Whole Ecosystem Warming Stimulates Methane Production from Plant Metabolites in Peatlands

The Science  

Northern freshwater wetlands, called peatlands, have cold, water-saturated, acidic conditions that slow microbial decomposition of plant matter into greenhouse gases, among other compounds. The Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment in northern Minnesota allows scientists to warm air and soil deep in a bog. This simulates the effects of climate change on the carbon cycle at the whole ecosystem scale over long time frames. After almost two years of warming, a multi-institutional team of scientists observed enhanced degradation of plant matter in soil and increased greenhouse gas production at the site. Methane production increased at a faster rate than carbon dioxide. The results further indicated that biomass degradation released plant-derived molecules that stimulated methane production. 

The Impact 

Soil carbon has accumulated over millennia in peatlands. Today, northern peatlands store approximately one-third of Earth’s terrestrial soil organic carbon. These results demonstrate that the vast, deep carbon stores in peatlands are vulnerable to microbial decomposition that fuels methane production in response to warming. Changes in vegetation type to more vascular plants, recently observed at the SPRUCE site, could result in higher inputs of degradable plant metabolites that are substrates for microbial methane production. 

Summary 

A multi-institutional team collected samples of soil and porewater from sites at the SPRUCE experiment that had been warmed to 2 meters deep. Then they analyzed the molecules in the samples using capabilities at EMSL, the Environmental Molecular Sciences Laboratory. The team used nuclear magnetic resonance spectrometry and several complementary forms of mass spectrometry for the analyses.  

In samples from the peat surface, they observed an increase in plant-derived molecules that microbes could easily degrade. This increase correlated significantly with warmer temperatures, as well as observed methane production. Genomic analyses of microbial community composition were performed at the DOE Joint Genome Institute and revealed the biochemical pathways by which soil microbes produce methane. 

Recent results from the SPRUCE site correlate warmer temperatures with declining moss cover and an increase in vascular plants such as shrubs or trees. Unlike mosses, vascular plants contain roots that release reactive carbon substrates such as sugars to the surrounding soil. Simple sugars were among the plant metabolites observed in this latest study with warming. These results suggest that as peatland vegetation trends toward increasing vascular plant cover with warming, peatlands could increasingly produce methane. This could increase greenhouse gas production and potential climate impacts from these ecosystems. 

Contact 

Joel E. Kostka, Georgia Institute of Technology 
joel.kostka@biology.gatech.edu  

Funding 

The U. S. Department of Energy, Office of Science, Biological and Environmental Research, Terrestrial Ecosystem Science program funded this research. A portion of the research used resources at the Environmental Molecular Sciences Laboratory and at the DOE Joint Genome Institute, which are Office of Science User Facilities. 

Publication 

R.M. Wilson*, M.M. Tfaily*, et al., “Soil metabolome response to whole ecosystem warming at the Spruce and Peatland Responses Under Changing Environments experiment.” Proceedings of the National Academy of Sciences 118, e2004192119 (2021). [DOI: 10.1073/pnas.2004192118]