Articles de revues : « Phytoplankton quantum yield for growth »

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Behrenfeld, M. J., T. K. Westberry, E. S. Boss, R. T. O'Malley, D. A. Siegel, J. D. Wiggert, B. A. Franz et al. « Satellite-detected fluorescence reveals global physiology of ocean phytoplankton ». Biogeosciences 6, n^o 5 (8 mai 2009) : 779–94. http://dx.doi.org/10.5194/bg-6-779-2009.

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Abstract. Phytoplankton photosynthesis links global ocean biology and climate-driven fluctuations in the physical environment. These interactions are largely expressed through changes in phytoplankton physiology, but physiological status has proven extremely challenging to characterize globally. Phytoplankton fluorescence does provide a rich source of physiological information long exploited in laboratory and field studies, and is now observed from space. Here we evaluate the physiological underpinnings of global variations in satellite-based phytoplankton chlorophyll fluorescence. The three dominant factors influencing fluorescence distributions are chlorophyll concentration, pigment packaging effects on light absorption, and light-dependent energy-quenching processes. After accounting for these three factors, resultant global distributions of quenching-corrected fluorescence quantum yields reveal a striking consistency with anticipated patterns of iron availability. High fluorescence quantum yields are typically found in low iron waters, while low quantum yields dominate regions where other environmental factors are most limiting to phytoplankton growth. Specific properties of photosynthetic membranes are discussed that provide a mechanistic view linking iron stress to satellite-detected fluorescence. Our results present satellite-based fluorescence as a valuable tool for evaluating nutrient stress predictions in ocean ecosystem models and give the first synoptic observational evidence that iron plays an important role in seasonal phytoplankton dynamics of the Indian Ocean. Satellite fluorescence may also provide a path for monitoring climate-phytoplankton physiology interactions and improving descriptions of phytoplankton light use efficiencies in ocean productivity models.

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Fanesi, Andrea, Heiko Wagner et Christian Wilhelm. « Phytoplankton growth rate modelling : can spectroscopic cell chemotyping be superior to physiological predictors ? » Proceedings of the Royal Society B : Biological Sciences 284, n^o 1848 (8 février 2017) : 20161956. http://dx.doi.org/10.1098/rspb.2016.1956.

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Climate change has a strong impact on phytoplankton communities and water quality. However, the development of robust techniques to assess phytoplankton growth is still in progress. In this study, the growth rate of phytoplankton cells grown at different temperatures was modelled based on conventional physiological traits (e.g. chlorophyll, carbon and photosynthetic parameters) using the partial least square regression (PLSR) algorithm and compared with a new approach combining Fourier transform infrared-spectroscopy and PLSR. In this second model, it is assumed that the macromolecular composition of phytoplankton cells represents an intracellular marker for growth. The models have comparable high predictive power ( R 2 > 0.8) and low error in predicting new observations. Interestingly, not all of the predictors present the same weight in the modelling of growth rate. A set of specific parameters, such as non-photochemical fluorescence quenching (NPQ) and the quantum yield of carbon production in the first model, and lipid, protein and carbohydrate contents for the second one, strongly covary with cell growth rate regardless of the taxonomic position of the phytoplankton species investigated. This reflects a set of specific physiological adjustments covarying with growth rate, conserved among taxonomically distant algal species that might be used as guidelines for the improvement of modern primary production models. The high predictive power of both sets of cellular traits for growth rate is of great importance for applied phycological studies. Our approach may find application as a quality control tool for the monitoring of phytoplankton populations in natural communities or in photobioreactors.

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Sinoir, Marie, Andrew R. Bowie, Mathieu Mongin, Edward C. V. Butler et Christel S. Hassler. « Zinc requirement for two phytoplankton strains of the Tasman Sea ». Marine and Freshwater Research 68, n^o 2 (2017) : 361. http://dx.doi.org/10.1071/mf15323.

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Zinc has been proposed as a limiting, or co-limiting, micronutrient for phytoplankton. In the Tasman Sea, extremely low zinc concentrations have been reported, raising the possibility there of limitation of phytoplankton growth by zinc. The pennate diatom Nitzschia closterium (CS-1) and the coccolithophorid Emiliania huxleyi (CS-812) were cultured in two low zinc concentrations (Zn2+ = 1.5 pmolL–1 and Zn2+ = 1.5 nmolL–1) mimicking conditions found in coastal and pelagic Tasman Sea. To monitor phytoplankton health and productivity, the maximum quantum yield (Fv/Fm), growth rate and cell size were analysed. These parameters showed that both strains were able to adapt and still grow. Short-term uptake experiments revealed an effect on Zn biological transport, with consequences for its bioavailability. When grown at low Zn2+ concentrations, E. huxleyi showed an induction of a two-transporter system, highly dependent on photosynthetic energy for Zn uptake. N. closterium was able to survive without inducing a higher-affinity Zn transporter. Its Zn uptake was also highly dependent on cellular energy and the ability to potentially access labile complexed forms of Zn. This strategy, thus, represented an advantage over E. huxleyi. Results are discussed in the context of the conditions found in the Tasman Sea.

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Kim, J. H., K. Y. Kim, E. J. Kang, K. Lee, J. M. Kim, K. T. Park, K. Shin, B. Hyun et H. J. Jeong. « Enhancement of photosynthetic carbon assimilation efficiency by phytoplankton in the future coastal ocean ». Biogeosciences 10, n^o 11 (21 novembre 2013) : 7525–35. http://dx.doi.org/10.5194/bg-10-7525-2013.

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Abstract. A mesocosm experiment was conducted to evaluate the influence of photosynthetic performance on the energetic balance of coastal phytoplankton, in relation to community production and autotrophic phytoplankton biomass in future coastal oceans. Natural phytoplankton assemblages were incubated in field mesocosms under ambient condition (control: ca. 400 μatm CO2 and ambient temperature), and two sets of potential future ocean conditions (acidification: ca. 900 μatm CO2 and ambient temperature; greenhouse: ca. 900 μatm CO2 and 3 °C warmer). The photosynthetic performances were estimated by in vivo fluorometry (effective quantum yield (ΦPSII), steady-state light response curves (LCs)) and in situ incorporation of 14C (photosynthesis-irradiance curves). The ΦPSII and rETRm,LC (relative maximum electron transport rate) clearly reduced under acidification, in particular, when phytoplankton were exposed to high light levels. However, PBmax (maximum photosynthetic rate) was the same in the ambient and acidification conditions. Thus, phytoplankton utilized less light under acidification condition, but could still assimilate a similar amount of carbon compared to the ambient condition. The PBmax and α (photosynthetic efficiency) under greenhouse condition were significantly higher than those under ambient condition without any difference in ΦPSII, rETRm,LC and α,LC (electron transport efficiency) between the treatments. Therefore, phytoplankton utilized the same amount of light under greenhouse condition, but could assimilate more carbon than under ambient condition. As a result, Chl a normalized primary production was higher in greenhouse than in other conditions. Nevertheless, the community production did not change between the experimental treatments. The main reason for the lack of a change in primary production under future climate conditions is the control of autotrophic phytoplankton biomass by grazing. Consequently, acidification and greenhouse environments have a potential to increase growth and primary production of phytoplankton by enhancing inorganic carbon assimilation efficiency when top-down regulation is negligible.

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Li, Zhou, Philippe Juneau, Yingli Lian, Wei Zhang, Shanquan Wang, Cheng Wang, Longfei Shu, Qingyun Yan, Zhili He et Kui Xu. « Effects of Titanium Dioxide Nanoparticles on Photosynthetic and Antioxidative Processes of Scenedesmus obliquus ». Plants 9, n^o 12 (10 décembre 2020) : 1748. http://dx.doi.org/10.3390/plants9121748.

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The effects of the photocatalytic toxicity of titanium dioxide nanoparticle (nano-TiO2) on phytoplankton are well understood. However, as UV light intensity decreases sharply with the depth of the water column, the effects of nano-TiO2 itself on deeper water phytoplankton, such as green algae, need further research. In this research, we investigated the effects of three sizes of TiO2 (10, 50 and 200 nm) on the photosynthetic and antioxidative processes of Scenedesmus obliquus in the absence of UV light. We found that 50 nm and 10 nm TiO2 (10 mg/L) inhibited growth rates and the maximal photosystem II quantum yield compared to the control in Scenedesmus obliquus. The minimal and maximal fluorescence yields, and the contents of reactive oxygen species and lipid peroxidation, increased, indicating that photosynthetic energy/electrons transferred to oxygen and induced oxidative stress in nano-TiO2-treated samples. In addition, we found that aggregations of algae and 10 nm TiO2 were present, which could induce cell membrane disruption, and vacuoles were induced to cope with nano-TiO2 stress in Scenedesmus obliquus. These results enhance our understanding of the effects of nano-TiO2 on the photosynthetic and antioxidative processes of green algae, and provide basic information for evaluating the ecotoxicity of nano-TiO2 in freshwater ecosystems.

