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 of agricultural soils
and the CH4 cycling microbial communities. 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 Methylocaldum
szegediense and methanogen Methanosarcina horonobensis, replacing the
indigenous methane cycling community members. However, multivariate
analyses did not point out type Ib methanotrophs like M. szegediense as
significant driving factors for the observed improved soil CH4 uptake
potential. Conventional type IIa methanotrophs like Methylocystis sp. also
had higher differential abundances in organic-amended soils and are
speculated to be contributing 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.