SOIL SOLUTION CHEMISTRY CONTROLLING THE FIELD DISTRIBUTION OF MELICA-CILIATA L

Germination, establishment and growth of Melica ciliata L., an ‘acidifuge’ species of rocky habitats in Europe, were studied experimentally and related to chemical properties of the soil solution, including pH, base cation composition, A1 concentration and speciatjon, and Mn concentration, M. ciliata failed to establish in acid leptite soil. However, it was able to grow in solution at pH 3-6 and exhibited vigorous growth at pH 3-9, a typical soil solution pH of leptite sites, which Melica is unable to colonize. Higher concentrations of Mn than those measured in any leptite soil solutions did not influence growth. Exposure to 0037 mmol r1 (1 mg l-1) of Al3+, a concentration usually exceeded in the soil solution of leptite sites, severely retarded root growth. Speciation technique applied to A1 in soil solutions obtained by centrifugation demonstrated a close relationship between H+and A1 concentrations and, in particular, between H+ and free ionic (quickly reacting) A1 species. Soil solution concentrations of free ionic A1 proved to be < 0-002 mmol l-1 in sites with Melica, but often >0-10 mmol l-1 in sites lacking Melica. It is concluded that the inability of M. ciliata to establish in acid soils is not primarily due to the high H+concentration but to the high soil solution concentrations of Al, especially free A1 ionic species at low soil pH. © 1993 Annals of Botany Company.