Effects of microplastics and acid rain on soil chemical properties, enzyme activity, and bacterial communities

While the adverse impacts of microplastics (MPs) on soil ecosystems have been extensively documented, their combined effects with acid rain (AR) remain poorly understood. In this study, we investigated the effects of low-density polyethylene (LDPE) and polylactic acid (PLA) on soil properties, enzyme activities, and bacterial communities in soils with different acid rain levels. The results showed that microplastics had negligible effects on soil pH but significantly altered available phosphorus content. Notably, 2 % PLA increased soil organic carbon and acid phosphatase activity, though AR did not further enhance acid phosphatase activity. In contrast, AR significantly stimulated β-D-glucosidase activity regardless of microplastic presence. Redundancy analysis identified available phosphorus and acid phosphatase as key drivers of microbial community structure. 16S rRNA sequencing revealed that 2 % PLA reduced bacterial α-diversity and reshaped community composition, with these effects being exacerbated under low AR level conditions. At the phylum level, 2 % PLA increased the relative abundance of Proteobacteria while decreasing that of Firmicutes. At the genus level, 2 % PLA enhanced the prevalence of Bradyrhizobium and Paraburkholderia but reduced that of Sinomonas. These findings bridge critical knowledge gaps regarding the risks of microplastics in acid rain-affected regions.