Changes in keystone species attenuate the complexity and stability of soil microbial networks during alpine meadow degradation

• Prokaryotic networks are more sensitive than fungal networks during the early stages of alpine meadow degradation. • Changes in keystone species attenuate microbial network stability and complexity. • Alpine meadow degradation increases the risk of soil carbon and nitrogen loss. In recent years, intensified human activities and climate change have led to the significant degradation of grasslands worldwide. Soil microbial network structure and function are crucial indicators of grassland degradation. Understanding how microbial networks and their associated functions respond to degradation can help guide interventions to mitigate grassland degradation. Here, we performed transect surveys across alpine meadows on the Qinghai-Tibet Plateau that ranged from non-degraded to severely degraded. Co-occurrence network and functional prediction analyses showed that as degradation intensified, the stability and complexity of the prokaryotic networks significantly decreased. Furthermore, prokaryotic networks were more sensitive to alpine meadow degradation early in the degradation process compared with fungal networks. Structural equation modeling revealed that variation in the abundance of keystone species in degraded meadows decreased the stability and complexity of microbial networks. The proportion of carbon-decomposing and nitrifying bacteria significantly increased during the degradation process, which potentially increased the risk of soil carbon and nitrogen loss, particularly via the decomposition of recalcitrant organic carbon (e.g., chitinolysis and cellulolysis). These findings greatly aid our understanding of the mechanism underlying microbial network complexity and stability during alpine meadow degradation and highlight the important role of keystone species in microbial networks.