Can Rhizosphere Effects Mitigate the Threat from Nanoplastics and Plastic Additives to Tomato (Solanum lycopersicum L.)?

Nanoplastics (NPs) and plastic additives inevitably coexist to threaten soil health and plant growth. Herein, in a root-box system isolating the rhizosphere and bulk soils, we explored the combined effects of NPs and a kind of typical plastic additive di-(2-ethylhexyl)phthalate (DEHP) on soil health via combining the evidence from in situ zymography, the microbiome, and metabolism. The plastic additive dominated the risks of plastic pollution to plants, and the coexistence of NPs did not mitigate the DEHP threat to microorganisms and increased that to food safety. Compared to single DEHP, combined NPs and DEHP inhibited β-glucosidase activity to limit soil organic carbon (C) decomposition and stimulated acid phosphatase activity to increase P uptake by tomato roots and enriched the relative abundance of C-fixed bacteria and P-dissolution bacteria, while inhibiting that of chemical heterotrophic bacteria in rhizosphere soils, which further stimulated the synthesis and metabolism of phospholipid and fatty acid and triphosphate cycle and increased nutrients bioavailability for plants. Therefore, rhizosphere effects optimized the root nutrient acquisition strategy, microbial community structure, and their metabolic processes to reduce the threat from NPs and plastic additives to plants. This study provides new insights for environmental risk control and agricultural management under plastic pollution.