Interior of an experimental chamber in a peatland in Minnesota. To better understand this carbon sink in danger, scientists are turning to tiny organisms that have long been overlooked. Image credit: Oak Ridge National Laboratory

Climate Change Alters the Hidden Microbial Food Web in Peatlands

Here's why that matters.

Not only are protists abundant -- collectively, they weigh twice as much as all the animals on the planet -- they also play a role in the overall movement of carbon between peatlands and the atmosphere.

The protist Paramecium bursaria is one of many moss-dwelling microbes common in peatlands. Credit: Daniel Wieczynski

That’s because as protists go about the business of life -- eating, reproducing -- they suck in and churn out carbon too.

Some protists draw in CO2 from the air to fuel their growth. Other protists are predators, gobbling up nitrogen-fixing bacteria the peatland mosses rely on to stay healthy.

In a bog in northern Minnesota, researchers led by Oak Ridge National Laboratory have built 10 open-topped enclosures, each 40 feet across, designed to mimic various global warming scenarios.

The enclosures are controlled at different temperatures, ranging from no warming all the way up to 9 degrees Celsius warmer than the surrounding peatland.

Half of the enclosures were grown in normal air. The other half were exposed to CO2 levels more than two times higher than today’s, which we could reach by the end of the century if the burning of fossil fuels is left unchecked.

Five years after the simulation experiment began, the Duke team was already seeing some surprising changes.

“The protists started behaving in ways that we didn't expect,” Kilner said.

At current CO2 levels, most of the more than 200,000 protists they measured became more abundant with warming. But under elevated CO2 that trend reversed.

What’s more, the combined effects of warming and elevated CO2 led to a reshuffling in the protists’ feeding habits and other traits known to influence how much CO2 they give off during respiration -- in other words, how much they contribute to climate change themselves.

Exactly what such changes could mean for peatlands’ future ability to mitigate climate change is unclear, but they’re likely to be important.

Overall, the results show that a neglected part of the peatlands’ microbial food web is sensitive to climate change too, and in ways that “are currently not accounted for in models that predict future warming,” Gibert said.

This research was supported by the U.S. Department of Energy (DE-SC0020362). Other authors include Alyssa Carrell, Dale Pelletier and David Weston of Oak Ridge National Laboratory; and Daniel Wieczynski, Samantha Votzke, Katrina DeWitt, Andrea Yammine, and Jonathan Shaw of Duke.

CITATION: "Temperature and CO2 Interactively Drive Shifts in the Compositional and Functional Structure of Peatland Protist Communities," Kilner et al. Global Change Biology, March 3, 2024. DOI: