HR: 0830h
AN: B31E-0361    [PDF]
TI: Stable Carbon Isotopic Signatures and Fractionations Occurring During Fungal Biosynthesis of Methyl Chloride
AU: * Shaw, S L
EM: slshaw@nature.berkeley.edu
AF: Ecosystem Sciences Division, Department of Environmental Science, Policy, and Management, University of California, Berkeley, 151 Hilgard Hall #3110, Berkeley, CA 94720 United States
AU: Henn, M R
EM: mh@nature.berkeley.edu
AF: Ecosystem Sciences Division, Department of Environmental Science, Policy, and Management, University of California, Berkeley, 151 Hilgard Hall #3110, Berkeley, CA 94720 United States
AU: Chapela, I H
EM: ichapela@nature.berkeley.edu
AF: Ecosystem Sciences Division, Department of Environmental Science, Policy, and Management, University of California, Berkeley, 151 Hilgard Hall #3110, Berkeley, CA 94720 United States
AU: Conrad, M E
EM: msconrad@lbl.gov
AF: Center for Isotope Geochemistry, Earth Sciences Division, E.O. Lawrence Berkeley National Laboratory, Building 70A 4418, 1 Cyclotron Road, Berkeley, CA 94720 United States
AU: Goldstein, A H
EM: ahg@nature.berkeley.edu
AF: Ecosystem Sciences Division, Department of Environmental Science, Policy, and Management, University of California, Berkeley, 151 Hilgard Hall #3110, Berkeley, CA 94720 United States
AB: Methyl halides are responsible for approximately 25% of the equivalent chlorine involved in stratospheric ozone depletion, yet quantitative understanding of their atmospheric budgets is still incomplete. The use of an isotopic mass balance to constrain these budgets is currently being investigated. The utility of this approach will depend not only on being able to measure the source signatures and loss kinetic isotope effects contributing to their atmospheric budgets, but also in our ability to assess the variability in these terms. Natural methyl halide sources and sinks due to microbial cycling, combined with their large and variable associated isotopic effects, should have discernable effects on the global atmospheric signature of these gases. Thus, we have begun investigating the isotopic signatures of methyl halides produced by fungi, and the fractionations occurring during their biosynthesis, using controlled laboratory cultures. Measurements of the stable carbon isotopic signatures of growth medium, biomass, respired CO$_{2}$, CH$_{3}$Cl, and the carbon mass balance were made over the growth cycle of {\it Inonotus andersonii}, a wood-rot fungus previously shown to emit methyl halides. Resulting CH$_{3}$Cl $\delta^{13}$C signatures were enriched by approximately 10\permil as compared to those previously reported for {\it Phellinus pomaceus}, another wood-rot species$^{1}$. Fractionations between substrate and biomass \{$\epsilon_{s-b}$\}, as well as biomass and gases \{$\epsilon_{b-g}$\}, were nearly constant during exponential and early stationary phase growth. Biomass was depleted by 1\permil compared to the $^{13}$C malt extract medium, and CH$_{3}$Cl and CO$_{2}$ were depleted by up to 5\permil compared to the biomass, implying the bulk of the final CH$_{3}$Cl signature is determined during CH$_{3}$Cl synthesis and not during uptake of the carbon substrate. However, the magnitude of these fractionations, and the direction of $\epsilon_{s-b}$, probably depends on the complexity of the substrate. Additionally, a survey of isotopic signatures of CH$_{3}$Cl produced by several fungal species on C3 and C4 substrates was begun to quantify likely variability in the natural source signature. \\ $^{1}$ Harper, DB., R.M. Kalin, J.T.G. Hamilton, and C. Lamb, Carbon Isotope Ratios for Chloromethane of Biological Origin: Potential Tool in Determining Biological Emissions, {\it Environ. Sci.Technol.}, 35, 3616-3619, 2001.
DE: 0315 Biosphere/atmosphere interactions
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
DE: 4840 Microbiology
DE: 4870 Stable isotopes
SC: Biogeosciences [B]
MN: 2003 Fall Meeting