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Evidence is mounting that extinctions are altering key processes important to the productivity and sustainability of Earth's ecosystems (1-4). Further species loss will accelerate change in ecosystem processes (5-8), 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 C[O.sub.2] and nutrient pollution. At intermediate levels, species loss generally had equal or greater effects on decomposition than did elevated C[O.sub.2] 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 (9)., A variety of global changes are driving rates of species extinction that greatly outpace background rates in the fossil record (10,11). If these trends continue, projections suggest that within (240) [...]

Increasing concentrations of atmospheric carbon dioxide (C[O.sub.2])can affect biotic and abiotic conditions in soil, such as microbial activity and water content (12). In turn, these changes might be expected to alter the production and consumption of the important greenhouse gases nitrous oxide ([N.sub.2]O) and methane (C[H.sub.4]) (refs 2, 3). However, studies on fluxes of [N.sub.2]O and C[H.sub.4] from soil under increased atmospheric C[O.sub.2] have not been quantitatively synthesized. Here we show, using meta-analysis, that increased C[O.sub.2] (ranging from 463 to 780 parts per million by volume) stimulates both [N.sub.2]O emissions from upland soils and C[H.sub.4] 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 C[O.sub.2] concentrations (4). Our results therefore suggest that the capacity of land ecosystems to slow climate warming has been overestimated., By burning fossil fuels, cutting down forests and changing land use in other ways, humans are rapidly increasing the amount of C[O.sub.2] in the atmosphere and warming the planet (5). [...]

A highly controversial issue in global biogeochemistry is the regulation of terrestrial carbon (C) sequestration by soil nitrogen (IV) availability. This controversy translates into great uncertainty in predicting future global [...]

Unprecedented nitrogen (N) inputs into terrestrial ecosystems have profoundly altered soil N cycling. Ammonia oxidizers and denitrifiers are the main producers of nitrous oxide (N2O), but it remains unclear how ammonia oxidizer and denitrifier abundances will respond to N loading and whether their responses can predict N‐induced changes in soil N2O emission. By synthesizing 101 field studies worldwide, we showed that N loading significantly increased ammonia oxidizer abundance by 107% and denitrifier abundance by 45%. The increases in both ammonia oxidizer and denitrifier abundances were primarily explained by N loading form, and more specifically, organic N loading had stronger effects on their abundances than mineral N loading. Nitrogen loading increased soil N2O emission by 261%, whereas there was no clear relationship between changes in soil N2O emission and shifts in ammonia oxidizer and denitrifier abundances. Our field‐based results challenge the laboratory‐based hypothesis that increased ammonia oxidizer and denitrifier abundances by N loading would directly cause higher soil N2O emission. Instead, key abiotic factors (mean annual precipitation, soil pH, soil C:N ratio, and ecosystem type) explained N‐induced changes in soil N2O emission. Altogether, these findings highlight the need for considering the roles of key abiotic factors in regulating soil N transformations under N loading to better understand the microbially mediated soil N2O emission. [ABSTRACT FROM AUTHOR]

Aim: Climate warming and biodiversity loss both alter plant productivity, yet we lack an understanding of how biodiversity regulates the responses of ecosystems to warming. In this study, we examine how plant diversity regulates the responses of grassland productivity to experimental warming using meta‐analytic techniques. Location: Global. Major taxa studied: Grassland ecosystems. Methods: Our meta‐analysis is based on warming responses of 40 different plant communities obtained from 20 independent studies on grasslands across five continents. Results: Our results show that plant diversity and its responses to warming were the most important factors regulating the warming effects on plant productivity, among all the factors considered (plant diversity, climate and experimental settings). Specifically, warming increased plant productivity when plant diversity (indicated by effective number of species) in grasslands was lower than 10, whereas warming decreased plant productivity when plant diversity was greater than 10. Moreover, the structural equation modelling showed that the magnitude of warming enhanced plant productivity by increasing the performance of dominant plant species in grasslands of diversity lower than 10. The negative effects of warming on productivity in grasslands with plant diversity greater than 10 were partly explained by diversity‐induced decline in plant dominance. Main conclusions: Our findings suggest that the positive or negative effect of warming on grassland productivity depends on how biodiverse a grassland is. This may mainly be due to differences in how warming may affect plant dominance and subsequent shifts in interspecific interactions in grasslands of different plant diversity levels. [ABSTRACT FROM AUTHOR]