Side Lighting Enhances Morphophysiology by Inducing More Branching and Flowering in Chrysanthemum Grown in Controlled Environment

Abstract

Light is one of the most important factors that influence plant growth and development. This study was conducted to examine how lighting direction affects plant morphophysiology by investigating plant growth parameters, leaf anatomy, epidermal cell elongation, stomatal properties, chloroplast arrangement, and physiological changes. In closed-type plant factory units, the rooted cuttings of two chrysanthemum (Chrysanthemum morifolium Ramat.) cultivars, ‘Gaya Glory’ and ‘Pearl Egg’, were subjected to a 10 h photoperiod with a 300 μmol∙m−2∙s−1 photosynthetic photon flux density (PPFD) provided by light-emitting diodes (LEDs) from three directions relative to the plant including the top, side, and bottom. Compared to the top or bottom lighting, the side lighting greatly enhanced the plant growth, improved the leaf internal structure and chloroplast arrangement, induced small stomata with a higher density, and promoted stomatal opening, which is associated with an increased stomatal conductance and photosynthetic efficiency. It is worth noting that the side lighting significantly enhanced the induction of branching and flowering for both cultivars., The plants grown with side lighting consistently exhibited the greatest physiological performance. We conclude that the lighting direction had a profound effect on the morphophysiological characteristics of chrysanthemum, and that side lighting dramatically promoted their growth and development, especially in their branching and flowering.

Lighting from Top and Side Enhances Photosynthesis and Plant Performance by Improving Light Usage Efficiency

“…The TS lighting increased the carbohydrate and soluble protein levels ( Figure 8 ), which was a result of a combination of splendid stomatal characteristics, excellent chlorophyll concentrations, and prominent light usage efficiency. These conclusions were in general agreement with those in prior studies, that the optimal lighting direction will improve the accumulation of the primary metabolites [ 13 , 14 ].…”

“…Various methods can be considered to improve the electrical energy use efficiency ( Figure 1 ) [ 12 ]. Consistent with our previous study, selecting the optimal lighting position, adjusting for a favorable lighting direction, and controlling the maximum leaf area exposed to light (the boxes marked in red Figure 1 ) enhanced plant performance via increased photosynthesis through a higher light use efficiency [ 13 , 14 ].…”

“…Compared to the other four lighting direction combinations, the TS lighting particularly enhanced branching ( Table 1 ). As was observed in our previous studies, adjusting the lighting direction from bottom and top to the side increased the light use efficiency, which significantly promoted flowering, branching, runner formation, and plant performance in chrysanthemum and strawberry [ 13 , 14 ]. In the present experiment, the chrysanthemums grown with the T lighting received light only from the top, which well-developed the terminal bud of the stem and made it grow preferentially, while the auxin produced was polar-transported to the lateral bud while inhibiting the lateral bud production, which is also known as apical dominance [ 45 ].…”

“…Morphology of the epidermis will be affected by variations in the lighting direction [ 13 , 14 , 39 ]. Plant shoots, especially the leaves, bend toward the light to be able to capture and more efficiently use the available light due to the positive phototropism [ 60 , 61 ].…”

“…However, studies have rarely focused on the influences of changes in the light usage efficiency induced by variations in the lighting direction combination on plant morphophysiology. According to previous studies, lettuces and chrysanthemums adapted to the solo light-direction variation from cellular to the individual level [ 13 , 14 , 39 ]. In this experiment, we investigated how chrysanthemum responds to the various lighting direction combinations to help fine-tune the growth environment for their development.…”