Objectives The symbiotic relationship between arbuscular mycorrhizal fungi (AMF) and crops bolstered their cadmium (Cd) tolerance. The impact of AMF inoculation on Cd uptake across different accumulation types remained unclear. This study investigated the influence of AMF inoculation on Cd absorption and accumulation in diverse pepper varieties under varying Cd concentrations, while elucidating the physiological and biochemical mechanisms enhancing pepper tolerance to Cd stress.

Methods A pot experiment was conducted, there were total of 12 treatments which were comprised by two AMF inoculation (with AMF and without AMF), three Cd addition levels (0, 5, 10 mg/kg, denoted as Cd0, Cd5, and Cd10), and two pepper cultivars (high Cd accumulation type ‘Layan 101’ and low Cd accumulation type ‘Layan 201’). Growth parameters, Cd content in various plant organs, and soil nutrient content were measured post-harvest.

Results Cd treatment hindered pepper growth, with plant height, above ground and root biomass decreasing significantly with increasing Cd concentration. In a high Cd environment (Cd10), AMF inoculation notably increased above ground biomass, with ‘Layan 101’ and ‘Layan 201’ experiencing increases of 31.72% and 20.09%, respectively. AMF inoculation exerted varied effects on root Cd content depending on the variety. Under Cd10 conditions, inoculation significantly decreased root Cd content in ‘Layan 101’ by 30.75%, whereas it increased by 41.93% in ‘Layan 201’; the transport coefficient (aboveground/root) of Cd in Layan 101 significantly increased by 48.96%, while Layan 201 decreased by 24.04%. Inoculation reduced Cd enrichment coefficient in pepper fruits across Cd concentrations. The inoculation of AMF changed the chemical composition and relative content of root exudates in chili peppers, and there were differences among different varieties. Structural equation modeling revealed a significant negative regulatory effect of inoculation and root Cd on Cd content in pepper fruits.

Conclusion Under Cd stress, AMF enhances root Cd content in low accumulation peppers (Layan 201), curbing Cd transport to aboveground parts and reducing Cd content in edible portions. Conversely, AMF boosts aboveground Cd content in high accumulation peppers (Layan 101), minimizing Cd transport to fruits and diminishing Cd content in edible parts.