Low Daily Light Integral Research Articles

Quantifying the Effects of Daily Light Integral or Photoperiod on Maize Morphology across Developmental Stage

Maize breeding and product development practices with transgenic and genome edited events use horticultural practices and controlled environment facilities for year-round production. In winter months, when ambient light is limited in the northern regions of the United States, tassel barrenness (lacking anthers) can be problematic due to reduced pollen production. Our objective was to quantify the tassel morphology of two maize inbred lines in response to low daily light integral (DLI) at different growth stages and identify a DLI threshold for tassel quality. Inbreds A and B were analyzed after being transferred from a high DLI equivalent (23.7 mol·m−2·d−1) to a low DLI equivalent (9.3 mol·m−2·d−1) for 7 days starting at vegetative growth stages (V) V4, V5, V6, V7, V8, V9, V10, V11, or V12 then placed back in the high DLI environment. Data were collected to characterize tassel morphology and barrenness in response to the low DLI stress. Inbred A tassels were more barren under low DLI during V7. Tassels of Inbred B plants responded similarly to the low DLI during V6. These results indicate that low DLI stress impacts tassel morphology of the two inbred lines tested during specific growth stages for 7 days. To identify the number of days required to negatively affect tassels, at the low DLI treatment, plants were subjected to 9.3 mol·m−2·d−1 at V6 on Inbred B for 0, 1, 2, 3, 4, 5, 6, or 7 days. Tassel height was shorter (by 9.2, 11.8, or 11.8 cm) for plants that received 5, 6, or 7 days (respectively) of low DLI stress during the V6 developmental stage compared with the high DLI control. These results highlight the importance of providing supplemental lighting if the DLI falls below a critical threshold that is likely well below 23.7 mol·m−2·d−1 for more than 5 days during tassel development. Photoperiod manipulation to increase DLI was investigated as a tool to suppress tassel barrenness. Inbreds A and B were subjected to a 16, 20, or 22-hour photoperiod during vegetative or reproductive growth. A longer photoperiod during vegetative growth resulted in an elongated tassel height for Inbred A (by 4.3 cm). For Inbred B, tassel branch number was less (by 3.5 branches), and barren tassel length was shorter (by 19.1 cm). Only Inbred A tassel morphology responded to the longer photoperiod during reproductive growth stages compared with the control, with a 1.4 cm longer tassel height, from 16 to 20 hours, and a 4.8 cm shorter tassel height from 16 to 22 hours, and a 6.2 cm shorter tassel height from 20 to 22 hours. These results indicate that a longer photoperiod can alter the tassel morphology of the two inbred lines during either vegetative or reproductive growth stages. Increasing the photoperiod too much can decrease tassel quality, for example, tassel branch number and viable tassel length decreased (by 4.5 branches and 23.6 cm) for Inbred A plants as the vegetative photoperiod increased from 20 to 22 hours.

Lowering the target daily light integrals following days with excessive lighting can reduce lettuce production costs

Given the fluctuating availability of natural lighting throughout the year, supplemental light is frequently employed to maintain the optimal daily light integral (DLI) levels necessary for adequate plant growth. However, the use of supplemental light translates into higher operational costs. Recent reports suggest that plants can tolerate a day with low DLI following exposure to a day with high DLI from natural light. This was referred to as the ‘carryover’ effect. In such cases, supplemental lighting may not be necessary, resulting in energy savings. In this study, we determined if plants can withstand such DLI fluctuations over multiple days without compromising plant growth. Additionally, we calculated the energy requirements for trese treatments to evaluate the potential energy savings of the carryover effect. To test this, we cultivated lettuce plants (Lactuca sativa cv. ‘Waldmand’s Dark Green’ and ‘Rouxai’) in a walk-in grow chamber, subjecting them to six different lighting treatments. Each treatment consisted of a day with a high DLI of 22.5 mol·m-2·d-1 followed by a varying number of consecutive days with low DLI, ranging from 1 to 5 days, with DLIs of 7.5, 11.25, 12.5, 13.13, and 13.5 mol·m-2·d-1 respectively. The combined DLI for each treatment, calculated as the average DLI across high and low DLI days, was maintained at 15 mol·m-2·d-1. Additionally, we included a control treatment where plants were exposed to a constant DLI of 15 mol·m-2·d-1. We measured plant growth rate, final fresh and dry weights, leaf number, leaf area, specific leaf area, light use efficiency, and relative pigment content to assess differences in plant growth under the different lighting regimes. We observed a decrease in biomass accumulation, as indicated by a 13% reduction in final dry weight only for the treatment involving one day of high DLI followed by one day of low DLI, compared to our control. We discovered that plants can tolerate multiple days of low DLI following a day with high DLI, in contrast to the optimal values reported in the literature. This finding can lead to reduced energy consumption for supplemental lighting and consequent operational cost savings.

