The Structure and Function of the Ericoid Mycorrhizal Root

The uniformity of structure of the anatomically simple ericoid mycorrhizal hair root across many plant families, including Epacridaceae, that are diagnostic of heathland, and the characteristic restriction of its occurrence to nutrient impoverished soils, are both emphasized. The extent to which the predominantly ascomycetous fungal endophytes of these roots are taxonomically related is discussed. In functional terms, the role of the mycorrhiza in nutrient mobilization is evaluated on the basis of experiments with ericaceous plants. The considerable saprotrophic potential of endophytes such as Hymenoscyphus ericae is demonstrated and the significance of this for nitrogen (N) and phosphorus (P) nutrition of plants growing in sclerophyllous litter of high C:N and C:P ratios is discussed. The need to carry out experiments using epacrid hosts is stressed. It is considered that the selective provision, by ericoid mycorrhizal fungi, of access to recalcitrant organic sources of N and P facilitates niche differentiation and so contributes to the maintenance of species diversity which is a feature of heaths with a significant component of epacrid or ericaceous plants particularly in the southern hemisphere.