DISSOLUTION OF IRON FROM IRON (HYDR)OXIDES BY MUGINEIC ACID

Mugineic acid (MA; (2S, 2'S, 3'S, 3 '' )-N-[3-carboxy-3-(3-carboxy-3-h ydroxy-propylamino) -2-hydroxypropyl]-azetidine-2-carboxylic acid), a multidentate complexing agent, is exuded by the roots of graminaceous plants (e.g. barley) growing under Fe-deficient conditions. The nature of the interactions of MA with Fe (hydr)oxide minerals in soils is th us of considerable practical importance. To examine the availability o f RIA in dissolving Fe (hydr)oxides, we investigated the amounts of Fe dissolved from 24 samples of Fe (hydr)oxides by 100 mu M MA (Fe-MA) a nd 200 mM NH4-oxalate (Fe-0). The Fe-0 values were much larger than th e Fe-MA ones, though the crystallinity of the Fe (hydr)oxides was a si gnificant factor. For Fe (hydr)oxides consisting of goethite, hematite , ferrihydrite, and their mixture, Fe-MA increased with the increase o f Fe-0, indicating that Fe-MA would be correlated with Fee, that is th e amount of short-range ordered Fe minerals including ferrihydrite. Fo r goethite, hematite, magnetite, maghemite, and lepidocrocite with a h igh crystallinity, MA was relatively ineffective in dissolving Fe, alt hough a part of crystalline magnetite, maghemite, and lepidocrocite co uld be dissolved by NH4-oxalate. For soils containing significant amou nts of magnetite, maghemite, lepidocrocite, it is unlikely therefore t hat Fe-0 would be a useful indicator of plant-available Fe.