L-Arginine Alleviates PVC Microplastic Toxicity in Oat through Ecophysiological and Rhizosphere Microbiome Modulation

L-arginine serves as an important protective agent against abiotic stress in plants, enhancing resilience and offering a potential strategy to mitigate environmental stressors. In contrast, microplastic toxicity has emerged as a serious concern in agricultural systems due to the widespread use of plastics, posing risks to plant growth even at low concentrations. Therefore, this study was conducted to evaluate the potential of L-arginine in alleviating the adverse effects of polyvinyl chloride (PVC) microplastics on oats (Avena sativa L.). A hydroponic experiment was performed using Hoagland’s nutrient solution with three levels of L-arginine (0, 25, and 50 µmol L⁻¹) and three levels of PVC microplastics (0, 2, and 4 mg L⁻¹). The study assessed morphological, physiological, biochemical, rhizosphere microbial, health risk, protein band pattern, and gene expression responses, along with ultrastructural observations using electron microscopy. The application of L-arginine significantly enhanced plant biomass and photosynthetic pigment levels while reducing oxidative stress through increased antioxidant activity and gene expression. It also modulated proline metabolism and improved the ascorbate–glutathione cycle. L-arginine enhanced rhizosphere microbial diversity and restored the relative abundance of beneficial microbial groups. Health risk indices, including chronic daily intake and cancer risk, were reduced in L-arginine-treated plants. At the molecular level, L-arginine enhanced the expression of antioxidant-related genes and modified protein band patterns, indicating improved cellular stability under stress. Furthermore, microplastic exposure induced stomatal closure, whereas L-arginine application partially restored stomatal function. Overall, L-arginine demonstrates strong potential as a sustainable strategy to mitigate microplastic-induced stress in plants by improving physiological performance, enhancing microbial stability, and strengthening gene expression–based defense responses.