This study investigated the relationships between ericoid mycorrhizal endophytes of the Ericaceae (Northern Hemisphere) and the Epacridaceae (Australia). Over 200 fungi were isolated from the roots of two species of Epacridaceae from Victoria, Australia. The isolates were divided into 12 groups by morphology on quarter-strength potato dextrose agar. All were slow-growing and most were dematiaceous, but groups varied from white through pink to dark olive. The ITS1–5.8S–ITS2 ribosomal DNA was amplified and sequenced from eight isolates, forming typical ericoid mycorrhizal morphology in Epacris impressa and one nonmycorrhizal isolate. Sequences were compared, by using similarities and maximum-parsimony analysis, with those of Hymenoscyphus ericae (Leotiales) and Oidiodendron species (Hyphomycetes), the most common endophytes of the Ericaceae. Maximum-parsimony analysis produced four clusters: (1) all Oidiodendron species (at least 90% similarity); (2) all five Victorian dark grey-olive isolates (at least 96% similarity); (3) one Victorian isolate and Cistella grevillei (88% similarity); (4) two light-coloured Victorian isolates and H. ericae (81% similarity). This suggests that these isolates from the Epacridaceae do not belong to the same species as those forming ericoid mycorrhiza in the Ericaceae.

In the ‘F’ horizons of acid mor-humus soils of heathland ecosystems, mycorrhizal roots of the dominant ericaceous species form a large fraction of the soil biomass. Rapid turnover of these roots provides the potential for recycling of substantial amounts of nitrogen contained in their fungal and plant components. Here, we first determine the amount of N in the biomass of ericoid roots growing in heathland and show it to constitute a large proportion of total soil N. In order to assess the accessibility of this N to ericaceous plants, experiments were then conducted using aseptically produced shoot and root necromass of Vaccinium macrocarpon Ait., the roots being grown with or without mycorrhizal colonization. These materials were provided as sole nitrogenous substrates in growth experiments using the ericoid mycorrhizal fungus Hymenoscyphus ericae (Read) Korf & Kernan in pure culture and V. macrocarpon in the mycorrhizal (M) or non-mycorrhizal (NM) condition as test organisms. The experiments were designed to test the hypothesis that the N contained in these substrates can be mobilized by the mycorrhizal endophyte. The ability of the endophyte to utilize the substrates was determined by measuring fungal yields and by assessing the presence of its extra-cellular protease and chitinase enzymes. Transfer of N to the host by the endophyte was determined through measurements of plant yield and tissue N contents. H. ericae produced a significantly greater yield on shoot and mycorrhizal root necromass than on non-mycorrhizal root necromass. The extra-cellular enzymes protease and chitinase were produced by the fungus when grown on the M root necromass. The fungus also transferred N to the host plant, up to 76% of N contained in the substrate being found in M plants whereas less than 5% was present in their NM counterparts.

The presence of host plants was found to be a key determinant of soil infectivity for endophytes of epacrids growing in south-west Australian jarrah forest carrying a sparse epacrid understorey. A comparable Banksia woodland with higher density of epacrids showed more uniform levels of infective endophytes, presumably because of closer overlap of host-supported patches of endophyte. Disturbed sites in jarrah forest, in which topsoil had been recently returned following bauxite mining, initially showed extremely low endophyte infectivity, probably due to disruption of the hyphal network, absence of host plants and/or increased competition from soil micro-organisms antagonistic to the endophytes. As the system stabilized and epacrids recruited and grew, inoculum potential of the soil re-established and by 12 yr it equalled that of adjacent undisturbed native forest. At disturbed sites with sparsely distributed adult members of the Epacridaceae, endophyte inoculum proved to be adequate only directly adjacent to the epacrids and declined steeply to negligible levels at only 40 cm radially distant from a host plant. The significance of live epacrid root systems on survival of endophyte inoculum in Banksia woodland was examined following removal of shoots of adult plants of the endemic epacrid, Leucopogon conostephioides DC. Coincident with demise of roots of the detopped plants, endophyte inoculum potential of closely adjacent soil declined by 50% during the growing season. However, the effect was short lived and infectivity rose the following year to equal that of undisturbed adjacent woodland as mycelial matrices supported by neighbouring epacrids invaded the depleted study areas.