Characteristics of the stem sap flux of Populus euphratica in the lower reaches of the Heihe River Basin, Northwest China

Populus euphratica trees are the sole natural perennial riparian woodlands native to the river oases in the lower reaches of Heihe River Basin in northwestern China. This study investigated characteristics of the stem sap flux of Populus euphratica and its relationship to environmental factors using the thermal dissipation probe (TDP) method. The results showed that (1) daily variation of sap flow of P. euphratica on clear days exhibited an obvious unimodal curve; sap flow rates in June, July, August, and September were 13.39, 12.07, 12.69, and 5.10 L/d, respectively; (2) the average transpiration of the Populus euphratica from June through September amounted to 1,309.84 L; (3) stem sap flow can be affected by a number of environmental factors that, in terms of the influential degree, can be arranged in the descending order of air temperature, soil moisture, relative humidity, total solar radiation, soil temperature, and wind velocity.