Study On Water Use Strategies Of Caragana Korshinskii In Ningxia Hedong Sandy Land Based On Stable Isotope Technology

This study took Caragana korshinskii as the research object,which grown in the Baijitan Nature Reserve in Hedong Sandy Land of Ningxia.Hydrogen and oxygen stable isotope tracer technology,a visual method and multivariate linear mixed model were used to analyze the main water sources of Caragana korshinskii during the growth period(May 2018?October 2018)in different site conditions,and to study water use strategies of Caragana korshinskii under different conditions.Using the long-term monitoring of environmental factors by meteorological stations in the study area to analyze the relationship between atmospheric precipitation and environmental factors.The excavation method was used to study the root distribution characteristics of Caragana korshinskii under different site conditions,combined with the water uptake and utilization of the root of Caragana korshinskii and the water cycle mechanism,to reveal the water use strategies of Caragana korshinskii in different ecological environments.It is expected that the study will provide the scientific basis for optimal allocation of regional water resources,vegetation restoration and ecological sustainable development.The result was shown that:(1)Analyze the hydrogen and oxygen isotope characteristics of the potential water sources(soil water,groundwater,plant water,atmospheric precipitation,irrigation water),the environmental effects of atmospheric precipitation stable isotopes,and seasonal changes during the growth period of Caragana korshinskii intermedia.The result was shown that:In the study area,from May 2018 to October 2018,the atmospheric precipitation line was ? D=6.5255? 18O-3.7443.Due to seasonal changes in water vapor sources,the slope of the atmospheric precipitation line in the study area is significantly smaller than the global atmospheric precipitation line,and there was a positive correlation between ?18O and temperature in precipitation.Atmospheric precipitation mainly replenishes 0?40 cm soil,which was the active layer of soil moisture;40-140 cm was the soil moisture transition layer,and 140?200 cm was the soil moisture stable layer.The soil evaporation line was ?D=4.761 1?18O-26.264,and the slope of the soil evaporation line was smaller than the slope of the atmospheric precipitation line,indicating that the soil water evaporation in the study area was stronger than precipitation replenishment,and the soil water has a fractionation effect.(2)Research and analysis of different potential water sources found that the change of groundwater?18O was relatively stable,and the seasonal variation range was relatively small.The slope of the soil evaporation line was smaller than the slope of the soil precipitation line.Due to the influence of evapotranspiration,the isotope fractionation effect occurs in the study area.The distribution of stable soil isotope ?18O in deep soil was close to that in groundwater,which shows that local groundwater has replenishment effect on deep groundwater.From the changes of stable isotopes in different water sources,it can be found that the soil moisture is recharged by precipitation and groundwater,and the variation range of ?D and ?18O are precipitation,soil water,and groundwater in that order.(3)The intuitive method and the multi-source linear mixed model were used to compare the hydrogen and oxygen isotopes of the xylem of Caragana korshinskii and the stable isotope characteristics of each potential water source under different site conditions.The results showed that the main water-absorbing layer of Caragana korshinskii became shallower with increasing slope.The multi-source linear mixed model was used to quantitatively study the contribution rate of each potential water source during the growth period of Caragana korshinskii.It was found that under irrigation conditions,the water use of plant roots was mostly selected as shallow soil,mainly using soil water above 80 cm;without irrigation The plant mainly absorbs and uses soil water below 80 cm in the early and middle growth period,and mainly uses 40 cm shallow soil water in the later growth period.Irrigation water supply can affect the soil layer above 80 cm.In addition,as the slope increases,the main water-absorbing layer of plants in the early and middle growth periods becomes shallower,while the main water-absorbing layer of plants in the later growth period becomes deeper.When the slope was 16°,the soil water and groundwater below 80 cm were mainly used in the early and middle growth period,and 60 cm soil water was mainly used in the later growth period;when the slope was 24°,the shallow soil of 20-40 cm was mainly used in the early and middle growth period,but mainly absorbs and utilizes deep soil water below 80 cm in the later growth period.(4)Under different site conditions,there are obvious differences in the distribution characteristics of plant roots,which are significantly affected by soil moisture and soil nutrients.When the soil moisture and nutrients are barren,the peak value of the plant root characteristic value shifts from the deep layer to the shallow layer,and the root biomass gradually decreases with the increase of the soil depth after the peak appears.