2017 ASHS Annual Conference

The photosynthetic rate of crops depends on growth environment factors, such as light intensity and temperature, and the photosynthetic efficiency varies with growth stage. The objective of this study was to develop a canopy photosynthetic model of romaine lettuce (Lactuca sativa L., Asia Heuk romaine) using light intensity, temperature and growth stage. The canopy photosynthetic rates of the plants were measured 4, 7, 14, 21, and 28 days after transplanting at closed acrylic chambers (1.0 × 0.8 × 0.5 m) using light-emitting diodes, in which the temperature and light intensity were changed to 19 to 28℃ and 50 to 500 μmol∙m^-2∙s^-1, respectively. At an initial CO₂ concentration of 2,000 μmol∙mol^-1, the canopy photosynthetic rate of lettuce began to calculate with the CO₂ decrement over time. Compared to the simple multiplication model expressed by simply multiplying a single variable model of rectangular hyperbola, the physiological model additionally considered photochemical efficiency, carboxylation conductance, and dark respiration which vary with temperature and growth stage. In validation, the R² value was 0.677 in the simple multiplication model, while it increased to 0.723 in the physiological model. It was found that the physiological model was more suitable than the simple multiplication model in order to express the photosynthetic rates affected by environmental factors.