The Assembly Mechanism Of Wetland Plant Community In The Middle And Lower Reaches Of The Yangtze River Based On ? Diversity

Community assembly mechanism is one of the core issues in the field of biogeography and ecology.Its research can provide an important reference for the protection of global and regional species diversity,which is important for biodiversity conservation and sustainable utilization.Although there are a lot of researches on the mechanism of plant community assembly,and it has been found that niche theory(environment filtering)and neutral theory(dispersal limitation)can better explain the mechanism of plant community assembly,while these researches mainly focus on terrestrial plant communities,the researches on wetland plant communities are relatively few,and whether the theory derived from terrestrial ecosystems is applicable to wetland ecosystems remains controversial.In this study,aquatic or hydrophyte plant communities in 10 different types of wetland ecosystems in the middle and lower reaches of the Yangtze River were selected as the research objects to investigate the main plant community types,species composition and environmental factors in each type of wetland.The main plant community types,species composition and environmental factors in each type of wetland were investigated,and PERMANOVA was used to analyze the?diversity of the investigated wetland plant communities;Mantel test and multicollinearity analysis were used to study the effects of environmental differences and geographical distance on wetland plant communities ? Diversity impact;the environmental factors significantly affecting the ? diversity of wetland plant community were screened through multicollinearity analysis,and then the multiple regression model(MRM)based on multiple regression on(dis)similarity matrices was used to study the relative variance contribution of environmental differences and geographical distance on the ? diversity of wetland plant community.Thus revealing the assembly mechanism of wetland plant community.The main results are as follows:(1)The main aquatic plant communities in different types of wetland ecosystems in the middle and lower reaches of the Yangtze River include Form.Hydrilla verticillata,Form.Myriophyllum spicatum,Form.Nelumbo nucifera,Form.Potamogeton crispus,Form.Zizania latifolia;The main hydrophyte plant communities were Form.Typha angustifolia,Form.Phragmites australis,Form.Imperata cylindrica,Form.Alternanthera philoxeroides,Form.Polygonum hydropiper.The Bray Curtis diversity index of aquatic plant community in different types of wetland ecosystem was as follows: Zhangjiazui reservoir(0.957),Ju river(0.955),Chong lake(0.943),Weishui reservoir(0.926),Dajiu lake(0.907),Fu river(0.891),East river(0.846),Hong river(0.782)and Yueliangwan(0.698),respectively.The Bray Curtis dissimilarity index of hydrophyte plant community in different types of wetland ecosystem was as follows: Dajiu river(0.982),Yuan'an(0.954),Hong river(0.935),Quanyitang(0.930),Zhangjiazui reservoir(0.921),Chong river(0.895),Fu river(0.880).PERMANOVA analysis showed that there were significant differences in ? diversity among different regions.(2)Mantel test results showed that environmental differences and geographical distance had significant correlation with Bray Curtis dissimilarity index of aquatic plant community and hydrophyte plant community(p<0.001);In terms ofcorrelation coefficient,Bray Curtis dissimilarity index of aquatic plant community and hydrophyte plant community had higher correlation with environmental differences than geographical distance.Among the environmental factors,Bray Curtis diversity index aquatic communities had the highest correlation with altitude(r=0.42),and the lowest correlation with total nitrogen(r=0.07).For the Bray Curtis dissimilarity index of hydrophyte community,the highest correlation was the mean temperature of warmest quarter(r=0.47),and the lowest correlation was the annual precipitation(r=0.15).(3)Environmental factors significantly affected the assembly of aquatic and hydrophyte communities,and the interpretation rates of aquatic and hydrophyte communities were17.83% and 21.66% respectively(p<0.01).Among all the environmental factors,the mean temperature of coldest quarter contributed the most to the assembly of aquatic,and hydrophyte communities,accounting for 15.44% and 19.53% of Bray Curtis dissimilarity index,respectively.However,the explanation rate of geographical distance on the assembly of aquatic and hydrophyte communities was much lower than that of environmental factors,which were 8.49% and 5.39% respectively.Moreover,geographical distance only had significant effect on aquatic plant communities(p<0.01),but had no significant effect on hydrophyte communities(p=0.27).The co-interpretation rates of environment filtering and dispersal limitation were 18.22% and 19.91%,respectively.The overall interpretation rates of environmental factors and geographical distance of MRM model to Bray Curtis dissimilarity index of aquatic and hydrophyte communities were 44.54% and 46.96% respectively,and the residual amounts were 55.46% and 53.04% respectively.The results showed that both environment filtering and dispersal limitation dominated the wetland plant assembly in the middle and lower reaches of the Yangtze River,and environment filtering had the greatest impact on the aquatic and hydrophyte communities in the region.