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Temperature and CO2 concentration affect the yield and quality of mushrooms. In particular, high CO2 concentration due to mushroom respiration induces specific physiological disorders of mushrooms. The objective of this study was to quantify the CO2 emission rate of King Oyster mushrooms (Pleurotus eryngii (DC.) Quel) as a function of temperature and growth stage during the cultivation including thinning processes. CO2 emission rates of the substrate including mycelium before and after thinning were significantly different. In the respiration model, the maintenance and CO2 production coefficients of fruit bodies were expressed as quadratic equations according to temperature. The total CO2 emission rate of a bottle of mushroom estimated by the model were validated with measured ones (R 2 = 0.71). The CO2 emission rates of the mushroom showed exponential and quadratical increases with growth stage and temperature at 16 to 25℃, respectively. The CO2 emission rate models developed for King Oyster mushroom can be utilized to control the CO2 concentration and temperature in mushroom cultivation facilities.

UV-B irradiation has been used to enhance the secondary metabolite content in plants, but its spatial effect on plants has not been considered. The objective of this study was to compare spatial photosynthetic traits and bioactive compound accumulation in kale (Brassica oleracea L. var Acephala) according to the distribution and length of UV-B exposure near harvest. Plants were exposed to UV-B of 0-3, 3-6 and 6-9 W m-2 for 4 h per day at 5 days (Exp. 1) and 4.2 W m-2 at 5, 4, 3, 2 or 1 days (Exp. 2) before harvest. In spatial distribution, the higher the UV-B intensity, the lower the mean Fv /Fm (maximal photochemical efficiency of PSII) and the higher the concentration of total flavonoid compound (TFC). With UV-B stress, Fv /Fm and fluorescence transient parameters decreased except for DI0 /CS (dissipated energy flux per cross section) and PIabs (performance index of PSII). When exposed to UV-B radiation for 2 days before harvest, the total phenolic compounds and TFC per plant were highest, not always proportional to the local Fv /Fm but affected by dry weight. Short-term UV-B stress near harvest would be more efficient for the accumulation of bioactive compounds by minimizing the loss of plant weight.

For developing a canopy photosynthesis model, an efficient method to measure the photosynthetic rate in a growth chamber is required. The objective of this study was to develop a method for establishing canopy photosynthetic rate curves of romaine lettuce (Lactuca sativa L.) with light intensity and CO2 concentration variables using controlled growth chamber. The plants were grown in plant factory modules, and the canopy photosynthesis rates were measured in sealed growth chambers made of acrylic (1.0 x 0.8 x 0.5 m). First, the canopy photosynthetic rates of the plants were measured, and then the time constants were compared between two application methods: 1) changing light intensity (340, 270, 200, and 130 μmol·m-2·s-1) at a fixed CO2 concentration (1,000 μmol·mol-1) and 2) changing CO2 concentration (600, 1,000, 1,400, and 1,800 μmol·mol-1) at a fixed light intensity (200 μmol·m-2·s-1). Second, the canopy photosynthetic rates were measured by changing the light intensity at a CO2 concentration of 1,000 μmol·mol-1 and compared with those measured by changing the CO2 concentration at a light intensity of 200 μmol·m-2·s-1. The time constant when changing the CO2 concentration at the fixed light intensity was 3.2 times longer, and the deviation in photosynthetic rate was larger than when changing the light intensity. The canopy photosynthetic rate was obtained stably with a time lag of one min when changing the light intensity, while a time lag of six min or longer was required when changing the CO2 concentration. Therefore, changing the light intensity at a fixed CO2 concentration is more appropriate for short-term measurement of canopy photosynthesis using a growth chamber.

