δ 15 N natural abundance may directly disclose perturbed soil when related to C:N ratio

RATIONALE 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. Copyright © 2013 John Wiley & Sons, Ltd.