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Diversity of ectotrophic mycobionts on outplanted seedlings of two oak species (Quercus rubra and Quercus prinus) was estimated at two sites in mature mixed forests in the southern Appalachian Mountains by sequencing nuclear 5.8S rRNA genes and the flanking internal transcribed spacer regions I and II (ITS). The seedlings captured a high diversity of mycorrhizal ITS-types and late-stage fungi were well represented. Total richness was 75 types, with 42 types having a frequency of only one. The first and second order jackknife estimates were 116 and 143 types, respectively. Among Basidiomycetes, tomentelloid/thelephoroid, russuloid, and cortinarioid groups were the richest. The ascomycete Cenococcum geophilum was ubiquitously present. Dominant fungi included a putative Tuber sp. (Ascomycetes), and Basidiomycetes including a putative Craterellus sp., and Laccaria cf. laccata. Diversity was lower at a drier high elevation oak forest site compared to a low elevation mesic cove--hardwood forest site. Fungal specificity for red oak vs. white oak seedlings was unresolved. The high degree of rarity in this system imposes limitations on the power of community analyses at finer scales. The high mycobiont diversity highlights the potential for seedlings to acquire carbon from mycelial networks and confirms the utility of using outplanted seedlings to estimate ectomycorrhizal diversity.

Sporocarps of Basidiomycetes belonging to families containing some species known to form ectomycorrhizae were enumerated in 12 plots (16 × 16 m) subdivided into contiguous 2 × 2 m quadrats during the growing seasons of 1981 – 1983. Plots were distributed equally between homogeneous second-growth red spruce stands and heterogeneous northern hardwood stands in southeastern West Virginia. A few major species accounted for most of the abundance, while most species fruited rarely, but abundance and phenology varied broadly from year to year, apparently in response to rainfall and temperature. Fungal species composition, spatial frequency, and sporocarp density in the two forest types differed as would be expected in light of the symbiotic nature of the fungi and trees considered. Of 54 fungal species encountered over 3 years, 19 occurred exclusively in spruce plots, 27 occurred exclusively in hardwood plots, and 8 occurred in both forest types. In both forest types, approximately 40% of the species were Russulaceae. Species frequency and sporocarp abundance were greater in spruce plots than in hardwood plots. The Shannon–Wiener index, the dominance–diversity curve, the species–area curve, and ordination confirmed that fungal species richness, equitability, and diversity were greater in the mixed-hardwood plots, which hosted many rare fungal species, than in the single-species coniferous plots, which were dominated by a few ubiquitous fungal species.

Assessing genetic variation within populations and genetic exchange between populations requires an understanding of the distribution and abundance of individual genotypes within the population. Previous workers have used somatic incompatibility testing to distinguish dones or individuals in natural populations of ectomycorrhizal fungi. However, somatic incompatibility tests performed with isolates of Suilus granulatus from a natural population revealed a lack of transitiveness, which brought into question the validity of this method. Subsequent studies of genetic identity of these isolates, using randomly amplified polymorphic DNA (RAPD) markers, conclusively showed that somatically compatible isolates are not necessarily genetically identical. RAPD marker analysis is more reliable and provides higher resolution of genotype distribution in natural populations than does somatic incompatibility testing. This is of particular importance in populations of organisms such as ectomycorrhizal fungi in which the mating systems are incompletely known.