Community Assembly Of Hygrophytes

Community assembly mechanism,that is,the formation and maintenance mechanism of community biodiversity has always been the core issue of ecological research.Exploring the model of plant community assembly on environmental and spatial gradients,in season periods and on research scales,combined with the species composition and phylogenetic relationship of the community,can more fully and accurately reveal the mechanism and driving factors of community assembly.In order to explore the diversity characteristics and assembly mechanism of the hygrophyte communities,this paper selects the hygrophytes in the plateau lakeside zone of Tibet and the riparian zone in the middle and lower reaches of the Yangtze River as the research object to study the diversity characteristics and community assembly mechanism of the hygrophyte communities from the two dimensions of plant community species diversity and phylogenetic diversity,using analysis methods such as correlation analysis,regression analysis,Mantel analysis,and order analysis.Then combined with environmental factors and spatial variables,the driving factors for the change of community assembly style were discussed.The main conclusions are as follows:(1)The ?-diversity of hygrophytes community during wet season is higher than that during dry season,and the ?-diversity in wet season is mainly positively related to water conditions,while the dry season is mainly related to temperature and soil total nitrogen content.The phylogenetic structure of the wet-season community showed an aggregation trend,suggesting that habitat filtration plays a leading role;However,NRT and NTI in the dry season showed different trends,suggesting the existence of recent community differentiation.The ?-diversity of the community is significantly related at the species level and the phylogenetic level,and its diversity level can be characterized to some extent.The assembly mechanism of the hygrophyte communities along the riparian zone in the middle and lower reaches of the Yangtze River differs at different times.The community assembly in the wet season is the result of the combined action of environmental screening and diffusion restrictions,and the environmental screening role is dominant;However,the community assembly in the dry season is only affected by a certain degree of environmental screening at the species level.Macro-habitat temperature and precipitation changes,micro-habitat soil moisture and nutrient conditions are the main driving factors influencing the differences in the hygrophyte communities in the riparian zone in the middle and lower reaches of the Yangtze River.(2)The Richness,Shannon index and Simpson index of the hygrophyte communities in the plateau lakeside zone of Tibet are significantly correlated with the phylogenetic diversity index Faith 'PD,showing a gradual increasing trend from west to east geographically.The wetland plant community in the plateau lakeside zone of Tibet showed divergent lineages in the overall phylogeny,and aggregated lineages in the end structure of the phylogeny,indicating recent community differentiation.In the long-term evolution of hygrophytes in the plateau lakeside zone of Tibet,the niche is conservative.The assembly of the hygrophyte community on the plateau lakeside zone of Tibet is mainly dominated by random processes,but deterministic processes driven by environmental and biological factors cannot be ruled out.Soil nutrient content and climatic conditions are the main limiting factors for the species diversity pattern of hygrophytes in the study area.(3)The study on the differences in the community structure characteristics of the plateau lakeside zone of Tibet and the riparian zone in the middle and lower reaches of the Yangtze River shows that: The species richness of the hygrophyte communities in the riparian zone in the middle and lower reaches of the Yangtze River is higher than that of the plateau lakeside zone of Tibet,but the species uniformity of the hygrophytes communities in the lakeside of the Tibetan Plateau is significantly higher.Because the habitat conditions of the lakeside wetlands on the plateau lakeside zone of Tibet are relatively poor,but the hydrological situation is relatively stable,the assembly of hygrophytes communities is dominated by a random process;The climate and soil conditions in the middle and lower reaches of the Yangtze River are suitable for the growth of coastal hygrophytes.However,due to the obvious changes in coastal hydrological conditions,the microenvironment at different locations is significantly different.Therefore,the hygrophytes in this area are clustered,and the community assembly is mainly affected by environmental screening.This result also implies that there are differences in the mechanism of plant community assembly at different research scales.