Mycorrhizal

Mycorrhizal describes a broad group of symbiotic associations between fungi and plant roots in which fungal hyphae colonize plant root tissues and extend into the surrounding soil. In exchange for photosynthetically derived carbon from the plant, the fungi assist with nutrient and water uptake, soil structure, and sometimes disease resistance. Mycorrhizal symbioses are nearly ubiquitous among land plants and are considered essential for many ecosystems.

Two major forms are ectomycorrhizae (ECM) and arbuscular mycorrhizae (AM, also called arbuscular mycorrhizal fungi). ECM fungi envelop the root tips with a hyphal sheath and form a network (Hartig net) between root cortical cells; they are common in many temperate and boreal trees such as pines, oaks and birches. AM fungi colonize root cortical cells without forming a mantle, producing arbuscules where nutrient exchange occurs; AMF belonging to Glomeromycota colonize the majority of vascular plants including most crops and many tropical species. Other forms include ericoid mycorrhizae in ericaceous shrubs and orchid mycorrhizae that enable orchid seed germination and seedling establishment.

Through their extensive hyphal networks, mycorrhizal fungi increase soil exploration, enhancing phosphorus, nitrogen, and micronutrient uptake, improve water acquisition, and contribute to soil aggregation via fungal byproducts such as glomalin. The plant supplies carbon to the fungi, often a significant portion of its photosynthate.

These associations influence plant community composition, succession, and nutrient cycling, and are exploited in sustainable agriculture, forestry, and habitat restoration by inoculation with compatible mycorrhizal fungi. However, outcomes can vary with plant species, soil conditions, and fungal partners. Disturbances, such as soil compaction, excessive fertilization, or fungicide use, can disrupt mycorrhizal communities.