Ambient UV-B Levels Research Articles

The influence of UV-B radiation on light-dependent photosynthetic performance in Sanionia uncinata (Hedw.) Loeske in Antarctica

Photosynthetic activity of the moss Sanionia uncinata (Hedw.) Loeske was investigated on Leonie Island (67°35'S, 68°20'W, Antarctic Peninsula) in response to short-term changes of UV-B radiation. The UV-environment of natural mat formations dominated by S. uncinata was altered using filter screens. Two filter experiments were conducted in the Antarctic summers 1998 and 1999. A third filter experiment was conducted during springtime ozone depletion in October 1998. Photosynthetic activity of S. uncinata was mainly determined by photosynthetically active photon flux density (PPFD). Light response of relative electron transport rate through photosystem II (rel ETR=ΔF/Fm'×PPFD) remained unaffected by ambient summer levels of UV-B radiation. The same was found for net photosynthesis and dark respiration. In October 1998, S. uncinata was mainly metabolically inactive due to low temperatures. No significant levels of DNA-damage measured as cyclobutane pyrimidine dimers (CPDs) were induced by ambient summer levels of UV-B. Artificially enhanced UV-B radiation supplying a Setlow-DNA-dose of 8.7 kJ m−2 day−1 UV-B led to formation of 7±3 CPD (106 nucleotides)–1. It is concluded that current ambient summer levels of UV-B radiation do not affect photosynthetic activity in S. uncinata.

Growth and production of buckwheat ( Fagopyrum esculentum) treated with reduced, ambient, and enhanced UV-B radiation

The effect of enhanced UV-B radiation on buckwheat ( Fagopyrum esculentum Moench. variety ‘Darja’), an important high elevation crop, was studied in order to estimate its vulnerability in changing UV-B environment. Plants were grown in outdoor experiments from July to October under reduced and ambient UV-B levels, and an UV-B level simulating 17% ozone depletion in Ljubljana. During the development the following parameters were monitored: light saturated photosynthetic activity, transpiration, potential and effective photochemical efficiencies of photosystem II, the contents of photosynthetic pigments and methanol soluble UV-B absorbing compounds. At the end of the experiment, growth rate and production of seeds were estimated. In the following growth season the seeds collected from plants exposed to different UV-B treatments were tested for germination capacity. Total UV-B absorbing compounds during plant development were increased by UV-B radiation, photosynthetic pigments (chlorophyll a and b and carotenoids) decreased. Photosynthetic rate was lowered in an early stage of development. UV-B treatment resulted in the increase in the transpiration rate and consequently the decrease in water use efficiency (WUE). The disturbances in water economy and in photosynthesis affected the reproduction potential negatively; the production of seeds in plants cultivated under ambient and enhanced UV-B was 57 and 39% of the production of specimens treated with reduced UV-B, respectively. The germination of seeds collected from treated plants revealed on average about 95% success, independently of the treatment, but the time needed for germination was the shortest for seeds developed under enhanced UV-B level treatment. Enhanced UV-B radiation affected water relations and production of buckwheat, but not the potential of seeds for germination.

The influence of enhanced UV-B radiation on Batrachium trichophyllum and Potamogeton alpinus — aquatic macrophytes with amphibious character

The responses of two amphibious species, Batrachium trichophyllum and Potamogeton alpinus to different UV-B environments were studied. Plant material from natural environments, as well as from outdoor treatments was examined. In long-term outdoor experiments plants were grown under three different levels of UV-B radiation: reduced and ambient UV-B levels, and a UV-B level simulating 17% ozone depletion. The following parameters were monitored: contents of total methanol soluble UV-absorbing compounds and chlorophyll a, terminal electron transport system (ETS) activity and optimal and effective quantum yield of photosystem II. No effect of the different UV-B levels on the measured parameters was observed. The amount of UV-B absorbing compounds seems to be saturated, since no differences were observed between treatments and no increase was found in peak season, when natural UV-B levels were the highest. Physiological measurements revealed no harmful effects; neither on potential and actual photochemical efficiency, nor on terminal ETS activity. The contents of UV-B absorbing compounds were examined also in plant material sampled in low and high altitude environments during the growth season. Both species exhibited no seasonal dynamics of production of UV-absorbing compounds. The contents were variable and showed no significant differences between high and low altitude populations.

