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Spatial and temporal changes in South African solar UV-B (280-315 nm) exposure were modeled and mapped at 2.5 km2resolution using ozone, relative humidity, cloud amount and elevation data. Computations indicated large natural gradients in UV-B exposure ranging from a 34.2% change over 14 deg. of latitude to a 44.2% change over 16 deg. of longitude. Modelling of future scenarios in annual UV-B exposure indicated small increases ranging from 2.5% in the year 2003 (best-case ozone depletion scenario) to 8.1 % in the year 2051 (worst-caseozone-depletion scenario). Notable were substantial increases in intra-annual variability in UV-B radiation with ozone depletion. Exposure exhibits a 12% increase during late autumn (May) in the year 2003 and a 35% increase during this season in the year 2051. Taxonomic, life form and functional attributes were analyzed in 2146 threatened (rare, endangered, vulnerable) species representing 468 genera and 103 families, and their distributions compared with modeled spatial and temporal UV-B distribution patterns. The high fractions of evergreen and succulent life forms and geophytes, present among threatened taxa, indicate a high degree of physiological resilience to increased solarUV-B stress, though some life forms, e.g. trees, appear relatively less resistant. Conceivable reductions in per capita reproductive output and overall plant fitness were indicated in some plant functional types, e.g. herbaceous annuals, which may lead to altered patterns ofspecies coexistence, floristic composition and diversity. [ABSTRACT FROM AUTHOR]

Adverse biological effects of ultraviolet-B (UV-B) radiation have been well documented for phytoplankton and zooplankton in both marine and freshwater ecosystems. However, investigations of interactions between UV-B and anthropogenic toxicants have focused primarily on the chemical interactions between UV-B and the toxicant. Here we investigate the potential for UV-B to increase the sensitivity of the rotifer Brachionus calyciflorus to either acute pentachlorophenol (PCP) or mercury toxicity, independent of UV-B effects on these toxicants. UV-B increased the toxicity of PCP and mercury to B. calyciflorus as much as five-fold, depending on duration of UV-B exposure and toxicant concentration. Reductions in the LC50 of up to 60% were also seen for both toxicants. UV-B alone effectively eliminated B. calyciflorus reproduction and reduced ingestion by up to 90%. These results demonstrate the potential for UV-B to increase rotifer sensitivity toanthropogenic stressors independent of photochemical reactions with toxicants. [ABSTRACT FROM AUTHOR]

Wheat plants (Triticum aestivum L.) were exposed to two levels of UV-B radiation (ambient UV-B and high UV-B, simulating a 20% reduction in the ozone layer) under mediterranean field-growth conditions. After 4 months of UV-B treatment, total plant biomass of high UV-B plantswas 18% lower compared to control plants. The decrease of biomass appears to be the result of changes in morphological and physiological processes. High UV-B treatment induces decreases in leaf area, net photosynthesis rate, transpiration rate and water use efficiency. Pigment analysis of leaf extracts showed increases in chlorophyll content and no effect on accumulation of UV-B absorbing pigments. The underlying mechanisms for these results are discussed. (c) 1999 Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]

The frog embryo teratogenesis assay-Xenopus (FETAX) was used to illustrate sublethal endpoints indicative of ultraviolet B (UV-B) radiation exposure in Xenopus laevis larvae. Xenopus laevis embryos were covered with plastic cutoff filters to manipulate UV dose, and irradiated under a light carriage consisting of two UV-B and three UVA bulbs. At the end of day 2, 20% of the tadpoles from all treatments were removed, and DNA was extracted. Frequency of pyrimidine dimers was estimated by quantifying single-strand breaks after incubating DNA with anendonuclease specific for cyclobutane pyrimidine dimers. Remaining tadpoles were sacrificed on day 5, and mortality, malformations, and growth data were recorded. Teratogenesis and growth inhibition were positively correlated with increasing UV-B dose in all tests. Photodamage to DNA in experiment 1 increased with higher UV-B doses. Teratogenesis positively correlated with the frequency of pyrimidine dimers. In experiment 2, significant variation with DNA photodamage in egg clutches was observed and no treatment effect was found. Usage of these sublethal endpoints in the field or laboratory would be helpful in discerning adaptational responses of developing amphibians to UV-B radiation, and interactive effects between UV and photosensitive chemicals. [ABSTRACT FROM AUTHOR]

