Evolution Characteristics And Driving Mechanism Of Aerobic Denitrifying Bacteria In Lake Baiyangdian Under Different Hydrological Scenarios

Taking Lake Baiyangdian as the research object,the representative sampling sites were collected and analyzed from four hydrological scenarios.The aim was to explore the evolution characteristics of different sub-communities of aerobic denitrifying bacteria and environmental driving factors,and to quantify the influence of key environmental factors on evolution of aerobic denitrifying bacteria in Lake Baiyangdian,based on the series of systematic research,it would provide significant support for futter understanding of the nitrogen cycle process and enrichment and acclimation of efficient aerobic denitrifying bacteria in Lake Baiyangdian.The main research results are as follows:1)There were significant differences for water quality indexes and dissolved organic matter（DOM）components during different hydrological scenarios in Lake Baiyangdian（P<0.05）.The water showed weak alkalescence all year round,and the water quality was poor in freezing period,in which the contents of NO₃^--N and TN were 2.97±1.25 and3.63±1.53 mg·L^-1,respectively.Tryptophanoid substances（P2,34.50-42.67%）and microbial metabolites（P4,25.32-40.24%）accounted for the majority proportion in the whole year.The DOM exhibited low humification degree and high bioavailability characteristic in Lake Baiyangdian.Moreover,the correlation between water quality and DOM compontnts showed obvious spatio-temporal differences.2)There were significant differences for aerobic denitrifiying bacterial community structure andα-diversity among different hydrological scenarios in Baiyangdian Lake（P<0.001）.Among each hydrological scenarios,Proteobacteria was the largest phylum,and the highest relative abundance of genus for abundant and rare taxon under each hydrological scenario were Magnetospirillum and Pseudomonas,respectively.In addition,the flora richness was highest in freezing season,and diversity and evenness of flora were highest in dry season and freezing season.Moreover,theα-diversity of rare taxa was much higher than that of abundant taxa.The difference of community similarity among different hydrological scenarios was highest in dry season and freezing season,and the smallest in rainy season and wet-to-dry transition season.The difference between sub-communities was the largest in dry season and the smallest in wet-to-dry transition season.3)The water quality driving factors were different among different hydrological scenarios and abundant/rare taxon,and the key water quality driving factors were T,DO,NO₃^--N and COD_Mn.Network analysis showed that the species associated with water quality drivers were different among different hydrological scenarios and sub-communities,and the main genera were unclassified,Magnetospirillum,Pseudomonas,Aeromonas and Thauera.At the same time,the interactions between key water quality factors and microflora exhibited obvious evolution characteristics,including water quality correlation categories,positive and negative interactions,and the species categories and abundant/rare taxon.Structural equation modeling（SEM）showed that T had the largest total effect onβ-diversity among hydrological scenarios,and was significantly negatively correlated with whole and rare taxon and positively correlated with abundant taxa.The quantitative effects of water quality factors for driving the evolution of abundant and rare taxon were different under different hydrological scenarios.4)The DOM driving factors differed among different hydrological scenarios and abundant/rare taxon.Network analysis showed that species related to DOM driving factors existed in different periods and sub-communities,and the main genera were unclassified,Magnetospirillum,Pseudomonas,Aeromonas,Sulfuritortus,Azoarcus and Limnohabitans.At the same time,the interactions between DOM components and microflora exhibited obvious evolution characteristics,including DOM correlation categories,positive and negative interactions between the key DOM components and flora,species categories and abundant/rare taxon.SEM showed that the quantitative effects of DOM components driving the evolution of communities were different in different hydrological scenarios and sub-communities,and humics-like substances（HDOM）had the largest total effect onβ-diversity of rainy season,showing a significant positive correlation.