Do hydraulic characteristics differ between woody plants from karst and non-karst forests?

Owing to rapid rainwater runoff and low surface soil moisture in karst environments, karst woody plants frequently experience drought and are highly vulnerable to climate change. However, recent studies have revealed that karst species can access reliable water sources from epikarst zones where have well-developed secondary porosity. The mechanisms by which woody plants cope with karst environments remains unclear. In this study, we established a stem and leaf hydraulic dataset for 696 karst and non-karst woody species (grown on soil substrates) from four climatic zones (tropical, subtropical, temperate, and Mediterranean), along with climate variables at each site. We aimed to address the following questions: How do karst and non-karst species differ in their hydraulic traits within the same climate? How do the hydraulic-climate relationships differ between the two plant groups? Our results showed that hydraulic efficiency, stem embolism resistance, and minimum leaf water potential were similar between karst and non-karst species in each climate zone. The stem hydraulic safety margin (HSMstem) was higher in karst species than in non-karst species in temperate and Mediterranean regions, but did not differ significantly in the other two climate zones. Leaf hydraulic safety-efficiency was significant and consistent between the two plant groups. However, at the stem level, the hydraulic trade-off was stronger in karst species than in non-karst species. Most hydraulic traits were significantly influenced by the aridity index in karst species, whereas in non-karst species leaf and stem hydraulic efficiencies were associated with the mean annual temperature and precipitation of the warmest quarter, respectively. With increasing aridity, HSMstem tended to increase in karst species but decrease in non-karst species. This comparative study enhances our understanding of the hydraulic strategies and drought risks associated with karst woody plants globally.