An in situ study of photosynthetic oxygen exchange and electron transport rate in the marine macroalga Ulva lactuca (Chlorophyta) (original) (raw)
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Photosynthesis Research, 2003
The relationship between O2-based gross photosynthesis (GP) and in vivo chlorophyll fluorescence of Photosystem II-based electron transport rate (ETR) as well as the relationship between effective quantum yield of fluorescence (ΦPSII) and quantum yield of oxygen evolution (ΦO_2) were examined in the green algae Ulva rotundata and Ulva olivascens and the red alga Porphyra leucosticta collected from the field and incubated for 3 days at 100 μmol m−2 s−1 in nutrient enriched seawater. Maximal GP was twice as high in Ulva species than that measured in P. leucosticta. In all species ETR was saturated at much higher irradiance than GP. The initial slope of ETR versus absorbed irradiance was higher than that of GP versus absorbed irradiance. Only under absorbed irradiances below saturation or at values of GP 2 m−2 s−1 a linear relationship was observed. In the linear phase, calculated O2 evolved /ETR molar ratios were closed to the theoretical value of 0.25 in Ulva species. In P. leucosticta, the estimated GP was associated to the estimated ETR only at high irradiances. ETR was determined under white light, red light emitting by diodes and solar radiation. In Ulva species the maximal ETR was reached under red light and solar radiation whereas in P. leucosticta the maximal ETR was reached under white light and minimal under red light. These results are in agreement with the known action spectra for photosynthesis in these species. In the case of P. leucosticta, GP and ETR were additionally determined under saturating irradiance in algae pre-incubated for one week under white light at different irradiances and at white light (100 μmol m−2 s−1) enriched with far-red light. GP and growth rate increased at a growth irradiance of 500 μmol m−2 s−1 becoming photoinhibited at higher irradiances, while ETR increased when algae were exposed to the highest growth irradiance applied (2000 μmol m−2 s−1). The calculated O2 evolved /ETR molar ratios were close to the theoretical value of 0.25 when algae were pre-incubated under 500–1000 μmol m−2 s−1. The enrichment by FR light provoked a decrease in both GP and ETR and an increase of nonphotochemical quenching although the irradiance of PAR was maintained at a constant level. In addition to C assimilation, other electron sinks, such as nitrogen assimilation, affected the GP–ETR relationship. The slopes of GP versus ETR or ΦPSII versus ΦO_2 were lower in the algae with the highest N assimilation capacity, estimated as nitrate reductase activity and internal nitrogen contents, i.e., Ulva rotundata and Porphyra leucosticta, than that observed in U. olivascens. The possible mechanisms to explain this discrepancy between GP and ETR are discussed.
European Journal of Phycology, 2004
Pulse amplitude modulated (PAM) fluorometry can be used for measuring photosynthetic electron transport rates (ETR) of marine angiosperms and macroalgae both in the laboratory and in situ. Regarding macroalgae, quantitative values and linear correlations between ETR and rates of photosynthetic O 2 evolution have so far been shown only for a few species under low irradiances. As a logical continuation of such work, the aim of the present study was to (a) assess to what degree high irradiances would limit such measurements and (b) evaluate whether PAM fluorometry could be used quantitatively also for other marine macroalgae from different phyla. This was done by comparing ETR with rates of gross O 2 evolution (net O 2 exhcange corrected for dark respiration) at various irradiances for the green alga Ulva lactuca grown at two irradiances, the brown algae Fucus serratus and Laminaria saccharina and the red algae Palmaria palmata and Porphyra umbilicalis. At low irradiances, there was a clear positive correlation between O 2 evolution and fluorescence-based ETR. At high irradiances, however, all algae featured an apparent decrease in ETR while O 2 evolution remained relatively constant, and this resulted in markedly increasing O 2 /ETR ratios. This anomaly could be nicely illustrated in plots of O 2 /ETR as a function of the effective quantum yield of photosystem II (Y). Such plots showed that the O 2 /ETR ratio generally started to increase when Y reached a critical low value of c. 0.1. It was further found that the irradiance at which this value was reached varied with species and previous light histories. Thus, it is the Y value, rather than the irradiance per se during PAM fluorescence measurements, that determines the upper limit for correct ETR measurements. Based on these results, it is recommended that Y be monitored during fluorescence measurements, and that ETR be used as a measure of photosynthetic rate only in cases where Y exceeds a critical low value, such as exemplified here.
Journal of Experimental Botany, 2020
Short-term effects of pCO2 (700–380 ppm; High carbon (HC) and Low carbon (LC), respectively) and nitrate content (50–5 µM; High nitrogen (HN) and Low nitrogen (LN), respectively on photosynthesis were investigated in Ulva rigida (Chlorophyta) under solar radiation (in-situ) and in the laboratory under artificial light (ex-situ). After six days of incubation at ambient temperature (AT), algae were subjected to a 4 °C temperature increase (AT+4 °C) for 3 d. Both in-situ and ex-situ maximal electron transport rate (ETRmax) and in situ gross photosynthesis (GP), measured by O2 evolution, presented highest values under HCHN, and lowest under HCLN, across all measuring systems. Maximal quantum yield (Fv/Fm), and ETRmax of photosystem (PS) II [ETR(II)max] and PSI [ETR(I)max], decreased under HCLN at AT+4 °C. Ex situ ETR was higher than in situ ETR. At noon, Fv/Fm decreased (indicating photoinhibition), whereas ETR(II)max and maximal non-photochemical quenching (NPQmax) increased. ETR(II)ma...
Russian Journal of Plant Physiology - RUSS J PLANT PHYSIOL-ENGL TR, 2000
The use of relative variable fluorescence (RVF) of chlorophyll, as measured in the presence of Diuron, an inhibitor of electron transfer, for the estimation of the photosynthetic activity of plankton microalgae was analyzed under a wide range of light intensities in the PAR region. Oxygen evolution rates (estimated by the method of light and dark bottles and the amperometric method), RVF, and chlorophyll a concentration were measured in parallel in natural algal cenoses and microecosystems. When the previously used regression equation, in the form A = b(?F/Fd)CchlI, where A is O2 evolution rate (g/(m3 h), ?F/Fd is RVF (relative units), Cchl is chlorophyll a concentration (mg/m3), and I is light intensity (W/m2), was verified in the PAR region, we observed a nonlinear dependence of the correction coefficient b on I, which can be described by the formula b = 6.227 × 103vI. This result agrees with the hypothesis that chlorophyll a fluorescence quenching comprises photochemical (qQ) and...
Photosynthetic rates ofUlva(Chlorophyta) measured by pulse amplitude modulated (PAM) fluorometry
European Journal of Phycology, 2000
In this work, we attempt to quantify pulse amplitude modulated (PAM) chlorophyll fluorescence measurements in marine macroalgae in terms of photosynthetic rates. For this, the effective electron transfer quantum yield of photosystem II measured for two Ulva species, at various irradiances and inorganic carbon (Ci) concentrations, was multiplied by the estimated flux of photons absorbed by the photosynthetic pigments associated with this photosystem. The rates of electron transport (ETR) calculated in this way were then compared with rates of photosynthetic O # evolution as measured in association with the fluorescence measurements. It was found that the calculated ETRs correlated linearly with rates of ' gross ' O # evolution (net O # exchange corrected for dark respiration as measured immediately after turning off each irradiance level) within the range of irradiances applied (up to 608 µmol photons m −# s −"). The average molar O # \ETR ratio was 0n238 for Ulva lactuca and 0n261 for Ulva fasciata, which is close to the theoretical maximal value of 0n25. Rates of O # evolution at various concentrations of Ci also showed linear correlations with ETR, and the average molar O # \ETR ratio was 0n249. These results show that PAM fluorometry can be used as a practical tool for quantifying photosynthetic rates at least under moderate irradiances in thin-bladed macroalgae such as Ulva possessing a CO #-concentrating system. A comparison between the PAM-101 (which was used in Sweden for the light-and Ci-response measurements of Ulva lactuca) and the newly developed portable Diving-PAM (used for Ulva fasciata in Israel) showed that such fluorescence-based photosynthetic rate measurements can also be carried out in situ.
