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Abstract
The influence of NH4 concentration on growth and mineral composition of chrysanthemum was examined in two cultivars, ‘Mountain Snow’ and ‘Fiesta’, found previously to differ in sensitivity to drought. Plants were grown for 18 days in modified Steinberg solution containing 51.7 mg l‐1 NO3 and NH4 concentrations ranging from 0 to 500 mg I‐1. Drought‐sensitive ‘Mountain Snow’ was found to be much more sensitive to NH4 toxicity (180 mg l‐1 or greater) than was drought tolerant‐'Fiesta’ as evidenced by increased chlorosis, a slower growth rate, and lower dry matter production. Growth reduction in ‘Mountain Snow’ was accompanied by decreased concentrations of Ca, K, and Zn in the lower leaves. Although the Ca concentration in ‘Fiesta’ leaf tissue was also significantly reduced by NH4 toxicity, concentrations of Mg, Mn, Fe, and Zn were unaffected. Ammonium tolerance in ‘Fiesta’ may have been associated with a greater ability to maintain root function and nutrient uptake in the presence of NH4.