Since kale (Brassica oleracea L. var. acephala) is one of the healthiest vegetables, its cultivation is increasing for either fresh consumption or as a source for functional foods and nutraceuticals. Plant factories are able to control the environment and trigger the accumulation of bioactive compounds with a stable supply by systematic cultivation methods. The objectives of this study were to evaluate the changes in the total phenolic compounds (TPCs), total flavonoid compounds (TFCs), glucosinolates (GLSs), and antioxidant capacity of kale in a plant factory and to determine an optimal harvest time for the maximum annual production. Two cultivars, namely ‘Manchoo collard’ and ‘Jangsoo collard’, were cultivated in a plant factory and thinned to avoid mutual shading. Both cultivars were harvested every week from 14 to 49 days after transplanting (DAT). The fresh weight (FW), dry weight (DW), projected leaf area (PLA), TPCs, TFCs, GLSs, and antioxidant capacity of both plants were measured every week. The annual production was calculated as follows: DW × the concentration × planting density × cultivation cycles per year. The optimal harvest time was determined based on the continuous phase of the production by modeling. The FW and DW of both cultivars exponentially increased, but the PLA hardly increased at 35 DAT. The TPCs, TFCs, and antioxidant capacity fluctuated or slightly changed, but the amount of substance per plant gradually increased. Their annual production increased with increasing harvest time, and only the production of TPCs in ‘Manchoo collard’ showed a local maximum when harvested at 35–42 DAT. Glucoiberin, sinigrin, and glucobrassicin were the major components of GLSs in both cultivars, and their contents fluctuated. The concentration of total GLSs was the highest at 42 DAT. Additionally, the annual production of the total and major GLSs showed the same results as the TPCs, TFCs, and antioxidant capacity. From the results, the optimum harvest time for production was determined to be 42 DAT.

UV-B (280–315 nm) radiation has been used as an effective tool to improve bioactive compound contents in controlled environments, such as plant factories. However, plant structure changes with growth progress induce different positional distributions of UV-B radiation interception, which cause difficulty in accurately evaluating the effects of UV-B on biosynthesis of bioactive compounds. The objective of this study was to quantitatively analyze the positional distributions of UV-B radiation interception and bioactive compound contents of kales (Brassica oleracea L. var. acephala) with growth progress and their relationships. Short-term moderate UV-B levels did not affect the plant growth and photosynthetic parameters. Spatial UV-B radiation interception was analyzed quantitatively by using 3D-scanned plant models and ray-tracing simulations. As growth progressed, the differences in absorbed UV-B energy between leaf positions were more pronounced. The concentrations of total phenolic compound (TPC) and total flavonoid compound (TFC) were higher with more cumulative absorbed UV-B energy. The cumulative UV energy yields for TFC were highest for the upper leaves of the older plants, while those for TPC were highest in the middle leaves of the younger plants. Despite the same UV-B levels, the UV-B radiation interception and UV-B susceptibility in the plants varied with leaf position and growth stage, which induced the different biosynthesis of TFC and TPC. This attempt to quantify the relationship between UV-B radiation interception and bioactive compound contents will contribute to the estimation and production of bioactive compounds in plant factories.

Ultraviolet-B (UV-B) acts as a regulatory stimulus, inducing the dose-dependent biosynthesis of phenolic compounds such as flavonoids at the leaf level. However, the heterogeneity of biosynthesis activation generated within a whole plant is not fully understood until now and cannot be interpreted without quantification of UV-B radiation interception. In this study, we analyzed the spatial UV-B radiation interception of kales (Brassica oleracea L. var. Acephala) grown under supplemental UV-B LED using ray-tracing simulation with 3-dimension-scanned models and leaf optical properties. The UV-B-induced phenolic compounds and flavonoids accumulated more, with higher UV-B interception and younger leaves. To distinguish the effects of UV-B energy and leaf developmental age, the contents were regressed separately and simultaneously. The effect of intercepted UV-B on flavonoid content was 4.9-fold that of leaf age, but the effects on phenolic compound biosynthesis were similar. This study confirmed the feasibility and relevance of UV-B radiation interception analysis and paves the way to explore the physical and physiological base determining the intraindividual distribution of phenolic compound in controlled environments.

