Abstract

Background and aims This study aimed to characterize the rhizosphere bacterial community structure associated with the cluster roots (CR) of the aluminum (Al)-accumulating plant, Gevuina avellana Mol. (Proteaceae) growing in soils with contrasting Al availability and evaluated the plant growth-promoting (PGP) traits of bacterial isolates in vitro.Methods Bulk soil and rhizosphere soil from CR and non-cluster roots (non-CR) of G. avellana were sampled at two natural sites with contrasting soil Al saturation: Oncol Park (75% Al saturation; + Al site) and Rucamanque Park (0.5% Al saturation; - Al site). Bacterial diversity and community structure were assessed through 16S rRNA gene metabarcoding, analyzed using QIIME2, LEfSe and FAPROTAX. Al-tolerant strains were additionally isolated and screened in vitro for PGP traits.Results Bacterial community structure was primarily shaped by site conditions rather than sample type (CR, non-CR or Bulk). Proteobacteria, Acidobacteriota and Planctomycetota were the dominant phyla in both sites. The + Al site was characterized by adapted taxa including Ktedonobacteraceae and Candidatus Xiphinematobacter but greater abundance of culturable Al-tolerant strains was found at -Al site. Isolates from both sites exhibited multiple PGP traits, including phosphate solubilization, siderophore production, ACC deaminase activity and phytohormone production.Conclusions Site-specific soil properties were the main drivers of rhizosphere bacterial community structure, whereas CR selectively harbored Al-tolerant bacteria with multiple PGP traits. These findings indicate that G. avellana associates with a functionally specialized microbiota adapted to acidic, Al-rich soils, providing a basis for future studies on plant-microbe interactions and the development of bioinoculants for acid soils.