Microplastics alter microbial structure and assembly processes in different soil types: Driving effects of environmental factors

Microplastics (MPs) are emerging pollutants with potential impacts on soil ecosystems. However, it is unclear how MPs-induced changes in the soil environment drive microbial structure and assembly in different soils. Here we investigated the responses of microbial structure, enzyme activities and soil properties to biodegradable polylactic acid (PLA) and conventional polythene (PE) with different doses in different soil types. Results showed that PLA generally decreased soil NH-N and NO-N levels but increased dissolved organic carbon (DOC) and pH, whereas PE exhibited contrasting effects depending on soil type. MPs significantly stimulated soil urease, sucrase, catalase and phosphatase activities, with dose-dependent responses observed under PLA treatments in fluvo-aquic soil. Additionally, MPs altered microbial composition and colonized specific bacterial taxa in different soils. In microbial assemblies dominated by stochastic processes, MPs, especially PE promoted the deterministic processes. Co-occurrence patterns showed lower microbial complexity under PLA treatments compared to PE. Notably, we revealed soil-type-specific response patterns: DOC emerged as the primary driver in red soil ecosystems, while pH exerted dominant control in fluvo-aquic soil systems. Furthermore, perturbation of microbial communities by MPs affected functions related to metabolism. These findings highlight that MPs-induced shifts in microbial communities and assembly processes are soil-type-specific and mediated by soil characteristics changes, providing critical insights for assessing the ecological risks of MPs in diverse agricultural soils.