EFFECTS OF PHOTOPERIOD, CO2 CONCENTRATION, AND LIGHT INTENSITY ON GROWTH AND NET PHOTOSYNTHETIC RATES OF LETTUCE AND TURNIP
At longer photoperiods, the growth rate and the net photosynthetic rate per plant of lettuce increased only slightly, whereas those of turnip increased remarkably, with increasing the CO2 concentration or the light intensity. It was observed that the tuber of turnip grew rapidly at a high intensity of 316 μE/m2/s and the photoperiod of 24 hrs. Also, at the light intensity of 237 μE/m2/s, the stomatal resistance and the CO2 compensation point of lettuce increased with increasing the photoperiod and the CO2 concentration. In the case of turnip, however, the stomatal resistance did not change appreciably and the CO2 compensation point increased to a lesser extent.
Thus, these substantial differences observed experimentally are considered to be attributable to the difference between the sink volumes of lettuce and turnip.