Jung Eek Son

Growth and phenolic compounds of Lactuca sativa L. grown in a closed-type plant production system with UV-A, -B, or -C lamp.

BACKGROUND The production of high-quality crops based on phytochemicals is a strategy for accelerating the practical use of plant factories. Previous studies have demonstrated that ultraviolet (UV) light is effective in improving phytochemical production. This study aimed to determine the effect of various UV wavelengths on growth and phenolic compound accumulation in lettuce (Lactuca sativa L.) grown in a closed-type plant production system. RESULTS Seven days, 1 day and 0.25 day were determined as the upper limit of the irradiation periods for UV-A, -B, and -C, respectively, in the lettuce based on physiological disorders and the fluorescence parameter F(v)/F(m). Continuous UV-A treatment significantly induced the accumulation of phenolic compounds and antioxidants until 4 days of treatment without growth inhibition, consistent with an increase in phenylalanine ammonia lyase (PAL) gene expression and PAL activity. Repeated or gradual UV-B exposure yielded approximately 1.4-3.6 times more total phenolics and antioxidants, respectively, than the controls did 2 days after the treatments, although both treatments inhibited lettuce growth. Repeated UV-C exposure increased phenolics but severely inhibited the growth of lettuce plants. CONCLUSION Our data suggest that UV irradiation can improve the accumulation of phenolic compounds with antioxidant properties in lettuce cultivated in plant factories.

Growth and phenolic content of sowthistle grown in a closed-type plant production system with a UV-A or UV-B lamp

This study was conducted to determine the effects of UV-A and UV-B wavelengths on the growth and content of antioxidant phenolic compounds in sowthistle (Ixeris dentata Nakai), a medicinal plant, grown in a closed plant-production system. In study I, sowthistle plants were continuously exposed to UV-A light. In study II, two UV treatments [repeated UV-B (R): 4 h·d−1 for 6 days, gradual UV-B (G): from 1 to 7 h·d−1 for 6 days] were applied to the sowthistle plants. As a result, contents of total phenolics and antioxidants in UV-A-treated plants were significantly (50 and 30%, respectively) higher than those in the control plants after 3 d of UV treatment without growth inhibition. Moreover, plants continuously exposed to UV-A for 5 d had 50% higher total flavonoid content than the control. The phenylalanine ammonia-lyase (PAL) activity supported the accumulation of phytochemicals in plants exposed to UV-A. The UV-B (R) treatment led to a more rapid decrease in the chlorophyll fluorescence ratio than UV-B (G) treatment. The UV-B (R) or UV-B (G) treatment produced more total phenolics, flavonoids, and antioxidants, although both UV-B treatments significantly inhibited plant growth measured at 2 days after treatment. The UV irradiation also enhanced PAL activity at 2 and 3 days after treatment, suggesting biosynthetic activation of secondary metabolites. Therefore, application of UV-A or UV-B light can be used as a strategy to improve antioxidant phenolic compounds of sowthistle plants grown in closed plant production systems.

Estimation of leaf number and leaf area of hydroponic pak-choi plants (Brassica campestns ssp,chinensis) using growing degree-days

Temperature is a principal environmental factor that directly affects the growth and timing of appearance for crop leaves. To estimate the leaf number and leaf area of ‘Seoul’ pak-choi plants (Brassica campestns ssp.chinensis), we applied the concept of growing degree-days GDD=(Tavg-Tbase) × days, where Tavg, Tbase and days were the daily average air temperature, base temperature, and days after transplanting, respectively. Leaves that were beginning to unfold with a leaf area ≥1 cm2 were counted every 2 to 3 d. Linear relationships were found between leaf number and days after transplanting as well as between leaf number and GDD. The rate of appearance and the number of leaves per GDD were 0.542 leaves d-1 and 0.051 leaves oC-1 d-1, respectively. In contrast, the relationship was non-linear between leaf number and leaf area, with the latter being calculated as [(128.9+11.6×GDD-0.03×GDD2)/1+(0.051×GDD+3.5) /13.7)-3.9] (cm2oC1 d-1). Using model validation, we found that the estimated leaf number and leaf area showed strong agreement with measured values. our results demonstrate the usefulness of modeling to estimate total leaf area and growth from hydroponically grown pak-choi plants.

Uptake of nutrients and water by paprika (Capsicum annuum L.) as affected by renewal period of recycled nutrient solution in closed soilless culture

One of the problems in closed soilless cultures is to find a solution in order to reduce ion imbalance in recycled nutrient solutions when the drained nutrient solution is re-used. To reduce ion imbalance in recycled nutrient solutions, determination of renewal period is required, since uptake of individual ion by plants changes throughout the growing period. The aims of this study are to determine the appropriate renewal period to reduce ion imbalance in the recycled nutrient solution and to investigate the uptake of nutrients and water by the paprika plant and to measure fruit yield and mineral contents in plant as influenced by renewal period of recycled nutrient solution in a closed soilless culture. Paprika plants were grown in rockwool slabs with either 4-, 8-, or 12-week renewal period in the closed as compared to the open hydroponic system (control). The electrical conductivity (EC), pH, and volume of the nutrient solutions were measured every three days. The nutrient solution in the reservoir tank was constantly maintained at EC 2.5 dS·m−1 and pH 5.5–6.5. As results, the uptake of K+ was significantly influenced by the renewal period. Changes of cation and anion ratio in the recycled nutrient solution could be reduced by discharging every 4 weeks. The significantly lowest fruit yield was observed in a closed hydroponic system using a 12-week renewal period. Regarding the ion balance in the recycled nutrient solution, renewing every 4 weeks was found to be the most effective in this study. However, considering the yield along with nutrients and water uptake, a 8-week interval could also be used.

