Differences in leaf heat and drought tolerance but not cold tolerance between karst and non-karst forest plants.

Abstract

Ongoing climate change and increasingly frequent extreme precipitation events pose greater threats to plant survival. Plants in the karst environment may face heightened risks because shallow soils and poor water retention amplify drought and temperature stresses, yet their physiological tolerances remain poorly understood. In this study, we aimed to investigate the leaf physiological tolerance strategies to drought and temperature stress in plants from karst versus non-karst forests, and to quantify the relative contributions of lithology and phylogeny to variation in these tolerances. In this study, we measured leaf photosynthetic heat and cold tolerance, leaf turgor loss points, and morphological and anatomical traits in 39 dominant woody species from karst and non-karst forests in Guangxi, China. We used Welch's t-tests to compare leaf trait differences between forest types, evaluated the trait relationships with Pearson correlation analysis, and partitioned the contributions of lithology and phylogeny to trait variation using phylogenetic eigenvector regression (PVR). Karst species exhibited more negative leaf turgor loss points (π_tlp) and lower heat tolerance (T50_heat) than non-karst species, whereas cold tolerance (T50_cold) did not differ between habitats. Leaf thickness (LT) and leaf mass per area (LMA) were positively correlated with T50_heat, suggesting that higher structural investments enhance heat tolerance, but are not correlated with T50_cold and π_tlp. Phylogeny predominantly explains the variation in T50_cold and the second principal component (PC2), whereas lithology primarily drove variation in π_tlp and T50_heat. Because karst species have lower heat tolerance, they may face a higher risk of thermal damage under future climate warming.