Iron nutrition dynamics - Differences between calcicole and calcifuge plants

One third of the earth´s soils is calcareous. Calcifuge plants are excluded from these soils, and one of the main causes is Fe deficiency, as Fe solubility in calcareous soil is very low. A lack of Fe lowers chlorophyll content, visible as yellowing of leaves, called chlorosis. It is demonstrated that the main cause of chlorosis in calcifuges is that a large part of the Fe in their leaf tissues is immobilized in a form that is not metabolically 'active', which is not the case in calcicole plants adapted to growth on such soils. The Fe fraction in leaves responsible for chlorophyll synthesis may be Fe2+ and can be extracted by synthetical chelators. 1,10-phenanthroline extractable Fe correlates well with degree of chlorosis. An additional cause of chlorosis in some calcifuges is a decreased Fe uptake by the root. Phosphorus concentration in the leaf tissue does not seem to have an influence on metabolically 'active' Fe, though phosphate addition to the soil may aggravate chlorosis. Studied were also other conditions of possible importance to calcicole-calcifuge behaviour, such as differences among plants in compartmentation of Fe between shoots, roots and the soil/root interface, as well as allocation of Fe and other plants nutrients to plant seeds. Iron immobilization in the tissue is ecologically important to the calcicole-calcifuge behaviour of plants, as it might decrease vitality in calcifuges and exclude them from calcareous soil