Biostimulant Effects of Rich Mannuronate-Alginate and Their Thermic-Acidic Depolymerized Derivates on Triticum aestivum

Wheat (<i>Triticum aestivum</i> L.) productivity is frequently compromised by environmental stressors such as drought, salinity, and nutrient deficiencies. The application of biostimulants has emerged as a promising strategy to mitigate these challenges by enhancing plant growth, resilience, and nutrient uptake. This study investigates the biostimulant effects of alginate gels and their depolymerized derivatives, particularly alginate oligosaccharides (AOS), on wheat seedling development. Treatments were applied in hydroponic systems at 50 and 500 mg/L to assess morphological and physiological responses. Depolymerized alginates, especially AOS at 500 mg/L, enhanced root length, compared to control by 40% (Kruskal-Wallis; <i>p</i>.adj ≤ 0.001). Smaller oligomers (<2 kDa) showed better biological activity compared to larger molecules (Mw > 2 kDa). Indeed, AOS application modulated oxidative stress by improving the ascorbate/dehydroascorbate (AsA/DHA) ratio as the control, indicating a stronger antioxidant response and a reduced ROS accumulation without stress. These findings suggest that AOS not only promotes root and shoot growth but also enhances the plant's endogenous ability to mitigate oxidative damage. The dual action, growth promotion and stress tolerance, position AOS as a promising biostimulant for improving wheat productivity in environmentally challenging conditions.