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  • Author or Editor: Joshua K. Craver x
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Electric lighting is often necessary to achieve a target daily light integral (DLI) for the production of high-quality young annual bedding plants (plugs). Early in production, plugs have a low leaf area index that limits light interception and likely results in wasted radiation supplied by electric sources. Previous research has shown that the addition of far-red radiation (700–780 nm) to the radiation spectrum in sole-source lighting experiments or the use of end-of-day far-red (EOD-FR) radiation treatments can promote an increase in leaf expansion and leaf area for many species. However, leaf expansion in response to far-red radiation may depend on other factors such as the ratio of red (600–699 nm) to far-red radiation (R:FR) and air temperature. Thus, the objectives of this work were to examine the effects of far-red radiation applied throughout the photoperiod and as an end-of-day radiation treatment on the morphology of petunia ‘Dreams Midnight’ seedlings grown under different temperature conditions. Specifically, petunia seed was sown in 128-cell trays and moved to one of two growth chambers set at 16 or 21 °C when cotyledons unfolded. Seedlings received an equal total photon flux density (400–780 nm) of 164 µmol·m−2·s−1 for a 17.25-hour photoperiod, and either a high (∼10.7) or low R:FR (0.5). Low R:FR-treated seedlings were grown at a constant temperature of either 16 or 21 °C and placed under blackout conditions at the end of the photoperiod. High R:FR-grown seedlings received either a 1-hour end-of-day white (EOD-W) or EOD-FR treatment at the end of the photoperiod, and were grown at a constant 16 or 21 °C; one EOD-FR treatment was also shifted from the 21 °C chamber to the 16 °C at the end of the photoperiod for both the EOD-FR treatment and subsequent dark period. Seedlings were harvested at 21 and 28 days after treatment initiation. For petunia seedlings grown at 21 °C, EOD-FR treatments had minimal effect on morphology or dry mass as all measured parameters, including total and average leaf area and stem length, were similar to EOD-W treatments. In contrast, low R:FR-treated seedlings showed responses characteristic of plants grown under shade, including significant stem elongation, an increase in total and average leaf area, and a reduction in leaf mass per unit area. As expected, production at 16 °C slowed the growth of petunia seedlings resulting in much smaller plants compared with the 21 °C grown plants, but shade responses such as elongated leaves and stems under a low R:FR were apparent. The EOD-FR–treated seedlings that received the diurnal temperature shift also showed reduced leaf area and dry mass compared with their constant 21 °C counterparts. Shade responses were observable at both 16 and 21 °C for low R:FR-grown plants, but the quantifiable impact of temperature on far-red responses could not be fully determined in the present study. Further research is warranted investigating crop responses to far-red radiation as well as potential interacting environmental factors as the promotion of morphological responses, such as leaf expansion, early in production may prove a useful strategy.

Open Access

Although crops often respond immediately to enriched CO2 concentrations (e.g., increased photosynthesis), this initial response is often not sustained throughout production, thus reducing the benefit of this input. For horticulture species, the timing and extent of these acclimation responses are still widely uncertain. Therefore, the objective of this research was to determine species-specific acclimation responses to elevated CO2 concentrations for pansy (Viola ×wittrockiana ‘Matrix Blue Blotch Improved’) and petunia (Petunia ×hybrida ‘Dreams Midnight’). Seedlings were transplanted to 11.5-cm pots and placed in growth chambers with air temperature, relative humidity, and radiation intensity setpoints of 21 °C, 55%, and 250 μmol⋅m 2⋅s 1, respectively. Carbon dioxide treatments were established using the two growth chambers with setpoints of either 400 (ambient) or 1000 μmol⋅mol−1 (elevated) maintained during a 16-hour photoperiod. In addition to data collected through destructive harvest, the rate of photosynthesis (A) in response to increasing internal leaf CO2 concentration (A-Ci) and at the operating CO2 concentration (A-Ca) were measured weekly with a portable leaf photosynthesis system at saturating [A-Ci (1000 μmol⋅m 2⋅s 1)] or production [A-Ca (250 μmol⋅m 2⋅s 1)] radiation intensities. For both pansy and petunia, elevated CO2 produced greater total shoot dry mass than ambient CO2 after 4 weeks. However, the decreased maximum rate of photosynthetic electron transport, maximum rate of Rubisco carboxylase, and triose phosphate utilization rate of both species were also observed under elevated CO2. Similarly, A measured at 400 and 1000 μmol⋅mol−1 was reduced for both pansy and petunia grown under the elevated compared with ambient CO2 concentration based on A-Ca responses after 7 days, indicating quick physiological acclimation to this input. These results provide information regarding the timing and extent of physiological acclimation in response to elevated CO2 concentrations. However, because of physiological acclimation potentially occurring within 7 days of treatment initiation, additional research is necessary to develop species-specific recommendations for controlled environment production.

