Isotopic signatures and trophic status of Ramaria

The genus Ramaria is composed of several subgenera that often correspond to specific trophic strategies. Because carbon and nitrogen isotopes can be used to assess fungal trophic status and nitrogen sources, we accordingly carried out an extensive survey of isotopic patterns in archived specimens of Ramaria from Germany and other locations. Isotopic patterns in species generally corresponded to subgeneric affiliations and to the range of different potential substrates, with fungi fruiting on wood and litter (subgenera Asteroramaria and Lentoramaria) much lower in δ¹⁵N (≈−3‰) than ectomycorrhizal taxa (≈12‰) (subgenus Ramaria) or taxa fruiting on soil (≈13‰) (subgenus Echinoramaria). Conversely, fungi fruiting on wood and litter were higher in δ¹³C (−23‰) than those fruiting on soil (≈−27‰), with ectomycorrhizal fungi intermediate (≈−24.5‰). Fungi colonizing mineral soil horizons were about 3‰ enriched in ¹⁵N relative to those colonizing both mineral and organic horizons. The high δ¹⁵N and low δ¹³C signatures of taxa fruiting on soil remains unexplained. The high degree of fidelity of isotopic signatures with subgeneric classifications and life history traits suggests that sporocarps are good integrators of patterns of carbon and nitrogen cycling for specific taxa. Archived specimens represent a useful trove of life history information that could be mined without requiring extensive supporting isotopic data from other ecosystem pools.