of the event are not well established .
Evidence in mid to low latitudes of the Southern Hemisphere , in particular , has remained perplexing .
The debate has in part focused on the behaviour of mountain glaciers in New Zealand , where previous research has found equivocal evidence for the precise timing of increased or reduced ice extent .
The interhemispheric behaviour of the climate system during the Younger Dryas thus remains an open question , fundamentally limiting our ability to formulate realistic models of global climate dynamics for this time period .
Here we show that New Zealand 's glaciers retreated after ~ 13 kyr bp , at the onset of the Younger Dryas , and in general over the subsequent ~ 1.5-kyr period .
Our evidence is based on detailed landform mapping , a high-precision 10Be chronology and reconstruction of former ice extents and snow lines from well-preserved cirque moraines .
Our late-glacial glacier chronology matches climatic trends in Antarctica , Southern Ocean behaviour and variations in atmospheric CO2 .
The evidence points to a distinct warming of the southern mid-latitude atmosphere during the Younger Dryas and a close coupling between New Zealand 's cryosphere and southern high-latitude climate .
These findings support the hypothesis that extensive winter sea ice and curtailed meridional ocean overturning in the North Atlantic led to a strong interhemispheric thermal gradient during late-glacial times , in turn leading to increased upwelling and CO2 release from the Southern Ocean , thereby triggering Southern Hemisphere warming during the northern Younger Dryas .

[2068] RNA-seq reveals cooperative metabolic interactions between two termite-gut spirochete species in co-culture

The hindguts of wood-feeding termites typically contain hundreds of microbial species .
Together with their insect host , these gut microbes degrade lignocellulose into usable catabolites .
Although past research revealed many facets of the stepwise flow of metabolites in this scheme , not much is known about the breadth of interactions occurring between termite-gut microbes .
Most of these microbes are thought to depend on , and to have co-speciated with , their host and each other for millions of years .
In this study , we explored the interactions of two spirochetes previously isolated from the very same termite species .
As hydrogen ( H2 ) is the central free intermediate in termite-gut lignocellulose digestion , we focused on interactions between two closely related termite-gut spirochetes possessing complementary H2 physiologies : one produces H2 , while the other consumes it .
In vitro , these two Treponema species markedly enhanced each other 's growth .
RNA sequencing resolved the transcriptomes of these two closely related organisms , revealing that co-cultivation causes comprehensive changes in global gene expression .
The expression of well over a 100 genes in each species was changed > twofold , with over a dozen changed > 10-fold .
Several changes implicating synergistic cross-feeding of known metabolites were validated in vitro .
Additionally , certain activities beneficial to the host were preferentially expressed during consortial growth .
However , the majority of changes in gene expression are not yet understandable , but indicate a broad , comprehensive and mutualistic interaction between these closely related , co-resident gut symbionts .
The results suggest that staggeringly intricate networks of metabolic and gene interactions drive lignocellulose degradation and co-evolution of termite gut microbiota .

[2069] Risk maps for Antarctic krill under projected Southern Ocean acidification

Marine ecosystems of the Southern Ocean are particularly vulnerable to ocean acidification .
Antarctic krill ( Euphausia superba ; hereafter krill ) is the key pelagic species of the region and its largest fishery resource .
There is therefore concern about the combined effects of climate change , ocean acidification and an expanding fishery on krill and ultimately , their dependent predators -- whales , seals and penguins .
However , little is known about the sensitivity of krill to ocean acidification .
Juvenile and adult krill are already exposed to variable seawater carbonate chemistry because they occupy a range of habitats and migrate both vertically and horizontally on a daily and seasonal basis .
Moreover , krill eggs sink from the surface to hatch at 700-1 ,000 m ( ref . )
, where the carbon dioxide partial pressure ( pCO2 ) in sea water is already greater than it is in the atmosphere .
Krill eggs sink passively and so can not avoid these conditions .
Here we describe the sensitivity of krill egg hatch rates to increased CO2 , and present a circumpolar risk map of krill hatching success under projected pCO2 levels .
We find that important krill habitats of the Weddell Sea and the Haakon VII Sea to the east are likely to become high-risk areas for krill recruitment within a century .
Furthermore , unless CO2 emissions are mitigated , the Southern Ocean krill population could collapse by 2300 with dire consequences for the entire ecosystem .

[2070] Making sense of palaeoclimate sensitivity

Many palaeoclimate studies have quantified pre-anthropogenic climate change to calculate climate sensitivity ( equilibrium temperature change in response to radiative forcing change ) , but a lack of consistent methodologies produces a wide range of estimates and hinders comparability of results .
Here we present a stricter approach , to improve intercomparison of palaeoclimate sensitivity estimates in a manner compatible with equilibrium projections for future climate change .
Over the past 65 million years , this reveals a climate sensitivity ( in K W-1 m2 ) of 0.3-1 .9 or 0.6-1 .3 at 95 % or 68 % probability , respectively .
The latter implies a warming of 2.2-4 .8 K per doubling of atmospheric CO2 , which agrees with IPCC estimates .

[2071] Contribution of anthropology to the study of climate change

Understanding the challenge that climate change poses and crafting appropriate adaptation and mitigation mechanisms requires input from the breadth of the natural and social sciences .
Anthropology 's in-depth fieldwork methodology , long engagement in questions of society-environment interactions and broad , holistic view of society yields valuable insights into the science , impacts and policy of climate change .
Yet the discipline 's voice in climate change debates has remained a relatively marginal one until now .
Here , we identify three key ways that anthropological research can enrich and deepen contemporary understandings of climate change .

[2072] Recent patterns and mechanisms of carbon exchange by terrestrial ecosystems

Knowledge of carbon exchange between the atmosphere , land and the oceans is important , given that the terrestrial and marine environments are currently absorbing about half of the carbon dioxide that is emitted by fossil-fuel combustion .
This carbon uptake is therefore limiting the extent of atmospheric and climatic change , but its long-term nature remains uncertain .
Here we provide an overview of the current state of knowledge of global and regional patterns of carbon exchange by terrestrial ecosystems .
Atmospheric carbon dioxide and oxygen data confirm that the terrestrial biosphere was largely neutral with respect to net carbon exchange during the 1980s , but became a net carbon sink in the 1990s .
This recent sink can be largely attributed to northern extratropical areas , and is roughly split between North America and Eurasia .
Tropical land areas , however , were approximately in balance with respect to carbon exchange , implying a carbon sink that offset emissions due to tropical deforestation .
The evolution of the terrestrial carbon sink is largely the result of changes in land use over time , such as regrowth on abandoned agricultural land and fire prevention , in addition to responses to environmental changes , such as longer growing seasons , and fertilization by carbon dioxide and nitrogen .
Nevertheless , there remain considerable uncertainties as to the magnitude of the sink in different regions and the contribution of different processes .

[2073] Contribution of ocean overturning circulation to tropical rainfall peak in the Northern Hemisphere

Rainfall in the tropics is largely focused in a narrow zonal band near the Equator , known as the intertropical convergence zone .
On average , substantially more rain falls just north of the Equator .
This hemispheric asymmetry in tropical rainfall has been attributed to hemispheric asymmetries in ocean temperature induced by tropical landmasses .
However , the ocean meridional overturning circulation also redistributes energy , by carrying heat northwards across the Equator .
Here , we use satellite observations of the Earth 's energy budget , atmospheric reanalyses and global climate model simulations to study tropical rainfall using a global energetic framework .
We show that the meridional overturning circulation contributes significantly to the hemispheric asymmetry in tropical rainfall by transporting heat from the Southern Hemisphere to the Northern Hemisphere , and thereby pushing the tropical rain band north .
This northward shift in tropical precipitation is seen in global climate model simulations when ocean heat transport is included , regardless of whether continents are present or not .
If the strength of the meridional overturning circulation is reduced in the future as a result of global warming , as has been suggested , precipitation patterns in the tropics could change , with potential societal consequences .

[2074] Correlation between Arabian Sea and Greenland climate oscillations of the past 110,000 years

Palaeoclimate studies have revealed the general high-frequency instability of Late Pleistocene climate -- for example , the so-called Dansgaard-Oeschger and Heinrich events -- on timescales of a few millennia , centuries or even decades .
Here we present evidence for a general relationship between low-latitude monsoonal climate variability and the rapid temperature fluctuations of high northern latitudes that are recorded in the Greenland ice records .
Sediment cores from the northeastern Arabian Sea show laminated , organic-carbon-rich bands , reflecting strong monsoon-induced biological productivity , that correlate with the mild interstadial climate events in the northern North Atlantic region .
In contrast , periods of lowered southwest monsoonal intensity , indicated by bioturbated , organic-carbon-poor bands , are associated with intervals of high-latitude atmospheric cooling and the injection of melt water into the North Atlantic basin .
Our records suggest that Dansgaard-Oeschger and Heinrich events are strongly expressed in low-latitude ( monsoonal ) climate variability , suggesting the importance of common forcing agents such as atmospheric moisture and other greenhouse gases .

[2075] Continuous flux of dissolved black carbon from a vanished tropical forest biome

Humans have used fire extensively as a tool to shape Earth 's vegetation .
The slash-and-burn destruction of Brazil 's Atlantic forest , which once covered over 1.3 million km2 of present-day Brazil and was one of the largest tropical forest biomes on Earth , is a prime example .
Here , we estimate the amount of black carbon generated by the burning of the Atlantic forest , using historical records of land cover , satellite data and black carbon conversion ratios .
We estimate that before 1973 , destruction of the Atlantic forest generated 200-500 million tons of black carbon .
We then estimate the amount of black carbon exported from this relict forest between 1997 and 2008 , using measurements of polycyclic aromatic black carbon collected from a large river draining the region , and a continuous record of river discharge .
We show that dissolved black carbon ( DBC ) continues to be mobilized from the watershed each year in the rainy season , despite the fact that widespread forest burning ceased in 1973 .
We estimate that the river exports 2,700 tons of DBC to the ocean each year .
Scaling our findings up , we estimate that 50,000-70 ,000 tons of DBC are exported from the former forest each year .
We suggest that an increase in black carbon production on land could increase the size of the refractory pool of dissolved organic carbon in the deep ocean .

[2076] CO2 regulator SLAC1 and its homologues are essential for anion homeostasis in plant cells

The continuing rise in atmospheric [ CO2 ] is predicted to have diverse and dramatic effects on the productivity of agriculture , plant ecosystems and gas exchange .
Stomatal pores in the epidermis provide gates for the exchange of CO2 and water between plants and the atmosphere , processes vital to plant life .
Increased [ CO2 ] has been shown to enhance anion channel activity proposed to mediate efflux of osmoregulatory anions ( Cl - and malate2 - ) from guard cells during stomatal closure .
However , the genes encoding anion efflux channels in plant plasma membranes remain unknown .
Here we report the isolation of an Arabidopsis gene , SLAC1 ( SLOW ANION CHANNEL-ASSOCIATED 1 , At1g12480 ) , which mediates CO2 sensitivity in regulation of plant gas exchange .
The SLAC1 protein is a distant homologue of bacterial and fungal C4-dicarboxylate transporters , and is localized specifically to the plasma membrane of guard cells .
It belongs to a protein family that in Arabidopsis consists of four structurally related members that are common in their plasma membrane localization , but show distinct tissue-specific expression patterns .
The loss-of-function mutation in SLAC1 was accompanied by an over-accumulation of the osmoregulatory anions in guard cell protoplasts .
Guard-cell-specific expression of SLAC1 or its family members resulted in restoration of the wild-type stomatal responses , including CO2 sensitivity , and also in the dissipation of the over-accumulated anions .
These results suggest that SLAC1-family proteins have an evolutionarily conserved function that is required for the maintenance of organic/inorganic anion homeostasis on the cellular level .

[2077] Hydrogen from catalytic reforming of biomass-derived hydrocarbons in liquid water

Concerns about the depletion of fossil fuel reserves and the pollution caused by continuously increasing energy demands make hydrogen an attractive alternative energy source .
Hydrogen is currently derived from nonrenewable natural gas and petroleum , but could in principle be generated from renewable resources such as biomass or water .
However , efficient hydrogen production from water remains difficult and technologies for generating hydrogen from biomass , such as enzymatic decomposition of sugars , steam-reforming of bio-oils and gasification , suffer from low hydrogen production rates and/or complex processing requirements .
Here we demonstrate that hydrogen can be produced from sugars and alcohols at temperatures near 500 K in a single-reactor aqueous-phase reforming process using a platinum-based catalyst .
We are able to convert glucose -- which makes up the major energy reserves in plants and animals -- to hydrogen and gaseous alkanes , with hydrogen constituting 50 % of the products .
We find that the selectivity for hydrogen production increases when we use molecules that are more reduced than sugars , with ethylene glycol and methanol being almost completely converted into hydrogen and carbon dioxide .
These findings suggest that catalytic aqueous-phase reforming might prove useful for the generation of hydrogen-rich fuel gas from carbohydrates extracted from renewable biomass and biomass waste streams .

[2078] A faster Rubisco with potential to increase photosynthesis in crops

In photosynthetic organisms , d-ribulose-1 ,5 - bisphosphate carboxylase/oxygenase ( Rubisco ) is the major enzyme assimilating atmospheric CO2 into the biosphere .
Owing to the wasteful oxygenase activity and slow turnover of Rubisco , the enzyme is among the most important targets for improving the photosynthetic efficiency of vascular plants .
It has been anticipated that introducing the CO2-concentrating mechanism ( CCM ) from cyanobacteria into plants could enhance crop yield .
However , the complex nature of Rubisco 's assembly has made manipulation of the enzyme extremely challenging , and attempts to replace it in plants with the enzymes from cyanobacteria and red algae have not been successful .
Here we report two transplastomic tobacco lines with functional Rubisco from the cyanobacterium Synechococcus elongatus PCC7942 ( Se7942 ) .
We knocked out the native tobacco gene encoding the large subunit of Rubisco by inserting the large and small subunit genes of the Se7942 enzyme , in combination with either the corresponding Se7942 assembly chaperone , RbcX , or an internal carboxysomal protein , CcmM35 , which incorporates three small subunit-like domains .
Se7942 Rubisco and CcmM35 formed macromolecular complexes within the chloroplast stroma , mirroring an early step in the biogenesis of cyanobacterial beta-carboxysomes .
Both transformed lines were photosynthetically competent , supporting autotrophic growth , and their respective forms of Rubisco had higher rates of CO2 fixation per unit of enzyme than the tobacco control .
These transplastomic tobacco lines represent an important step towards improved photosynthesis in plants and will be valuable hosts for future addition of the remaining components of the cyanobacterial CCM , such as inorganic carbon transporters and the beta-carboxysome shell proteins .

[2079] Within-host competition determines reproductive success of temperate bacteriophages

Within-host competition between parasites is frequently invoked as a major force for parasite evolution , yet quantitative studies on its extent in an organismal group are lacking .
Temperate bacteriophages are diverse and abundant parasites of bacteria , distinguished by their ability to enter a facultative dormant state in their host .
Bacteria can accumulate multiple phages that may eventually abandon dormancy in response to host stress .
Host resources are then converted into phage particles , whose release requires cell death .
To study within-host competition between phages , I used the bacterium Escherichia coli and 11 lambdoid phages to construct single and double lysogens .
Lysogenic bacterial cultures were then induced and time to host cell lysis and productivity of phages was measured .
In double lysogens , this revealed strong competitive interactions as in all cases productivity of at least one phage declined .
The outcome of within-host competition was often asymmetrical , and phages were found to vary hierarchically in within-host competitive ability .
In double infections , the phage with the shorter lysis time determined the timing of cell lysis , which was associated with a competitive advantage when time differences were large .
The results emphasize that within-host competition greatly affects phage fitness and that multiple infections should be considered an integral part of bacteriophage ecology .

[2080] The formation of cubic ice under conditions relevant to Earth 's atmosphere

An important mechanism for ice cloud formation in the Earth 's atmosphere is homogeneous nucleation of ice in aqueous droplets , and this process is generally assumed to produce hexagonal ice .
However , there are some reports that the metastable crystalline phase of ice , cubic ice , may form in the Earth 's atmosphere .
Here we present laboratory experiments demonstrating that cubic ice forms when micrometre-sized droplets of pure water and aqueous solutions freeze homogeneously at cooling rates approaching those found in the atmosphere .
We find that the formation of cubic ice is dominant when droplets freeze at temperatures below 190 K , which is in the temperature range relevant for polar stratospheric clouds and clouds in the tropical tropopause region .
These results , together with heat transfer calculations , suggest that cubic ice will form in the Earth 's atmosphere .
If there were a significant fraction of cubic ice in some cold clouds this could increase their water vapour pressure , and modify their microphysics and ice particle size distributions .
Under specific conditions this may lead to enhanced dehydration of the tropopause region .

[2081] Mangroves enhance the biomass of coral reef fish communities in the Caribbean

Mangrove forests are one of the world 's most threatened tropical ecosystems with global loss exceeding 35 % ( ref .
1 ) .
Juvenile coral reef fish often inhabit mangroves , but the importance of these nurseries to reef fish population dynamics has not been quantified .
Indeed , mangroves might be expected to have negligible influence on reef fish communities : juvenile fish can inhabit alternative habitats and fish populations may be regulated by other limiting factors such as larval supply or fishing .
Here we show that mangroves are unexpectedly important , serving as an intermediate nursery habitat that may increase the survivorship of young fish .
Mangroves in the Caribbean strongly influence the community structure of fish on neighbouring coral reefs .
In addition , the biomass of several commercially important species is more than doubled when adult habitat is connected to mangroves .
The largest herbivorous fish in the Atlantic , Scarus guacamaia , has a functional dependency on mangroves and has suffered local extinction after mangrove removal .
Current rates of mangrove deforestation are likely to have severe deleterious consequences for the ecosystem function , fisheries productivity and resilience of reefs .
Conservation efforts should protect connected corridors of mangroves , seagrass beds and coral reefs .

[2082] Opposing effects of target overexpression reveal drug mechanisms

Overexpression of a drug 's molecular target often increases drug resistance , offering a pathway for adaptive evolution and a tool for target identification .
It is unclear though why this phenomenon applies to some drugs but not others .
Here we gradually overexpressed antibiotic targets in Escherichia coli and found that drug resistance can increase , remain unchanged , decrease or even change non-monotonically .
Even a single target can produce opposing responses to its different inhibitors .
We explain these contradicting effects with quantitative models of enzyme inhibition that account for fitness costs and the biochemical activity or inactivity of drug-enzyme complexes .
Thus , target overexpression confers resistance or sensitivity as a predictable property of drug mechanism , explaining its variable presence in nature as a resistance mechanism .
Though overexpression screens may fail at identifying unknown targets , overexpressing known or putative targets provides a systematic approach to distinguish between simple inhibition and complex mechanisms of drug action .

[2083] Abrupt climate change in the Arctic

Semantic arguments about the definition of ` tipping points ' are distracting attention away from the causes and impacts of climate change in the Arctic .

[2084] Motion of an Antarctic glacier by repeated tidally modulated earthquakes

Between debris-laden glacial ice and bedrock , basal seismicity can develop that yields information about bed properties , stress distribution , outburst flooding , and crevassing and calving .
Basal seismicity in response to glacial motion is linked to variations in both stress and lubrication of bedrock by water and till .
Here we analyse data from the Transantarctic Mountains Seismic Experiment array in 2002-2003 to investigate seismic behaviour at David Glacier , a large outlet glacier that drains 4 % of East Antarctica 's ice sheet into the Ross Sea .
We identify about 20,000 seismic events that are larger in magnitude and duration than typical for glacial sources and repeat at regular intervals of about 25 min .
These events are consistent with stick-slip behaviour of debris-laden ice moving over a single obstacle of rough bedrock , modulated by relatively small stress changes from the ocean tides .
In the years before and after the interval of repeating events , seismic events with irregular and generally longer intervals were detected at the same location , and are consistent with combined stick-slip and continuous sliding of the subglacial interface .
We suggest that the observed transitions in seismicity patterns capture the dynamic behaviour of the ice stream , and that -- despite lower ice-flow velocities -- sliding in the stick-slip regime enhances subglacial erosion .

[2085] Sensitivity of collective action to uncertainty about climate tipping points

Despite more than two decades of diplomatic effort , concentrations of greenhouse gases continue to trend upwards , creating the risk that we may someday cross a threshold for ` dangerous ' climate change .
Although climate thresholds are very uncertain , new research is trying to devise ` early warning signals ' of an approaching tipping point .
This research offers a tantalizing promise : whereas collective action fails when threshold uncertainty is large , reductions in this uncertainty may bring about the behavioural change needed to avert a climate ` catastrophe ' .
Here we present the results of an experiment , rooted in a game-theoretic model , showing that behaviour differs markedly either side of a dividing line for threshold uncertainty .
On one side of the dividing line , where threshold uncertainty is relatively large , free riding proves irresistible and trust illusive , making it virtually inevitable that the tipping point will be crossed .
On the other side , where threshold uncertainty is small , the incentive to coordinate is strong and trust more robust , often leading the players to avoid crossing the tipping point .
Our results show that uncertainty must be reduced to this ` good ' side of the dividing line to stimulate the behavioural shift needed to avoid ` dangerous ' climate change .

[2086] Phanerozoic trends in skeletal mineralogy driven by mass extinctions

Marine calcifying organisms that produce sediments and build reefs generally have skeletons and shells that are composed of either aragonite or calcite .
Long-term changes in the estimated Mg/Ca ratios of sea water tend to correspond to changes in the prevailing mineralogy of these creatures .
High Mg/Ca ratios are expected to favour the spread of aragonitic organisms , whereas calcitic taxa are thought to benefit from low Mg/Ca ratios .
Here we test these patterns throughout the Phanerozoic eon and assess the relative impacts of changing ocean chemistry and mass extinctions on the evolutionary success of calcifying organisms .
We find that mass extinctions are more important in regulating long-term patterns of skeletal mineralogy than the Mg/Ca ratios of the global oceans .
Furthermore , selective recovery from mass extinctions is usually more important than selective extinction , in driving the Phanerozoic pattern of skeletal mineralogy .
But even in the recovery phase there is no clear connection between changes in the dominance of aragonite or calcite and the Mg/Ca ratio of the oceans , thus providing further evidence for the complexity of biotic recoveries .

[2087] Structural resilience of the gut microbiota in adult mice under high-fat dietary perturbations

Disruption of the gut microbiota by high-fat diet ( HFD ) has been implicated in the development of obesity .
It remains to be elucidated whether the HFD-induced shifts occur at the phylum level or whether they can be attributed to specific phylotypes ; additionally , it is unclear to what extent the changes are reversible under normal chow ( NC ) feeding .
One group ( diet-induced obesity , DIO ) of adult C57BL/6J mice was fed a HFD for 12 weeks until significant obesity and insulin resistance were observed , and then these mice were switched to NC feeding for 10 weeks .
Upon switching to NC feeding , the metabolic deteriorations observed during HFD consumption were significantly alleviated .
The second group ( control , CHO ) remained healthy under continuous NC feeding .
UniFrac analysis of bar-coded pyrosequencing data showed continued structural segregation of DIO from CHO on HFD .
At 4 weeks after switching back to NC , the gut microbiota in the DIO group had already moved back to the CHO space , and continued to progress along the same age trajectory and completely converged with CHO after 10 weeks .
Redundancy analysis identified 77 key phylotypes responding to the dietary perturbations .
HFD-induced shifts of these phylotypes all reverted to CHO levels over time .
Some of these phylotypes exhibited robust age-related changes despite the dramatic abundance variations in response to dietary alternations .
These findings suggest that HFD-induced structural changes of the gut microbiota can be attributed to reversible elevation or diminution of specific phylotypes , indicating the significant structural resilience of the gut microbiota of adult mice to dietary perturbations .

[2088] Biomimetic synthesis of struvite with biogenic morphology and implication for pathological biomineralization

Recent studies have found that certain urinary proteins can efficiently inhibit stone formation .
These discoveries are significant for developing effective therapies for stone disease , but the inhibition mechanism of crystallization remains elusive .
In the present study , polyaspartic acid ( PASP ) was employed as a model peptide to investigate the effect of urinary proteins on the crystallization and morphological evolution of struvite .
The results demonstrate that selective adsorption/binding of PASP onto the { 010 } and { 101 } faces of struvite crystals results in arrowhead-shaped morphology , which further evolves into X-shaped and unusual tabular structures with time .
Noticeably , these morphologies are reminiscent of biogenic struvite morphology .
Concentration-dependent experiments show that PASP can inhibit struvite growth and the inhibitory capacity increases with increasing PASP concentration , whereas aspartic acid monomers do not show a significant effect .
Considering that PASP is a structural and functional analogue of the subdomains of aspartic acid-rich proteins , our results reveal that aspartic acid-rich proteins play a key role in regulating biogenic struvite morphology , and aspartic acid residues contribute to the inhibitory capacity of urinary proteins .
The potential implications of PASP for developing therapeutic agents for urinary stone disease is also discussed .

[2089] Trophic cascades across ecosystems

Predation can be intense , creating strong direct and indirect effects throughout food webs .
In addition , ecologists increasingly recognize that fluxes of organisms across ecosystem boundaries can have major consequences for community dynamics .
Species with complex life histories often shift habitats during their life cycles and provide potent conduits coupling ecosystems .
Thus , local interactions that affect predator abundance in one ecosystem ( for example a larval habitat ) may have reverberating effects in another ( for example an adult habitat ) .
Here we show that fish indirectly facilitate terrestrial plant reproduction through cascading trophic interactions across ecosystem boundaries .
Fish reduce larval dragonfly abundances in ponds , leading to fewer adult dragonflies nearby .
Adult dragonflies consume insect pollinators and alter their foraging behaviour .
As a result , plants near ponds with fish receive more pollinator visits and are less pollen limited than plants near fish-free ponds .
Our results confirm that strong species interactions can reverberate across ecosystems , and emphasize the importance of landscape-level processes in driving local species interactions .

[2090] Mass and volume transport variability in an eddy-filled ocean

The possibility that the oceanic general circulation is undergoing changes as part , or the cause , of major climate shifts is being intensely discussed , with some published results relying on data from moorings spanning the North Atlantic Ocean .
The circulation is , however , extremely noisy .
Here , I use existing estimates of the frequency and wavenumber content of geostrophic eddies in the ocean to show that variations in ocean-wide integrated transport must appear even in the absence of a true long-term trend .
Expected fluctuations exceed + / -20 x109 kg s-1 ( or + / -20 x106 m3 s-1 ) and exhibit multi-year timescales .
Existing knowledge of the eddy field allows predictions of observed variability and produces lower bounds on the ( multi-decadal ) timescale required to detect true trends of a large magnitude .
Detecting and understanding the effect of climate change on the ocean circulation requires observations in three dimensions over long periods of time .

[2091] Influence of Preferred Orientation on the Electrical Conductivity of Fluorine-Doped Tin Oxide Films

Current development of high-performance transparent conductive oxide ( TCO ) films is limited with tradeoff between carrier mobility and concentration since none of them can be improved without sacrificing the other .
In this study , we prepare fluorine doped tin oxide ( FTO ) films by chemical vapor deposition with inclusions of different additives and report that the mobility can be varied from 0.65 to 28.5 cm2 V-1 s-1 without reducing the achieved high carrier concentration of 4 x 1020 cm-3 .
Such an increase in mobility is shown to be clearly associated with the development of ( 200 ) preferred orientation ( PO ) but concurrent degradation of ( 110 ) PO in films .
Thus , at a constant high carrier concentration , the electrical conductivity can be improved via carrier mobility simply by PO control .
Such a one-step approach avoiding conventional post-deposition treatment is suggested for developing next-generation FTO as well as other TCO films with better than ever conductivities .

[2092] A decade of seasonal dynamics and co-occurrences within freshwater bacterioplankton communities from eutrophic Lake Mendota , WI , USA

With an unprecedented decade-long time series from a temperate eutrophic lake , we analyzed bacterial and environmental co-occurrence networks to gain insight into seasonal dynamics at the community level .
We found that ( 1 ) bacterial co-occurrence networks were non-random , ( 2 ) season explained the network complexity and ( 3 ) co-occurrence network complexity was negatively correlated with the underlying community diversity across different seasons .
Network complexity was not related to the variance of associated environmental factors .
Temperature and productivity may drive changes in diversity across seasons in temperate aquatic systems , much as they control diversity across latitude .
While the implications of bacterioplankton network structure on ecosystem function are still largely unknown , network analysis , in conjunction with traditional multivariate techniques , continues to increase our understanding of bacterioplankton temporal dynamics .

[2093] The poleward migration of the location of tropical cyclone maximum intensity

Temporally inconsistent and potentially unreliable global historical data hinder the detection of trends in tropical cyclone activity .
This limits our confidence in evaluating proposed linkages between observed trends in tropical cyclones and in the environment .
Here we mitigate this difficulty by focusing on a metric that is comparatively insensitive to past data uncertainty , and identify a pronounced poleward migration in the average latitude at which tropical cyclones have achieved their lifetime-maximum intensity over the past 30 years .
The poleward trends are evident in the global historical data in both the Northern and the Southern hemispheres , with rates of 53 and 62 kilometres per decade , respectively , and are statistically significant .
When considered together , the trends in each hemisphere depict a global-average migration of tropical cyclone activity away from the tropics at a rate of about one degree of latitude per decade , which lies within the range of estimates of the observed expansion of the tropics over the same period .
The global migration remains evident and statistically significant under a formal data homogenization procedure , and is unlikely to be a data artefact .
The migration away from the tropics is apparently linked to marked changes in the mean meridional structure of environmental vertical wind shear and potential intensity , and can plausibly be linked to tropical expansion , which is thought to have anthropogenic contributions .

[2094] Field parameterization and experimental test of the neutral theory of biodiversity

Ecologists would like to explain general patterns observed across multi-species communities , such as species-area and abundance-frequency relationships , in terms of the fundamental processes of birth , death and migration underlying the dynamics of all constituent species .
The unified neutral theory of biodiversity and related theories based on these fundamental population processes have successfully recreated general species-abundance patterns without accounting for either the variation among species and individuals or resource-releasing processes such as predation and disturbance , long emphasized in ecological theory .
If ecological communities can be described adequately without estimating variation in species and their interactions , our understanding of ecological community organization and the predicted consequences of reduced biodiversity and environmental change would shift markedly .
Here , I introduce a strong method to test the neutral theory that combines field parameterization of the underlying population dynamics with a field experiment , and apply it to a rocky intertidal community .
Although the observed abundance-frequency distribution of the system follows that predicted by the neutral theory , the neutral theory predicts poorly the field experimental results , indicating an essential role for variation in species interactions .

[2095] Recent ecological transitions in China : greening , browning , and influential factors

Ecological conservation and restoration are necessary to mitigate environmental degradation problems .
China has taken great efforts in such actions .
To understand the ecological transition during 2000-2010 in China , this study analysed trends in vegetation change using remote sensing and linear regression .
Climate and socioeconomic factors were included to screen the driving forces for vegetation change using correlation or comparative analyses .
Our results indicated that China experienced both vegetation greening ( restoration ) and browning ( degradation ) with great spatial heterogeneity .
Socioeconomic factors , such as human populations and economic production , were the most significant factors for vegetation change .
Nature reserves have contributed slightly to the deceleration of vegetation browning and the promotion of greening ; however , a large-scale conservation approach beyond nature reserves was more effective .
The effectiveness of the Three-North Shelter Forest Program lay between the two above approaches .
The findings of this study highlighted that vegetation trend detection is a practical approach for large-scale ecological transition assessments , which can inform decision-making that promotes vegetation greening via proper socioeconomic development and ecosystem management .

[2096] Genome-wide identification of transcription factors and transcription-factor binding sites in oleaginous microalgae Nannochloropsis

Nannochloropsis spp .
are a group of oleaginous microalgae that harbor an expanded array of lipid-synthesis related genes , yet how they are transcriptionally regulated remains unknown .
Here a phylogenomic approach was employed to identify and functionally annotate the transcriptional factors ( TFs ) and TF binding-sites ( TFBSs ) in N. oceanica IMET1 .
Among 36 microalgae and higher plants genomes , a two-fold reduction in the number of TF families plus a seven-fold decrease of average family-size in Nannochloropsis , Rhodophyta and Chlorophyta were observed .
The degree of similarity in TF-family profiles is indicative of the phylogenetic relationship among the species , suggesting co-evolution of TF-family profiles and species .
Furthermore , comparative analysis of six Nannochloropsis genomes revealed 68 `` most-conserved '' TFBS motifs , with 11 of which predicted to be related to lipid accumulation or photosynthesis .
Mapping the IMET1 TFs and TFBS motifs to the reference plant TF - `` TFBS motif '' relationships in TRANSFAC enabled the prediction of 78 TF - `` TFBS motif '' interaction pairs , which consisted of 34 TFs ( with 11 TFs potentially involved in the TAG biosynthesis pathway ) , 30 TFBS motifs and 2,368 regulatory connections between TFs and target genes .
Our results form the basis of further experiments to validate and engineer the regulatory network of Nannochloropsis spp .
for enhanced biofuel production .

[2097] Direct observation of individual RecA filaments assembling on single DNA molecules

Escherichia coli RecA is essential for the repair of DNA double-strand breaks by homologous recombination .
Repair requires the formation of a RecA nucleoprotein filament .
Previous studies have indicated a mechanism of filament assembly whereby slow nucleation of RecA protein on DNA is followed by rapid growth .
However , many aspects of this process remain unclear , including the rates of nucleation and growth and the involvement of ATP hydrolysis , largely because visualization at the single-filament level is lacking .
Here we report the direct observation of filament assembly on individual double-stranded DNA molecules using fluorescently modified RecA .
The nucleoprotein filaments saturate the DNA and extend it ~ 1.6-fold .
At early time points , discrete RecA clusters are seen , permitting analysis of single-filament growth from individual nuclei .
Formation of nascent RecA filaments is independent of ATP hydrolysis but is dependent on the type of nucleotide cofactor and the RecA concentration , suggesting that nucleation involves binding of ~ 4-5 ATP-RecA monomers to DNA .
Individual RecA filaments grow at rates of 3-10 nm s-1 .
Growth is bidirectional and , in contrast to nucleation , independent of nucleotide cofactor , suggesting addition of ~ 2-7 monomers s-1 .
These results are in accord with extensive genetic and biochemical studies , and indicate that assembly in vivo is controlled at the nucleation step .
We anticipate that our approach and conclusions can be extended to the related eukaryotic counterpart , Rad51 ( see ref . )
, and to regulation by assembly mediators .

[2098] Efficient delivery of meteorites to the Earth from a wide range of asteroid parent bodies

Almost all meteorites come from asteroids , but identifying their specific parent bodies , and modelling their transport to the Earth , has proved to be difficult .
The usual model of delivery through orbital resonances with the major planets has recently been shown to deplete the supply of meteorites much too rapidly to explain either the observed flux at the Earth , or the length of time the meteorites have spent in space ( as measured by cosmic-ray exposure ages ) .
Independently , it has been found that a force arising from anisotropically emitted thermal radiation from asteroidal fragments ( the ` Yarkovsky effect ' ) influences the fragments ' orbits in important ways .
Here we report the results of a detailed model for the transport of meteorites to the Earth , which includes the Yarkovsky effect and collisional evolution of the asteroidal fragments .
We find that the Yarkovsky effect significantly increases the efficiency of the delivery of meteorites to the Earth , while at the same time allowing a much wider range of asteroids to contribute to the flux of meteorites .
Our model also reproduces the observed distribution of cosmic-ray exposure ages of stony meteorites .

[2099] September Arctic sea-ice minimum predicted by spring melt-pond fraction

The area of Arctic September sea ice has diminished from about 7 million km2 in the 1990s to less than 5 million km2 in five of the past seven years , with a record minimum of 3.6 million km2 in 2012 ( ref . )
.
The strength of this decrease is greater than expected by the scientific community , the reasons for this are not fully understood , and its simulation is an on-going challenge for existing climate models .
With growing Arctic marine activity there is an urgent demand for forecasting Arctic summer sea ice .
Previous attempts at seasonal forecasts of ice extent were of limited skill .
However , here we show that the Arctic sea-ice minimum can be accurately forecasted from melt-pond area in spring .
We find a strong correlation between the spring pond fraction and September sea-ice extent .
This is explained by a positive feedback mechanism : more ponds reduce the albedo ; a lower albedo causes more melting ; more melting increases pond fraction .
Our results help explain the acceleration of Arctic sea-ice decrease during the past decade .
The inclusion of our new melt-pond model promises to improve the skill of future forecast and climate models in Arctic regions and beyond .

[2100] Bacterial community succession and chemical profiles of subtidal biofilms in relation to larval settlement of the polychaete Hydroides elegans

Earlier studies have shown that biofilms can mediate the larval settlement of the polychaete Hydroides elegans and that changes in the bacterial community structure and density of biofilms often alter the larval settlement response .
However , the chemical cues that mediate this response remain unknown .
In this study , both successional changes in the bacterial community structure and the chemical profiles of subtidal biofilms are described and related to the larval settlement response .
Multispecies biofilms were developed on polystyrene Petri dishes and granite rock in the subtidal zone over a period of 20 days .
The effects of the substratum and age on the bacterial community structure and chemical profiles of the biofilms were evaluated with two molecular methods ( microarray ( PhyloChip ) and denaturing gradient gel electrophoresis ) and with gas chromatography-mass spectrometry , respectively .
Both age and substratum altered the bacterial community structures and chemical profiles of the biofilms .
Age had a greater effect in shaping the bacterial community structure than did the substratum .
In contrast , the type of substratum more strongly affected the chemical profile .
Extracts of biofilms of different ages , which developed on different substrata , were tested for the settlement of H. elegans larvae .
The extracts induced larval settlement in a biofilm-age-dependent manner , and extracts originating from different substrata of the same age showed no differences in larval settlement .
Our results suggest that the larval settlement response can not be predicted by the overall chemical composition of the biofilm alone .

[2101] Fjord insertion into continental margins driven by topographic steering of ice

Fjords commonly punctuate continental edges formerly occupied by Quaternary ice sheets , reaching kilometre depths and extending many tens of kilometres inland .
These features must have been created by late Cenozoic ice sheets , because rivers can not erode bedrock much below sea level .
Ice sheets drain primarily through fjords ; therefore , widespread fjord insertion may have altered ice-sheet size , shape and dynamics .
Here , we use a two-dimensional ice-sheet model to simulate the incision of fjords through a coastal mountain range .
We show that topographic steering of ice and erosion proportional to ice discharge are sufficient to form fjords .
Within one million years , kilometre-deep fjords punched through the mountain range owing to a robust positive feedback initiated by ice being steered towards mountain passes .
Enhanced erosion beneath thicker , faster ice deepens these passes , amplifying the topographic steering .
Simulated fjords are deepest through the highest topography and drain a large fraction of the interior ice .
Ice sheets simulated on landscapes with existing fjords are generally smaller and exhibit longer response times and larger responses to climate changes , suggesting that modern ice sheets are more sensitive to climate fluctuations than Early Quaternary ice sheets .

[2102] Tuning calcite morphology and growth acceleration by a rational design of highly stable protein-mimetics

In nature , proteins play a significant role in biomineral formation .
One of the ultimate goals of bioinspired materials science is to develop highly stable synthetic molecules that mimic the function of these natural proteins by controlling crystal formation .
Here , we demonstrate that both the morphology and the degree of acceleration or inhibition observed during growth of calcite in the presence of peptoids can be rationally tuned by balancing the electrostatic and hydrophobic interactions , with hydrophobic interactions playing the dominant role .
While either strong electrostatic or hydrophobic interactions inhibit growth and reduces expression of the { 104 } faces , correlations between peptoid-crystal binding energies and observed changes in calcite growth indicate moderate electrostatic interactions allow peptoids to weakly adsorb while moderate hydrophobic interactions cause disruption of surface-adsorbed water layers , leading to growth acceleration with retained expression of the { 104 } faces .
This study provides fundamental principles for designing peptoids as crystallization promoters , and offers a straightforward screening method based on macroscopic crystal morphology .
Because peptoids are sequence-specific , highly stable , and easily synthesized , peptoid-enhanced crystallization offers a broad range of potential applications .

[2103] Anthropogenic carbon dioxide transport in the Southern Ocean driven by Ekman flow

The Southern Ocean , with its large surface area and vigorous overturning circulation , is potentially a substantial sink of anthropogenic CO2 ( refs 1-4 ) .
Despite its importance , the mechanism and pathways of anthropogenic CO2 uptake and transport are poorly understood .
Regulation of the Southern Ocean carbon sink by the wind-driven Ekman flow , mesoscale eddies and their interaction is under debate .
Here we use a high-resolution ocean circulation and carbon cycle model to address the mechanisms controlling the Southern Ocean sink of anthropogenic CO2 .
The focus of our study is on the intra-annual variability in anthropogenic CO2 over a two-year time period .
We show that the pattern of carbon uptake is correlated with the oceanic vertical exchange .
Zonally integrated carbon uptake peaks at the Antarctic polar front .
The carbon is then advected away from the uptake regions by the circulation of the Southern Ocean , which is controlled by the interplay among Ekman flow , ocean eddies and subduction of water masses .
Although lateral carbon fluxes are locally dominated by the imprint of mesoscale eddies , the Ekman transport is the primary mechanism for the zonally integrated , cross-frontal transport of anthropogenic CO2 .
Intra-annual variability of the cross-frontal transport is dominated by the Ekman flow with little compensation from eddies .
A budget analysis in the density coordinate highlights the importance of wind-driven transport across the polar front and subduction at the subtropical front .
Our results suggest intimate connections between oceanic carbon uptake and climate variability through the temporal variability of Ekman transport .

[2104] Decreased stability of methane hydrates in marine sediments owing to phase-boundary roughness

Below water depths of about 300 metres , pressure and temperature conditions cause methane to form ice-like crystals of methane hydrate .
Marine deposits of methane hydrate are estimated to be large , amassing about 10,000 gigatonnes of carbon , and are thought to be important to global change and seafloor stability , as well as representing a potentially exploitable energy resource .
The extent of these deposits can usually be inferred from seismic imaging , in which the base of the methane hydrate stability zone is frequently identifiable as a smooth reflector that runs parallel to the sea floor .
Here , using high-resolution seismic sections of seafloor sediments in the Cascadia margin off the coast of Vancouver Island , Canada , we observe lateral variations in the base of the hydrate stability zone , including gas-rich vertical intrusions into the hydrate stability zone .
We suggest that these vertical intrusions are associated with upward flow of warmer fluids .
Therefore , where seafloor fluid expulsion and methane hydrate deposits coincide , the base of the hydrate stability zone might exhibit significant roughness and increased surface area .
Increased area implies that significantly more methane hydrate lies close to being unstable and hence closer to dissociation in the event of a lowering of pressure due to sea-level fall .

[2105] Orbit-related long-term climate cycles revealed in a 12-Myr continental record from Lake Baikal

Quaternary records of climate change from terrestrial sources , such as lake sediments and aeolian sediments , in general agree well with marine records .
But continuous records that cover more than the past one million years were essentially unavailable until recently , when the high-sedimentation-rate site of Lake Baikal was exploited .
Because of its location in the middle latitudes , Lake Baikal is highly sensitive to insolation changes and the entire lake remained uncovered by ice sheets throughout the Pleistocene epoch , making it a valuable archive for past climate .
Here we examine long sediment cores from Lake Baikal that cover the past 12 million years .
Our record reveals a gradual cooling of the Asian continental interior , with some fluctuations .
Spectral analyses reveal periods of about 400 kyr , 600 kyr and 1,000 kyr , which may correspond to Milankovitch periods ( reflecting orbital cycles ) .
Our results indicate that changes in insolation were closely related to long-term environmental variations in the deep continental interior , over the past 12 million years .

[2106] Ultrasound and pH Dually Responsive Polymer Vesicles for Anticancer Drug Delivery

Recently , smart polymer vesicles have attracted increasing interest due to their endless potential applications such as tunable delivery vehicles for the treatment of degenerative diseases .
However , the evolution of stimuli-responsive vesicles from bench to bedside still seems far away for the limitations of current stimuli forms such as temperature , light , redox , etc. .
Since ultrasound combined with chemotherapy has been widely used in tumor treatment and the pH in tumor tissues is relatively low , we designed herein a novel polymer vesicle that respond to both physical ( ultrasound ) and chemical ( pH ) stimuli based on a PEO-b-P ( DEA-stat-TMA ) block copolymer , where PEO is short for poly ( ethylene oxide ) , DEA for 2 - ( diethylamino ) ethyl methacrylate and TMA for ( 2-tetrahydrofuranyloxy ) ethyl methacrylate .
These dually responsive vesicles show noncytotoxicity below 250 mug/mL and can encapsulate anticancer drugs , exhibiting retarded release profile and controllable release rate when subjected to ultrasound radiation or varying pH in tris buffer at 37degreesC .

[2107] Anthropogenic noise playback impairs embryonic development and increases mortality in a marine invertebrate

Human activities can create noise pollution and there is increasing international concern about how this may impact wildlife .
There is evidence that anthropogenic noise may have detrimental effects on behaviour and physiology in many species but there are few examples of experiments showing how fitness may be directly affected .
Here we use a split-brood , counterbalanced , field experiment to investigate the effect of repeated boat-noise playback during early life on the development and survival of a marine invertebrate , the sea hare Stylocheilus striatus at Moorea Island ( French Polynesia ) .
We found that exposure to boat-noise playback , compared to ambient-noise playback , reduced successful development of embryos by 21 % and additionally increased mortality of recently hatched larvae by 22 % .
Our work , on an understudied but ecologically and socio-economically important taxon , demonstrates that anthropogenic noise can affect individual fitness .
Fitness costs early in life have a fundamental influence on population dynamics and resilience , with potential implications for community structure and function .

[2108] Fundamental shift in vitamin B12 eco-physiology of a model alga demonstrated by experimental evolution

A widespread and complex distribution of vitamin requirements exists over the entire tree of life , with many species having evolved vitamin dependence , both within and between different lineages .
Vitamin availability has been proposed to drive selection for vitamin dependence , in a process that links an organism 's metabolism to the environment , but this has never been demonstrated directly .
Moreover , understanding the physiological processes and evolutionary dynamics that influence metabolic demand for these important micronutrients has significant implications in terms of nutrient acquisition and , in microbial organisms , can affect community composition and metabolic exchange between coexisting species .
Here we investigate the origins of vitamin dependence , using an experimental evolution approach with the vitamin B12-independent model green alga Chlamydomonas reinhardtii .
In fewer than 500 generations of growth in the presence of vitamin B12 , we observe the evolution of a B12-dependent clone that rapidly displaces its ancestor .
Genetic characterization of this line reveals a type-II Gulliver-related transposable element integrated into the B12-independent methionine synthase gene ( METE ) , knocking out gene function and fundamentally altering the physiology of the alga .
The ISME Journal advance online publication , 19 December 2014 ; doi :10.1038 / ismej .2014.230

[2109] Last chance for carbon capture and storage

Anthropogenic energy-related CO2 emissions are higher than ever .
With new fossil-fuel power plants , growing energy-intensive industries and new sources of fossil fuels in development , further emissions increase seems inevitable .
The rapid application of carbon capture and storage is a much heralded means to tackle emissions from both existing and future sources .
However , despite extensive and successful research and development , progress in deploying carbon capture and storage has stalled .
No fossil-fuel power plants , the greatest source of CO2 emissions , are using carbon capture and storage , and publicly supported demonstration programmes are struggling to deliver actual projects .
Yet , carbon capture and storage remains a core component of national and global emissions-reduction scenarios .
Governments have to either increase commitment to carbon capture and storage through much more active market support and emissions regulation , or accept its failure and recognize that continued expansion of power generation from burning fossil fuels is a severe threat to attaining objectives in mitigating climate change .

[2110] Deep-water longline fishing has reduced impact on Vulnerable Marine Ecosystems

Bottom trawl fishing threatens deep-sea ecosystems , modifying the seafloor morphology and its physical properties , with dramatic consequences on benthic communities .
Therefore , the future of deep-sea fishing relies on alternative techniques that maintain the health of deep-sea ecosystems and tolerate appropriate human uses of the marine environment .
In this study , we demonstrate that deep-sea bottom longline fishing has little impact on vulnerable marine ecosystems , reducing bycatch of cold-water corals and limiting additional damage to benthic communities .
We found that slow-growing vulnerable species are still common in areas subject to more than 20 years of longlining activity and estimate that one deep-sea bottom trawl will have a similar impact to 296-1 ,719 longlines , depending on the morphological complexity of the impacted species .
Given the pronounced differences in the magnitude of disturbances coupled with its selectivity and low fuel consumption , we suggest that regulated deep-sea longlining can be an alternative to deep-sea bottom trawling .

[2111] Deterministic processes guide long-term synchronised population dynamics in replicate anaerobic digesters

A replicate long-term experiment was conducted using anaerobic digestion ( AD ) as a model process to determine the relative role of niche and neutral theory on microbial community assembly , and to link community dynamics to system performance .
AD is performed by a complex network of microorganisms and process stability relies entirely on the synergistic interactions between populations belonging to different functional guilds .
In this study , three independent replicate anaerobic digesters were seeded with the same diverse inoculum , supplied with a model substrate , alpha-cellulose , and operated for 362 days at a 10-day hydraulic residence time under mesophilic conditions .
Selective pressure imposed by the operational conditions and model substrate caused large reproducible changes in community composition including an overall decrease in richness in the first month of operation , followed by synchronised population dynamics that correlated with changes in reactor performance .
This included the synchronised emergence and decline of distinct Ruminococcus phylotypes at day 148 , and emergence of a Clostridium and Methanosaeta phylotype at day 178 , when performance became stable in all reactors .
These data suggest that many dynamic functional niches are predictably filled by phylogenetically coherent populations over long time scales .
Neutral theory would predict that a complex community with a high degree of recognised functional redundancy would lead to stochastic changes in populations and community divergence over time .
We conclude that deterministic processes may play a larger role in microbial community dynamics than currently appreciated , and under controlled conditions it may be possible to reliably predict community structural and functional changes over time .

[2112] A global standard for monitoring coastal wetland vulnerability to accelerated sea-level rise

Sea-level rise threatens coastal salt-marshes and mangrove forests around the world , and a key determinant of coastal wetland vulnerability is whether its surface elevation can keep pace with rising sea level .
Globally , a large data gap exists because wetland surface and shallow subsurface processes remain unaccounted for by traditional vulnerability assessments using tide gauges .
Moreover , those processes vary substantially across wetlands , so modelling platforms require relevant local data .
The low-cost , simple , high-precision rod surface-elevation table-marker horizon ( RSET-MH ) method fills this critical data gap , can be paired with spatial data sets and modelling and is financially and technically accessible to every country with coastal wetlands .
Yet , RSET deployment has been limited to a few regions and purposes .
A coordinated expansion of monitoring efforts , including development of regional networks that could support data sharing and collaboration , is crucial to adequately inform coastal climate change adaptation policy at several scales .

[2113] Methane oxidation coupled to oxygenic photosynthesis in anoxic waters

Freshwater lakes represent large methane sources that , in contrast to the Ocean , significantly contribute to non-anthropogenic methane emissions to the atmosphere .
Particularly mixed lakes are major methane emitters , while permanently and seasonally stratified lakes with anoxic bottom waters are often characterized by strongly reduced methane emissions .
The causes for this reduced methane flux from anoxic lake waters are not fully understood .
Here we identified the microorganisms and processes responsible for the near complete consumption of methane in the anoxic waters of a permanently stratified lake , Lago di Cadagno .
Interestingly , known anaerobic methanotrophs could not be detected in these waters .
Instead , we found abundant gamma-proteobacterial aerobic methane-oxidizing bacteria active in the anoxic waters .
In vitro incubations revealed that , among all the tested potential electron acceptors , only the addition of oxygen enhanced the rates of methane oxidation .
An equally pronounced stimulation was also observed when the anoxic water samples were incubated in the light .
Our combined results from molecular , biogeochemical and single-cell analyses indicate that methane removal at the anoxic chemocline of Lago di Cadagno is due to true aerobic oxidation of methane fuelled by in situ oxygen production by photosynthetic algae .
A similar mechanism could be active in seasonally stratified lakes and marine basins such as the Black Sea , where light penetrates to the anoxic chemocline .
Given the widespread occurrence of seasonally stratified anoxic lakes , aerobic methane oxidation coupled to oxygenic photosynthesis might have an important but so far neglected role in methane emissions from lakes .
The ISME Journal advance online publication , 13 February 2015 ; doi :10.1038 / ismej .2015.12

[2114] Late Cretaceous seasonal ocean variability from the Arctic

The modern Arctic Ocean is regarded as a barometer of global change and amplifier of global warming and therefore records of past Arctic change are critical for palaeoclimate reconstruction .
Little is known of the state of the Arctic Ocean in the greenhouse period of the Late Cretaceous epoch ( 65-99 million years ago ) , yet records from such times may yield important clues to Arctic Ocean behaviour in near-future warmer climates .
Here we present a seasonally resolved Cretaceous sedimentary record from the Alpha ridge of the Arctic Ocean .
This palaeo-sediment trap provides new insight into the workings of the Cretaceous marine biological carbon pump .
Seasonal primary production was dominated by diatom algae but was not related to upwelling as was previously hypothesized .
Rather , production occurred within a stratified water column , involving specially adapted species in blooms resembling those of the modern North Pacific subtropical gyre , or those indicated for the Mediterranean sapropels .
With increased CO2 levels and warming currently driving increased stratification in the global ocean , this style of production that is adapted to stratification may become more widespread .
Our evidence for seasonal diatom production and flux testify to an ice-free summer , but thin accumulations of terrigenous sediment within the diatom ooze are consistent with the presence of intermittent sea ice in the winter , supporting a wide body of evidence for low temperatures in the Late Cretaceous Arctic Ocean , rather than recent suggestions of a 15 degreesC mean annual temperature at this time .

[2115] A globally coherent fingerprint of climate change impacts across natural systems

Causal attribution of recent biological trends to climate change is complicated because non-climatic influences dominate local , short-term biological changes .
Any underlying signal from climate change is likely to be revealed by analyses that seek systematic trends across diverse species and geographic regions ; however , debates within the Intergovernmental Panel on Climate Change ( IPCC ) reveal several definitions of a ` systematic trend ' .
Here , we explore these differences , apply diverse analyses to more than 1,700 species , and show that recent biological trends match climate change predictions .
Global meta-analyses documented significant range shifts averaging 6.1 km per decade towards the poles ( or metres per decade upward ) , and significant mean advancement of spring events by 2.3 days per decade .
We define a diagnostic fingerprint of temporal and spatial ` sign-switching ' responses uniquely predicted by twentieth century climate trends .
Among appropriate long-term/large-scale/multi-species data sets , this diagnostic fingerprint was found for 279 species .
This suite of analyses generates ` very high confidence ' ( as laid down by the IPCC ) that climate change is already affecting living systems .

[2116] Recovery and resilience of tropical forests after disturbance

The time taken for forested tropical ecosystems to re-establish post-disturbance is of widespread interest .
Yet to date there has been no comparative study across tropical biomes to determine rates of forest re-growth , and how they vary through space and time .
Here we present results from a meta-analysis of palaeoecological records that use fossil pollen as a proxy for vegetation change over the past 20,000 years .
A total of 283 forest disturbance and recovery events , reported in 71 studies , are identified across four tropical regions .
Results indicate that forests in Central America and Africa generally recover faster from past disturbances than those in South America and Asia , as do forests exposed to natural large infrequent disturbances compared with post-climatic and human impacts .
Results also demonstrate that increasing frequency of disturbance events at a site through time elevates recovery rates , indicating a degree of resilience in forests exposed to recurrent past disturbance .

[2117] Control and benefits of CP4-57 prophage excision in Escherichia coli biofilms

Earlier , we discovered that the global regulator , Hha , is related to cell death in biofilms and regulates cryptic prophage genes .
Here , we show that Hha induces excision of prophages , CP4-57 and DLP12 , by inducing excision genes and by reducing SsrA synthesis .
SsrA is a tmRNA that is important for rescuing stalled ribosomes , contains an attachment site for CP4-57 and is shown here to be required for CP4-57 excision .
These prophages impact biofilm development , as the deletion of 35 genes individually of prophages , CP4-57 and DLP12 , increase biofilm formation up to 17-fold , and five genes decrease biofilm formation up to sixfold .
In addition , CP4-57 excises during early biofilm development but not in planktonic cells , whereas DLP12 excision was detected at all the developmental stages for both biofilm and planktonic cells .
CP4-57 excision leads to a chromosome region devoid of prophage and to the formation of a phage circle ( which is lost ) .
These results were corroborated by a whole-transcriptome analysis that showed that complete loss of CP4-57 activated the expression of the flg , flh and fli motility operons and repressed expression of key enzymes in the tricarboxylic acid cycle and of enzymes for lactate utilization .
Prophage excision also results in the expression of cell lysis genes that reduce cell viability ( for example , alpA , intA and intD ) .
Hence , defective prophages are involved in host physiology through Hha and in biofilm formation by generating a diversified population with specialized functions in terms of motility and nutrient metabolism .

