Maximum Quantum Yield Of Photosynthesis Research Articles

Impact of climate change on the kelp Laminaria digitata – simulated Arctic winter warming

The Arctic is seasonally exposed to long periods of low temperatures and complete darkness. Consequently, perennial primary producers have to apply strategies to maximize energy efficiency. Global warming is occurring in the Arctic faster than the rest of the globe. The highest amplitude of temperature rise occurs during Polar Night. To determine the stress resistance of the ecosystem-engineering kelp Laminaria digitata against Arctic winter warming, non-meristematic discs of adult sporophytes from Porsangerfjorden (Finnmark, Norway) were kept in total darkness at 0°C and 5°C over a period of three months. Physiological variables, namely maximum quantum yield of photosynthesis (Fv/Fm) and dry weight, as well as underlying biochemical variables including pigments, storage carbohydrates, total carbon and total nitrogen were monitored throughout the experiment. Although all samples remained in generally good condition with Fv/Fm values above 0.6, L. digitata performed better at 0°C than at 5°C. Depletion of metabolic products resulted in a constant decrease of dry weight over time. A strong decrease in mannitol and laminarin was observed, with greater reductions at 5°C than at 0°C. However, the total carbon content did not change, indicating that the sporophytes were not suffering from “starvation stress” during the long period of darkness. A decline was also observed in the accessory pigments and the pool of xanthophyll cycle pigments, particularly at 5°C. Our results indicate that L. digitata has a more active metabolism, but a lower physiological and biochemical performance at higher temperatures in the Arctic winter. Obviously, L. digitata is well adapted to Arctic Polar Night conditions, regardless of having its distributional center at lower latitudes. Despite a reduced vitality at higher temperatures, a serious decline in Arctic populations of L. digitata due to winter warming is not expected for the near future.

Activation of stress reactions in the dinophyte microalga Prorocentrum cordatum as a consequence of the toxic effect of ZnO nanoparticles and zinc sulfate

According to the results of the experimental study, the main regularities of changes in morphological, structural-functional and fluorescent indices of P. cordatum were established when zinc oxide nanoparticles ZnO NPs (0.3–6.4 mg L−1) and Zn in form of salt (0.09–0.4 mg L−1) were added to the medium. The studied pollutants have cytotoxic (growth inhibition, development of oxidative stress, destruction of cytoplasmic organelles, disorganization of mitochondria) and genotoxic (changes in the morphology of nuclei, chromatin condensation) effects on microalgae, affecting almost all aspects of cell functioning. Despite the similar mechanism of action of zinc sulfate and ZnO NPs on P. cordatum cells, the negative effect of ZnO NPs is also due to the inhibition of photosynthetic activity of cells (significant decrease in the maximum quantum yield of photosynthesis and electron transport rate), reduction of chlorophyll concentration from 3.5 to 1.8 pg cell−1, as well as mechanical effect on cells: deformation and damage of cell membranes, aggregation of NPs on the cell surface. Apoptosis-like signs of cell death upon exposure to zinc sulfate and ZnO NPs were identified by flow cytometry and laser scanning confocal microscopy methods: changes in cell morphology, cytoplasm retraction, development of oxidative stress, deformation of nuclei, and disorganization of mitochondria. It was shown that the first signs of cell apoptosis appear at 0.02 mg L−1 Zn and 0.6 mg L−1 ZnO NPs after 72 h of exposure. At higher concentrations of pollutants, a dose-dependent decrease in algal enzymatic activity (up to 5 times relative to control) and mitochondrial membrane potential (up to 4 times relative to control), and an increase in the production of reactive oxygen species (up to 4–5 times relative to control) were observed. The results of the presented study contribute to the disclosure of fundamental mechanisms of toxic effects of pollutants and prediction of ways of phototrophic microorganisms reaction to this impact.

