Critical Light Intensity Research Articles

The Effect of Decreasing Temperature up to Chilling Values on the in vivo F685/F735 Chlorophyll Fluorescence Ratio in Phaseolus vulgaris and Pisum sativum: The Role of the Photosystem I Contribution to the 735 nm Fluorescence Band ¶

The effect of leaf temperature (T), between 23 and 4°C, on the chlorophyll (Chl) fluorescence spectral shape was investigated under moderate (200 μE m−2 s−1) and low (30–35 μE m−2 s−1) light intensities in Phaseolus vulgaris and Pisum sativum. With decreasing temperature, an increase in the fluorescence yield at both 685 and 735 nm was observed. A marked change occurred at the longer emission band resulting in a decrease in the Chl fluorescence ratio, F685/F735, with reducing T. Our fluorescence analysis suggests that this effect is due to a temperature-induced state 1–state 2 transition that decreases and increases photosystem II (PSII) and photosystem I (PSI) fluorescence, respectively. Time-resolved fluorescence lifetime measurements support this interpretation. At a critical temperature (about 6°C) and low light intensity a sudden decrease in fluorescence intensity was observed, with a larger effect at 685 than at 735 nm. This is probably linked to a modification of the thylakoid membranes, induced by chilling temperatures, which can alter the spillover from PSII to PSI. The contribution of photosystem I to the long-wavelength Chl fluorescence band (735 nm) at room temperature was estimated by both time-resolved fluorescence lifetime and fluorescence yield measurements at 685 and 735 nm. We found that PSI contributes to the 735 nm fluorescence for about 40, 10 and 35% at the minimal (F0), maximal (Fm) and steady-state (Fs) levels, respectively. Therefore, PSI must be taken into account in the analysis of Chl fluorescence parameters that include the 735 nm band and to interpret the changes in the Chl fluorescence ratio that can be induced by different agents.

The Effects of Light, Rehilling, and Mulching on Greenshoulder and Internal Greening in Carrots

Greenshoulder (GS) and Internal greening (IG) in carrots (Daucus carota var. sativus) affect root appearance and can lead to significant economic loss. Experiments were conducted to quantify the critical light intensity that may trigger greening by exposing carrot hypocotyls to different light intensities. Chlorophyll a, b, and total chlorophyll were measured. The effects of rehilling on GS and IG were measured in a 2-yr field study with eight treatments imposed at various stages of growth. Another experiment to confirm the effects of rehilling by etiolating various genotypes was also conducted. Leaf area index, internal and external greening, and IG length were measured. Increasing light intensity enhanced chlorophyll a and b linearly and significantly. The highest amount of chlorophyll a, b, and total chlorophyll accumulation in hypocotyl occurred at the highest light intensity tested (320 μmol m -2 s -1 ). Rehilling reduced GS and IG significantly. However, the response varied significantly between seasons. In 2002, rehilling once at the early vegetative stage, initial bulking stage, or active bulking stage was effective in reducing GS and IG. In the 2003 field study, rehilling once at each of the three stages reduced GS and IG. Compared with the control, rehilling reduced GS by 10 to 21% and IG by 13 to 20%. Among the cultivars tested, mulching reduced GS only for Magno. The results suggest that GS and IG are induced at the hypoctoyl stage and that rehilling could reduce GS and IG considerably; however, the etiolation response appears to be genotype specific.

Thermooptical Properties of Gold Nanoparticles Embedded in Ice: Characterization of Heat Generation and Melting

We investigate the system of optically excited gold NPs in an ice matrix aiming to understand heat generation and melting processes at the nanoscale level. Along with the traditional fluorescence method, we introduce thermooptical spectroscopy based on phase transformation of a matrix. With this, we can not only measure optical response but also thermal response, that is, heat generation. After several recrystallization cycles, the nanoparticles are embedded into the ice film where the optical and thermal properties of the nanoparticles are probed. Spatial fluorescence mapping shows the locations of Au nanoparticles, whereas the time-resolved Raman signal of ice reveals the melting process. From the time-dependent Raman signals, we determine the critical light intensities at which the laser beam is able to melt ice around the nanoparticles. The melting intensity depends strongly on temperature and position. The position-dependence is especially strong and reflects a mesoscopic character of heat generation. We think that it comes from the fact that nanoparticles form small complexes of different geometry and each complex has a unique thermal response. Theoretical calculations and experimental data are combined to make a quantitative measure of the amount of heat generated by optically excited Au nanoparticles and agglomerates. The information obtained in this study can be used to design nanoscale heaters and actuators.

