Snow-melt water: An important water source for Picea crassifolia in Qilian Mountains

The tall mountains on the mainland are not only important for ecological barriers but also important for water -source bases. Forests play a key role in maintaining tall mountains' ecological and hydrological functions. Therefore, it is important to study the water sources to ensure the existence and growth of forests. We sampled precipitation, snow-melt water, soil, and Picea crassifolia at different altitudes in the Qilian Mountain and analyzed hydrogen and oxygen stable isotopes. The study showed that the snow-melt water contribution to Picea crassifolia water persisted throughout the growing season, and was detectable even in the late growing season, with snow-melt water accounting for 33% of Picea crassifolia water sources. The hydrogen and oxygen stable isotopes of Picea crassifolia xylem water showed that the plants mainly used snow-melt water in the dry season and rainfall in the rainy season. The snow-melt water greatly reduces the impact of spring and summer droughts on forests in the high mountain system in the mainland. Our findings mean that the recent rainfall changes reconstructed by hydrogen and oxygen stable isotopes of Picea crassifolia tree ring can not accurately reflect the water sources in the plant growing season. At the same time, the eco-hydrological model needs to be recon-sidered based on the assumption of the rapid transformation of precipitation-soil water-plant water.