The Investigate Of Plant Water Sources And Influencing Factors In Subalpine Shrubland On North Slope Of Qilian Mountains

Located in the northeastern edge of the Qinghai-Tibet Plateau in China,the Qilian Mountains are an important ecological barrier in the Northwest China.Subalpine shrublands are an important part of water conservation forests in the Qilian Mountains.Research on the water sources of subalpine shrubs in the Qilian Mountains is helpful to understand the eco-hydrological processes in the subalpine habitats.In this study,the stable isotopic composition of precipitation,soil water,xylem water,river water,and spring water as well as relevant environmental variables（meteorological and soil water variables）in the subalpine habitats on the northern slope of Qilian Mountains were monitored.The xylem waterline（XWL）equation and ANOVA were used to analyze the isotopic characteristics of subalpine shrubs.The Iso Source model was used to determine the potential water contribution rate of different subalpine shrubs,and the water sources of subalpine shrubs in the same habitat and different habitats were studied.The factors affecting the water source of subalpine shrubs were analyzed by the correlation analysis method.The following are the main conclusions:（1）There were differences in the XWL of the various subalpine shrubs in same habitat and the same subalpine shrubs in different habitats.For subalpine shrubs located in the same habitat,only theδ²H of xylem water was significantly different between Potentilla fruticosa and Caragana jubata on the semi-shaded slope（p<0.05）.There was no significant difference in theδ²H andδ¹⁸O values of xylem water between other subalpine shrubs.For the same subalpine shrubs located in different habitats,there was no significant difference in theδ²H andδ¹⁸O values between them.（2）The potential water sources of subalpine shrubs in the study area were consisitent.Shallow soil water at 0–30cm was the main water source for subalpine shrubs,and deep soil water below 30cm showed a small contribution rate.Only Potentilla fruticosa and Salix sclerophylla had higher water utilization rates for deep soil water below 30cm.The subalpine shrubs showed a higher utilization rate to surface soil water on the semi-shaded slope than on the semi-sunny slopet,and a higher utilization rate to deep soil water on the semi-sunny slope than on the semi-shaded slope.（3）During the sampling period,there were differences in the utilization ratio to soil water at different depths for subalpine shrubs.In date with less precipitation or large water demand,some subalpine shrubs increased the utilization of deep soil water to meet the water demand for growth,resulting in marked differences in the water sources of subalpine shrubs within the same habitat.Among them,the soil water below 30cm was used more by Salix sclerophylla on the semi-sunny slope,Potentilla fruticosa and Rhododendron anthopogonoides on the semi-shaded slope.Similarly,in the dry or growing season,subalpine shrubs increase the utilization of deep soil water on the semi-sunny or semi-shaded slope,resulting in marked differences in the water sources of the same subalpine shrub species under different habitats.Among them,the water sources of Potentilla fruticosa and Salix oritrepha were different in different habitats.（4）Correlation analysis showed that soil water content had a greater impact on the water source of subalpine shrubs.Affected by soil water content and the distribution depth of fine roots,subalpine shrubs in the study area mainly obtain water from the shallow soil layer.Under the context of climate change,some highly adapted subalpine shrubs（such as Salix cupularis,Salix oritrepha,Potentilla fruticosa,Salix sclerophylla,Caragana jubata）that switch water between shallow and deep soil layers may have a competitive advantage than other subalpine shrubs that only utilize shallow soil water.