Effect of ionic Al in culture solutions on the growth of Arnica montana L. and Deschampsia flexuosa (L.) Trin

The distribution ofArnica montana L., a hemicryptophytic plant of acid peaty heathlands on nutrientpoor humic podzols has declined in the Netherlands since 1950. The decline is significantly correlated with the 95-percentile of the SO2 concentration in the air over the winter period of 1978/1979. The resulting acid rain could have caused increased levels of ionic Al in low-buffered soils as ‘Haar’ and ‘Veld’ (humic) podzols. Ionic Al is generally considered to be an important growth-limiting factor in many acid soils which are often leached causing additionally low levels of Ca and Mg.The toxic effect of Al3+ on seedlings growth of Arnica and on the Al-tolerant, calcifugous grassDeschampsia flexuosa (L.) Trin. was investigated. Seedlings of both species were grown on complete nutrient solutions situated in a heated greenhouse. Various concentrations of Al3+ at high acidity (pH 3.8) were used. Relatively high and low levels of Ca and/or Mg were factorially combined.It appeared that Arnica and Deschampsia are Al tolerant, the former being somewhat less so. At relatively low concentrations (e.g. 5 mg l−1) of ionic Al, growth of shoot and roots of both species were stimulated. Tolerance to Al3+ is possibly due to an internal Al-chelating mechanism. The Ca and Mg supply did show an influence on growth (yield), but both divalent ions did not affect the magnitude of Al toxicity. These results may indicate that it is not likely that the decline of the regional distribution and abundance of Arnica since 1950 is regulated by ionic Al in the rooting zon