As global temperatures increase, the carbon stored in permafrost is at risk of being broken down by microbes. The enzyme latch theory suggests that polyphenols—antioxidants that neutralize harmful free radicals—should build up in saturated, waterlogged peatlands because the activity of an enzyme called phenol oxidase is reduced under these conditions. The accumulation of polyphenols would then inhibit microbial activity and help stabilize carbon in the soil.

However, research conducted in Stordalen Mire, an Arctic peatland in Sweden, found that while the phenol oxidase enzyme's activity decreased with increased water saturation, other predictions of the enzyme latch theory were not supported, and the expected accumulation of polyphenols and the resulting inhibition of microbes did not occur as predicted.

The research was published in Nature Microbiology.

Researchers used CAMPER, a tool designed to identify and categorize genes, to find a variety of enzymes in microbes that can break down polyphenols. These enzymes were found in different types of microbes and under various environmental conditions, challenging the idea that polyphenols stabilize carbon in saturated soils. This study highlights the importance of considering both oxic (oxygen-rich) and anoxic (oxygen-poor) environments when studying how polyphenols affect carbon cycling in ecosystems undergoing climate change.

Permafrost contains about 50% of global soil carbon. Thawing permafrost risks releasing this carbon, which microbes can decompose into carbon dioxide (CO₂) or methane (CH₄), further accelerating climate change. This study found no significant negative relationship between phenol oxidase activity and polyphenol concentrations or between polyphenols and microbial enzyme activity. Instead, polyphenol abundance was positively correlated with CO₂ concentrations, indicating that polyphenol metabolism may contribute to soil respiration.

The study found habitat—and depth-specific patterns in polyphenol metabolism, contradicting the enzyme latch theory and challenging the conventional belief that polyphenols only suppress microbial communities. It suggests that microbial communities adapt their polyphenol degradation strategies to their environment.

Microbial communities in Stordalen Mire expressed genes for polyphenol degradation across various environmental conditions, indicating that polyphenol transformations are integrated into carbon cycling networks, enhancing microbial metabolism and playing a role in producing carbon dioxide and carbon monoxide.

This research redefines the role of polyphenols in peatland carbon cycling, highlighting the diverse microbial metabolic strategies that degrade polyphenols and the need to consider these processes in understanding and predicting ecosystem biogeochemistry.

The study was led by Bridget B. McGivern, affiliated with the Department of Soil and Crop Science at Colorado State University, and Dylan R. Cronin, a Ph.D. Candidate from the Department of Microbiology at The Ohio State University. Other Ohio State co-authors included the Byrd Center Principal Investigators and microbiology Professors Matthew Sullivan, director of the Center of Microbiome Science, and Virginia Rich, lead PI and co-director of the EMERGE Biology Integration Institute. 

This research was a collaboration highlighting the interdisciplinary and cross-institutional nature of the study. In addition to Ohio State, it involved contributions from Colorado State University, Miami University, the University of Arizona, the University of New Hampshire, Florida State University, Emory University, and Queensland University of Technology.

Read more about this research by visiting "Microbial polyphenol metabolism is part of the thawing permafrost carbon cycle."