A Combination of Sunlight and Microbes Convert Arctic Carbon into Carbon Dioxide

Almost half of the organic carbon stored in soil globally is contained in Arctic permafrost, which has undergone rapid melting, and that organic material could be changed to greenhouse gases that would worsen global warming.

There is little shade in the Arctic, so when the permafrost melts, carbon is released into streams and lakes where a combination of sunlight and microbes converts it to carbon dioxide. (CREDIT - Rose Cory, University of Michigan)

When permafrost melts, microbial consumption of those carbon reserves creates carbon dioxide (CO2) much of which ultimately ends up in the atmosphere, but experts have been uncertain of just how the system functions.

A new research published recently in Nature Communications provides a framework of the mechanisms and highlights the significance of both sunlight and the correct microbial community as solutions to converting permafrost carbon to CO2. The research received support from the U.S. National Science Foundation and the Department of Energy.

We’ve long known that microbes convert the carbon into CO2, but previous attempts to replicate the Arctic system in laboratory settings have failed. As it turns out, that is because the laboratory experiments did not include a very important element – sunlight.

Byron Crump, Biogeochemist and Co-author on the study, Oregon State University

Crump added, “When the permafrost melts and stored carbon is released into streams and lakes in the Arctic, it gets exposed to sunlight, which enhances decay by some microbial communities, and destroys the activity for other communities. Different microbes react differently, but there are hundreds, even thousands of different microbes out there and it turns out that the microbes in soils are well-equipped to eat sunlight-exposed permafrost carbon.”

The Researchers from Oregon State and the University of Michigan were able to identify compounds that the microbes favor using high-resolution chemistry and genetic methods. They discovered that sunlight makes permafrost soils tastier for microbes as it converts it to the same kinds of carbon they already enjoy eating – the carbon they are adapted to metabolize.

The carbon we’re talking about moves from the soil into rivers and lakes, where it is completely exposed to sunlight. There are no trees and no shade, and in the summer, there are 24 hours a day of sunlight. That makes sunlight potentially more important in converting carbon into CO2 in the Arctic than in a tropical forest, for example.

Byron Crump, Biogeochemist and Co-author on the study, Oregon State University

As the climate carries on becoming warmer, there are interesting consequences for the Arctic, said Crump, who is a faculty member in OSU’s College of Earth, Ocean and Atmospheric Sciences.

The long-term forecast for the Arctic tundra ecosystem is for the warming to lead to shrubs and bigger plants replacing the tundra, which will provide shade from the sunlight. That is considered a negative feedback. But there also is a positive feedback, in that seasons are projected to expand. Spring will arrive earlier, and fall will be later, and more water and carbon will enter lakes and streams with more rapid degradation of carbon.

Byron Crump, Biogeochemist and Co-author on the study, Oregon State University

Crump added, “Which feedback will be stronger? No one can say for sure.”

The stakes are high, Crump said. Compared to the atmosphere, more carbon is stored in the frozen permafrost. It has collected over millions of years by plants growing and dying, with a very sluggish decaying process due to the freezing weather.

“Some of the organic matter is less tasty to microbes than others,” Crump said, “but bacterial communities are diverse, so there will be something out there that wants that energy and will use it.”

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