Among abiotic stresses, both drought and UV-B radiation effectively trigger the accumulation of secondary metabolites, and can be widely applied in plant factories. The objectives of this study were to investigate antioxidant accumulation under drought stress alone, or in combination with UV-B radiation near harvest, and to determine an optimal treatment time for maximum antioxidant production. Kale (Brassica oleracea L. var. acephala) plants were grown in a plant factory and harvested at 42 days after transplanting. The single and combination treatments lasted for 7 to 1 days and 4 to 2 days before harvest, respectively. The results of both Fv/Fm (maximal photochemical efficiency in photosystem II) and leaf water potential could ensure the function of photosynthesis and maintain normal leaf moisture in single drought treatments of less than 4 days. The total phenolic and flavonoid contents and antioxidant activities were significantly increased in both single and combination treatments for 3 to 4 days, compared to other treatments. The supplementary UV-B treatments showed no extra formation of antioxidants compared to the single drought treatments. As a result, drought for 3 days before harvest could achieve the highest potential value of kale as a source of natural antioxidants.

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.

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.

When designing a plant production system, it is crucial to perform advanced estimation of growth and productivity in relation to cultivation factors. In this study, we developed Planting-density Growth Harvest (PGH) charts to facilitate the estimation of crop growth and harvest factors such as growth rate, relative growth rate, shoot fresh weight, harvesting time, marketable rate, and marketable yield for quinoa (Chenopodium quinoa Willd.) and sowthistle (Ixeris dentata Nakai). The plants were grown in a nutrient film technique (NFT) system in a closed-type plant factory under fluorescent lamps with three-band radiation under a light intensity of 140 μmol·m-2 ·s-1, with a 12-h/12-h (day/night) photoperiod. We analyzed the growth and yield of quinoa and sowthistle grown in nutrient solution at EC 2.0 dS·m-1 under four planting densities: 15 cm between rows with a within-row distance of 15 × 10 cm (67 plants/m 2), 15 × 15 cm (44 plants/m2), 15 × 20 cm (33 plants/m2), and 15 × 25 cm (27 plants/m2). Crop growth rate, relative growth rate, and lost time were closely correlated with planting density. We constructed PGH charts based on the growth data and existing models. Using these charts, growth factors could easily be determined, including growth rate, relative growth rate, and lost time, as well as harvest factors such as shoot fresh weight, marketable yield per area, and harvesting time, based on at least two parameters, for instance, planting density and shoot fresh weight.

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 (C i ) 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.

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.

Light is a major environmental factor affecting the regulation of secondary metabolites, such as pigments and flavor. The Solanaceae plant family has diverse patterns of fruit metabolisms that serve as suitable models to understand the molecular basis of its regulation across species. To investigate light-dependent regulation for fruit pigmentation and volatile flavors, major fruit pigments, their biosynthetic gene expression, and volatiles were analyzed in covered fruits of tomato and bell pepper. Immature covered fruits were found to be ivory in color and no chlorophyll was detected in both plants. The total carotenoid content was found to be reduced in ripe tomato and bell pepper under cover. Naringenin chalcone decreased more than 7-fold in ripe tomato and total flavonoids decreased about 10-fold in immature and ripe pepper fruit under light deficiency. Light positively impacts fruit pigmentation in tomato and bell pepper by regulating gene expression in carotenoid and flavonoid biosynthesis, especially phytoene synthase and chalcone synthase, respectively. Nineteen volatile flavors were detected, and seven of these exhibited light-dependent regulations for both ripe tomato and pepper. This study will help in improving fruit quality and aid future research works to understand the molecular mechanisms regulating the influence of light-dependency on pigments and flavor volatiles.

