Mycorrhiza

A mycorrhiza (Greek: μυκός, mykós, "fungus" and ριζα, riza, "roots", pl. mycorrhizae or mycorrhizas) is a symbiotic association composed of a fungus and roots of a vascular plant. In a mycorrhizal association, the fungus colonizes the host plant's roots, either intracellularly as in arbuscular mycorrhizal fungi (AMF or AM), or extracellularly as in ectomycorrhizal fungi. They are an important component of soil life and soil chemistry. The association is generally mutualistic, but occasionally weakly pathogenic.

Mutualist dynamics

Fungi in mycorrhizae form a mutualistic relationship with the roots of most plant species. The roots in the relationship, and the plants themselves are referred to as mycorrhizal if mycorrhizae are formed. While only a small proportion of all species has been examined, 95% of those plant families are predominantly mycorrhizal. They are named after their presence in the plant's rhizosphere (root system).

Recent research with ectomycorrhizal plants in boreal forests has indicated that mycorrhizal fungi and plants have a relationship that may be more complex than simply mutualistic. This relationship was noted when mycorrhizal fungi were unexpectedly found hoarding nitrogen from plant roots in times of nitrogen scarcity. Researchers argue that some mycorrhizae distribute nutrients based upon the environment with surrounding plants and other mycorrhizae. Researchers go on to explain how this updated model explains why mycorrhizae do not alleviate plant nitrogen limitation, and why plants can switch abruptly from a mixed strategy with both mycorrhizal and nonmycorrhizal roots to a purely mycorrhizal strategy as soil nitrogen availability declines.