THE ROLE OF PHOSPHORUS CYCLING AND SOIL MINERALOGY IN DEFINING METHANOTROPH ECOLOGY IN ARCTIC SOILS

A large portion of the World’s terrestrial organic carbon is stored in Arctic permafrost soils and permafrost warming in these regions is leading to increasing fluxes of CH₄ (methane), a potent greenhouse gas, to the atmosphere. As patterns of CH₄ release from Arctic soils change there is an urgent need to better understand the basis of in situ CH₄ production by methanogens and oxidation rates and patterns by methanotrophs; the main biological mechanism for CH₄ consumption. To identify environmental controls on such releases, we characterized soil geochemistry and microbial community conditions in 13 near-surface Arctic soils collected across Kongsfjorden, Svalbard. Surveys of methane flux vary by five orders of magnitude across sites and do not correlate to methanotroph abundance. Instead bacterial and Type I methanotroph gene abundances co-vary with soil phosphorous (P) concentrations. Soils in this region are organic-rich and their mineral components derived from weathering of metamorphic silicates and carbonates, which contain apatite in their primary mineralogy. They are rich in clay minerals (smectite, kaolinite, and illite) and mix-valence iron oxyhydroxides derived from mica schists and variably enriched authigenic carbonates that exhibit methanogenic signatures based on ¹³C isotopic analyses. These soils do not contain detectable apatite nor other phosphate minerals, but instead P is sorbed to clay and iron minerals and its occurrence is pH dependent. Native methanotroph communities appear to be P-limited and respond to P addition with increases in biomass and CH₄ consumption. These data, taken in their entirety, suggest that phosphorus abundance and cycling in Arctic soils critically impact biological mediation of CH₄ flux by native methanotrophs and therefore, methane flux is likely to increase in these areas as thawing continues.