Development of A Three-Variable Canopy Photosynthetic Rate Model of Romaine Lettuce (Lactuca sativa L.) Grown in Plant Factory Modules Using Light Intensity, Temperature, and Growth Stage

Abstract

The photosynthetic rates of crops depend on growth environment factors, such as light intensity and temperature , and their photosynthetic efficiencies vary with growth stage. The objective of this study was to compare two different models expressing canopy photosynthetic rates of romaine lettuce (Lactuca sativa L., cv. Asia Heuk romaine) using three variables of 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 indoor temperature and light intensity were designed to change from 19 to 28? and 50 to 500 µmol·m-2 ·s-1 , respectively. At an initial CO 2 concentration of 2,000 µmol·mol-1 , the canopy photosyn-thetic rate began to be calculated with CO 2 decrement over time. A simple multiplication model expressed by simply multiplying three single-variable models and a modified rectangular hyperbola model were compared. The modified rectangular hyperbola model additionally included photochemical efficiency, carboxylation conductance, and dark respiration which vary with temperature and growth stage. In validation, R 2 value was 0.849 in the simple multiplication model, while it increased to 0.861 in the modified rectangular hyperbola model. It was found that the modified rectangular hyperbola model was more suitable than the simple multiplication model in expressing the canopy photosynthetic rates affected by environmental factors (light Intensity and temperature) and growth factor (growth stage) in plant factory modules. Additional key words : modified rectangular hyperbola model, regression model, simple multiplication model, three-variable model, validation 서 론 작물의 생산량을 증대시키기 위한 연구는 환경 요인의 영향을 정량화하여 생산량을 예측하거나, 원하는 작물 조직으로의 분배과정을 확인하는 등 다방면으로 진행되 고 있다(Heuvelink, 1996; Marcelis 등, 1998). 작물의 체내에서 일어나는 물질의 흐름은 광합성에 의한 동화 과정에서 시작하여 잎이나 줄기, 과실로 이동하는 형태 로 나타난다(Jones와 Tardieu, 1998; Prusinkiewicz, 1998). 이 중 광합성에 의한 동화 과정은 작물의 세포 내에서 일어나는 화학반응이므로, 광도와 온도, 이산화탄 소 농도 등의 환경 요인 의해 영향을 받아 증대되거나 감소한다(Kim과 Lieth, 2003; Caliskan 등, 2009). 환경 요인에 의한 광합성 속도 변화를 정량화 하려는 시도는 작물의 생산량을 예측하는 데 중요한 역할을 할 수 있 다. 최근에는 광합성에 영향을 미치는 환경 요인을 정량 화하는 연구 방법으로 모델링 기법이 각광받고 있다