Apparent surface conductance sensitivity to vapour pressure deficit in the absence of plants
Apparent surface conductance sensitivity to vapour pressure deficit in the absence of plants
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DOI：
10.1038/s44221-023-00147-9
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发表时间：
2023-10
期刊：
影响因子：
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通讯作者：
L. V. Vargas Zeppetello;K. McColl;Jeremiah A. Bernau;Brenda B. Bowen;Lois I. Tang;N. M. Holbrook;Pierre Gentine;Peter Huybers
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文献类型：
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作者：
L. V. Vargas Zeppetello;K. McColl;Jeremiah A. Bernau;Brenda B. Bowen;Lois I. Tang;N. M. Holbrook;Pierre Gentine;Peter Huybers
越来越多的文献认为，由于植物的气孔调节，生态系统规模的蒸散对大气干燥比对表面土壤湿度的减少更敏感。过去的研究分析了观测结果，很难最终控制植物生理学、可测量的状态变量（例如蒸气压不足（VPD）或土壤湿度）和生态系统规模的水通量之间的潜在关系。在这里，我们分析了在无植被但水文活跃的盐滩上进行的自然机制拒绝实验。在这些地点，生态系统规模的表面电导（gs，陆地表面如何影响蒸散量的主要衡量指标）对 VPD 的任何明显敏感性都不能归因于气孔关闭。在盐滩上，我们发现 VPD-gs 关系类似于通常归因于气孔关闭的关系，并使用排除植物的简约边界层模型重现了类似的关系。我们的结论是，观测研究可能夸大了生态系统规模的表面电导对大气干燥的敏感性，而低估了表面土壤湿度变化的重要性。这一发现对未来的生态系统具有广泛的影响，因为土壤湿度的人为趋势是不确定的且具有空间异质性，而全球变暖预计将导致普遍存在的大气干燥。
A growing literature argues that ecosystem-scale evapotranspiration is more sensitive to drying of the atmosphere because of stomatal regulation by plants than to reductions in surface soil moisture. Past studies analysed observations, for which it is difficult to conclusively control for potential relations among plant physiology, measurable state variables such as vapour pressure deficit (VPD) or soil moisture, and ecosystem-scale water flux. Here we analyse natural mechanism-denial experiments at non-vegetated but hydrologically active salt flats. At these sites, any apparent sensitivity of the ecosystem-scale surface conductance (gs, a bulk measure of how the land surface influences evapotranspiration) to VPD cannot be due to stomatal closure. Over the salt flats we find a VPD–gsrelation similar to that commonly attributed to stomatal closure, and reproduce similar relations using a parsimonious boundary layer model that excludes plants. We conclude that observational studies probably overstate the sensitivity of ecosystem-scale surface conductance to atmospheric drying and understate the importance of variations in surface soil moisture. This finding has broad implications for future ecosystems, because anthropogenic trends in soil moisture are uncertain and spatially heterogeneous whereas ubiquitous atmospheric drying is expected due to global warming.