ABSTRACT
Since the earliest report by Frank (1885), in which he documented the benefit of ectomycorrhizal fungi for their plant hosts, ecologists have been intrigued by the functional role of these fungi. Ectomycorrhizal fungi are known to play a principal role in supplementing the nutrient and water requirements of their plant hosts. Although these fungi are found on a relatively small number (ca. 3%) of plant taxa (Meyer, 1973), they are disproportionately represented in several plant families (e.g., Pinaceae and Fagaceae) in temperate and boreal forests in the northern hemisphere. The ectomycorrhizal root system is composed of a sheath or mantle of fungal tissue that envelopes the plant root, a network of fungal hyphae within the root (Hartig net), and an extensive ramifying system of hyphae that extends outwardly from the root and into the surrounding soil (extramatrical mycelium). Nutrients are captured by the hyphal network and transferred to the plant host in exchange for carbon (Finlay et al., 1989; Rousseau et al., 1994). In addition to their facilitation of plant nutrient acquisition, ectomycorrhizal fungi are also known to benefit their plant hosts in other ways, including enhanced plant pathogen resistance (Duchesne et al., 1989), increased plant drought tolerance (Parke et al., 1983), and heavy metal protection (Wilkins, 1991; Hartley et al., 1997) (see also, Fomina et al., Chapter 37 and Turneau and Kottke, Chapter 14, this volume
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. Although the overall importance of ectomycorrhizal fungi for plants is widely recognized, it is only recently that investigations have begun to focus on the functional role of ectomycorrhizal communities.
