Sang Gyu Lee

Effects of Air Temperature and Air Flow Rate Control on the Tipburn Occurrence of Leaf Lettuce in a Closed-type Plant Factory System

This study aimed to establish a practical method to reduce tipburn symptoms on leaf lettuce cultivars in a closed plant factory system, focusing on air temperature conversion at specific plant growth stages and artificial air flow application strategies using pre-screened tipburn-sensitive cultivars. Inter-conversion effect of day temperature among 18, 22, and 25°C, 12 days after transplanting on tipburn occurrences, were compared with stable day temperature condition. Horizontal air flow rates were controlled at 0.28 (Low), 0.55 (Medium), and 1.04 m·s−1 (High). Tipburn occurrences were highly variable depending on the lettuce cultivars tested. Following the initial screening of 28 leaf lettuce cultivars under 3 different light intensity conditions (ranging from 150 to 250 mol·m−2·s−1), two cultivars exhibiting relatively higher percentages of tipburn were selected for the following air temperature and air flow treatments. None of the temperature treatments effectively reduced tipburn symptom, while adjusting the temperature to a lower day temperatures at 12 days after transplanting only had a minor effect on lettuce growth and tipburn occurrence. In contrast, stable horizontal 24-hour air flow rates above 0.28 m·s−1 effectively reduced tipburn symptom, with no significant differences being found among the tested air flow rates, while above 65% of tipburned plants were found in the control plot of 0.08 m·s−1 flow rate. When stable air flow was applied, compared to the control, there was an increase in the absolute calcium content and a decrease in the calcium content difference between the inner and outer lettuce leaves. This calcium balance change may have occurred due to the enhanced transpiration in the inner parts of plants. This study showed that stable horizontal air flow application along cultivation beds is more effective than air temperature control in decreasing tipburn symptoms in a closed plant factory system.

Impacts of climate change on the growth, morphological and physiological responses, and yield of Kimchi cabbage leaves

We evaluated the effects of interacting climate change factors on the morphology, growth, physiological responses, and yield of Kimchi cabbage leaves. Kimchi cabbage was cultivated under two climate change scenarios predicted by the Intergovernmental Panel on Climate Change; Representative Concentration Pathway (RCP) 4.5 and RCP 8.5. For the RCP 4.5 and RCP 8.5 treatments, the air temperatures were maintained 3.4 and 6.0°C above the prevailing control air temperatures and the CO2 concentrations were maintained at 540 and 940 µmol·mol -1, respectively, using newly developed extreme weather growth-chambers. Control plants were grown outside during the autumn. The RCP 4.5 and RCP 8.5 treatments led to tipburn disorders and rough leaves. The light compensation and saturation points of control plants were greater than those of the treatment plants. The maximum carboxylation rate, maximum rate of electron transport, and triose phosphate utilization rate of the RCP 8.5 treatment plants were significantly lower than those of the control. The control plants had the greatest yield among the studied plants, with a 65% reduction in yield observed in the RCP 4.5 treatment plants. The RCP scenarios retarded the growth and assimilation rates, and negatively affected leaf morphology, photosynthesis efficiency, and yield. These results suggest that climate change scenarios may have a profound impact on the cultivation of Kimchi cabbage and that effective mitigation strategies may be needed to ensure that this economically important crop has the necessary resilience under such climate change.

Influence of air temperature on yield and phytochemical content of red chicory and garland chrysanthemum grown in plant factory

This study was conducted to improve the yield and quality of red chicory (Cichorium intybus L.) and garland chrysanthemum (Chrysanthemum coronarium L.) grown in a plant factory where fluorescent lamps were used as an artificial light source. Seeds of a chicory ‘Juck’ and garland chrysanthemum ‘Joongyupssuckgot’ were sown in a peat-lite germination mix. Twenty-day old seedlings with roots being washed off were anchored on a styrofoam board and were grown in hydroponics for 30 days. Plants were exposed to one of the three different air temperature regimes (20, 25, and 30°C during the day combined with 18°C during the night) which were being monitored with a sensor at 30 cm above the plant canopy. In all treatments, light intensity was maintained at 200 ± 20 μmol·m−2·s−1, day length was 12 hours, and relative humidity was 50–80%. Electrical conductivity (EC) and pH of the nutrient solution were 2.0 ± 0.2 dS·m−1 and 6.5–7.0, respectively, in all treatments. Increase in fresh weight was observed in chicory, but not in garland chrysanthemum, in both 25 and 30°C as compared to 20°C. Photosynthetic capacity and ascorbic acid content of chicory leaves were higher at 25°C than in other temperatures. In garland chrysanthemum, photosynthetic capacity was the greatest in both 20 and 25°C, while ascorbic acid content was the greatest in 25°C. Also plants grown at 25°C had the greatest contents of total phenol and flavonoid in both chicory and garland chrysanthemum. Hence, the optimum temperature appears to be 25°C for growing both chicory and garland chrysanthemum in the plant factory with fluorescent light as the sole souse of light.

