Effects of Ascorbic Acid and/or α-Tocopherol on Agronomic and Physio-Biochemical Traits of Oat (Avena sativa L.) under Drought Condition

Water stress is notably a critical environmental condition restricting plant growth and economic outputs in semi-arid and arid environments. In a pot experiment, we explored the potential function of alpha-tocopherol (alpha-toc) and/or ascorbic acid (AsA) on the agronomic and physio-biochemical features of oat grown in water-scarce conditions. Drought duration significantly reduced the soil electrical conductivity and pH but increased the soil temperature, influencing the nutrient availability and uptake. For example, post-drought (25 days) soil analysis indicated that electrical conductivity decreased from 597 to 306 mS/m, total dissolved solids from 298 to 153 mg/L, and pH from 7.5 to 6.3 in 25 days of drought. Further, the drought-stressed leaves also contained significantly lower metabolites, such as proline, protein, sugar, and glycine betaine, than the control leaves, indicating impaired plant defense mechanisms. Significantly increased enzymatic antioxidants in leaves (e.g., superoxide dismutase, ascorbate peroxidase, and peroxidase) suggested the inability of oat plants to overcome drought-induced oxidative damage. In contrast, AsA and/or alpha-toc significantly amplified the seed germination rates and plant growth. Taken together, our results demonstrate that AsA and alpha-toc have the capability to mitigate adverse effects of drought conditions on oat plants by improving leaf relative water contents, photosynthetic pigments, and the antioxidant defense system.