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Guo, Jiaying Abby, Robert Strzepek, Anusuya Willis, Aaron Ferderer et Lennart Thomas Bach. « Investigating the effect of nickel concentration on phytoplankton growth to assess potential side-effects of ocean alkalinity enhancement ». Biogeosciences 19, n^o 15 (5 août 2022) : 3683–97. http://dx.doi.org/10.5194/bg-19-3683-2022.

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Abstract. Ocean alkalinity enhancement (OAE) is a proposed method for removing carbon dioxide (CO2) from the atmosphere by the accelerated weathering of (ultra-)basic minerals to increase alkalinity – the chemical capacity of seawater to store CO2. During the weathering of OAE-relevant minerals relatively large amounts of trace metals will be released and may perturb pelagic ecosystems. Nickel (Ni) is of particular concern as it is abundant in olivine, one of the most widely considered minerals for OAE. However, so far there is limited knowledge about the impact of Ni on marine biota including phytoplankton. To fill this knowledge gap, this study tested the growth and photo-physiological response of 11 marine phytoplankton species to a wide range of dissolved Ni concentrations (from 0.07 to 50 000 nmol L−1). We found that the phytoplankton species were not very sensitive to Ni concentrations under the culturing conditions established in our experiments, but the responses were species-specific. The growth rates of 6 of the 11 tested species showed generally limited but still significant responses to changing Ni concentrations (36 % maximum change). Photosynthetic performance, assessed by measuring the maximum quantum yield (Fv/Fm) and the functional absorption cross-section (σPSII) of photosystem II (PSII), was sensitive to changing Ni in 3 out of 11 species (35 % maximum change) and 4 out of 11 species (16 % maximum change), respectively. The limited effect of Ni may be partly due to the provision of nitrate as the nitrogen source for growth as previous studies suggest higher sensitivities when urea is the nitrogen source. Furthermore, the limited influence may be due to the relatively high concentrations of synthetic organic ligands added to the growth media in our experiments. These ligands are commonly added to control trace metal bioavailability and therefore for example “free Ni2+” concentrations by binding the majority of the dissolved Ni. Our data suggest that dissolved Ni does not have a strong effect on phytoplankton under our experimental conditions, but we emphasize that a deeper understanding of nitrogen sources, ligand concentrations, and phytoplankton composition is needed when assessing the influence of Ni release associated with OAE.

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Durán-Romero, Cristina, Virginia E. Villafañe, Macarena S. Valiñas, Rodrigo J. Gonçalves et E. Walter Helbling. « Solar UVR sensitivity of phyto- and bacterioplankton communities from Patagonian coastal waters under increased nutrients and acidification ». ICES Journal of Marine Science 74, n^o 4 (22 janvier 2017) : 1062–73. http://dx.doi.org/10.1093/icesjms/fsw248.

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The effects of ultraviolet radiation (UVR) under future expected conditions of acidification and increase in nutrient inputs were studied on a post-bloom phytoplankton and bacterioplankton community of Patagonian coastal waters. We performed an experiment using microcosms where two environmental conditions were mimicked using a cluster approach: present (ambient nutrients and pH) and future (increased nutrients and acidification), and acclimating the samples for five days to two radiation treatments (full solar radiation [+UVR] and exclusion of UVR [–UVR]). We evaluated the short-term (hours) sensitivity of the community to solar UVR through chlorophyll a fluorescence parameters (e.g. the effective photochemical quantum yield of PSII [ΦPSII]) at the beginning, at the mid-point and at the end of the acclimation period. Primary production and heterotrophic bacterial production (HBP) were determined, and biological weighting functions were calculated, at the beginning and at the end of the acclimation period. Mid-term effects (days) were evaluated as changes in taxonomic composition, growth rates and size structure of the community. Although the UVR-induced inhibition on ΦPSII decreased in both clusters, samples remained sensitive to UVR after the 5 days of acclimation. Also, under the future conditions, there was, in general, an increase in the phytoplankton carbon incorporation rates along the experiment as compared to the present conditions. Bacterioplankton sensitivity to UVR changed along the experiment from inhibition to enhancement of HBP, and future environmental conditions stimulated bacterial growth, probably due to indirect effects caused by phytoplankton. Those changes in the microbial loop functioning and structure under future global change conditions might have important consequences for the carbon pump and thus for the carbon sequestration and trophodynamics of Patagonian coastal waters.

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Li, Futian, John Beardall et Kunshan Gao. « Diatom performance in a future ocean : interactions between nitrogen limitation, temperature, and CO2-induced seawater acidification ». ICES Journal of Marine Science 75, n^o 4 (4 janvier 2018) : 1451–64. http://dx.doi.org/10.1093/icesjms/fsx239.

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Abstract Phytoplankton cells living in the surface waters of oceans are experiencing alterations in environmental conditions associated with global change. Given their importance in global primary productivity, it is of considerable concern to know how these organisms will perform physiologically under the changing levels of pH, temperatures, and nutrients predicted for future oceanic ecosystems. Here we show that the model diatom, Thalassiosira pseudonana, when grown at different temperatures (20 or 24 °C), pCO2 (400 or 1000 µatm), and nitrate concentrations (2.5 or 102.5 µmol l−1), displayed contrasting performance in its physiology. Elevated pCO2 (and hence seawater acidification) under the nitrate-limited conditions led to decreases in specific growth rate, cell size, pigment content, photochemical quantum yield of PSII, and photosynthetic carbon fixation. Furthermore, increasing the temperature exacerbated the negative effects of the seawater acidification associated with elevated pCO2 on specific growth rate and chlorophyll content under the N-limited conditions. These results imply that a reduced upward transport of nutrients due to enhanced stratification associated with ocean warming might act synergistically to reduce growth and carbon fixation by diatoms under progressive ocean acidification, with important ramifications for ocean productivity and the strength of the biological CO2 pump.

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Budzałek, Gracjana, Sylwia Śliwińska-Wilczewska, Marek Klin, Kinga Wiśniewska, Adam Latała et Józef Maria Wiktor. « Changes in Growth, Photosynthesis Performance, Pigments, and Toxin Contents of Bloom-Forming Cyanobacteria after Exposure to Macroalgal Allelochemicals ». Toxins 13, n^o 8 (23 août 2021) : 589. http://dx.doi.org/10.3390/toxins13080589.

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Macroalgae can directly restrict the growth of various phytoplankton species by releasing allelopathic compounds; therefore, considerable attention should be paid to the allelopathic potential of these organisms against harmful and bloom-forming cyanobacteria. The main aim of this study was to demonstrate for the first time the allelopathic activity of Ulva intestinalis on the growth, the fluorescence parameters: the maximum PSII quantum efficiency (Fv/Fm) and the effective quantum yield of PSII photochemistry (ΦPSII), the chlorophyll a (Chl a) and carotenoid (Car) content, and the microcystin-LR (MC-LR) and phenol content of three bloom-forming cyanobacteria, Aphanizomenon sp., Nodularia spumigena, and Nostoc sp. We found both negative and positive allelopathic effects of U. intestinalis on tested cyanobacteria. The study clearly showed that the addition of the filtrate of U. intestinalis significantly inhibited growth, decreased pigment content and Fv/Fm and ΦPSII values of N. spumigena and Nostoc sp., and stimulated Aphanizomenon sp. The addition of different concentrations of aqueous extract also stimulated the cyanobacterial growth. It was also shown that the addition of extract obtained from U. intestinalis caused a significant decrease in the MC-LR content in Nostoc sp. cells. Moreover, it the phenol content in N. spumigena cells was increased. On the other hand, the cell-specific phenol content for Aphanizomenon sp. decreased due to the addition of the filtrate. In this work, we demonstrated that the allelopathic effect of U. intestinalis depends on the target species’ identity as well as the type of allelopathic method used. The study of the allelopathic Baltic macroalgae may help to identify their possible role as a significant biological factor influencing harmful cyanobacterial blooms in brackish ecosystems.

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Li, Futian, Jiekai Xu, John Beardall et Kunshan Gao. « Diurnally fluctuating pCO2 enhances growth of a coastal strain of Emiliania huxleyi under future-projected ocean acidification conditions ». ICES Journal of Marine Science 78, n^o 4 (4 mars 2021) : 1301–10. http://dx.doi.org/10.1093/icesjms/fsab036.

