Biodegradable mulch films (BDMs) are becoming increasingly popular in agriculture and are emerging as an alternative to conventional polyethylene (PE) films. However, the intricate details surrounding the establishment and growth of microorganisms on BDMs and PE during their degradation in agricultural fields remain unclear. In this study, the succession of bacterial communities in farmland soil and the plastispheres of PE and BDMs were compared through 16S rRNA gene high-throughput sequencing and real-time PCR. The results unveiled noteworthy distinctions in bacterial community structures across different samples. Specifically, the α-diversity in the BDM plastispheres was markedly lower than in the PE plastisphere. Hydrogenophaga and Variovorax genera were abundantly present in the BDM plastisphere, whereas Mycobacterium demonstrated significant enrichment in the PE plastisphere. Functional annotations indicated high abundances of degradation-related and pathogen-related functions in both BDM and PE plastispheres. Furthermore, the BDM plastisphere exhibited lower network complexity and modularity and stronger competitive interactions than the PE plastisphere. The conducted iCAMP analysis showed that stochastic community assembly processes largely govern the PE plastisphere, while deterministic processes prevailed in BDMs and increased significantly over time. These findings shed light on different mulching materials' effects in farmland ecosystems and provide insights into potential ecological risks linked to their usage.