The large amount of CO2 emitted from mushrooms during incubation and developmental stages can be utilized in plant production systems as a CO2 source. The objectives of this study were to measure the CO2 emission and absorption rates of mushroom and lettuce, respectively, and to analyze the CO2 concentrations at various ratios of mushroom and lettuce in a closed production system. The CO2 emission rate of king oyster mushrooms (Pleurotus eryngii (D C.) Quel) and CO 2 absorption rate of lettuces (Lactuca sativa L. cv. Asia Heuk Romaine) were measured by using two closed acryl chambers (1.0 m × 0.8 m × 0.5 m) in which indoor temperatures were maintained at 18°C and 22°C, respectively. The lettuce was grown at a light intensity of PPF 340 mol·m -2 ·s -1 and with nutrient solution at EC 1.2 dS·m -1 . The air was periodically circulated between the two chambers using a diaphragm pump. The CO2 emission rate of the mushroom increased until the 15 th day after scratching (DAS) and then decreased. The rate also increased with increased indoor temperature. In particular, the CO2 emission rate per fresh weight of fruit body increased by about 3.1 times after thinning compared to before thinning. In terms of CO2 balance, the CO2 emission rates from a bottle (950 mL) of the mushroom at 9, 12, and 14 DAS were equivalent to those of 3, 4.5, and 5.5 lettuce plants at 7, 10, and 12 DAT (days after transplanting), respectively. This work shows that balance in CO2 concentration could be achieved using an appropriate ratio of the two crops in a closed production system.

Since the moisture content (MC) of growing medium closely related with the crop transpiration, the MC should be included to the environmental factors to be considered for irrigation control in soilless culture. The objective of this study was to analyze the transpiration of paprika plants using daily mean solar radiation (RAD) and vapor pressure deficit (VPD) as well as the growth of the plants at different MCs of rockwool growing media. The starting points of irrigation were controlled by a moisture sensor with minimum set points of 40%, 50%, and 60% of MCs. The canopy transpirations were measured for 80 to 120 days after transplanting and analyzed. The transpirations were well regressed with a combination of both RAD and VPD rather than daily mean RAD only under the controlled MCs. The transpiration at 60% MC was higher than those at 50% and 40% MCs. Leaf area, leaf fresh and dry weights at 60% MC were higher than those at 50% and 40% MCs while the number of leaves had no significant difference among the MCs. There were no significant differences in number of fruits and fruit size among all the MCs, while fruit weight was significantly lower at 40% MC than other treatments. Fresh and dry fruit yields were the highest at 60% MC. Therefore it was concluded that the transpiration was affected by the MC of rockwool growing medium and the minimum set point of 50-60% MC of rockwool growing medium gave better effects on the growth of the paprika plants.

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.

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 Fv/Fm. 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. © 2013 Society of Chemical Industry

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/C i 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 plant's 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.

The measurement of total fresh weight of plants provides an essential indicator of crop growth for monitoring production. To measure fresh weight without damaging the vegetation, imagebased methods have been developed, but they have limitations. In addition, the total plant fresh weight is difficult to measure directly in hydroponic cultivation systems because of the amount of nutrient solution. This study aimed to develop a real-time, precise method to measure the total fresh weight of Romaine lettuce (Lactuca sativa L. cv. Asia Heuk Romaine) with growth stage in a plant factory using a nutrient film technique. The total weight of the channel, amount of residual nutrient solution in the channel, and fresh shoot and root weights of the plants were measured every 7 days after transplanting. The initial weight of the channel during nutrient solution supply (Wi) and its weight change per second just after the nutrient solution supply stopped were also measured. When no more draining occurred, the final weight of the channel (Ws) and the amount of residual nutrient solution in the channel were measured. The time constant (τ) was calculated by considering the transient values of Wi and Ws. The relationship of Wi, Ws, τ, and fresh weight was quantitatively analyzed. After the nutrient solution supply stopped, the change in the channel weight exponentially decreased. The nutrient solution in the channel slowly drained as the root weight in the channel increased. Large differences were observed between the actual fresh weight of the plant and the predicted value because the channel included residual nutrient solution. These differences were difficult to predict with growth stage but a model with the time constant showed the highest accuracy. The real-time fresh weight could be calculated from Wi, Ws, and τ with growth stage.

