Belowground bud bank depletion constrains productivity recovery in long established perennial pastures despite nitrogen enrichment

Belowground bud banks are the primary source of vegetative regeneration in perennial pastures and may indicate ecosystem regenerative capacity. However, whether bud bank dynamics reflect changes in regeneration potential during pasture development remains unclear. We investigated the responses of belowground bud banks to nitrogen (N) addition in Kentucky bluegrass ( Poa pratensis L.) pastures established for 4, 7, and 13 years. Three N addition levels, 0 g/m² (control), 5 g/m² (Low-N) and 15 g/m² (High-N), were applied to evaluate changes in belowground bud bank density and its relationships with tiller number and aboveground productivity. Nitrogen addition increased total bud density in 4- and 7-year pastures, with the strongest response under Low-N at year 7. Rhizome bud density declined under High-N addition, whereas tiller bud density remained relatively stable. Total bud density, tiller number, and aboveground biomass peaked at the year 7 and declined markedly by the year 13. No significant relationships were detected between belowground bud density and tiller number or aboveground biomass in the 13-year pasture. These results suggest that belowground bud bank dynamics track changes in tiller recruitment and productivity during pasture development. Their disappearance in long-established pastures suggests a weakening linkage between belowground bud banks, tiller recruitment, and productivity.