Differential response of root traits to arbuscular mycorrhizal fungi in two maize varieties alters cadmium speciation and migration in soil solution

Arbuscular mycorrhizal fungi (AMF) form symbiotic associations with crop roots, but their effects on the root traits of crops with different root system sizes and the subsequent influence of these traits on the migration of cadmium (Cd) within the maize-soil system remain unclear. In this study, two maize varieties with relatively large roots (Jingdian 8) and relatively small roots (Enyu 98) were selected as test plants. A compartmentalized soil culture experiment (Cd 17.4 mg/kg) was conducted to investigate the effects of AMF inoculation on the root traits, plant Cd content and accumulation, soil aggregates, preferential flow distribution, and solution Cd loss in both maize varieties. Compared with the non-inoculated treatment, AMF inoculation significantly promoted root growth of both maize varieties, resulting in increases in root length, root tip number, and branch number by 27–161%, and an increase in glomalin-related soil protein (GRSP) concentration by 57–84%. The number of large soil aggregates in the mycorrhizal compartment of Enyu 98 increased by 29% compared with the root compartment, and the distribution area of soil preferential flow increased by 23–185%. AMF significantly reduced soil available Cd concentration by 26–40%, soil solution Cd loss by 35–87%, and plant Cd content by 41–60%. Cd speciation in soil interflow and leachates were dominated by Cd²⁺ (96–98%), followed by CdSO₄(aq) (1–2%). Partial least squares structural equation modeling revealed that AMF promoted root growth in Jingdian 8, but weakened the mycorrhizal control on soil Cd loss; in contrast, AMF promoted root architecture and GRSP secretion in Enyu 98, and directly inhibited soil Cd loss through the "AMF-root traits-GRSP" pathway. This study identifies divergent root responses to AMF inoculation among different maize varieties and reveals how AMF reshapes cadmium migration pathways via differential regulation of root traits, while also providing theoretical support for applying AMF to remediate Cd-contaminated soils.