Irradiance Response Curve Research Articles

Photosynthetic characterization of three dominant plant species in the saline–alkaline soil of the Yellow River Delta, China

The diurnal variations of photosynthesis of three dominant species, including Glycine soja, Phragmites australis, and Cynanchum chinensis, in the Yellow River Delta in China have been studied under the same natural conditions using a Li-6400 portable photosynthesis system. The results showed that the curves of diurnal variations of net photosynthetic rate (PN) of the three plants were different. The diurnal variation of PN on C. chinensis was a midday depression pattern and had two peaks. However, PN of G. soja and P. australis showed single-peak curves. The transpiration rate (E) of G. soja was significantly higher than that of P. australis and C. chinensis, both showed single-peak curves. In general, the diurnal course of stomatal conductance (gs) followed the same pattern of PN. A similar diurnal pattern of intercellular CO2 concentration (Ci), vapor pressure deficit (VPD), and water use efficiency (WUE) was observed among different species. VPD showed single-peak curves, while WUE was characterized by double-peak curves, which was contrary to Ci. Linear correlations among photosynthetic variables and key environmental factors indicate high positive correlations between PN and E, PN and photosynthetic active radiation, PN and leaf temperature (Tleaf), PN and VPD, and between PN and gs except C. chinensis. Negative correlations among PN and relative humidity, PN and Ci were found. The irradiance response curves derived from the leaves were substantially affected by different species. C. chinensis showed highest apparent quantum efficiency, followed by P. australis and G. soja, while apparent dark respiration (Rd), convexity (k), light saturation point, and maximum gross CO2 assimilation rate (Pmax) of G. soja were higher than those of P. australis and C. chinensis. The irradiance response curve of PN and WUE of different plant species followed the same order: G. soja>C. chinensis>P. australis. They were both higher than most of other species. It was concluded that plant species adapting to the saline–alkaline habitat showed higher photosynthesis. In addition, G. soja is also effective to improve saline–alkaline soil quality.

Photosynthetic behavior of Spanish Arbequina and Italian Maurino olive (Olea europaea L.) cultivars under super-intensive grove conditions

The study was carried out in a four-year-old super-high density olive grove in Central Italy to compare leaf gas exchanges of Spanish Arbequina and Italian Maurino olive cultivars. Overall, from mid July to mid November, Maurino had a slightly higher maximum light-saturated net photosynthetic rate (PNmax) than Arbequina. The lowest and the highest PNmax values were recorded at the end of July and in mid November, respectively. Current-season leaves showed similar or slightly higher PNmax values than one-year-old leaves. During the day Maurino always had slightly higher values or values similar to Arbequina, with the highest PNmax being in the morning. Maurino had similar or higher dark respiration rate (RD) values compared to Arbequina. During the day, in both cultivars the RD was lower at 9:00 than in the afternoon. The pattern of the photosynthetic irradiance-response curve was similar in the two genotypes, but the apparent quantum yield (YQ) was higher in Maurino. In both cultivars intercellular CO2 concentration (Ci) tended to increase when PNmax decreased. The increase in Ci corresponded to a decrease in stomatal conductance (gs). The transpiration rate (E) increased from mid July to the beginning of August, then decreased in September and increased again in November. Particularly in the morning, the current-season leaves showed similar or slightly higher E values than the one-year-old leaves. During the day, in both cultivars and at both leaf ages, E was higher in the afternoon. No effects on leaf gas exchanges due to the presence or absence of fruit on the shoot were found. Overall, there was satisfactory physiological adaptation for Arbequina to the conditions of Central Italy and for Maurino to the superintensive grove conditions.

