Fig. 1. Schematic illustration of the growth chamber. The total pressure in the chamber
can be increased up to 0.6 MPa. The chamber has a caliber (ϕ) of 130 mm and an
inside height (h) of 330 mm. An air balloon is used for gas sampling in the experiment
under 0.1 MPa to extrude the gas from the chamber. A small fan is set in the
middle of the chamber.
sewer valve. Fluorescent tubes as light sources were set outside
the chamber. The photon flux density (PFD) was controlled in the
range of 0–100 mol/m2s by adjusting the distance between the
light sources and the chamber. A small fan consisting of a propeller
with three 40-mm-long blades and an electric motor (RF-500TB,
MABUCHI) was set in the middle of the chamber.
Fig. 2 shows a schematic illustration of the gas supply system.
The gaseous species in the gas cylinder were compressed air and
standard gases with controlled CO2 concentrations of 130, 190,
770 and 1140 ppm. The pressure of the gas was reduced to arbitrary
pressures using a regulator, and the gas was sterilized by a
clean filter and supplied into each chamber. The absolute humidity
of the gas was controlled arbitrarily by bubbling the gas from the
bottom of a 10 L pressure tank and by adjusting the flow rate and
volume of water. Thus, the absolute humidity of the gas was controlled
in the range of 5.1–14
×
10−3 kg/kg; it was 0.72
×
10−3 kg/kg
without bubbling. The fluctuation in temperature in the chamber
was suppressed by temperature-controlled air flowing around the
chamber. The absolute humidity and the temperature of the gas
were measured using a dew-point meter To evaluate the performance of the chamber for maintaining a controlled
environment, the pressure, temperature and humidity in
the chamber were kept constant for 24 h and analyzed at regular
time intervals. It was shown that the pressure in the chamber was