A moldy collaboration
Plants and molds have been working together for millions of years. Even before plants had their own root system, underground molds formed a network around the plant and collected nutrients from the soil. Thanks to molds, plants were able to colonize the land: the molds could extract minerals and nutrients from rocks that the plant roots couldn't reach. Then, the molds exchanged these nutrients for sugars produced by the plant. It was a win-win situation! With the nutrients from the molds, more and more plant species could evolve, all using CO2 from the atmosphere for photosynthesis. As a result, the CO2 level decreased to one-tenth of what it was before!
Carbon storage in the soil
Even today, almost all plants still work together with molds. These molds are called mycorrhiza. After millions of years of photosynthesis, 75% of all carbon on Earth is now stored underground. Until now, it was believed that this mainly happened because plants use CO2 to produce their own plant material. When the plants die, this material decomposes and ends up in the soil. However, the transfer of sugars from plants to mycorrhiza has often been left out of climate models because it's unclear how much carbon is involved.
Molds more powerful than we thought
Researchers from the University of Sheffield have now mapped out approximately how much CO2 is stored in the ground by all molds worldwide. In an extensive analysis evaluating common molds and their collaborations with plants, they concluded that the plant transfers 1 to 13% of the absorbed carbon to the mold. If you do the math, it adds up to 13.12 gigatons of CO2 per year passed on to underground molds worldwide. That's 36% of the annual amount of CO2 emitted by humans!
The mechanism
The researchers have discovered three reasons why molds store so much carbon in the soil. The first reason is that molds form such a large underground network that in grasslands, they make up 20 to 50% of the total biomass. These underground mold threads, called hyphae, store a lot of carbon. A second reason is that this mold network remains intact even when the mold dies. This means that the carbon stored during the mold's lifespan does not return to the soil. Finally, the molds release substances that contain carbon, such as sugars and organic acids. These substances bind to minerals in the soil, forming a very large and stable carbon storage.
Molds and the climate
The researchers emphasize the importance of not forgetting about molds when creating climate models. Additionally, the focus is often on conserving above-ground nature, such as forests. However, underground nature should also be in balance! Without healthy molds, plants also struggle. Moreover, it is clear that we need our molds to combat climate change!
Author: Noa Hudepol