Open Access

Greenhouse production of high-quality young annual bedding plants (plugs) at northern latitudes often requires supplemental lighting to compensate for a low natural daily light integral (DLI), but radiation interception by plugs is limited by a low leaf area index. Some species show an increase in leaf area in response to growth under a low ratio of red to far-red radiation (R:FR), and an early increase in leaf area may allow for more effective radiation capture by seedlings and a reduction in wasted radiation. Thus, the objective of this study was to examine the effects of end-of-day far-red (EOD-FR) radiation treatments varying in intensity, R:FR (600–700 nm/700–780 nm), and duration on early leaf expansion and plug quality for petunia (Petunia ×hybrida) ‘Wave Purple’ and ‘Dreams Midnight’. Seedlings were grown in 128-cell trays in a common greenhouse environment under a simulated winter DLI (∼5.3 mol·m−2·s−1) and received one of four EOD-FR treatments, control conditions (no EOD-FR or supplemental lighting), or supplemental lighting (target photosynthetic photon flux density of 70 μmol·m−2·s−1). The EOD-FR treatments were provided for 3 weeks on cotyledon emergence and included the following: 10 μmol·m−2·s−1 of far-red radiation for 30 minutes with a R:FR of ∼0.8 (EODFL), 10 or 20 μmol·m−2·s−1 of far-red radiation for 30 minutes with a R:FR of ∼0.15 (EOD10:30 and EOD20:30, respectively), or 20 μmol·m−2·s−1 of far-red radiation for 240 minutes with a R:FR of ∼0.15 (EOD20:240). Destructive data were collected 14 and 21 days after cotyledon emergence. Seedlings that received EOD-FR treatments did not show any increase in leaf area compared with control or supplemental lighting treatments. Stem length generally increased under EOD-FR treatments compared with supplemental lighting and control treatments; greater elongation was observed when the R:FR decreased from 0.8 to 0.15, and when treatment duration increased from 30 minutes to 240 minutes. However, at a R:FR of 0.15 and a treatment duration of 30 minutes, an increase in far-red radiation intensity from 10 to 20 μmol·m−2·s−1 did not promote further stem elongation resulting in similar stem lengths for both cultivars under EOD10:30 and EOD20:30. Results of this study indicate that under low DLIs, EOD-FR radiation applied in the first 3 weeks of seedling production does not promote early leaf area expansion, and generally decreases seedling quality for petunia. As responses to far-red radiation may vary based on study taxa, incident radiation, and DLI, future research examining EOD-FR–induced morphological changes is warranted.

Open Access

Student learning from producing crops in recirculating culture for a 6-week module in the Fall 2013 course HORT 570 Greenhouse Operations Management at Kansas State University was assessed. The module design followed Kolb’s experiential learning model, with teams of students responsible for production of lettuce (Lactuca sativa ‘Green Oak Leaf’) or basil (Ocimum basilicum ‘Italian Large Leaf’) and chives (Allium schoenoprasum ‘Purly’) crops in either a nutrient film technique (NFT) or in-pot recirculating culture system. Goals were to discern if this class experience would 1) improve student confidence and understanding of not only recirculating solution culture systems, but also general crop nutrient management; and 2) improve higher-order learning (HOL) skills of applying, analyzing, and evaluating information. Student learning was evaluated by administering the same survey, which included questions to evaluate student perception, lower-order learning (LOL), and HOL, at four separate times during the semester: 1) before mentioning plant nutrition, hydroponics, or recirculating solution culture; 2) after plant nutrition lectures but before the experiential module; 3) immediately upon completion of the experiential module; and 4) at the end of the semester. An increase in student confidence related to managing crop production in recirculating solution culture and nutrient management was perceived by students upon completion of the module. A significant increase in LOL occurred after the material was presented during the course lectures with an increase also occurring upon completion of the experiential module. In contrast, HOL did not significantly increase after the lecture material was presented, but significantly increased upon completion of the module. Both LOL and HOL was retained at the end of the semester. This evidence supports the role of experiential learning in improving student understanding and fostering HOL.

