title: Dual isotope and isotopomer signatures of nitrous oxide from fungal denitrification--a pure culture study.
abstract: BACKGROUND
  The contribution of fungal denitrification to the emission of the greenhouse gas nitrous oxide (N2O) from soil has not yet been sufficiently investigated. The intramolecular (15)N site preference (SP) of N2O could provide a tool to distinguish between N2O produced by bacteria or fungi, since in previous studies fungi exhibited much higher SP values than bacteria.
  
  
  METHODS
  To further constrain isotopic evidence of fungal denitrification, we incubated six soil fungal strains under denitrifying conditions, with either NO3(-) or NO2(-) as the electron acceptor, and measured the isotopic signature (δ(18)O, δ(15)Nbulk and SP values) of the N2O produced. The nitrogen isotopic fractionation was calculated and the oxygen isotope exchange associated with particular fungal enzymes was estimated.
  
  
  RESULTS
  Five fungi of the order Hypocreales produced N2O with a SP of 35.1 ± 1.7 ‰ after 7 days of anaerobic incubation independent of the electron acceptor, whereas one Sordariales species produced N2O from NO2(-) only, with a SP value of 21.9 ± 1.4 ‰. Smaller isotope effects of (15)Nbulk were associated with larger N2O production. The δ(18)O values were influenced by oxygen exchange between water and denitrification intermediates, which occurred primarily at the nitrite reduction step.
  
  
  CONCLUSIONS
  Our results confirm that SP of N2O is a promising tool to differentiate between fungal and bacterial N2O from denitrification. Modelling of oxygen isotope fractionation processes indicated that the contribution of the NO2(-) and NO reduction steps to the total oxygen exchange differed among the various fungal species studied. However, more information is needed about different biological orders of fungi as they may differ in denitrification enzymes and consequently in the SP and δ(18)O values of the N2O produced.
authors.affiliation: Thünen Institute of Climate-Smart Agriculture, Bundesallee 50, D-38116, Braunschweig, Germany; University of Göttingen, Department of Crop Sciences, Institute of Grassland Science, von-Siebold-Straße 8, D-37075, Göttingen, Germany.
authors.forename: Lena
authors.initials: L
authors.lastname: Rohe
authors.forename: Traute-Heidi
authors.initials: TH
authors.lastname: Anderson
authors.forename: Gesche
authors.initials: G
authors.lastname: Braker
authors.forename: Heinz
authors.initials: H
authors.lastname: Flessa
authors.forename: Anette
authors.initials: A
authors.lastname: Giesemann
authors.forename: Dominika
authors.initials: D
authors.lastname: Lewicka-Szczebak
authors.forename: Nicole
authors.initials: N
authors.lastname: Wrage-Mönnig
authors.forename: Reinhard
authors.initials: R
authors.lastname: Well
mesh_terms: D000693:Anaerobiosis; D002247:Carbon Isotopes / Q000032:analysis*; D058440:Denitrification; D008401:Gas Chromatography-Mass Spectrometry; D006999:Hypocreales / Q000378:metabolism* / Q000502:physiology; D009587:Nitrogen Isotopes / Q000032:analysis*; D009609:Nitrous Oxide / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D009609:Nitrous Oxide