Increasing atmospheric nitrogen (N) deposition would change soil N availability, and thereby changes N₂O production and emission from N-limiting forest soils. However, it is still unclear about the contrasting effects of different N ion (i.e., oxidized NO₃^--N and reduced NH₄⁺-N) deposition on soil N₂O emission in boreal forests. In the present study, a cold-temperate coniferous forest in the Great Khingan region was selected for conducting the manipulative N addition experiment, including three forms of N fertilizers (NH₄Cl, KNO₃, and NH₄NO₃) and four rates of N addition (0, 10, 20, and 40 kg N hm^-2 a^-1). Soil-atmospheric N₂O exchanging fluxes were measured four times per month using static chamber-gas chromatography. Simultaneously, soil temperature, moisture, and inorganic N contents were measured to explore how the main factors affect soil N₂O emission. The results showed that the types and doses of N addition significantly changed soil inorganic N contents, and the accumulation of soil NH₄⁺-N was significantly higher than that of soil NO₃^--N due to N addition. N addition increased N₂O emission from the boreal forest soil, and the NH₄NO₃ addition treatments promoted high soil N₂O fluxes, with an increase of 442% to 667%, which was higher than the global average (134%). There were positive correlations between soil N₂O fluxes and soil temperature, and between soil N₂O fluxes and soil NH₄⁺-N contents in the litter layer. Soil N₂O fluxes were driven by soil temperature, followed by soil NH₄⁺-N contents in the litter layer. These findings suggest that atmospheric N deposition cannot lead to a significant soil NO₃^--N leaching and loss in boreal forests over the short term, but it can significantly promote soil N₂O emission. Furthermore, exogenous NH₄⁺ and NO₃^- inputs into boreal forests have synergic effects on soil N₂O emission, which should be distinguished in N cycle and balance in terrestrial ecosystems using ¹⁵N tracer methods in the future.