Carbon use, nitrogen use, and isotopic fractionation of ectomycorrhizal and saprotrophic fungi in natural abundance and 13C-labeled cultures


Stable isotopes in fruit bodies from field studies have been used to infer ectomycorrhizal or saprotrophic status and to understand carbon and nitrogen use, but few controlled culture studies have correlated source and fungal isotopic patterns. Here, we measured natural abundances of 15N and 13C in ten strains of ectomycorrhizal fungi and seven strains of saprotrophic fungi grown on agar with three different primary carbon sources: glucose, glucose plus malt extract, and potato dextrose agar. Eight fungal strains were also grown using position-specific, 13C-labelled glucose (C-1 through C-6 labelled). Most fungi resembled nitrogen sources in δ15N, suggesting that growth on agar media minimizes isotopic fractionation on uptake compared to growth on liquid media, and that in general saprotrophic and mycorrhizal fungi process nitrogen similarly. Saprotrophic fungi were more depleted in 13C than ectomycorrhizal fungi on all media, presumably because of assimilation of 13C-depleted, agar-derived carbon. Results on 13C-enriched glucose indicated that saprotrophic fungi obtained up to 45% of their carbon from the agar substrate. Fungi generally incorporated the individual carbon atoms of glucose in the order, C-4 < C-1


Earth Systems Research Center

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Mycological Research



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© 2004 British Mycological Society. Published by Elsevier Ltd. All rights reserved.