Does strategy of resource acquisition in tropical woody species vary with life form, leaf texture, and canopy gradient?

Abstract

In order to test whether the strategy of resource acquisition varies with life form, leaf texture and canopy gradient, we measured light-saturated net photosynthetic capacity (A max-mass) and leaf nitrogen and phosphorus concentrations (N mass and P mass) for 127 woody species of understory (small shrubs and tree seedlings) and 47 woody species of canopy (large shrubs and tree adults) in a tropical montane rain forest of Hainan Island, South China. Photosynthetic nitrogen use efficiency (PNUE) and photosynthetic phosphorus use efficiency (PPUE) were studied by taking into account functional groups, which classified by either life form (FG1) or leaf texture (FG2). For FG1, there were significant (P < 0.05) differences between trees and shrubs in A mass, N mass and P mass, but not in PNUE and PPUE; whereas for FG2, there were significant (P < 0.05) differences between the papery-leaved species and those with leathery leaves in the measured leaf traits inclusive of PNUE and PPUE. Within the same classification systems, significant allometric scaling relationships were found in the leaf trait pairs of A mass-N mass and A mass-P mass. Considered separately, the slope and y-intercept of the linear regression between A mass and N mass did not differ among functional groups nor between understory and canopy, but those for the linear regression between A mass and P mass differed significantly (P = 0.001) between understory and canopy species regardless of functional groups. The results of phylogenetic comparative analyses were in accordance with the observed positive scaling relationships. The overall results indicate that there are no fundamentally different nitrogen capture strategies in tropical woody species regardless of their life form, leaf texture and canopy gradient. However, the strategies of phosphorus acquisition of tropical woody species differ with canopy layer increases. This variation may correspond to the special soil conditions in this ecosystem, as phosphorus is an element limiting plant growth in tropical areas.