Articoli di riviste: "Diel cycle"

1

Thomas, H., S. E. Craig, B. J. W. Greenan, W. Burt, G. J. Herndl, S. Higginson, L. Salt, E. H. Shadwick e J. Urrego-Blanco. "Direct observations of diel biological CO<sub>2</sub> fixation on the Scotian Shelf, northwestern Atlantic Ocean". Biogeosciences 9, n. 6 (27 giugno 2012): 2301–9. http://dx.doi.org/10.5194/bg-9-2301-2012.

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Abstract. Much of the variability in the surface ocean's carbon cycle can be attributed to the availability of sunlight, triggering surface heat flux and photosynthesis, which in turn regulate the biogeochemical cycling of carbon over a wide range of time scales. The critical processes of this carbon cycle regulation, occurring at time scales of a day or less, however, have undergone few investigations, most of which have been limited to time spans of several days to months. Optical methods have helped to infer short-term biological variability, but complementing investigations of the oceanic CO2 system are lacking. We employ high-frequency CO2 and optical observations covering the full seasonal cycle on the Scotian Shelf, northwestern Atlantic Ocean, in order to unravel diel periodicity of the surface ocean carbon cycle and its effects on annual budgets. Significant diel periodicity in the surface CO2 system occurs only if the water column is sufficiently stable as observed during seasonal warming. During that time biological CO2 drawdown, or net community production (NCP), is delayed for several hours relative to the onset of photosynthetically available radiation (PAR), due to diel cycles in chlorophyll a concentration and to grazing. In summer, NCP decreases by more than 90%, coinciding with the seasonal minimum of the mixed layer depth and resulting in the disappearance of the diel CO2 periodicity in the surface waters.

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Ball, Becky A., e Ross A. Virginia. "Controls on diel soil CO2 flux across moisture gradients in a polar desert". Antarctic Science 27, n. 6 (15 giugno 2015): 527–34. http://dx.doi.org/10.1017/s0954102015000255.

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AbstractThe McMurdo Dry Valleys of Antarctica are a climate-sensitive ecosystem, where future projected climate warming will increase liquid water availability to release soil biology from physical limitations and alter ecosystem processes. For example, many studies have shown that CO2 flux, an important aspect of the carbon cycle, is controlled by temperature and moisture, which often overwhelm biotic contributions in desert ecosystems. However, these studies used either single-point measurements during peak times of biological activity or diel cycles at individual locations. Here, we present diel cycles of CO2 flux from a range of soil moisture conditions and a variety of locations and habitats to determine how diel cycles of CO2 flux vary across gradients of wet-to-dry soil and whether the water source influences the diel cycle of moist soil. Soil temperature, water content and microbial biomass significantly influenced CO2 flux. Soil temperature explained most of the variation. Soil CO2 flux moderately increased with microbial biomass, demonstrating a sometimes small but significant role of biological fluxes. Our results show that over gradients of soil moisture, both geochemical and biological fluxes contribute to soil CO2 flux, and physical factors must be considered when estimating biological CO2 flux in systems with low microbial biomass.

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Thomas, H., S. E. Craig, B. J. W. Greenan, W. Burt, G. J. Herndl, S. Higginson, L. Salt, E. H. Shadwick e J. Urrego-Blanco. "Direct observations of diel biological CO<sub>2</sub> fixation in the oceans". Biogeosciences Discussions 9, n. 2 (24 febbraio 2012): 2153–68. http://dx.doi.org/10.5194/bgd-9-2153-2012.

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Abstract. Much of the variability in the surface ocean's carbon cycle can be attributed to the availability of sunlight, through processes such as heat fluxes and photosynthesis, which regulate over a wide range of time scales. The critical processes occurring on timescales of a day or less, however, have undergone few investigations, and most of these have been limited to a time span of several days to months, or exceptionally, for longer periods. Optical methods have helped to infer short-term biological variability, however corresponding investigations of the oceanic CO2 system are lacking. We employ high-frequency CO2and optical observations covering the full seasonal cycle on the Scotian Shelf, Northwestern Atlantic Ocean, in order to unravel diel periodicity of the surface ocean carbon cycle and its effects on annual budgets. Significant diel periodicity occurs only if the water column is sufficiently stable as observed during seasonal warming. During that time biological CO2 drawdown, or net community production (NCP), is delayed for several hours relative to the onset of photosynthetically available radiation (PAR), due to diel cycles in chlorophyll-a concentration and to grazing, both of which, we suggest, inhibit NCP in the early morning hours. In summer, NCP decreases by more than 90 %, coinciding with the seasonal minimum of the mixed layer depth and resulting in the disappearance of the diel CO2 periodicity in the surface waters.

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Fleming, Sean W., Peter Hudson e Edward J. Quilty. "Interpreting nonstationary environmental cycles as amplitude-modulated (AM) signalsA paper submitted to the Journal of Environmental Engineering and Science." Canadian Journal of Civil Engineering 36, n. 4 (aprile 2009): 720–31. http://dx.doi.org/10.1139/s08-051.

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Inspired by an analogy to AM radio signals, amplitude modulation (AM) is proposed here as a useful view of nonstationary environmental periodicities, and applied to hydrologic and air quality datasets. Both example time series considered exhibit seasonally evolving diel cycles, with large (small) daily cycle amplitudes in summer (winter). The carrier wave is taken to be a sinusoidal daily cycle; this is multiplied by an information signal consisting of a sinusoidal annual cycle, forming an envelope to the diel variations. Our results suggest that amplitude modulation may offer a novel, compact, and accessible perspective, both qualitatively and quantitatively, on the net phenomenological behaviour arising from highly complex, nonlinear, and diverse environmental process dynamics. Physical interpretations, synergies with common environmental time series processing or analysis methods (Kolmogorov-Zurbenko filtering, classical spectral analysis, and singular systems analysis), and potential future research directions are also explored.

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5

Sweeney, Colm. "The diel carbon cycle of the Biosphere 2 ocean". Ecological Engineering 13, n. 1-4 (giugno 1999): 235–47. http://dx.doi.org/10.1016/s0925-8574(98)00101-3.

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6

Kopec, B. G., A. M. Lauder, E. S. Posmentier e X. Feng. "The diel cycle of water vapor in west Greenland". Journal of Geophysical Research: Atmospheres 119, n. 15 (11 agosto 2014): 9386–99. http://dx.doi.org/10.1002/2014jd021859.

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Carniatto, Natália, Rosemara Fugi, Geuza Cantanhêde, Éder André Gubiani e Norma Segatti Hahn. "Effects of flooding regime and diel cycle on diet of a small sized fish associated to macrophytes". Acta Limnologica Brasiliensia 24, n. 4 (12 aprile 2013): 363–72. http://dx.doi.org/10.1590/s2179-975x2013005000007.

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AIM: In this paper we assessed the effects of flooding (low and high water period) on the feeding activity and diet composition of Serrapinus notomelas in patches of the macrophyte Eichhornia azurea in a shallow floodplain lake (upper Paraná River Floodplain, Brazil). We also assessed the variations of diet composition and feeding activity along the diel cycle. METHODS: Traps were used to catch the fish inside of macrophyte patches monthly from June/2007 to May/2008. A total of 1038 stomachs were examined. We assessed the feeding activity with the mean stomach fullness degree method. To summarize and support the results of diet composition in the different periods (low and high water periods) and times (dawn, light period, and dusk), was applied a nonmetric multidimensional scaling (NMS). RESULTS: The feeding activity of S. notomelas did not differ between low and high water periods, but it differed along the diel cycle. The feeding activity was higher during the light period and dusk, at both the low and high water period. The diet composition differed significantly between low and high water periods, and also along the diel cycle. In the low water the diet of S. notomelas was composed mainly by algae and in the high water by Cladocera. Algae were consumed mainly during the light period while Cladocera in dawn and dusk. CONCLUSIONS: Our results indicate that the oscillations in the water level affect the diet composition, but not the feeding activity of S. notomelas. These seasonal changes are probably related to the temporal abundance of food resources, thus, when Cladocera density was low (low water), S. notomelas consumed mainly algae but when Cladocera was more abundant (high water), it became a common food resource.