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Abstract The carbonate chemistry in coastal waters is more variable compared with that of open oceans, both in magnitude and time scale of its fluctuations. However, knowledge of the responses of coastal phytoplankton to dynamic changes in pH/pCO2 has been scarcely documented. Hence, we investigated the physiological performance of a coastal isolate of the coccolithophore Emiliania huxleyi (PML B92/11) under fluctuating and stable pCO2 regimes (steady ambient pCO2, 400 μatm; steady elevated pCO2, 1200 μatm; diurnally fluctuating elevated pCO2, 600–1800 μatm). Elevated pCO2 inhibited the calcification rate in both the steady and fluctuating regimes. However, higher specific growth rates and lower ratios of calcification to photosynthesis were detected in the cells grown under diurnally fluctuating elevated pCO2 conditions. The fluctuating pCO2 regime alleviated the negative effects of elevated pCO2 on effective photochemical quantum yield and relative photosynthetic electron transport rate compared with the steady elevated pCO2 treatment. Our results suggest that growth of E. huxleyi could benefit from diel fluctuations of pH/pCO2 under future-projected ocean acidification, but its calcification was reduced by the fluctuation and the increased concentration of CO2, reflecting a necessity to consider the influences of dynamic pH fluctuations on coastal carbon cycles associated with ocean global changes.

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Li, Ping, Qun Ma, Su Xu, Wenha Liu, Zengling Ma et Guangyan Ni. « Opposite Growth Responses of Alexandrium minutum and Alexandrium catenella to Photoperiods and Temperatures ». Plants 10, n^o 6 (25 mai 2021) : 1056. http://dx.doi.org/10.3390/plants10061056.

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Shift of phytoplankton niches from low to high latitudes has altered their experienced light exposure durations and temperatures. To explore this interactive effect, the growth, physiology, and cell compositions of smaller Alexandrium minutum and larger A. catenella, globally distributed toxic red tide dinoflagellates, were studied under a matrix of photoperiods (light:dark cycles of 8:16, 16:8, and 24:0) and temperatures (18 °C, 22 °C, 25 °C, and 28 °C). Under continuous growth light condition (L:D 24:0), the growth rate (µ) of small A. minutum increased from low to medium temperature, then decreased to high temperature, while the µ of large A. catenella continuously decreased with increasing temperatures. Shortened photoperiods reduced the µ of A. minutum, but enhanced that of A. catenella. As temperature increased, cellular Chl a content increased in both A. minutum and A. catenella, while the temperature-induced effect on RubisCO content was limited. Shortened photoperiods enhanced the Chl a but reduced RubisCO contents across temperatures. Moreover, shortened photoperiods enhanced photosynthetic capacities of both A. minutum and A. catenella, i.e., promoting the PSII photochemical quantum yield (FV/FM, ΦPSII), saturation irradiance (EK), and maximum relative electron transfer rate (rETRmax). Shortened photoperiods also enhanced dark respiration of A. minutum across temperatures, but reduced that of A. catenella, as well as the antioxidant activities of both species. Overall, A. minutum and A. catenella showed differential growth responses to photoperiods across temperatures, probably with cell size.

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Chen, Bokun, Jihua Liu, Ge Xu et Gang Li. « Lowering pO2 Interacts with Photoperiod to Alter Physiological Performance of the Coastal Diatom Thalassiosira pseudonana ». Microorganisms 9, n^o 12 (9 décembre 2021) : 2541. http://dx.doi.org/10.3390/microorganisms9122541.

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Exacerbating deoxygenation is extensively affecting marine organisms, with no exception for phytoplankton. To probe these effects, we comparably explored the growth, cell compositions, photosynthesis, and transcriptome of a diatom Thalassiosira pseudonana under a matrix of pO2 levels and Light:Dark cycles at an optimal growth light. The growth rate (μ) of T. pseudonana under a 8:16 L:D cycle was enhanced by 34% by low pO2 but reduced by 22% by hypoxia. Under a 16:8 L:D cycle, however, the μ decreased with decreasing pO2 level. The cellular Chl a content decreased with decreasing pO2 under a 8:16 L:D cycle, whereas the protein content decreased under a 16:8 L:D cycle. The prolonged photoperiod reduced the Chl a but enhanced the protein contents. The lowered pO2 reduced the maximal PSII photochemical quantum yield (FV/FM), photosynthetic oxygen evolution rate (Pn), and respiration rate (Rd) under the 8:16 or 16:8 L:D cycles. Cellular malondialdehyde (MDA) content and superoxide dismutase (SOD) activity were higher under low pO2 than ambient pO2 or hypoxia. Moreover, the prolonged photoperiod reduced the FV/FM and Pn among all three pO2 levels but enhanced the Rd, MDA, and SOD activity. Transcriptome data showed that most of 26 differentially expressed genes (DEGs) that mainly relate to photosynthesis, respiration, and metabolism were down-regulated by hypoxia, with varying expression degrees between the 8:16 and 16:8 L:D cycles. In addition, our results demonstrated that the positive or negative effect of lowering pO2 upon the growth of diatoms depends on the pO2 level and is mediated by the photoperiod.

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Xu, Juntian, Lennart T. Bach, Kai G. Schulz, Wenyan Zhao, Kunshan Gao et Ulf Riebesell. « The role of coccoliths in protecting Emiliania huxleyi ; against stressful light and UV radiation ». Biogeosciences 13, n^o 16 (18 août 2016) : 4637–43. http://dx.doi.org/10.5194/bg-13-4637-2016.

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Abstract. Coccolithophores are a group of phytoplankton species which cover themselves with small scales (coccoliths) made of calcium carbonate (CaCO3). The reason why coccolithophores form these calcite platelets has been a matter of debate for decades but has remained elusive so far. One hypothesis is that they play a role in light or UV protection, especially in surface dwelling species like Emiliania huxleyi, which can tolerate exceptionally high levels of solar radiation. In this study, we tested this hypothesis by culturing a calcified and a naked strain under different light conditions with and without UV radiation. The coccoliths of E. huxleyi reduced the transmission of visible radiation (400–700 nm) by 7.5 %, that of UV-A (315–400 nm) by 14.1 % and that of UV-B (280–315 nm) by 18.4 %. Growth rates of the calcified strain (PML B92/11) were about 2 times higher than those of the naked strain (CCMP 2090) under indoor constant light levels in the absence of UV radiation. When exposed to outdoor conditions (fluctuating sunlight with UV radiation), growth rates of calcified cells were almost 3.5 times higher compared to naked cells. Furthermore, the relative electron transport rate was 114 % higher and non-photochemical quenching (NPQ) was 281 % higher in the calcified compared to the naked strain, implying higher energy transfer associated with higher NPQ in the presence of calcification. When exposed to natural solar radiation including UV radiation, the maximal quantum yield of photosystem II was only slightly reduced in the calcified strain but strongly reduced in the naked strain. Our results reveal an important role of coccoliths in mitigating light and UV stress in E. huxleyi.

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Berman-Frank, Ilana, Jonathan Erez et Aaron Kaplan. « Changes in inorganic carbon uptake during the progression of a dinoflagellate bloom in a lake ecosystem ». Canadian Journal of Botany 76, n^o 6 (1 juin 1998) : 1043–51. http://dx.doi.org/10.1139/b98-075.

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The physiological, biochemical, and genetic aspects of inorganic (Ci) carbon uptake in aquatic plants and algae have been studied extensively. Yet, to date, few studies examined these questions on dominant phytoplankton populations in their natural environment. Lake Kinneret, Israel, provides a good example of a system in which changes in CO2 availability play a vital role in the ecophysiology of inorganic carbon uptake and in the population dynamics during the annual bloom of the dinoflagellate Peridinium gatunense Nygaard. In this study we investigated whether the availability of CO2(aq) limited growth rates and primary productivity of in situ populations of P. gatunense and focused on the role of adaptive mechanisms for Ci uptake. At the onset of the bloom, when epilimnetic pH was low ( = 8) and Ci concentrations were high ( = 2.5 mM), carbonic anhydrase activity and cellular affinity to CO2(aq) were comparatively low. At this time photosynthetic rates, quantum yields, and in situ growth rates were high. As P. gatunense biomass increased, inorganic carbon decreased by 40%, while CO2(aq) concentrations declined 50-fold to values less than 2 µM. The algae adapted by acquiring a CO2-concentrating mechanism indicated by (i) intracellular Ci-concentrations higher by a factor of 5-70 relative to the ambient Ci; (ii) levels of carbonic anhydrase activity higher by 5- to 50-fold than those at the beginning of the bloom; and (iii) enhanced affinity for Ci and CO2(aq) 3- and 40-fold higher, respectively, than affinities at the start of the bloom. These mechanistic changes in carbon uptake were reflected in declining photosynthetic rates and quantum yields as well as in the carbon isotopic composition with lower fractionation (13C enrichment) of the algae as the bloom progressed. Finally, despite induction of adaptive uptake mechanisms to low CO2 availability; scarcity of other nutrients combined with low CO2 concentrations, increased temperatures, and increased turbulence cause a decline in in situ growth rates and the collapse of the dinoflagellate biomass.Key words: dinoflagellates, inorganic carbon uptake, CCM, carbonic anhydrase, Peridinium gatunense.

