[Effects of Different Microplastics in Soil on Nitrogen Absorption and Metabolism in Lettuce （Lactuca sativa L.）]

To illuminate the differences in the effects of different types of microplastics （MPs， size<5 mm） on crop nitrogen absorption and metabolism， the degradable polylactic acid （PLA） and polybutylene terephthalate （PBAT） and undegradable polyethylene （PE） were selected for vegetable pot experiments with three doses （0.5%， 1%， and 3%）. The responses of inorganic nitrogen content， plant growth， nitrogen absorption， and metabolism enzyme activity to soil MPs pollution in the soil-lettuce （Lactuca sativa L.） system was investigated. The results showed that MPs significantly hindered the decomposition of soil organic carbon （SOC） and reduction and accumulation of nitrate （NO₃^--N） in lettuce， while increasing soil C/N and ammonium （NH₄⁺-N） content. The total nitrogen （TN） content of soil under the PE treatment was lower than that of the PLA and PBAT treatments for 0.25-0.52 g·kg^-1 and 0.33-0.52 g·kg^-1， respectively. PBAT treated lettuce had significantly lower dry weight and accumulated N uptake compared to those in the PLA and PE treatments （P<0.05）. The 1% dose resulted in the lowest antioxidant enzyme and nitrate reductase （NR） activities and the highest malondialdehyde （MDA） content， with NR activity and MDA content being 15.19%-42.0% and 2.68-3.11 times of the control， respectively. Regarding to the mechanism， N uptake by lettuce was significantly negatively correlated with SOC （P<0.01）. In summary， the MPs input to soil can reduce the activity of N metabolism enzymes in lettuce. The degradable PBAT significantly reduced the N uptake， and the oxidative damage to lettuce was greater under moderate pollution.