Ecotoxicological effects of polyethylene micro/nano-plastics and Cd on the physiological response, Cd migration, and their rhizosphere microbial community of Salix matsudana

The coexistence of micro/nano-plastics (MPs/NPs) and heavy metals in the environment has become inevitable. Existing published studies mainly focus on the effects of MPs and cadmium (Cd) coexistence on herbs, while relatively few studies are conducted on plants with high phytoremediation potential, especially woody plants. Our previous investigations identified Salix matsudana as potential phytoremediation species for Cd contamination. This study investigated the physiological response, accumulation, translocation, and distribution of Cd in S. matsudana seedlings, and their rhizosphere environment characteristics under the single or combined contamination of polyethylene (PE) MPs or NPs and Cd. Results showed that, when coexisted with Cd respectively, PE-MPs partially alleviated the phytotoxicity caused by Cd, while PE-NPs exacerbated it. Multiple pollution of PE-MPs, PE-NPs and Cd showed an intermediate phytotoxicity between PE-MPs and PE-NPs with Cd. PE-MPs reduced the absorption and translocation of Cd in plants, but PE-NPs promoted the process. Different detoxification strategies, like modifying Cd subcellular distribution and chemical forms, were adopted after PE-MPs or PE-NPs addition. Additionally, co-exposure of PE-MPs and Cd alleviated the inhibition of rhizosphere fertility and microbial community caused by Cd stress. In contrast, PE-NPs and Cd coexistence further reduced soil microbial community diversities and increased Cd availability. Soil fungal communities were more tolerant to Cd stress than bacterial communities. The results offer useful references for the toxicological characteristics of woody plants and their rhizosphere micro-environment under PE-MPs/NPs and Cd co-exposure, and provide a theoretical reference and empirical basis for implementing phytoremediation in the co-contaminated soils of MPs and Cd.