Red Photon Flux Research Articles

Investigating the influence of varied ratios of red and far-red light on lettuce (Lactuca sativa): effects on growth, photosynthetic characteristics and chlorophyll fluorescence.

Far red photon flux accelerates photosynthetic electron transfer rates through photosynthetic pigments, influencing various biological processes. In this study, we investigated the impact of differing red and far-red light ratios on plant growth using LED lamps with different wavelengths and Ca1.8Mg1.2Al2Ge3O12:0.03Cr3+ phosphor materials. The control group (CK) consisted of a plant growth special lamp with 450 nm blue light + 650 nm red light. Four treatments were established: F1 (650 nm red light), F2 (CK + 730 nm far-red light in a 3:2 ratio), F3 (650 nm red light + 730 nm far-red light in a 3:2 ratio), and F4 (CK + phosphor-converted far-red LED in a 3:2 ratio). The study assessed changes in red and far-red light ratios and their impact on the growth morphology, photosynthetic characteristics, fluorescence characteristics, stomatal status, and nutritional quality of cream lettuce. The results revealed that the F3 light treatment exhibited superior growth characteristics and quality compared to the CK treatment. Notably, leaf area, aboveground fresh weight, vitamin C content, and total soluble sugar significantly increased. Additionally, the addition of far-red light resulted in an increase in stomatal density and size, and the F3 treatments were accompanied by increases in net photosynthetic rate (Pn), transpiration rate (Tr), intercellular CO2 concentration (Ci), and stomatal conductance (Gs). The results demonstrated that the F3 treatment, with its optimal red-to-far-red light ratio, promoted plant growth and photosynthetic characteristics. This indicates its suitability for supplementing artificial light sources in plant factories and greenhouses.

Blue Photons from Broad-Spectrum LEDs Control Growth, Morphology, and Coloration of Indoor Hydroponic Red-Leaf Lettuce

For indoor crop production, blue + red light-emitting diodes (LEDs) have high photosynthetic efficacy but create pink or purple hues unsuitable for workers to inspect crops. Adding green light to blue + red light forms a broad spectrum (white light), which is created by: phosphor-converted blue LEDs that cast photons with longer wavelengths, or a combination of blue, green, and red LEDs. A broad spectrum typically has a lower energy efficiency than dichromatic blue + red light but increases color rendering and creates a visually pleasing work environment. Lettuce growth depends on the interactions of blue and green light, but it is not clear how phosphor-converted broad spectra, with or without supplemental blue and red light, influence crop growth and quality. We grew red-leaf lettuce 'Rouxai' in an indoor deep-flow hydroponic system at 22 °C air temperature and ambient CO2. Upon germination, plants received six LED treatments delivering different blue fractions (from 7% to 35%) but the same total photon flux density (400 to 799 nm) of 180 μmol·m-2·s-1 under a 20 h photoperiod. The six LED treatments were: (1) warm white (WW180); (2) mint white (MW180); (3) MW100 + blue10 + red70; (4) blue20 + green60 + red100; (5) MW100 + blue50 + red30; and (6) blue60 + green60 + red60. Subscripts denote photon flux densities in μmol·m-2·s-1. Treatments 3 and 4 had similar blue, green, and red photon flux densities, as did treatments 5 and 6. At the harvest of mature plants, lettuce biomass, morphology, and color were similar under WW180 and MW180, which had different green and red fractions but similar blue fractions. As the blue fraction in broad spectra increased, shoot fresh mass, shoot dry mass, leaf number, leaf size, and plant diameter generally decreased and red leaf coloration intensified. Compared to blue + green + red LEDs, white LEDs supplemented with blue + red LEDs had similar effects on lettuce when they delivered similar blue, green, and red photon flux densities. We conclude that the blue photon flux density in broad spectra predominantly controls lettuce biomass, morphology, and coloration.

