Comparison Of The Methods Of Stable Hydrogen And Oxygen Isotope In Distinguishing The Water Source Of Nitraria Tangutorum

The change of water will affect plants' distribution, because any kind of plants need water to support their growth. In the aridland region, water will be the key factor to restrict the growth of plants.Different plants absorbe water of different sources. When the plant water sources are ruducing, the territory of plants distribution will decrease too. So, the reserch of plant water sources will help to kown the time-space distribution pattern about plants under the background of global change. On the basis of isotope's mass-balance, the source of water will be determined by analyzing the stable oxygen and hydrogen isotope. The isotopic methods has also been improved. This paper used the two or three compartment linear mixing model, multiple sources linear mixing model, the model of mean depth of water uptake by plants and dynamic model to determine the N. tangutorum's water sources respectively. This paper also compared the advantages and disadvantages of each model.Results show that: N.tangutorum in golmud mainly use groundwater and soilwater of 50-100cm depths, more inclined to absorb soilwater in the depths of 70-100cm. The mean depth of soilwater uptaked by N. tangutorum is between 60cm and 95cm.The models have their own range of application and limitations. The two or three compartment linear mixing model will be used only in the situation of less than three sources. And the rusult ofδD andδ¹⁸O must have obvious difference.If the plant absorbs water more than three sources, we can simplify the sources, remove the sources which has less contribution to the plant's growth, until the sources was less than three. Or we can merge into three sources to simplify the analysis. Then, we can estimate the contribution of the water sources to the xylem water in plants. multiple sources linear mixing model can remedy the defects of two or three compartment linear mixing model. Multiple sources mixed-linear model can also compare more than three water sources' contribution to the plant at the same time and point out each source of water's contribution limits. Mixing models can not calculate the mean depth of the water that N.tangutorum absorbed. The model of mean depth of water will solve this problem. But the model of mean depth of water is confined to the absorption of soilwater,regardless the else sources of water. Multiple sources mixed-linear model and the model of mean depth of water can use hydrogen(oxygen) isotope separately.The result with the oxygen isotope should be more trustworthy, because the value of hygrogen isotope fractionation will be influented by external environment more easily. Control experiments often needed to do in using the dynamic model. This paper ultimately failed to use this model because the rainfall time and the precipitation. But control experiment and the application of dynamic model will play a large role in the study of plant space-time distribution after future precipitation pattern changes. Isotope technique will get more extensive application, because the stable hydrogen and oxygen isotope technique can distinguish the plant water sources.But there are some defects in using stable hygrogen and oxygen isotope to distinguising the plant's source of water. Determination of soilwater potential and rich deuterium water tracer method will perfect the stable isotope method.