Two Components of Nocturnal Locomotor Suppression by Light

In nocturnal rodents, millisecond light ("flash") stimuli can induce both a large circadian rhythm phase shift and an associated state change from highly active to quiescence followed by behavioral sleep. Suppression of locomotion ("negative masking") is an easily measured correlate of the state change. The present mouse studies used both flashes and longer light stimuli ("pulses") to distinguish initiation from maintenance effects of light on locomotor suppression and to determine whether the locomotor suppression exhibits temporal integration as is thought to be characteristic of phase shift responses to pulse, but not flash, stimuli. In experiment 1, locomotor suppression increased with irradiance (0.01-100 microW/cm( 2)), in accordance with previous reports. It also increased with stimulus duration (3-3000 sec), but interpretation of this result is complicated by the ability of light to both initiate and maintain locomotor suppression. In experiment 2, an irradiance response curve was determined using a stimulus series of 10 flashes, 2 msec each, with total flash energy varying from 0.0025 to 110.0 J/m(2). This included a test for temporal integration in which the effects of two equal energy series of flashes that differed in the number of flashes per series (10 vs 100), were compared. The 10 flash series more effectively elicited locomotor suppression than the 100 flash series, a result consistent with prior observations involving flash-induced phase shifts. In experiment 3, exposure of mice to an 11-h light stimulus yielded irradiance-dependent locomotor suppression that was maintained for the entire stimulus duration by a 100-microW/cm(2) stimulus. Light has the ability to initiate a time-limited (30-40 min) interval of locomotor suppression (initiation effect) that can be extended by additional light (maintenance effect). Temporal integration resembling that seen in phase-shifting responses to light does not exist for either phase shift or locomotor suppression responses to flashes or for locomotor suppression responses to light pulses. The authors present an alternative interpretation of data thought to demonstrate temporal integration in the regulation of phase shift responses to light pulses.

Photosynthetic response of wheat cultivar to long-term exposure to elevated temperature

Wheat (Triticum aestivum L. cv. HD 2285) was grown in control (C) and heated (H) open top chambers (OTCs) for entire period of growth and development till maturity. The mean maximum temperature of the entire period was 3 °C higher in H-compared to C-OTCs. Net photosynthetic rate (PN) measured at different temperature (20–40 °C) of C-and H-grown plants showed greater sensitivity to high temperature in H-plants. PN measured at respective growth temperature was lower in H-compared to C-plants. The CO2 and irradiance response curves of photosynthesis also showed lesser response in H-compared to C-plants. The initial slope of PNversus internal CO2 concentration (PN/Ci) curve was lower in H-than C-plants indicating ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) limitation. In irradiance response curve, the plateau was lower in H-compared to C-plants which is interpreted as RuBPCO limitation. RuBPCO content in the leaves of C-and H-plants, however, was not significantly different. Ribulose-1,5-bisphosphate carboxylase (RuBPC) initial activity was lower in H-plants, whereas activity of fully activated enzyme was not affected, indicating a decrease in activation state of the enzyme. This was further substantiated by the observed decrease in RuBPCO activase activity in H-compared to C-plants. RuBPCO activase was thus sensitive even to moderate heat stress. The decrease in PN under moderate heat stress was mainly due to a decrease in activation state of RuBPCO catalysed by RuBPCO activase.

Chlorella sp.의 광합성과 균체 성장에 대한 kinetic model의 적합도 분석

녹색 미세조류인 Chlorella sp.를 사용하여 광도에 따른 미세조류의 비성정속도와 광합성을 측정하였고, 여러 가지 kinetic model을 이용해 실측된 자료에 가장 적합한 kinetic model을 모색하였다. Chlorella sp.는 광독립영양조건 (photoautotroph condition)과 27, 54, 81, 140, 281 <TEX>${\mu}mol/m^2{\cdot}s$</TEX>의 광도 하에서 배양되었으며 kinetic model을 사용하여 P-I 반응선도와 <TEX>${\mu}-I$</TEX> 반응선도를 구하였다. Chlorella sp.의 비성장속도와 광합성은 81 <TEX>${\mu}mol/m^2{\cdot}s$</TEX>에서 0.35/day, 0.94 <TEX>$mgO_2/g{\cdot}h$</TEX>로 가장 높았다. 실측된 자료를 기질속도론 (Tamiya), 광포화모형(hyperbolic tangent, 포아송 함수)과 두가지 광저해모형(Steel 지수함수, Andrew 기질저해함수)을 이용하여 그게 따른 계수를 추정하고 비교 분석하였다. <TEX>${\mu}-I$</TEX> 반응선도에서는 포화모형의 일종인 hyperbolic tangent 모형이 적합하였으며, P-I 반응선도에서는 광저해가 현저히 관찰되어 Steele 지수함수의 적합도가 우수하였다. We investigated which is the best kinetic model for expression of microalgal growth and photosynthesis by irradiance in green microalgae, marine Chlorella sp. is cultivated under 5 light intensities (27, 54, 81, 140, and 281 <TEX>${\mu}mol/m^2{\cdot}s$</TEX>). The maximum of specific growth rate and photosynthesis at light intensity of 81 <TEX>${\mu}mol/m^2{\cdot}s$</TEX> were observed as 0.35/day and 0.94 <TEX>$mg0_2/g{\cdot}h$</TEX>, respectively. To describe the effect of irradiance, we adapted both types for kinetic model fitting, saturation and inhibition models, Tamiya's modified Michaelis- Menten equation, hyperbolic tangent and Poisson function as saturation model, Steele's exponential and Andrew's function as the other and made the specific growth rate- irradiance response curve and photosynthesis- irradiance response curve. In case of microalgal growth, one of the saturation models, the hyperbolic tangent function was the most suitable, otherwise, the Steele's exponential function, one of the inhibition models, was suitable for photosynthesis.