Design of artificial climate chamber for screening tea seedlings’ optimal light formulations

A multi-channel photon sensor (MPS) capable of measuring Red Photon Flux Density (RPFD), Blue Photon Flux Density (BPFD) and Photosynthetic Photon Flux Density (PPFD) based on silicon photodiodes and filters is designed. At the same time, the FPGA-based environmental control system realizes the closed-loop control of RPFD, BPFD and PPFD by reading the data collected by the MPS that slides up and down according to the height of the canopy of the plant and using the PWM signal to control the LED light board’s red and blue channel. Based on the above method, the article completed an Artificial Climate Chamber (ACC) that realizes the automatic regulation of PPFD and RPFD/BPFD (R/B) of plant canopy that are the key parameters for determining the light formulations of plant lighting and environmental parameters including temperature, relative humidity, CO2 concentration, photoperiod etc. At a significantly lower cost, the MPS’s photon response curve is close to the ideal value, and the linear response R2 of the calibration exceeds 0.999. After setting the parameters for 30 s, the RPFD, BPFD and PPFD control error of the ACC are 1.43%, 1.39% and 0.71%, respectively. The paper also used tea seedlings as materials to explore the physiological and biochemical indexes of leaves under different R/B and PPFD. By comparing the biomass accumulation, free amino acid, tea polyphenols, polyphenols / amino acid ratio and other key parameters, PPFD = 100μmol∙m-2∙s-1 and R/B = 1/3 is the optimal light formulations for artificial light cultivation of tea seedlings.

Far-red radiation interacts with relative and absolute blue and red photon flux densities to regulate growth, morphology, and pigmentation of lettuce and basil seedlings

Although outside the photosynthetic photon flux density (PPFD) waveband (400–700 nm), far-red (FR; 700–800 nm) radiation regulates photomorphogenesis and photochemistry, thereby meriting consideration in sole-source plant-lighting applications. We investigated how FR radiation interacted with the ratio of blue (B; 400–500 nm) to red (R; 600–700 nm) radiation (B:R) (experiment I) and PPFD (experiment II) to regulate seedling growth under sole-source lighting. We postulated that adding FR radiation to B + R radiation would increase leaf expansion and thus radiation capture to promote whole-plant photosynthesis, but that FR effects would depend on B:R and PPFD. In experiment I, lettuce (Lactuca sativa) ‘Rex’ and ‘Cherokee’ and basil (Ocimum basilicum) ‘Genovese’ were continuously irradiated by 180 μmol m–2 s–1 of B and/or R radiation [B30R150 (low B:R), B90R90 (high B:R), R180, or B180, where subscripts indicate respective photon flux densities in μmol m–2 s–1] with or without 30 μmol m–2 s–1 of FR radiation. Twelve and 16 days after seed sow for lettuce and basil, respectively, the addition of FR radiation increased leaf length and shoot weight of all crops with more pronounced impacts under high B:R than low B:R. It also increased root dry weight of basil and lettuce ‘Cherokee’. Adding FR to B + R radiation reduced specific chlorophyll content in lettuce by 10–20%, but not in basil. Red pigmentation of lettuce ‘Cherokee’ increased with increasing B:R but decreased with the inclusion of FR radiation. In experiment II, we grew lettuce ‘Rex’ (for 8 days) and ‘Rouxai’ (for 10 days) under B90R90 (low PPFD) or B180R180 (high PPFD) at the same B:R with or without FR radiation at 30 or 75 μmol m–2 s–1. Additional FR radiation increased lettuce shoot weight and extension growth but reduced relative specific chlorophyll content under both PPFDs, although FR effects were attenuated under the high PPFD. Shoot dry weight, relative specific chlorophyll content, and red foliage pigmentation increased with PPFD. We conclude that FR enrichment improves photosynthetic radiation capture and thus promotes crop growth under sole-source lighting, and that its effects are especially pronounced under high B:R and a low PPFD.

Carotenoid Production by Dunaliella salina under Red Light.

The halotolerant photoautotrophic marine microalga Dunaliella salina is one of the richest sources of natural carotenoids. Here we investigated the effects of high intensity blue, red and white light from light emitting diodes (LED) on the production of carotenoids by strains of D. salina under nutrient sufficiency and strict temperature control favouring growth. Growth in high intensity red light was associated with carotenoid accumulation and a high rate of oxygen uptake. On transfer to blue light, a massive drop in carotenoid content was recorded along with very high rates of photo-oxidation. In high intensity blue light, growth was maintained at the same rate as in red or white light, but without carotenoid accumulation; transfer to red light stimulated a small increase in carotenoid content. The data support chlorophyll absorption of red light photons to reduce plastoquinone in photosystem II, coupled to phytoene desaturation by plastoquinol:oxygen oxidoreductase, with oxygen as electron acceptor. Partitioning of electrons between photosynthesis and carotenoid biosynthesis would depend on both red photon flux intensity and phytoene synthase upregulation by the red light photoreceptor, phytochrome. Red light control of carotenoid biosynthesis and accumulation reduces the rate of formation of reactive oxygen species (ROS) as well as increases the pool size of anti-oxidant.

