HR: 1340h
AN: B43A-0892    [Abstracts]
TI: Isotopomers as a method for differentiating between bacterial and fungal production of nitrous oxide
AU: * Sutka, R L
EM: robin.sutka@gvinstruments.co.uk
AF: GV Instruments, Crewe Road, Manchester, M23 9BE, United Kingdom
AU: Adams, G
EM: gadams@msu.edu
AF: Michigan State University, 181 Wilson Road, East Lansing, MI 48824, United States
AU: Ostrom, N
EM: ostromn@msu.edu
AF: Michigan State University, 203 Natural Sciences, East Lansing, MI 48824, United States
AU: Ostrom, P
EM: ostrom@msu.edu
AF: Michigan State University, 203 Natural Sciences, East Lansing, MI 48824, United States
AB: In order to study the importance of fungi to nitrous oxide (N2O) production in the environment it is critical to have a non-intrusive method for differentiating between fungal and bacterial N2O production. Site preference (SP), the difference in d15N between the central and outer N atoms in N2O, has been used to differentiate between bacterial nitrification and denitrification. In this study we compare the SP, d15N and d18O of N2O produced by the two best-studied fungal denitrifiers, Fusarium oxysporum and Cylindrocarpon tonkinense, to data from our previous bacterial studies. Both d18O and SP values remained fairly constant during the course of nitrite reduction which likely reflects isotopic exchange with water in the case of d18O and conservative behavior in SP that has been observed previously (Sutka et al., 2006). We observed a wide range of fractionation factors for fungal denitrification, -74.7 to -6.6 ‰, and non-linear behavior indicating that fractionation was controlled by more than one step. We interpret the small degree of fractionation as reflecting fractionation during diffusion and the more negative values as being controlled by enzymatic fractionation. Data from this and our previous study of bacterial production (Sutka et al., 2006) reveals that N2O produced via nitrification by fungi can be differentiated from N2O produced by bacterial denitrification primarily on the basis of d18O. The site preference of N2O produced by F. oxysporum and C. tonkinense was 37.1 ± 2.5 ‰ and 36.9 ± 2.8 ‰, respectively. These results indicate that isotopomers can be used as a basis for differentiating bacterial and fungal denitrification. Our work further reveals the role that fungal and bacterial nitric oxide reductases have in determining site preference during N2O production.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0400 BIOGEOSCIENCES
DE: 0402 Agricultural systems
DE: 0469 Nitrogen cycling
DE: 0490 Trace gases
SC: Biogeosciences [B]
MN: 2007 Fall Meeting