Elevated CO2 and arbuscular mycorrhizal fungi enhanced black locust seedling defense under cadmium exposure by 13C isotopic tracer

Elevated CO 2 (eCO 2 ) and arbuscular mycorrhizal fungi (AMF) positively influence plant defense under heavy metal exposure individually, however, the combination of them and the contribution of eCO 2 were still unclear. The pot experiment was employed to explore the combined effect of eCO 2 (700 ppm) and Funneliformis mosseae on the defense of black locust ( Robinia pseudoacacia L.) grown in cadmium (Cd)-polluted soils by 13 C isotope tracer. Elevated CO 2 significantly caused an increase in Cd content, decreases in contents of malonaldehyde, carotenoids, soluble sugars and proteins, metallothioneins (MTs) and proline and activities of superoxide dismutase, catalase, peroxidase, ascorbate peroxidase and glutathione peroxidase and increases in ascorbic acid (AsA), glutathione (GSH), cysteine (Cys) and phytochelatins (PCs) in leaves under F. mosseae colonization. Additionally, the indirect contributions of eCO 2 to AsA, GSH, Car, proline, soluble sugars and proteins, Cys, PCs and MTs under eCO 2  +  F. mosseae were lower than that under eCO 2 alone. Overall, eCO 2 enhanced the defense of black locust colonized by F. mosseae under Cd exposure by stimulating AsA, GSH, PCs and Cys synthesis, which will provide some insights into the effect of global change on the resistance mechanism of plants colonized by AMF to heavy metals.