Photon Flux Levels Research Articles

Growth and photosynthesis of Chinese cabbage plants grown under light-emitting diode-based light source

We compared growth and the content of sugar, protein, and photosynthetic pigments, as well as chlorophyll fluorescence parameters in 15- and 27-day-old Chinese cabbage (Brassica chinensis L.) plants grown under a high-pressure sodium (HPS) lamps or a light source built on the basis of red (650 nm) and blue (470 nm) light-emitting diodes (LEDs) with a red to blue photon ratio of 7: 1. One group of plants was grown at a photosynthetic photon flux (PPF) level of 391 ± 24 μ mol/(m2 s) (normal level); the other, at a PPF level of 107 ± 9 μ mol/(m2 s) (low light). Plants of the third group were firstly grown at the low light and then (on the 12th day) transferred to the normal level. When grown at the normal PPF level, the plants grown under LEDs didn’t differ from plants grown under HPS lamps in shoot fresh weight, but they showed a lower root fresh and dry weights and the lower content of total sugar and sugar reserves in the leaves. No differences in the pigment content and photosystem II quantum yield were found; however, a higher Chl a/b ratio in plants grown under LEDs indicates a different proportion of functional complexes in thylakoid membranes. The response to low light conditions was mostly the same in plants grown under HPS lamps and LEDs; however, LED plants showed a lower growth rate and a higher nonphotochemical fluorescence quenching. In the case of the altered PPF level during growth, the plant photosynthetic apparatus adapted to new conditions of illumination within three days. Plants grown under HPS lamps at a constant normal PPF level and those transferred to the normal PPF level on the 12th day, on the 27th day didn’t differ in shoot fresh weight, but in plants grown under LEDs, the differences were considerable. Our results show that LED-based light sources can be used for plant growing. At the same time, some specific properties of plant photosynthesis and growth under these conditions of illumination were found.

Estimation of the degree of polarization from a single speckle intensity image with photon noise

It is demonstrated that, if not appropriately taken into account, photon noise leads to a biased estimation of the degree of polarization from a single speckle intensity image. A new method for estimating the degree of polarization from a single speckle intensity image acquired at low photon flux level is thus proposed. Its precision and the limit critical photon level that does not deteriorate the performance up to a given precision are determined.

Shifting cultivation effects on Brazil nut ( Bertholletia excelsa) regeneration

Brazil nut ( Bertholletia excelsa), has emerged as the cornerstone of the extractive economy in much of the Amazon, but the debate continues as to whether or not current harvest levels have a detrimental effect on Brazil nut seedling recruitment. While regeneration studies to date have been conducted solely within mature forest, our study provides further insight into current Brazil nut regeneration dynamics, with a unique first look at regeneration in swidden fallows within two multiple-use areas in Acre, Brazil. Recruitment of individuals ≤10 cm diameter at breast height (dbh) was evaluated within three 9 ha mature forest plots and six fallows of 0.5–1.0 ha each. Higher mean densities of B. excelsa seedlings (individuals <1.5 m in height) were observed in fallow than in mature forest (12.7 and 5.3 individuals ha −1, respectively). A generalized linear mixed model analysis revealed that in addition to forest type, proximity to seed sources also explained seedling densities. Height and diameter growth of young B. excelsa individuals was positively related to light availability. Photosynthetic photon flux density levels were over three times higher in fallows versus mature forest during peak sunlight hours. Results suggest that fallow environments may provide favorable conditions for B. excelsa regeneration. Not only can anthropogenic disturbance in the form of shifting cultivation play a positive role in B. excelsa regeneration, its historic presence on the landscape could explain current Brazil nut densities and distributions. Finally, swidden fallows could potentially be managed for enhanced Brazil nut densities, which may provide an opportunity for greater income for extractive families while contributing to the sustainability of Brazil nut extraction and forest conservation in the long term.