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Zhai, Peng-Wang, Emmanuel Boss, Bryan Franz, P. Werdell et Yongxiang Hu. « Radiative Transfer Modeling of Phytoplankton Fluorescence Quenching Processes ». Remote Sensing 10, n^o 8 (20 août 2018) : 1309. http://dx.doi.org/10.3390/rs10081309.

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We report the first radiative transfer model that is able to simulate phytoplankton fluorescence with both photochemical and non-photochemical quenching included. The fluorescence source term in the inelastic radiative transfer equation is proportional to both the quantum yield and scalar irradiance at excitation wavelengths. The photochemical and nonphotochemical quenching processes change the quantum yield based on the photosynthetic active radiation. A sensitivity study was performed to demonstrate the dependence of the fluorescence signal on chlorophyll a concentration, aerosol optical depths and solar zenith angles. This work enables us to better model the phytoplankton fluorescence, which can be used in the design of new space-based sensors that can provide sufficient sensitivity to detect the phytoplankton fluorescence signal. It could also lead to more accurate remote sensing algorithms for the study of phytoplankton physiology.

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McMinn, A., et E. N. Hegseth. « Quantum yield and photosynthetic parameters of marine microalgae from the southern Arctic Ocean, Svalbard ». Journal of the Marine Biological Association of the United Kingdom 84, n^o 5 (octobre 2004) : 865–71. http://dx.doi.org/10.1017/s0025315404010112h.

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The quantum yield and photosynthetic parameters of phytoplankton and sea ice microalgal communities were assessed from the Arctic Ocean and fjords of northern Svalbard. The phytoplankton community in Fram Strait was dominated by Phaeocystis while on Norskebanken it was dominated by diatoms. The quantum yield showed maximum values of 0·64 at 20–40 m below the surface and were consistent with nutrient replete waters elsewhere.Sea ice infiltration communities were widespread and dominated by Phaeocystis. This is the first record of an Arctic infiltration ice community. Quantum yields were relatively low (0·247). Bottom ice communities, which were dominated by Nitzschia frigida, were extremely restricted and had moderate quantum yields (0·427). Communities growing on multiyear ice had quantum yields of only 0·126. All ice communities were well adapted to their light environment.

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Raju*, Venkata Kesava, et Sreeramulu K. « Biofertilizer effect of free living nitrogen fixing bacterium on the growth and water quality properties of Penaeid prawn culture system ». International Journal of Bioassays 6, n^o 05 (6 mai 2017) : 5369. http://dx.doi.org/10.21746/ijbio.2017.05.001.

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The role of phytoplankton is significant in improving the yield of prawn culture. The growth of phytoplankton will be effected various factors viz. dissolved oxygen, production of natural food to shrimp larvae in control of ammonia. The growth of phytoplankton can be enhanced by application of nitrogeneous fertilizers to improve water quality and growth performance of Penaeus indicus. The present research work is focussed on a free-living nitrogen fixing bacterium Azotobacter chroococcum supplemented by nitrogeneous fertilizers to increase the content of proteins, carbohydrates and wet weight of P. indicus. Ten animals of juveniles of P. indicus were collected and grown in controlled conditions for fifteen days. The liquid suspension of free living nitrogen fixing bacteria A. chroococcum has been inoculated for experimental treatment purpose. The inoculum has been introduced to four treatments and for findings of water quality analysis andphytoplankton growth analysis by Strickland and Parsons method and biochemical analysis by Raymont et al., method. The research findings revealed that A. chroococcum supplemented with fertilizers will affect the growth of phytoplankton which is vital in prawn culture and enhance the growth of hormones and dry weight for improvement of the yield.

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Kishino, Motoaki, Noboru Okami, Masayuki Takahashi et Shun-ei Ichimura. « Light utilization efficiency and quantum yield of phytoplankton in a thermally stratified sea1 ». Limnology and Oceanography 31, n^o 3 (mai 1986) : 557–66. http://dx.doi.org/10.4319/lo.1986.31.3.0557.

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Maritorena, Stéphane, André Morel et Bernard Gentili. « Determination of the fluorescence quantum yield by oceanic phytoplankton in their natural habitat ». Applied Optics 39, n^o 36 (20 décembre 2000) : 6725. http://dx.doi.org/10.1364/ao.39.006725.

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Falkowski, Paul G., Hanzhi Lin et Maxim Y. Gorbunov. « What limits photosynthetic energy conversion efficiency in nature ? Lessons from the oceans ». Philosophical Transactions of the Royal Society B : Biological Sciences 372, n^o 1730 (14 août 2017) : 20160376. http://dx.doi.org/10.1098/rstb.2016.0376.

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Constraining photosynthetic energy conversion efficiency in nature is challenging. In principle, two yield measurements must be made simultaneously: photochemistry, fluorescence and/or thermal dissipation. We constructed two different, extremely sensitive and precise active fluorometers: one measures the quantum yield of photochemistry from changes in variable fluorescence, the other measures fluorescence lifetimes in the picosecond time domain. By deploying the pair of instruments on eight transoceanic cruises over six years, we obtained over 200 000 measurements of fluorescence yields and lifetimes from surface waters in five ocean basins. Our results revealed that the average quantum yield of photochemistry was approximately 0.35 while the average quantum yield of fluorescence was approximately 0.07. Thus, closure on the energy budget suggests that, on average, approximately 58% of the photons absorbed by phytoplankton in the world oceans are dissipated as heat. This extraordinary inefficiency is associated with the paucity of nutrients in the upper ocean, especially dissolved inorganic nitrogen and iron. Our results strongly suggest that, in nature, most of the time, most of the phytoplankton community operates at approximately half of its maximal photosynthetic energy conversion efficiency because nutrients limit the synthesis or function of essential components in the photosynthetic apparatus. This article is part of the themed issue ‘Enhancing photosynthesis in crop plants: targets for improvement’.

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Peperzak, L., H. J. van der Woerd et K. R. Timmermans. « Disparities between Phaeocystis ; in situ and optically-derived carbon biomass and growth rates : potential effect on remote-sensing primary production estimates ». Biogeosciences Discussions 11, n^o 4 (29 avril 2014) : 6119–49. http://dx.doi.org/10.5194/bgd-11-6119-2014.

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Abstract. The oceans play a pivotal role in the global carbon cycle. Unfortunately, the daily production of organic carbon, the product of phytoplankton standing stock and growth rate cannot be measured globally by discrete oceanographic methods. Instead, optical proxies from Earth-orbiting satellites must be used. To test the accuracy of optically-derived proxies of phytoplankton physiology and growth rate, standard ex situ data from the wax and wane of a Phaeocystis bloom in laboratory mesocosms were compared with hyperspectral reflectance data. Chlorophyll biomass could be estimated accurately from reflectance using specific chlorophyll absorption algorithms. However, the conversion of chlorophyll (Chl) to carbon (C) was obscured by the observed increase in C : Chl under nutrient-limited growth. C : Chl was inversely correlated (r2 = 0.88) with Photosystem II quantum efficiency (Fv/Fm), the in situ fluorometric oceanographic proxy for growth rate. In addition, the optical proxy for growth rate, the quantum efficiency of fluorescence &varphi; was linearly correlated to Fv/Fm (r2 = 0.84), but not – as by definition – by using total phytoplankton absorption, because during nutrient-limited growth the concentrations of non-fluorescent light-absorbing pigments increased. As a consequence, none of the three proxies (C : Chl, Fv/Fm, φ) was correlated to carbon or cellular phytoplankton growth rates. Therefore, it is concluded that although satellite derived estimates of chlorophyll biomass may be accurate, physiologically-induced non-linear shifts in growth rate proxies may obscure accurate phytoplankton growth rates and hence global carbon production estimates.

