中文摘要：

在季节性干旱区，水分是限制植物生长的关键因子．为了分析比较北京山区群落植物的水分利用特征，本文利用稳定同位素（D／H、埽O／…0）技术，探讨典型群落植物侧柏、荆条、构树和胡枝子的水分来源及其对各水源的利用比率．结果表明：群落内4种植物的水分来源不同，侧柏主要吸收利用40～60、60～80和80～100cm深度的土壤水，对这3层的利用率在23．3％～25．9％，对表层0～20和20～40cm的利用率分别为12．3％和13．0％；荆条主要吸收利用60～80和80～100cm深度的土壤水，利用率分别为51．9％和25．2％，对其他土壤水利用较少；构树主要吸收利用表层0～20am和20～40cm土壤水，利用率分别为47．5％和36．8％；胡枝子对5个水源层水分均有利用，对0～20、20～40和40—60cm深度土壤水的利用率在21．4％。22．8％，对60～80和踟～100c,m深度土壤水的利用率分别为15．2％和18．3％．侧柏和胡枝子的水分利用深度相似，两个树种混交可能会造成较大的水分竞争；荆条和构树的水分利用深唐恰好互补．适宦混交．研究结果可为恢复受损生态环境的最佳植物种组合方式提供参考．

英文摘要：

Water is the key factor limiting plant growth in seasonal arid area. In order to analyze the water sources of community plant （Platycladus orientalis, Vitex negundo var. heterophylla, Brous- sonetia papyrifera and Lespedeza bicolor） in Beijing mountainous area, we measured hydrogen and oxygen stable isotope ratio （δD and δ18O） values of their xylem water and potential water sources. The results showed the four species had different water sources. P. orientalis mainly absorbed water from 40-60, 60-80 and 80-100 cm soil layers, and the utilization ratio of the three layers was 23.3%-25.9%. It still grabbed water from 0-20 and 20-40 cm soil layers with the utilization ratio of 12.3% and 13.0%, respectively. V. negundo var. heterophylla mainly absorbed 60-80 and 80- 100 cm depth soil water, and the utilization rate was 51.9% and 25.2%, respectively, while it barely absorbed water in other soil layers. B. papyrifera mainly absorbed 0-20 and 20-40 cm depth soil water, and the utilization rate was 47.5% and 36.8%, respectively. L. bicolor used the water from five layers, and the utilization ratio of 0-20, 20-40 and 40-60 cm layer was 21.4%-22.8%, and that of 60-80 and 80-100 cm layer was 15.2%-18.3%, respectively. The competition was higher in mixed forest of P. orientalis and L. bicolor because they had similar water sources. It was better to mix V. negundo vat. heterophyUa and B. papyrifera because their water sources were com- plementary. The results could provide reference for the best combination of plant species to restore the damaged ecological environment.