[Water sources of and in the Tianshan Mountains in summer].

Water use patterns of trees and shrubs in the coniferous forest remain unclear, due to a lack of quantitative analysis on water use dynamics. In this study, the xylem water hydrogen and oxygen stable isotope compositions of and the companion shrub species were measured to detect their water sources. The IsoSource model was used to analyze the relative contribution of each potential water source for both species during summer. The results showed that during July, and mainly extracted water from the 0-60 cm soil layer due to the relatively sufficient soil water content, with the relative contributions being 73.8% and 63.2% for the two species, respectively. In August, with the decreases in soil water content, water source of remained stable, and the relative contribution of soil water above 60 cm was 69.5%. In contrast, reverted to water source from deeper soil layer, with the relative contribution of shallow soil (0-20 cm) water decreasing to 14.3% and that of middle (20-60 cm) to deep (60-100 cm) soil water increased to 67.7%. In September, with the increases of water content in the shallow soil layer, both species extracted water from shallow soil layers, with the relative contribution reaching to 95.0%. In summary, exhibited typical shallow root characteristics, while extracted water from the 0-100 cm soil profile and could flexibly change its water source corresponding to changes in soil water content to cope with changing environmental water condition.