Figure 1.
Average daytime and nighttime environmental conditions in the greenhouse during the cultivation period. (A) Mean day and night temperatures (°C). (B) Instantaneous light intensity (lux) inside and outside the greenhouse.
Figure 2.
Effects of supplemental UV-B exposure on lettuce seedlings after 12 days. (A) 'Caipira' and (B) 'Fortunas' cultivars. Top rows show control plants; middle and bottom rows show seedlings exposed to medium (4.8 kJ · m−2 · day−1) and high (9.6 kJ · m−2 · day−1) UV-B doses, respectively. UV-B, ultraviolet-B.
Figure 3.
Effects of supplemental UV-B on (A) plant height, (B) root length, (C) stem diameter, (D) true leaf count, (E) chlorophyll content (SPAD), (F) leaf dry matter, (G) root dry matter and (H) leaf width. The first three bars in each group represent 'Caipira', and the next three represent 'Fortunas'. Blue shades indicate increasing UV-B levels (lightest = control; darkest = 9.6 kJ · m−2 · day−1). Orange shades represent cultivar means (lightest = 'Caipira'; darkest = 'Fortunas'). Different lowercase letters denote statistically significant differences (LSD, p < 0.05). LSD, least significant difference; UV-B, ultraviolet-B.
Figure 4.
The impact of the supplemental UV-B on the colour parameter of the seedlings. (A) lightness (L*), (B) chroma (C*) and (C) hue (h°). Statistical significance (LSD test: p < 0.05) is denoted by differing lowercase letters. LSD, least significant difference; UV-B, ultraviolet-B.
Table 1.
The influence of the supplemental UV-B applications on micro (ppm) and macro nutrients (%) of the lettuce seedlings.
| Cultivars | ||||
|---|---|---|---|---|
| UV-B applications | 'Caipira' | 'Fortunas' | Average (Dose) | |
| Nitrogen (N)(%) | Control | 2.23 | 2.13 | 2.18 |
| 4.8 (kJ · m−2 · day−1) | 2.30 | 2.13 | 2.21 | |
| 9.6 (kJ · m−2 · day−1) | 2.23 | 2.26 | 2.25 | |
| Average (Cultivars) | 2.25 | 2.17 | ||
| Phosphorus (P)(%) | Control | 1.02 a | 0.23 | 0.62 a* |
| 4.8 (kJ · m−2 · day−1) | 0.39 b | 0.23 | 0.31 b | |
| 9.6 (kJ · m−2 · day−1) | 0.35 c | 0.23 | 0.29 c | |
| Average (Cultivars) | 0.59 a | 0.23 b | ||
| Potassium (K) (%) | Control | 4.90 b | 2.67 a | 3.78 b |
| 4.8 (kJ · m−2 · day−1) | 4.93 b | 2.50 b | 3.71 c | |
| 9.6 (kJ · m−2 · day−1) | 5.19 a | 2.56 ab | 3.88 a | |
| Average (Cultivars) | 5.00 a | 2.58 b | ||
| Calcium (Ca) (%) | Control | 1.38 b | 1.12 a | 1.25 b |
| 4.8 (kJ · m−2 · day−1) | 1.35 b | 1.02 b | 1.19 c | |
| 9.6 (kJ · m−2 · day−1) | 1.67 a | 1.04 b | 1.36 a | |
| Average (Cultivars) | 1.47 a | 1.06 b | ||
| Magnesium (Mg) (%) | Control | 0.30 | 0.45 | 0.37 ab |
| 4.8 (kJ · m−2 · day−1) | 0.29 | 0.42 | 0.36 b | |
| 9.6 (kJ · m−2 · day−1) | 0.35 | 0.44 | 0.40 a | |
| Average (Cultivars) | 0.31 b | 0.44 a | ||
| Zinc (Zn) (ppm) | Control | 140.6 b | 144.3 | 142.5 ab |
| 4.8 kJ · m−2 · day−1) | 138.3 b | 138.0 | 138.1 b | |
| 9.6 (kJ · m−2 · day−1) | 150.6 a | 143.0 | 146.8 a | |
| Average (Cultivars) | 143.2 | 141.7 | ||
| Copper (Cu) (ppm) | Control | 16.66 a | 4.66 | 10.66 a |
| 4.8 (kJ · m−2 · day−1) | 5.33 b | 4.00 | 5.16 b | |
| 9.6 (kJ · m−2 · day−1) | 6.00 b | 4.33 | 4.66 b | |
| Average (Cultivars) | 9.33 a | 4.33 b | ||
| Iron (Fe) (ppm) | Control | 57.00 b | 59.00 a | 58.00 |
| 4.8 (kJ · m−2 · day−1) | 53.66 b | 57.66 a | 55.66 | |
| 9.6 (kJ · m−2 · day−1) | 67.66 a | 48.66 b | 58.16 | |
| Average (Cultivars) | 59.44 a | 55.11 b | ||
| Manganese (Mn) (ppm) | Control | 14.3 | 34.6 a | 24.5 a |
| 4.8 (kJ · m−2 · day−1) | 13.0 | 28.6 c | 20.8 b | |
| 9.6 (kJ · m−2 · day−1) | 17.6 | 31.3 b | 24.5 a | |
| Average (Cultivars) | 15.0 b | 31.5 a | ||
Figure 5.
