Polyethylene Microplastics Alter the Microbial Functional Gene Abundances and Increase Nitrous Oxide Emissions from Paddy Soils

The accumulation of microplastics (MPs) in terrestrial ecosystems can affect greenhouse gases (GHGs) production by changing soil structure and microbial functions. In this study, microcosm experiments were conducted to investigate the impact of polyethylene (PE) MP addition on soil carbon dioxide (CO) and nitrous oxide (NO) emissions from paddy soils and their associated microbial functional genes. Methane was not considered due to the negligible emissions throughout the incubation. The amendment of both virgin and aged PE MPs did not significantly (p > 0.05) affect soil CO emissions, but significantly (p < 0.05) increased the abundances of microbial functional genes encoding enzymes involved in hemicellulose (abfA) and lignin (mnp) decomposition, indicating plastic particle has potential to stimulate soil organic carbon decomposition. The presence of PE MP significantly increased NO emissions by 3.7-fold, which was probably due to PE MP increased the abundances of nirS gene involved in nitrite reductase. In addition, compared with virgin PE MP treatment, artificially aged PE MP did not significantly (p > 0.05) influence soil CO and NO emissions. Our results provide evidence that PE MP likely cause a high risk of NO emission from paddy soils, this factor should be considered in future estimates of GHGs emissions from rice fields.