Exposure of red-legged frog embryos to ambient UV-B radiation in the field negatively affects larval growth and development.

Exposure to ultraviolet-B radiation (UV-B; 280-320nm) has a wide array of effects on aquatic organisms, including amphibians, and has been implicated as a possible factor contributing to global declines and range reductions in amphibian populations. Both lethal and sublethal effects of UV-B exposure have been documented for many amphibian species at various life-history stages. Some species, such as red legged frogs, Rana aurora, appear to be resistant to current ambient levels of UV-B, at least at the embryonic and larval stages, despite the fact that they have experienced range reductions in the Willamette Valley of Oregon, USA. However, UV-B is lethal to embryonic and larval R. aurora at levels slightly above those currently experienced during development. Therefore, we predicted that exposure of embryos to ambient UV-B radiation would result in sublethal effects on larval growth and development. We tested this by exposing R. aurora embryos to ambient UV-B in the field and then raising individuals in the laboratory for 1month after hatching. Larvae that were exposed to UV-B as embryos were smaller and less developed than the non-exposed individuals 1month post-hatching. These types of sublethal effects of UV-B exposure indicate that current levels of UV-B could already be influencing amphibian development.

Reduced UV-B in greenhouses decreases white clover response to enhance CO 2

The interaction between reduced UV-B radiation and elevated CO 2 on the growth, allocation and physiology of white clover ( Trifolium repens) was studied in greenhouses of different UV-B transmittance (82 and 88% of ambient) with either ambient (371 ppm) or elevated (521 μmol mol −1) CO 2 concentration. The 88% UV-B levels in increased growth and flowering, indicating an important role for ambient UV-B levels in plant functioning and growth. High CO 2 increased growth significantly only under the 88% UV-B level. The interaction between UV-B and CO 2 effects on total biomass was significant. Allocation was affected significantly by both UV-B (increased root growth, increased flowering) and CO 2 (increased flowering, reduced stem weight). The results clearly indicate the importance of using UV-B transmittant greenhouse or open-top chamber when conducting CO 2 studies, or at least stating the reduction in UV-B within greenhouses.

Influence of solar ultraviolet-B radiation on Antarctic terrestrial plants: results from a 4-year field study

We examined the influence of solar ultraviolet-B radiation (UV-B; 280–315 nm) on the performance of Antarctic vascular plants ( Colobanthus quitensis and Deschampsia antarctica) by placing filters that either absorbed or transmitted most solar UV-B over tundra along the Antarctic Peninsula for four consecutive growing seasons. The difference in biologically effective UV-B levels between our treatments was 65%, which was similar to the enhancement in ambient UV-B levels that appeared attributable to ozone depletion during the first 2 months of the growing season (November and December) at our site (62%). In both species, exposure to UV-B reduced vegetative growth, primarily through slower leaf elongation rates that led to shorter fully expanded leaves. In C. quitensis, exposure to UV-B also led to reductions in leaf longevity, branch production, cushion diameter growth, aboveground biomass, and thickness of the non-green cushion base and litter layer. Exposure to UV-B accelerated the development of reproductive structures and increased the number of panicles ( D. antarctica) and capsules ( C. quitensis) that reached maturity per unit of ground surface area covered by mother plants. However, this effect was offset by a tendency for these panicles and capsules to produce fewer spikelets and seeds. Ultimately, UV-B exposure did not effect the numbers of spikelets or seeds produced per unit of ground surface area. While seeds from plants exposed to UV-B tended to be lighter, germination rates were similar between UV-B treatments. The relative reductions in leaf elongation rates in D. antarctica attributable to UV-B exposure increased from the first (23%) through the fourth (43%) growing season, and relative reductions in leaf longevity in C. quitensis tended to increase from the first (9%) through the fourth (19%) growing season, suggesting that UV-B growth responses tended to be cumulative over successive years.

