Effects of biogas slurry-borne antibiotics and polypropylene microplastics on the rhizosphere microbiome and metabolome of Hybrid Pennisetum.

Antibiotic residues in biogas slurry and microplastic contamination are increasingly occurring in agricultural soils. However, their combined effects on rhizosphere ecological processes remain poorly understood. In this study, the individual and combined effects of polypropylene microplastics (PP-MPs, 1% w/w) and biogas slurry (BS, 0.5% w/w) on the rhizosphere soil of Hybrid Pennisetum were investigated by conducting an integrated analysis of 16S rRNA gene sequencing and untargeted metabolomics. The results revealed that PP-MPs alone significantly reduced soil bacterial α-diversity and inhibited urease, sucrase, and alkaline phosphatase activities while significantly increasing catalase and fluorescein diacetate hydrolase activities. BS amendment increased nutrient availability and microbial diversity. Notably, compared with BS alone, the coapplication of PP-MPs and BS induced significant soil acidification and increased the retention of multiple antibiotics, including tetracyclines, fluoroquinolones, and macrolides, in the rhizosphere. The combined treatment generated a unique bacterial community assemblage with increased Pseudomonadota and Bacteroidota abundances, restored microbial co-occurrence network complexity, and uniquely enriched pathways related to secondary metabolite biosynthesis and microbial metabolism in diverse environments. Procrustes analysis confirmed the tight coupling between shifts in the microbial community and metabolic reprogramming. Key hub metabolites, including prostaglandin derivatives and hydroxylated fatty acids, exhibited strong connectivity with genera frequently associated with antibiotic resistance potential, such as Pseudomonas, Bacillus, and Streptomyces. Overall, PP-MPs altered the ecological outcome of biogas slurry application by enhancing antibiotic persistence and coupling nutrient enrichment with contaminant-driven microbial and metabolic reprogramming. These results highlight the need to consider microplastic contamination when evaluating the agricultural safety of biogas slurry application in forage production systems.