Microplastics reshape rhizosphere microbial communities and nutrient cycling in tomato agroecosystems

BACKGROUND: Microplastics (MPs) are emerging soil contaminants increasingly recognized for their capacity to alter agroecosystem functioning; however, their impacts on horticultural crops and rhizosphere microbial processes remain insufficiently understood. RESULTS: We examined the impacts of MPs, polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC), on rhizosphere soil physicochemical properties, bacterial community structure, and functional genes associated with carbon (C), nitrogen (N), and phosphorus (P) cycling in tomato (Solanum lycopersicum L.), a major horticultural crop cultivated worldwide. Both PVC-MPs and PE-MPs significantly reduced soil ammonium nitrogen and available phosphorus contents, modifying rhizosphere elemental composition. In contrast, PP-MPs had no significant effects on these nutrients but significantly increased soil pH by 0.76% compared with the control (p < 0.05). PE-MPs exposure markedly reduced bacterial α-diversity and selectively enriching bacterial taxa involved in recalcitrant organic matter degradation and nitrogen cycling. High-throughput quantitative PCR (qPCR) revealed that MPs suppressed the degradation of labile carbon substrates, including starch, cellulose, and hemicellulose (as evidenced by downregulation of apu, manB, and xylA), as well as methane metabolism, while promoting carbon fixation and phosphorus cycling. CONCLUSIONS: Our results indicate selective reprogramming of bacterial carbon metabolism, enhancing recalcitrant carbon turnover while constraining labile carbon mineralization, thereby disrupting C-P metabolic coupling and promoting soil organic carbon accumulation. Additionally, MPs stimulated nitrogen fixation and nitrification while inhibiting denitrification, particularly under PE- and PVC-MPs treatments. These findings provide bacterial ecological insights into MPs-induced reshape rhizosphere processes and nutrient cycling dynamics in horticultural systems.