Iron oxide nanoparticles improving multimetal phytoextraction in Helianthus annuus

This study assessed the phytotoxicity of a mixture of five different trace elements (TEs) frequently found as pollutants in soils: arsenic, cadmium, copper, lead and zinc. On the other hand, the plant response to a magnetite (Fe3O4) nanoparticle amendment on this mixture as well as nanomagnetite remediation potential has been tested. Sunflower (Helianthus annuus) plants were grown for 90 days in soil contaminated with the five mentioned TEs at the limit levels of TEs in soils likely to receive sludge established by French legislation. Depending on the conditions, experimental set-ups were amended or not with 1% dry weight nanomagnetite (NPsMagn), citric acid-coated nanomagnetite (NPsMagn@CA) or micro-sized magnetite (μPs) in order to assess the behavior of nanomagnetites in a TEs-contaminated water-soil-plant system under repeated water-deficiency stress. The mixture of TEs did not induce phytotoxicity as estimated by plant growth, pigment content, maximum quantum yield of photosynthesis, oxidative impact and antioxidant response. Furthermore, both nanomagnetites treatments in a TEs-contaminated soil significantly increased biomass production by 64 % compared to control and antioxidant enzyme activities compared to control and TEs-treated plants. NPsMagn and NPsMagn@CA particularly enhance phytoextraction of Cd and Cu, increasing the amounts of TEs in aerial parts from 1.5 to 4.5 times compared to set-ups without nanomagnetites. Based on Cd, Cu, Pb and Zn contents in soil solutions, both nanomagnetites treatments improved TEs phytoextraction without increasing groundwater contamination. On the contrary, nanomagnetites significantly reduce arsenic uptake by plants and solubilization in dissolved phase. Our results show that modifying surface physicochemical properties of NPsMagn with citric acid coating does not improve their effects compared to bare NPsMagn. NPsMagn and NPsMagn@CA also appear to mitigate the effects of drought stress. This work highlights several positive environmental aspects related to the use of nanomagnetites in phytoremediation.

Interrelations between Canopy Architecture and Growth Yield Attribute on Selected Growth Habit Peanut Genotypes

Background: Crop architecture plays a major role in the growth and development of semi determinate crops like peanut.The orientation of branches and leaves in the plant canopy plays a major role in the radiation penetration, which influences the canopy photosynthetic rate and hence the crop productivity. Light penetration and radiation use efficiency effect the drymatter production of many crops. However, links between canopy orientation, growth attributes and yield potentiality of peanut are poorly understood. Hence the aim of the present study was to determine interrelationships among various growth habit peanut genotypes for canopy architecture, canopy photosynthesis, growth parameters and yield attributes. Methods: The experiment was laid out in a randomized block design with ten treatments and replicated thrice. Ten spanish bunch peanut genotypes varying in growth habits viz., decumbent-2, decumbent-3 and erect growth habit.Five plants were selected randomly in each plot by avoiding border rows and recorded canopy traits. Canopy photosynthetic parameters viz., light interception (Lux meter) and photosynthetic rate (IRGA) were recorded at the grand growth period (45 and 60 DAS). Result: Plant height had a significant negative correlation with peg to pod ratio. Among the various canopy architecture traits, wider angle between primary branch and main stem and number of secondary branches per plant established significantly positive correlation with rate of photosynthesis, radiation use efficiency, growth attributes, pod yield, shelling percentage and test weight. Spreading architecture exhibit a higher maximum quantum yield of photosynthesis.

The Change of Chlorophyll Content and Chlorophyll Efficiency in Epipremnum aureum by Water and pH

