Understanding Community Assembly Based On Functional Traits In A Mixed Broadleaved-korean Pine Forest

There are largely distinct biodiversity patters from temperate to tropical regions,but it has long confused community ecologists to understand why and how these patterns are presented and maintained.The two broadly debated ecological theories(i.e.,niche-based theory including abiotic filtering and competition exclusion,and neutral theory)both explain the classical biodiversity patterns partly,but their relative importance still remains unclear.The plenty of previous studies overwhelmingly focus on species identity-based patterns,however,recent studies suggest that species phylogenetic relationship and functional traits may improve our understanding of ecological processes.Therefore,based on the three insights(i.e.,species,phylogenetic relationship and functional traits)may be a better way for us to roundly understand the mechanisms of species coexistence and community assembly.The approach that decomposing the variation of species composition(i.e.,variation partitioning)is usually used by community ecologists to determine the relative importance of niche-and dispersal-based processes.But previous studies have suggested that including species traits into species composition may improve our understanding of these ecological processes,however the assumption has not been tested yet.Here we conducted our study on a 9 ha mixed broadleaved-Korean pine forest dynamics plot in the Heilongjiang LiangShui National Natural Reserve in northeastern China,to explore the influence of functional traits and their intraspecific trait variation among ontogenetic stages on our understanding of ecological processes.We compiled and measured eight functional traits leading the important ecological strategies of 41 co-existed species in the plot.We adapted the phylogenetic fuzzy weighting method to quantify species,phylogenetic and functional compositions and to compare the effects of these different response variables on the results of variation partitioning.We found that,relative to species identity,functional traits reduced the unexplained variation and environmental factors explained more variations of trait-based variables.However,when we ignored the intraspecific trait variation among ontogenetic stages,functional traits did not show a better performance than species identity.By adding the environmental variables as the covariates and decomposing the spatial variables,we found that medium-and fine-scaled spatial variables explained more variation of two dispersal-related traits(seed mass and maximum height).These results indicated that functional traits and including their intraspecific variation could improve our understanding of trait-and dispersal-based processes.To further explore the influence of niche-based process on community assembly,we divided the species into shrubs and trees.We selected three core leaf economics spectrum traits(i.e.,specific leaf area,leaf dry matter content and leaf phosphorus content),to explore their coordination at the community level(based on the abundance weighted trait mean values)and determined the environmental drivers on their spatial distributions.We found the coordination of a "leaf community economics spectrum" for shrub and tree communities,which was consistent to the widely reported correlations between species.Both topographical and soil factors drove the distributions of shrubs and trees,with a "acquisition community" was more likely found in the soil nutrient-rich conditions,which also implied the control of abiotic filtering process.Shrubs and trees responded differently to the environmental factors and their leaf community economics spectrum distributions were not spatially correlated,which indicated their niche differentiation.Overall,our results showed that functional traits and including their intraspecific variation could improve our understanding of niche-and dispersal-based processes.Relative to neutral process,niche processes such as abiotic filtering and niche differentiation controlled the assembly of this temperate forest in northeastern China.