Methane oxidation in contrasting soil types: responses to experimental warming with implication for landscape-integrated CH4 budget.

Abstract

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 insitu 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±0.03g CH4 -Cm-2 (8.1±1.2g CO2 -eqm-2 ) at ambient conditions, while the dry heath consumed 0.10±0.02g CH4 -Cm-2 (3.9±0.6g CO2 -eqm-2 ). These uptake rates were subsequently scaled to the entire study area of 0.15km2 , a landscape also consisting of wetlands with a seasonally integrated methane release of 0.10±0.01g CH4 -Cm-2 (3.7±1.2g CO2 -eqm-2 ). The result was a net landscape sink of 12.71kg 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.