Limitation of soil moisture on the response of transpiration to vapor pressure deficit in a subtropical coniferous plantation subjected to seasonal drought

•Multiplicative model was developed to quantify VPD and soil moisture contribution.•An exponential response of transpiration to VPD or soil moisture was appropriate.•Daily soil moisture contributes 17.8 ± 6.7% of limitation to maximum transpiration. Plant transpiration accounts for >60% of evapotranspiration and is affected by drought in various ways. Seasonal droughts are frequent in humid region, and co-occur with increasing atmospheric vapor pressure deficit (VPD) and decreasing soil moisture. Independent effects of atmospheric water demand and soil water supply on transpiration are still unclear. In this study, plant transpiration and environmental factors were monitored from April 2012 through December 2017 in a subtropical coniferous plantation, where low precipitation and high temperature occurred in summer and autumn. Our results confirmed the nonlinear relationship between atmospheric VPD and soil moisture and transpiration. A multiplicative model of atmospheric VPD and soil moisture on plant transpiration was developed to quantify their relative contributions to plant transpiration. The response of plant transpiration to atmospheric VPD or soil moisture followed an exponential function when they neither factor was limiting. Throughout the study period, atmospheric VPD and soil moisture explained on average 90.8% and 9.2% of the limitation on plant transpiration, respectively. While seasonal drought occurred during July to October, monthly mean contribution of soil moisture limitation to plant transpiration was 17.8 ± 6.7% with a maximum daily contribution of 86.8%. Our results showed that transpiration in this subtropical coniferous plantation would be further limited by soil moisture in conditions of future climate change.