HR: 1340h
AN: B43A-0897    [Abstracts]
TI: Isotopologue fractionation during nitrous oxide reduction in soil
AU: * Jinuntuya, M
EM: jinuntuy@msu.edu
AF: Department of Geological Sciences Michigan State University, 206 Natural Science building, East Lansing, MI 48824, United States
AU: Sutka, R L
EM: sutkarob@msu.edu
AF: GV Instruments, Crewe Road, Wythenshawe, Manchester, M23 9BE, United Kingdom
AU: Ostrom, P H
EM: ostrom@msu.edu
AF: Department of Geological Sciences Michigan State University, 206 Natural Science building, East Lansing, MI 48824, United States
AU: Gandhi, H
EM: gandhiha@msu.edu
AF: Department of Geological Sciences Michigan State University, 206 Natural Science building, East Lansing, MI 48824, United States
AU: Ostrom, N E
EM: ostromn@msu.edu
AF: Department of Geological Sciences Michigan State University, 206 Natural Science building, East Lansing, MI 48824, United States
AB: Reduction of N2O is a challenge to studies using isotope values to resolve global budgets and microbial sources of this critical greenhouse gas. Prior research has demonstrated that the difference in δ15N between the central (α) and outer (β) N atoms in the N2O can be used to distinguish N2O derived from nitrification and denitrification (Sutka et al., 2003; 2006; Toyoda et al., 2005). If the intramolecular distribution of 15N, however, is altered during reduction, apportionments of N2O to nitrification and denitrification will be inaccurate. Isotopologue analyses of N2O within soil mesocosm experiments were used to investigate fractionation during N2O reduction at four different levels of water filled pores space (WFPS) 60, 80, 100 and 110%. Uncultivated successional soils were obtained from the Kellogg Biological Station Long Term Ecological Research Site located in Michigan (KBS LTER). Isotopic enrichment factors (ε) for δ15N, δ18O, δ15Nα and δ15Nβ ranged from -4.2 to -9.0, -12.5 to -23.6, -6.4 to -10.0 and -2.0 to -7.9, respectively. With the exception of SP, lower fractionation factors were observed at higher WFPS demonstrating the importance of diffusion in limiting the expression of enzymatic fractionation. Isotopic discrimination in SP during N2O reduction was small and the ε values varied between -4.5 and 0 ‰. Strong correlations were evident between δ18O and δ15N during reduction and segregation against 18O was 2.7 times greater than 15N. Similarly, 18O was discriminated against approximately 2.0 times more than 15Nα. These relationships (1) provide a definitive means for establishing that isotope effects during reduction are present and (2) may provide a means to determine the source signatures even when reduction occurs.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting