Soil-Mediated Regulatory Mechanisms of Belowground Bud Banks in the Sustainable Management and Ecological Restoration of Degraded Alpine Grasslands

Alpine grasslands on the Qinghai–Tibet Plateau are highly sensitive to climate change and human disturbances, and their degradation poses serious threats to ecosystem stability and soil conservation. Belowground bud banks form the foundation of vegetative regeneration, yet their variation along degradation gradients and the soil factors regulating these changes remain insufficiently understood. In this study, we investigated the density and composition of belowground buds in grasses, sedges, and forbs across four degradation levels during the peak growing season and examined the soil controls shaping these responses. The results showed that moderate degradation significantly increased total bud density, indicating enhanced clonal renewal capacity, whereas severe degradation markedly reduced bud-bank potential. Bud types from different functional groups responded differently to soil conditions: rhizome buds of grasses were mainly driven by soil fertility, while tiller buds were more sensitive to soil compaction and carbon–nitrogen availability; rhizome buds of sedges could still develop in compact, nutrient-poor soils; and bud types of forbs were more responsive to variations in soil nutrient status or soil structure. Structural equation modeling further revealed that the formation of the belowground bud is primarily influenced by soil physico-chemical properties, particularly soil nutrients, which regulate regenerative capacity under degraded alpine grasslands. This study reveals the variation patterns of belowground bud banks along degradation gradients in alpine grasslands on the Qinghai–Tibet Plateau and their responses to soil factors, and it elucidates the pathways through which degradation mediates belowground bud bank dynamics via soil physico-chemical properties, particularly soil nutrients, thereby providing a scientific basis for understanding the regeneration potential of alpine grasslands and for the sustainable management and ecological restoration of degraded alpine grasslands.