ectomicorrizas

Ectomycorrhizas, or ectomycorrhizal associations (ECM), are mutualistic relationships between certain fungi and the roots of many trees and some shrubs. In these associations the fungal partner forms a dense mantle around the root tip and a network of hyphae called the Hartig net in the outer root cortex, while the fungal hyphae extend outward into the soil as an extensive extraradical mycelium.

ECM fungi belong primarily to basidiomycete and ascomycete lineages. The hyphae do not penetrate plant cell walls; instead, the Hartig net grows between epidermal and cortical cells, and the root tip is surrounded by a protective mantle. This structure enhances nutrient exchange while limiting disruption to plant cells.

During the symbiosis, plants supply carbon compounds to the fungus, while the fungus mobilizes and transfers inorganic nutrients, especially nitrogen and phosphorus, to the plant. The extraradical mycelium enlarges the soil-foraging zone, and enzymatic activities can decompose organic matter to release nutrients.

ECM associations are common in temperate and boreal forests and form with a wide range of host trees, including pines (Pinaceae), spruces, oaks (Fagaceae), beeches, and birches. Notable ECM fungal genera include Amanita, Suillus, Cortinarius, Laccaria, Lactarius, Russula, Boletus and Pisolithus.

Ecologically, ectomycorrhizas improve seedling establishment, tree growth, and resistance to drought and some pathogens. They are of interest in forestry and restoration, and inoculation with ECM fungi is used to enhance establishment of planted trees. ECM networks may connect multiple plants and influence nutrient sharing.