Lars Olof Björn

UV-B as an environmental factor in plant life: stress and regulation.

Recent studies indicate that increasing solar UV-B is not merely an environmental stress for plants. Solar UV-B can cause plant morphogenetic effects, which can, in turn, modify the architecture of plants and the structure of a vegetation, In addition, UV-B radiation affect the production of various secondary metabolites (such as flavonoids, tannins and lignin) with important physiological and ecological consequences.

Changes in biologically active ultraviolet radiation reaching the Earth's surface

Since publication of the 1998 UNEP Assessment, there has been continued rapid expansion of the literature on UV-B radiation. Many measurements have demonstrated the inverse relationship between column ozone amount and UV radiation, and in a few cases long-term increases due to ozone decreases have been identified. The quantity, quality and availability of ground-based UV measurements relevant to assessing the environmental impacts of ozone changes continue to improve. Recent studies have contributed to delineating regional and temporal differences due to aerosols, clouds, and ozone. Improvements in radiative transfer modelling capability now enable more accurate characterization of clouds, snow-cover, and topographical effects. A standardized scale for reporting UV to the public has gained wide acceptance. There has been increased use of satellite data to estimate geographic variability and trends in UV. Progress has been made in assessing the utility of satellite retrievals of UV radiation by comparison with measurements at the Earths surface. Global climatologies of UV radiation are now available on the Internet. Anthropogenic aerosols play a more important role in attenuating UV irradiances than has been assumed previously, and this will have implications for the accuracy of UV retrievals from satellite data. Progress has been made inferring historical levels of UV radiation using measurements of ozone (from satellites or from ground-based networks) in conjunction with measurements of total solar radiation obtained from extensive meteorological networks. We cannot yet be sure whether global ozone has reached a minimum. Atmospheric chlorine concentrations are beginning to decrease. However, bromine concentrations are still increasing. While these halogen concentrations remain high, the ozone layer remains vulnerable to further depletion from events such as volcanic eruptions that inject material into the stratosphere. Interactions between global warming and ozone depletion could delay ozone recovery by several years, and this topic remains an area of intense research interest. Future changes in greenhouse gases will affect the future evolution of ozone through chemical, radiative, and dynamic processes In this highly coupled system, an evaluation of the relative importance of these processes is difficult: studies are ongoing. A reliable assessment of these effects on total column ozone is limited by uncertainties in lower stratospheric response to these changes. At several sites, changes in UV differ from those expected from ozone changes alone, possibly as a result of long-term changes in aerosols, snow cover, or clouds. This indicates a possible interaction between climate change and UV radiation. Cloud reflectance measured by satellite has shown a long-term increase at some locations, especially in the Antarctic region, but also in Central Europe, which would tend to reduce the UV radiation. Even with the expected decreases in atmospheric chlorine, it will be several years before the beginning of an ozone recovery can be unambiguously identified at individual locations. Because UV-B is more variable than ozone, any identification of its recovery would be further delayed.

Effects of increased solar ultraviolet radiation on terrestrial ecosystems

Elevated solar UV-B radiation associated with stratospheric ozone reduction may exert effects on terrestrial ecosystems through actions on plants, microbes, and perhaps on some animals. At the ecosystem level, the effects are less well understood than at the molecular and organismal levels. Many of the most important, yet less predictable, consequences will be indirect effects of elevated UV-B acting through changes in the chemical composition and form of plants and through changes in the abiotic environment. These indirect effects include changes in the susceptibility of plants to attack by insects and pathogens in both agricultural and natural ecosystems; the direction of these changes can result in either a decrease or an increase in susceptibility. Other indirect effects of elevated UV-B include changes in competitive balance of plants and nutrient cycling. The direct UV-B action on plants that results in changes in form or function of plants appears to occur more often through altered gene activity rather than damage. The yield of some crop varieties can be decreased by elevated UV-B, but other varieties are not affected. Plant breeding and genetic engineering efforts should be able to cope with the potential threats to crop productivity due to elevated UV-B. For forest trees, this may be more difficult if effects of elevated UV-B accumulate over several years. All effects of elevated UV-B radiation must be considered in the context of other climate changes such as increased temperature and levels of carbon dioxide, which may alter the UV-B responses, especially for plants. The actions of elevated carbon dioxide and UV-B appear to be largely independent, but interactions occur between changes in UV-B and other factors. Other ecosystem-level consequences of elevated UV-B radiation are emerging and their magnitude and direction will not be easily predicted.

Ozone depletion and climate change: Impacts on UV radiation.

