The Science

Microbial activity in wetland soil is responsible for the emission of more methane to the atmosphere than all other natural sources combined. This flux is influenced by many factors, but in all cases, the generation of methane (methanogenesis) and any oxidation of CH4 (methanotrophy), which may attenuate emissions, are microbially mediated. Methane is a greenhouse gas with a greater ability to warm the earth than carbon dioxide. Wetlands are the largest natural source of methane to the atmosphere. Microbes in wetland soils are responsible for the generation of methane and the conversion of methane into carbon dioxide (a process called oxidation). Methane oxidation can be carried out by microbes that have different life requirements. This research investigated how a common wetland sedge (Carex aquatilis) affects microbes in wetland soil. It found that plants created a soil environment that favored methane-oxidizing microbes with specific life requirements met by resources released from plant roots. Without plants, microbes had more flexible life requirements.

The Impact

To understand future climate change, scientists need to predict the amount of methane released from wetlands. This work has advanced understanding of how plants affect the microbial communities generating and oxidizing methane within wetlands. This understanding will help scientist model and predict wetland methane emissions.

Summary

Microbial activity in wetland soil is responsible for the emission of more methane to the atmosphere than all other natural sources combined. This microbial activity is heavily impacted by plant roots, which influence the microbial community by exuding organic compounds and by leaking oxygen into an otherwise anoxic environment. This study compared the microbial communities of planted and unplanted wetland soil from an Alaskan bog to elucidate how plant growth influences populations and metabolisms of methanogens and methanotrophs. A common boreal wetland sedge, Carex aquatilis, was grown in the laboratory and DNA samples were sequenced from the rhizosphere, unplanted bulk soil, and a simulated rhizosphere with oxygen input but no organic carbon. The abundance of both methanogens and methanotrophs were positively correlated with methane emissions. Among the methanotrophs, both aerobic and anaerobic methane oxidizing microbes were more common in the rhizosphere of mature plants than in unplanted soil, while facultative methanotrophs capable of utilizing either methane or other molecules became relatively less common. These trends indicate that the roots in this experiment created an environment which favored highly specialized microbial metabolisms over generalist approaches. One aspect of this specialized microbiome is the presence of both aerobic and anaerobic metabolisms, which indicates that oxygen is present but is a limiting resource controlling competition.

Principal Investigator

Rebecca Neumann
University of Washington, Seattle
rbneum@uw.edu

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This material is based upon work supported by the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy’s (DOE) Office of Science (under Award Number DE‐SC‐ 0010338). A portion of this research was performed under the Facilities Integrating Collaborations for User Science (FICUS) program and used resources at the Environmental Molecular Sciences Laboratory (EMSL) and the DOE Joint Genome Institute (JGI), which are DOE Office of Science User Facilities sponsored by BER and operated under Contract Nos. DE-AC02-05CH11231 (JGI) and DE-AC05-76RL01830 (EMSL). This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education (ORISE) for DOE. ORISE is managed by ORAU under contract number DE-SC0014664. Students were additionally supported by the following fellowships and grants: University of Washington (UW) College of Engineering Dean’s Fellowship/Ford Motor Company Fellowship, UW Civil and Environmental Engineering Valle Scholarship, UW Mary Gates Scholarship, and the Carleton College Kolenkow Reitz Fellowship.

References