Intra-canopy LED lighting outperformed top LED lighting in improving tomato yield and expression of the genes responsible for lycopene, phytoene and vitamin C synthesis

Greenhouses located at high latitudes and in cloudy areas often experience a low quality and quantity of light, especially during autumn and winter. This low daily light integral (DLI) reduces production rate, quality, and nutritional value of many crops. This study was conducted on Sakhiya RZ F1 tomato plants to evaluate the impact of LED lights on the growth and nutritional value of tomatoes in a greenhouse with low daily light due to cloudy weather. The treatments included LED growth lights in three modes: top lighting, intra-canopy lighting, and combined top and intra-canopy lighting. The results showed that although the combined top and intra-canopy lighting reached the maximum increase in tomato yield, exposure to intra-canopy LED lighting alone outperformed in tomato fruit yield increase (28.46%) than exposure to top LED lighting alone (12.12%) when compared to no supplemental lighting during the entire production year. Intra-canopy exposure demonstrated the highest increase in tomato lycopene (31.3%), while top and intra-canopy lighting exhibited the highest increase in vitamin C content (123.4%) compared to the control. The LED light treatment also had a very positive effect on the expression of genes responsible for metabolic cycles, including Psy1, LCY-β, and VTC2 genes, which had collinearity with the increase in tomato fruit production.

Daily Light Integral, but Not the Photoperiod, Influences the Time to Flower and Finished Quality of Dianthus Specialty Cut Flowers

Because of the burgeoning year-round demand, greenhouse growers across the United States are increasingly becoming interested in producing specialty cut flowers for local and regional markets. However, outdoor or high tunnel production is not possible year-round in northern latitudes because of low temperatures and radiation intensities experienced during the winter and early spring. Additionally, natural short days in these seasons can limit which photoperiodic crops can be grown. Thus, our objectives were to quantify the influence of the photoperiod and daily light integral (DLI) on greenhouse-grown dianthus ‘Amazon Neon Cherry’ and ‘Amazon Rose Magic’ (Dianthus barbatus interspecific) cut flowers during the young plant and finishing stages. Seeds of both cultivars were sown under 9-, 10-, 11-, 12-, 13-, 15-, or 16-hour photoperiods and a DLI of either ≈5 or 10 mol⋅m−2⋅d−1. After 4 weeks, seedlings from several young-plant photoperiods were distributed across 11-, 12-, 13-, 14-, 15-, or 16-hour photoperiods or a 4-hour night interruption (NI) under a DLI of either ≈5 (low) or 14 (moderate) mol⋅m−2⋅d−1 for finishing. The young plant photoperiod generally had a statistical, but not commercial, influence on development and finished cut flower quality, whereas a 16-h finishing photoperiod marginally hastened development compared with an 11-hour finishing photoperiod. Additionally, stems were 11 to 13 cm longer when finished under the 16-hour photoperiod compared with those finished under the 11-hour photoperiod. Day length minimally influenced the time to flower and harvest, indicating a day-neutral flowering response. However, plants finished under a moderate DLI reached visible flower bud and were harvestable 9 to 10 days earlier than those finished under a low DLI. Additionally, ≈99% of cut flowers finished under a moderate DLI were harvestable, whereas only up to 32% and 57% of dianthus ‘Amazon Rose Magic’ and ‘Amazon Neon Cherry’, respectively, finished under a low DLI were harvestable. Although finished stem lengths were comparable between DLI treatments, cut flower stems were up to 29.6% thicker under a moderate DLI. These findings indicate that high-quality greenhouse-grown dianthus ‘Amazon Neon Cherry’ and ‘Amazon Rose Magic’ cut flowers can be produced when grown under any photoperiod between 9 and 16 hours for 4 weeks (during the young plant stage) and finished under any photoperiod between 11 and 16 hours or a 4-hour NI during finishing. If longer stems are desired, then plants can be finished under a 16-hour photoperiod. Young plants should be grown under a moderate DLI ≥10 mol⋅m−2⋅d−1 to promote biomass accumulation and reduce the young plant crop time. Additionally, plants should be finished under a moderate DLI ≥14 mol⋅m−2⋅d−1 to reduce crop time and increase stem thickness and yield.

