Fulvic Acid Alleviates Paper Sludge Toxicity in Canola (Brassica napus L.) by Reducing Cr, Cd, and Pb Uptake

Heavy metal toxicity reduces the growth and development of crop plants growing in metal-contaminated regions. Disposal of industrial waste in agricultural areas has negative effects on the physiochemical activities of plants. This research aimed to examine the fulvic acid (FA)-mediated efficacy of Brassica napus L. regarding stress tolerance in soil amended with paper sludge (PS). For this purpose, plants were grown for 90 days under greenhouse conditions at various concentrations of PS-amended soils (0, 5, 10, and 15%) being irrigated with water containing FA (0, 10, and 20%). All the physicochemical parameters of PS were carried out before and after plant transplantation. Paper sludge toxicity reduced the growth (shoot/root length, fresh/dry weight of shoot/root, numbers of flowers and leaves) and physicochemical characteristics of exposed B. napus plants. In comparison, FA application improved growth by reducing the metal uptake in the shoot of plants grown at various concentrations of PS. An increasing trend in antioxidant enzyme activity was observed by increasing the FA concentration (0%-10% and 20%). Post-harvest analysis indicated that the amount of tested metals was significantly reduced at all PS concentrations. Minimum metal uptake was observed at 0% concentration and maximum at 15% concentration of paper sludge. Additionally, FA application at 20% concentration reduced Chromium (Cr), Cadmium (Cd), and Lead (Pb) uptake in the shoot from 6.08, 34.42, and 20.6 mgkg^-1 to 3.62, 17.33, and 15.22 mgkg^-1, respectively. At this concentration of paper sludge in the root, 20% FA reduced Cr, Cd, and Pb uptake from 11.19, 44.11, and 35.5 mgkg^-1 to 7.88, 27.01, and 24.02 mgkg^-1, respectively. Thus, FA at 20% concentration was found to be an effective stimulant to mitigate the metal stress in B. napus grown in paper sludge-polluted soil by reducing metal uptake and translocation to various plant parts.