Study On Bacterial And Denitrifying Community Diversity Of Epiphytic Biofilms In Submerged Macrophytes

Eutrophication of water body has always been a hotspot in ecological research.Bioremediation methods have strong practicability and received widespread attention due to the characteristic of aesthetic,economic,and eco-friendly characteristics.Traditional research believes that aquatic plants play an important role in ecological restoration.It can not only regulate the physical and chemical environment of water body,improve dissolved oxygen and absorb nutrients,but also provide a suitable niche for microorganisms,algae,protozoa,etc.However,the important role of epiphytic biofilms on submerged macrophytes in water restoration has been ignored for a long time.In this study,a macrophytic lake the Caohai wetland was taken as the research object,and the samples of biofilms attached to the surface of submerged macrophytes were collected for many times.By using high-throughput sequencing,function prediction,gene quantification and other analysis methods to explore the structural and functional diversity differences between epiphytic bacteria community and planktonic bacteria community of a typical submerged macrophyte?Potamogeton lucens?,and Further explore the seasonal dynamic characteristics and influencing factors of the bacterial community of the epiphytic biofilms.Finally,explore the dynamic and seasonal characteristics of the denitrifying microbial community of the epiphytic biofilm,and the community assembly mechanism of denitrifying microorganisms was explored.The main results are as follows:?1?Epiphytic bacterial and planktonic bacterial communities have a higher ratio of common species composition,but each kind of community has some specific microbial groups.Proteobacteria and Bacteroidetes were dominant groups shared by the two kinds of communities.The structure of the epiphytic bacterial community is significantly different from the planktonic bacterial community,and the compositions of dominant OTUs different.?2?Functional prediction analysis?Prokaryotes for Functional Classification of Prokaryotes,FAPROTAX?found that epiphytic bacteria and planktonic bacteria are mainly heterotrophic functions,but compared with planktonic bacterial communities,epiphytic bacterial communities have more prominent fermentation and denitrification functions?Nitrate reduction,nitrate respiration and nitrite respiration?.?3?The bacterial communities of epiphytic biofilms showed significant structural differences between the growing period?July?and the declining period?November?of the submerged macrophytes.During the two seasons,the sharing rate of epiphytic bacterial species was higher,but the Alpha diversity index showed an upward trend?p<0.05?,and the16S gene abundance showed a certain downward trend?p<0.05?.?4?Firstly,water temperature is an important factor driving the seasonal dynamics of the epiphytic bacterial communities.Secondly,the pH,NH₄⁺concentration of the water body has a strong correlation with the seasonal dynamics of the Proteobacteria and Bacteroidetes groups;and the physicochemical characteristics of the biofilm also drive the seasonal dynamics of epiphytic bacterial communities.?5?The abundance of denitrification gene showed a downward trend with the growth to decline of plants,and the abundance of denitrification gene was significantly different among different plants.Proteobacteria?56.55%±22.15%?and Unclassified?bacteria?41.71%±22.17%?are the main groups of nirS-denitrifying bacteria.The seasonal dynamics of denitrifying bacterial communities were significant(R_ANOSIM=0.567,p=0.001),and the biofilm denitrifying functional bacterial communities among different host plants were less different.?6?Multiple regression analysis and redundancy analysis indicated the physicochemical factors of water body couldn't explain well of denitrifying bacterial diversification in the epiphytic biofilms?MRM's R²=0.238,RDA's R²=0.36?.The analysis of the null model showd that the dispersal limitation?randomness?plays a leading role in the process of denitrifying microbial community construction,followed by the undominated process.