Transpiration and Canopy Conductance of Poplar Trees and Its Relationship with Meteorological Factors in an Arid Region of China

摘要

Transpiration of a poplar tree in an arid region of China was determined using the heat dissipation technique. During the study period from 27 June to 7 November 2011, a diurnal rhythm of sap flow can be clearly seen. The diurnal fluctuation of sap flow was related to variations of meteorological factors. The daily sap flow velocity ranged from 9.1 cm/d to 223.5 cm/d with a mean value of 122.1 cm/d in the study period. The averaged monthly sap flow velocity varies insignificantly as the poplar tree took about 40% of water transpired from groundwater based on the partitioning of water sources of transpiration using stable isotopes. The average tree conductance in daytime was 3.34 mm s-1 and decreased exponentially with increasing vapor pressure deficit (VPD), indicating that stomata were controlled mainly by VPD. The averaged decupling factor was very low (0.09), indicating that the canopy of the poplar tree was strongly coupled to the atmosphere.