Similar low green absorptance was found in sunflower Helianthus annuus L. Brodersen and Vogelmann, , and spinach Vogelmann and Han, Absorption of red light decreased slower with increasing depth than that of blue light Vogelmann and Han, ; Brodersen and Vogelmann, Green light absorption peaked deeper into leaves, and was more evenly distributed throughout leaves, because of low absorption of green light by chlorophyll Vogelmann and Han, ; Brodersen and Vogelmann, The more even distribution of green light within leaves, as compared to red and blue light, can explain the interactive effects between PPFD and light spectrum on leaf photosynthesis.
The more uniform green light distribution within leaves may be a key contributor to higher leaf level QY inc under high PPFD because less heat dissipation of excess light energy is needed Nishio, ; Terashima et al. Reaction centers near the adaxial leaf surface receive more excitation energy under blue, and to a lesser extent under red light, than under green light, because of the differences in absorptance. Consequently, under high intensity blue light, NPQ is up-regulated in the chloroplasts near the adaxial leaf surface to dissipate some of the excitation energy Sun et al.
Since less green light is absorbed near the adaxial surface, less heat dissipation is required. This indicates more upregulation of heat dissipation in the top of the leaves under blue, than under green light Evans and Vogelmann, On the other hand, the bottom half of the leaves can still utilize the available light with relatively high QY inc , since the amount of light reaching the bottom half is relatively low, even under high PPFD Nishio, By channeling more light to the under-utilized bottom part of leaves, leaves could achieve higher QY inc even under high intensity green light.
In our study, high QY inc under green light and low QY inc under blue light at high PPFD Figure 6 can be thus explained by the large disparities in the light environment in chloroplasts from the adaxial to the abaxial side of leaves due to differences in leaf absorptance. Green light also resulted in a higher A g,max As discussed before, the high A g,max under green light resulted from the more uniform light distribution under green light, allowing deeper cell layers to photosynthesize more.
Overall, under high PPFD , the differences in light distribution throughout a leaf are important to quantum yield and assimilation rate, since it affects NPQ up-regulation Sun et al. We examined the effect of light quality and intensity on J and V c,max Figure 8. For the light-dependent reactions, the interactive effect between light spectra and PPFD found for CO 2 assimilation and quantum yield was also observed for J Figure 8A.
This similarly can be attributed to a more uniform energy distribution of green light among reaction centers throughout a leaf and weaker upregulation of non-photochemical quenching with increasing green light intensity Sun et al. Unlike J , V c,max was largely unaffected by light spectra Figure 8B and was not correlated with A g data not shown.
Similarly, Wullschleger noted a strong linear relationship between J and V c,max across C 3 species. The ratio between J and V c,max in our study 1. These results suggest that the interactive effect of light spectra and PPFD resulted from effects on J , which is associated with light energy harvesting by reaction centers, rather than from V c,max.
Figure 9. The color scheme representing the nine spectra is the same as Figure 8. The Emerson enhancement effect describes a synergistic effect between lights of different wavebands red and far-red on photosynthesis Emerson, McCree attempted to account for interactions between light with different spectra when developing photosynthetic action spectra and applied low intensity monochromatic lights from to nm with white background light to plants.
His results showed no interactive effect between those monochromatic lights and white light McCree, We tested different ratios of blue, green, and red light and different PPFD s, and similarly did not find any synergistic or antagonistic effect of different wavebands on any physiological parameters measured or calculated.
The interactive effect between PPFD and light quality demonstrates a remarkable adaptation of plants to different light intensities. Many early photosynthesis studies investigated the absorptance and action spectrum of photosynthesis of green algae, e. Extrapolating light absorptance of green algae and suspension of chlorophyll or chloroplast to whole leaves from can lead to an underestimation of absorptance of green light by whole leaves and the belief that green light has little photosynthetic activity Moss and Loomis, ; Smith et al.
Photosynthetic action spectra developed on whole leaves of higher plants, however, have long shown that green light effectively contributes to CO 2 assimilation, although with lower QY inc than red light Hoover, ; McCree, ; Inada, ; Evans, The importance of green light for photosynthesis was clearly established in more recent studies, emphasizing its role in more uniformly exciting all chloroplasts, which especially important under high PPFD Sun et al. The idea that red and blue light are more efficient at driving photosynthesis, unfortunately, still lingers, e.
Light-emitting diodes LEDs have received wide attention in recent years for use in controlled environment agriculture, as they now have superior efficacy over traditional lighting technologies Pattison et al. LEDs can have a narrow spectrum and great controllability. This provides unprecedented opportunities to fine tune light spectra and PPFD to manipulate crop growth and development.
Therefore, red and blue LEDs are sometimes considered optimal for driving photosynthesis. This claim holds true only under low PPFD. Green light plays an important role in photosynthesis, as it helps plants to adapt to different light intensities. The wavelength-dependent absorptance of chlorophylls channels green light deeper into leaves, resulting in more uniform light absorption throughout leaves and providing excitation energy to cells further from the adaxial surface.
