Studies on Techniques for Measuring Photosynthesis and Transpiration of Plant Stand in the Closed Plant Experiment Facility in the CEEF (Closed Ecology Experiment Facilities)

Abstract

Tests on performance and operation of the Closed Plant Experiment Facility (CPEF) of the Closed Ecology Experiment Facilities (CEEF) are currently under way. Tests on photosynthesis/transpiration measuring systems and procedures have been conducted since 1996. The CPEF has four independently controlled closed cultivation rooms, in which rates of photosynthesis and transpiration as the whole plant stand can be monitored simultaneously. Comparison of net photosynthetic (CO₂ exchange) rate of a 30m² rice stand calculated by multiplying the rate of CO₂ draw-down by room air volume, with the rate calculated from the mass of supplied CO₂ needed to hold steady state showed no difference exceeding 10% of each other between them. Changes in CO₂ exchange rate of rice stand calculated using the former method with changes in PPFD, temperature and CO₂ concentration were compared. Transpiration rate of rice stand with changes in PPFD, temperature and CO₂ concentration were also monitored by tracking both difference in water vapor concentrations calculated from inlet and outlet dew points and air flow rates.