Endomycorrhiza

Endomycorrhiza, commonly referred to as arbuscular mycorrhiza (AM), is a form of mycorrhizal symbiosis in which fungal hyphae colonize the root cortex of host plants and form intracellular structures called arbuscules within plant cortical cells, sometimes accompanied by vesicles used for storage. The fungal partners are mainly from the phylum Glomeromycota. Endomycorrhizal colonization is widespread across land plants and represents the most common type of mycorrhizal association.

The symbiosis involves two main interfaces for nutrient exchange. Intraradical hyphae penetrate root cortical cells and branch to form arbuscules, which are the primary sites of phosphorus and micronutrient transfer between fungus and plant. Vesicles may serve as storage. Exterior, branching hyphae extend into the soil and soil pore spaces, increasing the plant’s shared root surface area and enabling access to nutrients and water beyond the root zone. In return, the plant supplies carbon to the fungus in the form of sugars and other compounds. The association can also influence soil structure through fungal secretions such as glomalin.

Distribution and ecological role: AM is found in a vast majority of terrestrial plants, particularly in nutrient-poor soils where phosphorus is limited. It can enhance phosphorus and water uptake, improve tolerance to certain stresses, and participate in common mycorrhizal networks that connect multiple plants. Some plant groups, notably Brassicaceae, often do not form AM associations, depending on ecological context.

Taxonomy and life cycle: AMF are largely asexual and belong to Glomeromycota; they produce large multinucleate spores and do not form known sexual structures. The relationship is generally mutualistic, with benefits for both partners, though outcomes depend on soil conditions and plant and fungal genetics.

Applications: AM inoculation is used to improve nutrient acquisition and crop resilience, especially in low-input or degraded soils, though efficacy varies with host species and environment.