Time-varying Photosynthetic Photon Flux Density and Relative Spectral Photon Flux Density Distribution to Improve Plant Growth and Morphology in Plant Factories with Artificial Lighting

Abstract

In contrast to fluorescent lamps and high-power sodium lamps, the use of light-emitting diode (LED) lamps enables the control of not only photosynthetic photon flux density (PPFD) at the plant level, but also the relative spectral photon flux density distribution (RSPD) of light because of the variety, even at different times of day, of producible light emitted by LEDs of different types. Effects of the spectral photon flux density on plant growth and morphology have been investigated using several types of LEDs and plant species. However, few studies on lighting methods with time-varying PPFD or RSPD have been published to date. In this paper, we summarize the effects of time-varying PPFD on the net photosynthetic rate (P n) and those of time-varying RSPD on plant growth and morphology. Detailed modeling studies have been conducted on the reactions of the photosynthetic pathway under time-varying PPFD at a cycle of milliseconds to seconds. The results of these modeling studies and actual measurements of P n under pulsed light clearly indicate that pulsed light is not advantageous to improve P n. Although the integrated PPFD of blue and red light was unchanged, the growth of leaf lettuce was promoted by asynchronous irradiation with blue light and red light compared with growth under simultaneous irradiation. We think that blue-light monochromatic irradiation promotes leaf elongation through leaf expansion as a primary factor in the enhancement of plant growth. In addition, changes in leaf photosynthetic capacity caused by blue-light monochromatic irradiation may be involved in plant growth promotion. An increasing number of studies have investigated the effects of time-varying RSPD on plants. However, the mechanisms underlying these effects remain to be elucidated.

Varying the time of red light exposure influences leaf resistance to different Botrytis cinerea isolates in strawberry

“…In addition to plant response to biotic stresses, light methods with time-varying light qualities also have prominent effects on promoting plant growth (Jishi & Fujiwara, 2021). Blue light at the beginning of the photoperiod stimulated the growth of spinach with increased mesophyll cell number, and red light at the end of the day promoted spinach growth by increasing the mesophyll cell size (Hanyu & Shoji, 2002;Ohashi-Kaneko et al, 2010).…”

Rerouting Artificial Light for Efficient Crops Production: A Review of Lighting Strategy in PFALs

“…In a plant factory, however, the light environment is insusceptible to natural conditions and can be artificially created. Especially with the rise of light-emitting diodes (LEDs) and the developing of artificial intelligence, the light environment in plant factories can be custom-made from different dimensions [20][21][22][23][24]. Consequently, plenty of lighting modes that are quite different from the conventional ones were designed and their practical effects on crops have been investigated, such as intermittent lighting [25], alternate lighting [26], and continuous lighting [27].…”

LED Illumination for High-Quality High-Yield Crop Growth in Protected Cropping Environments

“…Several light spectra have been trialed for enhancing the yields of vegetables and herbs grown in indoor environments. A common approach has been widely investigated to examine the effects of photosynthetic photon flux density (PPFD) on the LED illumination spectrum [8,9]. The PPFD terminology has been used in the paper to quantify the light quality, as it is defined as the number of photosynthetically active photons that fall on a given plant surface each second (Table 1).…”