[2118] Gradual unlocking of plate boundary controlled initiation of the 2014 Iquique earthquake

On 1 April 2014 , Northern Chile was struck by a magnitude 8.1 earthquake following a protracted series of foreshocks .
The Integrated Plate Boundary Observatory Chile monitored the entire sequence of events , providing unprecedented resolution of the build-up to the main event and its rupture evolution .
Here we show that the Iquique earthquake broke a central fraction of the so-called northern Chile seismic gap , the last major segment of the South American plate boundary that had not ruptured in the past century .
Since July 2013 three seismic clusters , each lasting a few weeks , hit this part of the plate boundary with earthquakes of increasing peak magnitudes .
Starting with the second cluster , geodetic observations show surface displacements that can be associated with slip on the plate interface .
These seismic clusters and their slip transients occupied a part of the plate interface that was transitional between a fully locked and a creeping portion .
Leading up to this earthquake , the b value of the foreshocks gradually decreased during the years before the earthquake , reversing its trend a few days before the Iquique earthquake .
The mainshock finally nucleated at the northern end of the foreshock area , which skirted a locked patch , and ruptured mainly downdip towards higher locking .
Peak slip was attained immediately downdip of the foreshock region and at the margin of the locked patch .
We conclude that gradual weakening of the central part of the seismic gap accentuated by the foreshock activity in a zone of intermediate seismic coupling was instrumental in causing final failure , distinguishing the Iquique earthquake from most great earthquakes .
Finally , only one-third of the gap was broken and the remaining locked segments now pose a significant , increased seismic hazard with the potential to host an earthquake with a magnitude of > 8.5 .

[2119] A network-based analysis of systemic inflammation in humans

Oligonucleotide and complementary DNA microarrays are being used to subclassify histologically similar tumours , monitor disease progress , and individualize treatment regimens .
However , extracting new biological insight from high-throughput genomic studies of human diseases is a challenge , limited by difficulties in recognizing and evaluating relevant biological processes from huge quantities of experimental data .
Here we present a structured network knowledge-base approach to analyse genome-wide transcriptional responses in the context of known functional interrelationships among proteins , small molecules and phenotypes .
This approach was used to analyse changes in blood leukocyte gene expression patterns in human subjects receiving an inflammatory stimulus ( bacterial endotoxin ) .
We explore the known genome-wide interaction network to identify significant functional modules perturbed in response to this stimulus .
Our analysis reveals that the human blood leukocyte response to acute systemic inflammation includes the transient dysregulation of leukocyte bioenergetics and modulation of translational machinery .
These findings provide insight into the regulation of global leukocyte activities as they relate to innate immune system tolerance and increased susceptibility to infection in humans .

[2120] Potential contribution of wind energy to climate change mitigation

It is still possible to limit greenhouse gas emissions to avoid the 2 degreesC warming threshold for dangerous climate change .
Here we explore the potential role of expanded wind energy deployment in climate change mitigation efforts .
At present , most turbines are located in extra-tropical Asia , Europe and North America , where climate projections indicate continuity of the abundant wind resource during this century .
Scenarios from international agencies indicate that this virtually carbon-free source could supply 10-31 % of electricity worldwide by 2050 ( refs , ) .
Using these projections within Intergovernmental Panel on Climate Change Representative Concentration Pathway ( RCP ) climate forcing scenarios , we show that dependent on the precise RCP followed , pursuing a moderate wind energy deployment plan by 2050 delays crossing the 2 degreesC warming threshold by 1-6 years .
Using more aggressive wind turbine deployment strategies delays 2 degreesC warming by 3-10 years , or in the case of RCP4 .5 avoids passing this threshold altogether .
To maximize these climate benefits , deployment of non-fossil electricity generation must be coupled with reduced energy use .

[2121] Metagenomic mining for microbiologists

Microbial ecologists can now start digging into the accumulating mountains of metagenomic data to uncover the occurrence of functional genes and their correlations to microbial community members .
Limitations and biases in DNA extraction and sequencing technologies impact sequence distributions , and therefore , have to be considered .
However , when comparing metagenomes from widely differing environments , these fluctuations have a relatively minor role in microbial community discrimination .
As a consequence , any functional gene or species distribution pattern can be compared among metagenomes originating from various environments and projects .
In particular , global comparisons would help to define ecosystem specificities , such as involvement and response to climate change ( for example , carbon and nitrogen cycle ) , human health risks ( eg , presence of pathogen species , toxin genes and viruses ) and biodegradation capacities .
Although not all scientists have easy access to high-throughput sequencing technologies , they do have access to the sequences that have been deposited in databases , and therefore , can begin to intensively mine these metagenomic data to generate hypotheses that can be validated experimentally .
Information about metabolic functions and microbial species compositions can already be compared among metagenomes from different ecosystems .
These comparisons add to our understanding about microbial adaptation and the role of specific microbes in different ecosystems .
Concurrent with the rapid growth of sequencing technologies , we have entered a new age of microbial ecology , which will enable researchers to experimentally confirm putative relationships between microbial functions and community structures .

[2122] Potential influence of sulphur bacteria on Palaeoproterozoic phosphogenesis

All known forms of life require phosphorus , and biological processes strongly influence the global phosphorus cycle .
Although the record of life on Earth extends back to 3.8 billion years ago and the advent of biological phosphate processing can be tracked to at least 3.5 billion years ago , the earliest known P-rich deposits appeared only 2 billion years ago .
The onset of P deposition has been attributed to the rise of atmospheric oxygen 2.4-2 .3 billion years ago and the related profound biogeochemical shifts , which increased the riverine input of phosphate to the ocean and boosted biological productivity and phosphogenesis .
However , the P-rich deposits post-date the rise of oxygen by about 300 million years .
Here we use microfabric , trace element and carbon isotope analyses to assess the environmental setting and redox conditions of the 2-billion-year-old P-rich deposits of the vent - or seep-influenced Zaonega Formation , northwest Russia .
We identify phosphatized microorganism fossils that resemble modern methanotrophic archaea and sulphur-oxidizing bacteria , analogous to organisms found in modern seep settings and upwelling zones with a sharp redoxcline .
We therefore propose that the P-rich deposits in the Zaonega Formation were formed by phosphogenesis mediated by sulphur bacteria , similar to modern sites , and by the precipitation of calcium phosphate minerals on microbial templates during early diagenesis .

[2123] Biodiversity co-benefits of policies to reduce forest-carbon emissions

Climate change and biodiversity loss are leading environmental crises that converge most critically in tropical forests .
Policies for reducing emissions from deforestation and degradation are often portrayed as win-win solutions for forest-based climate change mitigation and biodiversity conservation .
However , the win-win narrative has obscured necessary trade-offs and a range of alternative policy approaches , insulating policymakers from difficult , potentially unpopular decisions .
We provide a typology that characterizes the five underlying policy approaches for linking forest-based climate change mitigation and biodiversity conservation and their related trade-offs .
Such clarification will enable policymakers and stakeholders to better articulate their positions in the protracted and controversial biodiversity co-benefits debate that is at the centre of contemporary conservation efforts .

[2124] Differential contributions of ammonia oxidizers and nitrite oxidizers to nitrification in four paddy soils

Rice paddy fields are characterized by regular flooding and nitrogen fertilization , but the functional importance of aerobic ammonia oxidizers and nitrite oxidizers under unique agricultural management is poorly understood .
In this study , we report the differential contributions of ammonia-oxidizing archaea ( AOA ) , bacteria ( AOB ) and nitrite-oxidizing bacteria ( NOB ) to nitrification in four paddy soils from different geographic regions ( Zi-Yang ( ZY ) , Jiang-Du ( JD ) , Lei-Zhou ( LZ ) and Jia-Xing ( JX ) ) that are representative of the rice ecosystems in China .
In urea-amended microcosms , nitrification activity varied greatly with 11.9 , 9.46 , 3.03 and 1.43 mug NO3 -- N g-1 dry weight of soil per day in the ZY , JD , LZ and JX soils , respectively , over the course of a 56-day incubation period .
Real-time quantitative PCR of amoA genes and pyrosequencing of 16S rRNA genes revealed significant increases in the AOA population to various extents , suggesting that their relative contributions to ammonia oxidation activity decreased from ZY to JD to LZ .
The opposite trend was observed for AOB , and the JX soil stimulated only the AOB populations .
DNA-based stable-isotope probing further demonstrated that active AOA numerically outcompeted their bacterial counterparts by 37.0 - , 10.5 - and 1.91-fold in 13C-DNA from ZY , JD and LZ soils , respectively , whereas AOB , but not AOA , were labeled in the JX soil during active nitrification .
NOB were labeled to a much greater extent than AOA and AOB , and the addition of acetylene completely abolished the assimilation of 13CO2 by nitrifying populations .
Phylogenetic analysis suggested that archaeal ammonia oxidation was predominantly catalyzed by soil fosmid 29i4-related AOA within the soil group 1.1 b lineage .
Nitrosospira cluster 3-like AOB performed most bacterial ammonia oxidation in the ZY , LZ and JX soils , whereas the majority of the 13C-AOB in the JD soil was affiliated with the Nitrosomona communis lineage .
The 13C-NOB was overwhelmingly dominated by Nitrospira rather than Nitrobacter .
A significant correlation was observed between the active AOA/AOB ratio and the soil oxidation capacity , implying a greater advantage of AOA over AOB under microaerophilic conditions .
These results suggest the important roles of soil physiochemical properties in determining the activities of ammonia oxidizers and nitrite oxidizers .
The ISME Journal advance online publication , 10 October 2014 ; doi :10.1038 / ismej .2014.194

[2125] Eutrophication causes speciation reversal in whitefish adaptive radiations

Species diversity can be lost through two different but potentially interacting extinction processes : demographic decline and speciation reversal through introgressive hybridization .
To investigate the relative contribution of these processes , we analysed historical and contemporary data of replicate whitefish radiations from 17 pre-alpine European lakes and reconstructed changes in genetic species differentiation through time using historical samples .
Here we provide evidence that species diversity evolved in response to ecological opportunity , and that eutrophication , by diminishing this opportunity , has driven extinctions through speciation reversal and demographic decline .
Across the radiations , the magnitude of eutrophication explains the pattern of species loss and levels of genetic and functional distinctiveness among remaining species .
We argue that extinction by speciation reversal may be more widespread than currently appreciated .
Preventing such extinctions will require that conservation efforts not only target existing species but identify and protect the ecological and evolutionary processes that generate and maintain species .

[2126] Observed and modelled stability of overflow across the Greenland-Scotland ridge

Across the Greenland-Scotland ridge there is a continuous flow of cold dense water , termed ` overflow ' , from the Nordic seas to the Atlantic Ocean .
This is a main contributor to the production of North Atlantic Deep Water that feeds the lower limb of the Atlantic meridional overturning circulation , which has been predicted to weaken as a consequence of climate change .
The two main overflow branches pass the Denmark Strait and the Faroe Bank channel .
Here we combine results from direct current measurements in the Faroe Bank channel for 1995-2005 with an ensemble hindcast experiment for 1948-2005 using an ocean general circulation model .
For the overlapping period we find a convincing agreement between model simulations and observations on monthly to interannual timescales .
Both observations and model data show no significant trend in volume transport .
In addition , for the whole 1948-2005 period , the model indicates no persistent trend in the Faroe Bank channel overflow or in the total overflow transport , in agreement with the few available historical observations .
Deepening isopycnals in the Norwegian Sea have tended to decrease the pressure difference across the Greenland-Scotland ridge , but this has been compensated for by the effect of changes in sea level .
In contrast with earlier studies , we therefore conclude that the Faroe Bank channel overflow , and also the total overflow , did not decrease consistently from 1950 to 2005 , although the model does show a weakening total Atlantic meridional overturning circulation as a result of changes south of the Greenland-Scotland ridge .

[2127] Interactions between Thaumarchaea , Nitrospira and methanotrophs modulate autotrophic nitrification in volcanic grassland soil

Ammonium/ammonia is the sole energy substrate of ammonia oxidizers , and is also an essential nitrogen source for other microorganisms .
Ammonia oxidizers therefore must compete with other soil microorganisms such as methane-oxidizing bacteria ( MOB ) in terrestrial ecosystems when ammonium concentrations are limiting .
Here we report on the interactions between nitrifying communities dominated by ammonia-oxidizing archaea ( AOA ) and Nitrospira-like nitrite-oxidizing bacteria ( NOB ) , and communities of MOB in controlled microcosm experiments with two levels of ammonium and methane availability .
We observed strong stimulatory effects of elevated ammonium concentration on the processes of nitrification and methane oxidation as well as on the abundances of autotrophically growing nitrifiers .
However , the key players in nitrification and methane oxidation , identified by stable-isotope labeling using 13CO2 and 13CH4 , were the same under both ammonium levels , namely type 1.1 a AOA , sublineage I and II Nitrospira-like NOB and Methylomicrobium - / Methylosarcina-like MOB , respectively .
Ammonia-oxidizing bacteria were nearly absent , and ammonia oxidation could almost exclusively be attributed to AOA .
Interestingly , although AOA functional gene abundance increased 10-fold during incubation , there was very limited evidence of autotrophic growth , suggesting a partly mixotrophic lifestyle .
Furthermore , autotrophic growth of AOA and NOB was inhibited by active MOB at both ammonium levels .
Our results suggest the existence of a previously overlooked competition for nitrogen between nitrifiers and methane oxidizers in soil , thus linking two of the most important biogeochemical cycles in nature .

[2128] Ruminococcus bromii is a keystone species for the degradation of resistant starch in the human colon

The release of energy from particulate substrates such as dietary fiber and resistant starch ( RS ) in the human colon may depend on the presence of specialist primary degraders ( or ` keystone species ' ) within the microbial community .
We have explored the roles of four dominant amylolytic bacteria found in the human colon in the degradation and utilization of resistant starches .
Eubacterium rectale and Bacteroides thetaiotaomicron showed limited ability to utilize RS2 - and RS3-resistant starches by comparison with Bifidobacterium adolescentis and Ruminococcus bromii .
In co-culture , however , R. bromii proved unique in stimulating RS2 and RS3 utilization by the other three bacterial species , even in a medium that does not permit growth of R. bromii itself .
Having previously demonstrated low RS3 fermentation in vivo in two individuals with undetectable populations of R. bromii-related bacteria , we show here that supplementation of mixed fecal bacteria from one of these volunteers with R. bromii , but not with the other three species , greatly enhanced the extent of RS3 fermentation in vitro .
This argues strongly that R. bromii has a pivotal role in fermentation of RS3 in the human large intestine , and that variation in the occurrence of this species and its close relatives may be a primary cause of variable energy recovery from this important component of the diet .
This work also indicates that R. bromii possesses an exceptional ability to colonize and degrade starch particles when compared with previously studied amylolytic bacteria from the human colon .

[2129] Nonlinear dynamics of ice-wedge networks and resulting sensitivity to severe cooling events

Patterns of subsurface wedges of ice that form along cooling-induced tension fractures , expressed at the ground surface by ridges or troughs spaced 10-30 m apart , are ubiquitous in polar lowlands .
Fossilized ice wedges , which are widespread at lower latitudes , have been used to infer the duration and mean temperature of cold periods within Proterozoic and Quaternary climates , and recent climate trends have been inferred from fracture frequency in active ice wedges .
Here we present simulations from a numerical model for the evolution of ice-wedge networks over a range of climate scenarios , based on the interactions between thermal tensile stress , fracture and ice wedges .
We find that short-lived periods of severe cooling permanently alter the spacing between ice wedges as well as their fracture frequency .
This affects the rate at which the widths of ice wedges increase as well as the network 's response to subsequent climate change .
We conclude that wedge spacing and width in ice-wedge networks mainly reflect infrequent episodes of rapidly falling ground temperatures rather than mean conditions .

[2130] Microbial expression profiles in the rhizosphere of willows depend on soil contamination

The goal of phytoremediation is to use plants to immobilize , extract or degrade organic and inorganic pollutants .
In the case of organic contaminants , plants essentially act indirectly through the stimulation of rhizosphere microorganisms .
A detailed understanding of the effect plants have on the activities of rhizosphere microorganisms could help optimize phytoremediation systems and enhance their use .
In this study , willows were planted in contaminated and non-contaminated soils in a greenhouse , and the active microbial communities and the expression of functional genes in the rhizosphere and bulk soil were compared .
Ion Torrent sequencing of 16S rRNA and Illumina sequencing of mRNA were performed .
Genes related to carbon and amino-acid uptake and utilization were upregulated in the willow rhizosphere , providing indirect evidence of the compositional content of the root exudates .
Related to this increased nutrient input , several microbial taxa showed a significant increase in activity in the rhizosphere .
The extent of the rhizosphere stimulation varied markedly with soil contamination levels .
The combined selective pressure of contaminants and rhizosphere resulted in higher expression of genes related to competition ( antibiotic resistance and biofilm formation ) in the contaminated rhizosphere .
Genes related to hydrocarbon degradation were generally more expressed in contaminated soils , but the exact complement of genes induced was different for bulk and rhizosphere soils .
Together , these results provide an unprecedented view of microbial gene expression in the plant rhizosphere during phytoremediation .

[2131] Global assessment of trends in wetting and drying over land

Changes in the hydrological conditions of the land surface have substantial impacts on society .
Yet assessments of observed continental dryness trends yield contradicting results .
The concept that dry regions dry out further , whereas wet regions become wetter as the climate warms has been proposed as a simplified summary of expected as well as observed changes over land , although this concept is mostly based on oceanic data .
Here we present an analysis of more than 300 combinations of various hydrological data sets of historical land dryness changes covering the period from 1948 to 2005 .
Each combination of data sets is benchmarked against an empirical relationship between evaporation , precipitation and aridity .
Those combinations that perform well are used for trend analysis .
We find that over about three-quarters of the global land area , robust dryness changes can not be detected .
Only 10.8 % of the global land area shows a robust ` dry gets drier , wet gets wetter ' pattern , compared to 9.5 % of global land area with the opposite pattern , that is , dry gets wetter , and wet gets drier .
We conclude that aridity changes over land , where the potential for direct socio-economic consequences is highest , have not followed a simple intensification of existing patterns .

[2132] Nutrient supply from fishes facilitates macroalgae and suppresses corals in a Caribbean coral reef ecosystem

On coral reefs , fishes can facilitate coral growth via nutrient excretion ; however , as coral abundance declines , these nutrients may help facilitate increases in macroalgae .
By combining surveys of reef communities with bioenergetics modeling , we showed that fish excretion supplied 25 times more nitrogen to forereefs in the Florida Keys , USA , than all other biotic and abiotic sources combined .
One apparent result was a positive relationship between fish excretion and macroalgal cover on these reefs .
Herbivore biomass also showed a negative relationship with macroalgal cover , suggesting strong interactions of top-down and bottom-up forcing .
Nutrient supply by fishes also showed a negative correlation with juvenile coral density , likely mediated by competition between macroalgae and corals , suggesting that fish excretion may hinder coral recovery following large-scale coral loss .
Thus , the impact of nutrient supply by fishes may be context-dependent and reinforce either coral-dominant or coral-depauperate reef communities depending on initial community states .

[2133] Implications of agricultural transitions and urbanization for ecosystem services

Historically , farmers and hunter-gatherers relied directly on ecosystem services , which they both exploited and enjoyed .
Urban populations still rely on ecosystems , but prioritize non-ecosystem services ( socioeconomic ) .
Population growth and densification increase the scale and change the nature of both ecosystem - and non-ecosystem-service supply and demand , weakening direct feedbacks between ecosystems and societies and potentially pushing social-ecological systems into traps that can lead to collapse .
The interacting and mutually reinforcing processes of technological change , population growth and urbanization contribute to over-exploitation of ecosystems through complex feedbacks that have important implications for sustainable resource use .

[2134] Temperature and solids retention time control microbial population dynamics and volatile fatty acid production in replicated anaerobic digesters

Anaerobic digestion is a widely used technology for waste stabilization and generation of biogas , and has recently emerged as a potentially important process for the production of high value volatile fatty acids ( VFAs ) and alcohols .
Here , three reactors were seeded with inoculum from a stably performing methanogenic digester , and selective operating conditions ( 37degreesC and 55degreesC ; 12 day and 4 day solids retention time ) were applied to restrict methanogenesis while maintaining hydrolysis and fermentation .
Replicated experiments performed at each set of operating conditions led to reproducible VFA production profiles which could be correlated with specific changes in microbial community composition .
The mesophilic reactor at short solids retention time showed accumulation of propionate and acetate ( 42 + / - 2 % and 15 + / - 6 % of CODhydrolyzed , respectively ) , and dominance of Fibrobacter and Bacteroidales .
Acetate accumulation ( > 50 % of CODhydrolyzed ) was also observed in the thermophilic reactors , which were dominated by Clostridium .
Under all tested conditions , there was a shift from acetoclastic to hydrogenotrophic methanogenesis , and a reduction in methane production by > 50 % of CODhydrolyzed .
Our results demonstrate that shortening the SRT and increasing the temperature are effective strategies for driving microbial communities towards controlled production of high levels of specific volatile fatty acids .

[2135] Deep Arctic Ocean warming during the last glacial cycle

In the Arctic Ocean , the cold and relatively fresh water beneath the sea ice is separated from the underlying warmer and saltier Atlantic Layer by a halocline .
Ongoing sea ice loss and warming in the Arctic Ocean have demonstrated the instability of the halocline , with implications for further sea ice loss .
The stability of the halocline through past climate variations is unclear .
Here we estimate intermediate water temperatures over the past 50,000 years from the Mg/Ca and Sr/Ca values of ostracods from 31 Arctic sediment cores .
From about 50 to 11 kyr ago , the central Arctic Basin from 1,000 to 2,500 m was occupied by a water mass we call Glacial Arctic Intermediate Water .
This water mass was 1-2 degreesC warmer than modern Arctic Intermediate Water , with temperatures peaking during or just before millennial-scale Heinrich cold events and the Younger Dryas cold interval .
We use numerical modelling to show that the intermediate depth warming could result from the expected decrease in the flux of fresh water to the Arctic Ocean during glacial conditions , which would cause the halocline to deepen and push the warm Atlantic Layer into intermediate depths .
Although not modelled , the reduced formation of cold , deep waters due to the exposure of the Arctic continental shelf could also contribute to the intermediate depth warming .

[2136] Comparing apples with oranges

The drivers and impacts of climate change extend beyond greenhouse gas emissions and rising temperature , especially when deforestation enters the picture .
In deciding how best to mitigate , we may need to favour direct calculations of cost over current means of measuring climate change .

[2137] A novel perspective on seed yield of broad bean ( Vicia faba L. ) : differences resulting from pod characteristics

Broad bean ( Vicia faba L. ) is an important crop worldwide .
An increase in seed yield would increase both the grain reserve and the profit for farmers .
Previous studies on increasing broad bean seed yield have focused mainly on increases at the whole population level .
Few studies have focused on the differences in plant type within populations .
In this study , we classified broad bean plants into four categories based on pod type , and then evaluated the ratio of each category in field-grown broad bean populations .
We analysed the seed and pod characteristics of each category , and their contributions to total seed yield .
The number of seeds per pod , and the number of pods or seeds per plant differed among the four plant categories , but the seed weight was relatively uniform .
There were significant differences in seed yield per plant among the four plant categories .
We calculated the effects of increasing the proportion of each plant category by 10 % or to 100 % on seed yield , and found that seed yield could be improved by increasing the ratio of plants with the highest seed production rate .
This study provides a novel perspective on estimating the seed yield of broad bean .

[2138] Allying with armored snails : the complete genome of gammaproteobacterial endosymbiont

Deep-sea vents harbor dense populations of various animals that have their specific symbiotic bacteria .
Scaly-foot gastropods , which are snails with mineralized scales covering the sides of its foot , have a gammaproteobacterial endosymbiont in their enlarged esophageal glands and diverse epibionts on the surface of their scales .
In this study , we report the complete genome sequencing of gammaproteobacterial endosymbiont .
The endosymbiont genome displays features consistent with ongoing genome reduction such as large proportions of pseudogenes and insertion elements .
The genome encodes functions commonly found in deep-sea vent chemoautotrophs such as sulfur oxidation and carbon fixation .
Stable carbon isotope ( 13C ) - labeling experiments confirmed the endosymbiont chemoautotrophy .
The genome also includes an intact hydrogenase gene cluster that potentially has been horizontally transferred from phylogenetically distant bacteria .
Notable findings include the presence and transcription of genes for flagellar assembly , through which proteins are potentially exported from bacterium to the host .
Symbionts of snail individuals exhibited extreme genetic homogeneity , showing only two synonymous changes in 19 different genes ( 13 810 positions in total ) determined for 32 individual gastropods collected from a single colony at one time .
The extremely low genetic individuality in endosymbionts probably reflects that the stringent symbiont selection by host prevents the random genetic drift in the small population of horizontally transmitted symbiont .
This study is the first complete genome analysis of gastropod endosymbiont and offers an opportunity to study genome evolution in a recently evolved endosymbiont .

[2139] Production and engineering of terpenoids in plant cell culture

Terpenoids are a diverse class of natural products that have many functions in the plant kingdom and in human health and nutrition .
Their chemical diversity has led to the discovery of over 40,000 different structures , with several classes serving as important pharmaceutical agents , including the anticancer agents paclitaxel ( Taxol ) and terpenoid-derived indole alkaloids .
Many terpenoid compounds are found in low yield from natural sources , so plant cell cultures have been investigated as an alternate production strategy .
Metabolic engineering of whole plants and plant cell cultures is an effective tool to both increase terpenoid yield and alter terpenoid distribution for desired properties such as enhanced flavor , fragrance or color .
Recent advances in defining terpenoid metabolic pathways , particularly in secondary metabolism , enhanced knowledge concerning regulation of terpenoid accumulation , and application of emerging plant systems biology approaches , have enabled metabolic engineering of terpenoid production .
This paper reviews the current state of knowledge of terpenoid metabolism , with a special focus on production of important pharmaceutically active secondary metabolic terpenoids in plant cell cultures .
Strategies for defining pathways and uncovering rate-influencing steps in global metabolism , and applying this information for successful terpenoid metabolic engineering , are emphasized .

[2140] Water balance of global aquifers revealed by groundwater footprint

Groundwater is a life-sustaining resource that supplies water to billions of people , plays a central part in irrigated agriculture and influences the health of many ecosystems .
Most assessments of global water resources have focused on surface water , but unsustainable depletion of groundwater has recently been documented on both regional and global scales .
It remains unclear how the rate of global groundwater depletion compares to the rate of natural renewal and the supply needed to support ecosystems .
Here we define the groundwater footprint ( the area required to sustain groundwater use and groundwater-dependent ecosystem services ) and show that humans are overexploiting groundwater in many large aquifers that are critical to agriculture , especially in Asia and North America .
We estimate that the size of the global groundwater footprint is currently about 3.5 times the actual area of aquifers and that about 1.7 billion people live in areas where groundwater resources and/or groundwater-dependent ecosystems are under threat .
That said , 80 per cent of aquifers have a groundwater footprint that is less than their area , meaning that the net global value is driven by a few heavily overexploited aquifers .
The groundwater footprint is the first tool suitable for consistently evaluating the use , renewal and ecosystem requirements of groundwater at an aquifer scale .
It can be combined with the water footprint and virtual water calculations , and be used to assess the potential for increasing agricultural yields with renewable groundwaterref .
The method could be modified to evaluate other resources with renewal rates that are slow and spatially heterogeneous , such as fisheries , forestry or soil .

[2141] Support for climate policy and societal action are linked to perceptions about scientific agreement

Although a majority of US citizens think that the president and Congress should address global warming , only a minority think it should be a high priority .
Previous research has shown that four key beliefs about climate change -- that it is real , human caused , serious and solvable -- are important predictors of support for climate policies .
Other research has shown that organized opponents of climate legislation have sought to undermine public support by instilling the belief that there is widespread disagreement among climate scientists about these points -- a view shown to be widely held by the public .
Here we examine if this misperception is consequential .
We show that the misperception is strongly associated with reduced levels of policy support and injunctive beliefs ( that is , beliefs that action should be taken to mitigate global warming ) .
The relationship is mediated by the four previously identified key beliefs about climate change , especially people 's certainty that global warming is occurring .
In short , people who believe that scientists disagree on global warming tend to feel less certain that global warming is occurring , and show less support for climate policy .
This suggests the potential importance of correcting the widely held public misperception about lack of scientific agreement on global warming .

[2142] Microbial production of short-chain alkanes

Increasing concerns about limited fossil fuels and global environmental problems have focused attention on the need to develop sustainable biofuels from renewable resources .
Although microbial production of diesel has been reported , production of another much in demand transport fuel , petrol ( gasoline ) , has not yet been demonstrated .
Here we report the development of platform Escherichia coli strains that are capable of producing short-chain alkanes ( SCAs ; petrol ) , free fatty acids ( FFAs ) , fatty esters and fatty alcohols through the fatty acyl ( acyl carrier protein ( ACP ) ) to fatty acid to fatty acyl-CoA pathway .
First , the beta-oxidation pathway was blocked by deleting the fadE gene to prevent the degradation of fatty acyl-CoAs generated in vivo .
To increase the formation of short-chain fatty acids suitable for subsequent conversion to SCAs in vivo , the activity of 3-oxoacyl-ACP synthase ( FabH ) , which is inhibited by unsaturated fatty acyl-ACPs , was enhanced to promote the initiation of fatty acid biosynthesis by deleting the fadR gene ; deletion of the fadR gene prevents upregulation of the fabA and fabB genes responsible for unsaturated fatty acids biosynthesis .
A modified thioesterase was used to convert short-chain fatty acyl-ACPs to the corresponding FFAs , which were then converted to SCAs by the sequential reactions of E. coli fatty acyl-CoA synthetase , Clostridium acetobutylicum fatty acyl-CoA reductase and Arabidopsis thaliana fatty aldehyde decarbonylase .
The final engineered strain produced up to 580.8 mg l-1 of SCAs consisting of nonane ( 327.8 mg l-1 ) , dodecane ( 136.5 mg l-1 ) , tridecane ( 64.8 mg l-1 ) , 2-methyl-dodecane ( 42.8 mg l-1 ) and tetradecane ( 8.9 mg l-1 ) , together with small amounts of other hydrocarbons .
Furthermore , this platform strain could produce short-chain FFAs using a fadD-deleted strain , and short-chain fatty esters by introducing the Acinetobacter sp .
ADP1 wax ester synthase ( atfA ) and the E. coli mutant alcohol dehydrogenase ( adhEmut ) .

[2143] Resilience of persistent Arctic mixed-phase clouds

The Arctic region is particularly sensitive to climate change .
Mixed-phase clouds , comprising both ice and supercooled liquid water , have a large impact on radiative fluxes in the Arctic .
These clouds occur frequently during all seasons in the region , where they often persist for many days at a time .
This persistence is remarkable given the inherent instability of ice-liquid mixtures .
In recent years it has emerged that feedbacks between numerous local processes , including the formation and growth of ice and cloud droplets , radiative cooling , turbulence , entrainment and surface fluxes of heat and moisture , interact to create a resilient mixed-phase cloud system .
As well as the persistent mixed-phase cloud state there is another distinct Arctic state , characterized by radiatively clear conditions .
The occurrence of either state seems to be related , in part , to large-scale environmental conditions .
We suggest that shifts in the large-scale environment could alter the prevalence of mixed-phase clouds , potentially affecting surface radiative fluxes and the Arctic energy budget .

[2144] Organic carbon transformations in high-Arctic peat soils : key functions and microorganisms

A substantial part of the Earths ' soil organic carbon ( SOC ) is stored in Arctic permafrost peatlands , which represent large potential sources for increased emissions of the greenhouse gases CH4 and CO2 in a warming climate .
The microbial communities and their genetic repertoire involved in the breakdown and mineralisation of SOC in these soils are , however , poorly understood .
In this study , we applied a combined metagenomic and metatranscriptomic approach on two Arctic peat soils to investigate the identity and the gene pool of the microbiota driving the SOC degradation in the seasonally thawed active layers .
A large and diverse set of genes encoding plant polymer-degrading enzymes was found , comparable to microbiotas from temperate and subtropical soils .
This indicates that the metabolic potential for SOC degradation in Arctic peat is not different from that of other climatic zones .
The majority of these genes were assigned to three bacterial phyla , Actinobacteria , Verrucomicrobia and Bacteroidetes .
Anaerobic metabolic pathways and the fraction of methanogenic archaea increased with peat depth , evident for a gradual transition from aerobic to anaerobic lifestyles .
A population of CH4-oxidising bacteria closely related to Methylobacter tundripaludum was the dominating active group of methanotrophs .
Based on the in-depth characterisation of the microbes and their genes , we conclude that these Arctic peat soils will turn into CO2 sources owing to increased active layer depth and prolonged growing season .
However , the extent of future CH4 emissions will critically depend on the response of the methanotrophic bacteria .

[2145] Integrating phylogeny , geographic niche partitioning and secondary metabolite synthesis in bloom-forming Planktothrix

Toxic freshwater cyanobacteria form harmful algal blooms that can cause acute toxicity to humans and livestock .
Globally distributed , bloom-forming cyanobacteria Planktothrix either retain or lose the mcy gene cluster ( encoding the synthesis of the secondary metabolite hepatotoxin microcystin or MC ) , resulting in a variable spatial/temporal distribution of ( non ) toxic genotypes .
Despite their importance to human well-being , such genotype diversity is not being mapped at scales relevant to nature .
We aimed to reveal the factors influencing the dispersal of those genotypes by analyzing 138 strains ( from Europe , Russia , North America and East Africa ) for their ( i ) mcy gene cluster composition , ( ii ) phylogeny and adaptation to their habitat and ( iii ) ribosomally and nonribosomally synthesized oligopeptide products .
Although all the strains from different species contained at least remnants of the mcy gene cluster , various phylogenetic lineages evolved and adapted to rather specific ecological niches ( for example , through pigmentation and gas vesicle protein size ) .
No evidence for an increased abundance of specific peptides in the absence of MC was found .
MC and peptide distribution rather depended on phylogeny , ecophysiological adaptation and geographic distance .
Together , these findings provide evidence that MC and peptide production are primarily related to speciation processes , while within a phylogenetic lineage the probability that strains differ in peptide composition increases with geographic distance .

[2146] Broadband evolution of phononic-crystal-waveguide eigenstates in real - and k-spaces

Control of sound in phononic band-gap structures promises novel control and guiding mechanisms .
Designs in photonic systems were quickly matched in phononics , and rows of defects in phononic crystals were shown to guide sound waves effectively .
The vast majority of work in such phononic guiding has been in the frequency domain , because of the importance of the phononic dispersion relation in governing acoustic confinement in waveguides .
However , frequency-domain studies miss vital information concerning the phase of the acoustic field and eigenstate coupling .
Using a wide range of wavevectors k , we implement an ultrafast technique to probe the wave field evolution in straight and L-shaped phononic crystal surface-phonon waveguides in real - and k-space in two spatial dimensions , thus revealing the eigenstate-energy redistribution processes and the coupling between different frequency-degenerate eigenstates .
Such use of k-t space is a first in acoustics , and should have other interesting applications such as acoustic-metamaterial characterization .

[2147] Estuarine and early-marine survival of transported and in-river migrant Snake River spring Chinook salmon smolts

Many juvenile Snake River Chinook salmon are transported downriver to avoid hydroelectric dams in the Columbia River basin .
As mortality to the final dam is ~ 50 % , transported fish should return as adults at roughly double the rate of nontransported fish ; however , the benefit of transportation has not been realized consistently .
`` Delayed '' mortality caused by transportation-induced stress is one hypothesis to explain reduced returns of transported fish .
Differential timing of ocean entry is another .
We used a large-scale acoustic telemetry array to test whether survival of transported juvenile spring Chinook is reduced relative to in-river migrant control groups after synchronizing ocean entry timing .
During the initial 750 km , 1 month long migration after release , we found no evidence of decreased estuarine or ocean survival of transported groups ; therefore , decreased survival to adulthood for transported Chinook is likely caused by factors other than delayed effects of transportation , such as earlier ocean entry .

[2148] Rise in carbon dioxide changes soil structure

Carbon in soil affects the formation and stabilization of aggregates ( groups of primary particles that adhere to each other more strongly than to surrounding soil particles ) .
Soil aggregation is important for preventing soil loss through wind and water erosion , and the size distribution and abundance of water-stable aggregates influences a range of physical , chemical , biological and agricultural properties of soil .
The effects on soil biota and nutrient cycling of increases in soil carbon availability , brought about by increased CO2 , are well studied , but the consequences for soil aggregation and structure have not been examined .
Here we show for three ecosystems that the water stability and size distribution of aggregates is affected by long-term CO2fumigation , and we propose a mechanism for this that involves the production by fungi of the glycoprotein glomalin .

[2149] A coupled physical and economic model of the response of coastal real estate to climate risk

Barring an unprecedented large-scale effort to raise island elevation , barrier-island communities common along the US East Coast are likely to eventually face inundation of the existing built environment on a timescale that depends on uncertain climatic forcing .
Between the present and when a combination of sea-level rise and erosion renders these areas uninhabitable , communities must choose levels of defensive expenditures to reduce risks and individual residents must assess whether and when risk levels are unacceptably high to justify investment in housing .
We model the dynamics of coastal adaptation as the interplay of underlying climatic risks , collective actions to mitigate those risks , and individual risk assessments based on beliefs in model predictions and processing of past climate events .
Efforts linking physical and behavioural models to explore shoreline dynamics have not yet brought together this set of essential factors .
We couple a barrier-island model with an agent-based model of real-estate markets to show that , relative to people with low belief in model predictions about climate change , informed property owners invest heavily in defensive expenditures in the near term and then abandon coastal real estate at some critical risk threshold that presages a period of significant price volatility .

[2150] Identification of iron-reducing microorganisms in anoxic rice paddy soil by 13C-acetate probing

In anoxic rice field soil , ferric iron reduction is one of the most important terminal electron accepting processes , yet little is known about the identity of iron-reducing microorganisms .
Here , we identified acetate-metabolizing bacteria by RNA-based stable isotope probing in the presence of iron ( III ) oxides as electron acceptors .
After reduction of endogenous iron ( III ) for 21 days , isotope probing with 13C-labeled acetate ( 2 mM ) and added ferric iron oxides ( ferrihydrite or goethite ) was performed in rice field soil slurries for 48 and 72 h. Ferrihydrite reduction coincided with a strong suppression of methanogenesis ( 77 % ) .
Extracted RNA from each treatment was density resolved by isopycnic centrifugation , and analyzed by terminal restriction fragment length polymorphism , followed by cloning and sequencing of 16S rRNA of bacterial and archaeal populations .
In heavy , isotopically labeled RNAs of the ferrihydrite treatment , predominant 13C-assimilating populations were identified as Geobacter spp .
( ~ 85 % of all clones ) .
In the goethite treatment , iron ( II ) formation was not detectable .
However , Geobacter spp .
( ~ 30 % ) , the delta-proteobacterial Anaeromyxobacter spp .
( ~ 30 % ) , and novel beta-Proteobacteria were predominant in heavy rRNA fractions indicating that 13C-acetate had been assimilated in the presence of goethite , whereas none were detected in the control heavy RNA .
For the first time , active acetate-oxidizing iron ( III ) - reducing bacteria , including novel hitherto unrecognized populations , were identified as a functional guild in anoxic paddy soil .

[2151] Synchronization of the climate system to eccentricity forcing and the 100,000-year problem

Over the past million years , glacial-interglacial cycles have had a period of about 100,000 years , similar to the 100,000-year period of change in the eccentricity of the Earth 's orbit .
However , the change in incoming solar radiation -- insolation -- at this timescale is small , and therefore difficult to reconcile with the amplitude of the glacial cycles .
This issue , known as the 100-kyr problem , is compounded by a lack of explanation for the transition of the length of the cycles from 41,000 to 100,000 years at the mid-Pleistocene transition 1.2 million years ago .
Individual discrepancies have been explained , for example , through interactions between other orbital frequencies such as obliquity and the 413,000-year period of eccentricity , but a unified explanation is lacking .
Here we show that climate oscillations over the past four million years can be explained by a single mechanism : the synchronization of nonlinear internal climate oscillations and the 413,000-year eccentricity cycle .
Using spectral analyses aided by a numerical model , we find that the climate system first synchronized to the 413,000-year eccentricity cycle about 1.2 million years ago and has remained synchronized ever since .
This synchronization results in a nonlinear transfer of power and frequency modulation that increases the amplitude of the 100,000-year cycle .
We conclude that the forced synchronization can explain the strong 100,000-year glacial cycles through the alignment of insolation changes and internal climate oscillations .

[2152] The equilibria that allow bacterial persistence in human hosts

We propose that microbes that have developed persistent relationships with human hosts have evolved cross-signalling mechanisms that permit homeostasis that conforms to Nash equilibria and , more specifically , to evolutionarily stable strategies .
This implies that a group of highly diverse organisms has evolved within the changing contexts of variation in effective human population size and lifespan , shaping the equilibria achieved , and creating relationships resembling climax communities .
We propose that such ecosystems contain nested communities in which equilibrium at one level contributes to homeostasis at another .
The model can aid prediction of equilibrium states in the context of further change : widespread immunodeficiency , changing population densities , or extinctions .

[2153] Evidence for deep-water production in the North Pacific Ocean during the early Cenozoic warm interval

The deep-ocean circulation is responsible for a significant component of global heat transport .
In the present mode of circulation , deep waters form in the North Atlantic and Southern oceans where surface water becomes sufficiently cold and dense to sink .
Polar temperatures during the warmest climatic interval of the Cenozoic era ( ~ 65 to 40 million years ( Myr ) ago ) were significantly warmer than today , and this may have been a consequence of enhanced oceanic heat transport .
However , understanding the relationship between deep-ocean circulation and ancient climate is complicated by differences in oceanic gateways , which affect where deep waters form and how they circulate .
Here I report records of neodymium isotopes from two cores in the Pacific Ocean that indicate a shift in deep-water production from the Southern Ocean to the North Pacific ~ 65 Myr ago .
The source of deep waters reverted back to the Southern Ocean 40 Myr ago .
The relative timing of changes in the neodymium and oxygen isotope records indicates that changes in Cenozoic deep-water circulation patterns were the consequence , not the cause , of extreme Cenozoic warmth .

[2154] Air traffic may increase cirrus cloudiness

High-level cirrus clouds can evolve , from the condensation trails of aircraft , which form as the mixture of warm , humid exhaust gases and colder , drier air exceeds water saturation .
In addition , the particles in exhaust plumes from aircraft may allow ice nucleation at lower supersaturations than those required under natural conditions .
This mechanism is sensitive to environmental conditions , but may occur downstream of the exhaust aerosol source regions .
Here I show that cirrus clouds increased in occurrence and coverage in the main air-traffic flight corridors between 1982 and 1991 .

[2155] Declines in insectivorous birds are associated with high neonicotinoid concentrations

Recent studies have shown that neonicotinoid insecticides have adverse effects on non-target invertebrate species .
Invertebrates constitute a substantial part of the diet of many bird species during the breeding season and are indispensable for raising offspring .
We investigated the hypothesis that the most widely used neonicotinoid insecticide , imidacloprid , has a negative impact on insectivorous bird populations .
Here we show that , in the Netherlands , local population trends were significantly more negative in areas with higher surface-water concentrations of imidacloprid .
At imidacloprid concentrations of more than 20 nanograms per litre , bird populations tended to decline by 3.5 per cent on average annually .
Additional analyses revealed that this spatial pattern of decline appeared only after the introduction of imidacloprid to the Netherlands , in the mid-1990s .
We further show that the recent negative relationship remains after correcting for spatial differences in land-use changes that are known to affect bird populations in farmland .
Our results suggest that the impact of neonicotinoids on the natural environment is even more substantial than has recently been reported and is reminiscent of the effects of persistent insecticides in the past .
Future legislation should take into account the potential cascading effects of neonicotinoids on ecosystems .

[2156] High-latitude controls of thermocline nutrients and low latitude biological productivity

The ocean 's biological pump strips nutrients out of the surface waters and exports them into the thermocline and deep waters .
If there were no return path of nutrients from deep waters , the biological pump would eventually deplete the surface waters and thermocline of nutrients ; surface biological productivity would plummet .
Here we make use of the combined distributions of silicic acid and nitrate to trace the main nutrient return path from deep waters by upwelling in the Southern Ocean and subsequent entrainment into subantarctic mode water .
We show that the subantarctic mode water , which spreads throughout the entire Southern Hemisphere and North Atlantic Ocean , is the main source of nutrients for the thermocline .
We also find that an additional return path exists in the northwest corner of the Pacific Ocean , where enhanced vertical mixing , perhaps driven by tides , brings abyssal nutrients to the surface and supplies them to the thermocline of the North Pacific .
Our analysis has important implications for our understanding of large-scale controls on the nature and magnitude of low-latitude biological productivity and its sensitivity to climate change .

[2157] Lake microbial communities are resilient after a whole-ecosystem disturbance

Disturbances act as powerful structuring forces on ecosystems .
To ask whether environmental microbial communities have capacity to recover after a large disturbance event , we conducted a whole-ecosystem manipulation , during which we imposed an intense disturbance on freshwater microbial communities by artificially mixing a temperate lake during peak summer thermal stratification .
We employed environmental sensors and water chemistry analyses to evaluate the physical and chemical responses of the lake , and bar-coded 16S ribosomal RNA gene pyrosequencing and automated ribosomal intergenic spacer analysis ( ARISA ) to assess the bacterial community responses .
The artificial mixing increased mean lake temperature from 14 to 20 degreesC for seven weeks after mixing ended , and exposed the microorganisms to very different environmental conditions , including increased hypolimnion oxygen and increased epilimnion carbon dioxide concentrations .
Though overall ecosystem conditions remained altered ( with hypolimnion temperatures elevated from 6 to 20 degreesC ) , bacterial communities returned to their pre-manipulation state as some environmental conditions , such as oxygen concentration , recovered .
Recovery to pre-disturbance community composition and diversity was observed within 7 ( epilimnion ) and 11 ( hypolimnion ) days after mixing .
Our results suggest that some microbial communities have capacity to recover after a major disturbance .

[2158] Experimental niche evolution alters the strength of the diversity-productivity relationship

The relationship between biodiversity and ecosystem functioning ( BEF ) has become a cornerstone of community and ecosystem ecology and an essential criterion for making decisions in conservation biology and policy planning .
It has recently been proposed that evolutionary history should influence the BEF relationship because it determines species traits and , thus , species ' ability to exploit resources .
Here we test this hypothesis by combining experimental evolution with a BEF experiment .
We isolated 20 bacterial strains from a marine environment and evolved each to be generalists or specialists .
We then tested the effect of evolutionary history on the strength of the BEF relationship with assemblages of 1 to 20 species constructed from the specialists , generalists and ancestors .
Assemblages of generalists were more productive on average because of their superior ability to exploit the environmental heterogeneity .
The slope of the BEF relationship was , however , stronger for the specialist assemblages because of enhanced niche complementarity .
These results show how the BEF relationship depends critically on the legacy of past evolutionary events .

[2159] Critically pressured free-gas reservoirs below gas-hydrate provinces

Palaeoceanographic data have been used to suggest that methane hydrates play a significant role in global climate change .
The mechanism by which methane is released during periods of global warming is , however , poorly understood .
In particular , the size and role of the free-gas zone below gas-hydrate provinces remain relatively unconstrained , largely because the base of the free-gas zone is not a phase boundary and has thus defied systematic description .
Here we evaluate the possibility that the maximum thickness of an interconnected free-gas zone is mechanically regulated by valving caused by fault slip in overlying sediments .
Our results suggest that a critical gas column exists below most hydrate provinces in basin settings , implying that these provinces are poised for mechanical failure and are therefore highly sensitive to changes in ambient conditions .
We estimate that the global free-gas reservoir may contain from one-sixth to two-thirds of the total methane trapped in hydrate .
If gas accumulations are critically thick along passive continental slopes , we calculate that a 5 degreesC temperature increase at the sea floor could result in a release of ~ 2,000 Gt of methane from the free-gas zone , offering a mechanism for rapid methane release during global warming events .

[2160] Reconciling complexity with stability in naturally assembling food webs

Understanding how complex food webs assemble through time is fundamental both for ecological theory and for the development of sustainable strategies of ecosystem conservation and restoration .
The build-up of complexity in communities is theoretically difficult , because in random-pattern models complexity leads to instability .
There is growing evidence , however , that nonrandom patterns in the strengths of the interactions between predators and prey strongly enhance system stability .
Here we show how such patterns explain stability in naturally assembling communities .
We present two series of below-ground food webs along natural productivity gradients in vegetation successions .
The complexity of the food webs increased along the gradients .
The stability of the food webs was captured by measuring the weight of feedback loops of three interacting ` species ' locked in omnivory .
Low predator-prey biomass ratios in these omnivorous loops were shown to have a crucial role in preserving stability as productivity and complexity increased during succession .
Our results show the build-up of food-web complexity in natural productivity gradients and pin down the feedback loops that govern the stability of whole webs .
They show that it is the heaviest three-link feedback loop in a network of predator-prey effects that limits its stability .
Because the weight of these feedback loops is kept relatively low by the biomass build-up in the successional process , complexity does not lead to instability .

[2161] Antarctic climate cooling and terrestrial ecosystem response

The average air temperature at the Earth 's surface has increased by 0.06 degreesC per decade during the 20th century , and by 0.19 degreesC per decade from 1979 to 1998 .
Climate models generally predict amplified warming in polar regions , as observed in Antarctica 's peninsula region over the second half of the 20th century .
Although previous reports suggest slight recent continental warming , our spatial analysis of Antarctic meteorological data demonstrates a net cooling on the Antarctic continent between 1966 and 2000 , particularly during summer and autumn .
The McMurdo Dry Valleys have cooled by 0.7 degreesC per decade between 1986 and 2000 , with similar pronounced seasonal trends .
Summer cooling is particularly important to Antarctic terrestrial ecosystems that are poised at the interface of ice and water .
Here we present data from the dry valleys representing evidence of rapid terrestrial ecosystem response to climate cooling in Antarctica , including decreased primary productivity of lakes ( 6-9 % per year ) and declining numbers of soil invertebrates ( more than 10 % per year ) .
Continental Antarctic cooling , especially the seasonality of cooling , poses challenges to models of climate and ecosystem change .

[2162] Leaf nitrogen and phosphorus of temperate desert plants in response to climate and soil nutrient availability

In desert ecosystems , plant growth and nutrient uptake are restricted by availability of soil nitrogen ( N ) and phosphorus ( P ) .
The effects of both climate and soil nutrient conditions on N and P concentrations among desert plant life forms ( annual , perennial and shrub ) remain unclear .
We assessed leaf N and P levels of 54 desert plants and measured the corresponding soil N and P in shallow ( 0-10 cm ) , middle ( 10-40 cm ) and deep soil layers ( 40-100 cm ) , at 52 sites in a temperate desert of northwest China .
Leaf P and N :P ratios varied markedly among life forms .
Leaf P was higher in annuals and perennials than in shrubs .
Leaf N and P showed a negative relationship with mean annual temperature ( MAT ) and no relationship with mean annual precipitation ( MAP ) , but a positive relationship with soil P. Leaf P of shrubs was positively related to soil P in the deep soil .
Our study indicated that leaf N and P across the three life forms were influenced by soil P. Deep-rooted plants may enhance the availability of P in the surface soil facilitating growth of shallow-rooted life forms in this N and P limited system , but further research is warranted on this aspect .

[2163] Metagenomic analysis of size-fractionated picoplankton in a marine oxygen minimum zone

Marine oxygen minimum zones ( OMZs ) support diverse microbial communities with roles in major elemental cycles .
It is unclear how the taxonomic composition and metabolism of OMZ microorganisms vary between particle-associated and free-living size fractions .
We used amplicon ( 16S rRNA gene ) and shotgun metagenome sequencing to compare microbial communities from large ( > 1.6 mum ) and small ( 0.2-1 .6 mum ) filter size fractions along a depth gradient in the OMZ off Chile .
Despite steep vertical redox gradients , size fraction was a significantly stronger predictor of community composition compared to depth .
Phylogenetic diversity showed contrasting patterns , decreasing towards the anoxic OMZ core in the small size fraction , but exhibiting maximal values at these depths within the larger size fraction .
Fraction-specific distributions were evident for key OMZ taxa , including anammox planctomycetes , whose coding sequences were enriched up to threefold in the 0.2-1 .6 mum community .
Functional gene composition also differed between fractions , with the > 1.6 mum community significantly enriched in genes mediating social interactions , including motility , adhesion , cell-to-cell transfer , antibiotic resistance and mobile element activity .
Prokaryotic transposase genes were three to six fold more abundant in this fraction , comprising up to 2 % of protein-coding sequences , suggesting that particle surfaces may act as hotbeds for transposition-based genome changes in marine microbes .
Genes for nitric and nitrous oxide reduction were also more abundant ( three to seven fold ) in the larger size fraction , suggesting microniche partitioning of key denitrification steps .
These results highlight an important role for surface attachment in shaping community metabolic potential and genome content in OMZ microorganisms .

[2164] Two-phase change in CO2 , Antarctic temperature and global climate during Termination II

The end of the Last Glacial Maximum ( Termination I ) , roughly 20 thousand years ago ( ka ) , was marked by cooling in the Northern Hemisphere , a weakening of the Asian monsoon , a rise in atmospheric CO2 concentrations and warming over Antarctica .
The sequence of events associated with the previous glacial-interglacial transition ( Termination II ) , roughly 136 ka , is less well constrained .
Here we present high-resolution records of atmospheric CO2 concentrations and isotopic composition of N2 -- an atmospheric temperature proxy -- from air bubbles in the EPICA Dome C ice core that span Termination II .
We find that atmospheric CO2 concentrations and Antarctic temperature started increasing in phase around 136 ka , but in a second phase of Termination II , from 130.5 to 129 ka , the rise in atmospheric CO2 concentrations lagged that of Antarctic temperature unequivocally .
We suggest that during this second phase , the intensification of the low-latitude hydrological cycle resulted in the development of a CO2 sink , which counteracted the CO2 outgassing from the Southern Hemisphere oceans over this period .

[2165] Tropical Atlantic temperature seasonality at the end of the last interglacial

The end of the last interglacial period , ~ 118 kyr ago , was characterized by substantial ocean circulation and climate perturbations resulting from instabilities of polar ice sheets .
These perturbations are crucial for a better understanding of future climate change .
The seasonal temperature changes of the tropical ocean , however , which play an important role in seasonal climate extremes such as hurricanes , floods and droughts at the present day , are not well known for this period that led into the last glacial .
Here we present a monthly resolved snapshot of reconstructed sea surface temperature in the tropical North Atlantic Ocean for 117.7 + / -0.8 kyr ago , using coral Sr/Ca and delta18O records .
We find that temperature seasonality was similar to today , which is consistent with the orbital insolation forcing .
Our coral and climate model results suggest that temperature seasonality of the tropical surface ocean is controlled mainly by orbital insolation changes during interglacials .

[2166] Iron solubility driven by speciation in dust sources to the ocean

Although abundant in the Earth 's crust , iron is present at trace concentrations in sea water and is a limiting nutrient for phytoplankton in approximately 40 % of the ocean .
Current literature suggests that aerosols are the primary external source of iron to offshore waters , yet controls on iron aerosol solubility remain unclear .
Here we demonstrate that iron speciation ( oxidation state and bonding environment ) drives iron solubility in arid region soils , glacial weathering products ( flour ) and oil combustion products ( oil fly ash ) .
Iron speciation varies by aerosol source , with soils in arid regions dominated by ferric ( oxy ) hydroxides , glacial flour by primary and secondary ferrous silicates and oil fly ash by ferric sulphate salts .
Variation in iron speciation produces systematic differences in iron solubility : less than 1 % of the iron in arid soils was soluble , compared with 2-3 % in glacial products and 77-81 % in oil combustion products , which is directly linked to fractions of more soluble phases .
We conclude that spatial and temporal variations in aerosol iron speciation , driven by the distribution of deserts , glaciers and fossil-fuel combustion , could have a pronounced effect on aerosol iron solubility and therefore on biological productivity and the carbon cycle in the ocean .

[2167] Acceleration of modern acidification in the South China Sea driven by anthropogenic CO2

Modern acidification by the uptake of anthropogenic CO2 can profoundly affect the physiology of marine organisms and the structure of ocean ecosystems .
Centennial-scale global and regional influences of anthropogenic CO2 remain largely unknown due to limited instrumental pH records .
Here we present coral boron isotope-inferred pH records for two periods from the South China Sea : AD 1048-1079 and AD 1838-2001 .
There are no significant pH differences between the first period at the Medieval Warm Period and AD 1830-1870 .
However , we find anomalous and unprecedented acidification during the 20th century , pacing the observed increase in atmospheric CO2 .
Moreover , pH value also varies in phase with inter-decadal changes in Asian Winter Monsoon intensity .
As the level of atmospheric CO2 keeps rising , the coupling global warming via weakening the winter monsoon intensity could exacerbate acidification of the South China Sea and threaten this expansive shallow water marine ecosystem .

[2168] The effects of 118 years of industrial fishing on UK bottom trawl fisheries

In 2009 , the European Commission estimated that 88 % of monitored marine fish stocks were overfished , on the basis of data that go back 20 to 40 years and depending on the species investigated .
However , commercial sea fishing goes back centuries , calling into question the validity of management conclusions drawn from recent data .
We compiled statistics of annual demersal fish landings from bottom trawl catches landing in England and Wales dating back to 1889 , using previously neglected UK Government data .
We then corrected the figures for increases in fishing power over time and a recent shift in the proportion of fish landed abroad to estimate the change in landings per unit of fishing power ( LPUP ) , a measure of the commercial productivity of fisheries .
LPUP reduced by 94 % -- 17-fold -- over the past 118 years .
This implies an extraordinary decline in the availability of bottom-living fish and a profound reorganization of seabed ecosystems since the nineteenth century industrialization of fishing .