Appropriate temperature control of seeds leads to uniform germination and efficient management of the production of seedling grafts, which are required for successful cultural practices. In this study, the base, optimum, and maximum temperatures of four hot pepper cultivars were used as scions as well as four hot pepper cultivars used as rootstocks were estimated using a quadratic model. Seeds of the cultivars were germinated in growth chambers at constant temperatures of 20°C, 25°C, 30°C, and 35°C. Cumulative germination was described using a logistic function. The base, optimum, and maximum temperatures were estimated by regressing the inverse of the time to 50% germination (1/GR50) against temperature. Although germination rates varied according to cultivar and temperature, the highest germination rates were observed at temperatures of 25°C and 30°C. Wongang 1 was the most tolerant at low temperature, whereas Koregon PR-380 and Wongang 1 were the most tolerant at high temperature. Further, we suggest appropriate combinations of scion and rootstock cultivars based on our cardinal temperature results for the eight hot pepper cultivars.

Recirculating subirrigation systems are frequently exposed to the risk of plant pathogens transmission, which may deteriorate the growth and quality of the plants. The transmission of Phytophthora nicotianae was examined using Kalanchoe blossfeldiana cv. New Alter in two recirculating subirrigation systems, a nutrient-flow wick culture (NFW) system and an ebb and flow (EBB) system. When the nutrient solution was infested, the pathogen was recovered from roots in both subirrigation systems. However, foliar blights and browning of roots appeared 4 and 7 weeks, respectively, after inoculation in the EBB system. Only a little discoloration appeared in the NFW system. The fresh and dry weights were lower in the EBB system than in the NFW system. When growing medium was inoculated, the pathogen was unable to be isolated from the plants in the NFW system. However, disease symptoms appeared in the EBB system 4 weeks after inoculation, and the pathogen was observed in the basal leaves and roots. Similar to the infested nutrient solution, the plant growth in the EBB system was inhibited. These results suggested that when the nutrient solution was infested, pathogen transmission could occur in plants in both systems, although differences existed with regard to disease symptoms and the time it took for symptoms to appear. However, we observed that when growing medium was inoculated the pathogen was not transmitted to adjacent plants in the NFW system using wick.

The distribution of humidity in a greenhouse was studied using three-dimensional (3-D) computational fluid dynamics (CFD). The calculations were validated using experimental data from a single-span greenhouse without plants. Two types of humidity distribution were considered: humidifying using a fog cooling system, and dehumidifying using refrigerative dehumidifiers in addition to a fog cooling system. The simulation errors of RH were 0.1–18.4% with a fog cooling system and 1.1–13.1% with a fog cooling system and refrigerative dehumidifiers at each observation point. Contour maps were obtained from the 3-D CFD simulations to locate any non-uniformity in humidity distribution. The use of refrigerative dehumidifiers reduced the overall difference of humidity between the middle and bottom zones of a greenhouse, but the local distribution of humidity was uneven, especially close to the dehumidifiers. This study suggests that the developed 3-D CFD model can be a useful tool in designing and evaluating greenhouses with various configurations.

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.

Non-destructive and mathematical approaches of modeling can be very convenient and useful for plant growth estimation. To predict individual leaf area, fresh weight, and dry weight of a cucumber ( Cucumis sativus L.), models were developed using leaf length, leaf width, SPAD value, and different combinations of these variables. Eight regression equations, commonly used for developing growth models, were compared for accuracy and adaptability. The three nonlinear models developed were as follows: individual leaf area (LA) = −210.61 + 13.358 W + 0.5356 LW ( R 2 = 0.980 *** ), fresh weight (FW) = −2.72 + 0.0135 LW + 0.00022 LWS ( R 2 = 0.956 *** ), and dry weight (DW) = 0.25 − 0.00102 LS + 0.000077 LWS ( R 2 = 0.956 *** ), where L is the leaf length, W the leaf width, S the SPAD value, and LWS = L × W × S . For validation of the model, estimated values for individual leaf area, fresh weight, and dry weight showed strong agreement with the measured values, respectively. Leaf dry weight, especially, was estimated with a higher degree of accuracy through the use of a SPAD value, as well as leaf length and width. Therefore, it is concluded that models presented herein may be useful for the estimation of the individual leaf area, fresh weight, and dry weight of a cucumber with a high degree of accuracy.

