Individual and combined effects of nano-silicon, silicate-solubilizing bacteria, and earthworm on wheat growth under...

Salinity stress disrupts plant physiology and inhibits plant growth. While microorganisms and silicon (Si) are known to mitigate salt stress, their combined effect with soil fauna like earthworms is underexplored. This study examined the effects of Si nanoparticles (Nano-Si: 0, 100, 200 mg kg⁻¹) and biological treatments (silicate-solubilizing bacteria (SSB) Bacillus subtilis (SSB1), Pseudomonas fluorescens (SSB2), earthworm Eisenia fetida (EWs)), and their combinations, on wheat under three salinity levels (0.97, 5, and 8 dS m⁻¹). Salinity reduced biomass, chlorophyll, relative water content (RWC), and potassium uptake, while increasing sodium, electrolyte leakage (EL), lipid peroxidation (MDA), and antioxidant enzyme activity. Nano-Si at 200 mg kg⁻¹ alleviated stress, increasing shoot dry weight (21.5%), chlorophyll (32.8%), and RWC (13.3%), while reducing MDA (17.3%) and EL (12.4%). SSB inoculation similarly improved growth and oxidative stress markers. The Nano-Si and SSB combination was most effective, enhancing the K⁺/Na⁺ ratio and reducing oxidative damage. Earthworms, especially with SSB, further improved soil conditions, increasing root length (up to 17.4%) and shoot Si concentration. We conclude that synergistic application of Nano-Si and SSB effectively enhances wheat salinity tolerance by improving photosynthesis, ion homeostasis, and antioxidant defense, with earthworms providing additional benefits for root development and Si uptake.