title: Isotope fractionation factors controlling isotopocule signatures of soil-emitted N₂O produced by denitrification processes of various rates.
abstract: BACKGROUND
  This study aimed (i) to determine the isotopic fractionation factors associated with N2O production and reduction during soil denitrification and (ii) to help specify the factors controlling the magnitude of the isotope effects. For the first time the isotope effects of denitrification were determined in an experiment under oxic atmosphere and using a novel approach where N2O production and reduction occurred simultaneously.
  
  
  METHODS
  Soil incubations were performed under a He/O2 atmosphere and the denitrification product ratio [N2O/(N2 + N2O)] was determined by direct measurement of N2 and N2O fluxes. N2O isotopocules were analyzed by mass spectrometry to determine δ(18)O, δ(15)N and (15)N site preference within the linear N2O molecule (SP). An isotopic model was applied for the simultaneous determination of net isotope effects (η) of both N2O production and reduction, taking into account emissions from two distinct soil pools.
  
  
  RESULTS
  A clear relationship was observed between (15)N and (18)O isotope effects during N2O production and denitrification rates. For N2O reduction, diverse isotope effects were observed for the two distinct soil pools characterized by different product ratios. For moderate product ratios (from 0.1 to 1.0) the range of isotope effects given by previous studies was confirmed and refined, whereas for very low product ratios (below 0.1) the net isotope effects were much smaller.
  
  
  CONCLUSIONS
  The fractionation factors associated with denitrification, determined under oxic incubation, are similar to the factors previously determined under anoxic conditions, hence potentially applicable for field studies. However, it was shown that the η(18)O/η(15)N ratios, previously accepted as typical for N2O reduction processes (i.e., higher than 2), are not valid for all conditions.
authors.affiliation: Thünen Institute of Climate-Smart Agriculture, Federal Research Institute for Rural Areas, Forestry and Fisheries, Bundesallee 50, D-38116, Braunschweig, Germany.|Institute of Geological Sciences, University of Wrocław, Cybulskiego 30, PL-50-205, Wroclaw, Poland.
authors.forename: Dominika
authors.initials: D
authors.lastname: Lewicka-Szczebak
authors.affiliation: Thünen Institute of Climate-Smart Agriculture, Federal Research Institute for Rural Areas, Forestry and Fisheries, Bundesallee 50, D-38116, Braunschweig, Germany.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Well
authors.affiliation: Forschungszentrum Jülich IBG-3, Wilhelm-Johnen-Straße, 52428, Jülich, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Bol
authors.affiliation: Rothamsted Research, Harpenden, AL5 2JQ, UK.
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Gregory
authors.affiliation: Faculty of Science & Environment, University of Plymouth, Plymouth, PL4 8AA, UK.
authors.forename: G Peter
authors.initials: GP
authors.lastname: Matthews
authors.affiliation: Rothamsted Research, North Wyke, Okehampton, EX20 2SB, UK.
authors.forename: Tom
authors.initials: T
authors.lastname: Misselbrook
authors.affiliation: Rothamsted Research, Harpenden, AL5 2JQ, UK.
authors.forename: W Richard
authors.initials: WR
authors.lastname: Whalley
authors.affiliation: Rothamsted Research, North Wyke, Okehampton, EX20 2SB, UK.
authors.forename: Laura M
authors.initials: LM
authors.lastname: Cardenas
mesh_terms: D058440:Denitrification; D013058:Mass Spectrometry; D009584:Nitrogen / Q000032:analysis*; D009585:Nitrogen Dioxide / Q000032:analysis*; D009587:Nitrogen Isotopes / Q000032:analysis; D010103:Oxygen Isotopes / Q000032:analysis; D012987:Soil / Q000737:chemistry; D012988:Soil Microbiology
chemical_list: D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D012987:Soil; D009584:Nitrogen; D009585:Nitrogen Dioxide