Histopathology of the skin of UV-B irradiated sole ( Solea solea) and turbot ( Scophthalmus maximus) larvae

Larval stages of two economically important flatfish, the sole ( Solea solea) and turbot ( Scophthalmus maximus) were exposed to ambient and elevated levels of UV-B. Sole larvae, which naturally occur in the plankton in early spring, demonstrated skin lesions at elevated levels of UV-B. Histopathology of the sole revealed cellular changes in the integument, characteristic of sunburn damage, with a reduction in the size of mucus-secreting cells and an increased epidermal thickening, especially at the highest doses of UV-B (2.15 KJ bio eff/m 2). Pigmentation in the sole is restricted to a few isolated melanocytes. The integrity of the heavily pigmented skin of turbot appeared to be unaffected by comparable doses of UV-B. Both species have protective mechanisms, which minimize the effects of naturally-occurring levels of UV-B. However, sole appear to be poorly adapted to accommodate any further increase in solar radiation.

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-BBE.(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.

Effects of ambient UV-B radiation on the above-ground biomass of seven temperate-zone plant species

Variations in the amount of solar ultraviolet-B radiation (UV-B) reaching the biosphere may alter productivity in non-agricultural plants. We examined how ambient levels of UV-B modify the biomass of seven temperatezone species including three grass species (Echinochloa crusgalli, Setaria faberi, Elymus virginicus), three forbs (Verbascum blattaria, Lactuca biennis, Oenothera parviflora), and one tree species (Quercus rubra). Plants were grown outside in enclosures near Morgantown, WV, USA (39 N, 79 W) for one season under near-ambient or no UV-B conditions. The different levels of UV-B were achieved using filters which differentially transmit UVB irradiance. There was a trend towards reduced above-ground biomass in L. biennis (14%) and significantly increased above-ground biomass in O. parviflora (10.2%) under ambient UV-B. The partitioning of biomass between individual plant parts was altered by ambient UV-B in O. parviflora. Leaf biomass was significantly increased (18%), and there were trends toward increased stem (6.7%) and reproductive (9%) biomass. In addition to biomass stimulations, O. parviflora grew significantly taller (5.3%) under ambient UV-B. This study provides evidence that some non-agricultural plants exhibit species-specific growth responses to variable UV-B, with shortlived forbs appearing to be the most sensitive. If the biomass and morphological alterations observed for the forbs in this study were to persist over several years, they might modify population dynamics, competitive interactions, and productivity in ecosystems as UV-B levels fluctuate in the future.

Community responses to UV radiation. I. Enhanced UVB effects on biomass and community structure of filamentous algal assemblages growing in a coral reef mesocosm

Four treatments (PAR; PAR+UVA; PAR + UVA+UVB enhanced by 20% from ambient levels; ambient levels of UVB) were performed using a combination of metal halide lights, UV lamps and cutoff filters over developing assemblages of filamentous algae in a coral reef mesocosm. Exposure to enhanced UVB initially reduced the standing crop by 67% as compared to the productivity of the assemblages grown under PAR and PAR+UVA. Treatment reversal from PAR to enhanced UVB restricted temporarily the growth of the brown alga Ectocarpus rhodochondroides. While the spores of this species are inhibited by UVB, the sporophytes seem to be capable of adapting to UVB exposure. The effects of ambient UVB levels on biomass production and community composition were less pronounced, while exposure to UVA did not affect productivity or community composition. All effects due to UVB exposure gradually diminished as succession progressed. Community composition and biomass production were fully restored 1 to 2 weeks after the cessation of exposure to enhanced UVB.

The cyanobacterium Synechococcus resists UV-B by exchanging photosystem II reaction-center D1 proteins.

