Calcium requirement of quaking aspen (Populus tremuloides Michx.) seedlings

To evaluate potential effects of Ca depletion on aspen productivity, I undertook a series of hydroponic and soil experiments to determine the levels of solution Ca required to achieve maximum growth in aspen seedlings and to examine other solution elements that influence the Ca requirement. Results from nine hydroponic experiments are summarized here.; Growth increased with solution Ca. Ninety percent of maximum elongation occurred at 61 muM for shoots and 88 muM for roots. Tissue Ca increased with solution Ca. Shoot and root elongation was positively correlated with tissue Ca. Ninety percent of maximum shoot elongation occurred at leaf Ca 0.46% (ODW) and root Ca 0.12%, and 90% of maximum root elongation at leaf Ca 0.56% and root Ca 0.13%. At 25 and 250 muM Ca, growth increased with solution pH (3.3 to 5.0). The need for solution Ca was higher at lower solution pH. Tissue Ca increased with solution pH.; High solution Mg reduced growth at low solution Ca. High solution NH 4 reduced root elongation at both 10 and 250 muM Ca. The need for solution Ca increased at higher solution Mg or NH4. Ninety percent of maximum elongation occurred at solution Ca/Mg molar ratio of 0.14 for shoots and 0.53 for roots, and 90% of maximum root elongation at solution Ca/NH 4 molar ratio of 2.44. High solution Mg and NH4 reduced tissue Ca.; Growth decreased with increasing solution Al and increased with solution Ca/Al. Ninety percent of maximum elongation occurred at solution Ca/Al molar ratios of 0.23 for shoots and 1.86 for roots. Solution Al reduced tissue Ca. Shoot elongation was positively correlated with root Ca/Al, and root elongation with root Ca. Ninety percent of maximum shoot elongation occurred at root Ca/Al weight ratio of 0.40, and 90% of maximum root elongation at root Ca 1.4%.; The reported soil solution Ca levels in Lakes States aspen forests are higher than those associated with Ca deficiency in my hydroponic experiments.