Refers to a close, symbiotic relationship between a fungus and the roots of a higher plant. Mycorrhiza (from the Greek myketos meaning fungus and rhiza meaning root) are common among trees in temperate and tropical forests. There are generally two forms—ectomycorrhiza, where the fungus forms a sheath around the plant roots, and endomycorrhiza, where the fungus penetrates into the cells of the plant roots. In both cases, the fungus acts as extended roots for the plant and therefore increase its total surface area. This allows for greater adsorption of water and nutrients vital to growth. Mycorrhiza even allow plants to utilize nutrients bound up in silicate minerals and phosphate-containing rocks that are normally unavailable to plant roots. They also can stimulate the plants to produce chemicals that hinder invading pathogens in the soil. In addition to the physical support, the mycorrhiza obtain carbohydrates from the higher, photosynthetic plant. This obligate relationship between fungi and plant roots is especially important in nutrient-impoverished soils. In fact, many trees will not grow without mycorrhiza.