Epipremnum aureum (pothos) is an herbaceous species and is originated to tropical or subtropical South East Asia and Solomon islands. This study investigated the effect of excessive moisture on chlorophyll content and photosynthesis efficiency on E. aureum. The chlorophyll a, b, and total (chlorophyll a + b) contents were measured by using spectrophotometer. Fluorescence analysis for chlorophyll efficiency was measured with the PAM Chlorophyll Fluorometer. The chlorophyll content increases when moisture increases to 30%, but gradually decreases when it exceeds 40%. When the soil moisture was 80%, the values of chlorophyll a and b were 0.317 mg/g and 0.126 mg/g, respectively. This decreased the chlorophyll a, b, and total contents by 38.1%, 46.6%, and 36.8%, respectively, compared to 30% in 80% moisture. The chlorophyll content was highest at pH 6.5 of the soil. The content for chlorophylls a, b, and total were 0.471, 0.219, and 0.446 mg/g at pH 6.5, respectively. The correlation coefficients were subjected of the chlorophyll efficiency as a function of moistures. The change of chlorophyll efficiency in the quenched state (Fv) was also increased at 30% of moisture and then decreased steeply. The maximal possible value for fluorescence (Fm) was varied from 4310 (40% moisture) to 4220 (80% moisture). The Fm was varied from 4098 (pH 4.0) to 4356 (pH 6.5). The maximum quantum yield of photosynthesis (Fv/Fm) was varied from 0.798 (30% moisture) to 0.810 (60% moisture). The slope factors of Fo, Fm, Fv, and Fv/Fm for chlorophyll efficient indicators were 0.938, -0.806, 0.013, and 0.846, respectively. Excess watering decreased chlorophyll a, chl b, and chl (a + b) contents, and the chl a/b ratio in the E. aureum. The growth of this species was not as sensitive to pH compared to moisture.

Physiological Responses of Sargassum muticum, a Potential Golden Tide Species, to Different Levels of Light and Nitrogen

Sargassum golden tides have bloomed frequently in many sea areas throughout the world, and negatively impacted on the local marine ecology. Sargassum muticum commonly inhabits rocky shores. It is now distributed worldwide due to its invasiveness, and recently drifting individuals have been observed on the coasts of Canary Islands. However, as a potential golden tide alga, physiological, and ecological studies of this species have not been frequently explored. To investigate the responses of S. muticum to light and nitrogen, two key environmental factors in golden tide formation, we established three light levels (LL, low light, 10 μmol photons m–2 s–1; ML, medium light, 60 μmol photons m–2 s–1, and HL, high light, 300 μmol photons m–2 s–1) and two nitrogen levels (LN, low nitrogen, 25.0 μM of natural seawater; HN, high nitrogen, 125.0 μM), and cultivated the thalli under different conditions for 12 days before measuring the physiological properties of alga. The results showed that higher light and/or nitrogen levels enhanced the relative algal growth rate. The maximum net photosynthesis rate of alga increased with the light, while it remained unaffected by the nitrogen. The HN treatment had no effect on the apparent photosynthetic efficiency of algae in the LL culture, while increased it in the ML and HL cultures. The irradiance saturation point of photosynthesis was approximately 300 μmol photons m–2 s–1 with no significant difference among the six treatments, except for a slight increase under HLHN in contrast to the LLHN and MLLN treatments. HL treatment decreased the maximum quantum yield of photosynthesis (Fv/Fm) in both nitrogen levels. In the HN culture, ML and HL led to lower values of photoinhibition, indicating higher survivability in the alga. The HN culture led to higher nitrogen uptake but had no effects on Fv/Fm and the contents of pigments and soluble protein, regardless of culture light level. Based on these results, we speculate that drifting individuals of S. muticum would be possible to form a golden tide owing to its rapid growth rate at light level of 300 μmol photons m–2 s–1, when they encountered the sustained lower light level on the sea surface (≤300 μmol photons m–2 s–1). A high nitrogen supply caused by eutrophication of seawater might facilitate this process. Our results provide an important reference for the prediction of golden tides formed by S. muticum.

Growing in Mixed Stands Increased Leaf Photosynthesis and Physiological Stress Resistance in Moso Bamboo and Mature Chinese Fir Plantations.

