EFFECTS OF ALUMINUM IONS ON UPTAKE OF CALCIUM, MAGNESIUM AND NITROGEN IN BETULA-PENDULA SEEDLINGS GROWING AT HIGH AND LOW NUTRIENT SUPPLY RATES

The effects of aluminium on plant nutrition in small birch plants (Betula pendula Roth) were investigated. By using relative addition rate (R(A), g g(-1) d(-1)) of nutrients as the growth-controlling variable, it was possible to grow the plants at very low external nutrient concentrations and to simulate plant requirements at two different fertility levels. Before aluminium addition the plants were at steady-slate relative growth rate, (R(G), g g(-1) d(-1)). The two addition rates were free access of nutrients with R(G) approximate to 0.215 d(-1), or nutrient-limited, R(A) and R(G) = 0.10 d(-1). Internal concentrations of calcium and magnesium decreased with increasing Al3+ conncentration in the nutrient solution while nitrogen concentrations in the plants remained unchanged or increased. It was demonstrated in both nutrition treatments that calcium and magnesium decrease per se does not reduce plant growth and that uptake has to be considered in relation to plant requirement at different growth rates. The interpretation of the effects of aluminium on Ca and Mg uptake and plant biomass development suggested that processes other than disturbances in Ca and Mg uptake are the cause of the decrease in growth.