[delta] super(15)N natural abundance may directly disclose perturbed soil when related to C:N ratio

RATIONALE Natural abundance [delta] super(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 [delta] super(15)N values may a priori indicate a perturbation. METHODS We analysed the [delta] super(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 [delta] super(15)N values from -4.8 to 9.7 ppt and in C:N ratio from 6.4 to 48.1. The [delta] super(15)N values were linearly proportional to the inverse of the square root of the C:N ratio (R super(2)=0.79). At any particular C:N ratio, 94 % of the [delta] super(15)N values of the unperturbed samples were within plus or minus 2.4 ppt, but 72 % of perturbed samples had values outside this range. CONCLUSIONS The [delta] super(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. Copyright [copy 2013 John Wiley & Sons, Ltd.