Browsing by Author "Meng, Qingwu"
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Item Blue Photons from Broad-Spectrum LEDs Control Growth, Morphology, and Coloration of Indoor Hydroponic Red-Leaf Lettuce(Plants, 2023-03-02) Meng, Qingwu; Runkle, Erik S.For indoor crop production, blue + red light-emitting diodes (LEDs) have high photosynthetic efficacy but create pink or purple hues unsuitable for workers to inspect crops. Adding green light to blue + red light forms a broad spectrum (white light), which is created by: phosphor-converted blue LEDs that cast photons with longer wavelengths, or a combination of blue, green, and red LEDs. A broad spectrum typically has a lower energy efficiency than dichromatic blue + red light but increases color rendering and creates a visually pleasing work environment. Lettuce growth depends on the interactions of blue and green light, but it is not clear how phosphor-converted broad spectra, with or without supplemental blue and red light, influence crop growth and quality. We grew red-leaf lettuce ‘Rouxai’ in an indoor deep-flow hydroponic system at 22 °C air temperature and ambient CO2. Upon germination, plants received six LED treatments delivering different blue fractions (from 7% to 35%) but the same total photon flux density (400 to 799 nm) of 180 μmol·m−2·s−1 under a 20 h photoperiod. The six LED treatments were: (1) warm white (WW180); (2) mint white (MW180); (3) MW100 + blue10 + red70; (4) blue20 + green60 + red100; (5) MW100 + blue50 + red30; and (6) blue60 + green60 + red60. Subscripts denote photon flux densities in μmol·m−2·s−1. Treatments 3 and 4 had similar blue, green, and red photon flux densities, as did treatments 5 and 6. At the harvest of mature plants, lettuce biomass, morphology, and color were similar under WW180 and MW180, which had different green and red fractions but similar blue fractions. As the blue fraction in broad spectra increased, shoot fresh mass, shoot dry mass, leaf number, leaf size, and plant diameter generally decreased and red leaf coloration intensified. Compared to blue + green + red LEDs, white LEDs supplemented with blue + red LEDs had similar effects on lettuce when they delivered similar blue, green, and red photon flux densities. We conclude that the blue photon flux density in broad spectra predominantly controls lettuce biomass, morphology, and coloration.Item Continuous light can promote growth of baby greens over diurnal light under a high daily light integral(Environmental and Experimental Botany, 2024-02-23) Meng, Qingwu; Severin, Stefanie N.Sole-source lighting with light-emitting diodes (LEDs) incurs high operating expenditure in indoor vertical farms, where crops are typically grown under diurnal light at a fixed photosynthetic photon flux density (PPFD). Under the same daily light integral (DLI), continuous light lowers the needed PPFD, thereby decreasing the initial capital investment on high-output LEDs and operating expenditure by lighting in the nighttime, when electricity rates are lower than in the daytime in some areas. However, little is known about how temporal light patterns influence baby green growth at varying DLIs. We performed an indoor experiment on baby greens of lettuce (Lactuca sativa) ‘Rouxai’, kale (Brassica oleracea var. acephala) ‘Red Russian’, and arugula (Eruca sativa) ‘Astro’ at ≈ 21 ºC air temperature and ≈ 70% relative humidity. At each of two DLIs (8.64 and 17.28 mol∙m–2∙d–1), each crop was grown under warm-white LEDs with three light patterns [100%, 75%, and 50% daytime DLI (first half of a 24-hour cycle), followed by 0%, 25%, and 50% nighttime DLI, respectively]. The 0% nighttime DLI treatments delivered diurnal light with a 12-h photoperiod, whereas the 25% and 50% nighttime DLI treatments delivered alternating light and continuous light, respectively, both with a 24-h photoperiod. Lettuce and kale generally had more pronounced growth responses to the light pattern under the higher DLI, whereas arugula growth was unaffected by the light pattern. Compared to diurnal light, continuous light increased lettuce shoot mass at both DLIs, but increased kale shoot mass only under the higher DLI. Compared to continuous light, alternating light decreased lettuce shoot mass only under the higher DLI, but did not influence most parameters of kale or arugula. Doubling the DLI increased the shoot