24 June 2024

Permafrost microbes may further accelerate climate change

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Permafrost microorganisms, explains a study by Colorado State University, are also able to break down polyphenols. A finding that could force an upward correction of CO2 emission previous estimates

by Matteo Cavallito

 

The thawing of permafrost, the perennially frozen portion of soil in cold regions, is known to be a threat to climate change. Estimates of the scale of the phenomenon take into account the ability of microbes to process organic carbon once awakened from hibernation. These predictions, however, may have to be revised. This is supported by a study from Colorado State University.

It’s all about polyphenols

“Currently, these models assume that this community of microorganisms – known as a microbiome – will break down some types of carbon but not others,” explains a statement released by the Colorado State University. The investigation, published in the journal Nature Microbiology, however, reveals how these microbes, once activated, “will go after a class of compounds previously thought to be untouchable under certain conditions: polyphenols.”

And the problem, the scholars add, is that “more carbon being broken down by microbial respiration will produce additional greenhouse gas emissions”.

A previously formulated theory known as ‘enzymatic latch’, the study says, hypothesised, in contrast, that polyphenols should accumulate in saturated peatlands due to diminished phenol oxidase (the enzyme that catalyses the aerobic oxidation of phenols, ed.) activity, inhibiting resident microbes and promoting carbon stabilization.” In the past, recalls Kelly Wrighton, professor and co-author of the research, “Not only did we think these microbes didn’t eat polyphenols, we thought that if the polyphenols were there it was like they were toxic and would lock the microbes into inactivity.” This claim, however, no longer appears convincing.

The investigation in Sweden

Together with her colleague at Colorado State, Bridget B. McGivern, Wrighton had already started formulating a different theory a few years ago. They thoght that permafrost microbes were actually able to break down polyphenols like the microbes living in the human digestive tract. This theory has been demonstrated in laboratory in 2021. In their latest study, however, researchers were able to verify this assumption in the field.

After creating a database with the results of gene sequencing obtained in the laboratory, the authors were able to compare these with information collected on samples from a research site: the Stordalen Mire peat bog in northern Sweden. “What we found was that genes across 58 different polyphenol pathways were expressed,” McGivern explained. “So, we’re saying not only can the microorganisms potentially do it, but they actually are, in the field, expressing the genes for this metabolism.”

All eyes on permafrost

The focus of international researchers on permafrost is particularly pronounced. As of today, says an estimate quoted by the University of Arizona, this peculiar type of soil contains, on a global scale, “a whopping 1,500 trillion grams of carbon (1,5 bn tonnes, ed.).” Or “twice as much as what’s stored in the atmosphere.”

According to research carried out last year by scientists at the same US university, forecast models suggest that under current global warming conditions, thawing would affect 20 per cent of the surface of Arctic permafrost and 60 per cent of that of Alpine permafrost in the future (but the time horizon is not defined).

In a study published last year, a team of scientists led by Donglin Guo, a researcher at the Chinese Academy of Sciences and Nanjing University, compared the current climate scenario with that of millions of years ago. They hypothesised that most of the surface permafrost could be gone by 2100.