Learn the Science

Mycorrhizae 101

A plain-English guide to how mycorrhizal fungi work - written by Dr. Mike Amaranthus, one of the world's leading mycorrhizal researchers.

By Dr. Mike Amaranthus, Ph.D. · Retired USDA Research Soil Scientist · Founder, Mycorrhizal Applications, Inc.

Myco-What?

We live on top of a hidden world. Beneath the soil surface is a fascinating combination of life forms interacting in an abundance of ways. The vast majority of plant species form a mutually beneficial living relationship - a "symbiosis" - with beneficial fungi. It's a 1+1=3 relationship.

The roots of an estimated 85% of the world's plant species are colonized by symbiotic fungi. We call this root/fungus combination a mycorrhiza (plural: mycorrhizae). Mycor-rhiza literally translates into "fungus-root." The mycorrhizal fungi are the network of fungal filaments that permeate into the soil from their home on the plant root.

The body of the mycorrhizal fungus consists of microscopic filaments called hyphae. An individual hypha is approximately 1/25th the diameter of a human hair and can grow 15 to 25 inches in length. These hyphal strands spread out from the root cells of the host plant into the surrounding soil, greatly increasing the effective surface area of the root system.

Just a teaspoon of healthy soil can contain up to several miles of fungal hyphae. This network acts as a massively extended root system - accessing water and nutrients the plant's own roots could never reach.

The Two Main Types

Mycorrhizal fungi fall into two major groups. Knowing which type your plants need is the key to choosing the right inoculant.

Endomycorrhizae ("Endo")

Forms with ~85% of plants - most crops, vegetables, fruits, ornamentals, and grasses. The fungus penetrates inside the root cells, forming branched structures called arbuscules that serve as the nutrient exchange point. Does not produce visible mushrooms; spores form in the soil.

Ectomycorrhizae ("Ecto")

Forms with ~10% of plants - mainly conifers, oaks, pines, and hardwood trees. The fungus wraps around the outside of root cells in a structure called the Hartig net and mantle, making roots appear swollen. Over 4,000 ecto species exist; mushrooms, truffles, and puffballs are their fruiting bodies.

What They Do for Your Plants

The mycorrhizal fungi act as the extended stomach of the plant - producing enzymes that digest and unlock nutrients in the soil, then transporting them back to the plant. Research confirms they are particularly important for accessing phosphorus, nitrogen, zinc, iron, calcium, magnesium, manganese, and sulfur.

Nutrient Uptake

Hyphae penetrate tiny soil pores roots can't reach, breaking "tightly held" chemical bonds and transporting nutrients back to the plant - often dramatically reducing fertilizer requirements.

Drought Tolerance

Mycorrhizal fungi find and retain water where plant roots cannot, slowly releasing it during dry periods. Plants in natural areas tolerate drought far better than cultivated ones largely due to this fungal network.

Disease Resistance

Mycorrhizae release suppressive compounds that inhibit fungal root pathogens including Phytophthora, Fusarium, Pythium, and Rhizoctonia. They also form a tough physical barrier made of chitin around root cells.

Carbon Sequestration

Mycorrhizal fungi produce glomalin - a sticky, carbon-rich compound that binds soil particles together. Glomalin may account for up to one-third of the world's soil carbon, making these fungi key players in climate stability.

The Underground Network

Much like the internet, mycorrhizae can link all plant species together into an underground network known as the "common mycelial network." New scientific evidence shows this network does more than transport water and nutrients - it acts as a communication system, sharing chemical signals between plants.

Studies have documented plants using this network to warn neighbors of aphid attacks, share defensive molecules against root pathogens, and even inhibit the growth of competing plants. Interplant communication via the common mycelial network is now well established in the scientific community.

Why Modern Soils Are Often Deficient

In natural, undisturbed soils, most plant roots become readily colonized by indigenous mycorrhizal fungi. But modern agricultural practices - tillage, heavy fertilizer use, fumigation, and soil disturbance - dramatically reduce or eliminate native mycorrhizal populations.

Plants that germinate or are planted in soil without a mycorrhizal network become colonized much more slowly, and sometimes not at all. That's where commercial inoculants come in: products containing mycorrhizal propagules ("fungal seeds") reintroduce the relationship and give plants an immediate advantage from day one.

Inoculation is most effective when the product is placed in direct contact with the root system at planting - in the hole, on the root ball, or worked into the growing medium.