Synergistic Effects of Salt-Tolerant PGPR and Foliar Silicon on Pak Choi Antioxidant Defense Under Salt Stress

Salinization severely impairs crop growth by inducing oxidative stress and disrupting cellular homeostasis. This study systematically investigates the synergistic effects of salt-tolerant plant-growth-promoting rhizobacteria (ST-PGPR) and foliar silicon fertilizer spraying (FSFS) on antioxidant responses in Pak choi under salt stress. Two-season pot experiments were carried out to evaluate key indicators, including antioxidant enzyme activities (superoxide dismutase: SOD; peroxidase: POD; catalase: CAT), oxidative stress (malondialdehyde: MDA), osmolyte accumulation (proline, soluble protein), and hormones (Jasmonic Acid: JA; Salicylic Acid: SA; Abscisic acid: ABA). The results demonstrate that combining ST-PGPR with FSFS significantly enhances SOD (6.18-2353.85%), POD (3.44-153.29%), and CAT (25.71-319.29%) activities while reducing MDA content (8.12-35.87%). Proline and soluble protein levels increased by 1.56-15.71% and 5.03-188.87%, respectively. Hormonal regulation increased JA, SA, and ABA levels by 1.05-31.81%, 2.09-34.29%, and 3.18-30.09%, respectively. Notably, ST-PGPR treatments at 10⁴ and 10⁶ cfu·mL^-1, combined with foliar silicon application, consistently ranked highest in overall antioxidant performance across both seasons based on a principal component analysis. These findings provide novel insights into microbial-mineral interactions for sustainable saline agriculture.