HR: 0830h
AN: B31D-0336    [PDF]
TI: Differentiating Nitrification and Denitrification Sources of Nitrous Oxide Based on the Isotopomeric Composition
AU: * Sutka, R L
EM: sutkarob@msu.edu
AF: Michigan State University, Department of Geological Sciences, East Lansing, MI 48824 United States
AU: Pitt, A J
EM: pittadam@msu.edu
AF: Michigan State University, Department of Geological Sciences, East Lansing, MI 48824 United States
AU: Ostrom, N E
EM: ostromn@msu.edu
AF: Michigan State University, Department of Geological Sciences, East Lansing, MI 48824 United States
AU: Ostrom, P H
EM: ostrom@msu.edu
AF: Michigan State University, Department of Geological Sciences, East Lansing, MI 48824 United States
AU: Gandhi, H
EM: gandhiha@msu.edu
AF: Michigan State University, Department of Geological Sciences, East Lansing, MI 48824 United States
AU: Breznak, J
EM: breznak@msu.edu
AF: Michigan State University, Department of Microbiology and Molecular Genetics, East Lansing, MI 48824 United States
AU: Bergsma, T
EM: tbergsma@kbs.msu.edu
AF: Michigan State University, Kellogg Biological Station, East Lansing, MI 48824 United States
AB: Atmospheric concentrations of nitrous oxide (N$_{2}$O) are steadily increasing primarily due to microbial activity in the environment. This has prompted efforts to apportion microbial sources of N$_{2}$O to specific microbial processes. We investigated the isotopomeric composition N$_{2}$O as a possible aid in differentiating microbial production mechanisms. Isotopomer refers not only to the isotopic abundance of N$_{2}$O ($\delta$$^{15}$N and $\delta$$^{18}$O), but also to the $^{15}$N abundance within each of the nitrogen atoms comprising this molecule. In the linear N$_{2}$O molecule, the central atom is referred to as alpha ($\alpha$) and the terminal nitrogen atom is referred to as beta ($\beta$). The site preference refers to the difference between $\delta$$^{15}$N$^{\alpha}$ and $\delta$$^{15}$N$^{\beta}$. We conducted experiments with pure bacterial cultures and agricultural soil mesocosms. Four microbial pathways for the production of N$_{2}$O were investigated including hydroxylamine oxidation via autotrophic nitrifiers and methane oxidizers and nitrite reduction via denitrifiers and autotrophic nitrifiers. We used concentrated cell suspensions of a nitrifier ({\it Nitrosomonas europaea}), a methane oxidizer ({\it Methylococcus capsulatus} Bath) and a denitrifier that lacks N$_{2}$O reductase ({\it Pseudomonas chlororaphis}). The average site preference of N$_{2}$O produced by the oxidation of hydroxylamine by M. {\it capsulatus} Bath (5.5 +/- 3.5 per mil) and N. {\it europaea}(-2.3 +/- 1.9 per mil) was significantly different. Nitrous oxide produced by the reduction of nitrite by N. {\it europaea} and P. {\it chlororaphis} had a site preference of -8.3 +/- 3.6 per mil and -8.1 +/- 3.4 per mil, respectively. These results demonstrate that site preference can distinguish N$_{2}$O produced by hydroxylamine oxidation by two distinct organisms. Furthermore, N$_{2}$O derived by hydroxylamine oxidation differed significantly from that derived from nitrite reduction by the same nitrifying organism. Soil mesocosm experiments were used to determine that consumption of N$_{2}$O did not change the isotopomeric composition. Since the site preference of the distinct pathways differ and N$_{2}$O reduction does not affect site preference, we have demonstrated that isotopomers can be used to apportion the production of N$_{2}$O by nitrification and denitrification in agricultural systems.
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting