Influence of solar ultraviolet radiation on photosynthesis and motility of marine phytoplankton

Abstract: The effects of solar ultraviolet radiation (UV) on carbon uptake, oxygen evolution and motility of marine phytoplankton were investigated in coastal waters at Kristineberg Marine Research Station on the west coast of Sweden (58° 30'N, 11° 30'E). The mean irradiances at noon above the water surface during the investigation period were: photosynthetic active radiation (PAR, 400–700 nm) 1670 μmol m⁻² s⁻¹; ultraviolet-A radiation (UV-A, 320–400 nm) 35.9 W m⁻² and ultraviolet-B radiation (UV-B, 280–320 nm) 1.7 W m⁻². UV-B radiation was much more attenuated with depth in the water column than were PAR and UV-A radiation. UV-B radiation could not be detected at depths greater than 100–150 cm. Inhibition of carbon uptake by UV-A and UV-B in natural phytoplankton populations was greatest at 50 cm depth and the effects of UV-B were greater than those of UV-A. At depths greater than 50 cm there was almost no effect of ultraviolet radiation on carbon uptake. PAR, UV-A and UV-B decreased oxygen evolution by the dinoflagellate Prorocentrum minimum . Inhibition of oxygen evolution was greater after 4 h than 2 h but it was not possible to distinguish the negative effects of the different light regimes. The motility of P. minimum was not affected by PAR, UV-A and UV-B. The importance of exposure of phytoplankton to different light regimes before being exposed to natural solar radiation is discussed.     

Effects of UV-B radiation on the structural and physiological diversity of bacterioneuston and bacterioplankton

The effects of UV radiation (UVR) on estuarine bacterioneuston and bacterioplankton were assessed in microcosm experiments. Bacterial abundance and DNA synthesis were more affected in bacterioplankton. Protein synthesis was more inhibited in bacterioneuston. Community analysis indicated that UVR has the potential to select resistant bacteria (e.g., Gammaproteobacteria), particularly abundant in bacterioneuston.     

UVR-induced photosynthetic inhibition dominates over DNA damage in marine dinoflagellates exposed to fluctuating solar radiation regimes

The combined effect of solar radiation (UV-B (280-315 nm), UV-A (315-400 nm) and PAR (400-700 nm)) and vertical mixing (i.e., fluctuating radiation regimes) on the marine dinoflagellates Gymnodinium chlorophorum, Heterocapsa triquetra and Prorocentrum micans was investigated during the austral spring in Patagonia, Argentina. Photosynthesis, measured as radiocarbon incorporation, and accumulation of DNA damage, as cyclobutane pyrimidine dimers (CPDs), were investigated under simulated mixed and non-mixed water column conditions using 3 h incubations centered at local noon. Static samples had significant UVR-induced photoinhibition that was higher in H. triquetra as compared to the other two species. Increasing mixing speed significantly increased UVR-induced inhibition of carbon fixation in G. chlorophorum and H. triquetra. No significant UVR effect was observed in P. micans under any of the mixing regimes. Most of the loss in carbon fixation in G. chlorophorum was due to UV-B while in H. triquetra it was due to UV-A. Part of these responses may be associated to the presence of UV-absorbing compounds which were abundant in P. micans, and low in H. triquetra and in G. chlorophorum. However, other variables such as cell size and active repair might have also influenced our results. We did not detect CPD accumulation in any of the species, probably because of the low solar angle that resulted in very low levels of DNA effective UV-B dose. Our results indicate that exposure to solar UVR in the Patagonia area during spring time (even during ozone depletion events) has a clear impact on photosynthesis and much less or negligible on DNA in the three studied species.     

Impact of solar ultraviolet-B radiation (290-320 nm) upon marine microalgae

For years scientists and laymen alike have casually noted the impact of solar ultraviolet radiation upon the non-human component of the biosphere. It was not until recently, when human activities were thought to threaten the protective stratospheric ozone shield, that researchers undertook intensive studies into the biological stress caused by the previously neglected short-wavelength edge of the global solar spectrum. Stratospheric ozone functions effectively as an ultraviolet screen by filtering out solar radiation in the 220–320 nm waveband as it penetrates through the atmosphere, thus allowing only small amounts of the longer wavelengths of radiation in this waveband to leak through to the surface of the earth. Although this ultraviolet radiation (UV-B radiation, 290–320 nm) comprises only a small fraction (less than 1%) of the total solar spectrum, it can have a major impact on biological systems due to its actinic nature. Many organic molecules, most notably DNA and proteins, absorb UV-B radiation which can initiate photochemical reactions. It is life's ability, or lack thereof, to cope with enhanced levels of solar UV-B radiation that has generated the concern over the potential depletion of stratospheric ozone. The defense mechanisms that serve to protect both plants and animals from current levels of UV-B radiation are quite varied. Whether these mechanisms will suffice for marine microalgae under conditions of enhanced levels of UV-B radiation is the subject of this review.     

Resistance of 5,10-methenyltetrahydrofolate to ultraviolet radiation

Aeration of aqueous solutions of 5,10-methenyltetrahydrofolic acid (MTHF) during exposure to ultraviolet irradiation (=300–390 nm, 240 W/m², 30 min) slowed down photolysis in comparison with deaerated solutions. The rate of photolysis in the presence of oxygen depended on the ionic strength of the buffer composition. MTHF degradation did not exceed 6% of the starting amount of MTHF. Photolysis of MTHF included opening of the imidazoline ring, dehydrogenation of the tetrahydropterin heterocycle, and elimination of the p-aminobenzoylglutamate moiety. 6,7-Dimethyltetrahydropterin was used as a model compound to show that protonation of the reduced pterin heterocycle increased its resistance to oxidation, and UV irradiation did not accelerate this process. The stabilizing effect of protonation of the pterin portion and the presence of the positively charged imidazoline moiety are assumed to hamper MTHF oxidation and photolysis. It is assumed that these factors favored the choice of MTHF molecules as photosensors in radiation-sensitive proteins in the course of evolution.__________Translated from Prikladnaya Biokhimiya i Mikrobiologiya, Vol. 41, No. 3, 2005, pp. 315–323.Original Russian Text Copyright © 2005 by Telegina, Lyudnikova, Zemskova, Sviridov, Kritsky.     

Photosynthetic acclimation to solar UV radiation of marine red algae from the warm-temperate coast of southern Spain: A review

A review is presented of the physiological mechanisms developed bybenthic macroalgae to cope with deleterious wavelengths, particularly UVradiation. Photoinhibition of photosynthesis, is a photoprotectivemechanism in various species studied in southern Spain. Incubations inoutdoor systems and transplantation experiments under natural radiationallowed to led to understanding of some the photoprotective strategies usedby red algae. Under conditions of enhanced UV-B radiation, algae inshallow sites show marked photoinhibition and rapid recovery ofphotosynthesis (dynamic photoinhibition), whereas algae from deeperlocations can suffer photodamage (chronic photoinhibition). Theexpression of this photoprotective strategy by intertidal species representsan efficient physiological adaptation to tolerate deleterious irradiance, whenlow tides coincide with the onset of solar radiation. Subtidal species canbe also exposed to high doses of UV radiation. This is particularly evidentin clear, Mediterranean waters, where light (including UV-B) can reach to10 m depth. The implications of photoacclimation processes formacroalgal ecology in warm-temperate littorals and the possibleconsequences for outdoor cultivation are outlined in terms of environmentalUV variability.     

Resistance to UVB radiation in Antarctic yeasts

Yeast cells were used as a model system to study the inter-relationship among free radicals, antioxidants and UV-induced cell damage. In particular, the effects of UV-radiation in newly isolated yeasts from the Antarctic have been studied.     

