Kyoung Sub Park

Sweet Pepper (Capsicum annuum L.) Canopy Photosynthesis Modeling Using 3D Plant Architecture and Light Ray-Tracing.

Canopy photosynthesis has typically been estimated using mathematical models that have the following assumptions: the light interception inside the canopy exponentially declines with the canopy depth, and the photosynthetic capacity is affected by light interception as a result of acclimation. However, in actual situations, light interception in the canopy is quite heterogenous depending on environmental factors such as the location, microclimate, leaf area index, and canopy architecture. It is important to apply these factors in an analysis. The objective of the current study is to estimate the canopy photosynthesis of paprika (Capsicum annuum L.) with an analysis of by simulating the intercepted irradiation of the canopy using a 3D ray-tracing and photosynthetic capacity in each layer. By inputting the structural data of an actual plant, the 3D architecture of paprika was reconstructed using graphic software (Houdini FX, FX, Canada). The light curves and A/Ci curve of each layer were measured to parameterize the Farquhar, von Caemmerer, and Berry (FvCB) model. The difference in photosynthetic capacity within the canopy was observed. With the intercepted irradiation data and photosynthetic parameters of each layer, the values of an entire plants photosynthesis rate were estimated by integrating the calculated photosynthesis rate at each layer. The estimated photosynthesis rate of an entire plant showed good agreement with the measured plant using a closed chamber for validation. From the results, this method was considered as a reliable tool to predict canopy photosynthesis using light interception, and can be extended to analyze the canopy photosynthesis in actual greenhouse conditions.

Development of a coupled photosynthetic model of sweet basil hydroponically grown in plant factories

For the production of plants in controlled environments such as greenhouses and plant factories, crop modeling and simulations are effective tools for configuring the optimal growth environment. The objective of this study was to develop a coupled photosynthetic model of sweet basil (Ocimum basilicum L.) reflecting plant factory conditions. Light response curves were generated using photosynthetic models such as negative exponential, rectangular hyperbola, and non-rectangular hyperbola functions. The light saturation and compensation points determined by regression analysis of light curves using modified non-rectangular hyperbola function in sweet basil leaves were 545.3 and 26.5 µmol·m-2·s-1, respectively. The non-rectangular hyperbola was the most accurate with complicated parameters, whereas the negative exponential was more accurate than the rectangular hyperbola and could more easily acquire the parameters of the light response curves of sweet basil compared to the non-rectangular hyperbola. The CO2 saturation and compensation points determined by regression analysis of the A-Ci curve were 728.8 and 85.1 µmol·mol-1, respectively. A coupled biochemical model of photosynthesis was adopted to simultaneously predict the photosynthesis, stomatal conductance, transpiration, and temperature of sweet basil leaves. The photosynthetic parameters, maximum carboxylation rate, potential rate of electron transport, and rate of triose phosphate utilization determined by Sharkey’s regression method were 102.6, 117.7, and 7.4 µmol·m-2·s-1, respectively. Although the A-Ci regression curve of the negative exponential had higher accuracy than the biochemical model, the coupled biochemical model enable to physiologically explain the photosynthesis of sweet basil leaves.

Spectral dependence of electrical energy-based photosynthetic efficiency at single leaf and canopy levels in green- and red-leaf lettuces

The spectrum of light affects both the electrical energy consumption by plants and photosynthetic efficiency. In a plant factory, where light-emitting diodes (LEDs) serve as an alternative to solar light, the optimal spectrum of light should be carefully chosen to maximize the rate of photosynthesis and the electrical energy efficiency of the crop. The objectives of this study were to investigate the photosynthetic rate of different colored lettuces (reddish and green leaves), to quantify the spectral dependence of photosynthetic efficiency, and to optimize the LED spectrum for maximum canopy photosynthesis and electrical energy consumption in lettuce grown in a plant factory. Two lettuce cultivars (Lactuca sativa L.), ‘JeokChukMyeon’ and ‘CheongChukMyeon’, were assessed for light absorption and photosynthetic efficiency at the single leaf and canopy levels, and the relative consumption of electrical energy from the LED lights was measured at 18 narrow wavelength bands of 10 nm from 400 to 700 nm. Anthocyanin and chlorophyll content (SPAD value) were measured and correlated with leaf color. Light interception by the canopy was estimated with light transmittance models. The light absorption was similar among the green and reddish lettuce cultivars at most wavelengths, but slightly higher in the reddish leaves around 550 nm (green region). In the reddish leaves, photosynthetic rates per incident photon of a single leaf had two peaks at 650-660 and 400-410 nm, while the photosynthetic rate per absorbed photon had three peaks at 650-660, 400-410, and 540-560 nm. In the green region of the light spectrum, both photosynthetic rates per incident photon and those per absorbed photon were lower in the reddish cultivars than in the green cultivars. The spectral dependence of light absorption at the canopy level was much weaker than that at the single leaf level. The quantum yield and absorption of green light at the canopy level were nearly same as those of blue and red lights, indicating that the photosynthetic efficiency of green light at the canopy level was higher than that at the single leaf level. The relative electrical energy consumption was lower in the green region than in the red and blue regions. Therefore, the photosynthetic efficiency based on electrical energy consumption at the canopy level was much lower with green LEDs than with blue or red LEDs. These results describe the plant response to the light spectrum at the canopy level and can be useful for optimizing artificial lighting sources for maximum plant productivity and energy-savings in a plant factory.

