Morphology, growth, and physiological traits of greenhouse cucumber seedlings as affected by supplementary white and blue LEDs

Abstract

Supplemental lighting can be applied in the greenhouse to obtain high-quality seedlings when the solar daily light integral (DLI) is insufficient. However, there is no optimal strategy for the supplementary light provided by white and blue light-emitting diodes (LEDs) with the same DLI in cucumber (Cucumis sativus L.) seedling production grown in the greenhouse in early spring. The objective of the study was to determine changes in morphology, photosynthesis, growth, and physiological characteristics in greenhouse-grown cucumber seedlings (cv. Tianjiao No. 5) depending on different supplementary fractions (28.5%, 33.5%, 38.5%, 43.5%, and 48.5%) of blue light (B) under constant DLI provided by combinations of white (B28.5% included) and blue LEDs, and cucumber seedlings were grown with sunlight only were set as the control. The results documented that supplementary light resulted in compact and robust greenhouse-grown cucumber seedlings with higher chlorophyll content and net photosynthetic rate compared to those grown without supplementary light. The plant height and hypocotyl length of cucumber seedlings decreased quadratically with an increase of blue light fractions provided by combinations of white and blue LEDs. Additionally, the leaf area and stem diameter of cucumber seedlings increased first and a decreased trend was observed subsequently with the increasing fraction of blue light in a quadratic function. Similar trends were found in root architecture (e.g., root length, root surface area, and root volume) and root activity of cucumber seedlings; however, no significant differences were exhibited as blue light fraction increased from 38.5% to 43.5% provided by supplementary light. Stem firmness and cellulose content increased by 26.2% and 23.4%, respectively, as 15% blue light was added to white LEDs. In conclusion, the 43.5% blue light created by supplementary broad-spectrum white and blue LEDs resulted in compact and stoutest cucumber seedlings along with well-developed root system and higher stem firmness, thus improving the mechanical strength of the greenhouse-grown cucumber seedlings for transplanting.

Supplementary White, UV-A, and Far-Red Radiation Differentially Regulates Growth and Nutritional Qualities of Greenhouse Lettuce

“…The chlorophyll content of lettuce grown under supplementary light was significantly higher compared with the control (Figure 1). Similar trends were observed under supplementary lighting in tomato [49] and cucumber seedlings [50] grown under greenhouse conditions. Light intensity and quality can regulate chlorophyll synthesis through a physiological process mediated by phytochromes [51].…”

The Combinations of White, Blue, and UV-A Light Provided by Supplementary Light-Emitting Diodes Promoted the Quality of Greenhouse-Grown Cucumber Seedlings

“…Considering the suitable DLI and supplementary duration [13] for growth of cucumber seedlings, they were grown under supplemental DLI at 6.5 mol m −2 d −1 with a light intensity and photoperiod at 180 µmol m −2 s −1 and 10 h d −1 , respectively, created by white LEDs (W) (Weifang Hengxin Electric Appliance Co., Ltd., Weifang, China), ultraviolet A LEDs (UV-A) (Xiamen Lumigro Technology Co., Ltd., Xiamen, China), the combinations of white and blue LEDs (WB) (Weifang Hengxin Electric Appliance Co., Ltd., Weifang, China), the combinations of white and UV-A LEDs (W-UVA), and the combinations of white, blue, and UV-A LEDs (WB-UVA), respectively. The ratio of combinations of blue and white LEDs and the spectral distribution of the LEDs were applied based on our previous study [37] and the supplemental light intensity of UV-A light was 15 µmol m −2 s −1 . Additionally, cucumber seedlings grown with natural light only was set as the control (DLI at 5.0 mol m −2 d −1 ).…”

“…Our previous study investigated the proper proportion created by white and blue LEDs for growth of greenhouse-grown cucumber seedlings [37]; nevertheless, hardly any studies have reported the influences of supplementary white or white plus blue LEDs combined with UV-A on the leaf morphology, pigment content, photosynthetic traits, biomass accumulation, root architecture, and hormone contents of cucumber seedlings grown in the greenhouse. The results could provide guidelines for the regulation of supplemental light strategies for greenhouse-grown cucumber seedlings produced in winter, early spring, or seasons with insufficient sunlight.…”