SENSITIVITY TO H- AND AL IONS LIMITING GROWTH AND DISTRIBUTION OF THEWOODLAND GRASS BROMUS-BENEKENII

One pH experiment and two aluminium experiments were conducted in orde r to investigate the effects of H- and Al ions on growth of Bromus ben ekenii. Continuously flowing solution cultures were used with ion conc entrations simulating natural soil solutions. In all experiments, trea tment effects were more pronounced on root than on shoot growth. In th e pH experiment, root growth decreased with decreasing pH within the p H range 4.5 to 3.5. The critical pH for root growth of Bromus benekeni i was between 3.8 and 4.0. In the Al experiments, root growth started to decrease at 20 muM of quickly reacting Al and almost ceased at 70 m uM Al. This characterizes Bromus benekenii as an Al sensitive species. In the pH experiment, shoot concentrations of Ca, Mg, K and P decreas ed with decreasing pH, but root concentrations were not affected. In t he Al experiments, the Al concentrations of both shoots and roots incr eased with Al in the nutrient solution. At treatments of 70 muM Al or higher, Ca, Mg, K and P concentrations in the shoots were reduced. The critical concentrations of H- and Al ions in the experiments were sim ilar to the highest concentrations found at field sites of Bromus bene kenii, analysed in soil solutions obtained by centrifugation technique . Both Al and H toxicity were considered to be of importance as limiti ng factors for the distribution of Bromus benekenii in south Sweden. P robably, Al toxicity starts to limit growth when also pH itself influe nces growth negatively. The importance of simulating natural soil solu tions in experiments is emphazised, in order to obtain information on the importance of chemical soil factors to the distribution of plants.