Coexisting plants restored in karst desertification areas cope with drought by changing water uptake patterns and improving water use efficiency

Abstract

As a result of global climate change, the frequency and intensity of droughts are increasing, severely impacting the functioning of forest ecosystems and even leading to tree mortality. However, the effects of natural droughts on the water use strategies of plants at seasonal scales remain unclear, limiting our understanding of how vegetation adapts to drought stress. In this study, we employed stable isotopes (δ²H, δ¹⁸O, and δ¹³C) to investigate the differences in the water use characteristics of the plants used in the restoration of subtropical karst areas during normal and drought years. The results indicated that the average water uptake proportions of the plants were similar throughout the study period, with water from shallow fissures soil being the predominant water source for all species (42.18 %−49.35 %). The proportional similarity (PS) was lowest among all the species (0.37–0.60) in July of the drought years, and water competition among the species was mitigated through water allocation. To improve adaptability to drought, shrubs increased the proportion of use of topsoil water (2.76 %−6.43 %) while decreasing the proportion of use of other deeper water sources (0.40 %−5.59 %), whereas trees decreased the proportion of use of topsoil water (4.76 %−9.59 %) but increased the proportion of use of deeper water sources (0.66 %−6.79 %). All the species presented an increase (3.05 %−57.81 %) in intrinsic water use efficiency (WUEi) during the drought year, with Cipadessa baccifera, Vitex negundo, and Koelreuteria bipinnata showing significantly (p < 0.05) greater mean WUEi values in the drought year than in the normal year. These results emphasize the importance of changing water uptake patterns and increasing WUEi to improve drought adaptation in plants used for the restoration of karst desertification areas. This study provides new insights into the water utilization characteristics of natural restoration plants in response to extreme natural drought.