Abstract: The degradation of alpine grasslands poses a threat to the ecological and environmental security of the Qinghai-Tibet Plateau. A comprehensive understanding of the changes in vegetation and soil properties during the degradation process of alpine grasslands is crucial for ecological restoration. In this study, we used space-for-time substitution to examine plant community composition, biomass, species diversity, soil factors, and their relationships in alpine steppes across a degradation gradient—intact, slightly degraded, moderately degraded, and severely degraded—in the Qinghai Lake Basin. The results showed that there were significant changes in the composition of plant community with the intensification of degradation. The importance value of grass species decreased significantly with increasing degradation degree, while the importance value of forb species exhibited an opposite trend. The degradation of alpine steppe did not significantly reduce species richness in plant community. Additionally, moderate and severe degradation significantly reduced aboveground biomass of grass species and belowground biomass (0-10 cm) of the community, and increased the aboveground biomass of forbs. Severe degradation resulted in a substantial increase in soil pH and a marked decrease in soil microaggregate content. Both moderate and severe degradation significantly reduced soil moisture. Moderate degradation led to a decrease in nutrient content in the topsoil (0-10 cm), while severe degradation resulted in a reduction in nutrient content across both the topsoil and subsurface soil layer (10-20 cm). Soil nutrients and the ecological processes related to nutrient formation and turnover were the main factors controlling the characteristics of plant communities in the alpine grasslands. Our results provided a theoretical basis for formulating restoration measures suitable for the degraded alpine grasslands in the Qinghai Lake Basin.

Key words: alpine steppe, grassland degradation, plant community characteristics, soil factor, Qinghai Lake Basin