Effects of elevated CO_2 on arbuscular mycorrhizal fungi associated with Robinia pseudoacacia L grown in cadmium-contaminated soils

摘要

As symbionts capable of reciprocal rewards, arbuscular mycorrhizal fungi (AMF) can alleviate heavy metal toxicity to host plants and are easily influenced by elevated CO_2 (ECO_2). Although the individual effects of ECO_2 and cadmium (Cd) on AMF have been widely reported, the response of AMF to ECO_2 + Cd receives little attention. We evaluated the combined effects of ECO_2 and Cd on AMF in the rhizosphere soil and roots of Robinia pseudoacacia L. seedlings. Under ECO_2 + Cd relative to Cd, AMF gene copies and richness in rhizosphere soils increased (p＜0.05) and the diversity reduced (p＜0.05) at 4.5 mg Cd kg~(-1) dry soil; whereas root AMF abundance at 4.5 mg Cd kg~(-1) dry soil and the diversity and richness reduced (p ＜ 0.05). Elevated CO_2 caused obvious differences in the dominant genera abundance between rhizosphere soils and roots upon Cd exposure. Responses of C, water-soluble organic nitrogen (WSON), pH, and diethylene triamine penta-acetic acid (DTPA)-Cd in rhizosphere soils and root N to ECO_2 shaped dominant genera in Cd-polluted rhizosphere soils. Levels of DTPA-Cd, WSON, C and pH in rhizosphere soils and C/N ratio, N, and Cd in roots to ECO_2 affected (p ＜ 0.05) dominant genera in roots under Cd exposure. AMF richness and diversity were lower in roots than in rhizosphere soils. Elevated CO_2 altered AMF communities in rhizosphere soils and roots of R. pseudoacacia seedlings exposed to Cd. AMF associated with R. pseudoacacia may be useful/interesting to be used for improving the phytoremediation of Cd under ECO_2.