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Prasad, K. S., et J. T. Hollibaugh. « Quantum yield estimates of phytoplankton on the Grand Banks for use in production models ». Limnology and Oceanography 37, n^o 6 (septembre 1992) : 1271–79. http://dx.doi.org/10.4319/lo.1992.37.6.1271.

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Evans, JR. « The Dependence of Quantum Yield on Wavelength and Growth Irradiance ». Functional Plant Biology 14, n^o 1 (1987) : 69. http://dx.doi.org/10.1071/pp9870069.

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The wavelength dependence of photosynthetic quantum yield was measured in a leaf disc oxygen electrode using narrow-band interference filters. Photorespiration was suppressed by measuring oxygen evolution in air containing ~ 1% CO2. Rates of oxygen evolution were determined as a function of absorbed irradiances between 0 and 100 �mol quanta m-2 s-1 and the slope was taken as the quantum yield. The wavelength-dependence previously observed in many species was confirmed for pea and spinach leaves. The maximum quantum yields obtained here and by others are close to 0.111 mol O2 mol-1 quanta for red light. Given the wavelength dependence of quantum yield and the spectral distribution of light, the quantum yields for various white lights were calculated to be around 85% of the red maximum. The quantum yields in white light were the same for plants grown at different irradiances. It is argued that the wavelength dependence of quantum yield reflects the distribution of quanta between the two photosystems with the quantum yield dropping at wavelengths strongly absorbed by chlorophyll b as this is mainly associated with photosystem II.

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McMinn, A., S. Sellah, W. A. Wan Ab Llah, M. Mohammad, F. Md Sidik Merican, W. M. Wan Omar, F. Samad et al. « Quantum yield of the marine benthic microflora of near-shore coastal Penang, Malaysia ». Marine and Freshwater Research 56, n^o 7 (2005) : 1047. http://dx.doi.org/10.1071/mf05007.

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Benthic microalgal communities often contribute more than 30% of the primary production of shallow coastal and estuarine areas. At Muka Head Penang (Pulau Pinang) and the Songsong Islands (Pulau Songsong), Kedah, Malaysia, high concentrations of suspended solids and phytoplankton biomass (10.6 mg Chl a m−3) has reduced water clarity such that the euphotic zone of these areas is less than 2 m and 3 m deep respectively. The benthic microalgal communities, which were composed of the diatom genera Cocconeis, Fragilaria, Paralia and Pleurosigma, had a low biomass, had low maximum quantum yields (0.325 ± 0.129), were poorly adapted to their light environment and were constantly light limited. These characteristics suggest that the benthic microalgal communities were likely to have made only a minor contribution to the total primary production of the area.

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Peperzak, L., H. J. van der Woerd et K. R. Timmermans. « Disparities between in situ and optically derived carbon biomass and growth rates of the prymnesiophyte Phaeocystis globosa ; ». Biogeosciences 12, n^o 6 (16 mars 2015) : 1659–70. http://dx.doi.org/10.5194/bg-12-1659-2015.

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Abstract. The oceans play a pivotal role in the global carbon cycle. It is not practical to measure the global daily production of organic carbon, the product of phytoplankton standing stock and its growth rate using discrete oceanographic methods. Instead, optical proxies from Earth-orbiting satellites must be used. To test the accuracy of optically derived proxies of phytoplankton physiology and growth rate, hyperspectral reflectance data from the wax and wane of a Phaeocystis bloom in laboratory mesocosms were compared with standard ex situ data. Chlorophyll biomass could be estimated accurately from reflectance using specific chlorophyll absorption algorithms. However, the conversion of chlorophyll (Chl) to carbon (C) was obscured by the non-linear increase in C : Chl under nutrient-limited growth. Although C : Chl was inversely correlated (r2 = 0.88) with the in situ fluorometric growth rate indicator Fv / Fm (Photosystem II quantum efficiency), none of them was linearly correlated to growth rate, constraining the accurate calculation of Phaeocystis growth or production rates. Unfortunately, the optical proxy &varphi;ph (quantum efficiency of fluorescence: the ratio of the number of fluoresced photons to the number of photons absorbed by the phytoplankton) did not show any correlation with Phaeocystis growth rate, and therefore it is concluded that &varphi;ph cannot be applied in the remotely sensed measurement of this species' carbon production rate.

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Carrick, Hunter J., Claire L. Schelske, Frederick J. Aldridge et Michael F. Coveney. « Assessment of Phytoplankton Nutrient Limitation in Productive Waters : Application of Dilution Bioassays ». Canadian Journal of Fisheries and Aquatic Sciences 50, n^o 10 (1 octobre 1993) : 2208–21. http://dx.doi.org/10.1139/f93-247.

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Excessive nutrient loads to aquatic systems can complicate otherwise predictable relationships between nutrient concentrations and phytoplankton biomass. We conducted six bioassays on surface phytoplankton assemblages collected from productive Lake Apopka, Florida, to measure the effect of nutrient reduction on phytoplankton growth and nutritional state. Lake water was mixed with one of three diluents to create a gradient of ambient nutrient concentrations; nitrogen (N) and phosphorus (P) limitation at each level of dilution was evaluated in a 2 × 2 factorial design. While the addition of N clearly increased the growth of phytoplankton in undiluted Lake Apopka water, the phytoplankton became more P limited with the reduction of particles (30–60% dilution). Regression of algal yields onto total P concentrations from our bottle experiments indicated that an 8 μg∙L−1 change in P leads to only a 1 μg∙L−1 change in chlorophyll yield, probably due to the high concentration of P in the lake. Because dilution influences factors in addition to ambient nutrient concentrations, results obtained with the technique must be carefully evaluated. Despite this, reduction of particles to improve water quality may, in concept, be a reasonable management scheme in lakes where a large fraction of the nutrients is particulate.

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Vanharanta, Mari, Samu Elovaara, Daniel J. Franklin, Kristian Spilling et Tobias Tamelander. « Viability of pico- and nanophytoplankton in the Baltic Sea during spring ». Aquatic Ecology 54, n^o 1 (11 novembre 2019) : 119–35. http://dx.doi.org/10.1007/s10452-019-09730-3.

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Abstract Phytoplankton cell death is an important process in marine food webs, but the viability of natural phytoplankton communities remains unexplored in many ecosystems. In this study, we measured the viability of natural pico- and nanophytoplankton communities in the central and southern parts of the Baltic Sea (55°21′ N, 17°06′ E–60°18′ N, 19°14′ E) during spring (4th–15th April 2016) to assess differences among phytoplankton groups and the potential relationship between cell death and temperature, and inorganic nutrient availability. Cell viability was determined by SYTOX Green cell staining and flow cytometry at a total of 27 stations representing differing hydrographic regimes. Three general groups of phytoplankton (picocyanobacteria, picoeukaryotes, and nanophytoplankton) were identified by cytometry using pigment fluorescence and light scatter characteristics. The picocyanobacteria and picoeukaryotes had significantly higher cell viability than the nanophytoplankton population at all depths throughout the study area. Viability correlated positively with the photosynthetic efficiency (Fv/Fm, maximum quantum yield of photosystem II) as measured on the total phytoplankton community. However, an anticipated correlation with dissolved organic carbon was not observed. We found that the abiotic factors suggested to affect phytoplankton viability in other marine ecosystems were not as important in the Baltic Sea, and other biotic processes, e.g. processes related to species succession could have a more pronounced role.

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Havens, Sonya M., Christel S. Hassler, Rebecca L. North, Stephanie J. Guildford, Greg Silsbe, Steven W. Wilhelm et Michael R. Twiss. « Iron plays a role in nitrate drawdown by phytoplankton in Lake Erie surface waters as observed in lake-wide assessments ». Canadian Journal of Fisheries and Aquatic Sciences 69, n^o 2 (février 2012) : 369–81. http://dx.doi.org/10.1139/f2011-157.

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Phytoplankton interactions with iron (Fe) were examined in surface waters of Lake Erie during summer thermal stratification. Lake-wide sampling in June and September 2005 was conducted using a continuous surface water sampler (1 m sampling depth) and in July at 18 hydrographic stations (5 m sampling depth). In situ measurements of photosynthetic efficiency (maximum quantum yield of photosystem II) and phytoplankton community composition were measured using fast repetition rate fluorometry and a phytoplankton pigment-specific fluorometer, respectively, during June and September. High ratios (73%–85%) of intracellular Fe to particulate Fe coincident with increases in chlorophyll a (Chl a) concentrations in the western and central basins in June and July imply that the majority of Fe in these regions was associated with intracellular pools. Correlations between intracellular Fe and Chl a were frequently observed when Heterokontophyta and Pyrrophyta dominated the phytoplankton community. Assimilation of Fe by the phytoplankton strongly influenced its partitioning between the dissolved and particulate phase. Dissolved iron (<0.45 µm) concentrations were proportional to Chl a concentrations and both dissolved iron and Chl a were inversely proportional to nitrate concentrations in July and September, suggesting that dissolved iron influenced both nitrate drawdown and Chl a concentrations in Lake Erie surface waters in summer.

