ORIGINAL ABSTRACT

Microplastics and pesticides are emerging contaminants that threaten soil ecosystems, yet their combined effects on soil health and soil fauna remain poorly understood. In this study, we constructed a microcosm to assess the individual and combined effects of microplastics and glyphosate on soil physicochemical properties, microbial communities, and the gut microbiome of soil invertebrates (Enchytraeus crypticus). Biodegradable polylactic acid (PLA) and conventional polyethylene terephthalate (PET) were introduced at environmentally relevant concentrations. Our results revealed that PLA had a stronger disruptive effect on soil microbial communities than PET, altering microbial diversity and functional composition. Glyphosate, in contrast, primarily influenced the gut microbiome of E. crypticus, reducing microbial diversity and inducing oxidative stress. Combined exposure to microplastics and glyphosate significantly intensified oxidative stress but did not amplify microbial dysbiosis beyond the effects of microplastics alone. Compare to PET, PLA combined with glyphosate had the most pronounced effects on both soil and gut microbiomes, suggesting that biodegradable microplastics may pose greater ecological risks than conventional microplastics when used alongside pesticides. These findings underscore the need for a reassessment of biodegradable plastic use in agriculture and highlight the complex interactions between microplastics and pesticides in shaping soil ecosystem health.