INFLUENCE OF SOIL OXYGEN DEPLETION ON IRON UPTAKE AND REDUCTION IN MANGO (MANGIFERA INDICA L.) ROOTS

摘要

In alkaline agricultural soils, such as those in south Florida, a large amount of chelated iron must often be applied to tropical fruit trees, including mango {Mangifera indica L.), to avoid iron deficiency. In calcareous soil, long-term lack of oxygen (anoxia) often results in iron deficiency due to increasing amounts of bicarbonate generated as a result of anaerobic metabolism in the root and microbial respiration. Short-term anoxia of alkaline soils may increase iron uptake as a result of iron becoming more soluble in the soil, reduced from the Fe3+ form to the Fe2+ form that is more readily available for plant uptake, and through biochemical changes in the roots as a result of anaerobic conditions. Experiments were conducted in a glasshouse to investigate short-term effects of root zone anoxia on physiological root responses of five-year-old 'Kitchener' mango trees. Oxygen was depleted from the rhizosphere by infusing root containers with gaseous nitrogen. Oxygen depletion reduced root respiration and resulted in an increased concentration of extractable NADH (nicotinamide adenine dinucleotide), a co-enzyme that functions as an electron carrier in the reduction of Fe3* to Fe2+. The role of these biochemical changes in the roots on increased iron uptake was supported by increased iron concentrations in roots of mango trees in an oxygen-depleted, alkaline medium.