DURHAM, N.C. – Slow-growing microbes found in low-latitude peatlands break down organic matter 30 times slower than their fast-growing cousins in peatlands up north, a new Duke University-led study shows.

This gives southern peatlands, whose chief vegetative cover is woody shrubs, a major leg up over northern Sphagnum-based peatlands in reducing the loss of their stored carbon during prolonged periods of heat and drought, conditions which are increasing common under climate change.

“Our study confirms that these wooded peatlands in tropical and subtropical areas are some of Earth’s most effective and important carbon sinks,” said Hongjun Wang, senior research scientist at the Duke University Wetland Center. “Their ability to retain carbon is three to five times higher than in boreal peatlands.”

Peatlands are wetlands that cover only 3 percent of Earth's land but store one-third of the planet's total soil carbon. Left undisturbed, they can lock away carbon in their organic soil for millennia due to natural antimicrobial compounds called phenolics and aromatics that prevent the waterlogged peat beneath their surface from decomposing.

Scientists have long known that wooded southern peatlands are less susceptible to carbon loss during times of drought or heat than Sphagnum-based boreal peatlands but haven’t known why. While low water levels and increased temperature accelerate decomposition, these factors alone do not explain why southern shrub dominated peatlands continue to store carbon.

“Our study answers that question by showing that shrubby southern peatlands are dominated by ancient slow-growing fungi only rarely found at higher latitudes,” said Curtis J. Richardson, director of the Duke Wetland Center.

The researchers analyzed the composition and ecological traits of microbial communities collected at peatland research sites in Minnesota and North Carolina, augmented by data from more than 200 other peatlands located between 2oS and 75oN latitudes, or roughly from just south of the Equator to the northern edge of Russia.

Their analysis showed that a class of slow-growing fungi called Archaeorhizomyces comprised up to 97% of the fungal communities in shrub-dominated peatlands but only 0.4% of the total community on average at Sphagnum-dominated sites, which were more likely to be dominated by faster-growing Pseudeurotium, Saccharomycetales, and Mortierella fungi.

This difference, combined with the fact that stems, bark and other woody litter from shrubs contain slow-decaying lignins, “essentially helps puts the brakes on the decomposition of carbon-rich organic matter locked away beneath the surface of shrub-dominated peatlands,” said Richardson, who is also the John O. Blackburn Distinguished University Professor of Resource Ecology at Duke’s Nicholas School of the Environment.

“This is one of the reasons why these peatlands, which cover hundreds of thousands of acres across the U.S. Southeast alone, should be protected or set aside for use as carbon farms,” Richardson said. “They are part of nature’s solution to store carbon for thousands of years, which reduces greenhouse gases entering the atmosphere.”

Wang, Richardson and their colleagues published their peer-reviewed findings March 26 in Communications Earth & Environment, a new Nature research journal.

Next up, Wang said, is to see if the slow-growing microbes can be engineered to protect higher-latitude Sphagnum-based peatlands in the face of climate change, and help regenerate healthier soil in worn-out farmland, as well.

Exploring why the north-south microbial divide occurs also requires further study, Wang said. Is it because only slow-growing fungi can survive in the shrub-dominated low-latitude peatlands or because faster-growing species have been driven out?

Wang and Richardson conducted the study with Jianqing Tian of the Duke Wetland Center and the Institute of Microbiology in Chinese Academy of Sciences (CAS); Huai Chen of the CAS Chengdu Institute of Biology; Zhao-Jun Bu of Northeast Normal University; Xingzhong Liu of the CAS Institute of Microbiology; and Mengchi Ho and Rytas Vilgalas, both of Duke.

Primary funding came from the U.S. Department of Energy Office of Science and the Duke University Wetland Center Endowment.

CITATION: “Vegetation and Microbes Interact to Preserve Carbon in Many Wooded Peatlands,” Hongjun Wang, Jianqing Tian, Huai Chen, Mengchi Ho, Rytas Vilgalys, Zhao-Jun Bu, Xingzhong Liu and Curtis J. Richardson; Communications Earth & Environment, March 26, 2021. DOI: https://doi.org/10.1038/s43247-021-00136-4