Uptake and distribution of calcium and phosphorus in beech (Fagus sylvatica) as influenced by aluminum and nitrogen

Abstract
We studied the effects of excess nitrogen added as nitrate (NO3) or ammonium (NH4+), or both, on mineral nutrition and growth of beech (Fagus sylvatica L.) plants grown at pH 4.2 in Al-free nutrient solution or in solutions containing 0.1 or 1.0 mM AlCl3. A high external concentration of NH4+ increased the concentration of nitrogen in roots, stems and leaves. The root/shoot dry weight ratio was less in plants grown in the presence of NH4+ than in plants grown in the presence of NO3. The concentration of phosphorus in the roots was increased and the concentration of potassium in all parts of the plant was decreased by NH4+. A high external concentration of NO3 caused a decrease in phosphorus concentrations of the root, stem and leaf. Uptake of 45Ca2+ by roots was reduced in the presence of high concentrations of NH4+ or NO3, and a combination of high concentrations of nitrogen and aluminum further reduced the uptake of 45Ca2+. Uptake of phosphate (32P) and concentrations of phosphorus in root and shoot were increased when plants were grown in the presence of 0.1 mM Al. Exposure to 1.0 mM Al, however, reduced the concentration of phosphorus in roots and shoots and the reduction was greater when plants were grown in the presence of a high external NO3 concentration. Aluminum binds to roots, and plants grown in the presence of 1.0 mM Al had a slightly higher concentration of aluminum in roots than plants grown in the presence of 0.1 mM Al, whereas the concentration of Al in the shoot was increased 2 to 3 times in plants exposed to 1.0 mm Al. Furthermore, the effects of 1.0 mM Al on uptake of other macronutrients were quite different from the effects of 0.1 mM Al. We conclude that 0.1 mM Al facilitates uptake and transport of phosphorus in beech and that between 0.1 and 1.0 mM Al there is a dramatic change in the effects of Al on uptake and transport of divalent cations and phosphorus.