Silica nanoparticles promote the growth of pepper under salt stress by improving photosynthesis and modulating the water relationship

• SiNP300 is a suspension containing 300 mg of silica nanoparticles per liter. • SiNP300 significantly improved the growth parameters of pepper under salt stress, such as stem diameter, leaf length, leaf width, fresh weight, dry weight, root length, root surface area, and average root diameter. • SiNP300 enhanced the net photosynthetic rate, transpiration rate, stomatal conductance, photosystem II efficiency maximum photochemical efficiency ( Fv / Fm ), and photosystem II actual photochemical efficiency ( Ф PSⅡ) of salt-stressed pepper. • SiNP300 reduced the relative electrolyte conductivity (REC), lipid peroxidation, and improve plasma membrane integrity of pepper under salt stress. Salinity stress is a global limitation to agricultural productivity. Silica nanoparticles (SiNPs) have been shown to enhance plant tolerance to salt stress. However, the precise mechanisms by which SiNPs regulate this response in pepper remain poorly understood. This study examined the effects of SiNP300 (300 mg L −1 SiNPs) on salt-stressed pepper plants. The findings revealed that SiNP300 significantly promoted pepper growth and biomass under salt stress conditions. Specifically, treatment with SiNP300 resulted in increases in total chlorophyll content (37.39%), net photosynthetic rate (583.14%), transpiration rate (121.08%), stomatal conductance (249.67 %), Fv / Fm (23.18 %), and Ф PSⅡ (43.67 %). In addition, SiNP300 enhanced relative water content, leaf water potential, and root vitality, indicating its role in maintaining water status under salt stress. Moreover, SiNP300 reduced reactive oxygen species (ROS) accumulation, contributing to a reduction in relative electrolyte conductivity (REC), while simultaneously boosting osmotic potential and preserving plasma membrane integrity. Further analysis demonstrated that SiNP300 increased soluble sugar levels in both leaves and roots, likely by modulating the activities of acid invertase (AI), neutral invertase (NI), and sucrose phosphate synthase (SPS), which may improve water status and osmotic regulation under salt stress. Additionally, SiNP300 modulated the expression of aquaporin (AQP) genes ( CaPIP1–1 and CaTIP1–1 )., thus regulating the water balance of pepper plants in saline conditions. This study provides valuable insights into the mechanisms by which SiNP300 alleviates salt stress and lays the groundwork for developing technologies aimed at enhancing plant resilience to abiotic stress.