Photosynthesis in relation to leaf nitrogen, phosphorus and specific leaf area of seedlings and saplings in tropical montane rain forests of Hainan Island, south China

Abstract

In order to make clear the relationships between photosynthesis and leaf N, leaf P and SLA of tropical trees, and test the differences in the relationships among life-form groups (trees, shrub-like trees and shrubs), seedlings and saplings of 101 species from a tropical montane rain forest, located in the Diaoluo Mountain of Hainan Island, were selected. The net photosynthesis based on area and mass (A area and A mass), leaf nitrogen content based on area and mass (N area and N mass), leaf phosphorus content based on area and mass (P area and P mass) and specific leaf area (SLA) were measured and/or calculated. The results showed that A area and A mass tended to follow the order of shrubs > trees > shrub-like trees. One-way ANOVA showed that the difference in A area between shrubs and shrub-like trees was significant (p<0.05), and for A mass there were significant differences between shrubs and shrub-like trees and between shrubs and tree species (p<0.05). The relationships between A area and N mass were highly significant in all three life-form groups and for all species (p<0.0001). The correlation between A area and P mass was highly significant in shrubs (p = 0.0038), shrub-like trees (p < 0.0002) and for all species (p<0.0001), but not significant in trees (p>0.05). The relationship between A area and SLAwas highly significant in shrubs (p = 0.0006), trees (p<0.0001) and for all species (p<0.0001), however this relation was not significant in shrub-like trees (p>0.05). The relationships between A mass and leaf N and SLA were highly significant in all three life-form groups and for all species (p<0.0001). For A mass and leaf P, there were significant correlations in tree groups (p = 0.0377) and highly significant correlations in shrub groups (p = 0.0004), shrub-like tree groups (p = 0.0018) and for all species (p < 0.0001). Stepwise regression showed that predicted A mass values were closer to the observed values than those for predicted A area values. Thus, it can be concluded that the relationships obtained from seedling and sapling measurements are close to those from mature individuals; correlations between photosynthesis and N mass, P mass and SLA traits are significant and the relationships are stronger and more stable for A mass than for A area. © 2009 Higher Education Press and Springer-Verlag GmbH.