Arbuscular mycorrhizal fungi regulate arsenic biotransformation and immobilization in contaminated soil through hyphosphere microbiome assembly

Soil arsenic (As) is a persistent environmental challenge driven by As toxicity, mobility, and bioavailability. Although arbuscular mycorrhizal fungi (AMF) are known to participate in soil As detoxification, how the hyphosphere microbiome contributes to this process remains elusive. Here, we established a controlled M. sativa – R. irregularis –microbiome system to investigate these mechanisms, The results showed that AMF colonization significantly enhanced soil As immobilization by increasing the residual As fraction. Concurrently, the AMF-recruited microbiome displayed a higher As transformation potential, driven by predominant transport-related pathways and the enrichment of critical genes such as arsABCHR, pstABCS and pgpA . Among the 72 recovered metagenome-assembled genomes, we identified 10 key bacterial taxa that collectively encoded gene modules for As transport, redox transformation, and methylation. Collectively, these findings demonstrate that AMF function as ecosystem engineers, constructing a cooperative As-detoxifying barrier in the hyphosphere through microbial recruitment, network reorganisation, and functional specialisation.