Photons at the ultraviolet-visible interface: Effects on leaf expansion and photoinhibition

Photons at the ultraviolet-visible interface: Effects on leaf expansion and photoinhibition

End-of-day Far-red Lighting with a Low Daily Light Integral Increases Stem Length But Does Not Promote Early Leaf Expansion for Petunia ×hybrida Seedlings

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.

Response of Flavor Substances in Tomato Fruit to Light Spectrum and Daily Light Integral.

Light-emitting diodes (LEDs) have been widely used as light sources for plant production in plant factories with artificial lighting (PFALs), and light spectrum and light amount have great impacts on plant growth and development. With the expansion of the product list of PFALs, tomato production in PFALs has received attention, but studies on fruit quality influenced by artificial light are lacking. In this study, precisely modulated LED light sources based on white light combined with additional red, blue, and green lights were used to investigate the effects of light spectrum and daily light integral (DLI) on the main quality indicators and flavor substances of "Micro-Tom" tomato fruits. The highest sugar-acid ratio was obtained under the white light with addition of red light with high DLI and blue light with low DLI. The contents of β-carotene, lycopene, and lutein were significantly increased by higher DLI conditions except for under the blue light treatment, and the cross-interactions between the light spectrum and DLI were observed. The accumulation of the main flavor substances in tomato fruits was decreased by addition of green light with a high DLI and red light with a low DLI; notably, the percentage of 2-isobutylthiazole, which is associated with fresh tomato aroma, was decreased by green light. This study provides insights for improving tomato fruit quality and flavor by regulating light conditions in PFALs.

Air temperature during cutting propagation of cold-intermediate and -sensitive crops can be reduced if root-zone heating is provided

Air temperature during cutting propagation of cold-intermediate and -sensitive crops can be reduced if root-zone heating is provided

Daily light integral and/or photoperiod during the young plant and finishing stages influence floral initiation and quality of witchgrass and marigold cut flowers

To produce consistent and high-quality specialty cut flowers throughout the year, growers in temperate climates must utilize controlled environment greenhouses. Research-based information on photoperiod management and supplemental lighting for specialty cut flowers is limiting. Therefore, our objectives were (1) to determine the effect of photoperiod during the young-plant and finishing stages on floral initiation and morphology of witchgrass ‘Frosted Explosion’ (Panicum capillare) and marigold ‘Xochi’ (Tagetes erecta) and (2) to quantify the effect of daily light integral (DLI) on floral initiation and morphology of witchgrass during the finishing stage. Seeds of marigold and multi-seed pellets of witchgrass were sown and placed under 9-, 11- (marigold only), 12-, 13-, 14-, 15-, 16-, 18-, or 24-h photoperiods or a 9-h short day with a 4-h night interruption (NI) from 2200 to 0200 h. Plugs were distributed among 10-, 11-, 12-, 13-, 14-, 15-, or 16-h photoperiods or a 4-h NI, for finishing. Witchgrass was finished under a very low or moderate DLI of ≈3 or 10 mol⋅m–2⋅d–1, respectively, while marigold was finished under a DLI of ≈10 mol⋅m–2⋅d–1. Marigold grown under a photoperiod ≥ 11 h or a 4-h NI during the young-plant stage and finished under an 11- or 12-h photoperiod had thick stems and consistently met the marketable stem length of ≥ 65 cm. Up to 29% and 107% more stems were harvestable under 11- and 12-h finishing photoperiods, respectively, compared to a 10-h finishing photoperiod. Marigold visible buds were delayed, and stems were not harvestable under photoperiods ≥ 13 h or a 4-h NI after 8 weeks. Young witchgrass plants grown under a photoperiod between 14- and 24-h or a 4-h NI and finished under photoperiods ≥ 14 h or a 4-h NI, and at least a moderate DLI, were reliably harvestable (≥ 50 cm long with a fully developed panicle). Witchgrass finished under day lengths < 13 h (rep. 1) or < 14 h (rep. 2) flowered prematurely and were roughly one-sixth the length of harvestable stems at an open flower. All witchgrass stems grown under a very low DLI were shorter and thinner than those grown under a moderate DLI, and none were harvestable. Therefore, we recommend growing marigold ‘Xochi’ young plants under a photoperiod ≥ 11 h or a 4-h NI and finishing under a 12-h photoperiod. Additionally, witchgrass ‘Frosted Explosion’ young plants should be grown under a photoperiod ≥ 14 h or a 4-h NI and finished under photoperiods ≥ 14 h or a 4-h NI to prevent premature flowering. Witchgrass and marigold cut flowers should be finished under a DLI of ≥ 10 mol⋅m–2⋅d–1 for consistent production of high-quality stems.

