Impacts of temperature and soil characteristics on methane production and oxidation in Arctic tundra

Rapid warming of Arctic ecosystems accelerates microbial decomposition of soil organic matter and leads to increased production of carbon dioxide (CO₂) and methane (CH₄). CH₄ oxidation potentially mitigates CH₄ emissions from permafrost regions, but it is still highly uncertain whether soils in high-latitude ecosystems will function as a net source or sink for CH₄ in response to rising temperature and associated hydrological changes. We investigated CH₄ production and oxidation potential in permafrost-affected soils from degraded ice-wedge polygons on the Barrow Environmental Observatory, Utqiagvik (Barrow), Alaska, USA. Frozen soil cores from flat and high-centered polygons were sectioned into organic, transitional, and permafrost layers, and incubated at -2, +4 and +8°C to determine potential CH₄ production and oxidation rates. Significant CH₄ production was only observed from the suboxic transition layer and permafrost of flat-centered polygon soil. These two soil sections also exhibited highest CH₄ oxidation potentials. Organic soils from relatively dry surface layers had the lowest CH₄ oxidation potential compared to saturated transition layer and permafrost, contradicting our original assumptions. Low methanogenesis rates are due to low overall microbial activities measured as total anaerobic respiration and the competing iron-reduction process. Our results suggest that CH₄ oxidation could offset CH₄ production and limit surface CH₄ emissions, in response to elevated temperature, and thus must be considered in model predictions of net CH₄ fluxes in Arctic polygonal tundra. Future changes in temperature and soil saturation conditions are likely to divert electron flow to alternative electron acceptors and significantly alter CH₄ production, which should also be considered in CH₄ models.