Mitigating cadmium-induced oxidative stress in Satureja hortensis using selenium and biochar: Impacts on plant growth and essential oil yield

Cadmium (Cd) contamination is an escalating threat to medicinal-crop production, yet practical mitigation strategies for Satureja hortensis L. remain unexplored. Here we tested the hypothesis that co-applying biochar and foliar selenium (Se) can synergistically alleviate Cd-induced oxidative damage and sustain essential oil (EO) yield. A full factorial pot experiment was conducted with three ecologically relevant Cd levels (0, 10, and 20 mg kg⁻¹ soil), two biochar rates (0 and 5 % of pot volume; 3 L pots), and three aqueous sodium selenate sprays (0, 5, and 10 mg L⁻¹, applied at 15-day intervals). Severe Cd exposure (20 mg kg⁻¹) depressed shoot fresh and dry biomass, total phenolics, flavonoids, relative water content (RWC), and EO yield by 21–38 % while accelerating osmolyte accumulation and antioxidant enzyme activity. Biochar or Se alone partially offsets these losses. However, the combined treatment was most effective: in mildly contaminated soil (10 mg kg⁻¹ Cd) the 5 % biochar + 5 mg L⁻¹ Se regime restored biomass to control levels and produced the highest EO content (0.98 %, +27 % versus untreated Cd stress). Across Cd doses, the dual amendment improved RWC (up to +19 %), total phenolics (+23 %), and flavonoids (+26 %) relative to Cd-only plants, indicating strengthened osmotic balance and antioxidant capacity. These results demonstrate, for the first time in summer savory, that a low-cost biochar–selenium combination can counteract Cd toxicity and safeguard both growth and EO profitability. The approach offers a scalable option for phytoprotection in Cd-affected agroecosystems and merits field-scale validation.