The influence of low concentrations of ozone (100 ppb) on nitrogen incorporation and the specific activity of superoxide dismutase (SOD) in 3-yr-old cloned spruce seedlings was studied under controlled conditions (potted plants in fumigation chambers). For the determination of nitrogen uptake, ¹⁵N tracer experiments were performed using emission spectrometric isotope analysis. Superoxide dismutase (SOD) activity was determined by inhibition of formazan formation.

Low doses of ozone led to a significant increase in both NO₃-N uptake from the soil and in specific SOD activity. The results show that stable isotope ¹⁵N tracer technique analysis is a suitable tool for the investigation of potential impacts of air pollutants on the nitrogen metabolism of plants.