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8

Watras, Carl J., Kenneth A. Morrison, Noah R. Lottig e Timothy K. Kratz. "Comparing the diel cycles of dissolved organic matter fluorescence in a clear-water and two dark-water Wisconsin lakes: potential insights into lake metabolism". Canadian Journal of Fisheries and Aquatic Sciences 73, n. 1 (gennaio 2016): 65–75. http://dx.doi.org/10.1139/cjfas-2015-0172.

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The cycling of organic carbon is fundamental to aquatic ecosystems, reflecting processes that extend from terrestrial watersheds to fish. Here, we use embedded fluorescence sensors that sample at high frequency to investigate the daily dynamics of a proxy for the major pool of organic carbon (chromophoric dissolved organic matter, CDOM) in a clear-water Wisconsin lake (∼3 mg C·L−1). We compare the diel CDOM cycle in this lake with cycles observed previously in two dark-water lakes (10 to 20 mg C·L−1). Despite differences in DOM quality and quantity, diel fluorescence cycles were evident in the epilimnia and hypolimnia of all three lakes. The amplitude differed among lakes, but the timing of the diel cycles was similar, with increases in fluorescence during nighttime and decreases during daylight (except in the aphotic hypolimnion of the darkest lake). The amplitude of the diel cycle increased with increasing DOM concentration, and estimates of DOM turnover based on the magnitude of oscillation ranged from 0.28 mg C·L−1·day−1 in the darkest lake to 0.14 mg C·L−1·day−1 in the clear lake. Independent estimates of free water metabolism based on the daily dynamics of O2 or CO2 were in general agreement, ranging from 0.32 to 0.06 mg C·L−1·day−1. Although absolute rates of turnover varied directly with DOM concentration, relative rates were highest in clear waters (∼5%·day−1). We conclude that these daily oscillations may be a common property of lakes and that they may provide insights into internal DOM processing over short time scales.

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9

Briggs, Nathan, Kristinn Guðmundsson, Ivona Cetinić, Eric D'Asaro, Eric Rehm, Craig Lee e Mary Jane Perry. "A multi-method autonomous assessment of primary productivity and export efficiency in the springtime North Atlantic". Biogeosciences 15, n. 14 (25 luglio 2018): 4515–32. http://dx.doi.org/10.5194/bg-15-4515-2018.

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Abstract. Fixation of organic carbon by phytoplankton is the foundation of nearly all open-ocean ecosystems and a critical part of the global carbon cycle. But the quantification and validation of ocean primary productivity at large scale remains a major challenge due to limited coverage of ship-based measurements and the difficulty of validating diverse measurement techniques. Accurate primary productivity measurements from autonomous platforms would be highly desirable due to much greater potential coverage. In pursuit of this goal we estimate gross primary productivity over 2 months in the springtime North Atlantic from an autonomous Lagrangian float using diel cycles of particulate organic carbon derived from optical beam attenuation. We test method precision and accuracy by comparison against entirely independent estimates from a locally parameterized model based on chlorophyll a and light measurements from the same float. During nutrient-replete conditions (80 % of the study period), we obtain strong relative agreement between the independent methods across an order of magnitude of productivities (r2=0.97), with slight underestimation by the diel cycle method (−19 ± 5 %). At the end of the diatom bloom, this relative difference increases to −58 % for a 6-day period, likely a response to SiO4 limitation, which is not included in the model. In addition, we estimate gross oxygen productivity from O2 diel cycles and find strong correlation with diel-cycle-based gross primary productivity over the entire deployment, providing further qualitative support for both methods. Finally, simultaneous estimates of net community productivity, carbon export, and particle size suggest that bloom growth is halted by a combination of reduced productivity due to SiO4 limitation and increased export efficiency due to rapid aggregation. After the diatom bloom, high Chl a-normalized productivity indicates that low net growth during this period is due to increased heterotrophic respiration and not nutrient limitation. These findings represent a significant advance in the accuracy and completeness of upper-ocean carbon cycle measurements from an autonomous platform.

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Liu, Riyue, Yaxin Liu, Yue Chen, Yuanchao Zhan e Qinglu Zeng. "Cyanobacterial viruses exhibit diurnal rhythms during infection". Proceedings of the National Academy of Sciences 116, n. 28 (24 giugno 2019): 14077–82. http://dx.doi.org/10.1073/pnas.1819689116.

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As an adaptation to the daily light–dark (diel) cycle, cyanobacteria exhibit diurnal rhythms of gene expression and cell cycle. The light–dark cycle also affects the life cycle of viruses (cyanophages) that infect the unicellular picocyanobacteriaProchlorococcusandSynechococcus, which are the major primary producers in the oceans. For example, the adsorption of some cyanophages to the host cells depends on light, and the burst sizes of cyanophages are positively correlated to the length of light exposure during infection. Recent metatranscriptomic studies revealed transcriptional rhythms of field cyanophage populations. However, the underlying mechanism remains to be determined, as cyanophage laboratory cultures have not been shown to exhibit diurnal transcriptional rhythms. Here, we studied variation in infection patterns and gene expression ofProchlorococcusphages in laboratory culture conditions as a function of light. We found three distinct diel-dependent life history traits in dark conditions (diel traits): no adsorption (cyanophage P-HM2), adsorption but no replication (cyanophage P-SSM2), and replication (cyanophage P-SSP7). Under light–dark cycles, each cyanophage exhibited rhythmic transcript abundance, and cyanophages P-HM2 and P-SSM2 also exhibited rhythmic adsorption patterns. Finally, we show evidence to link the diurnal transcriptional rhythm of cyanophages to the photosynthetic activity of the host, thus providing a mechanistic explanation for the field observations of cyanophage transcriptional rhythms. Our study identifies that cultured viruses can exhibit diurnal rhythms during infection, which might impact cyanophage population-level dynamics in the oceans.

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Forget, Marie-Hélène, Richard Carignan e Christiane Hudon. "Influence of diel cycles of respiration, chlorophyll, and photosynthetic parameters on the summer metabolic balance of temperate lakes and rivers". Canadian Journal of Fisheries and Aquatic Sciences 66, n. 7 (luglio 2009): 1048–58. http://dx.doi.org/10.1139/f09-058.

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Primary production, planktonic respiration, bacterial abundance, and chlorophyll a were measured in the epilimnion of two Canadian Shield lakes and in two large rivers to establish their metabolic balance and to contrast oligotrophic and oligo-mesotrophic systems. Pronounced diel respiration cycles were observed in all systems, with a minimum in the morning and a maximum in the evening. Respiration was positively correlated with water temperature, incident light, and chlorophyll a concentration. Diel cycles of chlorophyll a were discernible in both rivers and in the oligo-mesotrophic lake. Our results show that a single morning sampling underestimates both respiration and chlorophyll a, whereas a single sample taken at noon generally agrees better with the average of four daily measurements. In oligotrophic Lac Croche, the photosynthetic parameter αB remained constant throughout the day, whereas PBm increased by 12.5% between 0600 h and 1300 h. Ignoring the diel community respiration cycle resulted in a ~25% underestimation of daily respiration, whereas ignoring the PBm cycle induced a ~9% underestimation of the daily primary production. The net balance between production (P) and respiration (R) of the oligotrophic lake epilimnion remained positive during two summers, and the P:R ratio showed net autotrophy for all systems except for the oligotrophic river, which was slightly net heterotrophic.

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Dall'Olmo, G., T. K. Westberry, M. J. Behrenfeld, E. Boss, C. Courties, L. Prieur, N. Hardman-Mountford e T. Moutin. "Inferring phytoplankton carbon and eco-physiological rates from diel cycles of spectral particulate beam-attenuation coefficient". Biogeosciences Discussions 8, n. 2 (21 marzo 2011): 3009–50. http://dx.doi.org/10.5194/bgd-8-3009-2011.

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Abstract. The diurnal fluctuations in solar irradiance impose a fundamental frequency on ocean biogeochemistry. Observations of the ocean carbon cycle at these frequencies are rare, but could be considerably expanded by measuring and interpreting the inherent optical properties. A method is presented to analyze diel cycles in particulate beam-attenuation coefficient (cp) measured at multiple wavelengths. The method is based on fitting observations with a size-structured population and optical model to infer the particle size distribution and physiologically relevant parameters of the cells responsible for the measured diel cycle in cp. Results show that the information related to size and contained in the spectral data can be exploited to independently estimate growth and loss rates during the day and night. In addition, the model can characterize the population of particles affecting the cp diel variability. Application of this method to spectral cp measured at a station in the oligotrophic Mediterranean Sea suggests that most of the observed variations in cp can be ascribed to a synchronized population of cells with an equivalent spherical diameter between 1 and 4 μm. The inferred carbon biomass of these cells was about 8–13 mg m−3 and accounted for approximately 20% of the total particulate organic carbon. If successfully validated and implemented on autonomous platforms, this method could improve our understanding of the ocean carbon cycle.

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Levy, David A. "Reciprocal Diel Vertical Migration Behavior in Planktivores and Zooplankton in British Columbia Lakes". Canadian Journal of Fisheries and Aquatic Sciences 47, n. 9 (1 settembre 1990): 1755–64. http://dx.doi.org/10.1139/f90-199.

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Simultaneous comparison of planktivore and crustacean zooplankton distribution patterns in a set of British Columbia lakes suggested coupled diel vertical migration behavior in the two adjacent trophic levels. In lakes where juvenile sockeye salmon performed diel vertical migrations, most zooplankton were non-migratory and concentrated in shallow surface waters over the diel cycle. In contrast, in one lake where pelagic threespine sticklebacks were present, and where juvenile sockeye diel vertical migrations were periodically reversed, most zooplankton undertook diel vertical migrations. The presence of diel vertical migration behavior in zooplankton thus appears to be related to the presence or absence of the behavior in the predominant planktivores.

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Orlowski, Andrzej. "Experimental verification of the acoustic characteristics of the clupeoid diel cycle in the Baltic". ICES Journal of Marine Science 62, n. 6 (1 gennaio 2005): 1180–90. http://dx.doi.org/10.1016/j.icesjms.2005.02.013.

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Abstract This paper describes the results of a short-term experiment using measurements of sv from the diel, spatial, clupeoid distribution in the southern Baltic. The aim of the experiment was to verify fish-behaviour characteristics measured over the period from 1995 to 2001. It was also intended to estimate the dynamics of fish behaviour over one separate diel cycle. The studies were based on a 24 h continuous integration of fish echoes using an EY500 echosounder at 38 kHz. Measurements were carried out by RV “Baltica” travelling along the sides of a square of 4 nautical miles at a constant speed of 8 knots. The South Gotland Deep was chosen for the experiment because of the greatest amplitude there of fish vertical, diel migrations within the Polish EEZ. The duration of the experiment was limited by weather conditions, but nearly 300 EDSU samples were collected. 3-D distributions of echoes were correlated to the values of coincident environmental factors of time, depth, water temperature, salinity, and oxygen level. Fish distribution compared with environmental factors is described by different macrosounding visualizations, statistical, and mathematical models. Measurements are compared with the average characteristics of fish behaviour based on data from the autumn acoustic studies between 1995 and 2001 in a wider environment of the Gotland Deep. The results strongly confirmed the instability of the diel acoustic response of fish echoes in both situations. More precise measurements during the experiment indicated the biggest column-scattering strength (Svc) increase during the sunrise period, appearing simultaneously in the whole area. A similar increase was detected by analysis of 1995–2001 data from the South Gotland Deep environment. Major emphasis is given to the explanation of the diel irregularities. Diel instability of fish acoustic response can significantly effect the results of target-strength measurements (up to 400% during the sunrise) and, as a consequence, the calibration of acoustic fish stock-assessment models.

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Nalewajko, C., e H. Godmaire. "Extracellular products of Myriophyllum spicatum L. as a function of growth phase and diel cycle". Archiv für Hydrobiologie 127, n. 3 (9 giugno 1993): 345–56. http://dx.doi.org/10.1127/archiv-hydrobiol/127/1993/345.

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Shin, C. N., G.-Y. Rhee e J. Chen. "Phosphate Requirement, Photosynthesis, and Diel Cell Cycle of Scenedesmus obliquas Under Fluctuating Light". Canadian Journal of Fisheries and Aquatic Sciences 44, n. 10 (1 ottobre 1987): 1753–58. http://dx.doi.org/10.1139/f87-214.

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The effect of light fluctuation (0.06 Hz) on P requirement, photosynthesis, and the diel cell-division cycle was investigated in Scenedesmus obliquus in a chemostat under a 12 h day: 12 h night cycle. P requirement was much less under oscillating than under constant daylight of the same photon flux density. However, cell chlorophyll a was significantly higher, indicating an increased N requirement. There was little difference in photosynthetic efficiency (the slope of the photosynthesis–light regression) between oscillating and constant light, but photosynthetic capacity was higher in fluctuating light. Cell C was also higher. A strong diel rhythmicity in steady-state cell numbers was observed with little phase difference between oscillating and constant light. Although steady-state cell numbers under P limitation were significantly higher under fluctuating light, there was no difference in instantaneous growth rates and their diel distribution. At a dilution rate of 0.6∙d−1, cell death occurred at an average rate of −0.56∙d−1 between 4 h before and 5 h after the onset of the dark period.

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Benoit-Bird, Kelly J., Whitlow W. L. Au e Daniel W. Wisdoma. "Nocturnal light and lunar cycle effects on diel migration of micronekton". Limnology and Oceanography 54, n. 5 (25 luglio 2009): 1789–800. http://dx.doi.org/10.4319/lo.2009.54.5.1789.

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Baumann-Pickering, Simone, Marie A. Roch, Sean M. Wiggins, Hans-Ulrich Schnitzler e John A. Hildebrand. "Acoustic behavior of melon-headed whales varies on a diel cycle". Behavioral Ecology and Sociobiology 69, n. 9 (25 luglio 2015): 1553–63. http://dx.doi.org/10.1007/s00265-015-1967-0.

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Holtzendorff, J., F. Partensky, S. Jacquet, F. Bruyant, D. Marie, L. Garczarek, I. Mary, D. Vaulot e W. R. Hess. "Diel Expression of Cell Cycle-Related Genes in Synchronized Cultures of Prochlorococcus sp. Strain PCC 9511". Journal of Bacteriology 183, n. 3 (1 febbraio 2001): 915–20. http://dx.doi.org/10.1128/jb.183.3.915-920.2001.

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ABSTRACT The cell cycle of the chlorophyll b-possessing marine cyanobacterium Prochlorococcus is highly synchronized under natural conditions. To understand the underlying molecular mechanisms we cloned and sequenced dnaA and ftsZ, two key cell cycle-associated genes, and studied their expression. An axenic culture of Prochlorococcus sp. strain PCC 9511 was grown in a turbidostat with a 12 h–12 h light-dark cycle for 2 weeks. During the light periods, a dynamic light regimen was used in order to simulate the natural conditions found in the upper layers of the world's oceans. This treatment resulted in strong cell cycle synchronization that was monitored by flow cytometry. The steady-state mRNA levels of dnaA andftsZ were monitored at 4-h intervals during four consecutive division cycles. Both genes exhibited clear diel expression patterns with mRNA maxima during the replication (S) phase. Western blot experiments indicated that the peak of FtsZ concentration occurred at night, i.e., at the time of cell division. Thus, the transcript accumulation of genes involved in replication and division is coordinated in Prochlorococcus sp. strain PCC 9511 and might be crucial for determining the timing of DNA replication and cell division.

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Dall'Olmo, G., E. Boss, M. J. Behrenfeld, T. K. Westberry, C. Courties, L. Prieur, M. Pujo-Pay, N. Hardman-Mountford e T. Moutin. "Inferring phytoplankton carbon and eco-physiological rates from diel cycles of spectral particulate beam-attenuation coefficient". Biogeosciences 8, n. 11 (28 novembre 2011): 3423–39. http://dx.doi.org/10.5194/bg-8-3423-2011.

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Abstract. The diurnal fluctuations in solar irradiance impose a fundamental frequency on ocean biogeochemistry. Observations of the ocean carbon cycle at these frequencies are rare, but could be considerably expanded by measuring and interpreting the inherent optical properties. A method is presented to analyze diel cycles in particulate beam-attenuation coefficient (cp) measured at multiple wavelengths. The method is based on fitting observations with a size-structured population model coupled to an optical model to infer the particle size distribution and physiologically relevant parameters of the cells responsible for the measured diel cycle in cp. Results show that the information related to size and contained in the spectral data can be exploited to independently estimate growth and loss rates during the day and night. In addition, the model can characterize the population of particles affecting the diel variability in cp. Application of this method to spectral cp measured at a station in the oligotrophic Mediterranean Sea suggests that most of the observed variations in cp can be ascribed to a synchronized population of cells with an equivalent spherical diameter around 4.6±1.5 μm. The inferred carbon biomass of these cells was about 5.2–6.0 mg m−3 and accounted for approximately 10% of the total particulate organic carbon. If successfully validated, this method may improve our in situ estimates of primary productivity.

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Bahamon, Nixon, Francesc Sardà e Jacopo Aguzzi. "Fuzzy diel patterns in catchability of deep-water species on the continental margin". ICES Journal of Marine Science 66, n. 10 (8 luglio 2009): 2211–18. http://dx.doi.org/10.1093/icesjms/fsp190.

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Abstract Bahamon, N., Sardà, F., and Aguzzi, J. 2009. Fuzzy diel patterns in catchability of deep-water species on the continental margin. – ICES Journal of Marine Science, 66: 2211–2218. Exploited deep-water fish communities on continental margins are poorly understood in terms of variations in species composition and abundance by depth and season as a response to diel changes in light intensity and length of photoperiod. Innovative fuzzy clustering and traditional agglomerative hierarchical clustering methods were applied to data from bottom trawls collected continuously for 4 d in October and June, on the shelf (100–110 m) and upper slope (400–430 m). Fuzzy clustering was more effective than hierarchical clustering at characterizing diel variations in catches from the upper slope because the species assemblage did not show a distinct day and night structure. On the shelf, the species assemblages shifted abruptly between a diurnal and a nocturnal structure at sunset and sunrise, and the two clustering methods yielded similar results. Endobenthic decapods with marked crepuscular-nocturnal emergence from the substratum were mostly responsible for this pattern. No clearly discernible diel pattern was found with the dampening of light intensity with depth, weakening the behavioural response of endobenthos to the day–night cycle. The results indicated that the regulatory effect of the light cycle on diel activity rhythms weakens with depth.

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Hawes, Ian, e Paul Brazier. "Freshwater stream ecosystems of James Ross Island, Antarctica". Antarctic Science 3, n. 3 (settembre 1991): 265–71. http://dx.doi.org/10.1017/s0954102091000329.

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The freshwater streams of James Ross Island share many of the features common to other Antarctic streams. There is a diel variation in temperature and discharge, which follows the daily insolation cycle; catchments are barren; stream vegetation is predominantly algal, comprising mat-forming cyanobacteria and filamentous chlorophytes; and physical factors, particularly turbidity and bed stability are important in determining biomass and composition of algal assemblages. Nutrient concentrations vary from stream to stream and over a diel cycle, with minimum dissolved N in late afternoon. Biomass attained and photosynthetic and respiratory rates are also comparable to those recorded in other Antarctic streams, with low productivity/biomass ratios in perennial assemblages.

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Brinton, Cameron Patrick, e Mary Carla Curran. "Tidal and diel movement patterns of the Atlantic stingray (Dasyatis sabina) along a stream-order gradient". Marine and Freshwater Research 68, n. 9 (2017): 1716. http://dx.doi.org/10.1071/mf16073.

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The behaviour of the Atlantic stingray (Dasyatis sabina) is affected by environmental cues, including time of day and tide. The purpose of the present study was to determine whether these cycles and differences in creek geomorphology affected presence and movement patterns of Atlantic stingrays near Savannah, GA, USA. Forty-five stingrays were tagged with Vemco coded-acoustic transmitters and passively tracked in two creek systems between December 2012 and December 2014. The geomorphology of the creeks was classified using the Horton stream-order concept, with the smallest tributaries assigned to the first order. Stingrays moved most at dusk (0.26±0.09 movements day–1), followed by night (0.23±0.09 movements day–1). Stingrays were found in deeper water during the cold season than during the warm season. Patterns in creek usage across tidal stages were nearly consistent across seasons. However, the diel pattern varied; stingrays utilised all creek orders throughout the diel cycle in the warm seasons, but entered only shallow creeks during the day in the cold season. Because presence and movements of stingrays were affected by tidal and diel cycles, these environmental factors could also affect their foraging patterns and their influence as an ecosystem engineer.

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Rodrigo, María A., Antonio Camacho, Eduardo Vicente e María R. Miracle. "Microstratified vertical distribution and migration of phototrophic microorganisms during a diel cycle in Lake Arcas-2 (Spain)". Fundamental and Applied Limnology 145, n. 4 (26 luglio 1999): 497–512. http://dx.doi.org/10.1127/archiv-hydrobiol/145/1999/497.

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25

Levy, David A. "Acoustic Analysis of Diel Vertical Migration Behavior of Mysis relicta and Kokanee (Oncorhynchus nerka) within Okanagan Lake, British Columbia". Canadian Journal of Fisheries and Aquatic Sciences 48, n. 1 (1 gennaio 1991): 67–72. http://dx.doi.org/10.1139/f91-010.

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Abstract (sommario):

Dual-beam acoustic surveys of Okanagan Lake suggested active diel vertical migrations of Mysis relicta and kokanee (Oncorhynchus nerka) within the pelagic zone. Mysis relicta were situated between 90–150 m during the day and migrated upwards into the thermocline region of the water column at night. Two groups of kokanee targets were detected. The first undertook a diel vertical migration and coalesced at dusk with a second, shallow-oriented group of targets. Daytime target strength estimates taken while the two groups were vertically segregated in the water column suggested an 8–12 db lower target strength of the deeper group. The results provide acoustic evidence for a smaller body size in the deeper group and the occurrence of an ontogenetic shift in diel migratory behavior of kokanee within Okanagan Lake. Diel comparisons of depth distribution suggested spatial segregation of Mysis and kokanee over much of the diel cycle.

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26

Woltz, J. M., e D. A. Landis. "Comparison of sampling methods of Aphis glycines predators across the diel cycle". Journal of Applied Entomology 138, n. 7 (19 dicembre 2013): 475–84. http://dx.doi.org/10.1111/jen.12106.

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27

Woolway, Richard Iestyn, David M. Livingstone e Martin Kernan. "Altitudinal dependence of a statistically significant diel temperature cycle in Scottish lochs". Inland Waters 5, n. 4 (1 ottobre 2015): 311–16. http://dx.doi.org/10.5268/iw-5.4.854.

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28

Fahnenstiel, Gary L., Tyrone R. Patton, Hunter J. Carrick e Michael J. McCormick. "Diel Division Cycle and Growth Rates ofSynechococcus in Lakes Huron and Michigan1". Internationale Revue der gesamten Hydrobiologie und Hydrographie 76, n. 4 (1991): 657–64. http://dx.doi.org/10.1002/iroh.19910760415.

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29

Hynes, Annette M., Brad J. Blythe e Brian J. Binder. "An individual-based model for the analysis of Prochlorococcus diel cycle behavior". Ecological Modelling 301 (aprile 2015): 1–15. http://dx.doi.org/10.1016/j.ecolmodel.2015.01.011.

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30

Bollens, Stephen M., e Donald E. Stearns. "Predator-induced changes in the diel feeding cycle of a planktonic copepod". Journal of Experimental Marine Biology and Ecology 156, n. 2 (aprile 1992): 179–86. http://dx.doi.org/10.1016/0022-0981(92)90244-5.

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31

Gusareva, Elena S., Enzo Acerbi, Kenny J. X. Lau, Irvan Luhung, Balakrishnan N. V. Premkrishnan, Sandra Kolundžija, Rikky W. Purbojati et al. "Microbial communities in the tropical air ecosystem follow a precise diel cycle". Proceedings of the National Academy of Sciences 116, n. 46 (28 ottobre 2019): 23299–308. http://dx.doi.org/10.1073/pnas.1908493116.

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Abstract (sommario):

The atmosphere is vastly underexplored as a habitable ecosystem for microbial organisms. In this study, we investigated 795 time-resolved metagenomes from tropical air, generating 2.27 terabases of data. Despite only 9 to 17% of the generated sequence data currently being assignable to taxa, the air harbored a microbial diversity that rivals the complexity of other planetary ecosystems. The airborne microbial organisms followed a clear diel cycle, possibly driven by environmental factors. Interday taxonomic diversity exceeded day-to-day and month-to-month variation. Environmental time series revealed the existence of a large core of microbial taxa that remained invariable over 13 mo, thereby underlining the long-term robustness of the airborne community structure. Unlike terrestrial or aquatic environments, where prokaryotes are prevalent, the tropical airborne biomass was dominated by DNA from eukaryotic phyla. Specific fungal and bacterial species were strongly correlated with temperature, humidity, and CO2 concentration, making them suitable biomarkers for studying the bioaerosol dynamics of the atmosphere.

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32

Cohen, J. H., e R. B. Forward. "Diel vertical migration of the marine copepod Calanopia americana. I. Twilight DVM and its relationship to the diel light cycle". Marine Biology 147, n. 2 (22 febbraio 2005): 387–98. http://dx.doi.org/10.1007/s00227-005-1569-x.

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33

Reiman, Jeremy, e Y. Xu. "Diel Variability of pCO2 and CO2 Outgassing from the Lower Mississippi River: Implications for Riverine CO2 Outgassing Estimation". Water 11, n. 1 (27 dicembre 2018): 43. http://dx.doi.org/10.3390/w11010043.

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Abstract (sommario):

Carbon dioxide (CO2) outgassing from river surface waters is an important component of the global carbon cycle currently not well constrained. To test the hypothesis that riverine partial pressure of CO2 (pCO2) and CO2 outgassing rates differ between daylight and darkness, we conducted in-situ pCO2 and ambient water measurements over four 24-h periods in the spring and summer of 2018 in the Lower Mississippi River under varying flow regimes. We hypothesized that diel pCO2 variation will correlate inversely with solar radiation due to light-induced photosynthesis. Despite differing ambient conditions between seasons, we found a consistent diel cycle of riverine pCO2, with highest values before sunset and lowest values during peak daylight. Recorded pCO2 measurements varied by 206–607 µatm in spring and 344–377 µatm in summer, with significantly lower records during daylight in summer. CO2 outgassing was significantly lower during daylight in both seasons, with diel variation ranging between 1.5–4.4 mmol m−2 h−1 in spring and 1.9–2.1 mmol m−2 h−1 in summer. Daily outgassing rates calculated incorporating diel variation resulted in significantly greater rates (26.2 ± std. 12.7 mmol m−2 d−1) than calculations using a single daily pCO2 value. This study suggests a likely substantial underestimation of carbon outgassed from higher order rivers that make up a majority of the global river water surface. The findings highlight the need for high temporal resolution data and further research on diel CO2 outgassing in different climate regions to constrain uncertainties in riverine flux estimation.

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34

Ceusters, Nathalie, Stijn Luca, Regina Feil, Johan E. Claes, John E. Lunn, Wim Van den Ende e Johan Ceusters. "Hierarchical clustering reveals unique features in the diel dynamics of metabolites in the CAM orchid Phalaenopsis". Journal of Experimental Botany 70, n. 12 (11 aprile 2019): 3269–81. http://dx.doi.org/10.1093/jxb/erz170.

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Abstract (sommario):

Abstract Crassulacean acid metabolism (CAM) is a major adaptation of photosynthesis that involves temporally separated phases of CO2 fixation and accumulation of organic acids at night, followed by decarboxylation and refixation of CO2 by the classical C3 pathway during the day. Transitory reserves such as soluble sugars or starch are degraded at night to provide the phosphoenolpyruvate (PEP) and energy needed for initial carboxylation by PEP carboxylase. The primary photosynthetic pathways in CAM species are well known, but their integration with other pathways of central C metabolism during different phases of the diel light–dark cycle is poorly understood. Gas exchange was measured in leaves of the CAM orchid Phalaenopsis ‘Edessa’ and leaves were sampled every 2 h during a complete 12-h light–12-h dark cycle for metabolite analysis. A hierarchical agglomerative clustering approach was employed to explore the diel dynamics and relationships of metabolites in this CAM species, and compare these with those in model C3 species. High levels of 3-phosphoglycerate (3PGA) in the light activated ADP-glucose pyrophosphorylase, thereby enhancing production of ADP-glucose, the substrate for starch synthesis. Trehalose 6-phosphate (T6P), a sugar signalling metabolite, was also correlated with ADP-glucose, 3PGA and PEP, but not sucrose, over the diel cycle. Whether or not this indicates a different function of T6P in CAM plants is discussed. T6P levels were low at night, suggesting that starch degradation is regulated primarily by circadian clock-dependent mechanisms. During the lag in starch degradation at dusk, carbon and energy could be supplied by rapid consumption of a large pool of aconitate that accumulates in the light. Our study showed similarities in the diel dynamics and relationships between many photosynthetic metabolites in CAM and C3 plants, but also revealed some major differences reflecting the specialized metabolic fluxes in CAM plants, especially during light–dark transitions and at night.

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35

Connell, PE, F. Ribalet, EV Armbrust, A. White e DA Caron. "Diel oscillations in the feeding activity of heterotrophic and mixotrophic nanoplankton in the North Pacific Subtropical Gyre". Aquatic Microbial Ecology 85 (3 dicembre 2020): 167–81. http://dx.doi.org/10.3354/ame01950.

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Abstract (sommario):

Daily oscillations in photosynthetically active radiation strongly influence the timing of metabolic processes in picocyanobacteria, but it is less clear how the light-dark cycle affects the activities of their consumers. We investigated the relationship between marine picocyanobacteria and nanoplanktonic consumers throughout the diel cycle to determine whether heterotrophic and mixotrophic protists (algae with phagotrophic ability) display significant periodicity in grazing pressure. Carbon biomass of Prochlorococcus and Synechococcus was estimated continuously from abundances and cell size measurements made by flow cytometry. Picocyanobacterial dynamics were then compared to nanoplankton abundances and ingestion of fluorescently labeled bacteria measured every 4 h during a 4 d survey in the North Pacific Subtropical Gyre. Grazing of the labeled bacteria by heterotrophic nanoplankton was significantly greater at night than during the day. The grazing activity of mixotrophic nanoplankton showed no diel periodicity, suggesting that they may feed continuously, albeit at lower rates than heterotrophic nanoplankton, to alleviate nutrient limitation in this oligotrophic environment. Diel changes in Prochlorococcus biomass indicated that they could support substantial growth of nanoplankton if those grazers are the main source of picocyanobacterial mortality, and that grazers may contribute to temporally stable abundances of picocyanobacteria.

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36

Goulet, R. R., e F. R. Pick. "Diel changes in iron concentrations in surface-flow constructed wetlands". Water Science and Technology 44, n. 11-12 (1 dicembre 2001): 421–26. http://dx.doi.org/10.2166/wst.2001.0861.

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Abstract (sommario):

Diel changes in Fe concentrations were examined from spring to late fall at two surface-flow wetlands. The highest concentrations of ferrous, dissolved and total Fe were measured at night in the littoral zone, when oxygen and pH were low. The lowest Fe concentrations were measured during the day when oxygen and pH were highest. The amplitude of change over the day-night cycle was greatest in July and lowest in May and October. These diel changes were also observed at the outlet of both wetlands. Overall, O2 and pH explained 60% of the observed seasonal and diel variation in water Fe (R2=0.60, p=0.004). The treatment performance of wetlands can be overestimated when based on samples collected during the day.

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37

Andrade, Karen, Jörn Logemann, Karla B. Heidelberg, Joanne B. Emerson, Luis R. Comolli, Laura A. Hug, Alexander J. Probst et al. "Metagenomic and lipid analyses reveal a diel cycle in a hypersaline microbial ecosystem". ISME Journal 9, n. 12 (28 aprile 2015): 2697–711. http://dx.doi.org/10.1038/ismej.2015.66.

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38

Maurin-Defossez, Claire, e Yves Le Gal. "Diel periodicity of glutamine synthetase activity during the cell cycle of Emiliania huxleyi". Plant Physiology and Biochemistry 36, n. 3 (marzo 1998): 233–36. http://dx.doi.org/10.1016/s0981-9428(97)86880-5.

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39

VON CAEMMERER, SUSANNE, e HOWARD GRIFFITHS. "Stomatal responses to CO2during a diel Crassulacean acid metabolism cycle inKalanchoe daigremontianaandKalanchoe pinnata". Plant, Cell & Environment 32, n. 5 (maggio 2009): 567–76. http://dx.doi.org/10.1111/j.1365-3040.2009.01951.x.

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40

Revsbech, Niels Peter, Erik Trampe, Mads Lichtenberg, David M. Ward e Michael Kühl. "In SituHydrogen Dynamics in a Hot Spring Microbial Mat during a Diel Cycle". Applied and Environmental Microbiology 82, n. 14 (6 maggio 2016): 4209–17. http://dx.doi.org/10.1128/aem.00710-16.

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Abstract (sommario):

ABSTRACTMicrobes can produce molecular hydrogen (H2) via fermentation, dinitrogen fixation, or direct photolysis, yet the H2dynamics in cyanobacterial communities has only been explored in a few natural systems and mostly in the laboratory. In this study, we investigated the dielin situH2dynamics in a hot spring microbial mat, where various ecotypes of unicellular cyanobacteria (Synechococcussp.) are the only oxygenic phototrophs. In the evening, H2accumulated rapidly after the onset of darkness, reaching peak values of up to 30 μmol H2liter−1at about 1-mm depth below the mat surface, slowly decreasing to about 11 μmol H2liter−1just before sunrise. Another pulse of H2production, reaching a peak concentration of 46 μmol H2liter−1, was found in the early morning under dim light conditions too low to induce accumulation of O2in the mat. The light stimulation of H2accumulation indicated that nitrogenase activity was an important source of H2during the morning. This is in accordance with earlier findings of a distinct early morning peak in N2fixation and expression ofSynechococcusnitrogenase genes in mat samples from the same location. Fermentation might have contributed to the formation of H2during the night, where accumulation of other fermentation products lowered the pH in the mat to less than pH 6 compared to a spring source pH of 8.3.IMPORTANCEHydrogen is a key intermediate in anaerobic metabolism, and with the development of a sulfide-insensitive microsensor for H2, it is now possible to study the microdistribution of H2in stratified microbial communities such as the photosynthetic microbial mat investigated here. The ability to measure H2profiles within the mat compared to previous measurements of H2emission gives much more detailed information about the sources and sinks of H2in such communities, and it was demonstrated that the high rates of H2formation in the early morning when the mat was exposed to low light intensities might be explained by nitrogen fixation, where H2is formed as a by-product.

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41

Tsakalakis, Ioannis, Markus Pahlow, Andreas Oschlies, Bernd Blasius e Alexey B. Ryabov. "Diel light cycle as a key factor for modelling phytoplankton biogeography and diversity". Ecological Modelling 384 (settembre 2018): 241–48. http://dx.doi.org/10.1016/j.ecolmodel.2018.06.022.

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42

Kirchner, James W., Sarah E. Godsey, Madeline Solomon, Randall Osterhuber, Joseph R. McConnell e Daniele Penna. "The pulse of a montane ecosystem: coupling between daily cycles in solar flux, snowmelt, transpiration, groundwater, and streamflow at Sagehen Creek and Independence Creek, Sierra Nevada, USA". Hydrology and Earth System Sciences 24, n. 11 (5 novembre 2020): 5095–123. http://dx.doi.org/10.5194/hess-24-5095-2020.

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Abstract (sommario):

Abstract. Water levels in streams and aquifers often exhibit daily cycles during rainless periods, reflecting daytime extraction of shallow groundwater by evapotranspiration (ET) and, during snowmelt, daytime additions of meltwater. These cycles can aid in understanding the mechanisms that couple solar forcing of ET and snowmelt to changes in streamflow. Here we analyze 3 years of 30 min solar flux, sap flow, stream stage, and groundwater level measurements at Sagehen Creek and Independence Creek, two snow-dominated headwater catchments in California's Sierra Nevada mountains. Despite their sharply contrasting geological settings (most of the Independence basin is glacially scoured granodiorite, whereas Sagehen is underlain by hundreds of meters of volcanic and volcaniclastic deposits that host an extensive groundwater aquifer), both streams respond similarly to snowmelt and ET forcing. During snow-free summer periods, daily cycles in solar flux are tightly correlated with variations in sap flow, and with the rates of water level rise and fall in streams and riparian aquifers. During these periods, stream stages and riparian groundwater levels decline during the day and rebound at night. These cycles are reversed during snowmelt, with stream stages and riparian groundwater levels rising during the day in response to snowmelt inputs and falling at night as the riparian aquifer drains. Streamflow and groundwater maxima and minima (during snowmelt- and ET-dominated periods, respectively) lag the midday peak in solar flux by several hours. A simple conceptual model explains this lag: streamflows depend on riparian aquifer water levels, which integrate snowmelt inputs and ET losses over time, and thus will be phase-shifted relative to the peaks in snowmelt and evapotranspiration rates. Thus, although the lag between solar forcing and water level cycles is often interpreted as a travel-time lag, our analysis shows that it is mostly a dynamical phase lag, at least in small catchments. Furthermore, although daily cycles in streamflow have often been used to estimate ET fluxes, our simple conceptual model demonstrates that this is infeasible unless the response time of the riparian aquifer can be determined. As the snowmelt season progresses, snowmelt forcing of groundwater and streamflow weakens and evapotranspiration forcing strengthens. The relative dominance of snowmelt vs. ET can be quantified by the diel cycle index, which measures the correlation between the solar flux and the rate of rise or fall in streamflow or groundwater. When the snowpack melts out at an individual location, the local groundwater shifts abruptly from snowmelt-dominated cycles to ET-dominated cycles. Melt-out and the corresponding shift in the diel cycle index occur earlier at lower altitudes and on south-facing slopes, and streamflow integrates these transitions over the drainage network. Thus the diel cycle index in streamflow shifts gradually, beginning when the snowpack melts out near the gauging station and ending, months later, when the snowpack melts out at the top of the basin and the entire drainage network becomes dominated by ET cycles. During this long transition, snowmelt signals generated in the upper basin are gradually overprinted by ET signals generated lower down in the basin. The gradual springtime transition in the diel cycle index is mirrored in sequences of Landsat images showing the springtime retreat of the snowpack to higher elevations and the corresponding advance of photosynthetic activity across the basin. Trends in the catchment-averaged MODIS enhanced vegetation index (EVI2) also correlate closely with the late springtime shift from snowmelt to ET cycles and with the autumn shift back toward snowmelt cycles. Seasonal changes in streamflow cycles therefore reflect catchment-scale shifts in snowpack and vegetation activity that can be seen from Earth orbit. The data and analyses presented here illustrate how streams can act as mirrors of the landscape, integrating physical and ecohydrological signals across their contributing drainage networks.

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43

Thomaz, Sidinei M., Alex Enrich-Prast, José F. Gonçalves Jr., Anderson M. dos Santos e Francisco A. Esteves. "Metabolism and Gaseous Exchanges in Two Coastal Lagoons from Rio de Janeiro with Distinct Limnological Characteristics". Brazilian Archives of Biology and Technology 44, n. 4 (dicembre 2001): 433–38. http://dx.doi.org/10.1590/s1516-89132001000400015.

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Abstract (sommario):

The global metabolism and exchange of gases with the atmosphere were measured during a diel cycle in two tropical coastal lagoons, using the curves of carbon dioxide and dissolved oxygen. Heterotrophic metabolism (net CO2 production and net O2 consumption) was observed in a black water lagoon (Comprida), and autotrophic metabolism (net O2 production and net CO2 consumption) in a clear water lagoon (Imboassica). These differences were attributed to the limnological characteristics of both ecosystems, especially to dissolved organic carbon and the attenuation coefficient of light, which are much higher in the first environment. During the diel cycle analyzed there was a net release of carbon dioxide into the atmosphere in the first lagoon and a net uptake by the water in the second one. Thus, the importance of coastal lagoons for the global carbon budget deserves further study.

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44

Wyman, Michael. "Diel Rhythms in Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase and Glutamine Synthetase Gene Expression in a Natural Population of Marine Picoplanktonic Cyanobacteria (Synechococcusspp.)". Applied and Environmental Microbiology 65, n. 8 (1 agosto 1999): 3651–59. http://dx.doi.org/10.1128/aem.65.8.3651-3659.1999.

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Abstract (sommario):

ABSTRACT Diel periodicity in the expression of key genes involved in carbon and nitrogen assimilation in marine Synechococcus spp. was investigated in a natural population growing in the surface waters of a cyclonic eddy in the northeast Atlantic Ocean.Synechococcus sp. cell concentrations within the upper mixed layer showed a net increase of three- to fourfold during the course of the experiment (13 to 22 July 1991), the population undergoing approximately one synchronous division per day. Consistent with the observed temporal pattern of phycoerythrin (CpeBA) biosynthesis, comparatively little variation was found incpeBA mRNA abundance during either of the diel cycles investigated. In marked contrast, the relative abundance of transcripts originating from the genes encoding the large subunit of ribulose bisphosphate carboxylase/oxygenase (rbcL) and glutamine synthetase (glnA) showed considerable systematic temporal variation and oscillated during the course of each diel cycle in a reciprocal rhythm. Whereas activation of rbcL transcription was clearly not light dependent, expression of glnAappeared sensitive to endogenous changes in the physiological demands for nitrogen that arise as a natural consequence of temporal periodicity in photosynthetic carbon assimilation. The data presented support the hypothesis that a degree of temporal separation may exist between the most active periods of carbon and nitrogen assimilation in natural populations of marine Synecoccoccus spp.

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45

Tan, Maxine H., Sarah R. Smith, Kim K. Hixson, Justin Tan, James K. McCarthy, Adam B. Kustka e Andrew E. Allen. "The Importance of Protein Phosphorylation for Signaling and Metabolism in Response to Diel Light Cycling and Nutrient Availability in a Marine Diatom". Biology 9, n. 7 (6 luglio 2020): 155. http://dx.doi.org/10.3390/biology9070155.

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Abstract (sommario):

Diatoms are major contributors to global primary production and their populations in the modern oceans are affected by availability of iron, nitrogen, phosphate, silica, and other trace metals, vitamins, and infochemicals. However, little is known about the role of phosphorylation in diatoms and its role in regulation and signaling. We report a total of 2759 phosphorylation sites on 1502 proteins detected in Phaeodactylum tricornutum. Conditionally phosphorylated peptides were detected at low iron (n = 108), during the diel cycle (n = 149), and due to nitrogen availability (n = 137). Through a multi-omic comparison of transcript, protein, phosphorylation, and protein homology, we identify numerous proteins and key cellular processes that are likely under control of phospho-regulation. We show that phosphorylation regulates: (1) carbon retrenchment and reallocation during growth under low iron, (2) carbon flux towards lipid biosynthesis after the lights turn on, (3) coordination of transcription and translation over the diel cycle and (4) in response to nitrogen depletion. We also uncover phosphorylation sites for proteins that play major roles in diatom Fe sensing and utilization, including flavodoxin and phytotransferrin (ISIP2A), as well as identify phospho-regulated stress proteins and kinases. These findings provide much needed insight into the roles of protein phosphorylation in diel cycling and nutrient sensing in diatoms.

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46

Trotter, A. J., S. C. Battaglene e P. M. Pankhurst. "Buoyancy control and diel changes in swim-bladder volume in cultured striped trumpeter (Latris lineata) larvae". Marine and Freshwater Research 56, n. 4 (2005): 361. http://dx.doi.org/10.1071/mf04209.

