Integrative application of biochar and bacteria for mitigating antimony toxicity and bio-accessibility in sorghum

Antimony (Sb) toxicity is a serious concern due to its harmful effects on humans and plants. Biochar (BC) has become a popular amendment for remediating soils polluted with metals and metalloids. However, the exact interaction mechanism between BC, and microbes to remediate Sb-polluted soils remains unclear. To address this, a study was performed to determine the impacts of maize straw BC and a bacterial strain (Pseudomonas frederiksbergensis: PF) in mitigating the harmful effects of Sb toxicity on sorghum productivity. A pot experiment was set up with the following treatments: control, soil contaminated with Sb (1000 mg kg^-1), Sb-contaminated soil + BC (2 %), Sb-contaminated soil + PF, and Sb-contaminated soil + BC (2 %) + PF. Antimony toxicity significantly reduced sorghum biomass and grain yield while increasing hydrogen peroxide (H₂O₂: 32.63 %), malondialdehyde (MDA: 68.96 %) reducing chlorophyll a (95.65 %) and chlorophyll b synthesis (92 %), increasing Sb accumulation in plant parts and decreasing soil NPK (24.48 %, 8.01 % and 19.24 %) availability, soil organic carbon (SOC: 16.36 %), microbial biomass carbon (MBC: 10.80 %) and soil urease (76.31 %) and catalase (130.52 %) activity. The combined application of BC and bacteria enhanced the sorghum biomass and grain production by improving chlorophyll synthesis, antioxidant activity, osmolyte production, nutrient availability, SOC, MBC, soil enzymatic activities and reducing both H₂O₂ and MDA production. Co-application of BC and bacteria decreased soil Sb concentration by 38.84 % while they decreased Sb concentration in sorghum root, stem, leaves and grains by 54.58 %, 34.15 %, 30.96 % and 54.58 % respectively. The decrease of Sb concentration in soil and plant parts with BC and bacteria application was attributed to increase in soil pH, SOC, MBC, enzymes activities. Additionally, BC in combination with bacteria also reduced bio-accessible Sb concentration by 83.82 %, and bio-accessibility of Sb by 36.45 % indicating their appreciable potential to produce safer sorghum production in highly polluted Sb soils. Therefore, BC and PF can be used together to improve sorghum production and develop environmentally friendly approaches in Sb-contaminated soils.