Response Of Soil Microbial Community Structure And Functional Traits To Annually Water Level Fluctuation In Banghu Wetlands

Wetland is a special ecosystem in the amphibious staggered transitional zone,and the hydrological fluctuation is one of its important features.Wetland biotopes often respond to the dynamic changes of the water level rapidly.The response of soil microbials plays a vital role in the health of the wetland ecosystem.As one of the most important ecologically sensitive areas in China,the Poyang Lake Wetlands also play a safeguarding role in the ecological service function of the watershed;the interannual and seasonal heavily water level fluctuation affect the Poyang Lake Wetland ecosystem.In order to reveal the response mechanism of soil microbial community structure and functional activity to long-term water level changes,and to evaluate the impact of hydrological conditions on soil quality evolution and function stability,the Banghu Lake Wetland of Poyang Lake was selected was the study field.The effects of interannual water level changes on the physicochemical properties of wetland soil and the composition and metabolic function of soil microbial community were analyzed.The conclusions of this study are of great significance to the maintenance of Poyang Lake Wetland ecosystem,and provide basic scientific data for the rational protection and scientific management of Poyang Lake Wetlands.The preliminary results obtained in this study are as follows:?1?The hydrological environment of the water level detained year and normal flow years was conducive to increasing the accumulation of soil nutrient substances.Specifically,the water level detained year and normal flow years are beneficial to the accumulation of soil TOC,DOC,DON,AP and NH₄⁺-N.However,in terms of seasons,summer flooding conditions increased soil AFDM,TOC,TN,TP,DOC,DON and AP.The soil nutrient content of the Triarrhena Lutarioriparia plots was higher than that from the Cynodon dactylon and Carex cinerascens plots.?2?Higher soil nutrient resources in normal flow year increased the functional activity of soil microorganisms.In normal flow year,the functional indexes such as soil MBC,MBN,q MBC,q MBN and Bglu,Bxyl,NAG and Phos were significantly increased.The long-term flooded anaerobic environment posed physiological pressure on microorganisms and inhibited microbial activity.In the seasonal dimension,the increase of soil nutrients in summer wetlands enhanced the microbial biomass,and also increased the activities of the four hydrolytic enzymes.The MBC,MBN,q MBC,q MBN and soil hydrolase activity from Triarrhena Lutarioriparia and Cynodon dactylon plots were significantly higher than that from Carex cinerascens plots.?3?The interannual water level shifts changed the bacteria community composition,but did not change the Alpha-diversity.First of all,for the bacterial community diversity,there was no significant difference in the OTU number and Alpha-diversity index among three hydrological years,and the seasonal results were consistent with the years;while among different plots,the Alpha-diversity decreased with the elevation.Secondly,the bacterial community structure in the water level detained year is significantly different from that in normal flow year and high flow year,and there was a significant difference in community structure among different sites.The results of microbial community structure based on PLFA analysis were not completely consistent with the sequencing data.The performance of PLFA is more sensitive,and it still has certain advantages in reflecting the differences in community structures and the abundance of microorganisms.?4?The effect of interannual water level changes on the composition of bacterial communities in wetlands was smaller than that among plots,and the seasonal difference did not have a significant effect.Specifically,the LEf Se analysis found that there were only 11 different species during the inter-annual period,but no difference species were found during the seasons,and there were 174 species that were different among the plots.It involves 9 phylums,24 classes,35 orders,45 families,and 61 genus.In addition,based on the function prediction of bacterial community,it was also found that the metabolic function of soil bacteria was mainly clustered according to the plots,and the fixation of nitrogen,the production of streptomycin,the degradation of lignin,the chitin metabolism from Cynodon dactylon and Carex Cinerascens plots were stronger than the other plots.Functional predictions showed that the interannual and seasonal water level changes had no significant effect on the bacterial metabolic function.This was inconsistent with the functional activity index actually measured in this study,indicating that functional prediction based on bioinformatics may deviate from the actual situation.In summary,the interannual water level changes significantly changed the nutrient content of wetland soil,and changed the community structure and functional activity of soil microorganisms.However,this interannual hydrological change only affected the abundance of a small portion of bacterial species,and the seasonal changes had no significant impact,and the impact of plot differences on the composition of bacterial communities was even more pronounced.However,this was not consistent with the results from soil functional activity,indicating that the response of microbial community structure and function to environmental changes is not uniform.In addition,the formation of different water level elevation plots was the result of long-term hydrologic accumulation,which was more profound than the effects of short-term seasonal changes and medium-term interannual fluctuations.The results of this study show that the impact of wetland hydrological changes on wetland microbes is a long-term process.It also suggests that we should pay attention to the scale of the study in future studies.Research on different spatial and temporal scales will lead to different conclusions.