Ectomycorrhiza

An ectomycorrhiza (Gk. ἐκτός, ektos, "outside;" μυκός, mykós, "fungus;" ριζα, riza, "roots;" pl. ectomycorrhizas or ectomycorrhizae, abbreviated EcM) is a form of symbiotic relationship that occurs between a fungal symbiont and the roots of various plant species. The mycobiont tends to be predominantly from the phyla Basidiomycota and Ascomycota, although a few are represented in the phylum Zygomycota. Ectomycorrhizas form between fungi and the roots of around 2% of plant species. These tend to be composed of woody plants, including species from the birch, dipterocarp, myrtle, beech, willow, pine and rose families.

Unlike other mycorrhizal relationships, such as arbuscular mycorrhiza and ericoid mycorrhiza, ectomycorrhizal fungi do not penetrate their host’s cell walls. Instead, they form an entirely intercellular interface, consisting of highly branched hyphae forming a latticework between epidermal and cortical root cells, known as the Hartig net.

Ectomycorrhizas are further differentiated from other mycorrhizas by the formation of a dense hyphal sheath, known as the mantle, surrounding the root surface. This sheathing mantle can be up to 40 µm thick, with hyphae extending up to several centimeters into the surrounding soil. This hyphal network aids in water and nutrient uptake often helping the host plant to survive adverse conditions, and in exchange, the fungal symbiont is provided with access to carbohydrates.

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