Fungi and other decomposers generate nearly 10 times more carbon dioxide than humans. And as the planet warms, we might expect concentrations of the greenhouse gas to climb even higher with the increase of fungus activity. But according to a study published in Proceedings of the National Academy of Sciences this week, roly polies and other small soil crustaceans are likely to eat more fungi in response -- limiting the net increase in CO2 production and buffering the impacts of climate change.
By decomposing dead plants and animals, soil microbes release 50 billion to 75 billion metric tons of carbon into the atmosphere every year worldwide. This carbon takes the form of CO2 and methane. Based on current climate forecasts, increasing soil nitrogen levels will stimulate the growth of soil fungi, and more fungal activity means more CO2 production. This has the potential to become a horribly dangerous feedback cycle.
To see how natural ecosystems will be altered, a team led by Yale’s Thomas Crowther conducted a series of experiments at a long-term ecological research site on soil communities that contained fungi such as basidiomycetes as well as isopods (pillbugs and friends). With some manipulation, they established four levels of community complexity: plots with fungi and isopods, fungi but no isopods, isopods but no fungi, and finally, no fungi and no isopods.
"In disturbed environments, where soil animals are not present, the feedback between climate change and microbial carbon production was strong," Crowther says in a news release. "Meanwhile, when the soil community is healthy and diverse, we saw that animals feed on the microorganisms, limiting the feedback effects."
The small crustaceans, they found, play a regulatory role in soil ecosystems by feeding on microbes that trigger increased carbon emissions -- ultimately offsetting the increases in fungal decomposition and CO2 production.
However, this so-called "top-down" control only makes a difference when there are no limitations to nutrient production at the bottom of the food web -- which are exactly the conditions that will occur with atmospheric warming. "As a result of climate change, there's going to be more nitrogen deposition, it's going to be warmer -- many of the things that limit fungal growth are going to be alleviated," Crowther explains. "And by stimulating microbial activity it will trigger higher carbon emissions. So when those 'bottom up' limitations are gone, the grazing animals become even more important."