δ15N natural abundance may directly disclose perturbed soil when related to C:N ratio.

ABSTRACT

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 CN 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 CN ratio from 6.4 to 48.1. The δ(15)N values were linearly proportional to the inverse of the square root of the CN ratio (R(2) = 0.79). At any particular CN 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 CN 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.