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 (inline-formulaCO₂) and methane (inline-formulaCH₄). inline-formulaCH₄ oxidation potentially mitigates inline-formulaCH₄ 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 inline-formulaCH₄ in response to rising temperature and associated hydrological changes. We investigated inline-formulaCH₄ production and oxidation potential in permafrost-affected soils from degraded ice-wedge polygons on the Barrow Environmental Observatory, Utqiaġvik (Barrow), Alaska, USA. Frozen soil cores from flat and high-centered polygons were sectioned into organic, transitional, and permafrost layers, and incubated at inline-formula−2, inline-formula+4 and inline-formula+8 inline-formula^∘C to determine potential inline-formulaCH₄ production and oxidation rates. Significant inline-formulaCH₄ production was only observed from the suboxic transition layer and permafrost of flat-centered polygon soil. These two soil sections also exhibited highest inline-formulaCH₄ oxidation potentials. Organic soils from relatively dry surface layers had the lowest inline-formulaCH₄ 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 inline-formulaCH₄ oxidation could offset inline-formulaCH₄ production and limit surface inline-formulaCH₄ emissions, in response to elevated temperature, and thus must be considered in model predictions of net inline-formulaCH₄ 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 inline-formulaCH₄ production, which should also be considered in inline-formulaCH₄ models.