[Water source of typical plants in rocky mountain area of Beijing, China].

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, Broussonetia papyrifera and Lespedeza bicolor) in Beijing mountainous area, we measured hydrogen and oxygen stable isotope ratio (δD and δ18 O) 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 var. heterophylla and B. papyrifera because their water sources were complementary. The results could provide reference for the best combination of plant species to restore the damaged ecological environment.