Mixed-stand plantations are not always as beneficial for timber production and carbon sequestration as monoculture plantations. Systematic analyses of mixed-stand forests as potential ideal plantations must consider the physiological-ecological performance of these plantations. This study aimed to determine whether mixed moso bamboo (Phyllostachys pubescens (Pradelle) Mazel ex J. Houz.) and Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) stands exhibited better physiological-ecological performance than monoculture plantations of these species. We analyzed leaf photosynthesis, chlorophyll fluorescence, antioxidant enzyme activities, chlorophyll content and leaf chemistry in a moso bamboo stand, a Chinese fir stand and a mixed stand with both species. The results showed that both species in the mixed stand exhibited significantly higher leaf net photosynthesis rate (Amax), instantaneous carboxylation efficiency (CUE), chlorophyll content, maximum quantum yield of photosynthesis (Fv/Fm), photochemical quenching coefficient (qP), PSII quantum yield [Y(II)], leaf nitrogen content, and antioxidant enzyme activities than those in the monoculture plantations. However, the non-photochemical quenching (NPQ) in Chinese fir and 2-year-old moso bamboo was significantly lower in the mixed stand than in the monocultures. In addition, the water use efficiency (WUE) of Chinese fir was significantly higher in the mixed stand. The results suggest that the increase in leaf net photosynthetic capacity and the improved growth in the mixed stand could be attributed primarily to the (i) more competitive strategies for soil water use, (ii) stronger antioxidant systems, and (iii) higher leaf total nitrogen and chlorophyll contents in the plants. These findings suggest that mixed growth has beneficial effects on the leaf photosynthesis capacity and physiological resistance of moso bamboo and Chinese fir.

Light, Not Age, Underlies the Maladaptation of Maize and Miscanthus Photosynthesis to Self-Shading.

Zea mays and Miscanthus × giganteus use NADP-ME subtype C4 photosynthesis and are important food and biomass crops, respectively. Both crops are grown in dense stands where shaded leaves can contribute a significant proportion of overall canopy productivity. This is because shaded leaves, despite intercepting little light, typically process light energy very efficiently for photosynthesis, when compared to light-saturated leaves at the top of the canopy. However, an apparently maladaptive loss in photosynthetic light-use efficiency as leaves become shaded has been shown to reduce productivity in these two species. It is unclear whether this is due to leaf aging or progressive shading from leaves forming above. This was resolved here by analysing photosynthesis in leaves of the same chronological age in the centre and exposed southern edge of field plots of these crops. Photosynthetic light-response curves were used to assess maximum quantum yield of photosynthesis; the key measure of photosynthetic capacity of a leaf in shade. Compared to the upper canopy, maximum quantum yield of photosynthesis of lower canopy leaves was significantly reduced in the plot centre; but increased slightly at the plot edge. This indicates loss of efficiency of shaded leaves is due not to aging, but to the altered light environment of the lower canopy, i.e., reduced light intensity and/or altered spectral composition. This work expands knowledge of the cause of this maladaptive shade response, which limits productivity of some of the world’s most important crops.

Leaf gas exchanges responses of atemoya scion grafted onto Annona rootstocks

We examined the hypothesis that leaf gas exchange of scion is affected by different rootstocks in wood plants. We investigated daily courses of gas exchange and photosynthetic potential using the CO2 assimilation rates as a function of photosynthetic photon flux density, and then assessed CO2 response curves in atemoya scion (Annona × atemoya Mabb.) grafted onto araticum-de-terra-fria [A. emarginata (Schltdl.) H. Rainer var. terra-fria]: ATF, araticum-mirim [A. emarginata (Schltdl.) H. Rainer var. mirim]: ATM, biriba [A. mucosa (Bail.) H. Rainer]: ATB, atemoya (autograft): ATA, and in ungrafted atemoya plants: CTR. Throughout the entire evaluation period, the net assimilation rate (Anet) and stomatal conductance (gs) of CTR plants remained practically constant, being lower than those of grafted plants between 08:00 a.m. and 12:00 a.m., regardless of the rootstock used. Moreover, ATM plants proved to be more efficient in keeping the stomata open, even during the hottest hours of the day, improving Anet and carboxylation use efficiency. However, this occurred at the lowest maximum carboxylation rate of ribulose-1,5-bisphosphate (Vcmax). Overall, ATF plants presented a low light saturation point and photosynthetic electron transport rates, though increased maximum quantum yield of photosynthesis was observed. Thus, we accept our hypothesis and conclude that grafting might affect the photosynthetic metabolism of the atemoya hybrid, regardless of the combination used, which promotes enhanced Anet and low Vcmax and light saturation points.

Exploring Relationships between Canopy Architecture, Light Distribution, and Photosynthesis in Contrasting Rice Genotypes Using 3D Canopy Reconstruction.

