Roles of rhizospheric organic acids and microorganisms in mercury accumulation and translocation to different winter wheat cultivars

Elevated mercury concentrations in wheat grains pose a potential health risk to human. In this study, we selected two low-mercury-accumulating wheat cultivars (Nongda-3163, Gaocheng-8901) and two high-mercury-accumulating wheat cultivars (Jimai-21, Taishan-21) to investigate the role of rhizospheric organic acids and microorganisms in mercury accumulation and translocation to different wheat plants. The wheat grew in greenhouse with three levels of mercury treatment: control (no added mercury), low treatment (1 mg kg−1 total mercury) and high treatment (5 mg kg−1 total mercury). Under low mercury treatment condition, Jimai-21 and Taishan 21 had significantly higher mercury concentrations in roots and secreted higher amounts of oxalic acid and citric acid in the rhizosphere soil than Nongda-3163 and Gaocheng-8901. Meanwhile, abundances of gram positive bacteria, gram negative bacteria and fungi in the rhizosphere soil of Jimai-21 were significantly higher than those of Nongda-3163 and Gaocheng-8901, while abundance of protozoa in the rhizosphere soil of Jimai-21 was significantly lower than those of Gaocheng-8901. These facts may lead to higher mercury concentrations in grains of Jimai-21 and Taishan-21 than those of Nongda-3163 and Gaocheng-8901. In the current study, the oxalic acid had the largest contribution on mercury accumulation and translocation (p = .002), followed by citric acid (p = .002) and protozoa (p = .038) under low mercury treatment condition. Under high mercury treatment condition, Jimai-21 and Taishan-21 had significantly higher translocation factors from roots to leaves, glumes and grains than Nongda-3163 and Gaocheng-8901, and the significant contribution sequentially were citric acid (p = .002), fungi (p = .02) and gram positive bacteria (p = .018). Improving the beneficial relationship among rhizospheric organic acids, microorganisms and wheat cultivars was a realizable strategy to ensure wheat safety for mercury.