The Response Of Bacterioplankton Community To Water Nutritional Condition In Poyang Lake

Freshwater lakes are an important part of the terrestrial hydrosphere,which stores the limited freshwater resources that human beings depend on for survival.However,in recent years,the problem of eutrophication pollution has become more and more serious worldwide,and the prevention and remediation of eutrophication pollution in freshwater lakes has received more and more attention.As decomposers in nature,microorganisms are an important part of the lake ecosystem and play an important role in maintaining the stability of the structure and function of the lake ecosystem.However,little is known about the responses of the microbial community to eutrophication and the effects of different nutrient forms on the microbial community.For this purpose,we took the bacterioplankton community as the research object and carried out the following two research contents in Poyang Lake-the largest freshwater lake in China:(1)Through in-situ observation experiments to study the structure,function,and interspecific effects of bacterioplankton communities in lakes with different trophic levels;(2)The effects of different forms of nitrogen and phosphorus nutrient addition on bacterioplankton communities were studied through microcosm simulation experiments the study.In this study,we used 16 S r RNA gene highthroughput sequencing technology combined with functional prediction,network construction,and random forest model construction to analyze the changes in community structure,function,and interspecific interaction of bacterioplankton.The main conclusions were as follows:1.During the transition from mesophication to light eutrophication(The TLI index from 31 to 54),the content of nitrogen and phosphorus in the lake increased significantly,the diversity of bacterioplankton increased,the community composition changed,the carbon and nitrogen metabolism functions were enhanced,and the stability of the bacterioplankton community decreased,and the ecosystem became more fragile.The specific results were as follows:(1)The ? diversity of the bacterioplankton community in the eutrophic lake was significantly higher than that in the mesotrophic lake,and the ? diversity index was significantly positively correlated with the trophic level index,indicating that the higher diversity of the bacterioplankton community was conducive to the adaptation of microorganisms to eutrophication.(2)The dominant composition of the bacterioplankton communities in the light eutrophic and mesotrophic lake did not changed,and they were all composed of Actinobacteria,Proteobacteria,Cyanobacteria,Deinococcus-Thermus,Bacteroidetes,and Verrucomicrobia.The difference in composition is mainly reflected in the light eutrophication enrichment of rare abundance groups such as Chloroflexi and Acidobacteria.Function prediction shows that bacteria have a higher carbon metabolism and nitrogen metabolism related function in eutrophic lakes,shows that eutrophication screened out taxa with stronger nutritional competitive advantages and promoted the adaptive transformation of microbial community functions to the implementation of elemental chemical cycles.(3)Network analysis results show that the light eutrophication compared with the mesotrophication,the interspecies interaction of the bacterioplankton community has changed,the species richness and connectivity in the bacterial network are reduced,and reduced the stability of the bacterioplankton community,which reduces the ability of the community to resist environmental interference and is more prone to changes.2.The effect of the enrichment of organic nitrogen and phosphorus on the community structure and function of bacterioplankton was greater than that of inorganic nitrogen and phosphorus.The diversity of the bacterioplankton community was decreased by the addition of high nitrogen and phosphorus,but only phosphorus significantly affected the function of the bacterioplankton community.Enrichment of inorganic and organic nitrogen and phosphorus reduces the stability of the microbial community and makes the ecosystem more fragile.The specific results were as follows:(1)The addition of a high concentration of nitrogen(+5 mg/L,+10 mg/L)and phosphorus(+0.04 mg/L,+0.1 mg/L)significantly reduced the ? diversity of the bacterioplankton community,and the ? diversity of the bacterioplankton community was significantly lower in the treatment with organic nutrient than that in the treatment with inorganic nutrient.(2)Inorganic nitrogen input increased the abundance of Actinobacteria and Cyanobacteria,and decreased the abundance of Proteobacteria and Chloroflexi,while organic nitrogen input decreased the abundance of Actinobacteria and Bdellovibrionota,and increased the abundance of Proteobacteria,Cyanobacteria,and Bacteroidetes.The input of inorganic form phosphorus increased the abundance of Actinobacteria and Armatimonadota but decreased the abundance of Proteobacteria and Patescibacteria.However,the input of organic form phosphorus decreased the abundance of Actinobacteria,Bacteroidetes,and Armatimonadota,but increased the abundance of Proteobacteria.The results showed that the microorganism had a preference for different forms of nutrients,and thus change the composition of the bacterioplankton community.(3)Neither inorganic nor organic nitrogen input significantly changed the community function of bacterioplankton.Inorganic phosphorus treatment significantly increased the functions related to nitrogen metabolism of the bacterial community,while organic phosphorus treatment significantly increased the functions related to photosynthesis and reduced the functions related to chemotherapeutics.The results suggest that the addition of organic phosphorus increases the autotrophic capacity of the bacterial community and reduces the heterotrophic capacity.(4)The network analysis showed that the addition of inorganic nitrogen increased the species richness and connectivity in the network,while the input of organic nitrogen decreased the species richness and connectivity in the network.The input of inorganic and organic phosphorus nutrients significantly increased the species richness and connectivity in the bacterioplankton community network.However,the addition of inorganic and organic nitrogen and phosphorus increased the species turnover rate and spatial heterogeneity of the bacterioplankton community and decreased the community stability and the ability to resist environmental disturbance.3.The hgcI?clade in the bacterioplankton community is the most important indicator group for predicting the nutritional status of lakes.The results of the random forest model showed that the hgcI?clade was the most important indicator group to predict the nutrient status of the lake.The hgcI?clade was positively correlated with nitrogen and negatively correlated with phosphorus in the lake water.In conclusion,in the process of eutrophication,bacterioplankton can enhance the metabolism of nutrient elements by changing the community structure,to adapt to the increase of eutrophication.However,the high concentration of inorganic and organic nutrient elements is not conducive to maintaining a high community diversity and ecosystem stability.The enrichment of organic phosphorus enhanced the competition between the bacterioplankton taxa,weakened the chemochemical heterotrophic metabolism of bacteria,and enhanced the photosynthetic nutrient metabolism,which damaged the community diversity and was not conducive to maintaining the stability of the ecological community.The results of this study clarified the response of bacterioplankton communities to the lake with different nutrient status,deepened our understanding of the eutrophication process,and provided a scientific basis for the prevention and control of freshwater lake eutrophication and the scientific control of lake ecosystem in the future.