Effects Of Salinity On The Community Structure And Activity Of Aerobic Methanotrophic Bacteria In Lakeside Wetland Soils On The Qinghai-Tibet Plateau

Methane is an important greenhouse gas.Wetlands are one of the main sources of methane emissions.Methanotrophs in wetland aerobic soil layer can oxidize most of the methane produced in wetland soil before it is released into the atmosphere,which plays an important role in methane cycle.As an important part of natural wetland,lakeshore wetland is the link between aquatic ecosystem and terrestrial ecosystem.Soil physical and chemical properties of lakeshore wetlands are often affected by lake water and show some spatial heterogeneity.In particular,the expansion and contraction of lakes would lead to changes in soil salt content and soil water content,which would affect the number,community composition and activity of methanotrophs.In order to find out the effects of salinity on the abundance,community structure and activity of methanotrophs in lakeshore soil,the methane oxidation potential of freshwater Yang lake,saline Qinghai Lake and Chaka hyposaline lake on the Qinghai-Tibet Plateau were measured.We detected the variation characteristics of soil total organic carbon(TOC),total nitrogen(TN),total phosphorus(TP),nitrate nitrogen(NO₃^--N),ammonium nitrogen(NH₄⁺-N),p H value,conductivity and salinity.Using q PCR and Miseq sequencing analysis,we studied the abundance,diversity and community structure of methanotrophs.DNA stable-isotope probing followed by sequencing was used to determine how active methanotrophic populations differed in the lakeshore soils with a gradient salinity.The main results are as follows:1.There were significant differences in the abundance,diversity and community composition of bacteria and methanotrophs in lakeshore soils from different lakes and locations.In particular,the abundance and diversity of microorganisms(including bacteria and methanotrophs)in Chaka lakeshore soils were significantly lower than those in other lakeshore soils.Proteobacteria and Actinobacteriota were the dominant bacterial phyla in situ lakeshore soils.Methylocystis was the most dominant methanotrophs in most soils.The YL-b lakeshore sediment was dominated by Methylobacter.The community composition of methanotrophs in QHL-a lakeshore sediment was more diverse and dominated by type I methanotrophs,including uncultured RPC-1,FW,Methylomonas,and Methylobacter.The QHL-a meadow soil was dominated by atmospheric methane oxidizers USC-?.2.The methane oxidation potential of the lakeshore soils of Yang Lake and Qinghai Lake decreased with the increase of salt concentration and showed certain adaptability to high salt concentration.Salt stress significantly reduced the abundance and diversity of methanotrophs and changed the community structure of methanotrophs.The relative abundance of type Ia methanotrophs increased with the increasing soil salinity,but different methanotrophs adapted to different salinity.The relative abundance of an uncultured type Ia methanotrophs in lakeshore soils of Yang Lake increased significantly with the increase of salinity,but decreased sharply in soils with a salinity higher than 15 g L^-1.The relative abundance of Methylomicrobium in lakeshore sediment of Qinghai Lake increased with the increase of salinity,reaching?50%at high salinity(50 g L^-1).3.Methylobacter was the most active methanotrophs in lakeshore soils of Yang Lake at salinity of 0-15 g L^-1.In the lakeshore soils of Qinghai Lake,Methylovulum was the most active methanotrophs at salinity of 0-15 g L^-1;however,Methylobacter and Methylomicrobium were the most active methanotrophs in soils at salinity of 25-50g L^-1.The bacterial network increased in connectedness with low salinity(7.5 g L^-1)stimulus.The higher salinity(15-25 g L^-1)reduced the connectivity but increased the modularity of the network.Under the disturbance of salt,the key nodes in the microbial co-occurrence network were transformed.Methylobacter and other type I methanotrophs were the key nodes to maintain the stability of the co-occurrence network.Members of Sphingomonadaceae family might be the key taxa to help maintain the activity of methanotrophs under medium and high salinity conditions.This study fills the blank of the effects of salinity on the abundance,diversity,conmmunity structure and activity of methanotrophs in lakeshore soils on the Tibetan Plateau.The results of this study deepen the understanding of the methane cycle in lakeshore wetlands and have important implication for the interpretation of the regional and global carbon cycle and climate change.