15N natural abundance in fruit bodies of different functional groups of fungi in relation to substrate utilization

Natural abundances of N-15 and N concentrations of 34 fruit bodies from 24 species of ectomycorrhizal and saprophytic fungi were measured in a temperate Central European mixed forest stand. The fungi of the two life forms are known to be capable of utilizing different types of N sources (organic N compounds from the humus, inorganic N from the soil and N from litter or wood) differing by their N-15 natural abundance values. Based on the two life forms and the three different N sources, four functional groups of fungi were distinguished: (1) ectomycorrhizal fungi capable of utilizing organic N from the humus; (2) ectomycorrhizal fungi known to depend on inorganic N compounds in the soil; (3) saprophytes capable of utilizing organic N from the humus; and (4) saprophytes utilizing N from dead wood or litter. Large differences were found between species in the delta(15)N values (-3.0 to 3.3 parts per thousand,) and in the N concentrations (0.84 to 6.61 mmol eq N g dw(-1)) of the fruit bodies. In most cases fungi were more enriched in N-15 than their respective bulk N source was. Fungi living in humus, and presumably having access to organic N compounds (groups 1 and 3), were significantly more enriched in N-15 than fungi which are known to depend on inorganic N (e.g. Laccaria, group 2), or fungi living on litter or wood (group 4), irrespective of whether they were ectomycorrhizal or saprophytic species. Fungi living in humus had significantly higher N concentrations than fungi living on litter or wood.