Fig 1.
Spectral composition and peak wavelength of light in the two light quality treatments including (a). low percentage of blue (L) and (b). high percentage of blue (H) light. The variable light treatments were created by shifting plants from L to H and vice versa on the 21st day of the experiment and exposing to the new treatment for 10 days.
Fig 2.
Canopy area estimation from plant images.
The RGB and fluorescent images were captured by a camera, A mask was developed from the fluorescent image was used to remove background or segment plant in the RGB image. The plant pixel numbers are counted using the segmented image, pixel area was determined by multiplying total pixels with individual pixel area, and the canopy area was calculated by multiplying total pixel area with a magnification factor.
Fig 3.
Experimental layout showing light fixtures and arrangement of plants in treatments associated with main, first split, and second split plots in a replication.
Fig 4.
Th photosynthetic photon flux density (PPFD) of total, red, and blue light in the two light quality treatments.
The measurements were collected using a spectroradiometer at four different locations. Total PPFD can be visualized by the size of the overall bar. Error bars represent the standard error of the mean of each light quality treatment. Numbers inside the bars indicate percentages of red and blue light in the total light.
Table 1.
Effect of light quality (LQ) and lighting method (LM) on canopy area on day 21 (CA21), total leaf area (LA), biomass per unit area (BMA), and shoot dry weight (SDW) in green romaine lettuce.
Least-square means with standard error of the model (in parenthesis) are shown in the table. Statistical significance of the main and interaction effects of the fitted model is shown below the table. The symbols ‘*’ and ‘**’, indicate P values ≤ 0.05 and 0.005, respectively, and ‘n.s.’ indicates no statistical significance. The least-square means with a different letter are statistically different (Tukey-Kramer procedure).
Fig 5.
Representative green romaine lettuce plants from different light treatments.
(a). low blue or L, (b). low to high blue or LH, (c). high blue or H, and (d). high to low blue or HL.
Table 2.
Effect of light quality (LQ) and lighting method (LM) on the levels of beta-carotene (beta-car) and anthocyanin (antho) in green romaine lettuce.
Least-square means with standard error of the model (in parenthesis) are shown in the table. Statistical significance of main and interaction effects of the fitted model is shown below the table. The symbols ‘*’, ‘**’, and ‘***’ indicate P values ≤ 0.05, 0.005, and 0.0005 respectively, and ‘n.s.’ indicate no statistical significance. The least-square means with a different letter are statistically different (Tukey-Kramer procedure).
Fig 6.
Proposed model for changes in vegetative growth, beta carotene, and anthocyanin in green romaine lettuce exposed to the two variable lighting treatments.
The left panel shows the variable lighting method with a low percentage of blue radiation initially followed by a high percentage of blue radiation during the final growth stage and vice versa for the right panel.
Fig 7.
Representative red romaine lettuce plants from different light treatments.
(a). low blue or L, (b). low to high blue or LH, (c). high blue or H, and (d). high to low blue or HL.
Table 3.
Effect of light quality (LQ) and lighting method (LM) on canopy area on day 21 (CA21), total leaf area (LA), biomass per unit area (BMA), and shoot dry weight (SDW) in red romaine lettuce.
Least-square means with standard error of the model (in parenthesis) are shown in the table. Statistical significance of the main and interaction effects of the fitted model is shown below the table. The symbol ‘*’ and ‘n.s.’ indicate P values ≤ 0.05 and no statistical significance, respectively. In addition, P values close to statistical significance are shown. The least-square means with a different letter are statistically different (Tukey-Kramer procedure).
Table 4.
Effect of light quality (LQ) and lighting method (LM) on the levels of beta-carotene (beta-car) and anthocyanin (antho) in red romaine lettuce.
Least-square means with standard error of the model (in parenthesis) are shown in the table. Statistical significance of the main and interaction effects of the fitted model is shown below the table. The symbol ‘n.s.’ indicates no statistical significance. The least-square means with a same letter are not statistically different based on the Tukey-Kramer procedure.