The influence of Al on the metabolism of spruce needles

Aluminium toxicity as a consequence of increasing soil acidity is discussed as a primary factor in forest decline in middle Europe. Ecologically relevant concentrations of Al disturbed root systems of hydroponically grown spruce (Picea abies Karst.) seedlings. The needles, with a much lower Al content in comparison to the roots, were also affected by Al at these external concentrations. In this investigation needle chlorosis as the visible symptom of Al toxicity, was accompanied by decreasing pigment concentrations and photosynthetic rates as well as increasing starch levels and transpiration rates. The magnesium concentrations of roots and needles were lowered by treatment with Al. By feeding the needles directly with Mg, it was possible to differentiate between direct and indirect effects of Al on needle metabolism. Magnesium deficiency was found to drive all the experimental variables except transpiration.