Estimation of solar radiation environment

This paper derives a model,from a review of published literature and U.S. Army technical reports, for calculating the total heat imposed per unit surface area by direct sunlight. Factors considered include solar zenith angle, water vapor and dust content of the air and terrestrial elevation. Unlike the usual meteorological measurement of total hemispheric radiation, calculated values are obtained for direct solar intensity and also diffuse sky radiation, thus allowing separation of the solar radiation impinging on horizontal surfaces from that on vertical or perpendicular surfaces. Representative calculated values for 9 major climatic regions of the world agree with the limited comparable measured values available.

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Zusammenfassung Diese Arbeit beschreibt mittels eines Rückblicks auf die veröffentlichte Literatur und die Technischen Berichte der U.S. Army ein Modell für die Berechnung der totalen Wärmemenge, die einer Oberflächeneinheit durch die direkte Sonnenstrahlung zugeführt wird. Die betrachteten Faktoren schliessen den Einfallswinkel, den Wasserdampf, den Staubgehalt der Luft sowie die Höhenlage ein.Im Gegensatz zur üblichen meteorologischen Messung der totalen hemisphärischen Strahlung erhält man so berechnete Werte für die direkte Strahlungsintensität und auch für die diffuse Himmelstrahlung, so dass damit die Strahlung auf horizontale Flächen von der auf vertikale oder geneigte Flächen getrennt werden kann. Repräsentative berechnete Werte für 6 Hauptklimagebiete der Erde stimmen mit den wenigen vergleichbaren Werten überein, die verfügbar sind.

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Resume Dans le présent mémoire, on décrit un modèle permettant de calculer la quantité totale de chaleur reçue par une surface unité par suite du rayonnement solaire direct. Pour ce faire, on a passé en revue les travaux publiés en la matiére et les rapports techniques de l'armée des Etats-Unis. Les éléments considérés sont:l'angle d'incidence, la vapeur d'eau, la teneur en poussières de l'atmosphère et l'altitude. Au contraire des mesures météologiques usuelles indiquant le rayonnement total reçu par un hémisphère on obtient ici des valeurs calculées pour l'intensité du rayonnement direct ainsi que pour le rayonnement diffus. On peut ainsi distinguer le rayonnement tombant sur une surface horizontale de celui atteignant une surface verticale ou ayant une inclinaison quelconque. Des valeurs représentatives calculées pour 6 zones climatiques de la terre correspondent bien aux quelques valeurs comparatives dont on dispose.

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Dr.Roller was a Senior Postdoctoral Visiting Research Associate of the National Academy of Sciences-National Research Council on leave of absence from the Department of Agricultural Engineering, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, Ohio.     

Predicted inactivation of viruses of relevance to biodefense by solar radiation

UV radiation from the sun is the primary germicide in the environment. The goal of this study was to estimate inactivation of viruses by solar exposure. We reviewed published reports on 254-nm UV inactivation and tabulated the sensitivities of a wide variety of viruses, including those with double-stranded DNA, single-stranded DNA, double-stranded RNA, or single-stranded RNA genomes. We calculated D(37) values (fluence producing on average one lethal hit per virion and reducing viable virus to 37%) from all available data. We defined "size-normalized sensitivity" (SnS) by multiplying UV(254) sensitivities (D(37) values) by the genome size, and SnS values were relatively constant for viruses with similar genetic composition. In addition, SnS values were similar for complete virions and their defective particles, even when the corresponding D(37) values were significantly different. We used SnS to estimate the UV(254) sensitivities of viruses for which the genome composition and size were known but no UV inactivation data were available, including smallpox virus, Ebola, Marburg, Crimean-Congo, Junin, and other hemorrhagic viruses, and Venezuelan equine encephalitis and other encephalitis viruses. We compiled available data on virus inactivation as a function of wavelength and calculated a composite action spectrum that allowed extrapolation from the 254-nm data to solar UV. We combined our estimates of virus sensitivity with solar measurements at different geographical locations to predict virus inactivation. Our predictions agreed with the available experimental data. This work should be a useful step to understanding and eventually predicting the survival of viruses after their release in the environment.     

