Threshold of vapour–pressure deficit constraint on light use efficiency varied with soil water content

Understanding the constraints on light-use efficiency (LUE) induced by high evaporative water demand (vapour–pressure deficit; VPD) and soil stress (soil moisture content; SMC) is crucial for understanding simulating vegetation productivity, particularly in arid semi-arid regions. However, relative impacts of VPD SMC LUE are unclear, as we lack a mechanistic their interactions. In this study, quantified roles limiting analysed interactions among VPD, using data from CO2 flux stations weather along climatic gradient Heihe River Basin, China. We found threshold constraint LUE; above threshold, decreased at only 3.6% to 23.1% rate below threshold. As decreased, however, increased, reduction caused significantly, which more than half that moister Therefore, both played essential limitation stress. A also existed heat correlation between strength first then increased with increasing VPD. Our results clarified LUE, can improve simulation prediction plant productivity.