Fertile island effects across developmental stages of Caragana korshinskii nebkhas drive microbial nutrient cycling in arid ecosystems

Nebkhas, such as those formed by Caragana korshinskii, play a critical role in restoring degraded arid landscapes through the fertile island effect. However, the influence of C. korshinskii nebkhas developmental stages on soil microbial structure and function remains unclear. In this study, we investigated microbial diversity, enzyme activities, and soil properties across three developmental stages (growing, mature, and recession) and two soil depths (0–10 cm and 10–20 cm) in the desert steppe of northern China. The results showed that bacterial and fungal α-diversity indices were significantly higher in 0–10 cm soils and peaked during the mature stage. Soil NAG enzyme activity was significantly enhanced in mature-stage nebkhas (P < 0.05), and correlation analysis revealed that SOC, AP, and enzyme activities were strongly associated with microbial community composition. A total of 8331 bacterial and 1584 fungal OTUs were identified, with dominant taxa including Actinobacteriota and Ascomycota. These findings confirm that the fertile island effect intensifies with nebkha development, enhancing microbially mediated nutrient cycling. This study provides new insights into the role of shrub successional stages in soil ecosystem functioning and offers practical guidance for vegetation-based restoration in arid environments.