Enhancing rice productivity in wastewater-irrigated saline Cd-contaminated soils using microbial-nanoparticle synergy

Soil salinity and cadmium (Cd) contamination pose significant threats to agricultural productivity and food security, particularly in rice-growing regions. This study investigates the synergistic effects of plant growth-promoting rhizobacteria (PGPRs) (Pseudomonas koreensis, Bacillus coagulans, and Pseudomonas stutzeri) and selenium nanoparticles (SeNPs) in remediating saline Cd-contaminated soils and enhancing rice (Oryza sativa L.) performance. Over two consecutive growing seasons (2022–2023), the combined application of PGPRs and SeNPs significantly improved soil health, reducing soil pH from 8.50 to 8.02 and electrical conductivity (EC_e) from 5.97 to 4.01 dS m⁻¹ , while increasing soil organic matter (SOM) by 6.5 % and cation exchange capacity (CEC) by 25.6 %. The treatment also reduced soil Cd content by 34.6 %, from 0.81 to 0.53 mg kg⁻¹ , and decreased Cd accumulation in rice roots, shoots, and seeds by 56.7 %, 65.0 %, and 50.0 %, respectively, ensuring safer rice grain production. Furthermore, SeNPs significantly enhanced selenium (Se) content in rice shoots and seeds, with Se levels increasing from 0.55 to 1.47 µg g⁻¹ in shoots and from 0.01 to 0.51 µg g⁻¹ in seeds, highlighting their role in improving rice nutritional quality. Physiological analyses revealed enhanced photosynthetic pigment concentrations, with chlorophyll a increasing by 112.3 % and carotenoids by 213.6 %, alongside a 101.9 % increase in superoxide dismutase (SOD) activity under the combined treatment. These improvements translated into a 25.0 % increase in grain yield, from 5.76 to 7.24 ton ha⁻¹ , and a 21.4 % increase in 1000-grain weight. The findings highlight the efficacy of PGPRs and SeNPs in mitigating oxidative stress, improving nutrient uptake, reducing Cd toxicity, and enhancing rice productivity under combined salinity and Cd stress. This study provides a novel, eco-friendly strategy for sustainable soil remediation and crop production in contaminated environments, offering significant implications for global food security and agricultural sustainability.