Effect of Light Intensity, Carbon Dioxide Concentration, and Leaf Temperature on Gas Exchange of Spray Carnation Plants

The rates of CO2 assimilation by potted spray carnation plants (cv. Cerise Royalette) were determined over a wide range of light intensities (45-450 W m~ PAR), CO2 concentrations (200-3100 vpm), and leaf temperatures (5-35 °C). Assimilation rates varied with these factors in a way similar to the response of single leaves of other temperate crops, although the absolute values were lower. The optimal temperature for CO2 assimilation was between 5 and 10 °C at 45 W m~ PAR but it increased progressively with increasing light intensity and CO2 concentration up to 27 °C at 450 W m~ PAR and 3100 vpm CO2 as expressed by the equation 2\>pt = —6-47 + 2-336 In C + 0-031957 where C is CO2 concentration in vpm and I is photosynthetically active radiation in W m~. CO2 enrichment also increased stomatal resistance, especially at high light intensities. The influence of these results on optimalization of temperatures and CO2 concentrations for carnation crops subjected to daily light variation, and the discrepancy between optimal temperatures for growth and net photosynthesis, are discussed briefly.