Agricultural film microplastics counteract root exudate-induced cadmium behavior changes in soil revealed by PLS-PM analysis

Microplastics (MPs), as emerging contaminants, have attracted increasing global attention. MPs in the soil might interact with the root exudates, thus influencing the environmental behavior of cadmium (Cd). However, their complex roles and impact mechanisms are unclear. This study investigated how polyethylene agricultural film microplastics (PE MPs) and ramie root exudates (RE) affect Cd behaviors, soil properties, and microbial diversity. The results revealed that RE increased Cd availability with changing soil properties, enzymes activity and microbial community structure. The addition of PE MPs decreased acid extractable Cd, plant-available Cd and toxicity characteristic leaching procedure (TCLP) Cd by 3.88%-7.41%, 18.92%-28.04% and 3.06%-16.50%, respectively, while PE MPs increased soil pH and soil aggregate mean diameter. Meanwhile, the activity of urease, phosphatase, catalase and the bacterial community abundance were changed by PE MPs. Compared to the only RE treatments, PE MPs decreased the abundance of Acidobacteria, Bacteroidetes and Actinobacteria but increased the activity of Proteobacteria in the soil. The Partial Least Squares Path Modeling (PLS-PM) showed that PE MPs could mitigate Cd availability increase induced by RE, through altering soil characteristics and bacterial community structure. This is the first study investigating the combined effects of PE MPs and RE on Cd behaviors in soil. This study suggests that PE MPs might counteract RE-induced changes in heavy metal activity, which is of significance for the safe production of agricultural products and soil phytoremediation.