Current ambient UV-B levels can significantly depress productivity in aquatic habitats, largely because UV-B inhibits several steps of photosynthesis, including the photooxidation of water catalyzed by photosystem II. We show that upon UV-B exposure the cyanobacterium Synechococcus sp. PCC 7942 rapidly changes the expression of a family of three psbA genes encoding photosystem II D1 proteins. In wild-type cells the psbAI gene is expressed constitutively, but strong accumulations of psbAII and psbAIII transcripts are induced within 15 min of moderate UV-B exposure (0.4 W/m2). This transcriptional response causes an exchange of two distinct photosystem II D1 proteins. D1:1 is encoded by psbAI, but on UV-B exposure, it is largely replaced by the alternate D1:2 form, encoded by both psbAII and psbAIII. The total content of D1 and other photosystem II reaction center protein, D2, remained unchanged throughout the UV exposure, as did the content and composition of the phycobilisome. Wild-type cells suffered only slight transient inhibition of photosystem II function under UV-B exposure. In marked contrast, under the same UV-B treatment, a mutant strain expressing only psbAI suffered severe (40%) and sustained inhibition of photosystem II function. Another mutant strain with constitutive expression of psbAII and psbAIII was almost completely resistant to the UV-B treatment, showing no inhibition of photosystem II function and only a slight drop in electron transport. In Synechococcus the rapid exchange of alternate D1 forms, therefore, accounts for much of the cellular resistance to UV-B inhibition of photosystem II activity and photosynthetic electron transport. This molecular plasticity may be an important element in community-level responses to UV-B, where susceptibility to UV-B inhibition of photosynthesis changes diurnally.

The ratio UV-B/photosynthetically active radiation (PAR) determines the sensitivity of rye to increased UV-B radiation

To evaluate the effect of different naturally occurring irradiation conditions on the sensitivity of rye ( Secale cereale L.) to increased UV-B levels, plants were grown under eight different light treatments. In the control series (at ambient levels of UV-B), UV-B and visible light were decreased in parallel, resulting in four different total irradiation treatments with the same UV-B/photosynthetically active radiation (PAR) ratios. A second series with a 30% increase in UV-B irradiation at each PAR level was used to investigate the effect of UV-B under the varying total irradiance levels. The different total irradiance levels resulted in significant differences in total dry weight, specific leaf weight, photosynthesis-light response and pigment concentrations. A 30% increase in UV-B resulted in equal reductions in total dry weight (from 20.0 to 28.6%) and effective photosynthesis for all light levels. The accumulation of protective pigments in the leaves was stimulated by PAR and even more by UV-B, except at the highest UV-B irradiation, where a small decrease was noted. These results indicate that rye plants are able to adapt to changes in the natural light environment as long as the ratio UV-B/PAR is constant.

An estimate of the total UV-B exposure for outdoor workers during a south-east Queensland summer.

A numerical model was used to calculate the facial UV-B exposure received during summer (December-February) by typical outdoor farm workers in south-east Queensland (27.5 degrees S), a population among the groups at highest risk of skin cancer. The exposure was calculated using new, more detailed measurements of the probability of outdoor activity of farmers (FO-measured by the Fraction of time spent Outside), the distribution of incident solar radiation on the human face (ER-the Exposure Ratio, measured by the fraction of the ambient radiation which falls on each site) and the ambient UV-B levels (AE-the Ambient Exposure) for the region. Only the exposure of unprotected faces was considered. An analysis of the distribution of exposure over a typical working day and of the likely spread of exposures is also presented. The group average of exposures at three facial sites (the forehead, nose and cheek) were 8.7 J cm(-2), 14.0 J cm(-2), and 9.5 J cm(-2), respectively, which is substantially higher than estimates for summer made for populations in more temperate latitudes.

The combined effects of CO2 concentration and solar UV-B radiation on faba bean grown in open-top chambers.

