Freshwater ecosystems, such as urban lake sediments, have been identified as important sources of greenhouse gases (GHGs) to the atmosphere, as well as persistent sinks for ubiquitous microplastics due to the high population density and frequent anthropogenic activity. The potential impacts of microplastics on GHG production, however, remain underexplored. In this study, four types of common biodegradable microplastics (BMPs) versus four conventional non-biodegradable microplastics (NBMPs) were artificially exposed to urban lake sediments to investigate the responses of nitrous oxide (N2O) and methane (CH4) production, and make a comparison regarding how the biodegradability of microplastics affected GHG emissions. Importantly, results suggested that BMPs aggravated N2O and CH4 production in urban lake sediments more severely than conventional NBMPs. The production rates of N2O and CH4 increased by 48.78–71.88 % and 30.87–69.12 %, respectively, in BMPs groups, while those increased by only 0–25.69 % and 6.46–10.46 % with NBMPs exposure. Moreover, BMPs insignificantly affected nitrification but facilitated denitrification, while NBMPs inhibited both processes. BMPs not only created more oxygen-limited microenvironment, greatly promoting N2O production via nitrifier denitrification pathway, but also provided dissolved organic carbon favoring heterotrophic denitrification, which was primarily supported by the enriched denitrifiers and functional genes. In contrast, NBMPs slightly upregulated nitrifier denitrification pathway to generate N2O, and showed a toxic inhibition on both nitrifiers and denitrifiers. In addition, both BMPs and NBMPs promoted hydrogen-dependent methanogenic pathway but suppressed acetate-dependent pathway. The greater enhancement of CH4 production with BMPs exposure was attributed to the additional organic carbon substrates derived from BMPs and the stimulated microbial methane metabolism activities.

中文翻译：

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与传统微塑料相比，可生物降解的微塑料更严重地加剧了城市湖泊沉积物的温室气体排放


淡水生态系统，如城市湖泊沉积物，已被确定为大气中温室气体 （GHG） 的重要来源，并且由于人口密度高和人为活动频繁，无处不在的微塑料会持续下降。然而，微塑料对温室气体生产的潜在影响仍未得到充分探索。在这项研究中，将四种常见的可生物降解微塑料 （BMP） 与四种传统的不可生物降解微塑料 （NBMP） 人工暴露在城市湖泊沉积物中，以研究一氧化二氮 （N2O） 和甲烷 （CH4） 产生的反应，并比较微塑料的生物降解性如何影响温室气体排放。重要的是，结果表明，BMP 比传统的 NBMP 更严重地加剧了城市湖泊沉积物中 N2O 和 CH4 的产生。BMPs 组 N2O 和 CH4 的生成速率分别增加了 48.78-71.88 % 和 30.87-69.12 %，而 NBMP 暴露组的 N2O 和 CH4 的生成速率仅增加了 0-25.69% 和 6.46-10.46%。此外，BMPs 对硝化作用的影响不显著，但促进了反硝化作用，而 NBMP s 抑制了这两个过程。BMPs 不仅创造了更多的限氧微环境，通过硝化剂反硝化途径极大地促进了 N2O 的产生，而且还提供了有利于异养反硝化的溶解有机碳，这主要由富集的反硝化剂和功能基因支持。相比之下，NBMPs 略微上调硝化剂反硝化途径生成 N2O，并对硝化剂和反硝化剂均表现出毒性抑制作用。此外，BMPs 和 NBMPs 均促进氢依赖性产甲烷途径，但抑制乙酸盐依赖性途径。 BMPs 暴露对 CH4 产生的更大增强归因于 BMP 衍生的额外有机碳底物和刺激的微生物甲烷代谢活动。