ISHS Acta Horticulturae 711: V International Symposium on Artificial Lighting in Horticulture
GAS EXCHANGE AND CHL-A FLUORESCENCE OF LEAVES OF BARLEY SEEDLINGS GROWN UNDER BLUE LIGHT ENRICHMENT |
| Authors: | B. Yaakoubd, M. Dorais |
| Keywords: | LED, PSII efficiency, QB non transferring centers, photosynthesis |
| Abstract:
HPS lamps are the most commonly used type of light source for greenhouse production. Although they have an appropriate light spectral distribution for photosynthesis, HPS lamps are poor in blue (B) compared to solar spectrum. It is well known that B light promotes stomatal opening and influences the biochemical properties of photosynthesis. The use of B enrichment provided by monochromatic light source such as LEDs might thus be a useful way to correct these deficits and to modulate physiological responses in order to increase photosynthetic efficiency and consequently crop productivity. In a short term experiment (Ménard et al., 2005), we observed that B light enrichment at low levels (7.5 and 16 µmol m-2 s-1) increased CO2 assimilation rate of cucumber under PPF of 500 to 1000 µmol m-2 s-1, resulting in 30% increase of fruit yield. However, the effect of high levels of B light enrichment that could occur in an inner canopy lighting system on leaf gas exchange and Chl-a fluorescence remain unclear. The goal of this study was to investigate the effect of high levels of B light enrichment on plant photosynthetic capacity. To achieve this we compared the photosynthetic capacity of Hordeum vulgare cv Acca, grown under four B light regimes: 1- HPS+ 0 µmol m-2 s-1 B (455 nm); 2- HPS + 2.5 µmol m-2 s-1 B (455 nm); 3- HPS + 100 µmol m-2 s-1 B (455 nm); and 4- HPS + 250 µmol m-2 s-1 B (455 nm). Light (A/Q) response curves and Chl-a fluorescence parameters were measured after 7 days of treatments. Our results showed that B light enrichment of 2.5 and 100 µmol m-2 s-1 did not affect CO2 assimilation rate of barley leaves. Extended daylength with 100 µmol m-2 s-1 B increased the gs without any negative effect on the maximum quantum yield of PSII, qP and qN, while low level of B enrichment (2.5 µmol m-2 s-1) increased the ETR and qp under high ambient PPF. However, level of 250 µmol m-2 s-1 B decreased CO2 assimilation rate and PSII-efficiency, and increased the amount of PSII inactive centers. | |
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