The synergistic effect of applying Bacillus and biochar on restoration of lead-zinc tailings by Leptolyngbya

Heavy metal (HM) toxicity and nutrient deficiency pose major challenges to the ecological restoration of tailings area. As the primary stage of soil microbial community succession, biological soil crusts (BSCs) play an important role in stabilizing the soil surface and accelerating nutrient cycling in tailings area. Nevertheless, little information is available. In this study, microalgae and bacteria isolated from tailings area were inoculated onto the lead‑zinc tailing sand combined with exogenous biochar to induce the formation of BSCs. After 60 d of inoculation, chlorophyll a, total DNA, soil humic substances, soluble proteins and species abundance of induced BSCs increased significant in comparison with the control check (CK). Soil C, N and P nutrients, soil saturated moisture, cation exchange capacity and enzyme activities of induced BSCs soils also increased significantly, however, the available forms of lead and zinc, soluble salt, and microbial-derived fulvic acid significantly decreased. The expression of nitrification genes, denitrification genes, and P cycling genes significantly increased. Principal component analysis ranked the differences of each treatment group, and revealing that the combined microalgae-bacteria-biochar treatment group resulted in improving soil properties and higher expression of N/P cycling genes compared to the sole microalgae inoculation. These results indicated that utilizing indigenous microorganism inoculation could effectively improve the ecological function of tailings sand by increasing N/P cycling and provides a potential method for accelerating the ecological restoration of tailings sand. •Induced BSCs were successfully formed and developed on the surface of tailing sand.•Induced BSCs reduced the DTPA-Pb/Zn content in the tailing soil.•The addition of bacteria and biochar improved the soil properties and nutrients (C, N and P) of tailing soil better than that of microalgae alone.