Improved methane mitigation potential and modulated methane cycling microbial communities in arable soil by compost addition

The global atmospheric concentration of the potent greenhouse gas methane (CH₄) is rising rapidly, and agriculture is responsible for 30%-50% of the yearly CH₄ emissions. To limit its global warming effects, strong and sustained reductions are needed. Sustainable agricultural management strategies, as the use of organic amendments like compost, have previously proven to have a potent CH₄ mitigation effect in laboratory experiments. Here we investigated, using an extensive field study, the effect of organic amendments on the CH₄ mitigation potential and CH₄ cycling microbial communities of arable soils. Organic-amended soils had higher potential CH₄ uptake rates and an improved potential to oxidize CH₄ to sub-atmospheric concentrations. Also, we showed for the first time that the methanotrophic and methanogenic microbial communities of arable soils were unequivocally altered after organic amendment application by increasing in size while getting less diverse. Compost-amended soils became dominated by the compost-originating methanotroph <i>Methylocaldum szegediense</i> and methanogen <i>Methanosarcina horonobensis</i>, replacing the indigenous methane cycling community members. However, multivariate analyses didn't point out type Ib methanotrophs like <i>M. szegediense</i> as significant driving factors for the observed improved soil CH₄ uptake potential. Conventional type IIa methanotrophs like <i>Methylocystis</i> sp. also had higher differential abundances in organic-amended soils and are speculated to contribute to the improved CH₄ uptake potential. Altogether, the results showed that compost serves as a vector for the introduction of CH₄ cycling microbes and improves the soil's CH₄ uptake potential, which emphasizes the potential of organic fertilization with compost to contribute to CH₄ mitigation in agricultural soils.