Synergistic application of biochar and mercury-resistant Bacillus cereus enhances phytoremediation efficiency and stress tolerance in sorghum (Sorghum bicolor L.) grown in mercury-contaminated soil

Abstract

Mercury (Hg) contamination in agricultural soils threatens crop productivity and ecosystem sustainability. This study investigates the synergistic effects of Pieris japonica-derived biochar and the Hg-resistant bacterium Bacillus cereus B2 in mitigating Hg toxicity in sorghum (Sorghum bicolor L.) grown in Hg-contaminated soils (0, 15, 20, and 25 mg Hg kg⁻¹). Hg stress significantly inhibited plant growth, gas exchange, and photosynthetic pigments, with the greatest reductions at 25 mg kg⁻¹ Hg. The combined application of biochar (4%) and B. cereus B2 notably enhanced plant height (34.7%), stomatal conductance (50.1%), photosynthetic rate (24.5%), transpiration rate (60.2%), water-use efficiency (24.5%), chlorophyll a (75.8%), chlorophyll b (29.3%), carotenoids (27.0%), and total chlorophyll (59.5%) compared to individual treatments. This synergistic approach also stimulated antioxidant defenses, increasing activities of ascorbate peroxidase (20.1%), catalase (25.2%), superoxide dismutase (34.9%), and peroxidase (49.7%), while reducing reactive oxygen species (H₂O₂ and O₂⁻) and lipid peroxidation (MDA). Furthermore, Hg accumulation in sorghum roots and shoots was significantly reduced under the combined treatment, indicating lower Hg bioavailability. These findings demonstrate the novel synergistic potential of P. japonica biochar and B. cereus B2 in enhancing Hg immobilization, improving plant physiological resilience, and strengthening antioxidant defenses in sorghum, providing an effective and sustainable strategy for Hg-contaminated soil remediation.

Graphical abstract

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