Photoperiod can be used to enhance growth and improve feeding efficiency in farmed rainbow trout, Oncorhynchus mykiss

The current studies examined whether photoperiod techniques could be successfully transferred to commercial freshwater rainbow trout farming practices, with the key aim being to enhance winter grow-out and production in “open/uncovered systems”. Four experiments were undertaken to assess the effects of photoperiod in relation to: growth and feeding regime in tank reared fry; light intensity and growth in tank reared fry; growth and feeding efficiency in cages; and the use of different lighting technologies (bulb colour temperature) in cages. Commercial field trials conducted over a 3-year period showed that exposure of different developmental stages of rainbow trout to periods of constant light from autumn to spring appeared to enhance growth rates and could improve feed conversion. Furthermore, exposure to higher light intensities appeared to promote greater growth and feeding efficiency in all stages of production. The importance of even light distribution in the culture system rather than a critical light intensity was also evident. The outcome of artificial light regimes has been the ability to increase growth rates by up to 25%, alter stock out times, and reduce production time by as much as 2 months.

Tingkat Kritis Intensitas Cahaya Relatif Lima Genotip Kacang Hijau (Vigna radiatus L.)

The aim of this experiment was to determine the critical relative light intensities (RLI) level of mungbean. The critical level was determined by 50% decreasing of grain yield. The experiment was conducted at the ILETRI (Indonesian Legume and Tuber Crops Research Institute), Malang, from February to May 2004. Five genotypes of mungbean, i.e. VC2768B, Kenari, Local Wongsorejo, Nuri and MLG 431 were grown in four relative light intensities (RLI) levels, respectively 100%, 75%, 50% and 25%, that were prepared before planting with artificial shading. The experimental design was a randomized complete block with three replicates. The results showed that reducing RLI increased specific leaf area, but decreased leaf number, leaf area, leaf, stem and root dry weight, as well as pod number, pod dry weight and grain yield per plant. Reducing RLI from 100% to 75%, 50% and 25% did result in 15%, 56% and 71% decreased grain yield of mungbean. The critical level of RLI on mungbean was 48% or was found at 52% shading. Key words: Vigna radiatus L., genotype, critical level, relative light intensities, growth, yield

Estimation of light requirement for the growth of Zostera marina in central Japan

: The present study was designed to estimate the critical light intensity required for growth of Zostera marina and that which determines its depth limit. Seeds of Z. marina collected at Matsunase, Ise Bay, Mie Prefecture, central Japan were germinated and grown to young plants of 10 cm in length. The young Z. marina were cultured for 1 week in various water temperatures, and their photosynthesis and respiration were measured under various photon irradiances. The daily compensation point was estimated by a mathematical model based on photosynthetic activity and diurnal changes in solar irradiance. The estimated daily compensation point of young Z. marina was 5.7% of sea surface. The depth limit was determined by the Beer–Lambert law concerning the relative solar irradiance on the sea surface and the extinction coefficient. Almost all previous studies report a shallower growing depth of Z. marina than the present result, but the lowest reported data agreed well with the current estimated depth limit. Therefore, the mathematical model in the present study can estimate the production and critical growing depth of Z. marina. The results suggest that the compensation depth is controlled mainly by the solar irradiance reaching the Z. marina beds.

Predicting the spatial dominance of phytoplankton in a light limited and incompletely mixed eutrophic water column using the PROTECH model

