Study on the impact of microplastic characteristics on ecological function, microbial community migration and...

Saline-alkali soils constrain agricultural production due to high salt-alkali stress, and the microplastics introduced during agricultural improvement processes, such as through agricultural film residue and irrigation inputs, may have complex effects on soil ecological functions. As a new type of pollutant, microplastics are widely distributed in soils, water, and the atmosphere. However, the interactions between microplastics in the saline-alkali soil remediation process and the environment remain unclear. This study systematically analyzed the ecological effects of PE, PP, and PBAT microplastics during the remediation of saline-alkali soils with biogas slurry through laboratory simulation experiments. The results showed that microplastics significantly affect carbon-nitrogen cycle-related indicators (such as ammonia nitrogen and DOC) by altering the pH, electrical conductivity, and organic matter decomposition process of saline-alkali soils, and strongly correlate with the microbial community composition and functional pathways. Microplastics triggered the activation of redox enzyme activity and the co-expression of heavy metal resistance/carbon-nitrogen cycle genes, driving the adaptive reconstruction of microbial communities. Conventional microplastics (PE/PP) exhibited slow surface oxidation in saline-alkali soils, with physical adsorption dominating their ecological effects. They inhibited microbial diffusion, induced ecological niche competition, and selectively enriched hydrocarbon-degrading bacteria Alcanivorax and salt-alkali-resistant actinobacteria Nitriliruptoraceae. Their community assembly was mainly driven by random processes, and high microplastic abundance (10 wt%) showed a threshold effect on bacterial composition compared to control samples. In contrast, as the particle size decreased, the degradable PBAT accelerated degradation due to ester bond hydrolysis (CO functional group decreased from 52.50 % to 34.92 %), releasing decomposition products that drove deterministic community assembly and reconstructed microbial communities (enriching Proteobacteria, Firmicutes, and Halomonas). The rapid degradation of PBAT may exacerbate short-term ecological disturbances, while the chemical inertness of PE/PP poses a long-term retention risk. This study provides key data for risk management of microplastics in saline-alkali soil remediation. Although microplastic pollution may accelerate soil remediation by promoting microbial metabolic activity, further microplastic safety risk assessment during saline-alkali soil remediation is still needed.