Species level patterns in 13 C and 15 N abundance of ectomycorrhizal and saprotrophic fungal sporocarps.

•   The natural abundance of 13 C (δ13 C) and 15 N (δ15 N) of saprotrophic and ectomycorrhizal (ECM) fungi has been investigated on a number of occasions, but the significance of observed differences within and between the two trophic groups remains unclear. •   Here, we examine the influence of taxonomy, site, host and time upon isotopic data from 135 fungal species collected at two forest sites in Sweden. •   Mean δ13 C and δ15 N values differed significantly between ECM and saprotrophic fungi, with only a small degree of overlap even at the species level. Among ECM fungi, intraspecific variation in δ15 N was low compared with interspecific and intergeneric variation. Significant variation due to site, year and host association was found. •   At broad scales a number of factors clearly influence δ13 C and δ15 N values making interpretation problematic. We suggest that values are essentially site-specific within the two trophic groups, but that species-level patterns exist potentially reflecting ecophysiological attributes of species. The species is therefore highlighted as the taxonomic level at which most information may be obtained from fungal δ13 C and δ15 N data.