Synergistic Effects of Arbuscular Mycorrhizal Fungi and Mycorrhiza Helper Bacteria Alter Cucumber Rhizosphere Fungal Community and Reduce Soil Cadmium Contamination

Cadmium (Cd) contamination in agricultural soils severely impairs plant growth, disrupts microbial communities, and threatens food safety due to its high toxicity and mobility. Conventional remediation methods are often expensive and environmentally unsustainable. In contrast, plant–microbiome interactions offer an eco-friendly solution to reduce Cd accumulation and improve plant growth. Arbuscular mycorrhizal fungi (AMF) and mycorrhiza helper bacteria (MHB) are known to improve plant growth and resilience in Cd-contaminated soils. However, the mechanisms by which AMF and MHB co-inoculation could reduce soil Cd contamination by altering the rhizosphere fungal community remain unclear. This study aimed to evaluate how co-inoculation with AMF (Funneliformis mosseae) and MHB (Alcaligenes faecalis) affects plant Cd uptake and soil Cd content, and how it reshapes the cucumber rhizosphere fungal community. A greenhouse experiment was conducted with four treatments: CK (no inoculation), Fm (AMF inoculation), Af (MHB inoculation), and FA (AMF + MHB co-inoculation). Co-inoculation with AMF and MHB (FA) significantly reduced Cd concentrations in both plant tissues and soil. Fungal communities were profiled using Illumina MiSeq sequencing of the ITS region, and diversity metrics and structural changes were assessed through PCoA and DESeq2. Co-inoculation (FA) significantly reshaped the fungal community, increasing the relative abundances of beneficial phyla such as Mortierellomycota, Basidiomycota and Glomeromycota, while decreasing the abundance of potentially pathogenic Ascomycota. Double inoculation with AMF and MHB also enhanced fungal diversity, as measured by the Simpson index, and enriched specific OTUs. This study uncovers the mechanisms through which AMF–MHB co-inoculation reduces Cd concentrations in both plants and soil by altering the cucumber rhizosphere fungal community composition. These findings demonstrate that AMF–MHB co-inoculation is an effective, biologically driven strategy for remediating Cd-contaminated soils by restructuring cucumber rhizosphere fungal communities.