The term mycorrhiza describes the symbiotic relationship between diverse assemblages of fungi and plant roots. Mycorrhizal associations are considered mutualistic because they are both the normal state (Smith and Read 1997) and a constant feature (Smith 1995) of most plants under most ecological conditions. There are several types of mycorrhizae characterized with respect to the organisms involved in the symbiosis and their anatomy and function. The most common is called an arbuscular mycorrhiza (AM). The AM fungi (Glomales, Zygomycetes) occur in most terrestrial environments (Allen et al. 1995; Janos 1980) and are the dominant association in grassland, shrubland, and agricultural ecosystems. These fungi are characterized by the formation of arbuscules, thinly branched hyphal structures within root cortical cells responsible for transfer of immobile nutrients such as phosphorous (P) from fungi to plant. Arbuscular mycorrhizae fungi are obligate biotrophs, obtaining all of their carbon from a host plant, which makes culturing and mass-producing fungal isolates for large-scale inoculation efforts extremely difficult. The second most common mycorrhizal type is ectomycorrhiza (EM). The majority of EM fungi are basidiomycetes and ascomycetes, with few species of zygomycetus fungi in the genus Endogone (Smith and Read 1997). These fungi associate almost exclusively with woody plants in the Pinaceae and Fagaceae (Allen et al. 1995). Ectomycorrhizae fungi do not penetrate the plant cell walls but surround them forming a Hartig net and encase individual roots with a mantle of fungal tissue. These fungi are used extensively in forest reclamation worldwide, the most common being Pisolithus tinctorius (Marx and Cordell 1989; Marx et al. 1976), Rhizopogon spp. (Trappe 1977), and Suillus spp. (Chapela et al. 2001). Lastly, other less dominant mycorrhizal types that form important species-specific associations with ericaceous and orchidaceous plants should also be included in their restoration efforts.
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