Impact of moderate and extreme climate change scenarios on growth, morphological features, photosynthesis, and fruit production of hot pepper

Abstract Horticultural crop production and changes in physiological aspects during the growing season may be affected by climate change factors (CC), which include increased temperature and the associated doubling or tripling of atmospheric CO2 concentrations. However, the potential effects are complex and many parameters might impact on the observed effects. To evaluate the effects of CC, the growth, yield, fruit characteristics, photosynthetic traits, and morphological characteristics of hot peppers were investigated. The hot peppers were grown under two CC scenarios, with the Representative Concentration Pathway (RCP) of 4.5 (Temp.; +3.4°C, CO2 conc.; 540 μmol/mol, Precipitation +17.3%) and RCP 8.5 (Temp.; +6.0°C and CO2 conc.; 940 μmol/mol, Precipitation +20.3%), respectively, using extreme weather simulators. This was compared with existing weather conditions occurring in Jeonju, South Korea in terms of air temperature, relative humidity, radiation, and precipitation. Overall, the plant height showed the highest under moderate CC conditions (RCP 4.5) among all the treatments tested. The number of leaves in the RCP 8.5 condition showed 7,739/plants, which was 2.2 times higher than that of the control. In addition, fruit shape was shortened and percentage dry matter was also the highest. The yield of hot pepper in the CC RCP 4.5 and 8.5 conditions were decreased by 21.5% and 89.2% when compared with that of the control, respectively. The days to harvest in the condition of CC scenarios were shortened from 5 to 13 compared with that of control, predominantly due to the increased air temperature. The results indicated that the severe RCP CC scenarios made reduction in the yields and negative affection on the fruit qualities. Overall, hot pepper was tolerant of mild CC scenarios of temperature × CO2 but was significantly affected by more extreme CC interacting parameter concentrations (or similar).

Influence of Air Temperature and Soil Moisture Conditions on the Growth and Yield of Hot Pepper under a Plastic Tunnel Culture

This study was conducted to determine the effects of high temperature and deficit irrigation on growth and yield of hot pepper. Hot pepper was subjected to four irrigation treatments: fully irrigation (FI), 10, 20, and 30 days deficit irrigation (DI) combination with high temperature treatment. Control plants were grown natural environment and conventional culture methods. The plant height treated with high temperature was significantly higher than that of control plant. At FI combination with high temperature treatment, growth parameters such as stem diameter, leaf area, fresh and dry weight were the greatest. The yield was the greatest (2,036 kg/10a) under control, DI combination with high temperature treatment decreased by approximately 42% compare with FI combination with high temperature treatment. The number of abnormal fruits was approximately 38/plant under control, which was the smallest and that of 30 days DI combination with high temperature was higher 3.3 times compare with control. Flower abscission and calcium deficiency induced by DI treatments, especially those physiological disorder promoted by increasing DI treatments period. Results indicated that yield of hot pepper reduced by DI treatments, these results suggest that the growers should irrigate to proper soil moisture for preventing reduction of total fruit yield.

Characteristics of root growth and sugar translocation in yellowing symptom of melon

This study was carried out to investigate the causal factors of yellowing symptom of melon that has recently increased in major production areas in Korea and to characterize root growth, sugar content and morphology of melon with the yellowing symptom. The growth characteristics were not significantly different between normal plants (control) and plants that two-thirds of roots were removed (root pruning). The root length of plants of the control and root pruning were 1,197 and 1,120 cm, respectively, but plants showing yellowing symptom were 696 cm. The root volume was greatest in control (10.31 cm3) and the lowest in plants showing yellow symptom (6.99 cm3). The contents of glucose, fructose, and sucrose in leaves were greatest in plant showing yellowing symptom than the normal plants and sugars in stems, fruits, and roots were also slightly low in plants with the yellowing symptom. In a scanning electron microscope (SEM) observation of mesophyll, sieve tubes were closed in the plants with yellowing symptom. This result suggested that the occurrence of yellowing symptom and lowered root mass are closely related and the high sugar contents in leaves with yellowing symptom might be caused by poor translocation of free sugars produced in leaves to other organs by closed sieve tubes.