Abstract:Present study determined the effect of soil moisture condition on leaf carbon isotope composition (δ13C), photosynthesis and current year branch growth of Reaumuria soongorica in the pot experiment. The branch growth and δ13C of R. soongorica growing in different degraded area were investigated, and their relationship with soil moisture content that plant stand were analyzed. The results showed that:(1) The current year branch biomass (DM), length of first grade branches (LFG), number of second grade branches (NSG), net photosynthesis rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of R. soongorica were largely reduced as water supplies decreased in the pot experiments. δ13C and water use efficiency(WUE) increased as water supplies reduced, and a significant negative correlation was observed between δ13C and DM,LFG,NSG,Pn,Gs and Tr. (2) In the field, δ13C decreased from light degraded sites to severe degraded one and significantly negatively correlated with soil water content at a depth of 30-60 cm and 60-100 cm. A negative relationship was also observed between δ13C and biomass per unit canopy area (BCA) and number of first grade branch per unit canopy area (NCA). These results suggested that δ13C is a good indicator of R. soongorica response to water stress both under potted and field conditions and R. soongorica mainly utilize water in deeper soil and utilize water more efficiently in light degraded area than that in severe degraded area. This conclusion may improve understanding water use strategies of R. soongorica in the arid environments, and have practical use in grassland management and restoration.