dry mass of all crops by 44–150% and the shoot fresh mass of arugula by 38–73% across light patterns. The shoot fresh mass of lettuce and kale increased with an increasing DLI under continuous or diurnal light. We conclude that the light pattern and DLI had interactive and crop-specific effects on the growth of baby greens. Under the same DLI, continuous light can increase growth of lettuce and kale, but not arugula, baby greens over diurnal light, especially under a high DLI.Item Day-extension Blue Light Inhibits Flowering of Chrysanthemum When the Short Main Photoperiod Includes Far-red Light(Journal of the American Society for Horticultural Science, 2023-03-16) Kohler, Annika E.; Birtell, Eva M.; Runkle, Erik S.; Meng, QingwuChrysanthemum (Chrysanthemum ×morifolium) is a common ornamental crop with a qualitative short-day flowering response. Extending a short day with moderate blue [B (400–500 nm)] light inhibits flowering in greenhouse conditions with sunlight but does not indoors (without sunlight) under B + red [R (600–700 nm)] light or white light. We postulated that the contrasting responses to B light as a day extension depended on far-red [FR (700–800 nm)] light during the day, which is plentiful under sunlight but lacking indoors under B+R or white light-emitting diodes. To study this response in three chrysanthemum cultivars, we delivered indoor lighting treatments at two locations with an 11-hour main photoperiod of B, green [G (500–600 nm)], R, and FR light, where subscript values indicate the photon flux density (in µmol·m−2·s−1) of each waveband: B60R120, B60G60R60, and B60R60FR60. After each short main photoperiod, plants received 0 or 4 hours of day-extension lighting of 60 µmol·m−2·s−1 of B light (B60). Under all treatments except B60R60FR60 with day-extension B60, it took ‘Chelsey Pink’, ‘Gigi Gold’, and ‘Gigi Yellow’ 13 to 17 days to reach the first visible inflorescence and 42 to 51 days to the first open flower. In contrast, plants grown under B60R60FR60 with day-extension B60 took 41 to 67 days to reach the first visible inflorescence with few plants developing open flowers. Plants were tallest at the first open flower and after 9 weeks of treatments when grown under B60R60FR60 with day-extension B60. These results indicate that the inclusion of FR light, but not G light, in the main photoperiod is necessary for day-extension B light to inhibit flowering in chrysanthemum. On the basis of these results and those of other studies, we postulate that the spectral dependence of flowering in chrysanthemum depends on whether and how the phytochrome photoequilibrium changes during the day. In particular, a sufficiently high daytime phytochrome photoequilibrium (e.g., under B+R and B+G+R light) could establish a predominant mode of floral signaling that prevents perception of subsequent B light as a long day.Item Efficacy and Optimal Timing of Warm-white or Red + Far-red LED Lamps in Regulation of Flowering in Long-day Ornamentals(HortScience, 2024-04-30) Meng, Qingwu; Kelly, IanWhen natural days are short, photoperiodic lighting at the end or beginning of the day (day extension) or in the middle of the night (night break) promotes flowering of long-day plants. The objective of this study was to compare broad-spectrum warm-white light-emitting diodes (LEDs) and red (R) + far-red (FR) LEDs at flowering regulation when delivered at different timings in the night period. We performed a greenhouse experiment on four long-day ornamentals [coreopsis (Coreopsis grandiflora) ‘Early Sunrise’, snapdragon (Antirrhinum majus) ‘Liberty Classic Yellow’, petunia (Petunia ×hybrida) ‘Easy Wave Burgundy Star’, and petunia ‘Wave Purple Improved’]. We grew plants under a truncated 8-hour photoperiod with or without low-intensity (∼2 μmol·m−2·s−1) nighttime lighting from warm-white or R+FR LEDs. For each light quality, we delivered four timings: 1) 8 hours after dusk; 2) 8 hours before dawn; 3) 4 hours after dusk + 4 hours before dawn; and 4) 4-hour night break. The effectiveness of floral promotion was determined by time from the treatment onset to the first open flower. Coreopsis flowered similarly under all lighting treatments, irrespective of light quality and timing, but did not flower under the short-day treatment by the end of the experiment. At flowering, coreopsis was 18% to 19% shorter under white than R+FR