Transplant lettuce response to different blue:red photon flux ratios in indoor LED sole-source lighting production

Transplant lettuce response to different blue:red photon flux ratios in indoor LED sole-source lighting production

Photosynthetic apparatus plays a central role in photosensitive physiological acclimations affecting spinach (Spinacia oleracea L.) growth in response to blue and red photon flux ratios

Relative abundance of blue (B) and red (R) photons in the incident light plays a major role in regulating the morphology and physiology of plants. Many studies have been carried out to determine the R:B photon flux ratio (PFR) required for eliciting desired traits in various plant species. However, studies investigating the impact of R:B PFR on the underlying metabolic events and their mutual interactions are limited. In the present study, spinach (Spinacia oleracea L. cv. All Green) plants were raised in a plant growth chamber under R:B PFRs of 100R:0B, 75R:25B, 50R:50B, 25R:75B and 0R:100B provided by customized light-emitting diode (LED) panels. Data related to plant growth, status of photosynthetic apparatus, nitrogen metabolism, metabolite profile, oxidative stress and antioxidant defense response were collected. A putative mechanistic concept highlighting the interplay between photosynthesis, C- and N-assimilation and oxidative stress response in regulating plant growth under changing R:B PFR has been presented. Steady growth under B and R combined treatments was associated with high chlorophyll content, PSII quantum yield (Fv/Fm, Fv/Fo, ΦPSII) and vitality index (RFd) along with proper C- and N-assimilation. Reduction in non-photochemical quenching (NPQ) and oxidative stress was also observed under 25R:75B to 75R:25B light treatments. Subdued photosynthetic activity under deficiency of B waveband resulted in arrested growth due to suboptimal C- and N-assimilation. Monochromatic B lighting caused damage to the photosynthetic apparatus due to increased photooxidation. Presence of B photons was favorable for eliciting enzymatic and non-enzymatic antioxidant defense responses. However, the antioxidant machinery was unable to ameliorate the excessive oxidative damage under 0R:100B treatment resulting in suboptimal plant growth. Integrity and proper functionality of the photosynthetic apparatus under B and R combined light quality treatments was found to play a pivotal role in coordinating the non-photosynthetic light-sensitive metabolic processes in response to changing R:B PFR for ensuring proper plant growth.

Growth, Water-Use Efficiency, Stomatal Conductance, and Nitrogen Uptake of Two Lettuce Cultivars Grown under Different Percentages of Blue and Red Light

The objective of this study was to characterize growth, water-use efficiency (WUE), stomatal conductance (gs), SPAD index values, and shoot nitrogen uptake of two lettuce cultivars grown under different percentages of blue and red light. The treatments evaluated were 100% red; 7% blue + 93% red; 26% blue + 74% red; 42% blue + 58% red; 66% blue + 34% red; and 100% blue. Broad-spectrum (19% blue, 43% green, and 38% red) light was used to observe the effects of wavelength interactions. All of the treatments provided an average daily light integral (DLI) of 17.5 mol·m‒2·d‒1 (270 ± 5 µmol·m‒2·s‒1 over an 18-h photoperiod). The experiment was replicated three times over time; each terminated 21 days after treatment initiation. Leaf area, specific leaf area (SLA), and SPAD index had a similar response in that all of the parameters increased with up to 66% blue light, and slightly decreased or remained constant with 100% blue light. In contrast, leaf number, shoot dry mass, and WUE generally decreased in response to blue light. Conversely, for every 10% increase in blue light, gs increased by 10 mmol·m‒2·s‒1. Nitrogen uptake was unaffected by light quality. Our findings indicate that when grown under different blue and red photon flux ratios, the WUE of lettuce significantly decreases under higher blue light, which could be attributed to a reduction in plant growth (leaf number and dry mass), and an increase in gs. However, green light within broad-spectrum lamps might counteract blue-light mediated effects on gs and WUE in lettuce.

