Spatiotemporal Differentiation And Assembly Processes Of Root Microbial Community Of Typha Orientalis In Semi-Constructed Wetland

Plants coexist with diverse microbes in their life process.Plant hosts and microorganisms coevolve to form a complex“holobiont”and affect plant health and ecological functions.Emergent plants in semi-constructed wetlands release oxygen to the rhizosphere environment and provide carbon sources for the growth of microorganisms through root exudates,providing a suitable growth environment for various microorganisms and playing an important role in the removal of pollutants in the wetland ecosystem.There were significant differences in root microbial communities in soils with different Physicochemical properties.Plant species and their growth and developmental stage all affected the interactions and functions of root microorganisms.At present,all these studies focus on terrestrial plants.Emergent plants are affected by both soil and water,and the driving process of root microbial community assembly is still lacking.In this study,Typha orientalis P.and Scirpus validus V.,two emergent plants in the constructed wetland,were selected as the research materials,and three different sampling sites were set at the inlet,middle and outlet of the flowing area of the wetland.Water,bulk soil,rhizosphere soil roots of plant in wetland were sampled at seedling stage（April）,mature stage（July）and wilting stage（October）,respectively.The diversity and composition of microbial community were analyzed by high-throughput sequencing and physicochemical properties,RDA and Mantel methods were used to analyze the microbial community structure and its relationship with environmental factors,The co-occurrence network was used to analyze the interactions of microbial community taxa and keystones,The potential function of microbial community was analyzed by functional prediction method,The source and assembly process of root microbial community of wetland plants were investigated by using a null model and Source Tracker method.The main results were as the followings:（1）Characteristics and differences of root-associated microbial communities of T.orientalis and S.validusPlant species had significant effects on theα-diversity andβ-diversity of rhizosphere fungal communities,bacterial communities in rhizosphere soil and root endosphere（P<0.05）;The dominant bacterial and fungal communities of rhizosphere soil and root endosphere were similar between T.orientalis and S.validus.There were significant differences in relative abundance between classes and families（P<0.05）,which were related to the physical and chemical properties of the soil in the rhizosphere.It was found that rhizosphere soil p H and urease activity had the most significant influence on bacterial and fungal community structure in the rhizosphere soil of T.orientalis（P<0.05）,while rhizosphere soil p H and alkaline phosphatase activity had the most significant impact on bacterial and fungal community structure in root endosphere（P<0.05）.Co-occurrence network analysis indicated that the topological properties of rhizosphere and root endosphere networks of T.orientalis and S.validus were different,and the network of rhizosphere bacterial was more complex than the that of root endosphere.The network of rhizosphere bacterial of S.validus was more complex than that of T.orientalis,The bacterial network in root endosphere was more complex than that of S.validus.The taxa of bacterial keystones in rhizosphere soil and root endosphere were different between T.orientalis and S.validus,and the keystones of fungi were also different.NMDS analysis based on PICRUSt2 function prediction showed that the bacterial community functions in rhizosphere between T.orientalis and S.validus were significantly different（P<0.05）,whereas the bacterial community function of root endosphere did not differ significantly（P>0.05）,the opposite was true for the fungal communities.Analysis of functional groups of bacteria and fungi by FAPROTAX and FUNGuild showed that there were significant differences in some functional groups of bacteria in rhizosphere and root endosphere between T.orientalis and S.validus（P<0.05）.Functional groups of fungi in rhizosphere were not significantly different,while one functional group of fungi in root endosphere was significantly different（P<0.05）.