Abstract
Nasturtium (Tropaeolum majus L.), as a medicinal plant, has a high phenolic content in its leaves and flowers. It is often used in salads as a dietary vegetable. Attracting strong demand, it could be a good candidate crop for a plant factory with artificial lighting (PFAL) that can achieve the mass production of high-quality crops with high productivity by regulating environmental conditions such as light. In this study, two experiments were conducted to investigate the effects of continuous lighting (CL) and different daily light integrals (DLIs) under CL on the growth, secondary metabolites, and light use efficiency (LUE) of nasturtium, all of which are essential in the successful cultivation in PFALs. In Experiment 1, two lighting models, the same DLI of 17.3 mol m−2 d−1 but different light periods (24 and 16 h) with different light intensities (200 and 300 µmol m−2 s−1, respectively), were applied to nasturtium. The results showed that leaf production, secondary metabolites, and LUE were higher under the 24-h CL treatment than under the 16-h non-CL treatment. In Experiment 2, three DLI levels (17.3, 25.9, and 34.6 mol m−2 d−1) under the CL condition were applied. The results showed that the growth parameters were positively correlated with the DLI levels under CL. The lowest DLI had the highest LUE. We conclude that the mass production of nasturtium under CL in PFALs is feasible, and the yield increases as DLI increases from 17.3 to 34.6 mol m−2 d−1 under CL without causing physiological stress on plants.
Highlights
Nasturtium (Tropaeolum majus L.) is a medicinal plant, and its leaves and flowers are rich in health-beneficial ingredients such as polyphenols and glucosinolates
During the earlier growth stages of the first and the second weeks, the mean levels of the growth parameters were unanimously higher for T24-200 than for T16-300, with all the mean differences that were statistically significant, while, at the end of the third week, there was no significant mean differences found for all the growth parameters, except for the dry masses of the leaves and shoots
This study found that nasturtium grown under continuous lighting (CL) (T24-200) attained a heavier plant biomass and faster relative growth rate (RGR) compared to the plant grown under 16 h (T16-300) (Figure 2 and Table 2), without causing any physiological leaf injuries (Fv/Fmax > 0.8; Table 2)
Summary
Nasturtium (Tropaeolum majus L.) is a medicinal plant, and its leaves and flowers are rich in health-beneficial ingredients such as polyphenols and glucosinolates. The demand for nasturtium leaves and flowers increases rapidly, and the technology development for mass production in a plant factory has become important [1]. A positive linear relationship between the DLI and leaf fresh weight (FW) of hydroponic lettuce was observed by increasing the DLI from 6.48 to 17.28 mol m−2 d−1, provided by LED lamps [2]. Their results indicated that the leaf FW of lettuce slightly decreased when the DLI increased from
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