Biodegradable microplastics can cause more serious loss of soil organic carbon by priming effect than conventional microplastics in farmland shelterbelts

<ol><li>Globally, the widespread utilization of plastic products has resulted in the accumulation of microplastics (MPs) in the soil. MPs have the potential to impact the loss of soil organic carbon (SOC). Nevertheless, the influence of different types of MPs on SOC loss remains uncertain.</li><li>In this study, a 38 day incubation experiment with two kinds of conventional MPs (polyethylene, polypropylene) as well as two kinds of biodegradable MPs (polyhydroxyalkanoate [PHA], polylactic acid [PLA]) were added into three types of soil (loam, sandy loam, and sandy soil) in farmland shelterbelts, and the sources of CO2 emissions was distinguished by the difference in C-13 isotope abundance between the biodegradable MPs (PHA and PLA) (-10.02 parts per thousand to -9.92 parts per thousand) and the soil (-24.39 parts per thousand to -22.86 parts per thousand) (>10 parts per thousand).</li><li>In conjunction with the structural characterization of MPs, as well as soil physicochemical properties and microbial characteristics, we observed that the conventional MPs did not degrade in short term incubation, but significantly enhance soil-derived CO2 emissions by altering the dissolved N content (-N and dissolved total N [DTN]) and reducing microbial biomass carbon content only in sandy loam soil (p < 0.05). Biodegradable MPs degraded significantly, and enhanced soil-derived CO2 emissions by reducing soil DTN and -N contents in loam, sandy loam and sandy soil (p < 0.05).</li><li>Overall, the input of biodegradable MPs causes a more serious loss of SOC than conventional MPs as the soil sand content increased in short term incubation, which needs to be considered in predicting the global impact of increasing biodegradable MPs pollution.</li> </ol>