TITLE:
The Effect of Supplemental Blue, Red and Far-Red Light on the Growth and the Nutritional Quality of Red and Green Leaf Lettuce
AUTHORS:
Myungjin Lee, Jingwen Xu, Weiqun Wang, C. B. Rajashekar
KEYWORDS:
LEDs, Lettuce, Micronutrients, Nutritional Quality, Phytochemicals, Spectral Quality
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.10 No.12,
December
25,
2019
ABSTRACT: Spectral quality of radiation has a major impact on
the growth, development and nutritional quality of crops. The effect of
supplemental radiation (blue, red and far-red) on the growth and nutritional
quality with regard to health-promoting phytochemical and micronutrient composition of two lettuce (Lactuca sativa) varieties (red leaf “New Red Fire” and green leaf “Two
Star”) was studied. Supplemental radiation was provided by blue (450 nm), red
(660 nm) or far-red (730 nm) LEDs against a background of white light
(fluorescent lighting, PAR; 270 μmol/m2/s) in a growth chamber study. All the supplemental
radiation treatments increased dry shoot biomass in both varieties. However,
supplemental far-red radiation increased both fresh and dry shoot biomass in both
varieties. In addition, supplemental far-red radiation produced distinct
morphological characteristics in lettuce plants. It produced the largest shoot
biomass, bigger and taller plants, fewer leaves but with larger leaf area
compared to the control, similar to the shade avoidance response. With regard
to the accumulation of phytochemicals, supplemental blue radiation enhanced the
total phenolic compound concentration in both varieties. In addition,
supplemental blue radiation sharply increased the accumulation of several
phenolic compounds in green leaf lettuce including chlorogenic acid, chicoric acid, rutin, kaempferol, luteolin and apigenin. For example, the leaf
concentration of rutin in green leaf lettuce increased by 20-fold under
supplemental blue radiation. Similarly, supplemental red radiation increased
the concentration of many of these
phenolic compounds in red leaf lettuce. However, supplemental far-red radiation
had an inhibitory effect on the accumulation of chlorogenic acid, chicoric acid, rutin and kaempferol in red leaf
lettuce. While supplemental radiation did not affect the accumulation of most
of the micronutrients, it had a negative impact on the accumulation of some micronutrients, the response being variety
dependent. The results show that supplementing white light with specific
spectral quality has a major impact on the biomass accumulation, morphology and
on the accumulation of many health-promoting phytochemicals and micronutrients
in lettuce. While it had a large positive effect in enhancing the accumulation
of several phytochemicals, it also suppressed the accumulation of some
micronutrients.