Erik S. Runkle

Flowering of cyclamen is accelerated by an increase in temperature, photoperiod, and daily light integral

Summary Cyclamen (Cyclamen persicum Mill.) crop production times can be reduced by increasing the greenhouse temperature, but alternative methods to accelerate crop development are desirable when energy costs for heating are high. The effects of photoperiod and increasing daily light integral (DLI) on cyclamen remain unclear. We performed experiments to examine the effect of DLI using two temperatures (16°C or 20°C) and three photoperiods (8, 12, or 16 h) delivering DLI values of 4.9, 7.3, or 9.8 mol m–2 d–1, respectively, and the effect of night interruption (NI) lighting from incandescent lamps (IL), on the flowering of cyclamen ‘Metis Purple Flame’. Plants grown at 20°C reached the visible flower bud (VB) stage earlier than plants grown at 16°C under all photoperiods. NI hastened flower bud initiation by 22 – 29 d compared with an 8-h photoperiod at both temperatures. Plants grown under the 8-h photoperiod with an NI treatment (DLI = 4.9 mol m–2 d–1) flowered at a similar time as plants grown under the 12-h photoperiod (DLI = 7.3 mol m–2 d–1). In addition, plants grown at 16°C with an NI reached the VB stage in a similar time to plants grown at 20°C with an 8-h photoperiod. Therefore, the effects of increasing the DLI, providing NI lighting, or increasing the temperature can be compared, so that growers can determine which strategies can reduce the greenhouse production time of cyclamen most cost-effectively.

Controlled Flowering of Herbaceous Perennial Plants

We have determined the juvenility, cold (vernalization), photoperiod, and cultural requirements necessary to flower many herbaceous perennials on specific dates and at specified sizes. We identified the long-day (LD) requirement by conducting critical photoperiod experiments in which critical photoperiod is defined as the photoperiod that elicits a complete, rapid, uniform flowering response in a population. The LD requirement for all herbaceous perennials tested can be met by either a continual photoperiod of 16 hours or more, or by four hours of light as an interruption in the middle of the night. Nightinterruption lighting for two hours is adequate for rapid, uniform flowering in some species. Incandescent, cool-white fluorescent, metal halide, and high-pressure sodium lamps effectively promote an LD response; differences among the irradiance levels required for flower induction are horticulturally insignificant. To maintain vegetative growth on quantitative and qualitative LD species, photoperiods should be 10 hours or fewer.

INFLUENCE OF NIR-REFLECTING SHADING PAINT ON GREENHOUSE ENVIRONMENT, PLANT TEMPERATURE, AND GROWTH AND FLOWERING OF BEDDING PLANTS

During greenhouse production, growers often utilize shading strategies to reflect shortwave radiation (SWR; 300 to 2,700 nm) and reduce the thermal load inside a greenhouse. Greenhouse glazing or shading materials that photoselectively filter more near-infrared radiation (NIR; 770 to 2,700 nm) than photosynthetically active radiation (PAR; 400 to 700 nm) can be used to reduce thermal energy transmission. We quantified environmental conditions and bedding plant growth and flowering inside a glass-glazed greenhouse (lat. 42.7° N) that received an application of either a commercially available NIR-reflecting (NIR-R) or neutral (N) shading paint. During two summer seasons, shading paints were applied to the glazing exterior of different greenhouses so that the mean daily transmission of PAR was similar. Poinsettia (Euphorbia pulcherrima Willd. ex Klotz) or bedding plants were grown inside each greenhouse. The NIR-R paint transmitted 67%, 8%, 24%, 30%, and 29% less ultraviolet-A (315 to 380 nm), red (R; 600 to 700 nm), far-red (FR; 700 to 800 nm), NIR, and SWR, respectively, than the N paint. Transmission of blue (400 to 500 nm) and green (500 to 600 nm) light was 4.7% and 4.5% greater, respectively, under the NIR-R versus N paint. The ratio of transmitted PAR per unit of SWR under the N and NIR-R paints was 1.8 and 2.6 µmol W-1 s-1, respectively. During the day (1100 to 1800 h), mean greenhouse air, shoot-tip, and leaf temperatures were 0.4°C to 1.5°C, 0.4°C to 1.2°C, and 0.7°C to 1.5°C higher, respectively, under the N paint compared with the NIR-R paint. From 0900 to 1700 h, the ratio of R to FR light under the NIR-R paint ranged from 1.44 to 1.79, whereas the N paint and outside the greenhouse had an R:FR ratio of 1.11 to 1.22. Blue salvia (Salvia farinacea Benth.), pansy (Viola × wittrockiana Hook.), and petunia (Petunia ×hybrida Vilm.-Andr.) flowered a mean of 1 to 3 d earlier under the N versus NIR-R paint, but plant heights were similar.

