Enhancing the resistance of hyperaccumulator with arbuscular mycorrhizal fungi in cadmium-contaminated saline soil: A physiological and transcriptional mechanistic study

To address the issue of poor phytoremediation in Cd-contaminated saline soil caused by the biotoxicity of Cd-salinity, we constructed a symbiotic system of arbuscular mycorrhizal fungi (AMF) and the hyperaccumulator Solanum nigrum, and systematically elucidated the response strategies of Solanum nigrum and the enhancement mechanism of AMF for plant tolerance through cytological, physiological, and transcriptomic methods. The findings showed that Cd-salinity stress had synergistic aggravated Cd/Na enrichment, ultrastructural damage, photosynthetic inhibition, water loss, and reactive oxygen species (ROS) accumulation in plants. In response to the heterogeneity of Cd/salinity stress, AMF smartly regulated the Cd/salinity tolerance of host plants: AMF decreased intercellular CO₂ concentration (Ci) under Cd stress to alleviate non-stomatal limitation induced by Cd, but increased Ci under salinity stress to alleviate the stomatal limitation induced by salinity; the role of AMF in strengthening the osmoregulation system was more prominent under salinity stress, thereby alleviated the more severe osmotic imbalance induced by salinity. AMF also enhanced signal transduction to consolidate resistance defense, upregulated antioxidant genes to activate antioxidant enzymes, and strengthened the AsA-GSH cycle to mitigate oxidative damage. The enhancement of tolerance improved plant growth and Cd enrichment. Under high Cd-high salinity combined stress, Cd concentrations in shoots and roots increased by 14.28 % and 38.85 %, respectively, and the biomass also increased by over 30.00 % after AMF inoculation. In summary, inoculation with AMF serves as an effective and sustainable phytoremediation enhancement strategy that improves the host plants’ stress resistance through multiple pathways, thereby increasing the phytoremediation potential.