Critical evaluation of organic acid mediated iron dissolution in the rhizosphere and its potential role in root iron uptake

✍ Scribed by David L. Jones; Peter R. Darah; Leon V. Kochian

• Publisher: Springer
• Year: 1996
• Tongue: English
• Weight: 716 KB
• Volume: 180
• Category: Article
• ISSN: 0032-079X
• DOI: 10.1007/bf00015411

✦ Synopsis

Both experimental extractions and theoretical calculations were undertaken to assess whether organic acid-mediated Fe dissolution could play a significant role in elevating the concentration of Fe-complexes in the rhizosphere, and further, whether this could satisfy the Fe demands of a plant utilizing ferric reduction to acquire Fe. Using a mathematical computer model, it was predicted that organic acids released from and diffusing away from the root would result in a solution organic acid concentration at the root surface of between 1 to 50 #M. Over 99% of the organic acids lost by the root were predicted to remain within 1 mm of the root surface. The experimental results indicated that citrate-mediated Fe dissolution of amorphous Fe(OH)3, was rapid in comparison with citrate dissolution of the Fe-oxides, Fe203 and Fe304. The rate of citrate and malate mediated Fe-dissolution was dependent on many factors such as pH, metal cations and phosphate saturation of the Fe(OH)3 surface. At pH values < 6.8, citrate formed stable complexes with Fe and dissolution proceeded rapidly. Under optimal growth conditions for a plant utilizing a reductive-bound mechanism of Fe acquisition (dicots and non-grass monocots), it can be expected that citrate and malate may be able to satisfy a significant proportion of the plant's Fe demand through the formation of plant-available organic-Fe 3+ complexes in the rhizosphere. In high pH soils (pH >7.0), the plant must rely on other sources of Fe, as citrate-mediated Fe dissolution is slow and Fe-citrate complexes are unstable. Alternatively, the root acidification of the rhizosphere could allow the formation of stable Fe-organic complexes.