A high daily light integral can influence photoperiodic flowering responses in long day herbaceous ornamentals

A high daily light integral can influence photoperiodic flowering responses in long day herbaceous ornamentals

Effect of Pre-Harvest Supplemental UV-A/Blue and Red/Blue LED Lighting on Lettuce Growth and Nutritional Quality

Blue light and ultra-violet (UV) light have been shown to influence plant growth, morphology, and quality. In this study, we investigated the effects of pre-harvest supplemental lighting using UV-A and blue (UV-A/Blue) light and red and blue (RB) light on growth and nutritional quality of lettuce grown hydroponically in two greenhouse experiments. The RB spectrum was applied pre-harvest for two days or nights, while the UV-A/Blue spectrum was applied pre-harvest for two or four days or nights. All pre-harvest supplemental lighting treatments had a same duration of 12 h with a photon flux density (PFD) of 171 μmol m−2 s−1. Results of both experiments showed that pre-harvest supplemental lighting using UV A/Blue or RB light can increase the growth and nutritional quality of lettuce grown hydroponically. The enhancement of lettuce growth and nutritional quality by the pre-harvest supplemental lighting was more effective under low daily light integral (DLI) compared to a high DLI and tended to be more effective when applied during the night, regardless of spectrum.

Modeling growth and development of hydroponically grown dill, parsley, and watercress in response to photosynthetic daily light integral and mean daily temperature.

In controlled environments, crop models that incorporate environmental factors can be developed to optimize growth and development as well as conduct cost and/or resource use benefit analyses. The overall objective of this study was to model growth and development of dill ‘Bouquet’ (Anethum graveolens), parsley ‘Giant of Italy’ (Petroselinum crispum), and watercress (Nasturtium officinale) in response to photosynthetic daily light integral (DLI) and mean daily temperature (MDT). Plants were grown hydroponically in five greenhouse compartments with MDTs ranging from 9.7 to 27.2 °C under 0%, 30%, or 50% shade cloth to create DLIs ranging from 6.2 to 16.9 mol·m‒2·d‒1. MDT and DLI interacted to influence dill fresh mass and height, and watercress maximum quantum yield of dark adapted leaves (Fv/Fm), height, and branch number while only MDT affected dill leaf number and watercress fresh mass and branch length. Besides dry matter concentration (DMC), parsley was influenced by MDT and not DLI. Increasing MDT from ≈10 to 22.4 °C (parsley) or 27.2 °C (dill and watercress), linearly or near-linearly increased fresh mass. For dill, increasing DLI decreased fresh mass when MDT was low (9.7 to 13.9 °C) and increased fresh mass when MDT was high (18.4 to 27.2 °C). DMC of dill, parsley, and watercress increased as MDT decreased or DLI increased, indicating a higher proportion of plant fresh mass is water at higher MDTs or lower DLIs. With these data we have created growth and development models for culinary herbs to aid in predicting responses to DLI and MDT.

