Synergistic superiority of AMF and biochar in enhancing rhizosphere microbiomes to support plant growth under Cd stress

Abstract Arbuscular mycorrhizal fungi (AMF) and biochar (BC) exhibit considerable potential for remediation of Cd-contaminated soil. However, studies addressing the combined impact of AMF and BC on soil microbiomes under Cd stress across soils of varying fertility are lacking. In this study, bioinformatics methods were used to discern the distinctive microbiome in rhizosphere soil of Cd-contaminated plants after the application of AMF and BC, among which the representative cultivable bacterial strains were chosen for the construction of synthetic communities (SynComs). The co-application of AMF and BC effectively alleviated the detrimental impacts of Cd stress on plants, with significantly superior remediation efficacy observed in barren soils compared to fertile soil. Co-occurrence network analysis revealed that Cd-contaminated soils harbored more complex microbial interactions, and competitive interactions between bacteria were enhanced. Based on in vitro co-culture experiments (isolation of 34 strains from Cd-contaminated rhizosphere soil) and bioinformatics analysis (targeting differentially abundant taxa and co-occurrence network keystone species), 23 candidate strains for SynComs were screened. Based on the superior growth-promoting capabilities of single strains and their pairwise non-antagonistic interactions, we have constructed eight substitute SynComs. One of the SC3 (dominated by Bacillaceae and Sphingomonadaceae ) based on the microbiome increased shoot biomass by 242.73% in barren soil and 350.24% in fertile soil, under Cd-contaminated conditions, showing the highest growth-promoting efficiency. This study provides a novel strategy for the ecological restoration and sustainable utilization of soil contaminated by heavy metals. Graphical Abstract