Roots and soil on a cross-section of Minnesota prairie.
Prairie soils (what scientists call mollisols) are as complex, if not more so, than the prairie community above ground. In Minnesota prairie soils developed since the last glaciers retreated, over the past 10-15 thousand years. Soil formation can be influenced by geologic parent material, topography, climate, organisms, and time. It can take anywhere from 100 to 1,000 years to form an inch of topsoil. Healthy prairie soils are vital to the long-term resilience of prairies.
Water infiltration and storage
Soils act as a sponge, and along with the layers of prairie vegetation, improve infiltration and reduce runoff from rainstorms. This action increases groundwater recharge, provides flood control, and reduces erosion.
Prairie soils are carbon-rich. Carbon is found in living plant roots and in soil organic matter. This is also where carbon is stored in the soil after plants capture it from the atmosphere. When plant roots die, microorganisms break them down into rich organic matter, further enhancing the carbon storage capacity.
Prairies have dense and diverse root systems. Roots trap and filter both water and nutrients, which sustain prairies though extreme drought or flooding. The majority of prairie plant roots extend beyond 2 feet in depth and some roots are 3 times deeper than the plants are tall.
Soil biota (plants, animals, fungi, etc.)
Prairie soils have vast underground ecosystems; healthy soils are alive! There are more microbes in a teaspoon of healthy soil than there are people on earth (7 billion). Our prairies have literally tons of bacteria and fungi with unique relationships.
An example is arbuscular mycorrhizal fungi (AMF) that colonizes prairie roots. They form symbiotic partnerships with prairie plants and help the plants function. They help plants uptake and transport phosphorus, promote plant growth, and enhance a plant's stress tolerance, such as during extreme climate events (e.g., drought). AMF can even provide some resistance to pathogens.