Natural ultraviolet-B Radiation Research Articles

Effects of natural solar UV-B radiation on three Arabidopsis accessions are strongly affected by seasonal weather conditions

Large numbers of studies have reported on the responses of plants that are exposed to a specific dose of ultraviolet-B (UV-B) radiation. However, in the natural environment UV-B is a highly dynamic variable with UV-B intensities depending on, amongst others, geographic, temporal, weather and climatic factors. Furthermore, UV-B effects on plants can potentially be modulated by other environmental variables, and vice versa. This study aimed to characterize UV-B effects on plant morphology and accumulation of UV-screening pigments within the context of an oceanic climate and to assess the potential seasonality of plant UV-B responses. Arabidopsis thaliana was grown outdoors under UV-blocking or transmitting filters. Genotypic differences in the adaptive response to UV-B were assessed at seven time-points over a 12 month period and involved the Arabidopsis accessions Ler, Col-0, and Bur-0. Strong seasonal effects were found on rosette morphology and total UV-screening pigment concentrations across the three accessions. Low temperatures were the main determinant of accumulation of UV-absorbing pigments, with no clear UV-B effect observed at any time throughout the year. There was a significant UV effect on morphology during the summer months, and this was most likely associated with stress. This study shows that UV-effects need to be analysed in the context of weather, and other co-occurring natural factors, and emphasizes the importance of a holistic, multifactorial approach for the investigation of environmentally relevant UV-effects.

Effects of UVB radiation on net community production in the upper global ocean

AbstractAimErosion of the stratospheric ozone layer together with oligotrophication of the subtropical ocean is leading to enhanced exposure to ultraviolet B (UVB) radiation in ocean surface waters. The impact of increased exposure to UVB on planktonic primary producers and heterotrophs is uncertain. Here we test the null hypothesis that net community production (NCP) of plankton communities in surface waters of the tropical and subtropical ocean is not affected by ambient UVB radiation and extend this test to the global ocean, including the polar oceans and the Mediterranean Sea using previous results.LocationWe conducted experiments with 131 surface communities sampled during a circumnavigation cruise along the tropical and subtropical ocean and combined these results with 89 previous reports encompassing the Atlantic, Pacific, Arctic and Southern Oceans and the Mediterranean Sea.MethodsThe use of quartz (transparent to UVB radiation) and borosilicate glass materials (opaque to most UVB) for incubations allowed us to compare NCP between communities where UVB is excluded and those receiving natural UVB radiation.ResultsWe found that NCP varies when exposed to natural UVB radiation compared to those where UVB was removed. NCP of autotrophic communities tended to decrease under natural UVB radiation, whereas the NCP of heterotrophic communities tended to increase. However, these variations showed the opposite trend under higher levels of UVB radiation.Main conclusionsOur results suggest that earlier estimates of NCP for surface communities, which were hitherto derived using materials blocking UVB radiation were biased, with the direction and magnitude of this bias depending on the metabolic status of the communities and the underwater penetration of UVB radiation.

Effects of Elevated Ultraviolet‐B Radiation on Productive Tillers, Spikelet Sterility and Grain Characteristics of Southern US Rice (Oryza sativa L.) Cultivars

AbstractDepletion of the stratospheric ozone layer is leading to an increase in ultraviolet‐B (UVB) radiation (280–320 nm) reaching the Earth’s surface, which can alter crop productivity. The objective of this study was to determine the effects of elevated UVB radiation on rice production with special emphasis on grain characteristics in southern US rice cultivars (six inbred cultivars and three hybrids). Due to the spectral characteristics of the greenhouse glass, plants received no natural UVB radiation; hence, plants were provided with supplemental UVB lighting. Plants were exposed to UVB radiation of 0, 8 (ambient) or 16 (twice ambient) kJ m−2 day−1. There was no significant effect of elevated UVB radiation on the number of productive tillers in any cultivar except ‘Sierra’. All the cultivars except ‘Sierra’ showed increased spikelet sterility with an increase in UVB radiation. There were decreases in main‐stem panicle length, number of primary branches per panicle, and grain width with an increase in UVB radiation in most of the inbred cultivars. Elevated UVB radiation decreased plant grain yield in all the cultivars, however the per cent decrease in plant grain yield varied among the cultivars (31–79 %). The hybrid ‘Clearfield XL729’ performed best among the selected southern US rice cultivars under an elevated UVB environment.

