Grassland bud and shoot demography depend on both amount and frequency of nitrogen addition

Abstract The amount and frequency of atmospheric nitrogen (N) deposition have dramatically increased, profoundly influencing population regeneration, community composition and productivity in grasslands. Perennial species in grasslands primarily grow and expand clonally, yet it remains unclear how their below‐ground buds and above‐ground shoots respond to the amount and frequency of N deposition. We conducted a long‐term (2008–2022) N addition experiment in a semiarid grassland. The experiment included nine addition amounts (0, 1, 2, 3, 5, 10, 15, 20 and 50 g N m −2 year −1 ) and two addition frequencies: low frequency (twice per year) and high frequency (once per month). This allowed us to assess the interactive effects of N addition amount and frequency on bud density, shoot density and the ratio of bud to shoot density (meristem limitation index, MLI) in semiarid grasslands. We found a significant interaction between N addition amount and frequency on community bud and shoot densities. Community bud and shoot densities declined with increasing N amount under low addition frequency but remained stable under high addition frequency. However, community MLI was unchanged under low addition frequency but increased with increasing N amount under high addition frequency. Both N addition amount and frequency significantly altered the composition of community buds and shoots, with more pronounced effects under low versus high addition frequency. Bud and shoot densities and MLI declined with N amount under both addition frequencies for bunchgrasses. In contrast, rhizomatous grasses exhibited increased bud density and MLI under high N addition frequency, while shoot density remained unchanged regardless of addition frequency. These demographic responses did not alter above‐ground net primary productivity (ANPP) but shifted community composition toward greater dominance of rhizomatous grasses under N addition. Synthesis. These results suggest that grassland bud and shoot responses to N deposition depend on both the deposition amount and frequency. Commonly used low frequency N addition experiments may lead to inaccurate plant demographic and community responses to chronic N deposition.