The 15N natural abundance and N concentrations of fruit
bodies from 70 species (23 genera) of ectomycorrhizal
fungi found in boreal forests are presented. Large intraspecific and
intrageneric differences were found, e.g. 8·3‰ 15N
in the species Dermocybe crocea and 12·6‰ in the
genus
Cortinarius. In addition, significant differences in both
δ15N and %N were found between different parts of fruit
bodies, with cap material giving consistently higher
values. Proteins and amino acids were enriched by
9·7±0·4‰
(mean±1 SE) relative to chitin, irrespective of the
part of the fruit body examined. Chitin had δ15N values
similar to that of plant hosts. The higher δ15N and %N
values of the caps than of the stipes probably reflect a higher portion
of
proteins and amino acids in the caps. The
δ15N 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 flux of N from the soil through the fungus to
the plant, make it difficult, at present,
to make inferences about sources of N based on δ15N values
alone. No effect of sample drying temperature on δ15N
values of fungal material was detected.