Arbuscular mycorrhizal fungi facilitate Astragalus adsurgens growth and stress tolerance in cadmium and lead contaminated saline soil by regulating rhizosphere bacterial community

Abstract

Soil worldwide has been severely damaged by various stresses, particularly heavy metal pollution in natural saline soils. The rhizosphere microbial community and arbuscular mycorrhizal fungi (AMF) can effectively facilitate the phytoremediation of contaminated soil. However, the effects of heavy metals and AMF on plant growth and rhizosphere bacterial community in natural saline soils remain uncertain. Here, pot experiments (orthogonal experiments) were designed to investigate the effects of cadmium (Cd) and lead (Pb) on the rhizosphere bacterial community of Astragalus adsurgens with or without AMF, and the microbial regulation mechanism of AMF in promoting phytoremediation of Cd and Pb contaminated saline soil. The results showed that heavy metals inhibited plant growth with and without AMF, however, AMF significantly increased shoot biomass by 536 %–970 % and root biomass by 272 %–382 %. Heavy metals reduced the richness and diversity of the rhizosphere bacterial community without AMF, however, no significant reduction was observed with AMF. In all four treatments, AMF significantly enhanced the richness and diversity of the rhizosphere bacterial community. Linear discriminant analysis effect size revealed that heavy metals significantly enriched heavy metal-tolerant rhizosphere bacteria with and without AMF. AMF significantly enriched more beneficial rhizosphere bacteria (mainly Rhodobacter, Archangium, and Longimicrobium) that tolerated heavy metals and promoted plant growth. Network analysis showed that heavy metals weakened bacterial interactions without AMF, but did not influence it with AMF. AMF strengthened the interaction and enhanced negative correlation ratio between bacteria, suggesting less stress and a stable and healthy environment. Finally, the structural equation model confirmed that AMF could improve the phytoremediation efficiency by regulating the rhizosphere bacterial community. This study enables us to understand the influence of heavy metals and AMF on plants and rhizosphere bacterial community, providing a theoretical basis for further improving the phytoremediation of heavy metal-contaminated saline soils.