Polypropylene microplastics reshape diazotrophic community composition and interactions in the plastisphere without affecting the rhizosphere of Capsicum annuum L.

Interactions between microorganisms and microplastics play a crucial role in soil biological processes; however, the response of microbial functional groups in the presence of microplastics (MP) remains unclear. In this study, we investigated the diversity and composition of free-living nitrogen-fixing microorganisms (diazotrophs) in the rhizosphere and plastisphere of pepper (Capsicum annuum L.) across three growth stages under MP stress, using an optimized pipeline for functional nifH gene sequence analysis. Our results showed that MP addition suppressed plant growth, although soil properties were not significantly altered, except for soil pH, which was significantly reduced at each plant growth stage. Notable differences in diazotrophic community composition were observed between the rhizosphere and plastisphere, with the genus Rubrivax exhibiting a significantly lower relative abundance in the plastisphere. Moreover, we found strong deterministic assembly processes and intense network structures of diazotrophs in the plastisphere. Interestingly, MP addition did not significantly alter the diversity, composition, or network properties of diazotrophic communities in the rhizosphere compared to control soils. Our study provides insights into the interactions between microbial functional groups and microplastics, enhancing our understanding of the biological processes that drive ecological nutrient cycling and balance in changing environments.