Elevated atmospheric CO 2 generally improved soluble sugars content in the rhizosphere soil of black locust seedlings under cadmium exposure

Aims Sugars in soils play vital roles in soil aggregation and microbial activity, which is easily affected by environmental factors. Here, we investigated the accumulation of total sugars and monosaccharides in the rhizosphere soil of black locust seedlings exposed to the contamination of elevated atmospheric CO 2 (eCO 2 ) and cadmium (Cd) and its driving factors. Results Under eCO 2 + Cd compared to Cd, glucose, galactose, arabinose, mannose, and xylose concentrations in the rhizosphere soil increased and the increases were significant at 4.5 mg Cd kg −1 ( p < 0.05). Glucose was the most abundant sugar. The GM/AX ratio increased ( p < 0.05) under eCO 2 + Cd relative to Cd, suggesting that sugars in rhizosphere soils might be mainly from microbial synthesis under eCO 2 + Cd. In addition, CO 2 , Cd, and CO 2 + Cd influenced ( p < 0.05) total sugar and monosaccharide concentrations and the (galactose + mannose)/(arabinose + xylose) (GM/AX) ratio. Sugars concentrations in rhizosphere soils were affected ( p < 0.05) by responses of leaf and root biomass, Cd in roots, S in leaves, leaf C/N ratio, and pH and C in rhizosphere soils to eCO 2 . However, the contribution of sugars in the roots to those in rhizosphere soils was not significant under elevated CO 2 + Cd exposure. Conclusions Elevated CO 2 stimulated sugar concentrations in the rhizosphere soil of black locusts exposed to Cd, which was helpful to understand the contribution of global change scenarios to sugar accumulation in the rhizosphere of plants grown in heavy metal-contaminated soils.