Nitrogen (N) deposition may trigger soil nutrient imbalances, exerting a profound impact on nutrient cycling and microbial metabolism in forest ecosystems. Due to nutrient deficiencies in the Wudalianchi volcanic lava platform, vegetation restoration in this area is constrained by nutrient conditions. Little is known about whether soil microorganisms in this region exhibit a synergistic response to plant nutrient limitations. To explore the impact of exogenous N addition on microbial metabolic limitations in the soil of the Populus koreana elfin forest—an important pioneer tree community in this region— in-situ simulated N deposition experiments and enzymatic stoichiometry methods were employed to reveal the limitation patterns of carbon, nitrogen, and phosphorus in microbial metabolism. Our results showed that N addition significantly increased the activities of Carbon(C)-, Nitrogen(N)-, and Phosphorus(P)-acquiring enzymes. With the increase of N addition, the activities of the three enzymes first increased and then decreased. The activities of C-acquiring and P-acquiring enzymes were highest under the N3 treatment, while the activity of N-acquiring enzymes was highest under the N2 treatment. (2) The EEAC:P and EEAN:P of soil extracellular enzymes first increased and then decreased, reaching the highest under the N2 treatment, while EEAC:N first decreased, then increased, and then decreased again, reaching the highest under the N3 treatment. (3) The enzyme vector analysis revealed that the vector angles of the soil in all treatments were greater than 45°, and they first decreased and then increased with the increase of the nitrogen addition. (4) Redundancy analysis showed that soil nutrients were the key factors affecting the activities of extracellular enzymes and the stoichiometric ratios of extracellular enzymes. Total phosphorus (TP) had a significant positive correlation with vector length and vector angle (P < 0.05). These findings demonstrate that nitrogen deposition enhances soil extracellular enzyme activity, modulates microbial nutrient limitations, and accelerates soil biogeochemical cycling, providing critical scientific evidence for adaptive management of forest ecosystems under climate change.