| Summary: | Currently, microplastic pollution poses a great threat to diverse ecosystems. Microplastics can potentially change soil characteristics and impact soil microorganisms, and then affect the production of CO<sub>2</sub>, CH<sub>4</sub> and other greenhouse gases. However, experimental study on different ecological soils is lacking. Herein, we experimentally analyzed the CO<sub>2</sub> and CH<sub>4</sub> production potential affected by four types of microplastics in freshwater (Poyang Lake in Jiangxi province, paddy soil in Hunan province) and saltwater (Salt marsh in Shandong province, mangrove soil in Fujian province) ecosystems. Microplastics promoted CO<sub>2</sub> production, of which polyethylene terephthalate (PET) had the greatest impact. In our study, the microplastics that had the greatest impact on CH<sub>4</sub> concentration emissions were high-density polyethylene (1276 umol·g<sup>−1</sup>·L<sup>−1</sup>), followed by polyvinyl chloride (384 umol·g<sup>−1</sup>·L<sup>−1</sup>), polyethylene terephthalate (198 umol·g<sup>−1</sup>·L<sup>−1</sup>), and polyamide (134 umol·g<sup>−1</sup>·L<sup>−1</sup>). In addition, the largest impact on CO<sub>2</sub> concentration emissions was displayed by polyethylene terephthalate (2253 umol·g<sup>−1</sup>·L<sup>−1</sup>), followed by polyvinyl chloride (2194 umol·g<sup>−1</sup>·L<sup>−1</sup>), polyamide (2006 umol·g<sup>−1</sup>·L<sup>−1</sup>), and high-density polyethylene (1522 umol·g<sup>−1</sup>·L<sup>−1</sup>). However, the analysis results based on one-way ANOVA showed that CO<sub>2</sub> emission was most significantly affected by soil properties rather than microplastics types. In comparison, the influencing factor on CH<sub>4</sub> production changed from soil types to the interaction between soil types and microplastics, and finally to the microplastics with the increase in incubation time. Further, by comparing CO<sub>2</sub> and CH<sub>4</sub> production and Global Warming Equivalent (GWE) affected by microplastics, freshwater ecosystems were more sensitive than saltwater. For all the soil types used in this study, high-density polyethylene had the greatest impact on CH<sub>4</sub> production potential. In conclusion, our study provided basic data for further understanding the effects of microplastics on soil greenhouse gas emissions from different sources.
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