Effect of the NH4+:NO3- Ratio on Net Photosynthesis of Carnation1

Abstract

Productivity of carnation ( Dianthus caryophyllus L.), was increased to levels attained by C4 plants, such as corn, by adjusting the ratio of ammonium to nitrate N supplied to seasonal solar radiation levels. During periods of low solar radiation, the optimum ratio was one third ammonium and two thirds nitrate N. During periods of highest solar radiation, 100% nitrate was best. At high radiant intensity, reduction of nitrate N in carnation, a C3 plant, apparently increased net CO 2 assimilation (growth) by decreasing photorespiration. Nitrate reduction served as an alternate sink for excess photosynthetic energy.