Mycorrhizas

Mycorrhizas are symbiotic associations between fungi and plant roots that enhance nutrient exchange and plant growth. In these partnerships, fungal hyphae colonize root tissues and extend the effective root surface through networks in the soil, increasing nutrient and water uptake. The relationship is mutualistic, though the plant must supply carbohydrates to the fungi.

There are several major types. Ectomycorrhizas form a sheath around the root and a mantle, with fungal hyphae penetrating the spaces between root cortical cells to form a Hartig net; they are common in many trees, including pines and oaks. Arbuscular mycorrhizas, also called endomycorrhizas, involve arbuscules formed inside cortical cells by Glomeromycota fungi and are associated with most flowering plants. Mycorrhizal associations are widespread and can involve complex networks that connect multiple plants.

Functions include enhanced uptake of phosphorus and other nutrients from soil, improved water acquisition, and increased resistance to soil pathogens. The fungi receive carbon compounds from the plant in exchange. In addition, mycorrhizas contribute to soil structure through hyphal networks and can influence plant community dynamics and resilience to drought or salinity.

Ecology and evolution: Mycorrhizas are widespread in terrestrial ecosystems and are considered ancient, with evidence tracing back to early land plants. Phosphorus fertilization and soil disturbances can reduce colonization, while the fungi influence nutrient cycling, carbon storage, and plant competition. Environmental changes can alter the balance of mutualism in some contexts.

In forestry and agriculture, mycorrhizal inoculation is used to improve establishment and growth, though benefits depend on host species and conditions. Understanding mycorrhizas is important for sustainable soil management, agroforestry, and restoration efforts.