What Important Role Do Fungi Play in Many Ecosystems?

Fungi are among the most influential organisms on the planet, quietly driving processes that keep ecosystems functional, from recycling dead matter and feeding living plants to holding soil together and regulating which tree species thrive in a forest. They operate largely out of sight, yet without them, terrestrial life as we know it would stall. Their roles span decomposition, nutrient exchange, soil formation, carbon storage, population control, and even post-disaster recovery, and the science behind each of these functions is richer than most people realize.

Breaking Down What Nothing Else Can

The most familiar role of fungi is decomposition, but the scope of what they accomplish goes well beyond rotting a fallen log. Plant material is made largely of lignocellulose, a tough composite of cellulose, hemicellulose, and lignin. Lignin in particular is an extraordinarily resistant polymer that gives wood its rigidity. Bacteria can barely touch it. Fungi, especially white-rot basidiomycetes, are the only organisms that can break lignin down efficiently. They do this using a combination of enzymes including laccases and peroxidases, along with non-enzymatic systems that generate highly reactive molecules capable of attacking lignin’s chemical bonds.¹ They also deploy cellulases and hemicellulases that dismantle the polysaccharide components of plant cell walls.²

This decomposition work is not just cleanup. It is the bottleneck through which carbon, nitrogen, and phosphorus locked in dead plant tissue get released back into forms that other organisms can use. Without fungal decomposers, dead wood and leaf litter would pile up indefinitely, and the nutrient cycles that sustain forests, grasslands, and wetlands would grind to a halt.

Mycorrhizal Networks and the Underground Economy

Roughly 80% of terrestrial plant species form partnerships with mycorrhizal fungi.³ In these relationships, fungal threads called hyphae extend far beyond what plant roots alone can reach, absorbing water and mineral nutrients from the soil and delivering them to the plant. In return, the plant supplies the fungus with sugars produced through photosynthesis. The physical interface where this exchange happens varies by type: in arbuscular mycorrhizas, fungal hyphae penetrate root cell walls but remain separated from the cell’s interior by a plant-derived membrane, creating a specialized zone optimized for nutrient transfer.⁴

What makes these networks especially fascinating is that they can connect multiple plants. A single fungal network can link neighboring trees and shrubs underground, forming what researchers call a common mycelial network. Through these connections, plants can exchange not just nutrients but also chemical signals. When one plant is attacked by an herbivore or a pathogen, neighboring plants connected to the same network can up-regulate their own defense mechanisms, as though they received a warning.⁵ The likely mechanism is a direct transfer of signaling molecules through the fungal hyphae themselves.⁶ These changes can include rapid shifts in physiology, gene activity, and defense chemistry across entire plant communities.⁷

Holding Soil Together and Storing Carbon

Fungi do not just live in soil; they physically build it. Mycorrhizal fungi produce a glycoprotein called glomalin, which acts as a kind of biological glue. Glomalin binds tiny soil particles into larger, more stable clumps known as aggregates. These aggregates resist erosion by wind and water, improve the soil’s ability to hold moisture, and create the pore spaces that roots and other organisms need to thrive.³ Experimental work has confirmed that higher concentrations of glomalin in soil correlate with larger and more stable aggregates, and that fungal hyphae and glomalin together are dominant factors regulating soil stability, even in contaminated environments.⁸

Fungi are also major players in carbon storage. When fungal cells die, the residual organic material, called necromass, persists in soil and contributes to long-term carbon reserves. A recent global analysis found that fungal necromass carbon is the single largest contributor to soil organic carbon across the top meter of soil worldwide, outpacing both bacterial necromass and plant-derived carbon like lignin residues. The study estimated global fungal necromass carbon stocks in topsoil at around 211 billion tonnes.⁹ Part of what makes fungal necromass so persistent is the pigment melanin, which slows decomposition. In peatlands, initial melanin content in fungal tissue was the strongest predictor of how much mass remained after two years of decay.¹⁰

Regulating Forest Diversity

Fungi do not just support plant life; they also regulate which plants succeed and which fail, shaping the composition of entire forests. One of the clearest examples involves soil-borne fungal pathogens that preferentially attack seedlings growing near their parent trees. Because pathogen pressure is highest right under an adult of the same species, seeds that land close to their parent face steep mortality, while those that disperse farther have a better chance. This pattern, known as the Janzen-Connell effect, prevents any single tree species from dominating a forest and promotes diversity.

