Effects Of Different Combinations Of Three Aquatic Plants On Purification And Microbial Diversity Of Farm Tail Water

Ecological interception ditch can effectively intercept and remove pollutants such as nitrogen and phosphorus from farmland tail water,which is one of the important ways to reduce farmland pollution.Plant species and combinations play a key role in water purification,pollutant interception and ecological stability of the ecological interception ditch system.In order to understand the purification potential of native aquatic plants in farmland ditches for farmland tail water,in this study,three native aquatic plants,Vallisneria natans(submerged plants),Nymphaea tetragona(floating plants)and Zizania latifolia(emergent plants),were selected as the research objects by constructing a small tail water treatment tank.The farmland tail water in Junshan District of Yueyang City was used as the water source to be treated.The purification effects of three plant combinations of Vallisneria natans,Vallisneria natans+Nymphaea tetragona,Vallisneria natans+Nymphaea tetragona+Zizania latifolia(with no plants as the blank control group)on farmland tail water pollutants were observed and analyzed,and the correlation between rhizosphere soil microbial community structure characteristics and water quality was explored.In order to provide scientific basis for the selection,construction and maintenance management of ecological ditch plants in farmland tail water treatment,the plant combinations and effective dominant flora with good purification effect were screened out.The main results are as follows:(1)There are differences in the purification effects of the three plant combinations on the main pollutants in the tail water of farmland.In the whole process of the experiment(within 210 days),the removal efficiency of total nitrogen and total phosphorus was the best,which were 17.61%and 42.45%,respectively.The best nitrite removal effect was Vallisneria natans+Nymphaea tetragona+Zizania latifolia,and the removal rate was 7.14%.The best removal effect of ammonia nitrogen was Vallisneria natans+Nymphaea tetragona,the removal rate was 4.48%.In the vigorous growth period(120d),the best removal effects of total nitrogen and nitrite nitrogen were Vallisneria natans+Nymphaea tetragona,with removal rates of 17.84%and 20%.The removal efficiency of total phosphorus and ammonia nitrogen was the best,which were 29.25%and 44.51%,respectively.It is considered that bittergrass has the best purification effect in the long-term water purification process.(2)There were differences in rhizosphere microbial community structure and diversity among different plant combinations.The richness and diversity of rhizosphere soil fungal communities in the control group were the highest,and the lowest in the Vallisneria natans+Nymphaea tetragona + Zizania latifolia group.The dominant fungi in the rhizosphere of the three plant combinations were Ascomycota and Basidiomycota.The dominant bacteria were Sordariomycetes,Agaricomycetes and Dothideomycetes.The abundance of Sordariomycetes in the rhizosphere soil of Vallisneria natans group was relatively high.The richness and diversity of bacterial community in the rhizosphere soil of Vallisneria natans+Nymphaea tetragona+Zizania latifolia were the highest,and those of Vallisneria natans+Nymphaea tetragona were the lowest.The dominant bacteria in the rhizosphere soil of the three plant combinations were Chloroflexi,Proteobacteria and Acidobacteriota.The dominant bacteria were Anaerolineae,Vicinamibacteria,Gammaproteobacteria and Alphaproteobacteria.The abundance of Chloroflexi and Anaerolineae in the rhizosphere soil of Vallisneria natans group and Vallisneria natans+Nymphaea group was higher.(3)There is a correlation between microbial community structure diversity and environmental factors of tail water.Among fungi,Ascomycota was positively correlated with TDS and NN,and Basidiomycota was positively correlated with BOD5,DO,AN and pH.Among the bacteria,Chloroflexi and Hypocreales were positively correlated with TN,TP,AN and DO,Proteobacteria was positively correlated with DO,BOD5,NN and pH,and Acidobacteriota was positively correlated with TN,TP and TDS.On the whole,the key factors causing differences in the structure and composition of rhizosphere microbial communities in different plant communities were TN,AN and NN in tail water.In summary:three native aquatic plants have good purification effect on farmland tail water during the test period,among which evergreen submerged plants have the best purification effect;the structure and diversity of rhizosphere microbial community in the purification system were closely related to plant composition and TN,AN and NN in tail water.