On the Automatic CO₂ Controlling and Recording System

Abstract

Some characteristics on the control of CO₂concentration were tested with the automatic CO₂controlling and recording system, which was attached to the newly constructed phytotron.
The mode of action of this system is as follows (see Fig. 1) ;
1, The CO₂concentration in the chamber (90 × 90 × 120 cm³) or room is able to be controlled at arbitral concentration from 0 to 3, 000 ppm. And CO₂uptake and exhaust are measured at the same time.
2. In the light, CO₂enriched air of arbitral concentration, which is selected to be most suitable for the control of the concentration in the chamber or room, is stored in a gas holder by on-off action, and is flown to the chamber or room through the controlling system.
3. CO₂concentration in the chamber or room is controlled by compound PID (parallel, integral and differential) action of flow rate control valuve from the result of CO₂analysis.
4. In the dark, CO₂increase is controlled by CO₂free air from CO₂absorbing column of moleculer shieve.
5. In the natural light condition, the shift of action from the light to the dark or its reverse action is switched automatically by the signal from the CO₂analyzer of the chamber or room (Fig. 2) .
Using this system, the effect of inlet CO₂concentration upon CO₂uptake of tobacco plants was measured. The CO₂uptake was not affected by the inlet CO₂concentration, however (Table 1) .
Also the effect of CO₂concentration in the chamber upon the CO₂uptake by the plants was tested. The satulation point to CO₂concentration under the artificial light condition of 0.75 cal⋅cm^-2⋅min^-1 was about 1, 200 ppm (Fig. 3) .
The photosynthesis-light curves were figured from the results of the measurement of diurnal changes in net CO₂exchange. Then it was obseved that the tobacco plants in the chamber were satulated with light at the light intensity about 0.75 cal⋅cm^-2⋅min^-1 (Figs. 4, 5) .