Spatial and Temporal Characteristics of Stem Sap Flow of Populus euphratica

The sap flow rate of Populus euphratica and its relationship with environmental factors has been observed for one year in Ejin oasis at lower Heihe river by using HPVR, TDR and ICT systems. The result showed the following regularities: the diurnal variation of sap flow rate of Populus euphratica appears single-peak; there is little sap flow rate in morning and night; there is the same variation trend at different points; the velocity increases with the depth increase, and there is the maximum at 15 mm depth; but the velocity decreases when the depth exceeds 15 mm. In the direction, the velocity in south and west is higher than in north and east. Due to water intimidation, sap flow rate has the character of fluctuation. With the relationship of sap flow rate with weather factor, the amount of evapotranspiration can be predicted.