Effects of supplemental lighting to a lower leaf using light-emitting diodes with different spectra on the leaf photosynthetic rate in sweet pepper

Abstract

Intracanopy lighting (IL) is a newly proposed supplemental lighting technique, irradiating lower leaves of plants from light sources placed between plant stands in high-wire grown vegetable production in a greenhouse. Light-emitting diodes (LEDs) are an appropriate light source for IL because of their compactness and low operating temperatures. To take advantage of features of LEDs, which emit light with a narrow band of wavelengths, we investigated short-term effects of spectra on instantaneous photosynthesis and long-term effects on a decrease in photosynthesis during the senescence of irradiated lower leaves of chamber-grown sweet pepper plants. First, the instantaneous photosynthetic rate of each plant's fifth leaf was measured under white and monochromatic blue, green and red LED lights at a photosynthetic photon flux density (PPFD) of 150 µmol m -2 s -1 . We confirmed that the rate was low under green light. Second, we grew plants for five weeks in five treatments: four treatments with the fifth leaves irradiated with white, blue, green and red LEDs at a PPFD of 150 µmol m -2 s -1 , and one treatment without irradiation. After the treatments, photosynthetic rates of the irradiated leaves were measured to investigate the long-term effects. Measurements were performed at PPFDs of 300 and 1500 µmol m -2 s -1 with red and blue LEDs, irrespective of the treatments. The lighting treatments seemed to retard the decreases in photosynthetic rates irrespective of the spectra, but stomatal conductance (g s ) of the leaves grown under green light tended to be low compared to those measured under the other colors. In addition to the lower instantaneous photosynthesis, green light might have less enhancing effects on the photosynthesis of the irradiated leaves from the viewpoint of long-term effects. Based on these results, we concluded that green LEDs are not appropriate as an IL light source from the viewpoint of single-leaf photosynthesis.

Interaction between the spectral photon flux density distributions of light during growth and for measurements in net photosynthetic rates of cucumber leaves

“…the responses of P n to changes in PFD and/or C i ). Several studies have reported that the SPD of the ML affected the P n of leaves (McCree , Inada , Hogewoning et al , Murakami et al ). To eliminate this direct effect, measurements of photosynthetic parameters should be made under identical SPD conditions, irrespective of the SPD of GL.…”

LED Lighting: A Grower’s Guide to Light Spectra

“…Fluctuating light and shade-flecks due to shading from the upper canopy have been associated with reduced growth (Kaiser et al 2018;; however, the addition of intracanopy lighting can improve light distribution throughout the canopy (Frantz et al 2000;Pettersen et al 2010), increasing photosynthesis in lower leaves that would otherwise present a significant metabolic burden for the plant (Frantz et al 2000). It should be noted that any increases in photosynthesis by intracanopy lighting remain sensitive to the choice of light spectrum (Murakami et al 2013), and fine-tuning of light spectra may affect rates of photosynthesis more than morphology and fruit yield (G omez and Mitchell 2016b). Although intracanopy lighting is another tool for light spectrum-based manipulation of plant morphology and performance, we note that evidence of impact remains ambiguous.…”

Effect of Light Treatment and Maturity Stage on Biomass Production and Bioactive Compounds of Two Pepper Cultivars under a Deep Water Culture Hydroponic System

“…Light has an impact on plant physiology, flowering, secondary metabolite accumulation, nutrient transport and plant quality [14][15][16][17][18][19]. Different light spectra can influence the processes of plant part growth.…”