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An ectomycorrhiza (Gk. ἐκτός, ''ektos'', "outside;" μυκός, ''mykós'', "fungus;" ριζα, ''riza'', "roots;" pl. ''ectomycorrhizas'' or ''ectomycorrhizae'', abbreviated EcM) is a form of symbiotic relationship that occurs between a fungal symbiont and the roots of various plant species. The mycobiont tends to be predominantly from the phyla Basidiomycota and Ascomycota, although a few are represented in the phylum Zygomycota. Ectomycorrhizas form between fungi and the roots of around 2% of plant species.〔 These tend to be composed of woody plants, including species from the birch, dipterocarp, myrtle, beech, willow, pine and rose families. Unlike other mycorrhizal relationships, such as arbuscular mycorrhiza and ericoid mycorrhiza, ectomycorrhizal fungi do not penetrate their host’s cell walls. Instead, they form an entirely intercellular interface, consisting of highly branched hyphae forming a latticework between epidermal and cortical root cells, known as the Hartig net. Ectomycorrhizas are further differentiated from other mycorrhizas by the formation of a dense hyphal sheath, known as the mantle, surrounding the root surface. This sheathing mantle can be up to 40 µm thick, with hyphae extending up to several centimeters into the surrounding soil. This hyphal network aids in water and nutrient uptake often helping the host plant to survive adverse conditions,〔 and in exchange, the fungal symbiont is provided with access to carbohydrates. Many EcM fungal fruiting bodies are well known. These include the economically important and edible truffle (''Tuber'') and the deadly death caps and destroying angels (''Amanita''). They also form on many common temperate forest trees, such as pines (''Pinus''), oaks (''Quercus''), willows (''Salix''), Douglas firs (''Pseudotsuga''), eucalypts (''Eucalyptus''), beeches (''Fagus'') and birches (''Betula''). There have been tremendous advances in research concerning ectomycorrhizal identification and ecological importance over the past few years. This has led to a more complete understanding of the intricate and varied roles ectomycorrhizas play in the ecosystem. These advances in knowledge have led to increased applicability in areas such as ecosystem management and restoration, forestry and agriculture. == Evolution == Mycorrhizal symbioses, in general, are ubiquitous in terrestrial ecosystems, and it is possible that these associations helped to facilitate land colonization by plants. Paleobiological and molecular evidence suggest that arbuscular mycorrhizas (AM), in particular, originated at least 460 million years ago. EcM plants and fungi exhibit a wide taxonomic distribution and are similarly present across all continents (apart from Antarctica), suggesting the EcM symbiosis has ancient evolutionary roots, as well.〔 Pinaceae represents the oldest extant plant family in which symbiosis with EcM fungi occurs, and fossils from this family date back to 156 million years ago. A popular theory proposed by Read postulates that habitat type and the distinct functions of different mycorrhizas help determine the particular symbiosis that will become predominant. In this theory, EcM symbioses evolved in relatively productive ecosystems, such as boreal forests, but in which nutrient cycling could still be limiting. In this scenario, ectomycorrhizas are a somewhat intermediate form, having greater mineralization capacities than arbuscular mycorrhizas and less so than types such as ericoid mycorrhizas. This is supported by several studies, some of which also purport arbuscular mycorrhizas to be the ancestral trait. According to this data, many non-mycorrhizal and other mycorrhizal forms represent evolutionary specializations. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ectomycorrhiza」の詳細全文を読む スポンサード リンク
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