Effects of Stand Age on Underground Bud-Bank Structure of Alpine Artificial Poa pratensis Grasslands

Underground bud banks are important components contributing to the persistence and renewal of perennial grasslands, yet how their structure differs among establishment stages of alpine artificial grasslands remains poorly understood. Here, we investigated alpine artificial Poa pratensis grasslands with 4, 5, 8, and 9 years of establishment to evaluate changes in underground bud-bank structure and their relationships with soil properties. Stand age, bud type, and their interaction significantly affected bud density, length, and diameter. Tiller buds dominated across all establishment stages, but their relative contribution decreased from 81% in the 4th year to 70% in the 9th year, whereas the contribution of rhizome buds increased from 19% to 30%. Older stands exhibited more developed rhizome internodes and nodes, and rhizome buds consistently showed larger dimensions and more developed vascular structures. Soil water content, inorganic nitrogen, and available phosphorus were lower in older stands, with soil water content declining from 28.86% in the 5th year to 22.30% in the 9th year and NH4+–N decreasing from 7.06 to 5.24 mg kg−1. The relationships between soil properties and bud density varied among establishment stages. After accounting for stand age, most soil factors showed no independent relationships with bud density, except for the interaction between soil organic carbon (SOC) and stand age on tiller bud density. These findings indicate that different establishment stages are associated with changes in underground bud-bank composition and structural characteristics rather than simple changes in bud abundance, highlighting the importance of considering stand age when evaluating underground regeneration characteristics and long-term persistence of alpine artificial grasslands.