The effects of deposited nitrogen (N) on forest ecosystems largely depend on the amount of N retained in the ecosystems and its partitioning among ecosystem pools. However, our understanding of the capacity of tropical plantations to retain deposited N is limited. To evaluate the retention of deposited N in a human-disturbed pine plantation in southern China and compare the result with previous findings in an adjacent old-growth forest, we added ¹⁵N-tracer monthly to the forest floor for one year and determined its recovery in ecosystem compartments four months after the last addition. We monitored ¹⁵N recoveries in soil solution monthly to quantify leaching losses. The pine forest retained about 58 ± 5% of the ¹⁵N-labeled deposited N, which is lower than that reported in the adjacent old-growth forest (72 ± 6%). Both forests experience chronic N deposition (recently measured at 51 kg N ha⁻¹ yr⁻¹) and we attribute the difference in retention to effects of previous disturbance mainly understory and litter harvesting in the pine plantation. Only 3 kg N ha⁻¹ yr⁻¹ (5% of the ¹⁵N-labeled deposited N) out of the measured total leaching (54 kg N ha⁻¹ yr⁻¹) originated from deposited (and labeled) N from the measurement year, suggesting that N leaching is dominated by unlabeled N sources. Furthermore, results from our study and other similar ¹⁵N labeling experiments together show similar patterns of total ecosystem retention of deposited N in tropical and temperate forests, but here we demonstrate a decreasing retention of N with increased N deposition in these forests. Our findings indicate that plantation forests that experience human-disturbance and chronic N deposition have lower N retention compared to old-growth forests, and thus elevated N inputs in such ecosystems can cause risk of hydrological N losses, soil acidification, and freshwater pollution.