Saprotrophic fungi represent an important resource for a number of fungivorous and omnivorous soil animals,but little is known about the patterns of isotopic fractionation by soil fungi.We grew five common species of saprotrophic microfungi in laboratory cultures on simple artificial substrate based on carbohydrates derived either from C3orC4 plants.Fungal cultures were kept at15,20 or 25 C. Isotopic composition of carbon(13C/12C) and nitrogen(15N/14N) in bulk fungal tissue was determined after 11,21and32days.The fractionation of carbon and nitrogen stable isotopes was species-specific, but generally did not differ in C3-andC4-based growth media.The Zygomycete Mucor plumbeus did not differ in d13C from the carbon source used,though Ascomycetes(Alternaria alternata, Cladosporium cladosporioides, Trichoderma harzianum and Ulocladium botrytis) were depleted in heavy carbon relative to the carbon source by 0.5–0.9%. Three species were significantly depleted in 15N relative to the sodium nitrate that was used as a single source of nitrogen.In all species, d15N but not d13C tended to increase with the age of fungal colonies.The effect of temperature on d15N was weak and in consistent in different species.In contrast,all fungi except T. harzianum accumulated more 13C at25 1C than at 15 1C. The overall variation in the isotopic signatures of saprotrophic fungi growing in identical conditions reached 8%0 for d15N and 2.5%0 for d13C due to species-specific differences in the isotopic fractionation and the age of individual fungal colonies.This variation should be incorporated into the interpretation of the isotopic composition of fungivorous soil animals.
doi:10.1016/j.pedobi.2009.11.001