Response of red spruce and balsam fir seedlings to aluminum toxicity in nutrient solutions

Abstract

Red spruce (Picearubens Sarg.) and balsam fir (Abiesbalsamea (L.) Mill.) were grown in nutrient solutions containing 0, 25, 50, 100, and 200 mg/L aluminum (Al) at pH 3.8. Seedlings died only when placed directly in solutions containing Al without first being conditioned to growth in a hydroponic system. In preconditioned seedlings, no evidence of Al injury was noted in the tops of seedlings at any level of Al, except for small reductions in shoot growth. Aluminum toxicity symptoms in roots, however, were well developed, though spruce showed less tolerance than fir. Inhibition of root growth in both species was first evident at 50 mg/L Al, root lengths decreasing with increasing concentrations of Al. Spruce seedlings at Al concentrations of 100 mg/L and higher were characterized by thickened, stunted, dark brown roots. Root deterioration was caused by Al-induced destruction of epidermal and cortical cells. Although root elongation was severely restricted in spruce and fir, root dry weight was not significantly reduced. Aluminum decreased seedling uptake of most mineral elements; manganese, magnesium, and zinc were affected most and boron and phosphorus least.