Floral Induction in the Short-Day Plant Chrysanthemum Under Blue and Red Extended Long-Days

Shorter photoperiod and lower daily light integral (DLI) limit the winter greenhouse production. Extending the photoperiod by supplemental light increases biomass production but inhibits flowering in short-day plants such as Chrysanthemum morifolium. Previously, we reported that flowering in growth-chamber grown chrysanthemum with red (R) and blue (B) LED-light could also be induced in long photoperiods by applying only blue light during the last 4h of 15h long-days. This study investigates the possibility to induce flowering by extending short-days in greenhouses with 4h of blue light. Furthermore, flower induction after 4h of red light extension was tested after short-days RB-LED light in a growth-chamber and after natural solar light in a greenhouse. Plants were grown at 11h of sole source RB light (60:40) in a growth-chamber or solar light in the greenhouse (short-days). Additionally, plants were grown under long-days, which either consisted of short-days as described above extended with 4h of B or R light to long-days or of 15h continuous RB light or natural solar light. Flower initiation and normal capitulum development occurred in the blue-extended long-days in the growth-chamber after 11h of sole source RB, similarly as in short-days. However, when the blue extension was applied after 11h of full-spectrum solar light in a greenhouse, no flower initiation occurred. With red-extended long-days after 11h RB (growth-chamber) flower initiation occurred, but capitulum development was hindered. No flower initiation occurred in red-extended long-days in the greenhouse. These results indicate that multiple components of the daylight spectrum influence different phases in photoperiodic flowering in chrysanthemum in a time-dependent manner. This research shows that smart use of LED-light can open avenues for a more efficient year-round cultivation of chrysanthemum by circumventing the short-day requirement for flowering when applied in emerging vertical farm or plant factories that operate without natural solar light. In current year-round greenhouses’ production, however, extension of the natural solar light during the first 11 h of the photoperiod with either red or blue sole LED light, did inhibit flowering.

Optimizing production of ‘Fascination’ and ‘Carnivor’ transplants for grafting using lower daily light integral and higher CO2

Optimizing production of ‘Fascination’ and ‘Carnivor’ transplants for grafting using lower daily light integral and higher CO₂

Quality of Cut Spray Roses Grown in a Seasonal Cultivation Environment of a Smart Farm in Honam, Korea

In this study we assessed the quality of cut spray roses grown in a seasonal cultivation environment at a smart farm in the Honam area of Korea. The smart farm consists of a multi-span glass greenhouse that can be monitored in real time through CCTV. This farm is among those that are the first generation of smart farms. In the cultivation environment of the greenhouse the maximum temperature during summer was higher than at other seasons, and the daily light integral was less than the minimum light requirements during the winter. In addition, relative humidity was significantly higher in fall and winter, with a vapor pressure deficit of 0.3 kPa in winter. The change in pH of the nutrient solution was insignificant, but the electronic conductivity was found to be out of the proper range in spring and summer. Morphological characteristics and vase life were investigated for the rose cultivars ‘Egg Tart’, ‘Flash Dance’, ‘Pink Yoyo’, and ‘Super Sensation’, which are widely cultivated at smart farms. Stem length increased for most varieties but stem diameter was smaller, floret number was lower, and the flower diameter was less in winter than in other seasons. The Hunter value L was higher in summer, owing to higher discoloration in summer than in winter. The cultivars ‘Flash Dance’, ‘Pink Yoyo’, and ‘Super Sensation’ exhibited the longest vase life in the fall, and all three cultivars were found to have shorter vase life in winter and summer. Based on these results, we conclude that high temperatures in the summer and low daily light integral and high relative humidity in the winter have negative effects on flower size, petal color, and vase life. Therefore, in order to produce high-quality cut roses, it is necessary to improve the smart farm environment control system. In the smart farm in this study, the complex environment of the ground can be controlled. Once a large enough set of data is analyzed and a decision support system is designed based on the accumulated data, the development of more advanced smart farms will be facilitated.

Nutrient Solution Strength Does Not Interact with the Daily Light Integral to Affect Hydroponic Cilantro, Dill, and Parsley Growth and Tissue Mineral Nutrient Concentrations

