中文摘要：

植物水分来源取决于环境中有效水分的分布及植物获取水分的能力，对植物水分来源的研究有助于在全球变化背景下了解植被（类型和分布）的变化规律，以及退化生态系统修复过程中合适植物种的选择．本文利用直接相关法、二源或三源线型混合模型以及多元线性混合模型分别对华北土石山区栓皮栎旱季的水分来源进行了研究，发现栓皮栎在旱季不同时期的水分来源有差异，春季水分来源集中在表层土壤（0-30cm），秋季水分来源主要为下层土壤（〉30cm）．在研究方法上，各有优点和不足：直接相关法能够快速判断出植物水分主要来源的季节差异，但无法给出各水源的贡献率；直接相关法和二源或三源线性混合模型的结合能够快速得到各主要水源的贡献率，由于只能在水分来源不超过3个的情况下运行，比较适合于在土层浅薄，且降雨后土壤层同位素特征均一化的条件下运行；而多元线性混合模型弥补了端元线型混合模型对水分来源的限制，可以同时比较多种水源对栓皮栎的贡献率范围和均值，但是在华北土石山区，降雨量超过一定阈值后，运行不如端元混合模型适用．

英文摘要：

Plant water source depends on the distribution of available water in the environment, and the capability of plants in capturing water. The study of plant water source will help to understand the vegetation variation（ type and distribution）under the context of global change, as well as the selection of suitable plant species in the process of degraded ecosystem restoration. Stable isotope of hydrogen and oxygen were considered to be a good tool and have been used to identify the source of water, because different water sources possess different hydrogen or oxygen isotope signatures. In this study, we used three different methods to estimate the sources of water used by Quercus variabilis, the dominant species in the rocky mountain areas of Northern China. Furthermore, the advantages and disadvantages of the three methods were compared. The three methods are as follows：the method of direct reference, a two-three compartment linear mixing model, a multiple sources linear mixing model. Results displayed that： Quercus variabilis extracted different water sources in different season during dry. season, the main water source concentrated in surface soil layer （0--30cm） in spring, and sublayers （ 〉 30cm） in fall. The three methods we used in this study have their own range of application and limitations. The method of direct reference could rapidly distinguish the seasonal differences of main water sources, but could not get the contribution rates of different sources. The method of integrating the direct reference with two-three compartment linear mixing model could quickly calculated the contributed proportions of the main water sources, however, could use only in the situation that only less than three water sources were available, and more suitable to operate in the condition that the soil layer is shallow, and homogeneous isotopic characteristics of some soil layer after the rainfall The multiple sources mixed-linear model can remedy the defects of two- three compartment linear mixing model, theref