Growth rate differences between four Chilean populations of edible seaweedChondracanthus chamissoi(Rhodophyta, Gigartinales)

The effects of temperature, photon flux density and photoperiod on the growth rate of female gametophytic and tetrasporophytic thalli of Chondracanthus chamissoi from four populations along the Chilean coast were studied in vitro. Both reproductive phases survived and grew under all the conditions tested, with growth rates varying between 0.1 and 7.5% day−1. The results showed higher growth rates with increases in temperature and photon flux density levels. The growth rate was higher in female gametophytic thalli in almost all treatments. The photoperiod did not cause significant differences in the growth rate for either reproductive phases in any of the populations studied. Temperature was the principal factor affecting the growth rate of C. chamissoi.

The Effects of CO2 Enrichment, Increased Light Irradiance, and Reduced Sucrose Concentration on Acclimatization of Micropropagated American Ginseng Plantlets

ABSTRACT American ginseng (Panax quinquefolius L.) plantlets produced by somatic embryogenesis were pre-acclimatized for four weeks inside growth chambers in a factorial design. The three factors of the experiment were CO2 concentration (400 and 3000 μL L−1), photosynthetic photon flux (30 and 50 μmol m−2 s−1) and sucrose concentration (0 and 15 g L−1) in the culture medium. The plantlets were subsequently transferred into a greenhouse where they were acclimatized for two weeks. Regardless of photosynthetic photon flux and sucrose levels, CO2 enrichment during the pre-acclimatization phase significantly increased (6.3%) the fresh mass of American ginseng plantlets in the growth chambers. This positive effect resulted in a 26.4% increase in fresh mass after the acclimatization phase in the greenhouse. CO2 enrichment during the pre-acclimatization phase also significantly increased (32%) leaf area after acclimatization, but had no significant effect on dry mass, height nor survival. Increased light irradiance and reduced sucrose concentration had no significant effects on the growth parameters and survival of American ginseng plantlets. Despite the biological and ecological constraints that limit growth and development of this species, CO2 enrichment could enhance its acclimatization.

Numerical Simulations of HH 555

We present three-dimensional (3D) gasdynamic simulations of the Herbig Haro object HH 555. HH 555 is a bipolar jet emerging from the tip of an elephant trunk entering the Pelican Nebula from the adjacent molecular cloud. Both beams of HH 555 are curved away from the center of the H II region. This indicates that they are being deflected by a sidewind probably coming from a star located inside the nebula or by the expansion of the nebula itself. HH 555 is most likely an irradiated jet emerging from a highly embedded protostar, which has not yet been detected. In our simulations we vary the incident photon flux, which in one of our models is equal to the flux coming from a star 1 pc away emitting 5 × 1048 ionizing (i.e., with energies above the H Lyman limit) photons per second. An external, plane-parallel flow (a sidewind) is coming from the same direction as the photoionizing flux. We have made four simulations, decreasing the photon flux by a factor of 10 in each simulation. We discuss the properties of the flow, and we compute Hα emission maps (integrated along lines of sight). We show that the level of the incident photon flux has an important influence on the shape and visibility of the jet. If the flux is very high, it causes a strong evaporation of the neutral clump, producing a photoevaporated wind traveling in the direction opposite to the incident flow. The interaction of the two flows creates a double shock surface around the clump, protecting it and the jet from the external flow. The jet only starts to curve when it penetrates through the working surface.

Enhancement of phenylpropanoid enzymes and lignin in Phalaenopsis orchid and their influence on plant acclimatisation at different levels of photosynthetic photon flux

Effects of three levels of photosynthetic photon flux (PPF: 60, 160 and 300 µmol m−2s−1) were investigated in one-month-old Phalaenopsis plantlets acclimatised ex vitro. Optimal growth, chlorophyll and carotenoid concentations, and a high carotenoid:chlorophyll a ratio were obtained at 160 µmol m−2s−1, while net CO2 assimilation (A), stomatal conductance (g), transpiration rate (E) and leaf temperature peaked at 300 µmol m−2s−1, indicating the ability of the plants to grow ex vitro. Adverse effects of the highest PPF were reflected in loss of chlorophyll, biomass, non-protein thiol and cysteine, but increased proline. After acclimatisation, glucose-6-phosphate dehydrogenase, shikimate dehydrogenase, phenylalanine ammonia-lyase (PAL) and cinnamyl alcohol dehydrogenase (CAD) increased, as did lignin. Peroxidases (POD), which play an important role in lignin synthesis, were induced in acclimatised plants. Polyphenol oxidase (PPO) and β-glucosidase (β-GS) activities increased to a maximum in acclimatised plants at 300 µmol m−2s−1. A positive correlation between PAL, CAD activity and lignin concentration was observed, especially at 160 and 300 µmol m−2s−1. The study concludes that enhancement of lignin biosynthesis probably not only adds rigidity to plant cell walls but also induces defence against radiation stress. A PPF of 160 µmol m−2s−1was suitable for acclimatisation when plants were transferred from in vitro conditions.

