Responses of Five Species of Conifer Seedlings to Aluminum Stress

Abstract

Seedlings of red, white and black spruce, and white and jack pine were tested for their response to a range of Al concentrations, when grown for 12 to 14 weeks in sand culture in the greenhouse. Nutrients were supplied in solution of pH 3.8 to which Al was supplied at 0, 5, 10, 20, 40, 80 and 160 mg/L. Red and white spruce were inhibited in growth from 5 mg/L upwards, while black spruce was equally inhibited only at concentrations > 20 mg/L. In contrast, white pine was stimulated by 5 to 20 mg Al/L and was always more tolerant than the other 4 species at every Al level used. Jack pine was intermediate in its response. There was a positive linear relationship between P and Al accumulation in the shoots of red spruce. This was in contrast to the other 4 species in which P concentrations in the shoot decreased with an increase in Al concentrations. In localization studies on jack pine using a modified hematoxylin stain, Al was shown to accumulate in the root cap of root tips, and in the epidermal and outer cortical walls of older roots. EDAX-SEM analysis confirmed the tissue distribution of Al and revealed its coincidental distribution with P in roots.