[2169] Anatomical regulation of ice nucleation and cavitation helps trees to survive freezing and drought stress

Water in the xylem , the water transport system of plants , is vulnerable to freezing and cavitation , i.e. to phase change from liquid to ice or gaseous phase .
The former is a threat in cold and the latter in dry environmental conditions .
Here we show that a small xylem conduit diameter , which has previously been shown to be associated with lower cavitation pressure thus making a plant more drought resistant , is also associated with a decrease in the temperature required for ice nucleation in the xylem .
Thus the susceptibility of freezing and cavitation are linked together in the xylem of plants .
We explain this linkage by the regulation of the sizes of the nuclei catalysing freezing and drought cavitation .
Our results offer better understanding of the similarities of adaption of plants to cold and drought stress , and offer new insights into the ability of plants to adapt to the changing environment .

[2170] Oceanography : Ocean oxygenation

Biogeosciences 9 , 1159 - 1172 ( 2012 ) Increased global temperatures could lead to an expansion of low oxygen waters ( dead zones ) in the open ocean .
Reduced oxygen solubility and increased stratification are expected to cause this increase , which would have wide reaching implications for marine life .

[2171] Weakening of tropical Pacific atmospheric circulation due to anthropogenic forcing

Since the mid-nineteenth century the Earth 's surface has warmed , and models indicate that human activities have caused part of the warming by altering the radiative balance of the atmosphere .
Simple theories suggest that global warming will reduce the strength of the mean tropical atmospheric circulation .
An important aspect of this tropical circulation is a large-scale zonal ( east-west ) overturning of air across the equatorial Pacific Ocean -- driven by convection to the west and subsidence to the east -- known as the Walker circulation .
Here we explore changes in tropical Pacific circulation since the mid-nineteenth century using observations and a suite of global climate model experiments .
Observed Indo-Pacific sea level pressure reveals a weakening of the Walker circulation .
The size of this trend is consistent with theoretical predictions , is accurately reproduced by climate model simulations and , within the climate models , is largely due to anthropogenic forcing .
The climate model indicates that the weakened surface winds have altered the thermal structure and circulation of the tropical Pacific Ocean .
These results support model projections of further weakening of tropical atmospheric circulation during the twenty-first century .

[2172] Micron-scale mapping of sulfur cycling across the oxycline of a cyanobacterial mat : a paired nanoSIMS and CARD-FISH approach

The metabolic activities of microbial mats have likely regulated biogeochemical cycling over most of Earth 's history .
However , the relationship between metabolic activity and the establishment of isotopic geochemical gradients in these mats remains poorly constrained .
Here we present a parallel microgeochemical and microbiological study of micron-scale sulfur cycling within hypersaline microbial mats from Guerrero Negro , Baja California Sur , Mexico .
Dissolved sulfide within the mats was captured on silver discs and analyzed for its abundance and delta34S isotopic composition using high-resolution secondary ion mass spectrometry ( nanoSIMS ) .
These results were compared to sulfide and oxygen microelectrode profiles .
Two-dimensional microgeochemical mapping revealed well-defined laminations in sulfide concentration ( on scales from 1 to 200 mum ) , trending toward increased sulfide concentrations at depth .
Sulfide delta34S decreased from ~ +10 / 1000 to -20 / 1000 in the uppermost 3 mm and oscillated repeatedly between -10 / 1000 and -30 / 1000 down to a depth of 8 mm .
These variations are attributed to spatially variable bacterial sulfate reduction within the mat .
A parallel examination of the spatial distribution of known sulfate-reducing bacteria within the family Desulfobacteraceae was conducted using catalyzed reporter deposition fluorescence in situ hybridization .
Significant concentrations of Desulfobacteraceae were observed in both oxic and anoxic zones of the mat and occurred in several distinct layers , in large aggregates and heterogeneously dispersed as single cells throughout .
The spatial distribution of these microorganisms is consistent with the variation in sulfide concentration and isotopic composition we observed .
The parallel application of the methodologies developed here can shed light on micron-scale sulfur cycling within microbially dominated sedimentary environments .

[2173] Coral record of increased sediment flux to the inner Great Barrier Reef since European settlement

The effect of European settlement on water quality in the Great Barrier Reef of Australia is a long-standing and controversial issue .
Erosion and sediment transport in river catchments in this region have increased substantially since European settlement , but the magnitude of these changes remains uncertain .
Here we report analyses of Ba/Ca ratios in long-lived Porites coral from Havannah Reef -- a site on the inner Great Barrier Reef that is influenced by flood plumes from the Burdekin river -- to establish a record of sediment fluxes from about 1750 to 1998 .
We find that , in the early part of the record , suspended sediment from river floods reached the inner reef area only occasionally , whereas after about 1870 -- following the beginning of European settlement -- a five - to tenfold increase in the delivery of sediments is recorded with the highest fluxes occurring during the drought-breaking floods .
We conclude that , since European settlement , land-use practices such as clearing and overstocking have led to major degradation of the semi-arid river catchments , resulting in substantially increased sediment loads entering the inner Great Barrier Reef .

[2174] Effects of rising temperature on the viability of an important sea turtle rookery

A warming world poses challenges for species with temperature-dependent sex determination , including sea turtles , for which warmer incubation temperatures produce female hatchlings .
We combined in situ sand temperature measurements with air temperature records since 1850 and predicted warming scenarios from the Intergovernmental Panel on Climate Change to derive 250-year time series of incubation temperatures , hatchling sex ratios , and operational sex ratios for one of the largest sea turtles rookeries globally ( Cape Verde Islands , Atlantic ) .
We estimate that light-coloured beaches currently produce 70.10 % females whereas dark-coloured beaches produce 93.46 % females .
Despite increasingly female skewed sex ratios , entire feminization of this population is not imminent .
Rising temperatures increase the number of breeding females and hence the natural rate of population growth .
Predicting climate warming impacts across hatchlings , male-female breeding ratios and nesting numbers provides a holistic approach to assessing the conservation concerns for sea turtles in a warming world .

[2175] Evolution of magma-poor continental margins from rifting to seafloor spreading

The rifting of continents involves faulting ( tectonism ) and magmatism , which reflect the strain-rate and temperature dependent processes of solid-state deformation and decompression melting within the Earth .
Most models of this rifting have treated tectonism and magmatism separately , and few numerical simulations have attempted to include continental break-up and melting , let alone describe how continental rifting evolves into seafloor spreading .
Models of this evolution conventionally juxtapose continental and oceanic crust .
Here we present observations that support the existence of a zone of exhumed continental mantle , several tens of kilometres wide , between oceanic and continental crust on continental margins where magma-poor rifting has taken place .
We present geophysical and geological observations from the west Iberia margin , and geological mapping of margins of the former Tethys ocean now exposed in the Alps .
We use these complementary findings to propose a conceptual model that focuses on the final stage of continental extension and break-up , and the creation of a zone of exhumed continental mantle that evolves oceanward into seafloor spreading .
We conclude that the evolving stress and thermal fields are constrained by a rising and narrowing ridge of asthenospheric mantle , and that magmatism and rates of extension systematically increase oceanward .

[2176] Eddy transport as a key component of the Antarctic overturning circulation

The exchange of water masses across the Antarctic continental shelf break regulates the export of dense shelf waters to depth as well as the transport of warm , mid-depth waters towards ice shelves and glacial grounding lines .
The penetration of the warmer mid-depth waters past the shelf break has been implicated in the pronounced loss of ice shelf mass over much of west Antarctica .
In high-resolution , regional circulation models , the Antarctic shelf break hosts an energetic mesoscale eddy field , but observations that capture this mesoscale variability have been limited .
Here we show , using hydrographic data collected from ocean gliders , that eddy-induced transport is a primary contributor to mass and property fluxes across the slope .
Measurements along ten cross-shelf hydrographic sections show a complex velocity structure and a stratification consistent with an onshore eddy mass flux .
We show that the eddy transport and the surface wind-driven transport make comparable contributions to the total overturning circulation .
Eddy-induced transport is concentrated in the warm , intermediate layers away from frictional boundaries .
We conclude that understanding mesoscale dynamics will be critical for constraining circumpolar heat fluxes and future rates of retreat of Antarctic ice shelves .

[2177] Successional changes in bacterial communities during the development of black band disease on the reef coral , Montipora hispida

Black band disease ( BBD ) consists of a mat-forming microbial consortium that migrates across coral colonies causing rapid tissue loss .
Although BBD-associated microbial communities have been well characterized , little is known regarding how these complex bacterial consortia develop .
This study analyzed successional changes in microbial communities leading to the development of BBD .
Long-term monitoring of tagged corals throughout outbreaks of BBD in the central Great Barrier Reef documented cyanobacterium-infected lesions , herein termed cyanobacterial patch ( es ) ( CP ) , which were macroscopically distinct from BBD and preceded the onset of BBD in 19 % of the cases .
Dominant cyanobacteria within CP lesions were morphologically distinct from ones dominating BBD lesions .
Clone libraries and terminal restriction fragment length polymorphism analysis confirmed shifts within cyanobacterial assemblages , from Blennothrix sp.-affiliated sequences dominating CP lesions , to Oscillatoria sp.-affiliated sequences , similar to those retrieved from other BBD samples worldwide , dominating BBD lesions .
Bacterial 16S ribosomal RNA clone libraries also showed shifts in bacterial ribotypes during transitions from CP to BBD , with Alphaproteobacteria-affiliated sequences dominant in CP libraries , whereas gammaproteobacterial and cyanobacterial ribotypes were more abundant in BBD clone libraries .
Sequences affiliated with organisms identified in sulfur cycling were commonly retrieved from lesions showing characteristic field signs of BBD .
As high sulfide concentrations have been implicated in BBD-mediated coral tissue degradation , proliferation of a microbial community actively involved in sulfur cycling potentially contributes to the higher progression rates found for BBD compared with CP lesions .
Results show how microbial colonization of indistinct lesions may facilitate a common coral disease with proven ecological effects on coral populations .

[2178] Multi-gas assessment of the Kyoto Protocol

The Kyoto Protocol allows reductions in emissions of several ` greenhouse ' gases to be credited against a CO2-equivalent emissions limit , calculated using ` global warming potential ' indices for each gas .
Using an integrated global-systems model , it is shown that a multi-gas control strategy could greatly reduce the costs of fulfilling the Kyoto Protocol compared with a CO2-only strategy .
Extending the Kyoto Protocol to 2100 without more severe emissions reductions shows little difference between the two strategies in climate and ecosystem effects .
Under a more stringent emissions policy , the use of global warming potentials as applied in the Kyoto Protocol leads to considerably more mitigation of climate change for multi-gas strategies than for the -- supposedly equivalent -- CO2-only control , thus emphasizing the limits of global warming potentials as a tool for political decisions .

[2179] Dynamics of ammonia-oxidizing archaea and bacteria populations and contributions to soil nitrification potentials

It is well known that the ratio of ammonia-oxidizing archaea ( AOA ) and bacteria ( AOB ) ranges widely in soils , but no data exist on what might influence this ratio , its dynamism , or how changes in relative abundance influences the potential contributions of AOA and AOB to soil nitrification .
By sampling intensively from cropped-to-fallowed and fallowed-to-cropped phases of a 2-year wheat/fallow cycle , and adjacent uncultivated long-term fallowed land over a 15-month period in 2010 and 2011 , evidence was obtained for seasonal and cropping phase effects on the soil nitrification potential ( NP ) , and on the relative contributions of AOA and AOB to the NP that recovers after acetylene inactivation in the presence and absence of bacterial protein synthesis inhibitors .
AOB community composition changed significantly ( P0 .0001 ) in response to cropping phase , and there were both seasonal and cropping phase effects on the amoA gene copy numbers of AOA and AOB .
Our study showed that the AOA : AOB shifts were generated by a combination of different phenomena : an increase in AOA amoA abundance in unfertilized treatments , compared with their AOA counterparts in the N-fertilized treatment ; a larger population of AOB under the N-fertilized treatment compared with the AOB community under unfertilized treatments ; and better overall persistence of AOA than AOB in the unfertilized treatments .
These data illustrate the complexity of the factors that likely influence the relative contributions of AOA and AOB to nitrification under the various combinations of soil conditions and NH4 + - availability that exist in the field .

[2180] Glacial-interglacial changes in bottom-water oxygen content on the Portuguese margin

During the last and penultimate glacial maxima , atmospheric CO2 concentrations were lower than present , possibly in part because of increased storage of respired carbon in the deep oceans .
The amount of respired carbon present in a water mass can be calculated from its oxygen content through apparent oxygen utilization ; the oxygen content can in turn be calculated from the carbon isotope gradient within the sediment column .
Here we analyse the shells of benthic foraminifera occurring at the sediment surface and the oxic/anoxic interface on the Portuguese Margin to reconstruct the carbon isotope gradient and hence bottom-water oxygenation over the past 150,000 years .
We find that bottom-water oxygen concentrations were 45 and 65 mumol kg-1 lower than present during the last and penultimate glacial maxima , respectively .
We calculate that concentrations of remineralized organic carbon were at least twice as high as today during the glacial maxima .
We attribute these changes to decreased ventilation linked to a reorganization of ocean circulation and a strengthened global biological pump .
If the respired carbon pool was of a similar size throughout the entire glacial deep Atlantic basin , then this sink could account for 15 and 20 per cent of the glacial PCO2 drawdown during the last and penultimate glacial maxima .

[2181] Imaging energy status in live cells with a fluorescent biosensor of the intracellular ATP-to-ADP ratio

The ATP : ADP ratio is a critical parameter of cellular energy status that regulates many metabolic activities .
Here we report an optimized genetically encoded fluorescent biosensor , PercevalHR , that senses the ATP : ADP ratio .
PercevalHR is tuned to the range of intracellular ATP : ADP expected in mammalian cells , and it can be used with one - or two-photon microscopy in live samples .
We use PercevalHR to visualize activity-dependent changes in ATP : ADP when neurons are exposed to multiple stimuli , demonstrating that it is a sensitive reporter of physiological changes in energy consumption and production .
We also use PercevalHR to visualize intracellular ATP : ADP while simultaneously recording currents from ATP-sensitive potassium ( KATP ) channels in single cells , showing that PercevalHR enables the study of coordinated variation in ATP : ADP and KATP channel open probability in intact cells .
With its ability to monitor changes in cellular energetics within seconds , PercevalHR should be a versatile tool for metabolic research .

[2182] Comparative genomics reveals adaptations of a halotolerant thaumarchaeon in the interfaces of brine pools in the Red Sea

The bottom of the Red Sea harbors over 25 deep hypersaline anoxic basins that are geochemically distinct and characterized by vertical gradients of extreme physicochemical conditions .
Because of strong changes in density , particulate and microbial debris get entrapped in the brine-seawater interface ( BSI ) , resulting in increased dissolved organic carbon , reduced dissolved oxygen toward the brines and enhanced microbial activities in the BSI .
These features coupled with the deep-sea prevalence of ammonia-oxidizing archaea ( AOA ) in the global ocean make the BSI a suitable environment for studying the osmotic adaptations and ecology of these important players in the marine nitrogen cycle .
Using phylogenomic-based approaches , we show that the local archaeal community of five different BSI habitats ( with up to 18.2 % salinity ) is composed mostly of a single , highly abundant Nitrosopumilus-like phylotype that is phylogenetically distinct from the bathypelagic thaumarchaea ; ammonia-oxidizing bacteria were absent .
The composite genome of this novel Nitrosopumilus-like subpopulation ( RSA3 ) co-assembled from multiple single-cell amplified genomes ( SAGs ) from one such BSI habitat further revealed that it shares ~ 54 % of its predicted genomic inventory with sequenced Nitrosopumilus species .
RSA3 also carries several , albeit variable gene sets that further illuminate the phylogenetic diversity and metabolic plasticity of this genus .
Specifically , it encodes for a putative proline-glutamate ` switch ' with a potential role in osmotolerance and indirect impact on carbon and energy flows .
Metagenomic fragment recruitment analyses against the composite RSA3 genome , Nitrosopumilus maritimus , and SAGs of mesopelagic thaumarchaea also reiterate the divergence of the BSI genotypes from other AOA .

[2183] High-amplitude fluctuations and alternative dynamical states of midges in Lake Myvatn

Complex dynamics are often shown by simple ecological models and have been clearly demonstrated in laboratory and natural systems .
Yet many classes of theoretically possible dynamics are still poorly documented in nature .
Here we study long-term time-series data of a midge , Tanytarsus gracilentus ( Diptera : Chironomidae ) , in Lake Myvatn , Iceland .
The midge undergoes density fluctuations of almost six orders of magnitude .
Rather than regular cycles , however , these fluctuations have irregular periods of 4-7 years , indicating complex dynamics .
We fit three consumer-resource models capable of qualitatively distinct dynamics to the data .
Of these , the best-fitting model shows alternative dynamical states in the absence of environmental variability ; depending on the initial midge densities , the model shows either fluctuations around a fixed point or high-amplitude cycles .
This explains the observed complex population dynamics : high-amplitude but irregular fluctuations occur because stochastic variability causes the dynamics to switch between domains of attraction to the alternative states .
In the model , the amplitude of fluctuations depends strongly on minute resource subsidies into the midge habitat .
These resource subsidies may be sensitive to human-caused changes in the hydrology of the lake , with human impacts such as dredging leading to higher-amplitude fluctuations .
Tanytarsus gracilentus is a key component of the Myvatn ecosystem , representing two-thirds of the secondary productivity of the lake and providing vital food resources to fish and to breeding bird populations .
Therefore the high-amplitude , irregular fluctuations in midge densities generated by alternative dynamical states dominate much of the ecology of the lake .

[2184] Insolation and CO2 contribution to the interglacial climate before and after the Mid-Brunhes Event

Reconstructions of climate from marine sediment and ice cores show that the amplitude of glacial-interglacial climate cycles increased substantially after the Mid-Brunhes Event , about 430,000 years ago .
Interglacial periods before the event seem to be characterized by larger continental ice sheets , lower sea level , cooler temperatures in Antarctica and lower atmospheric CO2 concentrations , relative to the more recent interglacials .
Here we use an Earth system model of intermediate complexity to assess the contributions of insolation and greenhouse-gas concentrations to the climate associated with the peaks of all the interglacials over the past 800,000 years .
Our simulations recreate the expected warmer interglacials after the Mid-Brunhes Event and suggest that later interglacials are warmer primarily because of increased global mean temperatures during Northern Hemisphere winters .
This warmth arises from increased insolation during this season , relative to the interglacials that preceded the Mid-Brunhes Event , in conjunction with increased atmospheric greenhouse-gas concentrations .
The effect of boreal winters and of the Southern Hemisphere , which is also warmer during austral winters , on the carbon cyle should be assessed when investigating the underlying causes of the higher CO2 concentrations during the later interglacials .

[2185] Unprecedented recent warming of surface temperatures in the eastern tropical Pacific Ocean

Through its intimate connection with the El Nino/Southern Oscillation system , climate variability in the tropical Pacific Ocean influences climate across much of the planet .
But the history of temperature change in the tropical Pacific Ocean during recent millennia is poorly known : the available annually resolved records are discontinuous and rarely span more than a few centuries .
Longer records at coarser temporal resolution suggest that significant oceanographic changes , observed at multi-year to multi-century resolution , have had important effects on global climate .
Here we use a diatom record from El Junco Lake , Galapagos , to produce a calibrated , continuous record of sea surface temperature in the eastern tropical Pacific Ocean at subdecadal resolution , spanning the past 1,200 years .
Our reconstruction reveals that the most recent 50 years are the warmest 50-year period within the record .
Because our diatom-based sea surface temperature index resembles Northern Hemisphere temperature reconstructions , we suggest that with continued anthropogenic warming , the eastern tropical Pacific Ocean may continue to warm .

[2186] Phytoplankton distribution patterns in the northwestern Sargasso Sea revealed by small subunit rRNA genes from plastids

Phytoplankton species vary in their physiological properties , and are expected to respond differently to seasonal changes in water column conditions .
To assess these varying distribution patterns , we used 412 samples collected monthly over 12 years ( 1991-2004 ) at the Bermuda Atlantic Time-Series Study site , located in the northwestern Sargasso Sea .
We measured plastid 16S ribosomal RNA gene abundances with a terminal restriction fragment length polymorphism approach and identified distribution patterns for members of the Prymnesiophyceae , Pelagophyceae , Chrysophyceae , Cryptophyceae , Bacillariophyceae and Prasinophyceae .
The analysis revealed dynamic bloom patterns by these phytoplankton taxa that begin early in the year , when the mixed layer is deep .
Previously , unreported open-ocean prasinophyte blooms dominated the plastid gene signal during convective mixing events .
Quantitative PCR confirmed the blooms and transitions of Bathycoccus , Micromonas and Ostreococcus populations .
In contrast , taxa belonging to the pelagophytes and chrysophytes , as well as cryptophytes , reached annual peaks during mixed layer shoaling , while Bacillariophyceae ( diatoms ) were observed only episodically in the 12-year record .
Prymnesiophytes dominated the integrated plastid gene signal .
They were abundant throughout the water column before mixing events , but persisted in the deep chlorophyll maximum during stratified conditions .
Various models have been used to describe mechanisms that drive vernal phytoplankton blooms in temperate seas .
The range of taxon-specific bloom patterns observed here indicates that different ` spring bloom ' models can aptly describe the behavior of different phytoplankton taxa at a single geographical location .
These findings provide insight into the subdivision of niche space by phytoplankton and may lead to improved predictions of phytoplankton responses to changes in ocean conditions .

[2187] New particle formation in forests inhibited by isoprene emissions

It has been suggested that volatile organic compounds ( VOCs ) are involved in organic aerosol formation , which in turn affects radiative forcing and climate .
The most abundant VOCs emitted by terrestrial vegetation are isoprene and its derivatives , such as monoterpenes and sesquiterpenes .
New particle formation in boreal regions is related to monoterpene emissions and causes an estimated negative radiative forcing of about -0.2 to -0.9 W m-2 .
The annual variation in aerosol growth rates during particle nucleation events correlates with the seasonality of monoterpene emissions of the local vegetation , with a maximum during summer .
The frequency of nucleation events peaks , however , in spring and autumn .
Here we present evidence from simulation experiments conducted in a plant chamber that isoprene can significantly inhibit new particle formation .
The process leading to the observed decrease in particle number concentration is linked to the high reactivity of isoprene with the hydroxyl radical ( OH ) .
The suppression is stronger with higher concentrations of isoprene , but with little dependence on the specific VOC mixture emitted by trees .
A parameterization of the observed suppression factor as a function of isoprene concentration suggests that the number of new particles produced depends on the OH concentration and VOCs involved in the production of new particles undergo three to four steps of oxidation by OH .
Our measurements simulate conditions that are typical for forested regions and may explain the observed seasonality in the frequency of aerosol nucleation events , with a lower number of nucleation events during summer compared to autumn and spring .
Biogenic emissions of isoprene are controlled by temperature and light , and if the relative isoprene abundance of biogenic VOC emissions increases in response to climate change or land use change , the new particle formation potential may decrease , thus damping the aerosol negative radiative forcing effect .

[2188] July 2012 Greenland melt extent enhanced by low-level liquid clouds

Melting of the world 's major ice sheets can affect human and environmental conditions by contributing to sea-level rise .
In July 2012 , an historically rare period of extended surface melting was observed across almost the entire Greenland ice sheet , raising questions about the frequency and spatial extent of such events .
Here we show that low-level clouds consisting of liquid water droplets ( ` liquid clouds ' ) , via their radiative effects , played a key part in this melt event by increasing near-surface temperatures .
We used a suite of surface-based observations , remote sensing data , and a surface energy-balance model .
At the critical surface melt time , the clouds were optically thick enough and low enough to enhance the downwelling infrared flux at the surface .
At the same time they were optically thin enough to allow sufficient solar radiation to penetrate through them and raise surface temperatures above the melting point .
Outside this narrow range in cloud optical thickness , the radiative contribution to the surface energy budget would have been diminished , and the spatial extent of this melting event would have been smaller .
We further show that these thin , low-level liquid clouds occur frequently , both over Greenland and across the Arctic , being present around 30-50 per cent of the time .
Our results may help to explain the difficulties that global climate models have in simulating the Arctic surface energy budget , particularly as models tend to under-predict the formation of optically thin liquid clouds at supercooled temperatures -- a process potentially necessary to account fully for temperature feedbacks in a warming Arctic climate .

[2189] Opposite metabolic responses of shoots and roots to drought

Shoots and roots are autotrophic and heterotrophic organs of plants with different physiological functions .
Do they have different metabolomes ?
Do their metabolisms respond differently to environmental changes such as drought ?
We used metabolomics and elemental analyses to answer these questions .
First , we show that shoots and roots have different metabolomes and nutrient and elemental stoichiometries .
Second , we show that the shoot metabolome is much more variable among species and seasons than is the root metabolome .
Third , we show that the metabolic response of shoots to drought contrasts with that of roots ; shoots decrease their growth metabolism ( lower concentrations of sugars , amino acids , nucleosides , N , P , and K ) , and roots increase it in a mirrored response .
Shoots are metabolically deactivated during drought to reduce the consumption of water and nutrients , whereas roots are metabolically activated to enhance the uptake of water and nutrients , together buffering the effects of drought , at least at the short term .

[2190] Atmospheric chemistry : A new player in climate change

Land-use change from pre-industrial times to the present day has altered Earth 's surface energy balance .
Until now , the role of volatile hydrocarbons , emitted by plants , in controlling this balance and driving climate change has been overlooked .

[2191] Red coral extinction risk enhanced by ocean acidification

The red coral Corallium rubrum is a habitat-forming species with a prominent and structural role in mesophotic habitats , which sustains biodiversity hotspots .
This precious coral is threatened by both over-exploitation and temperature driven mass mortality events .
We report here that biocalcification , growth rates and polyps ' ( feeding ) activity of Corallium rubrum are significantly reduced at pCO2 scenarios predicted for the end of this century ( 0.2 pH decrease ) .
Since C. rubrum is a long-living species ( > 200 years ) , our results suggest that ocean acidification predicted for 2100 will significantly increases the risk of extinction of present populations .
Given the functional role of these corals in the mesophotic zone , we predict that ocean acidification might have cascading effects on the functioning of these habitats worldwide .

[2192] Increased damage from fires in logged forests during droughts caused by El Nino

In 1997-98 , fires associated with an exceptional drought caused by the El Nino/Southern Oscillation ( ENSO ) devastated large areas of tropical rain forests worldwide .
Evidence suggests that in tropical rainforest environments selective logging may lead to an increased susceptibility of forests to fire .
We investigated whether this was true in the Indonesian fires , the largest fire disaster ever observed .
We performed a multiscale analysis using coarse - and high-resolution optical and radar satellite imagery assisted by ground and aerial surveys to assess the extent of the fire-damaged area and the effect on vegetation in East Kalimantan on the island of Borneo .
A total of 5.2 + / - 0.3 million hectares including 2.6 million hectares of forest was burned with varying degrees of damage .
Forest fires primarily affected recently logged forests ; primary forests or those logged long ago were less affected .
These results support the hypothesis of positive feedback between logging and fire occurrence .
The fires severely damaged the remaining forests and significantly increased the risk of recurrent fire disasters by leaving huge amounts of dead flammable wood .

[2193] Climate change : A nasty surprise in the greenhouse

The Kyoto Protocol aims to reduce emissions of greenhouse gases such as methane .
But it seems that the fall in human-induced methane emissions in the 1990s was only transitory , and atmospheric methane might rise again .

[2194] Rapid circulation of warm subtropical waters in a major glacial fjord in East Greenland

The recent rapid increase in mass loss from the Greenland ice sheet is primarily attributed to an acceleration of outlet glaciers .
One possible cause of this acceleration is increased melting at the ice-ocean interface , driven by the synchronous warming of subtropical waters offshore of Greenland .
However , because of the lack of observations from Greenland 's glacial fjords and our limited understanding of their dynamics , this hypothesis is largely untested .
Here we present oceanographic data collected in Sermilik Fjord , East Greenland , by ship in summer 2008 and from moorings .
Our data reveal the presence of subtropical waters throughout the fjord .
These waters are continuously replenished through a wind-driven exchange with the shelf , where they are present all year .
The temperature and renewal of these waters indicate that they currently cause enhanced submarine melting at the glacier terminus .
Key controls on the melting rate are the volume and properties of the subtropical waters on the shelf , and the patterns of along-shore winds , suggesting that the glaciers ' acceleration has been triggered by a combination of atmospheric and oceanic changes .
Our measurements provide evidence for a rapid advective pathway for the transmission of oceanic variability to the ice-sheet margins .

[2195] Psychrophilic methanogenic community development during long-term cultivation of anaerobic granular biofilms

Granular biomass was temporally sampled from a cold ( 4-15 degreesC ) anaerobic bioreactor , which was inoculated with mesophilic biomass and used to treat industrial wastewater in a long-term ( 3.4 year ) study .
Data from 16S rRNA gene clone libraries , quantitative PCR and terminal restriction fragment length polymorphism analyses indicated that microbial community structure was dynamic , with shifts in the archaeal and bacterial communities ' structures observed following start-up and during temperature decreases from 15 to 9.5 degreesC ( phase 1 ) .
Specifically , the relative abundance of architecturally important Methanosaeta-like ( acetoclastic ) methanogens decreased , which was concomitant with granule disintegration and the development of a putatively psychrophilic hydrogenotrophic methanogenic community .
Genetic fingerprinting suggested the development of a psychroactive methanogenic community between 4 and 10 degreesC ( phase 2 ) , which was dominated by acetogenic bacteria and Methanocorpusculum-like ( hydrogenotrophic ) methanogens .
High levels of Methanosaeta-like acetoclastic methanogens and granular biofilm integrity were maintained during phase 2 .
Overall , decreasing temperature resulted in distinctly altered microbial community structure during phase 1 , and the development of a less dynamic psychroactive methanogenic consortium during phase 2 .
Moreover , psychrophilic H2-oxidizing methanogens emerged as important members of the psychroactive consortia after > 1200 days of low-temperature cultivation .
The data suggest that prolonged psychrophilic cultivation of mesophilic biomass can establish a well-functioning psychroactive methanogenic consortium , thus highlighting the potential of low-temperature anaerobic digestion technology .

[2196] Predatory cannibalism in Drosophila melanogaster larvae

Hunting live prey is risky and thought to require specialized adaptations .
Therefore , observations of predatory cannibalism in otherwise non-carnivorous animals raise questions about its function , adaptive significance and evolutionary potential .
Here we document predatory cannibalism on larger conspecifics in Drosophila melanogaster larvae and address its evolutionary significance .
We found that under crowded laboratory conditions younger larvae regularly attack and consume ` wandering-stage ' conspecifics , forming aggregations mediated by chemical cues from the attacked victim .
Nutrition gained this way can be significant : an exclusively cannibalistic diet was sufficient for normal development from eggs to fertile adults .
Cannibalistic diet also induced plasticity of larval mouth parts .
Finally , during 118 generations of experimental evolution , replicated populations maintained under larval malnutrition evolved enhanced propensity towards cannibalism .
These results suggest that , at least under laboratory conditions , predation on conspecifics in Drosophila is a functional , adaptive behaviour , which can rapidly evolve in response to nutritional conditions .

[2197] Water stress impacts on bacterial carbon monoxide oxidation on recent volcanic deposits

Water availability oscillates dramatically on young volcanic deposits , and may control the distribution and activity of microbes during early stages of biological succession .
Carbon monoxide ( CO ) - oxidizing bacteria are among the pioneering colonists on volcanic deposits and are subjected to these water stresses .
We report here the effects of water potential on CO-oxidizing bacteria in unvegetated ( bare ) and vegetated ( canopy ) sites on a 1959 volcanic deposit on Kilauea Volcano ( Hawai'i ) .
Time course measurements of water potential showed that average water potentials in the surface layer ( 0-1 cm ) of canopy soil remained between -0.1 and 0 MPa , whereas dramatic diurnal oscillations ( for example , between -60 and 0 MPa ) occur in bare site surface cinders .
During a moderate drying event in situ ( -1.7 to 0 MPa ) , atmospheric CO consumption by intact bare site cores decreased 2.7-fold .
For bare and canopy surface samples , maximum potential CO oxidation rates decreased 40 and 60 % , respectively , when water potentials were lowered from 0 to -1.5 MPa in the laboratory .
These observations indicated that CO oxidation is moderately sensitive to changes in water potential .
Additional analyses showed that CO oxidation resumes within a few hours of rehydration , even after desiccation at -150 MPa for 63 days .
Samples from both sites exposed to multiple cycles of drying and rewetting ( -80 to 0 MPa ) , lost significant activity after the first cycle , but not after subsequent cycles .
Similar responses of CO oxidation in both sites suggested that active CO-oxidizing communities in bare and canopy sites do not express differential adaptations to water stress .

[2198] Geomagnetic intensity variations over the past 780 kyr obtained from near-seafloor magnetic anomalies

Knowledge of past variations in the intensity of the Earth 's magnetic field provides an important constraint on models of the geodynamo .
A record of absolute palaeointensity for the past 50 kyr has been compiled from archaeomagnetic and volcanic materials , and relative palaeointensities over the past 800 kyr have been obtained from sedimentary sequences .
But a long-term record of geomagnetic intensity should also be carried by the thermoremanence of the oceanic crust .
Here we show that near-seafloor magnetic anomalies recorded over the southern East Pacific Rise are well correlated with independent estimates of geomagnetic intensity during the past 780 kyr .
Moreover , the pattern of absolute palaeointensity of seafloor glass samples from the same area agrees with the well-documented dipole intensity pattern for the past 50 kyr .
A comparison of palaeointensities derived from seafloor glass samples with global intensity variations thus allows us to estimate the ages of surficial lava flows in this region .
The record of geomagnetic intensity preserved in the oceanic crust should provide a higher-time-resolution record of crustal accretion processes at mid-ocean ridges than has previously been obtainable .

[2199] Regulation of nif gene expression and the energetics of N2 fixation over the diel cycle in a hot spring microbial mat

Nitrogen fixation , a prokaryotic , O2-inhibited process that reduces N2 gas to biomass , is of paramount importance in biogeochemical cycling of nitrogen .
We analyzed the levels of nif transcripts of Synechococcus ecotypes , NifH subunit and nitrogenase activity over the diel cycle in the microbial mat of an alkaline hot spring in Yellowstone National Park .
The results showed a rise in nif transcripts in the evening , with a subsequent decline over the course of the night .
In contrast , immunological data demonstrated that the level of the NifH polypeptide remained stable during the night , and only declined when the mat became oxic in the morning .
Nitrogenase activity was low throughout the night ; however , it exhibited two peaks , a small one in the evening and a large one in the early morning , when light began to stimulate cyanobacterial photosynthetic activity , but O2 consumption by respiration still exceeded the rate of O2 evolution .
Once the irradiance increased to the point at which the mat became oxic , the nitrogenase activity was strongly inhibited .
Transcripts for proteins associated with energy-producing metabolisms in the cell also followed diel patterns , with fermentation-related transcripts accumulating at night , photosynthesis - and respiration-related transcripts accumulating during the day and late afternoon , respectively .
These results are discussed with respect to the energetics and regulation of N2 fixation in hot spring mats and factors that can markedly influence the extent of N2 fixation over the diel cycle .

[2200] Validated predictive modelling of the environmental resistome

Multi-drug-resistant bacteria pose a significant threat to public health .
The role of the environment in the overall rise in antibiotic-resistant infections and risk to humans is largely unknown .
This study aimed to evaluate drivers of antibiotic-resistance levels across the River Thames catchment , model key biotic , spatial and chemical variables and produce predictive models for future risk assessment .
Sediment samples from 13 sites across the River Thames basin were taken at four time points across 2011 and 2012 .
Samples were analysed for class 1 integron prevalence and enumeration of third-generation cephalosporin-resistant bacteria .
Class 1 integron prevalence was validated as a molecular marker of antibiotic resistance ; levels of resistance showed significant geospatial and temporal variation .
The main explanatory variables of resistance levels at each sample site were the number , proximity , size and type of surrounding wastewater-treatment plants .
Model 1 revealed treatment plants accounted for 49.5 % of the variance in resistance levels .
Other contributing factors were extent of different surrounding land cover types ( for example , Neutral Grassland ) , temporal patterns and prior rainfall ; when modelling all variables the resulting model ( Model 2 ) could explain 82.9 % of variations in resistance levels in the whole catchment .
Chemical analyses correlated with key indicators of treatment plant effluent and a model ( Model 3 ) was generated based on water quality parameters ( contaminant and macro - and micro-nutrient levels ) .
Model 2 was beta tested on independent sites and explained over 78 % of the variation in integron prevalence showing a significant predictive ability .
We believe all models in this study are highly useful tools for informing and prioritising mitigation strategies to reduce the environmental resistome .
The ISME Journal advance online publication , 13 February 2015 ; doi :10.1038 / ismej .2014.237

[2201] A ` snowball Earth ' climate triggered by continental break-up through changes in runoff

Geological and palaeomagnetic studies indicate that ice sheets may have reached the Equator at the end of the Proterozoic eon , 800 to 550 million years ago , leading to the suggestion of a fully ice-covered ` snowball Earth ' .
Climate model simulations indicate that such a snowball state for the Earth depends on anomalously low atmospheric carbon dioxide concentrations , in addition to the Sun being 6 per cent fainter than it is today .
However , the mechanisms producing such low carbon dioxide concentrations remain controversial .
Here we assess the effect of the palaeogeographic changes preceding the Sturtian glacial period , 750 million years ago , on the long-term evolution of atmospheric carbon dioxide levels using the coupled climate-geochemical model GEOCLIM .
In our simulation , the continental break-up of Rodinia leads to an increase in runoff and hence consumption of carbon dioxide through continental weathering that decreases atmospheric carbon dioxide concentrations by 1,320 p.p.m. .
This indicates that tectonic changes could have triggered a progressive transition from a ` greenhouse ' to an ` icehouse ' climate during the Neoproterozoic era .
When we combine these results with the concomitant weathering effect of the voluminous basaltic traps erupted throughout the break-up of Rodinia , our simulation results in a snowball glaciation .

[2202] Oceanographic structure drives the assembly processes of microbial eukaryotic communities

Arctic Ocean microbial eukaryote phytoplankton form subsurface chlorophyll maximum ( SCM ) , where much of the annual summer production occurs .
This SCM is particularly persistent in the Western Arctic Ocean , which is strongly salinity stratified .
The recent loss of multiyear sea ice and increased particulate-rich river discharge in the Arctic Ocean results in a greater volume of fresher water that may displace nutrient-rich saltier waters to deeper depths and decrease light penetration in areas affected by river discharge .
Here , we surveyed microbial eukaryotic assemblages in the surface waters , and within and below the SCM .
In most samples , we detected the pronounced SCM that usually occurs at the interface of the upper mixed layer and Pacific Summer Water ( PSW ) .
Poorly developed SCM was seen under two conditions , one above PSW and associated with a downwelling eddy , and the second in a region influenced by the Mackenzie River plume .
Four phylogenetically distinct communities were identified : surface , pronounced SCM , weak SCM and a deeper community just below the SCM .
Distance-decay relationships and phylogenetic structure suggested distinct ecological processes operating within these communities .
In the pronounced SCM , picophytoplanktons were prevalent and community assembly was attributed to water mass history .
In contrast , environmental filtering impacted the composition of the weak SCM communities , where heterotrophic Picozoa were more numerous .
These results imply that displacement of Pacific waters to greater depth and increased terrigenous input may act as a control on SCM development and result in lower net summer primary production with a more heterotroph dominated eukaryotic microbial community .
The ISME Journal advance online publication , 17 October 2014 ; doi :10.1038 / ismej .2014.197

[2203] Noise and determinism in synchronized sheep dynamics

A major debate in ecology concerns the relative importance of intrinsic factors and extrinsic environmental variations in determining population size fluctuations .
Spatial correlation of fluctuations in different populations caused by synchronous environmental shocks , , is a powerful tool for quantifying the impact of environmental variations on population dynamics , .
However , interpretation of synchrony is often complicated by migration between populations , .
Here we address this issue by using time series from sheep populations on two islands in the St Kilda archipelago .
Fluctuations in the sizes of the two populations are remarkably synchronized over a 40-year period .
A nonlinear time-series model shows that a high and frequent degree of environmental correlation is required to achieve this level of synchrony .
The model indicates that if there were less environmental correlation , population dynamics would be much less synchronous than is observed .
This is because of a threshold effect that is dependent on population size ; the threshold magnifies random differences between populations .
A refined model showsthat part of the required environmental synchronicity can be accounted for by large-scale weather variations .
These results underline the importance of understanding the interaction between intrinsic and extrinsic influences on population dynamics .

[2204] Persistent 400,000-year variability of Antarctic ice volume and the carbon cycle is revealed throughout the Plio-Pleistocene

Marine sediment records from the Oligocene and Miocene reveal clear 400,000-year climate cycles related to variations in orbital eccentricity .
These cycles are also observed in the Plio-Pleistocene records of the global carbon cycle .
However , they are absent from the Late Pleistocene ice-age record over the past 1.5 million years .
Here we present a simulation of global ice volume over the past 5 million years with a coupled system of four three-dimensional ice-sheet models .
Our simulation shows that the 400,000-year long eccentricity cycles of Antarctica vary coherently with delta13C data during the Pleistocene , suggesting that they drove the long-term carbon cycle changes throughout the past 35 million years .
The 400,000-year response of Antarctica was eventually suppressed by the dominant 100,000-year glacial cycles of the large ice sheets in the Northern Hemisphere .

[2205] Inclusion of soil carbon lateral movement alters terrestrial carbon budget in China

The lateral movement of soil carbon has a profound effect on the carbon budget of terrestrial ecosystems ; however , it has never been quantified in China , which is one of the strongest soil erosion areas in the world .
In this study , we estimated that the overall soil erosion in China varies from 11.27 to 18.17 Pg yr-1 from 1982 to 2011 , accounting for 7-21 % of total soil erosion globally .
Soil erosion induces a substantial lateral redistribution of soil organic carbon ranging from 0.64 to 1.04 Pg C yr-1 .
The erosion-induced carbon flux ranges from a 0.19 Pg C yr-1 carbon source to a 0.24 Pg C yr-1 carbon sink in the terrestrial ecosystem , which is potentially comparable in magnitude to previously estimated total carbon budget of China ( 0.19 to 0.26 Pg yr-1 ) .
Our results showed that the lateral movement of soil carbon strongly alters the carbon budget in China , and highlighted the urgent need to integrate the processes of soil erosion into the regional or global carbon cycle estimates .

[2206] Collapse and rapid resumption of Atlantic meridional circulation linked to deglacial climate changes

The Atlantic meridional overturning circulation is widely believed to affect climate .
Changes in ocean circulation have been inferred from records of the deep water chemical composition derived from sedimentary nutrient proxies , but their impact on climate is difficult to assess because such reconstructions provide insufficient constraints on the rate of overturning .
Here we report measurements of 231Pa/230Th , a kinematic proxy for the meridional overturning circulation , in a sediment core from the subtropical North Atlantic Ocean .
We find that the meridional overturning was nearly , or completely , eliminated during the coldest deglacial interval in the North Atlantic region , beginning with the catastrophic iceberg discharge Heinrich event H1 , 17,500 yr ago , and declined sharply but briefly into the Younger Dryas cold event , about 12,700 yr ago .
Following these cold events , the 231Pa/230Th record indicates that rapid accelerations of the meridional overturning circulation were concurrent with the two strongest regional warming events during deglaciation .
These results confirm the significance of variations in the rate of the Atlantic meridional overturning circulation for abrupt climate changes .

[2207] In glucose-limited continuous culture the minimum substrate concentration for growth , smin , is crucial in the competition between the enterobacterium Escherichia coli and Chelatobacter heintzii , an environmentally abundant bacterium

The competition for glucose between Escherichia coli ML30 , a typical copiotrophic enterobacterium and Chelatobacter heintzii ATCC29600 , an environmentally successful strain , was studied in a carbon-limited culture at low dilution rates .
First , as a base for modelling , the kinetic parameters mumax and Ks were determined for growth with glucose .
For both strains , mumax was determined in batch culture after different precultivation conditions .
In the case of C. heintzii , mumax was virtually independent of precultivation conditions .
When inoculated into a glucose-excess batch culture medium from a glucose-limited chemostat run at a dilution rate of 0.075 h-1 C. heintzii grew immediately with a mumax of 0.17 + / -0.03 h-1 .
After five transfers in batch culture , mumax had increased only slightly to 0.18 + / -0.03 h-1 .
A different pattern was observed in the case of E. coli .
Inoculated from a glucose-limited chemostat at D = 0.075 h-1 into glucose-excess batch medium E. coli grew only after an acceleration phase of ~ 3.5 h with a mumax of 0.52 h-1 .
After 120 generations and several transfers into fresh medium , mumax had increased to 0.80 + / -0.03 h-1 .
For long-term adapted chemostat-cultivated cells , a Ks for glucose of 15 mug l-1 for C. heintzii , and of 35 mug l-1 for E. coli , respectively , was determined in 14C-labelled glucose uptake experiments .
In competition experiments , the population dynamics of the mixed culture was determined using specific surface antibodies against C. heintzii and a specific 16S rRNA probe for E. coli .
C. heintzii outcompeted E. coli in glucose-limited continuous culture at the low dilution rates of 0.05 and 0.075 h-1 .
Using the determined pure culture parameter values for Ks and mumax , it was only possible to simulate the population dynamics during competition with an extended form of the Monod model , which includes a finite substrate concentration at zero growth rate ( smin ) .
The values estimated for smin were dependent on growth rate ; at D = 0.05 h-1 , it was 12.6 and 0 mug l-1 for E. coli and C. heintzii , respectively .
To fit the data at D = 0.075 h-1 , smin for E. coli had to be raised to 34.9 mug l-1 whereas smin for C. heintzii remained zero .
The results of the mathematical simulation suggest that it is not so much the higher Ks value , which is responsible for the unsuccessful competition of E. coli at low residual glucose concentration , but rather the existence of a significant smin .

[2208] Fingerprints of global warming on wild animals and plants

Over the past 100 years , the global average temperature has increased by approximately 0.6 degreesC and is projected to continue to rise at a rapid rate .
Although species have responded to climatic changes throughout their evolutionary history , a primary concern for wild species and their ecosystems is this rapid rate of change .
We gathered information on species and global warming from 143 studies for our meta-analyses .
These analyses reveal a consistent temperature-related shift , or ` fingerprint ' , in species ranging from molluscs to mammals and from grasses to trees .
Indeed , more than 80 % of the species that show changes are shifting in the direction expected on the basis of known physiological constraints of species .
Consequently , the balance of evidence from these studies strongly suggests that a significant impact of global warming is already discernible in animal and plant populations .
The synergism of rapid temperature rise and other stresses , in particular habitat destruction , could easily disrupt the connectedness among species and lead to a reformulation of species communities , reflecting differential changes in species , and to numerous extirpations and possibly extinctions .

[2209] Macrotene chromosomes provide insights to a new mechanism of high-order gene amplification in eukaryotes

Copy number variation of chromosomal segments is now recognized as a major source of genetic polymorphism within natural populations of eukaryotes , as well as a possible cause of genetic diseases in humans , including cancer , but its molecular bases remain incompletely understood .
In the baker 's yeast Saccharomyces cerevisiae , a variety of low-order amplifications ( segmental duplications ) were observed after adaptation to limiting environmental conditions or recovery from gene dosage imbalance , and interpreted in terms of replication-based mechanisms associated or not with homologous recombination .
Here we show the emergence of novel high-order amplification structures , with corresponding overexpression of embedded genes , during evolution under favourable growth conditions of severely unfit yeast cells bearing genetically disabled genomes .
Such events form massively extended chromosomes , which we propose to call macrotene , whose characteristics suggest the products of intrachromosomal rolling-circle type of replication structures , probably initiated by increased accidental template switches under important cellular stress conditions .

[2210] Limiting global warming to 2 degreesC is unlikely to save most coral reefs

Mass coral bleaching events have become a widespread phenomenon causing serious concerns with regard to the survival of corals .
Triggered by high ocean temperatures , bleaching events are projected to increase in frequency and intensity .
Here , we provide a comprehensive global study of coral bleaching in terms of global mean temperature change , based on an extended set of emissions scenarios and models .
We show that preserving > 10 % of coral reefs worldwide would require limiting warming to below 1.5 degreesC ( atmosphere-ocean general circulation models ( AOGCMs ) range : 1.3-1 .8 degreesC ) relative to pre-industrial levels .
Even under optimistic assumptions regarding corals ' thermal adaptation , one-third ( 9-60 % , 68 % uncertainty range ) of the world 's coral reefs are projected to be subject to long-term degradation under the most optimistic new IPCC emissions scenario , RCP3-PD .
Under RCP4 .5 this fraction increases to two-thirds ( 30-88 % , 68 % uncertainty range ) .
Possible effects of ocean acidification reducing thermal tolerance are assessed within a sensitivity experiment .

[2211] El Nino/Southern Oscillation and tropical Pacific climate during the last millennium

Any assessment of future climate change requires knowledge of the full range of natural variability in the El Nino/Southern Oscillation ( ENSO ) phenomenon .
Here we splice together fossil-coral oxygen isotopic records from Palmyra Island in the tropical Pacific Ocean to provide 30-150-year windows of tropical Pacific climate variability within the last 1,100 years .
The records indicate mean climate conditions in the central tropical Pacific ranging from relatively cool and dry during the tenth century to increasingly warmer and wetter climate in the twentieth century .
But the corals also document a broad range of ENSO behaviour that correlates poorly with these estimates of mean climate .
The most intense ENSO activity within the reconstruction occurred during the mid-seventeenth century .
Taken together , the coral data imply that the majority of ENSO variability over the last millennium may have arisen from dynamics internal to the ENSO system itself .

[2212] Bacterial growth at -15 degreesC ; molecular insights from the permafrost bacterium Planococcus halocryophilus Or1

Planococcus halocryophilus strain Or1 , isolated from high Arctic permafrost , grows and divides at -15 degreesC , the lowest temperature demonstrated to date , and is metabolically active at -25 degreesC in frozen permafrost microcosms .
To understand how P. halocryophilus Or1 remains active under the subzero and osmotically dynamic conditions that characterize its native permafrost habitat , we investigated the genome , cell physiology and transcriptomes of growth at -15 degreesC and 18 % NaCl compared with optimal ( 25 degreesC ) temperatures .
Subzero growth coincides with unusual cell envelope features of encrustations surrounding cells , while the cytoplasmic membrane is significantly remodeled favouring a higher ratio of saturated to branched fatty acids .
Analyses of the 3.4 Mbp genome revealed that a suite of cold and osmotic-specific adaptive mechanisms are present as well as an amino acid distribution favouring increased flexibility of proteins .
Genomic redundancy within 17 % of the genome could enable P. halocryophilus Or1 to exploit isozyme exchange to maintain growth under stress , including multiple copies of osmolyte uptake genes ( Opu and Pro genes ) .
Isozyme exchange was observed between the transcriptome data sets , with selective upregulation of multi-copy genes involved in cell division , fatty acid synthesis , solute binding , oxidative stress response and transcriptional regulation .
The combination of protein flexibility , resource efficiency , genomic plasticity and synergistic adaptation likely compensate against osmotic and cold stresses .
These results suggest that non-spore forming P. halocryophilus Or1 is specifically suited for active growth in its Arctic permafrost habitat ( ambient temp .
~ -16 degreesC ) , indicating that such cryoenvironments harbor a more active microbial ecosystem than previously thought .

[2213] Structure-guided discovery of the metabolite carboxy-SAM that modulates tRNA function

The identification of novel metabolites and the characterization of their biological functions are major challenges in biology .
X-ray crystallography can reveal unanticipated ligands that persist through purification and crystallization .
These adventitious protein-ligand complexes provide insights into new activities , pathways and regulatory mechanisms .
We describe a new metabolite , carboxy-S-adenosyl-l-methionine ( Cx-SAM ) , its biosynthetic pathway and its role in transfer RNA modification .
The structure of CmoA , a member of the SAM-dependent methyltransferase superfamily , revealed a ligand consistent with Cx-SAM in the catalytic site .
Mechanistic analyses showed an unprecedented role for prephenate as the carboxyl donor and the involvement of a unique ylide intermediate as the carboxyl acceptor in the CmoA-mediated conversion of SAM to Cx-SAM .
A second member of the SAM-dependent methyltransferase superfamily , CmoB , recognizes Cx-SAM and acts as a carboxymethyltransferase to convert 5-hydroxyuridine into 5-oxyacetyl uridine at the wobble position of multiple tRNAs in Gram-negative bacteria , resulting in expanded codon-recognition properties .
CmoA and CmoB represent the first documented synthase and transferase for Cx-SAM .
These findings reveal new functional diversity in the SAM-dependent methyltransferase superfamily and expand the metabolic and biological contributions of SAM-based biochemistry .
These discoveries highlight the value of structural genomics approaches in identifying ligands within the context of their physiologically relevant macromolecular binding partners , and in revealing their functions .

[2214] Temperature responses of carbon monoxide and hydrogen uptake by vegetated and unvegetated volcanic cinders

Ecosystem succession on a large deposit of volcanic cinders emplaced on Kilauea Volcano in 1959 has resulted in a mosaic of closed-canopy forested patches and contiguous unvegetated patches .
Unvegetated and unshaded surface cinders ( Bare ) experience substantial diurnal temperature oscillations ranging from moderate ( 16 degreesC ) to extreme ( 55 degreesC ) conditions .
The surface material of adjacent vegetated patches ( Canopy ) experiences much smaller fluctuations ( 14-25 degreesC ) due to shading .
To determine whether surface material from these sites showed adaptations by carbon monoxide ( CO ) and hydrogen ( H2 ) consumption to changes in ambient temperature regimes accompanying succession , we measured responses of CO and H2 uptake to short-term variations in temperature and long-term incubations at elevated temperature .
Based on its broader temperature optimum and lower activation energy , Canopy H2 uptake was less sensitive than Bare H2 uptake to temperature changes .
In contrast , Bare and Canopy CO uptake responded similarly to temperature during short-term incubations , indicating no differences in temperature sensitivity .
However , during extended incubations at 55 degreesC , CO uptake increased for Canopy but not Bare material , which indicated that the former was capable of thermal adaptation .
H2 uptake for material from both sites was completely inhibited at 55 degreesC throughout extended incubations .
These results indicated that plant development during succession did not elicit differences in short-term temperature responses for Bare and Canopy CO uptake , in spite of previously reported differences in CO oxidizer community composition , and differences in average daily and extreme temperatures .
Differences associated with vegetation due to succession did , however , lead to a notable capacity for thermophilic CO uptake by Canopy but not Bare material .

[2215] Reduced drag coefficient for high wind speeds in tropical cyclones

The transfer of momentum between the atmosphere and the ocean is described in terms of the variation of wind speed with height and a drag coefficient that increases with sea surface roughness and wind speed .
But direct measurements have only been available for weak winds ; momentum transfer under extreme wind conditions has therefore been extrapolated from these field measurements .
Global Positioning System sondes have been used since 1997 to measure the profiles of the strong winds in the marine boundary layer associated with tropical cyclones .
Here we present an analysis of these data , which show a logarithmic increase in mean wind speed with height in the lowest 200 m , maximum wind speed at 500 m and a gradual weakening up to a height of 3 km .
By determining surface stress , roughness length and neutral stability drag coefficient , we find that surface momentum flux levels off as the wind speeds increase above hurricane force .
This behaviour is contrary to surface flux parameterizations that are currently used in a variety of modelling applications , including hurricane risk assessment and prediction of storm motion , intensity , waves and storm surges .

[2216] The rise of oxygen in Earth 's early ocean and atmosphere

The rapid increase of carbon dioxide concentration in Earth 's modern atmosphere is a matter of major concern .
But for the atmosphere of roughly two-and-half billion years ago , interest centres on a different gas : free oxygen ( O2 ) spawned by early biological production .
The initial increase of O2 in the atmosphere , its delayed build-up in the ocean , its increase to near-modern levels in the sea and air two billion years later , and its cause-and-effect relationship with life are among the most compelling stories in Earth 's history .

[2217] Large-scale distribution of Atlantic nitrogen fixation controlled by iron availability

Oceanic fixed-nitrogen concentrations are controlled by the balance between nitrogen fixation and denitrification .
A number of factors , including iron limitation , can restrict nitrogen fixation , introducing the potential for decoupling of nitrogen inputs and losses .
Such decoupling could significantly affect the oceanic fixed-nitrogen inventory and consequently the biological component of ocean carbon storage and hence air-sea partitioning of carbon dioxide .
However , the extent to which nutrients limit nitrogen fixation in the global ocean is uncertain .
Here , we examined rates of nitrogen fixation and nutrient concentrations in the surface waters of the Atlantic Ocean along a north-south 10,000 km transect during October and November 2005 .
We show that rates of nitrogen fixation were markedly higher in the North Atlantic compared with the South Atlantic Ocean .
Across the two basins , nitrogen fixation was positively correlated with dissolved iron and negatively correlated with dissolved phosphorus concentrations .
We conclude that inter-basin differences in nitrogen fixation are controlled by iron supply rather than phosphorus availability .
Analysis of the nutrient content of deep waters suggests that the fixed nitrogen enters North Atlantic Deep Water .
Our study thus supports the suggestion that iron significantly influences nitrogen fixation , and that subsequent interactions with ocean circulation patterns contribute to the decoupling of nitrogen fixation and loss .

