Immobilization of tissue iron on calcareous soil: differences between calcicole and calcifuge plants

Deficiency of P and sometimes of micronutrients; especially Fe, is of impor tance to the calcicole-calcifuge behaviour of plants. Calcifuge species are unable to solubilize these elements or keep them metabolically active in s ufficient amounts on calcareous soils. To demonstrate if calcicole, calcifu ge and 'soil indifferent' species differ in Fe nutrition dynamics, samples of such species were transplanted on a slightly acid silicate soil (pH BaCl 2 ca 4.0) and on a calcareous soil (pH BaCl2 ca 7.2). Plants were grown in a computer-controlled greenhouse at a soil moisture content of 50-60% water holding capacity and with additional light (ca 160 mu E s(-1) m(-2), 12 h d(-1)) if ambient light was < 120 mu E s(-1) m(-2). The calcifuge species developed chlorosis when grown on the calcareous soil , whereas the other species did not. Calcareous-soil grown plants had less 1,10-phenanthroline extractable Fe in their leaf tissues than the silicate- grown plants whereas total leaf Fe showed more species specific properties. The ratio of 1;10-phenanthroline extractable to total Fe in the leaves was significantly lower in the calcifuges than in the calcicoles when grown on the calcareous soil. 'Soil indifferent' species did not differ much from t he calcicoles. Root Fe, fractioned as DCB extractable 'plaque' on the root surface and Fe remaining in the root after DCB extraction, showed no distin ct pattern of DCB-Fe related to the different categories, but remaining roo t Fe tended to be lower in the calcifuges compared to the two other categor ies. Leaf colour estimated by a colour scale correlated well with chlorophy ll a + b content measured in the leaves of two calcifuges. Leaf P concentra tions did not differ between the different categories but were more species dependent. We conclude that chlorosis in calcifuge species is related to an immobiliza tion of Fe in physiologically less active forms in the tissue, if plants ar e forced to grow on a calcareous soil, whereas calcicole and 'soil indiffer ent' species are able to retain a much higher share of their leaf Fe in met abolically active form. This probably decreases the vitality and may exclud e calcifuge plants from calcareous soil. We consider this property, previou sly almost unconsidered in an ecological context, as important to the calci fuge-calcicole behaviour of plants.