Comparison of centroid computation algorithms in a Shack-Hartmann sensor

Analytical theory is combined with extensive numerical simulations to compare different flavours of centroiding algorithms: thresholding, weighted centroid, correlation, quad cell (QC). For each method, optimal parameters are defined in function of photon flux, readout noise and turbulence level. We find that at very low flux the noise of QC and weighted centroid leads the best result, but the latter method can provide linear and optimal response if the weight follows spot displacements. Both methods can work with average flux as low as 10 photons per subaperture under a readout noise of three electrons. At high-flux levels, the dominant errors come from non-linearity of response, from spot truncations and distortions and from detector pixel sampling. It is shown that at high flux, centre of gravity approaches and correlation methods are equivalent (and provide better results than QC estimator) as soon as their parameters are optimized. Finally, examples of applications are given to illustrate the results obtained in the paper.

Effect of Photosynthetic Photon Flux and Temperature on Floral Evocation and Development in the Vernalization-sensitive Ornamental Perennial Salvia ×superba `Blaukönigin'

Varying photothermal ratios (PTR) were supplied to Salvia ×superba Stapf `Blaukönigin' during pre-inductive vegetative development with the exception of a short germination period under uniform conditions. In addition, both unvernalized plants and plants receiving a saturating vernalization treatment of 6 weeks at 5 °C were given two photosynthetic photon flux (PPF) levels (50 or 200 μmol·m-2·s-1) during subsequent inductive 16-hour long days. There were no effects of PTR treatments during vegetative development on subsequent flowering. However, the higher PPF level during inductive long days significantly accelerated floral evocation in unvernalized plants, lowering the leaf number at flowering. The effect was practically negligent after the vernalization requirement was saturated. In a second experiment, varying periods (4, 7, 10, and 14 days or until anthesis) at a PPF of 200 μmol·m-2·s-1 during 20-hour days were given at the beginning of a long-day treatment, either with or without preceding vernalization treatment. Flowering percentage increased considerably as the period at 200 μmol·m-2·s-1 was extended compared with plants grown at a lower PPF of 50 μmol·m-2·s-1. However, the leaf number on flowering plants was not affected, except in unvernalized plants receiving the highest PPF continuously until anthesis, where leaf number was reduced by almost 50%. We propose that the PPF-dependent flowering is facilitated either by the rate of ongoing assimilation or rapid mobilization of stored carbohydrates at the time of evocation. Abortion of floral primordia under the lower PPF (50 μmol·m-2·s-1) irrespective of vernalization treatment indicates that the assimilate requirement for flower bud development is independent of the mechanism for floral evocation.

Model-based Moisture Prediction of Root Medium and Irrigation Control in Potted Plant Production using Nutrient-flow Wick Culture (NFW) System

The uptake of water and nutrient in potted plants is greatly affected by irrigation conditions, and it influences the plant growth. This study aimed to examine the correlations between basic environmental parameters and plant growth in potted plants (kalanchoe) and to develop the models for adequate irrigation control. Growth chambers were developed for the experiments, and four levels of photosynthetic photon flux (PPF) were treated by using different numbers of shading films and lamps. Kalanchoe blossfeldiana cv. New Alter, grown in the nutrient-flow wick culture (NFW) system, was used. The 7-cm pots were filled with a 7:3 mixture of peat moss and perlite medium (v/v). The initial water content was set at about 26%. A total of 150 pots and plants with different growth stage were prepared for 4 weeks. A wick [12 × 1 cm (L × W)] was used in each pot. Leaf areas of plants and surface areas of the medium were analyzed by a plant image analysis system. For measuring the water losses of plants and pots during the growth stage, the initial water content of the substrates was maintained at about 55%. Water losses were measured at 9, 11, 13, 15, and 17 hours for all experiment periods by using an electron balance. Two models were developed for estimating water losses by evapotranspiration and water intake by water absorption. Finally, a model for estimating water content in the medium was tried. Growth and environment parameters showed high correlations with transpiration and evaporation, respectively. There was an interactive effect of VPD and PPF on the change of evapotranspiration. The amount of absorption was increased by time and decreased with increase of initial water content.

