Abstract:Water is often the main limiting factor for plant growth in arid and semi-arid areas. Plants of different life-forms have different water use patterns and strategies, which reflect the balance and interrelationships between species characteristics and water distribution. These water use patterns and strategies may be subject to great variability in response to climate change. Malus toringoides is a native tree species of the sub-alpine arid areas in Luhuo County of Ganzi Region in Sichuan Provence. It is often used for ornamental horticulture because of its beautiful tree form, and for vegetation restoration along dry river valleys and south-facing hillsides in degraded ecosystem because of its well-developed root system and its drought tolerance to water-stressed conditions. M. toringoides also has other commercial values; its young new leaves can be processed to make tea with natural and green nutrients that can be used as health supplement. Berberis aemulans is a shallow root species and lives often in close association with M. toringoides as an accompanying species. The growth and reproduction of M. toringoides are increasingly affected by severe shortage of water in the arid area due to changing climate. Therefore, it is of importance to examine water use patterns of M. toringoides and Berberis aemulans. In this study, we used hydrogen stable isotope composition (δD) to examine water utilization pattern of M. toringoides and B. aemulans. Stable isotope techniques is considered as an effective tools to help understanding relationships between plants and their environment conditions and provides quantitative information about water use strategies and efficiencies of plants. By comparing δD value of water in xylem of M. toringoides and B. aemulans with potential water sources (rainfall, soil water, and river water), the results showed that the water utilization source for M. toringoides and B. aemulans was mainly from rain water and soil water from deep layers of the soil profile. M. toringoides did not take up river water even though it grew on river banks. After a rain event of 10-20 mm in the dry season, M. toringoides had a precipitation utilization rate of 33.50%-70.06%, while B. aemulans was 26.17%-45.17%. After a rain event of 10-25 mm in the wet season, M. toringoides and B. aemulans had rain utilization rates of 40.64%-69.01% and 28.44%-71.41%, respectively. The results showed that the utilization rates of precipitation were not significantly different (P>0.05) between the two seasons for either of the two plant species. After rain events, the water use patterns of M. toringoides and B. aemulans were similar regardless of the dry or wet season, and the utilization rate of precipitation of M. ertoringoides was significantly higher than that of B. aemulans (P<0.01). The water use patterns of M. toringoides and B. aemulans were consistent with the distribution patterns of their root systems: well-developed for M. toringoides and shallow for B. aemulans. Consequently, the two species can co-exist in the same vegetation communities. The results can contribute to in-depth understanding of growth, breeding and improvement, propagation of M. toringoides. In addition, we recommend that M. toringoides and B. aemulans be used together for ecological vegetation restoration by taking advantage of their co-beneficial water use strategies with different water sources.