Abstract: Hippophae rhamnoides plantations mitigate Gobi expansion and ameliorate soil quality, yet their effects on microbial communities in rhizosphere versus bulk soils across plantation ages remain unclear. Here, we investigated rhizosphere and bulk soils from 4, 12, and 15 yr H. rhamnoides plantations using high-throughput 16S rRNA and ITS sequencing to evaluate microbial succession and soil carbon-nitrogen associations. As stand age increased, the rhizosphere bacterial community shifted from Pseudomonadota to Actinomycetota, whereas fungi remained dominated by Ascomycota. Bacterial and fungal α-diversity showed no significant changes in the rhizosphere, whereas β-diversity indicated that stand age had a significant effect on community composition. In bulk soil, Actinomycetota and Ascomycota remained dominant. Bacterial α-diversity (shannon) significantly increased by 12.21%, whereas fungal α-diversity showed no significant difference; β-diversity was influenced by stand age. Functional analysis showed that rhizosphere bacteria shifted from amino acid synthesis to secondary metabolism and fungi shifted from pathogenic–saprophytic to multi-trophic lifestyles. In bulk soil, bacterial carbon fixation pathways increased, whereas fungi alternated between pathogenic and symbiotic states. Community assembly in rhizosphere bacteria shifted from drift to homogeneous selection and dispersal limitation, whereas rhizosphere fungi and bulk soil communities were governed by homogeneous selection, dispersal limitation, and drift. Total carbon, total nitrogen, and organic carbon increased with stand age. Key microbial groups associated with carbon and nitrogen accumulation shifted across developmental stages, indicating that microbial contributions to soil nutrient dynamics were age-dependent. These findings reveal stand-age-driven microbial succession coupled with nutrient accumulation, offering microbiological evidence for Gobi soil restoration via afforestation.

Key words: Hippophae rhamnoides plantation, high-throughput sequencing, microbial community structure, community assembly, soil carbon and nitrogen coupling