Proposed product label for electric lamps used in the plant sciences

Electric lamps are widely used to supplement sunlight (supplemental lighting) and daylength extension (photoperiodic lighting) for the production of horticultural crops in greenhouses and controlled environments. Recent advances in light-emitting diode (LED) technology nowprovide the horticultural industrywith multiple lighting options. However, growers are unable to compare technologies and LED options because of insufficient data on lamp performance metrics. Here, we propose a standardized product label that facilitates the comparison of lamps across manufacturers. This label includes the photosynthetically active radiation (PAR) efficacy, PAR conversion efficiency, photon flux density output in key wave bands, as well as the phytochrome photostationary state (PSS), red/far red ratio, and graphs of the normalized photon flux density across the 300–900 nm wave band and a horizontal distribution of the light output.

LED lighting for Urban agriculture

The benefits of using light-emitting diodes (LEDs) in urban agriculture are discussed, along with the necessity of introducing information and communication technology (ICT). The incorporation of ICT into urban agriculture is now economically viable because the marginal costs of information processing, storage, and transfer are approaching zero. Electricity generated from renewable resources such as solar energy and biomass is also becoming cost-competitive with that generated from fossil fuel and nuclear power. Internet-connected plant factories lit with LEDs and greenhouses with LED supplemental lighting will serve as key components in urban agriculture. The potential for combined applications of ICT, artificial intelligence, and the Internet of Things in urban agriculture is described briefly. Finally, the concept of closed plant production system (CPPS) and its application in plant factory with LED lighting are described.

The application of blue light as a growth regulator

Alternatives of agricultural chemicals such as growth retardant is awaited from the environmental point of view. Blue light would have potential to shorten plant height, and growth analysis may make effective timing and period of application of blue light clear. And it will be one of the basic data to construct a quantitative model to describe the relation between internode and/or stem elongation and light condition. This technique would provide growers with an environmental friendly ways to regulate plant growth of ornamental crops. Experiments were conducted in a controlled environment cabinet that equipped temperature control, eight controllable fluorescent lamps, blue LEDs. A turn table was used to increase efficiency of experiments. A CCD camera which had sensitivity in infrared region and an infrared illuminator were employed to obtain an image of plants during day and night.. The plant images were obtained every 10 minutes over three weeks. Two light conditions were planned for the experiments, that is to say, Exp I :12hrs light(0600 to 1800), 12 hrs dark(1800 to 0600) with 4 hrs night interrupt(2200 to 0200) by a fluorescent lamp, and Exp.II : 12hrs light(0600 to 1800), 12 hrs dark(1800 to 0600) with 4 hrs night interrupt (2200 to 0200) by blue LEDs (0400 to 0600). It was observed that the growth speed of internode length was slow under in the light period, and it became fast in the dark, and that the average value of the amount of internode elongation per day was reduced even to about 60% by blue LED, and that the inhibitory effect of internode elongation by blue LED was maintained not only in the night interruption period irradiating blue LED but in the dark and light periods following it.

Improving greenhouse environmental control using crop-model-driven multi-objective optimization

Optimal control of greenhouse environments can be improved by using a combined microclimate-crop-yield model to allow selection of greenhouse designs and control algorithms to maximize the profit margin. However, classical methods for optimal greenhouse control are not adequate to establish the tradeoffs between multiple objectives. We use NSGA-II to evolve the setpoints for microclimate control in a greenhouse simulation and define two objectives: minimizing variable costs and maximizing the value of the tomato crop yield. Results show that the evolved setpoints can provide the grower a variety of better solutions, resulting in greater profitability compared to prior simulated results. The Pareto front also provides additional information to the grower, showing the economic tradeoffs between variable costs and tomato crop yield, which can aid in decision making.