Experimental tests have confirmed just how potent this mechanism can be. In one study, fungal pathogens drove 100% mortality in field seedlings planted at high density near conspecific adults within four weeks of germination. Treating the soil with fungicide eliminated this density-dependent die-off entirely.¹¹ Other work has shown that the effect follows evolutionary relatedness: seedlings survive better in soil near a distant relative than in soil near a close one, and this phylogenetic signal disappears when fungicide is applied, confirming that host-specific fungal pathogens are the cause.¹² Meanwhile, mycorrhizal fungi can partially counteract this pathogen pressure, creating a tension between two fungal forces that collectively shape tree community structure.¹³

Feeding Animals and Hitching Rides

Fungi are woven into food webs in ways that go far beyond decomposition. Many mammals eat fungi as a regular part of their diet, and this relationship creates a two-way exchange that benefits both parties. A global review found viable fungal spores in the droppings of at least 40 mammal species, including spores from at least 58 mycorrhizal fungal species that survived passage through the gut.¹⁴ Animals get nutrition; fungi get their spores carried to new locations. This dispersal service is so important that it likely drove the evolution of truffle-like fruiting bodies, underground structures that depend entirely on being dug up and eaten to spread their spores.¹⁵

After disturbances like timber harvests, small mammals such as rodents and shrews become especially important mycorrhizal dispersers. By carrying spores from intact forest into freshly disturbed ground, they help re-establish the fungal partnerships that seedlings need to survive during forest regeneration.¹⁶

Insect Farmers and Their Fungal Crops

Some of the most sophisticated animal-fungus partnerships involve insects that actively cultivate fungi. Leaf-cutter ants harvest plant material not to eat it themselves but to feed it to a mutualistic fungus they grow inside their nests. The fungus breaks down the tough plant biomass, and the ants eat the fungus. This obligate partnership is roughly 50 million years old and helped some leaf-cutter species become dominant herbivores in the Neotropics, building colonies of enormous size.¹⁷

Ambrosia beetles follow a parallel strategy. They carry fungal spores in specialized body structures called mycangia, bore into wood, and inoculate it with their fungi, which grow into “gardens” the beetles feed on. Recent experimental work demonstrated that this is genuine farming: when beetles were present, their preferred fungal species grew significantly more abundantly than when beetles were absent, while competing mold species declined.¹⁸ These mycangia represent one of the oldest known mutualistic systems, housing not just fungi but also bacteria and yeasts in a portable microbial ecosystem.¹⁹

Recovery After Fire

When wildfire sweeps through a forest, it strips the soil of organic matter, destroys root systems, and leaves the ground vulnerable to erosion. A specialized group of pyrophilous (fire-loving) fungi rapidly colonize burned soil and begin stabilizing it. Experimental work showed that burned soil became up to 30% more aggregated when pyrophilous fungi were present, with improvements visible within ten days and sustained over a 40-day period.²⁰ Beyond soil binding, these fungi decompose charred organic material, capture nitrogen that would otherwise be lost from the burned landscape, and sequester carbon. Genomic analysis of fungi isolated after a major California wildfire revealed expansions of genes involved in breaking down the hydrophobic compounds and pyrolyzed organic matter that coat post-fire soils, suggesting these organisms are equipped specifically to restore soil function after burning.²¹

