Effects of Continuous or End-of-Day Far-Red Light on Tomato Plant Growth, Morphology, Light Absorption, and Fruit Production

Abstract

Shading by sunlit leaves causes a low red (R) to far-red (FR) ratio that results in a low phytochrome stationary state (PSS). A low PSS induces an array of shade avoidance responses that influence plant architecture and development. It has often been suggested that this architectural response is advantageous for plant growth due to its positive effect on light interception. In contrast to sunlight, artificial light sources such as LEDs often lack FR, resulting in a PSS value higher than solar light (∼0.70). The aim of this study was to investigate how PSS values higher than solar radiation influence the growth and development of tomato plants. Additionally, we investigated whether a short period of FR at the end of the day (EOD-FR) could counteract any potentially negative effects caused by a lack of FR during the day. Tomato plants were grown at four PSS levels (0.70, 0.73, 0.80, and 0.88), or with a 15-min end-of-day far-red (EOD-FR) application (PSS 0.10). Photosynthetic Active Radiation (PAR; 150 μmol m -2 s -1 ) was supplied using red and blue (95/5%) LEDs. In an additional experiment, the same treatments were applied to plants receiving supplementary low-intensity solar light. Increasing PSS above solar PSS resulted in increased plant height. Leaf area and plant dry mass were lower in the treatments completely lacking FR than treatments with FR. EOD-FR-treated plants responded almost similarly to plants grown without FR, except for plant height, which was increased. Simulations with a 3D-model for light absorption revealed that the increase in dry mass was mainly related to an increase in light absorption due to a higher total leaf area. Increased petiole angle and internode length had a negative influence on total light absorption. Additionally, the treatments without FR and the EOD-FR showed strongly reduced fruit production due to reduced fruit growth associated with reduced source strength and delayed flowering. We conclude that growing tomato plants under artificial light without FR during the light period causes a range of inverse shade avoidance responses, which result in reduced plant source strength and reduced fruit production, which cannot be compensated by a simple EOD-FR treatment.

Substituting Far-Red for Traditionally Defined Photosynthetic Photons Results in Equal Canopy Quantum Yield for CO2 Fixation and Increased Photon Capture During Long-Term Studies: Implications for Re-Defining PAR

“…This difference between short-term and long-term responses indicates that the efficiency of light utilization for photosynthesis may have acclimated to far-red radiation during long-term growth. Possible changes include modifications in leaf thickness, chlorophyll content (Table 1), chl a:b ratio (Gommers et al, 2013;Kalaitzoglou et al, 2019), PSI:PSII ratio, electron transport and photosynthetic capacity, rubisco content and activity (Chow et al, 1990a;Chow et al, 1990b;Anderson et al, 1995), as well as in the biosynthesis of photoprotective pigments carotenoids and anthocyanins (Li and Kubota, 2009;Stutte et al, 2009;Kalaitzoglou et al, 2019).…”

“…Perhaps the most powerful effect is the simulation of shade through FR supplementation, often without reducing light intensity in the PAR region. This change has been reported to promote leaf expansion in various leafy greens, fruiting vegetables, and ornamental species, which increases growth primarily through increased radiation capture (Casal et al, 1987;Goins et al, 2001;Li and Kubota, 2009;Stutte et al, 2009;Park and Runkle, 2017;Kalaitzoglou et al, 2019).…”

Morphophysiological responses of tomato phytochrome mutants under sun and shade conditions

“…As for the light quality, low R-to-FR ratios increased the accumulation of biomass into the stems at the expense of leaves. However, fruit production was improved under these light conditions possibly due to a positive impact on flowering acceleration (Kalaitzoglou et al 2019).…”

The role of far-red light (FR) in photomorphogenesis and its use in greenhouse plant production

“…Apart from plant morphological alterations, changes in the R : FR ratio also lead to the redistribution of growth and dry matter within the plants, as indicated by an increased shoot/root ratio and soluble sugar levels under radiation with a low R : FR ratio. Kalaitzoglou et al (2019) reported that additional FR light applied as continuous and EOD treatment increased total dry mass of tomato plants in the vegetative growth stage, as well as the fruit number per plant, fresh fruit weight per plant and average fruit fresh mass. Similarly, higher total plant dry mass and higher fruit yield in tomato grown under additional FR radiation were reported by Zhang et al (2019b).…”