Objective Water use efficiency (WUE) is an important indicator of carbon and water coupling in ecosystems, and its relationship with environmental factors has attracted much attention. However, the adaptation mechanism of plant potential water use capacity to environmental change has been rarely reported. This study was to explore the seasonal dynamics of potential leaf water use efficiency and its environmental controls in Vitex negundo var. heterophylla, the dominant shrub species of Pinus tabuliformis in Beijing.
Method We measured the photosynthesis and transpiration of photosynthesis-light response curves and calculated corresponding instantaneous water use efficiency (WUEi) from June to October, 2021 using a portable photosynthesis analyzer. In addition, the micrometeorological in situ observation method was used to determine the environmental factors such as air temperature (Ta), soil moisture content (SWC), air vapor pressure deficit (VPDa) and so on. Fitting model of WUEi against light was used to get the maximum water use efficiency (WUEmax). On this basis, the seasonal dynamics of WUEmax and the relationship between WUEmax and environmental factors were analyzed.
Result Consequently, the WUEmax descended first and then stayed steady during the growing season, ranging from 2.84 to9.17 μmol/mmol, with a mean of 4.79 μmol/mmol. Seasonal variations in WUEmax were mainly affected by SWC and Ta. Among them, SWC was the key environmental factor regulating WUEmax. WUEmax was negatively correlated with SWC, and SWC was mainly affected WUEmax through leaf stomatal conductance (gc). WUEmax was positively correlated with Ta, and Ta mainly affected WUEmax by regulating photosynthetic carboxylase activity.
Conclusion In the humid environment, Vitex negundo var. heterophylla mainly adapts to the environment through the water resource acquisition strategy. High SWC and Ta are inhibitory factors for WUEmax in leaves of Vitex negundo var. heterophylla.