Season and depth differences of soil moisture use for tree growth across wet and dry gradients in the Tibetan Plateau

Abstract Soil moisture has an important influence on tree growth in climate-sensitive regions. However, the seasonality of soil moisture utilization by trees in the Tibetan Plateau, a typical climate-sensitive region, and the mechanisms of depth of uptake are still unclear. Therefore, the spatial and temporal differences in the soil moisture use dynamics of tree growth were analyzed under wet and dry gradients on the Tibetan Plateau using tree-ring δ18O (δ18OTR). The results showed that: 1) soil moisture during the growing season was the main influencing factor on tree growth under different wet and dry gradients on the Tibetan Plateau. 2) The response of δ18OTR to soil moisture had a lag in arid areas than in wet areas. 3) In wet areas, trees absorbed the soil moisture in surface, while absorbed the soil moisture in deep in arid areas. And meanwhile, trees could develop more lateral and deep root systems using soil moisture from all soil layers to cope with climatic stress. In the future, more lateral and deep root systems of trees will be better suited to survive in complex habitats on the Tibetan Plateau, and that monitoring of trees in single water use areas should be enhanced. Further, it is of great significance to study soil water use strategies of tree growth under different wet and dry gradients for predicting forest ecosystem changes in complex environments.