Transpiration, the dominant component of terrestrial evapotranspiration (ET), directly connects the water, energy and carbon cycles and is typically restricted by soil and atmospheric (for example, the vapour pressure deficit (VPD)) moisture stresses through plant hydraulic processes. These sources of stress are likely to diverge under climate change, with a globally enhanced VPD but more variable and uncertain changes in soil moisture. Here, using a model–data fusion approach, we demonstrate that the common empirical approach used in most Earth system models to evaluate the ET response to soil moisture and VPD, which neglects plant hydraulics, underestimates ET sensitivity to VPD and compensates by overestimating the sensitivity to soil moisture stress. A hydraulic model that describes water transport through the plant better captures ET under high VPD conditions for wide-ranging soil moisture states. These findings highlight the central role of plant hydraulics in regulating the increasing importance of atmospheric moisture stress on biosphere–atmosphere interactions under elevated temperatures.
Bibliographical noteFunding Information:
We acknowledge S. C. Schmidler for providing suggestions on statistical inference. A.G.K. and Y.L. were funded by NASA Terrestrial Ecology (award 80NSSC18K0715) through the New Investigator programme. A.G.K. was also funded by the NOAA under grant NA17OAR4310127. M.K. acknowledges support from the National Science Foundation (NSF, EAR-1856054 and EAR-1920425). G.G.K. acknowledges support from the National Science Foundation (NSF-AGS-1644382 and NSF-IOS-1754893).
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