Effects Of Long-term Greenhouse Cultivation On Soil CH₄ Uptake And Underlying Microbial Mechanisms In A Subtropical Agricultural Ecosystem

In recent years,with the increasing demand for vegetables and grains,greenhouse cultivation areas have developed rapidly,which will cause a series of negative effects on agricultural ecosystem functions.As an important ecosystem function,soil methane?CH₄?uptake has attracted wide attentions and its small emissions into the atmosphere can cause marked positive feedback on global warming.Previous studies mainly focused on the effect of short-term greenhouse cultivation on soil CH₄ oxidation capacity,including in situ CH₄ efflux and its relationship with abiotic factors.However,the effect of long-term greenhouse cultivation on soil CH₄ uptake and associated microbial mechanisms still remain elusive.Based on this,we selected after 9 years?mid-term?and 21 years?long-term?two greenhouse cultivation,as well as nearby ambient control site without greenhouse cultivation in the Fengxian District,Shanghai.Soil in situ CH₄ fluxes were monitered for a growing season.Soil samples were collected periodically and soil physicochemical properties?i.e.,soil moisture contents,salinity contents,extractable organic nitrogen and so on?were measured.The effects of long-term greenhouse cultivation on methanotrophic activity were measured via laboratory incubations and the Michaelis Menten equation was used to quantify the effects of long-term greenhouse cultivation on soil physiological groups of methanotrophic communities.In addition,we analyzed the changes of community structure and abundance of methanotrophs by pmoA-based high-throughput sequencing and metagenomic sequencing as well as quantitative PCR,respectively.The main results are as follows:?1?Soil CH₄ efflux is negative,indicating that subtropical agricultural soils act as sinks of atmospheric CH₄.Long-term greenhouse cultivation significantly decreased soil CH₄ uptake.Moreover,the structural equation model showed that salinity is a major driver for soil CH₄ uptake.?2?Long-term greenhouse cultivation significantly reduced methanotrophic activity.The results of Michaelis Menten equation showed that long-term greenhouse cultivation leads to the transformation of methanotrophs?type I methanotrophs to type II methanotrophs?.Moreover,the structural equation model showed that salinity was the main driving factor for changes in methanotrophic activities and differences in methanotrophic groups in this region.?3?Based on pmoA high-throughput sequencing analysis,we found that long-term greenhouse cultivation altered methanotrophic community structure,and significantly decreased the richness of methanotrophic community.In general,type I methanotrophs were dominated in soils.Long-term greenhouse cultivation significantly reduced the relative abundance of type I methanotrophs,while it significantly increased the relative abundance of type II methanotrophs,which was consistent with the above-mentioned changes in physiological groups of methanotrophs.In addition,long-term greenhouse cultivation significantly reduced methanotrophic abundances,which were consistent with lower soil CH₄ uptake.The results of the structural equation model showed that salinity changed soil CH₄ oxidation capacity mainly by affected methanotrophic abundance.In conclusion,long-term greenhouse cultivation can lead to soil salinity content accumulation,resulting in lower soil CH₄ uptake.However,when we comprehensively considered the effects of methanotrophic abundance,salinity,and other soil physical and chemical factors on the CH₄ oxidation,we found that salinity mainly affected soil CH₄ oxidation capacity by changing methanotrophic abundance.Our results improve our understanding of the effects of long-term greenhouse cultivation onsoil CH₄ uptake and underlying methanotrophic communities in subtropical agricultural soils,which will be helpful for better agricultural management practices for sustainable agricultural production and mitigation of CH₄ emissions in this region.