Abstract: Atmospheric nitrogen (N) deposition includes inorganic N (IN) and organic N (ON). IN enrichment trends to reduce species richness greater than ON, likely lowering ecosystem stability, as species richness and ecosystem stability are usually positively related. However, previous field experiments evaluating N deposition effects on ecosystem stability used either IN or ON additions, likely biasing results. We assessed the effects of IN:ON ratios (0:10, 3:7, 5:5, 7:3, and 10:0) at 10 g N m^–2 year^–1 on the temporal stability of plant community productivity in a temperate meadow grassland using 6-year (2017–2022) data from a long-term N addition experiment established in 2014. Species richness, species asynchrony, population stability, and dominant species stability were investigated to explore mechanisms underlying community stability changes. We found that IN:ON ratio showed no significant effect on community stability, although all N addition significantly reduced community stability (averaged 26.7% reduction). However, IN decreased species richness more than ON (54.1% reduction in 10:0 vs. 31.8% reduction in 0:10). IN:ON ratio showed no significant effect on species asynchrony, population stability or dominant species stability. Species asynchrony and dominant species stability were both positively related to community stability, while population stability showed no significant association. It implies that species asynchrony and dominant species stability maintained community stability across IN:ON ratios. Overall, our findings suggest that, despite IN reducing species richness greater than ON, it may be reasonable to assess N deposition effects on ecosystem stability using either IN or ON addition.

Key words: dominant species, grassland, nitrogen deposition, nitrogen composition, population stability, species asynchrony