Background and aims <p>Artificial biocrusts play a crucial role as a carbon pool in reversing desertification. However, current research has focused predominantly on the microbes, not the specific interaction between biocrusts and clay minerals, such as montmorillonite, in the biocrust carbon pump.</p> Methods <p>This study established clay-based artificial biocrusts and investigated the effects of a clay mineral on the dynamics of soil organic carbon (SOC) accumulation. Montmorillonite and <i>Microcoleus vaginatus</i> were co-inoculated, and parameters related to SOC accumulation were determined, including microbial biomass carbon, SOC content, and chlorophyll a (Chl-<i>a</i>).</p> Results <p>The experimental results demonstrate that on day 84, the SOC contents in the montmorillonite-algae (≥ 1.4&#xa0;g&#xa0;dm⁻²) inoculated microcosms were over 3.45 times higher than in those inoculated with algae, identifying 1.4&#xa0;g&#xa0;dm⁻² as the optimal areal mass density of montmorillonite addition. Furthermore, montmorillonite played a crucial role in microbial growth and SOC stability, with microbial proliferation being the primary driver of SOC accumulation. Moreover, montmorillonite favored microorganisms with strong photosynthetic capabilities.</p> Conclusion <p>The experimental results indicate that montmorillonite promoted microbial growth and SOC accumulation in artificial biocrusts. Thus, montmorillonite may act as an accelerator for the microbial carbon pump during artificial biocrusts&#xa0;construction. Further field trials examining the positive effects of montmorillonite on artificial biocrust construction and organic carbon accumulation in the long-term are needed in the future.&#xa0;</p> Graphical Abstract <p></p>