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【Nature Climate Change 等】生态系统碳水通量与大气蒸发
发布时间:2016-10-31  来源:土壤与农业可持续发展国家重点实验室  浏览:522

【生态系统碳水通量与大气蒸发】Kimberly A. Novick, Darren L. Ficklin, Paul C. Stoy, Christopher A. Williams, Gil Bohrer, A. Christopher Oishi, Shirley A. Papuga, Peter D. Blanken, Asko Noormets, Benjamin N. Sulman, Russell L. Scott, Lixin Wang & Richard P. Phillips. The increasing importance of atmospheric demand for ecosystem water and carbon fluxes. Nature Climate Change 6, 1023–1027 (2016) doi:10.1038/nclimate3114

Abstract

Soil moisture supply and atmospheric demand for water independently limit—and profoundly affect—vegetation productivity and water use during periods of hydrologic stress1, 2, 3, 4. Disentangling the impact of these two drivers on ecosystem carbon and water cycling is difficult because they are often correlated, and experimental tools for manipulating atmospheric demand in the field are lacking. Consequently, the role of atmospheric demand is often not adequately factored into experiments or represented in models5, 6, 7. Here we show that atmospheric demand limits surface conductance and evapotranspiration to a greater extent than soil moisture in many biomes, including mesic forests that are of particular importance to the terrestrial carbon sink8, 9. Further, using projections from ten general circulation models, we show that climate change will increase the importance of atmospheric constraints to carbon and water fluxes in all ecosystems. Consequently, atmospheric demand will become increasingly important for vegetation function, accounting for >70% of growing season limitation to surface conductance in mesic temperate forests. Our results suggest that failure to consider the limiting role of atmospheric demand in experimental designs, simulation models and land management strategies will lead to incorrect projections of ecosystem responses to future climate conditions.


【黄土高原植被恢复已接近承载力阈值】Xiaoming Feng, Bojie Fu, Shilong Piao, Shuai Wang, Philippe Ciais, Zhenzhong Zeng, Yihe Lü, Yuan Zeng, Yue Li, Xiaohui Jiang & Bingfang Wu. Revegetation in China’s Loess Plateau is approaching sustainable water resource limits. Nature Climate Change 6, 1019–1022 (2016) doi:10.1038/nclimate3092

Abstract

Revegetation of degraded ecosystems provides opportunities for carbon sequestration and bioenergy production1, 2. However, vegetation expansion in water-limited areas creates potentially conflicting demands for water between the ecosystem and humans3. Current understanding of these competing demands is still limited4. Here, we study the semi-arid Loess Plateau in China, where the ‘Grain to Green large-scale revegetation programme has been in operation since 1999. As expected, we found that the new planting has caused both net primary productivity (NPP) and evapotranspiration (ET) to increase. Also the increase of ET has induced a significant (p < 0.001) decrease in the ratio of river runoff to annual precipitation across hydrological catchments. From currently revegetated areas and human water demand, we estimate a threshold of NPP of 400 ± 5gCm−2yr−1 above which the population will suffer water shortages. NPP in this region is found to be already close to this limit. The threshold of NPP could change by −36% in the worst case of climate drying and high human withdrawals, to +43% in the best case. Our results develop a new conceptual framework to determine the critical carbon sequestration that is sustainable in terms of both ecological and socio-economic resource demands in a coupled anthropogenic–biological system.


【大气CO2季节变化与陆地生产力】Sabrina Wenzel, Peter M. Cox, Veronika Eyring & Pierre Friedlingstein. Projected land photosynthesis constrained by changes in the seasonal cycle of atmospheric CO2. Nature 538, 499–501 (27 October 2016) doi:10.1038/nature19772

Abstract

Uncertainties in the response of vegetation to rising atmospheric CO2 concentrations1, 2 contribute to the large spread in projections of future climate change3, 4. Climate–carbon cycle models generally agree that elevated atmospheric CO2 concentrations will enhance terrestrial gross primary productivity (GPP). However, the magnitude of this CO2 fertilization effect varies from a 20 per cent to a 60 per cent increase in GPP for a doubling of atmospheric CO2 concentrations in model studies5, 6, 7. Here we demonstrate emergent constraints8, 9, 10, 11 on large-scale CO2 fertilization using observed changes in the amplitude of the atmospheric CO2 seasonal cycle that are thought to be the result of increasing terrestrial GPP12, 13, 14. Our comparison of atmospheric CO2 measurements from Point Barrow in Alaska and Cape Kumukahi in Hawaii with historical simulations of the latest climate–carbon cycle models demonstrates that the increase in the amplitude of the CO2 seasonal cycle at both measurement sites is consistent with increasing annual mean GPP, driven in part by climate warming, but with differences in CO2 fertilization controlling the spread among the model trends. As a result, the relationship between the amplitude of the CO2 seasonal cycle and the magnitude of CO2 fertilization of GPP is almost linear across the entire ensemble of models. When combined with the observed trends in the seasonal CO2 amplitude, these relationships lead to consistent emergent constraints on the CO2 fertilization of GPP. Overall, we estimate a GPP increase of 37 ± 9 per cent for high-latitude ecosystems and 32 ± 9 per cent for extratropical ecosystems under a doubling of atmospheric CO2 concentrations on the basis of the Point Barrow and Cape Kumukahi records, respectively.


【利用气候模型评价全球观测数据库质量】François Massonnet1,2,*, Omar Bellprat1, Virginie Guemas1,3, Francisco J. Doblas-Reyes1,4. Using climate models to estimate the quality of global observational data sets. Science  28 Oct 2016: Vol. 354, Issue 6311, pp. 452-455 DOI: 10.1126/science.aaf6369

Abstract

Observational estimates of the climate system are essential to monitoring and understanding ongoing climate change and to assessing the quality of climate models used to produce near- and long-term climate information. This study poses the dual and unconventional question: Can climate models be used to assess the quality of observational references? We show that this question not only rests on solid theoretical grounds but also offers insightful applications in practice. By comparing four observational products of sea surface temperature with a large multimodel climate forecast ensemble, we find compelling evidence that models systematically score better against the most recent, advanced, but also most independent product. These results call for generalized procedures of model-observation comparison and provide guidance for a more objective observational data set selection.


【极地沉积物中氮循环过程】N. D. McTigue, W. S. Gardner, K. H. Dunton & A. K. Hardison. Biotic and abiotic controls on co-occurring nitrogen cycling processes in shallow Arctic shelf sediments. Nature Communications 7,  Article number: 13145 (2016) doi:10.1038/ncomms13145

Abstract

The processes that convert bioavailable inorganic nitrogen to inert nitrogen gas are prominent in continental shelf sediments and represent a critical global sink, yet little is known of these pathways in the Arctic where 18% of the world’s continental shelves are located. Moreover, few data from the Arctic exist that separate loss processes like denitrification and anaerobic ammonium oxidation (anammox) from recycling pathways like dissimilatory nitrate reduction to ammonium (DNRA) or source pathways like nitrogen fixation. Here we present measurements of these co-occurring processes using 15N tracers. Denitrification was heterogeneous among stations and an order of magnitude greater than anammox and DNRA, while nitrogen fixation was undetectable. No abiotic factors correlated with interstation variability in biogeochemical rates; however, bioturbation potential explained most of the variation. Fauna-enhanced denitrification is a potentially important but overlooked process on Arctic shelves and highlights the role of the Arctic as a significant global nitrogen sink.

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