Evaluating the phytoremediation capacity of Verbesina encelioides through lead-induced morphological and biochemical shifts

Abstract

Soil contamination with heavy metals, particularly lead (Pb), has become a critical environmental issue due to rapid urbanization and industrial activities. This study was undertaken to evaluate the tolerance, physiological responses, and Pb accumulation behaviour of Verbesina encelioides under increasing Pb stress, in order to assess its potential for phytoremediation, particularly phytostabilization, in contaminated soils. To achieve this, a controlled pot experiment was conducted using graded Pb concentrations (0–500 mg kg⁻¹ soil), and plant responses were evaluated at different growth stages. Lead stress adversely affected the growth and physiological performance of V. encelioides. Lead stress impaired the growth and physiological functions of V. encelioides. Exposure to 500 mg kg⁻¹ Pb reduced shoot length and dry weight by approximately 45 and 60%, respectively and root length and weight 17–32 and 42% respectively, compared to the control (p ≤ 0.05), while leaf area declined by over 50%. Lead accumulation was predominantly confined to roots, with concentrations up to eightfold higher than in aerial parts, indicating restricted translocation. Photosynthetic pigments were severely affected, with chlorophyll a and total chlorophyll decreasing by more than 50% at the highest Pb level. Biochemically, the plant activated defence mechanisms, as shown by an increase in proline content and the activities of peroxidase (3–11 fold) and catalase (4–10 fold) by several-fold at 500 mg kg⁻¹ compared with the control (p ≤ 0.05). These morphological inhibitions and biochemical adjustments suggest that resources are preferentially allocated to stress mitigation processes, thereby constraining growth performance. Lead accumulation was predominantly root-localized, with shoot bioaccumulation factor (BAF) values remaining below unity (0.01–0.27) across all treatments and sampling intervals, indicating lead immobilization and restricted translocation to aerial tissues. Overall, the findings indicate that V. encelioides possesses adaptive traits that may support its use in phytostabilization rather than phytoextraction under controlled experimental conditions.