Seaweed biostimulant supplementation improves maize resilience to saline-alkaline stress

Saline-alkaline stress impedes maize growth, reducing yield and quality; however, mechanisms underlying maize responses to seaweed biostimulant treatment under these conditions remain poorly understood. This study investigated the physiological and molecular mechanisms of saline-alkaline resistance in the maize cultivar ‘Tuntian 168′ using seaweed biostimulant at 1, 5, 10, and 15 g/Kg soil. Saline-alkaline stress inhibited ‘Tuntian 168′ maize growth, but 10 g/Kg seaweed biostimulant treatment increased plant height, shoot and root biomass, chlorophyll content, and photosynthetic rate by 13.90, 64.73, 23.65, 20.15, and 47.07 %, respectively, compared to saline-alkaline controls. Treatment with 10 g/Kg seaweed biostimulant reduced the Na⁺/K⁺ ratio in shoots and roots by 54.98 and 79.79 %, respectively, likely via upregulated genes for Na⁺ efflux and K⁺ uptake. Treatment with 10 g/Kg seaweed biostimulant significantly enhanced the expression of genes involved in N, P, Fe, Mg, and Zn uptake and transport, thereby improving nutrient acquisition and distribution. This improved nutrient acquisition capacity may also be closely linked to the formation of a broader root network induced by the treatment. Moreover, treatment with 10 g/Kg seaweed biostimulant significantly increased shoots catalase (76.18 %), superoxide dismutase (37.49 %), and peroxidase (32.17 %) activities, mitigating oxidative stress, and elevated shoots proline (123.59 %) and soluble sugars (76.23 %), enhancing osmotic regulation. This study demonstrates that applying seaweed biostimulant effectively alleviates saline-alkaline stress in maize ‘Tuntian 168’, enhancing growth by improving nutrient uptake, lowering Na⁺/K⁺ ratios, and boosting antioxidant and osmotic regulation capacities. This provides a practical strategy for maize production in saline-alkaline soils.