A coupled model of photosynthesis and stomatal conductance for the ice plant (Mesembryanthemum crystallinum L.), a facultative CAM plant

The ice plant (Mesembryanthemum crystallinum L.), a medicinal plant with well-known effects on retarding diabetes mellitus, is increasingly being produced in plant factories in Asia. The ice plant is a Crassulacean Acid Metabolism (CAM) plant, but performs C3 photosynthesis during the juvenile period. The objective of this study was to develop a photosynthetic model of ice plants growing under plant factory conditions. C3 photosynthesis was observed in juvenile plants in plant factory growth conditions and a conversion from C3 to CAM photosynthesis was observed under salt-stressed condition at an electrical conductivity (EC) of 6.0 dS·m-1. The light saturation and compensation points, determined by a regression analysis of C3 light curves for the ice plant leaves, were 609.4 and 53.2 μmol·m-2·s-1, respectively. The accuracy of the light response was compared between negative exponential and non-rectangular hyperbolic function models. The non-rectangular hyperbola was more accurate with complicated parameters while the negative exponential function was more practical with simple parameters in the light response curves. Measurement of net CO2 assimilation rate (A) and intercellular CO2 concentration (Ci) allowed construction of the A-Ci curve and regression analysis of this curve revealed the CO2 saturation and compensation points as 632.9 and 117.2 μmol·mol-1, respectively. A coupled photosynthetic model was developed for the simultaneous prediction of photosynthesis, stomatal conductance, transpiration, and temperature of the ice plant leaves. Sharkey’s regression method was used to determine the photosynthetic parameters of maximum carboxylation rate, the potential rate of electron transport, and the rate of triose phosphate utilization, which were 222.3, 234.9, and 13.0 μmol·m-2·s-1, respectively. The parameters of minimum stomatal conductance of water vapor at the light compensation point (b) and the empirical coefficient (m) for the sensitivity of stomatal conductance and relative humidity in the Ball, Woodrow and Berry model could be solved as b = 0.0487 and m = 0.0012 by linear regression analysis using the measured A-Ci values. Although the A-Ci curve of the negative exponential function had higher accuracy than the biochemical model, the coupled biochemical model could physiologically explain the photosynthesis of the ice plant leaves under plant factory conditions.

Erratum to: Modeling the canopy photosynthetic rate of romaine lettuce (Lactuca sativa L.) grown in a plant factory at varying CO2 concentrations and growth stages

Photosynthetic models of crops are essential for predicting the optimum CO2 concentrations that should be maintained for crop productivity in closed systems throughout the growth period. The objective of this study was to develop a canopy photosynthetic model of romaine lettuce (Lactuca sativa L., cv. Asia Heuk romaine) incorporating CO2 concentration and plant growth stage. The canopy photosynthetic rates of the plants were measured 4, 7, 14, 21, and 28 days after transplanting using closed acrylic chambers, in which the temperature was maintained at 24°C and a 200 µmol · m -2 · s-1 light intensity was provided by an 8:1:1 ratio of RBW light-emitting diodes. The canopy photosynthetic rate of the lettuce was calculated by measuring the reduction in CO2 within the chamber over time, from an initial concentration of 2,000 µmol · mol -1. The canopy photosynthetic rate became saturated as the CO2 concentration increased, while it exponentially decreased with the plant growth stage. Among the previously published models available, the Thornley model was suitable for the expression of the canopy photosynthetic rate; however, it had to be adapted to take into account growth stage, resulting in an R2 of 0.985. The canopy photosynthetic rates estimated by the models showed good agreement with those actually measured (R2 = 0.939). Based on these results, the established model may be helpful in determining the optimum level of CO2 required for crop production and in calculating the decreasing CO2 requirements throughout the cultivation period.

Optical Characteristics of Two New Functional Films and Their Effect on Leaf Vegetables Growth and Yield

Three leaf vegetables, namely green lettuce, red lettuce (Lactuca sativa) and red-veined chicory (Cichorium intybus) were grown in minigreenhouses covered with two new functional films and conventional polyethylene film (PE). Seedlings of leaf vegetables were transplanted in a plastic troughs filled with soil-perlite mixture. Two functional films were made from polyolefin (PO) material. Measurement of optical characteristics showed that polyolefin films have better transmittance for the photosynthetic active radiation (PAR, 400-700nm) and higher absorptance for the ultraviolet radiation (UV, 300-400nm) in comparison with the conventional PE film. After three months of utilization higher loss in PAR transmittance was observed for conventional PE film. Leaf vegetables growth was enhanced and yield was increased in greenhouses covered by new functional films.

Effect of monochromatic UV-A LED irradiation on the growth of tomato seedlings

Effect of 376 nm UV-A LED irradiation on the growth and morphology of tomato seedlings was studied. Tomato seedlings were grown under the 658 nm red LEDs or the red LED supplemented with two irradiation levels of the UV-A. The growth and development of tomato seedlings were significantly enhanced under the red light supplemented with the UV-A. Under the UV-A treatments, the tomato seedlings became more compact, the growth of plant organs was balanced, the leaf area was increased, and the total plant fresh and dry weights were also enhanced. Our findings suggested that the 376 nm UV-A from LEDs had a beneficial effect on the growth and development of tomato seedlings as similarly to the blue light.