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

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 (g s) 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.

Spectral effects of blue and red light on growth, anatomy, and physiology of lettuce

“…Similarly, research has shown that plants grown under monochromatic blue light have longer stems (Liu et al 2011, Nanya et al, 2012, Wollaeger & Runkle, 2014, Kong et al, 2018) and may produce less biomass than those grown under blue‐enriched light supplemented with other wavebands (Hernández et al, 2016; Hernández & Kubota, 2016). However, when used as part of dynamic spectral lighting within a 24‐h period (Chinchilla et al, 2018; Jishi et al, 2016) or during the cropping cycle (H. Spalholz 2019. Thesis, North Carolina State University, Raleigh, NC, USA), monochromatic blue light has been shown to promote lettuce growth by increasing leaf area expansion.…”

Plant Production in Controlled Environments

“…The goal has been to use less electrical energy to achieve the same yield and quality. In this special issue, Chinchilla et al [2] evaluated growth and physiological responses of two lettuce cultivars exposed to small changes in light quality and intensity within a 24-h period. They found that 1 h of low intensity end-of-day 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.…”

“…With the advancement of LED technologies, customized light spectra have been made possible. Thus, manipulating light quality (or the spectrum) and light intensity to enhance plant growth and quality has become one of the most popular research fields in recent years, and this special issue has three articles on this subject [1][2][3].…”

Lettuce growth promoted by artificial lighting using light-emitting diodes (LED)

“…In addition, LED lamps have technical advantages over conventional artificial lighting sources such as HPS (High Pressure Sodium Lamp) lamps. A useful feature of LEDs is their inherent ability to provide spectral control with luminous flux customization, which allows plant photoreceptors to perceive light signals that can control morphology and improve product quality (CHINCHILLA et al, 2018).…”