Aerobic Wetlands Emit High Levels of Methane

The Science

A paradigm—microbial methane production can only occur in habitats devoid of oxygen—has been widely incorporated into soil biogeochemical models. However a recent study revealed clear geochemical and biological evidence for methane production in well-oxygenated soils of a freshwater wetland.

The Impact

This study provides the first genomic level evidence for existence of a novel methanogenic microbial species that is not only globally distributed, but a major contributor to methane emissions from freshwater wetlands. By challenging a widely held assumption about methane production, the findings could have significant implications for global methane estimates and earth system modeling.

Summary

Currently, biogeochemical models and biological studies typically discount microbial methane production in oxygen-rich surface soils. Scientists have traditionally assumed microbial enzymes involved in methane production are inactivated by oxygen, and methane-producing microbes do not compete well with other microorganisms in oxygenated environments. Challenging these assumptions, a team of researchers from The Ohio State University, University of Colorado Denver, Pacific Northwest National Laboratory and Lawrence Berkeley National Laboratory recently provided the first ecosystem-scale demonstration of methane production in oxygen-rich soils. The researchers assessed biological methane production and emissions across multiple spatial and temporal gradients in freshwater wetland soils at the shore of Lake Erie. Surprisingly, there was approximately 10 times more  methane production in oxygenated soils than in oxygen-depleted soils. In this particular wetland, it was estimated that up to 80 percent of the methane originated from oxygenated soil layers. Metabolomic responses were characterized using complementary capabilities at EMSL, the Environmental Molecular Sciences Laboratory, and JGI, the Joint Genome Institute, both DOE Office of Science user facilities. Combining the 800 MHz NMR Denali (liquids) and 600 MHz NMR Hood (metabolomics) spectrometers at EMSL and metagenomic and metatranscriptomic sequencing at JGI, the researchers provided the first holistic insight into methane-producing microbes active in oxygen-rich environments, recovering the first near complete genomes for a new species of methanogenic Archaea, Candidatus Methanothrix paradoxum. By mining public databases, the researchers discovered this organism is prevalent in diverse habitats spanning the globe. Taken together, the findings demonstrate the significant extent of methane production in oxygen-rich soils. If used to refine earth system models, the findings could lead to more accurate predictions of net wetland methane emissions and their effects on global biogeochemical processes.

Funding
This work was supported by the U.S. Department of Energy’s Office of Science (Office of Biological and Environmental Research), including support of the Environmental Molecular Sciences Laboratory (EMSL) and the Joint Genome Institute (JGI), both DOE Office of Science user facilities. Additional support came from the Office of Biological and Environmental Research’s Early Career Program and Office of Science’s Ameriflux Management Project.

Principal Investigator(s)

Kelly Wrighton
The Ohio State University
[email protected]

Funding

This work was supported by the U.S. Department of Energy’s Office of Science (Office of Biological and Environmental Research), including support of the Environmental Molecular Sciences Laboratory (EMSL) and the Joint Genome Institute (JGI), both DOE Office of Science user facilities. Additional support came from the Office of Biological and Environmental Research’s Early Career Program and Office of Science’s Ameriflux Management Project.

References

Angle, J.C., T.H. Morin, L.M. Solden, A.B. Narrowe, G.J. Smith, M.A. Borton, C. Rey-Sanchez, R.A. Daly, G. Mirfenderesgi, D.W. Hoyt, W.J. Riley, C.S. Miller, G. Bohrer, and K.C. Wrighton. “Methanogenesis in oxygenated soils is a substantial fraction of wetland methane emissions.” Nature Communications, 8 (1): Article no. 1567 (2017). [DOI: 10.1038/s41467-017-01753-4]