Abstract

This study evaluated the antioxidant enzyme responses of rice (Oryza sativa L.) to salinity stress and solid biofertilizer application under controlled conditions at the Department of Plant Biology and Biotechnology Botanic Garden, University of Benin. Soil samples were collected, bulked, and distributed into 66 bags, Soil salinity was induced using (NaNO₃) sodium nitrate at concentrations of 100, 1000, and 10,000 ppm for six weeks to simulate saline conditions The activities of key antioxidant enzymes Superoxide Dismutase (SOD), Catalase (CAT), Ascorbate (Vit. C), and Glutathione Peroxidase (GPx) as well as malondialdehyde (MDA), ascorbate content, and total protein were assessed to determine oxidative stress responses. Results showed that salinity stress altered antioxidant enzyme activities, while solid biofertilizer application modulated these effects. The control recorded an SOD activity of 4.38 u/g protein, whereas treatments such as S1A (6.90 u/g) and S3D (6.76 u/g) showed increased activity, indicating enhanced antioxidant defense. Conversely, some treatments exhibited reduced SOD activity. CAT activity decreased under moderate salinity (S2A–S2E) but increased markedly at higher salinity levels with biofertilizer application (S3A–S3E). GPx activity was significantly enhanced in selected treatments, reaching up to 10.93 u/g. Lipid peroxidation, measured by MDA content, declined in most biofertilizer-treated plants, suggesting reduced oxidative damage. Ascorbate and protein contents also improved, particularly in biofertilizer-amended soils. Overall, the findings demonstrate that solid biofertilizer application can enhance stress tolerance in rice by improving antioxidant defense systems and reducing oxidative damage under saline conditions (p < 0.05). Proper biofertilizer management is therefore crucial for optimizing plant resilience in salinity-affected soils.

Keywords: Salinity stress, Oryza sativa L., Biofertilizers, Antioxidant defense system, Oxidative stress, Soil health, Crop productivity