Dissolution of iron by mugineic acid from soils and comparison with DTPA soil test

Abstract

Mugineic acid (MA), which is a multidentate phytosiderophore, is exuded to the rhizosphere by the roots of graminaceous plants (e.g. barley) growing under Fe-deficient conditions, resulting in the dissolution of Fe as a form of MA-Fe111 complex (MAFe). To clarify the effects of soil chemical properties on the amount of Fe dissolved by MA, an experiment to study the reaction of MA using 38 soil samples was conducted, and the concentrations of free MA (uncomplexed and non-adsorbed MA) and MAFe in solution and the amounts of MA adsorbed on the soils were determined after the reaction. Soil pH value was a good indicator to predict the behavior of MA in soils. A large proportion of added MA was adsorbed on soils or formed MAFe in solution in acidic soils, whereas it did not react with soils and occurred as free MA in alkaline soils. These features were in good agreement with the interaction of MA with Fe (hydr)oxides, as reported in previous papers. Other soil chemical properties, such as soil organic carbon (SOC) content and the amount of amorphous (hydr)oxide components, also affected the behavior of MA in the soils. The Fe dissolution ability of MA was compared with that of diethylenetriaminepentaacetic acid (DTPA) soil test. Although the amounts of extractable Fe were similar between the MA extraction and DTPA soil test, factors influencing the amount of Fe dissolved (formation constant with Fe111, reaction pH, rate constant, etc.) were different between both chelating compounds.