| Afforestation has long been regarded as an important approach for ecological restoration worldwide.With looming water crisis under climate change, knowledge concerning water consumption by large scale plantation is pressingly needed. We selected a poplar plantation located in Yufa Forest Farm, Daxing District, Beijing to conduct sapflow study. Poplar is one of the most common planted speices in northern China. Stand transpiration was monitored with thermal dissipation probes and simultaneous climate and soil condition were measured in order to study the transpiration pattern in relation to environmental drivers. The results showed that:whole tree transpiration was not significantly correlated (R2=-0.135, P=0.057, n=200) with volumetric soil water content (VWC) due to the absence of soil moisture stress during growing season. Hysteresis existed between sap flow and net radiation (Rn), as well as vapor pressure deficit (VPD). However, the latter two shared significant correlation (P=0.00) with sap flow. Moreover, VPD was the dominant influence on nocturnal sap flow(P<0.05). Throughout the growing season, low Rn and air temperature surpressed stand transpiration during spring. Such control of Rn persisted into summer when sufficient soil water was availiable. However, VPD became more important during autumn. Estimated value from models incorporating environmental variables to predict sap flow agreed well with the observed value. The agreement was better on hourly scale than daily. |
