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Bostrom, B; Compstedt, D; Ekblad, A. 2008. Can isotopic fractionation during respiration explain the C-13-enriched sporocarps of ectomycorrhizal and saprotrophic fungi? NEW PHYTOLOGIST. 177(4):1012-1019. Address: Bostrom, B, Univ Orebro, Dept Nat Sci, SE-70182 Orebro, Sweden
The mechanism behind the C-13 enrichment of fungi relative to plant materials is unclear and constrains the use of stable isotopes in studies of the carbon cycle in soils. Here, we examined whether isotopic fractionation during respiration contributes to this pattern by comparing delta C-13 signatures of respired CO2, sporocarps and their associated plant materials, from 16 species of ectomycorrhizal or saprotrophic fungi collected in a Norway spruce forest. The isotopic composition of respired CO2 and sporocarps was positively correlated. The differences in delta C-13 between CO2 and sporocarps were generally small, < +/- 1 parts per thousand in nine out of 16 species, and the average shift for all investigated species was 0.04 parts per thousand. However, when fungal groups were analysed separately, three out of six species of ectomycorrhizal basidiomycetes respired C-13-enriched CO2 (up to 1.6 parts per thousand), whereas three out of five species of polypores respired C-13-depleted CO2 (up to 1.7 parts per thousand; P < 0.05). The CO2 and sporocarps were always C-13-enriched compared with wood, litter or roots. Loss of C-13-depleted CO2 may have enriched some species in C-13. However, that the CO2 was consistently C-13-enriched compared with plant materials implies that other processes must be found to explain the consistent C-13-enrichment of fungal biomass compared with plant materials.
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