Study On Functional Diversity And Phylogeny Of Jianfengling Tropical Montane Rainforest Canopy On Hainan Island

The functional ecological processes and formative reasons as well as maintained machanism of biodiversity in tropical rainforest canopy is one of the hotspots in modern ecological research. Functional traits are treated as a direct proxy of plants who adapted to biotic and abiotic interaction around them. This provided a perspective for studying functional ecology of tropical rainforest canopy. Integrating phylogenetic relatedness of tropical rainforest canopy assemblies with characteristics of plant functional traits is helpful for not only understanding community phylogenetic strcture and dynamics of the canopy, but also for potentially predicting its responses to climate change. In this study, communities ecological investigation, environmental factors measurements, phylogenetic establishment, functional traits chosen and measurements were conducted in Jianfengling tropical montane rainforest canopy on Hainan Island. Our aims were to figure out coupling process of functional traits at respective species and community levels of the canopies and the canopy‘s survival strategies; to analyse phylogenetic signal, correlation and evolved pattern(i.e., convergence or divergence) of major functional traits of the canopy; to compare impact of size classes and species abundance on phylogenetic relatedness of woody plants in the tropical montane rainforest community; to illustrate pattern of functional diversity of the canopy and its formative reasons, and ultimately to assess the specific effects of abiotic filtering on the distribution of major functional traits of the canopy and its community assemblies. This work established a scientific foundation, in some degree, for deeply illustrating distribution patterns of functional diversity of the canopy and its maintained mechanism as well as ecosystem function of Jianfengling tropical montane rainforest. Additionally, this work could seem as a reference to ecological researches in the other types of forest canopy. The primary results were as follows.(1) There existed a relative significance for the local habitat heterogeneity at the 20 m×20 m spatial scale in Jiafengling tropical montane rainforest. Generally, soil organism content, soil total nitrogen and phosphorous content increased when the mountain‘s elevation increased. In contrast, soil pH-value, density and water content declined as elevation increased.(2) Coefficient of variation of each major functional traits was greater than 17.26% excepted for leaf total organism content at the species level of Jianfengling tropical montane rainforest canopy. And the varied coefficients of inter-communities were slight compared with those at the species level. Specific leaf area(SLA) was significantly positive correlative with leaf nitrogen(LNC), phosphorous(LPC) and potassium(LKC) content at both species and community levels. However, almost no relationships between SLA and vein density(VD) were found at the both levels. Additionally the more important was that the predicted power of SLA to most of the rest of functional traits at community level was obviously stronger than its performance at the species level. Contrary, the predicted power of VD to the remained traits was remarkly weaker either at the species or community level.(3) It was likely to keep a ?module‘ effect for the major functional traits of Jiafengling tropical montane rainforest canopy. Those traits highly associated with photosynthesis, such as leaf area(LA), LNC, LPC and LKC, tended to cluster on the first principal component axis in order to regulating the trade-off between leaf structure investment and photosynthate accumulation of the forest canopy. And the first principal component explained 31.9% of the variance among major functional traits. Additionary for those functional traits(i.e., leaf thickness, leaf water content, VD and leaf dry matter content) which tightly correlative with evapotraspiration and defence usually clustered closely to the second principal component axis, which could explain 26.5% of the variance.(4) All major functional traits showed significant but weak phylogenetic signal except for LA, LT and potential maximum height(Hmax). Functional traits of closely relative species were more similar than those of distantly relative species(i.e., phylogenetic conservatism). Phylogenetic indepedent contrast(PICs) showed a convergent or divergent pattern among most of these major functional traits in their evolved process. Furthermore, the inter-specific divergent pattern of each functional trait seems like a funnel-shaped according to time dynamics.(5) The whole community assemblies were phylogenetic overdispersion(NRI < 0) whereas patiral branches of the phylogeny were phylogenetic clustering(NTI>0) at a 20 m×20 m spatial scale of Jianfengling tropical montane rainforest. This indicated the whole community assemblies in this region had a distant genetic relationship whereas partial branches of the community phylogeny kept a closer relationship. Additionally, community phylogenetic structure of small and middle size classes(i.e., DBH<5 cm or 5 cm≤DBH<15 cm) usually affected by species abundance. If only considering presence or not of species and without taking their abundance informations into mind, the community phylogenetic diversity would be overestimated obviously.(6) Canopy functional diversity was exponential associated with species abundance at community level of Jianfengling tropical montane rainforest(F=80.36,r2=0.524,P<0.001). The size of canopy functional trait-space and the functional diverisity in the relatively fertile habitats were comparatively larger/greater than thoses relatively poor habitats. This indicated that species functional traits were likely to be overdispersed in fertile habitat whereas clustering in the infertile habitat. Additionally, variance of canopy functional diversity among communitieswas best predicted based on all major functional traits in Jianfengling tropical montane rainforest.(7) Variance of canopy functional diversity was mainly explained by environmental factor at the community level in Jianfengling tropical montane rainforest. The purely environmental effect could explain more than 30% of the variance of the functional diversity for most of the major functional traits of the canopy community. Purely environmental factor had a highest explained rate(i.e., 74.0%) for the variance when functional diversity quantified using standardize effect size of species abundance weighted mean nearest taxon distance(S.E.S-AWMNTD) based on all major functional traits.(8) The first axis of extended RLQ(i.e., R-mode linked to Q-mode) analysis of abiotic filtering could approximately explain 98.24% of the co-variation of environment, space, functional traits and phylogeny of Jianfengling tropical montane rainforest canopy. Phylogenetic basal species in Lauraceae and Magnoliaceae, accompanied with long evolutionary history, were likely to distribute at a relatively more fertile habitat, in which soil total organism content and nitrogen content were richer. As a result, the canopy trees had a higher content of leaf total organism and dry mass. However, a vast majority of eudicotyledon such as species in Fagaceae and Symplocaceae tended to appear in the habitat with higher soil pH-value and micro-element content and therefore keeping a greater SLA.