The δ18O and δ2H showed significant correlations in plant water, precipitation, and soil water during the study period (Figure 5). The equation δ2H =7.89 × δ18O +17.79 (R2 = 0.97; p < 0.05) was used to describe the local meteoric water line (LMWL), the slope was smaller than the global meteoric water line, GMWL: δ2H = 8.17 × δ18O + 10.35; (Rozanski et al., 1993), indicating that evaporation is a main reason of arid climate and kinetic fractionation. The slopes and intercepts of the soil water line equations at both sites were smaller than those of the LMWL (Figure 5), indicating that the ongoing evaporation influence soil water (Yang&Fu, 2017). The linear relationships of δ18O and δ2H in soil water between shrub and grassland sites, which were δ2H = 5.83 × δ18O – 4.83 (R2 = 0.71) and δ2H = 5.46 × δ18O – 8.66 (R2 = 0.84), respectively, were significant, indicating that soil water evaporation was significantly different for plants between shrub and grassland sites. Moreover, the relationships between δ18O and δ2H were δ2H = 1.54 × δ18O – 33.75 (R2 = 0.96) for plant water at the shrub site, and δ2H = 2.46 × δ18O – 24.57 (R2 = 0.57) at the grassland site.