Ectomycorrhizal symbiosis

Article By:

Taylor, Andy F. S. Macaulay Institute, University of Aberdeen, Aberdeen, United Kingdom.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.900136

An obligate association formed between the roots of many plant species, especially trees, and a diverse range of soil fungi. The fungi and the finest, terminal root tips interact to form joint organs called ectomycorrhizas (Fig. 1). In ectomycorrhizal (ECM) symbiosis, the fungi exchange soil-derived nutrients for carbohydrates from the host plant. Nutrient uptake into the host is enhanced by the efficient spatial exploitation of the soil by the fungi and via access to nutrients, particularly organic sources, which would not be directly available to the plant. The percentage of root tips converted to ectomycorrhizas is usually close to 100%, which means that the belowground absorptive surfaces of most ECM plants are effectively isolated from the soil environment by a 30–80-micrometers (μm)-wide layer of fungal tissue (the mantle) [Fig. 2]. Nutrients and water taken up by the ECM trees and any carbon that enters the soil environment from the tree roots must pass through this structure. Consequently, by occupying the interface between the soil and the absorptive root surface, the ECM symbiosis can have a considerable influence not only on the nutrition of the host trees but also upon the soil environment in which they grow. See also: Forest soil; Fungi; Mutualism; Mycorrhizae; Root (botany)

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