Effect of microplastics on soil aggregate stability and organic carbon mineralization under flooding condition

Microplastics (MPs) are environmental emerging contaminant in soil owing to their ecological risks to terrestrial ecosystems. However, their impacts on the transformation of soil organic carbon (SOC) formation, especially on storage and emission mechanisms, remain unclear. Thus, we investigated the soil aggregate stability and SOC mineralization in the MPs polluted soil on under flooded conditions, and two particle sizes and three concentrations of MPs were considered. Meanwhile, the partial least squares structural equation model (PLS-SEM) was used to ananlyze the direct and indirect influences of soil property variables mineralization rate. Results showed that MPs enhanced the increase in percentage of aggregate destruction (PAD), indicating a decrease in soil aggregate stability. Soil dissolved organic carbon (DOC) and particulate organic carbon (POC) content increased significantly as MPs content rose, while DOC showed a downward trend with flooded time prolonged. Moreover, MPs significantly changed the aromaticity, biological, and humification index of dissolved organic matter (DOM) in soil, and particle size and concentration are regarded control factors. MPs significantly increased mineralization rate, and smaller-sized MPs showed a more significant promotion on SOC mineralization. PLS-SEM analysis demonstrated significant associations among MPs concentration, PAD, DOC, POC, and mineralization rate. MPs can significantly weaken the stability of soil aggregates, expedite SOC mineralization, and enhance SOC form transformation. Particle size and concentration could be considered control factors in these processes. This study can provide critical insights for predicting carbon flux responses to MP contamination in paddy and wetland soils.