Greenhouse gas release from thawing permafrost is among the biggest uncertainties for the future of our climate. Permafrost, or permanently frozen ground that’s mostly found in the Arctic and sub-Arctic, covers a quarter of the Northern Hemisphere’s land. Many studies project that carbon dioxide (CO₂) will be increasingly released from this warming permafrost. But a recent study, led by Drs. Sylvain Monteux and Ellen Dorrepaal at Umeå University and published in late November in Nature Geosciences, points to a previously ignored possibility: an increasingly diverse bacterial community in the soil as it warms. Without considering this, projections may be significantly underestimating CO₂ release from the warming Arctic.

All dirt has bacteria, which breaks down decayed organic matter and spews out greenhouse gases in the process. Bacterial communities in most soil are diverse and abundant, but permafrost is normally too cold to support that kind of prosperity. For decades, scientists have figured this. They warmed Arctic soil samples in lab and saw that the amount of bacteria increases, with a corresponding increase in greenhouse gas release. But this misses something: new bacteria could be introduced to soil from migrating animals; as the soil gets warmer and thus more comfortable for those foreign bacteria, they might stick around instead of dying from the cold.

Monteux and Dorrepaal considered that a more diverse bacterial community could be even better at digesting dead matter. Some bacteria can’t break down certain things, while others can. By having a larger variety of bacteria in soil, more things can get consumed–with correspondingly more greenhouse gas production. Studies that don’t account for this could therefore be underestimating CO₂ release from warming permafrost. To test their hypothesis, the researchers collected soil samples from Northern Alaska, the only part of the USA with permafrost. Before warming them up as usual, they took half the samples and added just a bit of soil from more temperate environments. They then incubated their samples for five months. After all that warming, they found that the amount of bacteria had increased in all of the samples, as expected. But for samples with temperate soil added, both the bacteria from the Alaskan soil and the community from temperate soil thrived. In these samples, CO₂ production was 40% higher than in the samples that were merely warmed up.

The authors bring to light a way that we might be underestimating the future climate impact of the warming Arctic. These warming Arctic regions are also getting greener, so it is possible that burgeoning plants may take up enough carbon dioxide as they grow to offset greenhouse gases produced by the bacteria. Still, this latest finding further raises the concern that the future planet may be warmer than scientists expect.

Sylvain Monteux is a poctdoctoral researcher at Umeå University. Ellen Dorrepaal is an associate professor of ecology and environmental science at Umeå University.

Managing Correspondent: Jordan Wilkerson

Original Science Article: Carbon and nitrogen cycling in Yedoma permafrost controlled by microbial functional limitations

Image Credit: flickr, National Park Service