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Carder, K. L., Z. P. Lee, J. Marra, R. G. Steward et M. J. Perry. « Calculated quantum yield of photosynthesis of phytoplankton in the Marine Light-Mixed Layers (59°N, 21°W) ». Journal of Geophysical Research 100, n^o C4 (1995) : 6655. http://dx.doi.org/10.1029/94jc02793.

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Hiscock, M. R., V. P. Lance, A. M. Apprill, R. R. Bidigare, Z. I. Johnson, B. G. Mitchell, W. O. Smith et R. T. Barber. « Photosynthetic maximum quantum yield increases are an essential component of the Southern Ocean phytoplankton response to iron ». Proceedings of the National Academy of Sciences 105, n^o 12 (18 mars 2008) : 4775–80. http://dx.doi.org/10.1073/pnas.0705006105.

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Falkowski, PG, et Z. Kolber. « Variations in Chlorophyll Fluorescence Yields in Phytoplankton in the World Oceans ». Functional Plant Biology 22, n^o 2 (1995) : 341. http://dx.doi.org/10.1071/pp9950341.

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The ocean is optically thin and lends itself to large-scale measurements of in vivo chlorophyll fluorescence. In the open ocean, however, phytoplankton chlorophyll concentrations average only 0.2 μg L-1, and hence high sensitivity is required for precise measurements of the fluorescence yields. Over the past decade, we have developed two approaches to achieve the required sensitivity; these are the pump- and probe-technique and a fast repetition rate (FRR) method. Both methods have been adapted for in situ studies and are used to rapidly measure the maximum change in the quantum yield (Δ�max) of photosystem II (PSII), as well as the effective absorption cross-section of PSII (σPSII). Sections of variable fluorescence across the Pacific and Atlantic Oceans reveal the influence of geophysical processes in controlling the quantum yields of phytoplankton photosynthesis. Areas of upwelling, such as off the coast of north-westem Africa, have Fv/Fm values of 0.65, which are close to the maximum achievable values in nutrient-replete cultures. Throughout most of the nutrient-deficient central ocean basins, this quantum efficiency is reduced by more than 50%. In high-nutrient, low- chlorophyll regions of the eastern Equatorial Pacific, the deliberate, large-scale addition of nanomolar iron directly to the ocean leads to a rapid increase in quantum efficiency of the natural phytoplankton community, thereby revealing that in these regions phytoplankton photosynthetic energy conversion efficiency is iron limited. Diel patterns of variation in the upper ocean display midday, intensity- dependent reductions in both upsII and A�max. We interpret the former as indicative of non- photochemical quenching in the antenna, while the latter is a consequence of both rapidly reversible and slowly reversible damage to reaction centres. From knowledge of the incident spectral irradiance, Δ�max, σPSII, and photochemical quenching, the absolute photosynthetic electron transport rate can be derived in real-time. Using unattended, moored continuous measurements of in vivo fluorescence parameters, the derived in situ electron transport rates can be related to satellite observations of the global ocean with basin-scale, seasonal estimates of phytoplankton carbon fixation. Thus, unlike any other photosynthetic parameter, chlorophyll fluorescence can be used to bridge the scales of biophysical responses to ecosystem dynamics.

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Kim, Hyungjin, Geun Ho Ahn, Joy Cho, Matin Amani, James P. Mastandrea, Catherine K. Groschner, Der-Hsien Lien et al. « Synthetic WSe2 monolayers with high photoluminescence quantum yield ». Science Advances 5, n^o 1 (janvier 2019) : eaau4728. http://dx.doi.org/10.1126/sciadv.aau4728.

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In recent years, there have been tremendous advancements in the growth of monolayer transition metal dichalcogenides (TMDCs) by chemical vapor deposition (CVD). However, obtaining high photoluminescence quantum yield (PL QY), which is the key figure of merit for optoelectronics, is still challenging in the grown monolayers. Specifically, the as-grown monolayers often exhibit lower PL QY than their mechanically exfoliated counterparts. In this work, we demonstrate synthetic tungsten diselenide (WSe2) monolayers with PL QY exceeding that of exfoliated crystals by over an order of magnitude. PL QY of ~60% is obtained in monolayer films grown by CVD, which is the highest reported value to date for WSe2 prepared by any technique. The high optoelectronic quality is enabled by the combination of optimizing growth conditions via tuning the halide promoter ratio, and introducing a simple substrate decoupling method via solvent evaporation, which also mechanically relaxes the grown films. The achievement of scalable WSe2 with high PL QY could potentially enable the emergence of technologically relevant devices at the atomically thin limit.

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Behrenfeld, Michael J., Kelsey M. Bisson, Emmanuel Boss, Peter Gaube et Lee Karp-Boss. « Phytoplankton community structuring in the absence of resource-based competitive exclusion ». PLOS ONE 17, n^o 9 (16 septembre 2022) : e0274183. http://dx.doi.org/10.1371/journal.pone.0274183.

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Under most natural marine conditions, phytoplankton cells suspended in the water column are too distantly spaced for direct competition for resources (i.e., overlapping cell boundary layers) to be a routine occurrence. Accordingly, resource-based competitive exclusion should be rare. In contrast, contemporary ecosystem models typically predict an exclusion of larger phytoplankton size classes under low-nutrient conditions, an outcome interpreted as reflecting the competitive advantage of small cells having much higher nutrient ‘affinities’ than larger cells. Here, we develop mechanistically-focused expressions for steady-state, nutrient-limited phytoplankton growth that are consistent with the discrete, distantly-spaced cells of natural populations. These expressions, when encompassed in a phytoplankton-zooplankton model, yield sustained diversity across all size classes over the full range in nutrient concentrations observed in the ocean. In other words, our model does not exhibit resource-based competitive exclusion between size classes previously associated with size-dependent differences in nutrient ‘affinities’.

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Kwangdinata, Raymond, Indah Raya et Muhammad Zakir. « Production of Biodiesel from Lipid of Porphyridium cruentum through Ultrasonic Method ». ISRN Renewable Energy 2014 (10 mars 2014) : 1–6. http://dx.doi.org/10.1155/2014/107278.

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A research on production of biodiesel from lipid of phytoplankton Porphyridium cruentum through ultrasonic method has been done. In this research, we carried out a series of phytoplankton cultures to determine the optimum time of growth and biodiesel synthesis process from phytoplankton lipids. Process of biodiesel synthesis consists of two steps, that is, isolation of phytoplankton lipids and biodiesel synthesis from those lipids. Oil isolation process was carried out by ultrasonic extraction method using ethanol 96%, while biodiesel synthesis was carried out by transesterification reaction using methanol and KOH catalyst under sonication. Weight of biodiesel yield per biomass Porphyridium cruentum is 40,27%. Characterization of biodiesel was well carried out in terms of physical properties which are density and viscosity and chemical properties which are FFA content, saponification value, and iodine value. These values meet the American Society for Testing and Materials (ASTM D6751) standard levels, except for the density value which was 0.9461 g·cm−3 and the FFA content which was 4.6671%.

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Li, Xiao-li, Thomas Kiran Marella, Ling Tao, Li-li Dai, Liang Peng, Chao-feng Song et Gu Li. « The application of ceramsite ecological floating bed in aquaculture : its effects on water quality, phytoplankton, bacteria and fish production ». Water Science and Technology 77, n^o 11 (25 avril 2018) : 2742–50. http://dx.doi.org/10.2166/wst.2018.187.

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Abstract In recent years, biological floating bed technology has been applied increasingly in aquaculture ponds. In this study we developed a novel floating bed made from ceramsite and studied its effect on water quality, phytoplankton, bacteria and fish growth. Water quality was effectively regulated and controlled in ceramsite floating bed (CFB) ponds with an average transparency of 23.18 cm, ammonia nitrogen (NH4+-N) of 2.30 mg L−1, total nitrogen (TN) of 5.09 mg L−1 and total phosphate (TP) of 1.32 mg L−1 which are lower than in control ponds without CFB. Increased phytoplankton species diversity, bacterial number, metabolic activity and microbial diversity was observed with CFB. At the end of growth stage, feed conversion ratio (FCR) was reduced with a total fish yield of 14,838 kg ha−1 at a survival rate of 77.2% in CFB ponds, which is significantly higher than control (P < 0.05). These results emphasize the potential of ecological floating bed to improve water quality, microalgal diversity, reduce the risk of harmful algal blooms and increase the number, activity and diversity of microorganisms as well as fish yield.

