DIFFERENCES BETWEEN CALCIFUGE AND ACIDIFUGE PLANTS IN ROOT EXUDATION OF LOW-MOLECUIAR ORGANIC-ACIDS

The nature and quantity of low-molecular organic acids (LOAs) exuded b y the roots of nine species of calcifuge and nine species of acidifuge wild plants from northern Europe were determined by ion chromatograph y. Particular attention was paid to differences between the calcifuge and the acidifuge species in the proportions of different LOAs in thei r root exudates. Great differences in mol% root exudation between the calcifuge and the acidifuge species were found in some acids. The calc ifuge species exuded more acetic acid, the acidifuge species more oxal ic acid and much more citric acid. In three calcifuge species, however , root exudation of oxalic acid was appreciable, whereas acetic acid e xudation was low in these species. The phosphate- and Fe-solubilizing ability of eight LOAs in a rhizosphere limestone soil was also tested. Oxalic acid was the most efficient phosphate solubilizer and citric a cid, by far, the most efficient Fe-solubilizer at the concentration (1 0 mM) tested. It might be hypothesized that acidifuge species use oxal ate to solubilize phosphate and citrate to solubilize Fe, in limestone soil. The inability of calcifuge species to grow in limestone soil mi ght, therefore, be due to low root exudation of these acids and, as a result, inability to solubilize phosphate and Fe in limestone soil.