Community Assembly And Primary Productivity Regulation Mechanisms Of Wetland Plants In The Shandong Section Of Yellow River And The South Coast Of Laizhou Bay

Biodiversity loss has become a common problem for all mankind.Although human beings have made a lot of efforts to curb the decline of biodiversity,the speed of biodiversity loss and species extinction is still accelerating.The loss of biodiversity will lead to the decline of ecosystem functions,and productivity has attracted people's attention as an ecosystem functioning closely related to humans.Community assembly process determines the formation and maintenance of biodiversity,which is a prerequisite for biodiversity protection.Wetland vegetation distributes at the transition zone between water and land and its environment is relatively fragile.It plays an important role in carbon stock,biodiversity conservation,wetland restoration and maintains important ecosystem functioning.In wetland vegetation,there are relatively few studies on the key ecological processes of "community assembly-biodiversity pattern-ecosystem productivity",which is an urgent problem to be solved in wetland vegetation research and has important practical significance.In this study,riparian marsh in the Shandong section of Yellow River and coastal marsh on the south coast of Laizhou Bay were selected as our research area.In order to explore the species composition and community types,the change pattern of biodiversity and functional traits composition,the mechanism of plant community assembly and the regulation mechanism of primary productivity,this study chose plant community on marshes as the research object and quantified the environmental conditions,functional traits composition,biodiversity,and primary productivity based on field investigation.Based on the above study contents,the main results are as follows:(1)The soil salt content is the main factor affecting the distribution of plant community types on riparian marshes.Due to the blocking of seawater by the dam,soil moisture content is the main factor affecting the distribution of plant community types on coastal marshes.Based on the field investigation,this study sorted out the species list and counted the species composition of wetland plant community according to Flora of China.This study divided the community types by cluster analysis,named it by using the dominant species,and then explored the distribution of community types using canonical ordination.The results show that there are 46 plant species in riparian marsh of the Shandong section of Yellow River,belonging to 19 families and 37 genera.There are 21 plant species in coastal marsh of the south coast of Laizhou Bay,belonging to 9 families and 20 genera.The largest family was Poaceae,followed by Asteraceae,the families with single species are more.The riparian plant community is affected by hydrological events and human disturbance,so there are shrub species in the coastal wetland and no tall woody plants in riparian marshes.The riparian plant community on marshes can be divided into 9 types:Calamagrostis pseudophragmites meadow,Digitaria ciliaris var.chrysoblephala meadow,Polygonum hydropiper meadow,Suaeda salsa meadow,Imperata cylindrica meadow,Calamagrostis pseudophragmites+Potentilla supina meadow,Calamagrostis pseudophragmites+Phragmites australis meadow,Phragmites australis meadow and Miscanthus sacchariflorus meadow.There are 4 types on coastal marshes:Artemisia scoparia meadow,Artemisia scoparia+Artemisia capillaris+Setaria viridis meadow,Erigeron canadensis meadow and Setaria viridis meadow.The main factors that cause the different types and distribution of riparian and coastal plant community on marshes are the environmental differences between the two areas.The soil salt content represented by soil electrical conductivity is the main factor affecting the distribution of community types of plant community on riparian marshes.Due to the blocking of seawater by the dam,soil moisture content is the main factor affecting the distribution of plant community on coastal marshes.(2)In the riparian marshes of the Shandong section of Yellow River,functional composition and biodiversity increased with the decrease of soil salinity;in the coastal marshes on the south coast of the Laizhou Bay,functional composition increased with the increase of soil nutrients,and the biodiversity did not change significantly along the environmental gradient.This study quantified the relative proportion of interspecific and intraspecific traits variability by measuring plant functional traits in different habitats to explore the source of differences in plant functional traits.Then,the functional traits composition(Community weighted traits value)and biodiversity were quantified to explore the change pattern along the environmental gradient.The results show that the variability of plant functional traits mainly come from interspecific differences,and the intraspecific variability of different regions and different functional traits are very large,reflect the response of functional traits to environmental changes.There is a general positive correlation between the biodiversity of different dimensions in plant community on marshes.This article found that leaf nitrogen and phosphorus concentration increased with the decrease of soil salinity,indicating salt stress limits the absorption of nutrient in riparian species.With the increase of soil nutrients in coastal marsh,leaf nitrogen and phosphorus concentration increased,while leaf dry matter content decreased,indicating that with the increase of soil nutrients,species tend to adopt the life history strategy of rapid growth.There was no significant change in biodiversity of plant community on coastal marshes along the environmental gradient.