Abstract
A computer-controlled whole-plant cuvette system is described that allows precise and independent control of temperature (+/- 0.05 degrees C), vapor pressure (+/- 0.02 kPa), CO(2) concentration (+/- 2 micro mol mol(-1)) and photosynthetic photon flux density (+/- 5 micro mol m(-2) s(-1)), and allows the continuous measurement of net photosynthesis and transpiration rates. Vapor pressure is controlled by circulating chamber air through a CaSO(4) desiccant column supported on a digital balance. Transpiration rate is calculated from the change in desiccant mass with time. Photosynthesis rate is measured by integrating the output of a mass flow controller used to inject CO(2) into the chamber to compensate for that assimilated by the plant. The control system can be driven by set points that can be varied, for example, as a function of time, or held constant. We were able to simulate weather data obtained from climate stations and accurately follow, in real time, the output of sensors measuring outside conditions. Experiments on well-watered one- and two-year-old nursery-raised western red cedar (Thuja plicata Donn.) and white spruce (Picea glauca (Moench) Voss) seedlings showed that if the mean daily temperature was increased from 20 to 22 degrees C with vapor pressure remaining constant at 1 kPa, CO(2) concentrations must almost double to compensate for the decrease in net photosynthesis rate.
Published Version
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