The Function of Fungi in Soil
Why fungal networks matter for healthy, living landscapes
In any thriving soil ecosystem, fungi are not just present — they are essential. These often unseen organisms are key players in the biological life of the soil, forming vast underground networks that support plant health, nutrient cycling, soil structure, and long-term ecological resilience.
Below the surface, fungi perform a range of critical functions that can’t be replicated by fertilisers or conventional soil additives. Understanding their role is central to building and maintaining living, regenerative soils.
1. Decomposition and Nutrient Cycling
Fungi are nature’s most efficient decomposers. They break down complex, carbon-rich materials — such as lignin, cellulose, and hemicellulose — that bacteria cannot easily process. This process:
Releases locked-up nutrients like nitrogen, phosphorus, and potassium
Converts organic matter into stable humic compounds
Supports the steady formation of high-quality topsoil
Key players:
Saprophytic fungi (e.g. Trichoderma, Penicillium)
White rot and brown rot fungi on woody material
These fungi thrive in carbon-rich environments — such as thatch, wood chips, and forest litter — making them especially active in the decomposition zones of mulches like Soil Builder™.
2. Symbiotic Relationships: Mycorrhizal Fungi
Certain fungi form mutualistic relationships with plant roots. These mycorrhizal fungi colonise root systems and extend their reach through the soil via fine-threaded hyphae. In return for carbohydrates from the plant, they offer:
Enhanced access to water and immobile nutrients (especially phosphorus and zinc)
Increased drought tolerance and disease resistance
Improved root structure and seedling establishment
Types of mycorrhizae:
Arbuscular mycorrhizae (AMF): common in most crops and herbaceous plants
Ectomycorrhizae: typical in trees such as pines, oaks, and eucalypts
3. Soil Structure and Aggregation
Fungal hyphae act as biological binders within the soil, physically holding together particles of sand, silt, and clay. This stabilises soil aggregates, which improves:
Airflow and gas exchange
Water infiltration and retention
Resistance to erosion
In addition, certain fungi exude sticky proteins such as glomalin, which further cement soil particles and enhance the structural integrity of the soil.
4. Biological Defence and Pathogen Suppression
Many soil fungi play a protective role by outcompeting or directly inhibiting plant pathogens. Some species produce antibiotics or enzymes that break down the cell walls of harmful organisms.
Examples include:
Trichoderma spp. – known for suppressing root pathogens and stimulating plant immunity
Beauveria and Metarhizium – entomopathogenic fungi that target soil-dwelling insect pests
These biological controls are part of a balanced soil ecosystem where diversity limits disease outbreaks naturally.
5. Carbon
Fungi are central to the long-term storage of carbon in soil. Unlike fast-decomposing bacterial biomass, fungal residues (especially melanised hyphae) persist longer and contribute to the formation of stable soil organic matter.
This makes fungal-dominant systems particularly valuable in gathering CO₂ from the atmosphere and setting it into the soil.
Encouraging Fungal Activity
Healthy fungal populations require:
Minimal soil disturbance (avoid over-tilling)
A consistent supply of carbon-rich material (e.g., mulch, compost, cover crops)
Avoidance of harsh chemical inputs that disrupt microbial communities
Moist, aerated environments that allow hyphae to expand
Inputs like Soil Builder™ — which include raw carbon, green nutrients, and microbial inoculants — create the ideal substrate for fungal colonisation, especially in degraded or biologically poor soils.
In Summary
Fungi are not a supplement to soil health — they are fundamental to it. From decomposing organic matter and forming symbiotic relationships with roots, to improving structure and suppressing disease, their functions are complex, interconnected, and vital.
Supporting fungi in your soil isn’t just good practice. It’s the basis of building a living, resilient landscape — from the ground up.