Abstract
Biocrusts are essential for soil stabilization and nutrient cycling in arid ecosystems, yet their formation is often limited by coarse texture, low fertility, and extremely low cyanobacterial biomass in shifting sands. To address these constraints, this study conducted a field experiment in the Gurbantunggut Desert using four treatments that combined two inocula, crushed natural cyanobacteria dominated biocrust fragments and laboratory-cultured cyanobacteria, with or without the addition of sepiolite. The results showed that sepiolite addition significantly enhanced biocrust development by promoting exopolysaccharides accumulation, biocrust thickness and structural integrity. It also improved soil organic carbon, microbial biomass carbon, and some enzymes activities involved in carbon and nitrogen cycling, especially β-glucosidase. Furthermore, a general C limitation was observed across all biocrust groups, and the addition of sepiolite effectively alleviate N limitation. Microbial α-diversity remained unchanged, but β-diversity and community composition were distinctly shaped by both sepiolite and inoculum type. Notably, although sepiolite facilitated biocrust formation in both inoculation strategies, crushed natural biocrusts outperform cyanobacterial monoculture in enhancing recovery efficiency, indicated by achieving much higher microbial biomass, stability, enzyme activities and nutrient levels. Overall, sepiolite addition plays multiple key roles in promoting the biocrust restoration in arid sandy soils by improving soil microhabitats and supporting microbial assembly and nutrient cycling, thereby enhancing biocrust development. These results provide new field-based evidence that integrating functional clay minerals with microbial inoculation can effectively overcome abiotic barriers to biocrust formation.