[2218] Southern Ocean origin for the resumption of Atlantic thermohaline circulation during deglaciation

During the two most recent deglaciations , the Southern Hemisphere warmed before Greenland .
At the same time , the northern Atlantic Ocean was exposed to meltwater discharge , which is generally assumed to reduce the formation of North Atlantic Deep Water .
Yet during deglaciation , the Atlantic thermohaline circulation became more vigorous , in the transition from a weak glacial to a strong interglacial mode .
Here we use a three-dimensional ocean circulation model to investigate the impact of Southern Ocean warming and the associated sea-ice retreat on the Atlantic thermohaline circulation .
We find that a gradual warming in the Southern Ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation , triggered by increased mass transport into the Atlantic Ocean via the warm ( Indian Ocean ) and cold ( Pacific Ocean ) water route .
This effect prevails over the influence of meltwater discharge , which would oppose a strengthening of the thermohaline circulation .
A Southern Ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of Southern and Northern hemispheric climate change at times of deglaciation , in agreement with the available proxy records .

[2219] Ocean oxygenation in the wake of the Marinoan glaciation

Metazoans are likely to have their roots in the Cryogenian period , but there is a marked increase in the appearance of novel animal and algae fossils shortly after the termination of the late Cryogenian ( Marinoan ) glaciation about 635 million years ago .
It has been suggested that an oxygenation event in the wake of the severe Marinoan glaciation was the driving factor behind this early diversification of metazoans and the shift in ecosystem complexity .
But there is little evidence for an increase in oceanic or atmospheric oxygen following the Marinoan glaciation , or for a direct link between early animal evolution and redox conditions in general .
Models linking trends in early biological evolution to shifts in Earth system processes thus remain controversial .
Here we report geochemical data from early Ediacaran organic-rich black shales ( ~ 635-630 million years old ) of the basal Doushantuo Formation in South China .
High enrichments of molybdenum and vanadium and low pyrite sulphur isotope values ( Delta34S values > = 65 per mil ) in these shales record expansion of the oceanic inventory of redox-sensitive metals and the growth of the marine sulphate reservoir in response to a widely oxygenated ocean .
The data provide evidence for an early Ediacaran oxygenation event , which pre-dates the previous estimates for post-Marinoan oxygenation by more than 50 million years .
Our findings seem to support a link between the most severe glaciations in Earth 's history , the oxygenation of the Earth 's surface environments , and the earliest diversification of animals .

[2220] Reconciling the temperature dependence of respiration across timescales and ecosystem types

Ecosystem respiration is the biotic conversion of organic carbon to carbon dioxide by all of the organisms in an ecosystem , including both consumers and primary producers .
Respiration exhibits an exponential temperature dependence at the subcellular and individual levels , but at the ecosystem level respiration can be modified by many variables including community abundance and biomass , which vary substantially among ecosystems .
Despite its importance for predicting the responses of the biosphere to climate change , it is as yet unknown whether the temperature dependence of ecosystem respiration varies systematically between aquatic and terrestrial environments .
Here we use the largest database of respiratory measurements yet compiled to show that the sensitivity of ecosystem respiration to seasonal changes in temperature is remarkably similar for diverse environments encompassing lakes , rivers , estuaries , the open ocean and forested and non-forested terrestrial ecosystems , with an average activation energy similar to that of the respiratory complex ( approximately 0.65 electronvolts ( eV ) ) .
By contrast , annual ecosystem respiration shows a substantially greater temperature dependence across aquatic ( approximately 0.65 eV ) versus terrestrial ecosystems ( approximately 0.32 eV ) that span broad geographic gradients in temperature .
Using a model derived from metabolic theory , these findings can be reconciled by similarities in the biochemical kinetics of metabolism at the subcellular level , and fundamental differences in the importance of other variables besides temperature -- such as primary productivity and allochthonous carbon inputs -- on the structure of aquatic and terrestrial biota at the community level .

[2221] Hydrogen Photogeneration Promoted by Efficient Electron Transfer from Iridium Sensitizers to Colloidal MoS2 Catalysts

We report the utilization of colloidal MoS2 nanoparticles ( NPs ) for multicomponent photocatalytic water reduction systems in cooperation with a series of cyclometalated Ir ( III ) sensitizers .
The effects of the particle size and particle dispersion of MoS2 NPs catalyst , reaction solvent and the concentration of the components on hydrogen evolution efficiency were investigated .
The MoS2 NPs exhibited higher catalytic performance than did other commonly used water reduction catalysts under identical experiment conditions .
The introduction of the carboxylate anchoring groups in the iridium complexes allows the species to be favorably chem-adsorbed onto the MoS2 NPs surface to increase the electron transfer , resulting in enhancement of hydrogen evolution relative to the non-attached systems .
The highest apparent quantum yield , which was as high as 12.4 % , for hydrogen evolution , was obtained ( lambda = 400 nm ) .

[2222] A seasonal cycle in the export of bottom water from the Weddell Sea

Dense water formed over the Antarctic continental shelf rapidly descends into the deep ocean where it spreads throughout the global ocean as Antarctic Bottom Water .
The coldest and most voluminous component of this water mass is Weddell Sea bottom water .
Here we present observations over eight years of the temperature and salinity stratification in the lowermost ocean southeast of the South Orkney Islands , marking the export of Weddell Sea bottom water .
We observe a pronounced seasonal cycle in bottom temperatures , with a cold pulse in May/June and a warm one in October/November , but the timing of these phases varies each year .
We detect the coldest bottom water in 1999 and 2002 , whereas there was no cold phase in 2000 .
On the basis of current velocities and water mass characteristics , we infer that the pulses originate from the southwest Weddell Sea .
We propose that the seasonal fluctuations of Weddell Sea bottom-water properties are governed by the seasonal cycle of the winds over the western margin of the Weddell Sea .
Interannual fluctuations are linked to the variability of the wind-driven Weddell Sea gyre and hence to large-scale climate phenomena such as the Southern Annular Mode and El Nino/Southern Oscillation .

[2223] Flow velocities of Alaskan glaciers

Our poor understanding of tidewater glacier dynamics remains the primary source of uncertainty in sea level rise projections .
On the ice sheets , mass lost from tidewater calving exceeds the amount lost from surface melting .
In Alaska , the magnitude of calving mass loss remains unconstrained , yet immense calving losses have been observed .
With 20 % of the global new-water sea level rise coming from Alaska , partitioning of mass loss sources in Alaska is needed to improve sea level rise projections .
Here we present the first regionally comprehensive map of glacier flow velocities in Central Alaska .
These data reveal that the majority of the regional downstream flux is constrained to only a few coastal glaciers .
We find regional calving losses are 17.1 Gt a-1 , which is equivalent to 36 % of the total annual mass change throughout Central Alaska .

[2224] Stochastic signalling rewires the interaction map of a multiple feedback network during yeast evolution

During evolution , genetic networks are rewired through strengthening or weakening their interactions to develop new regulatory schemes .
In the galactose network , the GAL1/GAL3 paralogues and the GAL2 gene enhance their own expression mediated by the Gal4p transcriptional activator .
The wiring strength in these feedback loops is set by the number of Gal4p binding sites .
Here we show using synthetic circuits that multiplying the binding sites increases the expression of a gene under the direct control of an activator , but this enhancement is not fed back in the circuit .
The feedback loops are rather activated by genes that have frequent stochastic bursts and fast RNA decay rates .
In this way , rapid adaptation to galactose can be triggered even by weakly expressed genes .
Our results indicate that nonlinear stochastic transcriptional responses enable feedback loops to function autonomously , or contrary to what is dictated by the strength of interactions enclosing the circuit .

[2225] Climate Science : Enduring extremes

No matter how well we understand the climate system , the possibility of extreme temperature increases is unlikely be ruled out entirely Past attempts at narrowing down the range of predicted climate sensitivity -- the long-term change in global temperatures with doubling atmospheric carbon dioxide concentrations -- have not been met with much success .
A new theoretical study shows that even a much better understanding of the Earth 's responses to increasing greenhouse gases is not likely to make a difference to this problem .

[2226] Links between viral and prokaryotic communities throughout the water column in the ( sub ) tropical Atlantic Ocean

Viral and prokaryotic abundance , production and diversity were determined throughout the water column of the subtropical Atlantic Ocean to assess potential variations in the relation between viruses and prokaryotes .
Prokaryotic abundance and heterotrophic activity decreased by one and three orders of magnitude , respectively , from the epi - to the abyssopelagic layer .
Although the lytic viral production ( VP ) decreased with depth , lysogenic VP was variable throughout the water column and did not show any trend with depth .
The bacterial , archaeal and viral community composition were depth-stratified as determined by the automated ribosomal intergenic spacer analysis , terminal-restriction fragment length polymorphism and randomly amplified polymorphic DNA-PCR , respectively .
Generally , the number of operational taxonomic units ( OTUs ) did not reveal consistent trends throughout the water column .
Viral and prokaryotic abundance were strongly related to heterotrophic prokaryotic production , suggesting similar linkage strength between the viral and prokaryotic communities from the lower epi - to the abyssopelagic layer in the Atlantic Ocean .
Strikingly , the prokaryotic and viral parameters exhibited a similar variability throughout the water column down to the abyssopelagic layers , suggesting that the dark ocean is as dynamic a system as is the lower epipelagic layer .
It also indicates that viruses are apparently having a similar role for prokaryotic mortality in the dark oceanic realm as in surface waters .
The more than twofold increase in bacterial OTUs from 2750 m depth to > 5000 m depth and the concurrent decrease in viral OTUs , however , suggests that viruses might exhibit a wider host range in deep waters than in surface waters .

[2227] Consequences of biodiversity loss for litter decomposition across biomes

The decomposition of dead organic matter is a major determinant of carbon and nutrient cycling in ecosystems , and of carbon fluxes between the biosphere and the atmosphere .
Decomposition is driven by a vast diversity of organisms that are structured in complex food webs .
Identifying the mechanisms underlying the effects of biodiversity on decomposition is critical given the rapid loss of species worldwide and the effects of this loss on human well-being .
Yet despite comprehensive syntheses of studies on how biodiversity affects litter decomposition , key questions remain , including when , where and how biodiversity has a role and whether general patterns and mechanisms occur across ecosystems and different functional types of organism .
Here , in field experiments across five terrestrial and aquatic locations , ranging from the subarctic to the tropics , we show that reducing the functional diversity of decomposer organisms and plant litter types slowed the cycling of litter carbon and nitrogen .
Moreover , we found evidence of nitrogen transfer from the litter of nitrogen-fixing plants to that of rapidly decomposing plants , but not between other plant functional types , highlighting that specific interactions in litter mixtures control carbon and nitrogen cycling during decomposition .
The emergence of this general mechanism and the coherence of patterns across contrasting terrestrial and aquatic ecosystems suggest that biodiversity loss has consistent consequences for litter decomposition and the cycling of major elements on broad spatial scales .

[2228] Limited overlap between the seismic gap and coseismic slip of the great 2010 Chile earthquake

The Mw 8.8 mega-thrust earthquake and tsunami that occurred on 27 February 2010 offshore the Maule region , Chile , was not unexpected .
A clearly identified seismic gap existed in an area where tectonic loading has been accumulating since the great 1835 earthquake .
Here we jointly invert tsunami and geodetic data to derive a robust model for the coseismic slip distribution and induced coseismic stress changes .
We compare these with past earthquakes and the preseismic locking distribution , to assess if the Maule earthquake has filled the seismic gap .
We find that the main slip patch is located to the north of the gap , overlapping the rupture zone of the Mw 8.0 earthquake that occurred in 1928 , with a secondary concentration of slip to the south .
The seismic gap was only partially filled and a zone of high preseismic locking remains unbroken , inconsistent with the assumption that distributions of seismic rupture might be correlated with preseismic locking .
Moreover , we conclude that increased stress on the unbroken patch may in turn have increased the probability of another major to great earthquake there in the near future .

[2229] Geochemical evidence for widespread euxinia in the Later Cambrian ocean

Widespread anoxia in the ocean is frequently invoked as a primary driver of mass extinction as well as a long-term inhibitor of evolutionary radiation on early Earth .
In recent biogeochemical studies it has been hypothesized that oxygen deficiency was widespread in subsurface water masses of later Cambrian oceans , possibly influencing evolutionary events during this time .
Physical evidence of widespread anoxia in Cambrian oceans has remained elusive and thus its potential relationship to the palaeontological record remains largely unexplored .
Here we present sulphur isotope records from six globally distributed stratigraphic sections of later Cambrian marine rocks ( about 499 million years old ) .
We find a positive sulphur isotope excursion in phase with the Steptoean Positive Carbon Isotope Excursion ( SPICE ) , a large and rapid excursion in the marine carbon isotope record , which is thought to be indicative of a global carbon cycle perturbation .
Numerical box modelling of the paired carbon sulphur isotope data indicates that these isotope shifts reflect transient increases in the burial of organic carbon and pyrite sulphur in sediments deposited under large-scale anoxic and sulphidic ( euxinic ) conditions .
Independently , molybdenum abundances in a coeval black shale point convincingly to the transient spread of anoxia .
These results identify the SPICE interval as the best characterized ocean anoxic event in the pre-Mesozoic ocean and an extreme example of oxygen deficiency in the later Cambrian ocean .
Thus , a redox structure similar to those in Proterozoic oceans may have persisted or returned in the oceans of the early Phanerozoic eon .
Indeed , the environmental challenges presented by widespread anoxia may have been a prevalent if not dominant influence on animal evolution in Cambrian oceans .

[2230] SLC38A9 is a component of the lysosomal amino acid sensing machinery that controls mTORC1

Cell growth and proliferation are tightly linked to nutrient availability .
The mechanistic target of rapamycin complex 1 ( mTORC1 ) integrates the presence of growth factors , energy levels , glucose and amino acids to modulate metabolic status and cellular responses .
mTORC1 is activated at the surface of lysosomes by the RAG GTPases and the Ragulator complex through a not fully understood mechanism monitoring amino acid availability in the lysosomal lumen and involving the vacuolar H + - ATPase .
Here we describe the uncharacterized human member 9 of the solute carrier family 38 ( SLC38A9 ) as a lysosomal membrane-resident protein competent in amino acid transport .
Extensive functional proteomic analysis established SLC38A9 as an integral part of the Ragulator-RAG GTPases machinery .
Gain of SLC38A9 function rendered cells resistant to amino acid withdrawal , whereas loss of SLC38A9 expression impaired amino-acid-induced mTORC1 activation .
Thus SLC38A9 is a physical and functional component of the amino acid sensing machinery that controls the activation of mTOR .

[2231] Heterothermy in growing king penguins

A drop in body temperature allows significant energy savings in endotherms , but facultative heterothermy is usually restricted to small animals .
Here we report that king penguin chicks ( Aptenodytes patagonicus ) , which are able to fast for up to 5 months in winter , undergo marked seasonal heterothermy during this period of general food scarcity and slow-down of growth .
They also experience short-term heterothermy below 20 degreesC in the lower abdomen during the intense ( re ) feeding period in spring , induced by cold meals and adverse weather .
The heterothermic response involves reductions in peripheral temperature , reductions in thermal core volume and temporal abandonment of high core temperature .
Among climate variables , air temperature and wind speed show the strongest effect on body temperature , but their effect size depends on physiological state .
The observed heterothermy is remarkable for such a large bird ( 10 kg before fasting ) , which may account for its unrivalled fasting capacity among birds .

[2232] The temperature response of soil microbial efficiency and its feedback to climate

Soils are the largest repository of organic carbon ( C ) in the terrestrial biosphere and represent an important source of carbon dioxide ( CO2 ) to the atmosphere , releasing 60-75 Pg C annually through microbial decomposition of organic materials .
A primary control on soil CO2 flux is the efficiency with which the microbial community uses C. Despite its critical importance to soil-atmosphere CO2 exchange , relatively few studies have examined the factors controlling soil microbial efficiency .
Here , we measured the temperature response of microbial efficiency in soils amended with substrates varying in lability .
We also examined the temperature sensitivity of microbial efficiency in response to chronic soil warming in situ .
We find that the efficiency with which soil microorganisms use organic matter is dependent on both temperature and substrate quality , with efficiency declining with increasing temperatures for more recalcitrant substrates .
However , the utilization efficiency of a more recalcitrant substrate increased at higher temperatures in soils exposed to almost two decades of warming 5 degreesC above ambient .
Our work suggests that climate warming could alter the decay dynamics of more stable organic matter compounds , thereby having a positive feedback to climate that is attenuated by a shift towards a more efficient microbial community in the longer term .

[2233] Dispersal network structure and infection mechanism shape diversity in a coevolutionary bacteria-phage system

Resource availability , dispersal and infection genetics all have the potential to fundamentally alter the coevolutionary dynamics of bacteria-bacteriophage interactions .
However , it remains unclear how these factors synergise to shape diversity within bacterial populations .
We used a combination of laboratory experiments and mathematical modeling to test how the structure of a dispersal network affects host phenotypic diversity in a coevolving bacteria-phage system in communities of differential resource input .
Unidirectional dispersal of bacteria and phage from high to low resources consistently increased host diversity compared with a no dispersal regime .
Bidirectional dispersal , on the other hand , led to a marked decrease in host diversity .
Our mathematical model predicted these opposing outcomes when we incorporated modified gene-for-gene infection genetics .
To further test how host diversity depended on the genetic underpinnings of the bacteria-phage interaction , we expanded our mathematical model to include different infection mechanisms .
We found that the direction of dispersal had very little impact on bacterial diversity when the bacteria-phage interaction was mediated by matching alleles , gene-for-gene or related infection mechanisms .
Our experimental and theoretical results demonstrate that the effects of dispersal on diversity in coevolving host-parasite systems depend on an intricate interplay of the structure of the underlying dispersal network and the specifics of the host-parasite interaction .

[2234] Increased estimates of air-pollution emissions from Brazilian sugar-cane ethanol

Accelerating biofuel production has been promoted as an opportunity to enhance energy security , offset greenhouse-gas emissions and support rural economies .
However , large uncertainties remain in the impacts of biofuels on air quality and climate .
Sugar-cane ethanol is one of the most widely used biofuels , and Brazil is its largest producer .
Here we use a life-cycle approach to produce spatially and temporally explicit estimates of air-pollutant emissions over the whole life cycle of sugar-cane ethanol in Brazil .
We show that even in regions where pre-harvest field burning has been eliminated on half the croplands , regional emissions of air pollutants continue to increase owing to the expansion of sugar-cane growing areas , and burning continues to be the dominant life-cycle stage for emissions .
Comparison of our estimates of burning-phase emissions with satellite estimates of burning in Sao Paulo state suggests that sugar-cane field burning is not fully accounted for in satellite-based inventories , owing to the small spatial scale of individual fires .
Accounting for this effect leads to revised regional estimates of burned area that are four times greater than some previous estimates .
Our revised emissions maps thus suggest that biofuels may have larger impacts on regional climate forcing and human health than previously thought .

[2235] Synthetic apatite nanoparticles as a phosphorus fertilizer for soybean ( Glycine max )

Some soluble phosphate salts , heavily used in agriculture as highly effective phosphorus ( P ) fertilizers , cause surface water eutrophication , while solid phosphates are less effective in supplying the nutrient P .
In contrast , synthetic apatite nanoparticles could hypothetically supply sufficient P nutrients to crops but with less mobility in the environment and with less bioavailable P to algae in comparison to the soluble counterparts .
Thus , a greenhouse experiment was conducted to assess the fertilizing effect of synthetic apatite nanoparticles on soybean ( Glycine max ) .
The particles , prepared using one-step wet chemical method , were spherical in shape with diameters of 15.8 + / - 7.4 nm and the chemical composition was pure hydroxyapatite .
The data show that application of the nanoparticles increased the growth rate and seed yield by 32.6 % and 20.4 % , respectively , compared to those of soybeans treated with a regular P fertilizer ( Ca ( H2PO4 ) 2 ) .
Biomass productions were enhanced by 18.2 % ( above-ground ) and 41.2 % ( below-ground ) .
Using apatite nanoparticles as a new class of P fertilizer can potentially enhance agronomical yield and reduce risks of water eutrophication .

[2236] Microbial oceanography

It is now commonly accepted that the world is changing as a result of human activity .
The rise in atmospheric carbon dioxide -- which increases the amount of CO 2 dissolved in the ocean and reduces the pH of the water -- as well as higher temperatures will probably have a detrimental effect on the oceans ' ecosystems .

[2237] Escherichia coli transcription factor YncC ( McbR ) regulates colanic acid and biofilm formation by repressing expression of periplasmic protein YbiM ( McbA )

Quorum-sensing signal autoinducer 2 ( AI-2 ) stimulates Escherichia coli biofilm formation through the motility regulator MqsR that induces expression of the putative transcription factor encoded by yncC .
Here , we show that YncC increases biofilm formation by repressing overproduction of the exopolysaccharide identified as colanic acid ( corroborated by decreasing mucoidy and increased sensitivity to bacteriophage P1 infection ) .
Differential gene expression and gel shift assays demonstrated that YncC is a repressor of the predicted periplasmic protein-encoding gene , ybiM , which was corroborated by the isogenic yncC ybiM double mutation that repressed the yncC phenotypes ( biofilm formation , colanic acid overproduction , mucoidy and bacteriophage resistance ) .
Through nickel-enrichment DNA microarrays and additional gel shift assays , we found that the putative transcription factor B3023 ( directly upstream of mqsR ) binds the yncC promoter .
Overexpressing MqsR , AI-2 import regulators LsrR/LsrK and AI-2 exporter TqsA induced yncC transcription , whereas the AI-2 synthase LuxS and B3023 repressed yncC .
MqsR has a toxic effect on E. coli bacterial growth , which is partially reduced by the b3023 mutation .
Therefore , AI-2 quorum-sensing control of biofilm formation is mediated through regulator MqsR that induces expression of the transcription factor YncC .
YncC inhibits the expression of periplasmic YbiM , which prevents overproduction of colanic acid ( excess colanic acid causes mucoidy ) and prevents YbiM from inhibiting biofilm formation .

[2238] West Nile virus emergence and large-scale declines of North American bird populations

Emerging infectious diseases present a formidable challenge to the conservation of native species in the twenty-first century .
Diseases caused by introduced pathogens have had large impacts on species abundances , including the American chestnut , Hawaiian bird species and many amphibians .
Changes in host population sizes can lead to marked shifts in community composition and ecosystem functioning .
However , identifying the impacts of an introduced disease and distinguishing it from other forces that influence population dynamics ( for example , climate ) is challenging and requires abundance data that extend before and after the introduction .
Here we use 26 yr of Breeding Bird Survey ( BBS ) data to determine the impact of West Nile virus ( WNV ) on 20 potential avian hosts across North America .
We demonstrate significant changes in population trajectories for seven species from four families that concur with a priori predictions and the spatio-temporal intensity of pathogen transmission .
The American crow population declined by up to 45 % since WNV arrival , and only two of the seven species with documented impact recovered to pre-WNV levels by 2005 .
Our findings demonstrate the potential impacts of an invasive species on a diverse faunal assemblage across broad geographical scales , and underscore the complexity of subsequent community response .

[2239] Global change : A question of litter quality

One aspect of how terrestrial ecosystems will respond to rising levels of CO2in the atmosphere is potential changes in the decomposition rate of leaf litter - a central factor in plant growth .
It had been thought that the decomposition rate would decline in high CO2conditions , but this long-established hypothesis was laid to rest at a meeting in September of plant physiologists , ecologists and soil scientists .

[2240] Solution-Processed VO2-SiO2 Composite Films with Simultaneously Enhanced Luminous Transmittance , Solar Modulation Ability and Anti-Oxidation property

Recently , researchers spare no efforts to fabricate desirable vanadium dioxide ( VO2 ) film which provides simultaneously high luminous transmittance and outstanding solar modulation ability , yet progress towards the optimization of one aspect always comes at the expense of the other .
Our research devotes to finding a reproducible economic solution-processed strategy for fabricating VO2-SiO2 composite films , with the aim of boosting the performance of both aspects .
Compare to VO2 film , an improvement of 18.9 % ( from 29.6 % to 48.5 % ) in the luminous transmittance as well as an increase of 6.0 % ( from 9.7 % to 15.7 % ) in solar modulation efficiency is achieved when the molar ratio of Si/V attains 0.8 .
Based on the effective medium theory , we simulate the optical spectra of the composite films and the best thermochromic property is obtained when the filling factor attains 0.5 , which is consistent with the experimental results .
Meanwhile , the improvement of chemical stability for the composite film against oxidation has been confirmed .
Tungsten is introduced to reduce the phase transition temperature to the ambient temperature , while maintain the thermochromism required for application as smart window .
Our research set forth a new avenue in promoting practical applications of VO2-based thermochromic fenestration .

[2241] Predator-induced reduction of freshwater carbon dioxide emissions

Predators can influence the exchange of carbon dioxide between ecosystems and the atmosphere by altering ecosystem processes such as decomposition and primary production , according to food web theory .
Empirical knowledge of such an effect in freshwater systems is limited , but it has been suggested that predators in odd-numbered food chains suppress freshwater carbon dioxide emissions , and predators in even-numbered food chains enhance emissions .
Here , we report experiments in three-tier food chains in experimental ponds , streams and bromeliads in Canada and Costa Rica in the presence or absence of fish ( Gasterosteus aculeatus ) and invertebrate ( Hesperoperla pacifica and Mecistogaster modesta ) predators .
We monitored carbon dioxide fluxes along with prey and primary producer biomass .
We found substantially reduced carbon dioxide emissions in the presence of predators in all systems , despite differences in predator type , hydrology , climatic region , ecological zone and level of in situ primary production .
We also observed lower amounts of prey biomass and higher amounts of algal and detrital biomass in the presence of predators .
We conclude that predators have the potential to markedly influence carbon dioxide dynamics in freshwater systems .

[2242] Intraspecific genotypic richness and relatedness predict the invasibility of microbial communities

Biological invasions can lead to extinction events in resident communities and compromise ecosystem functioning .
We tested the effect of two widespread biodiversity measurements , genotypic richness and genotypic dissimilarity on community invasibility .
We manipulated the genetic structure of bacterial communities ( Pseudomonas fluorescens ) and submitted them to invasion by Serratia liquefaciens .
We show that the two diversity measures impact on invasibility via distinct and additive mechanisms .
Genotypic dissimilarity of the resident communities linearly increased productivity and in parallel decreased invasion success , indicating that high dissimilarity prevents invasion through niche pre-emption .
By contrast , genotypic richness exerted a hump-shaped effect on invasion and was linked to the production of toxins antagonistic to the invader .
This effect peaked at intermediate richness , suggesting that high richness levels may increase invasibility .
Invasibility could be well predicted by the combination of these two mechanisms , documenting that both genotypic richness and dissimilarity need to be considered , if we are to understand the biotic properties determining the susceptibility of ecosystems to biological invasions .

[2243] Soil clay content underlies prion infection odds

Environmental factors -- especially soil properties -- have been suggested as potentially important in the transmission of infectious prion diseases .
Because binding to montmorillonite ( an aluminosilicate clay mineral ) or clay-enriched soils had been shown to enhance experimental prion transmissibility , we hypothesized that prion transmission among mule deer might also be enhanced in ranges with relatively high soil clay content .
In this study , we report apparent influences of soil clay content on the odds of prion infection in free-ranging deer .
Analysis of data from prion-infected deer herds in northern Colorado , USA , revealed that a 1 % increase in the clay-sized particle content in soils within the approximate home range of an individual deer increased its odds of infection by up to 8.9 % .
Our findings suggest that soil clay content and related environmental properties deserve greater attention in assessing risks of prion disease outbreaks and prospects for their control in both natural and production settings .

[2244] Oceanic Cd/P ratio and nutrient utilization in the glacial Southern Ocean

During glacial periods , low atmospheric carbon dioxide concentration has been associated with increased oceanic carbon uptake , particularly in the southern oceans .
The mechanism involved remains unclear .
Because ocean productivity is strongly influenced by nutrient levels , palaeo-oceanographic proxies have been applied to investigate nutrient utilization in surface water across glacial transitions .
Here we show that present-day cadmium and phosphorus concentrations in the global oceans can be explained by a chemical fractionation during particle formation , whereby uptake of cadmium occurs in preference to uptake of phosphorus .
This allows the reconstruction of past surface water phosphate concentrations from the cadmium/calcium ratio of planktonic foraminifera .
Results from the Last Glacial Maximum show similar phosphate utilization in the subantarctic to that of today , but much smaller utilization in the polar Southern Ocean , in a model that is consistent with the expansion of glacial sea ice and which can reconcile all proxy records of polar nutrient utilization .
By restricting communication between the ocean and atmosphere , sea ice expansion also provides a mechanism for reduced CO2 release by the Southern Ocean and lower glacial atmospheric CO2 .

[2245] Payback time for soil carbon and sugar-cane ethanol

The effects of land-use change ( LUC ) on soil carbon ( C ) balance has to be taken into account in calculating the CO2 savings attributed to bioenergy crops .
There have been few direct field measurements that quantify the effects of LUC on soil C for the most common land-use transitions into sugar cane in Brazil , the world 's largest producer .
We quantified the C balance for LUC as a net loss ( carbon debt ) or net gain ( carbon credit ) in soil C for sugar-cane expansion in Brazil .
We sampled 135 field sites to 1 m depth , representing three major LUC scenarios .
Our results demonstrate that soil C stocks decrease following LUC from native vegetation and pastures , and increase where cropland is converted to sugar cane .
The payback time for the soil C debt was eight years for native vegetation and two to three years for pastures .
With an increasing need for biofuels and the potential for Brazil to help meet global demand , our results will be invaluable for guiding expansion policies of sugar-cane production towards greater sustainability .

[2246] Novel hydrated graphene ribbon unexpectedly promotes aged seed germination and root differentiation

It is well known that graphene ( G ) induces nanotoxicity towards living organisms .
Here , a novel and biocompatible hydrated graphene ribbon ( HGR ) unexpectedly promoted aged ( two years ) seed germination .
HGR formed at the normal temperature and pressure ( 120 days hydration ) , presented 17.1 % oxygen , 0.9 % nitrogen groups , disorder-layer structure , with 0.38 nm thickness ribbon morphology .
Interestingly , there were bulges around the edges of HGR .
Compared to G and graphene oxide ( GO ) , HGR increased seed germination by 15 % root differentiation between 52 and 59 % and enhanced resistance to oxidative stress .
The metabonomics analysis discovered that HGR upregulated carbohydrate , amino acid , and fatty acids metabolism that determined secondary metabolism , nitrogen sequestration , cell membrane integrity , permeability , and oxidation resistance .
Hexadecanoic acid as a biomarker promoted root differentiation and increased the germination rate .
Our discovery is a novel HGR that promotes aged seed germination , illustrates metabolic specificity among graphene-based materials , and inspires innovative concepts in the regulation of seed development .

[2247] Possible evolution of mobile animals in association with microbial mats

Complex animals first evolved during the Ediacaran period , between 635 and 542 million years ago , when the oceans were just becoming fully oxygenated .
In situ fossils of the mobile forms of these animals are associated with microbial sedimentary structures , and the animal 's trace fossils generally were formed parallel to the surface of the seabed , at or below the sediment-water interface .
This evidence suggests the earliest mobile animals inhabited settings with high microbial populations , and may have mined microbially bound sediments for food resources .
Here we report the association of mobile animals -- insect larvae , oligochaetes and burrowing shore crabs -- with microbial mats in a modern hypersaline lagoon in Venezuela .
The lagoon is characterized by low concentrations of dissolved O2 and pervasive biomats dominated by oxygen-producing cyanobacteria , both analogous to conditions during the Ediacaran .
We find that , during the day , O2 levels in the biomats are four times higher than in the overlying water column .
We therefore conclude that the animals harvest both food and O2 from the biomats .
In doing so , the animals produce horizontal burrows similar to those found in Ediacaran-aged rocks .
We suggest that early mobile animals may have evolved in similar environments during the Ediacaran , effectively exploiting oases rich in O2 that formed within low oxygen settings .

[2248] The nexus of chromatin regulation and intermediary metabolism

Living organisms and individual cells continuously adapt to changes in their environment .
Those changes are particularly sensitive to fluctuations in the availability of energy substrates .
The cellular transcriptional machinery and its chromatin-associated proteins integrate environmental inputs to mediate homeostatic responses through gene regulation .
Numerous connections between products of intermediary metabolism and chromatin proteins have recently been identified .
Chromatin modifications that occur in response to metabolic signals are dynamic or stable and might even be inherited transgenerationally .
These emerging concepts have biological relevance to tissue homeostasis , disease and ageing .

[2249] Pyroclastic passage zones in glaciovolcanic sequences

Volcanoes are increasingly recognized as agents and recorders of global climate variability , although deciphering the linkages between planetary climate and volcanism is still in its infancy .
The growth and emergence of subaqueous volcanoes produce passage zones , which are stratigraphic surfaces marking major transitions in depositional environments .
In glaciovolcanic settings , they record the elevations of syn-eruptive englacial lakes .
Thus , they allow for forensic recovery of minimum ice thicknesses .
Here we present the first description of a passage zone preserved entirely within pyroclastic deposits , marking the growth of a tephra cone above the englacial lake level .
Our discovery requires extension of the passage-zone concept to accommodate explosive volcanism and guides future studies of hundreds of glaciovolcanic edifices on Earth and Mars .
Our recognition of pyroclastic passage zones increases the potential for recovering transient paleolake levels , improving estimates of paleo-ice thicknesses and providing new constraints on paleoclimate models that consider the extents and timing of planetary glaciations .

[2250] Parallel evolution of the make-accumulate-consume strategy in Saccharomyces and Dekkera yeasts

Saccharomyces yeasts degrade sugars to two-carbon components , in particular ethanol , even in the presence of excess oxygen .
This characteristic is called the Crabtree effect and is the background for the ` make-accumulate-consume ' life strategy , which in natural habitats helps Saccharomyces yeasts to out-compete other microorganisms .
A global promoter rewiring in the Saccharomyces cerevisiae lineage , which occurred around 100 mya , was one of the main molecular events providing the background for evolution of this strategy .
Here we show that the Dekkera bruxellensis lineage , which separated from the Saccharomyces yeasts more than 200 mya , also efficiently makes , accumulates and consumes ethanol and acetic acid .
Analysis of promoter sequences indicates that both lineages independently underwent a massive loss of a specific cis-regulatory element from dozens of genes associated with respiration , and we show that also in D. bruxellensis this promoter rewiring contributes to the observed Crabtree effect .

[2251] Carbon isotope equilibration during sulphate-limited anaerobic oxidation of methane

Collectively , marine sediments comprise the largest reservoir of methane on Earth .
The flux of methane from the sea bed to the overlying water column is mitigated by the sulphate-dependent anaerobic oxidation of methane by marine microbes within a discrete sedimentary horizon termed the sulphate-methane transition zone .
According to conventional isotope systematics , the biological consumption of methane leaves a residue of methane enriched in 13C ( refs , , ) .
However , in many instances the methane within sulphate-methane transition zones is depleted in 13C , consistent with the production of methane , and interpreted as evidence for the intertwined anaerobic oxidation and production of methane .
Here , we report results from experiments in which we incubated cultures of microbial methane consumers with methane and low levels of sulphate , and monitored the stable isotope composition of the methane and dissolved inorganic carbon pools over time .
Residual methane became progressively enriched in 13C at sulphate concentrations above 0.5 mM , and progressively depleted in 13C below this threshold .
We attribute the shift to 13C depletion during the anaerobic oxidation of methane at low sulphate concentrations to the microbially mediated carbon isotope equilibration between methane and carbon dioxide .
We suggest that this isotopic effect could help to explain the 13C-depletion of methane in subseafloor sulphate-methane transition zones .

[2252] Warming experiments underpredict plant phenological responses to climate change

Warming experiments are increasingly relied on to estimate plant responses to global climate change .
For experiments to provide meaningful predictions of future responses , they should reflect the empirical record of responses to temperature variability and recent warming , including advances in the timing of flowering and leafing .
We compared phenology ( the timing of recurring life history events ) in observational studies and warming experiments spanning four continents and 1,634 plant species using a common measure of temperature sensitivity ( change in days per degree Celsius ) .
We show that warming experiments underpredict advances in the timing of flowering and leafing by 8.5-fold and 4.0-fold , respectively , compared with long-term observations .
For species that were common to both study types , the experimental results did not match the observational data in sign or magnitude .
The observational data also showed that species that flower earliest in the spring have the highest temperature sensitivities , but this trend was not reflected in the experimental data .
These significant mismatches seem to be unrelated to the study length or to the degree of manipulated warming in experiments .
The discrepancy between experiments and observations , however , could arise from complex interactions among multiple drivers in the observational data , or it could arise from remediable artefacts in the experiments that result in lower irradiance and drier soils , thus dampening the phenological responses to manipulated warming .
Our results introduce uncertainty into ecosystem models that are informed solely by experiments and suggest that responses to climate change that are predicted using such models should be re-evaluated .

[2253] The impact of temperature on marine phytoplankton resource allocation and metabolism

Marine phytoplankton are responsible for ~ 50 % of the CO2 that is fixed annually worldwide , and contribute massively to other biogeochemical cycles in the oceans .
Their contribution depends significantly on the interplay between dynamic environmental conditions and the metabolic responses that underpin resource allocation and hence biogeochemical cycling in the oceans .
However , these complex environment-biome interactions have not been studied on a larger scale .
Here we use a set of integrative approaches that combine metatranscriptomes , biochemical data , cellular physiology and emergent phytoplankton growth strategies in a global ecosystems model , to show that temperature significantly affects eukaryotic phytoplankton metabolism with consequences for biogeochemical cycling under global warming .
In particular , the rate of protein synthesis strongly increases under high temperatures even though the numbers of ribosomes and their associated rRNAs decreases .
Thus , at higher temperatures , eukaryotic phytoplankton seem to require a lower density of ribosomes to produce the required amounts of cellular protein .
The reduction of phosphate-rich ribosomes in warmer oceans will tend to produce higher organismal nitrogen ( N ) to phosphate ( P ) ratios , in turn increasing demand for N with consequences for the marine carbon cycle due to shifts towards N-limitation .
Our integrative approach suggests that temperature plays a previously unrecognized , critical role in resource allocation and marine phytoplankton stoichiometry , with implications for the biogeochemical cycles that they drive .

[2254] Digestion in sea urchin larvae impaired under ocean acidification

Larval stages are considered as the weakest link when a species is exposed to challenging environmental changes .
Reduced rates of growth and development in larval stages of calcifying invertebrates in response to ocean acidification might be caused by energetic limitations .
So far no information exists on how ocean acidification affects digestive processes in marine larval stages .
Here we reveal alkaline ( ~ pH 9.5 ) conditions in the stomach of sea urchin larvae .
Larvae exposed to decreased seawater pH suffer from a drop in gastric pH , which directly translates into decreased digestive efficiencies and triggers compensatory feeding .
These results suggest that larval digestion represents a critical process in the context of ocean acidification , which has been overlooked so far .

[2255] Large-scale impoverishment of Amazonian forests by logging and fire

Amazonian deforestation rates are used to determine human effects on the global carbon cycle and to measure Brazil 's progress in curbing forest impoverishment , , .
But this widely used measure of tropical land use tells only part of the story .
Here we present field surveys of wood mills and forest burning across Brazilian Amazonia which show that logging crews severely damage 10,000 to 15,000 km2 yr-1 of forest that are not included in deforestation mapping programmes .
Moreover , we find that surface fires burn additional large areas of standing forest , the destruction of which is normally not documented .
Forest impoverishment due to such fires may increase dramatically when severe droughts provoke forest leaf-shedding and greater flammability ; our regional water-balance model indicates that an estimated 270,000 km2 of forest became vulnerable to fire in the 1998 dry season .
Overall , we find that present estimates of annual deforestation for Brazilian Amazonia capture less than half of the forest area that is impoverished each year , and even less during years of severe drought .
Both logging and fire increase forest vulnerability to future burning , and release forest carbon stocks to the atmosphere , potentially doubling net carbon emissions from regional land-use during severe El Nino episodes .
If this forest impoverishment is to be controlled , then logging activities need to be restricted or replaced with low-impact timber harvest techniques , and more effective strategies to prevent accidental forest fires need to be implemented .

[2256] Interannual atmospheric variability forced by the deep equatorial Atlantic Ocean

Climate variability in the tropical Atlantic Ocean is determined by large-scale ocean-atmosphere interactions , which particularly affect deep atmospheric convection over the ocean and surrounding continents .
Apart from influences from the Pacific El Nino/Southern Oscillation and the North Atlantic Oscillation , the tropical Atlantic variability is thought to be dominated by two distinct ocean-atmosphere coupled modes of variability that are characterized by meridional and zonal sea-surface-temperature gradients and are mainly active on decadal and interannual timescales , respectively .
Here we report evidence that the intrinsic ocean dynamics of the deep equatorial Atlantic can also affect sea surface temperature , wind and rainfall in the tropical Atlantic region and constitutes a 4.5-yr climate cycle .
Specifically , vertically alternating deep zonal jets of short vertical wavelength with a period of about 4.5 yr and amplitudes of more than 10 cm s-1 are observed , in the deep Atlantic , to propagate their energy upwards , towards the surface .
They are linked , at the sea surface , to equatorial zonal current anomalies and eastern Atlantic temperature anomalies that have amplitudes of about 6 cm s-1 and 0.4 degreesC , respectively , and are associated with distinct wind and rainfall patterns .
Although deep jets are also observed in the Pacific and Indian oceans , only the Atlantic deep jets seem to oscillate on interannual timescales .
Our knowledge of the persistence and regularity of these jets is limited by the availability of high-quality data .
Despite this caveat , the oscillatory behaviour can still be used to improve predictions of sea surface temperature in the tropical Atlantic .
Deep-jet generation and upward energy transmission through the Equatorial Undercurrent warrant further theoretical study .

[2257] Rapid adaptation to food availability by a dopamine-mediated morphogenetic response

Food can act as a powerful stimulus , eliciting metabolic , behavioural and developmental responses .
These phenotypic changes can alter ecological and evolutionary processes ; yet , the molecular mechanisms underlying many plastic phenotypic responses remain unknown .
Here we show that dopamine signalling through a type-D2 receptor mediates developmental plasticity by regulating arm length in pre-feeding sea urchin larvae in response to food availability .
Although prey-induced traits are often thought to improve food acquisition , the mechanism underlying this plastic response acts to reduce feeding structure size and subsequent feeding rate .
Consequently , the developmental programme and/or maternal provisioning predetermine the maximum possible feeding rate , and food-induced dopamine signalling reduces food acquisition potential during periods of abundant resources to preserve maternal energetic reserves .
Sea urchin larvae may have co-opted the widespread use of food-induced dopamine signalling from behavioural responses to instead alter their development .

[2258] Southern Annular Mode-like changes in southwestern Patagonia at centennial timescales over the last three millennia

Late twentieth-century instrumental records reveal a persistent southward shift of the Southern Westerly Winds during austral summer and autumn associated with a positive trend of the Southern Annular Mode ( SAM ) and contemporaneous with glacial recession , steady increases in atmospheric temperatures and CO2 concentrations at a global scale .
However , despite the clear importance of the SAM in the modern/future climate , very little is known regarding its behaviour during pre-Industrial times .
Here we present a stratigraphic record from Lago Cipreses ( 51degreesS ) , southwestern Patagonia , that reveals recurrent ~ 200-year long dry/warm phases over the last three millennia , which we interpret as positive SAM-like states .
These correspond in timing with the Industrial revolution , the Mediaeval Climate Anomaly , the Roman and Late Bronze Age Warm Periods and alternate with cold/wet multi-centennial phases in European palaeoclimate records .
We conclude that SAM-like changes at centennial timescales in southwestern Patagonia represent in-phase interhemispheric coupling of palaeoclimate over the last 3,000 years through atmospheric teleconnections .

[2259] Recent Walker circulation strengthening and Pacific cooling amplified by Atlantic warming

An unprecedented strengthening of Pacific trade winds since the late 1990s ( ref . )
has caused widespread climate perturbations , including rapid sea-level rise in the western tropical Pacific , strengthening of Indo-Pacific ocean currents , and an increased uptake of heat in the equatorial Pacific thermocline .
The corresponding intensification of the atmospheric Walker circulation is also associated with sea surface cooling in the eastern Pacific , which has been identified as one of the contributors to the current pause in global surface warming .
In spite of recent progress in determining the climatic impacts of the Pacific trade wind acceleration , the cause of this pronounced trend in atmospheric circulation remains unknown .
Here we analyse a series of climate model experiments along with observational data to show that the recent warming trend in Atlantic sea surface temperature and the corresponding trans-basin displacements of the main atmospheric pressure centres were key drivers of the observed Walker circulation intensification , eastern Pacific cooling , North American rainfall trends and western Pacific sea-level rise .
Our study suggests that global surface warming has been partly offset by the Pacific climate response to enhanced Atlantic warming since the early 1990s .

[2260] Substantial contribution to sea-level rise during the last interglacial from the Greenland ice sheet

During the last interglacial period ( the Eemian ) , global sea level was at least three metres , and probably more than five metres , higher than at present .
Complete melting of either the West Antarctic ice sheet or the Greenland ice sheet would today raise sea levels by 6-7 metres .
But the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the West Antarctic ice sheet , with model studies attributing only 1-2 m of sea-level rise to meltwater from Greenland .
This result was considered consistent with ice core evidence , although earlier work had suggested a much reduced Greenland ice sheet during the last interglacial period .
Here we reconsider the Eemian evolution of the Greenland ice sheet by combining numerical modelling with insights obtained from recent central Greenland ice-core analyses .
Our results suggest that the Greenland ice sheet was considerably smaller and steeper during the Eemian , and plausibly contributed 4-5 .5 m to the sea-level highstand during that period .
We conclude that the high sea level during the last interglacial period most probably included a large contribution from Greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the West Antarctic ice sheet .

[2261] Biodiversity and ecosystem stability in a decade-long grassland experiment

Human-driven ecosystem simplification has highlighted questions about how the number of species in an ecosystem influences its functioning .
Although biodiversity is now known to affect ecosystem productivity , its effects on stability are debated .
Here we present a long-term experimental field test of the diversity-stability hypothesis .
During a decade of data collection in an experiment that directly controlled the number of perennial prairie species , growing-season climate varied considerably , causing year-to-year variation in abundances of plant species and in ecosystem productivity .
We found that greater numbers of plant species led to greater temporal stability of ecosystem annual aboveground plant production .
In particular , the decadal temporal stability of the ecosystem , whether measured with intervals of two , five or ten years , was significantly greater at higher plant diversity and tended to increase as plots matured .
Ecosystem stability was also positively dependent on root mass , which is a measure of perenniating biomass .
Temporal stability of the ecosystem increased with diversity , despite a lower temporal stability of individual species , because of both portfolio ( statistical averaging ) and overyielding effects .
However , we found no evidence of a covariance effect .
Our results indicate that the reliable , efficient and sustainable supply of some foods ( for example , livestock fodder ) , biofuels and ecosystem services can be enhanced by the use of biodiversity .

[2262] Nutritional stress induces exchange of cell material and energetic coupling between bacterial species

Knowledge of the behaviour of bacterial communities is crucial for understanding biogeochemical cycles and developing environmental biotechnology .
Here we demonstrate the formation of an artificial consortium between two anaerobic bacteria , Clostridium acetobutylicum ( Gram-positive ) and Desulfovibrio vulgaris Hildenborough ( Gram-negative , sulfate-reducing ) in which physical interactions between the two partners induce emergent properties .
Molecular and cellular approaches show that tight cell-cell interactions are associated with an exchange of molecules , including proteins , which allows the growth of one partner ( D. vulgaris ) in spite of the shortage of nutrients .
This physical interaction induces changes in expression of two genes encoding enzymes at the pyruvate crossroads , with concomitant changes in the distribution of metabolic fluxes , and allows a substantial increase in hydrogen production without requiring genetic engineering .
The stress induced by the shortage of nutrients of D. vulgaris appears to trigger the interaction .

[2263] 124,000-year periodicity in terrestrial vegetation change during the late Pliocene epoch

The late Pliocene ( ~ 3-2 .6 million years ago ) is an interval of exceptional interest for understanding the Earth 's climate system .
It was a time of progressive global cooling , resulting in the growth of large terrestrial ice sheets and the initiation of extensive Northern Hemisphere glaciation , .
The build up of the ice sheets was cyclical and apparently paced by the orbitally driven oscillations in incoming solar radiation ( Milankovitch cycles ) at periods of approximately 41 kyr ( obliquity ) and 23-19 kyr ( precession ) .
Here we present a high-resolution continental record of late Pliocene climate change , detailing the response of terrestrial vegetation to this interval of dramatic global environmental change .
The annually laminated sequence of lake sediments from Pula maar , in Hungary , represents approximately 320 kyr of accumulation between ~ 3.0 and 2.6 million years ago .
Spectral analyses of the record indicate terrestrial responses to incoming solar radiation at obliquity and precession periodicities , but the strongest response appears at a period of ~ 124 kyr .
Calculations indicate that variations in insolation forcing at this periodicity were negligible at this time .
The Pula record thus demonstrates that internally driven nonlinear responses of the climate system , at a period of ~ 124 kyr , were at least as important as external forcing at the orbital frequencies of precession and obliquity in driving late Pliocene large-scale environmental change .

[2264] Interspecific bacterial sensing through airborne signals modulates locomotion and drug resistance

Bacteria use chemical signals to sense each other and to regulate various physiological functions .
Although it is known that some airborne volatile organic compounds function as bacterial signalling molecules , their identities and effects on global gene expression and bacterial physiological processes remain largely unknown .
Here we perform microarray analyses of Escherichia coli exposed to volatile organic compounds emitted from Bacillus subtilis .
We find that 2,3-butanedione and glyoxylic acid mediate global changes in gene expression related to motility and antibiotic resistance .
Volatile organic compound-dependent phenotypes are conserved among bacteria and are regulated by the previously uncharacterized ypdB gene product through the downstream transcription factors soxS , rpoS or yjhU .
These results strongly suggest that bacteria use airborne volatile organic compounds to sense other bacteria and to change master regulatory gene activity to adapt .

[2265] Spatial-temporal model for silencing of the mitotic spindle assembly checkpoint

The spindle assembly checkpoint arrests mitotic progression until each kinetochore secures a stable attachment to the spindle .
Despite fluctuating noise , this checkpoint remains robust and remarkably sensitive to even a single unattached kinetochore among many attached kinetochores ; moreover , the checkpoint is silenced only after the final kinetochore-spindle attachment .
Experimental observations have shown that checkpoint components stream from attached kinetochores along microtubules towards spindle poles .
Here we incorporate this streaming behaviour into a theoretical model that accounts for the robustness of checkpoint silencing .
Poleward streams are integrated at spindle poles , but are diverted by any unattached kinetochore ; consequently , accumulation of checkpoint components at spindle poles increases markedly only when every kinetochore is properly attached .
This step change robustly triggers checkpoint silencing after , and only after , the final kinetochore-spindle attachment .
Our model offers a conceptual framework that highlights the role of spatiotemporal regulation in mitotic spindle checkpoint signalling and fidelity of chromosome segregation .

[2266] Climate change : Future rise in rain inequality

Rainfall disparities are expected to intensify in response to anthropogenic climate change .
Model simulations suggest that wet regions and seasons will get wetter , and that a warmer equator will get wetter too .

[2267] Threat to future global food security from climate change and ozone air pollution

Future food production is highly vulnerable to both climate change and air pollution with implications for global food security .
Climate change adaptation and ozone regulation have been identified as important strategies to safeguard food production , but little is known about how climate and ozone pollution interact to affect agriculture , nor the relative effectiveness of these two strategies for different crops and regions .
Here we present an integrated analysis of the individual and combined effects of 2000-2050 climate change and ozone trends on the production of four major crops ( wheat , rice , maize and soybean ) worldwide based on historical observations and model projections , specifically accounting for ozone-temperature co-variation .
The projections exclude the effect of rising CO2 , which has complex and potentially offsetting impacts on global food supply .
We show that warming reduces global crop production by > 10 % by 2050 with a potential to substantially worsen global malnutrition in all scenarios considered .
Ozone trends either exacerbate or offset a substantial fraction of climate impacts depending on the scenario , suggesting the importance of air quality management in agricultural planning .
Furthermore , we find that depending on region some crops are primarily sensitive to either ozone ( for example , wheat ) or heat ( for example , maize ) alone , providing a measure of relative benefits of climate adaptation versus ozone regulation for food security in different regions .

[2268] Nitrification by plants that also fix nitrogen

Nitrification is a key stage in the nitrogen cycle ; it enables the transformation of nitrogen into an oxidized , inorganic state .
The availability of nitrates produced by this process often limits primary productivity and is an important determinant in plant community ecology and biodiversity .
Chemoautotrophic prokaryotes are recognized as the main facilitators of this process , although heterotrophic nitrification by fungi may be significant under certain conditions .
However , there has been neither biochemical nor ecological evidence to support nitrification by photoautotrophic plants .
Here we show how certain legumes that accumulate the toxin , 3-nitropropionic acid , generate oxidized inorganic nitrogen in their shoots , which is returned to the soil in their litter .
In nitrogen-fixing populations this ` new ' nitrate and nitrite can be derived from the assimilation of nitrogen gas .
Normally , the transformation of elemental nitrogen from the atmosphere into a fixed oxidized form ( as nitrate ) is represented in the nitrogen cycle as a multiphasic process involving several different organisms .
We show how this can occur in a single photoautotrophic organism , representing a previously undescribed feature of this biogeochemical cycle .

[2269] Fungal community on decomposing leaf litter undergoes rapid successional changes

Fungi are considered the primary decomposers of dead plant biomass in terrestrial ecosystems .
However , current knowledge regarding the successive changes in fungal communities during litter decomposition is limited .
Here we explored the development of the fungal community over 24 months of litter decomposition in a temperate forest with dominant Quercus petraea using 454-pyrosequencing of the fungal internal transcribed spacer ( ITS ) region and cellobiohydrolase I ( cbhI ) genes , which encode exocellulases , to specifically address cellulose decomposers .
To quantify the involvement of phyllosphere fungi in litter decomposition , the fungal communities in live leaves and leaves immediately before abscission were also analysed .
The results showed rapid succession of fungi with dramatic changes in the composition of the fungal community .
Furthermore , most of the abundant taxa only temporarily dominated in the substrate .
Fungal diversity was lowest at leaf senescence , increased until month 4 and did not significantly change during subsequent decomposition .
Highly diverse community of phyllosphere fungi inhabits live oak leaves 2 months before abscission , and these phyllosphere taxa comprise a significant share of the fungal community during early decomposition up to the fourth month .
Sequences assigned to the Ascomycota showed highest relative abundances in live leaves and during the early stages of decomposition .
In contrast , the relative abundance of sequences assigned to the Basidiomycota phylum , particularly basidiomycetous yeasts , increased with time .
Although cellulose was available in the litter during all stages of decomposition , the community of cellulolytic fungi changed substantially over time .
The results indicate that litter decomposition is a highly complex process mediated by various fungal taxa .

[2270] Faster growth of the major prokaryotic versus eukaryotic CO2 fixers in the oligotrophic ocean

Because maintenance of non-scalable cellular components -- membranes and chromosomes -- requires an increasing fraction of energy as cell size decreases , miniaturization comes at a considerable energetic cost for a phytoplanktonic cell .
Consequently , if eukaryotes can use their superior energetic resources to acquire nutrients with more or even similar efficiency compared with prokaryotes , larger unicellular eukaryotes should be able to achieve higher growth rates than smaller cyanobacteria .
Here , to test this hypothesis , we directly compare the intrinsic growth rates of phototrophic prokaryotes and eukaryotes from the equatorial to temperate South Atlantic using an original flow cytometric 14CO2-tracer approach .
At the ocean basin scale , cyanobacteria double their biomass twice as frequently as the picoeukaryotes indicating that the prokaryotes are faster growing CO2 fixers , better adapted to phototrophic living in the oligotrophic open ocean -- the most extensive biome on Earth .

[2271] El Nino and health risks from landscape fire emissions in southeast Asia

Emissions from landscape fires affect both climate and air quality .
Here , we combine satellite-derived fire estimates and atmospheric modelling to quantify health effects from fire emissions in southeast Asia from 1997 to 2006 .
This region has large interannual variability in fire activity owing to coupling between El Nino-induced droughts and anthropogenic land-use change .
We show that during strong El Nino years , fires contribute up to 200 mug m-3 and 50 ppb in annual average fine particulate matter ( PM2 .5 ) and ozone surface concentrations near fire sources , respectively .
This corresponds to a fire contribution of 200 additional days per year that exceed the World Health Organization 50 mug m-3 24-hr PM2 .5 interim target and an estimated 10,800 ( 6,800-14 ,300 ) - person ( ~ 2 % ) annual increase in regional adult cardiovascular mortality .
Our results indicate that reducing regional deforestation and degradation fires would improve public health along with widely established benefits from reducing carbon emissions , preserving biodiversity and maintaining ecosystem services .

[2272] Forest cutting and impacts on carbon in the eastern United States

Forest cutting is a major anthropogenic disturbance that affects forest carbon ( C ) storage and fluxes .
Yet its characteristics and impacts on C cycling are poorly understood over large areas .
Using recent annualized forest inventory data , we estimated cutting-related loss of live biomass in the eastern United States was 168 Tg C yr-1 from 2002 to 2010 ( with C loss per unit forest area of 1.07 Mg ha-1 yr-1 ) , which is equivalent to 70 % of the total U.S. forest C sink or 11 % of the national annual CO2 emissions from fossil-fuel combustion over the same period .
We further revealed that specific cutting-related C loss varied with cutting intensities , forest types , stand ages , and geographic locations .
Our results provide new insights to the characteristics of forest harvesting activities in the eastern United States and highlight the significance of partial cutting to regional and national carbon budgets .

