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We used molecular genetic methods to test two hypotheses, (i) that host plant specificity among ectomycorrhizal fungi would be common in a closed-canopy, mixed Pinus contorta-Picea engelmannii forest in Yellowstone National Park and (ii) that specificity would be more common in the early successional tree species, P. contorta, than in the invader, P. engelmannii. We identified 28 ectomycorrhizal fungal species collected from 27 soil cores. The proportion of P. engelmannii to P. contorta ectomycorrhizae was nearly equal (52 and 48%, respectively). Of the 28 fungal species, 18 composed greater than 95% of the fungal community. No species was associated exclusively with P. contorta, but four species, each found in only one core, and one species found in two cores were associated exclusively with P. engelmannii. These fungi composed less than 5% of the total ectomycorrhizae. Thus, neither hypothesis was supported, and hypothesized benefits of ectomycorrhizal specificity to both trees and fungi probably do not exist in this system. Ectomycorrhizal (EM) mutualisms (interactions betweenfungi and plant roots) provide plants with increased access to resources, such as water, nitrogen, and phosphorus (1,18,21,31). They also protect plants from disease (3, 17), from chemical extremes, such as high pH, and from heavy-metal contamination (10, 11) and can facilitate establishment of pioneer plants in harsh environments, such as mine tailings (13,38). While EM fungi are functionally similar in their roles as mycorrhizae (4), individual species may differ in physiological functions, e.g., the ability to degrade litter (16,26); in responses to environmental conditions, such as soil temperature and moisture (4, 12); and in the specificity of interactions with host plants (28).EM specificity is thought to influence ecosystem function and to benefit both plant and fungal partners (reviewed by Molina et al. [28]). For example, specificity could enhance carbon transfer to the fungal partner (15) and could benefit an early-successional plant by protecting portions of its root system from mycorrhizal parasitism by invading tree species. Specificity could also partition soil resources and provide "exclusive avenues" for nutrient transfer from the soil to the plant host, and because EM associations are required by many plants for survival, specificity may limit the ability of some plants to migrate and establish and thus influence the rates and directions of ecosystem change. Therefore, assessment of EM specificity patterns is critical to our understanding of ecosystem function, though it is yet unclear whether this phenomenon is common in nature.Early specificity experiments indicated that most EM fungi could establish symbioses with most EM plants (27). Closer examination of specificity patterns reveals that the interaction phenomenon is complex and that combinations of specificity and nonspecificity occur simultaneously to influence ecosystem function and successional processes (28). Fruiting body assessments and long-term fungal comm...

Effects of clear-cutting on the ectomycorrhizal (EM) fungus community in a Pinus contorta Dougl. ex Loud. forest near Yellowstone National Park, Wyoming, U.S.A., were assessed using molecular techniques. Samples were taken by soil core in both undisturbed and clear-cut sites by randomized block design. Species overlap was compared between clear-cut and undisturbed sites and ascomycete-basidiomycete ratio was determined, using PCR-RFLP methods. Fifty species of EM fungi were detected in the clear-cut sites, the most common being Cenococcum geophilum Fr., Suillus sp., a member of the suilloid group, a Russulaceae species, and a Thelephoraceae species. Sixty-six species were detected in the undisturbed sites, which were dominated by a Suilloid species, a Tricholomataceae species, Cortinarius sp., and Cenococcum geophilum. Species composition in the clear-cut sites differed significantly from that in the undisturbed sites (P = 0.0001). However, 9 of the 14 species most commonly found in the clear-cut sites were also found in the undisturbed sites, but in much lower abundance, while species rank curves of both stand types mirrored each other. There were no significant differences in species richness, root-tip abundance, or ascomycete-basidiomycete ratio between the clear-cut and undisturbed sites. However, species richness was lower in the clear-cut sites than in the undisturbed sites. An overall loss of species richness after clear-cutting and significant changes in species composition indicate that clear-cutting can negatively alter the EM fungal community, and this may have profound effects on ecosystem function.Key words: ectomycorrhizae, community structure, clear-cutting, molecular techniques.

Molecular genetic methods were used to determine whether artificial defoliation affects ectomycorrhizal (EM) colonization, EM fungal species richness, and species composition in a mixed Pinus contorta (lodgepole pine)/Picea engelmannii (Engelmann spruce) forest in Yellowstone National Park, Wyoming. All lodgepole pines in three replicate plots were defoliated 50%, while Engelmann spruce were left untreated. This was done to determine how defoliation of one conifer species would affect EM mutualisms of both treated and neighboring, untreated conifers. The results indicated no significant effect on either EM colonization (142.0 EM tips/core in control plots and 142.4 in treatment plots) or species richness (5.0 species/core in controls and 4.5 in treatments). However, the relative abundance of EM of the two tree species shifted from a ratio of approximately 6:1 without treatment (lodgepole EM:spruce EM), to a near 1:1 ratio post-treatment. This shift may be responsible for maintaining total EM colonization and species richness following defoliation. In addition, EM species composition changed significantly post-defoliation; the system dominant, an Inocybe species, was rare in defoliation plots, while Agaricoid and Suilloid species that were rare in controls were dominant in treatments. Furthermore, species of EM fungi associating with both lodgepole pine and Engelmann spruce were affected, which indicates that changing the photosynthetic capacity of one species can affect mycorrhizal associations of neighboring non-defoliated trees.

We complied a 5.8S nuclear ribosomal gene sequence database for animals, plants, and fungi using both newly generated and GenBank sequences. We demonstrate the utility of this database as an internal check to determine whether the target organism and not a contaminant has been sequenced, as a diagnostic tool for ecologists and evolutionary biologists to determine the placement of asexual fungi within larger taxonomic groups, and as a tool to help identify fungi that form ectomycorrhizae.