| Island ecosystem is a “natural laboratory" for studying the mechanism of plant community assembly.Studying plant species diversity,plant functional traits and community phylogenetic structure of islands is of great significance for understanding the species coexistence of island plant communities and the mechanism of plant community assembly.In order to protect and restore the island vegetation ecosystem,the temperate typical island: Xiaoqin Island plant communities were taken as the research objects.The species composition,growth status and growth environment characteristics of the vegetation community in Xiaoqin Island were investigated for three consecutive years from 2016 to 2018.From the four aspects of species,species diversity,plant functional traits and phylogenetic structure,using variance analysis,correlation analysis,RDA redundancy analysis and other methods to explore the differences in species diversity and plant functional traits on different habitat gradients,as well as the environmental driving factors affecting community assembly.the community phylogenetic structure,the phylogenetic index is used to reveal the importance of niche theory and neutral theory,Suggestions for plant restoration in islands were provided.The results show:(1)Distribution of species composition and flora,a total of 121 species of plants were recorded in 176 plots,belonging to 42 families and 104 genera.The orders of different levels of families,genera and species are herbaceous layer > shrub layer > arbor layer,among which there are many species of Gramineae,Compositae and Liliaceae.Mainly in the world,Mainly cosmopolitan,most of its genus and species are mainly produced in temperate zones.The temperate distribution families is relatively wide.Tropical and subtropical families have distribution,It reflects that the flora of Xiaoqin Island has a long historical origin and has a certain tropical relationship.Most of the plants are monotypic in Xiaoqin Island.Compared with other islands,the species richness is relatively low,which is consistent with the “Species area relationship”.(2)Species diversity and its maintenance mechanisms.The order of Shannon-Wiener Index,Simpson Index and Species Richness Index of different life types in Xiaoqin Island was herbaceous layer > shrub layer > tree layer,Pielou Index was herbaceous layer > herbaceous layer > tree layer,herbaceous species diversity index was the highest and species were the most abundant.Herbaceous plant species diversity index is highest,species is the most abundant,The arbor is artificially planted and is mainly affected by human disturbance.Species diversity has significant differences in slope gradient(p<0.05).Slope orientation is the main topographic factor affecting species diversity.Soil water content is the main soil factor affecting species diversity.(3)Evolution of plant functional traits and their environmental drivers.The variation of spatial variation of plant functional traits is mainly reflected in the change of slope position.Slope position is the most critical topographic factor affecting plant functional traits.With the increase of the slope position,the total nitrogen,specific leaf area and plant height of the leaves gradually decreased,and the stem density gradually increased.Hydrothermal nutrient conditions become the main limiting factor for plant growth.Available K and available P is the main soil factors affecting plant functional traits by affecting plant photosynthesis.(4)The community phylogenetic structure can explain the influence of evolutionary processes and ecological processes on community species combinations.By analyzing the NRI and NTI indices,it is found that the phylogenetic structure of most of the plant communities in Xiaoqin Island is divergent,indicating that the competitive exclusion between community species plays a leading role in community assembly.The positive and negative NRI and NTI of the three communities are opposite,indicating that the species niche overlap of the plot community is high,and the competition for species competition is fierce.The community assembly process may be affected by factors such as species bio-characteristics,disturbances,diseases,drought stress,etc.,which aggravates the instability of the dynamic process of community species.Comprehensive analysis of species,biodiversity,plant functional traits and community phylogenetic structure,the species composition is affected by the historical regional process.Sea isolation limits the effective exchange of species.Regional processes cannot explain the reasons for their species coexistence.Species diversity and plant functional traits are mainly limited by hydrothermal conditions caused by topographic factors,and there are significant differences in slope direction and slope position,respectively.The community phylogenetic structure explains from the perspective of evolution and ecological processes that plant community species competition plays a dominant role in community assembly. |
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