[2273] Selective progressive response of soil microbial community to wild oat roots

Roots moving through soil induce physical and chemical changes that differentiate rhizosphere from bulk soil , and the effects of these changes on soil microorganisms have long been a topic of interest .
The use of a high-density 16S rRNA microarray ( PhyloChip ) for bacterial and archaeal community analysis has allowed definition of the populations that respond to the root within the complex grassland soil community ; this research accompanies compositional changes reported earlier , including increases in chitinase - and protease-specific activity , cell numbers and quorum sensing signal .
PhyloChip results showed a significant change compared with bulk soil in relative abundance for 7 % of the total rhizosphere microbial community ( 147 of 1917 taxa ) ; the 7 % response value was confirmed by16S rRNA terminal restriction fragment length polymorphism analysis .
This PhyloChip-defined dynamic subset was comprised of taxa in 17 of the 44 phyla detected in all soil samples .
Expected rhizosphere-competent phyla , such as Proteobacteria and Firmicutes , were well represented , as were less-well-documented rhizosphere colonizers including Actinobacteria , Verrucomicrobia and Nitrospira .
Richness of Bacteroidetes and Actinobacteria decreased in soil near the root tip compared with bulk soil , but then increased in older root zones .
Quantitative PCR revealed rhizosphere abundance of beta-Proteobacteria and Actinobacteria at about 108 copies of 16S rRNA genes per g soil , with Nitrospira having about 105 copies per g soil .
This report demonstrates that changes in a relatively small subset of the soil microbial community are sufficient to produce substantial changes in functions observed earlier in progressively more mature rhizosphere zones .

[2274] Underestimation of volcanic cooling in tree-ring-based reconstructions of hemispheric temperatures

The largest eruption of a tropical volcano during the past millennium occurred in AD 1258-1259 .
Its estimated radiative forcing was several times larger than the 1991 Pinatubo eruption .
Radiative forcing of that magnitude is expected to result in a climate cooling of about 2 degreesC ( refs , , , ) .
This effect , however , is largely absent from tree-ring reconstructions of temperature , and is muted in reconstructions that employ a mix of tree-rings and other proxy data .
This discrepancy has called into question the climate impact of the eruption .
Here we use a tree-growth model driven by simulated temperature variations to show that the discrepancy between expected and reconstructed temperatures is probably an artefact caused by a reduced sensitivity to cooling in trees that grow near the treeline .
This effect is compounded by the secondary effects of chronological errors due to missing growth rings and volcanically induced alterations of diffuse light .
We support this conclusion with an assessment of synthetic proxy records created using the simulated temperature variations .
Our findings suggest that the evidence from tree rings is consistent with a substantial climate impact of volcanic eruptions in past centuries that is greater than that estimated by tree-ring-based temperature reconstructions .

[2275] The cause of the fragile relationship between the Pacific El Nino and the Atlantic Nino

El Nino , the most prominent climate fluctuation at seasonal-to-interannual timescales , has long been known to have a remote impact on climate variability in the tropical Atlantic Ocean , but a robust influence is found only in the northern tropical Atlantic region .
Fluctuations in the equatorial Atlantic are dominated by the Atlantic Nino , a phenomenon analogous to El Nino , characterized by irregular episodes of anomalous warming during the boreal summer .
The Atlantic Nino strongly affects seasonal climate prediction in African countries bordering the Gulf of Guinea .
The relationship between El Nino and the Atlantic Nino is ambiguous and inconsistent .
Here we combine observational and modelling analysis to show that the fragile relationship is a result of destructive interference between atmospheric and oceanic processes in response to El Nino .
The net effect of El Nino on the Atlantic Nino depends not only on the atmospheric response that propagates the El Nino signal to the tropical Atlantic , but also on a dynamic ocean-atmosphere interaction in the equatorial Atlantic that works against the atmospheric response .
These results emphasize the importance of having an improved ocean-observing system in the tropical Atlantic , because our ability to predict the Atlantic Nino will depend not only on our knowledge of conditions in the tropical Pacific , but also on an accurate estimate of the state of the upper ocean in the equatorial Atlantic .

[2276] Formation of the ` Great Unconformity ' as a trigger for the Cambrian explosion

The transition between the Proterozoic and Phanerozoic eons , beginning 542 million years ( Myr ) ago , is distinguished by the diversification of multicellular animals and by their acquisition of mineralized skeletons during the Cambrian period .
Considerable progress has been made in documenting and more precisely correlating biotic patterns in the Neoproterozoic-Cambrian fossil record with geochemical and physical environmental perturbations , but the mechanisms responsible for those perturbations remain uncertain .
Here we use new stratigraphic and geochemical data to show that early Palaeozoic marine sediments deposited approximately 540-480 Myr ago record both an expansion in the area of shallow epicontinental seas and anomalous patterns of chemical sedimentation that are indicative of increased oceanic alkalinity and enhanced chemical weathering of continental crust .
These geochemical conditions were caused by a protracted period of widespread continental denudation during the Neoproterozoic followed by extensive physical reworking of soil , regolith and basement rock during the first continental-scale marine transgression of the Phanerozoic .
The resultant globally occurring stratigraphic surface , which in most regions separates continental crystalline basement rock from much younger Cambrian shallow marine sedimentary deposits , is known as the Great Unconformity .
Although Darwin and others have interpreted this widespread hiatus in sedimentation on the continents as a failure of the geologic record , this palaeogeomorphic surface represents a unique physical environmental boundary condition that affected seawater chemistry during a time of profound expansion of shallow marine habitats .
Thus , the formation of the Great Unconformity may have been an environmental trigger for the evolution of biomineralization and the ` Cambrian explosion ' of ecologic and taxonomic diversity following the Neoproterozoic emergence of animals .

[2277] Air-pollution emission ranges consistent with the representative concentration pathways

The fifth phase of the Coupled Model Intercomparison Project uses four representative concentration pathways ( RCPs ) that span the literature range of total anthropogenic radiative forcing but not necessarily of each single forcing agent .
We here explore a wide range of air-pollutant emissions over the twenty-first century consistent with the global CO2 paths of the RCPs , by varying assumptions on air-pollution controls and accounting for the possible phase-out of CO2-emitting sources .
We show that global air-pollutant emissions in the RCPs ( including ozone and aerosol precursors ) compare well to and are at times higher than cases that assume an extrapolation of current and planned air-pollution legislation in the absence of new policies to improve energy access for the poor .
Stringent pollution controls and clean energy policies can thus further reduce the global atmospheric air-pollution loading below the RCP levels .
When assuming pollution control frozen at 2005 levels , the RCP8.5-consistent loading of all species either stabilizes or increases during the twenty-first century , in contrast to RCP4 .5 and RCP2 .6 , which see a consistent decrease in the long term .
Our results inform the possible range of global aerosol loading .
However , the net aerosol forcing depends strongly on the geographical location of emissions .
Therefore , a regional perspective is required to further explore the range of compatible forcing projections .

[2278] Flood risk of natural and embanked landscapes on the Ganges-Brahmaputra tidal delta plain

The Ganges-Brahmaputra river delta , with 170 million people and a vast , low-lying coastal plain , is perceived to be at great risk of increased flooding and submergence from sea-level rise .
However , human alteration of the landscape can create similar risks to sea-level rise .
Here , we report that islands in southwest Bangladesh , enclosed by embankments in the 1960s , have lost 1.0-1 .5 m of elevation , whereas the neighbouring Sundarban mangrove forest has remained comparatively stable .
We attribute this elevation loss to interruption of sedimentation inside the embankments , combined with accelerated compaction , removal of forest biomass , and a regionally increased tidal range .
One major consequence of this elevation loss occurred in 2009 when the embankments of several large islands failed during Cyclone Aila , leaving large areas of land tidally inundated for up to two years until embankments were repaired .
Despite sustained human suffering during this time , the newly reconnected landscape received tens of centimetres of tidally deposited sediment , equivalent to decades ' worth of normal sedimentation .
Although many areas still lie well below mean high water and remain at risk of severe flooding , we conclude that elevation recovery may be possible through controlled embankment breaches .

[2279] Gulf Stream density structure and transport during the past millennium

The Gulf Stream transports approximately 31 Sv ( 1 Sv = 106 m3 s-1 ) of water and 1.3 x 1015 W of heat into the North Atlantic ocean .
The possibility of abrupt changes in Gulf Stream heat transport is one of the key uncertainties in predictions of climate change for the coming centuries .
Given the limited length of the instrumental record , our knowledge of Gulf Stream behaviour on long timescales must rely heavily on information from geologic archives .
Here we use foraminifera from a suite of high-resolution sediment cores in the Florida Straits to show that the cross-current density gradient and vertical current shear of the Gulf Stream were systematically lower during the Little Ice Age ( ad ~ 1200 to 1850 ) .
We also estimate that Little Ice Age volume transport was ten per cent weaker than today 's .
The timing of reduced flow is consistent with temperature minima in several palaeoclimate records , implying that diminished oceanic heat transport may have contributed to Little Ice Age cooling in the North Atlantic .
The interval of low flow also coincides with anomalously high Gulf Stream surface salinity , suggesting a tight linkage between the Atlantic Ocean circulation and hydrologic cycle during the past millennium .

[2280] The evolutionary inheritance of elemental stoichiometry in marine phytoplankton

Phytoplankton is a nineteenth century ecological construct for a biologically diverse group of pelagic photoautotrophs that share common metabolic functions but not evolutionary histories .
In contrast to terrestrial plants , a major schism occurred in the evolution of the eukaryotic phytoplankton that gave rise to two major plastid superfamilies .
The green superfamily appropriated chlorophyll b , whereas the red superfamily uses chlorophyll c as an accessory photosynthetic pigment .
Fossil evidence suggests that the green superfamily dominated Palaeozoic oceans .
However , after the end-Permian extinction , members of the red superfamily rose to ecological prominence .
The processes responsible for this shift are obscure .
Here we present an analysis of major nutrients and trace elements in 15 species of marine phytoplankton from the two superfamilies .
Our results indicate that there are systematic phylogenetic differences in the two plastid types where macronutrient ( carbon : nitrogen : phosphorus ) stoichiometries primarily reflect ancestral pre-symbiotic host cell phenotypes , but trace element composition reflects differences in the acquired plastids .
The compositional differences between the two plastid superfamilies suggest that changes in ocean redox state strongly influenced the evolution and selection of eukaryotic phytoplankton since the Proterozoic era .

[2281] Effects of ciprofloxacin on salt marsh sediment microbial communities

Fluoroquinolones , a widely used class of antibiotics , are frequently detected in sediments and surface waters .
Given their antimicrobial properties , the presence of these compounds may alter the composition of microbial communities and promote antibiotic resistance in the environment .
The purpose of this study was to measure sorption , and effects of ciprofloxacin on microbial community composition , in sediment samples from three California salt marshes .
Sediments were exposed to a ciprofloxacin concentration gradient ( 0-200 mug ml-1 ciprofloxacin ) and microbial community composition characterized using phospholipid fatty acid ( PLFA ) analysis .
Sorption coefficients , expressed as log Kd , were calculated from fits using the Freundlich isotherm model .
Ciprofloxacin strongly sorbed to all sediments and had log Kd values , ranging from 2.9 to 4.3 .
Clay content was positively ( r2 = 0.98 ) and pH negatively ( r2 = 0.99 ) correlated to Kd values .
Biomass , PLFA richness , sulfate reducer and Gram-negative bacteria markers increased with ciprofloxacin concentrations , while the 17 cy/precursor and saturated/unsaturated biomarker ratios , indicators of starvation stress , decreased .
The magnitude of the effect of ciprofloxacin on microbial communities was inversely correlated to the degree of sorption to the sediments .
Despite the fact that ciprofloxacin is a wide-spectrum antibiotic , its impact on sediment microbial communities was selective and appeared to favor sulfate-reducing bacteria and Gram-negative bacteria .

[2282] Hdsp , a horizontally transferred gene required for social behavior and halotolerance in salt-tolerant Myxococcus fulvus HW-1

Myxococcus fulvus HW-1 , a salt-tolerant bacterial strain , which was isolated from a coastal environment , changes its behavior with different salinities .
To study the relationship between behavioral shifts and the adaption to oceanic conditions , the HW-1 strain was randomly mutagenized using transposon insertion , producing a dispersed-growing mutant , designated YLH0401 .
The mutant did not develop fruiting bodies and myxospores , was deficient in S-motility , produced less extracellular matrix and was less salt tolerant .
The YLH0401 strain was determined to be mutated by a single insertion in a large gene of unknown function ( 7011 bp in size ) , which is located in a horizontally transferred DNA fragment .
The gene is expressed during the vegetative growth stage , as well as highly and stably expressed during the development stage .
This horizontally transferred gene may allow Myxococcus to adapt to oceanic conditions .

[2283] Consistent patterns and the idiosyncratic effects of biodiversity in marine ecosystems

Revealing the consequences of species extinctions for ecosystem function has been a chief research goal and has been accompanied by enthusiastic debate .
Studies carried out predominantly in terrestrial grassland and soil ecosystems have demonstrated that as the number of species in assembled communities increases , so too do certain ecosystem processes , such as productivity , whereas others such as decomposition can remain unaffected .
Diversity can influence aspects of ecosystem function , but questions remain as to how generic the patterns observed are , and whether they are the product of diversity , as such , or of the functional roles and traits that characterize species in ecological systems .
Here we demonstrate variable diversity effects for species representative of marine coastal systems at both global and regional scales .
We provide evidence for an increase in complementary resource use as diversity increases and show strong evidence for diversity effects in naturally assembled communities at a regional scale .
The variability among individual species responses is consistent with a positive but idiosyncratic pattern of ecosystem function with increased diversity .

[2284] Past constraints on the vulnerability of marine calcifiers to massive carbon dioxide release

Increasing concentrations of carbon dioxide in sea water are driving a progressive acidification of the ocean .
Although the associated changes in the carbonate chemistry of surface and deep waters may adversely affect marine calcifying organisms , current experiments do not always produce consistent results for a given species .
Ocean sediments record past biological responses to transient greenhouse warming and ocean acidification .
During the Palaeocene-Eocene thermal maximum , for example , the biodiversity of benthic calcifying organisms decreased markedly , whereas extinctions of surface dwellers were very limited .
Here we use the Earth system model GENIE-1 to simulate and compare directly past and present environmental changes in the marine realm .
In our simulation of future ocean conditions , we find an undersaturation with respect to carbonate in the deep ocean that exceeds that experienced during the Palaeocene-Eocene thermal maximum and could endanger calcifying organisms .
Furthermore , our simulations show higher rates of environmental change at the surface for the future than the Palaeocene-Eocene thermal maximum , which could potentially challenge the ability of plankton to adapt .

[2285] Climate warming and Mediterranean seagrass

To the Editor We have a limited understanding of how seagrass communities will respond to climate change .
A dramatic decline of Posidonia oceanica seagrass meadows around the Balearics , even under active conservation , is forecasted by Jorda et al .
after linking the modelled increase in sea surface temperature with a purported decline in shoot demography .

[2286] Sensitivity of coccolithophores to carbonate chemistry and ocean acidification

About one-third of the carbon dioxide ( CO2 ) released into the atmosphere as a result of human activity has been absorbed by the oceans , where it partitions into the constituent ions of carbonic acid .
This leads to ocean acidification , one of the major threats to marine ecosystems and particularly to calcifying organisms such as corals , foraminifera and coccolithophores .
Coccolithophores are abundant phytoplankton that are responsible for a large part of modern oceanic carbonate production .
Culture experiments investigating the physiological response of coccolithophore calcification to increased CO2 have yielded contradictory results between and even within species .
Here we quantified the calcite mass of dominant coccolithophores in the present ocean and over the past forty thousand years , and found a marked pattern of decreasing calcification with increasing partial pressure of CO2 and concomitant decreasing concentrations of CO32 - .
Our analyses revealed that differentially calcified species and morphotypes are distributed in the ocean according to carbonate chemistry .
A substantial impact on the marine carbon cycle might be expected upon extrapolation of this correlation to predicted ocean acidification in the future .
However , our discovery of a heavily calcified Emiliania huxleyi morphotype in modern waters with low pH highlights the complexity of assemblage-level responses to environmental forcing factors .

[2287] Regionally differentiated contribution of mountain glaciers and ice caps to future sea-level rise

The contribution to sea-level rise from mountain glaciers and ice caps has grown over the past decades .
They are expected to remain an important component of eustatic sea-level rise for at least another century , despite indications of accelerated wastage of the ice sheets .
However , it is difficult to project the future contribution of these small-scale glaciers to sea-level rise on a global scale .
Here , we project their volume changes due to melt in response to transient , spatially differentiated twenty-first century projections of temperature and precipitation from ten global climate models .
We conduct the simulations directly on the more than 120,000 glaciers now available in the World Glacier Inventory , and upscale the changes to 19 regions that contain all mountain glaciers and ice caps in the world ( excluding the Greenland and Antarctic ice sheets ) .
According to our multi-model mean , sea-level rise from glacier wastage by 2100 will amount to 0.124 + / -0.037 m , with the largest contribution from glaciers in Arctic Canada , Alaska and Antarctica .
Total glacier volume will be reduced by 21 + / -6 % , but some regions are projected to lose up to 75 % of their present ice volume .
Ice losses on such a scale may have substantial impacts on regional hydrology and water availability .

[2288] Sediment Type Affects Competition between a Native and an Exotic Species in Coastal China

Different types of sediments in salt marsh have different physical and chemical characters .
Thus sediment type plays a role in plant competition and growth in salt marsh ecosystems .
Spartina anglica populations have been increasingly confined to upper elevation gradients of clay , and the niche sediment has changed .
Because the niches of S. anglica and the native species Scirpus triqueter overlap , we conducted a greenhouse experiment to test the hypothesis that plant competition has changed under different types of sediments .
Biomass and asexual reproduction were analyzed , and inter - and intraspecific competition was measured by log response ratio for the two species in both monoculture and combination under three sediment types ( sand , clay and mixture of sand and clay ) .
For S. anglica , biomass , ramet number and rhizome length in combination declined significantly compared with those in monoculture , and the intensity of interspecific competition was significantly higher than that of intraspecific competition under all sediments .
For S. triqueter , the intensities of intra - and interspecific competition were not significantly different .
This indicates that S. triqueter exerts an asymmetric competitive advantage over S. anglica across all sediments , but especially clay .
Thus the sediment type changes competition between S. anglica and S. triqueter .

[2289] The drivers of tropical speciation

Since the recognition that allopatric speciation can be induced by large-scale reconfigurations of the landscape that isolate formerly continuous populations , such as the separation of continents by plate tectonics , the uplift of mountains or the formation of large rivers , landscape change has been viewed as a primary driver of biological diversification .
This process is referred to in biogeography as vicariance .
In the most species-rich region of the world , the Neotropics , the sundering of populations associated with the Andean uplift is ascribed this principal role in speciation .
An alternative model posits that rather than being directly linked to landscape change , allopatric speciation is initiated to a greater extent by dispersal events , with the principal drivers of speciation being organism-specific abilities to persist and disperse in the landscape .
Landscape change is not a necessity for speciation in this model .
Here we show that spatial and temporal patterns of genetic differentiation in Neotropical birds are highly discordant across lineages and are not reconcilable with a model linking speciation solely to landscape change .
Instead , the strongest predictors of speciation are the amount of time a lineage has persisted in the landscape and the ability of birds to move through the landscape matrix .
These results , augmented by the observation that most species-level diversity originated after episodes of major Andean uplift in the Neogene period , suggest that dispersal and differentiation on a matrix previously shaped by large-scale landscape events was a major driver of avian speciation in lowland Neotropical rainforests .

[2290] Marine microbial symbiosis heats up : the phylogenetic and functional response of a sponge holobiont to thermal stress

Large-scale mortality of marine invertebrates is a major global concern for ocean ecosystems and many sessile , reef-building animals , such as sponges and corals , are experiencing significant declines through temperature-induced disease and bleaching .
The health and survival of marine invertebrates is often dependent on intimate symbiotic associations with complex microbial communities , yet we have a very limited understanding of the detailed biology and ecology of both the host and the symbiont community in response to environmental stressors , such as elevated seawater temperatures .
Here , we use the ecologically important sponge Rhopaloeides odorabile as a model to explore the changes in symbiosis during the development of temperature-induced necrosis .
Expression profiling of the sponge host was examined in conjunction with the phylogenetic and functional structure and the expression profile of the symbiont community .
Elevated temperature causes an immediate stress response in both the host and symbiont community , including reduced expression of functions that mediate their partnership .
Disruption to nutritional interdependence and molecular interactions during early heat stress further destabilizes the holobiont , ultimately leading to the loss of archetypal sponge symbionts and the introduction of new microorganisms that have functional and expression profiles consistent with a scavenging lifestyle , a lack virulence functions and a high growth rate .
Previous models have postulated various mechanisms of mortality and disease in marine invertebrates .
Our study suggests that interruption of symbiotic interactions is a major determinant for mortality in marine sessile invertebrates .
High symbiont specialization and low functional redundancy , thus make these holobionts extremely vulnerable to environmental perturbations , including climate change .

[2291] Future sea-level rise from Greenland 's main outlet glaciers in a warming climate

Over the past decade , ice loss from the Greenland Ice Sheet increased as a result of both increased surface melting and ice discharge to the ocean .
The latter is controlled by the acceleration of ice flow and subsequent thinning of fast-flowing marine-terminating outlet glaciers .
Quantifying the future dynamic contribution of such glaciers to sea-level rise ( SLR ) remains a major challenge because outlet glacier dynamics are poorly understood .
Here we present a glacier flow model that includes a fully dynamic treatment of marine termini .
We use this model to simulate behaviour of four major marine-terminating outlet glaciers , which collectively drain about 22 per cent of the Greenland Ice Sheet .
Using atmospheric and oceanic forcing from a mid-range future warming scenario that predicts warming by 2.8 degrees Celsius by 2100 , we project a contribution of 19 to 30 millimetres to SLR from these glaciers by 2200 .
This contribution is largely ( 80 per cent ) dynamic in origin and is caused by several episodic retreats past overdeepenings in outlet glacier troughs .
After initial increases , however , dynamic losses from these four outlets remain relatively constant and contribute to SLR individually at rates of about 0.01 to 0.06 millimetres per year .
These rates correspond to ice fluxes that are less than twice those of the late 1990s , well below previous upper bounds .
For a more extreme future warming scenario ( warming by 4.5 degrees Celsius by 2100 ) , the projected losses increase by more than 50 per cent , producing a cumulative SLR of 29 to 49 millimetres by 2200 .

[2292] Cryptic prophages help bacteria cope with adverse environments

Phages are the most abundant entity in the biosphere and outnumber bacteria by a factor of 10 .
Phage DNA may also constitute 20 % of bacterial genomes ; however , its role is ill defined .
Here , we explore the impact of cryptic prophages on cell physiology by precisely deleting all nine prophage elements ( 166 kbp ) using Escherichia coli .
We find that cryptic prophages contribute significantly to resistance to sub-lethal concentrations of quinolone and beta-lactam antibiotics primarily through proteins that inhibit cell division ( for example , KilR of rac and DicB of Qin ) .
Moreover , the prophages are beneficial for withstanding osmotic , oxidative and acid stresses , for increasing growth , and for influencing biofilm formation .
Prophage CPS-53 proteins YfdK , YfdO and YfdS enhanced resistance to oxidative stress , prophages e14 , CPS-53 and CP4-57 increased resistance to acid , and e14 and rac proteins increased early biofilm formation .
Therefore , cryptic prophages provide multiple benefits to the host for surviving adverse environmental conditions .

[2293] Legume-based cropping systems have reduced carbon and nitrogen losses

In agricultural systems , optimization of carbon and nitrogen cycling through soil organic matter can improve soil fertility and yields while reducing negative environmental impact .
A basic tenet that has guided the management of soil organic matter for decades has been that equilibrium levels of carbon and nitrogen are controlled by their net input and that qualitative differences in these inputs are relatively unimportant .
This contrasts with natural ecosystems in which there are significant effects of species composition and litter quality on carbon and nitrogen cycling , .
Here we report the net balances of carbon and nitrogen from a 15-year study in which three distinct maize/soybean agroecosystems are compared .
Quantitative differences in net primary productivity and nitrogen balance across agroecosystems do not account for the observed changes in soil carbon and nitrogen .
We suggest that the use of low carbon-to-nitrogen organic residues to maintain soil fertility , combined with greater temporal diversity in cropping sequences , significantly increases the retention of soil carbon and nitrogen , which has important implications for regional and global carbon and nitrogen budgets , sustained production , and environmental quality .

[2294] The oceanic biological pump modulates the atmospheric transport of persistent organic pollutants to the Arctic

Semivolatile persistent organic pollutants have the potential to reach remote environments , such as the Arctic Ocean , through atmospheric transport and deposition .
Here we show that this transport of polychlorinated biphenyls to the Arctic Ocean is strongly retarded by the oceanic biological pump .
A simultaneous sampling of atmospheric , seawater and plankton samples was performed in July 2007 in the Greenland Current and Atlantic sector of the Arctic Ocean .
The atmospheric concentrations declined during atmospheric transport over the Greenland Current with estimated half-lives of 1-4 days .
These short half-lives can be explained by the high air-to-water net diffusive flux , which is similar in magnitude to the estimated settling fluxes in the water column .
Therefore , the decrease of atmospheric concentrations is due to sequestration of atmospheric polychlorinated biphenyls by enhanced air-water diffusive fluxes driven by phytoplankton uptake and organic carbon settling fluxes ( biological pump ) .

[2295] Mega-heatwave temperatures due to combined soil desiccation and atmospheric heat accumulation

The recent European mega-heatwaves of 2003 and 2010 broke temperature records across Europe .
Although events of this magnitude were unprecedented from a historical perspective , they are expected to become common by the end of the century .
However , our understanding of extreme heatwave events is limited and their representation in climate models remains imperfect .
Here we investigate the physical processes underlying recent mega-heatwaves using satellite and balloon measurements of land and atmospheric conditions from the summers of 2003 in France and 2010 in Russia , in combination with a soil-water-atmosphere model .
We find that , in both events , persistent atmospheric pressure patterns induced land-atmosphere feedbacks that led to extreme temperatures .
During daytime , heat was supplied by large-scale horizontal advection , warming of an increasingly desiccated land surface and enhanced entrainment of warm air into the atmospheric boundary layer .
Overnight , the heat generated during the day was preserved in an anomalous kilometres-deep atmospheric layer located several hundred metres above the surface , available to re-enter the atmospheric boundary layer during the next diurnal cycle .
This resulted in a progressive accumulation of heat over several days , which enhanced soil desiccation and led to further escalation in air temperatures .
Our findings suggest that the extreme temperatures in mega-heatwaves can be explained by the combined multi-day memory of the land surface and the atmospheric boundary layer .

[2296] The proportionality of global warming to cumulative carbon emissions

The global temperature response to increasing atmospheric CO2 is often quantified by metrics such as equilibrium climate sensitivity and transient climate response .
These approaches , however , do not account for carbon cycle feedbacks and therefore do not fully represent the net response of the Earth system to anthropogenic CO2 emissions .
Climate-carbon modelling experiments have shown that : ( 1 ) the warming per unit CO2 emitted does not depend on the background CO2 concentration ; ( 2 ) the total allowable emissions for climate stabilization do not depend on the timing of those emissions ; and ( 3 ) the temperature response to a pulse of CO2 is approximately constant on timescales of decades to centuries .
Here we generalize these results and show that the carbon-climate response ( CCR ) , defined as the ratio of temperature change to cumulative carbon emissions , is approximately independent of both the atmospheric CO2 concentration and its rate of change on these timescales .
From observational constraints , we estimate CCR to be in the range 1.0-2 .1 degreesC per trillion tonnes of carbon ( Tt C ) emitted ( 5th to 95th percentiles ) , consistent with twenty-first-century CCR values simulated by climate-carbon models .
Uncertainty in land-use CO2 emissions and aerosol forcing , however , means that higher observationally constrained values can not be excluded .
The CCR , when evaluated from climate-carbon models under idealized conditions , represents a simple yet robust metric for comparing models , which aggregates both climate feedbacks and carbon cycle feedbacks .
CCR is also likely to be a useful concept for climate change mitigation and policy ; by combining the uncertainties associated with climate sensitivity , carbon sinks and climate-carbon feedbacks into a single quantity , the CCR allows CO2-induced global mean temperature change to be inferred directly from cumulative carbon emissions .

[2297] Nonlinear dynamics of lava dome extrusion

During the eruption of the Soufriere Hills volcano , Montserrat ( 1995-99 ) , and several other dome eruptions , shallow seismicity , short-lived explosive eruptions and ground deformation patterns indicating large overpressures ( of several megapascals ) in the uppermost few hundred metres of the volcanic conduit have been observed .
These phenomena can be explained by the nonlinear effects of crystallization and gas loss by permeable flow , which are here incorporated into a numerical model of conduit flow and lava dome extrusion .
Crystallization can introduce strong feedback mechanisms which greatly amplify the effect on extrusion rates of small changes of chamber pressure , conduit dimensions or magma viscosity .
When timescales for magma ascent are comparable to timescales for crystallization , there can be multiple steady solutions for fixed conditions .
Such nonlinear dynamics can cause large changes in dome extrusion rate and pulsatory patterns of dome growth .

[2298] Impact of internal waves on the spatial distribution of Planktothrix rubescens ( cyanobacteria ) in an alpine lake

The vertical and horizontal distribution of the cyanobacterium , Planktothrix rubescens , was studied in a deep alpine lake ( Lac du Bourget ) in a 2-year monitoring program with 11 sampling points , and a 24-h survey at one sampling station .
This species is known to proliferate in the metalimnic layer of numerous deep mesotrophic lakes in temperate areas , and also to produce hepatotoxins .
When looking at the distribution of P. rubescens at the scale of the entire lake , we found large variations ( up to 10 m ) in the depth of the biomass peak in the water column .
These variations were closely correlated to isotherm displacements .
We also found significant variations in the distribution of the cyanobacterial biomass in the northern and southern parts of the lake .
We used a physical modeling approach to demonstrate that two internal wave modes can explain these variations .
Internal waves are generated by wind events , but can still be detected several days after the end of these events .
Finally , our 24-h survey at one sampling point demonstrated that the V1H1 sinusoidal motion could evolve into nonlinear fronts .
All these findings show that internal waves have a major impact on the distribution of P. rubescens proliferating in the metalimnic layer of a deep lake , and that this process could influence the growth of this species by a direct impact on light availability .

[2299] Origins of extrinsic variability in eukaryotic gene expression

Variable gene expression within a clonal population of cells has been implicated in a number of important processes including mutation and evolution , determination of cell fates and the development of genetic disease .
Recent studies have demonstrated that a significant component of expression variability arises from extrinsic factors thought to influence multiple genes simultaneously , yet the biological origins of this extrinsic variability have received little attention .
Here we combine computational modelling with fluorescence data generated from multiple promoter-gene inserts in Saccharomyces cerevisiae to identify two major sources of extrinsic variability .
One unavoidable source arising from the coupling of gene expression with population dynamics leads to a ubiquitous lower limit for expression variability .
A second source , which is modelled as originating from a common upstream transcription factor , exemplifies how regulatory networks can convert noise in upstream regulator expression into extrinsic noise at the output of a target gene .
Our results highlight the importance of the interplay of gene regulatory networks with population heterogeneity for understanding the origins of cellular diversity .

[2300] Under-water superoleophobic Glass : Unexplored role of the surfactant-rich solvent

Preparing low energy liquid-repellant surfaces ( superhydrophobic or superoleophobic ) have attracted tremendous attention of late .
In all these studies , the necessary liquid repellency is achieved by irreversible micro-nano texturing of the surfaces .
Here we show for the first time that a glass surface , placed under water , can be made superoleophobic ( with unprecedented contact angles close to 180 degrees and roll off angles only a few fractions of 1 degree ) by merely changing the surfactant content of the water medium in which the oil ( immiscible in water ) has been dispersed .
Therefore , we propose a paradigm shift in efforts to achieve liquid-repellant systems , namely , altering the solvent characteristics instead of engineering the surfaces .
The effect occurs for a surfactant concentration much larger than the critical micelle concentration , and is associated to strong adsorption of surfactant molecules at the solid surface , triggering an extremely stable Cassie-Baxter like conformation of the oil droplets .

[2301] Efficient aquatic bacterial metabolism of dissolved low-molecular-weight compounds from terrestrial sources

Carboxylic acids ( CAs ) , amino acids ( AAs ) and carbohydrates ( CHs ) in dissolved free forms can be readily assimilated by aquatic bacteria and metabolized at high growth efficiencies .
Previous studies have shown that these low-molecular-weight ( LMW ) substrates are released by phytoplankton but also that unidentified LMW compounds of terrestrial origin is a subsidy for bacterial metabolism in unproductive freshwater systems .
We tested the hypothesis that different terrestrially derived CA , AA and CH compounds can offer substantial support for aquatic bacterial metabolism in fresh waters that are dominated by allochthonous dissolved organic matter ( DOM ) .
Drainage water from three catchments of different characters in the Krycklan experimental area in Northern Sweden were studied at the rising and falling limb of the spring flood , using a 2-week bioassay approach .
A variety of CA , AA and CH compounds were significantly assimilated by bacteria , meeting 15-100 % of the bacterial carbon demand and explaining most of the observed variation in bacterial growth efficiency ( BGE ; R2 = 0.66 ) .
Of the 29 chemical species that was detected , acetate was the most important , representing 45 % of the total bacterial consumption of all LMW compounds .
We suggest that LMW organic compounds in boreal spring flood drainage could potentially support all in situ bacterial production in receiving lake waters during periods of weeks to months after the spring flood .

[2302] Carbon , nitrogen and O2 fluxes associated with the cyanobacterium Nodularia spumigena in the Baltic Sea

Photosynthesis , respiration , N2 fixation and ammonium release were studied directly in Nodularia spumigena during a bloom in the Baltic Sea using a combination of microsensors , stable isotope tracer experiments combined with nanoscale secondary ion mass spectrometry ( nanoSIMS ) and fluorometry .
Cell-specific net C - and N2-fixation rates by N. spumigena were 81.6 + / -6.7 and 11.4 + / -0.9 fmol N per cell per h , respectively .
During light , the net C : N fixation ratio was 8.0 + / -0.8 .
During darkness , carbon fixation was not detectable , but N2 fixation was 5.4 + / -0.4 fmol N per cell per h. Net photosynthesis varied between 0.34 and 250 nmol O2 h-1 in colonies with diameters ranging between 0.13 and 5.0 mm , and it reached the theoretical upper limit set by diffusion of dissolved inorganic carbon to colonies ( > 1 mm ) .
Dark respiration of the same colonies varied between 0.038 and 87 nmol O2 h-1 , and it reached the limit set by O2 diffusion from the surrounding water to colonies ( > 1 mm ) .
N2 fixation associated with N. spumigena colonies ( > 1 mm ) comprised on average 18 % of the total N2 fixation in the bulk water .
Net NH4 + release in colonies equaled 8-33 % of the estimated gross N2 fixation during photosynthesis .
NH4 + concentrations within light-exposed colonies , modeled from measured net NH4 + release rates , were 60-fold higher than that of the bulk .
Hence , N. spumigena colonies comprise highly productive microenvironments and an attractive NH4 + microenvironment to be utilized by other ( micro ) organisms in the Baltic Sea where dissolved inorganic nitrogen is limiting growth .

[2303] The genetic legacy of the Quaternary ice ages

Global climate has fluctuated greatly during the past three million years , leading to the recent major ice ages .
An inescapable consequence for most living organisms is great changes in their distribution , which are expressed differently in boreal , temperate and tropical zones .
Such range changes can be expected to have genetic consequences , and the advent of DNA technology provides most suitable markers to examine these .
Several good data sets are now available , which provide tests of expectations , insights into species colonization and unexpected genetic subdivision and mixture of species .
The genetic structure of human populations may be viewed in the same context .
The present genetic structure of populations , species and communities has been mainly formed by Quaternary ice ages , and genetic , fossil and physical data combined can greatly help our understanding of how organisms were so affected .

[2304] Minimising hydrogen sulphide generation during steam assisted production of heavy oil

The majority of global petroleum is in the form of highly viscous heavy oil .
Traditionally heavy oil in sands at shallow depths is accessed by large scale mining activities .
Recently steam has been used to allow heavy oil extraction with greatly reduced surface disturbance .
However , in situ thermal recovery processes can generate hydrogen sulphide , high levels of which are toxic to humans and corrosive to equipment .
Avoiding hydrogen sulphide production is the best possible mitigation strategy .
Here we use laboratory aquathermolysis to reproduce conditions that may be experienced during thermal extraction .
The results indicate that hydrogen sulphide generation occurs within a specific temperature and pressure window and corresponds to chemical and physical changes in the oil .
Asphaltenes are identified as the major source of sulphur .
Our findings reveal that for high sulphur heavy oils , the generation of hydrogen sulphide during steam assisted thermal recovery is minimal if temperature and pressure are maintained within specific criteria .
This strict pressure and temperature dependence of hydrogen sulphide release can allow access to the world 's most voluminous oil deposits without generating excessive amounts of this unwanted gas product .

[2305] Archaeal ammonia oxidizers and nirS-type denitrifiers dominate sediment nitrifying and denitrifying populations in a subtropical macrotidal estuary

Nitrification and denitrification are key steps in nitrogen ( N ) cycling .
The coupling of these processes , which affects the flow of N in ecosystems , requires close interaction of nitrifying and denitrifying microorganisms , both spatially and temporally .
The diversity , temporal and spatial variations in the microbial communities affecting these processes was examined , in relation to N cycling , across 12 sites in the Fitzroy river estuary , which is a turbid subtropical estuary in central Queensland .
The estuary is a major source of nutrients discharged to the Great Barrier Reef near-shore zone .
Measurement of nitrogen fluxes showed an active denitrifying community during all sampling months .
Archaeal ammonia monooxygenase ( amoA of AOA , functional marker for nitrification ) was significantly more abundant than Betaproteobacterial ( beta-AOB ) amoA .
Nitrite reductase genes , functional markers for denitrification , were dominated by nirS and not nirK types at all sites during the year .
AOA communities were dominated by the soil/sediment cluster of Crenarchaeota , with sequences found in estuarine sediment , marine and terrestrial environments , whereas nirS sequences were significantly more diverse ( where operational taxonomic units were defined at both the threshold of 5 % and 15 % sequence similarity ) and were closely related to sequences originating from estuarine sediments .
Terminal-restriction fragment length polymorphism ( T-RFLP ) analysis revealed that AOA population compositions varied spatially along the estuary , whereas nirS populations changed temporally .
Statistical analysis of individual T-RF dominance suggested that salinity and C : N were associated with the community succession of AOA , whereas the nirS-type denitrifier communities were related to salinity and chlorophyll-alpha in the Fitzroy river estuary .

[2306] Linkage between bacterial and fungal rhizosphere communities in hydrocarbon-contaminated soils is related to plant phylogeny

Phytoremediation is an attractive alternative to excavating and chemically treating contaminated soils .
Certain plants can directly bioremediate by sequestering and/or transforming pollutants , but plants may also enhance bioremediation by promoting contaminant-degrading microorganisms in soils .
In this study , we used high-throughput sequencing of bacterial 16S rRNA genes and the fungal internal transcribed spacer ( ITS ) region to compare the community composition of 66 soil samples from the rhizosphere of planted willows ( Salix spp . )
and six unplanted control samples at the site of a former petrochemical plant .
The Bray-Curtis distance between bacterial communities across willow cultivars was significantly correlated with the distance between fungal communities in uncontaminated and moderately contaminated soils but not in highly contaminated ( HC ) soils ( > 2000 mg kg-1 hydrocarbons ) .
The mean dissimilarity between fungal , but not bacterial , communities from the rhizosphere of different cultivars increased substantially in the HC blocks .
This divergence was partly related to high fungal sensitivity to hydrocarbon contaminants , as demonstrated by reduced Shannon diversity , but also to a stronger influence of willows on fungal communities .
Abundance of the fungal class Pezizomycetes in HC soils was directly related to willow phylogeny , with Pezizomycetes dominating the rhizosphere of a monophyletic cluster of cultivars , while remaining in low relative abundance in other soils .
This has implications for plant selection in phytoremediation , as fungal associations may affect the health of introduced plants and the success of co-inoculated microbial strains .
An integrated understanding of the relationships between fungi , bacteria and plants will enable the design of treatments that specifically promote effective bioremediating communities .

[2307] Metabolic streamlining in an open-ocean nitrogen-fixing cyanobacterium

Nitrogen ( N2 ) - fixing marine cyanobacteria are an important source of fixed inorganic nitrogen that supports oceanic primary productivity and carbon dioxide removal from the atmosphere .
A globally distributed , periodically abundant N2-fixing marine cyanobacterium , UCYN-A , was recently found to lack the oxygen-producing photosystem II complex of the photosynthetic apparatus , indicating a novel metabolism , but remains uncultivated .
Here we show , from metabolic reconstructions inferred from the assembly of the complete UCYN-A genome using massively parallel pyrosequencing of paired-end reads , that UCYN-A has a photofermentative metabolism and is dependent on other organisms for essential compounds .
We found that UCYN-A lacks a number of major metabolic pathways including the tricarboxylic acid cycle , but retains sufficient electron transport capacity to generate energy and reducing power from light .
Unexpectedly , UCYN-A has a reduced genome ( 1.44 megabases ) that is structurally similar to many chloroplasts and some bacteria , in that it contains inverted repeats of ribosomal RNA operons .
The lack of biosynthetic pathways for several amino acids and purines suggests that this organism depends on other organisms , either in close association or in symbiosis , for critical nutrients .
However , size fractionation experiments using natural populations have so far not provided evidence of a symbiotic association with another microorganism .
The UCYN-A cyanobacterium is a paradox in evolution and adaptation to the marine environment , and is an example of the tight metabolic coupling between microorganisms in oligotrophic oceanic microbial communities .

[2308] Climate change : The 20-year forecast

Policy-makers need short-term climate predictions to develop strategies for coping with climate change over the typical two-decade planning horizon .
Two new studies increase our confidence in these predictions .

[2309] Explosive volcanism on the ultraslow-spreading Gakkel ridge , Arctic Ocean

Roughly 60 % of the Earth 's outer surface is composed of oceanic crust formed by volcanic processes at mid-ocean ridges .
Although only a small fraction of this vast volcanic terrain has been visually surveyed or sampled , the available evidence suggests that explosive eruptions are rare on mid-ocean ridges , particularly at depths below the critical point for seawater ( 3,000 m ) .
A pyroclastic deposit has never been observed on the sea floor below 3,000 m , presumably because the volatile content of mid-ocean-ridge basalts is generally too low to produce the gas fractions required for fragmenting a magma at such high hydrostatic pressure .
We employed new deep submergence technologies during an International Polar Year expedition to the Gakkel ridge in the Arctic Basin at 85degrees E , to acquire photographic and video images of ` zero-age ' volcanic terrain on this remote , ice-covered ridge .
Here we present images revealing that the axial valley at 4,000 m water depth is blanketed with unconsolidated pyroclastic deposits , including bubble wall fragments ( limu o Pele ) , covering a large ( > 10 km2 ) area .
At least 13.5 wt % CO2 is necessary to fragment magma at these depths , which is about tenfold the highest values previously measured in a mid-ocean-ridge basalt .
These observations raise important questions about the accumulation and discharge of magmatic volatiles at ultraslow spreading rates on the Gakkel ridge and demonstrate that large-scale pyroclastic activity is possible along even the deepest portions of the global mid-ocean ridge volcanic system .

[2310] Genomic properties of Marine Group A bacteria indicate a role in the marine sulfur cycle

Marine Group A ( MGA ) is a deeply branching and uncultivated phylum of bacteria .
Although their functional roles remain elusive , MGA subgroups are particularly abundant and diverse in oxygen minimum zones and permanent or seasonally stratified anoxic basins , suggesting metabolic adaptation to oxygen-deficiency .
Here , we expand a previous survey of MGA diversity in O2-deficient waters of the Northeast subarctic Pacific Ocean ( NESAP ) to include Saanich Inlet ( SI ) , an anoxic fjord with seasonal O2 gradients and periodic sulfide accumulation .
Phylogenetic analysis of small subunit ribosomal RNA ( 16S rRNA ) gene clone libraries recovered five previously described MGA subgroups and defined three novel subgroups ( SHBH1141 , SHBH391 , and SHAN400 ) in SI .
To discern the functional properties of MGA residing along gradients of O2 in the NESAP and SI , we identified and sequenced to completion 14 fosmids harboring MGA-associated 16S RNA genes from a collection of 46 fosmid libraries sourced from NESAP and SI waters .
Comparative analysis of these fosmids , in addition to four publicly available MGA-associated large-insert DNA fragments from Hawaii Ocean Time-series and Monterey Bay , revealed widespread genomic differentiation proximal to the ribosomal RNA operon that did not consistently reflect subgroup partitioning patterns observed in 16S rRNA gene clone libraries .
Predicted protein-coding genes associated with adaptation to O2-deficiency and sulfur-based energy metabolism were detected on multiple fosmids , including polysulfide reductase ( psrABC ) , implicated in dissimilatory polysulfide reduction to hydrogen sulfide and dissimilatory sulfur oxidation .
These results posit a potential role for specific MGA subgroups in the marine sulfur cycle .

[2311] Morphology of seahorse head hydrodynamically aids in capture of evasive prey

Syngnathid fish ( seahorses , pipefish and sea dragons ) are slow swimmers yet capture evasive prey ( copepods ) using a technique known as the ` pivot ' feeding , which involves rapid movement to overcome prey escape capabilities .
However , this feeding mode functions only at short range and requires approaching very closely to hydrodynamically sensitive prey without triggering an escape .
Here we investigate the role of head morphology on prey capture using holographic and particle image velocimetry ( PIV ) .
We show that head morphology functions to create a reduced fluid deformation zone , minimizing hydrodynamic disturbance where feeding strikes occur ( above the end of the snout ) , and permits syngnathid fish to approach highly sensitive copepod prey ( Acartia tonsa ) undetected .
The results explain how these animals can successfully employ short range ` pivot ' feeding effectively on evasive prey .
The need to approach prey with stealth may have selected for a head shape that produces lower deformation rates than other fish .

[2312] Interior pathways of the North Atlantic meridional overturning circulation

To understand how our global climate will change in response to natural and anthropogenic forcing , it is essential to determine how quickly and by what pathways climate change signals are transported throughout the global ocean , a vast reservoir for heat and carbon dioxide .
Labrador Sea Water ( LSW ) , formed by open ocean convection in the subpolar North Atlantic , is a particularly sensitive indicator of climate change on interannual to decadal timescales .
Hydrographic observations made anywhere along the western boundary of the North Atlantic reveal a core of LSW at intermediate depths advected southward within the Deep Western Boundary Current ( DWBC ) .
These observations have led to the widely held view that the DWBC is the dominant pathway for the export of LSW from its formation site in the northern North Atlantic towards the Equator .
Here we show that most of the recently ventilated LSW entering the subtropics follows interior , not DWBC , pathways .
The interior pathways are revealed by trajectories of subsurface RAFOS floats released during the period 2003-2005 that recorded once-daily temperature , pressure and acoustically determined position for two years , and by model-simulated ` e-floats ' released in the subpolar DWBC .
The evidence points to a few specific locations around the Grand Banks where LSW is most often injected into the interior .
These results have implications for deep ocean ventilation and suggest that the interior subtropical gyre should not be ignored when considering the Atlantic meridional overturning circulation .

[2313] Carbon Emission Flow in Networks

As the human population increases and production expands , energy demand and anthropogenic carbon emission rates have been growing rapidly , and the need to decrease carbon emission levels has drawn increasing attention .
The link between energy production and consumption has required the large-scale transport of energy within energy transmission networks .
Within this energy flow , there is a virtual circulation of carbon emissions .
To understand this circulation and account for the relationship between energy consumption and carbon emissions , this paper introduces the concept of `` carbon emission flow in networks '' and establishes a method to calculate carbon emission flow in networks .
Using an actual analysis of China 's energy pattern , the authors discuss the significance of this new concept , not only as a feasible approach but also as an innovative theoretical perspective .

[2314] Slowing of the Atlantic meridional overturning circulation at 25degrees N

The Atlantic meridional overturning circulation carries warm upper waters into far-northern latitudes and returns cold deep waters southward across the Equator .
Its heat transport makes a substantial contribution to the moderate climate of maritime and continental Europe , and any slowdown in the overturning circulation would have profound implications for climate change .
A transatlantic section along latitude 25degrees N has been used as a baseline for estimating the overturning circulation and associated heat transport .
Here we analyse a new 25degrees N transatlantic section and compare it with four previous sections taken over the past five decades .
The comparison suggests that the Atlantic meridional overturning circulation has slowed by about 30 per cent between 1957 and 2004 .
Whereas the northward transport in the Gulf Stream across 25degrees N has remained nearly constant , the slowing is evident both in a 50 per cent larger southward-moving mid-ocean recirculation of thermocline waters , and also in a 50 per cent decrease in the southward transport of lower North Atlantic Deep Water between 3,000 and 5,000 m in depth .
In 2004 , more of the northward Gulf Stream flow was recirculating back southward in the thermocline within the subtropical gyre , and less was returning southward at depth .

[2315] Productivity-biodiversity relationships depend on the history of community assembly

Identification of the causes of productivity-species diversity relationships remains a central topic of ecological research .
Different relations have been attributed to the influence of disturbance , consumers , niche specialization and spatial scale .
One unexplored cause is the history of community assembly , the partly stochastic sequential arrival of species from a regional pool of potential community members .
The sequence of species arrival can greatly affect community structure .
If assembly sequence interacts with productivity to influence diversity , different sequences can contribute to variation in productivity-diversity relationships .
Here we report a test of this hypothesis by assembling aquatic microbial communities at five productivity levels using four assembly sequences .
About 30 generations after assembly , productivity-diversity relationships took various forms , including a positive , a hump-shaped , a U-shaped and a non-significant pattern , depending on assembly sequence .
This variation resulted from idiosyncratic joint effects of assembly sequence , productivity and species identity on species abundances .
We suggest that the history of community assembly should be added to the growing list of factors that influence productivity-biodiversity patterns .

[2316] Temporary refugia for coral reefs in a warming world

Climate-change impacts on coral reefs are expected to include temperature-induced spatially extensive bleaching events .
Bleaching causes mortality when temperature stress persists but exposure to bleaching conditions is not expected to be spatially uniform at the regional or global scale .
Here we show the first maps of global projections of bleaching conditions based on ensembles of IPCC AR5 ( ref . )
models forced with the new Representative Concentration Pathways ( RCPs ) .
For the three RCPs with larger CO2 emissions ( RCP 4.5 , 6.0 and 8.5 ) the onset of annual bleaching conditions is associated with ~ 510 ppm CO2 equivalent ; the median year of all locations is 2040 for the fossil-fuel aggressive RCP 8.5 .
Spatial patterns in the onset of annual bleaching conditions are similar for each of the RCPs .
For RCP 8.5 , 26 % of reef cells are projected to experience annual bleaching conditions more than 5 years later than the median .
Some of these temporary refugia include the western Indian Ocean , Thailand , the southern Great Barrier Reef and central French Polynesia .
A reduction in the growth of greenhouse-gas emissions corresponding to the difference between RCP 8.5 and 6.0 delays annual bleaching in ~ 23 % of reef cells more than two decades , which might conceivably increase the potential for these reefs to cope with these changes .

[2317] A field guide to bacterial swarming motility

How bacteria regulate , assemble and rotate flagella to swim in liquid media is reasonably well understood .
Much less is known about how some bacteria use flagella to move over the tops of solid surfaces in a form of movement called swarming .
The focus of bacteriology is changing from planktonic to surface environments , and so interest in swarming motility is on the rise .
Here , I review the requirements that define swarming motility in diverse bacterial model systems , including an increase in the number of flagella per cell , the secretion of a surfactant to reduce surface tension and allow spreading , and movement in multicellular groups rather than as individuals .

[2318] Ammonia oxidation and ammonia-oxidizing bacteria and archaea from estuaries with differing histories of hypoxia

Nitrification , the oxidation of NH4 + to NO2 - and subsequently to NO3 - , plays a central role in the nitrogen cycle and is often a critical first step in nitrogen removal from estuarine and coastal environments .
The first and rate-limiting step in nitrification is catalyzed by the enzyme ammonia monooxygenase ( AmoA ) .
We evaluate the relationships between the abundance of ammonia-oxidizing archaea ( AOA ) and ammonia-oxidizing bacteria ( AOB ) amoA genes ; potential nitrification rates and environmental variables to identify factors influencing AOA abundance and nitrifier activity in estuarine sediments .
Our results showed that potential nitrification rates increased as abundance of AOA amoA increased .
In contrast , there was no relationship between potential nitrification rates and AOB amoA abundance .
This suggests that AOA are significant in estuarine nitrogen cycling .
Surprisingly , more of the variability in potential nitrification rates was predicted by salinity and pore water sulfide than by dissolved oxygen history .

[2319] Pervasive density-dependent recruitment enhances seedling diversity in a tropical forest

Negative density-dependent recruitment of seedlings , that is , seeds of a given species are less likely to become established seedlings if the density of that species is high , has been proposed to be an important mechanism contributing to the extraordinary diversity of tropical tree communities because it can potentially prevent any particular species from usurping all available space , either in close proximity to seed sources or at relatively larger spatial scales .
However , density-dependent recruitment does not necessarily enhance community diversity .
Furthermore , although density-dependent effects have been found at some life stages in some species , no study has shown that density-dependent recruitment affects community diversity .
Here we report the results of observations in a lowland , moist forest in the Republic of Panama in which the species identities of 386,027 seeds that arrived at 200 seed traps were compared with the species identities of 13,068 seedlings that recruited into adjacent plots over a 4-year period .
Across the 200 sites , recruit seedling diversity was significantly higher than seed diversity .
Part of this difference was explained by interspecies differences in average recruitment success .
Even after accounting for these differences , however , negative density-dependent recruitment contributes significantly to the increase in diversity from seeds to seedling recruits .

[2320] Growth of non-phototrophic microorganisms using solar energy through mineral photocatalysis

Phototrophy and chemotrophy are two dominant modes of microbial metabolism .
To date , non-phototrophic microorganisms have been excluded from the solar light-centered phototrophic metabolism .
Here we report a pathway that demonstrates a role of light in non-phototrophic microbial activity .
In lab simulations , visible light-excited photoelectrons from metal oxide , metal sulfide , and iron oxide stimulated the growth of chemoautotrophic and heterotrophic bacteria .
The measured bacterial growth was dependent on light wavelength and intensity , and the growth pattern matched the light absorption spectra of the minerals .
The photon-to-biomass conversion efficiency was in the range of 0.13-1 .90 / 1000 .
Similar observations were obtained in a natural soil sample containing both bacteria and semiconducting minerals .
Results from this study provide evidence for a newly identified , but possibly long-existing pathway , in which the metabolisms and growth of non-phototrophic bacteria can be stimulated by solar light through photocatalysis of semiconducting minerals .

[2321] Co-overexpression of geraniol-10-hydroxylase and strictosidine synthase improves anti-cancer drug camptothecin accumulation in Ophiorrhiza pumila

Camptothecin ( CPT ) belongs to a group of monoterpenoidindole alkaloids ( TIAs ) and its derivatives such as irinothecan and topothecan have been widely used worldwide for the treatment of cancer , giving rise to rapidly increasing market demands .
Genes from Catharanthus roseus encoding strictosidine synthase ( STR ) and geraniol 10-hydroxylase ( G10H ) , were separately and simultaneously introduced into Ophiorrhiza pumila hairy roots .
Overexpression of individual G10H ( G lines ) significantly improved CPT production with respect to non-transgenic hairy root cultures ( NC line ) and single STR overexpressing lines ( S lines ) , indicating that G10H plays a more important role in stimulating CPT accumulation than STR in O. pumila .
Furthermore , co-overexpression of G10H and STR genes ( SG Lines ) caused a 56 % increase on the yields of CPT compared to NC line and single gene transgenic lines , showed that simultaneous introduction of G10H and STR can produce a synergistic effect on CPT biosynthesis in O. pumila .
The MTT assay results indicated that CPT extracted from different lines showed similar anti-tumor activity , suggesting that transgenic O. pumila hairy root lines could be an alternative approach to obtain CPT .
To our knowledge , this is the first report on the enhancement of CPT production in O. pumila employing a metabolic engineering strategy .

[2322] Atmospheric Science : A boost in big El Nino

Computer models and theory do not offer a consensus on how El Nino will change under global warming .
Despite this disagreement , a study indicates a robust increase in the frequency of extreme El Nino episodes .

[2323] Spontaneous assembly and real-time growth of micrometre-scale tubular structures from polyoxometalate-based inorganic solids

We report the spontaneous and rapid growth of micrometre-scale tubes from crystals of a metal oxide-based inorganic solid when they are immersed in an aqueous solution containing a low concentration of an organic cation .
A membrane immediately forms around the crystal , and this membrane then forms micrometre-scale tubes that grow with vast aspect ratios at controllable rates along the surface on which the crystal is placed .
The tubes are composed of an amorphous mixture of polyoxometalate-based anions and organic cations .
It is possible for liquid to flow through the tubes , and for the direction of growth and the overall tube diameter to be controlled .
We demonstrate that tube growth is driven by osmotic pressure within the membrane sack around the crystal , which ruptures to release the pressure .
These robust , self-growing , micrometre-scale tubes offer opportunities in many areas , including the growth of microfluidic devices and the self-assembly of metal oxide-based semipermeable membranes for diverse applications .