An automatically operated system for simulating global change temperature and ultraviolet B radiation increases: application to the study of aquatic ecosystem responses in mesocosm experiments

We report on a new, automatically operated system that can provide accurate simulations of the increases in ultraviolet‐B radiation (UVBR: 280‐320 nm) and temperature predicted by climate change scenarios. The system was employed in mesocosms using a factorial design. The originality of this system is that the increases in UVBR and water temperature are proportional to the prevailing ambient levels. In this system, a 20% increase above natural UVBR generated by UV lamps, and a 3°C increase in water temperature generated by submersible heating elements, are both regulated within very short time scales (0.5 s for UVBR and 30 s for water temperature). Thus, the system follows the natural fluctuations that the control mesocosms experience, and so reproduces the high degree of environmental variability that is inherent to aquatic systems. In 2006, eight mesocosms were set up and moored at the Mediterranean platform for Marine Ecosystem Experimental Research (South of France), and 4 treatments were applied in duplicate over a period of 13 d: (i) Control; (ii) a 20% increase in UVBR above ambient UVBR incident at the water surface of the control mesocosms, (iii) a 3°C increase in water temperature above that of control mesocosms, and (iv) a combination of the increased UVBR and temperature. The system proved highly reliable, and therefore represents an adaptable, robust, and accurate tool that can realistically mimic scenarios for temperature and UVBR increases linked to global change to study the effects on aquatic organisms.

Response of Rice (Oryza sativa L.) Tillering to Sub‐ambient Levels of Ultraviolet‐B Radiation

AbstractThe negative impact of enhanced ultraviolet‐B (UV‐B) radiation has been demonstrated for rice, but few studies have examined the effects of low UV‐B radiation on rice growth and physiology. The objective of this study was to determine the effects of low UV‐B radiation on rice physiology with special emphasis on tiller initiation and development in two popular US rice cultivars, ‘Cocodrie’ and ‘Clearfield 161 (CL161)’. Plants received no natural UV‐B radiation because of the UV‐absorption characteristics of the greenhouse glass, hence UV‐B was artificially supplied by supplemental UV‐B lighting. Plants were grown in soil collected from research plots, and were exposed to UV‐B radiation of 0, 4 (sub‐ambient) or 8 kJ m−2 day−1 (ambient) for 29 days in one experiment and 87 days in a second experiment. ‘Cocodrie’ had no differential response among 0, 4 and 8 kJ m−2 day−1 UV‐B treatments for all the parameters measured except for plant height, which showed 5% decrease at ambient UV‐B conditions. For ‘CL161’ sub‐ambient UV‐B radiation exposure decreased vegetative tiller production (25%) and total panicle dry weight (15%). The decrease in tiller production was not due to a decrease in carbohydrate content or increase in auxin content under the low UV‐B radiation.

Ultraviolet‐B Radiation Effects on the Structure and Function of Lower Trophic Levels of the Marine Planktonic Food Web

The impact of UV-B radiation (UVBR; 280-320 nm) on lower levels of a natural plankton assemblage (bacteria, phytoplankton and microzooplankton) from the St. Lawrence Estuary was studied during 9 days using several immersed outdoor mesocosms. Two exposure treatments were used in triplicate mesocosms: natural UVBR (N treatment, considered as the control treatment) and lamp-enhanced UVBR (H treatment, simulating 60% depletion of the ozone layer). A phytoplankton bloom developed after day 3, but no significant differences were found between treatments during the entire experiment for phytoplankton biomass (chlorophyll a and cell carbon) nor for phytoplankton cell abundances from flow cytometry and optical microscopy of three phytoplankton size classes (picoplankton, nanoplankton and microplankton). In contrast, bacterial abundances showed significantly higher values in the H treatment, attributed to a decrease in predation pressure due to a dramatic reduction in ciliate biomass (approximately 70-80%) in the H treatment relative to the N treatment. The most abundant ciliate species were Strombidinium sp., Prorodon ovum and Tintinnopsis sp.; all showed significantly lower abundances under the H treatment. P. ovum was the less-affected species (50% reduction in the H treatment compared with that of the N control), contrasting with approximately 90% for the other ones. Total specific phytoplanktonic and bacterial production were not affected by enhanced UVBR. However, both the ratio of primary to bacterial biomass and production decreased markedly under the H treatment. In contrast, the ratio of phytoplankton to bacterial plus ciliate carbon biomass showed an opposite trend than the previous results, with higher values in the H treatment at the end of the experiment. These results are explained by the changes in the ciliate biomass and suggest that UVBR can alter the structure of the lower levels of the planktonic community by selectively affecting key species. On the other hand, linearity between particulate organic carbon (POC) and estimated planktonic carbon was lost during the postbloom period in both treatments. On the basis of previous studies, our results can be attributed to the aggregation of carbon released by cells to the water column in the form of transparent exopolymer particles (TEPs) under nutrient limiting conditions. Unexpectedly, POC during such a period was higher in the H treatment than in controls. We hypothesize a decrease in the ingestion of TEPs by ciliates, in coincidence with increased DOC release by phytoplankton cells under enhanced UVBR. The consequences of such results for the carbon cycle in the ocean are discussed.

