title: Isotopic evidence indicates saprotrophy in post-fire Morchella in Oregon and Alaska.
abstract: We assessed the nutritional strategy of true morels (genus Morchella) collected in 2003 and 2004 in Oregon and Alaska, 1 or 2 y after forest fires. We hypothesized that the patterns of stable isotopes (δ(13)C and δ(15)N) in the sporocarps would match those of saprotrophic fungi and that radiocarbon (Δ(14)C) analyses would indicate that Morchella was assimilating old carbon not current-year photosynthate. We compared radiocarbon and stable isotopes in Morchella with values from concurrently collected foliage, the ectomycorrhizal Geopyxis carbonaria (Alb. & Schwein.) Sacc., the saprotrophic Plicaria endocarpoides (Berk.) Rifai, and with literature to determine isotopic values for ectomycorrhizal or saprotrophic fungi. Geopyxis, Plicaria and Morchella, respectively, were 3‰, 5‰ and 6‰ higher in 13C than foliage and 5‰, 7‰ and 7‰ higher in (15)N. High (15)N enrichment in Morchella indicated that recent litter was not the primary source for Morchella nitrogen, and similar (13)C and (15)N enrichments to Plicaria suggest that Morchella assimilates its carbon and nitrogen from the same source pool as this saprotrophic fungus. From radiocarbon analyses Morchella averaged 11 ± 6 y old (n = 19), Plicaria averaged 17 ± 5 y old (n = 3), foliage averaged 1 ± 2 y old (n = 8) and Geopyxis (n = 1) resembled foliage in Δ(14)C. We conclude that morels fruiting in post-fire environments in our study assimilated old carbon and were saprotrophic.
authors.affiliation: Earth Systems Research Center, University of New Hampshire, Durham, New Hampshire 03824 Erik.Hobbie@unh.edu.
authors.forename: Erik A
authors.initials: EA
authors.lastname: Hobbie
authors.affiliation: Earth Systems Research Center, University of New Hampshire, Durham, New Hampshire 03824.
authors.forename: Samuel F
authors.initials: SF
authors.lastname: Rice
authors.affiliation: Department of Forest Ecosystems and Society, Oregon State University, 2160 NW Beechwood Place, Corvallis, Oregon 97330.
authors.forename: Nancy S
authors.initials: NS
authors.lastname: Weber
authors.affiliation: US Department of Agriculture, Forest Service, Pacific Northwest Research Station, Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, Oregon 97331.
authors.forename: Jane E
authors.initials: JE
authors.lastname: Smith
mesh_terms: D000413:Alaska; D001203:Ascomycota / Q000378:metabolism*; D005390:Fires; D020387:Food Chain; D007554:Isotopes / Q000032:analysis; D009922:Oregon
chemical_list: D007554:Isotopes
keywords: carbon sources; ectomycorrhizal; life history; post-fire; saprotrophy