Ecosystem water use efficiency in a warm-temperate mixed plantation in the North China

Abstract

Water use efficiency (WUE) at the ecosystem level is an important ecophysiological index reflecting the coupling relationship between water and carbon cycles. CO2 and water vapor fluxes were measured by the eddy covariance method during the period 2006–2010 over a warm-temperate mixed plantation in the North China. The seasonal and interannual variations of gross primary productivity (GPP), evapotranspiration (ET) and ecosystem WUE were analyzed, and the impacts of climatic variables and soil moisture on GPP, ET and WUE were discussed. At the monthly scale, GPP and ET had similar relations with solar radiation, air temperature, vapor pressure deficit (VPD) and precipitation. It is suggested that photosynthesis and evapotranspiration were driven by climatic variables at the approximately equal strength. During the growing season, WUE decreased significantly with the increase of VPD and solar radiation. Cloudiness can improve photosynthesis and enhance WUE. GPP was 9–39% greater but ET was 8–26% lower under cloudy sky conditions than that under sunny sky conditions. Therefore, WUE was 29–72% higher under cloudy skies in comparison with that under sunny skies. Annual average WUE ranged from 1.76 to 2.41 g C kg−1 H2O. The major driver of interannual variability in WUE was soil water content in May.