LEDs. In contrast, snapdragon flowered 9 to 20 days later under white than R+FR LEDs, when delivered for 8 hours at night, but flowered similarly under these two lamp types as a 4-hour night break. Compared with the short-day treatment, white and R+FR LEDs promoted flowering of both petunia cultivars, although flowering generally occurred later under white than R+FR LEDs. Snapdragon and petunia ‘Easy Wave Burgundy Star’ developed 30% to 122% more lateral branches under white than R+FR LEDs, when delivered for 8 hours at night. The effectiveness of warm-white LEDs was generally unaffected by timing, although it was most promotive of flowering in snapdragon when delivered for 8 hours before dawn. For R+FR LEDs, 8-hour day-extension lighting was generally more effective than 4-hour night-break lighting, irrespective of timing. We conclude when delivered for 8 hours at night, warm-white LEDs are generally less effective than R+FR LEDs at promoting flowering of long-day ornamentals but similarly effective as 4-hour night-break lighting. The effectiveness of day-extension lighting is generally independent of timing, although for R+FR LEDs, 8 hours after-dusk and/or before-dawn lighting was generally more effective than 4-hour night-break lighting.Item Far-red Light and Nitrogen Concentration Elicit Crop-specific Responses in Baby Greens under Superelevated CO2 and Continuous Light(Journal of the American Society for Horticultural Science, 2024-03-05) Kennebeck, Emily J.; Meng, QingwuBaby greens are becoming increasingly popular in the consumer market because of their desired flavor and leaf size. The short life cycles and fast response times to environmental stimuli make baby greens ideal for testing environmental conditions for space crop production. Additionally, far-red (FR) light has been used for microgreen and baby green research to enhance stem elongation, leaf expansion, and biomass; however, how it interacts with nutrient solution nitrogen (N) concentrations remains unclear. During this ground-based study, we characterized how FR light and N concentrations influenced the growth and morphology of Chinese cabbage (Brassica rapa var. chinensis cv. Tokyo Bekana) and kale (Brassica oleracea var. sabellica cv. Red Russian) baby greens under similar superelevated CO2 and low relative humidity to levels observed in spaceflight. Plants were subject to combinations of four sole-source light spectra and three N concentrations (75, 125, and 175 mg⋅L−1). At the same total photon flux density (PFD) of 200 μmol⋅m−2⋅s−1, we maintained the same blue and green PFDs at 25 μmol⋅m−2⋅s−1 each; the remaining 150 μmol⋅m−2⋅s−1 comprised four red (R) and FR PFD combinations (FR: 0, 25, 50, and 75 μmol⋅m−2⋅s−1). Increasing the FR PFD enhanced the typical shade-avoidance morphology of Chinese cabbage ‘Tokyo Bekana’ and kale ‘Red Russian’, exhibiting leaf length increases of 20% to 26% and 31% to 61%, respectively. Edible biomass did not increase with increasing FR PFDs for either species, regardless of the N concentration. Increasing the N concentration increased the Chinese cabbage ‘Tokyo Bekana’ fresh mass and dry mass by 32% to 59% and 37% to 74%, respectively, except under 25 μmol⋅m−2⋅s−1 of FR light, with which shoot fresh mass increased by 55% with an increasing N concentration from 75 to 125 mg⋅L−1; however, the shoot dry mass was unaffected. Increasing the N concentration did not affect kale ‘Red Russian’ growth under various FR PFDs. We conclude that partially substituting incremental FR light for R light elicits the shade-avoidance response, with little influence on the growth, of Chinese cabbage ‘Tokyo Bekana’ and kale ‘Red Russian’ baby greens under superelevated CO2 and continuous light, and that the former, but not the latter, crop can benefit from increased N fertilization.Item Mustard ‘Amara’ Benefits from Superelevated CO2 While Adapting to Far-red Light Over Time(HortScience, 2024-01-05) Kennebeck, Emily J.; Meng, QingwuCompared with the ambient Earth carbon dioxide concentration (≈415 μmol⋅mol–1), the International Space Station has superelevated carbon dioxide (≈2800 μmol⋅mol–1), which can be a stressor to certain crops. Far-red light can drive plant photosynthesis and increase extension growth and biomass. However, the effects of far-red light under superelevated carbon dioxide are unclear. We grew hydroponic mustard (Brassica carinata) ‘Amara’ seedlings in four growth chambers using a randomized complete block design with two carbon dioxide concentrations (415 and 2800 μmol⋅mol–1), two lighting treatments, and two blocks at temperature and relative humidity set points of 22 °C and 40%, respectively. Each growth chamber had two lighting treatments at the same total photon flux density of 200 μmol⋅m–2⋅s–1. Under the same blue and green light at 50 μmol⋅m–2⋅s–1 each, plants received either red light at 100 μmol⋅m–2⋅s–1 or red + far-red light at 50 μmol⋅m–2⋅s–1 each. At day 15 after planting, far-red light did not influence shoot fresh or dry mass at 415 μmol⋅mol–1 carbon dioxide, but decreased both parameters by 22% to 23% at 2800 μmol⋅mol–1 carbon dioxide. Increasing the carbon dioxide concentration increased shoot fresh and dry mass 27% to 49%, regardless of the lighting treatment. Far-red light decreased leaf area by 16% at 2800 μmol⋅mol–1 carbon dioxide, but had no effect at 415 μmol⋅mol–1 carbon dioxide. Increasing the carbon dioxide concentration increased leaf area by 21% to 33%, regardless of far-red light. Regardless of the carbon dioxide concentration, far-red light promoted stem elongation and decreased chlorophyll concentrations by 39% to 42%. These responses indicate far-red light elicited a crop-specific shade avoidance response in mustard ‘Amara’, increasing extension growth but decreasing leaf area, thereby reducing light interception and biomass. In addition, carbon dioxide enrichment up to 2800 μmol⋅mol–1 increased the biomass of mustard ‘Amara’ but decreased the biomass of other crops, indicating crop-specific tolerance to superelevated carbon dioxide. In conclusion, mustard ‘Amara’ seedlings benefit from superelevated carbon dioxide, but exhibit growth reduction under far-red light under superelevated carbon dioxide.Item Nutrient Solution Application of a Calcium-mobilizing Biostimulant Mitigates Tipburn without Decreasing Biomass of Greenhouse Hydroponic Lettuce(HortScience, 2024-01-01) Biradar, Kishan; Meng, QingwuLettuce tipburn is a physiological disorder characterized by marginal necrosis and curling of inner, younger leaves caused by localized calcium deficiency, especially in low evapotranspiration environments that restrict mass flow and thus calcium mobility. Severe tipburn negatively affects the marketability and quality of greenhouse-grown hydroponic lettuce. We aimed to assess the effectiveness of a chemical-based, calcium-mobilizing biostimulant for mitigating lettuce tipburn when applied in hydroponic nutrient solutions. Butterhead lettuce (Lactuca sativa ‘Rex’) was grown indoors under warm-white light-emitting diodes at a mean photosynthetic photon flux density of 300 μmol⋅m−2⋅s−1 for 11 days. Subsequently, we transplanted seedlings into deep-water-culture hydroponic trays in a greenhouse at an air temperature of 24.6 ± 1.2 °C, relative humidity of 76.2% ± 7.4%, and 20-hour photoperiod with supplemental lighting from high-pressure sodium lamps. The plants were grown in nutrient solutions with and without the biostimulant codenamed CC US-2105 at two concentrations (22 and 220 μL⋅L−1). Data were collected from plant samples at three harvests at 14, 21, and 28 days after transplant (DAT). At 14 DAT, there was no tipburn under any treatments. Compared with the control, the biostimulant at 22 μL⋅L−1 increased shoot dry mass by 31%. At 21 DAT, the biostimulant at 220 μL⋅L−1 eliminated tipburn, and the biostimulant increased shoot fresh weight by 28%, irrespective of the concentration. At 28 DAT, despite sufficient calcium in the whole plant and the remaining nutrient solution, severe tipburn still occurred in plants that did not receive the biostimulant (control). Compared with the control, the biostimulant at the higher concentration of 220 μL⋅L−1 decreased the tipburn rating by 88% and the number of leaves with tipburn by 85%, increased the plant diameter by 11%, increased the total leaf number by six, and accumulated higher levels of manganese and zinc. In contrast, these parameters remained unaffected at the lower biostimulant concentration of 22 μL⋅L−1. At 28 DAT, shoot biomass was unaffected by the biostimulant. In conclusion, the calcium-mobilizing biostimulant is an effective strategy to mitigate hydroponic lettuce tipburn without decreasing biomass accumulation in greenhouse conditions.