© 1990 Heron Publishing—Victoria, Canada
Effects of aluminum on growth and nutrient status of Douglas-fir seedlings grown in culture solution
W. G. Keltjens
Department of Soil Science and Plant Nutrition, Wageningen Agricultural University, Dreijenplein 10, 6703 HB Wageningen, The
Netherlands / Received May 10, 1989
Summary
Effects of Al on growth, nutrient uptake and proton efflux were studied in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings grown for about nine months in culture solutions with a pH between 3.4 and 3.6 and with both calcium
and magnesium (Ca + Mg) at a concentration of 0.1, 0.5 or 2.5 mM.
In the absence of Al, plant dry matter production and root development increased with increasing concentrations of (Ca + Mg)
in the culture solution. At the low and intermediate (Ca + Mg) concentrations, optimal root and shoot development were observed
at an Al concentration of 4 mg l–1. At the highest (Ca + Mg) concentration, Al up to 4 mg l–1 did not affect growth, but at higher concentrations, it significantly reduced both shoot and root growth.
As the concentration of (Ca + Mg) in the nutrient solution increased, the concentrations of Ca and Mg increased in shoots
and roots also. The concentrations of Ca and Mg in the roots were unaffected by the presence of Al, whereas in the shoots
they were either unaffected, or increased, by Al. Concentrations of Al in, or on, roots, or in shoots, did not change in response
to changing concentrations of Ca + Mg in the nutrient medium. In general, concentrations of P and K in shoots and roots were
higher in seedlings grown in nutrient solutions containing Al.
Stimulation of growth by moderate concentrations of Al, which was observed at suboptimal (Ca + Mg)
concentrations, was associated with a low NH4 preference and a low root proton efflux. The Al-induced increase in internal K concentration and reduction in NH4 preference may be explained by a lower efflux of K and NO3, respectively.
