Effect of the air pollution component ammonium sulphate on the VAM infection rate of three heathland species

Three heathand species, Antennaria dioica, Arnica montana and Hieracium pilosella, were artificially rained with ammonium sulphate solutions at increasing concentrations in a greenhouse experiment. The same species were also artificially rained with increasing ammonium sulphate solutions under field conditions. Dry weights of the plants in the field experiments did not change with increasing ammonium sulphate applications. Nor did the dry weights of plants in the greenhouse experiments change with increasing ammonium sulphate concentrations, except for Arnica montana, which showed an increase in dry weight. VAM infection percentage of Antennaria dioica increased in both the greenhouse and the field experiment. The results of the field experiment show that VAM infection rates are reduced after two years of artificial rain in the plant species Arnica montana, which grows naturally under nutrient poor conditions and is presently declining in its natural habitat in the Netherlands. In the greenhouse experiment, VAM infection of Arnica montana did not change with increasing ammonium sulphate concentrations. VAM infection rates of Hieracium pilosella, which presently is not declining, did not change with increasing ammonium sulphate concentrations.