Adding Far-Red to Red-Blue Light-Emitting Diode Light Promotes Yield of Lettuce at Different Planting Densities

Abstract

The economic viability and energy use of vertical farms strongly depend on the efficiency of the use of light. Increasing far-red radiation (FR, 700–800 nm) relative to photosynthetically active radiation (PAR, 400–700 nm) may induce shade avoidance responses including stem elongation and leaf expansion, which would benefit light interception, and FR might even be photosynthetically active when used in combination with PAR. The aims of this study are to investigate the interaction between FR and planting density and to quantify the underlying components of the FR effects on growth. Lettuce (Lactuca sativa cv. Expertise RZ) was grown in a climate chamber under two FR treatments (0 or 52 μmol m–2 s–1) and three planting densities (23, 37, and 51 plants m–2). PAR of 89% red and 11% blue was kept at 218 μmol m–2 s–1. Adding FR increased plant dry weight after 4 weeks by 46–77% (largest effect at lowest planting density) and leaf area by 58–75% (largest effect at middle planting density). Radiation use efficiency (RUE: plant dry weight per unit of incident radiation, 400–800 nm) increased by 17–42% and incident light use efficiency (LUEinc: plant dry weight per unit of incident PAR, 400–700 nm) increased by 46–77% by adding FR; the largest FR effects were observed at the lowest planting density. Intercepted light use efficiency (LUEint: plant dry weight per unit of intercepted PAR) increased by adding FR (8–23%). Neither specific leaf area nor net leaf photosynthetic rate was influenced by FR. We conclude that supplemental FR increased plant biomass production mainly by faster leaf area expansion, which increased light interception. The effects of FR on plant dry weight are stronger at low than at high planting density. Additionally, an increased LUEint may contribute to the increased biomass production.

Combined Effect of Salinity and LED Lights on the Yield and Quality of Purslane (Portulaca oleracea L.) Microgreens

“…In our experiment, the addition of FR to the spectrum did not result in a yield increase. However, Jin et al [30] showed an increase in shoot weight when FR radiation was added to B+R radiation in lettuce 28 days after transplanting and Meng and Runkle [31] in lettuce and basil seedlings, a phenomenon that could be associated with faster leaf area expansion, which would ultimately result in increased light interception [30]. Possibly, in the current experiment, given that microgreens are harvested at early stage, the beneficial effects on leaf elongation induced by FR radiation were negligible, and therefore did not allow for increased light interception.…”

Solar Radiation Effects on Dry Matter Accumulations and Transfer in Maize

“…Also, assimilates in the vegetative organs gradually move to the grain in the late growth stage (Yang et al, 1997 ; Ma et al, 2008 ; Gao et al, 2017 ). Modern maize grain yield improvements are highly dependent on increasing plant density while enabling the plants to intercept more solar radiation (Liu et al, 2017 , 2021c ; Hou et al, 2020 ), and planting density affects light quality and other environmental factors that influence the yield as well (Jin et al, 2020 ). Also, planting density has important effects on maize dry matter partitioning between vegetative and reproductive organs (Wei et al, 2019 ), as planting density increases, the numbers of vegetative organs increase while that of reproductive organs decrease (Liu et al, 2011 ).…”

LED versus HPS Lighting: Effects on Water and Energy Consumption and Yield Quality in Lettuce Greenhouse Production

“…It could also be possible that the application period was too short, as longer tomato experiments with the same experimental setup as described in our study resulted in a higher light use efficiency and higher yields in favor of the LED treatment [13]. Other research groups added far-red with an intensity of 52 µmol m −2 s −1 [28] or 26 µmol m −2 s −1 [29] to red-blue LEDs, which increased the plant biomass production of lettuce. The far-red radiation caused by the new LED fixture in the present study (4 µmol m −2 s −1 ) was not sufficient to achieve the same effects.…”