Ultraviolet-B radiation effects on natural phytoplankton assemblages of central San Francisco Bay

Since the discovery of a depletion of the stratospheric ozone layer over Antarctica in 1979, scientific attention has been directed towards the effects of increased doses of ultraviolet radiation on phytoplankton in other ecosystems. Little is known about the effects of ultraviolet-B (280–320 nm) radiation (UVBR) on temperate estuarine phytoplankton. Freshly collected phytoplankton samples from Central San Francisco Bay were exposed to ambient UVBR in quartz bottles and monitored for biomass and nutrient uptake rates for comparison with phytoplankton dispensed into bottles made of polycarbonate that effectively filtered out the UVBR to evaluate response to natural UVBR exposure. Short-term (10–12 h) exposure experiments were carried out monthly from October 1998 to October 1999. No significant effect of UVBR on chlorophylla concentrations was found but a clear deleterious effect of UVBR on nutrient uptake was observed.

Non-synergistic effects of water-soluble crude oil and enhanced ultraviolet-B radiation on a natural plankton assemblage

The present study demonstrates the effects of the water-soluble fraction (WSF) of a crude oil, enhanced ultraviolet-B radiation (UVBR: 280 to 320 nm), and the combination of WSF and en- hanced UVBR on a natural plankton assemblage (<150 μm) isolated from the lower St. Lawrence Estu- ary. To study the separate and dual effects of WSF and UVBR, 12 microcosms (9 l) were immersed in the water column of larger mesocosms (polyethylene bags; 1800 l), providing 4 treatments, each in triplicate: (1) NUVBR + WSF (natural UVBR with WSF), (2) HUVBR + WSF (enhanced UVBR with WSF), (3) NUVBR (natural UVBR without WSF), and (4) HUVBR (enhanced UVBR without WSF). Dur- ing 5 d we monitored the incident radiation, WSF and nutrient concentrations, abundance and produc- tion of heterotrophic bacteria and phytoplankton. Strong deleterious effects of WSF and lower effects of UVBR were observed on the phytoplankton assemblage, with a decrease in growth rates accompa- nied by an increase in mean cell size which reflected a perturbation of the cell division cycle. Using the NUVBR treatement as reference conditions, the above effects resulted in a reduction of 84, 79 and 60% of total abundance of the phytoplankton fraction <20 μm in the HUVBR + WSF, NUVBR + WSF and HUVBR treatments, respectively. Significant higher values of bacterial abundances were ob- served in the WSF-added treatments compared to NUVBR without WSF. However, bacterial thymi- dine incorporation exhibited diel variations, suggesting cumulative UVBR-induced DNA and/or PAH- induced DNA damages, and possible repair mechanisms with the co-occurrence of more available growth substrates from stressed phytoplankton. The absence of significant differences between both WSF-added treatments under the 2 different UVBR conditions suggests that there is no additive inter- action between WSF and UVBR. This study provides therefore the first evidence of a non-synergistic interaction between both stresses, and suggests that UVBR-induced effects on marine microorganisms can be completely masked by the strong deleterious effects of soluble petroleum hydrocarbons.

