Unravelling how biochar and dung amendments determine the functional structure and community assembly related to methane metabolisms in grassland soils

Abstract

Biochar and dung amendments have been extensively employed in soil remediation and fertilization of grasslands, which are the largest terrestrial sinks for methane. However, how these exogenous amendments regulate methane metabolisms at the molecular and community levels remains elusive. In this study, we investigated the functional genes and community assemblies of methanogens and methanotrophs using Geochip 5.0 and high-throughput sequencing to reveal the impacts of biochar and dung on soil methanogenesis and methane oxidation. The interactions between methane metabolic genes and other biogeochemical genes were also examined. According to Geochip microarrays, methanogenic gene mcrA decreased and increased with dung or biochar amendment, respectively; The methanotrophic gene pmoA showed a reverse but not significant tendency. Undominated processes contributed 65.51% to replace homogeneous selections as primary driving forces of methanogen assembly after dung amendment; the contribution of dispersal limitation increased to 46.13% in methanotroph assembly after biochar amendment. The diversity and association of co-occurrence networks for carbon–nitrogen cycling genes decreased after exogenous amendments. These results indicated that biochar and dung amendments prominently regulated the functional genes and community assembly involved in methane metabolisms. The co-existence patterns of methane metabolic genes and other related geochemical genes were also shaped by these amendments. This study provides the scientific reference for the development of grassland management in the context of global warming.

Highlight

1.	Biochar amendment impeded methanogenesis and facilitated methane oxidation whereas dung amendment facilitated methanogenesis and impeded methane oxidation in grassland  soils.
2.	Dung amendment generated undominated processes rather than homogeneous selection as the primary driving force in the community assembly of methanogen.
3.	Biochar amendment raised the contribution of dispersal limitation in the community assembly of  methanotrophs.
4.	Diversity and association of the network among the functional genes involved in carbon and nitrogen cycling decreased after biochar and dung amendments.

Funding

Ministry of Science and Technology of the People's Republic of China(2018YFD0800403)