Nutritionally Important Pigments in Baby Chinese Kale Are Higher Under Narrow Band LED Light than Under Fluorescent/Incandescent Lighting in Controlled Environments

Narrow-band wavelengths of light from light-emitting diodes (LED) can improve nutritional quality parameters in specialty vegetable crops.  Work by our group has demonstrated the ability to increase brassica microgreen shoot tissue pigments using short and long-term exposure to LED light with higher percentages of blue wavelengths.  The objectives of this study were to measure the impacts of: 1) different percentages of blue LED light; and 2) different levels of nutrient fertility on the concentrations of nutritionally important pigment in Chinese kale (Brassica oleracea var. alboglabra L.) grown to the 30-d baby greens stage.  A comparison of kale pigment responses between incandescent/fluorescent light and LED light was also conducted.  ‘Green Lance’ Chinese kale was grown hydroponically in controlled environments under the light treatments of: 1) fluorescent/incandescent light; 2) 10% blue / 90% red; 3) 20% blue / 80% red; and 4) 40% blue / 60% red wavelengths from LEDs.  The growing air temperature was set at 22 °C with a 16-h photoperiod using a light intensity of 250 µmol·m^-2·sec^-1 for all light treatments.  Plants within light treatments were cultured in either a ½ strength or a ¼ strength Hoagland’s #2 nutrient solution.  Three complete experimental runs were conducted.  All plants were harvested 30 d after seeding and analyzed for nutritionally important shoot pigments.  Kale under the fluorescent/incandescent light treatment had significantly higher shoot fresh and dry mass compared to plants under all other LED light treatments.  Shoot tissue violaxanthin, neoxanthin, antheraxanthin, lutein, beta-carotene, chlorophyll a, and chlorophyll b concentrations were significantly lower under the fluorescent/incandescent light treatment.  Higher fertility levels resulted in higher shoot tissue concentrations for most of these same pigments.  Results from the current study support previous data showing stimulation of nutritionally important shoot tissue pigment concentrations following exposure to higher percentages of blue light wavelengths from LEDs.