Scientists working at the ongoing Department of Energy's (DOE) Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment use the site's northern Minnesota bog as a laboratory. SPRUCE allowed scientists to warm the air and soil by zero to 9 degrees C above ambient temperatures to depths more than 2 m below ground.
This warming simulates the effects of climate change on the carbon cycle at the whole ecosystem scale over the long term. The research found that the production of the potent greenhouse gas methane increased at a faster rate than carbon dioxide in response to warming. The results indicate that carbon dioxide release and methane production are stimulated by plants' release of metabolites, chemicals that plants create for protection and other functions.
Soil carbon has accumulated over millennia in peatlands. These results demonstrate that peatlands' vast, deep carbon stores are vulnerable to microbial decomposition in response to warming. This research suggests that as climate change causes peatland vegetation to have a greater proportion of vascular plants relative to mosses, peatlands will produce more methane and amplify their contribution to climate change.
Northern peatlands store approximately one-third of Earth's terrestrial soil organic carbon due to their cold, water-saturated, acidic conditions, which slow decomposition. To study these soils, researchers leveraged the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment, where they combined air and peat warming in a whole ecosystem warming treatment. The team included Georgia Institute of Technology, Florida State University, the University of Arizona, Pacific Northwest National Laboratory, Oak Ridge National Laboratory, Chapman University, the University of Oregon, and the U.S. Department of Agriculture Forest Service.
The scientists hypothesized that warming would enhance the production of plant-derived metabolites, resulting in increased labile organic matter inputs to the surface peat, thereby enhancing microbial activity and greenhouse gas production. In support of this hypothesis, the researchers observed significant correlations between metabolites and temperature consistent with increased availability of labile substrates, which may stimulate more rapid turnover of microbial proteins.
An increase in the abundance of methanogenic genes in response to the increase in the abundance of labile substrates was accompanied by a shift towards acetoclastic- and methylotrophic methanogenesis. The results suggest that peatland vegetation trends towards increasing vascular plant cover with warming will be accompanied by a concomitant shift towards increasingly methanogenic conditions and amplified climate-peatland feedbacks.
This material is based upon work supported by the DOE Office of Science, Office of Biological and Environmental Research program. A portion of this research was performed using the Environmental Molecular Sciences Laboratory, a DOE Office of Science User Facility at the Pacific Northwest National Laboratory. Metagenome sequence data were produced by the DOE Joint Genome Institute in collaboration with the user community.