Supplemental Light-Emitting Diode Inter-Lighting Increases Tomato Fruit Growth Through Enhanced Photosynthetic Light Use Efficiency and Modulated Root Activity

Abstract

We investigated the effect of supplemental LED inter-lighting (80% red, 20% blue; 70 W m −2 ; light period 04:00-22:00) on the productivity and physiological traits of tomato plants (Flavance F1) grown in an industrial greenhouse with high pressure sodium (HPS) lamps (235 W m −2 , 420 µmol m −2 s −1 at canopy). Physiological trait measurements included diurnal photosynthesis and fruit relative growth rates, fruit weight at specific positions in the truss, root pressure, xylem sap hormone and ion compositions, and fruit quality. In the control treatment with HPS lamps alone, the ratio of far-red to red light (FR:R) was 1.2 at the top of the canopy and increased to 5.4 at the bottom. The supplemental LED interlighting decreased the FR:R ratio at the middle and low positions in the canopy and was associated with greener leaves and higher photosynthetic light use efficiency (PLUE) in the leaves in the lower canopy. The use of LED inter-lighting increased the biomass and yield by increasing the fruit weight and enhancing plant growth. The PLUE of plants receiving supplemental LED light decreased at the end of the light period, indicating that photosynthesis of the supplemented plants at the end of the day might be limited by sink capacity. The supplemental LED lighting increased the size of fruits in the middle and distal positions of the truss, resulting in a more even size for each fruit in the truss. Diurnal analysis of fruit growth showed that fruits grew more quickly during the night on the plants receiving LED light than on unsupplemented control plants. This faster fruit growth during the night was related to an increased root pressure. The LED treatment also increased the xylem levels of the phytohormone jasmonate. Supplemental LED inter-lighting increased tomato fruit weight without affecting the total soluble solid contents in fruits by increasing the total assimilates available for fruit growth and by enhancing root activity through an increase in root pressure and water supply to support fruit growth during the night.

Supplemental LED Increases Tomato Yield in Mediterranean Semi-Closed Greenhouse

“…However, during the period that SL was switched on, the DLI under LEDs was in the optimal range for tomato crops [23,25], while the plants grown under NL had less light compared to optimal conditions ( Figure 1). The DLI obtained under LEDs was a great result when compared with Northern European countries, such as Norway (58 • 42 49.2" N 5 • 31 51.0" E), where from October to February, the natural DLI in the greenhouse is always under 10 mol m −2 d −1 and it never reaches 25 mol m −2 d −1 with LED SL [27]. In detail, considering a tomato cycle from September to march, the total light integral (TLI) of natural light in the greenhouse in Norwegian conditions is around 1040 mol m −2 [25], while at the latitude in our study, TLI was almost 3 times higher (Figure 1).…”

Increase of Yield, Lycopene, and Lutein Content in Tomatoes Grown Under Continuous PAR Spectrum LED Lighting

“…Although the role of carotenoids in photosynthesis is well appreciated, wavelengths other than red and blue had rarely been used in academic studies on the effect of LED lightings in tomato production. Consequently, there is a lot of information about the effect of red and blue light used as overhead-lighting, interlighting or hybrid-lighting (LEDs + HPS) on plant growth and yield of tomatoes (Dueck et al, 2011;Hogewoning et al, 2012;Gajc-Wolska et al, 2013;Gomez et al, 2013;Deram et al, 2014;Gómez and Mitchell, 2015;Tewolde et al, 2016;Gilli et al, 2018;Lanoue et al, 2019;Paponov et al, 2019). These studies showed that photosynthesis under a combination of red and blue light tends to be higher than under HPS lighting, but fruit yield is equal.…”

Effects of Supplemental Lighting on Potassium Transport and Fruit Coloring of Tomatoes Grown in Hydroponics

“…The use of supplemental lighting increased the biomass and yield of tomatoes by increasing the fruit weight and enhancing plant growth [ 4 ]. In this study, the K accumulation, biomass, and yield of tomatoes were all increased by SL at both K supply levels ( Figure 1 A,C), and the increase percentage was higher in red SL or red combined blue SL than in blue SL.…”

“…K uptake by the cells of the root to shoot via the vessels was linearly related to water flux [ 35 ]. A recent study demonstrated that supplemental LED lighting increased tomato fruit growth through modulated root pressure [ 4 ]. In this study, the K uptake was higher under red SL during fruit development, but it was higher under blue SL than red SL during fruit ripening ( Figure 3 B).…”

“…In recent years, supplemental LED lighting (SL) has been used as an efficient light source to meet the demand for high irradiance during plant growth and fruit development and to maintain the productivity of greenhouse tomatoes, particularly during the low irradiance seasons [ 2 , 3 , 4 , 5 , 6 ]. We accelerated the tomato fruit coloring process, and promoted lycopene synthesis in tomato fruits by applying supplemental blue or/and red light during winter to early-spring growing seasons [ 7 ].…”