Transpiration of a Linze jujube orchard in an arid region of China

摘要

As an important source of income in the region's economy, the jujube plantations are very common in arid north-western China, and their planted areas continue to expand. In the central Heihe River Basin of arid north-western China, Linze jujube (Zizyphus jujuba Mill. var. inermis (Bunge) Rehd.) plantations cover more than 10,000 ha, too. Water use by this species is expected to change or modify catchment hydrological process. To our knowledge, there is no information on the transpiration and canopy conductance of the jujube plantations in arid north-western China. Therefore, Transpiration and canopy conductance were monitored in a 14-year-old Linze jujube orchard. The experiment was carried out in the central Heihe River Basin, near Pingchuan Town (Linze County, Gansu Province, China) during growing season of 2006, from May to the first ten days of October. Eight trees were used to measure sap flow using the heat-pulse-velocity method. The orchard was irrigated adequately during the study. Transpiration was estimated from the sap flow measurements. During the experiment, the transpiration rate of the orchard ranged from 0.32 to 1.40 mm per day. Canopy conductance was obtained from estimated daily transpiration and climatic variables measured on a half-hour basis, and canopy conductance for water vapour transfer was between 1.20 to 82.57 mm s~(-1) with a mean of 11.86 ±6.84 mm s~(-1) during the observation period. Air temperature and vapour-pressure deficit exhibited a linear relationship with sap flow velocity and the relationship between these factors and canopy conductance could be represented by an exponential decay function.