Effects of ultraviolet‐B radiation and vertical mixing on nitrogen uptake by a natural planktonic community shifting from nitrate to silicic acid deficiency

We investigated the combined effects of mixing regimes and ultraviolet‐B radiation (UVBR: 280–320 nm) on the uptake of nitrate, ammonium, and urea by an estuarine phytoplankton community during a 10‐d mesocosm experiment in July 1997. The experiment was conducted in eight mesocosms (1,500 liters each) subjected to varying conditions of UVBR and mixing: (1) natural UVBR and fast mixing, (2) enhanced UVBR and fast mixing, (3) natural UVBR and slow mixing, and (4) enhanced UVBR and slow mixing. The study was carried out during a typical midsummer period of low nutrient concentrations. Throughout the experiment, the phytoplankton community was dominated by a mixed community composed mainly of centric diatoms, cyanobacteria, and prymnesiophytes, with larger algal cells (&gt;5 µm) representing &gt;70% of the total chlorophyll a biomass. The phytoplankton nutrient status changed over the experiment. Algal cells were nitrate‐deficient until the occurrence of a nitrification event on day 7, and then became silicic acid‐deficient. Mesocosms with different mixing rates showed significant differences in ambient nutrient concentrations, nitrogen uptake rates, and phytoplankton species composition. In general, no significant difference was detected between the N transport rates from samples incubated close to the surface and close to the bottom of the mesocosms, and no difference was detected between the UVBR treatments on all the other studied biological and chemical variables measured during the experiment. It is only under the slow mixing regime that the enhanced UVBR treatments significantly depress both the transport and the chlorophyll a—specific transport rates of dissolved organic nitrogen (urea). The UVBR effects observed only in the slow mixing regime could be a consequence of an inherent difference in the uptake capacity of the different communities under the two mixing regimes. Both nutrient conditions and mixing regime influenced the natural phytoplankton physiology and composition toward a community more sensitive to UVBR enhancement under a slower mixing regime.

Photobiosynthetic Opportunity and Ability for UV-B Generated Vitamin D Synthesis in Free-Living House Geckos (Hemidactylus turcicus) and Texas Spiny Lizards (Sceloporus olivaceous)

The opportunity and ability to photobiosynthesize vitamin D3 by exposing skin to ultraviolet-B (UVB) irradiation from the sun was compared using the nocturnal/crepuscular Mediterranean House Gecko Hemidactylus turcicus and the diurnal Texas Spiny Lizard Sceloporus olivaceous. Texas spiny lizards had a greater opportunity for photobiosynthetic production of vitamin D3 than geckos. This was revealed by vitamin D3 photoproduct production in models (ampoules containing an alcohol solution of vitamin D3 precursor) placed at locations inhabited by free-living lizards at similar times of occupancy. Alternatively, geckos seemed able to maximize their limited photobiosynthetic opportunity with a higher rate of conversion of provitamin D3 to photoproducts. This was revealed by photoproduct conversion in patches of lizard skin exposed to ultraviolet lamps in the laboratory. Stomach-content analysis showed the spiny lizards to have dietary sources of vitamin D3, the geckos may or may not. This is the first documentation that mostly nocturnal geckos may rely on photobiosynthesis of vitamin D3 and that they might have a more sensitive mechanism than diurnal lizards to compensate for their limited exposure to natural UVB radiation. Future studies should investigate sexual, seasonal, age, and species differences in photobiosynthetic opportunity and ability.

Bacterivory of a natural heterotrophic protozoan community exposed to different intensities of ultraviolet-B radiation

