ALUMINUM TOXICITY AND TOLERANCE IN 3 HEATHLAND SPECIES

Arnica montana and Cirsium dissectum are characteristic species of spe cies-rich heathlands and adjacent grasslands, which declined during th e last decades in the Netherlands. It has been shown in a recent field survey that the decline of A. montana and C. dissectum might be cause d by soil acidification. Calluna vulgaris is not susceptible to soil a cidification. It was hypothesized that increased aluminium concentrati ons in the soil as a result of acidifying atmospheric inputs caused th e decline of A, montana and C. dissectum whereas C. vulgaris would not be sensitive to enhanced aluminium concentrations. We studied the eff ects of different Al:Ca-ratios and of Al concentrations on the develop ment of A. montana, C. dissectum and C. vulgaris in nutrient solution experiments. All three species showed aluminium accumulation in the sh oots related with increased aluminium concentrations in the nutrient s olutions. This accumulation was correlated with a reduction in growth when plants were cultured at high Al concentrations (200-500 mu mol l( -1)), in both A. montana and C. dissectum. In addition, indications of Al toxicity were observed in these plant species, e.g. poor root deve lopment, yellowish leaves and reduced contents of Mg and P in the plan ts. C. vulgaris did not show reduced growth or poor plant development due to high Al concentrations. The negative effects of aluminium in A. montana and C. dissectum were partly counterbalanced when plants were grown on the same Al concentrations but with increased Ca concentrati ons, resulting in lower Al:Ca-ratios. No effects of enhanced calcium c oncentrations on C. vulgaris have been observed.