Interference of microplastics on autotrophic microbiome in paddy soils: Shifts in carbon fixation rate, structure, abundance, co-occurrence, and assembly process.

Autotrophic microorganisms play a crucial role in soil CO2 assimilation. Although microplastic pollution is recognized as a significant global concern, its precise impact on carbon sequestration by autotrophic microorganisms in agroecosystem soil remains poorly understood. This study conducted microcosm experiments to explore how conventional polystyrene (PS) and biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) microplastics affect carbon fixation rates (CFRs) and the community characteristics of soil autotrophic microorganisms in paddy agroecosystems. The results showed that compared with the control groups, 0.5 % and 1 % microplastic treatments significantly reduced soil CFRs by 11.8 - 24.5 % and 18.7 - 32.3 %, respectively. PS microplastics exerted a stronger inhibition effect on CFRs than PHBV microplastics in bulk soil. However, no significant difference was observed in the inhibition of CFRs by both types of microplastics in rhizosphere soils. Additionally, PS and PHBV microplastics altered the structure of autotrophic microbial communities, resulting in more stochastically dominated assembly and looser, more fragile coexistence networks compared to control groups. Moreover, microplastics drove the changes in autotrophic microbial carbon fixation primarily through their direct interference and the indirect effect by increasing soil organic carbon levels. Our findings enhance the understanding and predictive capabilities regarding the impacts of microplastic pollution on carbon sinks in agricultural soils.

"Microplastic communities" in different environments: Differences, links, and role of diversity index in source analysis.

Microplastics have been detected in various environments, yet the differences between microplastics in different environments are still largely unknown. Scientists have proposed the concept of the "microplastic cycle," but the evidence for the movement of microplastics between different environments is still scarce. By screening the literature and extracting information, we obtained microplastic data from 709 sampling sites in freshwater, seawater, freshwater sediment, sea sediment, and soil in China. Based on the similarity between microplastics and biological communities, here we propose the concept of a "microplastic community" and examine the differences, links, and diversity of microplastic communities in different environments. Wilcoxon sign-ranks test, Kruskal-Wallis test, and analysis of similarities (ANOSIM) showed that there were significant differences in abundance, proportion of small microplastics, and community composition (shape, color, and polymer types) of microplastics in different environments. The Mantel test showed that there were significant correlations between microplastic community composition in different environments. Network analysis based on community similarity further confirmed the links between microplastic communities. The distance decay models revealed that the links weakened with the increase of geographic distance, suggesting that sampling sites with closed geographical locations had similar pollution sources and more easily to migrate or exchange microplastics. The microplastic diversity integrated index (MDII) was established based on the diversity of microplastic shape, color, and polymer types, and its indication of the number of microplastic pollution sources was verified by the statistical fitting relationship between the number of industrial pollution sources and MDII. Our study provides new insight into the differences and links between microplastics in different environments, which contributes to the microplastic risk assessment and demonstrates the "microplastic cycle." The establishment of the microplastic diversity integrated index could be used in source analysis of microplastics.

Impact of microplastics on microbial community in sediments of the Huangjinxia Reservoir-water source of a water diversion project in western China.

Microplastics have been of great concern in recent years due to bioaccumulation and their toxic effects on organisms. However, few studies have focused on microplastics in the natural river ecosystem and the relationship between microplastics and microbes. Therefore, to understand the concentration and characteristics of microplastics and explore the impact of microplastics on the microbial community, sediment samples were collected from the Huangjinxia Reservoir, which is the water source of a water diversion project in western China. Results showed that the concentration of microplastics in the study area ranged from 233.33 ± 70.24 items·kg-1 to 870 ± 238.12 items·kg-1, with an average of 558.10 ± 291.45 items·kg-1. After clustering the sediments according to the microplastic concentration, there was a significant difference in the Chao1 index of microbial community between groups, indicating that microplastics might have affected microbial diversity of the sediments. Additionally, Anosim, MRPP, and Amova analyses indicated that microplastics might have an impact on the structure and composition of microbial communities. Moreover, function prediction assays suggested that microplastics might have differential impacts on various microbial community functions. To our knowledge, this is the first study to explore the impact of microplastics on microbes in sediments of a natural river ecosystem, providing a basis for further study of the interaction between microplastics and microbes in similar habitats.