ectomycorrhiza

Ectomycorrhiza is a form of symbiotic association between certain soil fungi and the roots of many woody plants, including most temperate and boreal trees. In this relationship the fungal hyphae envelop the root tip with a sheath (mantle) and extend into the surrounding soil as an extensive extraradical network. Unlike some other mycorrhizas, ectomycorrhizal fungi do not penetrate the cortical cell plasma membranes; instead they form a Hartig net in the intercellular spaces of the root cortex where nutrient exchange occurs.

The plant supplies carbohydrates to the fungal partner, while the fungus enhances the host's uptake of mineral nutrients, particularly nitrogen and phosphorus, and often improves water absorption. The extraradical mycelium explores soil beyond the root depletion zone, accessing organic and mineral nutrients that the plant alone cannot reach and buffering the plant against drought and soil acidity.

A wide range of woody plants forms ectomycorrhizas, especially conifers and many hardwoods. ECM fungi include many basidiomycetes and some ascomycetes, such as Amanita, Cortinarius, Suillus, Laccaria, Pisolithus, Rhizopogon, and Cenococcum geophilum. Interactions can vary from highly specific to broadly compatible, depending on the plant and fungal species involved.

Ecologically, ectomycorrhizas play a key role in nutrient cycling and forest health. They influence plant community composition, litter decomposition rates, and soil structure. Ectomycorrhizal networks can connect multiple plants, potentially facilitating cross-plant transfer of carbon and nutrients, though the extent and ecological significance of such transfers are context-dependent. These associations are especially important in nutrient-poor soils and in boreal and temperate forest ecosystems.