Field-type growth chambers such as open-top chambers (OTC) and temperature gradient chambers (TGC) are widely used by plant scientists for research on global climate change. However, because of differences in air temperature - plant growth relationships between chamber and open field experiments, it has been suggested that an unknown "chamber effect" exists. In this paper we 1) measured the effects of an enclosure on the relationships between air, soil and rice plant temperatures and 2) compared rice plant growth in the chamber with that of plants grown outside.
In one experiment, two small wind tunnels were covered with either polyvinyl chloride (PVC) or polyethylene (PE). The solar radiation transmittance of both tunnels were the same, but the long-wave radiation transmittance was 0.28 for the PVC film and 0.85 for the PE film. The wind speed in the tunnels was controlled at either 3 m/s or at 0.3 m/s. Under clear sky conditions, the difference of the soil minus air temperature was 1.6 to 3.5 deg C larger under PVC compared to PE. Compared to PVC, the greater dissipation of long-wave radiation under PE decreased the soil temperature to a greater extent. The increase in the soil temperature in relation to the air temperature decreased as the wind speed increased. Compared to a wind speed of 3.0m/s, soil temperature was 3.0 to 4.5 deg C higher at 0.3m/s.
In the second experiment, a TGC at the Tohoku National Agricultural Experiment Station was used. The TGC was a pipe-structured greenhouse with a pre-air-conditioning system, where the inlet air temperature was lower than outside and a temperature difference of 8 to 10 deg C existed along the longitudinal axis. The solar radiation transmittance of the TGC was 0.60 and the long-wave radiation transmittance of the covering film (a fluoro-polymer) was 0.44. The wind speed in the TGC varied from 0.1 to 0.7 m/s in order to control the temperature gradient. Both outside and in the TGC, soil temperature was higher than air temperature during the growing season (May to August 1997) with the difference being 1.5 deg C outside and from 2 to 5 deg C in the TGC. Rice plants grown at the location in the TGC where the seasonal mean air temperature was equal to the outside air temperature grew much faster than the outside plants. By comparing the leaf emergence rate in the TGC with that outside, we calculated that the "chamber effect" of this TGC was equivalent to an air temperature increase of 5 deg C. In contrast, the relationships between soil temperature and growth rate in the TGC were similar to those outside and the shift in soil temperature coincided with the shift in plant growth in the chamber.
These results suggest that :
1) a plant response analysis on an air temperature basis is perturbed by the shift in temperature regime inherent in a chamber and
2) it is likely that the chamber effect is primarily a temperature effect together with the influence of other environmental factors (e.g. light, humidity) associated with the chamber.