Differentiation in the Underground Bud-Bank Structure of Poa pratensis Across Contrasting Alpine Grassland Habitats on the Eastern Qinghai–Tibetan Plateau

Underground bud banks play a critical role in vegetative regeneration of alpine grassland plants, but how species-level underground regenerative structures vary across contrasting habitats remains unclear. This study investigated the widely distributed clonal grass Poa pratensis across alpine steppe and alpine meadow habitats on the Qinghai–Tibetan Plateau, focusing on the differentiation of underground bud density, morphological traits, ultrastructure, and associated soil environmental conditions. Compared with alpine steppe, alpine meadow populations exhibited significantly higher tiller bud density, bud length, and bud diameter, whereas rhizome buds were observed exclusively in alpine meadow. Furthermore, underground buds in alpine meadow showed larger dimensions and more developed surface appendages. Principal component and correlation analyses revealed that underground bud traits were associated with soil resource conditions, with higher soil moisture and nutrient availability corresponding to enhanced bud development. Collectively, the integrated differentiation of underground bud “quantity–type–structure” in P. pratensis suggests that environmental heterogeneity may shape belowground regenerative strategies of alpine grassland plants.