[Effects of Microplastics Addition on Soil Organic Carbon Mineralization in Citrus Orchard]

To investigate the effects of microplastics on soil organic carbon mineralization and the changes in soil enzyme activities, an incubation experiment was conducted whereby single applications of either microplastics or straw, and combined application of both, were added to Dangyang citrus orchard soil. The results showed that the combined application of straw and microplastics significantly affected organic carbon mineralization in the soil, but the single addition of microplastics had no significant effect. Compared with straw alone, the application of a small combined amount of microplastics and straw significantly increased soil organic carbon mineralization by 8.20%, while medium and high amounts of the combined application significantly inhibited soil organic carbon mineralization. The lowest amount of organic carbon mineralization occurred with the highest amount of combined microplastics and straw, 10.13% lower than with straw alone. The addition of microplastics significantly reduced the activity of β-glucosidase. In particular, a high amount of microplastics significantly decreased the activity of β-glucosidase, compared with the control, by 20.52%, 43.93%, and 17.79% on the day 1, 6, and 35, respectively. However, straw application alleviated the inhibition effect of microplastic application on soil β-glucosidase activity. The soil organic carbon mineralization rate was significantly positively correlated with DOC, MBC and β-glucosidase activity.