Comparing the Potential of Silicon Nanoparticles and Conventional Silicon for Salinity Stress Alleviation in Soybean (Glycine max L.): Growth and Physiological Traits and Rhizosphere/Endophytic Bacterial Communities

In this study, 20-day-old soybean plants were watered with 100 mL of 100 mM NaCl solution and sprayed with silica nanoparticles (SiO₂ NPs) or potassium silicate every 3 days over 15 days, with a final dosage of 12 mg of SiO₂ per plant. We assessed the alterations in the plant’s growth and physiological traits, and the responses of bacterial microbiome within the leaf endosphere, rhizosphere, and root endosphere. The result showed that the type of silicon did not significantly impact most of the plant parameters. However, the bacterial communities within the leaf and root endospheres had a stronger response to SiO₂ NPs treatment, showing enrichment of 24 and 13 microbial taxa, respectively, compared with the silicate treatment, which led to the enrichment of 9 and 8 taxonomic taxa, respectively. The rhizosphere bacterial communities were less sensitive to SiO₂ NPs, enriching only 2 microbial clades, compared to the 8 clades enriched by silicate treatment. Furthermore, SiO₂ NPs treatment enriched beneficial genera, such as Pseudomonas, Bacillus, and Variovorax in the leaf and root endosphere, likely enhancing plant growth and salinity stress resistance. These findings highlight the potential of SiO₂ NPs for foliar application in sustainable farming by enhancing plant-microbe interactions to improve salinity tolerance.