Micro(nano)plastic (MNP) pollution in soil environments is a major concern, but the effects of different sizes of MNPs on soil microbial communities, which are crucial in nutrient cycling, has not been well investigated. In this study, we aimed to determine the effects of polystyrene (PS) MNPs of different sizes (0.05-, 0.5-, and 5-μm) on soil microbial activity and community composition. Changes in inorganic N concentration, microbial biomass, and extracellular enzyme activities were determined in soils treated with 100 and 1000 μg PS MNPs g⁻¹ soil during a 40-d incubation experiment. Soil microbial biomass was significantly lowered when soils were treated with 0.5- or 5-μm MNPs at 100 and 1000 μg PS MNPs g⁻¹ soil. NH₄⁺ concentration was higher in soils treated with 5-μm MNPs at 100 and 1000 μg g⁻¹ soil than in the control soils at day 1, suggesting that MNPs inhibited the soil nitrification in short term. In contrast, extracellular enzyme activity was not altered by MNPs. The composition of microbial communities analyzed by Illumina MiSeq sequencing changed; particularly, the relative abundance of several bacteria related to N cycling, such as the genus Rhizomicrobium belonging to Alphaproteobacteria was decreased by 0.5- and 5-μm MNPs. Our study shows that the size of MNPs is an important factor that can determine their effects on soil microbial communities. Therefore, the size effects need to be considered in assessing the environmental impacts of MNPs.

土壤环境中的微（纳米）塑料 (MNP) 污染是一个主要问题，但不同大小的 MNP 对土壤微生物群落的影响（这在养分循环中至关重要）尚未得到很好的研究。在本研究中，我们旨在确定不同尺寸（0.05、0.5 和 5 μm）的聚苯乙烯 (PS) MNP 对土壤微生物活性和群落组成的影响。在 40 天的培养实验中，测定了用 100 和 1000 μg PS MNPs g ^-1土壤处理过的土壤中无机氮浓度、微生物生物量和胞外酶活性的变化。^{当在 100 和 1000 μg PS MNPs g −1}土壤中用 0.5 或 5 μm MNP 处理土壤时，土壤微生物生物量显着降低。氨氮₄ ⁺在第 1 天，在100 和 1000 μg g ^-1土壤中用 5 μm MNPs 处理的土壤中的浓度高于对照土壤，表明 MNPs 在短期内抑制了土壤硝化作用。相反，细胞外酶活性没有被 MNPs 改变。Illumina MiSeq测序分析的微生物群落组成发生变化；特别是，与 N 循环相关的几种细菌的相对丰度，例如属于Alphaproteobacteria的Rhizomicrobium属，被 0.5 和 5 μm MNP 降低了。我们的研究表明，MNP 的大小是决定其对土壤微生物群落影响的重要因素。因此，在评估 MNP 的环境影响时需要考虑规模效应。