Inoculation of cadmium-tolerant bacteria mitigates the impact of cadmium pollution on soil bacterial community assembly processes

Abstract

Cadmium (Cd)-tolerant bacteria show significant potential for remediating Cd-contaminated soils, particularly in plant-microbe combined remediation. However, their effects on soil microbial communities, especially community assembly processes remain largely unexplored. To address this, we conducted an experiment inoculating two strains of Cd-tolerant bacteria in combination with Lolium perenne cultivation, in soils with varying Cd contamination levels. We investigated the effects of both Cd-tolerant bacteria and Cd pollution on bacterial communities, with a focus on the different responses of rare and abundant subcommunities. Our results indicated that Cd pollution exhibited more pronounced impacts on bacterial communities than Cd-tolerant bacteria incubation. Cd pollution significantly reduced alpha diversity and altered community structure, while incubation with Cd-tolerant bacteria showed minimal effects on both alpha and beta diversity. Cd pollution also resulted in a higher number of indicator species compared to inoculation treatments. However, inoculation with Cd-tolerant bacteria exerted effects contrasting with those of Cd pollution on bacterial community assembly processes. Specifically, the inoculation strengthened the networks of the abundant community while weakening those of the rare community, enhanced stochastic processes in community assembly, alleviated dispersal limitation, and expanded niche breadth – all effects opposite to those induced by Cd pollution. These results demonstrate that Cd-tolerant bacteria can mitigate the detrimental effects of Cd pollution on soil microorganisms, primarily by modulating bacterial community assembly processes. In addition, the distinct responses of the abundant and rare subcommunities underscore their unique assembly dynamics and adaptive strategies. This study offers valuable insights into the role of Cd-tolerant bacteria in shaping soil bacterial communities, providing foundations for optimizing plant-microbe combined remediation strategies for Cd-contaminated soils.