Controls on soil carbon loss with permafrost thaw in Alaskan peatland ecosystems

High latitudes are experiencing effects of climate change such as soil warming, thawing permafrost, altered hydrology, and longer growing seasons due to warmer temperatures. An estimated 50% of the global below-ground soil organic carbon pool (SOC) is stored in high latitudes and a significant amount is found in peatlands. Using an experimental approach, we quantified release of methane (CH4) and carbon dioxide (CO2) from soil cores from northern permafrost peatlands and explored mechanisms responsible for SOC mineralization in response to temperature and soil moisture. We conducted experiments using replicate cores from two boreal and two tundra peatland sites with intact permafrost to represent Alaskan peatlands. Cores were exposed to a range of temperature and moisture to represent typical field conditions, and we measured production of CO2 and CH4. We also characterized total microbial biomass, dissolved organic carbon, and peat chemistry. In these incubations, CO2 production over 30-days ranged from 1.20 to 394.5 umol CO2 g-1 and CH4 production over 30-days ranged from -0.134 umol CH4 g-1 (net uptake) to 2.167 umol CH4 g-1. All soil types demonstrated similar rates of potential C production at lower temperatures. However, at high temperatures, arctic active layer soils showed higher rates of potential CH4 production and boreal active layer soils showed higher rates of potential CO2 production. Differences in potential C fluxes between ecosystems (boreal vs. arctic peatlands) and depths (active layer vs. permafrost) at higher temperatures are likely due to inherent differences in peat properties, microbial biomass, and redox status. Therefore, the response of soil C mineralization to climate change will vary by ecosystem type and depend on the magnitude of temperature increase.