Methanotrophs' Niche Differentiation And Its Driving Mechanism

Methanotrophs are an indispensable part of the global carbon cycle.They are the key of reducing global methane emissions and have important ecological significance.In recent decades,the newly discovered sulfate-dependent anaerobic methane oxidation(sulfate-AOM),nitrate-AOM and nitrite-AOM processes combine the methane cycle with the sulfur cycle and the nitrogen cycle,which has a significant impact on the biogeochemical cycle and global climate change.Soil is an important carrier of the biogeochemical cycles and regarded as an important methane sink,which has special significance in the global methane cycle.The complex soil environment contains a variety of electron acceptors,which allows different methanotrophs to coexist in the soil habitat.However,the research on anaerobic methanotrophs in soil habitats has not been reported,and their contribution to methane emission reduction remains unknown.To this end,this thesis took 3 types of typical soil habitats(forest,grassland and cropland)as the research object,and soil samples in 4 major climate zones in China(subtropical monsoon climate,temperate monsoon climate,temperate continental climate,plateau mountain climate)were collected.All known methanotrophs(including the conventional proteobacterial aerobic methanotrophic bacteria,verrucomicrobial methanotrophic bacteria,NC10 phylum methanotrophic bacteria,and anaerobic methanotrophic archaea)were investigated to explore the niche differentiation of methanotrophs in typical soil habitats and their environment-driven mechanism.Furthermore,the driving mechanism of nitrogen input on methanotrophs in intertidal zone and paddy field was explored.The results will help to improve the global methane cycle and carbon cycle,and provide a theoretical basis for the regulation of methane emission reduction.The main findings are as follows.1)The niche differentiation characteristics of methanotrophs in typical soil habitatsMethanotrophs exhibited vertical spatial niche differentiation in soil habitats.The top soil was dominated by aerobic methane oxidizing bacteria,the sub-surface soil was dominated by NC10 phylum methanotrophic bacteria,and the deep soil was dominated by anaerobic methanotrophic(ANME) archaea.There were significant differences in the distribution of methanotrophs in different land use types.The methane oxidation processes in cropland soil were the most active,and the corresponding methanotrophs also exhibited the highest abundance.The potential methane oxidation rates and the abundance of methanotrophs in grassland soil and forest soil ranked second and third respectively.Sulfate-AOM could occur in terrestrial soil habitats,but ANME-2d archaea might be the potential functional microorganisms performing this bioprocess in terrestrial soil habitats,which is different from marine habitats.2)Key functional species of methanotrophs in typical soil habitatsAerobic methane-oxidizing bacteria participated in the construction of microbial molecular networks in 47.2% of all the soil samples.Methylacidiphilaceae,Methylomonaceae and Methylococcaceae were the keystone families in the deep layer of grassland soil in Northeast China,deep layer of forest soil in Tibet,and surface layer of grassland soil in Tibet,respectively.Methylomirabilaceae within NC10 phylum and Beijerinckiaceae within Alphaproteobacteria were the core families in terrestrial soil habitats.They existed in all soil habitat samples.In forest soil habitats,Type ? methane oxidizing bacteria were the main dominant methane oxidizing bacteria.In grassland soil habitats,Type ? or NC10 methane oxidizing bacteria were the dominant bacteria.In cropland soil habitats,Type ?,Type ? or NC10 methane-oxidizing bacteria were the dominant methanotrophs.In terrestrial soil habitats,ANME-2d archaea occupied an absolute dominant position in ANME archaea.In addition,a special cluster of ANME-1 were recovered in grassland and cropland soil,which was different from those in marine habitats.3)Environmental factors affecting the niche differentiation of methanotrophsClimate zones,land use types and depth had significant effects on the structure of soil habitat microbial communities and the abundance of genes involved in methane cycle.Human activities such as rice cultivation made the microbial community structure in cropland soil from different climate zones similar.pH value,temperature and inorganic nitrogen caused the niche differentiation of methanotrophs.Proteobacterial methanotrophic bacteria,NC10 methanotrophic bacteria and ANME archaea prefer to grow and perform methane oxidation in a neutral p H and moderate temperature environment,while verrucomicrobial methane oxidizing bacteria prefer acidic environments.Ammonia showed an extremely significant positive correlation with the proteobacterial pmo A gene and ANME-2d archaea mcr A gene abundance,as well as the aerobic methane oxidation rate.Nitrate and non-ANME-2d ANME archaeal mcr A gene abundance were significantly negatively correlated.4)Response mechanism of methane-oxidizing microorganisms to nitrogen inputNitrogen input reshaped the methane cycle in intertidal zone.Nitrogen input improved the abundance and activity of denitrifying methanotrophs,as well as their contribution rates to methane oxidation in intertidal zone.Nitrogen input reshaped the methane cycle in paddy soil,with NC10 phylum methane-oxidizing bacteria and ANME-2d archaea being the dominant species in paddy soil.Thus,denitrifying anaerobic methane oxidation became the dominant methane oxidation process in growing season,accounting for 71.9% of the total methane removal in paddy soil.