Adaptation of Antioxidant Enzymes in Robinia Pseudoacacia L. Grown in Cadmium-Contaminated Soils under Elevated CO2 to Arbuscular Mycorrhizal Symbiosis

The coexistence of heavy metal-contaminated soils and increasing atmospheric CO2 significantly affect plant growth. Arbuscular mycorrhizal fungi (AMF) can regulate the oxidative stress of adverse environments on plants. This study focused on the regulation of AMF on antioxidant enzymes in leaves of Robinia pseudoacacia grown in cadmium-contaminated soils under elevated CO2 (ECO2). Funneliformis mosseae was selected to study the regulation of AMF on antioxidant enzymes in R. pseudoacacia grown in sterilized cadmium (Cd)-contaminated soils (added 4.5 mg kg(-1) dry weight soil) under 750 ppm ECO2 provided by plant incubators. Elevated CO2 decreased F. mosseae colonization rate in roots by 8.8% under Cd exposure. F. mosseae enhanced Cd in root by 87.9% but reduced Cd in leaves by 72.8% under ECO2. F. mosseae led to (p < 0.05) lower malondialdehyde in leaves under ECO2 + Cd. F. mosseae up-regulated (p < 0.05) Cu/Zn-superoxide dismutase (SOD) gene expression and down-regulated catalase (CAT) gene expression under ECO2 + Cd. F. mosseae inoculation significantly reduced SOD activity under ECO2 + Cd, however, the changes in POD and CAT activities were insignificant. Additionally, the combination of ECO2 and F. mosseae reduced (p < 0.05) SOD and POD activities under Cd exposure. Cadmium and carbon in the roots significantly influenced the three antioxidant enzymes. Gene expression and activities of SOD and POD enzymes generally showed inconsistent patterns in responses to F. mosseae under ECO2 + Cd. The results will improve our understanding of the regulation of AMF on antioxidant system in plants grown in heavy metal-contaminated soils under increasing CO2 scenarios.