RESUMEN
Plastic mulch film is often believed to be a significant contributor to microplastic pollution in farmland soil, however, its direct impact in areas with high human activities remains unclear due to the presence of multiple pollution sources. This study aims to address this knowledge gap by investigating the impact of plastic film mulching on microplastic pollution in farmland soils in Guangdong province, China's largest economic province. The macroplastic residues in soils were investigated in 64 agricultural sites, and the microplastics were analyzed in typical plastic film mulched and nearby non-mulched farmland soils. The average concentration of macroplastic residues was 35.7 kg/ha and displayed a positive correlation with mulch film usage intensity. Contrarily, no significant correlation was found between macroplastic residues and microplastics, which exhibited an average abundance of 22,675 particles/kg soil. The pollution load index (PLI) model indicated that the microplastic pollution level was category I and comparatively higher in mulched farmland soils. Interestingly, polyethylene accounted for only 2.7% of the microplastics, while polyurethane was found to be the most abundant microplastic. According to the polymer hazard index (PHI) model, polyethylene posed a lower environmental risk than polyurethane in both mulched and non-mulched soils. These findings suggest that multiple sources other than plastic film mulching primarily contribute to microplastic pollution in farmland soils. This study enhances our understanding of microplastic sources and accumulation in farmland soils, offering crucial information on potential risks to the agroecosystem.
RESUMEN
To investigate the effects of plastic film mulches and their residual films after use on soil bacterial communities, mulching experiment and the subsequent residual film experiment were conducted on winter-planting potato field in two locations. During mulching experiment, treatments biodegradable film mulch (BM) and PE film mulch (PM) reduced soil nutrient regarding available nitrogen and available potassium, as well as microbial biomass carbon (MBC), but increased urease activity, as compared to treatment no film mulch (NM). Soil moisture was significantly elevated by mulching practices and correlated with more microbial phyla than the other tested soil properties, indicating its important role in shaping soil bacterial communities. In addition, mulching practices increased alpha diversity of soil bacteria, although location heterogeneity was observed. Network analyses showed that both treatments BM and PM promoted the interrelations within bacterial communities and harbored more keystone taxa than treatment NM. During residual film experiment, residual films from BM and PM were incorporated into soil after harvest of potato. Treatment residual biodegradable film (RBF) significantly increased the content of MBC and activity of ß-glucosidase (BG) as compared to treatments residual PE film (RPF) and no residual film (NRF), and BG had the most correlations with microbial phyla among all the tested soil properties. Treatments RBF and RPF increased the relative abundance of some dominant bacterial phyla, including Bacteroidetes, Actinobacteria, and Chlorofexi, and enhanced the interrelations within bacterial community, whereas more keystone taxa were harbored by treatment RBF, due to the increase of keystone taxa in phyla Acidobacteria, Actinobacteria, Bacteroidetes, and Proteobacteria. These results indicate that the indirect effects of biodegradable and PE film mulch as a soil surface barrier on soil are similar, whereas their direct effects via incorporation into soil as residual films show specificity.