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.