Interspecific variation in branch and leaf traits among three Syzygium tree species from different successional...

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.