Combined application of nanobiochar, silicon, and iron nanoparticles mitigates multiple heavy metal stress in tomato (Solanum lycopersicum)

This study evaluated the efficacy of nanobiochar (NB) and foliar Si/Fe nanoparticles in mitigating multiple heavy metal stress (HMS) in tomato. A three-factor factorial greenhouse experiment (completely randomized design, five replications) was conducted in 2023: soil amendment (control vs. 1% w/w NB), foliar spray (control, Si, Fe, Si + Fe at 2 g L⁻¹), and growth condition (normal vs. HMS from wastewater). HMS induced significant oxidative stress, as evidenced by increased H₂O₂ and malondialdehyde (MDA) levels, reduced photosynthetic pigment levels, and lower fruit yield. However, NB plus foliar nanoparticles, especially in combination, markedly alleviated HMS toxicity. The most effective treatment (NB + Si + Fe) increased key antioxidant enzymes (CAT, SOD, APX) and non-enzymatic antioxidants (proline, sugars, phenols, flavonoids), thereby decreasing H₂O₂ and MDA levels. Consequently, chlorophyll a , b , and carotenoid content increased under HMS. This treatment also reduced Cd, Pb, Cr, Cu, and Zn uptake in plant tissues and enhanced fruit yield by more than 57.14% compared to the stressed control. Integrated Biomarker Response version 2 (IBRv2) showed that NB + Fe (I = − 0.01) and NB + Si+Fe (I = − 0.02) produced the smallest negative deviation in growth indices and the greatest increase in antioxidant defense. Co-application of nanobiochar with Si + Fe nanoparticles is a highly effective strategy for sustaining tomato productivity in heavy-metal-contaminated soils, offering a promising nano-remediation approach for sustainable agriculture that warrants field-scale validation.