Abstract
Tomato and cucumber seedlings were grown in a growth chamber to evaluate the effects of different cycles of light–dark exposure conditions (T0 (control treatment) (1 cycle of 24 h distributed in 18 h of light exposure and six hours of dark), T1 (two cycles of 12 h distributed in nine hours of light exposure and three hours of dark) and T2 (three cycles of eight hours distributed in six hours of light exposure and two hours of dark) on growth, nutrient status, pigment concentration and physiological changes. Total dry weight showed different behaviors in both species, since in tomato the total dry weight remained unchanged under varying light–dark cycles, whereas in cucumber seedlings there was a clear decrease compared to the control treatment. In both species, plants grown under T2 showed the best water content. Nitrogen, P and K content—as well as partitioning in the different organs of the plants—displayed different patterns under varying cycles of light–dark conditions in both species. Chlorophyll (b and a + b) concentration decreased significantly in both species in T1 and T2 compared to the control treatment (T0). At physiological level, the concentration of total soluble sugars and proline in leaf showed the highest value in the control treatment with 18 h of light and six hours of dark.
Highlights
Light is one of the most important environmental regulators for the growth of crop species since it provides essential energy input and triggers various signaling pathways for the dynamic growth regulation of crops [1].Nowadays, the production of horticultural seedlings in southern Spain totals around 1,800,000,000 seedling plants
In the case of cucumber seedlings, no variation in phosphorus content between treatments can be ascribed to a non-relationship between changes in circadian rhythms and phosphorous uptake capacity being not in line with the findings reported by Versaw et al [43] who reported the presence of one phosphate transporter enhanced by cyrcadian rhythms in Arabidopsis thaliana plants
The consequent decrease of leaf proline concentration in both species under increasing cycles may be ascribed to the fact that changes in the circadian clock can result changes in proline synthesis as reported by Hayashi et al [54]. The results of this experiment show that the increasing cycles of light–dark conditions led to no variations in fresh and dry weight in tomato seedlings, they showed higher size, but reduced shoot diameter
Summary
Light is one of the most important environmental regulators for the growth of crop species since it provides essential energy input and triggers various signaling pathways for the dynamic growth regulation of crops [1]. The production of horticultural seedlings in southern Spain totals around 1,800,000,000 seedling plants. Supplementary artificial lighting has been considered as economically practical since it allows growers to improve profits, mainly due to a faster development and quality of plants, improving their sales [2]. A wide variety of lamps have been used to increase the yields. Growth improvements have been obtained by using lamps to increase the irradiance received by the crop. Fluorescent lamps (FL) and high intensity discharge (HID) lamps (e.g., high-pressure sodium (HPS))
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