The arrangement of leaf material is critical in determining the light environment, and subsequently the photosynthetic productivity of complex crop canopies. However, links between specific canopy architectural traits and photosynthetic productivity across a wide genetic background are poorly understood for field grown crops. The architecture of five genetically diverse rice varieties—four parental founders of a multi-parent advanced generation intercross (MAGIC) population plus a high yielding Philippine variety (IR64)—was captured at two different growth stages using a method for digital plant reconstruction based on stereocameras. Ray tracing was employed to explore the effects of canopy architecture on the resulting light environment in high-resolution, whilst gas exchange measurements were combined with an empirical model of photosynthesis to calculate an estimated carbon gain and total light interception. To further test the impact of different dynamic light patterns on photosynthetic properties, an empirical model of photosynthetic acclimation was employed to predict the optimal light-saturated photosynthesis rate (Pmax) throughout canopy depth, hypothesizing that light is the sole determinant of productivity in these conditions. First, we show that a plant type with steeper leaf angles allows more efficient penetration of light into lower canopy layers and this, in turn, leads to a greater photosynthetic potential. Second the predicted optimal Pmax responds in a manner that is consistent with fractional interception and leaf area index across this germplasm. However, measured Pmax, especially in lower layers, was consistently higher than the optimal Pmax indicating factors other than light determine photosynthesis profiles. Lastly, varieties with more upright architecture exhibit higher maximum quantum yield of photosynthesis indicating a canopy-level impact on photosynthetic efficiency.

Halocarbon emissions by selected tropical seaweeds: species-specific and compound-specific responses under changing pH.

Five tropical seaweeds, Kappaphycus alvarezii (Doty) Doty ex P.C. Silva, Padina australis Hauck, Sargassum binderi Sonder ex J. Agardh (syn. S. aquifolium (Turner) C. Agardh), Sargassum siliquosum J. Agardh and Turbinaria conoides (J. Agardh) Kützing, were incubated in seawater of pH 8.0, 7.8 (ambient), 7.6, 7.4 and 7.2, to study the effects of changing seawater pH on halocarbon emissions. Eight halocarbon species known to be emitted by seaweeds were investigated: bromoform (CHBr3), dibro­momethane (CH2Br2), iodomethane (CH3I), diiodomethane (CH2I2), bromoiodomethane (CH2BrI), bromochlorometh­ane (CH2BrCl), bromodichloromethane (CHBrCl2), and dibro­mochloromethane (CHBr2Cl). These very short-lived halocarbon gases are believed to contribute to stratospheric halogen concentrations if released in the tropics. It was observed that the seaweeds emit all eight halocarbons assayed, with the exception of K. alvarezii and S. binderi for CH2I2 and CH3I respectively, which were not measurable at the achievable limit of detection. The effect of pH on halocarbon emission by the seaweeds was shown to be species-specific and compound specific. The highest percentage changes in emissions for the halocarbons of interest were observed at the lower pH levels of 7.2 and 7.4 especially in Padina australis and Sargassum spp., showing that lower seawater pH causes elevated emissions of some halocarbon compounds. In general the seaweed least affected by pH change in terms of types of halocarbon emission, was P. australis. The commercially farmed seaweed K. alvarezii was very sensitive to pH change as shown by the high increases in most of the compounds in all pH levels relative to ambient. In terms of percentage decrease in maximum quantum yield of photosynthesis (Fv∕Fm) prior to and after incubation, there were no significant correlations with the various pH levels tested for all seaweeds. The correlation between percentage decrease in the maximum quantum yield of photosynthesis (Fv∕Fm) and halocarbon emission rates, was significant only for CH2BrCl emission by P. australis (r = 0.47; p ≤ 0.04), implying that photosynthesis may not be closely linked to halocarbon emissions by the seaweeds studied. Bromine was the largest contributor to the total mass of halogen emitted for all the seaweeds at all pH. The highest total amount of bromine emitted by K. alvarezii (an average of 98% of total mass of halogens) and the increase in the total amount of chlorine with decreasing seawater pH fuels concern for the expanding seaweed farming activities in the ASEAN region.

Inhibition of five natural products from Chinese herbs on the growth of Chattonella marina.

The effects of five natural products from Chinese herbs including evodiamine, curcumin, 4-methoxysalicylaldehyde, esculin hydrate, and gramine on the growth of Chattonella marina, one of the most noxious red tide algae, were observed. Among them, gramine exhibited the highest inhibitory rate with LC50, 96h of 0.51mg/l. After exposure to gramine, the activities of superoxide dismutase (SOD) and catalase (CAT), and content of malondialdehyde (MDA) increased in C. marina, suggesting that gramine could induce microalgae oxidative stress. In addition, chlorophyll a and the maximum quantum yield of photosynthesis (Fv/Fm) decreased following exposure to gramine, indicating the inhibition of photosynthesis activity in the microalgae. Combined with the fast inhibition against the algal cells and environmentally friendly character of gramine, we proposed that gramine might be a potential algaecide against marine harmful algae and that the oxidative damage and photosynthesis inhibition might be responsible for the toxicity of gramine on harmful algae.

Influence of culture medium recycling on the performance of Arthrospira platensis cultures

To reduce the water footprint of microalgae biomass production, it is essential to recycle the culture medium. The influence of medium recycling on the performance of the cyanobacterium Arthrospira platensis, the most widely cultivated microalgae, was investigated. Arthrospira was harvested with a 20μmmesh size microstrainer, which is the benchmark harvesting technology for Arthrospira production. Repeated recycling of the culture medium resulted in a decline in growth rate and the maximum quantum yield of photosynthesis (Fv/Fm) when compared to a control culture in fresh medium. This decline was accompanied by accumulation of organic matter in the culture medium (up to 104mgCL−1). This organic matter consists of 70% of sugars, mostly rhamnose-rich polysaccharides with uronic acids. Accumulation of polysaccharides resulted in a decrease in the filtration rate through the microstrainer used for harvesting. Part of the biomass escaped harvesting and was returned to the culture with the recycled medium. This resulted in a change in the Arthrospira population and reduction in the harvesting efficiency, but this change in population had no effect on the growth rate. The growth rate of Arthrospira in the recycled culture medium was primarily influenced by organic matter that accumulated in the medium.

The use of grafting to improve the net photosynthesis of cucumber

Grafting induces significant changes in the growth and development of plants. Additionally, photosynthesis is directly proportional to light, and the stomatal aperture decreases with decreases in irradiance. The present study aimed to evaluate daily gas exchange rates and the response curve of the CO2 assimilation rate as a function of photosynthetic photon flux density in grafted and non-grafted Japanese cucumber plants with the objective of studying the underlying physiology. Two similar experiments were conducted in 2009 and 2010. The Japanese cucumber hybrid ‘Taisho’ was grafted on the pumpkin hybrid ‘Excitte Ikki’ using the tongue approach method. The results indicated that grafting affected photosynthetic metabolism. As a result of this metabolic change, the grafted plants had a higher net CO2 assimilation rate, a lower maximum quantum yield of photosynthesis and a higher transpiration rate than the non-grafted plants. Furthermore, the non-grafted plants appeared to be more sensitive to environmental conditions, as they showed a higher water use efficiency, indicating an improved water saving capability a lower saturation point of photosynthesis by light than the grafted plants. This result suggests that grafted plants tend to tolerate higher radiance levels than non-grafted plants.

Spatial patterns and links between microbial community composition and function in cyanobacterial mats.

We imaged reflectance and variable fluorescence in 25 cyanobacterial mats from four distant sites around the globe to assess, at different scales of resolution, spatial variabilities in the physiological parameters characterizing their photosynthetic capacity, including the absorptivity by chlorophyll a (Achl), maximum quantum yield of photosynthesis (Ymax), and light acclimation irradiance (Ik). Generally, these parameters significantly varied within individual mats on a sub-millimeter scale, with about 2-fold higher variability in the vertical than in the horizontal direction. The average vertical profiles of Ymax and Ik decreased with depth in the mat, while Achl exhibited a sub-surface maximum. The within-mat variability was comparable to, but often larger than, the between-sites variability, whereas the within-site variabilities (i.e., between samples from the same site) were generally lowest. When compared based on averaged values of their photosynthetic parameters, mats clustered according to their site of origin. Similar clustering was found when the community composition of the mats' cyanobacterial layers were compared by automated ribosomal intergenic spacer analysis (ARISA), indicating a significant link between the microbial community composition and function. Although this link is likely the result of community adaptation to the prevailing site-specific environmental conditions, our present data is insufficient to identify the main factors determining these patterns. Nevertheless, this study demonstrates that the spatial variability in the photosynthetic capacity and light acclimation of benthic phototrophic microbial communities is at least as large on a sub-millimeter scale as it is on a global scale, and suggests that this pattern of variability scaling is similar for the microbial community composition.

Chemical Diversity as a Function of Temperature in Six Northern Diatom Species

In this study, we investigate how metabolic fingerprints are related to temperature. Six common northern temperate diatoms (Attheya longicornis, Chaetoceros socialis, Chaetoceros furcellatus, Porosira glacialis, Skeletonema marinoi, and Thalassiosira gravida) were cultivated at two different temperatures, 0.5 and 8.5 °C. To exclude metabolic variations due to differences in growth rates, the growth rates were kept similar by performing the experiments under light limited conditions but in exponential growth phase. Growth rates and maximum quantum yield of photosynthesis were measured and interpreted as physiological variables, and metabolic fingerprints were acquired by high-resolution mass spectrometry. The chemical diversity varied substantially between the two temperatures for the tested species, ranging from 31% similarity for C. furcellatus and P. glacialis to 81% similarity for A. longicornis. The chemical diversity was generally highest at the lowest temperature.

Carbon allocation under light and nitrogen resource gradients in two model marine phytoplankton(1).

Marine phytoplankton have conserved elemental stoichiometry, but there can be significant deviations from this Redfield ratio. Moreover, phytoplankton allocate reduced carbon (C) to different biochemical pools based on nutritional status and light availability, adding complexity to this relationship. This allocation influences physiology, ecology, and biogeochemistry. Here, we present results on the physiological and biochemical properties of two evolutionarily distinct model marine phytoplankton, a diatom (cf. Staurosira sp. Ehrenberg) and a chlorophyte (Chlorella sp. M. Beijerinck) grown under light and nitrogen resource gradients to characterize how carbon is allocated under different energy and substrate conditions. We found that nitrogen (N)-replete growth rate increased monotonically with light until it reached a threshold intensity (~200μmol photons·m(-2) ·s(-1) ). For Chlorella sp., the nitrogen quota (pg·μm(-3) ) was greatest below this threshold, beyond which it was reduced by the effect of N-stress, while for Staurosira sp. there was no trend. Both species maintained constant maximum quantum yield of photosynthesis (mol C·molphotons(-1) ) over the range of light and N-gradients studied (although each species used different photophysiological strategies). In both species, C:chl a (g·g(-1) ) increased as a function of light and N-stress, while C:N (mol·mol(-1) ) and relative neutral lipid:C (rel. lipid·g(-1) ) were most strongly influenced by N-stress above the threshold light intensity. These results demonstrated that the interaction of substrate (N-availability) and energy gradients influenced C-allocation, and that general patterns of biochemical responses may be conserved among phytoplankton; they provided a framework for predicting phytoplankton biochemical composition in ecological, biogeochemical, or biotechnological applications.

