The natural abundance of 13C and 15N was measured in basidiocarps of at least 115 species in 88 genera of
ectomycorrhizal, wood-decomposing and litter-decomposing fungi from Japan and Malaysia. The natural
abundance of 13C and 15N was also measured in leaves, litter, soil and wood from three different sites. 15N and 13C
were enriched in ectomycorrhizal and wood-decomposing fungi, respectively, relative to their substrates.
Ectomycorrhizal and wood-decomposing fungi could be distinguished on the basis of their δ13C and δ15N
signatures. Although there was high variability in the isotopic composition of fungi, the following isotope-
enrichment factors (ε, mean±SD) of the fungi relative to substrates were observed:
εectomycorrhizal fungi/litter = 6.1±0.4‰ 15N
εectomycorrhizal fungi/wood = 1.4±0.8‰ 13C
εwood-decomposing fungi/wood = −0.6±0.7‰ 15N
εwood-decomposing fungi/wood = 3.5±0.9‰ 13C
The basis of isotope fractionation in C metabolism from wood to wood-decomposing fungus is discussed.