Alternating Red and Blue Light-Emitting Diodes Allows for Injury-Free Tomato Production With Continuous Lighting

Abstract

Plant biomass is largely dictated by the total amount of light intercepted by the plant [daily light integral (DLI) — intensity × photoperiod]. Continuous light (CL, 24 h lighting) has been hypothesized to increase plant biomass and yield if CL does not cause any injury. However, lighting longer than 18 h causes leaf injury in tomato characterized by interveinal chlorosis and yield is no longer increased with further photoperiod extension in tomatoes. Our previous research indicated the response of cucumbers to long photoperiod of lighting varies with light spectrum. Therefore, we set out to examine greenhouse tomato production under supplemental CL using an alternating red (200 µmol m−2 s−1, 06:00–18:00) and blue (50 µmol m−2 s−1, 18:00–06:00) spectrum in comparison to a 12 h supplemental lighting treatment with a red/blue mixture (200 µmol m−2 s−1 red + 50 µmol m−2 s−1 blue, 06:00–18:00) at the same DLI. Our results indicate that tomato plants grown under supplemental CL using the red and blue alternating spectrum were injury-free. Furthermore, parameters related to photosynthetic performance (i.e., Pnmax, quantum yield, and Fv/Fm) were similar between CL and 12 h lighting treatments indicating no detrimental effect of growth under CL. Leaves under CL produced higher net carbon exchange rates (NCER) during the subjective night period (18:00–06:00) compared to plants grown under 12 h lighting. Notably, 53 days into the treatment, leaves grown under CL produced positive NCER values (photosynthesis) during the subjective night period, a period typically associated with respiration. At 53 days into the growth cycle, it is estimated that leaves under CL will accumulate approximately 800 mg C m−2 more than leaves under 12 h lighting over a 24 h period. Leaves grown under CL also displayed similar diurnal patterns in carbohydrates (glucose, fructose, sucrose, and starch) as leaves under 12 h lighting indicating no adverse effects on carbohydrate metabolism under CL. Taken together, this study provides evidence that red and blue spectral alternations during CL allow for injury-free tomato production. We suggest that an alternating spectrum during CL may alleviate the injury typically associated with CL production in tomato.

Producing Enhanced Yield and Nutritional Pigmentation in Lollo Rosso Through Manipulating the Irradiance, Duration, and Periodicity of LEDs in the Visible Region of Light

“…The lower total PPFD in the night break treatment (545 compared to 830 µmol m −2 s −1 ) may allow most incident B photons to be photochemically quenched explaining the high and unaffected F V /F M ' and the low level of NPQ. B light application in the night period was reported to increase carbon export and enhance fruit production (Lanoue et al, 2019), and the night break produced the highest biomass of our diel treatments. The higher percentage of B in the total PPF, 100% in the midnight treatment compared to 75% in PAR LEDs supplemented with B radiation, may explain the greater effectiveness at inducing anthocyanins of the supplemental B night break since anthocyanin content has been reported to increase with the percentage of B (Hernández et al, 2016).…”

Salt stress and fluctuating light have separate effects on photosynthetic acclimation, but interactively affect biomass

“…The photoperiod (16 hr) and daily integral (11.5 mol m −2 d −1 ) of photosynthetic photon flux density (PPFD) were equal between constant irradiance (C, 200 μmol m −2 s −1 ) and fluctuating irradiance (FL, following a sinusoidal pattern during the day and on top of that changing every 5 min in the range of 5–650 μmol m −2 s −1 ; Figure 1). Fluctuations were chosen to be substantial, but not stressful: maximum light intensity was 650 μmol m −2 s −1 , which is typically far from the light saturation point of photosynthesis in tomato leaves (Lanoue et al, 2019; Zhang, Kaiser, Zhang, Yang, & Li, 2019). The FL pattern was repeated daily.…”

Continuous Light Does Not Compromise Growth and Yield in Mini-Cucumber Greenhouse Production with Supplemental LED Light

“…Long photoperiods of lighting have an economic advantage over a short period of lighting in achieving the same DLI with less light fixtures (capital) costs. More recently, the trend towards continuous (24 h) supplemental lighting has received much interest due to the potential for increased yield and its inherent reduction in energy input [ 1 , 2 , 3 , 4 ]. The use of continuous light (CL) theoretically can increase the production as there is constant light energy to drive photosynthesis and carbon assimilation [ 5 ].…”

“…The ability to adequately express CAB-13 throughout a CL period may allow for the hypothesized increase in plant production. More recently, a greenhouse trial using an alternating red and blue light-emitting diode (LED) CL strategy was the first of its kind to show that tomatoes can be grown for a full production season without showing the typical signs of chlorosis associated with CL-injury [ 4 ]. This, along with other studies investigating the role of photoreceptors [ 10 ], has raised the question of what role spectral quality can play in CL tolerance and the adoption of CL strategies for production.…”

“…This is due both to the decrease in vegetative growth [ 20 ] and yield reduction [ 15 ], which occurred when cucumbers were grown under CL. However, based on our recent finding using dynamic spectral changes to eliminate leaf injury on tomatoes [ 4 ], it may be feasible to overcome CL-related injury in greenhouse cucumbers. Therefore, we set out to examine the morphological, physiological, and yield characteristics of mini-cucumber production during CL with wavelength-specific LEDs and its potential as a viable production strategy.…”