2018 ASHS Annual Conference
Growth and Physiological Responses of Lettuce Grown Under Pre-Dawn or End-of-Day Sole-Source Light-Quality Treatments
Growth and Physiological Responses of Lettuce Grown Under Pre-Dawn or End-of-Day Sole-Source Light-Quality Treatments
Wednesday, August 1, 2018
International Ballroom East/Center (Washington Hilton)
In order to understand the physiological factors that drive plant responses to spectral changes over time, the objective of this study was to evaluate growth and gas-exchange of ‘Cherokee’ and ‘Waldmann’s Green’ lettuce (Lactuca sativa) treated with light-quality changes within a 24-hour period. Three pre-dawn (PD; 0600 to 0700 HR) and three end-of-day (EOD; 2100 to 2200 HR) treatments were evaluated in the study, each providing 50 ± 2 µmol·m‒2·s‒1 of either blue, red, or white light from light-emitting diodes (LEDs). To account for the main daily light integral (DLI), white LEDs provided 210 ± 2 µmol·m‒2·s‒1 from 0700 to 2200 HR or from 0600 to 2100 HR 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 HR. All treatments provided a DLI of 11.5 mol·m‒2·d‒1 a 17-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 (FM) 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 potential to promote lettuce growth by increasing leaf area and FM when the main DLI from sole-source lighting is provided by white light. Furthermore, they indicate that regardless of light-quality, short-term exposure to EOD-light stimulates higher gs and E during the day, which may increase the photosynthetic efficiency of plants during the light period.