Assessing the combined impacts of microplastics and nickel oxide nanomaterials on soybean growth and nitrogen fixation potential

The excessive presence of polystyrene microplastic (PS-MPx) and nickel oxide nanomaterials (NiO-NPs) in agriculture ecosystem have gained serious attention about their effect on the legume root-nodule symbiosis and biological nitrogen fixation (BNF). However, the impact of these contaminants on the root-nodule symbiosis and biological N-fixation have been largely overlooked. The current findings highlighted that NiO-NMs at 50 mg kg improved nodule formation and N-fixation potential, leading to enhanced N uptake by both roots and shoots, resulting in increased plant growth and development. While single exposure of PS-MPx (500 mg kg) significantly reduced the photosynthetic pigment (8-14 %), phytohormones (9-25 %), nodules biomass (24 %), N-related enzymes (12-17 %) that ultimately affected the N-fixation potential. Besides, co-exposure of MPx and NiO at 100 mg kg altered the nodule morphology. Additionally, single and co-exposure of MPx and NiO-NMs at 100 mg kg reduced the relative abundance of Proteobacteria, Gemmatimonadota, Actinobacteria, Firmicutes, and Bacteroidetes is associated with N-cycling and N-fixation potential. The findings of this study will contribute to understanding the potential risks posed by MPx and NiO-NMs to leguminous crops in the soil environment and provide scientific insights into the soybean N-fixation potential.