Methanotroph populations and CH(4) oxidation potentials in high-Arctic peat are altered by herbivory induced vegetation change

Methane oxidizing bacteria (methanotrophs) within the genus Methylobacter constitute the biological filter for methane (CH(4)) in many Arctic soils. Multiple Methylobacter 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 CH(4) 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 CH(4) concentrations and lower oxygen (O(2)) concentrations than exclosed peat. Correspondingly, the highest CH(4) oxidation potentials were closer to the O(2) 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 Methylobacter. Further analyses of pmoA transcripts revealed that several Methylobacter 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 CH(4) filter and that different Methylobacter populations are responsible for CH(4) oxidation depending on the environmental conditions.