Potassium Silicate Partially Alleviates Salt-Induced Inhibition of Growth, Photosynthetic Performance, PSII Energy Partitioning, and Oxidative Injury in Cucumber Seedlings

Salt stress restricts cucumber seedling establishment by impairing root development, photosynthesis, ion homeostasis, and redox balance. This study examined whether potassium silicate (K2SiO3) could partially alleviate these responses under hydroponic sodium chloride (NaCl) stress. Cucumber seedlings were exposed to six treatments: a nutrient-solution control, K2SiO3 alone supplying 1.0 mmol L−1 silicon (Si), 75 mmol L−1 NaCl, and NaCl combined with K2SiO3 supplying 0.5, 1.0, or 2.0 mmol L−1 Si. Growth, root morphology, photosynthetic pigments, gas exchange, chlorophyll fluorescence, photosystem II (PSII) energy partitioning, oxidative injury, antioxidant enzyme activities, osmotic adjustment, and ion status were evaluated at 7 and 14 d. NaCl markedly reduced seedling growth, root development, net photosynthetic rate, PSII photochemical performance, and electron transport, while increasing leaf sodium (Na+), malondialdehyde accumulation, non-photochemical quenching, non-regulated energy loss, proline, and soluble sugar. K2SiO3 partially alleviated these changes. The treatment supplying 1.0 mmol L−1 Si produced the strongest integrated recovery of growth, root activity, photosynthetic performance, PSII function, and oxidative status. The treatment supplying 2.0 mmol L−1 Si resulted in the lowest leaf Na+ concentration and the highest leaf potassium (K+)/Na+ ratio among salt-stressed seedlings but did not produce the greatest growth recovery. These findings suggest coordinated changes in photosynthesis, photochemical energy use, redox status, and ion balance. Because K2SiO3 supplied both Si and K+, the results represent responses to K2SiO3 supplementation rather than Si-specific effects.