Impacts of temperature and soil characteristics on methane production and oxidation in Arctic polygonal tundra
Methane (CH<sub>4</sub>) oxidation mitigates CH<sub>4</sub> emission from soils. However, it is still highly uncertain whether soils in high-latitude ecosystems will function as a net source or sink for this important greenhouse gas. We investigated CH<sub>4</sub> production and oxidation potential in permafrost-affected soils from degraded ice-wedge polygons with carbon-rich soils at the Barrow Environmental Observatory, Utqiaġvik (Barrow) Alaska, USA. Frozen soil cores from flat and
... flat and high-centered polygons were sectioned into active layers, transition zones, and permafrost, and incubated at &minus;2, +4 and +8&thinsp;°C to determine potential CH<sub>4</sub> production and oxidation rates. Organic acids produced by fermentation fueled methanogenesis and competing iron reduction processes responsible for most anaerobic respiration. Significant CH<sub>4</sub> oxidation was observed from the suboxic transition zone and permafrost of flat-centered polygon soil, which also exhibited higher CH<sub>4</sub> production rates during the incubations. Although CH<sub>4</sub> production showed higher temperature sensitivity than CH<sub>4</sub> oxidation, potential rates of CH<sub>4</sub> oxidation exceeded methanogenesis rates at each temperature. Assuming no diffusion limitation, our results suggest that CH<sub>4</sub> oxidation could offset CH<sub>4</sub> production and limit surface CH<sub>4</sub> emissions, in response to elevated temperature, and thus should be considered in model predictions of net CH<sub>4</sub> fluxes in Arctic polygonal tundra.