Root biochemical, uptake, and transport behaviors of kochia ( Kochia scoparia  L.) to cadmium and lead contaminated soil

Contamination of agricultural soils with cadmium (Cd) and lead (Pb) poses significant risks to forage production and food chain safety in arid and semi-arid regions. Kochia (Kochia scoparia L.) is a fast-growing, stress-tolerant forage species with potential for phytoremediation. This study evaluated the biochemical, uptake, and translocation responses of kochia roots to soil contaminated with Cd or Pb at concentrations of 25-800 mg kg^-1. Key parameters assessed included non-enzymatic antioxidants (e.g., phenols, flavonoids, proline, glycine betaine), enzymatic activities (catalase, peroxidase, superoxide dismutase, ascorbate peroxidase), hydrogen peroxide content, osmolyte accumulation (water-soluble carbohydrates and proteins), and metal bioconcentration factor (BCF), biological accumulation coefficient (BAC), translocation factor (TF), and translocation efficiency (TE %). Results demonstrated that kochia accumulated substantial Cd and Pb in roots, with maximum root concentrations correlating positively with soil levels (polynomial relationships; R² > 0.95). Cd exhibited high root-to-shoot translocation (TF up to 1.5 at 800 mg kg^-1; TE % up to 60%), while Pb was predominantly sequestered in roots (TF < 0.5; TE % < 30%). Cd induced stronger oxidative stress, evidenced by greater elevations in hydrogen peroxide (up to 115.2% increase at 800 mg kg^-1), antioxidant enzymes (e.g., ascorbate peroxidase increased 79.3% at 800 mg kg^-1), and osmoprotectants (e.g., proline 33.9%, glycine betaine 66.9%) compared to Pb (proline 27%, glycine betaine 50.1%). Biomass declined more severely under Cd (shoot dry weight reduced 83.4% at 800 mg kg^-1) than Pb (67.6%). BCF and BAC were highest at 25 mg kg^-1 (BCF > 4 for both metals) and decreased with concentration. These findings position kochia as an effective Cd phytoremediator due to high translocation, but highlight food chain risks from shoot Cd accumulation when used as forage, necessitating strict biomass management in contaminated sites.