[2324] Geological constraints on tidal dissipation and dynamical ellipticity of the Earth over the past three million years

The evolution of the Solar System has been shown to be chaotic , which limits our ability to retrace the orbital and precessional motion of the Earth over more than 35-50 Myr ( ref .
2 ) .
Moreover , the precession , obliquity and insolation parameters can also be influenced by secular variations in the tidal dissipation and dynamical ellipticity of the Earth induced by glacial cyclicity and mantle convection .
Here we determine the average values of these dissipative effects over the past three million years .
We have computed the optimal fit between an exceptional palaeoclimate record from the eastern Mediterranean Sea and a model of the astronomical and insolation history by testing a number of values for the tidal dissipation and dynamical ellipticity parameters .
We find that the combined effects of dynamical ellipticity and tidal dissipation were , on average , significantly lower over the past three million years , compared to their present-day values ( determined from artificial satellite data and lunar ranging ) .
This secular variation associated with the Plio-Pleistocene ice load history has caused an average acceleration in the Earth 's rotation over the past 3 Myr , which needs to be considered in the construction of astronomical timescales and in research into the stationarity of phase relations in the ocean-climate system through time .

[2325] reply : Parameters for global ecosystem models

Tian et al. reply -- Our model-based analysis of the effects of interannual climate variability and increasing atmospheric CO2concentration on carbon storage in Amazonian ecosystems focused on CO2exchanges between the atmosphere and undisturbed forests and other upland eco-systems of the region .
Crutzen et al. urge us to add the emissions of isoprene and other volatile organic compounds ( VOCs ) to our analysis .
They argue that ignoring these emissions could lead to an overestimation of annual net carbon storage ( net ecosystem production ) in the Amazon Basin .

[2326] Trends in hourly rainfall statistics in the United States under a warming climate

It is now widely accepted that the mean world climate has warmed since the beginning of climatologically significant anthropogenic emission of greenhouse gases .
Warming may be accompanied by changes in the rate of extreme weather events such as severe storms and drought .
Here we use hourly precipitation data from 13 stations in the 48 contiguous United States to determine trends in the frequency of such events , taking the normalized variance and a renormalized fourth moment of the precipitation measurements , averaged over decades , as objective measures of the frequency and severity of extreme weather .
Using data mostly from the period 1940-1999 but also two longer data series , periods that include the rapid warming that seems to have begun at approximately 1970 , we find a significant increase of 6.5 + / -1.3 % ( 1sigma ) per decade in the normalized variance at a site on the Olympic Peninsula at which it is low .
We place statistical limits on any trend at the remaining 12 sites , where the normalized variance and its uncertainty are larger .
At most sites these limits are consistent with the same rate of linear increase as at the Olympic Peninsula site , but exclude the same rate of percentage increase .

[2327] Toward defining the autoimmune microbiome for type 1 diabetes

Several studies have shown that gut bacteria have a role in diabetes in murine models .
Specific bacteria have been correlated with the onset of diabetes in a rat model .
However , it is unknown whether human intestinal microbes have a role in the development of autoimmunity that often leads to type 1 diabetes ( T1D ) , an autoimmune disorder in which insulin-secreting pancreatic islet cells are destroyed .
High-throughput , culture-independent approaches identified bacteria that correlate with the development of T1D-associated autoimmunity in young children who are at high genetic risk for this disorder .
The level of bacterial diversity diminishes overtime in these autoimmune subjects relative to that of age-matched , genotype-matched , nonautoimmune individuals .
A single species , Bacteroides ovatus , comprised nearly 24 % of the total increase in the phylum Bacteroidetes in cases compared with controls .
Conversely , another species in controls , represented by the human firmicute strain CO19 , represented nearly 20 % of the increase in Firmicutes compared with cases overtime .
Three lines of evidence are presented that support the notion that , as healthy infants approach the toddler stage , their microbiomes become healthier and more stable , whereas , children who are destined for autoimmunity develop a microbiome that is less diverse and stable .
Hence , the autoimmune microbiome for T1D may be distinctly different from that found in healthy children .
These data also suggest bacterial markers for the early diagnosis of T1D .
In addition , bacteria that negatively correlated with the autoimmune state may prove to be useful in the prevention of autoimmunity development in high-risk children .

[2328] Miocene shift of European atmospheric circulation from trade wind to westerlies

The modern European climatic regime is peculiar , due to its unitary winter but diverse summer climates and a pronounced Mediterranean climate in the south .
However , little is known on its evolution in the deep time .
Here we reconstruct the European summer climate conditions in the Tortonian ( 11.62-7 .246 Ma ) using plant fossil assemblages from 75 well-dated sites across Europe .
Our results clearly show that the Tortonian Europe mainly had humid to subhumid summers and no arid climate has been conclusively detected , indicating that the summer-dry Mediterranean-type climate has not yet been established along most of the Mediterranean coast at least by the Tortonian .
More importantly , the reconstructed distribution pattern of summer precipitation reveals that the Tortonian European must have largely been controlled by westerlies , resulting in higher precipitation in the west and the lower in the east .
The Tortonian westerly wind field appears to differ principally from the trade wind pattern of the preceding Serravallian ( 13.82-11 .62 Ma ) , recently deduced from herpetofaunal fossils .
Such a shift in atmospheric circulation , if ever occurred , might result from the development of ice caps and glaciers in the polar region during the Late Miocene global cooling , the then reorganization of oceanic circulation , and/or the Himalayan-Tibetan uplift .

[2329] Marine control of biological production in the eastern equatorial Pacific Ocean

The eastern equatorial Pacific Ocean is the site of approximately 20-50 % of new biological production in the global oceans .
This region is also responsible for the greatest efflux of CO2 from oceans to the atmosphere .
New production , which fixes carbon in response to external inputs of nutrients as opposed to supply from local nutrient recycling , is thought to modulate the CO2 release .
But what controls new production in this region is less clear .
Here we present a quantitative reconstruction of biological production in the surface ocean for this region over the past 130,000 years , which shows that the equatorial Pacific Ocean exhibits higher-frequency variations than the South Equatorial Current .
Comparison of these records with palaeotemperature reconstructions indicates that atmospherically driven mechanisms -- such as aeolian flux of iron or wind-driven changes in upwelling rate of nutrient-rich waters -- are unlikely to have influenced longer-term rates of production in this region .
Instead , biological production appears to be governed by changes in ocean circulation and the chemical composition of upwelled water .

[2330] Effect of organic forms of phosphorus and variable concentrations of sulfide on the metabolic generation of soluble-reactive phosphate by sulfur chemolithoautotrophs : a laboratory study

In aquatic systems , recycling of phosphorus ( P ) is strongly influenced by microbial metabolic responses .
This study was designed to look at the generation of P ( as soluble-reactive phosphate ( SRP ) ) from organic P-enriched sediments by benthic sulfur chemolithoautotrophs .
The study revealed that microbial density was greater in organic P-enriched sediments when compared to sediments without added organic P and the presence of organic P significantly influenced mobilization of SRP from sediment .
Generation of SRP by sediment microbes was cumulative , dependent on time .
The results indicated dissolved sulfide ( S2 - ) to be necessary for initiation of the metabolism-related mobilization of P : there was no statistically significant effect of variations in ambient concentrations of sulfide ( S2 - ) .
The results elucidate possible outcomes of addition of organic P in aquatic ecosystems .

[2331] Evolution of land surface air temperature trend

The global climate has been experiencing significant warming at an unprecedented pace in the past century .
This warming is spatially and temporally non-uniform , and one needs to understand its evolution to better evaluate its potential societal and economic impact .
Here , the evolution of global land surface air temperature trend in the past century is diagnosed using the spatial-temporally multidimensional ensemble empirical mode decomposition method .
We find that the noticeable warming ( > 0.5 K ) started sporadically over the global land and accelerated until around 1980 .
Both the warming rate and spatial structure have changed little since .
The fastest warming in recent decades ( > 0.4 K per decade ) occurred in northern mid-latitudes .
From a zonal average perspective , noticeable warming ( > 0.2 K since 1900 ) first took place in the subtropical and subpolar regions of the Northern Hemisphere , followed by subtropical warming in the Southern Hemisphere .
The two bands of warming in the Northern Hemisphere expanded from 1950 to 1985 and merged to cover the entire Northern Hemisphere .

[2332] Effect of temperature and cycle length on microbial competition in PHB-producing sequencing batch reactor

The impact of temperature and cycle length on microbial competition between polyhydroxybutyrate ( PHB ) - producing populations enriched in feast-famine sequencing batch reactors ( SBRs ) was investigated at temperatures of 20 degreesC and 30 degreesC , and in a cycle length range of 1-18 h .
In this study , the microbial community structure of the PHB-producing enrichments was found to be strongly dependent on temperature , but not on cycle length .
Zoogloea and Plasticicumulans acidivorans dominated the SBRs operated at 20 degreesC and 30 degreesC , respectively .
Both enrichments accumulated PHB more than 75 % of cell dry weight .
Short-term temperature change experiments revealed that P. acidivorans was more temperature sensitive as compared with Zoogloea .
This is particularly true for the PHB degradation , resulting in incomplete PHB degradation in P. acidivorans at 20 degreesC .
Incomplete PHB degradation limited biomass growth and allowed Zoogloea to outcompete P. acidivorans .
The PHB content at the end of the feast phase correlated well with the cycle length at a constant solid retention time ( SRT ) .
These results suggest that to establish enrichment with the capacity to store a high fraction of PHB , the number of cycles per SRT should be minimized independent of the temperature .

[2333] Tumour-on-a-chip provides an optical window into nanoparticle tissue transport

Nanomaterials are used for numerous biomedical applications , but the selection of optimal properties for maximum delivery remains challenging .
Thus , there is a significant interest in elucidating the nano-bio interactions underlying tissue accumulation .
To date , researchers have relied on cell culture or animal models to study nano-bio interactions .
However , cell cultures lack the complexity of biological tissues and animal models are prohibitively slow and expensive .
Here we report a tumour-on-a-chip system where incorporation of tumour-like spheroids into a microfluidic channel permits real-time analysis of nanoparticle ( NP ) accumulation at physiological flow conditions .
We show that penetration of NPs into the tissue is limited by their diameter and that retention can be improved by receptor targeting .
NP transport is predominantly diffusion-limited with convection improving accumulation mostly at the tissue perimeter .
A murine tumour model confirms these findings and demonstrates that the tumour-on-a-chip can be useful for screening optimal NP designs prior to in vivo studies .

[2334] The impact of specialized enemies on the dimensionality of host dynamics

Although individual species persist within a web of interactions with other species , data are usually gathered only from the focal species itself .
We ask whether evidence of a species ' interactions be detected and understood from patterns in the dynamics of that species alone .
Theory predicts that strong coupling between a prey and a specialist predator/parasite should lead to an increase in the dimensionality of the prey 's dynamics , whereas weak coupling should not .
Here we describe a rare test of this prediction .
Two natural enemies were added separately to replicate populations of a moth .
For biological reasons that we identify here , the prediction of increased dimensionality was confirmed when a parasitoid wasp was added ( although this increase had subtleties not previously appreciated ) , but the prediction failed for an added virus .
Thus , an imprint of the interactions may be discerned within time-series data from component species of a system .

[2335] Reductive glutamine metabolism is a function of the alpha-ketoglutarate to citrate ratio in cells

Reductively metabolized glutamine is a major cellular carbon source for fatty acid synthesis during hypoxia or when mitochondrial respiration is impaired .
Yet , a mechanistic understanding of what determines reductive metabolism is missing .
Here we identify several cellular conditions where the alpha-ketoglutarate/citrate ratio is changed due to an altered acetyl-CoA to citrate conversion , and demonstrate that reductive glutamine metabolism is initiated in response to perturbations that result in an increase in the alpha-ketoglutarate/citrate ratio .
Thus , targeting reductive glutamine conversion for a therapeutic benefit might require distinct modulations of metabolite concentrations rather than targeting the upstream signalling , which only indirectly affects the process .

[2336] Climate change : Late leaf fall

The shift of autumnal colouring of leaves to later in the year is due to high ambient atmospheric carbon dioxide concentrations and is independent of temperature .

[2337] Geophysical limits to global wind power

There is enough power in Earth 's winds to be a primary source of near-zero-emission electric power as the global economy continues to grow through the twenty-first century .
Historically , wind turbines are placed on Earth 's surface , but high-altitude winds are usually steadier and faster than near-surface winds , resulting in higher average power densities .
Here , we use a climate model to estimate the amount of power that can be extracted from both surface and high-altitude winds , considering only geophysical limits .
We find wind turbines placed on Earth 's surface could extract kinetic energy at a rate of at least 400 TW , whereas high-altitude wind power could extract more than 1,800 TW .
At these high rates of extraction , there are pronounced climatic consequences .
However , we find that at the level of present global primary power demand ( ~ 18 TW ; ref . )
, uniformly distributed wind turbines are unlikely to substantially affect the Earth 's climate .
It is likely that wind power growth will be limited by economic or environmental factors , not global geophysical limits .

[2338] Ecology : Fungal feedbacks to climate change

Climate change is known to affect the carbon balance of Arctic tundra ecosystems by influencing plant growth and decomposition .
Less predictable climate-driven biotic events , such as disease outbreaks , are now shown to potentially shift these ecosystems from net carbon sinks to sources .

[2339] The role of mineral-dust aerosols in polar temperature amplification

Changes in global temperature are generally more marked in high than in low latitudes , an effect referred to as polar amplification .
Model simulations of future climate suggest a marked response of high-latitude climate due to elevated greenhouse-gas concentrations and associated albedo feedbacks .
However , most climate models struggle to reproduce the amplitude of polar temperature change observed in palaeoclimatic archives and may carry this bias into future predictions .
With the example of mineral dust we show that some atmospheric aerosols experience an amplified high-latitude response to global changes as well , a phenomenon generally not captured by the models .
Using a synthesis of observational and model data we reconstruct atmospheric dust concentrations for Holocene and Last Glacial Maximum ( LGM ) conditions .
Radiative forcing calculations based on our new dust concentration reconstructions suggest that the impact of aerosols in polar areas is underestimated in model simulations for dustier-than-modern conditions .
In the future , some simulations predict an increase in aridity in dust source areas .
Other aerosols such as black carbon and sulphates are likely to increase as well .
We therefore suggest that the inclusion of the amplified high-latitude response of aerosols in atmospheric models would improve the assessment of LGM and future polar amplification .

[2340] Structural and Thermodynamic Factors of Suppressed Interdiffusion Kinetics in Multi-component High-entropy Materials

We report multi-component high-entropy materials as extraordinarily robust diffusion barriers and clarify the highly suppressed interdiffusion kinetics in the multi-component materials from structural and thermodynamic perspectives .
The failures of six alloy barriers with different numbers of elements , from unitary Ti to senary TiTaCrZrAlRu , against the interdiffusion of Cu and Si were characterized , and experimental results indicated that , with more elements incorporated , the failure temperature of the barriers increased from 550 to 900degreesC .
The activation energy of Cu diffusion through the alloy barriers was determined to increase from 110 to 163 kJ/mole .
Mechanistic analyses suggest that , structurally , severe lattice distortion strains and a high packing density caused by different atom sizes , and , thermodynamically , a strengthened cohesion provide a total increase of 55 kJ/mole in the activation energy of substitutional Cu diffusion , and are believed to be the dominant factors of suppressed interdiffusion kinetics through the multi-component barrier materials .

[2341] The role of the SST-thermocline relationship in Indian Ocean Dipole skewness and its response to global warming

A positive Indian Ocean Dipole ( IOD ) tends to have stronger cold sea surface temperature anomalies ( SSTAs ) over the eastern Indian Ocean with greater impacts than warm SSTAs that occur during its negative phase .
Two feedbacks have been suggested as the cause of positive IOD skewness , a positive Bjerknes feedback and a negative SST-cloud-radiation ( SCR ) feedback , but their relative importance is debated .
Using inter-model statistics , we show that the most important process for IOD skewness is an asymmetry in the thermocline feedback , whereby SSTAs respond to thermocline depth anomalies more strongly during the positive phase than negative phase .
This asymmetric thermocline feedback drives IOD skewness despite positive IODs receiving greater damping from the SCR feedback .
In response to global warming , although the thermocline feedback strengthens , its asymmetry between positive and negative IODs weakens .
This behaviour change explains the reduction in IOD skewness that many models display under global warming .

[2342] Global radiative forcing from contrail cirrus

Aviation makes a significant contribution to anthropogenic climate forcing .
The impacts arise from emissions of greenhouse gases , aerosols and nitrogen oxides , and from changes in cloudiness in the upper troposphere .
An important but poorly understood component of this forcing is caused by ` contrail cirrus ' -- a type of cloud that consist of young line-shaped contrails and the older irregularly shaped contrails that arise from them .
Here we use a global climate model that captures the whole life cycle of these man-made clouds to simulate their global coverage , as well as the changes in natural cloudiness that they induce .
We show that the radiative forcing associated with contrail cirrus as a whole is about nine times larger than that from line-shaped contrails alone .
We also find that contrail cirrus cause a significant decrease in natural cloudiness , which partly offsets their warming effect .
Nevertheless , net radiative forcing due to contrail cirrus remains the largest single radiative-forcing component associated with aviation .
Our findings regarding global radiative forcing by contrail cirrus will allow their effects to be included in studies assessing the impacts of aviation on climate and appropriate mitigation options .

[2343] Interactions between bacterial carbon monoxide and hydrogen consumption and plant development on recent volcanic deposits

Patterns of microbial colonization and interactions between microbial processes and vascular plants on volcanic deposits have received little attention .
Previous reports have shown that atmospheric CO and hydrogen contribute significantly to microbial metabolism on Kilauea volcano ( Hawaii ) deposits with varied ages and successional development .
Relationships between CO oxidation and plant communities were not clear , however , since deposit age and vegetation status covaried .
To determine plant-microbe interactions in deposits of uniform ages , CO and hydrogen dynamics have been assayed for unvegetated tephra on a 1959 deposit at Pu'u Puai ( PP-bare ) , at the edge of tree ` islands ' within the PP deposit ( PP-edge ) and within PP tree islands ( PP-canopy ) .
Similar assays have been conducted for vegetated and unvegetated sites on a 1969 Mauna Ulu ( MU ) lava flow .
Net in situ atmospheric CO uptake was highest at PP-edge and PP-bare sites ( 2.2 + / -0.5 and 1.3 + / -0.1 mg CO m-2 day-1 , respectively ) , and least for PP-canopy ( -3.2 + / -0.9 mg CO m-2 day-1 , net emission ) .
Respiration rates , microbial biomass and maximum CO uptake potential showed an opposing pattern .
Comparisons of atmospheric CO uptake and CO2 production rates indicate that CO contributes significantly to microbial metabolism in PP-bare and MU-unvegetated sites , but negligibly where vegetation is well developed .
Nonetheless , maximum potential CO uptake rates indicate that CO oxidizer populations increase with increasing plant biomass and consume CO actively .
Some of these CO oxidizers may contribute to elevated nitrogen fixation rates ( acetylene reduction ) measured within tree islands , and thus , support plant successional development .

[2344] Uncertainty in climate change

Climate modelling has produced varying projections of possible global rises in temperature .
A simple statistical method brings several such projections into closer agreement and includes an indication of potential accuracy .

[2345] Links between eccentricity forcing and the 100,000-year glacial cycle

Variations in the eccentricity ( 100,000 yr ) , obliquity ( 41,000 yr ) and precession ( 23,000 yr ) of Earth 's orbit have been linked to glacial-interglacial climate cycles .
It is generally thought that the 100,000-yr glacial cycles of the past 800,000 yr are a result of orbital eccentricity .
However , the eccentricity cycle produces negligible 100-kyr power in seasonal or mean annual insolation , although it does modulate the amplitude of the precession cycle .
Alternatively , it has been suggested that the recent glacial cycles are driven purely by the obliquity cycle .
Here I use statistical analyses of insolation and the climate of the past five million years to characterize the link between eccentricity and the 100,000-yr glacial cycles .
Using cross-wavelet phase analysis , I show that the relative phase of eccentricity and glacial cycles has been stable since 1.2 Myr ago , supporting the hypothesis that 100,000-yr glacial cycles are paced by eccentricity .
However , I find that the time-dependent 100,000-yr power of eccentricity has been anticorrelated with that of climate since 5 Myr ago , with strong eccentricity forcing associated with weaker power in the 100,000-yr glacial cycle .
I propose that the anticorrelation arises from the strong precession forcing associated with strong eccentricity forcing , which disrupts the internal climate feedbacks that drive the 100,000-yr glacial cycle .
This supports the hypothesis that internally driven climate feedbacks are the source of the 100,000-yr climate variations .

[2346] Pink marine sediments reveal rapid ice melt and Arctic meltwater discharge during Dansgaard-Oeschger warmings

The climate of the last glaciation was interrupted by numerous abrupt temperature fluctuations , referred to as Greenland interstadials and stadials .
During warm interstadials the meridional overturning circulation was active transferring heat to the north , whereas during cold stadials the Nordic Seas were ice-covered and the overturning circulation was disrupted .
Meltwater discharge , from ice sheets surrounding the Nordic Seas , is implicated as a cause of this ocean instability , yet very little is known regarding this proposed discharge during warmings .
Here we show that , during warmings , pink clay from Devonian Red Beds is transported in suspension by meltwater from the surrounding ice sheet and replaces the greenish silt that is normally deposited on the north-western slope of Svalbard during interstadials .
The magnitude of the outpourings is comparable to the size of the outbursts during the deglaciation .
Decreasing concentrations of ice-rafted debris during the interstadials signify that the ice sheet retreats as the meltwater production increases .

[2347] Uncovering loss mechanisms in silver nanoparticle-blended plasmonic organic solar cells

There has been much controversy over the incorporation of organic-ligand-encapsulated plasmonic nanoparticles in the active layer of bulk heterojunction organic solar cells , where both enhancement and detraction in performance have been reported .
Here through comprehensive transient optical spectroscopy and electrical characterization , we demonstrate evidence of traps responsible for performance degradation in plasmonic organic solar cells fabricated with oleylamine-capped silver nanoparticles blended in the poly ( 3-hexylthiophene ) : [ 6,6 ] - phenyl-C 61-butyric acid methyl ester active layer .
Despite an initial increase in exciton generation promoted by the presence of silver nanoparticles , transient absorption spectroscopy reveals no increase in the later free polaron population -- attributed to fast trapping of polarons by nearby nanoparticles .
The increased trap-assisted recombination is also reconfirmed by light intensity-dependent electrical measurements .
These new insights into the photophysics and charge dynamics of plasmonic organic solar cells would resolve the existing controversy and provide clear guidelines for device design and fabrication .

[2348] Significant contribution of insolation to Eemian melting of the Greenland ice sheet

During the Eemian interglacial period , 130,000 to 114,000 years ago , the volume of the Greenland ice sheet was about 30-60 % smaller than the present-day volume .
Summer temperatures in the Arctic region were about 2-4 K higher than today , leading to the suggestion that Eemian conditions could be considered an analogue for future warming , particularly for the future stability of the Greenland ice sheet .
However , Northern Hemisphere insolation was much higher during the Eemian than today , which could affect the reliability of this analogy .
Here we use a high-resolution regional climate model with a realistic ice-sheet surface representation to assess the surface mass balance of the Greenland ice sheet during the Eemian .
Our simulations show that Eemian climate led to an 83 % lower surface mass balance , compared with the preindustrial simulation .
Our sensitivity experiments show that only about 55 % of this change in surface mass balance can be attributed to higher ambient temperatures , with the remaining 45 % caused by higher insolation and associated nonlinear feedbacks .
We show that temperature-melt relations are dependent on changes in insolation .
Hence , we suggest that projections of future Greenland ice loss on the basis of Eemian temperature-melt relations may overestimate the future vulnerability of the ice sheet .

[2349] Thermophilic anaerobic oxidation of methane by marine microbial consortia

The anaerobic oxidation of methane ( AOM ) with sulfate controls the emission of the greenhouse gas methane from the ocean floor .
AOM is performed by microbial consortia of archaea ( ANME ) associated with partners related to sulfate-reducing bacteria .
In vitro enrichments of AOM were so far only successful at temperatures 25 degreesC ; however , energy gain for growth by AOM with sulfate is in principle also possible at higher temperatures .
Sequences of 16S rRNA genes and core lipids characteristic for ANME as well as hints of in situ AOM activity were indeed reported for geothermally heated marine environments , yet no direct evidence for thermophilic growth of marine ANME consortia was obtained to date .
To study possible thermophilic AOM , we investigated hydrothermally influenced sediment from the Guaymas Basin .
In vitro incubations showed activity of sulfate-dependent methane oxidation between 5 and 70 degreesC with an apparent optimum between 45 and 60 degreesC .
AOM was absent at temperatures 75 degreesC .
Long-term enrichment of AOM was fastest at 50 degreesC , yielding a 13-fold increase of methane-dependent sulfate reduction within 250 days , equivalent to an apparent doubling time of 68 days .
The enrichments were dominated by novel ANME-1 consortia , mostly associated with bacterial partners of the deltaproteobacterial HotSeep-1 cluster , a deeply branching phylogenetic group previously found in a butane-amended 60 degreesC-enrichment culture of Guaymas sediments .
The closest relatives ( Desulfurella spp. ; Hippea maritima ) are moderately thermophilic sulfur reducers .
Results indicate that AOM and ANME archaea could be of biogeochemical relevance not only in cold to moderate but also in hot marine habitats .

[2350] Examining the global distribution of dominant archaeal populations in soil

Archaea , primarily Crenarchaeota , are common in soil ; however , the structure of soil archaeal communities and the factors regulating their diversity and abundance remain poorly understood .
Here , we used barcoded pyrosequencing to comprehensively survey archaeal and bacterial communities in 146 soils , representing a multitude of soil and ecosystem types from across the globe .
Relative archaeal abundance , the percentage of all 16S rRNA gene sequences recovered that were archaeal , averaged 2 % across all soils and ranged from 0 % to > 10 % in individual soils .
Soil C : N ratio was the only factor consistently correlated with archaeal relative abundances , being higher in soils with lower C : N ratios .
Soil archaea communities were dominated by just two phylotypes from a constrained clade within the Crenarchaeota , which together accounted for > 70 % of all archaeal sequences obtained in the survey .
As one of these phylotypes was closely related to a previously identified putative ammonia oxidizer , we sampled from two long-term nitrogen ( N ) addition experiments to determine if this taxon responds to experimental manipulations of N availability .
Contrary to expectations , the abundance of this dominant taxon , as well as archaea overall , tended to decline with increasing N .
This trend was coupled with a concurrent increase in known N-oxidizing bacteria , suggesting competitive interactions between these groups .

[2351] Mitigation policy : Health co-benefits

Efforts to tackle climate change have met significant financial and political barriers that have been difficult to overcome .
Research now shows that such measures are justified on grounds other than mitigation of climate change .

[2352] Universal species-area and endemics-area relationships at continental scales

Despite the broad conceptual and applied relevance of how the number of species or endemics changes with area ( the species-area and endemics-area relationships ( SAR and EAR ) ) , our understanding of universality and pervasiveness of these patterns across taxa and regions has remained limited .
The SAR has traditionally been approximated by a power law , but recent theories predict a triphasic SAR in logarithmic space , characterized by steeper increases in species richness at both small and large spatial scales .
Here we uncover such universally upward accelerating SARs for amphibians , birds and mammals across the world 's major landmasses .
Although apparently taxon-specific and continent-specific , all curves collapse into one universal function after the area is rescaled by using the mean range sizes of taxa within continents .
In addition , all EARs approximately follow a power law with a slope close to 1 , indicating that for most spatial scales there is roughly proportional species extinction with area loss .
These patterns can be predicted by a simulation model based on the random placement of contiguous ranges within a domain .
The universality of SARs and EARs after rescaling implies that both total and endemic species richness within an area , and also their rate of change with area , can be estimated by using only the knowledge of mean geographic range size in the region and mean species richness at one spatial scale .

[2353] Subcellular metal imaging identifies dynamic sites of Cu accumulation in Chlamydomonas

We identified a Cu-accumulating structure with a dynamic role in intracellular Cu homeostasis .
During Zn limitation , Chlamydomonas reinhardtii hyperaccumulates Cu , a process dependent on the nutritional Cu sensor CRR1 , but it is functionally Cu deficient .
Visualization of intracellular Cu revealed major Cu accumulation sites coincident with electron-dense structures that stained positive for low pH and polyphosphate , suggesting that they are lysosome-related organelles .
Nano-secondary ion MS showed colocalization of Ca and Cu , and X-ray absorption spectroscopy was consistent with Cu + accumulation in an ordered structure .
Zn resupply restored Cu homeostasis concomitant with reduced abundance of these structures .
Cu isotope labeling demonstrated that sequestered Cu + became bioavailable for the synthesis of plastocyanin , and transcriptome profiling indicated that mobilized Cu became visible to CRR1 .
Cu trafficking to intracellular accumulation sites may be a strategy for preventing protein mismetallation during Zn deficiency and enabling efficient cuproprotein metallation or remetallation upon Zn resupply .

[2354] Population level functional diversity in a microbial community revealed by comparative genomic and metagenomic analyses

In microbial mat communities of Yellowstone hot springs , ribosomal RNA ( rRNA ) sequence diversity patterns indicate the presence of closely related bacterial populations along environmental gradients of temperature and light .
To identify the functional bases for adaptation , we sequenced the genomes of two cyanobacterial ( Synechococcus OS-A and OS-B ' ) isolates representing ecologically distinct populations that dominate at different temperatures and are major primary producers in the mat .
There was a marked lack of conserved large-scale gene order between the two Synechococcus genomes , indicative of extensive genomic rearrangements .
Comparative genomic analyses showed that the isolates shared a large fraction of their gene content at high identity , yet , differences in phosphate and nitrogen utilization pathways indicated that they have adapted differentially to nutrient fluxes , possibly by the acquisition of genes by lateral gene transfer or their loss in certain populations .
Comparisons of the Synechococcus genomes to metagenomic sequences derived from mats where these Synechococcus stains were originally isolated , revealed new facets of microbial diversity .
First , Synechococcus populations at the lower temperature regions of the mat showed greater sequence diversity than those at high temperatures , consistent with a greater number of ecologically distinct populations at the lower temperature .
Second , we found evidence of a specialized population that is apparently very closely related to Synechococcus OS-B ' , but contains genes that function in the uptake of reduced ferrous iron .
In situ expression studies demonstrated that these genes are differentially expressed over the diel cycle , with highest expression when the mats are anoxic and iron may be in the reduced state .
Genomic information from these mat-specific isolates and metagenomic information can be coupled to detect naturally occurring populations that are associated with different functionalities , not always represented by isolates , but which may nevertheless be important for niche partitioning and the establishment of microbial community structure .

[2355] Dependence of riverine nitrous oxide emissions on dissolved oxygen levels

Nitrous oxide is a potent greenhouse gas , and it destroys stratospheric ozone .
Seventeen per cent of agricultural nitrous oxide emissions come from the production of nitrous oxide in streams , rivers and estuaries , in turn a result of inorganic nitrogen input through leaching , runoff and sewage .
The Intergovernmental Panel on Climate Change and global nitrous oxide budgets assume that riverine nitrous oxide emissions increase linearly with dissolved inorganic nitrogen loads , but data are sparse and conflicting .
Here we report measurements over two years of nitrous oxide emissions in the Grand River , Canada , a seventh-order temperate river that is affected by agricultural runoff and outflow from a waste-water treatment plant .
Emissions were disproportionately high in urban areas and during nocturnal summer periods .
Moreover , annual emission estimates that are based on dissolved inorganic nitrogen loads overestimated the measured emissions in a wet year and underestimated them in a dry year .
We found no correlations of nitrous oxide emissions with nitrate or dissolved inorganic nitrogen , but detected negative correlations with dissolved oxygen , suggesting that nitrate concentrations did not limit emissions .
We conclude that future increases in nitrate export to rivers will not necessarily lead to higher nitrous oxide emissions , but more widespread hypoxia most likely will .

[2356] Meteorology : Hurricanes and global warming

Arising from : K. Emanuel Nature 436 , 686-688 ( 2005 ) ; K. Emanuel reply .
Anthropogenic climate change has the potential for slightly increasing the intensity of tropical cyclones through warming of sea surface temperatures .
Emanuel has shown a striking and surprising association between sea surface temperatures and destructiveness by tropical cyclones in the Atlantic and western North Pacific basins .
However , I question his analysis on the following grounds : it does not properly represent the observations described ; the use of his Atlantic bias-removal scheme may not be warranted ; and further investigation of a substantially longer time series for tropical cyclones affecting the continental United States does not show a tendency for increasing destructiveness .
These factors indicate that instead of `` unprecedented '' tropical cyclone activity having occurred in recent years , hurricane intensity was equal or even greater during the last active period in the mid-twentieth century .

[2357] Seasonal changes in predator community switch the direction of selection for prey defences

Insect communities consist of aposematic species with efficient warning colours against predation , as well as abundant examples of crypsis .
To understand such coexistence , we here report results from a field experiment where relative survival of artificial larvae , varying in conspicuousness , was estimated in natural bird communities over an entire season .
This takes advantage of natural variation in the proportion of naive predators : naivety peaks when young birds have just fledged .
We show that the relative benefit of warning signals and crypsis changes accordingly .
When naive birds are rare ( early and late in the season ) , conspicuous warning signals improve survival , but conspicuousness becomes a disadvantage near the fledging time of birds .
Such temporal structuring of predator-prey relationships facilitates the coexistence of diverse antipredatory strategies and helps explain two patterns we found in a 688-species community of Lepidoterans : larval warning signals remain rare and occur disproportionately often in seasons when predators are educated .

[2358] A successful real-time forecast of the 2010-11 La Nina event

During 2010-11 , a La Nina condition prevailed in the tropical Pacific .
An intermediate coupled model ( ICM ) is used to demonstrate a real-time forecast of sea surface temperature ( SST ) evolution during the event .
One of the ICM 's unique features is an empirical parameterization of the temperature of subsurface water entrained into the mixed layer ( Te ) .
This model provided a good prediction , particularly of the `` double dip '' evolution of SST in 2011 that followed the La Nina event peak in October 2010 .
Thermocline feedback , explicitly represented by the relationship between Te and sea level in the ICM , is a crucial factor affecting the second cooling in 2011 .
Large negative Te anomalies were observed to persist in the central equatorial domain during 2010-11 , inducing a cold SST anomaly to the east during July-August 2011 and leading to the development of a La Nina condition thereafter .

[2359] Genomic deletions disrupt nitrogen metabolism pathways of a cyanobacterial diatom symbiont

Diatoms with symbiotic N2-fixing cyanobacteria are often abundant in the oligotrophic open ocean gyres .
The most abundant cyanobacterial symbionts form heterocysts ( specialized cells for N2 fixation ) and provide nitrogen ( N ) to their hosts , but their morphology , cellular locations and abundances differ depending on the host .
Here we show that the location of the symbiont and its dependency on the host are linked to the evolution of the symbiont genome .
The genome of Richelia ( found inside the siliceous frustule of Hemiaulus ) is reduced and lacks ammonium transporters , nitrate/nitrite reductases and glutamine :2 - oxoglutarate aminotransferase .
In contrast , the genome of the closely related Calothrix ( found outside the frustule of Chaetoceros ) is more similar to those of free-living heterocyst-forming cyanobacteria .
The genome of Richelia is an example of metabolic streamlining that has implications for the evolution of N2-fixing symbiosis and potentially for manipulating plant-cyanobacterial interactions .

[2360] Climate change : Out-of-reach goal to limit warming

Even if the world makes long-term cuts to carbon emissions of 90 % relative to 2009 levels , it will miss the target of limiting global warming to 2 degreesC by the end of the millennium .
Only if larger cuts are made -- both long term and globally , starting in the next couple of decades -- at an annual rate of at least 3 % could that target be met .

[2361] The impact of human-environment interactions on the stability of forest-grassland mosaic ecosystems

Forest-grassland mosaic ecosystems can exhibit alternative stables states , whereby under the same environmental conditions , the ecosystem could equally well reside either in one state or another , depending on the initial conditions .
We develop a mathematical model that couples a simplified forest-grassland mosaic model to a dynamic model of opinions about conservation priorities in a population , based on perceptions of ecosystem rarity .
Weak human influence increases the region of parameter space where alternative stable states are possible .
However , strong human influence precludes bistability , such that forest and grassland either co-exist at a single , stable equilibrium , or their relative abundance oscillates .
Moreover , a perturbation can shift the system from a stable state to an oscillatory state .
We conclude that human-environment interactions can qualitatively alter the composition of forest-grassland mosaic ecosystems .
The human role in such systems should be viewed as dynamic , responsive element rather than as a fixed , unchanging entity .

[2362] Epiphytic leafy liverworts diversified in angiosperm-dominated forests

Recent studies have provided evidence for pulses in the diversification of angiosperms , ferns , gymnosperms , and mosses as well as various groups of animals during the Cretaceous revolution of terrestrial ecosystems .
However , evidence for such pulses has not been reported so far for liverworts .
Here we provide new insight into liverwort evolution by integrating a comprehensive molecular dataset with a set of 20 fossil age constraints .
We found evidence for a relative constant diversification rate of generalistic liverworts ( Jungermanniales ) since the Palaeozoic , whereas epiphytic liverworts ( Porellales ) show a sudden increase of lineage accumulation in the Cretaceous .
This difference is likely caused by the pronounced response of Porellales to the ecological opportunities provided by humid , megathermal forests , which were increasingly available as a result of the rise of the angiosperms .

[2363] Formation and fate of oxidized mercury in the upper troposphere and lower stratosphere

Mercury contamination affects many aquatic ecosystems .
The atmosphere is the main transport route for this toxicant .
According to aircraft measurements , the upper troposphere and lower stratosphere are depleted in gaseous elemental mercury but enriched in oxidized , particle-bound mercury .
It is therefore assumed that mercury is oxidized in the stratosphere , and then incorporated into stratospheric aerosols .
However , direct evidence for mercury oxidation in the stratosphere is missing .
Here , we present simultaneous measurements of elemental and oxidized mercury concentrations in air of stratospheric origin , collected during an aircraft campaign over North America and Europe in 2010 .
We show that levels of oxidized mercury are strongly correlated with tracers of stratospheric air .
Concentrations of total and elemental mercury , in contrast , are negatively correlated with these tracers .
Together , the findings indicate that elemental mercury is oxidized in stratospheric air masses .
We develop a numerical model of atmospheric mercury , based on the assumption that mercury is oxidized in the upper troposphere and lower stratosphere .
The resultant vertical profiles -- which depict a rapid decline in mercury concentrations with increasing stratospheric height -- resemble those seen in other studies , and indicate that mercury has a relatively short stratospheric lifetime .
We suggest that following oxidation , mercury is removed from the stratosphere by sedimentation and entrainment processes common to all stratospheric particles .

[2364] The significance of nitrification for oceanic new production

The flux of organic material sinking to depth is a major control on the inventory of carbon in the ocean .
To first order , the oceanic system is at equilibrium such that what goes down must come up .
Because the export flux is difficult to measure directly , it is routinely estimated indirectly by quantifying the amount of phytoplankton growth , or primary production , fuelled by the upward flux of nitrate .
To do so it is necessary to take into account other sources of biologically available nitrogen .
However , the generation of nitrate by nitrification in surface waters has only recently received attention .
Here we perform the first synthesis of open-ocean measurements of the specific rate of surface nitrification and use these to configure a global biogeochemical model to quantify the global role of nitrification .
We show that for much of the world ocean a substantial fraction of the nitrate taken up is generated through recent nitrification near the surface .
At the global scale , nitrification accounts for about half of the nitrate consumed by growing phytoplankton .
A consequence is that many previous attempts to quantify marine carbon export , particularly those based on inappropriate use of the f-ratio ( a measure of the efficiency of the ` biological pump ' ) , are significant overestimates .

[2365] Promoting interdisciplinarity through climate change education

Climate change is a complex scientific and social problem .
Effectively dealing with it presents an immense challenge , yet educating students about it offers educators in science , technology , engineering and mathematics ( STEM ) fruitful opportunities for promoting interdisciplinarity , retaining talented young people in STEM fields and enhancing multiple literacies of all students .
We offer three illustrative examples of interdisciplinary climate change-related STEM education projects .
Each of these models is designed deliberately for implementation in the first two years of collegiate-level STEM courses ; thus , they may be employed in both four - and two-year institutions .
The scientific community can use climate change education opportunities to help further transform STEM education in the US and increase production of high-quality STEM graduates .

[2366] Cooler winters as a possible cause of mass extinctions at the Eocene/Oligocene boundary

The Eocene/Oligocene boundary , at about 33.7 Myr ago , marks one of the largest extinctions of marine invertebrates in the Cenozoic period .
For example , turnover of mollusc species in the US Gulf coastal plain was over 90 % at this time .
A temperature change across this boundary -- from warm Eocene climates to cooler conditions in the Oligocene -- has been suggested as a cause of this extinction event , but climate reconstructions have not provided support for this hypothesis .
Here we report stable oxygen isotope measurements of aragonite in fish otoliths -- ear stones -- collected across the Eocene/Oligocene boundary .
Palaeotemperatures reconstructed from mean otolith oxygen isotope values show little change through this interval , in agreement with previous studies .
From incremental microsampling of otoliths , however , we can resolve the seasonal variation in temperature , recorded as the otoliths continue to accrete new material over the life of the fish .
These seasonal data suggest that winters became about 4 degreesC colder across the Eocene/Oligocene boundary .
We suggest that temperature variability , rather than change in mean annual temperature , helped to cause faunal turnover during this transition .

[2367] Contemporary fisherian life-history evolution in small salmonid populations

The relative importance of natural selection and random drift in phenotypic evolution has been discussed since the introduction of the first population genetic models .
The empirical evidence used to evaluate the evolutionary theories of Fisher and Wright remains obscure because formal tests for neutral divergence or sensitive attempts to separate the effects of selection and drift are scarce , subject to error , and have not been interpreted in the light of well-known population demography .
We combined quantitative genetic and microsatellite DNA analyses to investigate the determinants of contemporary life-history evolution in isolated populations of grayling ( Thymallus thymallus , Salmonidae ) that originated from a common source 80-120 years ago .
Here we show that natural selection was the dominant diversifying agent in the evolution of the quantitative traits .
However , the populations were founded by a small number of individuals , exhibit very low microsatellite-based effective sizes and show genetic imprints of severe ` bottlenecks ' ; which are conditions often suggested to constrain selection and favour drift .
This study demonstrates a very clear case of fisherian evolution in small natural populations across a contemporary timescale .

[2368] Climate extremes and the carbon cycle

The terrestrial biosphere is a key component of the global carbon cycle and its carbon balance is strongly influenced by climate .
Continuing environmental changes are thought to increase global terrestrial carbon uptake .
But evidence is mounting that climate extremes such as droughts or storms can lead to a decrease in regional ecosystem carbon stocks and therefore have the potential to negate an expected increase in terrestrial carbon uptake .
Here we explore the mechanisms and impacts of climate extremes on the terrestrial carbon cycle , and propose a pathway to improve our understanding of present and future impacts of climate extremes on the terrestrial carbon budget .

[2369] The transcriptional regulator BBX24 impairs DELLA activity to promote shade avoidance in Arabidopsis thaliana

In response to canopy shade , plant vegetative structures elongate to gain access to light .
However , the mechanism that allows a plastic transcriptional response to canopy shade light is not fully elucidated .
Here we propose that the activity of PIF4 , a key transcription factor in the shade signalling network , is modulated by the interplay between the BBX24 transcriptional regulator and DELLA proteins , which are negative regulators of the gibberellin ( GA ) signalling pathway .
We show that GA-related targets are enriched among genes responsive to BBX24 under shade and that the shade-response defect in bbx24 mutants is rescued by a GA treatment that promotes DELLA degradation .
BBX24 physically interacts with DELLA proteins and alleviates DELLA-mediated repression of PIF4 activity .
The proposed molecular mechanism provides reversible regulation of the activity of a key transcription factor that may prove especially relevant under fluctuating light conditions .

[2370] Allee effects and pulsed invasion by the gypsy moth

Biological invasions pose considerable threats to the world 's ecosystems and cause substantial economic losses .
A prime example is the invasion of the gypsy moth in the United States , for which more than $ 194 million was spent on management and monitoring between 1985 and 2004 alone .
The spread of the gypsy moth across eastern North America is , perhaps , the most thoroughly studied biological invasion in the world , providing a unique opportunity to explore spatiotemporal variability in rates of spread .
Here we describe evidence for periodic pulsed invasions , defined as regularly punctuated range expansions interspersed among periods of range stasis .
We use a theoretical model with parameter values estimated from long-term monitoring data to show how an interaction between strong Allee effects ( negative population growth at low densities ) and stratified diffusion ( most individuals disperse locally , but a few seed new colonies by long-range movement ) can explain the invasion pulses .
Our results indicate that suppressing population peaks along range borders might greatly slow invasion .

[2371] Shallow fault-zone dilatancy recovery after the 2003 Bam earthquake in Iran

Earthquakes radiate from slip on discrete faults , but also commonly involve distributed deformation within a broader fault zone , especially near the surface .
Variations in rock strain during an earthquake are caused by heterogeneity in the elastic stress before the earthquake , by variable material properties and geometry of the fault zones , and by dynamic processes during the rupture .
Stress changes due to the earthquake slip , both dynamic and static , have long been thought to cause dilatancy in the fault zone that recovers after the earthquake .
Decreases in the velocity of seismic waves passing through the fault zone due to coseismic dilatancy have been observed followed by postseismic seismic velocity increases during healing .
Dilatancy and its recovery have not previously been observed geodetically .
Here we use interferometric analysis of synthetic aperture radar images to measure postseismic surface deformation after the 2003 Bam , Iran , earthquake and show reversal of coseismic dilatancy in the shallow fault zone that causes subsidence of the surface .
This compaction of the fault zone is directly above the patch of greatest coseismic slip at depth .
The dilatancy and compaction probably reflects distributed shear and damage to the material during the earthquake that heals afterwards .
Coseismic and postseismic deformation spread through a fault zone volume may resolve the paradox of shallow slip deficits for some strike-slip fault ruptures .

[2372] Population diversity and the portfolio effect in an exploited species

One of the most pervasive themes in ecology is that biological diversity stabilizes ecosystem processes and the services they provide to society , a concept that has become a common argument for biodiversity conservation .
Species-rich communities are thought to produce more temporally stable ecosystem services because of the complementary or independent dynamics among species that perform similar ecosystem functions .
Such variance dampening within communities is referred to as a portfolio effect and is analogous to the effects of asset diversity on the stability of financial portfolios .
In ecology , these arguments have focused on the effects of species diversity on ecosystem stability but have not considered the importance of biologically relevant diversity within individual species .
Current rates of population extirpation are probably at least three orders of magnitude higher than species extinction rates , so there is a pressing need to clarify how population and life history diversity affect the performance of individual species in providing important ecosystem services .
Here we use five decades of data from Oncorhynchus nerka ( sockeye salmon ) in Bristol Bay , Alaska , to provide the first quantification of portfolio effects that derive from population and life history diversity in an important and heavily exploited species .
Variability in annual Bristol Bay salmon returns is 2.2 times lower than it would be if the system consisted of a single homogenous population rather than the several hundred discrete populations it currently consists of .
Furthermore , if it were a single homogeneous population , such increased variability would lead to ten times more frequent fisheries closures .
Portfolio effects are also evident in watershed food webs , where they stabilize and extend predator access to salmon resources .
Our results demonstrate the critical importance of maintaining population diversity for stabilizing ecosystem services and securing the economies and livelihoods that depend on them .
The reliability of ecosystem services will erode faster than indicated by species loss alone .

[2373] Whole-lake carbon-13 additions reveal terrestrial support of aquatic food webs

Ecosystems are supported by organic carbon from two distinct sources .
Endogenous carbon is produced by photosynthesis within an ecosystem by autotrophic organisms .
Exogenous carbon is produced elsewhere and transported into ecosystems .
Consumers may use exogenous carbon with consequent influences on population dynamics , predator-prey relationships and ecosystem processes .
For example , exogenous inputs provide resources that may enhance consumer abundance beyond levels supported by within-system primary production .
Exogenous fluxes of organic carbon to ecosystems are often large , but this material is recalcitrant and difficult to assimilate , in contrast to endogenously produced organic matter , which is used more easily .
Here we show , by the experimental manipulation of dissolved inorganic 13C in two lakes , that internal primary production is insufficient to support the food webs of these ecosystems .
Additions of NaH13CO3 enriched the 13C content of dissolved inorganic carbon , particulate organic carbon , zooplankton and fish .
Dynamics of 13C indicate that 40-55 % of particulate organic carbon and 22-50 % of zooplankton carbon are derived from terrestrial sources , showing that there is significant subsidy of these ecosystems by organic carbon produced outside their boundaries .

[2374] Integrated metagenomics and network analysis of soil microbial community of the forest timberline

The forest timberline responds quickly and markedly to climate changes , rendering it a ready indicator .
Climate warming has caused an upshift of the timberline worldwide .
However , the impact on belowground ecosystem and biogeochemical cycles remain elusive .
To understand soil microbial ecology of the timberline , we analyzed microbial communities via 16s rRNA Illumina sequencing , a microarray-based tool named GeoChip 4.0 and a random matrix theory-based association network approach .
We selected 24 sampling sites at two vegetation belts forming the timberline of Shennongjia Mountain in Hubei Province of China , a region with extraordinarily rich biodiversity .
We found that temperature , among all of measured environmental parameters , showed the most significant and extensive linkages with microbial biomass , microbial diversity and composition at both taxonomic and functional gene levels , and microbial association network .
Therefore , temperature was the best predictor for microbial community variations in the timberline .
Furthermore , abundances of nitrogen cycle and phosphorus cycle genes were concomitant with NH4 + - N , NO3 -- N and total phosphorus , offering tangible clues to the underlying mechanisms of soil biogeochemical cycles .
As the first glimpse at both taxonomic and functional compositions of soil microbial community of the timberline , our findings have major implications for predicting consequences of future timberline upshift .

[2375] Distinct effects of anthropogenic aerosols on tropical cyclones

Long-term observations have revealed large amplitude fluctuations in the frequency and intensity of tropical cyclones ( TCs ; refs , , , ) , but the anthropogenic impacts , including greenhouse gases and particulate matter pollution , remain to be elucidated .
Here , we show distinct aerosol effects on the development of TCs : the coupled microphysical and radiative effects of anthropogenic aerosols result in delayed development , weakened intensity and early dissipation , but an enlarged rainband and increased precipitation under polluted conditions .
Our results imply that anthropogenic aerosols probably exhibit an opposite effect to that of greenhouse gases , highlighting the necessity of incorporating a realistic microphysical-radiative interaction of aerosols for accurate forecasting and climatic prediction of TCs in atmospheric models .

[2376] Fewer large waves projected for eastern Australia due to decreasing storminess

Extratropical cyclones are the main generators of the strong winds that cause large ocean waves in temperate regions of the world .
The severity of the winds associated with these storms is poorly represented by the coarse resolution of current global climate models ( GCMs ) , making it challenging to produce projections of the future climate of large waves .
Wind data from GCMs can be downscaled in resolution using dynamical methods , resulting in a successful reproduction of the mean wave climate , but a suboptimal reproduction of the storm wave climate .
Projections of large wave occurrence can also be produced using statistical downscaling methods , although such methods have previously been applied only to three or less GCMs , preventing a robust assessment of confidence in projections based on variation between models .
Consequently , considerable uncertainty remains in projections of the future storm wave climate .
Here we apply a statistical diagnostic of large wave occurrence in eastern Australia to 18 different GCMs , allowing model variations to be examined in greater detail than previously possible .
Results are remarkably consistent between different GCMs , allowing anthropogenic influences to be clearly demonstrated , with fewer days with large waves expected to occur in eastern Australia due to increasing greenhouse gas concentrations .

[2377] Defining seasonal marine microbial community dynamics

Here we describe , the longest microbial time-series analyzed to date using high-resolution 16S rRNA tag pyrosequencing of samples taken monthly over 6 years at a temperate marine coastal site off Plymouth , UK .
Data treatment effected the estimation of community richness over a 6-year period , whereby 8794 operational taxonomic units ( OTUs ) were identified using single-linkage preclustering and 21 130 OTUs were identified by denoising the data .
The Alphaproteobacteria were the most abundant Class , and the most frequently recorded OTUs were members of the Rickettsiales ( SAR 11 ) and Rhodobacteriales .
This near-surface ocean bacterial community showed strong repeatable seasonal patterns , which were defined by winter peaks in diversity across all years .
Environmental variables explained far more variation in seasonally predictable bacteria than did data on protists or metazoan biomass .
Change in day length alone explains > 65 % of the variance in community diversity .
The results suggested that seasonal changes in environmental variables are more important than trophic interactions .
Interestingly , microbial association network analysis showed that correlations in abundance were stronger within bacterial taxa rather than between bacteria and eukaryotes , or between bacteria and environmental variables .

[2378] Helium Ion Microscopy ( HIM ) for the imaging of biological samples at sub-nanometer resolution

Scanning Electron Microscopy ( SEM ) has long been the standard in imaging the sub-micrometer surface ultrastructure of both hard and soft materials .
In the case of biological samples , it has provided great insights into their physical architecture .
However , three of the fundamental challenges in the SEM imaging of soft materials are that of limited imaging resolution at high magnification , charging caused by the insulating properties of most biological samples and the loss of subtle surface features by heavy metal coating .
These challenges have recently been overcome with the development of the Helium Ion Microscope ( HIM ) , which boasts advances in charge reduction , minimized sample damage , high surface contrast without the need for metal coating , increased depth of field , and 5 angstrom imaging resolution .
We demonstrate the advantages of HIM for imaging biological surfaces as well as compare and contrast the effects of sample preparation techniques and their consequences on sub-nanometer ultrastructure .

[2379] Regional population collapse followed initial agriculture booms in mid-Holocene Europe

Following its initial arrival in SE Europe 8,500 years ago agriculture spread throughout the continent , changing food production and consumption patterns and increasing population densities .
Here we show that , in contrast to the steady population growth usually assumed , the introduction of agriculture into Europe was followed by a boom-and-bust pattern in the density of regional populations .
We demonstrate that summed calibrated radiocarbon date distributions and simulation can be used to test the significance of these demographic booms and busts in the context of uncertainty in the radiocarbon date calibration curve and archaeological sampling .
We report these results for Central and Northwest Europe between 8,000 and 4,000 cal .
BP and investigate the relationship between these patterns and climate .
However , we find no evidence to support a relationship .
Our results thus suggest that the demographic patterns may have arisen from endogenous causes , although this remains speculative .

[2380] Catastrophic shifts in ecosystems

All ecosystems are exposed to gradual changes in climate , nutrient loading , habitat fragmentation or biotic exploitation .
Nature is usually assumed to respond to gradual change in a smooth way .
However , studies on lakes , coral reefs , oceans , forests and arid lands have shown that smooth change can be interrupted by sudden drastic switches to a contrasting state .
Although diverse events can trigger such shifts , recent studies show that a loss of resilience usually paves the way for a switch to an alternative state .
This suggests that strategies for sustainable management of such ecosystems should focus on maintaining resilience .

[2381] Impact of oceanic-scale interactions on the seasonal modulation of ocean dynamics by the atmosphere

Ocean eddies ( with a size of 100-300 km ) , ubiquitous in satellite observations , are known to represent about 80 % of the total ocean kinetic energy .
Recent studies have pointed out the unexpected role of smaller oceanic structures ( with 1-50 km scales ) in generating and sustaining these eddies .
The interpretation proposed so far invokes the internal instability resulting from the large-scale interaction between upper and interior oceanic layers .
Here we show , using a new high-resolution simulation of the realistic North Pacific Ocean , that ocean eddies are instead sustained by a different process that involves small-scale mixed-layer instabilities set up by large-scale atmospheric forcing in winter .
This leads to a seasonal evolution of the eddy kinetic energy in a very large part of this ocean , with an amplitude varying by a factor almost equal to 2 .
Perspectives in terms of the impacts on climate dynamics and future satellite observational systems are briefly discussed .

[2382] Untangling aerosol effects on clouds and precipitation in a buffered system

It is thought that changes in the concentration of cloud-active aerosol can alter the precipitation efficiency of clouds , thereby changing cloud amount and , hence , the radiative forcing of the climate system .
Despite decades of research , it has proved frustratingly difficult to establish climatically meaningful relationships among the aerosol , clouds and precipitation .
As a result , the climatic effect of the aerosol remains controversial .
We propose that the difficulty in untangling relationships among the aerosol , clouds and precipitation reflects the inadequacy of existing tools and methodologies and a failure to account for processes that buffer cloud and precipitation responses to aerosol perturbations .

[2383] Stability of Climate Networks with Time

The pattern of local daily fluctuations of climate fields such as temperatures and geopotential heights is not stable and hard to predict .
Surprisingly , we find that the observed relations between such fluctuations in different geographical regions yields a very robust network pattern that remains highly stable during time .
Using a new systematic methodology we track the origins of the network stability .
It is found that about half of this network stability is due to the spatial 2D embedding of the network , and half is due to physical coupling between climate in different locations .
We also find that around the equator , the contribution of the physical coupling is significantly less pronounced compared to off-equatorial regimes .
Finally , we show that there is a gradual monotonic modification of the network pattern as a function of altitude difference .