Our objectives were to quantify the growth and tissue mineral nutrient concentrations of cilantro (Coriandrum sativum ‘Santo’), dill (Anethum graveolens ‘Fernleaf’), and parsley (Petroselinum crispum ‘Giant of Italy’) in response to nutrient solution electrical conductivity (EC) under low and high photosynthetic daily light integrals (DLI). Three-week old seedlings of cilantro, dill, and parsley were transplanted into nutrient-film technique hydroponic systems with one of five nutrient solution EC treatments (0.5, 1.0, 2.0, 3.0, or 4.0 dS·m−1) in greenhouses under a low (~7.0 mol·m−2·d−1) or high (~18.0 mol·m−2·d−1) DLI. The DLI, but not nutrient solution EC, affected culinary herb growth. For example, fresh mass increased by 21.0 (154%), 17.1 (241%), or 13.3 g (120%) for cilantro, dill, and parsley, respectively, for plants grown under high DLI compared to those grown under a low DLI; dry mass followed a similar trend. Tissue nutrient concentrations were generally affected by either DLI or EC. For those nutrients affected by DLI, concentrations increased with increasing DLI, except for potassium (K; all species) and manganese (Mn; dill). For those nutrients affected by EC, Ca and Mg decreased with increasing EC, while the remaining increased with increasing EC. When our tissue nutrient data are compared to recommended tissue concentrations, the vast majority of elements were either within or above recommended tissue ranges for cilantro, dill, and parsley. Our results demonstrate cilantro, dill, and parsley can be successfully grown across a range of EC, regardless of the light intensity of the growing environment.

Contrasting responses of the coral Acropora tenuis to moderate and strong light limitation in coastal waters

Contrasting responses of the coral Acropora tenuis to moderate and strong light limitation in coastal waters

Effects of Nutrient Solution Concentration and Daily Light Integral on Growth and Nutrient Concentration of Several Basil Species in Hydroponic Production

Our objective was to quantify the effect of mineral nutrient concentration of a nutrient solution on the growth of basil species and cultivars grown under high and low photosynthetic daily light integrals (DLIs). Sweet basil (Ocimum basilicum ‘Nufar’), lemon basil (O. ×citriodorum ‘Lime’), and holy basil (O. tenuiflorum ‘Holy’) seedlings were transplanted into nutrient-film technique (NFT) systems with different nutrient solution electrical conductivities (EC; 0.5, 1.0, 2.0, 3.0, or 4.0 dS·m–1) in greenhouses with a low (≈7 mol·m–2·d–1) or high (≈15 mol·m–2·d–1) DLI. Although nutrient solution EC did not affect growth and morphology, increasing DLI did. For example, when sweet basil was grown under a high DLI, the fresh and dry weight, height, and node number increased by 144%, 178%, 20%, and 18%, respectively, compared with plants grown under the low DLI, and branching was also stimulated. In contrast, DLI had little effect on tissue nutrient concentration, although nutrient solution did. Most tissue nutrient concentrations increased with increasing EC, with the exception of Mg and Ca. For example, N in sweet basil increased by 0.6% to 0.7% whereas Mg decreased by 0.2% as EC increased from 0.5 to 4.0 dS·m–1. Across treatments and basil species, tissue nutrient concentrations were generally within recommended ranges with no visible deficiencies. Based on our results, nutrient solution concentrations for hydroponic basil production can be selected based on factors such as other species grown in the same solution or by reducing fertilizer inputs.

Promotion of Flowering from Far-red Radiation Depends on the Photosynthetic Daily Light Integral

