Study region: The Daliyabuyi Oasis at the terminal of the Keriya River, China. Study Focus: Water scarcity acts as the primary limiting factor for vegetation growth in arid regions. However, studies on the response of desert vegetation to changes in water conditions remain limited. This study used stable isotope method combined with the MixSIAR model, and stem sap flow measurement methods to analyze the seasonal variations in water use patterns and transpiration of vegetation under different water conditions. New hydrological insights: The results showed that as the groundwater depth increased, the water use pattern of Populus euphratica (p. euphratica) trees shifts from shallow soil water to deep water sources. Compared with the shallow groundwater depth sample plots, the proportion of shallow soil water use by p. euphratica in the deep groundwater depth sample plot decreased by 16.66%, while the use of near-groundwater layer soil water and groundwater increased by14.23% and by13.07%, respectively. The influence of tree age on the water use pattern is weak. Throughout the growing season, transpiration of P. euphratica gradually increased from May to July and decreased from August to October.The daily average transpiration of large and small trees was 87.43 L & sdot;d-1 and 11.24 L & sdot;d-1 , respectively. Meanwhile, as transpiration of p. euphratica increased, groundwater use significantly increased. Compared with May, the use of groundwater by p. euphratica in July increased by 26.64%. In addition, flood replenishment increased shallow soil water use by p. euphratica (12.05%), and enhanced transpiration. This study provides insights into water use and adaptability of p. euphratica.