Natural ¹⁵N abundance in fruit bodies of ectomycorrhizal fungi from boreal forests

Abstract

The ¹⁵ N 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‰¹⁵ N in the species Dermocybe crocea and 12.6‰ in the genus Cortinarius. In addition, significant differences in both δ¹⁵ N 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 δ¹⁵ N values similar to that of plant hosts. The higher δ¹⁵ N and %N values of the caps than of the stipes probably reflect a higher portion of proteins and amino acids in the caps. The δ¹⁵ 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 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 δ¹⁵ N values alone. No effect of sample drying temperature on δ¹⁵ values of fungal material was detected.