Silicon Confers Salt Tolerance in Potato in a Concentration-Dependent Manner via Coordinated Antioxidant and Osmotic Regulation

Soil salinization restricts potato yield by inducing excessive reactive oxygen species (ROS) accumulation and oxidative damage. Exogenous silicon (Si) can alleviate salt-induced oxidative injury, yet the concentration-dependent mechanisms remain unclear in potato. Here, we conducted a tiered investigation combining phenotypic, physiological, and transcriptomic analyses. An in vitro gradient screening under 0.3% NaCl stress identified 1.0 mM Si as optimal. Compared with NaCl-alone treatment, 1.0 mM Si enhanced Catalase (CAT), Peroxidase (POD), and Superoxide Dismutase (SOD) activities by approximately 2.1-fold, 2.3-fold, and 1.3-fold, respectively. This Si supplementation also dramatically reduced ROS accumulation and membrane lipid peroxidation, as evidenced by 3,3′-diaminobenzidine (DAB) and nitroblue tetrazolium (NBT) staining and decreased Malondialdehyde (MDA) content. Subsequent pot experiments under 100 and 200 mM NaCl confirmed that 2.0 mM Si most effectively alleviated oxidative injury, accompanied by increased proline, higher relative water content, and reduced ROS and MDA. These data demonstrated that Si exerts dose-dependent protection by orchestrating both enzymatic (SOD, POD, CAT) and non-enzymatic (proline, glutathione) antioxidant systems. Transcriptome profiling coupled with Weighted Gene Co-expression Network Analysis (WGCNA) and RT-qPCR revealed eight candidate hub genes, with antioxidant defense-related StGSH1 (glutathione synthesis) and StPRX52 (peroxidase) as key components, alongside genes involved in protein homeostasis and osmotic adjustment. Collectively, our findings establish optimal Si regimes and demonstrate that Si mitigates salt injury primarily through enhancing antioxidative capacity and ROS detoxification, providing candidate genes for antioxidative breeding in potato.