• Journal of Bio-Environment Control
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• v.27 no.2
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• pp.132-139
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• 2018

The photosynthetic rate is an indicator of the growth state and growth rate of crops and is an important factor in constructing efficient production systems. The objective of this study was to develop a canopy photosynthetic rate model of romaine lettuce using the three variables of $CO_2$ concentration, light intensity, and growth stage. The canopy photosynthetic rates of the lettuce were measured at five different $CO_2$ concentrations ($600-2,200{\mu}mol{\cdot}mol^{-1}$), five light intensities ($60-340{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$), and four growth stages (5-20 days after transplanting) in three closed acrylic chambers ($1.0{\times}0.8{\times}0.5m$). A simple multiplication model expressed by multiplying three single-variable models and the modified rectangular hyperbola model including photochemical efficiency, carboxylation conductance, and dark respiration, which vary with growth stage, were also considered. In validation, the $R^2$ value was 0.923 in the simple multiplication model, while it was 0.941 in the modified rectangular hyperbola model. The modified rectangular hyperbola model appeared to be more appropriate than the simple multiplication model in expressing canopy photosynthetic rates. The model developed in this study will contribute to the determination of an optimal $CO_2$ concentration and light intensity with the growth stage of lettuce in plant factories.

• Journal of Bio-Environment Control
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• v.26 no.4
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• pp.268-275
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• 2017

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 ($1.0{\times}0.8{\times}0.5m$) using light-emitting diodes, in which indoor temperature and light intensity were designed to change from 19 to $28^{\circ}C$ and 50 to $500{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$, respectively. At an initial $CO_2$ concentration of $2,000{\mu}mol{\cdot}mol^{-1}$, the canopy photosynthetic 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.

• Journal of Bio-Environment Control
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• v.28 no.4
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• pp.279-285
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• 2019

To estimate daily canopy photosynthesis, accurate estimation of canopy light interception according to a daily solar position is needed. However, this process needs a lot of cost, time, manpower, and difficulty when measuring manually. Various modeling approaches have been applied so far, but it was difficult to accurately estimate light interception by conventional methods. The objective of this study is to estimate the spatial distributions of light interception and photosynthetic rate of paprika with time by using 3D-scanned plant models and optical simulation. Structural models of greenhouse paprika were constructed with a portable 3D scanner. To investigate the change in canopy light interception by surrounding plants, the 3D paprika models were arranged at $1{\times}1$ and $9{\times}9$ isotropic forms with a distance of 60 cm between plants. The light interception was obtained by optical simulation, and the photosynthetic rate was calculated by a rectangular hyperbola model. The spatial distributions of canopy light interception of the 3D paprika model showed different patterns with solar altitude at 9:00, 12:00, and 15:00. The total canopy light interception decreased with an increase of surrounding plants like an arrangement of $9{\times}9$, and the decreasing rate was lowest at 12:00. The canopy photosynthetic rate showed a similar tendency with the canopy light interception, but its decreasing rate was lower than that of the light interception due to the saturation of photosynthetic rate of upper leaves of the plants. In this study, by using the 3D-scanned plant model and optical simulation, it was possible to analyze the light interception and photosynthesis of plant canopy under various conditions, and it can be an effective way to estimate accurate light interception and photosynthesis of plants.