Using stable isotopes to quantify water uptake by Cyclobalanopsis glauca in typical clusters of karst peaks in China

In this study, stable isotopes (¹⁸O and ²H) were used to determine the sources of water for Cyclobalanopsis glauca in two habitats: limestone outcrops and thin soils in clusters of karst peaks in southwest China, where soils are scattered only in rock gaps and are underlain by rigid carbonate rocks. We used a direct inference approach and the IsoSource mixing model to estimate the contributions of different sources to the plant xylem water. The results showed that adult C. glauca growing on limestone outcrops mainly used water from soils in rock gaps, which comprised 65 % of all water sources during the rainy season, and water from rainwater sources during the rain-dry season and dry season; the proportion of deep water used increased during the dry season. In contrast, young C. glauca growing on limestone outcrops relied on a mixture of rainwater and soil water during the rainy and the rain-dry seasons, and on rainwater in the dry season, accounting for 66.3 and 64.0 % of water use, respectively. Adult C. glauca on thin soils mainly used soil water in rainy seasons, a mixture of soil water and rain water in the rain-dry season, and rainwater in the dry season. Water held within bedrock was essential for meeting plant transpiration requirements in karst peak cluster areas. The results will provide knowledge for the effective protection of vulnerable karst environments and for the recovery of vegetation on karst rocky desertification areas.