Photosynthesis of Plant under Continuous Illumination

Abstract

To propose an efficient illumination method of plant cultural system in a CELSS, net photosynthetic rates per plant (NPR) of lettuce and turnip were investigated under the conditions of 12 -24hr photoperiod, 400-3200 ppm CO₂ concentrations, and 140-320 μ mol/m²/s light intensities.
At 24hr photoperiod (continuous illumination), NPR of lettuce decreased remarkably as compared to that at 12hr photoperiod, whereas NPR of turnip did not change appreciably, with increasing the light intensity or the CO₂ concentration.
In order to avoid the decrease in light efficiency, the condition of a continuous illumination of low light intensity (less than 140 μ mol/m²/s) is effective in the case of plants with the small sink volume like letuce.