Lead-Induced morpho-physiological and antioxidant responses of Pistia stratiotes L.: Insights into its role as a bioindicator and phytoremediator in aquatic environments

Heavy metal contamination in aquatic ecosystems represents a significant environmental challenge due to its persistence, toxicity, and propensity for bioaccumulation. This study investigated the impact of lead [Pb(C₂H₃O₂)₂] on the growth, photosynthetic pigments, and antioxidant responses of Pistia stratiotes exposed to concentrations of 0 µM (control), 200 µM, 300 µM, 400 µM, and 500 µM Pb for 7 days at 37 ± 1°C, 85% RH. Relative growth rate (RGR) increased progressively up to 400 µM (1.100 gg⁻¹day⁻¹) before declining at 500 µM (0.730 gg⁻¹ day⁻¹), although growth remained above control values. Lead accumulation in plant tissues exhibited a strong concentration-dependent increase from 10.410 mg/kg (control) to 8182.000 mg/kg (500 µM), confirming P. stratiotes as a potential lead hyperaccumulator. Chlorophyll content decreased from 1.365±0.006 mg/g (control) to 1.306±0.022 mg/g (500 µM) under Pb stress, indicative of photoinhibition and potential biomass loss. Concurrently, levels of ascorbic acid, malondialdehyde (MDA), proline, and total antioxidant capacity significantly increased with Pb concentration, reflecting the activation of antioxidative defense mechanisms and oxidative stress responses. Bioconcentration factor (BCF= 0.056), tolerance index (TI= 106.25%) at 400 µM, and Pb uptake measurements demonstrated the species’ high efficiency in phytoextraction and rhizofiltration processes. Collectively, these findings underscore the substantial tolerance and accumulation capacity of P. stratiotes under moderate Pb stress (400 µM), highlighting its suitability as a phytoremediator for lead-contaminated aquatic environments and as an effective bioindicator for environmental monitoring. • Pistia stratiotes exhibited strong lead tolerance, achieving peak growth and antioxidant activation at 400 µM Pb exposure. • The species demonstrated hyperaccumulation potential, with Pb content rising from 10.41 mg/kg to 8182 mg/kg across treatments. • Photosynthetic pigments declined under high Pb levels, indicating early photoinhibition and stress sensitivity. • Enhanced proline, MDA, ascorbic acid, and antioxidant activity confirmed robust oxidative stress defense mechanisms. • High bio-concentration and tolerance indices highlight P. stratiotes as a promising phytoremediator and bioindicator for Pb-polluted aquatic systems.