Ozone in the atmosphere, mainly in the stratosphere, absorbs most of the ultraviolet-B (wavelength 280-315 nm) radiation from the sun, which can destroy DNA and other biologically important molecules and,thereby, damage living organisms. Due to the pollution of the atmosphere by humans, the ozone layer is presently being depleted, more rapidly at higher latitudes than at lower, and more rapidly over Scandinavia than over most geographical regions at corresponding latitudes. Ultraviolet-B radiation is generally more intense in mountain regions than at sea level. We have experiments in progress in which we simulate the effects of further ozone depletion on terrestrial ecosystems (mountain heaths, bogs, tundra) by irradiating them with artificial ultraviolet-B radiation. Effects on the growth of dwarf-shrubs and mosses and on plant lifter decomposition are described. [ABSTRACT FROM AUTHOR]

A high arctic polar semidesert and a subarctic dwarf-shrub heath were subjected to increases in the concentration of nutrients, elevated temperatures and greater summer precipitation over five growing seasons. The aim of the study was to determine the sensitivity and resilience of the two contrasting European arctic ecosystems to components of projected global environmental change. Both ecosystems were sensitive to environmental change, with nutrient eliciting the greatest responses, followed by temperature, and then water, which exerted little measurable influence. The direction, magnitude and timing of responses differed markedly between ecosystems and species responded individualistically. Some of the observed responses were similar to those from parallel studies in Alaskan wet tussock tundra and other European subarctic communities. but underlying mechanisms may not always be the same. Community level changes at the subarctic dwarf-shrub heath were mediated through the responses of a few key species which were already present in the community, whilst at the high Arctic polar semidesert, responses were determined by both existing and invading species. Responses of arctic plants and communities to nutrient enrichment and temperature are greater than those reported in response to elevated CO, or enhanced fluxes of UV-B radiation, although interactions between variables may be important in determining responses to current environmental change scenarios. [ABSTRACT FROM AUTHOR]

The current knowledge on conifer responses to enhanced ultraviolet-B(UV-B) radiation is mainly based on greenhouse or growth chamber experiments of one growing season in duration. However, the biomass losses observed in greenhouses do not occur in field-grown trees in theirnatural habitats. Moreover, the majority of the 20 conifer species studied have been 1-year-old seedlings, and no studies have been undertaken on mature trees. Fully grown needles, with their glaucous waxy surfaces and thick epidermal cells with both soluble and wall-bound UV-B screening metabolites, are well protected against UV-B radiation.However, it is not known whether these are sufficient protectants inyoung emerging needles or during the early spring period of high UV-B levels reflected from snow. In order to understand all the mechanisms that result in the protection of conifer needles against UV-B radiation, future research should focus on the epidermal layer, separating the waxes, cuticle and epidermal and hypodermal cells. Parallel studies should consist of wall-bound and soluble secondary metabolite analysis, antioxidant measurements and microscopic observations. [ABSTRACT FROM AUTHOR]

The impact on plant growth of the simultaneously changing factors ofthe global climate, rising tropospheric O3 concentrationsand increasing UV-B radiation fluxes, has been tested in a combined glasshouse and growth chamber experiment. The saltmarsh grass speciesElymus athericus was sequentially fumigated for two weeks with O3 and for another two weeks irradiated with UV-B (vv). Exposure to elevated UV-B did not negatively affect photosynthesis or plant growth. Fumigation with O3 had a depressing effect on net photosynthesis, the number and biomass of flowers, the number of leaves and the number of shoots. O3-induced damage only was observed in plants which had been fumigated during the last two weeks of the experiment. Since interactive responses were not observed, results suggest different primary target sites for O3 and UV-Bwithin the plant. [ABSTRACT FROM AUTHOR]

Like most other environmental and economic sectors, forestry worldwide looks set to encounter a growing number of surprises in the sense of major divergencies from established trends. These surprises will be largely environmental or economic or both at once. Unless we do a better job of identifying them ahead of time, these surprises will often be of a scale to overwhelm our anticipatory and preventive capacities. Indeed and as this paper demonstrates, the most likely as well as the most taxing forestry problems of the future will often be the ones we have scarcely thought of. Fortunately, the same applies to forestry opportunities. In these circumstances, there is a premium on not only supplying answers to recognized questions but on raising entirely new questions. [ABSTRACT FROM AUTHOR]

