The study measured and compared the rates of total soil respiration, heterotrophic respiration, and autotrophic respiration under short-term nitrogen addition conditions. Additionally, it examined the effects of environmental factors on the respiration rates of heterotrophic and autotrophic processes within the soils of young forests. The aim was to reveal the implications of prospective nitrogen deposition for soil respiration and carbon cycling in young forests in Northeast China. The research focused on an artificially mixed young forest in Shulan, Northeast China, where three simulated nitrogen addition treatments were designed: a control group (CK, 0 kg/hm²), a low nitrogen group (LN, 50 kg/hm²), and a high nitrogen group (HN, 100 kg/hm²). During the growing seasons spanning 2021 to 2023, measurements of soil respiration rates, soil pH, and fine root biomass density were conducted. Relationships between soil total respiration and its components under different nitrogen addition treatments were analyzed, considering factors such as soil temperature, soil pH, and fine root biomass density. Results: (1) Nitrogen enrichment substantially affected the soil respiration components without markedly altering the proportional contributions of heterotrophic and autotrophic respiration. Specifically, low nitrogen addition stimulated soil respiration and increased the respiration rates of its components, whereas high nitrogen addition suppressed total soil respiration primarily by enhancing soil acidification and restricting heterotrophic respiration rates. (2) Nitrogen addition altered the soil environment, including soil temperature, volumetric water content at a 5 cm depth, and soil pH, as well as the growth of plant fine roots. Specifically, low nitrogen addition significantly promoted the growth of saplings and increased fine root biomass density in the soil. In contrast, high nitrogen addition had an inhibitory effect on both sapling growth and fine root biomass density. Both nitrogen addition treatments caused soil acidification, but the impact was more pronounced with high nitrogen addition. (3) Soil temperature, fine root biomass density, and soil pH exhibited significant positive correlations with soil respiration rates. Notably, soil temperature had a significant exponential relationship with both total soil respiration and heterotrophic respiration rates, accounting for 20.2% to 45.4% of the variation in soil respiration rates and serving as the primary influencing factor. The results highlighted the significant impact of nitrogen addition on soil respiration rates, primarily through its effects on the soil environment and plant fine root biomass density. Among the various nitrogen addition treatments, low nitrogen addition notably increased soil respiration rates, whereas high nitrogen addition led to a decrease. This indicated that future changes in nitrogen deposition could exert a considerable impact on soil carbon cycling. During the experimental period, variations in soil volumetric water content were found to be a poor predictor of soil respiration rates. Additionally, nitrogen addition intensified soil acidification, which was contrary to previous research findings. Notably, neither nitrogen addition, soil pH, nor fine root biomass density had a significant effect on the contribution rates of soil heterotrophic respiration. This suggests that further exploration and explanation in this area are necessary.