Physiologia Plantarum
Chlorophyll a fluorescence is a powerful tool for estimating photosynthetic efficiency, but there are still unanswered questions that hinder the use of its full potential. The present results describe a caveat in estimation of photosynthetic performance with so-called rapid light curves (RLCs) with pulse amplitude modulation fluorometers. RLCs of microalgae show a severe decrease in photosynthetic performance in high light, although a similar decrease cannot be seen with other methods. We show that this decrease cannot be assigned to energy-dependent non-photochemical quenching or photoinhibition or to the geometry of the algal sample. The measured decrease in electron transfer rate is small in the tested siphonaceuous algae and higher plants, but very notable in all planktonic species, exhibiting species-dependent variation in extent and reversibility. We performed in-depth analysis of the phenomenon in the diatom Phaeodactylum tricornutum, in which the decrease is the most pronounced and reversible among the tested organisms. The results suggest that quenching of fluorescence by oxidized plastoquinone alone cannot explain the phenomenon, and alternative quenching mechanisms within PSII need to be considered.
Flora - Morphology, Distribution, Functional Ecology of Plants, 2011
An optode device for net-photosynthesis measurements, based on oxygen-depending quenching of fluorescence from O 2-specific sensors, and PAM fluorometry have been used to study diurnal courses of net-photosynthesis and the F v /F m ratio of the submerged plant Lagarosiphon major. Plants were precultivated and studied in large mesocosm flow-through outdoor tanks under 50% and 80% shade cloth, respectively. Growth under the different shade cloths resulted in similar light compensation points (∼20 mol photons m −2 s −1), but strongly different light saturation levels, with about 150 mol m −2 s −1 for plants grown under 80% shade cloth and about 350 mol m −2 s −1 for plants grown under 50% shade cloth. Plants under both growth conditions showed a transient reduction of the maximum F v /F m value in the afternoon (down to 70% of the morning control values under 80% shade cloth and down to 85% under 50% shade cloth), which was not accompanied by a reduction of the net photosynthetic rate. This indicated that the fluorescence parameter F v /F m must not be a reliable indicator of the rate of photosynthesis under all conditions. The new photo-optical device became evidenced as a valuable tool not only for laboratory experiments, but also for field studies of gas exchange of submerged plants.
Measuring photosynthetic parameters in individual algal cells by Fast Repetition Rate fluorometry
1999
A Single Cell Fast Repetition Rate (SCFRR) fluorometer was developed to measure the quantum yield of photochemistry, the functional absorption cross section of PS II and the kinetics of electron transport on the acceptor side of PS II in individual algal cells. These parameters are used to quantify the cell-specific photosynthetic performance in natural phytoplankton assembledges in aquatic ecosystems. The SCFRR technique measures chlorophyll fluorescence transients induced by a precisely controlled series of excitation flashlets that cumulatively saturate PS II within 120 µs. To meet the requirement in the analysis for single algal cells, the measurements are conducted in micro volumes, such that the probability of probing more than one cell at a time is vanishingly low. We designed a novel, computer-controlled hydromechanical system to deliver a portion of the sample into the measuring chamber and, following measurement, remove it into one of six sorting containers. The fluorescence signal is induced by a series of high frequency flashlets obtained from high luminosity blue light-emitting diodes and is acquired by a novel red-sensitive PMT-based detection system exhibiting both high sensitivity and a very wide dynamic range. The wide dynamic range of the detector allows SCFRR measurements for a wide variety of cell sizes ranging from 1 to 100 µm equivalent spherical diameter. The compact and light-weight design makes the SCFRR Fluorometer applicable for both laboratory and field studies.