Iron nutrition of sunflower and corn plants in mono and mixed culture

Sunflower (Helianthus annuus L. var. Giganteus) and corn plants (Zea mays L. var. Velox) were grownin mono and mixed culture for 11 days in nutrient solution containing no iron, inorganic Fe3+ and FeEDTA (2 ppm Fe each) respectively to evaluate the interaction between both plant species on their ability for iron uptake. Both plant species developed chlorosis under iron stress (no iron, inorganic Fe3+); however, due to the ability of sunflower plants to lower the pH of the nutrient solution under iron stress conditions, in presence of inorganic Fe3+ the pH lowering was followed by regreening of sunflower in mono and mixed culture. In mixed culture but not in mono culture corn plants also regreened under these conditions. With respect to iron accumulation, therefore, the sunflower plants promoted the uptake and translocation of iron to the shoot of corn plants, i.e. an ‘Fe-efficient’ species can improve the iron nutrition of an ‘Fe-inefficient’ one. In contrast to this corn plants had little or no effect on the iron nutrition of sunflower plants. The corn variety used in this experiment developed chlorosis even in presence of 2 ppm Fe in form of EDTA. This high susceptibility to iron chlorosis was related to the P/Fe ratio in the shoot rather than to the capacity of the plants for absorption and translocation of iron, because sunflower plants with the same or even lower iron content but lower phosphorus content were green.