The Montreal Protocol is working, but it will take several decades for ozone to return to 1980 levels. The atmospheric concentrations of ozone depleting substances are decreasing, and ozone column amounts are no longer decreasing. Mid-latitude ozone is expected to return to 1980 levels before mid-century, slightly earlier than predicted previously. However, the recovery rate will be slower at high latitudes. Springtime ozone depletion is expected to continue to occur at polar latitudes, especially in Antarctica, in the next few decades. Because of the success of the Protocol, increases in UV-B radiation have been small outside regions affected by the Antarctic ozone hole, and have been difficult to detect. There is a large variability in UV-B radiation due to factors other than ozone, such as clouds and aerosols. There are few long-term measurements available to confirm the increases that would have occurred as a result of ozone depletion. At mid-latitudes UV-B irradiances are currently only slightly greater than in 1980 (increases less than ~5%), but increases have been substantial at high and polar latitudes where ozone depletion has been larger. Without the Montreal Protocol, peak values of sunburning UV radiation could have been tripled by 2065 at mid-northern latitudes. This would have had serious consequences for the environment and for human health. There are strong interactions between ozone depletion and changes in climate induced by increasing greenhouse gases (GHGs). Ozone depletion affects climate, and climate change affects ozone. The successful implementation of the Montreal Protocol has had a marked effect on climate change. The calculated reduction in radiative forcing due to the phase-out of chlorofluorocarbons (CFCs) far exceeds that from the measures taken under the Kyoto protocol for the reduction of GHGs. Thus the phase-out of CFCs is currently tending to counteract the increases in surface temperature due to increased GHGs. The amount of stratospheric ozone can also be affected by the increases in the concentration of GHGs, which lead to decreased temperatures in the stratosphere and accelerated circulation patterns. These changes tend to decrease total ozone in the tropics and increase total ozone at mid and high latitudes. Changes in circulation induced by changes in ozone can also affect patterns of surface wind and rainfall. The projected changes in ozone and clouds may lead to large decreases in UV at high latitudes, where UV is already low; and to small increases at low latitudes, where it is already high. This could have important implications for health and ecosystems. Compared to 1980, UV-B irradiance towards the end of the 21st century is projected to be lower at mid to high latitudes by between 5 and 20% respectively, and higher by 2-3% in the low latitudes. However, these projections must be treated with caution because they also depend strongly on changes in cloud cover, air pollutants, and aerosols, all of which are influenced by climate change, and their future is uncertain. Strong interactions between ozone depletion and climate change and uncertainties in the measurements and models limit our confidence in predicting the future UV radiation. It is therefore important to improve our understanding of the processes involved, and to continue monitoring ozone and surface UV spectral irradiances both from the surface and from satellites so we can respond to unexpected changes in the future.

Environmental effects of ozone depletion and its interactions with climate change: progress report, 2011

The Environmental Effects Assessment Panel (EEAP) is one of three Panels that regularly informs the Parties (countries) to the Montreal Protocol on the effects of ozone depletion and the consequences of climate change interactions with respect to human health, animals, plants, biogeochemistry, air quality, and materials. The Panels provide a detailed assessment report every four years. The most recent 2014 Quadrennial Assessment by the EEAP was published as a special issue of seven papers in 2015 (Photochem. Photobiol. Sci., 2015, 14, 1-184). The next Quadrennial Assessment will be published in 2018/2019. In the interim, the EEAP generally produces an annual update or progress report of the relevant scientific findings. The present progress report for 2015 assesses some of the highlights and new insights with regard to the interactive nature of the effects of UV radiation, atmospheric processes, and climate change.

Biodiversity, distributions and adaptations of arctic species in the context of environmental change

Abstract The individual of a species is the basic unit which responds to climate and UV-B changes, and it responds over a wide range of time scales. The diversity of animal, plant and microbial species appears to be low in the Arctic, and decreases from the boreal forests to the polar deserts of the extreme North but primitive species are particularly abundant. This latitudinal decline is associated with an increase in super-dominant species that occupy a wide range of habitats. Climate warming is expected to reduce the abundance and restrict the ranges of such species and to affect species at their northern range boundaries more than in the South: some Arctic animal and plant specialists could face extinction. Species most likely to expand into tundra are boreal species that currently exist as outlier populations in the Arctic. Many plant species have characteristics that allow them to survive short snow-free growing seasons, low solar angles, permafrost and low soil temperatures, low nutrient availability and physical disturbance. Many of these characteristics are likely to limit species. responses to climate warming, but mainly because of poor competitive ability compared with potential immigrant species. Terrestrial Arctic animals possess many adaptations that enable them to persist under a wide range of temperatures in the Arctic. Many escape unfavorable weather and resource shortage by winter dormancy or by migration. The biotic environment of Arctic animal species is relatively simple with few enemies, competitors, diseases, parasites and available food resources. Terrestrial Arctic animals are likely to be most vulnerable to warmer and drier summers, climatic changes that interfere with migration routes and staging areas, altered snow conditions and freeze-thaw cycles in winter, climate-induced disruption of the seasonal timing of reproduction and development, and influx of new competitors, predators, parasites and diseases. Arctic microorganisms are also well adapted to the Arctics climate: some can metabolize at temperatures down to −39°C. Cyanobacteria and algae have a wide range of adaptive strategies that allow them to avoid, or at least minimize UV injury. Microorganisms can tolerate most environmental conditions and they have short generation times which can facilitate rapid adaptation to new environments. In contrast, Arctic plant and animal species are very likely to change their distributions rather than evolve significantly in response to warming.

