Effects of Heavy Metal-immobilizing Bacteria on Reducing Wheat Uptake Cd by Regulation Soil Iron Oxides

Abstract

Iron oxides are widely distributed in soils and have large specific surface areas and strong affinities with heavy metals, and thus play a significant role in the transformation of heavy metals in soils. Pot experiments were conducted to study the effects of heavy metal-immobilizing bacteria Bacillus megaterium N3, Serratia liquefaciens H12, and strain N3 combination with H12 on the absorption of Cd by ZM-3 (Triticum aestivum L.). The effects of different treatments on soil pH, iron oxide content, and relative abundance of iron oxide bacteria, clay particle mineral composition, and aggregates in wheat rhizosphere were also measured. The results showed that strains N3, H12, and N3+H12 significantly (P<0.05) increased the dry weight (36.5%-75.3%) of wheat grains, and significantly (P<0.05) decreased the content of Cd (30.2%-84.9%) in wheat grains. Furthermore, compared with the single application of strain N3 or H12, the application of strain N3 combined with H12 had a stronger ability to reduce the absorption of Cd by ZM-3. The results suggested that strain N3, combined with H12, decreased the uptake of Cd in wheat by:①increasing the pH (from 6.74 to 7.08) of wheat rhizosphere soil; ② increasing the Fe oxide (67.9%) and goethite contents of wheat rhizosphere soil; ③ increasing the relative abundance of iron-oxidizing bacteria (Leptothrix spp. and Gallionella spp.), and ④ increasing the content of small particle size (<0.25 mm) aggregates. The results provide a theoretical basis and technical support for the use of heavy metal-immobilizing bacteria to repair farmland contaminated by heavy metals.