Lighting strategies for morphological and physiological characteristics of horticultural crops often focus on the proper daily light integral (DLI); however, a suitable combination of photosynthetic photon flux density (PPFD) and photoperiod at the same DLI is conducive to optimize the light environment management in vegetable seedling production. In the present study, cucumber seedlings ( Cucumis sativus L. cv. Tianjiao No. 5) were grown for 21 days under six different combinations of PPFD and photoperiod at a constant DLI of 11.5 mol⋅m ⁻² ⋅d ⁻¹ , corresponding to a photoperiod of 7, 10, 13, 16, 19, and 22 h⋅d ⁻¹ provided by white light-emitting diodes (LEDs) under a controlled environment. Results showed that plant height, hypocotyl length, and specific leaf area of cucumber seedlings decreased quadratically with increasing photoperiod, and the opposite trend was observed in seedling quality index of cucumber seedlings. In general, pigment content and fresh and dry weight of cucumber seedlings increased as photoperiod increased from 7 to 16 h⋅d ⁻¹ , and no significant differences were found in fresh and dry weight of shoot and root as photoperiod increased from 16 to 22 h⋅d ⁻¹ . Sucrose and starch content of cucumber leaves increased by 50.6% and 32.3%, respectively, as photoperiod extended from 7 to 16 h⋅d ⁻¹ . A longer photoperiod also led to higher cellulose content of cucumber seedlings, thus improving the mechanical strength of cucumber seedlings for transplanting. CsCesA1 relative expression level showed a trend similar to cellulose content. We propose that CsCesA1 is the key gene in the response to cellulose biosynthesis in cucumber seedlings grown under different combinations of PPFD and photoperiod. In summary, prolonging the photoperiod and lowering PPFD at the same DLI increased the quality of cucumber seedlings. An adaptive lighting strategy could be applied to increase seedling quality associated with the reduction of capital cost in cucumber seedling production.

The relatively low light intensity during autumn–winter or early spring and inclement weather such as rain or fog may lead to extended production periods and decreased quality of greenhouse-grown tomato seedlings. To produce high-quality tomato seedlings rapidly, the influences of supplementary lights with different spectra on the morphological and physiological traits of tomato seedlings were measured in a greenhouse. Supplemental lighting with the same daily light integrals (DLI) of 3.6 mol m⁻²d⁻¹ was provided by white (W) light-emitting diodes (LEDs), white plus red (WR) LEDs, and red plus blue (RB) LEDs, respectively, and tomato seedlings grown under only sunlight irradiation were regarded as the control. Our results demonstrate that raised DLI by supplementary light improved the growth and development of greenhouse-grown tomato seedlings, regardless of the spectral composition. Under conditions with the equal DLI, the tomato seedlings grown under supplementary WR LEDs with a red to blue light ratio (R:B ratio) of 1.3 obtained the highest values of the shoot and root fresh weights, net photosynthetic rate, and total chlorophyll content. The best root growth and highest root activity of tomato seedlings were also found under the supplementary WR LEDs. Supplementary WR LEDs remarkably increased the stem firmness of the greenhouse-grown tomato seedlings, and increased the starch content in the leaves of greenhouse-grown tomato seedlings compared to the control. However, statistically significant differences did not occur in the sucrose, carotenoid contents, superoxide dismutase (SOD), and catalase (CAT) activities among the different supplemental lighting treatments. In conclusion, supplemental LED lighting could promote the growth and development of greenhouse-grown tomato seedlings grown under insufficient sunlight conditions. In addition, WR LEDs could obtain tomato seedlings with a higher net photosynthetic rate, higher root activity, and higher starch content compared with other treatments, which could be applied as supplementary lights in greenhouse-grown tomato seedlings grown in seasons with insufficient light.

In this study, gibberellic acid 3 (GA3) and uniconazole were applied as the means of improving of cadmium (Cd) polluted site phytoremediation using maize (Zea mays L.). The results showed that GA3 (40 mg/L), and uniconazole (800 mg/L) could increase the biomass, plant height, stem diameter, leaf area, and root parameters of maize plants under Cd stress (0.4 mg/L) by foliar spraying. GA3 (40 mg/L) could increase the SPAD value of maize leaves by 23.45% and the net photosynthetic rate by 645.93%. Both plant regulators could alleviate the oxidative damage of maize and increase the activity of SOD and POD up to 11.44~58.41% and 35.00~99.55%, respectively. The content of MDA and H2O2 could be reduced by GA3 to 31.91% and 24.77%, respectively. GA3 at 40 mg/L could significantly increase the accumulation of Cd ions in the shoots, roots and whole plants of maize by 222.01%, 603.13% and 341.70%, respectively, showing the best effect among tested treatments. It was found that the application of plant growth regulators (PGRs) could increase the biomass and Cd concentration in maize organs, ultimately achieving the purpose of improving the remediation efficiency of Cd by increasing the absolute content of Cd in maize biomass.

Two eggplant cultivars (Brigitte and Dalong) were stored under ambient conditions for 8 days to examine the postharvest quality and shelf life. Results indicated that the respiration rate, firmness and springiness, and nutritional quality of both eggplant cultivars decreased with the extension of shelf life. On the contrary, opposite trends were observed in weight loss, gumminess, and chewiness of eggplant fruits. In addition, the weight loss of ‘Brigitte’ eggplant fruits was 3.3% and 6.9% lower compared with ‘Dalong’ eggplant fruits at 4 and 8 days after storage. Thicknesses of epidermal cells and the stratum corneum, the epicuticular wax content of ‘Brigitte eggplant fruits increased by 42.9%, 766.7%, and 58.8% compared with ‘Dalong’ eggplant fruits, respectively, with a concomitant increase in the dense wax layer structure. In conclusion, the storage tolerance of ‘Brigitte’ eggplant fruits was higher than that of ‘Dalong’ eggplant fruits due to the higher epicuticular wax content and dense wax layer structure.

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. Keywords: blue light, hypocotyl length, photosynthetic capacity, stem firmness, supplementary light DOI: 10.25165/j.ijabe.20221506.7351 Citation: Yan Z N, Wang L, Cheng J, Lin D, Yang Y J. Morphology, growth, and physiological traits of greenhouse cucumber seedlings as affected by supplementary white and blue LEDs. Int J Agric & Biol Eng, 2022; 15(6): 60–66.