SWES-MEL/ClimateWire

ARCTIC: Newly discovered microbe appears to be key player with methane emissions Christa Marshall, E&E reporter Published: Friday, October 24, 2014

A tiny organism that can only be seen with a microscope may play a key role in determining how much methane is eventually released from thawing permafrost, according to a new study. The research provides insight into some of the main questions about thawing soil -- how much do microbes within it control greenhouse gas release, and how much is permafrost releasing CO2 versus methane? It appears that it's not only important to know the general branch of microbes producing greenhouse gases in permafrost, but specific species, according to the researchers.

In this case, a single microbe species discovered earlier this year -- Methanoflorens stordalenmirensis -- seems to help predict how much methane versus CO2 is released with thaw, at least at one location. It also seems to help predict the chemical fingerprint of methane, which is important for determining where measured methane in the atmosphere as a whole comes from. If scientists don't consider Methanoflorens, their models of methane release from permafrost in the future may be wrong, according to the study.

"In Methanoflorens, we discovered the microbial equivalent of an elephant, or an organism that plays an enormously important role in what happens to the whole ecosystem," said Scott Saleska, an associate professor at the University of Arizona Department of Ecology and co-author of the paper in Nature.

While there are many methane-producing microbes in thawing Arctic peatlands, Methanoflorens by far had the best prediction ability of the chemical fingerprint of released methane at a study site in Sweden. Its abundance also was a good predictor of eventual CO2 versus methane release at the site in Abisko National Park, north of the Arctic Circle. The study site is ideal, the researchers said, because it contains permafrost with various stages of melt.

"We're saying not all microbes are the same," said Carmody McCalley, lead author of the study and a scientist at the University of New Hampshire who conducted the research during doctoral work at the University of Arizona.

Methane leaves different 'fingerprints'

Methane has different forms, in that some is lighter or heavier depending on the ratio of isotopes, or chemical variations, of carbon in methane molecules.

Soil microbes make methane in one of two ways. Their food supply is either acetate -- which comes from living and decomposing plants -- or CO2 and hydrogen coming from decomposing plants. They breathe out different forms of lighter or heavier methane depending on the food source. Methane from gas production is even heavier.

"You can think of the isotopic signature of the methane as a fingerprint or a tracer. ... It tells us something about where methane came from. Did it come from fossil fuels? Or did it come from microbes that use acetate?" McCalley said.

Previously, there was an assumption that the methane coming from permafrost might only be from acetate microbes. But the researchers found via tests of both permafrost samples and air that is not the case -- instead there is a significance presence of CO2-hydrogen-produced methane, particularly during initial stages of thaw. Methanoflorens is a CO2-hydrogen microbe. With more extensive thaw, the studied permafrost region shifted to more acetate-produced methane, indicating that the methane type was not constant during stages of melt.

That shift is important, McCalley said, because models in the future will overestimate the amount of global methane coming from permafrost and underestimate the amount coming from fossil fuel burning, if scientists are only assuming acetate-fueled methane.

In that case, they'll think the overall amount of methane from permafrost is heavier than it actually is, as CO2-hydrogen methane is even lighter than acetate methane. That in turn will throw off estimates of the amount of methane released from permafrost, which are based partly on assessing the isotope signature.

"They'll think more methane came from permafrost than actually did," McCalley said. Future estimates could be inaccurate by one or two times, according to simulations performed in the study, she said.

'Pioneer organism' unveiled

She compared the analysis to knowing what an overall light-green paint looks like. To know the right amount of blue paint making it up, you have to assume the right amount of yellow paint.

The abundance of Methanoflorens, meanwhile, was a harbinger -- when there was more of it, the methane fingerprint looked like methane that comes from CO2-hydrogen and less like methane coming from acetate, McCalley said.

Saleska explained that there are ongoing measurements of methane providing an overall estimate of the greenhouse gas. Determining where that methane came from -- shale gas fields, rice paddies or the Arctic -- depends on getting the isotope ratios right, he said.

Methanoflorens seems to be a pioneer organism, in that it seems to get other microbes going, Saleska said. This pioneer status may be one reason why it's such a good predictor of the greenhouse gas emissions of permafrost generally, he said. A next step will be to do similar tests at other locations, he added.

Permafrost contains about 50 percent of the global soil carbon, the study notes. But scientists to date have not had a good grasp of exactly which microbes are in the world's thawing permafrost, whether they are releasing methane versus carbon dioxide, and what quantity of greenhouse gases they are spewing into the atmosphere (ClimateWire, Sept. 27, 2013).

Byron Crump, a microbial ecologist at Oregon State University who reviewed the paper, said it was significant, especially for its detail on climate impacts down to the species level.

"The potential for worsening global climate change due to carbon release from permafrost is enough to make any details of the process worth learning about. Every detail might matter," he said.