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Karst and non-karst forests occur in the same region in south-west China, but the soil water and mineral nutrients availability are different between the forests. Our hypothesis was that the leaves of karst trees would be better adapted to dry, nutrient-poor conditions than those of trees in a nearby non-karst forest. We compared the gas exchange, anatomical characteristics and mineral nutrient concentrations in leaves from 21 tree species in a tropical karst forest and 19 species in a nearby non-karst forest in south-west China. We found that the leaves of karst trees had higher P concentrations, photosynthetic capacity and water use efficiency, and greater adaxial and abaxial epidermis thickness than leaves of non-karst forest trees. Evergreen and deciduous trees differed more significantly in leaf functional traits in the karst forest than in the non-karst forest. The leaf palisade:spongy mesophyll thickness ratio was positively correlated with stomatal conductance and negatively correlated with photosynthetic water use efficiency in the karst forest but not in the non-karst forest. Our findings indicate that karst forest trees are more conservative in water use, whereas soil P deficiency could be a major limiting factor for the growth of non-karst forest trees.

Plant functional traits are closely associated with plant habitats. In this study, we investigated the interspecific variations in stem and leaf hydraulics, xylem and leaf anatomy, gas-exchange rates and leaf pressure-volume relationships among three Syzygium tree species in early, mid- and late successional tropical forests. The objective was to understand the response and adaptation of congeneric species, in terms of branch and leaf functional traits, to different environments. A consistent pattern of decline with succession was evident in leaf and sapwood specific hydraulic conductivity (ks), maximum leaf hydraulic conductance (Kleaf), and photosynthetic rates for the three Syzygium species. Variations of ks and Kleaf were correlated with changes in vessel anatomy (i.e. vessel density and diameter) and leaf flux-related structure (i.e. stomatal pore index and vein density) respectively. However, specific leaf area and leaf to sapwood area ratio did not significantly differ among the three species. In addition, the mid-successional species had the lowest values of leaf water potential at full turgor and turgor loss point and 50% loss of Kleaf, but the greatest value of xylem water potential at 50% loss of ks. Our results demonstrate that leaf and branch traits associated with photosynthesis and/or hydraulic conductance, rather than those associated with drought tolerance, are the key factors underlying the response and adaptation of the three Syzygium tree species along the tropical forest succession.