A new, small-scale controlled environment plant growth chamber is described, which permits accurately controlled temperatures from ambient (c. 20°C) down to −5°C in the day or −15°C at night. The system also allows controlled injection of pollutant gases.
The chamber is based on a modified commercial chest freezer with temperature control achieved through by-passing the cooling coils in the inner walls of the freezer. This by-pass is controlled by a BBC microcomputer which gives nominal temperature control to 0·1°C over definable diurnal temperature profiles. Photoperiod is also controlled by the microcomputer. The chamber forms a virtually closed system to which pollutant gases are added by injection from low concentration cylinders, regulated using mass flow controllers. The accuracy with which pollutant concentrations are controlled is increased by filtration of the air-stream after passing over the experimental plants: i.e. a ‘single-pass’ system is adopted.
In operation air temperatures across the chambers are controlled to within 1-1·5°C of the pre-set value over the range 25 to −10°C. Leaf temperatures are 2·5-3·0°C above air temperatures during the day, with a total energy input of c. 180 Wm−2 from two 400 W metal halide lamps. The lamps provide a photon fluence rate of 270±30 μmol quanta PAR m−2 s−1 at plant height. During the dark, leaf temperatures deviate less than 1·0°C from air temperature. Soil temperatures are controlled separately from air temperature and are held above zero at all times. To date, fumigation, with NO2 and SO2 has been confined to the daytime. At pre-set concentrations of 20 nl litre−1 variations during fumigation were less than 2·0–2·5 nl litre−1 and 0·5 nl litre−1, respectively.