Water use efficiency of dominant tree species during natural restoration of vegetation in karst peak-cluster depression.

We measured water use efficiency (WUE) of dominant species across three distinct restoration stages (shrub, secondary forest, and primary forest) in karst peak-cluster depression region using stable carbon isotope technology. The results showed that foliar δ¹³C values of 12 dominant tree species ranged from -32.1‰ to -29.0‰. The WUE for these dominant species ranged from 18.25 μmoL·moL^-1 to 36.23 μmoL·moL^-1, with the lowest WUE in Pittosporum tobira and the highest WUE in Pterolobium punctatum. The hierarchy of WUE across different restoration stages was in order of shrub > secondary forest > primary forest. The WUE for a particular species was higher during early-stage vegetation recovery compared to late-stage. Furthermore, when considering different life forms, WUE was in order of liana > shrub > tree. From the shrub stage to the primary forest stage, deciduous species exhibited higher WUE than evergreen species. In summary, plant WUE gradually declined with the ongoing vegetation restoration process in this region. Enhancing WUE was one of the principal strategies for plant adaptation to drought-prone habitats within karst peak cluster depression region. Therefore, priority should be given to lianas and shrubs characterized by high WUE when selecting appropriate species for reforestation efforts in karst regions subject to seasonal or geological droughts.