Integrating Morphological and Physiological Responses of Tomato Plants to Light Quality to the Crop Level by 3D Modeling

Abstract

Next to its intensity, the spectral composition of light is one of the most important factors affecting plant growth and morphology. The introduction of light emitting diodes (LEDs) offers perspectives to design optimal light spectra for plant production systems. However, knowledge on the effects of light quality on physiological plant processes is still limited. The aim of this study is to determine the effects of six light qualities on growth and plant architecture of young tomato plants, and to upscale these effects to the crop level using a multispectral, functional-structural plant model. Young tomato plants were grown under 210 μmol m^-2 s^-1 blue, green, amber, red, white or red/blue (92%/8%) LED light with a low intensity of sunlight as background. Plants grown under blue light were shorter and developed smaller leaves which were obliquely oriented upward. Leaves grown under blue light contained the highest levels of light harvesting pigments, but when exposed to blue light only, they had the lowest rate of leaf photosynthesis. However, when exposed to white light these leaves had the highest rate of photosynthesis. Under green light, tomato plants were taller and leaves were nearly horizontally oriented, with a high specific leaf area. The open plant structure combined with a high light transmission and reflection at the leaf level allowed green light to penetrate deeper into the canopy. Plants grown under red, amber and white light were comparable with respect to height, leaf area and biomass production. The 3D model simulations indicated that the observed changes in plant architecture had a significant impact on light absorbance at the leaf and crop level. The combination of plant architecture and spectrum dependent photosynthesis was found to result in the highest rate of crop photosynthesis under red light in plants initially grown under green light. These results suggest that dynamic light spectra may offer perspectives to increase growth and production in high value production systems such as greenhouse horticulture and vertical farming.

Keywords: blue light; functional-structural plant model; green light; photomorphogenesis; red light; spectral composition of light.

FIGURE 1

Effect of spectral composition of the light on plant morphology of tomato plants grown under white, red, blue, green, amber and red/blue LED light during 21 days.

FIGURE 2

Effects of spectral composition of the light during 21 days on plant height (A), internode length (B), leaf area (C) and specific leaf area (SLA) of the 6th leaf (D), recorded at the end of the experiments (n = 2, average of 10 plants). Vertical bars indicate the standard error of mean (n = 2). Different letters indicate significant differences (P < 0.05).

FIGURE 3

Effects of spectral composition of the light during 21 days on dry weights of the stem (A), leaves (B) and total plant (C, excluding roots) (n = 2, average of 10 plants). Vertical bars indicate the standard error of mean (n = 2). Different letters indicate significant differences (P < 0.05).

FIGURE 4

Light transmission (A), reflection (B) and absorption (C) of tomato leaves grown under blue, green, amber, red, white, and red/blue light during 21 days (n = 2, average of 4 leaves).

FIGURE 5

Simulated image of the 3D crop where the intensity of the pink color illustrates the light distribution of 95% red and 5% blue LEDs placed directly above the middle row.