基于稳定氧同位素确定植物水分来源不同方法的比较

Comparison of different methods for determining plant water sources based on stable oxygen isotope

利用稳定同位素技术确定植物水分来源,对提高生态水文过程的认识和对干旱半干旱区的生态管理至关重要。目前基于稳定同位素技术确定植物水分来源的方法众多,但不同方法之间对比的研究较少。本研究基于原位样品采集,室内实验测试,利用直接对比法、多元线性混合模型(IsoSource)、贝叶斯混合模型(MixSIR、MixSIAR)和吸水深度模型分析植物水分来源,并对比各方法的优缺点。结果表明:相对于多元线性混合模型(IsoSource)而言,贝叶斯混合模型(MixSIR、MixSIAR)具有更好的水源区分性能,但对数据要求较高,且植物木质部水和潜在水源同位素组成的标准差越小,模型运行结果的可信度更高。本研究中贝叶斯混合模型(MixSIR)为最优解。在利用稳定氢氧同位素技术确定植物水分来源时,可先通过直接对比法定性判断植物可能利用的潜在水源,然后再用多元线性混合模型(IsoSource)、贝叶斯混合模型(MixSIR、MixSIAR)计算出各潜在水源对植物的贡献率和贡献范围,必要时可评估模型性能,选择出最优模型,定量分析植物的水分来源。若植物主要吸收利用不同土层深度的土壤水,可结合吸水深度模型计算出植物吸收土壤水的平均深度。本研究为干旱半干旱地区利用同位素技术确定植物水分来源方法的选择提供了理论依据。

Using stable isotope technique to determine the sources of plant water is essential to improve our understanding of eco-hydrological process and ecological management in arid and semi-arid regions.There are many methods for determining plant water sources using stable isotope technique,but few studies have tried to compare outcomes of different methods.Based on empirical data,we used direct comparison method,multivariate linear mixed model(IsoSource),Bayesian mixing models(MixSIR,Mix SIAR)and water absorption depth model,analyzed the water sources of vegetation,and compared the merit and demerit of each method.The results showed that Bayesian mixing models(MixSIR,MixSIAR)performed better in water source apportionment than IsoSource.The Bayesian models have higher requirements for data.The smaller the standard deviation of isotopic composition of vegetation xylem water and potential water source,the higher the reliability of model operation results.Bayesian hybrid model(MixSIR)is the optimal solution in this study.When determining plant water source by stable isotopes of hydrogen and oxygen,the potential water source of vegetation can be determined by direct comparison method.Furthermore,the contribution rate and range for each potential water source of plants could be calculated by the multivariate linear mixed model(Iso Source),and Bayesian mixing models(MixSIR,MixSIAR).When needed,the optimal model of quantitative analysis of plant water sources should be selected by evaluating the performance of models.If plant mainly absorbs soil water at different soil depths,the average depth of soil water absorbed by plants can be calculated by combining water absorption depth model.This study provides theoretical basis for the selection of method for identifying plant water sources by isotope techniques in arid and semiarid regions.