| Summary: | Climate change exacerbates flooding problems due to hurricanes followed by heavy rains, particularly in sub-tropical regions. Consequently, submerged plants experience hypoxia stress which limits agronomic and horticultural crop growth and production. Hypoxia causes oxidative damage by accelerating the lipid peroxidation associated with O<sub>2</sub>- and H<sub>2</sub>O<sub>2</sub> levels. Additionally, hypoxia increases the accumulation of organic osmoprotectants and antioxidant activity, whereas it decreases the macronutrient (N, P, K, and Zn) uptake. This study aimed at investigating the effects of flooding-induced hypoxia stress on the growth and the physiological, biochemical, and nutritional characteristics of the hydroponically grown southern highbush blueberry (cv. Jewel) plants. In addition, the hypoxia-mitigating effects of conventional silicon (Si-C) and silicon nanoparticles (SiNPs) and their application methods (foliar vs. foliar and rootzone application) were also appraised. Both the Si-C and the SiNPs efficiently alleviated hypoxia-induced oxidative and osmotic damage to cells by enhancing the activities of the enzymatic antioxidants (ascorbate peroxidase, catalase, dehydroascorbate reductase, superoxide dismutase, peroxidase, guaiacol peroxidase, monodehydroascorbate, reductase); the non-enzymatic antioxidants (ascorbic acid and glutathione contents); and the accumulation of compatible solutes (proline and glycinebetaine) in leaves and roots. However, the SiNPs were more effective than Si-C at improving antioxidant activities and osmolytes formation. A strong negative correlation between the antioxidant activities and the lipid peroxidation rate was observed in the SiNP-treated plants under hypoxia stress. The SiNPs also regulated nutrient uptake by increasing the K, N, P, and Zn concentrations while decreasing Fe and Mn concentrations to a less toxic level. Blueberry plants treated with SiNPs responded more effectively to hypoxia stress by maintaining higher antioxidant and osmoprotectant concentrations than blueberry plants treated with Si-C. Additionally, the foliar and rootzone applications yielded better results than the foliar applications only.
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