Silicon-mediated regulation of photosynthesis, ion homeostasis and antioxidant defense improves salinity tolerance in Agropyron cristatum × A. desertorum cv. Hycrest-Mengnong

Abstract Soil salinity is a major abiotic stress that severely limits plant growth and productivity worldwide, particularly under changing climate conditions. Silicon (Si) has emerged as a promising approach for improving plant tolerance to salinity stress; however, its integrated physiological effects in perennial forage grasses remain insufficiently understood. This study investigated the role of Si in alleviating salinity stress in Agropyron cristatum × A. desertorum cv. Hycrest-Mengnong under controlled conditions. Plants were exposed to 0, 100, and 200 mM NaCl with or without Si application, and growth, physiological, biochemical, and ionic responses were evaluated. Salinity stress significantly reduced plant height, biomass, leaf area, photosynthetic performance, chlorophyll content, and PSII efficiency, with the strongest inhibitory effects observed at 200 mM NaCl. Salinity also increased oxidative damage, as indicated by higher malondialdehyde (MDA) content, promoted proline accumulation associated with osmotic adjustment, enhanced antioxidant enzyme activities, and disrupted ionic homeostasis through excessive Na⁺ accumulation and reduced K⁺/Na⁺ ratio. Si application markedly alleviated these adverse effects by improving growth, maintaining photosynthetic efficiency and chlorophyll stability, enhancing antioxidant defense, promoting osmotic adjustment, and regulating ion balance through reduced Na⁺ accumulation and improved K⁺ retention. These findings demonstrate that Si enhances salinity tolerance through coordinated regulation of physiological, biochemical, and ionic mechanisms. The study provides a mechanistic framework for understanding Si-mediated salinity tolerance in perennial forage grasses and highlights the potential application of Si for improving forage productivity under saline conditions.