Microbial inoculant and microalgae fertilizer improved the growth and quality of Salvia miltiorrhiza cultivated in lead-contaminated soil

Abstract

Excessive Pb accumulation in medicinal plants compromises the safety and therapeutic efficacy of herbal products, posing significant health risks to consumers. This study evaluated the potential of the Bacillus microbial inoculant and the microalgae fertilizer to mitigate Pb stress in Salvia miltiorrhiza by assessing their effects on plant growth, Pb uptake, active ingredient accumulation, antioxidant activity and rhizosphere microbial composition. The results showed that microalgae application markedly enhanced peroxidase activity (by 38.62 %) and salvianolic acid B content (by 50.32 %) while lowering root Pb concentration, whereas microbial inoculant tended to elevate tanshinone levels and improve soil potassium availability. Moreover, biofertilizer application reshaped the rhizosphere microbial communities, recruiting abundant metal-tolerant and nutrient-cycling taxa (such as Bacillus, Cupriavidus, and Pseudomonas) in the rhizosphere and suppressing the pathogenic fungi, potentially supporting improved plant performance. When applied in combination, total tanshinone content was further increased. However, co-application showed no synergistic effects on plant growth or Pb accumulation, and even led to a significant reduction in root biomass. Overall, microalgae fertilizer appears more effective for enhancing Pb tolerance and medicinal quality in Salvia miltiorrhiza, likely through the activation of antioxidant defenses, soil quality improvement, and beneficial restructuring of the rhizosphere microbiome. The absence of synergy in the combined treatment indicates that co-application protocols require further optimization before practical implementation.