Abstract
The spectrum of light significantly influences the growth of plants cultivated in closed systems. Five lettuce cultivars with different leaf colours were grown under white light (W, 170 μmol m−2 s−1) and under white light with the addition of red (W + R) or blue light (W + B) (230 μmol m−2 s−1). The plants were grown until they reached the seedling phase (30 days). Each cultivar reacted differently to the light spectrum applied. The red-leaved cultivar exhibited the strongest plasticity in response to the spectrum. The blue light stimulated the growth of the leaf surface in all the plants. The red light negatively influenced the length of leaves in the cultivars, but it positively affected their number in red and dark-green lettuce. It also increased the relative chlorophyll content and fresh weight gain in the cultivars containing anthocyanins. When the cultivars were grown under white light, they had longer leaves and higher value of the leaf shape index. The light-green cultivars had a greater fresh weight. Both the addition of blue and red light significantly increased the relative chlorophyll content in the dark-green cultivar. The spectrum enhanced with blue light had positive influence on most of the parameters under analysis in butter lettuce cultivars. These cultivars were also characterised by the highest absorbance of blue light.
Highlights
Artificial lighting is one of the main parameters of cultivation, which significantly affects the growth and quality of plants cultivated in closed systems, controlled environment agriculture (CEA) or vertical farms
Naznin et al [3] observed that coriander plants cultured under different ratios of red to blue light from light-emitting diodes (LEDs) had higher content of fresh and dry matter than the plants cultured under 100% red light
Some authors observed the highest fresh weight of lettuce under dominant R light [21,26]. These differences in the results show that lettuce exhibits high plasticity and sensitivity to the applied spectral composition of light
Summary
Artificial lighting is one of the main parameters of cultivation, which significantly affects the growth and quality of plants cultivated in closed systems, controlled environment agriculture (CEA) or vertical farms. A combination of red and blue light from LEDs proved to effectively stimulate the growth of various plant species, including lettuce, in controlled environments [4,5]. Schwalb et al [6] studied the effect of different ratios of red (660 nm) and blue (435 nm) light from LEDs on the photosynthesis of lettuce and petunia seedlings grown with and without background broadband high-pressure sodium radiation. They observed that the optimum photosynthesis occurred when lettuce was grown within a red-to-blue ratio of 5:1–15:1. This means that plant development and physiology is strongly influenced by blue or red light [8]
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