Plant Physiol.
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Plant Physiology 79:609-613 (1985)
© 1985 American Society of Plant Biologists

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Articles

Effects of Nitrate Application on Amaranthus powellii Wats. 1

I. Changes in Photosynthesis, Growth Rates, and Leaf Area

E. Raymond Hunt, Jr.2, James A. Weber and David M. Gates

University of Michigan Biological Station, University of Michigan, Ann Arbor, Michigan 48109

Physiological effects of different nitrate applications were studied using the C4 plant, Amaranthus powellii Wats. Plants were grown in a controlled environment chamber and watered daily with nutrient solutions containing 45, 10, 5, or 1 millimolar nitrate. Chloride and sulfate were used to keep the cation and phosphate concentrations constant. Total leaf nitrogen concentration, chlorophyll concentration, specific leaf mass, leaf area, relative growth rate, relative leaf growth rate, unit leaf rate (increase of dry mass per unit leaf area per day), net photosynthetic rate, and incident quantum yield decreased with decreasing nitrate concentration. The per cent decrease of unit leaf rate was similar to the decrease of light-saturated net photosynthetic rate; however, the decrease in relative growth rate was less than that of unit leaf rate because leaf area ratio (leaf area per unit dry mass) increased with decreasing nitrate concentration. Essential mineral concentrations per unit leaf area were about equal among all treatments. Leaf expansion, determined by stomatal density, decreased except for the 1 millimolar treatment which showed relatively more cell expansion but less cell division. Decreased nitrate application was correlated with higher osmotic potentials and lower pressure potentials (determined by pressure-volume curves), whereas leaf water potentials were equal among treatments. Even though total leaf area and shoot mass decreased with decreasing applied nitrate, the increase of the leaf area ratio may be related to selection for the highest possible growth rate.

2 Present address: Laboratory of Biomedical and Environmental Sciences, UCLA, 900 Veteran Ave., Los Angeles, CA 90024.

1 Funded in part by Department of Energy contract DE-AC02-76EV02164.






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Copyright © 1985 by the American Society of Plant Biologists