Methane oxidation in contrasting soil types: responses to experimental warming with implication for...

Arctic ecosystems are characterized by a wide range of soil moisture conditions and thermal regimes and contribute differently to the net methane (CH₄ ) budget. Yet, it is unclear how climate change will affect the capacity of those systems to act as a net source or sink of CH₄ . Here, we present results of in situ CH₄ flux measurements made during the growing season 2014 on Disko Island (west Greenland) and quantify the contribution of contrasting soil and landscape types to the net CH₄ budget and responses to summer warming. We compared gas flux measurements from a bare soil and a dry heath, at ambient conditions and increased air temperature, using open-top chambers (OTCs). Throughout the growing season, bare soil consumed 0.22 ± 0.03 g CH₄ -C m^-2 (8.1 ± 1.2 g CO₂ -eq m^-2 ) at ambient conditions, while the dry heath consumed 0.10 ± 0.02 g CH₄ -C m^-2 (3.9 ± 0.6 g CO₂ -eq m^-2 ). These uptake rates were subsequently scaled to the entire study area of 0.15 km² , a landscape also consisting of wetlands with a seasonally integrated methane release of 0.10 ± 0.01 g CH₄ -C m^-2 (3.7 ± 1.2 g CO₂ -eq m^-2 ). The result was a net landscape sink of 12.71 kg CH₄ -C (0.48 tonne CO₂ -eq) during the growing season. A nonsignificant trend was noticed in seasonal CH₄ uptake rates with experimental warming, corresponding to a 2% reduction at the bare soil, and 33% increase at the dry heath. This was due to the indirect effect of OTCs on soil moisture, which exerted the main control on CH₄ fluxes. Overall, the net landscape sink of CH₄ tended to increase by 20% with OTCs. Bare and dry tundra ecosystems should be considered in the net CH₄ budget of the Arctic due to their potential role in counterbalancing CH₄ emissions from wetlands - not the least when taking the future climatic scenarios of the Arctic into account.