Fungi are woven into nearly every terrestrial ecosystem. About 90 percent of land plants form mycorrhizal partnerships, symbiotic associations between plant roots and fungal hyphae. In these exchanges, the fungus dramatically increases the plant's uptake of water and nutrients such as phosphorus and nitrogen, while the plant supplies the fungus with sugars produced through photosynthesis. Mycorrhizal fungi come in two main forms: ectomycorrhizae wrap around the outside of root cells, often associating with trees like oaks and pines, while endomycorrhizae penetrate into root cells, forming tree-like arbuscules where the nutrient exchange takes place. Inside these structures, fungi produce glycoproteins like glomalin that contribute to soil carbon storage and help bind soil particles into stable aggregates.
Wood-decay fungi specialize in breaking down dead trees and fallen logs. White rot fungi decompose both lignin and cellulose, leaving behind whitish, fibrous wood, while brown rot fungi attack mainly cellulose and leave brown, crumbly, cubical remnants. Beyond decay, fungi connect living trees through underground mycelial networks often called the wood wide web, a concept popularized by ecologist Suzanne Simard. Through these networks, trees can share sugars, water, and chemical signals, and forests become more than collections of competing individuals. Some of the most dramatic examples of fungal scale are fairy rings, circles of mushrooms formed by a single mycelium expanding outward, and the enormous Armillaria mycelium in Oregon, which covers roughly 2,385 acres and is considered the largest known organism on Earth.
Fungi also collaborate with animals and other microbes. Leaf-cutter ants and certain termites practice fungiculture, cultivating specific fungi in their colonies and feeding on the fungal tissue. Lichens are intimate symbioses between fungi and algae or cyanobacteria, with newer research showing that multiple microbial partners are often involved. Endophytic fungi live harmlessly inside plant tissues, while epiphytic fungi grow on plant surfaces. Decomposition itself is a team effort; the trinity of decay describes how fungi, bacteria, and invertebrates together recycle about 90 percent of dead organic matter on land, releasing nutrients for new life and maintaining soil fertility. A rotting log is a microcosm where this diversity unfolds, supporting insects, slime molds, bacteria, and countless fungi in a single log. Fungi also play a major role in carbon cycling, both storing carbon in soils through mycorrhizal networks and releasing it through decomposition, which ties their fate directly to the global climate.