By Eva Schwarz, Graduate Fellow
August 26, 2025
For our summer 2025 field crew, an essential part of packing for early mornings in the field was remembering to load a large red cooler in the trunk of the car. Anyone looking inside it for popsicles would be disappointed; the cooler was not for refreshing drinks or tasty midday field snacks, but rather several dozen bags of soil.
When we think about climate change, we often think about carbon dioxide in the atmosphere, or the plants that take carbon dioxide out of the atmosphere and use it to grow. But there is another important pool of carbon larger than the amount stored in the air and in living things combined: the soil! To understand carbon on earth, we need to understand carbon in soils, and one major determinant of soil carbon is fungi. Fungi can release carbon into the atmosphere as they decompose dead things. They can also store carbon in the soil through symbiotic partnerships with plants.
So, when are fungi contributing to climate change, and when are they helping us combat it? An ongoing experiment at Cedar Creek Ecosystem Science Reserve called Forests and Biodiversity 2, or FAB2, helps us explore this question. FAB2 is a patchwork of small, square forests made up of different combinations of tree species, which allows us to study how forests change fungal communities and how those fungal communities in turn impact how carbon is stored in the soil. Crawling along the dense layer of duff under the varied canopies of these tiny forests, there are lots of signs of fungal life. Mushrooms pop up all over the experiment, and in many plots the dead leaves and pine needles on the ground are covered in a thin, creeping veil of white mycelia (the filamentous, non-reproductive tissue that makes up the body of many fungi).
However, much like with climate change itself, there is only so much we can learn from what we can see with the naked eye. Fungi are known for the fruiting bodies, or mushrooms, that many of them produce, but much of their lifecycle and most of their biomass is microscopic or hidden underground. Many species of fungi never even produce mushrooms. So, when we want to study soil fungal communities like the ones in FAB2, we have to start with the soil itself. We use DNA sequencing to find out which fungi are in our soil, we use chloroform (following strict safety protocols!) to separate fungi from the soil and measure their biomass, and we combust soils at high heat to quantify how much carbon they hold. This is all to better understand what soil fungi are doing with carbon: how much are they storing and how much are they releasing? Knowing how these metrics change as forest composition changes could help us manage forests to maximize soil carbon sequestration.
This brings us back to the red cooler. As much as I thought studying soil fungi would involve identifying cool mushrooms in the woods, that part is mostly a side perk. The real work is getting to know the soils: how they change as you go from the surface downwards, which parts hold on to carbon, how far roots reach, where the microbes hang out, and to tie it all together, what methods you use to answer these questions. Step one often looks something like this: collect a baggie of soil and keep it cool.
Eva Schwarz is a PhD student and MW CASC graduate fellow at the University of Minnesota, Twin Cities in the Ecology Evolution and Behavior program. She is advised by Dr. Peter Kennedy and Dr. Sarah Hobbie, and her research focuses on soil fungal communities, their interactions with plant communities, and their relationship to global change.