Anthropogenic impacts on natural nitrogen isotope variations in Pinus sylvestris stands in an industrially polluted area Original Research Article

Natural variations of the nitrogen isotopes 15N/14N (Δ15N values) and the N concentrations of one-year-old needles from 7–12-year-old pine trees (Pinus sylvestris L.) were determined on 27 sites in the heavily polluted Leipzig-Halle region (former GDR). At three selected sites measurements were repeated over a period of 2 years. N concentrations and Δ15N values in different needle age classes were compared at the three sites. The Δ15N values of the N in the humus layer and the potential plant available N in the Ah horizon of the local soil were determined. The 15N/14N isotope ratios (Δ15N values) of one-year-old pine needles in the region of Leipzig-Halle were found to vary depending on their specific location by a factor of up to one order of magnitude (−9.6‰ to + 0.4‰). N concentrations in one-year-old pine needles varied between 0.71 and 1.38 mmol eq N g dw−1. Pine stands with positive or slightly negative Δ15N values and high N concentrations in one-year-old needles were concentrated around the cities of Leipzig and Halle and in the industrial areas. More negative Δ15N values and lower N concentrations in one-year-old pine needles were found on sites at greater distances from the industrial agglomerations, mainly in the NE forested part. Site specific differences in the Δ15N values of the N in the humus layer from three selected sites were similar to those found for the needles. No site specific differences, however, were found for the Δ15N values of the water soluble nitrogen fraction from the mineral soil horizons of the same sites.