Water Sources Of Dominant Plants Of The Subalpine Shrub And Its Water Supply Relations In The Eastern Of Qilian Mountains,China

The hydrological process in high-cold area is one of the significant links to ecosystem,and the hydrothermal conditions directly determine the ecological environment.The study on the hydrological cycle and the water sources and utilization strategies of dominant plants can provide theoretical basis for the improvement of eco-environment in high-cold areas.Under the background of global climate change,the change of precipitation pattern will have vital impact on water sources and utilization strategies of plant individual,vegetation distribution as well as ecosystem water balance.The use of stable hydrogen and oxygen isotopes has become an effective tool for tracing the source of plant water because of its high sensitivity and accuracy.But it is started relatively late in China,mainly in arid and semi-arid areas and humid areas,so there are few studies on high-cold areas.Subalpine shrub is an important vegetation type in Qilian Mountains,and has high water conservation capacity.However,under the influence of climate change and agricultural and pastoral activities,the degradation and destruction of shrub are more serious in Qilian Mountains,which have a certain impact on the hydrological processes in cold regions.Therefore,it is necessary to research on hydrogen and oxygen of stable isotope characteristics of dominant plants of subalpine shrub in Qilian Mountains,so as to explore the water use strategies of typical plants.In this study,six species of dominant subalpine shrub plants in the eastern Qilian Mountains were selected to analyze the water sources of different plants in the same biotope landscape and the water source changes of the same plant in different growth stages using multivariate linear mixed models(Isosource).1.The local meteoric water line(LMWL)equation was ?D = 7.775 ?18O + 12.34(R2 = 0.871,P< 0.001),which showed that the study area has the characteristics of strong evaporation,low temperature and high humidity.Most of the isotope of plant water were located at lower right of the atmospheric precipitation line,with indicated that the isotopic enrichment is evident during the transpiration of the plant.The hydrogen and oxygen isotopes of river water were between that of precipitation,groundwater and soil water,and the recharge of water was obvious.2.The isotope ratios of hydrogen and oxygen in different plants were different,and were significantly different at different times.Comparing the ?D of precipitation during the whole sampling period,it was found that the fluctuation ranges of hydrogen isotope ratios were relatively large from July to August,and the values at the end of July were significantly higher than other periods,reflecting the heavy isotope enriched during this period.The isotope ratios of hydrogen and oxygen in soil water for different soil layers were significantly different at different times.The isotope ratios of hydrogen and oxygen in river and groundwater were relatively stable and were little variation at different times.3.For six dominant species of subalpine shrub,the utilization of precipitation was the highest in the eastern of Qilian Mountains,secondly was soil water underground from 0cm to 10 cm,while it was the lowest for contribution of groundwater.The utilizations to soil water underground from 10 to 80 cm were relatively higher for Rhododendron capitatum Maxim,Spiraea Salicifolia L.,Salix cupularis,Rhododendron thymifolium Maximthan,Salix oritrepha Schneid and Potentilla fruticosa Linn.The six dominant plant species changed the proportions of different water sources utilized during the sampling period.On July,the six dominant plant species mainly used precipitation and shallow soil water.The contribution rates of precipitation and soil water underground from 0cm to 10 cm were similar for S.salicifolia,R.capitatum Maxim,and R.thymifolium Maximwere,but other three species mainly used precipitation.On August,the main water sources of all six species were precipitation.The utilized efficiencies of precipitation were higher for S.Salicifolia,S.cupularis,and R.thymifolium Maxim than S.oritrepha Schneid,R.capitatum Maxim and P.fruticosa Linn,but those of underground water were higher for the latter than the former.4.Based on the estimation of the river recharge sources in the study area,the contribution rates of groundwater to river water were more than 50% on July 23,August 2 and August 14,which were the main sources of recharge for runoff.With the changing of time,the supply of precipitation to groundwater decreased firstly and then increased,and the recharge of groundwater by soil water increased firstly and then decreased.Soil water was the main source of recharged groundwater,with a contribution rate more than 50%,and the change of precipitation was positively correlated with the contribution of precipitation to groundwater.From July to August,groundwater was the main source of soil water for the contribution rate of groundwater to soil water more than 50%.