The response of faba bean seedlings to the combined effects of increased atmospheric CO2 concentrations ([CO2]) and solar UV-B irradiance was studied using open-top chambers transparent to UV-B radiation. The purpose of the study was to determine whether effects of increased [CO2] on growth and physiology are modified by the present solar UV-B fluence rate in the Netherlands. Seedlings were exposed to 350 or 700 micromoles mol-1 CO2. At both [CO2], solar UV-B irradiance was either present or reduced using polyester foil opaque to UV-B radiation. To obtain information on the time dependence of increased [CO2] and UV-B radiation effects, three harvests were performed during the experiment. CO2 enrichment resulted in increased biomass production at all harvests. At the final harvest, UV-B radiation did not affect biomass production but a significant decrease was observed after 14 d of treatment. A reduction of the UV-B fluence increased shoot length at both [CO2] throughout the experiment. UV-B radiation slightly altered biomass allocation. Plants grown at reduced levels of UV-B radiation invested less biomass in flowers and more in stem material compared to plants grown at ambient UV-B levels. CO2 enrichment resulted in a stimulation of net photosynthesis after 26 and 38 d of treatment. UV-B reduction did not alter this response. After 26 d of treatment, photosynthetic acclimation to CO2 enrichment was observed, which was probably the result of accumulation of carbohydrates in the leaves. After 38 d, photosynthetic acclimation was no longer present. The UV absorbance of methanolic leaf extracts was increased by CO2 enrichment only. Both CO2 enrichment and solar UV-B reduced the transmittance of radiation through intact attached leaves. Interaction between [CO2] and UV-B radiation was limited to UV-A transmittance of leaves. Under prevalent experimental conditions, UV-B radiation did not affect the measured physiological parameters. Most open-top chambers used for climate change research are constructed of materials which do not transmit UV-B radiation. Our results indicate that part of the 'chamber effects' on plant height often described in the literature might be explained by the absence of solar UV-B radiation in these chambers.

Exclusion of UV-B radiation from normal solar spectrum on the growth of mung bean and maize

The increase in UV-B radiation due to depletion of the ozone layer has potentially harmful effects on plant growth and performance. The bulk of these studies conducted in growth chambers, greenhouses or in the field use different types of exposure systems which may be responsible for differences in the sensitivity of a crop to UV-B radiation. A field study using selective filters to remove the UV-B portion of the solar spectrum was conducted with mung bean (a dicotyledonous C 3 plant) and maize (a monocotyledonous C 4 plant) to determine the sensitivity of these crop plants to ambient UV-B levels without disturbing the microenvironment. Mung bean was found to be sensitive to ambient UV-B levels in terms of leaf area development, plant height attained and net photosynthesis, while maize was found to be unaffected by ambient UV-B levels (22.8 |GmW cm −2 nm −1) found in Delhi, India (28°38′N, 77°13′E). The level of ambient UV-B radiation thus appears to be inhibitory for optimal growth of plants, especially dicotyledonous mung bean.

Considerations for evaluating ultraviolet radiation-induced genetic damage relative to Antarctic ozone depletion.

Springtime ozone depletion over the Antarctic results in increased UVB in local marine environments. It has been established that decreases in primary productivity occur with decreases in ozone concentrations, but the impact of increased UVB on the functioning and stability of the ecosystem has not yet been determined. Very little has been done to evaluate the potential for genetic damage caused by the increase in UVB, and this type of damage is most significant relative to the fitness and maintenance of populations. An essential problem in evaluating genotoxic effects is the lack of appropriate techniques to sample and quantify genetic damage in field populations under ambient UVB levels. In addition, it is currently not feasible to estimate exposure levels for organisms in their natural habitats.

PERSONAL DOSIMETRY OF SOLAR UV RADIATION FOR DIFFERENT OUTDOOR ACTIVITIES

Quantifying individual exposure to ultraviolet radiation (UVR) is critical to understanding the etiology of a number of diseases including nonmelanotic and melanotic skin cancers. Measurements of personal exposure to solar UVR were made in Hobart, Tasmania in February (summer) 1991 for six different outdoor activities using UVR-sensitive polysulfone (PS) film attached at seven anatomical sites. Concurrent behavioral and environmental observations were also made. To date many studies have relied on subject recall to quantify past solar UVR exposures. To gain insight into the accuracy of subject recall the measured UVR exposures received by different subjects using the PS film were compared to those calculated from personal diaries and ambient solar UVB levels from a monitoring station. In general, when UVR exposure activities took place under close supervision, good correlations were obtained between the PS badges and the ambient measurements/diaries approach. Ultraviolet radiation exposures for the field study involving 94 subjects engaged in a number of outdoor activities are presented.