Control of Morphology by Manipulating Light Quality and Daily Light Integral Using LEDs
In northern latitudes, supplemental lighting is utilized to increase the photosynthetic daily light integral in greenhouses during the winter months, which can fall as low as 1–5 mol m−2 d−1. Traditionally, supplemental lighting has been provided by high-
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Control of Morphology by Manipulating Light Quality and Daily Light Integral Using LEDs Joshua K. Craver and Roberto G. Lopez
Abstract In northern latitudes, supplemental lighting is utilized to increase the photosynthetic daily light integral in greenhouses during the winter months, which can fall as low as 1–5 mol m 2 d 1. Traditionally, supplemental lighting has been provided by high-intensity discharge (HID) lamps, but light-emitting diode (LED) technologies are now available for many greenhouse applications. The use of LEDs for supplemental lighting can be beneficial because wavelengths of light can be selected for applications such as the control of plant growth, development, morphology, and leaf color. However, delivering these precise wavelengths at moderately low intensities with ambient light already present in the greenhouse may prove ineffective at eliciting desired morphological characteristics. Regardless, LEDs have proven to be a viable option to provide supplemental lighting in the many controlled environments. Keywords Extension growth • Floriculture crops • Light-emitting diodes • Photomorphogenesis • Phytochrome • Seedling growth • Sole-source lighting • Supplemental lighting
15.1
Introduction
Light-emitting diodes (LEDs) provide a novel approach to greenhouse lighting that has yet to be fully researched (Mitchell et al. 2012; Morrow 2008). To date, little research has been published involving the use of LEDs in greenhouses where plants are also subjected to solar radiation. The use of LEDs in a greenhouse production scenario could involve supplemental, photoperiodic, or photomorphogenic lighting J.K. Craver Department of Horticulture and Landscape Agriculture, Purdue University, 625 Agriculture Mall Drive, West Lafayette, IN 47907-2010, USA R.G. Lopez (*) Department of Horticulture, Michigan State University, 1066 Bogue Street, East Lansing, MI 48824-1325, USA e-mail: [email protected] © Springer Science+Business Media Singapore 2016 T. Kozai et al. (eds.), LED Lighting for Urban Agriculture, DOI 10.1007/978-981-10-1848-0_15
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for select high-value crops (Mitchell et al. 2012; Morrow 2008). While the quantity (intensity) of light supplied to a plant is often a major focus during greenhouse crop production, the quality of light administered can also influence plant growth, development, and morphology.
15.2
Effects of DLI on Plant Morphology
Daily light integral (DLI) describes the cumulative number of photosynthetically active photons (400–700 nm) received during a 24-h period. Numerous studies have reported that DLI influences plant growth and morphology measured in terms of biomass accumulation, leaf area, branch and flower number, and height. For example, Currey and Lopez (2015) reported that leaf, stem, and root biomass accumulation increased linearly with DLI by 122 %, 118 %, and 211 % for geranium (Pelargonium hortorum), New Guinea impatiens (Impatiens hawkeri), and petunia (Petunia hybrida) cuttings, respectively, as DLI during propagation incre
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