Effects on the function of arctic ecosystems in the short- and long-term perspectives

Abstract Species individualistic responses to warming and increased UV-B radiation are moderated by the responses of neighbors within communities, and trophic interactions within ecosystems. All of these responses lead to changes in ecosystem structure. Experimental manipulation of environmental factors expected to change at high latitudes showed that summer warming of tundra vegetation has generally led to smaller changes than fertilizer addition. Some of the factors manipulated have strong effects on the structure of Arctic ecosystems but the effects vary regionally, with the greatest response of plant and invertebrate communities being observed at the coldest locations. Arctic invertebrate communities are very likely to respond rapidly to warming whereas microbial biomass and nutrient stocks are more stable. Experimentally enhanced UV-B radiation altered the community composition of gram-negative bacteria and fungi, but not that of plants. Increased plant productivity due to warmer summers may dominate food-web dynamics. Trophic interactions of tundra and sub-Arctic forest plant-based food webs are centered on a few dominant animal species which often have cyclic population fluctuations that lead to extremely high peak abundances in some years. Population cycles of small rodents and insect defoliators such as the autumn moth affect the structure and diversity of tundra and forest-tundra vegetation and the viability of a number of specialist predators and parasites. Ice crusting in warmer winters is likely to reduce the accessibility of plant food to lemmings, while deep snow may protect them from snowsurface predators. In Fennoscandia, there is evidence already for a pronounced shift in small rodent community structure and dynamics that have resulted in a decline of predators that specialize in feeding on small rodents. Climate is also likely to alter the role of insect pests in the birch forest system: warmer winters may increase survival of eggs and expand the range of the insects. Insects that harass reindeer in the summer are also likely to become more widespread, abundant and active during warmer summers while refuges for reindeer/caribou on glaciers and late snow patches will probably disappear.

UV Radiation: Balancing Risks and Benefits

We use action spectra published by the International Commission on Illumination to examine diurnal, seasonal and latitudinal variations in erythemally weighted (sunburning) UV—a health risk, and vitamin D‐weighted UV—a health benefit. Vitamin D‐weighted UV is more strongly dependent on ozone and solar zenith angle. Consequently, its diurnal, seasonal and geographic variability is more pronounced than for erythemally weighted UV. We then investigate relationships between the two quantities. An algorithm is developed and used to relate vitamin D production to the widely used UV index, to help the public to optimize their exposure to UV radiation. In the summer at noon, there should at mid‐latitudes be sufficient UV to photosynthesize optimal vitamin D in ∼1 min for full body exposure, whereas skin damage occurs after ∼15 min. Further, while it should be possible to photosynthesize vitamin D in the winter at mid‐latitudes, the amount of skin that must be exposed is larger than from the hands and face alone. This raises the question of whether the action spectrum for vitamin D production is correct, since studies have reported that production of vitamin D is not possible in the winter at mid‐latitudes.

The effect of ultraviolet radiation on the accumulation of medicinal compounds in plants

A review is given of how the production by plants of compounds useful as medicines or raw materials for manufacture of medicines is influenced by ultraviolet radiation, particularly by UV-B radiation (280-315 nm wavelength). The compounds considered in this review are flavonoids and other phenolics, alkaloids (especially indole terpenoid and purine alkaloids), essential oils and other terpenoids, cannabinoids, glucosinolates and isothiocyanates, and compounds having human hormone activity. A short account is also given of ultraviolet signalling in plants. The review concludes with a discussion of the possible evolutionary mechanisms that have led to the evolution of UV-B regulation of secondary metabolite accumulation.

The Effects of Enhanced UV-B Radiation on the Growth of Dwarf Shrubs in a Subarctic Heathland

In a field irradiation experiment UV-B radiation was enhanced to simulate 15% ozone depletion under clear sky conditions in northern Sweden. This was accomplished by using UV-B fluorescent lamps mounted on metal frames raised over a naturally growing plant community. 2. The study area consisted of a dwarf shrub heath mainly composed of the four species Vaccinium vitis-idaea, V. myrtillus, V. uliginosum and Empetrum hermaphroditum. The absolute annual stem growth, relative stem growth and absolute leaf growth were recorded for different years. 3. The relative growth was significantly reduced by UV-B enhancement in the two evergreen species V. vitis-idaea (27% after 2 years of enhanced UV-B) and E. hermaphroditum (14% after 1 year and 33% after 2 years). The two deciduous species also showed a tendency for decreased relative growth under enhanced UV-B, but this effect was not statistically significant. 4. The leaf thickness of V. vitis-idaea increased both during 1992 (9%) and 1993 (4%). In contrast, the two deciduous species V. myrtillus and V. uliginosum developed thinner leaves under enhanced UV-B both during 1992 (4% for V. myrtillus, 6% for V. uliginosum) and 1993 (9% for V. myrtillus, 10% for V. uliginosum). (Less)