Mycorrhizal effectiveness of Rhizopogon spores recovered from faecal pellets of small forest-dwelling mammals

Abstract

Mature basidiomes of the hypogeous ectomycorrhizal fungi Rhizopogon vinicolor and R. truncatus were fed to three species of mycophagous mammals in captivity. Spores which passed through the digestive tract of the mammals were isolated from faecal pellets. The metabolic activity and mycorrhizal effectiveness of these spores was assessed. Flouricene-diacetate (a vital stain) was used to assess spore metabolic activity. Mycorrhizal effectiveness was determined by inoculating Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) seedlings with spore slurries. The same assays were performed on spores isolated from uneaten basidiomes. Spores from R. vinicolor were viable after passage through the gut of each mammal species but the digestive process did not substantially enhance or detract from the ability of spores to form ectomycorrhizas relative to spores from uneaten basidiomes. Spores recovered from faeces of Californian red-backed vole (Clethrionomys californicus) and Townsend's chipmunk (Tamias townsendii) had significantly higher metabolic activity than spores from uneaten basidiomes and those recovered from northern flying squirrel (Glaucomys sabrinus) faeces. Spores from eaten and uneaten basidiomes of R. truncatus failed to show any signs of metabolic activity and largely failed to form ectomycorrhizas on seedlings. The reasons for this are unclear but we suggest that germination of spores from this fungus may depend upon other factors. Our findings add to the growing body of literature demonstrating that spores of at least some species of hypogeous fungi remain viable after passage through the digestive tract of mycophagous animals.