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Previous research has shown high-quality annual bedding plant seedlings can be produced in controlled environments using light-emitting diode (LED) sole-source lighting (SSL). However, when only red and blue radiation are used, a delay in time to flower may be present when seedlings of some long-day species are subsequently finished in a greenhouse. Thus, our objective was to evaluate the effects of various radiation qualities and intensities under SSL on the morphology, nutrient uptake, and subsequent flowering of annual bedding plant seedlings with a long-day photoperiodic response. Coreopsis (Coreopsis grandiflora ‘Sunfire’), pansy (Viola ×wittrockiana ‘Matrix Yellow’), and petunia (Petunia ×hybrida ‘Purple Wave’) seedlings were grown at radiation intensities of 105, 210, or 315 µmol·m−2·s−1, achieved from LED arrays with radiation ratios (%) of red:blue 87:13 (R87:B13), red:far-red:blue 84:7:9 (R84:FR7:B9), or red:green:blue 74:18:8 (R74:G18:B8). Four-week-old seedlings were subsequently transplanted and grown in a common greenhouse environment. Stem caliper, root dry mass, and shoot dry mass of seedlings generally increased for all three species as the radiation intensity increased from 105 to 315 µmol·m−2·s−1, regardless of radiation quality. Similarly, stem length of all three species was generally shorter as the radiation intensity increased. Macro- and micronutrient concentrations were also generally lower as the radiation intensity increased for all three species. Pansy seedlings grown under R84:FR7:B9 flowered an average of 7 and 5 days earlier than those under R87:B13 and R74:G18:B8, respectively. These results provide information regarding the specific radiation parameters from commercially available LEDs necessary to produce high-quality seedlings under SSL, with radiation intensity appearing to be the dominant factor in determining seedling quality. Furthermore, the addition of far-red radiation can reduce time to flower after transplant and allow for a faster greenhouse turnover of some species with a long-day photoperiodic response.

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High-quality young plant production in northern latitudes requires supplemental lighting (SL) to achieve a recommended daily light integral (DLI) of 10 to 12 mol·m−2·d−1. High-pressure sodium (HPS) lamps have been the industry standard for providing SL in greenhouses. However, high-intensity light-emitting diode (LED) fixtures providing blue, white, red, and/or far-red radiation have recently emerged as a possible alternative to HPS lamps for greenhouse SL. Therefore, the objectives of this study were to 1) quantify the morphology and nutrient concentration of common and specialty bedding plant seedlings grown under no SL, or SL from HPS lamps or LED fixtures; and 2) determine whether SL source during propagation or finishing influences finished plant quality or flowering. The experiment was conducted at a commercial greenhouse in West Lafayette, IN. Seeds of New Guinea impatiens (Impatiens hawkeri ‘Divine Blue Pearl’), French marigold (Tagetes patula ‘Bonanza Deep Orange’), gerbera (Gerbera jamesonii ‘Terracotta’), petunia (Petunia ×hybrida ‘Single Dreams White’), ornamental millet (Pennisetum glaucum ‘Jester’), pepper (Capsicum annuum ‘Hot Long Red Thin Cayenne’), and zinnia (Zinnia elegans ‘Zahara Fire’) were sown in 128-cell trays. On germination, trays were placed in a double-poly greenhouse under a 16-hour photoperiod of ambient solar radiation and photoperiodic lighting from compact fluorescent lamps providing a photosynthetic photon flux density (PPFD) of 2 µmol·m−2·s−1 (ambient conditions) or SL from either HPS lamps or LED fixtures providing a PPFD of 70 µmol·m−2·s−1. After propagation, seedlings were transplanted and finished under SL provided by the same HPS lamps or LED fixtures in a separate greenhouse environment. Overall, seedlings produced under SL were of greater quality [larger stem caliper, increased number of nodes, lower leaf area ratio (LAR), and greater dry mass accumulation] than those produced under no SL. However, seedlings produced under HPS or LED SL were comparable in quality. Although nutrient concentrations were greatest under ambient conditions, select macro- and micronutrient concentrations also were greater under HPS compared with LED SL. SL source during propagation and finishing had little effect on flowering and finished plant quality. Although these results indicate little difference in plant quality based on SL source, they further confirm the benefits gained from using SL for bedding plant production. In addition, with both SL sources producing a similar finished product, growers can prioritize other factors related to SL installations such as energy savings, fixture price, and fixture lifespan.

