Change in terrestrial ecosystem water‐use efficiency over the last three decades |
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| Authors: | Mengtian Huang Shilong Piao Yan Sun Philippe Ciais Lei Cheng Jiafu Mao Ben Poulter Xiaoying Shi Zhenzhong Zeng Yingping Wang |
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| Affiliation: | 1. Sino‐French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University, Beijing, China;2. Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Center for Excellence in Tibetan Earth Science, Chinese Academy of Sciences, Beijing, China;3. LSCE, UMR CEA‐CNRS, Bat. 709, CE, L'Orme des Merisiers, Gif‐sur‐Yvette, France;4. CSIRO Land and Water Flagship, Canberra, ACT, Australia;5. Climate Change Science Institute and Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA;6. Institute on Ecosystems and the Department of Ecology, Montana State University, Bozeman, MT, USA;7. CSIRO Ocean and Atmosphere Flagship, PMB 1, Aspendale, Vic., Australia |
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| Abstract: | Defined as the ratio between gross primary productivity (GPP) and evapotranspiration (ET), ecosystem‐scale water‐use efficiency (EWUE) is an indicator of the adjustment of vegetation photosynthesis to water loss. The processes controlling EWUE are complex and reflect both a slow evolution of plants and plant communities as well as fast adjustments of ecosystem functioning to changes of limiting resources. In this study, we investigated EWUE trends from 1982 to 2008 using data‐driven models derived from satellite observations and process‐oriented carbon cycle models. Our findings suggest positive EWUE trends of 0.0056, 0.0007 and 0.0001 g C m?2 mm?1 yr?1 under the single effect of rising CO2 (‘CO2’), climate change (‘CLIM’) and nitrogen deposition (‘NDEP’), respectively. Global patterns of EWUE trends under different scenarios suggest that (i) EWUE‐CO2 shows global increases, (ii) EWUE‐CLIM increases in mainly high latitudes and decreases at middle and low latitudes, (iii) EWUE‐NDEP displays slight increasing trends except in west Siberia, eastern Europe, parts of North America and central Amazonia. The data‐driven MTE model, however, shows a slight decline of EWUE during the same period (?0.0005 g C m?2 mm?1 yr?1), which differs from process‐model (0.0064 g C m?2 mm?1 yr?1) simulations with all drivers taken into account. We attribute this discrepancy to the fact that the nonmodeled physiological effects of elevated CO2 reducing stomatal conductance and transpiration (TR) in the MTE model. Partial correlation analysis between EWUE and climate drivers shows similar responses to climatic variables with the data‐driven model and the process‐oriented models across different ecosystems. Change in water‐use efficiency defined from transpiration‐based WUEt (GPP/TR) and inherent water‐use efficiency (IWUEt, GPP×VPD/TR) in response to rising CO2, climate change, and nitrogen deposition are also discussed. Our analyses will facilitate mechanistic understanding of the carbon–water interactions over terrestrial ecosystems under global change. |
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| Keywords: | climate change CO2 enrichment nitrogen deposition process‐based model remote‐sensing water‐use efficiency |
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