1. A phytoplankton community model [Phytoplankton RespOnses To Environmental CHange (PROTECH)] was used to examine the effect of a wide range of varied light intensities and mixed depths upon simulated phytoplankton populations. Two different column lengths of the simulated water body were examined (the upper 5 m and the whole 14.5 m water column) for each scenario.2. The hypotheses tested were that: (i) under low light intensity and/or deep mixing the simulated community will be dominated by a phytoplankter with a low critical light intensity; (ii) at high light intensity and shallow mixing the simulated community will be dominated by small, fast‐growing phytoplankters; (iii) under all conditions, except deep mixing, the largest proportion of phytoplankton biomass will be found near the surface.3. It was found under most conditions that, although there was a bloom in the upper column (dominated by algae such as Chlorella, Ceratium or Rhodomonas), the largest phytoplankton biomass in the water column was located 9 m below the surface and consisted of solely Asterionella. This bloom was missed by the 5‐m samples. Thus, using the whole column sample lengths, hypothesis (i) was not rejected but hypotheses (ii) and (iii) were refuted.4. The inclusion of specific movement characteristics of phytoplankton in the model allowed the possibility of the dominance of multiple spaces within the water column and should be included in any model‐based investigation of this topic. Further, the results from the model suggest that a reduced depth of mixing creates greater environmental heterogeneity, allowing more species to persist.

Effects of Illuminations at Night on Heading, Yield, and its Components in Rice Grown in the Early Season in Miyazaki Prefecture.

近年, 宮崎県においても夜間営業店舗や街路・道路上に設置された夜間照明が早期水稲の出穂遅延を引き起こし, 水稲に対する問題が生じてきている.本研究では夜間照明が早期水稲品種の出穂遅延に及ぼす影響および夜間照明時期と強さが早期水稲品種の出穂および収量並びにその構成要素に及ぼす影響を宮崎県総合農業試験場内の水田ほ場試験で検討した.夜間照明による出穂遅延はコシヒカリがきらり宮崎より大きく, 移植から出穂期までの長期照明ではコシヒカリが約4Lx, きらり宮崎が約30Lxの照度から出穂の遅延が認められた.夜間照明によるコシヒカリの出穂遅延は, 幼穂形成始期前18～3日の照明で最も大きく, 次いで幼穂形成始期前2～後12日において大きかった.分げつ期から出穂期までの照明では約6Lxから遅延し, 照度117Lxで約25日の遅れがみられ, また長稈となる傾向を示した.幼穂形成始期前2日～出穂期の照明では登熟歩合が低下した.コシヒカリの収量低下は幼穂形成始期後13日から出穂期までの照明で最も大きく, 夜間照明の時期が出穂に近いほど登熟歩合が低下し, 減収傾向が大きくなると考えられた.コシヒカリときらり宮崎の夜間照明に対する出穂反応の差から, 街灯等に近いところの水田には, きらり宮崎を栽培することによって被害の軽減が期待される.

Optical Switching Due to Local Kerr Nonlinearity in Attenuated Total Reflection Geometry

By employing attenuated total reflection geometries, we have numerically analyzed optical switching due to local Kerr nonlinearity by the coupled mode theory for a lossy polydiacetylene waveguide and explored the possibility of realizing the observation of optical attenuated total reflection (ATR) switching. We have adopted a Gaussian incident beam and have taken into account beam spread. It has been found that the choice of a proper beam spread of the incident Gaussian light leads to a considerable decrease of the critical light power and the critical light intensity required for the optical switching. Moreover, the effect of the incident beam width and guided layer thickness on the critical incident intensity and the critical incident power has been discussed.

The effect of decreasing temperature up to chilling values on the in vivo F685/F735 chlorophyll fluorescence ratio in Phaseolus vulgaris and Pisum sativum: the role of the photosystem I contribution to the 735 nm fluorescence band.

The effect of leaf temperature (T), between 23 and 4 degrees C, on the chlorophyll (Chl) fluorescence spectral shape was investigated under moderate (200 microE m-2 s-1) and low (30-35 microE m-2 s-1) light intensities in Phaseolus vulgaris and Pisum sativum. With decreasing temperature, an increase in the fluorescence yield at both 685 and 735 nm was observed. A marked change occurred at the longer emission band resulting in a decrease in the Chl fluorescence ratio, F685/F735, with reducing T. Our fluorescence analysis suggests that this effect is due to a temperature-induced state 1-state 2 transition that decreases and increases photosystem II (PSII) and photosystem I (PSI) fluorescence, respectively. Time-resolved fluorescence life-time measurements support this interpretation. At a critical temperature (about 6 degrees C) and low light intensity a sudden decrease in fluorescence intensity was observed, with a larger effect at 685 than at 735 nm. This is probably linked to a modification of the thylakoid membranes, induced by chilling temperatures, which can alter the spill-over from PSII to PSI. The contribution of photosystem I to the long-wavelength Chl fluorescence band (735 nm) at room temperature was estimated by both time-resolved fluorescence lifetime and fluorescence yield measurements at 685 and 735 nm. We found that PSI contributes to the 735 nm fluorescence for about 40, 10 and 35% at the minimal (F0), maximal (Fm) and steady-state (Fs) levels, respectively. Therefore, PSI must be taken into account in the analysis of Chl fluorescence parameters that include the 735 nm band and to interpret the changes in the Chl fluorescence ratio that can be induced by different agents.

