Exogenous Fe(II) enhanced iron plaque formation influences the adsorption and immobilization of Cd in rice root.

Background: Iron plaque on the rice rhizoplane could potentially prevent cadmium (Cd) entry into plant roots. A hydroponic experiment was conducted to study the morphological characteristics and mineral compositions of iron plaque, Cd immobilization mechanism by iron plaque, and its effect on Cd uptake and transport in rice.

Results: Exogenous divalent iron ion (Fe(II)) could induce the formation of deep-red iron plaque on rice rhizoplane, which primarily consisted of ferrihydrite, goethite, hematite, iron phosphate, and iron sulfate compounds. The results of X-ray photoelectron spectroscopy and X-ray diffraction indicated that the conversion of Fe(II) into ferric ion (Fe(III)) during the formation of iron plaque could promote the adsorption and immobilization of Cd in iron plaque. Meanwhile, Cd content in amorphous and crystalline fractions of iron plaque increased by 29.9-97.3% and 13.6-97.9%, respectively, during the formation of iron plaque. Correlation analysis indicated that fractions of amorphous and crystalline Fe might effectively combine with Cd in the iron plaque on rice rhizoplane. Furthermore, the content of Cd in the above-ground parts of rice decreased by 2.75-35.2% during the formation of iron plaque. Also, the translocation factors of Cd from rice roots to shoots showed a gradually decreasing trend with increasing Fe(II) concentration in the solution.

Conclusion: Cd could be effectively adsorbed on iron plaque and immobilized on rice rhizoplane, thus further reducing the transport of Cd from roots to the above-ground parts in rice. © 2025 Society of Chemical Industry.