Effects of different types of microplastics in soil on nitrogen absorption and metabolism of quinoa

To reveal the effects of different types of microplastics (particle size < 5 mm) on crop nitrogen absorption and metabolism, biodegradable microplastics made of polylactic acid (PLA) and polybutylene terephthalate (PBAT) andnonbiodegradable microplastics made ofpolyethylene (PE) were selected for plant pot experiments atthree mass fractions(0.5%, 1% and 3%, respectively). The responses of inorganic nitrogen content, crop growth, nitrogen absorption and nitrogen-metabolizing enzyme activity to soil microplastic pollution in the soil-Chenopodium quinoa system were studied. The results revealed that microplastics significantly limited the decomposition of soil organic carbon (SOC), reduced the accumulation of quinoa nitrate nitrogen (NO₃^- -N), and increased the soil C/N ratio. The total nitrogen (TN) content under the PE treatment was lower than that under the PLA and PBAT treatments by 0.03-0.60 g·kg^-1 and 0.27-0.31 g·kg^-1, respectively. The dry weight and cumulative nitrogen absorption of quinoa treated with PBAT were significantly lower than those of quinoa treated with PLA or PE (P < 0.05). The activities of antioxidant enzymes and nitrate reductase (NR) were the lowestin the 1% microplastic treatment, and the content of malondialdehyde (MDA) was the highest; the activities of NR and the MDA content were 40.3-54.3% and 2.54-2.61 times greater in the 1% treatment than in the control, respectively. In terms of mechanism, nitrogen absorption inquinoa was significantly negatively correlated with soil SOC content (P < 0.01). In conclusion, the input of microplastics to the soil can reduce the activity of nitrogen-metabolizing enzymes in quinoa, and biodegradable PBAT significantly reducednitrogen absorption inquinoa. Oxidative damage in quinoa wasgreater when the degree of pollution wasmoderate.