Phosphate Requirement, Photosynthesis, and Diel Cell Cycle of Scenedesmus obliquas Under Fluctuating Light

1987 ◽  
Vol 44 (10) ◽  
pp. 1753-1758 ◽  
Author(s):  
C. N. Shin ◽  
G-Y Rhee ◽  
J. Chen
Keyword(s):  
Steady State ◽  
Average Rate ◽  
Scenedesmus Obliquus ◽  
Constant Light ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Cell Numbers ◽  
P Limitation ◽  
Fluctuating Light ◽  
Light Fluctuation

The effect of light fluctuation (0.06 Hz) on P requirement, photosynthesis, and the diel cell-division cycle was investigated in Scenedesmus obliquus in a chemostat under a 12 h day: 12 h night cycle. P requirement was much less under oscillating than under constant daylight of the same photon flux density. However, cell chlorophyll a was significantly higher, indicating an increased N requirement. There was little difference in photosynthetic efficiency (the slope of the photosynthesis–light regression) between oscillating and constant light, but photosynthetic capacity was higher in fluctuating light. Cell C was also higher. A strong diel rhythmicity in steady-state cell numbers was observed with little phase difference between oscillating and constant light. Although steady-state cell numbers under P limitation were significantly higher under fluctuating light, there was no difference in instantaneous growth rates and their diel distribution. At a dilution rate of 0.6∙d−1, cell death occurred at an average rate of −0.56∙d−1 between 4 h before and 5 h after the onset of the dark period.

Rate Limitation of Non-Steady-State Photosynthesis by Ribulose-1,5-Bisphosphate Carboxylase in Spinach

1989 ◽  
Vol 16 (6) ◽  
pp. 487 ◽  
Author(s):  
IE Woodrow ◽  
KA Mott
Keyword(s):  
Relaxation Time ◽  
Steady State ◽  
Spinacia Oleracea ◽  
Exponential Phase ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Mathematical Framework ◽  
Bisphosphate Carboxylase ◽  
Quantitative Expression ◽  
Spinacia Oleracea L

A mathematical framework was developed to analyse rate limitation of non-steady-state photosynthesis following an increase in photon flux density (PFD). This analysis was employed to resolve an exponential phase of the photosynthetic response of Spinacia oleracea L. to a step increase from darkness to moderate PFD. This phase had a relaxation time of approximately 5 min, similar to the relaxation time for the activation of ribulose-1,5-bisphosphate carboxylase (Rubisco) as determined by freeze-clamp experiments following the same change in PFD. Furthermore, as the time in darkness prior to illumination was increased, the exponential phase contributed more to the overall trajectory of photosynthesis following the increase in light. The relaxation time for the increase in the contribution of this phase was 24 min. Freeze-clamp studies showed a relaxation time of 28 min for Rubisco deactivation in the dark. These results, together with measurements of RuP2 levels, suggest that the exponential phase resolved from gas exchange experiments was limited by activation of Rubisco and that Rubisco deactivation in the dark was the reason that this phase contributed more to the overall photosynthetic trajectory as time in darkness increased. A quantitative expression for the amount of extra photosynthesis that could have been obtained had Rubisco activated instantly following an increase in PFD was derived and discussed in relation to optimal functioning of the system under different environmental conditions.

scholarly journals Effects of Artificially Reproduced Fluctuations in Sunlight Spectral Distribution on the Net Photosynthetic Rate of Cucumber Leaves

2021 ◽  
Vol 12 ◽  
Author(s):  
Ryo Matsuda ◽  
Hiroki Ito ◽  
Kazuhiro Fujiwara
Keyword(s):  
Steady State ◽  
Net Photosynthetic Rate ◽  
Flux Density ◽  
Photosynthetic Rate ◽  
Photosynthetic Photon Flux Density ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Simulation Studies ◽  
Overall Ratio ◽  
Flux Density Distribution