Effects of temperature, CO 2/O 2 concentrations and light intensity on cellular multiplication of microalgae, Euglena gracilis

Microalgae culture is likely to play an important role in aquatic food production modules in bioregenerative systems for producing feeds for fish, converting CO 2 to O 2 and remedying water quality as well as aquatic higher plants. In the present study, the effects of culture conditions on the cellular multiplication of microalgae, Euglena gracilis, was investigated as a fundamental study to determine the optimum culture conditions for microalgae production in aquatic food production modules including both microalgae culture and fish culture systems. E. gracilis was cultured under conditions with five levels of temperatures (25–33 °C), three levels of CO 2 concentrations (2–6%), five levels of O 2 concentrations (10–30%), and six levels of photosynthetic photon flux (20–200 μmol m −2 s −1). The number of Euglena cells in a certain volume of solution was monitored with a microscope under each environmental condition. The multiplication rate of the cells was highest at temperatures of 27–31 °C, CO 2 concentration of 4%, O 2 concentration of 20% and photosynthetic photon flux of about 100 μmol m −2 s −1. The results demonstrate that E. gracilis could efficiently produce biomass and convert CO 2 to O 2 under relatively low light intensities in aquatic food production modules.

QUALITY MONITORING OF POTATO TRANSPLANTS USING THERMAL AND VISUAL IMAGES

ISHS VII International Symposium on Protected Cultivation in Mild Winter Climates: Production, Pest Management and Global Competition QUALITY MONITORING OF POTATO TRANSPLANTS USING THERMAL AND VISUAL IMAGES

Optically nonlinear energy transfer in light-harvesting dendrimers.

Dendrimeric polymers are the subject of intense research activity geared towards their implementation in nanodevice applications such as energy harvesting systems, organic light-emitting diodes, photosensitizers, low-threshold lasers, and quantum logic elements, etc. A recent development in this area has been the construction of dendrimers specifically designed to exhibit novel forms of optical nonlinearity, exploiting the unique properties of these materials at high levels of photon flux. Starting from a thorough treatment of the underlying theory based on the principles of molecular quantum electrodynamics, it is possible to identify and characterize several optically nonlinear mechanisms for directed energy transfer and energy pooling in multichromophore dendrimers. Such mechanisms fall into two classes: first, those where two-photon absorption by individual donors is followed by transfer of the net energy to an acceptor; second, those where the excitation of two electronically distinct but neighboring donor groups is followed by a collective migration of their energy to a suitable acceptor. Each transfer process is subject to minor dissipative losses. In this paper we describe in detail the balance of factors and the constraints that determines the favored mechanism, which include the excitation statistics, structure of the energy levels, laser coherence factors, chromophore selection rules and architecture, possibilities for the formation of delocalized excitons, spectral overlap, and the overall distribution of donors and acceptors. Furthermore, it transpires that quantum interference between different mechanisms can play an important role. Thus, as the relative importance of each mechanism determines the relevant nanophotonic characteristics, the results reported here afford the means for optimizing highly efficient light-harvesting dendrimer devices.

