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MYCORRHIZAL VS. SAPROTROPHIC STATUS OF FUNGI: THE ISOTOPIC EVIDENCE
Citation:
Hobbie, E. A., N. S. Weber, AND J. M. Trappe. MYCORRHIZAL VS. SAPROTROPHIC STATUS OF FUNGI: THE ISOTOPIC EVIDENCE. NEW PHYTOLOGIST. Blackwell Science, Inc., Malden, MA, 150:601-610, (2001).
Description:
Relative abundance of carbon (C) and nitrogen (N) isotopes in fungal sporocarps may prove useful in unraveling fungal roles in ecosystems. Sporocarps of known mycorrhizal or saprotrophic genera were collected from a single site in Oregon and isotopically compared to foliage, litter, and soils collected from the same site. On average, mycorrhizal fungi were 2.9??1.7? depleted in 13C and 5.1??2.9? enriched in 15N relative to saprotrophic fungi. Brown-rot and white-rot fungi did not differ isotopically in 13C, suggesting that white-rot fungi incorporated little 13C-depleted, lignin-derived carbon. In a separate experiment, the 13C of saprotrophic fungi and their woody substrates were compared, with the fungi enriched on average 3.5??0.3? relative to wood. Measurements of 13C of cellulose extracted from foliage and litter samples were combined with the above data to derive relationships of isotopic fractionation occurring in 15N and 13C among soils, fungi, and plants. The clear differences in 15N and 13C values between saprotrophic and mycorrhizal fungi were then used to determine the trophic strategies of archived specimens of the Pezizales from the western U.S. The phylogenetic pattern of trophic strategies was compared to a recent study of molecular phylogeny of these taxa to determine to what degree trophic strategies were evolutionarily conserved. In across-site studies, it appears that 13C measurements are better indicators of trophic strategies than 15N measurements, presumably because of large variations in 15N that depend on site history and climate. In general, 13C measurements suggested that mycorrhizal or saprotrophic status was conserved within families of the Pezizales, with the Discinaceae and Morchellaceae being largely saprotrophic, and the Helvellaceae and Tuberaceae mycorrhizal. In contrast to prior speculations, the disturbance fungi Aleuria and Sowerbyella both appeared mycorrhizal. Isotopic measurements are a powerful new tool to exami