Spectral effects of light-emitting diodes on plant growth, visual color quality, and photosynthetic photon efficacy: White versus blue plus red radiation

Arrays of blue (B, 400−500 nm) and red (R, 600−700 nm) light-emitting diodes (LEDs) used for plant growth applications make visual assessment of plants difficult compared to a broad (white, W) spectrum. Although W LEDs are sometimes used in horticultural lighting fixtures, little research has been published using them for sole-source lighting. We grew seedlings of begonia (Begonia ×semperflorens), geranium (Pelargonium ×horturum), petunia (Petunia ×hybrida), and snapdragon (Antirrhinum majus) at 20°C under six sole-source LED lighting treatments with a photosynthetic photon flux density (PPFD) of 160 μmol∙m–2∙s–1 using B (peak = 447 nm), green (G, peak = 531 nm), R (peak = 660 nm), and/or mint W (MW, peak = 558 nm) LEDs that emitted 15% B, 59% G, and 26% R plus 6 μmol∙m−2∙s−1 of far-red radiation. The lighting treatments (with percentage from each LED in subscript) were MW100, MW75R25, MW45R55, MW25R75, B15R85, and B20G40R40. At the transplant stage, total leaf area, and fresh and dry weight were similar among treatments in all species. Surprisingly, when petunia seedlings were grown longer (beyond the transplant stage) under sole-source lighting treatments, the primary stem elongated and had flower buds earlier under MW100 and MW75R25 compared to under B15R85. The color rendering index of MW75R25 and MW45R55 were 72, and 77, respectively, which was higher than those of other treatments, which were ≤64. While photosynthetic photon efficacy of B15R85 (2.25 μmol∙J–1) was higher than the W light treatments (1.51−2.13 μmol∙J–1), the dry weight gain per unit electric energy consumption (in g∙kWh–1) of B15R85 was similar to those of MW25R75, MW45R55, and MW75R25 in three species. We conclude that compared to B+R radiation, W radiation had generally similar effects on seedling growth at the same PPFD with similar electric energy consumption, and improved the visual color quality of sole-source lighting.

Recent Developments in Plant Lighting

There is substantial interest among commercial growers and plant hobbyists, academics, and lighting manufacturers in the development of new lighting technologies and lighting applications. LEDs are of particular interest because of the ability to control the light spectrum to regulate crop growth characteristics as well as their increasing energy efficiency. This chapter briefly discusses recent developments in plant lighting including an international light symposium held in 2016, a new book on horticultural lighting, and the development of lighting standards for plant applications, which are especially needed for LEDs.

Control of Flowering Using Night-Interruption and Day-Extension LED Lighting

Flowering of photoperiodic plants is regulated by the duration of the continuous night (dark) period during each 24-h period. When the natural photoperiod is short, longer days (shorter nights) may be desired by commercial growers of ornamentals and other specialty crops to promote flowering of long-day plants or inhibit flowering of short-day plants. To create short nights, electric lighting can extend the daylength (day extension, DE) or interrupt the night (night interruption, NI). Conventional lamps such as incandescent (INC), halide, and compact fluorescent (CFL) can serve this purpose, but they are energy inefficient, have a short life span, and/or emit photons at wavelengths that have little or no effect on regulating flowering. Recent advancements in solid-state lighting enable horticultural applications including regulation of flowering, especially in (semi-) controlled environments. Light-emitting diodes (LEDs) with customized spectra suitable for control of flowering are at least as effective as conventional lamps, last longer, and are more energy efficient. Narrowband radiation from LEDs facilitates research on the role of specific wavelengths in mediating flowering and plant morphology, which are important in commercial production of many specialty crops produced in controlled environments. In addition, applied lighting research helps elucidate how photoreceptors, such as phytochromes and cryptochromes, mediate these physiological processes in plants. LEDs will increasingly replace conventional lamps to regulate flowering of commercial photoperiodic crops as their energy efficiency increases and manufacturing costs decrease.