Lipoxygenase activity and proline accumulation in leaves and roots of olive trees in response to drought stress

The olive tree (Olea europaea L.) is commonly grown in the Mediterranean basin and is able to resist severe and prolonged drought. Levels of proline (PRO) and malondialdehyde (MDA), and the lipoxygenase (LOX) activity were determined in 2-year-old olive plants (cv. 'Coratina') grown in environmental conditions characterized by high temperatures and high photosynthetic photon flux density levels and gradually subjected to a controlled water deficit for 20 days. Before and during the experimental period, leaf and root samples were collected and analysed for PRO and MDA. The levels of PRO increased in parallel with the severity of drought stress in both leaves and roots. Significant increases of LOX activity and MDA content were also observed during the progressive increment of drought stress in both leaf and root tissues. Measurements of transpiration and photosynthetic rate, stomatal conductance and substomatal CO(2) concentration were carried out during the experiment. The accumulation of PRO indicates a possible role of PRO in drought tolerance. The increases of MDA content and LOX activity show that the water deficit is associated with lipid peroxidation mechanisms.

The Growth and Photosynthetic Characteristics of Potato (Solanum tuberosum L.) Plantlets as Affected by Hydroponic Solution pH and EC, Light, and CO2

In vitro nodal cuttings of potato (Solanum tuberosum L.) `Atlantic' and `Russet Burbank' from bioreactor culture were hydroponically cultured for 28 days using a deep flow technique (DFT) system. The response of plant growth and photosynthesis to different levels of solution electrical conductivity (EC; 0.08, 0.15, 0.22 and 0.36 S·cm-1) and pH (3, 4, 5, 6 and 7) were studied. The best growth, characters of shoot length, total shoot and root fresh and dry weight, were obtained in nutrient solution of pH 6.0 and EC 0.15 S·cm-1 for `Atlantic', while pH 7.0 and EC 0.15 S·cm-1 were found to be best for `Russet Burbank'. Plantlet growth was reduced by low solution pH (3.0) and high EC level (0.36 S·cm-1). Photosynthetic rate, stomatal conductance, and transpiration rate were also found to be affected by EC levels. Down regulation of photosynthesis, as indicated by chlorophyll fluorescence results, were observed when potato plantlets were cultured under nutrient solution of higher EC level. Plantlet growth and photosynthetic rate increased as photosynthetic photon flux (PPF) levels increased from 50 to 250 μmol·m-2·s-1. Particularly, increasing PPF level had a more distinctive effect on plantlet growth than CO2 enrichment condition. It was apparent from this study that nutrient solution of pH 6.0 and 0.15 S·cm-1 EC in combination with high PPF level (250 μmol·m-2·s-1) were suitable for hydroponic culture of potato plantlets as it would maximize net photosynthetic rate, and achieve the highest growth rates.

Physiology of effects of temporary immersion bioreactors on micropropagated pineapple plantlets

Summary Temporary immersion bioreactors are an efficient tool for plant mass propagation because they increase multiplication rate and plant quality. Little knowledge is available on the ecosystem and physiological behavior of plantlets when using this new culture technique. In order to evaluate the effects of the conditions on physiological change of pineapple plantlets, a factorial experiment was conducted, where axillary clusters were cultured under two levels of photosynthetic photon flux (PPF): 80mmol m 22 s 21 (low) and 225mmol m 22 s 21 (high), using two culture methods (conventional micropropagation in liquid medium and a temporary immersion bioreactor) during the elongation phase. CO2 concentration in the headspace volume container was measured during a whole cycle of temporary immersion (3 h). At the time before the next immersion period, the levels of CO2 increased significantly to 14 171mmol mol 21 at high PPF. The maximal photosynthetic rate as well as the maximum quantum yield of photosystem II were low for plantlets cultivated in the temporary immersion bioreactor at high PPF. However, these plantlets showed large increases in sugar and nitrogen uptake and also increases in dry weight and foliar area. These results indicate that shoot growth did not totally depend on the photosynthesis process. In vitro pineapple plantlets appeared to use more nutrients in the culture medium than those from photosynthesis. In summary, temporary immersion bioreactor-derived plantlets showed remarkable nutrient uptake, indicating a higher photo-mixotrophic metabolism.

