δ15N 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.

δ15N natural abundance in permafrost soil indicates impact of fire on nitrogen cycle.

The impact of fire on the nitrogen (N) cycle of natural ecosystems is arguable. Here we report and interpret an observation from boreal ecosystems in the Lena River basin, Sakha Republic (Yakutia), Russian Federation. Different types of permafrost soil (0-30 cm depth) were sampled along transects (60-150 m length) from the forest edge towards the centre of four separate thermokarst depressions under grassland.