The seaweed <i>Ascophyllum nodosum</i>-based biostimulant enhances salt stress tolerance in rice (<i>Oryza sativa</i> L.) by remodeling physiological, biochemical, and metabolic responses

This study explores the role of a biostimulant derived from the seaweed Ascophyllum nodosum (AN) in mitigating salt stress in rice plants. The weekly (S+W) and biweekly (S+B) biostimulant treatments exhibited enhanced shoot and root biomass, maintained ionic balance, and increased pigment content (total chlorophyll increased by 26.35% and 31%, carotenoids by 11.90% and 16.67% in S+W and S+B treatments, respectively) compared to untreated salt-stressed plants (CS). Improved gas exchange parameters and PSII efficiency were observed in S+W and S+B treatments. AN-biostimulant treatments mitigated salt-induced oxidative stress by positively regulating the antioxidant defense system. Notably, a strong negative correlation was observed between antioxidants and oxidative markers. Furthermore, AN-biostimulant treatments induced key metabolites (organic acids, sugars, amino acids, flavonoids), emphasizing the integrated role of multiple pathways in enhancing salt tolerance in rice. These findings highlight the potential of AN biostimulants as eco-friendly tools for crop enhancement in challenging environments.