NATURAL N-15 ABUNDANCE IN FRUIT BODIES OF ECTOMYCORRHIZAL FUNGI FROM BOREAL FORESTS

The N-15 natural abundance and N concentrations of fruit bodies from 7 0 species (23 genera) of ectomycorrhizal fungi found in boreal forests are presented. Large intraspecific and intrageneric differences were found, e.g. 8.3 parts per thousand N-15 in the species Dermocybe croce a and 12.6 parts per thousand in the genus Cortinarius. In addition, s ignificant differences in both delta(15)N and %N were found between di fferent parts of fruit bodies, with cap material giving consistently h igher values. Proteins and amino acids were enriched by 9.7 +/- 0.4 pa rts per thousand (mean +/- SE) relative to chitin, irrespective of the part of the fruit body examined. Chitin had delta(15)N values similar to that of plant hosts. The higher delta(15)N and %N values of the ca ps than of the stipes probably reflect a higher portion of proteins an d amino acids in the caps. The delta(15)N of mycorrhizal fungi can be a function of the N species used (organic N, NH4+, NO3-), the depth of soil at which the mycelium occurs, and metabolic fractionations. The metabolic fractionations, e.g. potential transaminations during the fl ux of N from the soil through the fungus to the plant, make it difficu lt, at present, to make inferences about sources of N based on delta(1 5)N values alone. No effect of sample drying temperature on delta(15)N values of fungal material was detected.