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 20:59-74 (1999) - doi:10.3354/ame020059 Bacterivory of a natural heterotrophic protozoan community exposed to different intensities of ultraviolet-B radiation Khaled Chatila1, Serge Demers1,*, Behzad Mostajir1, Michel Gosselin1, Jean-Pierre Chanut1, Patrick Monfort2 1Groupe de Recherche en Environnement Côtier, Institut des Sciences de la Mer de Rimouski (ISMER), Université du Québec à Rimouski, 310 Allée des Ursulines, Rimouski (Québec) G5L 3A1, Canada 2Laboratoire d'Hydrobiologie Marine et Continentale, Unité mixte de Recherche 'Écosystèmes lagunaires', Université Montpellier II, CNRS (UMR 5556), Case 093, 34095 Montpellier Cedex 05, France *Corresponding author. E-mail: serge_demers@uqar.uquebec.ca ABSTRACT: The effects of ultraviolet-B radiation (UVBR) on the bacterivory of a natural marine protozoan community were examined as part of a 7 d experiment designed to study the effects of different UVBR intensities on the summer planktonic assemblage of the lower St. Lawrence Estuary, Québec, Canada. The experiment was conducted in large containers (mesocosms) subjected to 1 of the following UVBR regimes: excluded UVBR (WUVB), natural UVBR (NUVB), and natural UVBR enhanced with either 2 lamps (LUVB) or 3 lamps (HUVB). Incubations with fluorescently labeled bacteria were conducted daily as a tool to understand the interaction between the potential bacterivores (heterotrophic ciliates and nanoflagellates) and bacteria within the studied system. UVBR intensities had no significant effects on the estimated clearance and ingestion rates (CR and IR, respectively) until Day 5 of the experiment. During the following 2 d, characterized by low nutrient concentration, both CR and IR decreased with the increase of the daily UVBR (at 305 and 320 nm) doses received. The maximum difference between treatments was observed on Day 7, where both clearance and ingestion rate values in the NUVB, LUVB and HUVB treatments were significantly lower than the WUVB treatment. Our data suggest that over a 1 d period and under conditions of high nutrient concentrations, protozoan bacterivory is not affected by UVBR increases. When nutrient concentrations become low, bacterivores become more susceptible to damaging UVBR effects. We think that the deterioration of food quality, itself resulting from the synergistic action of nutrients and UVBR stresses, is responsible for the increased sensitivity of bacterivores to UVBR. UVBR-induced decreases in bacterivory would represent a considerable loss to the higher tropic levels that feed upon bacterivores. KEY WORDS: Ultraviolet-B · Protozoa · Bacterivory · Bacterioplankton · Clearance rate · Ingestion rate · St. Lawrence Estuary Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 20, No. 1. Publication date: November 30, 1999 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1999 Inter-Research.

Does ambient UV-B radiation influence marine diatom-dominated microbial mats? A case study

Intact natural microbial mats collected from a shallow microtidal bay were incubated in the presence or absence of ambient ultraviolet-B radiation (UVBR) in an outdoor flow-through system for 2 and 6 wk, respectively. The microbial mats were cohesive and dominated by a large, motile diatom species, Gyrosigma balticum (Ehrenberg) Rabenhorst. The variables studied included biomass, composition of microalgae and meiofauna, bacterial biomass, pigment composition and presence of UV-absorbing compounds. Carbon assimilation and sediment oxygen microprofiles were measured as indicators of photosynthetic and respiratory activity. No significant effects were found on any of the measured variables when natural UVBR was excluded, suggesting that ambient UVBR did not exert any strong selective pressure on the particular type of microbial mat studied Biochemical screening by UV-absorbing compounds did not appear to be of major importance for avoiding UVBR damage. Visual observations, and to some extent oxygen profiles, indicated downward migration of the dominant diatom species as a response to high light levels. This may have been an important strategy also to avoid exposure to UVBR. Thus, vertical migration of benthic diatoms appears to be a factor that should be further investigated in relation to effects of both present and enhanced levels of UVBR.

Ultraviolet-B radiation and bacterial metabolism in coastal waters

The impact of ultraviolet-B (UV-B) radiation on bacterial density and production and on extracellular enzymatic activity was investigated the northern Adriatic Sea. Samples were incubated in quartz bottles and exposed to natural solar radiation (0.5 W m -2 ) as well as to artificial UV-B (0.4 W m -2 ) sources. Exposure to artificial UV-B sources over a period of 12 h revealed a constant decline in bacterial density to about 60% of the corresponding dark value. Total lipase and leucine-aminopeptidase activity showed a decrease to 38.8 and 21.9%, respectively, of the dark control; dissolved leucine-aminopeptidase activity was significantly more affected (15.3 % of the corresponding dark value) than dissolved lipase activity (43.2 % of the corresponding dark value). Samples exposed for 6 h to artificial UV-B or for 4 h to natural solar radiation exhibited rapid recovery during subsequent dark incubation. Following UV-B exposure (0.4 W m -2 ) bacterial density recovered rapidly from 74.6 % to 84.1%, lipase activity recovered from 64 % to 80 % and leucine-aminopeptidase activity from 53 % to 71% of the corresponding dark values during 6 h of subsequent dark incubation. Recovery of bacteria following exposure to natural solar UV-B radiation with similar intensity was even higher. In these experiments bacterial density reached similar values as in the dark control, bacterial production even exceeded the dark control production rates after 6 h of dark incubation following UV-B exposure. This difference might be attributed to photorepair induced by UV-A and to increased availability of dissolved organic matter due to UV-B mediated photolysis. UV-B radiation levels of 0.4 W m -2 as used in this study are detectable in the surface layers of the northern Adriatic Sea up to 0.5 m depth for at least 3 to 5 h d -1 during summer. Thus our results suggest that microbial life might be affected by UV-B radiation and consequently also the carbon and energy flow in aquatic systems.

VARIATION IN UV‐B SENSITIVITY IN PLANTS FROM A 3,000‐m ELEVATIONAL GRADIENT IN HAWAII

Interest in the potential consequences of stratospheric ozone depletion has led to numerous studies that have evaluated the effects of ultraviolet‐B (UV‐B) radiation on plant growth and productivity. However, few studies have been conducted on plants from natural ecosystems. Differences in solar UV‐B radiation along latitudinal or elevational gradients may have resulted in plants from diverse habitats developing contrasting sensitivities to UV‐B radiation. In this study, seeds were collected along a 3,000‐m elevational gradient in Hawaii and then germinated and grown in an unshaded greenhouse with either no UV‐B radiation or one of two daily UV‐B irradiances, 15.5 or 23.1 kj m2. Seedlings were grown for 12 weeks and harvested to determine whether UV‐B radiation altered plant biomass. The responses to UV‐B radiation varied among species, but, in general, sensitivity to UV‐B radiation was reduced as the elevation of seed collection increased. Of the 33 species tested, UV‐B radiation significantly reduced plant height in 14 species and biomass in eight species. Biomass increased in four species grown under UV‐B radiation. This study provides clear evidence that natural plant populations exhibit wide variation in UV‐B radiation sensitivity and that this variation is related to the natural (ambient) UV‐B radiation environment in which these plants grow.

Variation in UV-B Sensitivity in Plants from a 3,000-m Elevational Gradient in Hawaii

Interest in the potential consequences of stratospheric ozone depletion has led to numerous studies that have evaluated the effects of ultraviolet-B (UV-B) radiation on plant growth and productivity. However, few studies have been conducted on plants from natural ecosystems. Differences in solar UV-B radiation along latitudinal or elevational gradients may have resulted in plants from diverse habitats developing contrasting sensitivities to UV-B radiation. In this study, seeds were collected along a 3,000-m elevational gradient in Hawaii and then germinated and grown in an unshaded greenhouse with either no UV-B radiation or one of two daily UV-B irradiances, 15.5 or 23.1 kj m2. Seedlings were grown for 12 weeks and harvested to determine whether UV-B radiation altered plant biomass. The responses to UV-B radiation varied among species, but, in general, sensitivity to UV-B radiation was reduced as the elevation of seed collection increased. Of the 33 species tested, UV-B radiation significantly reduced plant height in 14 species and biomass in eight species. Biomass increased in four species grown under UV-B radiation. This study provides clear evidence that natural plant populations exhibit wide variation in UV-B radiation sensitivity and that this variation is related to the natural (ambient) UV-B radiation environment in which these plants grow.

Protective mechanisms and acclimation to solar ultraviolet-B radiation in Oenothera stricta

Plant adaptations ameliorating or repairing the damaging effects of ultraviolet-B (UV-B) radiation on plant tissue were investigated. The degree of phenotype plasticity in UV protective mechanisms and acclimation in relation to the natural solar UV-B radiation flux and in an enhanced UV-B irradiance environment was also examined. Mechanisms by which plants avoid radiation, adaptations altering the path of radiation incident on the leaf, and repair processes were considered. Attenuation of UV-B by tissues, UV-B irradiation into the leaf, and the effects of UV-B on photosynthesis were investigated.