Photosynthetic rates ofUlva(Chlorophyta) measured by pulse amplitude modulated (PAM) fluorometry (original) (raw)
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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.
Photosynthesis Research, 2002
Direct comparisons between photosynthetic O2 evolution rate and electron transport rate (ETR) were made in situ over 24 h using the benthic macroalga Ulva lactuca (Chlorophyta), growing and measured at a depth of 1.8 m, where the midday irradiance rose to 400–600 μmol photons m−2 s−1. O2 exchange was measured with a 5-chamber data-logging apparatus and ETR with a submersible pulse amplitude modulated (PAM) fluorometer (Diving-PAM). Steady-state quantum yield ((Fm′−Ft)/Fm′) decreased from 0.7 during the morning to 0.45 at midday, followed by some recovery in the late afternoon. At low to medium irradiances (0–300 μmol photons m−2 s−1), there was a significant correlation between O2 evolution and ETR, but at higher irradiances, ETR continued to increase steadily, while O2 evolution tended towards an asymptote. However at high irradiance levels (600–1200 μmol photons m−2 s−1) ETR was significantly lowered. Two methods of measuring ETR, based on either diel ambient light levels and fluorescence yields or rapid light curves, gave similar results at low to moderate irradiance levels. Nutrient enrichment (increases in [NO3−], [NH4+] and [HPO42-] of 5- to 15-fold over ambient concentrations) resulted in an increase, within hours, in photosynthetic rates measured by both ETR and O2 evolution techniques. At low irradiances, approximately 6.5 to 8.2 electrons passed through PS II during the evolution of one molecule of O2, i.e., up to twice the theoretical minimum number of four. However, in nutrient-enriched treatments this ratio dropped to 5.1. The results indicate that PAM fluorescence can be used as a good indication of the photosynthetic rate only at low to medium irradiances.
Functional Plant Biology, 2021
This study documents the first validation of the suitability of the most common parameters and protocols used in marine ecophysiology to characterise photosynthesis by means of chlorophyll a fluorescence tools. We demonstrate that the effective yield of PSII (DF/Fm') is significantly underestimated when using short inductions times (1 min) following the rapid light curve protocol (RLC). The consequent electron transport rates (ETR) underestimations are species-specific and highly variable with irradiance and the photoacclimatory condition of the sample. Our analysis also questions the use of relative descriptors (relETR), as they not only overestimate photosynthesis, but overlook one of the fundamental components of the photosynthetic response: light absorption regulation. Absorptance determinations were fundamental to characterise the ETR response of low-pigmented seagrass leaves, and also uncovered relevant differences between two coral species and the accclimatory response of a cultured dinoflagellate to temperature. ETR and oxygen evolution determinations showed close correlations for all organisms tested with the expected slope of 4 e– per O2 molecule evolved, when correct photosynthesis inductions and light absorption determinations were applied. However, ETR curves cannot be equated to conventional photosynthetic response to irradiance (P vs E) curves, and caution is needed when using ETR to characterise photosynthesis rates above photosynthesis saturation (Ek). This validation strongly supports the utility of fluorescence tools, underlining the need to correct two decades of propagation of erroneous concepts, protocols and parameters in marine eco-physiology. We aim also to emphasise the importance of optical descriptions for understanding photosynthesis, and for interpreting fluorescence measurements. In combination with conventional gross photosynthesis (GPS) approaches, optical characterisations open an extraordinary opportunity to determine two central parameters of photosynthesis performance: the quantum yield (fmax) of the process and its minimum quantum requirements (1/fmax). The combination of both approaches potentiates the possibilities of chlorophyll a fluorescence tools to characterise marine photosynthesis biodiversity.
Measuring photosynthetic rates in seagrasses by pulse amplitude modulated (PAM) fluorometry
Marine Ecology Progress Series, 1998
Photosynthetic rates of seagrasses have until recently been measured a s gas exchange of chamber-enclosed leaves mainly in the laboratory, and in situ measurements under natural conditions are scarce. In this work we explore the possibility of rneasunng such rates by pulse amplitude modulated (PAM) fluorometry, using a newly developed underwater device. This was done by first comparing photosynthetic O2 evolution (net photosynthesis corrected for dark respiration) with rates of electron transport (ETR) derived from fluorescen.ce measurements of the effective quantum yield of photosystem I1 multiplied with the estlnlated photon flux of photosynthetic active radiation absorbed by this photosystem. In the field, ETRs were then measured both as rapid light curves (RLCs) and by in situ point measurements under ambient light during the day. Photosynthetic O2 volution showed a linear relationship with ETR within a range of irradiances for the Mediterranean seagrass Cymodocea nodosa, while the tropical Halophila stipulacea and a temperate intertidal population of Zostera marina exhibited decreasing O2 evolution rates relative to ETRs at high lrradiances. These differences are likely due to photorespiration, w h~c h is absent in C. nodosa. The molar ratio between photosynthetic O2 evolution and ETR within the range of their linear relationship was found to be 0.3 for C. nodosa, which is close to the theoretical stoichiometric ratio of 0.25, but was higher and lower for 2. manna and H. stjpulacea, respectively. Point measurements of ETR in the field showed good agreements wlth rates derived from RLCs for H. stipulacea and Z. marina, but values varied greatly between replicate measurements for C. nodosa a t high irradiances. It is speculated that this variation was partly due to lightflecks caused by waves in the shallow water where these measurements were done. In all, this work shows that PAM fluorometry can efficiently yield photosynthetic rates for seagrasses in the laboratory, without the typical lag experienced by O2 electrodes, a s well a s in situ under natural conditions which are not disturbed by enclosures. KEY WORDS. Marine angiosperms Photosynthesis . PAM fluorometry . Seagrasses O Inter-Research 1998 Resale of full article not permitted
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...