Species Dynamics in Phytoplankton Blooms: Incomplete Mixing and Competition for Light.

With the eutrophication of many freshwaters and coastal environments, phytoplankton blooms have become a common phenomenon. This article uses a reaction-diffusion model to investigate the implications of mixing processes for the dynamics and species composition of phytoplankton blooms. The model identifies four key parameters for bloom development: incident light intensity, background turbidity, water column depth, and turbulent mixing rates. The model predicts that the turbulent mixing rate is a major determinant of the species composition of phytoplankton blooms. In well-mixed environments, the species with lowest "critical light intensity" should become dominant. But at low mixing rates, the species with lowest critical light intensity is displaced if other species obtain a better position in the light gradient. Instead of a gradual change in species composition, the model predicts steep transitions between the dominance regions of the various species. The model predicts a low species diversity: phytoplankton blooms in eutrophic environments should be dominated by one or a few species only. The model predictions are consistent with laboratory competition experiments and many existing field data. We recommend examining competition in phytoplankton blooms under well-controlled laboratory conditions, and we derive scaling rules that facilitate translation from the laboratory to the field.

Predictors of light-limited growth and competition of phytoplankton in a well-mixed water column

Based on a model of light limited growth, Huisman and Weissing found that in a well mixed water column with constant light supply (energy reaching the water surface), equilibrium growth and competition of phytoplankton for light can be characterised by a critical light intensity at the base of the column (I*out). The present study attempts to give a further insight into this model. We first analyse the dependence of the critical light intensity on four parameters: initial slope of the photosynthesis-intensity (p-I) curve, maximal photosynthetic rate, the light-saturated parameter Ikand specific carbon loss rate. Increases in the first two parameters tend to reduce the critical light intensity and increases in the last two tend to increase the critical light intensity. Then we analyse the performance of a model under variable light supply with a time-scale of 1 day (24 hr). Within this time-scale, the critical light intensity changes with time. However, the equilibrium growth and the outcome of competition for light can be adequately characterised by critical light extinction defined as the upper limit of total light extinction due to both biomass and non-living matter in the water column. Under constant light supply, a critical light intensity uniquely corresponds to a critical light extinction. Therefore, critical light extinction can be utilised to predict the equilibrium growth and the outcome of competition under both constant and variable light supply. By changing the maximal light supply at noon, seasonal succession of species composition of communities is investigated. The possible effect of two typical photoresponses, photoadaptation and photoinhibition, on growth and competiton are discussed. Copyright 1999 Academic Press.

COMPETITION FOR LIGHT BETWEEN PHYTOPLANKTON SPECIES: EXPERIMENTAL TESTS OF MECHANISTIC THEORY

According to recent competition theory, the population dynamics of phy- toplankton species in monoculture can be used to make a priori predictions of the dynamics and outcome of competition for light. The species with lowest ''critical light intensity'' should be the superior light competitor. To test this theory, we ran monoculture experiments and competition experiments with two green algae (Chlorella vulgaris and Scenedesmus protuberans) and two cyanobacteria (Aphanizomenon flos-aquae and a Microcystis strain) in light-limited continuous cultures. We used the monoculture experiments to estimate the critical light intensities of the species. Scenedesmus had by far the highest critical light intensity. The critical light intensities of Chlorella, Aphanizomenon,and Microcystis were rather similar. According to observation, Aphanizomenonhad a slightly lower critical light intensity than Chlorella and Microcystis. However, according to a model fit to the mono- culture experiments, Chlorella had a slightly lower critical light intensity than Microcystis, which in turn had a slightly lower critical light intensity than Aphanizomenon.These subtle differences between observed and fitted critical light intensities could be attributed to differences in the light absorption spectra of the species. The competition experiments were all consistent with the competitive ordering of the species according to the fitted critical light intensities: Chlorella displaced all three other species, Microcystis displaced both Aphanizomenon and Scenedesmus, and Aphanizomenon only displaced Scenedesmus. Not only the final outcomes, but also the time courses of competition predicted by the theory, were in excellent agreement with the experimental results for nearly all species combi- nations.

