Abstract. The impact of atmospheric nitrogen (N) deposition on nitrous oxide (N₂O) emissions in forest ecosystems is still unclear. Our study assessed the direct contribution of N deposition to N₂O emissions in temperate forests exposed to chronic high N depositions using a ¹⁵N labelling technique. In a Norway spruce stand (Picea abies) and in a beech stand (Fagus sylvatica) at the Solling, Germany, we used a low concentrated ¹⁵N-labelled ammonium-nitrate solution to simulate N deposition. Nitrous oxide fluxes and ¹⁵N isotope abundances in N₂O were measured using the closed chamber method combined with ¹⁵N isotope analyses. Emissions of N₂O were higher in the beech stand (2.6 ± 0.6 kg N ha⁻¹ yr⁻¹) than in the spruce stand (0.3 ± 0.1 kg N ha⁻¹ yr⁻¹). We observed a direct effect of N input on ¹⁵N-N₂O emissions, which lasted for less than three weeks and was mainly caused by denitrification. No further increase in ¹⁵N enrichment of N₂O occurred during a one-year experiment, which was probably due to immobilisation of deposited N. The annual emission factor for N₂O from deposited N was 0.1% for the spruce stand and 0.6% for the beech stand. Standard methods used in the literature applied to the same stands grossly overestimated emission factors with values of up to 25%. Only 6–13% of the total N₂O emissions were derived from direct N depositions. Whether the remaining emissions resulted from accumulated anthropogenic N depositions or native soil N, could not be distinguished with the applied methods. The ¹⁵N tracer technique is a useful tool, which may improve estimates of the current contribution of N deposition to N₂O emissions.