An experimental comparison of aluminium and manganese susceptibility in Antennaria dioica, Arnica montana, Viola canina, Filago minima and Deschampsia flexuosa

Antennaria dioica, Arnica montana, Viola canina and Filago minima are declining in The Netherlands and are even locally extinct. This process of decline has been associated with an increased rate of acidification of soils and an increased availability of aluminium and manganese to plants up to potentially phytotoxic levels. This paper examines whether, and to what extent, aluminium and manganese are important environmental variables in determining the decline in plant species. Susceptibility to ionic aluminium and manganese was studied in three experiments under controlled conditions. Young plants were grown on a complete nutrient solution containing variable concentrations of aluminium, manganese or aluminium plus manganese (pH 3-8). Responses (dry weights after 5 weeks of growth) were compared to those of Deschampsia flexuosa, known to be aluminium and manganese resistant. Arnica montana was the most resistant, up to concentrations of 80 mg 1“1 aluminium, Antennaria dioica and Viola canina somewhat less, and Filago minima was relatively sensitive. All the species were relatively manganese-resistant up to concentrations of 312- smgl ~1 manganese, with the exception of the relatively sensitive Filago minima. Arnica montana, Viola canina and even Deschampsia flexuosa, were adversely affected by high concentrations of aluminium (80 mg 1“') and manganese (300 mg I-1), when supplied simultaneously. It was concluded from these results that increased amounts of aluminium and manganese available in the plants’ rooting zone are unlikely to account for the decline in the investigated species of the alliance Violion caninae. The sensitivity to aluminium and manganese of Filago minima may, however, be responsible for its decline. The potential significance of other possible (interacting) environmental factors is discussed.