The effects of photosynthetic photon flux density (PPFD) fluctuations in sunlight have already been investigated; however, the spectral photon flux density distribution (SPD) has hardly been considered. Here, sunlight SPD fluctuations recorded for 200 min in October in Tokyo, Japan were artificially reproduced using an LED-artificial sunlight source system. The net photosynthetic rate (Pn) of cucumber leaves under reproduced sunlight was measured and compared with the Pn estimated from a steady-state PPFD–Pn curve for the same leaves. The measured and estimated Pn agreed except when the PPFD was low, where the measured Pn was lower than the estimated Pn. The ratio of measured Pn to estimated Pn was 0.94–0.95 for PPFD ranges of 300–700 μmol m–2 s–1, while the value was 0.98–0.99 for 900–1,300 μmol m–2 s–1, and the overall ratio was 0.97. This 3% reduction in the measured Pn compared with the Pn estimated from a steady-state PPFD–Pn curve was significantly smaller than the approximately 20–30% reduction reported in previous experimental and simulation studies. This result suggests that the loss of integral net photosynthetic gain under fluctuating sunlight can vary among days with different fluctuation patterns or may be non-significant when fluctuations in both PPFD and relative SPD of sunlight are taken into consideration.

scholarly journals Effect of Pre-Harvest Supplemental UV-A/Blue and Red/Blue LED Lighting on Lettuce Growth and Nutritional Quality

Horticulturae ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 80
Author(s):  
Triston Hooks ◽  
Joseph Masabni ◽  
Ling Sun ◽  
Genhua Niu
Keyword(s):  
Blue Light ◽  
Nutritional Quality ◽  
Uv Light ◽  
Ultra Violet ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Daily Light Integral ◽  
Lettuce Growth ◽  
Supplemental Lighting

Blue light and ultra-violet (UV) light have been shown to influence plant growth, morphology, and quality. In this study, we investigated the effects of pre-harvest supplemental lighting using UV-A and blue (UV-A/Blue) light and red and blue (RB) light on growth and nutritional quality of lettuce grown hydroponically in two greenhouse experiments. The RB spectrum was applied pre-harvest for two days or nights, while the UV-A/Blue spectrum was applied pre-harvest for two or four days or nights. All pre-harvest supplemental lighting treatments had a same duration of 12 h with a photon flux density (PFD) of 171 μmol m−2 s−1. Results of both experiments showed that pre-harvest supplemental lighting using UV A/Blue or RB light can increase the growth and nutritional quality of lettuce grown hydroponically. The enhancement of lettuce growth and nutritional quality by the pre-harvest supplemental lighting was more effective under low daily light integral (DLI) compared to a high DLI and tended to be more effective when applied during the night, regardless of spectrum.

scholarly journals Light Quality Affects Water Use of Sweet Basil by Changing Its Stomatal Development

Agronomy ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 303
Author(s):  
Sungeun Lim ◽  
Jongyun Kim
Keyword(s):  
Stomatal Conductance ◽  
Blue Light ◽  
Water Use ◽  
Growth Parameters ◽  
Stomatal Density ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Stomatal Development ◽  
Sweet Basil ◽  
Stomatal Responses

Different light qualities affect plant growth and physiological responses, including stomatal openings. However, most researchers have focused on stomatal responses to red and blue light only, and the direct measurement of evapotranspiration has not been examined. Therefore, we quantified the evapotranspiration of sweet basil under various red (R), green (G), and blue (B) combinations using light-emitting diodes (LEDs) and investigated its stomatal responses. Seedlings were subjected to five different spectral treatments for two weeks at a photosynthetic photon flux density of 200 µmol m−2 s−1. The ratios of the RGB light intensities were as follows: R 100% (R100), R:G = 75:25 (R75G25), R:B = 75:25 (R75B25), R:G:B = 60:20:20 (R60G20B20), and R:G:B = 31:42:27 (R31G42B27). During the experiment, the evapotranspiration of the plants was measured using load cells. Although there were no significant differences in growth parameters among the treatments, the photosynthetic rate and stomatal conductance were higher in plants grown under blue LEDs (R75B25, R60G20B20, and R31G42B27) than in the R100 treatment. The amount of water used was different among the treatments (663.5, 726.5, 728.7, 778.0, and 782.1 mL for the R100, R75G25, R60G20B20, R75B25, and R31G42B27 treatments, respectively). The stomatal density was correlated with the blue light intensity (p = 0.0024) and with the combined intensity of green and blue light (p = 0.0029); therefore, green light was considered to promote the stomatal development of plants together with blue light. Overall, different light qualities affected the water use of plants by regulating stomatal conductance, including changes in stomatal density.

scholarly journals LED Illumination Spectrum Manipulation for Increasing the Yield of Sweet Basil (Ocimum basilicum L.)

