ECTOMYCORRHIZAL DIVERSITY ON BETULA-PAPYRIFERA AND PSEUDOTSUGA-MENZIESII SEEDLINGS GROWN IN THE GREENHOUSE OR OUTPLANTED IN SINGLE-SPECIES AND MIXED PLOTS IN SOUTHERN BRITISH-COLUMBIA

The inoculum potential and diversity of the ectomycorrhizal fungal com munity usually decrease on a site following logging. The objective of this study was to determine if planting a mixture of tree species foll owing logging retains a higher diversity of ectomycorrhizal fungi than planting a single species. Paper birch (Betula papyrifera Marsh.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were planted eithe r alone or in mixture and in different proportions and densities on ea ch of three sites in the southern interior of British Columbia. Ectomy corrbizal types were characterized following detailed morphological ex amination on 12 seedlings per plot at 4, 16, and 28 months following o ut planting (field bioassay). Thelephora, E-strain, Rhizpogon (for Dou glas-fir only), Mycelium radicis atrovirens, and Cenococcum mycorrhiza e were the most abundant. The Thelephora mycorrhizae decreased in domi nance over the sampling period from 82 to 41% of ectomycorrhizae on bi rch and from 26 to 15% on Douglas-fir. Rhizopogon mycorrhizae remained consistently abundant an Douglas-fir roots (36% of mycorrhizae at 4 m onths to 37% at 28 months). By 28 mouths, 91% of birch and 56% of Doug las-fir mycorrhizae were types common to the two species. This has imp ortant implications for possible nutrient of carbon transfer between t he two species. At 16 (P = 0.068) and 28 months (P = 0.088) following outplanting, the evenness of the ectomycorrhizal community on Douglas- fir root systems was higher in mixed than in single-species plots. Ric hness (number of ectomycorrhizal types) and Simpson's diversity index per seedling were not affected by tree mixture treatments. Planting de nsity did not affect richness, evenness, or diversity. The ectomycorrh izae that developed an Douglas-fir or birch seedlings grown in the gre enhouse in soils from these sites were very similar to those that deve loped in the field. This demonstrates that greenhouse bioassays can be used to predict which types of ectomycorrbizae will form on seedlings grown on disturbed sites, at least for the first few years following outplanting.