Understory N deposition amplifies the contrasting effects of organic and inorganic N on soil N2O emissions in a Moso bamboo forest

Enhanced anthropogenic nitrogen (N) deposition has intensified nitrous oxide (N 2 O) emissions from forest soils, thereby exacerbating global warming. However, most previous studies have relied solely on understory N addition for N deposition simulation, overlooking the influence of the forest canopy. Moreover, the majority of these studies have focused exclusively on inorganic N, with limited research addressing organic N deposition. Here, a three-year in situ study was performed in a Moso bamboo ( Phyllostachys edulis ) forest to differentiate the influences of different N forms (inorganic vs. organic) under different N deposition simulation approaches (canopy vs. understory). Our findings disclosed that the annual cumulative soil N 2 O emissions under understory inorganic N deposition were 25.1% higher than that under understory organic N deposition. This discrepancy was mainly caused by the greater mineral N supply, gene abundances and lower pH under understory inorganic N deposition. In contrast, no significant difference was observed between canopy organic and inorganic N deposition. For different simulation approaches, annual cumulative soil N 2 O emissions were always markedly higher under understory N deposition compared to canopy N deposition, but prolonged N deposition diminished the differences between the two approaches. This was mainly attributed to the narrowed discrepancy in nitrifying enzyme activities between the two approaches. The N 2 O emission factor from N deposition (EF 4 ) under canopy N deposition (0.76%) was lower compared to understory N deposition (1.63%). Using EF 4 derived only from understory deposition would lead to an overestimation of soil N 2 O emissions from Chinese bamboo forests by ∼2.29 Gg yr −1 . Overall, our findings demonstrate that understory-only N addition experiments may substantially overestimate regional N 2 O emissions, particularly when inorganic N is applied, and underscore the necessity of incorporating canopy processes in future assessments of atmospheric N deposition impacts.