Phytotoxic effects and rhizosphere microecological responses of peanut to oxytetracycline and microplastic co-exposure.

Abstract

Microplastics (MPs) and antibiotics represent escalating emerging contaminants in global agricultural soils, posing substantial threats to crop health and ecosystem functionality worldwide. However, a comprehensive understanding of their joint toxicity and the underlying rhizosphere mechanisms under co-contamination remains elusive, leaving a critical knowledge gap. This study conducted a pot experiment using the globally cultivated peanut (Arachis hypogaea) exposed to polystyrene (PS) or polylactic acid (PLA) MPs (0.25 and 2% w/w) and oxytetracycline (OTC, 10 mg·kg⁻¹), integrating metagenomic sequencing and untargeted metabolomics to elucidate root-zone microecological responses. High-concentration co-exposures significantly suppressed peanut shoot biomass, and OTC was identified as the primary contributor to reduced leaf catalase activity (CAT) (p < 0.01). Metagenomic profiling revealed that co-exposure significantly reshaped the rhizosphere microbiota (R2 = 0.939, p = 0.001), enriching Pseudomonadota while inhibiting Actinobacteriota. Untargeted metabolomics detected 3789 metabolites, revealing that co-exposure significantly regulated the accumulation of defensive flavonoids (taxifolin and daidzin) and stress-responsive steroids (ponasterone A). Particularly, the combined exposure of PLA MPs and OTC induced the most severe metabolic disruption in the rhizosphere, generating 374 differential metabolites compared to the PLA-alone treatment. Procrustes analysis confirmed a tight coupling between microbial communities and metabolomes (M2 = 0.619, p = 0.004). Network analysis further identified key regulatory nodes (Nocardioides and taxifolin) that bridge the associations between the rhizosphere microenvironment and plant growth traits. This study demonstrates that microbial shifts and metabolic adjustments are essential in mediating plant responses to multi-pollutant stress, providing crucial theoretical and mechanistic insights for global agricultural environmental risk assessment under co-contamination scenarios.