Soluble carbohydrates of red pine (Pinus resinosa) mycorrhizas and mycorrhizal fungi

In the field, the concentrations of several soluble carbohydrates in mycorrhizas of red pine varied seasonally. Fructose, glucose, sucrose and trehalose concentrations were negatively correlated with soil temperature, while myo-inositol and mannitol concentrations were positively correlated. The patterns for the concentrations of fungal carbohydrates (trehalose and mannitol) were consistent with their previously-reported functions. Trehalose may serve as a storage carbohydrate, accumulating during the winter when host carbohydrate is plentiful and when fungal growth is reduced. In contrast, mannitol may serve a translocatory role, increasing in concentration in warmer months when fungal growth is more rapid and when sporocarps are formed. The carbohydrates of six species of ectomycorrhizal fungi grown at room temperature and at reduced temperatures were also analysed to determine the extent to which seasonal variation in concentrations of fungal carbohydrates of mycorrhizas may be due to fungal acclimation to temperature. Variation in carbohydrate concentration occurred both among fungal species and due to cooling treatment. The variation due to cooling was relatively small, generally less than the variation among species, and less than the seasonal variation observed in field-collected mycorrhizas. This suggests that seasonal variation in the fungal carbohydrate trehalose in mycorrhizas could possibly be due to shifts in host carbohydrate supply rather than to independent shifts by the fungi in response to temperature. Production of a distinct pattern of carbohydrate concentrations by different ectomycorrhizal fungi suggests that fungal carbohydrates may be of taxonomic significance. This was further demonstrated using discriminant analysis of fungal carbohydrates.