micorhize

Mycorrhiza is a symbiotic association between a fungus and the roots of a plant that enhances nutrient and water uptake for the plant while providing the fungus with carbohydrates and lipids. The relationship is typically mutualistic, though conditions can influence its net benefit for the host.

Two major forms are ectomycorrhizas and arbuscular mycorrhizas. Ectomycorrhizal fungi form a sheath, or mantle, around the root tip and grow a Hartig net between root cortical cells, increasing nutrient absorption from the soil for many trees and woody plants. Arbuscular mycorrhizal fungi colonize the root cortex and create highly branched arbuscules inside plant cells, facilitating exchange of nutrients such as phosphorus and micronutrients. Lesser forms include ericoid mycorrhizae, associated with heath plants, and orchid mycorrhizae, essential for many orchid germinations.

Structure and function involve extensive extraradical mycelium that explores soil beyond the root zone, aiding water uptake, soil aggregation, and defense against some soil pathogens. In return, the plant provides carbon compounds to the fungal partner. The balance of benefits depends on soil fertility, moisture, and plant species.

Ecologically, mycorrhizae are widespread and crucial in many ecosystems, influencing plant community composition, nutrient cycling, and resilience to stress. They are ancient associations, with evidence dating back hundreds of millions of years, and are a focus of agricultural and ecological applications, including inoculants for crops and rehabilitation of degraded lands. Methods to study them include microscopy, molecular markers, and isotopic tracing of carbon and nutrients.