（2）Spatial differentiation of T.orientalis root microbial communitySome physical and chemical indexes of water,bulk soil and rhizosphere soil showed environmental gradient with the direction of water flow.There were significant differences in theα-diversity of bacterial communities in water and bulk soil at different sampling sites（P<0.05）,and the fungal communities in the rhizosphere and root endosphere of Typha orientalis were significantly different（P<0.05）.The sampling sites had significant effects onβ-diversity of bacterial and fungal communities in water,bulk soil,rhizosphere and root endosphere（P<0.05）.The physicochemical indexes(Temp,p H,DO,EC,NO^3--N)of water were significantly correlated with the structure of bacterial and fungal communities（P<0.05）.The bacterial and fungal community structure of bulk soil was significantly correlated with TS and urease activities（P<0.05）,and the fungal community was also significantly affected by NH4+-N and sucrase activities（P<0.05）.The fungal community structure in rhizosphere soil was significantly correlated with the physical and chemical properties and enzyme activities of rhizosphere soil（P<0.05）.Rhizosphere soil p H and alkaline phosphatase activity were significantly correlated with bacterial and fungal communities in rhizosphere soil（P<0.05）.Fungal community structure was also significantly correlated with other rhizosphere soil physicochemical properties and enzyme activities（P<0.05）.Co-occurrence network analysis indicated that the interaction intensity of bacterial community was higher in bulk soil than rhizosphere soil than root endosphere than water,and the interaction intensity of fungal community was higher in bulk soil than rhizosphere soil than water than root endosphere.NMDS analysis based on PICRUSt2 function prediction showed that bacterial community functions in water,bulk,rhizosphere and root endosphere were spatially different at different sampling sites（P<0.05）,and the function of fungal communiiies were different in water and bulk soil（P<0.05）.（3）Temporal dynamics of root microbial communities in different developmental stages of T.orientalisPhysicochemical properties of water,bulk soil,and rhizosphere soil changed significantly with plant developmental stages（P<0.05）.The diversity and composition of microbial communities in water,bulk soil,rhizosphere soil and root endosphere significant changed during development stages of T.orientalis.The richness index of bacterial communities were the highest in the wilting stage,and the fungal richness index in water was the highest in the wilting stage,while the fungal richness index in bulk soil and root endosphere were the higher in mature stage.The dominant classes of bacteria and fungi differ significantly in water,bulk soil,rhizosphere soil and root endosphere at three developmental stages.The co-occurrence network of microbial community changed significantly in different developmental stages,and the network connectivity was higher in the mature stage.The keystone taxa and ecological role of bacterial and fungal communities in root endosphere shifted significantly with plant development.Bacteria play an important role in maintaining plant health and nutrient requirements at the early stages,while fungi take an increasingly greater role as the decomposer at later stages.（4）Assembly process of T.orientalis root associated microbial communityThe microbial diversity and composition along the water-soil-plant continuum were related to their niche（17.2-37.9%）and the developmental stage of the T.orientalis（6.6-7.7%）,but the sampling site has little influence.As a plant barrier,roots selectively recruit specific microbial taxa primarily from water（bacteria:18.9%,fungi:19.1%）and rhizosphere soils（bacteria:39.9%,fungi:27.3%）.The Assembly processes of bacteria and fungi were different.While bacterial communities were dominated by deterministic processes（|βNTI|≥2）,and fungal communities were instead driven by stochastic processes（|βNTI|<2）.The community structure of bacteria and fungi in water was closely related to temperature,p H,dissolved oxygen,electrical conductivity,nitrate and ammonium content.In bulk soil,bacterial community structure was closely related to ammonium and total phosphorus,while fungal community structure was closely related to organic carbon.In rhizosphere soil,fungal community structure was only significantly correlated with ammonium.The bacterial community structure in the root was significantly affected by the total sulfur and ammonium in the rhizosphere.In conclusion,the composition,structure,interaction relationship and function of the semi-constructed wetland microbial community differ significantly with plant species,different ecological niche and different development stages of plants.Moreover,the construction process of bacterial and fungal communities in wetland is different,and the root endophytic microbial community is enriched by water and rhizosphere microbial communities.This study provides data support for the research on the construction process and potential functions of the root microbial community of wetland plants,and provides theoretical and data support for the ecological functions of wetland plants such as nutrient metabolism and pollutant removal and the application of synthetic microbial community.