Modeling of Transpiration of Paprika (Capsicum annuum L.) Plants Based on Radiation and Leaf Area Index in Soilless Culture

Modeling of crop transpiration is important to manage the irrigation strategy in soilless culture. In this study, the transpiration of paprika plants (Capsicum annuum L.) grown in rockwool was analyzed considering the relationship between incident radiation (RAD) and leaf area index (LAI). Coefficients of the simplified Penman-Monteith formula were calibrated in order to calculate the transpiration rate of the crop (Tr). Transpiration rate per floor area was measured by weighing plants with load cells. The following model was developed: Tr = a [1 − exp(−k × LAI)] × RAD /λ + b for estimating transpiration of paprika. Determination coefficient for the linear regression between estimations and measurements of daily transpiration was 0.80 with a slope of 0.93. In validation, the model showed high agreement between estimated and measured values of daily transpiration. Radiation showed a great effect on transpiration of paprika plants. The results indicated the simplified Penman- Monteith formula could be used to predict water requirements and improve irrigation control in soilless culture. However the model coefficients require parameter adjustments for specific climate and crop conditions.

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.

Transpiration, Growth, and Water Use Efficiency of Paprika Plants (Capsicum annuum L.) as Affected by Irrigation Frequency

Irrigation frequency is one of the major factors required for adequate irrigation control in soilless culture. In order to investigate the effect of irrigation frequency on transpiration, growth, fruit yield, and water use efficiency, the paprika plants (Capsicum annuum L.) were compared under different irrigation frequencies based on solar radiation in soilless culture systems. The plants were grown on rockwool slabs following the vertical trellis “V” technique. Irrigation started whenever cumulative solar radiation reached the set value. Two set values of 120 J·cm−2 (high irrigation frequency, HIF) and 160 J·cm−2 (low irrigation frequency, LIF) were applied from 25 days after transplanting. Irrigation amount was controlled to keep a drain ratio at 20–30% of the total supply in order to avoid the salt accumulation in the root medium. Total water amount supplied to the plants in LIF was 94% of that in HIF. Transpiration in LIF or HIF was similar to that of estimated transpiration by Penman-Monteith equation, but slightly lower or higher value was observed, respectively. Leaf area and marketable fruit yield were not affected by the irrigation treatment. The both ratios of total transpiration to marketable fruit yield and total irrigation to marketable fruit yield were a little higher in LIF than in HIF. We concluded that water use efficiency in HIF was considered to be similar to or a little higher than that in LIF, but irrigation frequency did not affect the growth and production of paprika plants in open-loop system.

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.

Growth characteristics of sowthistle (Ixeris dentata Nakai) under different levels of light intensity, electrical conductivity of nutrient solution, and planting density in a plant factory

The objective of this study was to investigate the growth characteristics of sowthistle (Ixeris dentata Nakai) under different levels of light intensity (photosynthetic photon flux, PPF), electrical conductivity (EC) of nutrient solution, and planting density for efficient production in a closed-type plant factory system. Growth and yield of the plants were analyzed at EC 1.5 and 2.0 dS·m−1 with PPF 100 and 200 μmol·m−2·s−1. Further, growth and yield were measured under four different planting densities: a 15-cm between-row distance with within-row distances of 10, 15, 20, and 25 cm. Shoot dry weight and leaf photosynthetic rate all increased with increasing EC and light intensity. Shoot fresh and dry weights, chlorophyll content, and leaf photosynthetic rate were maximal at EC 2.0 dS·m−1 with PPF 200 μmol·m−2·s−1. For all planting densities, number of leaves and leaf width were not significantly different. Shoot fresh and dry weights per plant were not significantly different, however, shoot fresh and dry weights per area decreased with increasing plating densities. A linear relationship was observed between the number of leaves and days after transplantation. Based on the results, we suggest a nutrient solution of EC 2.0 dS·m−1, PPF 200 μmol·m−2 · s−1, and planting density of 15×10 cm for maximal growth and yield of sowthistle in a closed-type plant factory.

Leaf photosynthetic rate, growth, and morphology of lettuce under different fractions of red, blue, and green light from light-emitting diodes (LEDs)

Current LED-based artificial lights for crop cultivation consist of red and blue lights because these spectra effectively promote leaf photosynthesis. However, the absence of green light could be disadvantageous for crop production, as green light plays an important role in plant development. The objective of this study was to investigate whether adding green light to different proportions of red and blue light would affect the leaf photosynthetic rate, growth, and morphology of lettuce plants. Plants were transplanted and grown hydroponically for 25 days under different combinations of red, blue (0, 10, 20, and 30%), and green (0 and 10%) light at 150 ± 15 μmol•m-2•s-1 of photosynthetic photon flux density (PPFD). The leaf photosynthetic rate was highest under 80% red and 20% blue light and decreased significantly with the addition of green light and the absence of blue light. As the fraction of blue light increased, leaf size and plant growth decreased significantly. However, while the addition of green light considerably reduced the leaf photosynthetic rate, it did not reduce plant growth. In the absence of blue light, the plants showed symptoms of the shade avoidance response, which possibly enhanced their growth by improving their light interception. Therefore, the addition of 10% (15 μmol•m-2•s-1) green light did not have a positive effect on the growth of lettuce. Further study using higher intensities of green light is required to investigate the effects of green light on plant growth.