Important contributions of winter and spring precipitation to the water sources of a montane shrub community in the Tianshan Mountains of China

Study region Tianshan Mountains (Xinjiang, China). Study Focus Precipitation exhibits distinct spatiotemporal variability in arid-region temperate forests, and the contributions of summer and winter precipitation to the plant water supply throughout the growing season are not well understood. Clarifying the seasonal water sources utilized by forest species is essential for accurately predicting ecosystem responses to future climate change. This study examined seasonal soil moisture dynamics in montane shrub communities on the northern slopes of the Tianshan Mountains, using soil water content, isotopic signatures of soil water and precipitation, and the seasonal origin index (SOI) method to trace water sources for two dominant shrubs ( Cotoneaster melanocarpus and Berberis heteropoda ) during the growing season. Soil water SOI values reached their minimum (near −1) at 0–40 cm in April, partly exceeded 0 in August–September, and fluctuated between −0.5 and 0 from May to July. These patterns indicate that snowmelt-derived winter precipitation dominated soil moisture in April, which was subsequently mixed with spring rainfall by May. Summer precipitation had limited influence, penetrating only the surface layer (0–20 cm) and mixing with pre-existing soil water. Xylem water SOI values followed similar seasonal trends. B. heteropoda showed lower SOI values in May–June, indicating strong dependence on winter and spring precipitation during early summer. In contrast, C. melanocarpus maintained SOI values between −0.6 and 0 throughout the growing season, reflecting consistent use of mixed water sources. New Hydrological Insights for the Region These results underscore the ecological importance of spring and winter precipitation in enhancing plant water availability in this region. Under future climate scenarios, shifts in seasonal precipitation and increased winter snowfall and increased winter snowfall may play a critical role in sustaining arid temperate forest ecosystems.