(3)Environmental filtering based on the niche theory drives the processes of plant community assembly in the Shandong section of Yellow River and the south coast of the Laizhou Bay.Soil salinity drives the processes of plant community assembly on riparian marshes.Spatial variables affect the processes of plant community assembly on coastal marshes.Based on the phylogenetic tree and functional cluster tree,the key community assembly process was inferred by quantifying functional trait and phylogenetic structures(Nearest taxa index),testing the phylogenetic signals of functional traits and change of functional trait and phylogenetic structures along the environmental gradient.Through the methods of redundancy analysis and variance partitioning,explored the influence of environmental(edaphic and climatic)and spatial factors to functional trait and phylogenetic structures.The results show that significant phylogenetic signals were detected for all traits in plant community on riparian marshes,indicating that the evolution of functional traits was in line with the phylogenetic conservation.The phylogenetic and functional traits structures were clustered,which indicated that the processes of community assembly were dominated by deterministic process.The significant changes in structures of functional traits along the environmental gradient indicated that the changes in structures of functional traits were caused by environmental changes.In the coastal marshes,it was found that seed mass had a significant phylogenetic signal,the structure of seed mass wase significantly clustered and tended to overdispersion along the environmental gradient.These evidences indicate that the processes of community assembly are dominated by environmental filtering in the Shandong section of Yellow River and the south coast of the Laizhou Bay.The results of redundancy analysis and variance partitioning showed that community assembly of riparian plant community was greatly affected by soil factors,and soil salt content was the key soil factor affecting its assemble process.The assembly process of coastal plant community is greatly affected by spatial variables,which indicates that the species diffusion ability affects the assembly process of coastal plant community.(4)Environmental factors affect primary productivity mainly through biodiversity and functional traits composition.The maximum plant height is the best predictor of primary productivity.Through the analysis of the bivariate relationship of "environmental factors-primary productivity" and "biodiversity and functional traits composition-primary productivity",explored the effects of environment,biodiversity,and functional traits composition on primary productivity.Random forest analysis,linear mixed effect model and model selection were used to extract the predictor affecting primary productivity.The structural equation model was used to explore the cascade regulation mechanism of primary productivity.Then,combined with the process of community assembly,the effects of community assembly on primary productivity was explored.The results show that available nitrogen increased primary productivity of riparian plant community.The effect of environmental factor on primary productivity of coastal plant community was not significant.The maximum plant height was positive with primary productivity.There are negative relationships between different dimensions of biodiversity and primary productivity.When considering the effects of environmental factors,biodiversity,and functional traits composition on the primary productivity of plant community together,the maximum plant height was the best predictor of primary productivity.Environmental factors affect primary productivity indirectly through biodiversity and functional traits composition.In coastal marsh,Tamarix chinensis directly promotes the primary productivity,reflects its "fertile island" effect and the facilitation of herbaceous species.The plant functional traits mediate the relationship between the community assembly and primary productivity.In riparian marshes,plant maximum height responds to environmental filtering and drives the change of primary productivity.In coastal marsh,seed mass not only responds to environmental changes,but also affects primary productivity.This study found a negative correlation between biodiversity and primary productivity in the Shandong section of Yellow River and the south coast of the Laizhou Bay.The facilitation of shrub species Tamarix chinensis on primary productivity of the lower meadow was found in coastal marsh,and the influence of Tamarix chinensis on the plant community was integrated into the cascade regulation mechanism of primary productivity.These findings provide new ideas for wetland management and restoration.In conclusion,this study provides experimental evidence for wetland community assembly and the regulation mechanism of ecosystem functionings,provides theoretical basis for predicting the possible change trend of wetland vegetation under global climate change,and provides scientific support for wetland ecological restoration,improvement of ecological environment and efficient utilization of plant resources.