[2384] Expression profiling of the bloom-forming cyanobacterium Nodularia CCY9414 under light and oxidative stress conditions

Massive blooms of toxic cyanobacteria frequently occur in the central Baltic Sea during the summer .
In the surface scum , cyanobacterial cells are exposed to high light ( HL ) intensity , high oxygen partial pressure and other stresses .
To mimic these conditions , cultures of Nodularia spumigena CCY9414 , which is a strain isolated from a cyanobacterial summer bloom in the Baltic Sea , were incubated at a HL intensity of 1200 mumol photons m-2 s-1 or a combination of HL and increased oxygen partial pressure .
Using differential RNA sequencing , we compared the global primary transcriptomes of control and stressed cells .
The combination of oxidative and light stresses induced the expression of twofold more genes compared with HL stress alone .
In addition to the induction of known stress-responsive genes , such as psbA , ocp and sodB , Nodularia cells activated the expression of genes coding for many previously unknown light - and oxidative stress-related proteins .
In addition , the expression of non-protein-coding RNAs was found to be stimulated by these stresses .
Among them was an antisense RNA to the phycocyanin-encoding mRNA cpcBAC and the trans-encoded regulator of photosystem I , PsrR1 .
The large genome capacity allowed Nodularia to harbor more copies of stress-relevant genes such as psbA and small chlorophyll-binding protein genes , combined with the coordinated induction of these and many additional genes for stress acclimation .
Our data provide a first insight on how N. spumigena became adapted to conditions relevant for a cyanobacterial bloom in the Baltic Sea .
The ISME Journal advance online publication , 17 February 2015 ; doi :10.1038 / ismej .2015.16

[2385] Control of crystal nucleation by patterned self-assembled monolayers

An important requirement in the fabrication of advanced inorganic materials , such as ceramics and semiconductors , is control over crystallization .
In principle , the synthetic growth of crystals can be guided by molecular recognition at interfaces .
But it remains a practical challenge to control simultaneously the density and pattern of nucleation events , and the sizes and orientations of the growing crystals .
Here we report a route to crystal formation , using micropatterned self-assembled monolayers , , which affords control over all these parameters .
We begin with a metal substrate patterned with a self-assembled monolayer having areas of different nucleating activity -- in this case , an array of acid-terminated regions separated by methyl-terminated regions .
By immersing the patterned substrates in a calcium chloride solution and exposing them to carbon dioxide , we achieve ordered crystallization of calcite in the polar regions , where the rate of nucleation is fastest ; crystallization can be completely suppressed elsewhere by a suitable choice of array spacing , which ensures that the solution is undersaturated in the methyl-terminated regions .
The nucleation density ( the number of crystals formed per active site ) may be controlled by varying the area and distribution of the polar regions , and we can manipulate the crystallographic orientation by using different functional groups and substrates .

[2386] The worldwide leaf economics spectrum

Bringing together leaf trait data spanning 2,548 species and 175 sites we describe , for the first time at global scale , a universal spectrum of leaf economics consisting of key chemical , structural and physiological properties .
The spectrum runs from quick to slow return on investments of nutrients and dry mass in leaves , and operates largely independently of growth form , plant functional type or biome .
Categories along the spectrum would , in general , describe leaf economic variation at the global scale better than plant functional types , because functional types overlap substantially in their leaf traits .
Overall , modulation of leaf traits and trait relationships by climate is surprisingly modest , although some striking and significant patterns can be seen .
Reliable quantification of the leaf economics spectrum and its interaction with climate will prove valuable for modelling nutrient fluxes and vegetation boundaries under changing land-use and climate .

[2387] Understanding the thermal evolution of deep-water continental margins

Areas of exploration for new hydrocarbons are changing as the hydrocarbon industry seeks new resources for economic and political reasons .
Attention has turned from easily accessible onshore regions such as the Middle East to offshore continental shelves .
Over the past ten years , there has been a marked shift towards deep-water continental margins ( 500-2 ,500 m below sea level ) .
In these more hostile regions , the risk and cost of exploration is higher , but the prize is potentially enormous .
The key to these endeavours is a quantitative understanding of the structure and evolution of the thinned crust and lithosphere that underlie these margins .

[2388] Nitrification driven by bacteria and not archaea in nitrogen-rich grassland soils

The oxidation of ammonia to nitrate , nitrification , is a key process in the nitrogen cycle .
Ammonia-oxidizing archaea are present in large numbers in the ocean and soils , suggesting a potential role for archaea , in addition to bacteria , in the global nitrogen cycle .
However , the importance of archaea to nitrification in agricultural soils is not well understood .
Here , we examine the contribution of ammonia-oxidizing archaea and bacteria to nitrification in six grassland soils in New Zealand using a quantitative polymerase chain reaction .
We show that although ammonia-oxidizing archaea are present in large numbers in these soils , neither their abundance nor their activity increased with the application of an ammonia substrate , suggesting that their abundance was not related to the rate of nitrification .
In contrast , the number of ammonia-oxidizing bacteria increased 3.2-10 .4 - fold and their activity increased 177-fold , in response to ammonia additions .
Indeed , we find a significant relationship between the abundance of ammonia-oxidizing bacteria and the rate of nitrification .
We suggest that nitrification is driven by bacteria rather than archaea in these nitrogen-rich grassland soils .

[2389] Barrier island bistability induced by biophysical interactions

Barrier islands represent about 10 % of the world 's coastline , sustain rich ecosystems , host valuable infrastructure and protect mainland coasts from storms .
Future climate-change-induced increases in the intensity and frequency of major hurricanes and accelerations in sea-level rise will have a significant impact on barrier islands -- leading to increased coastal hazards and flooding -- yet our understanding of island response to external drivers remains limited .
Here , we find that island response is intrinsically bistable and controlled by previously unrecognized dynamics : the competing , and quantifiable , effects of storm erosion , sea-level rise , and the aeolian and biological processes that enable and drive dune recovery .
When the biophysical processes driving dune recovery dominate , islands tend to be high in elevation and vulnerability to storms is minimized .
Alternatively , when the effects of storm erosion dominate , islands may become trapped in a perpetual state of low elevation and maximum vulnerability to storms , even under mild storm conditions .
When sea-level rise dominates , islands become unstable and face possible disintegration .
This quantification of barrier island dynamics is supported by data from the Virginia Barrier Islands , USA and provides a broader context for considering island response to climate change and the likelihood of potentially abrupt transitions in island state .

[2390] The role of quorum sensing signalling in EPS production and the assembly of a sludge community into aerobic granules

Quorum sensing ( QS ) signalling has been extensively studied in single species populations .
However , the ecological role of QS in complex , multi-species communities , particularly in the context of community assembly , has neither been experimentally explored nor theoretically addressed .
Here , we performed a long-term bioreactor ecology study to address the links between QS , organization and composition of complex microbial communities .
The conversion of floccular biomass to highly structured granules was found to be non-random , but strongly and positively correlated with N-acyl-homoserine-lactone ( AHL ) - mediated QS .
Specific AHLs were elevated up to 100-fold and were strongly associated with the initiation of granulation .
Similarly , the levels of particular AHLs decreased markedly during the granular disintegration phase .
Metadata analysis indicated that granulation was accompanied by changes in extracellular polymeric substance ( EPS ) production and AHL add-back studies also resulted in increased EPS synthesis .
In contrast to the commonly reported nanomolar to micromolar signal concentrations in pure culture laboratory systems , QS signalling in the granulation ecosystem occurred at picomolar to nanomolar concentrations of AHLs .
Given that low concentrations of AHLs quantified in this study were sufficient to activate AHL bioreporters in situ in complex granular communities , AHL mediated QS may be a common feature in many natural and engineered ecosystems , where it coordinates community behaviour .

[2391] Glacial-interglacial changes in ocean surface conditions in the Southern Hemisphere

The stable-isotope signatures of oxygen and hydrogen in the water of preserved ice and snow are both widely used to infer local temperatures of past environments .
A derived quantity based on these two signatures , the ` deuterium excess ' , provides additional palaeoclimatic information , as this parameter depends on the meteorological and oceanic characteristics of the water 's source-regions ( in particular , their temperature , and relative humidity ) .
Published studies mainly focus on records from the past 40,000 years .
Here we present a deuterium-excess history obtained from ice cores from Vostok , East Antarctica , spanning the full glacial-interglacial cycle of the past 150,000 years .
The deuterium-excess record shows a strong anticorrelation with the Earth 's orbital obliquity ( ~ 41,000-year periodicity ) , and values are markedly higher during the cold stage 5d ( following the last interglacial ) than during the other cold stages .
We interpret the relationship with obliquity as resulting from changes in the latitudinal insolation gradient affecting ocean surface conditions and , thus , the delivery of moisture to the polar region .
We argue that the high 5d values , relative to other cold stages , are driven by relatively less moisture delivered from high latitudes , and more from low latitudes .
The deuterium-excess in Antarctic precipitation thus provides long-term , spatially integrated information on ocean surface conditions and ocean/atmosphere circulations in the Southern Hemisphere .

[2392] Loss of neuronal 3D chromatin organization causes transcriptional and behavioural deficits related to serotonergic dysfunction

The interior of the neuronal cell nucleus is a highly organized three-dimensional ( 3D ) structure where regions of the genome that are linearly millions of bases apart establish sub-structures with specialized functions .
To investigate neuronal chromatin organization and dynamics in vivo , we generated bitransgenic mice expressing GFP-tagged histone H2B in principal neurons of the forebrain .
Surprisingly , the expression of this chimeric histone in mature neurons caused chromocenter declustering and disrupted the association of heterochromatin with the nuclear lamina .
The loss of these structures did not affect neuronal viability but was associated with specific transcriptional and behavioural deficits related to serotonergic dysfunction .
Overall , our results demonstrate that the 3D organization of chromatin within neuronal cells provides an additional level of epigenetic regulation of gene expression that critically impacts neuronal function .
This in turn suggests that some loci associated with neuropsychiatric disorders may be particularly sensitive to changes in chromatin architecture .

[2393] Thermal tolerance and the global redistribution of animals

The redistribution of life on Earth has emerged as one of the most significant biological responses to anthropogenic climate warming .
Despite being one of the most long-standing puzzles in ecology , we still have little understanding of how temperature sets geographic range boundaries .
Here we show that marine and terrestrial ectotherms differ in the degree to which they fill their potential latitudinal ranges , as predicted from their thermal tolerance limits .
Marine ectotherms more fully occupy the extent of latitudes tolerable within their thermal tolerance limits , and are consequently predicted to expand at their poleward range boundaries and contract at their equatorward boundaries with climate warming .
In contrast , terrestrial ectotherms are excluded from the warmest regions of their latitudinal range ; thus , the equatorward , or ` trailing ' range boundaries , may not shift consistently towards the poles with climate warming .
Using global observations of climate-induced range shifts , we test this prediction and show that in the ocean , shifts at both range boundaries have been equally responsive , whereas on land , equatorward range boundaries have lagged in response to climate warming .
These results indicate that marine species ' ranges conform more closely to their limits of thermal tolerance , and thus range shifts will be more predictable and coherent .
However , on land , warmer range boundaries are not at equilibrium with heat tolerance .
Understanding the relative contribution of factors other than temperature in controlling equatorward range limits is critical for predicting distribution changes , with implications for population and community viability .

[2394] Integrating abundance and functional traits reveals new global hotspots of fish diversity

Species richness has dominated our view of global biodiversity patterns for centuries .
The dominance of this paradigm is reflected in the focus by ecologists and conservation managers on richness and associated occurrence-based measures for understanding drivers of broad-scale diversity patterns and as a biological basis for management .
However , this is changing rapidly , as it is now recognized that not only the number of species but the species present , their phenotypes and the number of individuals of each species are critical in determining the nature and strength of the relationships between species diversity and a range of ecological functions ( such as biomass production and nutrient cycling ) .
Integrating these measures should provide a more relevant representation of global biodiversity patterns in terms of ecological functions than that provided by simple species counts .
Here we provide comparisons of a traditional global biodiversity distribution measure based on richness with metrics that incorporate species abundances and functional traits .
We use data from standardized quantitative surveys of 2,473 marine reef fish species at 1,844 sites , spanning 133 degrees of latitude from all ocean basins , to identify new diversity hotspots in some temperate regions and the tropical eastern Pacific Ocean .
These relate to high diversity of functional traits amongst individuals in the community ( calculated using Rao 's Q ) , and differ from previously reported patterns in functional diversity and richness for terrestrial animals , which emphasize species-rich tropical regions only .
There is a global trend for greater evenness in the number of individuals of each species , across the reef fish species observed at sites ( ` community evenness ' ) , at higher latitudes .
This contributes to the distribution of functional diversity hotspots and contrasts with well-known latitudinal gradients in richness .
Our findings suggest that the contribution of species diversity to a range of ecosystem functions varies over large scales , and imply that in tropical regions , which have higher numbers of species , each species contributes proportionally less to community-level ecological processes on average than species in temperate regions .
Metrics of ecological function usefully complement metrics of species diversity in conservation management , including when identifying planning priorities and when tracking changes to biodiversity values .

[2395] Metagenomic analysis of a permafrost microbial community reveals a rapid response to thaw

Permafrost contains an estimated 1672 Pg carbon ( C ) , an amount roughly equivalent to the total currently contained within land plants and the atmosphere .
This reservoir of C is vulnerable to decomposition as rising global temperatures cause the permafrost to thaw .
During thaw , trapped organic matter may become more accessible for microbial degradation and result in greenhouse gas emissions .
Despite recent advances in the use of molecular tools to study permafrost microbial communities , their response to thaw remains unclear .
Here we use deep metagenomic sequencing to determine the impact of thaw on microbial phylogenetic and functional genes , and relate these data to measurements of methane emissions .
Metagenomics , the direct sequencing of DNA from the environment , allows the examination of whole biochemical pathways and associated processes , as opposed to individual pieces of the metabolic puzzle .
Our metagenome analyses reveal that during transition from a frozen to a thawed state there are rapid shifts in many microbial , phylogenetic and functional gene abundances and pathways .
After one week of incubation at 5 degreesC , permafrost metagenomes converge to be more similar to each other than while they are frozen .
We find that multiple genes involved in cycling of C and nitrogen shift rapidly during thaw .
We also construct the first draft genome from a complex soil metagenome , which corresponds to a novel methanogen .
Methane previously accumulated in permafrost is released during thaw and subsequently consumed by methanotrophic bacteria .
Together these data point towards the importance of rapid cycling of methane and nitrogen in thawing permafrost .

[2396] Short-lived uncertainty ?

Short-lived greenhouse gases and black-carbon aerosols have contributed to past climate warming .
Curbing their emissions and quantifying the forcing by all short-lived components could both mitigate climate change in the short term and help to refine projections of global warming .

[2397] Bacterial community responses to a gradient of alkaline mountaintop mine drainage in Central Appalachian streams

Microbial community composition and diversity change along chemical gradients , leading to the expectation that microbial community information might provide new gradient characterizations .
Here we examine stream bacteria composition and diversity along a strong chemical gradient in Central Appalachian streams .
Coal mining in the region generates alkaline mine drainage ( AlkMD ) , causing dramatic increases in conductivity , alkalinity , sulfate and metals sufficient to degrade stream macrobiota communities throughout the ecoregion .
In this study , we examined the relationship between water and biofilm chemistry and biofilm bacteria taxonomic composition in streams where active and reclaimed surface coal mines occupied 0-96 % of watershed surface area .
We incubated wood veneers in each stream site for 4 months to develop biofilms on similar substrates .
We sampled water chemistry at the time of deployment and collection , and after 1 month .
Following incubation , we collected biofilms for microbial and chemical characterization .
Microbial composition was determined by pyrosequencing 16S rRNA amplicons .
Biofilm subsamples were analyzed by inductively coupled plasma mass spectrometry to determine metal concentrations .
Our results show that microbial community composition differed significantly between AlkMD-exposed and AlkMD-unexposed sites , and that compositional dissimilarity increased with AlkMD loading .
Diversity was not correlated with pH or extent of upstream mining , but instead correlated with biofilm concentrations of Cd , Mn , Zn and Ni .
Within mined sites , the extent of upstream mining was negatively correlated with taxonomic richness .
Despite major compositional shifts , functional capacity predicted with PICRUSt ( Phylogenetic Investigation of Communities by Reconstruction of Unobserved States ) correlated with mining in only 3 of 43 level-2 KEGG ( Kyoto Encyclopedia of Genes and Genomes ) Orthology groups .
The ISME Journal advance online publication , 12 December 2014 ; doi :10.1038 / ismej .2014.222

[2398] Particle-size distributions and seasonal diversity of allergenic and pathogenic fungi in outdoor air

Fungi are ubiquitous in outdoor air , and their concentration , aerodynamic diameters and taxonomic composition have potentially important implications for human health .
Although exposure to fungal allergens is considered a strong risk factor for asthma prevalence and severity , limitations in tracking fungal diversity in air have thus far prevented a clear understanding of their human pathogenic properties .
This study used a cascade impactor for sampling , and quantitative real-time PCR plus 454 pyrosequencing for analysis to investigate seasonal , size-resolved fungal communities in outdoor air in an urban setting in the northeastern United States .
From the 20 libraries produced with an average of ~ 800 internal transcribed spacer ( ITS ) sequences ( total 15 326 reads ) , 12 864 and 11 280 sequences were determined to the genus and species levels , respectively , and 558 different genera and 1172 different species were identified , including allergens and infectious pathogens .
These analyses revealed strong relationships between fungal aerodynamic diameters and features of taxonomic compositions .
The relative abundance of airborne allergenic fungi ranged from 2.8 % to 10.7 % of total airborne fungal taxa , peaked in the fall , and increased with increasing aerodynamic diameter .
Fungi that can cause invasive fungal infections peaked in the spring , comprised 0.1-1 .6 % of fungal taxa and typically increased in relative abundance with decreasing aerodynamic diameter .
Atmospheric fungal ecology is a strong function of aerodynamic diameter , whereby through physical processes , the size influences the diversity of airborne fungi that deposit in human airways and the efficiencies with which specific groups of fungi partition from outdoor air to indoor environments .

[2399] Methane uptake in forest soils along an urban-to-rural gradient in Pearl River Delta , South China

We investigated soil CH4 fluxes from six forests along an urban-to-rural gradient in Guangzhou City metropolitan area , South China .
The most significant CH4 consumption was found in the rural site , followed by suburban , and then urban forest sites .
The rates of CH4 uptake were significantly higher ( by 38 % and 44 % , respectively for mixed forest and broadleaf forest ) in the rural than in the urban forest site .
The results indicate that soil water filled pore space ( WFPS ) is the primary factor for controlling CH4 consumption in subtropical forests .
The reductions of soil CH4 uptake in urban forests were also influenced by the higher rates of atmospheric nitrogen ( N ) deposition and increases in soil nitrate ( NO3 - ) and aluminum ( Al3 + ) contents as a result of urbanization .
Results from this work suggest that environmental changes associated with urbanization could decrease soil CH4 consumption in subtropical forests and potentially contribute to increase of atmospheric CH4 concentration .

[2400] Facing the future

Global Change Biol .
14 , 2910 - 2922 ( 2008 ) The influence of elevated atmospheric CO 2 on soil 's ability to store carbon is a matter of great debate , with some studies reporting increases in soil organic matter -- and hence carbon storage -- and others , no change or even a loss .
Now , a nine-year investigation suggests that increased litterfall could enhance soil carbon storage in a greenhouse world .

[2401] Culture and molecular-based profiles show shifts in bacterial communities of the upper respiratory tract that occur with age

The upper respiratory tract ( URT ) is a crucial site for host defense , as it is home to bacterial communities that both modulate host immune defense and serve as a reservoir of potential pathogens .
Young children are at high risk of respiratory illness , yet the composition of their URT microbiota is not well understood .
Microbial profiling of the respiratory tract has traditionally focused on culturing common respiratory pathogens , whereas recent culture-independent microbiome profiling can only report the relative abundance of bacterial populations .
In the current study , we used both molecular profiling of the bacterial 16S rRNA gene and laboratory culture to examine the bacterial diversity from the oropharynx and nasopharynx of 51 healthy children with a median age of 1.1 years ( range 1-4 .5 years ) along with 19 accompanying parents .
The resulting profiles suggest that in young children the nasopharyngeal microbiota , much like the gastrointestinal tract microbiome , changes from an immature state , where it is colonized by a few dominant taxa , to a more diverse state as it matures to resemble the adult microbiota .
Importantly , this difference in bacterial diversity between adults and children accompanies a change in bacterial load of three orders of magnitude .
This indicates that the bacterial communities in the nasopharynx of young children have a fundamentally different structure from those in adults and suggests that maturation of this community occurs sometime during the first few years of life , a period that includes ages at which children are at the highest risk for respiratory disease .
The ISME Journal advance online publication , 9 January 2015 ; doi :10.1038 / ismej .2014.250

[2402] Vulnerability of coastal aquifers to groundwater use and climate change

Climate change and human population growth are expected to have substantial impacts on global water resources throughout the twenty-first century .
Coastal aquifers are a nexus of the world 's oceanic and hydrologic ecosystems and provide a water source for the more than one billion people living in coastal regions .
Saltwater intrusion caused by excessive groundwater extraction is already impacting diverse regions of the globe .
Synthesis studies and detailed simulations have predicted that rising sea levels could negatively impact coastal aquifers through saltwater intrusion and/or inundation of coastal regions .
However , the relative vulnerability of coastal aquifers to groundwater extraction and sea-level rise has not been systematically examined .
Here we show that coastal aquifers are more vulnerable to groundwater extraction than to predicted sea-level rise under a wide range of hydrogeologic conditions and population densities .
Only aquifers with very low hydraulic gradients are more vulnerable to sea-level rise and these regions will be impacted by saltwater inundation before saltwater intrusion .
Human water use is a key driver in the hydrology of coastal aquifers , and efforts to adapt to sea-level rise at the expense of better water management are misguided .

[2403] Water and the martian landscape

Over the past 30 years , the water-generated landforms and landscapes of Mars have been revealed in increasing detail by a succession of spacecraft missions .
Recent data from the Mars Global Surveyor mission confirm the view that brief episodes of water-related activity , including glaciation , punctuated the geological history of Mars .
The most recent of these episodes seems to have occurred within the past 10 million years .
These new results are anomalous in regard to the prevailing view that the martian surface has been continuously extremely cold and dry , much as it is today , for the past 3.9 billion years .
Interpretations of the new data are controversial , but explaining the anomalies in a consistent manner leads to potentially fruitful hypotheses for understanding the evolution of Mars in relation to Earth .

[2404] Past temperature and delta18O of surface ocean waters inferred from foraminiferal Mg/Ca ratios

Determining the past record of temperature and salinity of ocean surface waters is essential for understanding past changes in climate , such as those which occur across glacial-interglacial transitions .
As a useful proxy , the oxygen isotope composition ( delta18O ) of calcite from planktonic foraminifera has been shown to reflect both surface temperature and seawater delta18O , itself an indicator of global ice volume and salinity .
In addition , magnesium/calcium ( Mg/Ca ) ratios in foraminiferal calcite show a temperature dependence due to the partitioning of Mg during calcification .
Here we demonstrate , in a field-based calibration experiment , that the variation of Mg/Ca ratios with temperature is similar for eight species of planktonic foraminifera ( when accounting for Mg dissolution effects ) .
Using a multi-species record from the Last Glacial Maximum in the North Atlantic Ocean we found that past temperatures reconstructed from Mg/Ca ratios followed the two other palaeotemperature proxies : faunal abundance and alkenone saturation .
Moreover , combining Mg/Ca and delta18O data from the same faunal assemblage , we show that reconstructed surface water delta18O from all foraminiferal species record the same glacial-interglacial change -- representing changing hydrography and global ice volume .
This reinforces the potential of this combined technique in probing past ocean-climate interactions .

[2405] Electrical conductivity during incipient melting in the oceanic low-velocity zone

The low-viscosity layer in the upper mantle , the asthenosphere , is a requirement for plate tectonics .
The seismic low velocities and the high electrical conductivities of the asthenosphere are attributed either to subsolidus , water-related defects in olivine minerals or to a few volume per cent of partial melt , but these two interpretations have two shortcomings .
First , the amount of water stored in olivine is not expected to be higher than 50 parts per million owing to partitioning with other mantle phases ( including pargasite amphibole at moderate temperatures ) and partial melting at high temperatures .
Second , elevated melt volume fractions are impeded by the temperatures prevailing in the asthenosphere , which are too low , and by the melt mobility , which is high and can lead to gravitational segregation .
Here we determine the electrical conductivity of carbon-dioxide-rich and water-rich melts , typically produced at the onset of mantle melting .
Electrical conductivity increases modestly with moderate amounts of water and carbon dioxide , but it increases drastically once the carbon dioxide content exceeds six weight per cent in the melt .
Incipient melts , long-expected to prevail in the asthenosphere , can therefore produce high electrical conductivities there .
Taking into account variable degrees of depletion of the mantle in water and carbon dioxide , and their effect on the petrology of incipient melting , we calculated conductivity profiles across the asthenosphere for various tectonic plate ages .
Several electrical discontinuities are predicted and match geophysical observations in a consistent petrological and geochemical framework .
In moderately aged plates ( more than five million years old ) , incipient melts probably trigger both the seismic low velocities and the high electrical conductivities in the upper part of the asthenosphere , whereas in young plates , where seamount volcanism occurs , a higher degree of melting is expected .

[2406] The impact of hot charge carrier mobility on photocurrent losses in polymer-based solar cells

A typical signature of charge extraction in disordered organic systems is dispersive transport , which implies a distribution of charge carrier mobilities that negatively impact on device performance .
Dispersive transport has been commonly understood to originate from a time-dependent mobility of hot charge carriers that reduces as excess energy is lost during relaxation in the density of states .
In contrast , we show via photon energy , electric field and film thickness independence of carrier mobilities that the dispersive photocurrent in organic solar cells originates not from the loss of excess energy during hot carrier thermalization , but rather from the loss of carrier density to trap states during transport .
Our results emphasize that further efforts should be directed to minimizing the density of trap states , rather than controlling energetic relaxation of hot carriers within the density of states .

[2407] Evolution of long-toothed fishes and the changing nature of fish-benthos interactions on coral reefs

Interactions between fishes and the benthos have shaped the development of marine ecosystems since at least the early Mesozoic .
Here , using the morphology of fish teeth as an indicator of feeding abilities , we quantify changes over the last 240 million years of reef fish evolution .
Fossil and extant coral reef fish assemblages reveal exceptional stasis in tooth design over time , with one notable exception , a distinct long-toothed form .
Arising only in the last 40 million years , these long-toothed fishes have bypassed the invertebrate link in the food chain , feeding directly on benthic particulate material .
With the appearance of elongated teeth , these specialized detritivores have moved from eating invertebrates to eating the food of invertebrates .
Over evolutionary time , fishes have slid back down the food chain .

[2408] Shale gas can be a double-edged sword for climate change

Shale gas can be a powerful tool in combating climate change .
However , its exploitation may also lead to undesired environmental effects that can conversely worsen climate change .

[2409] Global warming and amphibian losses ; The proximate cause of frog declines ?

( Reply )
Alford et al. question the working model underlying our test for a link between global warming and amphibian disappearances , and Di Rosa et al. criticize our emphasis on a single proximate agent , the chytrid fungus Batrachochytrium dendrobatidis .
Both teams report key pieces of the amphibian-decline puzzle and new evidence from different parts of the world that climate change is a factor in these losses .
Here we show why our working model was appropriate and highlight the complexity of the imminent threat to species survival that results as global warming conspires with various other agents .

[2410] Palaeoceanographic implications of genetic variation in living North Atlantic Neogloboquadrina pachyderma

The shells of the planktonic foraminifer Neogloboquadrina pachyderma have become a classical tool for reconstructing glacial-interglacial climate conditions in the North Atlantic Ocean .
Palaeoceanographers utilize its left - and right-coiling variants , which exhibit a distinctive reciprocal temperature and water mass related shift in faunal abundance both at present and in late Quaternary sediments .
Recently discovered cryptic genetic diversity in planktonic foraminifers now poses significant questions for these studies .
Here we report genetic evidence demonstrating that the apparent ` single species ' shell-based records of right-coiling N. pachyderma used in palaeoceanographic reconstructions contain an alternation in species as environmental factors change .
This is reflected in a species-dependent incremental shift in right-coiling N. pachyderma shell calcite delta18O between the Last Glacial Maximum and full Holocene conditions .
Guided by the percentage dextral coiling ratio , our findings enhance the use of delta18O records of right-coiling N. pachyderma for future study .
They also highlight the need to genetically investigate other important morphospecies to refine their accuracy and reliability as palaeoceanographic proxies .

[2411] Feast and famine -- microbial life in the deep-sea bed

The seabed is a diverse environment that ranges from the desert-like deep seafloor to the rich oases that are present at seeps , vents , and food falls such as whales , wood or kelp .
As well as the sedimentation of organic material from above , geological processes transport chemical energy -- hydrogen , methane , hydrogen sulphide and iron -- to the seafloor from the subsurface below , which provides a significant proportion of the deep-sea energy .
At the sites on the seafloor where chemical energy is delivered , rich and diverse microbial communities thrive .
However , most subsurface microorganisms live in conditions of extreme energy limitation , with mean generation times of up to thousands of years .
Even in the most remote subsurface habitats , temperature rather than energy seems to set the ultimate limit for life , and in the deep biosphere , where energy is most depleted , life might even be based on the cleavage of water by natural radioisotopes .
Here , we review microbial biodiversity and function in these intriguing environments .

[2412] Dual RNA-seq of pathogen and host

A comprehensive understanding of host-pathogen interactions requires a knowledge of the associated gene expression changes in both the pathogen and the host .
Traditional , probe-dependent approaches using microarrays or reverse transcription PCR typically require the pathogen and host cells to be physically separated before gene expression analysis .
However , the development of the probe-independent RNA sequencing ( RNA-seq ) approach has begun to revolutionize transcriptomics .
Here , we assess the feasibility of taking transcriptomics one step further by performing ` dual RNA-seq ' , in which gene expression changes in both the pathogen and the host are analysed simultaneously .

[2413] Glacial cycles : Atmosphere and ocean chemistry

Low atmospheric carbon dioxide concentrations during glacial periods must have been accompanied by changes in surface-ocean carbonate chemistry .
But it is unclear whether concurrent changes in the deep sea contributed to the glacial carbon dioxide decline .

[2414] Biodiversity in the dark

A multitude of organisms makes soils the fertile factories of food and fibre production , decomposition and nutrient cycling that they are .
But tying changes in soil biodiversity to shifts in ecosystem function is a daunting task .

[2415] Substrate-induced growth and isolation of Acidobacteria from acidic Sphagnum peat

Fluorescence in situ hybridization ( FISH ) was applied to estimate the population size of the poorly characterized phylum Acidobacteria in acidic peat sampled from nine different Sphagnum-dominated wetlands of Northern Russia .
The cell numbers of these bacteria in oxic peat layers ranged from 0.4 x 106 to 1.3 x 107 cells per g of wet peat , comprising up to 4 % of total bacterial cells .
Substrate-induced growth of acidobacteria was observed after amendment of peat samples with glucose , pectin , xylan , starch , ethanol and methanol , while weak or no response was obtained for acetate , pyruvate , mannitol and cellobiose .
Using low-nutrient media and FISH-mediated monitoring of the isolation procedure , we succeeded in obtaining nine strains of acidobacteria in pure cultures .
These strains belonged to subdivisions 1 and 3 of the Acidobacteria and represented strictly aerobic , heterotrophic organisms .
Except for methanol , the substrate utilization patterns of these isolates matched the results obtained in our substrate-amendment experiments with native peat .
All strains were also capable of utilizing galacturonic acid , a characteristic component of the cell wall in Sphagnum spp , which is released during moss decomposition .
Most isolates from subdivision 1 were truly acidophilic organisms with the growth optimum at pH 3.5-4 .5 , while the isolates from subdivision 3 grew optimally at pH 5.5-6 .5 .
Another important phenotypic trait of novel strains was their capability of active growth at low temperatures .
Both acidophily and low-temperature growth are consistent with the occurrence of acidobacteria in cold and acidic northern wetlands .

[2416] Sunlight modulates the relative importance of heterotrophic bacteria and picophytoplankton in DMSP-sulphur uptake

There is a large body of evidence supporting a major role of heterotrophic bacteria in dimethylsulphoniopropionate ( DMSP ) utilisation as a source of reduced sulphur .
However , a role for phototrophic microorganisms has been only recently described and little is known about their contribution to DMSP consumption and the potential modulating effects of sunlight .
In an attempt to ascertain the relative quantitative roles of heterotrophic bacteria and picophytoplankton in the osmoheterotrophic uptake of DMSP-sulphur upon exposure to natural sunlight conditions , we incubated northwestern Mediterranean waters under various optical filters and used an array of bulk and single-cell activity methods to trace the fate of added 35S-DMSP .
Flow cytometry cell sorting confirmed dark 35S uptake by Prochlorococcus , Synechococcus and heterotrophic bacteria , the latter being the most efficient in terms of uptake on a cell volume basis .
Under exposure to full sunlight , however , the relative contribution of Synechococcus was significantly enhanced , mainly because of the inhibition of heterotrophic bacteria .
Microautoradiography showed a strong increase in the proportion of Synechococcus cells actively taking up 35S-DMSP , which , after full sunlight exposure , made up to 15 % of total active Bacteria .
Parallel incubations with 3H-leucine generally showed no clear responses to light .
Finally , size-fractionated assimilation experiments showed greater relative cyanobacterial assimilation during the day than at night compared with that of heterotrophic bacteria .
Our results show for the first time a major influence of sunlight in regulating the competition among autotrophic and heterotrophic picoplankton for DMSP uptake at both the daily and seasonal time scales .

[2417] Fitness and stability of obligate cross-feeding interactions that emerge upon gene loss in bacteria

Cross-feeding interactions , in which bacterial cells exchange costly metabolites to the benefit of both interacting partners , are very common in the microbial world .
However , it generally remains unclear what maintains this type of interaction in the presence of non-cooperating types .
We investigate this problem using synthetic cross-feeding interactions : by simply deleting two metabolic genes from the genome of Escherichia coli , we generated genotypes that require amino acids to grow and release other amino acids into the environment .
Surprisingly , in a vast majority of cases , cocultures of two cross-feeding strains showed an increased Darwinian fitness ( that is , rate of growth ) relative to prototrophic wild type cells -- even in direct competition .
This unexpected growth advantage was due to a division of metabolic labour : the fitness cost of overproducing amino acids was less than the benefit of not having to produce others when they were provided by their partner .
Moreover , frequency-dependent selection maintained cross-feeding consortia and limited exploitation by non-cooperating competitors .
Together , our synthetic study approach reveals ecological principles that can help explain the widespread occurrence of obligate metabolic cross-feeding interactions in nature .

[2418] Hydrothermal contribution to the oceanic dissolved iron inventory

Iron limits phytoplankton growth and hence the biological carbon pump in the Southern Ocean .
Models assessing the impacts of iron on the global carbon cycle generally rely on dust input and sediment resuspension as the predominant sources .
Although it was previously thought that most iron from deep-ocean hydrothermal activity was inaccessible to phytoplankton because of the formation of particulates , it has been suggested that iron from hydrothermal activity may be an important source of oceanic dissolved iron .
Here we use a global ocean model to assess the impacts of an annual dissolved iron flux of approximately 9x108 mol , as estimated from regional observations of hydrothermal activity , on the dissolved iron inventory of the world 's oceans .
We find the response to the input of hydrothermal dissolved iron is greatest in the Southern Hemisphere oceans .
In particular , observations of the distribution of dissolved iron in the Southern Ocean ( Chever et al. , manuscript in preparation ; Bowie et al. , manuscript in preparation ) can be replicated in our simulations only when our estimated iron flux from hydrothermal sources is included .
As the hydrothermal flux of iron is relatively constant over millennial timescales , we propose that hydrothermal activity can buffer the oceanic dissolved iron inventory against shorter-term fluctuations in dust deposition .

[2419] Erosion and climate

To the Editor The calculations offered by Quinton et al .
raise the unfortunate notion that soil erosion generates an unintentional benefit for climate , owing to the long-term burial of soil organic carbon .
But limiting the assessment of the impact of soil erosion on climate change to organic carbon burial ignores , apart from economic and social damages , the coupling between biogeochemical cycles .

[2420] Community proteogenomics highlights microbial strain-variant protein expression within activated sludge performing enhanced biological phosphorus removal

Enhanced biological phosphorus removal ( EBPR ) selects for polyphosphate accumulating microorganisms to achieve phosphate removal from wastewater .
We used high-resolution community proteomics to identify key metabolic pathways in ` Candidatus Accumulibacter phosphatis ' ( A. phosphatis ) - mediated EBPR and to evaluate the contributions of co-existing strains within the dominant population .
Overall , 702 proteins from the A. phosphatis population were identified .
Results highlight the importance of denitrification , fatty acid cycling and the glyoxylate bypass in EBPR .
Strong similarity in protein profiles under anaerobic and aerobic conditions was uncovered ( only 3 % of A. phosphatis-associated proteins exhibited statistically significant abundance differences ) .
By comprehensive genome-wide alignment of 13 930 orthologous proteins , we uncovered substantial differences in protein abundance for enzyme variants involved in both core-metabolism and EBPR-specific pathways among the A. phosphatis population .
These findings suggest an essential role for genetic diversity in maintaining the stable performance of EBPR systems and , hence , demonstrate the power of integrated cultivation-independent genomics and proteomics for the analysis of complex biotechnological systems .

[2421] Magmatic and amagmatic seafloor generation at the ultraslow-spreading Gakkel ridge , Arctic Ocean

A high-resolution mapping and sampling study of the Gakkel ridge was accomplished during an international ice-breaker expedition to the high Arctic and North Pole in summer 2001 .
For this slowest-spreading endmember of the global mid-ocean-ridge system , predictions were that magmatism should progressively diminish as the spreading rate decreases along the ridge , and that hydrothermal activity should be rare .
Instead , it was found that magmatic variations are irregular , and that hydrothermal activity is abundant .
A 300-kilometre-long central amagmatic zone , where mantle peridotites are emplaced directly in the ridge axis , lies between abundant , continuous volcanism in the west , and large , widely spaced volcanic centres in the east .
These observations demonstrate that the extent of mantle melting is not a simple function of spreading rate : mantle temperatures at depth or mantle chemistry ( or both ) must vary significantly along-axis .
Highly punctuated volcanism in the absence of ridge offsets suggests that first-order ridge segmentation is controlled by mantle processes of melting and melt segregation .
The strong focusing of magmatic activity coupled with faulting may account for the unexpectedly high levels of hydrothermal activity observed .

[2422] A pigment-binding protein essential for regulation of photosynthetic light harvesting

Photosynthetic light harvesting in plants is regulated in response to changes in incident light intensity .
Absorption of light that exceeds a plant 's capacity for fixation of CO2 results in thermal dissipation of excitation energy in the pigment antenna of photosystem II by a poorly understood mechanism .
This regulatory process , termed nonphotochemical quenching , maintains the balance between dissipation and utilization of light energy to minimize generation of oxidizing molecules , thereby protecting the plant against photo-oxidative damage .
To identify specific proteins that are involved in nonphotochemical quenching , we have isolated mutants of Arabidopsis thaliana that can not dissipate excess absorbed light energy .
Here we show that the gene encoding PsbS , an intrinsic chlorophyll-binding protein of photosystem II , is necessary for nonphotochemical quenching but not for efficient light harvesting and photosynthesis .
These results indicate that PsbS may be the site for nonphotochemical quenching , a finding that has implications for the functional evolution of pigment-binding proteins .

[2423] Sea level as a stabilizing factor for marine-ice-sheet grounding lines

Climate change could potentially destabilize marine ice sheets , which would affect projections of future sea-level rise .
Specifically , an instability mechanism has been predicted for marine ice sheets such as the West Antarctic ice sheet that rest on reversed bed slopes , whereby ice-sheet thinning or rising sea level leads to irreversible retreat of the grounding line .
However , existing analyses of this instability mechanism have not accounted for deformational and gravitational effects that lead to a sea-level fall at the margin of a rapidly shrinking ice sheet .
Here we present a suite of predictions of gravitationally self-consistent sea-level change following grounding-line migration .
Our predictions vary the initial ice-sheet size and also consider the contribution to sea-level change from various subregions of the simulated ice sheet .
Using these results , we revisit a canonical analysis of marine-ice-sheet stability and demonstrate that gravity and deformation-induced sea-level changes local to the grounding line contribute a stabilizing influence on ice sheets grounded on reversed bed slopes .
We conclude that accurate treatments of sea-level change should be incorporated into analyses of past and future marine-ice-sheet dynamics .

[2424] Photophysiology and albedo-changing potential of the ice algal community on the surface of the Greenland ice sheet

Darkening of parts of the Greenland ice sheet surface during the summer months leads to reduced albedo and increased melting .
Here we show that heavily pigmented , actively photosynthesising microalgae and cyanobacteria are present on the bare ice .
We demonstrate the widespread abundance of green algae in the Zygnematophyceae on the ice sheet surface in Southwest Greenland .
Photophysiological measurements ( variable chlorophyll fluorescence ) indicate that the ice algae likely use screening mechanisms to downregulate photosynthesis when exposed to high intensities of visible and ultraviolet radiation , rather than non-photochemical quenching or cell movement .
Using imaging microspectrophotometry , we demonstrate that intact cells and filaments absorb light with characteristic spectral profiles across ultraviolet and visible wavelengths , whereas inorganic dust particles typical for these areas display little absorption .
Our results indicate that the phototrophic community growing directly on the bare ice , through their photophysiology , most likely have an important role in changing albedo , and subsequently may impact melt rates on the ice sheet .

[2425] Greenhouse-gas emissions from energy use in the water sector

Water management faces great challenges over the coming decades .
Pressures include stricter water-quality standards , increasing demand for water and the need to adapt to climate change , while reducing emissions of greenhouse gases .
The processes of abstraction , conveyance and treatment of fresh water and wastewater all demand energy .
Energy use in the water sector is growing , yet its importance is under-recognized , and gaps remain in our knowledge .
Here we define the need to integrate energy use further into water resource management and identify opportunities for the water sector to understand and describe more effectively its role in greenhouse-gas emissions .

[2426] No extreme bipolar glaciation during the main Eocene calcite compensation shift

Major ice sheets were permanently established on Antarctica approximately 34 million years ago , close to the Eocene/Oligocene boundary , at the same time as a permanent deepening of the calcite compensation depth in the world 's oceans .
Until recently , it was thought that Northern Hemisphere glaciation began much later , between 11 and 5 million years ago .
This view has been challenged , however , by records of ice rafting at high northern latitudes during the Eocene epoch and by estimates of global ice volume that exceed the storage capacity of Antarctica at the same time as a temporary deepening of the calcite compensation depth ~ 41.6 million years ago .
Here we test the hypothesis that large ice sheets were present in both hemispheres ~ 41.6 million years ago using marine sediment records of oxygen and carbon isotope values and of calcium carbonate content from the equatorial Atlantic Ocean .
These records allow , at most , an ice budget that can easily be accommodated on Antarctica , indicating that large ice sheets were not present in the Northern Hemisphere .
The records also reveal a brief interval shortly before the temporary deepening of the calcite compensation depth during which the calcite compensation depth shoaled , ocean temperatures increased and carbon isotope values decreased in the equatorial Atlantic .
The nature of these changes around 41.6 million years ago implies common links , in terms of carbon cycling , with events at the Eocene/Oligocene boundary and with the ` hyperthermals ' of the Early Eocene climate optimum .
Our findings help to resolve the apparent discrepancy between the geological records of Northern Hemisphere glaciation and model results that indicate that the threshold for continental glaciation was crossed earlier in the Southern Hemisphere than in the Northern Hemisphere .

[2427] Deep-sea hydrothermal vent animals seek cool fluids in a highly variable thermal environment

The thermal characteristics of an organism 's environment affect a multitude of parameters , from biochemical to evolutionary processes .
Hydrothermal vents on mid-ocean ridges are created when warm hydrothermal fluids are ejected from the seafloor and mixed with cold bottom seawater ; many animals thrive along these steep temperature and chemical gradients .
Two-dimensional temperature maps at vent sites have demonstrated order of magnitude thermal changes over centimetre distances and at time intervals from minutes to hours .
To investigate whether animals adapt to this extreme level of environmental variability , we examined differences in the thermal behaviour of mobile invertebrates from aquatic habitats that vary in thermal regime .
Vent animals were highly responsive to heat and preferred much cooler fluids than their upper thermal limits , whereas invertebrates from other aquatic environments risked exposure to warmer temperatures .
Avoidance of temperatures well within their tolerated range may allow vent animals to maintain a safety margin against rapid temperature fluctuations and concomitant toxicity of hydrothermal fluids .

[2428] Involvement of dietary salt in shaping bacterial communities in European sea bass ( Dicentrarchus labrax )

Bacteria associated with the digestive tract of multicellular organisms have been shown to play a major role in their hosts ' functioning .
In fish , it has been proposed that food fermentation occurs inside the pyloric ceca , pouch like organs found in their digestive tract .
However , this notion remains controversial .
Furthermore , changes in pyloric cecal bacterial populations under different diets have yet to be demonstrated in fish .
In this study , we explore the changes occurring in the bacterial community residing in the pyloric ceca of carnivorous fish fed different diets , which were shown to induce different growth rates .
Our results revealed that different diets do indeed induce distinct bacterial compositions within the pyloric ceca .
We found that , when salt was added to a low fish meal diet , the bacterial changes were accompanied by a significant enhancement in weight gain , hinting at a possible involvement of the bacterial community in energy harvest .

[2429] Biodiversity conservation : Effects of changes in climate and land use

Arising from : C. D. Thomas et al. .
Nature 427 , 145-148 ( 2004 ) ) ; see also communication from Thuiller et al. and communication from Harte et al. ; Thomas et al. replyThomas et al. argue , contrary to Sala et al. , that climate change poses an equal or greater threat to global biodiversity than land-use change .
We contest this claim , however , on the grounds that Thomas et al. incorrectly apply species-area relationships .

[2430] Spread of white-nose syndrome on a network regulated by geography and climate

Wildlife and plant diseases can reduce biodiversity , disrupt ecosystem services and threaten human health .
Emerging pathogens have displayed a variety of spatial spread patterns due to differences in host ecology , including diffusive spread from an epicentre ( West Nile virus ) , jump dispersal on a network ( foot-and-mouth disease ) , or a combination of these ( Sudden oak death ) .
White-nose syndrome is a highly pathogenic infectious disease of bats currently spreading across North America .
Understanding how bat ecology influences this spread is crucial to management of infected and vulnerable populations .
Here we show that white-nose syndrome spread is not diffusive but rather mediated by patchily distributed habitat and large-scale gradients in winter climate .
Simulations predict rapid expansion and infection of most counties with caves in the contiguous United States by winter 2105-2106 .
Our findings show the unique pattern of white-nose syndrome spread corresponds to ecological traits of the host and suggest hypotheses for transmission mechanisms acting at the local scale .

[2431] How to conserve the tropics as they warm

To make tropical forests more resilient to climate change , we need a coordinated effort to refocus conservation tools at regional and international levels .
The tools include expansion of protected areas , control of fires , and application of REDD policy ( ` reduced emissions from deforestation and forest degradation ' ) .

[2432] Small influence of solar variability on climate over the past millennium

The climate of the past millennium was marked by substantial decadal and centennial scale variability in the Northern Hemisphere .
Low solar activity has been linked to cooling during the Little Ice Age ( AD 1450-1850 ; ref . )
and there may have been solar forcing of regional warmth during the Medieval Climate Anomaly ( AD 950-1250 ; ref . )
.
The amplitude of the associated changes is , however , poorly constrained , with estimates of solar forcing spanning almost an order of magnitude .
Numerical simulations tentatively indicate that a small amplitude best agrees with available temperature reconstructions .
Here we compare the climatic fingerprints of high and low solar forcing derived from model simulations with an ensemble of surface air temperature reconstructions for the past millennium .
Our methodology also accounts for internal climate variability and other external drivers such as volcanic eruptions , as well as uncertainties in the proxy reconstructions and model output .
We find that neither a high magnitude of solar forcing nor a strong climate effect of that forcing agree with the temperature reconstructions .
We instead conclude that solar forcing probably had a minor effect on Northern Hemisphere climate over the past 1,000 years , while , volcanic eruptions and changes in greenhouse gas concentrations seem to be the most important influence over this period .

[2433] Penguin tissue as a proxy for relative krill abundance in East Antarctica during the Holocene

Antarctic krill ( Euphausia superba ) is a key component of the Southern Ocean food web .
It supports a large number of upper trophic-level predators , and is also a major fishery resource .
Understanding changes in krill abundance has long been a priority for research and conservation in the Southern Ocean .
In this study , we performed stable isotope analyses on ancient Adelie penguin tissues and inferred relative krill abundance during the Holocene epoch from paleodiets of Adelie penguin ( Pygoscelis adeliae ) , using inverse of delta15N ( ratio of 15N/14N ) value as a proxy .
We find that variations in krill abundance during the Holocene are in accord with episodes of regional climate changes , showing greater krill abundance in cold periods .
Moreover , the low delta15N values found in modern Adelie penguins indicate relatively high krill availability , which supports the hypothesis of krill surplus in modern ages due to recent hunt for krill-eating seals and whales by humans .

[2434] Measurement challenges

Tools and methodologies for reducing uncertainties in climate change knowledge are now available , but it is disputed to what extent increased confidence in data will lead to increased action on carbon emissions .

[2435] Collapse and recovery of marine fishes

Over-exploitation and subsequent collapse of marine fishes has focused attention on the ability of affected populations to recover to former abundance levels and on the degree to which their persistence is threatened by extinction .
Although potential for recovery has been assessed indirectly , actual changes in population size following long-term declines have not been examined empirically .
Here I show that there is very little evidence for rapid recovery from prolonged declines , in contrast to the perception that marine fishes are highly resilient to large population reductions .
With the possible exception of herring and related species that mature early in life and are fished with highly selective equipment , my analysis of 90 stocks reveals that many gadids ( for example , cod , haddock ) and other non-clupeids ( for example , flatfishes ) have experienced little , if any , recovery as much as 15 years after 45-99 % reductions in reproductive biomass .
Although the effects of overfishing on single species may generally be reversible , the actual time required for recovery appears to be considerable .
To exempt marine fishes from existing criteria used to assign extinction risk would be inconsistent with precautionary approaches to fisheries management and the conservation of marine biodiversity .

[2436] The Phaeodactylum genome reveals the evolutionary history of diatom genomes

Diatoms are photosynthetic secondary endosymbionts found throughout marine and freshwater environments , and are believed to be responsible for around one-fifth of the primary productivity on Earth .
The genome sequence of the marine centric diatom Thalassiosira pseudonana was recently reported , revealing a wealth of information about diatom biology .
Here we report the complete genome sequence of the pennate diatom Phaeodactylum tricornutum and compare it with that of T. pseudonana to clarify evolutionary origins , functional significance and ubiquity of these features throughout diatoms .
In spite of the fact that the pennate and centric lineages have only been diverging for 90 million years , their genome structures are dramatically different and a substantial fraction of genes ( ~ 40 % ) are not shared by these representatives of the two lineages .
Analysis of molecular divergence compared with yeasts and metazoans reveals rapid rates of gene diversification in diatoms .
Contributing factors include selective gene family expansions , differential losses and gains of genes and introns , and differential mobilization of transposable elements .
Most significantly , we document the presence of hundreds of genes from bacteria .
More than 300 of these gene transfers are found in both diatoms , attesting to their ancient origins , and many are likely to provide novel possibilities for metabolite management and for perception of environmental signals .
These findings go a long way towards explaining the incredible diversity and success of the diatoms in contemporary oceans .

[2437] Snowdrift game dynamics and facultative cheating in yeast

The origin of cooperation is a central challenge to our understanding of evolution .
The fact that microbial interactions can be manipulated in ways that animal interactions can not has led to a growing interest in microbial models of cooperation and competition .
For the budding yeast Saccharomyces cerevisiae to grow on sucrose , the disaccharide must first be hydrolysed by the enzyme invertase .
This hydrolysis reaction is performed outside the cytoplasm in the periplasmic space between the plasma membrane and the cell wall .
Here we demonstrate that the vast majority ( ~ 99 per cent ) of the monosaccharides created by sucrose hydrolysis diffuse away before they can be imported into the cell , serving to make invertase production and secretion a cooperative behaviour .
A mutant cheater strain that does not produce invertase is able to take advantage of and invade a population of wild-type cooperator cells .
However , over a wide range of conditions , the wild-type cooperator can also invade a population of cheater cells .
Therefore , we observe steady-state coexistence between the two strains in well-mixed culture resulting from the fact that rare strategies outperform common strategies -- the defining features of what game theorists call the snowdrift game .
A model of the cooperative interaction incorporating nonlinear benefits explains the origin of this coexistence .
We are able to alter the outcome of the competition by varying either the cost of cooperation or the glucose concentration in the media .
Finally , we note that glucose repression of invertase expression in wild-type cells produces a strategy that is optimal for the snowdrift game -- wild-type cells cooperate only when competing against cheater cells .

[2438] Early Cretaceous chalks from the North Sea giving evidence for global change

Among calcareous nannofossils , important primary producers in Jurassic and Cretaceous oceans , nannoconids were carbonate rock-forming organisms .
During the late Barremian and early Aptian ( ~ 126 to 122 million years ago ) , nannoconids went through a crisis culminating during the Oceanic Anoxic Event 1a .
Here we present nannofossil and geochemical data from a section of early Barremian-early Aptian age from the North Sea , recording the earliest chalks ever known in the Boreal Realm .
These middle-late Barremian chalks were generated by blooming of endemic nannoconids under relative warm and arid conditions .
A subsequent decrease of nannoconids in the latest Barremian coincides with increased nutrient and clay input .
This nannoconid decline , also detected at low latitudes , was associated with the Ontong Java Plateau emplacement .
We conclude that nannoconids were rock forming also at high latitudes , under clear and oligotrophic waters .
Their decline was related to increased continental runoff under reinforced greenhouse conditions .

[2439] Diatoms in a future ocean -- stirring it up : reply from Falkowski and Oliver

We have suggested that future warming climate scenarios will result in a shift in the phytoplankton community in the central ocean gyres towards smaller cells , and that under such conditions , diatoms , especially large-celled species , would be at a competitive disadvantage .
We also suggested that a warming climate will simultaneously enhance the productivity of large phytoplankton , such as diatoms , in coastal regions , owing to increased wind-driven upwelling .

[2440] Recovery of methanotrophs from disturbance : population dynamics , evenness and functioning

Biodiversity is claimed to be essential for ecosystem functioning , but is threatened by anthropogenic disturbances .
Prokaryotes have been assumed to be functionally redundant and virtually inextinguishable .
However , recent work indicates that microbes may well be sensitive to environmental disturbance .
Focusing on methane-oxidizing bacteria as model organisms , we simulated disturbance-induced mortality by mixing native with sterilized paddy soil in two ratios , 1:4 and 1:40 , representing moderate and severe die-offs .
Disturbed microcosms were compared with an untreated control .
Recovery of activity and populations was followed over 4 months by methane uptake measurements , pmoA-qPCR , pmoA-based terminal restriction fragment length polymorphism and a pmoA-based diagnostic microarray .
Diversity and evenness of methanotrophs decreased in disturbed microcosms , but functioning was not compromised .
We consistently observed distinctive temporal shifts between type I and type II methanotrophs , and a rapid population growth leading to even higher cell numbers comparing disturbed microcosms with the control .
Overcompensating mortality suggested that population size in the control was limited by competition with other bacteria .
Overall , methanotrophs showed a remarkable ability to compensate for die-offs .

[2441] Comparative transcriptomics of two environmentally relevant cyanobacteria reveals unexpected transcriptome diversity

Prochlorococcus is a genus of abundant and ecologically important marine cyanobacteria .
Here , we present a comprehensive comparison of the structure and composition of the transcriptomes of two Prochlorococcus strains , which , despite their similarities , have adapted their gene pool to specific environmental constraints .
We present genome-wide maps of transcriptional start sites ( TSS ) for both organisms , which are representatives of the two most diverse clades within the two major ecotypes adapted to high - and low-light conditions , respectively .
Our data suggest antisense transcription for three-quarters of all genes , which is substantially more than that observed in other bacteria .
We discovered hundreds of TSS within genes , most notably within 16 of the 29 prochlorosin genes , in strain MIT9313 .
A direct comparison revealed very little conservation in the location of TSS and the nature of non-coding transcripts between both strains .
We detected extremely short 5 ' untranslated regions with a median length of only 27 and 29 nt for MED4 and MIT9313 , respectively , and for 8 % of all protein-coding genes the median distance to the start codon is only 10 nt or even shorter .
These findings and the absence of an obvious Shine-Dalgarno motif suggest that leaderless translation and ribosomal protein S1-dependent translation constitute alternative mechanisms for translation initiation in Prochlorococcus .
We conclude that genome-wide antisense transcription is a major component of the transcriptional output from these relatively small genomes and that a hitherto unrecognized high degree of complexity and variability of gene expression exists in their transcriptional architecture .