POPULATION DYNAMICS OF LIGHT-LIMITED PHYTOPLANKTON: MICROCOSM EXPERIMENTS

This paper investigates the extent to which the predictions of an elementary model for light-limited growth are matched by laboratory experiments with light-limited phytoplankton. The model and experiments link the population dynamics of phytoplankton species with changes in the light gradient caused by phytoplankton shading. The model predicts that a phytoplankton population should continue to grow until, at steady state, the light intensity at the bottom of the water column equals its critical light intensity. The experimental results were in good agreement with the theoretical predictions: (1) the steady-state population density increased with an increase of the incident light intensity, (2) the steady-state population density (per unit volume) was inversely proportional to mixing depth, (3) the steady-state population size (per unit area) decreased linearly with mixing depth, (4) the critical light intensity decreased with an increase of the incident light intensity, (5) the critical light intensity was approximately the same at each mixing depth, and (6) the time courses predicted by the model were in line with the observed time courses of population density and light penetration. Implications for phytoplankton ecology and aquatic production biology are discussed.

Species Dynamics in Phytoplankton Blooms: Incomplete Mixing and Competition for Light

With the eutrophication of many freshwaters and coastal environments, phytoplankton blooms have become a common phenomenon. This article uses a reaction‐diffusion model to investigate the implications of mixing processes for the dynamics and species composition of phytoplankton blooms. The model identifies four key parameters for bloom development: incident light intensity, background turbidity, water column depth, and turbulent mixing rates. The model predicts that the turbulent mixing rate is a major determinant of the species composition of phytoplankton blooms. In well‐mixed environments, the species with lowest “critical light intensity” should become dominant. But at low mixing rates, the species with lowest critical light intensity is displaced if other species obtain a better position in the light gradient. Instead of a gradual change in species composition, the model predicts steep transitions between the dominance regions of the various species. The model predicts a low species diversity: phytoplankton blooms in eutrophic environments should be dominated by one or a few species only. The model predictions are consistent with laboratory competition experiments and many existing field data. We recommend examining competition in phytoplankton blooms under well‐controlled laboratory conditions, and we derive scaling rules that facilitate translation from the laboratory to the field.

Synchronous Crepuscular Flight of Female Asian Gypsy Moths: Relationships of Light Intensity and Ambient and Body Temperatures

Female gypsy moths (Lymantria dispar) of Asian heritage studied in central Siberia and Germany exhibit a highly synchronous flight at dusk, after light intensity falls to about 2 lux. This critical light intensity sets the timing of flight behaviors independent of ambient temperature. Flight follows several minutes of preflight wing fanning during which females in Germany and those from a laboratory colony (derived from Siberian stock) raised their thoracic temperatures to 32–33°C at ambient temperatures of 19–22°C. Thoracic temperature of females in free flight exceeded the air temperature (19–22°C) by approximately 11–13°C. The duration of wing fanning was strongly dependent on ambient temperature. In Germany, where ambient temperatures at dusk ranged between 21 and 25°C, females wing fanned for only 2.1 ± 0.2 (SE) min; in the much colder temperatures prevalent at dusk in Bellyk, central Siberia (11–13°C), females spent 11.2 ± 0.6 min in preflight wing fanning. The majority (≤80%) of mated and even virgin females initiated flight during the evening of the day they eclosed. However, in Bellyk, a small proportion (12%) of females wing fanned for an extended time but then stopped, whereas others (8%) never wing fanned and, therefore, did not take flight. Females also were capable of flight when disturbed during the daylight hours in Germany where the maximal temperature was high (27–30°C), but not in Siberia, where temperatures peaked at only 17–19°C. However, Siberian females were able to propel themselves off the tree on which they were perched by executing several vigorous wing flicks when approached by the predaceous tettigoniid, Tettigonia caudata.