Under natural short days, growers can use photoperiodic lighting to promote flowering of long-day plants and inhibit flowering of short-day plants. Unlike traditional lamps used for photoperiodic lighting, low-intensity light-emitting diode (LED) lamps allow for a wide array of adjustable spectral distributions relevant to regulation of flowering, including red (R) and white (W) radiation with or without far-red (FR) radiation. Our objective was to quantify how day-extension (DE) photoperiodic lighting from two commercially available low-intensity LED lamps emitting R + W or R + W + FR radiation interacted with daily light integral (DLI) to influence stem elongation and flowering of several ornamental species. Long-day plants [petunia (Petunia ×hybrida Vilm.-Andr. ‘Dreams Midnight’) and snapdragon (Antirrhinum majus L. ‘Oh Snap Pink’)], short-day plants [african marigold (Tagetes erecta L. ‘Moonsong Deep Orange’) and potted sunflower (Helianthus annuus L. ‘Pacino Gold’)], and day-neutral plants [pansy (Viola ×wittrockiana Gams. ‘Matrix Yellow’) and zinnia (Zinnia elegans Jacq. ‘Magellan Cherry’)] were grown at 20/18 °C day/night air temperatures and under low (6–9 mol·m−2·d−1) or high (16–19 mol·m−2·d−1) seasonal photosynthetic DLIs from ambient solar radiation combined with supplemental high-pressure sodium lighting and DE LED lighting. Photoperiods consisted of a truncated 9-hour day (0800–1700 hr) with additional 1-hour (1700–1800 hr, 10 hours total), 4-hour (1700–2100 hr, 13 hours total), or 7-hour (1700–2400 hr, 16 hours total) R + W or R + W + FR LED lighting at 2 μmol·m−2·s−1. Days to visible bud, plant height at first open flower, and time to first open flower (TTF) of each species were influenced by DLI, lamp type, and photoperiod though to different magnitudes. For example, plant height of african marigold and potted sunflower at first open flower was greatest under R + W + FR lamps, high DLIs, and 16-hour photoperiods. Petunia grown under R + W lamps, high DLI, and 10- and 13-hour photoperiods were the most compact. For all species, TTF was generally reduced under high DLIs. For example, regardless of the lamp type, flowering of african marigold occurred fastest under a high DLI and 10-hour photoperiod. Flowering of petunia and snapdragon occurred fastest under a high DLI, R + W + FR lamps, and a 16-hour photoperiod. However, only under high DLIs, R + W or R + W + FR lamps were equally effective at promoting flowering when used to provide DE lighting. Our data suggest that under low DLIs, flowering of long-day plants (petunia and snapdragon) occurs more rapidly under lamps providing R + W + FR, whereas under high DLIs, flowering is promoted similarly under either R + W or R + W + FR lamps.

Geranium and Purple Fountain Grass Leaf Pigmentation Is Influenced by End-of-Production Supplemental Lighting with Red and Blue Light-emitting Diodes

Under low-light greenhouse conditions, anthocyanin pigmentation in vegetative tissues of red- or purple-leafed floricultural crops is not fully expressed and, consequently, plants are not as visually appealing to consumers. Our objective was to quantify the effect of end-of-production (EOP; before shipping) supplemental lighting (SL) of different light sources, qualities, and intensities on foliage color of geranium (Pelargonium ×hortorum L.H. Bailey ‘Black Velvet’) and purple fountain grass [Pennisetum ×advena Wipff and Veldkamp (formerly known as Pennisetum setaceum Forsk. Chiov. ‘Rubrum’)]. Plants were finished under early (Expt. 1) and late (Expt. 2) seasonal greenhouse ambient solar light and provided with 16 hours of day-extension lighting from low-intensity light-emitting diode (LED) lamps [7:11:33:49 blue:green:red:far-red light ratio (%); control] delivering 4.5 μmol·m−2·s−1, or 16 hours of EOP SL from high-pressure sodium (HPS) lamps delivering 70 μmol·m−2·s−1, or LED arrays (100:0, 87:13, 50:50, or 0:100 red:blue) delivering 100 μmol·m−2·s−1, or 0:100 red:blue LEDs delivering 25 or 50 μmol·m−2·s−1. Geranium and fountain grass chlorophyll content and leaf color were estimated using a SPAD-502 chlorophyll meter and Minolta tristimulus colorimeter, respectively. Relative chlorophyll content (RCC) and foliage L* (lightness), C* (chroma; a measure of saturation), and h° (hue angle; a measure of tone) values were significantly influenced by EOP SL and days of exposure. Generally, RCC of geranium and fountain grass increased from 3 to 14 days of exposure to EOP SL from HPS lamps and LEDs delivering 100 μmol·m−2·s−1. Under low daily light integrals (DLIs) [8.6 mol·m−2·d−1 (geranium) and 9.4 mol·m−2·d−1 (purple fountain grass)] EOP SL providing 100 μmol·m−2·s−1 of 100:0, 87:13, 50:50, or 0:100 red:blue light for ≥14 days resulted in lower L* (darker foliage), C* (saturated), and h° (orange to violet-red hues). Our data indicate that a minimum of 14 days of EOP SL providing 100 μmol·m−2·s−1 of 50:50 or 0:100 red:blue light enhanced foliage color of geranium and fountain grass leaves when plants were grown under a low greenhouse DLI ≤ 9 mol·m−2·d−1.