Plants ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 344
Author(s):  
Md Momtazur Rahman ◽  
Mikhail Vasiliev ◽  
Kamal Alameh
Keyword(s):  
Growth Rate ◽  
Fold Increase ◽  
Photosynthetic Photon Flux Density ◽  
Ocimum Basilicum ◽  
Photon Flux ◽  
Photon Flux Density ◽  
White Led ◽  
Experimental Conditions ◽  
Sweet Basil ◽  
Optimal Illumination

Manipulation of the LED illumination spectrum can enhance plant growth rate and development in grow tents. We report on the identification of the illumination spectrum required to significantly enhance the growth rate of sweet basil (Ocimum basilicum L.) plants in grow tent environments by controlling the LED wavebands illuminating the plants. Since the optimal illumination spectrum depends on the plant type, this work focuses on identifying the illumination spectrum that achieves significant basil biomass improvement compared to improvements reported in prior studies. To be able to optimize the illumination spectrum, several steps must be achieved, namely, understanding plant biology, conducting several trial-and-error experiments, iteratively refining experimental conditions, and undertaking accurate statistical analyses. In this study, basil plants are grown in three grow tents with three LED illumination treatments, namely, only white LED illumination (denoted W*), the combination of red (R) and blue (B) LED illumination (denoted BR*) (relative red (R) and blue (B) intensities are 84% and 16%, respectively) and a combination of red (R), blue (B) and far-red (F) LED illumination (denoted BRF*) (relative red (R), blue (B) and far-red (F) intensities are 79%, 11%, and 10%, respectively). The photosynthetic photon flux density (PPFD) was set at 155 µmol m−2 s−1 for all illumination treatments, and the photoperiod was 20 h per day. Experimental results show that a combination of blue (B), red (R), and far-red (F) LED illumination leads to a one-fold increase in the yield of a sweet basil plant in comparison with only white LED illumination (W*). On the other hand, the use of blue (B) and red (R) LED illumination results in a half-fold increase in plant yield. Understanding the effects of LED illumination spectrum on the growth of plant sweet basil plants through basic horticulture research enables farmers to significantly improve their production yield, thus food security and profitability.

Effect of leaf age on photosynthesis and transpiration of cassava (Manihot esculenta)

1977 ◽  
Vol 55 (17) ◽  
pp. 2288-2295 ◽  
Author(s):  
M. Aslam ◽  
S. B. Lowe ◽  
L. A. Hunt
Keyword(s):  
Chlorophyll Content ◽  
Manihot Esculenta ◽  
Leaf Age ◽  
Gas Analysis ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Genotypic Differences ◽  
Specific Leaf Weight ◽  
Manihot Esculenta Crantz ◽  
Leaf Weight

The effect of plant and leaf age on CO2-exchange rates (CER) and transpiration rates in 15 genotypes of cassava (Manihot esculenta Crantz) was measured in situ by infrared gas analysis. The plants were grown in a controlled-environment room with a 14-h photoperiod, day–night temperatures of 29–24 °C, and 60–70% relative humidity.Plant age had no effect on leaf CER, whereas transpiration rates in 14-week-old plants were significantly greater than those in 7-week-old plants. Both CER and transpiration rates decreased with leaf age. The decline was negligible when measured at low photosynthetic photon flux density. At saturating light, however, both CER and transpiration rates decreased significantly in most of the genotypes. Significant genotypic differences were observed in the pattern of decline. Both stomatal (rs) and residual (rr) resistances to the diffusion of CO2 increased with leafage in all the genotypes. The relative increase in rr was much greater than the increase in rs. In all the genotypes the ratio rr:rs was greater than unity, suggesting that rr is the major component of the total resistance to photosynthesis. Chlorophyll content and specific leaf weight also varied significantly among the genotypes. However, chlorophyll content decreased and specific leaf weight increased with leaf age.

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