When we think of fungi, we probably think of mushrooms. But mushrooms are only fruiting bodies, analogous to apples on a tree. Most fungi live out of sight, yet make up a massively diverse kingdom of organisms that support and sustain nearly all living systems. The more we learn about fungi, the less makes sense without them.
Had we understood in the early 1900s, what we now understand of the complexity, prevalence and importance of symbiotic* relationships in nature, perhaps we could have avoided much of the collapse of biodiversity, and much of the global heating we are witnessing now. With that understanding, it would have been obvious how much collateral damage would be caused by the disturbance of the soil, and the biocides (pesticides, herbicides and fungicides) that modern agriculture is now dependent on.
We now know that around 90% of plants depend on mycorrhizal fungal networks to extend their own root systems, deliver the water and nutrients they need, and even deliver chemical warnings of threats elsewhere on the network. In ploughing the soil, we destroy these delicate connections, leaving plants susceptible to drought, disease and malnutrition, and dependent on irrigation, biocides and chemical fertilisers.
* Symbiosis is any type of close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasitic. – https://en.wikipedia.org/wiki/Symbiosis
Fungi in the carbon cycle
More carbon is contained in the earth’s soils than in its plants and atmosphere combined, and one of the processes by which it gets there involves mycorrhizal fungi. The water and nutrient transport services that these fungal networks provide to plants are often provided in exchange for carbon. Plants, with their green leaves exposed to the sun and the carbon dioxide in the atmosphere, are able to combine these two resources using photosynthesis to produce carbohydrates, much of which they require for their own energy needs, but a portion of which are passed on to their fungal partners. The mycorrhizal fungi use these carbohydrates, which they can not source on their own, to grow and to produce glomalin, a glue-like protein that they use to prevent leaching of water and minerals during transport. Glomalin additionally helps to bind soil particles together, and improves water retention. So long as the soil increases in depth, and is not eroded, this process results in sequestration of carbon from the atmosphere to the soil.
Fungi in the nutrient cycle
Fungi play two distinct roles in the nutrient cycle. As well as connecting with plant roots to provide a sophisticated water and mineral delivery network, they are also instrumental (with the help of bacteria and other soil organisms), in decomposing both organic and inorganic matter to make those minerals available in a useful, soluble form.