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About mycorrhizas |
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The traditional text book view of the plant:soil interaction. For virtually all plants this explanation is inaccurate since it totally ignores the existence of mycorrhizas, which are formed by almost all plants in nature. Most simplistically, a mycorrhiza is an association between a fungus and a plant root that results in the formation of distinct structures (from the Greek mukes-fungus and rhiza=root).
More encompassing definitions include: "A structure in which a symbiotic union between a fungus and a plant root increases the fitness of both partners" (Read, 1997) and "Dual organs of absorption formed when symbiotic fungi inhabit healthy organs of most land plants" (Trappe, 1996).
There are several types of mycorrhiza such as those that form distinctive mantles around host (mostly trees) roots that are known as ectomycorrhizas.....
....and those in which distinctive structures are only formed inside the host roots (in the UK, mostly non-woody vegetation), which are known as endomycorrhizas. This photograph shows an arbuscule; this intra cellular structure is the namesake to a subgroup of endomycorrhiza and is responsible for nutrient and carbon exchange between host and fungus. Arbuscular mycorrhizas are commonly associated with grasslands.
Common to all mycorrhizal types is the extra radical mycelium. This finely branched structure is central to nutrient turnover in ecosystems, for which it is ideally suited both biochemically and physically to exploit the soil matrix. It is a major conduit and source of carbon in soil and in some circumstances it can form links between different plants. Much of the research in the Aberdeen Mycorrhiza Research Group aims to understand the complex processes and interactions of the external mycelium.