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Multilayer vertical production systems using sole-source (SS) lighting can be used for the production of microgreens; however, traditional SS lighting methods can consume large amounts of electrical energy. Light-emitting diodes (LEDs) offer many advantages over conventional light sources, including high photoelectric conversion efficiencies, narrowband spectral light quality (LQ), low thermal output, and adjustable light intensities (LIs). The objective of this study was to quantify the effects of SS LEDs of different light qualities and intensities on growth, morphology, and nutrient content of Brassica microgreens. Purple kohlrabi (Brassica oleracea L. var. gongylodes L.), mizuna (Brassica rapa L. var. japonica), and mustard [Brassica juncea (L.) Czern. ‘Garnet Giant’] were grown in hydroponic tray systems placed on multilayer shelves in a walk-in growth chamber. A daily light integral (DLI) of 6, 12, or 18 mol·m−2·d−1 was achieved from commercially available SS LED arrays with light ratios (%) of red:green:blue 74:18:8 (R74:G18:B8), red:blue 87:13 (R87:B13), or red:far-red:blue 84:7:9 (R84:FR7:B9) with a total photon flux (TPF) from 400 to 800 nm of 105, 210, or 315 µmol·m−2·s−1 for 16 hours. Regardless of LQ, as the LI increased from 105 to 315 µmol·m−2·s−1, hypocotyl length (HL) decreased and percent dry weight (DW) increased for kohlrabi, mizuna, and mustard microgreens. With increasing LI, leaf area (LA) of kohlrabi generally decreased and relative chlorophyll content (RCC) increased. In addition, nutrient content increased under low LIs regardless of LQ. The results from this study can help growers to select LIs and LQs from commercially available SS LEDs to achieve preferred growth characteristics of Brassica microgreens.

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Indoor production of bedding plant seedlings using sole-source radiation may present value in increasing uniformity and consistency compared with greenhouse production. However, information on physiological acclimation related to growth and photosynthesis in seedlings exposed to high-intensity blue radiation and elevated CO2 is limited. Seedlings of petunia (Petunia ×hybrida) ‘Dreams Midnight’ were exposed to red (peak = 660 nm):blue (peak = 451 nm) radiation ratios of 50:50 (R50:B50) or 90:10 (R90:B10) and radiation intensities of 150 or 300 µmol·m−2·s–1 under two CO2 regimes of 450 or 900 µmol·mol–1. Shoot dry mass (SDM), leaf area index (LAI), internode length, and whole-plant photosynthesis and light-use efficiency (LUE) responses to increasing radiation intensity were measured. In addition, leaf photosynthetic rate (A) was measured at ambient and supra-optimal CO2 concentrations for plants grown under 450 µmol·mol–1 CO2. Our results indicated growth (based on SDM, LAI, and internode length) was lowered for seedlings produced under R50:B50 compared with R90:B10. However, we observed an increase in whole-plant light-saturated photosynthesis (Ag,max) and whole-plant light saturation point (LSP) under R50:B50 compared with R90:B10. In addition, we observed lower LUE below and higher LUE above a radiation intensity of 500 µmol·m−2·s–1 in seedlings grown under R50:B50 compared with R90:B10. Based on our results, seedling growth was lowered under a high proportion of blue radiation mainly due to lower radiation interception (due to lower LAI and shorter internode length) and LUE of intercepted radiation at the intensities used. Higher Ag,max and LSP in R50:B50 compared with R90:B10 under higher radiation intensities was likely in part due to higher LUE. Further investigation revealed A was higher at both optimal and supra-optimal CO2 concentrations under R50:B50 compared with R90:B10, indicating a lack of stomatal effects of a higher proportion of blue radiation on carboxylation and LUE. We hypothesize that higher LUE in R50:B50 compared with R90:B10 under higher radiation intensities is due to improved photochemical quenching from increased biosynthesis of carotenoids and anthocyanins. The results from our study generated fundamental information on growth and photosynthetic responses to excess blue radiation, data that can be further used in optimizing plant production in controlled environments.