Effects of Temperature on Photosynthetic Rates in Korean Fir (Abies koreana) between Healthy and Dieback Population

The present study was carried out on natural Korean fir forests (Abies koreana) growing in Mount Halla in Jeju Island, Korea (33 degrees 13-36' N and 126 degrees 12-57' E). Mount Halla is the highest mountain (1,950 m a.s.l.) in South Korea. On the Korean fir forests near the top of Mount Halla in Korea, we established permanent plots between dieback and healthy population. Each permanent plot includes both dieback and relatively healthy Korean fir individuals. Three sites in this study showed similar altitude, topographic position, aspects, slope, diameter at breast height, average height and ages. Net photosynthetic rates (P(N)) on different temperature regimes were evaluated to explain the forest dieback phenomenon on Korean fir populations. Light response curves were determined on three different temperature regimes: 15 degrees C, 20 degrees C and 25 degrees C. The irradiance response curve showed higher values in lower air temperatures. Generally, irradiance response curves of healthy Korean fir populations were higher than the dieback population at all sites.

Temperature Sensitivity of Photosynthesis in Lolium perenne Swards: A Comparison of Two Methods for Deriving Photosynthetic Parameters from in vivo Measurements

The seasonal variation in photosynthetic rate of grass swards is partly the result of changes in the environment and partly the result of changes in the photosynthetic capacity of the sward itself. We evaluated two types of photosynthesis equations regarding their capacity to analyse seasonal and short-term temperature effects on photosynthesis of ryegrass (Lolium perenne L.). Intact cores of a field-grown ryegrass sward were taken to the laboratory 10 d after cutting for measurement of photosynthesis under controlled conditions. This was done during two four-week periods, in summer and autumn. Net photosynthetic rate (PN) of the sward was lower in autumn than in summer. Both a simple negatively exponential photosynthesis irradiance-response curve and the Farquhar equations for photosynthesis were applied to the in vivo canopy measurements. Application of the irradiance-response curve showed that irradiance-saturated gross photosynthetic rate increased linearly with increasing temperature and was higher in summer than in autumn. The initial radiation use efficiency did not differ between the seasons but decreased with the temperature rise. This explains the observation that total canopy photosynthetic rate decreased after short-term temperature increases in both seasons. The parameters in Farquhar equations that represent the temperature sensitivity of the maximum electron transport rate and of the Michaelis-Menten constants for CO2 and O2 fixation could not be quantified satisfactorily. Parameterisation of the Farquhar equations was hampered by a lack of robust information on many biochemical parameters, and the use of simple empirical response-functions may be preferable in the case of in vivo canopy measurements on grass swards.