Under high PPFD , this can increase leaf photosynthesis. Plant evolved under sunlight for hundreds of millions of years, and it seems likely that the relatively low absorptance of green light contributes to the overall photosynthetic efficiency of plants Nishio, There was an interactive effect of light spectrum and PPFD on leaf photosynthesis.
The strong absorption of blue light by chlorophyll creates a large light gradient from the top to the bottom of leaves. The large amount of excitation energy near the adaxial side of a leaf results in upregulation of nonphotochemical quenching, while chloroplasts near the bottom of a leaf receive little excitation energy under blue light. The more uniform distribution of green light absorption within leaves reduces the need for nonphotochemical quenching near the top of the leaf, while providing more excitation energy to cells near the bottom of the leaf.
We also found that the interactive effect of light spectrum and PPFD on photosynthesis was a result of the light-dependent reactions; gross assimilation and J were strongly correlated. We detected no synergistic or antagonistic interactions between blue, green, and red light. The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.
JL and MI designed the experiment, discussed the data, and revised the manuscript. JL performed the experiment, analyzed data, and prepared the first draft. Both authors contributed to the article and approved the submitted version.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Note that the initial increase in QY inc became more pronounced after correction of light suppressed respiration. Note that the pattern of QY inc after correcting of alternative electron sink B is similar to quantum yield of PSII measured by chlorophyll fluorescence by Weaver and van Iersel The light response curves are shown in Figure 3.
Atkin, O. Leaf respiration in light and darkness A comparison of slow- and fast-growing Poa species. Plant Physiol. Badger, M. Electron flow to oxygen in higher plants and algae: rates and control of direct photoreduction Mehler reaction and rubisco oxygenase. B Biol. Balegh, S. The photosynthetic action spectrum of the bean plant. Brodersen, C.
Do changes in light direction affect absorption profiles in leaves? Plant Biol. Brooks, A. Planta , — Campbell, W. Light activation of rubisco by rubisco activase and thylakoid membranes. Plant Cell Physiol. Chen, S.
The action spectrum for the photochemical evolution of oxygen by isolated chloroplasts. Craver, J. Acclimation of growth and photosynthesis in Petunia seedlings exposed to high-intensity blue radiation. Croce, R. Carotenoid-to-chlorophyll energy transfer in recombinant major light-harvesting complex LHCII of higher plants. Femtosecond transient absorption measurements. B , — Emerson, R. Dependence of yield of photosynthesis in long-wave red on wavelength and intensity of supplementary light.
Science , — Evans, J. The dependence of quantum yield on wavelength and growth irradiance. Profiles of 14C fixation through spinach leaves in relation to light absorption and photosynthetic capacity. Plant Cell Environ.
Haxo, F. Photosynthetic action spectra of marine algae. Half of the solar energy is in the infrared part of the spectrum and it is this which contributes an important part to heating the greenhouse. Because it is not needed for photosynthesis, shading out infrared heat radiation is a good idea. Light colour determines development The colour of the light also determines the development of the crop: the amount of elongation, how much it branches, when it flowers etc.
The intensity of light is very important for photosynthesis but for steering the development of the crop a much minor light differences can already be enough.
For example a very small amount of red light during a long night is enough to keep chrysanthemums vegetative. It is the relationship between the colours that gives light its steering effect. For example, the ratio between red and far red: More red results in more compact plants.
The ratio between red and blue is also important. Less blue and therefore more red leads to roses with longer stems. Keep in mind that it is always about the colour to colour ratio. In practice it is difficult to steer with light colours.
After all, there is always an ample amount of sunlight available. In order to change the ratios during the day, you would need to add a lot of the desired light colour. Son-T lamps contain so much red light that at low levels of natural light there is a definite red-light effect. Extended lighting at dusk to change the ratio red:far red can lead to more compact plants, according to research by Wageningen University Research on fuchsias.
Rose growers have had good experiences with the coating ReduFlex Blue which partly blocks blue light. They can harvest longer roses under this coating. In this case it is the ratio of red:blue light that causes the effect. There are many interesting developments in the field of light colours, but practical application or applying the results to other crops is still difficult. The plants sent more assimilates to the fruits.
It is still unclear whether such results can be applied to ornamental plants, like gerbera or rose. The market for ornamental products has declined drastically due to the coronavirus. Many growers have questions about slowing down their crop growth in order to lower or postpone production. June Lighting , Production.
Erik Runkle Erik Runkle is professor and floriculture Extension specialist in the department of horticulture at Michigan State University. Current Issue. Culture , Variety Info. Management , Production. Plant Trials , Variety Info. Video Library see all ». Latest News Greenhouse Product News. Greenhouse Product News. Education , Lighting. Latest Photos see all ». GPN recognizes 40 industry professionals under the age of 40 who are helping to determine the future of the horticulture industry.
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