Understanding Anaerobic Oxidation of Methane in a Climate-Manipulated Northern Peatland
MetadataShow full item record
Although peatlands cover < 3% of the Earth’s surface, they are among the most important terrestrial ecosystems partially because they are responsible for roughly 10% of global methane (CH_4) flux. The consumption of CH_4 (methanotrophy) is an important control on wetland emissions of this greenhouse gas. Anaerobic oxidation of methane (AOM) was thought to be unimportant in peatlands; however, recent studies suggest that this process is ubiquitous in freshwater wetlands, but report a wide range of rates of AOM in peatlands. Due to the lack of understanding of the magnitude and controls over AOM, it is not currently included in Earth system models. The Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE; http://mnspruce.ornl.gov) experiment is assessing how northern peatland ecosystems react to a changing climate with a regression-based, ecosystem-scale climate manipulation that incorporates surface and deep (up to 2 m depth) peat heating from 0 to +9 °C above ambient. Soil cores were collected throughout the 2016 growing season following 13 months of deep peat heating and 14 months of subsequent whole-ecosystem warming (surface and deep heating) at 30, 50, 75, 125, and 200 cm depths from each enclosure at the SPRUCE site. Samples were slurried with a 1:3 mixture of peat and porewater (collected from the same plot and depth) and anaerobically incubated within 1°C of in situ temperatures for approximately three weeks using a radioactive tracer method. AOM was measured by the accumulation of tritiated water over time and CH_4 production rates were determined with gas chromatography. We found that AOM was ubiquitous throughout the entire peat profile, with the highest rates occurring at the surface and then decreasing with depth. Additionally, rates of AOM were the greatest at the beginning of the incubation and decreased over time, indicating that organic or inorganic terminal electron acceptors may be driving this process in peatlands. Finally, there was suggestive evidence that temperature is positively correlated with rates of AOM. Collectively, these results suggest that AOM may be important process in northern peatlands, warranting further study and consideration in Earth system models.