Arbuscular mycorrhizal fungi and nitrilotriacetic acid regulated Suaeda salsa growth in Cd-contaminated saline soil by driving rhizosphere bacterial assemblages

Abstract Phytoremediation is an environmentally friendly method to remediate heavy metal contaminated saline soil. Arbuscular mycorrhizal fungi (AMF) and biodegradable chelators have potential roles in enhancing the phytoremediation efficiency, while their combined effects are largely unexplored. This study was objected to evaluate the effects of AMF and nitrilotriacetic acid (NTA) on phytoremediation using Suaeda salsa. A pot experiment consisting of four treatments (CK, AMF, NTA and AMF + NTA) was conducted for this purpose. The results showed that the shoot and root biomass of Suaeda salsa ranged from 1.84 to 5.86 mg kg-1 and 0.09 to 0.48 mg kg-1 respectively, and were the highest in the AMF + NTA treatment. The AMF + NTA treatment enhanced the Na accumulation by 116% and 490%, and enhanced Cd accumulation by 61% and 33%, respectively, in plant shoots and roots compared with the CK. The AMF treatment significantly promoted the dominance of Actinobacteria (mainly including Arenimonas, Gaiella, Nocardioides and Marmoricola), whereas the AMF + NTA treatment enhanced that of Proteobacteria (mainly including Aminobacter, Candidatus_Paracaedibacter, Longimicrobium and Flavitalea) in rhizosphere bacterial communities. Network analysis revealed that the bacteria related to Cd were independent from that related to Na in the AMF treatment, but they were consistent in the AMF + NTA treatment. Structural equation modeling further confirmed that single application of AMF or NTA affected plant growth both directly and indirectly, and their combined application could further promote phytoremediation efficiency by enhancing the interactions among bacteria, soil and plants. This study not only proved the benefit of the combined application of AMF and NTA to the improvement of phytoremediation efficiency, but also provided insights into the mechanisms for the improvement from the perspective of rhizosphere microbial community changes.