Silicon Combined with Activated Carbon Enhances Salt Tolerance in Strawberry (Fragaria × ananassa) by Reinforcing Ion–Redox Homeostasis and Reshaping the Rhizosphere Microbiome

Soil salinity severely constrains strawberry production by disrupting ion homeostasis and provoking oxidative injury. Here, we investigated whether soluble silicon (Si) and activated carbon (AC) act synergistically to enhance salt tolerance in strawberry (Fragaria × ananassa). Under NaCl stress, plants showed pronounced growth inhibition, increased Na⁺ accumulation and a deteriorated K⁺/Na⁺ balance, accompanied by elevated reactive oxygen species (ROS) and lipid peroxidation. In contrast, combined Si and AC treatment consistently provided the strongest protection, improving seedling vigor and survival, limiting Na⁺ build-up while maintaining a higher K⁺/Na⁺ ratio, and attenuating oxidative damage as reflected by reduced ROS and MDA levels together with enhanced activities of antioxidant enzymes (SOD, POD and CAT). Beyond plant responses, AC-containing treatments alleviated salt-induced increases in soil electrical conductivity and improved soil nutrient availability, coinciding with a clear restructuring of the rhizosphere bacterial community and enrichment of putatively beneficial taxa. Transcriptome profiling further supported coordinated reprogramming of ion transport, redox control and stress-responsive signaling pathways under the Si+AC regime. Collectively, our results indicate that Si and AC co-application enhances strawberry salt tolerance through an integrated soil–plant–microbiome mechanism that stabilizes ion homeostasis and reinforces redox homeostasis.