Methanotroph populations and CH 4 oxidation potentials in High Arctic peat are altered by herbivory induced vegetation change

Abstract

Methane oxidizing bacteria (methanotrophs) within the genus <i>Methylobacter</i> constitute the biological filter for methane (CH₄) in many Arctic soils. Multiple <i>Methylobacter</i> strains have been identified in these environments but we seldom know the ecological significance of the different strains. High-Arctic peatlands in Svalbard are heavily influenced by herbivory, leading to reduced vascular plant and root biomass. Here, we have measured potential CH₄ oxidation rates and identified the active methantrophs in grazed peat and peat protected from grazing by fencing (exclosures) for 18 years. Grazed peat sustained a higher water table, higher CH₄ concentrations and lower oxygen (O₂) concentrations than exclosed peat. Correspondingly, the highest CH₄ oxidation potentials were closer to the O₂ rich surface in the grazed than in the protected peat. A comparison of 16S rRNA genes showed that the majority of methanotrophs in both sites belong to the genus <i>Methylobacter</i>. Further analyses of pmoA transcripts revealed that several <i>Methylobacter</i> OTUs were active in the peat but that different OTUs dominated the grazed peat than the exclosed peat. We conclude that grazing influences soil conditions, the active CH₄ filter and that different <i>Methylobacter</i> populations are responsible for CH₄ oxidation depending on the environmental conditions.