Effects of Microplastics with Different Concentrations and Particle Sizes on N₂O Emissions from Agricultural Soils Under Different Temperature Conditions

ObjectiveMicroplastic (MP), with its small size and low degradability, is recognized as a potential persistent organic pollutant in terrestrial ecosystems. MP enters terrestrial ecosystems and affects the soil nitrogen cycling process by changing the soil's physical, chemical, and biological properties. These changes affect soil N2O emission. Despite having gained global attention, the key factors and mechanism of MP influence on soil N2O remain unclear. Therefore, this study aimed to investigate the effects of MP size and concentrations on N2O emission from agricultural soils at different temperatures and thus explore their potential mechanisms.MethodAgricultural soils were collected from plots in South China for indoor culture experiments, and five different treatment sets were selected under three temperature gradients(10 ℃, 20 ℃ and 30 ℃): (1) no microplastics (CK); (2) addition of microplastics with a mass concentration of 0.1% and a particle size of 74 μm(Nlp-0.1%); (3)addition of microplastics with a mass concentration of 0.5% and a particle size of 74 μm (Nlp-0.5%); (4)addition of microplastics with a mass concentration of 0.1% and a particle size of 25 μm(Nsp-0.1%); and (5) addition of microplastics with 0.5% mass concentration and a particle size of 25 μm (Nsp-0.5%). Afterward, soil N2O concentration as well as inorganic nitrogen and microbial functional genes were determined.ResultElevated temperature significantly increased soil N2O emissions from agricultural soils (P 2O emissions at 30 ℃ were 43.3 and 6.3 times higher than those at 10 ℃ and 20 ℃, respectively. In addition, soil NO3–-N content gradually increased with increasing temperature. The abundance of AOB amoA, Comammox(com2), nirS, nirK, and nosZ functional genes was the highest at 20℃ and lowest at 30℃. The effects of MP of different sizes on soil N2O emissions and related nitrogen cycle functional genes varied widely. Compared with the CK treatment, the Nlp treatment significantly increased soil N2O emission by 37.5% and 838.7% at 10 ℃ and 20 ℃(P com2 and nirK functional genes but significantly increased the abundance of nirS functional genes in soil (P 2O emission was significantly and positively correlated with temperature and the concentration of NO3–-N, but significantly and negatively correlated with the abundance of AOA amoA, nirK, nirS, and nosZ functional genes(P nosZ functional genes and temperature were the main factors affecting soil N2O emission.ConclusionElevated temperatures significantly increased N2O emissions from agricultural soils, and different particle sizes and concentrations of MPs had different effects on soil N2O emissions, and there was an interaction effect between microplastics and temperature. The results of this study can provide a scientific basis for investigating the mechanism of MP on N2O emissions from agricultural soils under global warming conditions and for risk assessment.