Succession Characteristics Of Rhizosphere Microbial Communities Of Submerged Plants And Their Effects On Nitrogen And Phosphorus Reduction

In recent years,lake eutrophication is still one of the serious water environment problems in China.Submerged plants play an important role in the treatment of eutrophic lakes,and submerged plant rhizosphere microorganisms play an important role in this process.In this study,Meiliang Bay of Taihu Lake was selected for basic investigation.Based on the analysis of the characteristics of nitrogen and phosphorus pollution in the study area and the current situation of sediment "sources and sinks",laboratory simulation experiments were carried out to study the changes of rhizosphere microbial communities,the physical and chemical properties of overlying water and sediment,and the dynamic changes of various nitrogen and phosphorus indicators during the growth of submerged plants under the conditions of source mud and sink mud,It is expected to provide a theoretical basis for the mechanism of the influence of submerged plant rhizosphere microorganisms on nitrogen and phosphorus release from the water sediment interface and the control of endogenous nitrogen and phosphorus release from the sediment of eutrophic lakes.The main research conclusions are as follows:The basic investigation results show that the average concentrations of TP and TN in the overlying water of the study area are 0.129 mg/L and 1.935 mg/L respectively;TP in surface sediments generally increased from the lake center to the lake shore,and TN gradually increased from the northwest to the southeast;The content of TP and various forms of phosphorus decreased from the surface layer downward in vertical direction,while the content of TN and various forms of nitrogen decreased from the surface layer downward in vertical direction or decreased first and then increased from the surface layer.Four principal components were extracted from the principal component analysis of pollution sources,including agricultural non-point source pollution,domestic sewage pollution,industrial wastewater pollution,aquatic plant residue degradation pollution and aquaculture pollution.The cumulative variance contribution rate was 95.711%.Surface sediments have a higher risk of nitrogen release,and lower temperature increases the risk of nitrogen release in middle and bottom sediments;In the table,the bottom sediment has a greater risk of phosphorus release.The phosphorus Qm of the sediment is shown as bottom>middle>surface,and the theoretical maximum adsorption amount reaches0.933 mg/g.The results of indoor simulation experiment showed that during the experiment,the p H and DO of the overlying water in the source mud group and the Malayan cabbage group showed a trend of first increasing and then stabilizing,and the p H and DO of the overlying water in the sink mud group were lower than those in the source mud group;The OM content of sediment in the source mud group decreased by0.47%,1.56% and 0.72% respectively in the control group,kukucao group and malayan cabbage group,and the OM content of sediment in the sink mud group accounted for less than that in the source mud group in each period;The growth indexes of submerged plants,such as leaf growth,stem number,fresh weight and root diameter,were gradually increasing.The content of nitrogen and phosphorus in the control group and submerged plant group decreased gradually,The content of nitrogen and phosphorus in the submerged plant group was significantly lower than that in the control group,and the submerged plant Malayan potherb group was greater than that in the bitter grass group(source mud: Malayan potherb N 36.72%,P38.51%>bitter grass N 31.80%,P 33.20%>control N 19.56%,P 21.93%,sink mud:Malayan potherb N 36.72%,P 38.51%>bitter grass N 18.10%,P 17.66%>control N17.85%,P 17.11%);The removal of phosphorus in the system is mainly realized by the reduction of DTP and SRP in the overlying water,and the reduction of Na OH-P content in the sediment.Compared with Huini Formation,the growth indexes of submerged plants in Yuanni Formation are better,and the growth of submerged plants in Yuanni Formation is more effective in reducing nitrogen and phosphorus in sediment water system.The results of microbial sequencing showed that the number of taxa,classes,orders,families and genera of microorganisms in sediment and plant root samples had increased to varying degrees in the early,middle and late stages.The growth rate of the experimental group was higher than that of the control group,and there was no significant difference between the bitter grass group and the Malayan cabbage group.Sediment and plant rhizosphere and sample microbial communities α Diversity analysis showed that there were significant differences among groups in Chao1 and Observed specifications,Faith’s PD and Good’s coverage indexes(P=0.013,0.012,0.033 and 0.025,respectively),and Shannon,Simpson and Pierou’s evenness indexes were extremely significant(P=0.0027,0.0027 and 0.0041);Beta diversity PCo A analysis showed that the microbial community composition in the sediment group was more similar,and the plant root community composition was significantly different;The results of hierarchical cluster analysis showed that the growth of plants under the source mud conditions was conducive to the diversity of microbial community species.The content of total nitrogen in overlying water,total nitrogen and organic phosphorus in sediment were negatively correlated with most of the microflora.Compared with Huini Formation,the source mud conditions hindered the structural succession of some microbial communities to some extent;The growth of two submerged plants,Vallisneria alopecuroides and Potamogeton malayi,significantly increased the relative abundance of microorganisms related to nitrogen cycle.