Abstract
Light quantity (intensity and photoperiod) and quality (spectral composition) affect plant growth and physiology and interact with other environmental parameters and cultivation factors in determining the plant behaviour. More than providing the energy for photosynthesis, light also dictates specific signals which regulate plant development, shaping and metabolism, in the complex phenomenon of photomorphogenesis, driven by light colours. These are perceived even at very low intensity by five classes of specific photoreceptors, which have been characterized in their biochemical features and physiological roles. Knowledge about plant photomorphogenesis increased dramatically during the last years, also thanks the diffusion of light-emitting diodes (LEDs), which offer several advantages compared to the conventional light sources, such as the possibility to tailor the light spectrum and to regulate the light intensity, depending on the specific requirements of the different crops and development stages. This knowledge could be profitably applied in greenhouse horticulture to improve production schedules and crop yield and quality. This article presents a brief overview on the effects of light spectrum of artificial lighting on plant growth and photomorphogenesis in vegetable and ornamental crops, and on the state of the art of the research on LEDs in greenhouse horticulture. Particularly, we analysed these effects by approaching, when possible, each single-light waveband, as most of the review works available in the literature considers the influence of combined spectra.
Highlights
Light is one of the main environmental parameters regulating plant physiology throughout the entire plant life cycle, as plants use light as both energy source for carbon fixation in photosynthesis, and signal to activate and regulate many other key processes related to plant growth and development (Devlin et al 2007).As their life depends on the assimilative function of light, plants evolved fine light-sensing mechanisms to maintain and maximize photosynthetic performance and fitness during their life span
In mini-cucumber, combinations of FR, R and B by top and bottom vertical light-emitting diodes (LEDs) resulted in more than 10% increase in fruit yield; plasma light supplemented with vertical B light from the top of the canopy reduced plant growth and fruit yield in the first month, while FR from the top of the canopy increased fruit yield compared to that from the bottom (Guo et al 2016; Table 2)
1 3 by cooling for 4 weeks followed by high phytochrome photoequilibria (PPE) light. These results suggested that hormones responsible for flowering in Phalaenopsis are stimulated by a high PPE during the induction period, and temperature and/or light spectrum in the second part of the treatment are more important to obtain multiple inflorescences, probably through the apical dominance suppression
Summary
Light is one of the main environmental parameters regulating plant physiology throughout the entire plant life cycle, as plants use light as both energy source for carbon fixation in photosynthesis (assimilative function), and signal to activate and regulate many other key processes related to plant growth and development (control function) (Devlin et al 2007). Green light penetrates deeply in the leaf mesophyll layers and reaches the lower and inner canopy levels, promoting photosynthesis in the deepest chloroplasts and in the less irradiated leaves and providing signals to respond to the environmental irradiance, improving crop productivity and yield (Smith et al 2017) These evidences show the importance of the different wavelengths of the light spectrum, alone or in combination, in eliciting morphological and physiological responses of plants (Devlin et al 2007; Folta and Childers 2008). This is important in noncontinuous canopies (e.g. young plants), where the incident light is only partially intercepted and photomorphogenetic responses have a relevant impact on plant growth and productivity (Hogewoning et al 2010) He et al (2019) highlighted that the impact of LED light quality on productivity can be linked to the induced modification of leaf traits more than the change in photosynthetic performance on a leaf area basis.
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