Photosynthesis and leaf development of cherry tomato seedlings under different LED-based blue and red photon flux ratios

We investigated the photosynthesis and leaf development of cherry tomato seedlings grown under five different combinations of red and blue light provided by light-emitting diodes (LEDs). Fresh biomass increased significantly under treatments with blue light percentages of 50, 60, and 75%, with 50% blue-light-grown seedlings accumulating significantly more dry mass. The 25% blue-light-grown seedlings were obviously weaker than those from the other LED treatments. An increase in net photosynthetic rate upon blue light exposure (25–60%) was associated with increases in leaf mass per unit leaf area, leaf area, leaf density, stomatal number, chloroplast and mesophyll cell development, and chlorophyll contents. Our results imply that photosynthesis and leaf development in cherry tomato seedlings are associated with both the proportion and quantity of blue light.

UV-B radiation dose requirement for suppressing intumescence injury on tomato plants

Intumescence injury is a physiological disorder characterized by watery tumors on a leaf surface associated with abnormal cell enlarge ment and cell division. This problematic intumescence injury has been observed on susceptible cultivars of tomato when grown under an ultraviolet radiation (UV) deficient light environment. In this study, different doses of UV-B radiation were applied after each photoperiod for ‘Beaufort’ interspecific tomato rootstock seedlings (Solanum lycopersicum × S. habrochaites) grown under light emitting diodes (10% blue and 90% red photon flux). The percent number of leaves exhibiting intumescences on leaves decreased linearly with increasing UV-B dose (measured in a 300–320 nm range) in the range examined (0–6.7 mmol m−2 d−1 or 0–2.6 kJ m−2 d−1 achieved by 0.31 μmol m−2 s−1 or 0.12 W m−2 UV-B photon flux for 0–6 h). The severity of intumescence injury was also linearly decreased by increasing UV-B dose. The intumescence incidence as well as severity was the highest in the non-treated control (66.0% leaves showing injury and 2.5–3.8 severity score out of 5) and the lowest (36.1% leaves showing injury and 0.6–1.6 severity score) at the highest dose of 6.7 mmol m−2 d−1 UV-B. The shoot dry weight of seedlings increased by 119% under the highest UV-B dose compared with that of non-treated control. T5-type white fluorescent lamps used for comparison emitted a moderate dose of UV-B (4.3 mmol m−2 d−1 at 0.07 μmol m−2 s−1 for 18 h d−1) and induced a moderate level of intumescent injury. Linear regression suggests that the UV-B dose eliminating intumescence was likely at around 12.3–14.0 mmol m−2 d−1 (4.7–5.3 kJ m−2 d−1), less than a UV-B dose received outdoors on a typical clear summer day. This level of UV-B is achievable under T12-type fluorescent lamps which emit more UV-B and explains why we typically do not see intumescence under T12 fluorescent lighting. The results obtained in this study will help to avoid intumescence in tomato plants grown under controlled environments.

Study of Plant Cultivation Using a Light-Emitting Diode Illumination System to Control the Spectral Irradiance Distribution

In plant cultivation, the number of photons is more important than the light energy from the chemical reactions that occur during photosynthesis. In addition, the blue and red photon flux (B/R) ratio is an important parameter for plant cultivation. Here we discuss the effect of the spectral irradiance distribution and the B/R ratio on plant cultivation. We cultivated lettuce seedlings, Lactuca sativa L. Cv. Okayama, using a light-emitting diode illumination system that can precisely control the spectral irradiance distribution and B/R ratio. The B/R ratio varied from 0.36 to 2.06 according to the intensity of the blue light when the photosynthetic photon flux density values were sufficient to ensure the 150 - 200 μmol⋅m−2⋅s−1. High photon flux densities of blue light result in reduced plant length, plant height, and leaf area, thereby suggesting its role in the suppression of leaf growth. Therefore, we conclude that a lower photon flux of blue light (B/R Ratio) is optimal for lettuce cultivation.

Tomato seedling physiological responses under different percentages of blue and red photon flux ratios using LEDs and cool white fluorescent lamps

