Acid tolerance of Pacific Northwest conifers in solution culture

Abstract

Seedlings of three Pacific northwest conifer species: Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and western redcedar (Thuja plicata Donn) were grown in acid nutrient solutions with and without aluminium present. The acid treatments were paired so as to differentiate the effects of aluminium from the hydrogen ion concentration that a specific level of Al-cations induces via hydrolysis reactions. Relative to agronomic plants, all the conifers were found tolerant of the acid solutions and high levels of aluminium. Species differed in their relative tolerance to H and Al-cations. Douglas-fir and western redcedar both displayed similar or better growth in nutrient containing 175 ppm Al than in solutions at the same pH (3.0) without aluminium. In contrast to the other species, western hemlock survived and thrived in acid solution of pH 3 while the presence of Al in acid solution adversely affected seedling root growth and tissue divalent cation concentrations, especially calcium and magnesium. Therefore, the ability of western hemlock to grow in acid conditions is postulated to be related to this species' physiological tolerance of excess H-cations in solution and low tissue requirements of Ca and Mg. This tolerance of H-cation concentrations found for western hemlock meant that the specific effects of high Al concentrations in solution could be differentiated in hemoock seedling growth and nutrition from those effects caused by increased H-concentration due to Al-hydrolysis.