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Abstract (sommario):

Body density, swim-bladder volume, buoyant force and feeding in relation to growth, photoperiod and light intensity were investigated in cultured striped trumpeter larvae. Prior to initial swim-bladder inflation, body density was negative during both the light and dark phases, regulated on a diel cycle from 1.0275 to 1.0290 g cm−3 (seawater: 1.0265 g cm−3). After initial swim-bladder inflation, body density decreased markedly during the dark phase as swim-bladder volume increased on a diel cycle. Downward buoyant force from dry matter increased with age and was compensated for by increasing relative swim-bladder volume. Greatest difference in body density between light (1.0260 g cm−3) and dark phase (1.0245 g cm−3) was when larvae were from 6.5 to 7.5 mm (standard length) (seawater: 1.0260 g cm−3). Density of larvae without a functional swim bladder was always greater than larvae with a functional swim bladder, and the former had reduced growth. Diel buoyancy control exhibited by striped trumpeter larvae with low amplitude changes in swim-bladder volume is similar to other transient physostomes. Mortality events previously observed in striped trumpeter culture are possibly related to negative buoyancy before first feeding and positive buoyancy during the dark phase following initial swim-bladder inflation.

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47

Perdomo, Juan Alejandro, Peter Buchner e Elizabete Carmo-Silva. "The relative abundance of wheat Rubisco activase isoforms is post-transcriptionally regulated". Photosynthesis Research 148, n. 1-2 (1 aprile 2021): 47–56. http://dx.doi.org/10.1007/s11120-021-00830-6.

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Abstract (sommario):

AbstractDiurnal rhythms and light availability affect transcription–translation feedback loops that regulate the synthesis of photosynthetic proteins. The CO2-fixing enzyme Rubisco is the most abundant protein in the leaves of major crop species and its activity depends on interaction with the molecular chaperone Rubisco activase (Rca). In Triticum aestivum L. (wheat), three Rca isoforms are present that differ in their regulatory properties. Here, we tested the hypothesis that the relative abundance of the redox-sensitive and redox-insensitive Rca isoforms could be differentially regulated throughout light–dark diel cycle in wheat. While TaRca1-β expression was consistently negligible throughout the day, transcript levels of both TaRca2-β and TaRca2-α were higher and increased at the start of the day, with peak levels occurring at the middle of the photoperiod. Abundance of TaRca-β protein was maximal 1.5 h after the peak in TaRca2-β expression, but the abundance of TaRca-α remained constant during the entire photoperiod. The redox-sensitive TaRca-α isoform was less abundant, representing 85% of the redox-insensitive TaRca-β at the transcript level and 12.5% at the protein level. Expression of Rubisco large and small subunit genes did not show a consistent pattern throughout the diel cycle, but the abundance of Rubisco decreased by up to 20% during the dark period in fully expanded wheat leaves. These results, combined with a lack of correlation between transcript and protein abundance for both Rca isoforms and Rubisco throughout the entire diel cycle, suggest that the abundance of these photosynthetic enzymes is post-transcriptionally regulated.

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48

Harmange, Clément, Vincent Bretagnolle, Nathan Chabaud, Mathieu Sarasa e Olivier Pays. "Diel cycle in a farmland bird is shaped by contrasting predation and human pressures". Biological Journal of the Linnean Society 134, n. 1 (17 giugno 2021): 68–84. http://dx.doi.org/10.1093/biolinnean/blab060.

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Abstract (sommario):

Abstract In human-dominated landscapes, human disturbances may contrast (spatially and/or temporally) with risk imposed by non-human predators. However, how prey adjust behaviour to minimize risk from multiple threats remains unclear. In Central-Western France, we investigated patterns of activity, space and habitat use, and causes of variations during the diel cycle of the grey partridge (captive-reared, released), a farmland bird facing multiple risks (nocturnal predation, diurnal hunting pressure). We also investigated influence of individual space use, relative to risk-related features on the fate of birds. Birds adjusted their behaviours in ways consistent with the reduction of risk from nocturnal carnivores at night and hunters during daytime. We recorded bimodal crepuscular activity, likely explained by commuting movements between spatially-separated diurnal and nocturnal sites composed of different habitats: selection of open terrains and avoidance of predator reservoirs at night vs. use of high-vegetation cover during daytime. We observed space use differences between surviving, hunted and predated birds. Predation and hunting activities act as contrasting pressures, selecting birds based on their spatial behaviour, which has likely shaped diel adjustments at the population level. An improved consideration of temporal variation in environmental pressures would help to reliably address factors constraining populations, so increasing wildlife management efficiency.

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49

Cartes, Joan E. "Day-night feeding by decapod crustaceans in a deep-water bottom community in the western Mediterranean". Journal of the Marine Biological Association of the United Kingdom 73, n. 4 (novembre 1993): 795–811. http://dx.doi.org/10.1017/s0025315400034731.

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Abstract (sommario):

Changes in the composition of the diet, foregut fullness, and the degree of digestion of ingested food were taken into account in determining diel feeding activity of the numerically dominant species of decapod crustaceans dwelling on the Catalan Sea Slope (western Mediterranean). Two 24-h periods were sampled at two different stations on the upper middle slope (between 400 and 710 m) using bottom trawls. Additional foregut fullness data for Aristeus antennatus and Acanthephyra eximia were recorded below 1000 m. The influence of the relatively shallow-living mesopelagic fauna (Pasiphaeidae, Sergestes arcticus, euphausiids, and fishes) over the 24-h cycle apparently had a large effect on the feeding activity rhythms in the deep-sea decapods studied. Species can be classified into two different groups according to their feeding patterns. Thus, species whose diet was based on pelagic prey (Plesionika edwardsi, Plesionika martia, and A. eximia) exhibited a feeding pattern conditioned to the availability of this type of prey. In contrast, in those species in which pelagic prey contributed only a small portion of the diet (A. antennatus, Plesionika acanthonotus, Polycheles typhlops, and Geryon longipes) no variations in the foregut fullness or in the percentage of undigested prey in foreguts during the diel feeding cycles were recorded. The decrease in the influence of the abundance of mesopelagic fauna with depth, with a commonly accepted boundary at around 1000 m would be responsible for the progressive flattening out of activity rhythms among the species dwelling on the lower slope. Foregut fullness values for certain species with broad depth distributions in the Catalan Sea (A. antennatus, A. eximia), would support this hypothesis.

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Hawley, Kate L., Carolyn M. Rosten, Thrond O. Haugen, Guttorm Christensen e Martyn C. Lucas. "Freezer on, lights off! Environmental effects on activity rhythms of fish in the Arctic". Biology Letters 13, n. 12 (dicembre 2017): 20170575. http://dx.doi.org/10.1098/rsbl.2017.0575.

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Abstract (sommario):

Polar regions are characterized by acute seasonal changes in the environment, with organisms inhabiting these regions lacking diel photoperiodic information for parts of the year. We present, to our knowledge, the first high-resolution analysis of diel and seasonal activity of free-living fishes in polar waters (74°N), subject to extreme variation in photoperiod, temperature and food availability. Using biotelemetry, we tracked two sympatric ecomorphs of lake-dwelling Arctic charr ( Salvelinus alpinus n = 23) over an annual cycle. Charr activity rhythms reflected the above-surface photoperiod (including under ice), with diel rhythms of activity observed. During the dark winter solstice period, charr activity became arrhythmic and much reduced, even though estimated light levels were within those at which charr can feed. When twilight resumed, charr activity ensued as diel vertical migration, which continued throughout spring and with increasing day length, despite stable water temperatures. Diel activity rhythms ceased during the polar day, with a sharp increase in arrhythmic fish activity occurring at ice-break. Despite contrasting resource use, circannual rhythms were mirrored in the two ecomorphs, although individual variability in activity rhythms was evident. Our data support conclusions of functionally adaptive periods of arrhythmicity in polar animals, suggesting maintenance of a circannual oscillator for scheduling seasonal behavioural and developmental processes.

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