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Horticulturae 2018, 4(2), 8; https://doi.org/10.3390/horticulturae4020008

Growth and Physiological Responses of Lettuce Grown under Pre-Dawn or End-Of-Day Sole-Source Light-Quality Treatments

1
Environmental Horticulture Department, University of Florida, 1549 Fifield Hall, Gainesville, FL 32611-0670, USA
2
Department of Agricultural Sciences, University of Naples Federico II, via Universitá 100, 80055 Portici, Italy
3
IFAS Statistical Consulting Unit and Agronomy Department, University of Florida, 404 McCarty Hall C, Gainesville, FL 32611-0500, USA
*
Author to whom correspondence should be addressed.
Received: 30 April 2018 / Revised: 29 May 2018 / Accepted: 4 June 2018 / Published: 7 June 2018
(This article belongs to the Special Issue Plant Production in Controlled Environment)
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Abstract

The objective of this study was to evaluate growth and physiological responses of ‘Cherokee’ and ‘Waldmann’s Green’ lettuce (Lactuca sativa) exposed to small changes in light quality and intensity within a 24-h period. Three pre-dawn (PD; 0600 to 0700) and three end-of-day (EOD; 2100 to 2200) treatments were evaluated in the study, each providing 50 ± 2 µmol·m−2·s−1 of either blue, red, or broadband white light from light-emitting diodes (LEDs). To account for the main daily light integral (DLI), broadband white LEDs provided 210 ± 2 µmol·m−2·s−1 from 0700 to 2200 or from 0600 to 2100 for the PD or EOD treatments, respectively. A control treatment was included which provided 200 ± 2 µmol·m−2·s−1 of white light from 0600 to 2200. All treatments provided a DLI of 11.5 mol·m−2·day−1 over a 16-h photoperiod. Regardless of cultivar, no treatment difference was measured for hypocotyl length or leaf number. However, plants grown under EOD-blue or PD-white had up to 26% larger leaves than those grown under PD-red and 20% larger leaves than control. In addition, plants grown under EOD-blue produced up to 18% more shoot fresh mass compared to those grown under control, EOD-red, or PD-red. Contrasts for gas-exchange data collected during the main photoperiod showed that light quality was not significant within PD or EOD for any of the parameters evaluated. However, regardless of light quality, stomatal conductance (gs) and transpiration (E) were up to 34% and 42% higher, respectively, for EOD-grown plants compared to control. Our results suggest that 1 h of low intensity EOD-blue light has the potential to promote lettuce growth by increasing leaf area and shoot fresh mass when the main DLI from sole-source lighting is provided by broadband white LEDs. View Full-Text
Keywords: blue light; Lactuca sativa; red light; spectral changes; stomatal conductance blue light; Lactuca sativa; red light; spectral changes; stomatal conductance
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Chinchilla, S.; Izzo, L.G.; van Santen, E.; Gómez, C. Growth and Physiological Responses of Lettuce Grown under Pre-Dawn or End-Of-Day Sole-Source Light-Quality Treatments. Horticulturae 2018, 4, 8.

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