Rhizosphere microbial metabolic reprogramming under plastic film stress: a potential mechanism for carbon pool dynamic disruption

Although plastic film mulching enhances tobacco yield and quality, its residues pose a threat to soil health. Herein, a field experiment was designed to investigate the impacts of polyethylene (PE) and poly (butylene adipate-co-terephthalate) (PBAT) residues on soil carbon pools throughout the tobacco growth cycle. Plastic film residues increased soil CO 2 and CH 4 emissions by 1.09-15.33% and 14.57-122.47%, respectively, with responses varying by polymer type and growth stage. PE residues inhibited the accumulation of soil organic carbon (SOC) fractions and weakened carbon pool stability, with the degree of inhibition regulated by residue concentration. Conversely, high levels of PBAT residues elevated total SOC but preferentially enriched active carbon pools, evidenced by a declining MAOC/SOC ratio. The rhizosphere microbial functional shifts driven by residual film accumulation are an important potential factor influencing soil carbon pool dynamics. Low-concentration PE residues had no significant impact on microbial functions, severe PE accumulation triggered oxidative stress and forced a selective gene function, shift toward efficient energy pathways, indicating metabolic inefficiency driven by stress. As an exogenous available carbon source, PBAT substantially enriched genes involved in carbon fixation and degradation, thereby stimulating microbial metabolism and accelerating rhizosphere carbon turnover. Enzyme activity measurements and targeted metabolomics analyses provided further evidence substantiating the microbial metabolic reprogramming processes suggested by functional gene profiling. This study elucidated how distinct plastic residues differentially regulate soil carbon cycling via microbial metabolic modulation, providing a scientific basis for the ecological risk assessment of mulch film residues.