HR: 0800h
AN: B21D-0916    [Abstracts]
TI: Radiocarbon-based assessments of the role of fungal species in decomposition
AU: * Treseder, K K
EM: treseder@uci.edu
AF: University of California Irvine, Earth System Science Dept and Ecology and Evolutionary Biology Dept, Irvine, CA 92697 United States
AU: * Treseder, K K
EM: treseder@uci.edu
AF: University of Pennsylvania, Dept of Biology, Philadelphia, PA 19104 United States
AU: Lansing, J L
EM: jllansin@yahoo.com
AF: University of Pennsylvania, Dept of Biology, Philadelphia, PA 19104 United States
AU: Choi, N
EM: nchoi@uci.edu
AF: University of California Irvine, Earth System Science Dept and Ecology and Evolutionary Biology Dept, Irvine, CA 92697 United States
AB: We used natural radiocarbon signatures to determine if species of decomposer fungi specialize on different pools of organic matter in the soil. Specifically, we examined natural radiocarbon signatures of mushrooms to estimate the average integrated age of C compounds metabolized by individual species. This method takes advantage of rapid changes in atmospheric radiocarbon signatures of carbon dioxide since the early 1960s, when several years of above-ground weapons testing produced a spike in atmospheric $\Delta$$^{14}$C. This signature has been rapidly declining since then. Therefore, we can measure radiocarbon signatures of tissues and determine the time at which their component C was originally photosynthesized. We conducted our study in a fire chronosequence in boreal forests near Delta Junction, Alaska. The chronosequence includes sites burned in severe fires during the summers of 1999, 1987, and 1956. A "control" site was established in a neighboring 80 yr old black spruce forest. In 2002, we collected mushrooms each week from six 50 m long transects in each site. Mushrooms were weighed and assigned to species based on morphological and molecular analyses (i.e. typing by restriction fragment length polymorphism). Saprotrophic species could be distinguished from ectomycorrhizal species based on $^{15}$N and $^{13}$C signatures. Specifically, saprotrophic mushrooms had $\delta$$^{15}$N values less than 4.66\permil and $\delta$$^{13}$C values greater than -23.1\permil. We then measured the $\Delta$$^{14}$C values of mushrooms from 20 of the most abundant saprotrophic species. Radiocarbon signatures varied widely among species, implying that species take up C from compounds that range in turnover time. For example, fungi of the Polyporaceae often grow on woody debris in our sites, and their $\Delta$$^{14}$C signatures (-65.1 to 15.0\permil) indicate the use of several decades-old, recalcitrant C. These fungi are known to possess the necessary enzymes for lignin degradation, so lignocellulose is a likely C source. In contrast, an unidentified saprotrophic gilled mushroom displayed a $\Delta$$^{14}$C signature close to that of the atmosphere (77.5\permil), which would occur if that species were taking up recently-photosynthesized, labile C. Species that incorporate older C (7 to 14 yr old C and $>$50 yr old C) were most abundant in the two youngest sites, potentially because woody debris from dead black spruce trees is common in both. Most fire-related woody debris had decomposed after 46 years, which may underlie the decline at that stage in populations of fungal species that use older C. Fungal species that use young C (0 to 7 yr old C) tend to proliferate in the intermediate-aged sites, where quaking aspens produce large quantities of litter. Our results suggest that fungal species perform different functions in decomposition in boreal forests, and that radiocarbon analyses can be used to examine the influence of fungal community composition on soil carbon dynamics.
DE: 1694 Instruments and techniques
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting