Winter wheat plants were grown in open top chambers either at 365 µmol mol-1 (AC) or at 700 µmol mol-1 (EC) air CO2 concentrations. The photosynthetic response of flag leaves at the beginning of flowering and on four vertical leaf levels at the beginning of grain filling were measured. Net photosynthetic rates (PN) were higher at both developmental phases in plants grown at EC coupled with larger leaf area and photosynthetic pigment contents. The widely accepted Farquhar net photosynthesis model was parameterised and tested using several observed data. After parameterisation the test results corresponded satisfactorily with observed values under several environmental conditions. and N. Harnos, Z. Tuba, K. Szente.
The paper presents a simple box model simulating the temporal variation of atmospheric 13CO2 concentration, atmospheric CO2 mixing ratio and 13C content of plant material. The model is driven by observed meteorological and measured biosphere-atmosphere CO2 exchange data. The model was calibrated and validated using measurements from a Hungarian atmospheric monitoring station. The simulated atmospheric stable carbon isotope ratio data agreed well with the measured ratios considering both the magnitude and the seasonal dynamics. Observed deviations between the measured and simulated δ13Cair values were systematically negative in winters, while deviations were random in sign and smaller by an order of magnitude during periods when the vegetation was photosynthetically active. This difference, supported by a significant correlation between the deviation and modeled fossil fuel contributions to CO2 concentration, suggests the increased contribution of 13C-depleted fossil fuel CO2 from heating and the lower boundary layer heights during winter. and D. Hidy ... [et al.].
Theoretical modelling is often overlooked in photosynthesis research even if it can significantly help with understanding of explored system. A new model of light-induced photosynthetic reactions occurring in and around thylakoid membrane is introduced here and used for theoretical modelling of not only the light-induced chlorophyll (Chl) a fluorescence rise (FLR; the O-J-I-P transient), reflecting function of photosystem II (PSII), but also of the 820 nmtransmittance signal (I820), reflecting function of photosystem I (PSI) and plastocyanin (PC), paralleling the FLR. Correctness of the model was verified by successful simulations of the FLR and I820 signal as measured with the control (no treatment) sample but also as measured with 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone- (inhibits electron transport in cytochrome b 6/f) and methylviologen- (accepts electrons from iron-sulphur cluster of PSI) treated samples and with the control sample upon different intensities of excitation light. From the simulations performed for the control sample, contribution of the oxidised donor of PSI, P700, and oxidised PC to the I820 signal minimum (reflects maximal accumulations of the two components) was estimated to be 75% and 25%, respectively. Further in silico experiments showed that PC must be reduced in the dark, cyclic electron transport around PSI must be considered in the model and activation of ferredoxin-NADP+-oxidoreductase (FNR) also affects the FLR. Correct simulations of the FLR and I820 signal demonstrate robustness of the model, confirm that the electron transport reactions occurring beyond PSII affect the shape of the FLR, and show usefulness and perspective of theoretical approach in studying of the light-induced photosynthetic reactions.
a1_Shallow ponds with rapidly photosynthesising cyanobacteria or eukaryotic algae are used for growing biotechnology feedstock and have been proposed for biofuel production but a credible model to predict the productivity of a column of phytoplankton in such ponds is lacking. Oxygen electrodes and Pulse Amplitude Modulation (PAM) fluorometer technology were used to measure gross photosynthesis (PG) vs. irradiance (E) curves (PG vs. E curves) in Chlorella (chlorophyta), Dunaliella salina (chlorophyta) and Phaeodactylum (bacillariophyta). PG vs. E curves were fitted to the waiting-in-line function [PG = (PGmax × E/Eopt) × exp(1 — E/Eopt)]. Attenuation of incident light with depth could then be used to model PG vs. E curves to describe PG vs. depth in pond cultures of uniformly distributed planktonic algae. Respiratory data (by
O2-electrode) allowed net photosynthesis (PN) of algal ponds to be modelled with depth. Photoinhibition of photosynthesis at the pond surface reduced PN of the water column. Calculated optimum depths for the algal ponds were: Phaeodactylum, 63 mm; Dunaliella, 71 mm and Chlorella, 87 mm. Irradiance at this depth is ≈ 5 to 10 μmol m-2 s-1 photosynthetic photon flux density (PPFD). This knowledge can then be used to optimise the pond depth. The total net P N [μmol(O2) m-2 s-1] were: Chlorella, ≈ 12.6 ± 0.76; Dunaliella, ≈ 6.5 ± 0.41; Phaeodactylum ≈ 6.1 ± 0.35. Snell’s and Fresnel’s laws were used to correct irradiance for reflection and refraction and thus estimate the time course of PN over the course of a day taking into account respiration during the day and at night. The optimum PN of a pond adjusted to be of optimal depth (0.1-0.5 m) should be approximately constant because increasing the cell density will proportionally reduce the optimum depth of the pond and vice versa., a2_Net photosynthesis for an optimised pond located at the tropic of Cancer would be [in t(C) ha-1 y-1]: Chlorella, ≈ 14.1 ± 0.66; Dunaliella, ≈ 5.48 ± 0.39; Phaeodactylum, ≈ 6.58 ± 0.42 but such calculations do not take weather, such as cloud cover, and temperature, into account., R. J. Ritchie, A. W. D. Larkum., and Obsahuje bibliografii a dodatky
Irradiance data software developed by the NREL Solar Radiation Laboratory (Simple Model of Atmospheric Radiative Transfer of Sunshine, SMARTS) has been used for modelling photosynthesis. Spectra and total irradiance were expressed in terms of quanta [mol m-2 s-1, photosynthetic photon flux density, PPFD (400-700 nm)]. Using the SMARTS software it is possible to (1) calculate the solar spectrum for a planar surface for any given solar elevation angle, allowing for the attenuating effects of the atmosphere on extraterrestrial irradiance at each wavelength in the 400-700 nm range and for the thickness of atmosphere the light must pass through during the course of a day, (2) calculate PPFD vs. solar time for any latitude and date and (3) estimate total daily irradiance for any latitude and date and hence calculate the total photon irradiance for a whole year or for a growing season. Models of photosynthetic activity vs. PPFD are discussed. Gross photosynthesis (Pg) vs. photosynthetic photon flux density (PPFD) (Pg vs. I) characteristics of single leaves compared to that of a canopy of leaves are different. It is shown that that the optimum irradiance for a leaf (Iopt) is the half-saturation irradiance for a battery of leaves in series. A C3 plant, with leaves having an optimum photosynthetic rate at 700 μmol m-2 s-1 PPFD, was used as a realistic worked example. The model gives good estimates of gross photosynthesis (Pg) for a given date and latitude. Seasonal and annual estimates of Pg can be made. Taking cloudiness into account, the model predicts maximum Pg rates of about 10 g(C) m-2 d-1, which is close to the maximum reported Pg experimental measurements. and R. J. Ritchie.
We propose a dynamic model specifically designed to simulate changes in the photosynthetic electron transport rate, which is calculated from fluorescence measurements when plants are exposed, for a short time, to a series of increasing photon flux densities. This model simulates the dynamics of the effective yield of photochemical energy conversion from the maximum and natural chlorophyll fluorescence yields, taking into account a cumulative effect of successive irradiations on photosystems. To estimate a characteristic time of this effect on photosystems, two series of experiments were performed on two benthic diatom culture concentrations. For each concentration, two different series of irradiations were applied. Simplified formulations of the model were established based on the observed fluorescence curves. The simplified versions of the model streamlined the parameters estimation procedure. For the most simplified version of the model (only 4 parameters) the order of magnitude of the characteristic time of the residual effect of irradiation was about 38 s (within a confidence interval between 20 and 252 s). The model and an appropriate calibration procedure may be used to assess the physiological condition of plants experiencing short time-scale irradiance changes in experimental or field conditions. and J.-M. Guarini, C. Moritz.
We developed transgenic rice plants (Oryza sativa L. cv. Daeribbyeo) overproducing cytosolic glutathione reductase (GR) using a GR gene from Brassica campestris and studied their response to photo-oxidative stress in the presence of methyl viologen (MV, 10 and 50 μM concentrations) under room (25 °C) and moderately elevated (35 °C) temperature by analysis of chlorophyll (Chl) a fluorescence parameters (FV/FM, qN, and qP) and of Chl content. Elevated temperature enhanced and accelerated the photo-oxidative damage to photosynthetic apparatus expressed mainly by a fast decrease of qN. Higher temperature supported the protective reaction in transformed rice plants for lower MV concentration (10 μM) and eliminated the enhanced tolerance of photosystem 2 photochemistry to photooxidative stress for higher (50 μM) MV concentration. Different mechanisms and temperature dependence of oxidative and protective reactions explain the results. and R. Kouřil ... [et al.].
Changes in pigment composition and chlorophyll (Chl) fluorescence parameters were studied in 20 year-old Scots pine (Pinus sylvestris L.) trees grown in environment-controlled chambers and subjected to ambient conditions (CON), doubled ambient CO2 concentration (EC), elevated temperature (ambient +2-6 °C, ET), or a combination of EC and ET (ECT) for four years. EC did not significantly alter the optimal photochemical efficiency of photosystem 2 (PS2; Fv/Fm), or Chl a+b content during the main growth season (days 150-240) but it reduced Fv/Fm and the Chl a+b content and increased the ratio of total carotenoids to Chl a+b during the 'off season'. By contrast, ET significantly enhanced the efficiency of PS2 in terms of increases in Fv/Fm and Chl a+b content throughout the year, but with more pronounced enhancement in the 'off season'. The reduction in Fv/Fm during autumn could be associated with the CO2-induced earlier yellowing of the leaves, whereas the temperature-stimulated increase in the photochemical efficiency of PS2 during the 'off season' could be attributed to the maintenance of a high sink capacity. The pigment and fluorescence responses in the case of ECT showed a similar pattern to that for ET, implying the importance of the temperature factor in future climate changes in the boreal zone. and K. Y. Wang, S. Kellomäki, T. Zha.
Chlorophyll fluorescence measurements showed that plasticity to salinity in stems of Salicornia ramosissima is expressed at a modular level, so intraplant variation should be considered in further studies. and S. Redondo-Gómez ... [et al.].
Determination of modulated chlorophyll fluorescence coupled to measurements of the net photosynthetic rate (P^) leaf water potential has heen assessed as a screening method to score a set of twenty genotypes of barley {Hordeum vulgare L.) for drought tolerance. These methods can be ušed as rapid screening tests for water stress tolerance in barley, although applied alone they are appropriate indicators for a severe water stress. For genotypes growing under a mild water stress, it is necessary to use several screening tests simultaneously. Drought tolerant genotypes show smaller variations of photochemical quenching, P^, water use efficiency and leaf temperature than the drought sensitive ones.