Mycorrhizal Fungi Funneliformis mosseae Mitigates Cadmium Bioavailability in Pepper Rhizosphere via Glomalin Production and pH Elevation

Cadmium (Cd) contamination in agricultural soils, especially in regions with a naturally high geochemical background such as Southwest China, poses a serious threat to food safety and the health of terrestrial ecosystems. Although arbuscular mycorrhizal fungi (AMFs) are known to enhance plant tolerance to heavy metals, the specific mechanisms by which dominant AMF species in karst soils—such as Funneliformis mosseae (Fm) and Rhizophagus intraradices (Ri)—immobilize Cd are not yet fully understood. In this study, a pot experiment with pepper plants was conducted to investigate the effects of Fm and Ri inoculation on Cd geochemistry in both the rhizosphere and bulk soil. Key results showed that AMF inoculation, especially with Fm, significantly reduced total Cd (by up to 33.8%) and bioavailable Cd (by up to 36.3%) concentrations in the soil, with a more pronounced effect within the rhizosphere. Accordingly, Cd content in pepper shoots was reduced by up to 15.0%. Inoculation also increased soil pH, organic matter, available phosphorus, and glomalin-related soil protein (GRSP) content. Redundancy analysis identified soil pH and total extractable GRSP as primary factors negatively correlated with Cd bioavailability. The study concludes that AMFs, particularly Fm, represent a potent bioremediation strategy by effectively immobilizing Cd in contaminated soils through mechanisms linked to GRSP production and pH elevation, thereby reducing its phytoavailability and translocation to edible plant parts.