Application of Parthenium biochar and Serratia marcescens reduced metal toxicity and uptake in Zea mays: An assessment via experimental and predictive modelling.

Biochar and metal-resistant bacteria are increasingly used to stabilize toxic metals in contaminated soils. Parthenium biochar and Serratia marcescens were applied in combination to assess their impact on plant growth parameters, physiological and biochemical attributes, metal uptake, soil metal fractions, and oxidative stress responses. Additionally, machine learning models, including support vector machine regression and elastic net, were used to predict and identify key factors influencing metal uptake. The combined treatment significantly enhanced plant biomass, root length, and shoot length by 56-78%. Chlorophyll content increased by 42-68%, membrane injury decreased by 25%, and cell viability improved by 33%, along with increases in proline (45%) and protein contents (35%). Metal uptake was reduced by 40-65%, while bioaccumulation decreased by 40%, and bioconcentration and translocation factors declined by 55% and 60%, respectively. Soil metal fractions (extractable, reducible, and oxidizable) decreased by 30-50%, reducing total metal concentrations by 45%. Integrated Biomarker Response analysis indicated reduced oxidative stress in both leaves and roots, supported by decreased antioxidant enzyme activity. Support vector machine regression showed superior predictive performance (R² = 0.97), whereas elastic net identified key predictors (R² = 0.85). The integrated application of biochar and S. marcescens was associated with improved plant growth, enhanced soil quality, and reduced metal toxicity under multimetal stress. These findings suggest that this approach may have potential for sustainable remediation of contaminated soils.