The impact of the supplemental UV-B on growth related parameters of plants at harvest. (A) plant height, (B) stem diameter, (C) SPAD content, (D) dry matter of leaves, (E) dry matter of roots, (F) the marketable head weight and (G) yield. Statistical significance (LSD test: p < 0.05) is denoted by differing lowercase letters. LSD, least significant difference; UV-B, ultraviolet-B.
Figure 6.
The impact of the supplemental UV-B on the colour parameter of the plants at harvest. (A) Lightness (L*), (B) Chroma (C*) and (C) Hue (h°). Statistical significance (LSD test: p < 0.05) is denoted by differing lowercase letters. LSD, least significant difference; UV-B, ultraviolet-B.
Table 2.
The impact of the additional UV-B applications on micro (ppm) and macro (%) nutrients of the lettuce plants at harvest.
| Cultivars | ||||
|---|---|---|---|---|
| UV-B applications | 'Caipira' | 'Fortunas' | Average (Dose) | |
| Nitrogen (N) (%) | Control | 2.75 | 4.03 | 3.39 |
| 4.8 (kJ · m−2 · day−1) | 2.93 | 3.20 | 3.06 | |
| 9.6 (kJ · m−2 · day−1) | 2.90 | 3.46 | 3.18 | |
| Average (Cultivars) | 2.86 b* | 3.56 a | ||
| Phosphorus (P) (%) | Control | 0.77 | 1.03 a | 0.90 a |
| 4.8 (kJ · m−2 · day−1) | 0.80 | 0.95 c | 0.87 b | |
| 9.6 (kJ · m−2 · day−1) | 0.77 | 1.01 b | 0.89 a | |
| Average (Cultivars) | 0.78 b | 0.99 a | ||
| Potassium (K) (%) | Control | 4.31 b | 3.75 c | 4.03 b |
| 4.8 (kJ · m−2 · day−1) | 4.49 b | 4.16 a | 4.30 a | |
| 9.6 (kJ · m−2 · day−1) | 4.72 a | 3.83 b | 4.27 a | |
| Average (Cultivars) | 4.49 a | 3.91 b | ||
| Calcium (Ca) (%) | Control | 2.13 c | 0.94 b | 1.53 c |
| 4.8 (kJ · m−2 · day−1) | 2.80 a | 1.11 a | 1.95 a | |
| 9.6 (kJ · m−2 · day−1) | 2.25 b | 0.95 b | 1.60 b | |
| Average (Cultivars) | 2.39 a | 1.00 b | ||
| Magnesium (Mg) (%) | Control | 0.55 c | 0.35 | 0.45 c |
| 4.8 (kJ · m−2 · day−1) | 0.81 a | 0.36 | 0.58 a | |
| 9.6 (kJ · m−2 · day−1) | 0.70 b | 0.35 | 0.52 b | |
| Average (Cultivars) | 0.69 a | 0.35 b | ||
| Zinc (Zn) (ppm) | Control | 112.0 b | 94.3 b | 103.1 b |
| 4.8 (kJ · m−2 · day−1) | 155.6 a | 91.3 c | 123.5 a | |
| 9.6 (kJ · m−2 · day−1) | 74.3 c | 97.6 a | 86.0 c | |
| Average (Cultivars) | 114.0 a | 94.4 b | ||
| Copper (Cu) (ppm) | Control | 14.00 a | 11.66 b | 12.83 a |
| 4.8 (kJ · m−2 · day−1) | 11.66 ab | 14.33 a | 13.00 a | |
| 9.6 (kJ · m−2 · day−1) | 8.66 b | 14.33 a | 11.50 b | |
| Average (Cultivars) | 11.44 b | 13.44 a | ||
| Iron (Fe) (ppm) | Control | 84.33 | 128.33 b | 106.3 b |
| 4.8 (kJ · m−2 · day−1) | 80.33 | 114.66 c | 97.5 c | |
| 9.6 (kJ · m−2 · day−1) | 84.66 | 157.33 a | 121.0 a | |
| Average (Cultivars) | 83.1 b | 133.4 a | ||
| Manganese (Mn) (ppm) | Control | 26.53 | 21.00 c | 23.76 |
| 4.8 (kJ · m−2 · day−1) | 23.66 | 24.00 a | 23.83 | |
| 9.6 (kJ · m−2 · day−1) | 92.66 | 22.66 b | 57.66 | |
| Average (Cultivars) | 47.62 | 22.55 | ||