Effects of co-exposure of antibiotic and microplastic on the rhizosphere microenvironment of lettuce seedlings.

Antibiotics and microplastics (MPs) often coexist in facility agriculture soils due to the prevalent use of animal manure and plastic films. However, their combined impacts on the rhizosphere environment of lettuce remain unclear. This study assessed the effects of individual and combined exposure to polyethylene (PE) MPs (2 g·kg) and oxytetracycline (OTC) (0, 5, 50, and 150 mg·kg) on the growth of lettuce seedlings and enzyme activities, physicochemical properties, metabolite profiles and bacterial communities of rhizosphere soil of lettuce. Exposure to 150 mg·kg OTC, either individually or combined, significantly increased lettuce seedling shoot biomass. All treatments decreased chlorophyll and carotenoid contents. Combined exposure notably increased the Simpson's index of rhizosphere bacterial communities and altered community composition. The number of differential genera of rhizosphere was less than that of non-rhizosphere. Combined exposure significantly changed both rhizosphere and non-rhizosphere metabolite profiles. Soil organic matter emerged as the key environmental factor influencing bacterial community variation. Mantel tests revealed strong positive associations between total potassium and rhizosphere bacterial communities under combined exposure. The correlation network identified stearic acid and palmitic acid as the core metabolites in the rhizosphere. These findings offer valuable insights into the impact of OTC combined with PE MPs on lettuce rhizosphere environment.