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Griffith, Derek J., Emma L. Bone, Sandy J. Thomalla et Stewart Bernard. « Calibration of an in-water multi-excitation fluorometer for the measurement of phytoplankton chlorophyll-a fluorescence quantum yield ». Optics Express 26, n^o 15 (10 juillet 2018) : 18863. http://dx.doi.org/10.1364/oe.26.018863.

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Kwangdinata, Raymond, Indah Raya et Muhammad Zakir. « Production of Biodiesel from Lipid of PhytoplanktonChaetoceros calcitransthrough Ultrasonic Method ». Scientific World Journal 2014 (2014) : 1–5. http://dx.doi.org/10.1155/2014/231361.

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A research on production of biodiesel from lipid of phytoplanktonChaetoceros calcitransthrough ultrasonic method has been done. In this research, we carried out a series of phytoplankton cultures to determine the optimum time of growth and biodiesel synthesis process from phytoplankton lipids. Process of biodiesel synthesis consists of two steps, that is, isolation of phytoplankton lipids and biodiesel synthesis from those lipids. Oil isolation process was carried out by ultrasonic extraction method using ethanol 96%, while biodiesel synthesis was carried out by transesterification reaction using methanol and KOH catalyst under sonication. Weight of biodiesel yield per biomassChaetoceros calcitransis 35.35%. Characterization of biodiesel was well carried out in terms of physical properties which are density and viscosity and chemical properties which are FFA content, saponification value, and iodine value. These values meet the American Society for Testing and Materials (ASTM D6751) standard levels, except for the viscosity value which was 1.14 g·cm−3.

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Sosik, Heidi M., et B. Greg Mitchell. « Absorption, fluorescence, and quantum yield for growth in nitrogen-limited Dunaliella tertiolecta ». Limnology and Oceanography 36, n^o 5 (juillet 1991) : 910–21. http://dx.doi.org/10.4319/lo.1991.36.5.0910.

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Titus, Stephen J., et Robert T. Morton. « Forest Stand Growth Models : What For ? » Forestry Chronicle 61, n^o 1 (1 février 1985) : 19–22. http://dx.doi.org/10.5558/tfc61019-1.

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Until very recently foresters have relied on infrequent inventories to provide static descriptions of large forest areas for management planning. With the quantum increases in computing power, the massing of forestry data, and the increasing pressure for effective management planning, it is becoming necessary to view the forest as dynamic, and subject to manipulation for management purposes. Prediction of changes to forest structure and yield must be made to update old data and project stands into the future. This paper reviews the current sources of literature on growth and yield, discusses basic types and components of growth models, and gives some examples of important uses for growth and yield models. The future will see increased use of computers for analysis of forestry data including even more sophisticated growth and yield models linked to both inventory and decision making processes.

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Greene, Richard M., Zbigniew S. Kolber, Dorothy G. Swift, Neil W. Tindale et Paul G. Falkowski. « Physiological limitation of phytoplankton photosynthesis in the eastern equatorial Pacific determined from variability in the quantum yield of fluorescence ». Limnology and Oceanography 39, n^o 5 (juillet 1994) : 1061–74. http://dx.doi.org/10.4319/lo.1994.39.5.1061.

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Morrison, J. Ruairidh. « In situ determination of the quantum yield of phytoplankton chlorophyll a fluorescence : A simple algorithm, observations, and a model ». Limnology and Oceanography 48, n^o 2 (mars 2003) : 618–31. http://dx.doi.org/10.4319/lo.2003.48.2.0618.

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Aiken, Jim, James Fishwick, Gerald Moore et Katharine Pemberton. « The annual cycle of phytoplankton photosynthetic quantum efficiency, pigment composition and optical properties in the western English Channel ». Journal of the Marine Biological Association of the United Kingdom 84, n^o 2 (avril 2004) : 301–13. http://dx.doi.org/10.1017/s0025315404009191h.

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Phytoplankton photosynthetic quantum efficiency (PQE), pigments, absorption characteristics, species composition (converted to phytoplankton carbon, Cph) and other variables were measured at an offshore site in the western English Channel throughout 2001, using an opportunistic weekly sampling schedule. The variation of chlorophyll-a (Chla) and other phytoplankton pigments followed the classical seasonal cycle, driven by incident light, patterns of stratification and nutrient availability. Phytoplankton and pigment concentrations were low in the winter, rising to a peak in the spring ‘bloom’, with episodic blooms throughout the summer, an autumn bloom and a decline to the winter minimum. Surface layer Chla and total pigment (Tpig) concentrations were highly correlated for the whole year, yet it was observed that the fraction of Chla in Tpig (Chla/Tpig) was not constant and had a distinct seasonal pattern, low in winter and higher in spring, summer and autumn blooms. Chlorophyll-a/Tpig was linearly correlated with recent ambient light fluxes and maximum PQE (PQEm) throughout most of the year, though more significantly within seasonal periods. Chlorophyll-a and Tpig were both linearly correlated to Cph and the Chla/Cph ratio was significantly correlated with both Chla/Tpig and PQEm. Also the optical absorption ratios, a674/a443 and a674/a490 were significantly correlated with PQE and Chla/Tpig, indicating probable optical signatures for these two parameters. The seasonal cycle of measurements of photosynthetic quantum efficiency provided a bench-mark against which all the photosynthetically-driven seasonal changes of biological properties can be understood, in terms of incident solar radiation and nutrient availability. We conclude that phytoplankton synthesize Chla preferentially to other pigments or carbon compounds in conditions beneficial to growth. The PQEm, the ratios of Chla/Tpig, Chla/Cph and a674/a443 are greater when plants are growing actively. In periods of nutrient sufficiency, PQEm, Chla/Tpig and a674/a443 are all linear functions of the mean total photon flux for the recent few days. Photosynthetically driven changes in Chla synthesis, cause observed changes of Chla/Tpig and Chla/Cph ratios.

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Soondur, Mouneshwar, Sundy Ramah, Ravindra Boojhawon, Deepeeka Kaullysing et Ranjeet Bhagooli. « Variations in abundance, diversity, photo-physiology and estimated productivity of micro-phytoplankton with depth at the Saya de Malha Bank, Mascarene Plateau ». Western Indian Ocean Journal of Marine Science, n^o 2/2021 (20 juillet 2022) : 53–68. http://dx.doi.org/10.4314/wiojms.si2021.2.4.

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The variations in micro-phytoplankton abundance, diversity, photo-physiology, chlorophyll a (Chla) concentration and estimated productivity were assessed at depth ranges of 0-4, 5-10, and 11-29 m with 100, 28 and 11% of irradiance, respectively, in Saya de Malha waters. The total micro-phytoplankton abundance (TMPA) differed significantly (P < 0.001) with depth ranges, and between day and night samples. Out of the 34 genera identified, 27 showed a decrease in abundance of over 40% with depth. Chaetoceros, Coscinodiscus, Navicula, Nitzschia and Ceratium were most dominant. The Shannon-Wiener (H’) diversity index did not differ among depth ranges and between samples collected during day and night, but diatoms were more diverse than dinoflagellates. The effective quantum yield (ΦPSII) and the light-use efficiency factor (α) tended to decrease, while the maximum relative electron transport rate (rETRmax), the photo-inhibitory factor (β) and the maximum non-photochemical quenching (NPQmax) varied insignificantly from morning to afternoon sampling points at all depth ranges studied. The estimated productivity, rETRmax and Chla concentration decreased with depth ranges. The higher diversity of diatoms, better photosynthetic performance in the morning hours and higher near-surface estimated productivity provide new insights into micro-phytoplankton dynamics and productivity in Saya de Malha waters.

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Jeon, Jueun, Dong Gil You, Wooram Um, Jeongjin Lee, Chan Ho Kim, Sol Shin, Seunglee Kwon et Jae Hyung Park. « Chemiluminescence resonance energy transfer–based nanoparticles for quantum yield–enhanced cancer phototheranostics ». Science Advances 6, n^o 21 (mai 2020) : eaaz8400. http://dx.doi.org/10.1126/sciadv.aaz8400.

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Chemiluminescence (CL) has recently gained attention for CL resonance energy transfer (CRET)–mediated photodynamic therapy of cancer. However, the short duration of the CL signal and low quantum yield of the photosensitizer have limited its translational applications. Here, we report CRET-based nanoparticles (CRET-NPs) to achieve quantum yield–enhanced cancer phototheranostics by reinterpreting the hidden nature of CRET. Owing to reactive oxygen species (ROS)–responsive CO2 generation, CRET-NPs were capable of generating a strong and long-lasting photoacoustic signal in the tumor tissue via thermal expansion–induced vaporization. In addition, the CRET phenomenon of the NPs enhanced ROS quantum yield of photosensitizer through both electron transfer for an oxygen-independent type I photochemical reaction and self-illumination for an oxygen-dependent type II photochemical reaction. Consequently, owing to their high ROS quantum yield, CRET-NPs effectively inhibited tumor growth with complete tumor growth inhibition in 60% of cases, even with a single treatment.

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LI, JUNWEI, YANG JIANG, YUGANG ZHANG, DI WU, ANQI LUO et ZHONGPING ZHANG. « AQUEOUS SYNTHESIS OF HIGH QUANTUM YIELD AND MONODISPERSED THIOL-CAPPED CdxZn1-xTe QUANTUM DOTS BASED ON ELECTROCHEMICAL METHOD ». Nano 07, n^o 02 (avril 2012) : 1250011. http://dx.doi.org/10.1142/s1793292012500117.

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A facile green approach has been developed to control the growth regime in the aqueous synthesis of CdxZn1-xTe semiconductor quantum dots (QDs) based on the electrochemistry method. The Low growth temperature and slow injection of Te precursor are used to prolong the diffusion controlled stage and thus suppress Ostwald ripening during the nanocrystal growth. The experimental results showed that a low concentration of Te precursor will definitely influence the growth procedure. The UV–visible absorption spectra, as well as transmission electron microscopy (TEM) shows the QDs a good monodispersity at any interval of the reaction procedure. The high-resolution transmission electron microscopy (HRTEM) images and powder X-ray diffraction (XRD) pattern suggested that the as-prepared QDs have high crystallinity and cubic structure. The size and composition-dependent fluorescent emission wavelength of the resultant CdxZn1-xTe alloyed QDs can be tuned from 460 to 610 nm, and their photoluminescent quantum yield can reach up to 70%. Especially in the wavelength range of 510–578 nm, the overall PL QYs of the as-prepared CdxZn1-xTe QDs were above 50%. The current work suggests that electrochemical method is an attractive approach to the synthesis of high-quality II-VI ternary alloyed semiconductor QDs at large-scale with a prominent cost advantage.

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Twiss, Michael R., Jean-Christian Auclair et Murray N. Charlton. « An investigation into iron-stimulated phytoplankton productivity in epipelagic Lake Erie during thermal stratification using trace metal clean techniques ». Canadian Journal of Fisheries and Aquatic Sciences 57, n^o 1 (1 janvier 2000) : 86–95. http://dx.doi.org/10.1139/f99-189.

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We tested the hypothesis that phytoplankton productivity in pelagic Lake Erie is limited by low Fe bioavailability during the period of thermal stratification. Iron enrichment (20 and 200 nM Fe) of water sampled from the eastern basin surface water (5 m depth) in July 1996 revealed a dramatic 180 and 30% increase in the standing crop of the picoplankton (0.2-2 µm) and nanoplankton (2-20 µm) size fractions, respectively. Light-saturated rates of photosynthesis for picoplankton increased 2.8 times that of the controls within 24 h. In contrast, simultaneous P and Fe enrichment experiments carried out in July 1997 and August 1998 with water samples from three pelagic stations revealed that P enrichment alone stimulated phytoplankton growth, although at several stations, phytoplankton yield was greater in combined P- and Fe-amended experiments relative to P-enriched treatments. Periodogram analysis of meteorological buoy wave height data and heat budgets calculated from thermal profiles in the eastern basin revealed important interyear differences in precruise conditioning of the epilimnion. Low-frequency, turbulent mixing events that characterized the 30-day precruise period in the years 1997 and 1998 relative to 1996 may have prevented Fe-stressed conditions in the phytoplankton community studied in 1997 and 1998.

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Markager, Stiig. « LIGHT ABSORPTION AND QUANTUM YIELD FOR GROWTH IN FIVE SPECIES OF MARINE MACROALGAE1 ». Journal of Phycology 29, n^o 1 (février 1993) : 54–63. http://dx.doi.org/10.1111/j.1529-8817.1993.tb00279.x.

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TANAKA, Yuji, Ryohei TSUDA, Minako MIZUTANI et Osamu MITAMURA. « Quantum Yield of Photosynthesis and Spectral Absorption of Phytoplankton during the Stratified Periods at the Northern Basin of Lake Biwa. » Japanese Journal of Limnology (Rikusuigaku Zasshi) 60, n^o 4 (1999) : 507–29. http://dx.doi.org/10.3739/rikusui.60.507.

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Sasai, Yoshikazu, Sherwood Lan Smith, Eko Siswanto, Hideharu Sasaki et Masami Nonaka. « Physiological flexibility of phytoplankton impacts modelled chlorophyll and primary production across the North Pacific Ocean ». Biogeosciences 19, n^o 20 (19 octobre 2022) : 4865–82. http://dx.doi.org/10.5194/bg-19-4865-2022.

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Abstract. Phytoplankton growth, and hence biomass, responds to variations in light and nutrient availability in the near-surface ocean. A wide variety of models have been developed to capture variable chlorophyll : carbon ratios due to photoacclimation, i.e. the dynamic physiological response of phytoplankton to varying light and nutrient availability. Although photoacclimation models have been developed and tested mostly against laboratory results, their application and testing against the observed flexible response of phytoplankton communities remains limited. Hence, the biogeochemical implications of photoacclimation in combination with ocean circulation have yet to be fully explored. We compare modelled chlorophyll and primary production from an inflexible phytoplankton functional type model (InFlexPFT), which assumes fixed carbon (C) : nitrogen (N) : chlorophyll (Chl) ratios, to that from a recently developed flexible phytoplankton functional type model (FlexPFT), which incorporates photoacclimation and variable C : N : Chl ratios. We couple each plankton model with a 3-D eddy-resolving ocean circulation model of the North Pacific and evaluate their respective performance versus observations (e.g. satellite imagery and vertical profiles of in situ observations) of Chl and primary production. These two models yield different horizontal and vertical distributions of Chl and primary production. The FlexPFT reproduces observed subsurface Chl maxima in the subtropical gyre, although it overestimates Chl concentrations. In the subtropical gyre (where light is sufficient), even at low nutrient concentrations, the FlexPFT yields higher chlorophyll concentrations and faster growth rates, which result in higher primary production in the subsurface, compared to the InFlexPFT. Compared to the FlexPFT, the InFlexPFT yields slower growth rates and lower Chl and primary production. In the subpolar gyre, the FlexPFT also predicts faster growth rates near the surface, where light and nutrient conditions are most favourable. Compared to the InFlexPFT, the key differences that allow the FlexPFT to better reproduce the observed patterns are its assumption of variable, rather than fixed, C : N : Chl ratios and interdependent, rather than strictly multiplicative, effects of light limitation (photoacclimation) and nutrient limitation (uptake). Our results suggest that incorporating these processes has the potential to improve chlorophyll and primary production patterns in the near-surface ocean in future biogeochemical models.

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Figueredo, Cleber Cunha, Alessandra Giani et José Pires Lemos Filho. « Photosynthetic capacity of three phytoplanktonic species measured by a pulse amplitude fluorometric method ». Brazilian Journal of Plant Physiology 21, n^o 3 (2009) : 167–74. http://dx.doi.org/10.1590/s1677-04202009000300001.

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During photosynthesis, absorbed energy that is not used in photochemical reactions dissipates as fluorescence. Fluorescence provides important information on the physiological conditions of the studied organisms and its measurement is widely used by plant physiologists and can be valuable in phytoplankton studies. We describe a method adapting a plant fluorometric equipment to measure the photosynthetic capacity of microalgae. Unialgal cultures of three planktonic chlorophytes were exposed to 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosystem II, at concentrations of 0.1, 1.0 and 10.0 µmol.L-1. Estimates were made of photosynthetic parameters, including operational and potential photosystem II quantum yield and electron transport rate between photosystems, using algal cells concentrated on glass-fiber filters. The technique allowed reliable measurements of fluorescence, and detection of distinct levels of inhibition. Physiological or morphological characteristics of the selected species might provide an explanation for the observed results: differences on the surface/volume ratio of the cells and colony morphology, for example, were associated with contrasting resistance to the toxicant. To characterize inhibition on phytoplanktonic photosynthesis, we suggest operational quantum yield and electron transport rate as best parameters, once they were more sensitive to the DCMU toxicity.

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