Altitudinal decline of vegetation restoration effects on soil microbial communities on high-altitude roadside slops: Environmental drivers and management implications

Construction activities in high-altitude regions have left many bare roadside slopes vulnerable to degradation, complicating restoration efforts. Soil microorganisms are vital for plant growth and nutrient cycling, yet their responses to restoration efforts at various altitudes remains uncertain. This study investigates soil microbial composition, network properties, ecological functions, keystone taxa, and environmental drivers across three restored vegetation types: herbaceous plants (H), shrubs + herbaceous plants (SH), and trees + shrubs + herbaceous plants (TSH) at elevations from 3100 to 3800 m. Our structural equation model identifies elevation and vegetation type as key factors influencing microbial communities, directly or indirectly, through their effects on plant and soil properties. We also found that bacterial α-diversity decreased with elevation, while fungal α-diversity increased, resulting in more complex but less stable microbial networks. R-strategists predominated in the herbaceous type (H) and at lower altitudes, whereas K-strategists dominated in the SH and TSH types, and at higher altitudes. Keystone species of type H, associated with pathotrophs and plant pathogens, showed a negative correlation with plant properties, which weakened at higher altitudes. Both bacterial and fungal communities were driven more by abiotic factors, especially ammonium (NH₄⁺-N) and dissolved organic nitrogen (DON) for bacteria and soil water content (SWC) for fungi. This study proposes managing restoration-sensitive microbes and keystone taxa associated with specific vegetation types for effective restoration at appropriate altitudes, especially those shared by SH and TSH. Furthermore, integrating suitable legume or nitrogen-fixing woody vegetation into restoration efforts at lower altitudes and herbaceous vegetation into higher altitudes has the potential to significantly enhance plant growth and health at high altitudes. This study offers valuable guidance for optimizing restoration strategies by effectively addressing key environmental factors and nurturing essential microbial species crucial for successful restoration efforts and global warming mitigation.