Inhibitory effect of nitrogen deposition on soil denitrifying activity in a subtropical forest

Aims Nitrogen (N) deposition, as a global environmental threat, has exhibited profound impacts on the nutrient cycling and ecosystem functioning of natural forests. However, little is known about how different N deposition levels influence the diversity, community composition, and structural complexity of the denitrifying bacteria. Methods Here we set up a field experiment to investigate the impacts of N deposition (0, 50, 100, and 150 kg N ha(-1) yr(-1)) on soil denitrification and underlying mechanisms in a subtropical forest. Results The denitrifying activity was significantly decreased by the high level of N deposition compared to the control. The abundances of denitrification functional genes were commonly increased by the lower rate of N deposition, while significantly suppressed by the higher levels of N deposition. Non-metric multidimensional scaling ordinations showed that the denitrifier assemblages were evidently clustered based on N deposition levels and soil layers, regardless of sampling seasons. Structural equation modeling analysis indicated that the denitrifier abundance and community composition directly explained 62% of the total variance of denitrifying activity. Soil pH exhibited profound effects on the denitrifier abundance, diversity, and community composition. Nitrogen deposition affected the denitrifier co-occurrence networks with increased complexity under the highest level of N deposition compared to the control. Conclusions This study emphasized the crucial role of denitrifier community composition in shaping soil denitrifying activity under N deposition, highlighting the importance of incorporating the dynamics of denitrifier communities together with soil environmental parameters into the models for accurately predicting ecosystem processes in forests.