Change in terrestrial ecosystem water‐use efficiency over the last three decades

• Published in: Global change biology Vol. 21; no. 6; pp. 2366 - 2378
• Main Authors: Huang, Mengtian, Piao, Shilong, Sun, Yan, Ciais, Philippe, Cheng, Lei, Mao, Jiafu, Poulter, Ben, Shi, Xiaoying, Zeng, Zhenzhong, Wang, Yingping
• Format: Journal Article
• Language: English
• Published: England Blackwell Science 01-06-2015; Blackwell Publishing Ltd; Wiley
• Subjects: Bioclimatology; Carbon Cycle; carbon dioxide; Carbon Dioxide - metabolism; climate; Climate Change; CO2 enrichment; Ecology, environment; Ecosystem; Ecosystems; ENVIRONMENTAL SCIENCES; evapotranspiration; evolution; latitude; Life Sciences; Models, Theoretical; nitrogen; Nitrogen - metabolism; nitrogen deposition; Photosynthesis; plant communities; Plant Transpiration; Plants - metabolism; primary productivity; process-based model; remote-sensing; stomatal conductance; Terrestrial ecosystems; vegetation; Water - metabolism; Water resources; water use efficiency; Central America; Amazonia; North America; Siberia; Russia, Siberia; South America, Amazonia; ANE, Europe; CO2 enrichment; process-based model; remote-sensing; nitrogen deposition; water-use efficiency; climate change
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.12873

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⁻¹under 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‐CO₂shows 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 CO₂reducing 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.