Modelling vertical migration of the cyanobacterium Microcystis

Computer models can be helpful tools to provide a better understanding of the mechanisms responsible for the complex movements of cyanobacteria resulting from changes in buoyancy and mixing of the water column in a lake. Kromkamp & Walsby (1990) developed a vertical migration model for Oscillatoria, that was based on the experimentally determined relationship between the rates of density change and photon irradiance in this cyanobacterium. To adapt this model to Microcystis, we determined related changes in carbohydrate content in cultures of Microcystis. Samples were incubated at various constant values of photon irradiance and then placed in the dark. The changes in carbohydrate content of the cells during these incubations were investigated. The relationship between the ratio of carbohydrate to protein and cell density in Microcystis was established to permit conversion of the rates of carbohydrate change to rates of density change. By plotting the calculated rates of density change against the values of photon irradiance experienced during the incubations, an irradiance-response curve of density change was established. The curve showed a distinct maximum at 278 mol photons m 2 s 1 . At higher values of photon irradiance, the rate of density change was strongly inhibited. A positive linear correlation was found between cell density and the rates of density decrease in the dark. The validity of the use of rate equations of density change, which are based on short-term incubations at constant values of photon irradiance, to predict density changes in Microcystis in fluctuating light regimes was tested. This was accomplished by measuring the time course of change in carbohydrate content of two continuous cultures of Microcystis, which were submitted to fluctuating light regimes, and comparing the results with the changes in the carbohydrate contents of these cultures predicted by the rate equations of carbohydrate change. The results showed good agreement: the rate equations of density change were therefore introduced into the model to simulate vertical migration of Microcystis .T he model predicts that the maximum migration depth of Microcystis will increase with colony size up to a maximum of 200 m radius. The effect of colony size on the net increase in cell density during the light period was also investigated with the model. It predicts that small colonies have a higher net increase in cell density than large colonies, but are inhibited at high photon irradiances at the surface.

Effects of UV radiation on photosynthesis of phytoplankton exposed to solar simulator light

A sunlight simulator was used to investigate the effects of short term irradiation on photosynthetic oxygen production and chlorophyll fluorescence in the unicellular algae Dunaliella salina and Ochromonas danica. Oxygen evolution was measured with a Clark-type electrode and initial ( F 0) and maximal ( F m) fluorescence were determined by means of a pulse amplitude-modulated (PAM) fluorometer. Using different long-pass filters, a UV exclusion study was performed comparing the effects of irradiation with full sun simulator light, with sun simulator light without UV-B and short wavelength UV-A radiation and without any UV component. In D. salina, exposure to full sun simulator light caused a marked drop in photochemical efficiency indicated by a decline in the initial slope of the irradiance-response curve for photosynthetic oxygen production and by a decrease in the ratio F v/ F m, whereas only a slight inhibition of photosynthetic activity was observed irradiating with PAR and UV-A radiation or with PAR alone. In the case of O. danica, a strong inhibition was observed under all irradiation conditions. The results are consistent with preliminary data obtained with outdoor experiments.

Photosynthetic light-response curves

Gradients in photosynthetic capacity through the leaf affect the shape of the irradiance-response curve. These gradients in photosynthetic capacity were manipulated by restraining leaves in different orientations. The shape or curvature of the light-response curve can be defined by Θ, where Θ=0 is a rectangular hyperbola and Θ=1 is a Blackman curve. Horizontal leaves had the highest Θ values when their adaxial (top) surface was illuminated and lowest Θ value when their abaxial (bottom) surface was illuminated

Photosynthetic light-response curves

Gradients in photosynthetic capacity through the leaf affect the shape of the irradiance-response curve. These gradients in photosynthetic capacity were manipulated by restraining leaves in different orientations. The shape or curvature of the light-response curve can be defined by Θ, where Θ=0 is a rectangular hyperbola and Θ=1 is a Blackman curve. Horizontal leaves had the highest Θ values when their adaxial (top) surface was illuminated and lowest Θ value when their abaxial (bottom) surface was illuminated. Vertical leaves had intermediate Θ values that were similar for illumination from either direction, indicating that both surfaces had similar photosynthetic capacities. The photosynthetic capacity near each surface was probed by measuring the resistance to photoinhibition by 2000 μmol quanta · m −2·s −1 for 2 h followed by 15 min dark relaxation. Resistance to photoinhibition was consistent with the amount of direct sunlight exposure during growth. By measuring three light-response curves for a given leaf, illuminating the leaf from either the adaxial or abaxial surface or with the adaxial and abaxial surfaces illiminated equally, it was possible to infer gradients in the light absorption and photosynthetic capacity of the leaf using a ten-layer model. The gradient in light absorption was not as steep as expected and the photosynthetic capacity declined from the adaxial surface but increased again approaching the abaxial surface, the increase being more pronounced in vertical leaves. The modelled gradients were qualitatively similar for dorsiventral and isolateral leaves. The gradients in light absorption and photosynthetic capacity were not identical and this results (1) in curvilinear relationships between the quantum efficiency of PSII determined by chlorophyll fluorescence and the quantum efficiency of leaf photosynthesis and (2) in light-response curves that slowly reach saturation rather than being abruptly truncated. The Θ value for the photosynthetic light-response curve will remain a parameter that has to be derived empirically, in contrast to the maximum quantum yield and photosynthetic capacity. The curvature factor, Θ, depends on CO2 partial pressure and the interplay between the gradients in light absorption and photosynthetic capacity through the leaf which can change depending on the light environment during growth.

