The Power of Far-Red Light at Night: Photomorphogenic, Physiological, and Yield Response in Pepper During Dynamic 24 Hour Lighting

Abstract

Supplemental light is needed during the winter months in high latitude regions to achieve the desired daily light integral (DLI) (photoperiod × intensity) for greenhouse pepper (Capsicum annuum) production. Peppers tend to have short internodes causing fruit stacking and higher labor time for plant maintenance when grown under supplemental light. Far-red light can increase internode length, and our previous study on tomatoes (Solanum lycopersicum) also discovered monochromatic blue light at night during continuous lighting (CL, 24 h) increased stem elongation. Furthermore, the use of low-intensity, long photoperiod lighting can reduce light fixture costs and overall electricity costs due to lower power prices during the night. Therefore, we investigated the use of blue and/or far-red light during the night period of CL to increase stem elongation. Three pepper cultivars with different internode lengths/growing characteristics (‘Maureno,’ ‘Gina,’ and ‘Eurix’) were used to investigate the effects on plant morphology in a short experiment, and one cultivar ‘Maureno’ was used in a long experiment to assess the impact on fruit yield. The five lighting treatments that were used are as follows: 16 h of white light during the day followed by either 8 h of darkness (16W – control), white light (24W), blue light only (16W + 8B), blue + far-red light (16W + 8BFR), or far-red light only (16W + 8FR). Calculated nighttime phytochrome photostationary state (PSS) was 0.833, 0.566, 0.315, and 0.186 for 24W, 16W + 8B, 16W + 8BFR, and 16W + 8FR respectively. All five treatments had the same DLI in photosynthetically active radiation (PAR) and far-red light. The 16W + 8BFR and 16W + 8FR treatments significantly increased internode length compared to 16W and 24W but neither was more impactful than the other. The 16W + 8B treatment also increased internode length but to a lesser extent than 16W + 8BFR and 16W + 8FR. This indicates that a nighttime PSS of 0.315 is sufficient to maximize stem elongation. Both 16W + 8B and 16W + 8BFR drove photosynthesis during the nighttime supporting a similar yield compared to 16W. Therefore, 16W + 8BFR is the most potential lighting strategy as it can lead to a greater reduction in the light fixture and electrical costs while maintaining yield and enhancing internode length.

LED Lighting: A Grower’s Guide to Light Spectra

“…FR has been associated with increased shoot weight and leaf expansion in seedlings and harvest yields of basil and lettuce (Jin et al 2021;. For fruiting plants, while FR increased the partitioning of dry weight into the stem and thus led to taller plants in both tomato and pepper (C. annuum), a higher fruit mass was also reported in tomato (Brown et al 1995;Kalaitzoglou et al 2019;Kim et al 2019a;Lanoue et al 2022). Although FR showed little effect on pepper fruit yield, it did induce longer internode length, which may prevent deformation of fruit shape (Lanoue et al 2022).…”

“…For fruiting plants, while FR increased the partitioning of dry weight into the stem and thus led to taller plants in both tomato and pepper (C. annuum), a higher fruit mass was also reported in tomato (Brown et al 1995;Kalaitzoglou et al 2019;Kim et al 2019a;Lanoue et al 2022). Although FR showed little effect on pepper fruit yield, it did induce longer internode length, which may prevent deformation of fruit shape (Lanoue et al 2022). FR also interacts with the daily light integral (DLI), influencing the Table 2.…”

Continuous lighting can improve yield and reduce energy costs while increasing or maintaining nutritional contents of microgreens

“…Even in collard greens and purple basil, the use of reduced electrical prices during the night lowered electricity cost in 24h treatments making them more cost effective than their 16h counterparts (Table 6). The microgreens studied here join a growing list of plants which can tolerate CL including other microgreen species (Shibaeva et al, 2022b), lettuces (Ohtake et al, 2018), cucumbers (Lanoue et al, 2021b), peppers (Lanoue et al, 2022), and tomatoes (Haque et al, 2017;Lanoue et al, 2019).…”

“…Specifically, since the plant is under constant light, it seems that components of the light harvesting complex are negatively affected causing reduced transcription leading to inadequate use and/or dissipation of light (Velez-Ramirez et al, 2014). More recent research in these two crops have provided evidence that dynamic CL, which involves a change in light spectrum between daytime and nighttime, can result in injury-free production (Lanoue et al, 2019;Lanoue et al, 2022). Some cultivars of lettuces and some members of the Brassicaceae microgreen family have also been shown to have positive interactions with CL (Ohtake et al, 2018;Shibaeva et al, 2022b).…”

Tomato and mini-cucumber tolerance to photoperiodic injury involves photorespiration and the engagement of nighttime cyclic electron flow from dynamic LEDs

“…Therefore, there is an upper limit on how much far-red can be added in a photoperiod, necessitating the reliance on EOD far-red to counteract most of the blue light plus extended photoperiod induced morphological responses. An example of this was found in greenhouse pepper, which becomes overly compact under continuous light but was completely alleviated if far-red was added to the nighttime phase of the alternating LED spectrum ( Lanoue et al., 2022 ). These considerations informed the implementation of far-red in addition to dim-blue during the nighttime spectra.…”