Co-inoculation of Cyanobacteria and Fungi Promotes Induced Biocrust Formation and Stabilization of Quartz Sand Tailings

Abstract Biocrust induction is increasingly explored to stabilize mine tailings, but the microbial interactions driving biocrust assembly, especially those between cyanobacteria and fungi, remain largely uncharacterized. In this study, five cyanobacterial strains ( Nostoc sp., Trichormus sp., Tolypothrix sp. , and two Chroococcidiopsis sp. ) and five fungal strains ( Penicillium oxalicum , Purpureocillium lilacinum , Aspergillus clavatus , Penicillium brasilianum , Talaromyces wortmannii ) were tested individually and in all cyanobacteria–fungi co-inoculations on quartz sand tailings. After 90 days of incubation, induced biocrust formation was assessed via scanning electron microscopy (SEM) imaging, chlorophyll- a and exopolysaccharides (EPS) production, fungal abundance, surface water repellency (WDPT), induced biocrust thickness, and sediment penetration resistance. SEM imaging revealed successful colonization, effective sediment particle binding, and EPS-mediated stabilization. The co-inoculation effects depended on the specific cyanobacteria–fungi combination. Certain co-inoculations led to substantial enhancements in chlorophyll‑ a , EPS, and water repellency (e.g. Tolypothrix sp. with Penicillium oxalicum ), as well as induced biocrust thickness and a minor increase in sediment stability (e.g. Trichormus sp. and Purpureocillium lilacinum ), far exceeding the effects of sole cyanobacterial inoculation. Conversely, other cyanobacteria–fungi combinations showed little impact or even caused significant reductions (e.g. Tolypothrix sp. with Penicillium brasilianum or Talaromyces wortmannii ), reflecting the strong dependence of co-inoculation benefits on the compatibility of the studied biocrust-forming microorganisms. Correlation analysis showed that chlorophyll‑ a and LB‑EPS were positively correlated with each other and with WDPT, while induced biocrust thickness was negatively correlated with WDPT, chlorophyll‑ a , and sediment penetration resistance, indicating contrasting responses among induced biocrust functional traits. Overall, co-inoculation promoted synergistic interactions in selected combinations, markedly enhancing induced biocrust formation and sediment stabilization. These results indicate that tailored cyanobacteria–fungi consortia can successfully establish induced biocrusts and improve degraded mine tailings, providing an effective induced biocrust-facilitated strategy for the rehabilitation of degraded substrates.