Mycorrhizal fungi of aspen forests: Natural occurrence and potential applications

Native mycorrhizal fungi associated with aspen were surveyed on three soil types in the north-central Rocky Mountains. Selected isolates were tested f or the ability to enhance aspen seedling growth in vitro. Over 50 species o f ectomycorrhizal fungi occur with Populus tremuloides in this region, prim arily basidiomycete fungi in the Agaricales. Almost one-third (30%) were ub iquitous with aspen and were found on all three soil types. Over one-third (37%) were restricted to the acidic, sandy soil of the smelter-impacted But te-Anaconda area, revealing a subset of fungi that tolerate these condition s. Mycorrhizal fungi were screened for their ability to enhance aspen growt h and establishment. Of nine selected isolates, all but one increased the b iomass of aspen seedlings 2-4 times. Stem diameter, height, and number of r oot tips increased with inoculation of some fungi. The native species Paxil lus vernalis, Tricholoma scalpturatum, Hebeloma mesophaem, Thelephora terre stris, and Laccaria spp. were most promising for further study. Pisolithus tinctorius (available as commercial inoculum) formed prolific mycorrhizae a nd stimulated plant growth but does not occur with aspen in the Rocky Mount ains.