Abstract
Light is essential for plant growth. Light intensity, photoperiod, and light quality all affect plant morphology and physiology. Compared to light intensity, photoperiod, little is known about the effects of different monochromatic lights on crop species. To investigate how different lighting conditions influence crops with heterogeneous colors in leaves, we examined photosynthetic characteristics and quality (regarding edibility and nutrition) of purple cabbage under different combinations of lights. Eight different treatments were applied including monochromic red (R), monochromic blue (B), monochromic yellow (Y), monochromic green (G), and the combination of red and blue (3/1, RB), red/blue/yellow (3/1/1, RBY), red/blue/green (3/1/1,RBG), and white light as the control. Our results indicate that RBY (3/1/1) treatment promotes the PSII activity of purple cabbage, resulting in improved light energy utilization. By contrast, both G and Y lights alone have inhibitory effect on the PSII activity of purple cabbage. In addition, RBY (3/1/1) significantly boosts the anthocyanin and flavonoids content compared with other treatments. Although we detected highest soluble protein and vitamin C content under B treatment (increased by 30.0 and 14.3% compared with the control, respectively), RBY (3/1/1) appeared to be the second-best lighting condition (with soluble protein and vitamin C content increased by 8.6 and 4.1%, respectively compared with the control). Thus we prove that the addition of yellow light to the traditional combination of red/blue lighting conditions is beneficial to synthesizing photosynthetic pigments and enables superior outcome of purple cabbage growth. Our results indicate that the growth and nutritional quality of purple cabbage are greatly enhanced under RBY (3/1/1) light, and suggest that strategical management of lighting conditions holds promise in maximizing the economic efficiency of plant production and food quality of vegetables grown in controlled environments.
Highlights
Light is one of the most important environment regulators for the growth of crop species
Our results suggested that blue light was beneficial for production of soluble protein and vitamin C in purple cabbage
Photosynthetic rate is the parameter reflecting the ability of plants to use light, to fix CO2 and to produce photosynthetic product
Summary
Light is one of the most important environment regulators for the growth of crop species. It provides essential energy input and triggers various signaling pathways for dynamic growth regulation of crops. The light refers to white light, which is a mixture of a wide range of different wavelengths (colors). There is controversy about the optimal ratio between the R and B in different backgrounds. It was reported that plantlets of strawberry and rapeseed, as well as cucumber seedlings gained highest fresh and dry weight with 7/3 ratio of B/R (Nhut et al, 2003), while other research showed that the optimal ratio is 1/3 (Li et al, 2013) and 9 (Hernandez and Kubota, 2016)
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