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

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 belowground buds and aboveground 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 yr-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 that community bud and shoot densities declined with
increasing N amount under biannual addition frequency but remained stable
under monthly addition frequency. However, community MLI was unchanged
under biannual addition frequency, but increased with increasing N amount
under monthly 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 application 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 monthly N addition, while shoot
density remained unchanged regardless of addition frequency. These
demographic responses did not alter aboveground 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.