Phylogenetic signals, correlations, and evolutionary patterns of some functional traits for forest canopy trees in Jianfengling tropical montane rainforest
The tropical rainforest canopy has enormous diversity of species, function, and phylogeny. It can significantly affect biogeochemical cycles of ecosystem,which can regulate the atmospheric water-heat balance,as well as relieve the negative effect brought by climate change and human disturbance. Thus, functional and phylogenetic ecology of tropical rainforest canopy are among the most burning topics of research in community ecology. The present study was conducted in the forest canopy of three 1 hm~2plots located in Jianfengling tropical montane rainforest on Hainan Island. We used inventory data set of canopy trees to construct a phylogenetic tree of forest canopy in these plots based on APG III phylogenetic structure. Indices of Blomber's K and Pagel's A, combined with phylogenetic independent contrasts method, were used to study the phylogenetic signals,correlations,and evolved patterns of eleven structural,stoichiometric,and hydraulic traits (i.e. leaf area, leaf thickness, leaf dry matter content, specific leaf area, leaf total organism content, leaf nitrogen content, leaf phosphorus content,leaf potassium content,vein density,leaf water content, potential maximum height) of the canopy trees. Our goal was to explore the effect of phylogenetic relatedness between species on the correlations of multi-dimensional functional traits and their dynamic evolutionary patterns at the canopy layer in Jianfengling tropical montane rainforest. The results showed that eight out of the eleven functional traits evolved with significant phylogenetic signals ( P<0.05),except for leaf area, leaf thickness, and potential maximum height; and their Blomber's K and Pagel's A values ranged from 0.202 to 0.392 and from 0.277 to 0.847,respectively. This indicated that phylogenetic conservatism commonly existed in these canopy functional traits in Jianfengling tropical montane rainforest. Furthermore, structural, stoichiometric, and hydraulic traits of canopy trees were universally associated with each other at the species level ( P<0.05) after considering species' phylogenetic relatedness, which demonstrated convergent or divergent evolution. The differentiated patterns of these functional traits displayed generally like a funnel-shape along with divergence of species. In addition, the variation of functional traits for sister nodes, occurring in the preliminary evolved phase (c.120 to 60 million years ago),was weaker than that in the middle and latest phases ( since about 60 million years ago) , which indicated the rapid expansion of traitspace for the forest canopy in the latter ones. However, a majority of phylogenetic independent contrast values obtained from the divergence of sister taxa on each of the phylogenetic internal node, given of evolution of each trait, were nonsignificantly different against the randomly simulated values generated by a null model. In summary, understanding the trade-off relationship of functional traits and their divergent patterns and temporal dynamics with evolution is a foundation for further exploration of the ecosystem functioning for tropical rainforest canopy.