Unraveling the mechanism of cadmium stress alleviation in Forsythia suspensa by SeNPs-enriched Rhodopseudomonas palustris via root metabolomics.

This study systematically investigated the effects and intrinsic mechanisms of inoculating SeNPs-enriched Rhodopseudomonas palustris (SR) on the physiological and biochemical traits, Cd accumulation, and root metabolome of Forsythia suspensa under Cd stress. A pot experiment was designed with a full factorial combination of three Cd concentrations (3.75, 7.5, and 15.0 mg kg-1 soil) and four SR inoculation levels (0.5 × 109, 1.0 × 109, 1.5 × 109, and 2.0 × 109 CFU mL-1). The results demonstrated that SR inoculation significantly reduced shoot Cd content by up to 54.14 % and dramatically enhanced shoot selenium content by 58-fold in F. suspensa. Physiologically, SR effectively alleviated Cd-induced growth inhibition. At the biochemical level, SR mitigated Cd-induced oxidative damage by elevating glutathione levels and enhancing the activities of antioxidant enzymes, thereby reducing the accumulation of malondialdehyde and hydrogen peroxide. Additionally, SR improved cellular osmotic balance by modulating osmotic substances and enhanced metal chelation capacity by upregulating root levels of metallothionein and phytochelatin synthase. Untargeted metabolomics analysis showed that, compared to Cd stress alone, SR inoculation (Cd7.5+SR2.0 treatment) significantly upregulated key metabolites including L-glutamate, L-aspartate, L-arginine, and scopoletin. These differentially expressed metabolites were primarily enriched in critical metabolic pathways such as amino acid metabolism, unsaturated fatty acid metabolism, ABC transporter biosynthesis, and glutathione metabolism. This study provides a theoretical basis for plant-microbe combined remediation of Cd-contaminated soils and offers novel insights into the mechanisms of SR-mediated Cd stress alleviation in medicinal plants.