HR: 0800h
AN: B21A-0852    [Abstracts]
TI: Characterization of Isotopomer Factionation During Consumption of Nitrous Oxide in Pure Culture and Soils
AU: * Ostrom, P H
EM: ostrom@msu.edu
AF: Department of Zoology, 203 Natural Sciences Building Michigan State University, East Lansing, MI 48824-1115 United States
AU: Pitt, A J
EM: pittadam00@hotmail.com
AF: Department of Zoology, 203 Natural Sciences Building Michigan State University, East Lansing, MI 48824-1115 United States
AU: Sutka, R L
EM: sutkarob@msu.edu
AF: Department of Zoology, 203 Natural Sciences Building Michigan State University, East Lansing, MI 48824-1115 United States
AU: Ostrom, N E
EM: ostromn@msu.edu
AF: Department of Zoology, 203 Natural Sciences Building Michigan State University, East Lansing, MI 48824-1115 United States
AU: Fang, L
EM: fli@math.iupui.edu
AF: Department of Mathematical Sciences, IUPUI, Science Building, LD 270D, 402 N. Blackford Street, Indianapolis, IN 46202-3216 United States
AU: Gandhi, H
EM: gandhiha@msu.edu
AF: Department of Zoology, 203 Natural Sciences Building Michigan State University, East Lansing, MI 48824-1115 United States
AB: Previous work in our laboratory demonstrates that the intermolecular distribution of $^{15}$N in the N$_{2}$O molecule can be used distinguish N$_{2}$O derived from nitrification and denitrification in pure culture. However, if consumption of N$_{2}$O during denitrification also imparts an isotopomeric effect, it needs to be accounted for. We determined fractionation factors associated with N$_{2}$O consumption for bulk $^{15}$N, $^{18}$O and site preference (difference in $\delta$$^{15}$N between the central and outer N atoms) in a pure culture of {\it Pseudomonas denitrificans} and soils from the Kellogg Biological Station's Long Term Ecosystem Research Site. The soils derive from a deciduous forest and agricultural fields with different management histories. Soils were collected by auger, homogenized and stored dry prior to initiation of mesocosm experiments. Denitrification in soil mesocosms was promoted by a headspace of pure N$_{2}$ and addition of water to near saturation levels. The isotopic enrichment factor, $\epsilon$ (defined as ($\alpha$-1)*1000)) for $^{15}$N, $^{18}$O and site preference during N$_{2}$O consumption by {\it Pseudomonas denitrificans} was found to be 10.9, 24.8, and 20.3 $\permil$, respectively. Isotopic enrichment factors in soils ranged from 1.0 to 9.2 $\permil$ for $^{15}$N, 2.7 to 24.5 $\permil$ for $^{18}$O, and 6 to 11.9 $\permil$ for the site preference. The enrichment factors in soils were generally less than those observed in pure culture. This likely reflects suppression of fractionation during diffusion in wet soils. Isotopic enrichment factors for nitrogen and oxygen were strongly correlated such that fractionation for $^{18}$O exceeded that associated with $^{15}$N by a factor of 2.5. This relationship may provide a basis to identify N$_{2}$O consumption and account for it in models of source apportionment.
DE: 1030 Geochemical cycles (0330)
DE: 1094 Instruments and techniques
DE: 1610 Atmosphere (0315, 0325)
DE: 0330 Geochemical cycles
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting