Abstract: Populus euphratica is the main tree species in desert riparian forests, with an important role in regulating climate, fixing sand, stabilizing river channel, and maintaining the stability of oasis community. In this study, we investigated P. euphratica near the riverbank at the tail of the Keriya River in the hinterland of Taklimakan Desert in northwestern China. Based on diameter at breast height (DBH), P. euphratica individuals were classified into four development stages, i.e., seedling (Basal diameter≤4 cm), sapling (4 cm<DBH≤10 cm), mature tree (10 cm<DBH≤40 cm), and overmature tree (DBH>40 cm). We measured oxygen stable isotope ratios (δ¹⁸O) in xylem water, soil water in different soil layers (0-300 cm depth), groundwater, and river water. Four potential water sources were classified: shallow soil water (0-140 cm), deep soil water (140-300 cm), groundwater, and river water. The ratios of different potential water sources used by P. euphratica were determined using the IsoSource model. Stable carbon isotope technology was used to examine the water use efficiency ofP. euphratica in different development stages. The result showed that δ¹⁸O value of xylem water of P. euphratica decreased with DBH, with a range of -6.10‰ to -5.67‰. Seedling, sapling, mature tree, and overmature tree of P. euphratica mainly used river water, with corresponding water use ranges of 0-74%, 0-77%, 7%-80%, and 17%-82%, respectively. Foliar δ¹³C of P. euphratica changed slightly with increasing DBH, ranging between -29.96‰ and -29.02‰. Our findings suggested that P. euphratica growing near the riverbank at the tail of the Keriya River have good water conditions and suffer little drought stress.

Key words: Populus euphratica, riverbank, stable isotope, water source, water use efficiency.