Aluminum toxicity and forest decline

The rate of root elongation in seedlings of Picea abies was drastically inhibited by exposure to AlCl(3) at 800 or 1200 mumol/dm(3) in nutrient solutions. A 35-day exposure to Al at 700 mumol/dm(3) reduced Mg and Ca in roots and needles of the seedlings. The Mg content of needles was reduced to levels considered to be critical for Mg deficiency. In investigations of (45)Ca uptake into roots, exposure to Al at 100-800 mumol/dm(3) reduced (45)Ca uptake by 77-92%, respectively. By using x-ray microanalysis, the distribution of Al, Mg, Ca, and K was found to be similar in roots of Picea abies seedlings grown in solution culture and in roots collected from declining spruce stands at Solling, F.R.G. In solution culture Al displaced Mg and Ca in the root cortex. A mechanism of Al toxicity for root growth and ion uptake is proposed, and its relevance to forest decline is discussed.