Rare Microbial Taxa Dominate the Microecological Landscape of Cadmium Exposure in Rice Rhizosphere

Cadmium (Cd) contamination in soil is a growing problem, posing a significant threat to soil microorganisms and plant growth. Understanding how Cd exposure disrupts the evolution of soil microbial communities and the mechanisms underlying community remodeling requires further investigation. In this study, the rice rhizosphere treated with 0 (CK), 2.5 (LC), 5 (MC), and 15 (HC) mg kg−1 Cd was used as a model and combined with 16S rRNA gene sequencing to systematically evaluate the response patterns of rice rhizosphere microbial communities under Cd gradient treatments. The study found that rice rhizosphere microbial communities responded to Cd exposure with a unimodal pattern of “low-promotion and high-suppression”. LC treatment significantly increased the alpha diversity of rare fungal taxa and significantly enriched rare genera such as Candidatus Solibacter and Penicillium. Network analysis further confirmed that LC treatment significantly enhanced symbiotic relationships within and across rare taxa. The assembly of abundant bacterial and fungal taxa was consistently dominated by stochastic diffusional constraints, while rare taxa were primarily driven by deterministic homogeneous selection. In summary, rice rhizosphere microbial communities showed specific response patterns under Cd gradient treatment. Rare fungal taxa, as core members, actively responded to Cd exposure, made prominent contributions to shaping the community composition, and played a crucial role in maintaining the complexity and stability of the microbial network.