Open Access

In northern latitudes, the photosynthetic daily light integral can be less than 5 mol·m–2·d–1, necessitating the use of supplemental lighting (SL) to reduce bedding plant seedling production time and increase quality. Our objectives were 1) to quantify seedling quality and production time under continuous 16-h or instantaneous threshold SL, continuous low-intensity photoperiodic lighting (PL) for 16 or 24 hours with and without far-red light, or no electric lighting; and 2) to determine whether the described lighting treatments during propagation impact finished plant quality or flowering. Seeds of begonia (Begonia ×semperflorens) ‘Bada Bing Scarlet’, gerbera (Gerbera jamesonii) ‘Jaguar Deep Orange’, impatiens (Impatiens walleriana) ‘Accent Premium Salmon’, petunia (Petunia ×hybrida) ‘Ramblin Peach Glo’, and tuberous begonia (Begonia ×tuberosa) ‘Nonstop Rose Petticoat’ were sown in 128-cell trays and grown under either SL, PL, or no electric lighting (control). SL treatments consisted of high-intensity light-emitting diode (LED) or high-pressure sodium (HPS) lamps providing a photosynthetic photon flux density (PPFD) of either 70 µmol·m–2·s–1 on continuously for 16 h·d–1 or 90 µmol·m–2·s–1 based on an instantaneous threshold. PL treatments consisted of low-intensity red:white (R:W) or red:white:far-red (R:W:FR) lamps for 16 h·d–1 or R:W:FR lamps for 24 h·d–1. Seedlings of gerbera, impatiens, and petunia from each treatment were subsequently transplanted and finished in a common greenhouse environment. The highest quality seedlings were grown under SL compared with PL or control conditions. When comparing SL treatments, seedlings produced under HPS or LED SL using an instantaneous threshold were of equal or greater quality compared with those under continuous SL with a 16-h photoperiod. Although the greater leaf area and internode elongation under PL may give growers the perception that seedling production time is reduced, PL did not increase biomass accumulation and seedling quality. Petunia seedlings propagated under HPS lamps using an instantaneous threshold flowered 4 to 11 days earlier compared with the other SL treatments. In addition, petunia propagated under R:W:FR PL for 16 h·d–1 flowered 5 to 7 days earlier compared with LED SL and the other PL treatments.

Free access

Multilayer vertical production systems using sole-source (SS) light-emitting diodes (LEDs) can be an alternative to more traditional methods of microgreens production. One significant benefit of using LEDs is the ability to select light qualities that have beneficial impacts on plant morphology and the synthesis of health-promoting phytochemicals. Therefore, the objective of this study was to quantify the impacts of SS LEDs of different light qualities and intensities on the phytochemical content of brassica (Brassica sp.) microgreens. Specifically, phytochemical measurements included 1) total anthocyanins, 2) total and individual carotenoids, 3) total and individual chlorophylls, and 4) total phenolics. Kohlrabi (Brassica oleracea var. gongylodes), mustard (Brassica juncea ‘Garnet Giant’), and mizuna (Brassica rapa var. japonica) were grown in hydroponic tray systems placed on multilayer shelves in a walk-in growth chamber. A daily light integral (DLI) of 6, 12, or 18 mol·m−2·d−1 was achieved from SS LED arrays with light ratios (percent) of red:blue 87:13 (R87:B13), red:far-red:blue 84:7:9 (R84:FR7:B9), or red:green:blue 74:18:8 (R74:G18:B8) with a total photon flux from 400 to 800 nm of 105, 210, or 315 µmol·m−2·s–1 for 16 hours, respectively. Phytochemical measurements were collected using spectrophotometry and high-performance liquid chromatography (HPLC). Regardless of light quality, total carotenoids were significantly lower under increasing light intensities for mizuna and mustard microgreens. In addition, light quality affected total integrated chlorophyll with higher values observed under the light ratio of R87:B13 compared with R84:FR7:B9 and R74:G18:B8 for kohlrabi and mustard microgreens, respectively. For kohlrabi, with increasing light intensities, the total concentration of anthocyanins was greater compared with those grown under lower light intensities. In addition, for kohlrabi, the light ratios of R87:B13 or R84:FR7:B9 produced significantly higher anthocyanin concentrations compared with the light ratio of R74:G18:B8 under a light intensity of 315 µmol·m−2·s−1. Light quality also influenced the total phenolic concentration of kohlrabi microgreens, with significantly greater levels for the light ratio of R84:FR7:B9 compared with R74:G18:B8 under a light intensity of 105 µmol·m−2·s−1. However, the impact of light intensity on total phenolic concentration of kohlrabi was not significant. The results from this study provide further insight into the selection of light qualities and intensities using SS LEDs to achieve preferred phytochemical content of brassica microgreens.

Free access