RESPONSES OFPOPULUS TREMULOIDESSEEDLINGS TO SOLUTION pH AND CALCIUM

Quaking aspen (Populus tremuloides Michx.) seedlings were grown in solution culture to investigate their response to a range of solution pH (3.3, 3.5, 3.7, 3.9, and 5.0) at two levels of solution Ca (25 and 250 μM). Both shoots and roots showed visible abnormalities at lower levels of solution pH and Ca. Growth increased significantly with increasing solution pH at both levels of solution Ca. Regardless of solution pH, seedlings were larger at 250 μM Ca than at 25 μM Ca. The results suggest that high solution Ca ameliorated the adverse effects of low pH on growth. Concentrations of leaf P, K, Ca, and Mg and root K, Ca, and Mg usually increased with increasing solution pH. At pH 3.9 and 5.0, concentrations of leaf P and Ca and root Ca were higher at 250 μM Ca than at 25 μM Ca. Shoot elongation was positively related to concentration of leaf P, and root elongation was positively related to concentrations of leaf P and Ca and root Ca. These results suggest that high solution Ca ameliorated the adverse effects of low pH on growth possibly by alleviating P and Ca deficiencies.