Rearrangement of light harvesting bacteriochlorophyll homologues as a response of green sulfur bacteria to low light intensities

The pigment composition of two species of green-colored BChl c-containing green sulfur bacteria (Chlorobium limicola and C. chlorovibrioides) and two species of brown-colored BChl e-containing ones (C. phaeobacteroides and C. phaeovibrioides) incubated at different light intensities have been studied. All species responded to the reduction of light intensity from 50 to 1 μEinstein(E) m(-2) s(-1) by an increase in the specific content of light harvesting pigments, bacteriochlorophylls and carotenoids. At critical light intensities (0.5 to 0.1 μE m(-2) s(-1)) only brown-colored chlorobia were able to grow, though at low specific rates (0.002 days(-1) mg prot(-1)). High variations in the relative content of farnesyl-bacteriochlorophyll homologues were found, in particular BChl e 1 and BChl e 4, which were tentatively identified as [M, E] and [I, E] BChlF e, respectively. The former was almost completely lost upon reduction of light intensity from 50 to 0.1 μE m(-2) s(-1), whereas the latter increased from 7.2 to 38.4% and from 13.6 to 42.0% in C. phaeobacteroides and C. phaeovibrioides, respectively. This increase in the content of highly alkylated pigment molecules inside the chlorosomes of brown species is interpreted as a physiological mechanism to improve the efficiency of energy transfer towards the reaction center. This study provides some clues for understanding the physiological basis of the adaptation of brown species to extremely low light intensities.

Nonlinear transient photovoltaic response in Al/C60/Au devices: Control of polarity with optical bias

We report fast (nanosecond) transient photovoltaic response and steady-state photovoltage of rectifying Al/C60/Au sandwich devices. The transient photovoltage changes polarity at a critical light intensity, which can be varied and controlled by applying steady-state light as bias. This ability to change the polarity of the transient photovoltaic response and to control the intensity at which the polarity changes sign offers potential for use in applications in the area of fast nonlinear optoelectronic detectors.

Growth and Competition in a Light Gradient

In this paper a general model for growth and competition in a light gradient is developed. The model is based on a few qualitative assumptions: (i) biomass is continuously distributed over depth; (ii) the light gradient is one-dimensional and uni-directional; (iii) photosynthesis is positively related to the local light intensity; and (iv) biomass growth is governed by the carbon balance. By introducing the concept of "quantum return", it is shown that growth can be quantified directly in terms of the light gradient. In monoculture, growth leads to a globally stable equilibrium, at which the light intensity at the bottom of the light gradient is reduced to a "critical light intensity" I*out, I*out is not affected by the background turbidity but negatively related to the light supply. When all species are similarly distributed over the light gradient, the outcome of competition can be inferred from this monoculture characteristic: the species with lowest I*out will competitively exclude all other species. In contrast, spatial differentiation of the competitors may lead to a completely different situation: several species may co-exist, and the species with lowest I*out may be competitively displaced by species with a better position in the light gradient.

Light‐Limited Growth and Competition for Light in Well‐Mixed Aquatic Environments: An Elementary Model

Light is never distributed homogeneously since it forms a gradient over biomass. As a consequence, the common theories on nutrient competition are not applicable to competition for light. In this paper, we investigate a model for light—limited growth and competition among phytoplankton species in a mixed water column. The model is based on standard assumptions such as Lambert—Beer's law of light absorption, a Monod equation for carbon uptake, and constant specific carbon losses. By introducing the concept of quantum return, we show that the dynamics of growth and competition can be quantified not only in terms of depth but also directly in terms of light availability. We argued that the crucial measure for phytoplankton growth is not a "critical depth" but a "critical light intensity," I*out. For each species, I*out corresponds to the equilibrium light intensity at the bottom of a water column when the species is grown in monoculture. I*out plays a role similar to the "critical nutrient concentration" R* used in models of nutrient—limited growth. For a constant light supply, the species with the lowest I*out will competitively exclude all other species. There are, however, some important differences between R* and I*out. Whereas R* reflects both the local and the total balance between nutrient uptake and nutrient losses, I*out only reflects the total carbon balance. Moreover, I*out decreases with increasing light supply, whereas R* is independent of the nutrient supply. As a consequence, (1) the outcome of competition for light may depend on the light supply, (2) the compensation point is not a good predictor for the outcome of competition, (3) the resource ratio hypothesis does not apply when species compete for both nutrients and light. The outcome of competition for nutrients and light may depend on the nutrient and light supply, on the mixing depth, and on the background turbidity due to inanimate substances.