Study On The Characteristics Of Soil Microbial Network And Carbon Metabolism Efficiency In The Riparian Zone Of Three Gorges Reservoir Area

Since the establishment of the Three Gorges Dam,a water-land ecotone（also known as riparian zone/water-level-fluctuating zone）with a total area of 349 km² has been formed on both banks of the reservoir area due to its unique hydrological operation mode of"storing water in winter and discharging water in summer".At present,researchers have done a lot of research on the geomorphological division,hydrological impact,vegetation colonization and biogeochemical interaction in the reservoir area,but the study on microbial community structure and network is relatively small,especially the study on microbial carbon metabolism efficiency is rarely reported.As the most active part of soil ecosystem,microorganism plays an important role in many aspects of ecosystem process.The coupling study of microbialα-diversity,community structure and composition,network interaction and microbial carbon metabolism efficiency will help to improve the understanding of microbial-mediated soil carbon cycle.In this study,the soil at 20 points along the riparian zone of the Three Gorges Reservoir Area in December 2021 and the soil at three elevations of typical tributary riparian zone（Gao Yang）from April to September 2022 were selected for study.The soil characteristics,soil enzyme activities,microbialαdiversity（including Chao,Shannon,Shannon even and PD index）,microbial community composition,key groups,generalized species and specialized species,microbial carbon metabolism efficiency and other related indicators were mainly analyzed,and the carbon metabolism efficiency,community structure and network interaction of soil microorganisms were mainly studied.The main conclusions are as follows:（1）Soil microbialα-diversity and microbial carbon metabolism efficiency in the riparian zone along the Three Gorges Reservoir have a clear trend of change.The microbialα-diversity and microbial carbon metabolism efficiency were analyzed by dividing the Three Gorges Reservoir into three different sections:upstream,middle and downstream.The results showed that the microbialαdiversity decreased continuously along the Three Gorges Reservoir,and the fungal communities in different sections showed significant differences.Carbon use efficiency（CUE）and microbial mass carbon（MBC）showed a trend of increasing and then decreasing,while microbial metabolic entropy（q CO₂）was completely opposite.（2）The metabolic efficiency of soil microbial carbon is influenced by multiple drivers.By constructing random forest model predictions,structural equation modeling,Pearson correlation,and redundancy analysis to analyze the factors influencing microbial carbon metabolism efficiency,it was found that the Myxococcota phylum in the bacterial community and the unclassified＿k＿Fungi phylum in the fungal community had a significant positive correlation with MBC（P<0.05）,the Desulfobacterota phylum in the bacterial Desulfobacterota and Nitrospirota in the fungal community had significant positive correlations with q CO₂（P<0.05）,while in the fungal community,Calcarisporiellomycota and Rozellomycota had significant positive correlations with Similar results were found in the correlation study of q CO₂.At the level of key genera,only the fungal genus unclassified＿k＿＿Fungi showed a significant positive correlation with MBC（P<0.05）,while microbial carbon metabolic efficiency was not significantly correlated with any of the remaining key genera.In addition,microbialα-diversity was hardly associated with microbial carbon metabolic efficiency by direct effect,but more by indirect effect by influencing soil enzyme activity,which plays a crucial role in driving microbial carbon metabolic efficiency.（3）Significant variability was observed among the indicators of soil properties,enzyme activity and microbialα-diversity at different elevations in the typical tributary riparian zone.In the study of soils at three different elevations at the Gaoyang site,it was found that soil total carbon（TC）,total nitrogen（TN）,different elemental molar ratios（containing C/N,C/P,N/P）,soil water content（SWC）,N-acetyl-β-D-glucosaminidase（NAG）,leucine aminopeptidase（LAP）,bacterial Shannon,bacterial Shannoneven,fungal Chao,fungal Shannon,fungal Shannoneven,and fungal PD indicators showed significant variability among elevations.（4）Bacterial and fungal networks were significantly different in the study of soil microbial network interactions of typical tributary riparian zones.Overall,the total number of nodes,edges,average degree,module number,niche breadth and node degree of bacterial community were significantly higher than those of fungal community.TC,C/N,C/P,N/P and LAP enzyme activities were important factors affecting bacterial and fungal communities.（5）Generalized and specialized species play an important role in the co-occurrence network,and their responses to external environmental factors are generally consistent with the responses of the whole bacterial and fungal communities to external environmental factors.About 1/3 of the total bacterial and fungal communities were composed of generalized species and specialized species.In the sub-network constructed by generalized species and specialized species,the specialized species of bacteria accounted for 69.16%,while the specialized species of fungi accounted for 91.28%.The network of generalized and specialized species could be clearly distinguished,especially the generalized species had a wider ecological niche width than the specialized species,while TC,C/N and C/P had highly significant positive effects on both generalized and specialized species（P<0.01）.