Mowing Modulates Nitrogen Saturation Thresholds of Aboveground Productivity in a Meadow Steppe via Dominant Species and Stoichiometric Regulation

Determining how nitrogen (N) addition and mowing jointly affect aboveground net primary productivity (ANPP) is crucial for assessing the sustainable utilization of grassland ecosystems under increasing N deposition. However, it remains unclear how these two factors together influence the thresholds of ANPP and N saturation as well as the underlying stoichiometric mechanisms. In a typical meadow steppe in Inner Mongolia, we established a field experiment with a gradient of N addition (0, 2, 5, 10, 20, and 50 g N m −2 year −1 ) and mown treatment. We analyzed their effects on ANPP and explored the roles of dominant species and their elemental stoichiometry (C:N, C:P, and N:P ratios) in driving the N saturation threshold. Our results showed that N addition rates significantly increased ANPP in a nonlinear manner. Mowing increased the N saturation threshold for ANPP from 11.7 to 16.7 g N m −2 year −1 . The Simpson dominance index, the absolute and relative biomass of Leymus chinensis exhibited similar response trends in response to increasing N addition, suggesting that changes in the dominance of this species are closely associated with ANPP responses under N enrichment. Whole aboveground plant tissue N concentrations and C:N ratios also exhibited nonlinear responses to N addition rates, with saturation thresholds. When N addition exceeded 10 g N m −2 year −1 , the total effects of N addition, N concentration, and C:N ratio on ANPP declined, collectively driving ANPP to saturation. These findings provide new evidence for understanding how N addition and mowing influence ANPP and N saturation threshold in grassland ecosystems, offering a threshold‐based framework for formulating rational N management and grassland utilization strategies. Practically, by integrating findings from this study, we cautiously recommend that no more than 10 g N m −2 year −1 be applied to balance productivity enhancement and biodiversity conservation in sustainable grassland management.