Study On The Relationship Between Microbial Community Structure Around Typical Plants Roots And Pollutants Removal In The Constructed Wetland

The constructed wetland has shown its attractions and been widely used to treat various types of wastewater due to low investment,energy consumption and operation cost.Substrates,aquatic plants and microorganisms are the main components that work in the water purification process in a constructed wetland.The rich microbial resources provide sufficient decomposers for the sewage treatment system.Factors such as plant species,growth dynamics all have an impact on the microbial community activity,population structure and spatial distribution around plant roots,which further affect the removal efficiency of pollutants.Previous researches on the water purification efficiency and microbial community mainly focused on seasonal changes,but there were few studies on the relationship between the dynamic microbial community around roots and the removal efficiency of pollutants both in the vegetative period and reproduction period of plants.In this research,the microbial community composition and structural dynamics around the roots of Butomus umbellatus,Phragmites australis and Typha orientalis were analyzed in the vegetative and reproduction periods.The correlation between the microbial community and the removal efficiency of pollutants in wetlands was also explored in different periods.Our result can provide a reliable scientific basis for the optimization of plant configuration,improvement of water purification efficiency and protection and management of wetland ecosystem in constructed wetlands.The main conclusions are as follows:?1?In the vegetative period,the average removal efficiencies of P.australis wetland for TN and NH₄⁺-N were the highest,which were 65.15% and 61.24%,respectively;the average removal efficiencies of B.umbellatus wetland for NO₃^--N,NO₂^--N,COD and TP were the highest,which were 85.69%,95.12%,61.58% and 78.29%,respectively.In the reproduction period,the average removal efficiencies of B.umbellatus wetland for TN,NH₄⁺-N,NO₂^--N,COD and TP were the highest,which were 72.26%,64.61%,99.07%,73.97% and 86%,respectively;the average removal efficiency of P.australis wetland for NO₃^--N was the highest and it reached 91.94%.The removal efficiencies of NO₃^--N,NO₂^--N,COD and TP were better in the reproduction period,than those in the vegetative period.?2?During the vegetative period,the contents of total phospholipid fatty acid?PLFAs?around the roots of B.umbellatus,P.australis and T.orientalis increased first and then decreased;the average contents of total PLFAs,bacteria,fungi,actinomycetes,arbuscular mycorrhizal fungi?AMF?around the root of P.australis were the highest,and the highest contents of protozoa presented around the root of B.umbellatus.During the reproduction period,the contents of total PLFAs around the roots of B.umbellatus and T.orientalis decreased first and then increased,however,those aroud the root of P.australis showed an increasing trend;the contents of total PLFAs,bacteria,fungi,protozoa around the root of P.australis were the highest,while the highest contents of AMF and actinomycetes presented around the roots of B.Umbellatus and T.Orientalis,respectively.Around the roots of the three plants,the bacteria belong to Alphaproteobacteria,Gammaproteobacteria and Acidobacteria were dominant in the vegetative period,while the bacteria belong to Alphaproteobacteria,Betaproteobacteria,Deltaproteobacteri were dominant in the propagation period.The contents of dominant bacteria varies greatly among different plant species.In general,the microbial biomass was the largest at the depth of 10-20 cm both in the vegetative period and reproduction period.The microbial biomass were higher in the vegetative period than that in the reproduction period.?3?The pollutants removal efficiency in different plant wetlands was related to different factors.During the vegetative period,the removal efficiency of COD was positively correlated with protozoan,and those of NH₄⁺-N,NO₃^--N and NO₂^--N were positively correlated with G⁺: G^-in the B.umbellatus wetland;the removal efficiencies of NO₃^--N and NO₂^--N were positively correlated with G⁺: G^-in the P.australis wetland;the removal efficiencies of TN,NH₄⁺-N and NO₂^--N were positively correlated with AMF in the T.orientalis wetland.During the reproduction period,the removal efficiency of COD was positively correlated with Aerobic: Anaerobic in the B.umbellatus wetland;the removal efficiencies of TN,NH₄⁺-N and TP were positively correlated with S: M in the P.australis wetland;the removal efficiencies of TN,NH₄⁺-N were positively correlated with Aerobic: Anaerobic in the T.orientalis wetland.?4?The removal efficiency of pollutants was affected by the bacterial phylum.During the vegetative period,the removal efficiency of COD was positively correlated with Proteobacteria,that of NH₄⁺-N was positively correlated with Chloroflexi in the B.umbellatus wetland;the removal efficiencies of NH₄⁺-N and COD were positively correlated with Bacteroidetes in the P.australis wetland;the removal efficiencies of NH₄⁺-N and COD were positively correlated with Bacteroidetes in the T.orientalis wetland.During the reproduction period,the removal efficiency of NH₄⁺-N was positively correlated with Nitrospirae in the B.umbellatus wetland;the removal efficiencies of NO₃^--N and NO₂^--N were positively correlated with Bacteroidetes in the P.australis wetland;the removal efficiencies of NH₄⁺-N was positively correlated with Proteobacteria in the T.orientalis wetland.?5?In the vegetative period,the removal efficiency of nitrogen by P.australis wetland was the highest,and that of COD and TP by B.umbellatus wetland were the highest.In the reproduction period,the removal efficiencies of COD and TP by B.umbellatus wetland were the highest.In the vegetative period,the removal efficiencies of NH₄⁺-N?NO₃^--N?NO₂^--N?TP were correlated with the microbial community around the roots of B.umbellatus,P.australis and T.orientalis,and the removal efficiencies of TN?NH₄⁺-N?NO₂^--N?COD were correlated with the microbial community around the roots of three plants in the reproduction period.