Backgound and aims <p>Afforestation and reforestation are essential for bolstering soil carbon stocks. Traditionally, vegetation restoration has relied on monoculture planting. However, mixed forests, with their relatively complex stand structures, are increasingly recognized as a more promising strategy. Owing to the resource limitations of limestone hills, the effects of arbor-shrub mixed vegetation restoration on soil organic carbon (SOC) storage and stability, as well as the mechanisms driving these effects, remain underexplored compared to monocultures.</p> Methods <p>We quantified biomass and chemical traits of litterfall and fine roots, soil physiochemical properties, SOC and its fractions, microbial necromass carbon (MNC), microbial traits, and enzyme activity. Pearson correlation analysis and structural equation modeling (SEM) were employed to explore the mechanisms influencing SOC storage and stability across vegetation restoration strategies.</p> Results <p>Arbor-shrub mixed vegetation restoration forests significantly enhanced SOC content, storage, and stability, primarily through a greater contribution of mineral-associated organic carbon (MAOC) to SOC and increased MNC content, compared to monoculture stands. These improvements were strongly associated with higher fine root biomass, reduced C/N and lignin/N ratios, enhanced fungal diversity, shifts in fungal phyla abundance, and elevated activities of peroxidase (POD) and sucrase (SC) enzymes. The quality of fine roots and fungal community dynamics accounted for most variations in SOC storage and stability, surpassing the influences of soil physicochemical properties, litterfall, or bacterial community dynamics.</p> Conclusions <p>Our findings highlight the effectiveness of arbor-shrub vegetation restoration strategies in enhancing soil carbon stocks in limestone hills, which contribute to optimizing afforestation strategies.</p>