The Community Assembly And Scale Dependence Of Secondary Forest Community In The Loess Plateau Based On Plant DNA Barcode And Functional Traits

The arrival of species in local regions and their subsequent formation of plant communities creates hotspots for community ecology,and the scale-dependency of community assembly is still one of the research focuses.Neutral process based on neutral theory and deterministic process related niche theory are two basic hypotheses to explain the mechanism of community formation.The loess plateau is one of the regions with the most serious soil and water loss in China.Quercus wutaishanicais the dominant species widely distributed in the Loess Plateau region,while the oak forestof Quercus wutaishanica is the climax community in the process of regional succession of the Loess Plateau region.The combination of DNA barcoding and functional trait analysis is increasingly used to provide an integrated view of the processes structuring communitiesand the discussion of scale-dependency of community assembly.Weare using three methods(cons.bar,uncons.bar,APG)toreconstruct the phylogenies of the co-existing woody species in the Quercus wutaishanica forest of the Loess Plateau,which are the climax community of succession stages,andthen compared the topological structure and resolution of species level of the phylogenentic trees.Three representative functional traits(height,specific leaf area(SLA),and seed mass)were also measured.The phylogenies of the main woody plants in the Loess Plateau at the species level were reconstructed and compared by using three types of construction trees(bar.cons,bar.uncons,APG).We compared the differences between the functional and phylogenetical structures of the Quercus wutaishanica forest in three spatial-scales(100,400,2 500 m~2)and two different vertical structural layers.The results showed that the constrained phylogenetic trees with the guides tree of APG III can provide better phylogenies than the unconstrained and APG trees.We found that although the total plant communities were phylogenetically random at all three scales,the shrub layer was phylogenetically overdispersed with increasing scales.The outcomes of scale dependence of the phylogenetic structure of shrub layers show that the ecological process played the dominant jole in shrub species assemblages have significant scale dependence.SLA showed functional convergence for total communities and tree layer,while seed mass and plant height showed functional divergence.For shrub layer,the functional structure of these three characters showed significant convergence on three spatial scales.The scale-dependency of the functional trait convergence in seed mass and plant height was stronger at the medium and lager scales(400 m~2 and 2 500 m~2)than that for the SLA.These results revealed different assembly patterns of the Quercus wutaishanica forest between the functional traits and phylogenies,which indicates combined actions of deterministic and stochastic processes in shaping the functional composition and genetic relationships of the coexisting species in the Loess Plateau.Specifically,the effects of the spatial scales on the assembly patterns heavily depend on the increasing species turnover at the shrub layer,suggesting that environmental filtering and niche differentiation play roles in the different forest layers of the Loess Plateau.