A mesocosm approach was adopted for the study of the impact of UV-B radiation on coastal planktonic communities. Experiments were conducted in eight land-based 1500 l mesocosms. The 2.25 m deep mesocosms reproduced the whole euphotic zone and vertical mixing ensured a homogeneous water column. While maintaining all other physical characteristics the same, UV-B levels were manipulated in different mesocosms by either increasing UV-B with lamps or by eliminating it using Mylar(R)sheet as a filter. The resulting spectral irradiance regime producedin the mesocosms was characterised by the daily irradiance averaged over the water column. Incident irradiance was measured every 10 minutes using an International Light IL-1700 radiometer and a Biospherical PUV-511 radiometer. Underwater spectral irradiance for the different treatments was determined using a Biospherical PUV-500 profiling radiometer. One of the present challenges of UV-B research is the extrapolation of results from laboratory and short-term field experiments to natural populations and ecosystems. The merits and limitations of using mesocosms are explored in this investigation with particular attention to the underwater spectral properties. [ABSTRACT FROM AUTHOR]

Risk assessment comprises four steps: hazard identification, dose-response assessment, exposure assessment, and risk characterization. Inthis study, the effects of increased ultraviolet B (UVB, 280--315 nm) radiation on immune functions and the immunological resistance to infectious diseases in rats were analyzed according to this strategy. In a parallelogram approach, nonthreshold mathematical methods were used to estimate the risk for the human population after increased exposure to UVB radiation. These data demonstrate, using a worst-case strategy (sensitive individuals, no adaptation), that exposure for approximately 90 min (local noon) at 40 deg.N in July might lead to 50% suppression of specific T-cell mediated responses to Listeria monocytogenes in humans who were not preexposed to UVB (i.e., not adapted). Additionally, a 5% decrease in the thickness of the ozone layer might shorten this exposure time by approximately 2.5%. These data demonstrate that UVB radiation, at doses relevant to outdoor exposure, may affect the specific cellular immune response to Listeria bacteria in humans. Whether this will also lead to a lowered resistance (i.e., increased pathogenic load) in humans is not known, although it was demonstrated that UVB-induccd immunosuppression in rats was sufficient to increase the pathogenic load. Epidemiology studies are needed to validate and improve estimates for the potential effects of increased UVB exposure on infectious diseases in humans. [ABSTRACT FROM AUTHOR]

Effects of ultraviolet radiation on microorganisms are of great interest in field of microbiology and planetary sciences. In the present study, we used Magnetospirillum magneticum AMB-1 as a model organism to examine the influence of ultraviolet-B (UV-B) radiation on cell growth and magnetite biomineralization of magnetotactic bacteria (MTB). Live AMB-1 cells were exposed to UV-B radiation for 60, 300 and 900 s, which correspond to radiation doses of 120 J/m(2), 600 J/m(2), and 1800 J/m(2), respectively. After irradiation, the amounts of cyclobutane pyrimidine dimers (CPD) and reactive oxygen species (ROS) of the cells were increased, and cell growth was stunted up to ~170 h, depending on the UV-B radiation doses. The UV-B irradiated cells also produced on average more magnetite crystals with larger grain sizes and longer chains, which results in changes of their magnetic properties.

Elevated carbon dioxide (CO2 ), temperature (T) and ultraviolet-B (UV-B) radiation may affect plant growth and secondary chemistry in different directions, but the effect of the combination of the three factors has seldom been tested. Here, we grew four dark-leaved willow (Salix myrsinifolia) clones under combinations of ambient or elevated CO2, T and UV-B radiation in top-closed chambers for 7 wk. Elevated UV-B had no effects on growth or phenolic compounds, and there were no significant interactions between UV-B, CO2 and T. CO2 alone increased most growth parameters, but the magnitude of the effect varied among the clones. Total phenolics increased at elevated CO2 , whereas they decreased at elevated T. The responses varied between the clones. The results imply that dark-leaved willow are fairly resistant to the applied three-factor climate change, probably because of high constitutive defense. However, the interactions between clone and climate change factors implies that some clones are more susceptible than the species as a whole., (© 2010 The Authors. New Phytologist © 2010 New Phytologist Trust.)