[2442] A meta-analysis of changes in bacterial and archaeal communities with time

Ecologists have long studied the temporal dynamics of plant and animal communities with much less attention paid to the temporal dynamics exhibited by microbial communities .
As a result , we do not know if overarching temporal trends exist for microbial communities or if changes in microbial communities are generally predictable with time .
Using microbial time series assessed via high-throughput sequencing , we conducted a meta-analysis of temporal dynamics in microbial communities , including 76 sites representing air , aquatic , soil , brewery wastewater treatment , human - and plant-associated microbial biomes .
We found that temporal variability in both within - and between-community diversity was consistent among microbial communities from similar environments .
Community structure changed systematically with time in less than half of the cases , and the highest rates of change were observed within ranges of 1 day to 1 month for all communities examined .
Microbial communities exhibited species-time relationships ( STRs ) , which describe the accumulation of new taxa to a community , similar to those observed previously for plant and animal communities , suggesting that STRs are remarkably consistent across a broad range of taxa .
These results highlight that a continued integration of microbial ecology into the broader field of ecology will provide new insight into the temporal patterns of microbial and ` macro ' - bial communities alike .

[2443] Microbial burden and diversity of commercial airline cabin air during short and long durations of travel

Total microbial burden and diversity associated with commercial airliner cabin air was assessed by molecular methods in 125 air samples from the business-class sections of 16 domestic and international flights .
Viable microbial burden within these cabin air parcels constituted only 1-10 % of the total microbial population and ranged from below detection limits to 1.2 x 104 cells m-3 as determined with a validated ATP-based technology .
Cultivable bacterial diversity was almost entirely limited to Gram-positive bacteria such as Staphylococcus and Bacillus .
In contrast , cloning and sequencing 16S rRNA gene directly from the samples without cultivation indicated a significantly broader diversity , as sequences representing more than 100 species , and encompassing 12 classes of bacteria , were retrieved in varying abundance .
Sequences of proteobacterial and Gram-positive lineage were retrieved most frequently ( 58 % and 31 % of all clone sequences , respectively ) , with Gram-positive and alpha-proteobacterial sequences dominating international flight samples and beta - and gamma-proteobacterial sequences comprising the largest portion of those retrieved from domestic flights .
Significant differences in bacterial load and diversity were noted between samples obtained on domestic and international flights .
The disparities observed in microbial abundance and diversity further underscore the immense value of state-of-the art molecular assays in augmenting traditional culture-based techniques .

[2444] Daedalus : Nuclear autumn

One way to counter global warming would be to increase cloud cover , and so reduce the amount of solar radiation reaching Earth .
Daedalus plans to do this with a save-the-planet diesel fuel which emits huge numbers of particles to act as cloud-condensation nuclei .
The downside , in cold , humid conditions , will be appalling fog on the motorways .

[2445] Trimethylamine induces migration of waterfleas

It has long been known that the waterflea Daphnia hyalina exhibits diel vertical migration in the water column , but the chemical that triggers this behaviour has not been identified .
We find that trimethylamine ( TMA ) , which is a major component of the odour produced by decaying fish , induces Daphnia to migrate to greater depths during the day , presumably to avoid predation by fish , .
We observed a gradual increase in average depth of Daphnia with increasing TMA concentration .
Changes in light intensity are known to trigger migration , and chemicals produced by their predators must also be present .
Because migration has demographic and physiological costs , this chemical cue ensures that zooplankton migration occurs only when fish are present .

[2446] Photosynthetic control of chloroplast gene expression

Redox chemistry -- the transfer of electrons or hydrogen atoms -- is central to energy conversion in respiration and photosynthesis .
In photosynthesis in chloroplasts , two separate , light-driven reactions , termed photosystem I and photosystem II , are connected in series by a chain of electron carriers .
The redox state of one connecting electron carrier , plastoquinone , governs the distribution of absorbed light energy between photosystems I and II by controlling the phosphorylation of a mobile , light-harvesting , pigment-protein complex .
Here we show that the redox state of plastoquinone also controls the rate of transcription of genes encoding reaction-centre apoproteins of photosystem I and photosystem II .
As a result of this control , the stoichiometry between the two photosystems changes in a way that counteracts the inefficiency produced when either photosystem limits the rate of the other .
In eukaryotes , these reaction-centre proteins are encoded universally within the chloroplast .
Photosynthetic control of chloroplast gene expression indicates an evolutionary explanation for this rule : the redox signal-transduction pathway can be short , the response rapid , and the control direct .

[2447] Pervasive oxygenation along late Archaean ocean margins

The photosynthetic production of oxygen in the oceans is thought to have begun by 2.7 billion years ago , several hundred million years before appreciable accumulation of oxygen in the atmosphere .
However , the abundance and distribution of dissolved oxygen in the late Archaean oceans is poorly constrained .
Here we present geochemical profiles from 2.6 - to 2.5-billion-year-old black shales from the Campbellrand-Malmani carbonate platform in South Africa .
We find a high abundance of rhenium and a low abundance of molybdenum , which , together with the speciation of sedimentary iron , points to the presence of dissolved oxygen in the bottom waters on the platform slope .
The water depth on the slope probably reached several hundred metres , implying the export of O2 below the photic zone .
Our data also indicate that the mildly oxygenated surface ocean gave way to an anoxic deep ocean .
We therefore suggest that the production of oxygen in the surface ocean was vigorous at this time , but was not sufficient to fully consume the deep-sea reductants .
On the basis of our results and observations from the Hamersley basin in Western Australia , we conclude that the productive regions along ocean margins during the late Archaean eon were sites of substantial O2 accumulation , at least 100 million years before the first significant increase in atmospheric O2 concentration .

[2448] Ecological stability in response to warming

That species ' biological rates including metabolism , growth and feeding scale with temperature is well established from warming experiments .
The interactive influence of these changes on population dynamics , however , remains uncertain .
As a result , uncertainty about ecological stability in response under warming remains correspondingly high .
In previous studies , severe consumer extinction waves in warmed microcosms were explained in terms of warming-induced destabilization of population oscillations .
Here , we show that warming stabilizes predator-prey dynamics at the risk of predator extinction .
Our results are based on meta-analyses of a global database of temperature effects on metabolic and feeding rates and maximum population size that includes species of different phylogenetic groups and ecosystem types .
To unravel population-level consequences we parameterized a bioenergetic predator-prey model and simulated warming effects within ecological , non-evolutionary timescales .
In contrast to previous studies , we find that warming stabilized population oscillations up to a threshold temperature , which is true for most of the possible parameter combinations .
Beyond the threshold level , warming caused predator extinction due to starvation .
Predictions were tested in a microbial predator-prey system .
Together , our results indicate a major change in how we expect climate change to alter natural ecosystems : warming should increase population stability while undermining species diversity .

[2449] Climate change : Southern see-saw seen

The bipolar see-saw hypothesis provides an explanation for why temperature shifts in the two hemispheres were out of phase at certain times .
The hypothesis has now passed a test of one of its predictions .

[2450] AhR sensing of bacterial pigments regulates antibacterial defence

The aryl hydrocarbon receptor ( AhR ) is a highly conserved ligand-dependent transcription factor that senses environmental toxins and endogenous ligands , thereby inducing detoxifying enzymes and modulating immune cell differentiation and responses .
We hypothesized that AhR evolved to sense not only environmental pollutants but also microbial insults .
We characterized bacterial pigmented virulence factors , namely the phenazines from Pseudomonas aeruginosa and the naphthoquinone phthiocol from Mycobacterium tuberculosis , as ligands of AhR .
Upon ligand binding , AhR activation leads to virulence factor degradation and regulated cytokine and chemokine production .
The relevance of AhR to host defence is underlined by heightened susceptibility of AhR-deficient mice to both P. aeruginosa and M. tuberculosis .
Thus , we demonstrate that AhR senses distinct bacterial virulence factors and controls antibacterial responses , supporting a previously unidentified role for AhR as an intracellular pattern recognition receptor , and identify bacterial pigments as a new class of pathogen-associated molecular patterns .

[2451] Eco-evolutionary feedbacks drive species interactions

In the biosphere , many species live in close proximity and can thus interact in many different ways .
Such interactions are dynamic and fall along a continuum between antagonism and cooperation .
Because interspecies interactions are the key to understanding biological communities , it is important to know how species interactions arise and evolve .
Here , we show that the feedback between ecological and evolutionary processes has a fundamental role in the emergence and dynamics of species interaction .
Using a two-species artificial community , we demonstrate that ecological processes and rapid evolution interact to influence the dynamics of the symbiosis between a eukaryote ( Saccharomyces cerevisiae ) and a bacterium ( Rhizobium etli ) .
The simplicity of our experimental design enables an explicit statement of causality .
The niche-constructing activities of the fungus were the key ecological process : it allowed the establishment of a commensal relationship that switched to ammensalism and provided the selective conditions necessary for the adaptive evolution of the bacteria .
In this latter state , the bacterial population radiates into more than five genotypes that vary with respect to nutrient transport , metabolic strategies and global regulation .
Evolutionary diversification of the bacterial populations has strong effects on the community ; the nature of interaction subsequently switches from ammensalism to antagonism where bacteria promote yeast extinction .
Our results demonstrate the importance of the evolution-to-ecology pathway in the persistence of interactions and the stability of communities .
Thus , eco-evolutionary dynamics have the potential to transform the structure and functioning of ecosystems .
Our results suggest that these dynamics should be considered to improve our understanding of beneficial and detrimental host-microbe interactions .

[2452] Assessing the risks associated with new agricultural practices

One key challenge for the twenty-first century is how to produce the food we need , yet ensure the landscape we want .
Genetically modified crops have focused our attention on how to answer this question for one part of agriculture .
The same principles could be applied to assess environmental impacts of future land-use change in a much broader context .

[2453] Expanding ester biosynthesis in Escherichia coli

To expand the capabilities of whole-cell biocatalysis , we have engineered Escherichia coli to produce various esters .
The alcohol O-acyltransferase ( ATF ) class of enzyme uses acyl-CoA units for ester formation .
The release of free CoA upon esterification with an alcohol provides the free energy to facilitate ester formation .
The diversity of CoA molecules found in nature in combination with various alcohol biosynthetic pathways allows for the biosynthesis of a multitude of esters .
Small to medium volatile esters have extensive applications in the flavor , fragrance , cosmetic , solvent , paint and coating industries .
The present work enables the production of these compounds by designing several ester pathways in E. coli .
The engineered pathways generated acetate esters of ethyl , propyl , isobutyl , 2-methyl-1-butyl , 3-methyl-1-butyl and 2-phenylethyl alcohols .
In particular , we achieved high-level production of isobutyl acetate from glucose ( 17.2 g l-1 ) .
This strategy was expanded to realize pathways for tetradecyl acetate and several isobutyrate esters .

[2454] Antarctic temperature at orbital timescales controlled by local summer duration

During the late Pleistocene epoch , proxies for Southern Hemisphere climate from the Antarctic ice cores vary nearly in phase with Northern Hemisphere insolation intensity at the precession and obliquity timescales .
This coherence has led to the suggestion that Northern Hemisphere insolation controls Antarctic climate .
However , it is unclear what physical mechanisms would tie southern climate to northern insolation .
Here we call on radiative equilibrium estimates to show that Antarctic climate could instead respond to changes in the duration of local summer .
Simple radiative equilibrium dictates that warmer annual average atmospheric temperatures occur as a result of a longer summer , as opposed to a more intense one , because temperature is more sensitive to insolation when the atmosphere is cooler .
Furthermore , we show that a single-column atmospheric model reproduces this radiative equilibrium effect when forced exclusively by local Antarctic insolation , generating temperature variations that are coherent and in phase with proxies of Antarctic atmospheric temperature and surface conditions .
We conclude that the duration of Southern Hemisphere summer is more likely to control Antarctic climate than the intensity of Northern Hemisphere summer with which it ( often misleadingly ) covaries .
In our view , near interhemispheric climate symmetry at the obliquity and precession timescales arises from a northern response to local summer intensity and a southern response to local summer duration .

[2455] Functional microarray analysis of nitrogen and carbon cycling genes across an Antarctic latitudinal transect

Soil-borne microbial communities were examined via a functional gene microarray approach across a southern polar latitudinal gradient to gain insight into the environmental factors steering soil N - and C-cycling in terrestrial Antarctic ecosystems .
The abundance and diversity of functional gene families were studied for soil-borne microbial communities inhabiting a range of environments from 51degreesS ( cool temperate - Falkland Islands ) to 72degreesS ( cold rock desert - Coal Nunatak ) .
The recently designed functional gene array used contains 24 243 oligonucleotide probes and covers > 10 000 genes in > 150 functional groups involved in nitrogen , carbon , sulfur and phosphorus cycling , metal reduction and resistance and organic contaminant degradation ( He et al. 2007 ) .
The detected N - and C-cycle genes were significantly different across different sampling locations and vegetation types .
A number of significant trends were observed regarding the distribution of key gene families across the environments examined .
For example , the relative detection of cellulose degradation genes was correlated with temperature , and microbial C-fixation genes were more present in plots principally lacking vegetation .
With respect to the N-cycle , denitrification genes were linked to higher soil temperatures , and N2-fixation genes were linked to plots mainly vegetated by lichens .
These microarray-based results were confirmed for a number of gene families using specific real-time PCR , enzymatic assays and process rate measurements .
The results presented demonstrate the utility of an integrated functional gene microarray approach in detecting shifts in functional community properties in environmental samples and provide insight into the forces driving important processes of terrestrial Antarctic nutrient cycling .

[2456] Different magnitudes of projected subsurface ocean warming around Greenland and Antarctica

The observed acceleration of outlet glaciers and ice flows in Greenland and Antarctica is closely linked to ocean warming , especially in the subsurface layer .
Accurate projections of ice-sheet dynamics and global sea-level rise therefore require information of future ocean warming in the vicinity of the large ice sheets .
Here we use a set of 19 state-of-the-art climate models to quantify this ocean warming in the next two centuries .
We find that in response to a mid-range increase in atmospheric greenhouse-gas concentrations , the subsurface oceans surrounding the two polar ice sheets at depths of 200-500 m warm substantially compared with the observed changes thus far .
Model projections suggest that over the course of the twenty-first century , the maximum ocean warming around Greenland will be almost double the global mean , with a magnitude of 1.7-2 .0 degreesC .
By contrast , ocean warming around Antarctica will be only about half as large as global mean warming , with a magnitude of 0.5-0 .6 degreesC .
A more detailed evaluation indicates that ocean warming is controlled by different mechanisms around Greenland and Antarctica .
We conclude that projected subsurface ocean warming could drive significant increases in ice-mass loss , and heighten the risk of future large sea-level rise .

[2457] Mesozoic Alpine facies deposition as a result of past latitudinal plate motion

The fragmentation of Pangaea as a consequence of the opening of the Atlantic Ocean is documented in the Alpine-Mediterranean region by the onset of widespread pelagic sedimentation .
Shallow-water sediments were replaced by mainly pelagic limestones in the Early Jurassic period , radiolarian cherts in the Middle-Late Jurassic period , and again pelagic limestones in the Late Jurassic-Cretaceous period .
During initial extension , basin subsidence below the carbonate compensation depth ( CCD ) is thought to have triggered the transition from Early Jurassic limestones to Middle-Late Jurassic radiolarites .
It has been proposed that the transition from radiolarites to limestones in the Late Jurassic period was due to an increase in calcareous nannoplankton abundance when the CCD was depressed below the ocean floor .
But in modern oceans , sediments below the CCD are not necessarily radiolaritic .
Here we present palaeomagnetic samples from the Jurassic-Cretaceous pelagic succession exposed in the Lombardian basin , Italy .
On the basis of an analysis of our palaeolatitudinal data in a broader palaeogeographic context , we propose an alternative explanation for the above facies tripartition .
We suggest that the Lombardian basin drifted initially towards , and subsequently away from , a near-equatorial upwelling zone of high biosiliceous productivity .
Our tectonic model for the genesis of radiolarites adds an essential horizontal plate motion component to explanations involving only vertical variations of CCD relative to the ocean floor .
It may explain the deposition of radiolarites throughout the Mediterranean and Middle Eastern region during the Jurassic period .

[2458] Disruption of Mediator rescues the stunted growth of a lignin-deficient Arabidopsis mutant

Lignin is a phenylpropanoid-derived heteropolymer important for the strength and rigidity of the plant secondary cell wall .
Genetic disruption of lignin biosynthesis has been proposed as a means to improve forage and bioenergy crops , but frequently results in stunted growth and developmental abnormalities , the mechanisms of which are poorly understood .
Here we show that the phenotype of a lignin-deficient Arabidopsis mutant is dependent on the transcriptional co-regulatory complex , Mediator .
Disruption of the Mediator complex subunits MED5a ( also known as REF4 ) and MED5b ( also known as RFR1 ) rescues the stunted growth , lignin deficiency and widespread changes in gene expression seen in the phenylpropanoid pathway mutant ref8 , without restoring the synthesis of guaiacyl and syringyl lignin subunits .
Cell walls of rescued med5a/5b ref8 plants instead contain a novel lignin consisting almost exclusively of p-hydroxyphenyl lignin subunits , and moreover exhibit substantially facilitated polysaccharide saccharification .
These results demonstrate that guaiacyl and syringyl lignin subunits are largely dispensable for normal growth and development , implicate Mediator in an active transcriptional process responsible for dwarfing and inhibition of lignin biosynthesis , and suggest that the transcription machinery and signalling pathways responding to cell wall defects may be important targets to include in efforts to reduce biomass recalcitrance .

[2459] Atmospheric oxidation capacity sustained by a tropical forest

Terrestrial vegetation , especially tropical rain forest , releases vast quantities of volatile organic compounds ( VOCs ) to the atmosphere , which are removed by oxidation reactions and deposition of reaction products .
The oxidation is mainly initiated by hydroxyl radicals ( OH ) , primarily formed through the photodissociation of ozone .
Previously it was thought that , in unpolluted air , biogenic VOCs deplete OH and reduce the atmospheric oxidation capacity .
Conversely , in polluted air VOC oxidation leads to noxious oxidant build-up by the catalytic action of nitrogen oxides ( NOx = NO + NO2 ) .
Here we report aircraft measurements of atmospheric trace gases performed over the pristine Amazon forest .
Our data reveal unexpectedly high OH concentrations .
We propose that natural VOC oxidation , notably of isoprene , recycles OH efficiently in low-NOx air through reactions of organic peroxy radicals .
Computations with an atmospheric chemistry model and the results of laboratory experiments suggest that an OH recycling efficiency of 40-80 per cent in isoprene oxidation may be able to explain the high OH levels we observed in the field .
Although further laboratory studies are necessary to explore the chemical mechanism responsible for OH recycling in more detail , our results demonstrate that the biosphere maintains a remarkable balance with the atmospheric environment .

[2460] Ice-cold hotspots

Science doi : 10.1126 / science .1142834 ( 2007 ) Rising global temperatures are causing Antarctic ice shelves to disintegrate , creating thousands of free-drifting icebergs in the nearby Weddell Sea .
A novel study has now found that these migrant icebergs serve as hot spots of ocean life , enhancing local primary production , which could increase the export of organic carbon to the deep sea .

[2461] Links between climate and sea levels for the past three million years

The oscillations between glacial and interglacial climate conditions over the past three million years have been characterized by a transfer of immense amounts of water between two of its largest reservoirs on Earth -- the ice sheets and the oceans .
Since the latest of these oscillations , the Last Glacial Maximum ( between about 30,000 and 19,000 years ago ) , ~ 50 million cubic kilometres of ice has melted from the land-based ice sheets , raising global sea level by ~ 130 metres .
Such rapid changes in sea level are part of a complex pattern of interactions between the atmosphere , oceans , ice sheets and solid earth , all of which have different response timescales .
The trigger for the sea-level fluctuations most probably lies with changes in insolation , caused by astronomical forcing , but internal feedback cycles complicate the simple model of causes and effects .

[2462] Undesired usage and the robust self-assembly of heterogeneous structures

Inspired by multiprotein complexes in biology and recent successes in synthetic DNA tile and colloidal self-assembly , we study the spontaneous assembly of structures made of many kinds of components .
The major challenge with achieving high assembly yield is eliminating incomplete or incorrectly bound structures .
Here , we find that such undesired structures rapidly degrade yield with increasing structural size and complexity in diverse models of assembly , if component concentrations reflect the composition ( that is , stoichiometry ) of the desired structure .
But this yield catastrophe can be mitigated by using highly non-stoichiometric concentrations .
Our results support a general principle of ` undesired usage ' -- concentrations of components should be chosen to account for how they are ` used ' by undesired structures and not just by the desired structure .
This principle could improve synthetic assembly methods , but also raises new questions about expression levels of proteins that form biological complexes such as the ribosome .

[2463] Nitrogen losses in anoxic marine sediments driven by Thioploca-anammox bacterial consortia

Ninety per cent of marine organic matter burial occurs in continental margin sediments , where a substantial fraction of organic carbon escapes oxidation and enters long-term geologic storage within sedimentary rocks .
In such environments , microbial metabolism is limited by the diffusive supply of electron acceptors .
One strategy to optimize energy yields in a resource-limited habitat is symbiotic metabolite exchange among microbial associations .
Thermodynamic and geochemical considerations indicate that microbial co-metabolisms are likely to play a critical part in sedimentary organic carbon cycling .
Yet only one association , between methanotrophic archaea and sulphate-reducing bacteria , has been demonstrated in marine sediments in situ , and little is known of the role of microbial symbiotic interactions in other sedimentary biogeochemical cycles .
Here we report in situ molecular and incubation-based evidence for a novel symbiotic consortium between two chemolithotrophic bacteria -- anaerobic ammonium-oxidizing ( anammox ) bacteria and the nitrate-sequestering sulphur-oxidizing Thioploca species -- in anoxic sediments of the Soledad basin at the Mexican Pacific margin .
A mass balance of benthic solute fluxes and the corresponding nitrogen isotope composition of nitrate and ammonium fluxes indicate that anammox bacteria rely on Thioploca species for the supply of metabolic substrates and account for about 57 + / - 21 per cent of the total benthic N2 production .
We show that Thioploca-anammox symbiosis intensifies benthic fixed nitrogen losses in anoxic sediments , bypassing diffusion-imposed limitations by efficiently coupling the carbon , nitrogen and sulphur cycles .

[2464] Global patterns in human consumption of net primary production

The human population and its consumption profoundly affect the Earth 's ecosystems .
A particularly compelling measure of humanity 's cumulative impact is the fraction of the planet 's net primary production that we appropriate for our own use .
Net primary production -- the net amount of solar energy converted to plant organic matter through photosynthesis -- can be measured in units of elemental carbon and represents the primary food energy source for the world 's ecosystems .
Human appropriation of net primary production , apart from leaving less for other species to use , alters the composition of the atmosphere , levels of biodiversity , energy flows within food webs and the provision of important ecosystem services .
Here we present a global map showing the amount of net primary production required by humans and compare it to the total amount generated on the landscape .
We then derive a spatial balance sheet of net primary production ` supply ' and ` demand ' for the world .
We show that human appropriation of net primary production varies spatially from almost zero to many times the local primary production .
These analyses reveal the uneven footprint of human consumption and related environmental impacts , indicate the degree to which human populations depend on net primary production ` imports ' and suggest policy options for slowing future growth of human appropriation of net primary production .

[2465] Bio-inspired nanocatalysts for the oxygen reduction reaction

Electrochemical conversions at fuel cell electrodes are complex processes .
In particular , the oxygen reduction reaction has substantial overpotential limiting the electrical power output efficiency .
Effective and inexpensive catalytic interfaces are therefore essential for increased performance .
Taking inspiration from enzymes , earth-abundant metal centres embedded in organic environments present remarkable catalytic active sites .
Here we show that these enzyme-inspired centres can be effectively mimicked in two-dimensional metal-organic coordination networks self-assembled on electrode surfaces .
Networks consisting of trimesic acid and bis-pyridyl-bispyrimidine coordinating to single iron and manganese atoms on Au ( 111 ) effectively catalyse the oxygen reduction and reveal distinctive catalytic activity in alkaline media .
These results demonstrate the potential of surface-engineered metal-organic networks for electrocatalytic conversions .
Specifically designed coordination complexes at surfaces inspired by enzyme cofactors represent a new class of nanocatalysts with promising applications in electrocatalysis .

[2466] Importance of rare taxa for bacterial diversity in the rhizosphere of Bt - and conventional maize varieties

Ribosomal 16S rRNA gene pyrosequencing was used to explore whether the genetically modified ( GM ) Bt-maize hybrid MON 89034 x MON 88017 , expressing three insecticidal recombinant Cry proteins of Bacillus thuringiensis , would alter the rhizosphere bacterial community .
Fine roots of field cultivated Bt-maize and three conventional maize varieties were analyzed together with coarse roots of the Bt-maize .
A total of 547 000 sequences were obtained .
Library coverage was 100 % at the phylum and 99.8 % at the genus rank .
Although cluster analyses based on relative abundances indicated no differences at higher taxonomic ranks , genera abundances pointed to variety specific differences .
Genera-based clustering depended solely on the 49 most dominant genera while the remaining 461 rare genera followed a different selection .
A total of 91 genera responded significantly to the different root environments .
As a benefit of pyrosequencing , 79 responsive genera were identified that might have been overlooked with conventional cloning sequencing approaches owing to their rareness .
There was no indication of bacterial alterations in the rhizosphere of the Bt-maize beyond differences found between conventional varieties .
B. thuringiensis-like phylotypes were present at low abundance ( 0.1 % of Bacteria ) suggesting possible occurrence of natural Cry proteins in the rhizospheres .
Although some genera indicated potential phytopathogenic bacteria in the rhizosphere , their abundances were not significantly different between conventional varieties and Bt-maize .
With an unprecedented sensitivity this study indicates that the rhizosphere bacterial community of a GM maize did not respond abnormally to the presence of three insecticidal proteins in the root tissue .

[2467] A push for political will

In his latest book Cool It : The Skeptical Environmentalist 's Guide to Global Warming , statistician Bjorn Lomborg argues that rather than pouring billions of dollars into mitigating climate change , we would do more global good and get better return for our buck by focusing on immediate problems such as disease prevention and poverty reduction .
On the basis of the Copenhagen Consensus -- an analysis of the world 's greatest challenges and their most cost-efficient solutions -- Lomborg tells us that a reduction in the toll of HIV/AIDS is first in the pecking order of global problems worth investing in and that tackling climate change through the Kyoto Protocol and carbon taxes are the last and least worthy .

[2468] Climate change and the South Asian summer monsoon

The vagaries of South Asian summer monsoon rainfall on short and long timescales impact the lives of more than one billion people .
Understanding how the monsoon will change in the face of global warming is a challenge for climate science , not least because our state-of-the-art general circulation models still have difficulty simulating the regional distribution of monsoon rainfall .
However , we are beginning to understand more about processes driving the monsoon , its seasonal cycle and modes of variability .
This gives us the hope that we can build better models and ultimately reduce the uncertainty in our projections of future monsoon rainfall .

[2469] Warming trends in Asia amplified by brown cloud solar absorption

Atmospheric brown clouds are mostly the result of biomass burning and fossil fuel consumption .
They consist of a mixture of light-absorbing and light-scattering aerosols and therefore contribute to atmospheric solar heating and surface cooling .
The sum of the two climate forcing terms -- the net aerosol forcing effect -- is thought to be negative and may have masked as much as half of the global warming attributed to the recent rapid rise in greenhouse gases .
There is , however , at least a fourfold uncertainty in the aerosol forcing effect .
Atmospheric solar heating is a significant source of the uncertainty , because current estimates are largely derived from model studies .
Here we use three lightweight unmanned aerial vehicles that were vertically stacked between 0.5 and 3 km over the polluted Indian Ocean .
These unmanned aerial vehicles deployed miniaturized instruments measuring aerosol concentrations , soot amount and solar fluxes .
During 18 flight missions the three unmanned aerial vehicles were flown with a horizontal separation of tens of metres or less and a temporal separation of less than ten seconds , which made it possible to measure the atmospheric solar heating rates directly .
We found that atmospheric brown clouds enhanced lower atmospheric solar heating by about 50 per cent .
Our general circulation model simulations , which take into account the recently observed widespread occurrence of vertically extended atmospheric brown clouds over the Indian Ocean and Asia , suggest that atmospheric brown clouds contribute as much as the recent increase in anthropogenic greenhouse gases to regional lower atmospheric warming trends .
We propose that the combined warming trend of 0.25 K per decade may be sufficient to account for the observed retreat of the Himalayan glaciers .

[2470] Planetary science : Climate change on Venus

Earth 's climate has changed significantly over the past several million years .
New theoretical work suggests that the climate of our nearest neighbour , Venus , may have also changed on similar timescales .

[2471] Consistent geographical patterns of changes in high-impact European heatwaves

Climate-change projections suggest that European summer heatwaves will become more frequent and severe during this century , consistent with the observed trend of the past decades .
The most severe impacts arise from multi-day heatwaves , associated with warm night-time temperatures and high relative humidity .
Here we analyse a set of high-resolution regional climate simulations and show that there is a geographically consistent pattern among climate models : we project the most pronounced changes to occur in southernmost Europe for heatwave frequency and duration , further north for heatwave amplitude and in low-altitude southern European regions for health-related indicators .
For the Iberian peninsula and the Mediterranean region , the frequency of heatwave days is projected to increase from an average of about two days per summer for the period 1961-1990 to around 13 days for 2021-2050 and 40 days for 2071-2100 .
In terms of health impacts , our projections are most severe for low-altitude river basins in southern Europe and for the Mediterranean coasts , affecting many densely populated urban centres .
We find that in these locations , the frequency of dangerous heat conditions also increases significantly faster and more strongly , and that the associated geographical pattern is robust across different models and health indicators .

[2472] Global change : Rice , microbes and methane

Rice agriculture is projected to expand by up to 70 % over the next 25 years , and is likely to mean much more intensive use of ammonium-based nitrogen fertilizers .
That is a worry because rice paddies are one of the main sources of methane ( a greenhouse gas ) in the atmosphere , and increased emissions would be undesirable .
It seems , however , that extra ammonium may stimulate soil bacteria that oxidize methane , and so reduce emissions .

[2473] Chytrid epidemics may increase genetic diversity of a diatom spring-bloom

Contrary to expectation , populations of clonal organisms are often genetically highly diverse .
In phytoplankton , this diversity is maintained throughout periods of high population growth ( that is , blooms ) , even though competitive exclusion among genotypes should hypothetically lead to the dominance of a few superior genotypes .
Genotype-specific parasitism may be one mechanism that helps maintain such high-genotypic diversity of clonal organisms .
Here , we present a comparison of population genetic similarity by estimating the beta-dispersion among genotypes of early and peak bloom populations of the diatom Asterionella formosa for three spring-blooms under high or low parasite pressure .
The Asterionella population showed greater beta-dispersion at peak bloom than early bloom in the 2 years with high parasite pressure , whereas the within group dispersion did not change under low parasite pressure .
Our findings support that high prevalence parasitism can promote genetic diversification of natural populations of clonal hosts .

[2474] A million-year record of fire in sub-Saharan Africa

Biomass burning today constitutes approximately one-third of annual anthropogenic CO2 emissions , and there is a sound theoretical base for expecting fire-related changes in vegetation patterns to affect climate , at least on a regional scale .
But despite the central role that fire has played in moulding many modern ecosystems , there is little information on the incidence of fire before the earliest time at which anthropogenic burning may have significantly affected natural fire regimes .
Here we present a million-year record of elemental carbon abundance from marine sediments on the Sierra Leone rise , ` downwind ' of sub-Saharan Africa .
Elemental carbon serves as a proxy for wind-blow debris derived from the combustion of sub-Sahara vegetation .
The inferred fire incidence in the region was low until about 400,000 years ago , but since that time intense episodes of vegetation fires have occurred during periods when global climate was changing from interglacial to glacial mode .
The occurrence of a peak in elemental carbon abundance within the present interglacial is unique in the past million years , suggesting that this peak is anthropogenic in origin , and that humans have exercised significant control over fire regimes in the region at least since Holocene times .

[2475] Coupled ocean-atmosphere dynamics in the Indian Ocean during 1997-98

Climate variability in the Indian Ocean region seems to be , in some aspects , independent of forcing by external phenomena such as the El Nino/Southern Oscillation .
But the extent to which , and how , internal coupled ocean-atmosphere dynamics determine the state of the Indian Ocean system have not been resolved .
Here we present a detailed analysis of the strong seasonal anomalies in sea surface temperatures , sea surface heights , precipitation and winds that occurred in the Indian Ocean region in 1997-98 , and compare the results with the record of Indian Ocean climate variability over the past 40 years .
We conclude that the 1997-98 anomalies -- in spite of the coincidence with the strong El Nino/Southern Oscillation event -- may primarily be an expression of internal dynamics , rather than a direct response to external influences .
We propose a mechanism of ocean-atmosphere interaction governing the 1997-98 event that may represent a characteristic internal mode of the Indian Ocean climate system .
In the Pacific Ocean , the identification of such a mode has led to successful predictions of El Nino ; if the proposed Indian Ocean internal mode proves to be robust , there may be a similar potential for predictability of climate in the Indian Ocean region .

[2476] Mesoscale vertical motion and the size structure of phytoplankton in the ocean

Phytoplankton size structure is acknowledged as a fundamental property determining energy flow through ` microbial ' or ` herbivore ' pathways .
The balance between these two pathways determines the ability of the ecosystem to recycle carbon within the upper layer or to export it to the ocean interior .
Small cells are usually characteristic of oligotrophic , stratified ocean waters , in which regenerated ammonium is the only available form of inorganic nitrogen and recycling dominates .
Large cells seem to characterize phytoplankton in which inputs of nitrate enter the euphotic layer and exported production is higher .
But the size structure of phytoplankton may depend more directly on hydrodynamical forces than on the source of available nitrogen .
Here we present an empirical model that relates the magnitude of mesoscale vertical motion to the slope of the size-abundance spectrum of phytoplankton in a frontal ecosystem .
Our model indicates that the relative proportion of large cells increases with the magnitude of the upward velocity .
This suggests that mesoscale vertical motion -- a ubiquitous feature of eddies and unstable fronts -- controls directly the size structure of phytoplankton in the ocean .

[2477] Benefits of tree mixes in carbon plantings

Increasingly governments and the private sector are using planted forests to offset carbon emissions .
Few studies , however , examine how tree diversity -- defined here as species richness and/or stand composition -- affects carbon storage in these plantings .
Using aboveground tree biomass as a proxy for carbon storage , we used meta-analysis to compare carbon storage in tree mixtures with monoculture plantings .
Tree mixes stored at least as much carbon as monocultures consisting of the mixture 's most productive species and at times outperformed monoculture plantings .
In mixed-species stands , individual species , and in particular nitrogen-fixing trees , increased stand biomass .
Further motivations for incorporating tree richness into planted forests include the contribution of diversity to total forest carbon-pool development , carbon-pool stability and the provision of extra ecosystem services .
Our findings suggest a two-pronged strategy for designing carbon plantings including : ( 1 ) increased tree species richness ; and ( 2 ) the addition of species that contribute to carbon storage and other target functions .

[2478] Delivery of marine-derived nutrients to streambeds by Pacific salmon

Marine fish that migrate to freshwater rivers to spawn deliver substantial quantities of marine-derived nutrients to terrestrial and freshwater environments .
These nutrients support riparian vegetation , terrestrial organisms , benthic macroinvertebrates , algae and other fish populations .
Although it is known that the quantity of nutrients delivered to these environments is influenced by the number of spawning salmon , little is known about the mechanisms of nutrient delivery .
Here , we present a pathway for nutrient delivery and retention in a Pacific salmon stream , which depends on the aggregation of inorganic and organic particulate matter .
We verify the existence of this pathway in the controlled environment conditions of a recirculating flume , replicating the hydrologic conditions of a stream environment .
We show that the addition of salmon organic matter and clay to the flume increases the formation of organic-inorganic aggregates in the water column , and the transfer of these aggregates to the stream bed .
We find that the formation of these aggregates is associated with an increase in the concentration of bacteria in the stream bed .
We suggest that bacterial aggregation of salmon organic matter and inorganic particulate matter delivers nutrients to streambeds , and thus plays an integral role in nutrient cycling in Pacific salmon streams .

[2479] Adult blood-feeding tsetse flies , trypanosomes , microbiota and the fluctuating environment in sub-Saharan Africa

The tsetse fly vector transmits the protozoan Trypanosoma brucei , responsible for Human African Trypanosomiasis , one of the most neglected tropical diseases .
Despite a recent decline in new cases , it is still crucial to develop alternative strategies to combat this disease .
Here , we review the literature on the factors that influence trypanosome transmission from the fly vector to its vertebrate host ( particularly humans ) .
These factors include climate change effects to pathogen and vector development ( in particular climate warming ) , as well as the distribution of host reservoirs .
Finally , we present reports on the relationships between insect vector nutrition , immune function , microbiota and infection , to demonstrate how continuing research on the evolving ecology of these complex systems will help improve control strategies .
In the future , such studies will be of increasing importance to understand how vector-borne diseases are spread in a changing world .

[2480] Melting during late-stage rifting in Afar is hot and deep

Investigations of a variety of continental rifts and margins worldwide have revealed that a considerable volume of melt can intrude into the crust during continental breakup , modifying its composition and thermal structure .
However , it is unclear whether the cause of voluminous melt production at volcanic rifts is primarily increased mantle temperature or plate thinning .
Also disputed is the extent to which plate stretching or thinning is uniform or varies with depth with the entire continental lithospheric mantle potentially being removed before plate rupture .
Here we show that the extensive magmatism during rifting along the southern Red Sea rift in Afar , a unique region of sub-aerial transition from continental to oceanic rifting , is driven by deep melting of hotter-than-normal asthenosphere .
Petrogenetic modelling shows that melts are predominantly generated at depths greater than 80 kilometres , implying the existence of a thick upper thermo-mechanical boundary layer in a rift system approaching the point of plate rupture .
Numerical modelling of rift development shows that when breakup occurs at the slow extension rates observed in Afar , the survival of a thick plate is an inevitable consequence of conductive cooling of the lithosphere , even when the underlying asthenosphere is hot .
Sustained magmatic activity during rifting in Afar thus requires persistently high mantle temperatures , which would allow melting at high pressure beneath the thick plate .
If extensive plate thinning does occur during breakup it must do so abruptly at a late stage , immediately before the formation of the new ocean basin .

[2481] ` Green ' reversible addition-fragmentation chain-transfer ( RAFT ) polymerization

Reversible addition-fragmentation chain-transfer ( RAFT ) polymerization has revolutionized the field of polymer synthesis as a versatile tool for the production of complex polymeric architectures .
As for all chemical processes , research and development in RAFT have to focus on the design and application of chemical products and processes that have a minimum environmental impact , and follow the principles of ` green ' chemistry .
In this Review , we summarize some of the green features of the RAFT process , and review the recent advances in the production of degradable polymers obtained from RAFT polymerization .
Its use to modify biodegradable and renewable inorganic and organic materials to yield more functional products with enhanced applications is also covered .
RAFT is a promising candidate for answering both the increasing need of modern society to employ highly functional polymeric materials and the global requirements for developing sustainable chemicals and processes .

[2482] Mechanotransduction through growth-factor shedding into the extracellular space

Physical forces elicit biochemical signalling in a diverse array of cells , tissues and organisms , helping to govern fundamental biological processes .
Several hypotheses have been advanced that link physical forces to intracellular signalling pathways , but in many cases the molecular mechanisms of mechanotransduction remain elusive .
Here we find that compressive stress shrinks the lateral intercellular space surrounding epithelial cells , and triggers cellular signalling via autocrine binding of epidermal growth factor family ligands to the epidermal growth factor receptor .
Mathematical analysis predicts that constant rate shedding of autocrine ligands into a collapsing lateral intercellular space leads to increased local ligand concentrations that are sufficient to account for the observed receptor signalling ; direct experimental comparison of signalling stimulated by compressive stress versus exogenous soluble ligand supports this prediction .
These findings establish a mechanism by which mechanotransduction arises from an autocrine ligand-receptor circuit operating in a dynamically regulated extracellular volume , not requiring induction of force-dependent biochemical processes within the cell or cell membrane .

[2483] Climate sciences : How plants helped Earth to stay cool

Plant growth spurred by rising levels of carbon dioxide pollution in the atmosphere has slowed the rate of global warming considerably .
Stephen Pacala of Princeton University in New Jersey and his colleagues used an Earth-system model to analyse historical emissions from industry and changes in land use , including deforestation and agricultural development .

[2484] Hydrogen production in photosynthetic microbial mats in the Elkhorn Slough estuary , Monterey Bay

Hydrogen ( H2 ) release from photosynthetic microbial mats has contributed to the chemical evolution of Earth and could potentially be a source of renewable H2 in the future .
However , the taxonomy of H2-producing microorganisms ( hydrogenogens ) in these mats has not been previously determined .
With combined biogeochemical and molecular studies of microbial mats collected from Elkhorn Slough , Monterey Bay , California , we characterized the mechanisms of H2 production and identified a dominant hydrogenogen .
Net production of H2 was observed within the upper photosynthetic layer ( 0-2 mm ) of the mats under dark and anoxic conditions .
Pyrosequencing of rRNA gene libraries generated from this layer demonstrated the presence of 64 phyla , with Bacteriodetes , Cyanobacteria and Proteobacteria dominating the sequences .
Sequencing of rRNA transcripts obtained from this layer demonstrated that Cyanobacteria dominated rRNA transcript pyrotag libraries .
An OTU affiliated to Microcoleus spp .
was the most abundant OTU in both rRNA gene and transcript libraries .
Depriving mats of sunlight resulted in an order of magnitude decrease in subsequent nighttime H2 production , suggesting that newly fixed carbon is critical to H2 production .
Suppression of nitrogen ( N2 ) - fixation in the mats did not suppress H2 production , which indicates that co-metabolic production of H2 during N2-fixation is not an important contributor to H2 production .
Concomitant production of organic acids is consistent with fermentation of recently produced photosynthate as the dominant mode of H2 production .
Analysis of rRNA % transcript : % gene ratios and H2-evolving bidirectional [ NiFe ] hydrogenase % transcript : % gene ratios indicated that Microcoelus spp .
are dominant hydrogenogens in the Elkhorn Slough mats .

[2485] Aerobic production of methane in the sea

Methane is a potent greenhouse gas that has contributed approximately 20 % to the Earth 's warming since pre-industrial times .
The world 's oceans are an important source of methane , comprising 1-4 % of annual global emissions .
But despite its global significance , oceanic methane production is poorly understood .
In particular , methane concentrations in the surface waters of most of the world 's oceans are supersaturated with respect to atmospheric concentrations , but the origin of this methane , which has been thought to be produced exclusively in anaerobic environments , is not known .
Here , we measure methane production in seawater samples amended with methylphosphonate , an organic , phosphorus-containing compound .
We show that methane is produced aerobically as a by-product of methylphosphonate decomposition in phosphate-stressed waters .
Methylphosphonate decomposition , and thus methane production , may be enhanced by the activity of nitrogen-fixing microorganisms .
We suggest that aerobic marine methane production will be sensitive to the changes in water-column stratification and nutrient limitation that are likely to result from greenhouse-gas-induced ocean warming .

[2486] Phenotypic plasticity in heterotrophic marine microbial communities in continuous cultures

Phenotypic plasticity ( PP ) is the development of alternate phenotypes of a given taxon as an adaptation to environmental conditions .
Methodological limitations have restricted the quantification of PP to the measurement of a few traits in single organisms .
We used metatranscriptomic libraries to overcome these challenges and estimate PP using the expressed genes of multiple heterotrophic organisms as a proxy for traits in a microbial community .
The metatranscriptomes captured the expression response of natural marine bacterial communities grown on differing carbon resource regimes in continuous cultures .
We found that taxa with different magnitudes of PP coexisted in the same cultures , and that members of the order Rhodobacterales had the highest levels of PP .
In agreement with previous studies , our results suggest that continuous culturing may have specifically selected for taxa featuring a rather high range of PP .
On average , PP and abundance changes within a taxon contributed equally to the organism 's change in functional gene abundance , implying that both PP and abundance mediated observed differences in community function .
However , not all functional changes due to PP were directly reflected in the bulk community functional response : gene expression changes in individual taxa due to PP were partly masked by counterbalanced expression of the same gene in other taxa .
This observation demonstrates that PP had a stabilizing effect on a community 's functional response to environmental change .
The ISME Journal advance online publication , 14 November 2014 ; doi :10.1038 / ismej .2014.206

[2487] Using experimental evolution to explore natural patterns between bacterial motility and resistance to bacteriophages

Resistance of bacteria to phages may be gained by alteration of surface proteins to which phages bind , a mechanism that is likely to be costly as these molecules typically have critical functions such as movement or nutrient uptake .
To address this potential trade-off , we combine a systematic study of natural bacteria and phage populations with an experimental evolution approach .
We compare motility , growth rate and susceptibility to local phages for 80 bacteria isolated from horse chestnut leaves and , contrary to expectation , find no negative association between resistance to phages and bacterial motility or growth rate .
However , because correlational patterns ( and their absence ) are open to numerous interpretations , we test for any causal association between resistance to phages and bacterial motility using experimental evolution of a subset of bacteria in both the presence and absence of naturally associated phages .
Again , we find no clear link between the acquisition of resistance and bacterial motility , suggesting that for these natural bacterial populations , phage-mediated selection is unlikely to shape bacterial motility , a key fitness trait for many bacteria in the phyllosphere .
The agreement between the observed natural pattern and the experimental evolution results presented here demonstrates the power of this combined approach for testing evolutionary trade-offs .

[2488] Numbers , biomass and cultivable diversity of microbial populations relate to depth and borehole-specific conditions in groundwater from depths of 4-450 m in Olkiluoto , Finland

Microbiology , chemistry and dissolved gas in groundwater from Olkiluoto , Finland , were analysed over 3 years ; samples came from 16 shallow observation tubes and boreholes from depths of 3.9-16 .2 m and 14 deep boreholes from depths of 35-742 m .
The average total number of cells ( TNC ) was 3.9 x 105 cells per ml in the shallow groundwater and 5.7 x 104 cells per ml in the deep groundwater .
There was a significant correlation between the amount of biomass , analysed as ATP concentration , and TNC .
ATP concentration also correlated with the stacked output of anaerobic most probable number cultivations of nitrate - , iron - , manganese - and sulphate-reducing bacteria , and acetogenic bacteria and methanogens .
The numbers and biomass varied at most by approximately three orders of magnitude between boreholes , and TNC and ATP were positively related to the concentration of dissolved organic carbon .
Two depth zones were found where the numbers , biomass and diversity of the microbial populations peaked .
Shallow groundwater down to a depth of 16.2 m on average contained more biomass and cultivable microorganisms than did deep groundwater , except in a zone at a depth of approximately 300 m where the average biomass and number of cultivable microorganisms approached those of shallow groundwater .
Starting at a depth of approximately 300 m , there were steep gradients of decreasing sulphate and increasing methane concentrations with depth ; together with the peaks in biomass and sulphide concentration at this depth , these suggest that anaerobic methane oxidation may be a significant process at depth in Olkiluoto .

[2489] The influence of rivers on marine boron isotopes and implications for reconstructing past ocean pH

Ocean pH is particularly sensitive to atmospheric carbon dioxide content .
Records of ocean pH can therefore be used to estimate past atmospheric carbon dioxide concentrations .
The isotopic composition of boron ( delta11B ) contained in the carbonate shells of marine organisms varies according to pH , from which ocean pH can be reconstructed .
This requires independent estimates of the delta11B of dissolved boron in sea water through time .
The marine delta11B budget , however , is still largely unconstrained .
Here we show that , by incorporating the global flux of riverine boron ( as estimated from delta11B measurements in 22 of the world 's main rivers ) , the marine boron isotope budget can be balanced .
We also derive ocean delta11B budgets for the past 120 Myr .
Estimated isotope compositions of boron in sea water show a remarkable consistency with records of delta11B in foraminiferal carbonates , suggesting that foraminifera delta11B records may in part reflect changes in the marine boron isotope budget rather than changes in ocean pH over the Cenozoic era .

[2490] The effects of disruptions in ribosomal active sites and in intersubunit contacts on ribosomal degradation in Escherichia coli

Although ribosomes are very stable under most conditions , ribosomal degradation does occur in diverse groups of organisms in response to specific stresses or environmental conditions .
While non-functional ribosome decay ( NRD ) in yeast is well characterized , very little is known of the mechanisms that initiate ribosomal degradation in bacteria .
Here we test ribosome degradation in growing Escherichia coli expressing mutant ribosomes .
We found that mutations in the 16S rRNA decoding centre ( G530U and A1492C ) and 23S rRNA active site ( A2451G ) do not lead to ribosomal degradation .
In contrast , 23S rRNA mutation U2585A causes degradation of both the large and small ribosomal subunits in E. coli .
We further tested mutations in 23S rRNA , which disrupt ribosomal intersubunit bridges B2a and B3 .
Deletion of helix 69 of 23S rRNA and the point mutation A1912G in the same helix did not destabilize ribosomes , while expression of mutations A1919G in H69 and A1960G in H71 led to degradation of both mutant and wild-type ribosomes .
Our results suggest an actively induced mechanism requiring de novo protein synthesis for ribosomal degradation in E. coli , which degrades both structurally inactive and active ribosomes .

[2491] Climate change : What 's in the rising tide ?

The nitrogen cycle rarely features in the grim litany of things at risk from global warming .
Nick Lane reports on research that might change this ?
with grave consequences for ocean chemistry .

[2492] Diversification of the gut symbiont Lactobacillus reuteri as a result of host-driven evolution

The vertebrate digestive tract , including that of humans , is the habitat to trillions of bacteria that are of significant importance to host biology and health .
Although these communities are often postulated to have coevolved with their hosts , evidence is lacking , yet critical for our understanding of microbial symbiosis in vertebrates .
To gain insight into the evolution of a gut symbiont , we have characterized the population genetic structure and phylogeny of Lactobacillus reuteri strains isolated from six different host species ( human , mouse , rat , pig , chicken and turkey ) using Amplified-Fragment Length Polymorphism ( AFLP ) and Multi-Locus Sequence Analysis ( MLSA ) .
The results revealed considerable genetic heterogeneity within the L. reuteri population and distinct monophyletic clades reflecting host origin but not provenance .
The evolutionary patterns detected indicate a long-term association of L. reuteri lineages with particular vertebrate species and host-driven diversification .
Results from a competition experiment in a gnotobiotic mouse model revealed that rodent isolates showed elevated ecological performance , indicating that evolution of L. reuteri lineages was adaptive .
These findings provide evidence that some vertebrate gut microbes are not promiscuous , but have diversified into host-adapted lineages by a long-term evolutionary process , allowing the development of a highly specialized symbiosis .

[2493] Oceanic forcing of the Marine Isotope Stage 11 interglacial

The interglacial known as Marine Isotope Stage 11 has been proposed to be analogous to the Holocene , owing to similarities in the amplitudes of orbital forcing .
It has been difficult to compare the periods , however , because of the long duration of Stage 11 and a lack of detailed knowledge of any extreme climate events that may have occurred .
Here we use the distinctive phasing between seasurface temperatures and the oxygen-isotope records of benthic foraminifera in the southeast Atlantic Ocean to stratigraphically align the Holocene interglacial with the first half of the Marine Isotope Stage 11 interglacial optimum .
This alignment suggests that the second half of Marine Isotope Stage 11 should not be used as a reference for ` pre-anthropogenic ' greenhouse-gas emissions .
By compiling benthic carbon-isotope records from sites in the Atlantic Ocean on a single timescale , we also find that meridional overturning circulation strengthened about 415,000 years ago , at a time of high orbital obliquity .
We propose that this mechanism transported heat to the high northern latitudes , inhibiting significant ice-sheet build-up and prolonging interglacial conditions .
We suggest that this mechanism may have also prolonged other interglacial periods throughout the past 800,000 years .

[2494] Air quality : Emissions versus climate change

Climate change is likely to offset some of the improvements in air quality expected from reductions in pollutant emissions .
A comprehensive analysis of future air quality over North America suggests that , on balance , the air will still be cleaner in coming decades .

[2495] Molecular evidence for genetic mixing of Arctic and Antarctic subpolar populations of planktonic foraminifers

Bipolarity , the presence of a species in the high latitudes separated by a gap in distribution across the tropics , is a well-known pattern of global species distribution .
But the question of whether bipolar species have evolved independently at the poles since the establishment of the cold-water provinces 16-8 million years ago , or if genes have been transferred across the tropics since that time , has not been addressed .
Here we examine genetic variation in the small subunit ribosomal RNA gene of three bipolar planktonic foraminiferal morphospecies .
We identify at least one identical genotype in all three morphospecies in both the Arctic and Antarctic subpolar provinces , indicating that trans-tropical gene flow must have occurred .
Our genetic analysis also reveals that foraminiferal morphospecies can consist of a complex of genetic types .
Such occurrences of genetically distinct populations within one morphospecies may affect the use of planktonic foraminifers as a palaeoceanographic proxy for climate change and necessitate a reassessment of the species concept for the group .

[2496] Genome sequence of Silicibacter pomeroyi reveals adaptations to the marine environment

Since the recognition of prokaryotes as essential components of the oceanic food web , bacterioplankton have been acknowledged as catalysts of most major biogeochemical processes in the sea .
Studying heterotrophic bacterioplankton has been challenging , however , as most major clades have never been cultured or have only been grown to low densities in sea water .
Here we describe the genome sequence of Silicibacter pomeroyi , a member of the marine Roseobacter clade ( Fig. 1 ) , the relatives of which comprise ~ 10-20 % of coastal and oceanic mixed-layer bacterioplankton .
This first genome sequence from any major heterotrophic clade consists of a chromosome ( 4,109,442 base pairs ) and megaplasmid ( 491,611 base pairs ) .
Genome analysis indicates that this organism relies upon a lithoheterotrophic strategy that uses inorganic compounds ( carbon monoxide and sulphide ) to supplement heterotrophy .
Silicibacter pomeroyi also has genes advantageous for associations with plankton and suspended particles , including genes for uptake of algal-derived compounds , use of metabolites from reducing microzones , rapid growth and cell-density-dependent regulation .
This bacterium has a physiology distinct from that of marine oligotrophs , adding a new strategy to the recognized repertoire for coping with a nutrient-poor ocean .

[2497] Microbial community successional patterns in beach sands impacted by the Deepwater Horizon oil spill

Although petroleum hydrocarbons discharged from the Deepwater Horizon ( DWH ) blowout were shown to have a pronounced impact on indigenous microbial communities in the Gulf of Mexico , effects on nearshore or coastal ecosystems remain understudied .
This study investigated the successional patterns of functional and taxonomic diversity for over 1 year after the DWH oil was deposited on Pensacola Beach sands ( FL , USA ) , using metagenomic and 16S rRNA gene amplicon techniques .
Gamma - and Alphaproteobacteria were enriched in oiled sediments , in corroboration of previous studies .
In contrast to previous studies , we observed an increase in the functional diversity of the community in response to oil contamination and a functional transition from generalist populations within 4 months after oil came ashore to specialists a year later , when oil was undetectable .
At the latter time point , a typical beach community had reestablished that showed little to no evidence of oil hydrocarbon degradation potential , was enriched in archaeal taxa known to be sensitive to xenobiotics , but differed significantly from the community before the oil spill .
Further , a clear succession pattern was observed , where early responders to oil contamination , likely degrading aliphatic hydrocarbons , were replaced after 3 months by populations capable of aromatic hydrocarbon decomposition .
Collectively , our results advance the understanding of how natural benthic microbial communities respond to crude oil perturbation , supporting the specialization-disturbance hypothesis ; that is , the expectation that disturbance favors generalists , while providing ( microbial ) indicator species and genes for the chemical evolution of oil hydrocarbons during degradation and weathering .
The ISME Journal advance online publication , 17 February 2015 ; doi :10.1038 / ismej .2015.5

[2498] Palaeoclimate : A fiery start to the Jurassic

The Triassic/Jurassic boundary was marked by widespread environmental changes , including greenhouse warming .
Palaeoecological reconstructions from East Greenland reveal a dramatic rise in fire activity , driven by vegetation shifts and climate change .

[2499] Evolutionary instability of ectomycorrhizal symbioses in basidiomycetes

Mycorrhizae , the symbiotic associations of plant roots and fungal hyphae , are classic examples of mutualisms .
In these ecologically important associations , the fungi derive photosynthetic sugars from their plant hosts , which in turn benefit from fungus-mediated uptake of mineral nutrients .
Early views on the evolution of symbioses suggested that all long-term , intimate associations tend to evolve toward mutualism .
Following this principle , it has been suggested that mycorrhizal symbioses are the stable derivatives of ancestral antagonistic interactions involving plant parasitic fungi .
Alternatively , mutualisms have been interpreted as inherently unstable reciprocal parasitisms , which can be disrupted by conflicts of interest among the partners .
To determine the number of origins of mycorrhizae , and to assess their evolutionary stability , it is necessary to understand the phylogenetic relationships of the taxa involved .
Here we present a broad phylogenetic analysis of mycorrhizal and free-living homobasidiomycetes ( mushroom-forming fungi ) .
Our results indicate that mycorrhizal symbionts with diverse plant hosts have evolved repeatedly from saprotrophic precursors , but also that there have been multiple reversals to a free-living condition .
These findings suggest that mycorrhizae are unstable , evolutionarily dynamic associations .

[2500] Climate change : Dichotomy of drought and deluge

Freshwater deficits and heavy rainfall have been projected to intensify in a warming climate .
An analysis of hydrological data suggests that past changes in wet and dry extremes were more complex than a simple amplification of existing patterns .