Biodegradable microplastics impact the uptake of Cd in rice: The roles of niche breadth and assembly process

Biodegradable microplastics (MPs) can impact the accumulation of cadmium (Cd) by plants, however, its mechanisms have not been fully understood. In this study, two biodegradable MPs, polypropylene carbonate (PPC) and polylactic acid (PLA), were used to examine their influences on the uptake of Cd in rice plants. Results showed that PPC significantly reduced the accumulation of Cd in rice root and aerial part, whereas PLA increased the Cd concentrations in rice root. The random forest analysis revealed that the bacterial biomarkers enriched by two MPs were different at genus level. Niche breadths were significantly reduced under Cd stress, and PPC alleviated this environmental pressure for entire bacterial community, whereas PLA reduced the niche breadth for whole community and abundant taxa, which was further verified by co-occurrence network and normalized stochasticity ratio model. The abundant taxa of group PPC were primarily governed by deterministic process while rare taxa were more driven by stochastic process. Structural equation model and Mantel analysis identified that the niche breadth imposed a strong selection on Cd accumulation after co-exposure. This study reveals the underlying mechanism of assembly process and niche breadth of rice rhizosphere microbiome on Cd accumulation by rice plants.