Nitrogen deposition affects the productivity of planted and natural forests by modulating forest climate and community functional traits

With global climate change, atmospheric nitrogen deposition is intensifying. However, the specific impact of nitrogen deposition on forest ecosystem productivity remains unclear. Additionally, due to the differences in the origin of planted and natural forests, it is not clear whether the effects of nitrogen deposition on different types of forest functions are consistent. This study utilizes data from 384 planted forests and 541 natural forests in China, collected through field surveys and literature research from 2005 to 2020, to explore the specific effects of nitrogen deposition on the productivity of natural and planted forests. The results show that the levels of six forms of nitrogen deposition (gaseous NO2, HNO3, NH3, and particulate NH4+, NO3- as well as total dry nitrogen deposition (TN)) are significantly higher in planted forests than in natural forests (P < 0.001). With increasing nitrogen deposition, the NPP (Net Primary Productivity) of planted forests significantly linear increased, while that of natural forests significantly decreased. Compared to natural forests, nitrogen deposition contributes more to the spatial variability of NPP in planted forests. Under the background of nitrogen deposition, forest climate factors (MAP, MAT) and soil phosphorus content have a positive effect on the NPP of natural and planted forests, while soil pH and soil nitrogen content have a negative effect. MAT is the dominant factor for the spatiotemporal variability of NPP in natural forests, while community functional traits (Trait PC1) are the dominant factor for the spatial variability of NPP in planted forests. Nitrogen deposition can not only directly affect the NPP of natural and planted forests but also indirectly through its impact on plant functional traits, forest climate, and soil nutrient factors. Our findings reveal the specific impacts of nitrogen deposition on the productivity of natural and planted forests, providing data support for effective forest management. •Nitrogen deposition in planted forests significantly exceeds that in natural forests P < 0.001•With rising nitrogen deposition, planted forests' NPP significantly rises, but natural forests' decreases (P < 0.001).•Nitrogen deposition not only directly affects forests' NPP but also indirectly through its impact on leaf traits, climate, and soil nutrients.