Lamp spectral customization can be a strategy to achieve desirable plant characteristics when plants are grown under sole-source electric lighting. Vegetable transplants can be efficiently and economically grown under indoor-production systems with electrical lighting; however, species-specific light recipes have to be developed to improve plant growth, development and morphology, as well as to reduce electrical consumption. The objective of this study was to evaluate the growth and morphology of tomato transplants to a broad range of blue to red (B:R) photon flux (PF) ratios under LEDs and cool white fluorescent lamps (CWF). Tomato ‘Komeett’ and ‘Beaufort’ seedlings were grown in a climate control growth chamber. Using LEDs, seven light treatments with different blue (B), green (G) and red (R) PF ratios were used: 100R, 10B:90R, 20B:28G:52R, 30B:70R, 50B:50R, 75B:25R and 100B. In addition, a CWF treatment served as the control. Hypocotyl length of ‘Komeett’ decreased with the increase of percent B PF up to 75% B. Plant leaf area was 64–72% greater under treatments emitting both B and R PF than in the 100 B and 100 R treatments. Similarly, tomato ‘Komeett’ fresh mass, dry mass, leaf number and chlorophyll concentration was comparable among the treatments containing B and R PF and greater than in 100 B and 100 R treatments. However, plant compactness in the 30B:70R treatment was 42% greater than in the 10B:90R treatment. Anthocyanin concentration increased with the increase of percent B PF up to 75% B. Also, plants in 30B:70R and 50B:50R had 39% and 36% greater dry mass than in CWF, respectively. In addition, 30B:70R and 50B:50R LEDs had 172% greater growing efficacy (gkWh−1) than high output fluorescent lamps. The addition of G light did not have any effects on tomato physiological responses. ‘Beaufort’ plant morphology and growth were severely affected by intumescences development and intumescence severity decreased under higher percentages of B PF. In summary, 30B:70R, 50B:50R were the best spectrums to produce tomato seedlings under LEDs tested here; however, plant quality under CWF, 10B:90R, 20B:28G:52R, and 75B:25R was also acceptable.

Morphological, Photosynthetic, and Physiological Responses of Rapeseed Leaf to Different Combinations of Red and Blue Lights at the Rosette Stage.

Rapeseed (Brassica napus L.) is sensitive to light quality. The factory production of rapeseed seedlings for vegetable use and for transplanting in the field requires an investigation of the responses of rapeseed to light quality. This study evaluated the responses of the leaf of rapeseed (cv. “Zhongshuang 11”) to different ratios of red-photonflux (RPF) and blue-photonflux (BPF) from light emitting diodes (LEDs). The treatments were set as monochromatic lights, including 100R:0B% and 0R:100B%, and compound lights (CLs), including 75R:25B%, 50R:50B%, and 25R:75B%. The total photonflux in all of the treatments was set as 550 μmolm−2s−1. With an increase of BPF, the rapeseed leaves changed from wrinkled blades and down-rolled margins to flat blades and slightly up-rolled margins, and the compact degree of palisade tissue increased. One layer of the cells of palisade tissue was present under 100R:0B%, whereas two layers were present under the other treatments. Compared to 100R:0B%, 0R:100B% enhanced the indexes of leaf thickness, leaf mass per area (LMA), stomatal density, chlorophyll (Chl) content per weight and photosynthetic capacity (Pmax), and the CLs with high BPF ratios enhanced these indexes. However, the 100R:0B% and CLs with high RPF ratios enhanced the net photosynthetic rate (Pn). The leaves under the CLs showed growth vigor, whereas the leaves under 100R:0B% or 0R:100B% were stressed with a low Fv/Fm (photosynthetic maximum quantum yield) and a high content of and H2O2. The top second leaves under 100R:0B% or 0R:100B% showed stress resistance responses with a high activity of antioxidase, but the top third leaves showed irreversible damage and inactivity of antioxidase. Our results showed that the rapeseed leaves grown under 0R:100B% or CLs with a high BPF ratio showed higher ability to utilize high photonflux, while the leaves grown under 100R:0B% or CLs with a low BPF ratio showed higher efficiency in utilizing low photonflux. Under different R:B photonflux ratios, red and blue lights may play mutual roles in Pn. When the blue light dominated, the Pn showed a B-preference. When the red light dominated, the Pn showed an R-preference. Furthermore, CLs were suitable for the Pn of rapeseed seedlings.

