Mycorrhizal networks are a major global carbon sink: ecosystems with plants that feed carbon to underground networks store an estimated 8 times more carbon compared to ecosystems with non-mycorrhizal vegetation. Underground fungal networks sequester carbon in three ways. First, fungi use carbon to build rapidly expanding networks in the soil. These networks are connected to plant roots, and act as nutrient highways. Second, sequestered carbon is used to create fungal exudates. Exudates are tough organic compounds that help form stronger soil aggregates, which act as a stable carbon reservoir, reducing erosion rates and maintaining soil structure. Third, sequestered carbon is stored in fungal necromass. Necromass describes underground networks that are no longer active, but whose complex architecture is structurally woven into the soil matrix. Microbial necromass is responsible for up to one-half of total soil organic matter and helps stabilize soils.

Fungi are expert foragers. They are able to acquire nutrients like phosphorus and nitrogen from the soil, and trade these nutrients to their plant partners for energy-containing carbon compounds, like sugars and fats. Modern industrial agriculture adds vast quantities of chemical fertilizer which interrupts the dynamics of exchange between plants and fungi. Phosphorus fertilizer is mined as rock phosphate: a non-renewable resource that takes millions of years to form. By 2040-2050, demand for phosphorus is projected to outpace supply, with dire consequences for food production. As rock phosphate becomes scarce, the importance of high-functioning fungal networks for agricultural systems will increase. Healthy networks decrease the quantity of nutrients leached out of the soil by rainfall by as much as 50%, and can increase the nutrient density of crops. Maximizing the health and functioning of fungal networks can help reduce the growing footprint of global food production.

Fungal networks are ecosystem engineers that help protect plants from a wide range of stresses. By protecting plants, fungal networks help increase plant biodiversity and ecosystem resilience. Fungal networks help prevent disease in plants, and boost the ability of plants to fight off attacks from insect pests by stimulating the production of defensive chemicals. Networks are also able to bind to heavy metals within their mycelium, protecting plants from toxicity, and can make plants less susceptible to drought and salt stress. Fungal networks also support entire ecosystems by excreting cement-like biopolymers that help reduce erosion. This helps increase biodiversity, maintain biogeochemical cycles and ecosystem productivity.