Nitrogen deposition accelerates litter decomposition in peri-urban forests with species-specific responses

Peri-urban forests at the urban-rural interface are increasingly affected by nitrogen (N) deposition driven by urbanization, which alters litter decomposition processes and disrupts nutrient turnover. To investigate the mechanisms underlying these changes, we conducted litterbag experiments in peri-urban forests with four levels of N addition [0 (CK), 30 (N30), 50 (N50), and 100 (N100) kg N ha^-1 yr^-1] to assess the effects of N input on the decomposition of Quercus acutissima and Pinus massoniana leaf litter, including nutrient release, soil chemical properties, microbial biomass, and soil bacterial community composition. The findings indicate that N enrichment significantly enhanced the breakdown of both litter types in peri-urban forests. The highest decomposition rates were observed under the N50 treatment for Q. acutissima and the N100 treatment for P. massoniana, with increases of 30.1 % and 29.9 %, respectively, compared to CK. A significantly higher decomposition constant was recorded for Q. acutissima litter than for P. massoniana, likely due to its lower lignin content and carbon-to-nitrogen ratio. N enrichment also significantly enhanced soil microbial biomass carbon and nitrogen in both stands, thereby promoting litter breakdown. In P. massoniana stands, N input markedly elevated soil nitrate-nitrogen concentration and triggered alterations in bacterial community composition, further contributing to the acceleration of litter decomposition. These findings underscore the importance of integrating litter quality, soil microbial dynamics, and environmental drivers when assessing the ecological impacts of N deposition. Q. acutissima litter exhibited a continuous release of carbon, nitrogen, and phosphorus throughout the decomposition period. In contrast, P. massoniana litter showed net immobilization of nitrogen and phosphorus in the later stage. Overall, this study demonstrates that N addition substantially accelerates litter breakdown in subtropical peri-urban forests. At the same time, the species-specific differences observed highlight the crucial role of plant community composition in regulating litter decomposition and nutrient cycling under urbanization-induced N input, thereby improving predictions of ecosystem functioning and informing management strategies under global change scenarios.