Taxonomic composition of Lake Baikal bacterioneuston communities

The taxonomic composition of microbial communities of Lake Baikal surface microlayer was studied by pyrosequencing of the 16S rDNA amplicons. Statistically reliable differences were found between bacterioneuston of the shallow and deep-water stations. The shallow station community was characterized by higher diversity than the deep-water one. While bacterioneuston communities were shown to be less diverse than the water column communities, their diversity was comparable to that of other biofilm associations. Microbial communities of Lake Baikal surface microlayer were shown to be similar to those of the water column in the composition of predominant phyla, while differing considerably at the genus level. Bacterioneuston of Lake Baikal was comparable to microbial communities of the surface microlayer of other freshwater basins, although it was characterized by high abundance of the Alphaproteobacteria and Verrucomicrobia. High abundance of photoheterotrophs compared to the water column communities of other freshwater basins was another distinctive feature of Lake Baikal bacterioneuston. Our results showed the Lake Baikal surface microlayer to be a specific microbial community with low species diversity and relatively high abundance of photoheterotrophic microorganisms.     

Energy advantages of orientation to solar radiation in three African ruminants

Animal orientation relative to incident solar radiation allows an animal to effectively adjust the amount of radiant heat gained from an environment. Yet recent literature found ruminants to primarily orientate north/south and proposed magnetic alignment as the most parsimonious explanation. To test whether such northerly orientation has an energy advantage, we used heated cylindrical models to estimate energy costs of thermoregulation associated with north and east orientations of three species of African ruminants under cool winter conditions. Concurrent behavioural observations revealed that eland, blue wildebeest and impala did not preferentially orientate north/south during warm summer or cool winter conditions. Instead, all three species preferred to orientate perpendicular to incident solar radiation during winter and parallel to incident solar radiation during summer, throughout the day. On clear winter days with little wind, more than 60% of animal orientation preference could be accounted for by the energy savings associated with that orientation. Thus energy demands are likely to be the primary driver of animal orientation preferences.     

Comparative sensitivity of six scleractinian corals to temperature and solar radiation

Scleractinian corals were exposed to 6 combinations of temperature and solar radiation to evaluate effects on coral bleaching, survival, and tissue surface area changes during and after exposure. A recirculating coral exposure system was coupled to a solar simulator to allow laboratory testing of 6 species of Caribbean corals (Diploria clivosa, Montastraea faveolata, Porites divaricata, Stephanocoenia intersepta, Siderastrea radians, and Siderastrea siderea). Significant bleaching occurred in all of the corals exposed to high irradiance except S. siderea. Elevated light levels resulted in a decrease in photochemical efficiency for all species during the exposure period, with S. siderea showing the smallest decrease. The most prominent reductions in photochemical efficiency occurred in M. faveolata and S. intersepta, and these species exhibited extensive tissue loss and the highest mortality. In contrast to high irradiance, high temperatures significantly decreased photochemical efficiency for only D. clivosa and did not lead to severe tissue loss for this species. These results demonstrate species-specific responses to solar radiation and temperatures, with M. faveolata and S. intersepta being the most susceptible to bleaching due to high irradiance.     

Potential solar radiation on plant shapes

The thesis is presented that most plant-shapes, especially trees, resemble a combination of geometrical shapes which present their non-opaque bodies to incoming radiation, which is partially absorbed by the foliage. Such a hypothesis makes possible the quantification of the budget of energy of the entire plant. This first report presents only the findings in regard to the receipt of direct and diffuse solar radiation from the sky (clear conditions), before reflection and absorption, on a variety of geometries which simulate common plant-shapes. An all-year simulation of potential insolation for such shapes was conducted for latitudes 0° to 90°. Each shape, latitude and each season exhibited its own characteristic patterns of the various energy cycles. Derived data differed materially from data applicable to horizontal surfaces. The simulated plant-shapes tended to avoid receipt of energy in the low latitudes, whereas the opposite occurred toward higher latitudes.