Absence of red-light enhancement of phototropism in pea seedlings at limiting irradiances of blue light

The kinetics of phototropism were determined from infrared video recordings of third internodes of intact 7 d etiolated pea seedlings (Pisum sativum L. cv Alcan) exposed to continuous, unilateral blue light (460 nm). Small but significant curvatures (ca. 1–2°) were observed after a 2 h stimulation at 0.8 pmol m-2 s-1. Both latency (i.e., lag time) and rate of curvature were dependent on irradiance between 0.8 and 80 pmol m-2 s-1. Maximum rates of curvature at the highest irradiance of blue light were 74% greater in seedlings that received 2 min red light (270 J m-2) 20 h earlier, but latency was unaffected. An irradiance-response curve for curvature at 2 h was obtained with unilateral, broad-spectrum blue light between 4 and 90,000 pmol m-2 s-1. Maximum tropistic response in dark-grown seedlings (ca. 25°) occurred between 30 and 1000 pmol m-2 s-1. Peak response for red light-treated seedlings (ca. 55°) was obtained at 1000 pmol m-2 s-1. Above this irradiance, phototropism declined by 12–15° for both red-treated and dark-grown plants. Red light did not significantly stimulate phototropism at lower, limiting irradiances of blue light. The data do not support the hypothesis that phytochrome affects the amount or activity of a photoreceptor for phototropism.

Interactions between irradiance, nitrogen nutrition, and water stress in the sun-shade responses of Solanum dulcamara.

When grown with adequate water and nitrogen (12 mM NO 3- ) four clones of Solanum dulcamara from sun or shade habitats in Europe showed similar potential for acclimation of photosynthesis to irradiance level during growth. When grown with limiting nitrogen (0.6 mM NO 3- ) all clones showed a low potential for acclimation of photosynthesis to irradiance during growth. If limiting nitrogen was accompanied by water stress at high irradiance, the initial slope of the irradiance response curve, and the irradiance saturated rate of photosynthesis were depressed, especially in a clone from a shaded habitat. These interactions are discussed in terms of earlier reports on the sunshade responses and sun-shade ecotypic differentiation in this species.

The biogenesis of anthocyanins: X. The action spectrum for anthocyanin formation in Spirodela oligorrhiza

Anthocyanin formation by Spirodela oligorrhiza has been determined as a function of irradiance. The highest yields resulted when the plants were incubated for 40 hours in the dark after irradiation. Saturation was reached in the red at about 20 k.ergs (1.3 × 10 −8 Einsteins) per square millimeter. The irradiance response curve for white fluorescent light, however, did not reach saturation at the highest values applied, namely 600 kiloergs per square millimeter, and possible explanations for this behavior are discussed. Using irradiances within the proportionality range, and calibrated intensities of monochromatic light from a high energy arc in a grating spectrograph, the action spectrum for anthocyanin synthesis was determined. The band widths for each point were less than 4 mμ. The resulting spectrum shows sharp peaks at 705 and (when number of fronds is used as parameter) at 300 mμ. The latter band in the ultraviolet has not yet been reported in other plants. Both blue and green light were relatively ineffective. In spite of many attempts, no evidence for control of anthocyanin formation by a red: far-red reversible system could be obtained.