From the Red Drop to the Z‐scheme of photosynthesis

In 1943, the US-American biophysicist Robert Emerson (see Fig. 1) and his collaborator, the physicist C. Charlton M. Lewis, were investigating the efficiency of photosynthesis, determined as its quantum yield, i.e., the number of light quanta required for the release of one molecule of oxygen, and its relationship to the wavelength of light.1 In the course of this work, they observed, at low light intensities, an unexpected sharp decline of photosynthetic efficiency in the far red, that is, from 685 nm towards the infrared region of the spectrum [5, p. 166]. This was the phenomenon that later became known as the “Red Drop” of photosynthesis efficiency (see Fig. 2). The puzzling fact was that at wavelengths even above 685 nm chlorophyll absorption was still rather high, and no pigments were known to compete with chlorophyll in this region, whichmight have caused the drop in efficiency. Emerson and Lewis were completely at a loss as to how to explain this finding. And as in the years afterwards, Emerson became involved in an atrocious controversy on the maximum quantum yield of photosynthesis with the eminent – and extremely stubborn – cell physiologist Otto Warburg, over the next ten years he did not investigate this curious phenomenon any further.2 It was only in 1955 that Emerson came back to his former line of enquiry, and he hit upon an even stranger effect. It turned out that the Red Drop of photosynthetic efficiency disappeared if a supplementary light beam of shorter wavelengths was provided (see [7]). As a possible explanation, Emerson and his co-workers, Ruth Chalmers and Carl Cederstrand, suggested that “the significance of the supple-

Photobiology of sea ice algae during initial spring growth in Kangerlussuaq, West Greenland: insights from imaging variable chlorophyll fluorescence of ice cores

We undertook a series of measurements of photophysiological parameters of sea ice algae over 12 days of early spring growth in a West Greenland Fjord, by variable chlorophyll fluorescence imaging. Imaging of the ice-water interface showed the development of ice algae in 0.3-0.4 mm wide brine channels between laminar ice crystals in the lower 4-6 mm of the ice, with a several-fold spatial variation in inferred biomass on cm scales. The maximum quantum yield of photosynthesis, F(v) /F(m), was initially low (~0.1), though this increased rapidly to ~0.5 by day 6. Day 6 also saw the onset of biomass increase, the cessation of ice growth and the time at which brine had reached <50 psu and >-2 °C. We interpret this as indicating that the establishment of stable brine channels at close to ambient salinity was required to trigger photosynthetically active populations. Maximum relative electron transport rate (rETR(max)), saturation irradiance (E(k)) and photosynthetic efficiency (α) had also stabilised by day 6 at 5-6 relative units, ~30 μmol photons m⁻² s⁻¹ and 0.4-0.5 μmol photons m⁻²s⁻¹, respectively. E(k) was consistent with under-ice irradiance, which peaked at a similar value, confirming that daytime irradiance was adequate to facilitate photosynthetic activity throughout the study period. Photosynthetic parameters showed no substantial differences with depth within the ice, nor variation between cores or brine channels suggesting that during this early phase of ice algal growth cells were unaffected by gradients of environmental conditions within the ice. Variable chlorophyll fluorescence imaging offers a tool to determine how this situation may change over time and as brine channels and algal populations evolve.

Effects of hydrogen peroxide on the content of major volatile halogenated compounds in the red alga Asparagopsis taxiformis (Bonnemaisoniaceae)

The genus Asparagopsis is a prolific source of halogenated metabolites. Due to its commercial applications, it has been intensively cultivated in southern Portugal. In the present study, we assess if the internal levels of the major halogenated metabolites (bromoform and dibromoacetic acid) in Asparagopsis taxiformis can be increased with hydrogen peroxide (H2O2) addition. Previous studies with red algae showed that the production/release of bromoform can be enhanced by exogenously supplying H2O2. However, no study has assessed if H2O2 supply enhances the content of secondary metabolites within the biomass. This detail is important as the objective of the proposed research is to enhance the content of these valuable metabolites in the produced biomass. Both the activity of the haloperoxidase enzyme and the metabolite content were assessed on short-term and long-term incubation periods to H2O2. To determine the susceptibility of A. taxiformis photosynthetic performance to the imposed oxidative stress, the in vivo fluorescence of photosystem II was monitored. A. taxiformis was shown to be physiologically vulnerable to H2O2, given the observed decrease of the maximum quantum yield of photosynthesis (F v/F m). Contrary to what was expected, the presence of H2O2 inhibited the activity of the iodoperoxidase enzyme. Nevertheless, the extracted halogenated metabolites were higher over the first hours of exposure to H2O2, decreasing after 48 h. These results are probably related to the prosthetic group of the halogenated enzyme in A. taxiformis and the long-term oxidative stress damage of H2O2 exposure. Considering the objective of the proposed research, addition of H2O2 to the cultures, prior (3 h) to biomass harvesting, increases the metabolite content.