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Effeltrich, Germany

Figueroa F.L.,University of Malaga | Conde-Alvarez R.,University of Malaga | Bonomi Barufi J.,Federal University of Santa Catarina | Celis-Pla P.S.,University of Malaga | And 5 more authors.
Aquatic Biology

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. © The authors 2014. Source

Klughammer C.,University of Wurzburg | Siebke K.,Heinz Walz GmbH | Schreiber U.,University of Wurzburg
Photosynthesis Research

Technical features and examples of application of a special emitter-detector module for highly sensitive measurements of the electrochromic pigment absorbance shift (ECS) via dual-wavelength (550-520 nm) transmittance changes (P515) are described. This device, which has been introduced as an accessory of the standard, commercially available Dual-PAM-100 measuring system, not only allows steady-state assessment of the proton motive force (pmf) and its partitioning into ΔpH and ΔΨ components, but also continuous recording of the overall charge flux driven by photosynthetic light reactions. The new approach employs a double-modulation technique to derive a continuous signal from the light/dark modulation amplitude of the P515 signal. This new, continuously measured signal primarily reflects the rate of proton efflux via the ATP synthase, which under quasi-stationary conditions corresponds to the overall rate of proton influx driven by coupled electron transport. Simultaneous measurements of charge flux and CO2 uptake as a function of light intensity indicated a close to linear relationship in the light-limited range. A linear relationship between these two signals was also found for different internal CO2 concentrations, except for very low CO2, where the rate of charge flux distinctly exceeded the rate of CO2 uptake. Parallel oscillations in CO2 uptake and charge flux were induced by high CO2 and O2. The new device may contribute to the elucidation of complex regulatory mechanisms in intact leaves. © 2013 The Author(s). Source

Pfundel E.E.,University of Wurzburg | Pfundel E.E.,Heinz Walz GmbH | Klughammer C.,Im Biefang 22 | Meister A.,Leibniz Institute of Plant Genetics and Crop Plant Research | Cerovic Z.G.,University Paris - Sud
Photosynthesis Research

The effect of stepwise increments of red light intensities on pulse-amplitude modulated (PAM) chlorophyll (Chl) fluorescence from leaves of A. thaliana and Z. mays was investigated. Minimum and maximum fluorescence were measured before illumination (F0 and FM, respectively) and at the end of each light step (F'0 and F'M, respectively). Calculated F'0 values derived from F0, FM and F'M fluorescence according to Oxborough and Baker (1997) were lower than the corresponding measured F'0 values. Based on the concept that calculated F'0 values are under-estimated because the underlying theory ignores PSI fluorescence, a method was devised to gain relative PSI fluorescence intensities from differences between calculated and measured F'0. This method yields fluorometer-specific PSI data as its input data (F0, FM, F'0 and F'M depend solely on the spectral properties of the fluorometer used. Under the present conditions, the PSI contribution to F0 fluorescence was 0.24 in A. thaliana and it was independent on the light acclimation status; the corresponding value was 0.50 in Z. mays. Correction for PSI fluorescence affected Z. mays most: the linear relationship between PSI and PSII photochemical yields was clearly shifted toward the one-to-one proportionality line and maximum electron transport was increased by 50 %. Further, correction for PSI fluorescence increased the PSII reaction center-specific parameter, 1/F0 - 1/FM, up to 50 % in A. thaliana and up to 400 % in Z. mays. © 2012 Springer Science+Business Media Dordrecht. Source

Porcar-Castell A.,University of Helsinki | Tyystjarvi E.,University of Turku | Atherton J.,University of Helsinki | Van Der Tol C.,University of Twente | And 5 more authors.
Journal of Experimental Botany

Chlorophyll a fluorescence (ChlF) has been used for decades to study the organization, functioning, and physiology of photosynthesis at the leaf and subcellular levels. ChlF is now measurable from remote sensing platforms. This provides a new optical means to track photosynthesis and gross primary productivity of terrestrial ecosystems. Importantly, the spatiotemporal and methodological context of the new applications is dramatically different compared with most of the available ChlF literature, which raises a number of important considerations. Although we have a good mechanistic understanding of the processes that control the ChlF signal over the short term, the seasonal link between ChlF and photosynthesis remains obscure. Additionally, while the current understanding of in vivo ChlF is based on pulse amplitude-modulated (PAM) measurements, remote sensing applications are based on the measurement of the passive solar-induced chlorophyll fluorescence (SIF), which entails important differences and new challenges that remain to be solved. In this review we introduce and revisit the physical, physiological, and methodological factors that control the leaf-level ChlF signal in the context of the new remote sensing applications. Specifically, we present the basis of photosynthetic acclimation and its optical signals, we introduce the physical and physiological basis of ChlF from the molecular to the leaf level and beyond, and we introduce and compare PAM and SIF methodology. Finally, we evaluate and identify the challenges that still remain to be answered in order to consolidate our mechanistic understanding of the remotely sensed SIF signal. © 2014 The Author. Source

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