Getting to the Root of Plant-Mediated Methane Emissions and Oxidation in a Thermokarst Bog

The Science

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. Working in a wetland that formed due to permafrost thaw, scientists used multiple methods to identify how wetland plants influence the amount of methane: generated by soil microbes (called production), converted by soil microbes into carbon dioxide (called oxidation), and transported from soil to the atmosphere (called emission). Plants appeared to increase methane production and to surprisingly decrease methane oxidation. Scientists created a theory for why plants increased methane emissions.

The Impact

To understand future climate change, scientists need to predict the amount of methane released from wetlands. This work has advanced understanding of plant‐soil interactions that contribute to wetland methane emissions within thawing permafrost landscapes. This understanding will help scientist model and predict wetland methane emissions.

Summary

In a permafrost‐thaw bog in Interior Alaska, scientists sought to disentangle mechanisms by which vascular vegetation affect methane emissions. Vegetation operated on top of baseline methane emissions, which varied with proximity to the thawing permafrost margin. Emissions from vegetated plots increased over the season, resulting in cumulative seasonal methane emissions that were ~4.5 g m−2 season−1 greater than unvegetated plots. Mass balance calculations signify these greater emissions were due to increased methane production and decreased methane oxidation. Minimal oxidation occurred along the plant‐transport pathway, and oxidation was suppressed outside the plant pathway. Suppression of methane oxidation was stimulated by root exudates fueling competition among microbes for electron acceptors. This contention is supported by the fact that methane oxidation and relative abundance of methanotrophs decreased over the season in the presence of vegetation, but methane oxidation remained steady in unvegetated treatments. Oxygen was not detected around plant roots but was detected around silicone tubes mimicking aerenchyma, and oxygen injection experiments suggested that oxygen consumption was faster in the presence of vascular vegetation. Root exudates are known to fuel methane production, and this work provides evidence they also decrease methane oxidation.

Principal Investigator

Rebecca Neumann
University of Washington, Seattle
[email protected]

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

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 (Award Number DE‐SC‐ 0010338 to R.B.N.), and the U.S. Geological Service (USGS) Land Change Science Program. Logistic support was provided by the Bonanza Creek Long-Term Ecological Research (LTER) Program, which is jointly funded by the National Science Foundation (DEB 1026415) and the U.S. Department of Agriculture’s (USDA) Forest Service, Pacific Northwest Research Station (PNW01‐ JV112619320‐16). Microbial data came from DOE’s Joint Genome Institute (JGI Proposal 1445).

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