HR: 0800h
AN: B21D-0920    [Abstracts]
TI: Sources of Variability in the Stable Carbon Isotopic Signatures of Fungal Methyl Chloride
AU: * Shaw, S L
EM: slshaw@nature.berkeley.edu
AF: Department of Environmental Science and Management, UC Berkeley, Hilgard Hall #3110, Berkeley, CA 94720 United States
AU: Henn, M R
EM: mhenn@duke.edu
AF: Department of Biological Sciences, Duke University, Box 90338, Durham, NC 27708 United States
AU: Chapela, I H
EM: ichapela@nature.berkeley.edu
AF: Department of Environmental Science and Management, UC Berkeley, Hilgard Hall #3110, Berkeley, CA 94720 United States
AU: Conrad, M S
EM: msconrad@lbl.gov
AF: Center for Isotope Geochemistry, Earth Science Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 United States
AU: Goldstein, A H
EM: ahg@nature.berkeley.edu
AF: Department of Environmental Science and Management, UC Berkeley, Hilgard Hall #3110, Berkeley, CA 94720 United States
AB: The atmospheric budgets of the stratospheric ozone-depleting methyl halides are currently poorly constrained by known sources and sinks. Use of an isotopic mass balance technique may clarify these budgets by constraining the magnitudes of unknown or previously estimated fluxes, or by suggesting potential additional sources or sinks. The utility of this approach will depend not only on being able to measure the relevant source signatures and loss kinetic isotope effects contributing to their atmospheric budgets, but also on our ability to assess the variability in these terms. We investigated sources of variability in the isotopic signatures associated with one component of the methyl chloride budget: production by wood-rot fungi. Using controlled laboratory cultures, measurements of the stable carbon isotopic signatures of growth medium, biomass, respired CO2, CH3Cl, and the carbon mass balance were made over the growth cycle of Inonotus andersonii. Fractionations between medium and biomass (1 permil), as well as biomass and gases (5 permil), were nearly constant during exponential and stationary phase growth. However, the signatures varied across fungal species and type of substrate. A survey of several Phellinus and Inonotus strains grown on C3 plant-derived medium resulted in CH3Cl with delta13C values ranging from -48.2 to -26.4 permil. Other species, including freshly isolated P. robustus and I. andersonii monocultures produced CH3Cl, but in insufficient quantities to determine the isotopic signature. Similarly, field samples of live and blue oak woods rotting through action of these two species did produce CH3Cl when augmented with 10 mM KCl/water solution, but in insufficient quantities to determine isotopic signature. Growth of I. andersonii on C4 plant-derived medium resulted in a larger depletion in the delta13C value of CH3Cl as compared to substrate (18 permil) than for C3 plant-derived medium (7 permil). The amount of available oxygen also plays a role in the capability of the fungi to produce CH3Cl. The range of isotopic signatures measured in this study, while large, is not unique enough from other known CH3Cl sources to change the average global signature of sources to the atmosphere.
DE: 4870 Stable isotopes
DE: 0315 Biosphere/atmosphere interactions
DE: 0322 Constituent sources and sinks
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting