Characteristics of microplastics and their effects on phthalates and microbial activity in greenhouse soil after long-term planting

As an exogenous pollutant, the microplastics accumulated in soil could alter microbial activity. The use of plastic mulch in greenhouse vegetable planting not only enhances vegetable yield and quality, but also leads to the formation and accumulation of microplastics in the soil over time. It is essential to determine the characteristics of microplastics and microorganisms in soils with varying years of planting is crucial for ensuring vegetable quality and quantity. Therefore, this study investigated the abundance and particle size of microplastics, the concentration of phthalates (PAEs), and the dynamics of soil microbial activity in greenhouse soils with different planting years (5, 10, 15, 20, 25, and 30 years). Results showed that microplastics increased in abundance, particle size, and PAEs concentration as planting years progressed. Specifically, the abundance of microplastics rose from 70.0 ± 8.7 to 224.0 ± 10.4 items/kg, with the proportion of microplastics sized 0–2 mm increasing from 14.02 to 69.11 %, and the total PAEs concentration in the soil escalating from 0.31 to 1.89 mg/kg. Additionally, Bacteroidetes and Actinobacteria levels increased, correlating with organic matter degradation. Metabolic pathway linked to degradation were enriched according to KEGG analysis. Correlation analysis revealed that microplastics notably decreased soil pH, creating an acidic environment that boosted urease activity and the relative abundance of Nitrospirae. This study sheds light on the accumulation characteristics of microplastics and their impact on soil microbial activity following prolonged planting.