Growth and morphology of vegetable seedlings under different blue and red photon flux ratios using light-emitting diodes as sole-source lighting

Growth and morphology of vegetable seedlings under different blue and red photon flux ratios using light-emitting diodes as sole-source lighting

Physiological responses of cucumber seedlings under different blue and red photon flux ratios using LEDs

Light emitting diodes (LEDs) are frequently regarded as a new light source for the production of horticultural crops under closed-type conditions. However, before use of LEDs as the sole source of light can be advanced, plant responses to light quality have to be investigated for important horticultural plants. The objective of the present study was to evaluate cucumber (Cucumis sativus) seedlings physiological responses to different blue (B) and red (R) photon flux (PF) ratios using LEDs. Cucumber seedlings (cv. Cumlaude) were grown in a growth chamber until the second true leaf stage (17 days) with LED lighting and 18-h photoperiod. The treatments consisted of 100μmolm−2s−1 photosynthetic photon flux (PPF) with B:R PF ratios of 0B:100R%, 10B:90R%, 30B:70R%, 50B:50R%, 75B:25R%, 100B:0R%. Another treatment consisted of B, green (G) and R PF ratio of 20B:28G:52R%. Peak wavelengths of LEDs were 455nm (B) and 661nm (R) for the in the B:R treatments and 473nm (B), 532nm (G), 660nm (R) in the B:G:R treatment. Hypocotyl length decreased with the increase of B PF up to the 75B:25R% treatment. Hypocotyl length in the 0B:100R% treatment was 164% greater than in the 75B:25R treatment. Plants under the 100B:0R% treatment had unexpected greater plant height, hypocotyl, and epicotyl length than plants under all other treatments. For example, the hypocotyl length under the 100B:0R% was 69% greater than in the 0B:100R treatment and 346% greater than in the 75B:25R% treatment. Leaf area decreased with the increase of B PF when plants were irradiated with the combination of B and R PF. The response of leaf area under the 100B:0R% treatment was unexpected since plants in the 100B:0R% treatment had 48% greater leaf area than plants in the 75B:25R% treatment. Chlorophyll content per leaf area, net photosynthetic rate, and stomatal conductance increased with the increase of B PF. Shoot dry and fresh mass decreased with the increase of B PF when plants were irradiated with the combination of B and R PF. Plants under 0B:100R% had the lowest dry and fresh mass from all the treatments and plants under 100B:0R% showed the greatest fresh mass from all the treatments and equal dry mass as the plants under 10B:90R% treatment. The addition of G PF to the spectrum did not have any influence in cucumber plant responses. For cucumber seedlings, morphological responses influenced plant growth since B PF responses in growth parameters (i.e., dry mass) closely matched those in morphological parameter (i.e., leaf area). More research is needed to find the optimal spectrum for the growth and development of horticultural crops under sole source electrical lighting such as LEDs.

Growth and morphological response of cucumber seedlings to supplemental red and blue photon flux ratios under varied solar daily light integrals

High intensity light-emitting diodes (LEDs) have the potential to be used as supplemental lighting technology in greenhouses. However, LED light quality requirements of greenhouse crops grown when supplementing the solar spectrum are unknown. In this study, to find the requirements, cucumber (Cucumis sativus L. cv. Cumlaude) seedlings were grown in a greenhouse with and without supplemental LED lighting (PPF: 54±1.1μmolm−2s−1) at varied blue (400–500nm with the peak at 455nm) and red (600–700nm with the peak at 661nm) photon flux (PF) ratios (B:R ratios) under different solar daily light integrals (DLI). The treatments were 0B:100R% (54μmolm−2s−1 red PF), 4B:96R% (2.3 and 52μmolm−2s−1 blue and red PF, respectively), 16B:84R% (8.5 and 46.2μmolm−2s−1 blue and red PF, respectively), and a control without supplemental lighting. The solar DLIs during the experiment were 5.2±1.2 and 16.2±5.3molm−2d−1 created inside a greenhouse using shade screen. Regardless of B:R ratio, morphological and growth parameters of the seedlings were all improved under supplemental LED lighting compared to the no-supplemental-light control. Under high DLI conditions, no significant differences were found for any parameters between the different B:R ratios. Under low DLI, chlorophyll concentration increased with increasing B:R ratio (i.e., increasing blue PF without increasing photosynthetic photon flux, PPF) of the supplemental lighting. Dry mass, leaf number, and leaf area decreased with increasing B:R ratio under low DLI conditions. The reduction in dry mass and leaf number were attributed to the reduction in leaf area. Leaf net photosynthetic rate measured under ambient CO2, ambient temperature, and 1000μmolm−2s−1 PPF (light source: tungsten halogen lamp) also showed no difference among treatments of B:R ratios, indicating that B:R ratio treatments did not cause any changes in plant photosynthetic apparatus. When used for supplemental lighting in the greenhouse, use of 100% red LED is preferred for cucumber seedlings, and additional blue LED was not beneficial.

Reductions in mesophyll and guard cell photosynthesis impact on the control of stomatal responses to light and CO2.

