Straw addition promotes biodegradable microplastic degradation and affects soil ecosystems: A comparative study across different soil types.

Biodegradable microplastics (bio-MPs), specifically poly(butylene adipate-co-terephthalate) microplastics (PBAT-MPs), are an emerging soil contaminant of significant concern. While straw incorporation is a common agricultural practice, the biochemical interactions between crop residues and PBAT-MPs across diverse soil habitats remain poorly understood. Specifically, it is unclear how soil texture and initial organic matter availability modulate the microbial response and subsequent plastic degradation. This study conducted a 120-day incubation experiment using loam and sandy soils to investigate these driving factors. Results indicated that straw incorporation significantly accelerated PBAT-MP degradation. The most pronounced effect was observed in organic-rich loam under high-dose (5%) straw treatment, where the carbonyl index (CI) decreased substantially, indicating enhanced polymer oxidation. Straw improved soil physicochemical properties, increasing organic matter (SOM) by 23.4% in loam and 76.0% in sandy soil. Furthermore, straw stimulated FDA hydrolase, β-glucosidase, and cellulase activities by up to 137.4%, 23.6%, and 64.0%, respectively, compared to microplastic-only treatments. Although straw promoted degradation in both soil types, the process was more efficient in loam. This is because native organic matter provided greater microbial metabolic stability and mitigated nutrient limitations during the co-metabolic breakdown of polymers. Partial least squares path analysis (PLS-PM) confirmed these findings. It revealed that straw-induced changes in microbial structure, particularly the enrichment of the Proteobacteria and Bacteroidetes phyla, were the primary drivers of accelerated PBAT degradation. Our findings highlight that the ecological benefits of straw return in mitigating plastic pollution are context-dependent and most effective in soils with higher intrinsic organic content.