ECTOMYCORRHIZAL FUNGAL COMMUNITY STRUCTURE OF PINYON PINES GROWING IN2 ENVIRONMENTAL EXTREMES

We used molecular techniques to examine the ectomycorrhizal fungal com munity associated with pinyon pine (Pinus edulis) growing in two soil types in a semiarid region of northern Arizona: cinder soils low in nu trients and moisture, and sandy-loam soils with higher moisture and nu trient levels. Pinyon performance (e.g., growth, reproduction, water s tress) has been shown to be markedly lower in cinder than in sandy-loa m environments. Fungal community composition and richness were determi ned using RFLP (restriction fragment length polymorphism) analysis of ectomycorrhizal root tips collected from three sites within each soil type. Several patterns emerged from these analyses. First, communities in both cinder and sandy-loam soils were dominated by one or a few ab undant ectomycorrhizal types, a species abundance pattern common to ma ny plant and animal communities. Second, unlike the pattern for many o ther organisms, ectomycorrhizal fungal type (species) richness was not correlated with measures of ecosystem productivity such as soil nutri ent and moisture levels; cinder and sandy-loam soils had similar numbe rs of ectomycorrhizal fungal types (range of 15-19 fungal types for bo th soil types). Third, soil type and fungal community composition were linked, as cluster analysis demonstrated greater similarity of fungal communities from sites within soil types than between them. Different ial amplification using primers with enhanced specificity for basidiom ycetes indicated that an average of 85% of the ectomycorrhiza found at the sandy-loam sites were members of the subphylum Basidiomycotina, w hereas over half (mean = 52%) of the ectomycorrhiza at the cinder site s were formed by members of other fungal groups, probably the subphylu m Ascomycotina. Fourth, a preliminary survey of 14-45 ectomycorrhizal root tips from each of 20 trees at one cinder site indicated that tree s were dominated by one or a few ectomycorrhizal RFLP types. However, the same RFLP types did not dominate on all trees, and dominant types showed considerable spatial variation. Fifth, the RFLP patterns of som e fungal sporocarps matched those of ectomycorrhizal root tips, but ma ny did not, indicating that many of the ectomycorrhizal fungi at these sites fruit infrequently, whereas other fungi with more abundant spor ocarps may not form ectomycorrhiza. This emphasizes the need to charac terize the ectomycorrhizal communities formed on the plant roots thems elves, rather than characterization based on sporocarps alone, particu larly in arid environments. Finally, the differences in ectomycorrhiza l fungal communities we observed between soil types supported the conc ept that conserving fungal diversity requires conservation of host pla nt species over their entire range, not just typical sites. If future studies corroborate these patterns, our results suggest that abiotical ly stressful environments are important to include in these conservati on efforts.