Photoautotrophic culture conditions and photosynthetic photon flux influence growth of Lilium bulblets in vitro

Lilium Asiatic hybrid ‘Mona’ bulblets were cultured in vitro for 100 d under photoautotrophic (CO2-enriched conditions and without sucrose in the medium) and heterotrophic (non-enriched CO2 conditions and sucrose-supplemented medium) methods and under various levels of photosynthetic photon flux (PPF). Bulblet growth and net photosynthetic rate (NPR) were analyzed. CO2− and PPF-enriched conditions enhanced the overall growth of bulblets, scale leaves, and roots. Heterotrophic conditions enhanced bulblet growth but higher PPF levels were inhibitory to the development of scale leaves. These results indicate the CO2− and PPF-enriched conditions (photoautotrophic conditions) are beneficial for the production of high-quality bulblets of Asiatic hybrid lilies in vitro

Broadband photon-number squeezing in light-emitting diodes at low photon-flux levels

We have investigated the squeezing of intensity-fluctuation below the full-shot-noise level in light-emitting diodes (LEDs) at low-photon flux levels. By using a tailor-made LED, the squeezing over a wide frequency range, near-dc to 1.5 GHz was achieved at an injection-current level as low as 100 μA. As a result, the number of photons, which can be expected in the sub-Poissonian light, was reduced to the order of 105 per pulse, nearly three orders of magnitude smaller than those obtained in commercial LEDs.

Regulation of eelgrass (Zostera marina) cover along depth gradients in Danish coastal waters

A large data set, collected under the national Danish monitoring program, was used to evaluate the importance of photon flux density (PFD), relative wave exposure (REI), littoral slope, and salinity in regulating eelgrass cover at different depth intervals in Danish coastal waters. Average eelgrass cover exhibited a bell-shaped pattern with depth, reflecting that different factors regulate eelgrass cover at shallow- and deep-water sites. The multiple logistic regression analysis was used to identify regulating factors and determine their role in relation to eelgrass cover at different depth intervals. PFD, REI, and salinity were main factors affecting eelgrass cover while littoral slope had no significant effect. Eelgrass cover increased with increasing PFD at water depths of more than 2 m, while cover was in versely related to REI in shallow water. This pattern favored eelgrass cover at intermediate depths where levels of PFD and REI were moderate. Salinity had a minor, but significant, effect on eelgrass cover that is most likely related to the varying costs of osmoregulation with changing salinity. The analysis provided a useful conceptual framework for understanding the factors that regulate eelgrass abundance with depth. Although the regression model was statistically significant and included the factors generally considered most important in regulating eelgrass cover, its explanatory power was low, especially in shallow water. The largest discrepancies between predicted and observed values of cover appeared in cases where no eelgrass occurred despite sufficient light and moderate levels of exposure (almost 50% of all observations). These discrepancies suggest that population losses due to stochastic phenomena, such as extreme wind events, played an important regulating role that is not adequately described by average exposure levels. A more thorough knowledge of the importance of such loss processes and the time scales involved in recovery of seagrass populations after a severe disturbance are necessary if we are to understand the regulation of seagrass distribution in shallow coastal areas more fully.

Photoautotrophic growth of sugarcane plantlets in vitro as affected by photosynthetic photon flux and vessel air exchanges

Explants of sugarcane, a C4 plant, were cultured in vitro for 18d on Floridalite (a solid cube consisting of vermiculite and cellulose fibers) used as supporting material with sugar-free Murashige and Skoog liquid medium with double-strength KH2PO4, MgSO4, FeSO4, and Na2-EDTA in the vessel with enhanced natural ventilation. CO2 concentration in the culture room was kept at 1500 μmol mol−1 (four times the atmospheric CO2 concentration) during the photoperiod. A factorial experiment was designed with two levels of photosynthetic photon flux (PPF) and three levels of N (number of air exchanges of the vessel). The results were compared with those in the control treatment (photomixotrophic culture using sugar-containing agar medium under low PPF and low N). PPF and N showed significant positive effects on the growth of sugarcane plantlets in vitro. In the photoautotrophic (using sugar-free medium) treatments with relatively high PPF (200–400 μmol m−2 s−1) and high N (2–10 h−1), the growth of plantlets was four to seven times greater than that in the control. Also, the culture period for multiplication and rooting was shortened from 30 d in the control to 18 d or less in the photoautotrophic, high PPF, and high N treatments. Use of porous supporting material in photoautotrophic treatments promoted rooting and plantlet growth significantly.