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.
A Monitoring-PAM fluorometer with high temporal resolution (every 5 min) was used to assess the effects on photosynthesis in Ulva rigida (Chlorophyta) during exposure to 2 different CO2 conditions: current (‘LC’, 390 ppm), and the predicted level for the year 2100 (‘HC’, 700 ppm) in a crossed combination with 2 different daily pulsed nitrate concentrations (‘LN’, 5 μM and ‘HN’, 50 μM) and 2 temperature regimes (ambient and ambient +4°C). Effective quantum yield (ΔF/Fm’) in the afternoon was lower under HCLN conditions than under the other treatments. The decrease in ΔF/Fm’ from noon to the afternoon was significantly lower under +4°C compared to ambient temperature. Maximal quantum yield (Fv/Fm) decreased during the night with a transient increase 1 to 3 h after sunset, whereas a transient increase in ΔF/Fm’ was observed after sunrise. These transient increases have been related to activation/deactivation of the electron transport rate and the relaxation of non-photochemical quenching. Relative electron transport rate was higher under the LC and +4°C treatment, but the differences were not significant due to high variability in daily irradiances. Redundancy analysis on the data matrix for the light periods indicates that photosynthetically active radiation through the day is the main variable determining the physiological responses. The effects of nutrient levels (mainly carbon) and experimental increase of temperature were low but significant. During the night, the effect of nutrient availability is of special importance with an opposite effect of nitrogen compared to carbon increase. The application of the Monitoring-PAM to evaluate the effects of environmental conditions by simulating climate change variations under outdoor-controlled, semi-controlled conditions is discussed.
Aquatic Biology, 2008
The present paper compares light-response patterns of electron transport rate (ETR) measured by imaging and conventional pulse-amplitude-modulated fluorescence (PAM) with that of gross O 2 evolution in naturally thin-leaved (Ulva lactuca) and thick-leaved (Fucus serratus) algae, as well as in 1 to 8 cell layer thick 'artificial thalli' built from layers of Enteromorpha intestinalis. At sub-saturating and saturating irradiances imaging ETR/ETR max provided a very accurate reflection of P/P max , which was different in thin and thick algae. There was no effect of tissue thickness on conventional ETR/ETR max , which was unrelated to P/P max at low irradiances. At super-saturating irradiances, imaging ETR/ETR max was reduced significantly compared to P/P max , which instead corresponded to conventional ETR/ETR max. Imaging F m was only related to thallus thicknesses from 1 to 4 cell layers but not beyond. Photoinhibition expressed by imaging PAM in thick thallus may have been compensated for by photosynthesis in deeper cells. Conventional F m was linearly related to thallus thickness from 1 to 8 cell layers. No photoinhibition was indicated at super-saturating irradiances by conventional PAM and O 2 evolution measurements that integrate the photosynthetic performance of the entire thallus of thick algae. At irradiances < 80 µmol m-2 s-1 , the O 2 /conventional ETR ratio was close to 0.25, whereas it decreased at higher irradiances in both thin and thick macroalgae. The O 2 /imaging ETR ratio was > 0.25 and increased further at super-saturating irradiances, in particular in thin algae. In conclusion, the type of PAM instrument may influence the light response of ETR. Likewise, the thallus thickness may affect the relationship between O 2 evolution and ETR. ETR recordings should be treated with caution and regarded as a compliment to O 2 measurements, particularly when thick-leaved macroalgae are studied.
Aquatic Botany, 2000
Pulse amplitude modulated (PAM) fluorometers can potentially be used for measurements of photosynthesis rates. In this work, we attempt to assess the validity of such measurements for two common tropical seagrass species using a newly marketed portable device. This was done by comparing calculated photosynthetic electron transport rates (ETRs), based on fluorescence parameters, with rates of photosynthetic O 2 evolution. While a linear relationship was found for Halophila ovalis over a wide range of photon irradiances, Halodule wrightii showed a curvilinear response with apparently lower rates of O 2 evolution at high irradiance. The apparent average molar ratio of O 2 evolution to ETR was 0.28 for H. stipulacea and 0.57 within the linear correlation range for H. wrightii; the deviation of the latter value from the theoretical maximal ratio of 0.25 mol O 2 evolved per mol electrons transported through the photosystems is discussed. Results from in situ fluorescence measurements of these two seagrasses in a shallow intertidal habitat at high natural irradiances show that photosynthesis of H. wrightii was significantly reduced at midday. The results demonstrate that PAM fluorometry can be used to measure photosynthetic performances in seagrasses. However, in order to quantify ETRs it may be necessary to determine the fraction of incident light absorbed by thicker-leaved species more exactly than was done in these initial trials.