Dynamics of Ectomycorrhizas and Actinorhizal Associations

A mycorrhiza is a symbiotic association between a plant root and a fungus. Mycorrhizas are classified into seven categories according to how the fungi penetrate the root cells, i.e., arbuscular mycorrhiza (forming a symbiotic association between more than 80% of vascular plants and zygomycetous fungi in the Glomales), ectomycorrhiza (an association between about 3% of seed plants and basidiomycetous fungi), ascomycetous and zygomycetous fungi, ericoid mycorrhiza, ectendomycorrhiza, arbutoid mycorrhiza, and monotropoid and orchidoid mycorrhiza (Smith and Read 1997; Raina et al. 2000). Mycorrhizal associations, both directly and indirectly, play a very important role in forest ecosystems: they enhance the uptake of water and plant nutrients, they promote plant growth, they increase resistance to drought, freezing, salinity, and root pathogens, they influence plant communities, and they play a role in the circulation of materials.