Methane oxidation in contrasting soil types: responses to experimental warming with implication for landscape-integrated CH 4 budget.

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.