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Zusammenfassung Die meisten Pflanzenumrisse, speziell Bäume, ähneln einer Kombination geometrischer Formen. Die Bäume sind nicht-undurchsichtige Körper für einkommende Strahlung, die durch die Blätter teilweise absorbiert wird. Nach der Hypothese ist es möglich, den Energiehaushalt für die gesamte Pflanze zu quantifizieren. Dieser erste Bericht befasst sich nur mit den Ergebnissen der direkten und diffusen Sonnenstrahlung vom Himmel bei klaren Bedingungen vor Reflexion und Absorption bei einer Anzahl simulierter geometrischer Formen, die auf allgemeinen Pflanzenumrissen basieren. Eine ganzjährige Simulation der potentiellen Besonnung dieser Formen wurde für alle Breiten von 0° bis 90° berechnet. Jede Form, Breite und Jahreszeit zeigt ihre eigenen charakteristischen Verläufe der verschiedenen Energiezyklen. Die abgeleiteten Werte unterscheiden sich von den Werten, die auf horizontale Oberflächen anwendbar sind. Die simulierten Pflanzenkörper neigten zur Vermeidung von Energieaufnahme in niedrigen Breiten, während bei höheren Breiten das Umgekehrte auftrat.

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Resume Les formes extérieures des plantes et plus spécialement celles des arbres peuvent se ramener à des combinaisons de formes géométriques. Les arbres ne constituent pas des corps opaques pour le rayonnement, mais celuici n'est que partiellement absorbé par la couronne. Selon l'hypothèse présentée ici, il est possible de déterminer quantitativement le bilan énergétique de la plante entière. Ce premier mémoire se restreint à l'étude de l'absorption du rayonnement direct et diffus, c'est-à-dire du soleil et d'un ciel serein. Ces résultats sont calculés avant toute réflexion ou absorption par d'autres corps et se rapportent à un certain nombre de formes géométriques simulant des profils typiques d'arbres. On a ainsi calculé le gain énergétique de ces formes pour toute l'année et pour toutes les latitudes de 0° à 90°. Chaque profil, chaque latitude et chaque saison présente des caractéristiques propres quant à l'évolution des différents cycles d'énergie. Les valeurs ainsi obtenues se distinguent nettement de valeurs correspondantes se rapportant à des surfaces horizontales. Les profils de plantes examinés tendent à absorber aussi peu d'énergie que possible dans les basses latitudes, alors que c'est le contraire qui se produit au voisinage des pôles.

     

Seasonal responses of six Poaceae to differential levels of solar UV-B radiation

The effects of changes in solar UV-B on the growth and pigmentation of six grass species from cold-temperate grasslands (Lolium perenne, Lolium multiflorum, Festuca arundinacea, Festuca rubra, Phleum pratense and Dactylis glomerata) in spring and summer were studied. The grasses were grown in greenhouses with different foils, resulting in three treatments: no UV-B, 80% of ambient and 90% of ambient UV-B_BE.(biologically effective UV-B). The results indicated important effects of ambient UV-B levels on grass, but the different species reacted in very different ways. Both morphology and biomass production were influenced by UV-B in some species. However, changes in biomass production did not necessarily occur within the same species as changes in morphology. The grasses were more sensitive in summer. Overall, only F. rubra was positively influenced by UV-B under all circumstances. The biomass of D. glomerata and L. perenne was reduced by UV-B in spring and summer. Morphological changes included reduced height and increased tillering. The sensitivity of the different species was partially explained by their ability to reduce their specific leaf area in response to UV-B. Only the more sensitive species showed increased production of protective pigments. Overall, there were important differences between the effect of a low level of UV-B, and the further increase in UV-B, indicating that several mechanisms are operating at different light levels.