Abstract
Variations in precipitation pattern under climate changes influence water availability that have important implications for plants water use and vegetation sustainability. However, the water use characteristic of the main tree species under different temporal-spatial of water availability remain poorly understood, especially in high temporal-spatial heterogeneity area, such as subtropical monsoon climate region of China. We investigated water use characteristics of the most widely and common natural trees, Mallotus philippensis and Celtis biondii , in edaphic and rocky habitats. We measured the δD and δ 18 O values of xylem and soil water and water potential of plant leaves during the wet season in 2020. The results showed that the two species mainly absorbed soil water from shallow layers and switched for deeper layers during the late of the wet season in both habitats. But the plant water sources were different in edaphic and rocky habitats when the antecedent precipitation was much high, deep layers soil water in the former and still shallow layers in the latter. The two species had no significant differences in water uptake depth, but notably distinction in the diurnal water potential ranges. M. philippensis maintained less negative predawn and midday water potential, whereas C. biondii showed higher diurnal water potential ranges. Besides, the water potential of C. biondii were negatively associated with antecedent precipitation amount. These results indicate that there is significant eco-physiological niche segregation but no ecohydrological segregation co-existing species in communities. Besides, antecedent precipitation amount and habitat differences were the main factors influencing the plant water uptake depth. While the relationship between leaf physiological traits and water availability was affected by the species types, rather than the habitats. Furthermore, during the long drought in growing season, there are probable divergent responses of M. philippensis and C. biondii , such as growth restriction and hydraulic failure. But when the precipitation is heavy and long, these natural species could increase the ecohydrological linkages between ecosystem and the deep-layer system in edaphic habitat.