Foliar application of inorganic fertilizers mitigates mercury and methylmercury accumulation in dryland Crops: A plant-soil-microorganism synergistic regulation.

Foliar application technology has received considerable research attention due to its potential to mitigate the accumulation of heavy metals such as cadmium and lead in crops. However, to date, there are very few inorganic foliar sprays reported to be capable of reducing mercury (Hg) and methylmercury (MeHg) in plants. In this study, common inorganic foliar sprays such as ZnSO4, Na2S, Na2SeO3, and MnCl2 were screened, among which ZnSO4 was confirmed to be the most effective in reducing Hg (32 %-72 %) and MeHg content (43 %-75 %) in various dryland plants (Lettuce, Chili, Maize and Bok choy). Further mechanistic studies showed that ZnSO4 application reduced organic acid concentrations and increased sulfate levels in the rhizosphere. These changes simultaneously shifted Hg speciation and altered the microbial community, favoring mercury-reducing bacteria while inhibiting mercury-methylating microorganisms. As a result, both bioavailable Hg and MeHg concentrations in the soil were effectively reduced. Moreover, foliar spraying of ZnSO4 enhanced the chelation of Hg by non-protein thiols in roots, the compartmentalization of cells, and the antagonistic absorption between mineral elements and Hg, thus reducing the absorption of Hg by plants. In contrast, spraying Na2SeO3 had no significant effect on mercury-methylating microorganisms in the soil. only enhanced cellular compartmentalization and slightly increased soil Se content and, slightly reduced soil bioavailable Hg and Hg content in stems, but had no significant effect on Hg content in leaves. These results suggest the potential of zinc sulfate foliar application for the safe use of mercury-contaminated soil.