为研究黑河下游额济纳三角洲典型河岸带植物胡杨(Populus euphratica)和多枝柽柳(Tamarix ramosissima)的水分来源及其时空变化特征, 于2015-2016年植物生长期在额济纳东、西河沿岸选取8处样点, 分别采集胡杨和多枝柽柳木质部、土壤以及降水、河水、地下水样品, 分析测试获取各样品的氧稳定同位素比率(δ¹⁸O), 并利用氧同位素直接对比法确定植物主要吸水层位, 利用IsoSource线性混合模型确定胡杨和多枝柽柳水分来源构成及比例。研究表明: 河水和地下水为胡杨和多枝柽柳的主要补给水源, 降水补给因雨水少且入渗浅可忽略不计; 胡杨和多枝柽柳吸收土壤水的层位因地下水位波动、土壤物理特性、河水对土壤水的侧向补给及漫溢补给等存在较大的空间差异, 但其利用河水和地下水的比例未见明显空间差异; 胡杨更多地利用河水(68%), 而多枝柽柳更多地利用地下水(65%); 植物水分来源对生态输水工程响应敏感, 河水贡献率在输水期增大至84%和48%, 非输水期下降至63%和30%, 地下水贡献率在输水期下降至16%和52%, 非输水期增大至37%和70%。值得指出的是, 河岸带地下水与河水交互作用强烈, 导致地下水与河水的δ¹⁸O较为接近, 使得源分解析定量具有不确定性。

Aims We aim to evaluate the water sources of typical riparian arbor species (Populus euphratica) and shrub species (Tamarix ramosissima), and analyze the spatial and temporal dynamics of plant water source in Ejina Delta, the lower reaches of the Heihe River, China.Methods Eight sampling sites were selected in the riparian zones along the East River and West River in Ejina. The plant xylem water, soil moisture, rainwater, stream water and groundwater were taken and pretreated during the growing season in 2015-2016, and the stable oxygen isotope ratio (δ¹⁸O) for each water sample was measured. The δ¹⁸O of plant xylem water and soil moisture were compared to estimate the dominant depth of root water uptake, and the linear-mixed model called “IsoSource” were applied to determine plant water sources and quantify their proportions.Important findings This study indicated that the main recharge sources for P. euphratica and T. ramosissima were stream water and groundwater. The contributions of rain water to them was negligible due to the limited amount and the shallow infiltration depth of local rainfall. As affected by groundwater level fluctuation, soil physical properties, as well as lateral and vertical recharge of stream water on soil moisture, the dominant depth of root water uptake spatially varied. However, the relative contributions of stream water or groundwater to plant water sources did not change significantly across space. Populus euphratica used more stream water (68%), while T. ramosissima used more groundwater (65%). Plant water sources were sensitive to environmental flow controls. The contributions of stream water to the water sources of the two species went up to 84% and 48% for P. euphratica and T. ramosissima respectively during the discharge period, but dropped to 63% and 30% during the non-discharge period. On the other hand, the contributions of groundwater decreased to 16% and 52% during the discharge period, but increased to 37% and 70% during non-discharge period. It is noteworthy that the high similarity of δ¹⁸O between stream water and groundwater due to extensive water exchange in the riparian zone made increase the uncertain in quantifying plant water sources.