Global warming results in more field soil suffering freeze-thaw cycles (FTCs). The environmental risk of microplastics-recognized as a global emerging contaminant-in soils undergoing FTCs remains unclear. In this study, the combined effects of FTCs and poly(butylene adipate-co-terephthalate) (PBAT) microplastics on microbial degradation of atrazine in Mollisols were investigated. Freeze-thaw cycles, rather than microplastics, significantly inhibited the biodegradation of atrazine in soil, with average inhibition ratios of 33.69% and 4.99% for FTCs and microplastics, respectively. Thawing temperature was the main factor driving the changes in soil microbial community structures and the degradation of atrazine. The degradable microplastics with an amendment level of 0.2% had different and limited effects on the dissipation of atrazine under different modes of FTCs. Among the four modes, microplastics only showed a trend toward promoting atrazine degradation under high-frequency and high-thawing-temperature FTCs. Across all modes, microplastics altered microbial interactions and ecological niches that included affecting specific bacterial abundance, module keystone species, microbial network complexity, and functional genes in soil. There's no synergistic effect between microplastics and FTCs on the degradation of atrazine in soil within a short-term period. This study provides critical insights into the ecological effects of the new biodegradable mulch film-derived microplastics in soil under FTCs.

Earthworms can expedite di-(2-ethylhexyl) phthalate (DEHP) degradation in soils, but limited information is available on the key DEHP-degradation pathways and related genes during the vermicomposting process. In this study, DEHP degradation, degradation-related genes and bac-terial communities were investigated by metagenomic analysis. DEHP degradation efficiency was significantly and 65.69% higher in vermicomposting treatment than natural soils. Earthworm supplement remarkably increased the contents of humic acid, humus and fulvic acid in soils. Both humic acid and earthworm gut positively stimulated soil microbes potentially responsible for DEHP degradation. Betaprotebacteria, Acidobacteria, Variovorax, Hydrogenophaga, Limnobacter, Ramlibacter, Pseudomonas, Acinetobacter, Paracoccus and Achromobacter significantly contributed to DEHP degradation pathways. From functional gene analysis, there were remarkable differences in dominant DEHP degradation pathways between soils (catechol pathway), earthworm cast (protocatechuate pathway), and earthworm gut (protocatechuate and catechol pathways). Our findings proposed two possible mechanisms of earthworms in accelerating DEHP degradation, stimulating the activities of indigenous degraders to augment the catechol pathway in soils and providing an extra protocatechuate pathway in earthworm gut. This study, for the first time, offers new insights into the impacts of vermicomposting on DEHP degradation genes and path-ways, providing valuable scientific evidence for improving DEHP bioremediation in contaminated agricultural soils.