To determine the adequate irrigation conditions in a nutrient-flow wick culture (NFW) system, the water contents of root media were analyzed with different wick lengths (2 and 3 cm), pot sizes (6-, 10-, and 15-cm diameter), and media compositions (mixtures of 5 peatmoss : 5 perlite and 7 peatmoss : 3 perlite). The growth of potted ‘New Alter’ kalanchoe (Kalanchoe blossfeldiana) in the NFW system was also compared with that of plants grown in other irrigation systems, such as nutrient-stagnant wick culture and ebb-and-flow culture. All factors, such as wick length, pot size, and medium composition, influenced the water content of the medium in the NFW system. Pots that included more peatmoss with a shorter wick could easily take up the nutrient solution. The water content of the media increased by more than 8% and 5% in 2- and 3-cm wick lengths within 15 minutes respectively. The fluctuation of water content became greater with a decrease of pot size in the NFW system. Kalanchoe plants grew well in the NFW system with four irrigations for 15 min per day each. The dry weight and leaf area of the plants were higher in the NFW system (4×) and considerably lower in the NFW system with two irrigations for 15 min per day each. Therefore, more precise irrigation is required in the NFW system than in other systems.

To compliment the current subirrigation systems used for production of potted plants, a nutrient-flow wick culture (NFW) system was developed and compared with other subirrigation systems, such as an ebb and flow culture (EBB) system and a nutrient-stagnant wick culture (NSW) system in relation to their system characteristics and plant growth. Kalanchoe ( Kalanchoe blossfeldiana cv. New Alter) was cultivated in a 6 cm pot for 10 weeks in each subirrigation system. The water-absorption pattern of the medium, water content of the medium, water loss, algal growth, salt-buildup and plant growth under various culture systems were observed. The water contents of medium under the NFW and EBB systems showed fluctuations from 30 to 40% and from 50 to 60% (by volume), respectively, whereas the water content under the NSW system gradually increased to over 40% without fluctuation. Relative to other systems, the water loss in the NFW system was 50–70% due to the reduction in the evaporation from the surfaces of the trough and medium. Algae appeared in the NSW system because the nutrient solution was always stagnant in the trough, while it was not observed under the NFW system. The dissolved oxygen in the nutrient solution was the highest during the irrigation period and the salinity in the medium was the lowest in the NFW system. With regard to system characteristics, the NFW system was simple, water-saving and efficient. In addition, the growth of kalanchoes in the NFW system was similar to those in the NSW and EBB systems at an irrigation frequency of five times a day.

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.

Supporting materials for rooting have a considerable influence on the growth and quality of in vitro plantlets. Various supporting materials (rockwool, perlite, vermiculite, and polyurethane) and nutrient supply cycles (12, 24, 36, and 48 hours) were examined to find the optimum conditions for photoautotrophic micropropagation of potato plantlets in the nutrient-circulated micropropagation (NCM) system. In the NCM system, nutrient solution was circulated between the culture vessel and the nutrient reservoir. A plug cell tray with 70 plantlets was placed inside. The number of air exchanges was 10 hours under forced ventilation. Nodal leafy cuttings of plantlets were cultured at CO2 concentrations (mol·mol-1)/PPF s (mol·m-2·s-1) of 350/80, 700/120, and 1500/250 on day 5-11, 12-18, and 19-28, respectively, for all treatments. All growth factors of in vitro plantlets grown for 28 days using rockwool, perlite and vermiculite were greater than those grown using polyurethane. Dry weight of plantlets grown using rockwool was eight times greater than those grown using polyurethane. The same results were obtained in the growth and survival percentages 14 days after transplanting to ex vitro conditions. Optimum nutrient supply cycles were 12, 24, and 48 hours when perlite, rockwool, and vermiculite were used as supporting materials, respectively. It was considered that the range of optimum nutrient supply cycle was affected by water retention characteristics of supporting materials. This study proved that the supporting material and the nutrient supply cycle were very important environmental factors in photoautotrophic mass propagation.