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Effects of polyethylene microplastics and cadmium co-contamination on the soybean-soil system: Integrated metabolic and rhizosphere microbial mechanisms
Summary
Researchers investigated how polyethylene microplastics and cadmium interact in soybean-soil systems and found that specific microplastic concentrations enhanced cadmium accumulation in roots under moderate contamination. Higher microplastic levels reduced beneficial soil bacteria like Sphingomonas and Bradyrhizobium and suppressed nitrogen-cycling functions. The study demonstrates that microplastics fundamentally alter heavy metal behavior through interconnected plant-metabolite-microbe interactions in agricultural soils.
The coexistence of microplastics (MPs) and heavy metals in agricultural soils presents complex and poorly understood ecological risks. While previous studies have examined the individual effects of these pollutants, the interactive mechanisms governing their combined impact on plant-soil systems, particularly through integrated metabolic and microbial pathways remain unclear. This study investigated the effects of polyethylene microplastics (PE-MPs) and cadmium (Cd) co-exposure on soybean-soil systems. Under moderate Cd exposure (20 mg/kg), specific PE-MPs concentrations (1 % and 5 %) enhanced Cd accumulation in soybean roots, whereas this trend reversed under high Cd levels (50 mg/kg). Co-exposure maintained stable shoot growth through activation of stress-response pathways (β-alanine, porphyrin, and pantothenate metabolism). Rhizosphere microbiome analysis revealed that 5 % and 10 % PE-MPs reduced the abundance of Sphingomonas and Bradyrhizobium in Cd-contaminated soil and suppressed nitrogen-cycling functionality. Integrated metabolite-microbe network analysis identified malonyldaidzin as a potential mediator linking soybean leaf metabolism with rhizobacterial interactions, associated with root Cd accumulation. These findings demonstrate that PE-MPs fundamentally alter Cd behavior through tripartite plant-metabolite-microbe interactions, thereby highlighting the need to incorporate MPs effects into ecological risk assessments of heavy metal contamination in agricultural ecosystems.