Biochemical insights into fulvic acid-driven drought tolerance in canola

• Fulvic acid improved root growth and stress resilience in drought-stressed canola. • FA enhanced antioxidant defenses by boosting GSH, CAT, and radical scavenging activity. • FA reduced lipid peroxidation and promoted proline-driven osmoprotection under drought. • Metabolomics showed FA modulated primary and secondary metabolism in canola. • Stress-related metabolites (e.g., phenolics, spermidine) increased with FA treatment. Sustainable food production is a critical driver of a consumer-led transformation taking place in agriculture. Among the available strategies, biostimulants represent a critical set of agronomic tools for enhancing crop productivity. This study evaluated the impact of drought stress on canola ( Brassica napus ) and the efficacy of fulvic acid (FA) to mitigate drought-induced damage by linking morphological changes with physiological and metabolic responses. Canola plants were subjected to four treatments: well-watered control (WWC), well-watered with FA (WWFA), drought control (DC), and drought with FA (DFA). FA application significantly improved root growth under drought. Across drought onset (do) and both 7- and 14-days post drought onset (dpdo), FA increased soluble protein, glutathione (GSH), and catalase (CAT) activity (WWC < WWFA < DC < DFA). Drought increased radical scavenging activity and malondialdehyde (MDA), while FA further elevated radical scavenging activity and significantly reduced lipid peroxidation. Proline accumulation was highest in DFA plants, suggesting enhanced osmoprotection. Metabolomic profiling revealed that FA modulated central and secondary metabolism, increasing levels of stress-related metabolites including proline, glucose, glutamine, phenolics (quercetin, ellagic acid), antioxidants, nitrogenous metabolites (trigonelline), and polyamines (spermidine). These shifts were associated with improved oxidative stress management and cellular resilience. Overall, FA treatment conferred broad protective effects against drought in canola by enhancing root growth, antioxidant defenses, and osmoprotection. These findings are supported by increased levels of stress-related metabolites in treated canola, highlighting FA as a promising biostimulant for improving drought tolerance.