Transgenic antisense tobacco plants with a range of reductions in sedoheptulose-1,7-bisphosphatase (SBPase) activity were used to investigate the role of photosynthesis in stomatal opening responses. High resolution chlorophyll a fluorescence imaging showed that the quantum efficiency of photosystem II electron transport (Fq′/Fm′) was decreased similarly in both guard and mesophyll cells of the SBPase antisense plants compared to the wild-type plants. This demonstrated for the first time that photosynthetic operating efficiency in the guard cells responds to changes in the regeneration capacity of the Calvin cycle. The rate of stomatal opening in response to a 30 min, 10-fold step increase in red photon flux density in the leaves from the SBPase antisense plants was significantly greater than wild-type plants. Final stomatal conductance under red and mixed blue/red irradiance was greater in the antisense plants than in the wild-type control plants despite lower CO2 assimilation rates and higher internal CO2 concentrations. Increasing CO2 concentration resulted in a similar stomatal closing response in wild-type and antisense plants when measured in red light. However, in the antisense plants with small reductions in SBPase activity greater stomatal conductances were observed at all Ci levels. Together, these data suggest that the primary light-induced opening or CO2-dependent closing response of stomata is not dependent upon guard or mesophyll cell photosynthetic capacity, but that photosynthetic electron transport, or its end-products, regulate the control of stomatal responses to light and CO2.

Spectral Irradiance Available for Turfgrass Growth in Sun and Shade

The spectral quality of solar radiance affects plant growth and development. The purpose of this study was to assess the spectral quality of deciduous shade, coniferous shade, building shade, and full sun in a natural environment common to turfgrass growth throughout a day and throughout a growing season. A spectroradiometer was used to acquire solar spectra in these four environments. Acquisitions were made on an hourly basis from 0730 to 1930 h, biweekly, from vernal equinox to autumnal equinox at The Ohio Turfgrass Foundation Research and Educational Center and from 10 April to 1 July 1997 at The Ohio State University campus. Data were tested for variation in spectral quality between morning hours and afternoon hours in full sun and among full sun and deciduous, coniferous, and building shade. Results indicated that changes in spectral quality occurred between morning and afternoon periods in full sun, but total (red + blue) photosynthetically active irradiance was not affected. Measurements indicated that a deciduous tree and a conifer tree filtered significantly more high activity (red + blue) quanta than a building. Blue irradiance relative to total irradiance increased and red irradiance decreased with increasing shade density. Significant differences were detected between full sun, tree shade, and building shade for blue photoreceptor potential (blue photon flux/far‐red photon flux) and phytochrome potential (red photon flux/far‐red photon flux). Results indicated that relationships among blue, red, and far‐red irradiance that influence many plant responses were affected by both shade source and shade density.

Influence of Covering Material and Shading on the Spectral Distribution of Light in Greenhouses

The solar photon flux distribution was measured in the range from 400 to 1100 nm under a twin-span glasshouse and under the same glasshouse with blanked roof, external shading net and internal aluminized shade-screen. Measurements were also carried out under a twin-span polyethylene greenhouse, a multi-span greenhouse with fibreglass and a polyethylene tunnel. For each greenhouse configuration, the measured solar photon flux spectra were used to calculate the solar transmission for the photosynthetically active radiation waveband (PAR), from 400 to 700 nm, the near infrared waveband (NIR), from 700 to 1100 nm, and the whole waveband (TOTAL), from 400 to 1100 nm. Other parameters having a physiological interest were also determined: the broadband PAR to TOTAL photon flux ratio and PAR to NIR photon flux ratio; and the morphogenesis-related parameters, such as the red to far red photon flux ratio, the phytochrome equilibrium, the relative cycling rate, the blue to red photon flux ratio and the blue to far red photon flux ratio. The results provided a better insight on the quantitative and qualitative properties of the light environment under each greenhouse configuration. Some significant differences in the values of blue light quality related parameters were found between greenhouses. Minor changes were observed on the PAR:TOTAL and PAR:NIR photon flux ratios, but indicated that glass and blanking tend to enrich the PAR content of the transmitted light, while the two plastic cover materials have the opposite effect, enriching the NIR content. These results stressed the need for a more precise characterization of modifications in light quality induced by greenhouse materials or shading devices as plant photosynthetic and photomorphogenetic responses may be significantly influenced by these modifications.