Northern peatlands store a significant amount of terrestrial carbon (C) but also function as the largest natural source of atmospheric methane (CH4). C losses in peatlands is projected to increase through future climate changes that potentially impact the balance of CO2 and CH4 sequestration and release. In particular, warming may accelerate the temperature-sensitive processes such as microbial decomposition and methanogenesis that increase the release of CO2 and CH4 from peat C. Enhanced plant productivity due to warming and elevated CO2 may increase peat aerobicity and substrate availability that alter the nature of trace gas production and emission. In order to determine the influences of warming, elevated CO2 and physical (i.e., micro-topography) factors on CH4 and CO2 emission, we performed an automated C-flux measurement at the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment. The experiment is located in a boreal Sphagnum moss - black spruce peat bog in northern Minnesota. The design combines whole ecosystem warming treatments at five different temperature differentials (0, +2.25, +4.5, +6.75, +9) in ten 12-m diameter open-top chambers, with half of the chambers exposed to elevated CO2 since August 2016.
Results/Conclusions
We analyzed CO2 and CH4 flux data and their δ13C composition from each experimental plot. Results show that both CH4 and CO2 flux increase with experimental warming from 0oC to +6.75oC above ambient temperature, but both decline at 9oC warming treatment. Elevated CO2 stimulates CO2 and CH4 emission at lower warming temperatures (0 oC to 4.5 oC), but not at higher warming temperatures (6.75oC and 9 oC). The δ 13C-CH4 increases with warming temperature, indicating an increasing contribution of acetoclastic methanogenesis to total CH4 production with warming. CH4 contribute to ~2% of seasonal C emission at SPRUCE. However, when adjusted for CO2 equivalents on a 100-year time scale, CH4 contribution ranged between 26% to 56% of total seasonal C emissions, with the highest proportion observed at 9 oC warming treatment. Our results demonstrate that warming increases CO2 and CH4 emissions from peatlands, supporting the prevailing view that warming of northern peatlands is potentially to enhance and amplify the terrestrial feedback on temperature change. We highlight the importance of continued measurements at SPRUCE experiment for ensuring the observed responses are sustained and not transient responses to novel conditions.