Fungi in Water, Deserts, and High Mountains

Fungal roles extend well beyond forests. In freshwater streams, aquatic fungi colonize submerged leaf litter and drive the early stages of decomposition. In the hyporheic zone, the waterlogged sediment layer beneath and alongside stream channels, fungal activity accounted for roughly 12% of leaf mass loss, two to three times more than under other conditions tested.²² In mangrove ecosystems, fungi play a parallel role, decomposing the abundant organic matter in waterlogged sediments and cycling nutrients in conditions where many other decomposers struggle.²³

In deserts, fungi are integral to biological soil crusts, the thin living layers on the soil surface composed of cyanobacteria, algae, fungi, lichens, and mosses. These crusts stabilize sandy and silty soils against wind erosion, fix nitrogen, redistribute water, and provide the only primary productivity in otherwise barren landscapes.²⁴ At the other extreme, dark septate endophytic fungi live inside the roots of plants at high altitudes and in harsh environments, boosting their hosts’ growth, nutrient uptake, and stress tolerance.²⁵ These fungi have been found in plant roots above 4,270 meters in the Andes and Rocky Mountains, suggesting they help plants survive where conditions are too harsh for most mycorrhizal partnerships.²⁶

Building Soil from Bare Rock

Before there is soil, there are often lichens, composite organisms made of fungi living in partnership with photosynthetic algae or cyanobacteria. Lichens are among the first colonizers of bare rock surfaces, and they actively create soil by weathering the stone beneath them. They do this both mechanically, as their hyphae penetrate cracks and expand and contract with moisture changes, and chemically, by secreting organic acids, particularly oxalic acid, that dissolve minerals and strip metallic elements from the rock surface. Over time, this process produces clay minerals, iron oxides, and fine particles that accumulate as primitive soil.²⁷ The partnership between fungi and photosynthetic organisms in this pioneering role is ancient. Molecular clock analyses suggest fungi and green algae were present on land roughly a billion years ago, with land plants appearing by around 700 million years ago, likely facilitated by symbiosis with fungi.²⁸

Natural Pest Control

Entomopathogenic fungi, species that infect and kill insects, serve as natural population regulators across ecosystems. Insect communities commonly harbor diverse assemblages of pathogenic fungi, which exert selective pressure on insect traits and behavior even when full-blown epidemics are rare.²⁹ This low-level but persistent pressure helps keep herbivorous insect populations in check, which in turn protects vegetation. Some beneficial endophytic fungi that live inside plant tissue without causing disease also discourage herbivores directly by producing compounds that reduce feeding, suppress pathogen growth, and enhance the plant’s own stress tolerance.³⁰

Cleaning Up Contaminated Environments

Fungi have a remarkable capacity to absorb and break down pollutants, a field known as mycoremediation. Some species can pull heavy metals out of contaminated soil and degrade pesticides simultaneously. In one study, a strain of Aspergillus fumigatus removed 98% of zinc, 95% of lead, and significant fractions of cadmium, chromium, nickel, and copper from media containing multiple metals and the pesticide lindane. The fungus also degraded 94% of the lindane within 72 hours.³¹ While laboratory conditions differ from field-scale cleanups, results like these highlight fungi as a potentially low-cost, low-energy tool for environmental restoration.

Shaping Plant Invasions

Fungal communities do not just support native ecosystems; they can also influence how invasive plants spread. Research on Canada goldenrod, a prolific invader in parts of Asia and Europe, found that arbuscular mycorrhizal fungi simultaneously boosted its growth and its competitive ability against native species, helping explain the plant’s invasion success.³² At the same time, invasive plants can rapidly reshape the fungal pathogen communities in the soil around them. One study found that an invasive species homogenized soil fungal pathogen assemblages even at low densities, potentially creating conditions where the invader faces fewer species-specific enemies in the soil, giving it a further edge over natives.³³ Understanding these dynamics is increasingly important for conservation, because managing fungal communities could become a lever for slowing invasions or restoring native plant dominance.