Methane Oxidation in Arctic Soils from High- and Flat-Centered Polygons

Abstract:

The premise of global warming will cause deeper permafrost thawing, followed by increased carbon mineralization and CH₄ formation in saturated tundra soils. Arctic tundra soils also serve as potential sinks for CH₄ in response to warming temperature, which might be a key process in the global CH₄ budget. Quantification of methane oxidation potential of Arctic tundra is an important component to constrain models assessing the Carbon-climate feedback from high latitude soils.

The signature polygonal ground of Arctic tundra generates high level of heterogeneity in soil hydrology and soil thermal regime. Thus, two distinct polygonal features were investigated in this study to evaluate CH₄ oxidation potentials under multiple biogeochemical controls. The rates, drivers, and temperature sensitivity of methane oxidation were compared between High- and Flat-Centered Polygons (HCP and FCP, respectively). A significant lag period of CO₂ production was observed in soil microcosms from HCP center, which might be attributed to microbial biomass limitations and the slow growth of anaerobic microbial populations that were sensitive to freezing. Prolonged thawing significantly accelerated carbon mineralization and CH₄ oxidation rates measured via methane oxidation assays (MOA) from both active and permafrost organic layers of HCP. Soil microcosms from FCP showed higher CO₂ production and CH₄ oxidation rates in the active organic layer, but not permafrost layer, which might be explained by the anoxic/oxic interface identified by Fe(II) content in active layer. MOAs with temperature manipulation demonstrated high temperature dependence of methane oxidation activity, mediated primarily by soluble methane monooxygenase based upon metagenomic analysis and PCR quantification. Future work will identify key variables controlling methane oxidation rate and develop parameterization that can be incorporated into Arctic terrestrial ecosystem models.