title: δ15N natural abundance may directly disclose perturbed soil when related to C:N ratio.
abstract: BACKGROUND
  Natural abundance δ(15) N values in soil samples analysed by isotope ratio mass spectrometry (IRMS) are often used to confirm a perturbation after it has been indicated by other parameters. We propose a concept of how δ(15)N values may a priori indicate a perturbation.
  
  
  METHODS
  We analysed the δ(15)N values and C:N ratios of 102 soil samples from five regions in northern Eurasia by using an elemental analyser coupled to an isotope ratio mass spectrometer.
  
  
  RESULTS
  Unperturbed samples ranged in δ(15)N values from -4.8 to 9.7 ‰ and in C:N ratio from 6.4 to 48.1. The δ(15)N values were linearly proportional to the inverse of the square root of the C:N ratio (R(2) = 0.79). At any particular C:N ratio, 94 % of the δ(15)N values of the unperturbed samples were within ±2.4 ‰, but 72 % of perturbed samples had values outside this range.
  
  
  CONCLUSIONS
  The δ(15)N natural abundance values, when related to the C:N ratios, may readily indicate perturbation of soil N cycling prior to other, more demanding investigations into related processes and extend the current use of IRMS in ecosystem research.
authors.affiliation: Department of Environmental Sciences, University of Basel, Basel, Switzerland. franz.conen@unibas.ch
authors.forename: Franz
authors.initials: F
authors.lastname: Conen
authors.forename: Mikhail V
authors.initials: MV
authors.lastname: Yakutin
authors.forename: Nina
authors.initials: N
authors.lastname: Carle
authors.forename: Christine
authors.initials: C
authors.lastname: Alewell