Biofunctionalized sulfur nanoparticles alleviate salinity-induced physio-oxidative damage by maintaining ionic homeostasis and modulating rhizosphere bacterial community in tomato

Soil salinization reduces crop yields and threatens agricultural productivity worldwide. This study investigated the potential of biogenically synthesized sulfur nanoparticles (SNPs) using neem leaf extract to mitigate salinity stress in tomato (Solanum lycopersicum L.) plants. The spherical SNPs, ranging 18–30 nm in size, were characterized using UV–visible spectrophotometry, FTIR, XRD, SEM, and TEM analyses. A greenhouse experiment demonstrated that SNPs (200 mg kg⁻¹) significantly improved plant growth (20.3 %), dry weight (33.0 %), and root length (32.0 %) compared to the control. SNPs application enhanced the chlorophyll a (16.9 %) and b (22.1 %), photosynthetic rate (34.0 %), and water use efficiency (44.0 %). SNPs amendments also led to the upregulation of antioxidant enzymes including superoxide dismutase (24.8 %), peroxidase (25.9 %), catalase (30.5 %) and ascorbate peroxidase (80.0 %), consequently reduced ROS activity and oxidative stress compared to plants treated with L-NaCl control. SNPs amendments restored the ionic homeostasis through reduced the Na⁺ accumulation and improved K⁺ uptake. Transmission electron microscopy revealed that SNPs preserved chloroplast integrity and cell membranes under salinity. High-throughput sequencing results showed that SNPs positively modulated rhizosphere microbial communities, enriching beneficial bacteria like Proteobacteria and Thiobacillus. These findings demonstrate that biogenic SNPs offer a sustainable, eco-friendly approach for managing salinity stress in tomato cultivation, enhancing both plant resilience and soil health through improved plant-microbe interactions.