Microplastics Can Inhibit Organic Carbon Mineralization by Influencing Soil Aggregate Distribution and Microbial Community Structure in Cultivated Soil: Evidence from a One-Year Pot Experiment

Microplastics (MPs) pollution has become a global pollution problem, potentially affecting soil carbon cycling and structure stability in agricultural systems. However, the effects of MPs pollution on soil organic carbon fractions/transformation and soil aggregate stability remain unknown. Thus, a combination of one-year pot and short-term mineralized incubation experiments that involved a reference (CK, with no MPs), different concentrations (0.1, 1, and 2 w/w % polyethylene (PE)), and types (0.1 w/w % PE, polypropylene (PP), and polyvinyl chloride (PVC)) of MPs were carried out to investigate the effects on the soil aggregate stability and organic carbon mineralization after one year of adding MPs. The results showed that the size distribution of the soil partial aggregates varied significantly as affected by the MP concentration and type (p ˂ 0.05). Compared with 0.1% PE, significant increases in the MWD (mean weight diameter) and GMD (geometric mean diameter) of 2% PE of 27.22% and 32.73%, respectively, were detected. In addition, high concentrations (>1%) of PE significantly decreased the dissolved organic carbon (DOC) (p ˂ 0.05), whereas they significantly increased the stable carbon fractions including the particulate organic carbon (POC) and mineral-bound organic carbon (MOC) (p ˂ 0.01). Meanwhile, compared with the CK, both MP types and doses significantly decreased the soil organic carbon mineralization rate (SOCMR) and cumulative mineralization amount (CM) (p ˂ 0.001). Moreover, the MPs significantly increased the total PLFA (phospholipid fatty acid) by 261.9–438.8% (p ˂ 0.01), and the soil pH and total PLFA were the dominant factors that affected the SOCMR as affected by MPs. Thus, a high concentration (>1%) of PE significantly decreased the SOCMR by influencing the soil pH, TN, and macroaggregate (R>0.25) content and microbial community composition. This study provided evidence of the feedback of MPs pollution on soil C dynamic and aggregates in cultivated soil in South China.