Increased ultraviolet-B Radiation Research Articles

Effects of enhanced UV-B radiation on the interaction between rice and Magnaporthe oryzae in Yuanyang terrace.

Enhanced ultraviolet-B (UV-B) radiation affected the growth of rice and Magnaporthe oryzae, and changed the interactions between them. Increased UV-B radiation (5.0 kJ m-2 d-1) on rice leaves in a Yuanyang terrace was conducted before, during, and after infection of the leaves with Magnaporthe oryzae. The relationship between rice blast and UV-B radiation on the disease resistance of rice and the pathogenicity of M. oryzae was studied, and the effects of enhanced UV-B radiation on the interactions between rice and M. oryzae were analysed. The results indicated the following: (1) enhanced UV-B radiation significantly reduced the rice blast disease index, but as infection progressed, the inhibitory effect of UV-B radiation on the disease was weakened. (2) UV-B radiation treatment before infection with M. oryzae (UV-B + M.) significantly increased the activity of the enzymes related to disease resistance (phenylalanine ammonia lyase, lipoxygenase, chitinase, and β-1,3-glucanase), and the plants exhibited light-induced resistance. (3) Exposure to UV-B radiation after M. oryzae infection (M. + UV-B) did not induce disease course-related protein (PR) activity, but the content of soluble sugar increased. The osmotic stress caused by pathogenic fungi infection was alleviated by active accumulation of soluble sugar; due to this lack of nutrients, it was difficult for the rice blast fungus to grow. (4) Enhanced UV-B radiation significantly inhibited the production of conidia by M. oryzae, and the expression of the pathogenic genes Chitinase, MGP1, MAGB, and CPKA was significantly downregulated. The pathogenicity of M. oryzae was reduced by UV-B radiation. The resistance of rice leaves was weakened by simultaneous exposure to UV-B radiation and M. oryzae (UV-B/M.). Hence, UV-B radiation can weaken the infectivity of M. oryzae, improve the resistance of traditional rice, and contain the disease.

Effects of UV-B radiation on phenolic accumulation, antioxidant activity and physiological changes in wheat (Triticum aestivum L.) seedlings

The production of secondary metabolites and the antioxidant defense systems could be activated in response to ultraviolet-B (UV-B). The effects of UV-B radiation on the phenolic content, antioxidant activity, and physiological changes in wheat seedlings were investigated. Results showed that the free, bound and total phenolic contents and antioxidant activities significantly increased in wheat seedlings after UV-B exposure from the third and fourth day. UV-B radiation of 20 μW/cm2 led to the highest accumulation of phenolics. Total phenolics, DPPH and ABTS values significantly increased by 26.3, 25.1 and 12.0%, respectively, on day 4 as compared to unirradiated wheat seedlings. The highest respiratory rate and phenylalanine ammonia-lyase activity were also observed with the radiation. The increased UV-B radiation intensified the lipid peroxidation in wheat seedlings and changed the activities of antioxidant enzymes involved in the scavenging of reactive oxygen species. The activities of superoxide dismutase, peroxidase and catalase decreased, while the ascorbate peroxidase activity increased with the enhanced UV-B radiation intensity. This study showed that wheat seedlings could be developed as a functional food ingredient after moderate UV-B radiation.

Contrasting Responses of Marine and Freshwater Photosynthetic Organisms to UVB Radiation: A Meta-Analysis

Ultraviolet-B (UVB) radiation is a global stressor that has profound impacts on freshwater and marine ecosystems. However, an analysis of the patterns of sensitivity to UVB radiation across aquatic photosynthetic organisms has not yet been published. Here, we performed a meta-analysis on results reported in 214 studies compiled from the published literature to quantify and compare the magnitude of responses of aquatic photosynthetic organisms to changes in UVB radiation. The meta-analysis was conducted on observations of marine (n = 893) and freshwater macroalgae (n = 126) and of marine (n = 1087) and freshwater (n = 2889) microalgae (total n = 4995). Most of these studies (85%) analysed the performance of organisms exposed to natural solar radiation when UVB was partially or totally reduced compared with the organismal performance under the full solar radiation spectrum, whereas the remaining 15% of the studies examined the responses of organisms to elevated UVB radiation mostly using artificial lamps. We found that marine photosynthetic organisms tend to be more sensitive than freshwater photosynthetic organisms to UVB radiation; responses to either decreased or increased UVB radiation vary among taxa; the mortality rate is the most sensitive of the trait responses to elevated UVB radiation, followed by changes in cellular and molecular traits; the sensitivity of microalgae to UVB radiation is dependent on size, with small-celled microalgae more sensitive than large-celled microalgae to UVB radiation. Thick macroalgae morphotypes were the less sensitive to UVB, but this effect could not be separated from phylogenetic differences. The high sensitivity of marine species, particularly the smallest photosynthetic organisms, to increased UVB radiation suggests that the oligotrophic ocean, a habitat comprising 70 % of the world’s oceans with high UVB penetration and dominated by picoautotrophs, is extremely vulnerable to changes in UVB radiation.

Effect of increased UV-B radiation on carotenoid accumulation and total antioxidant capacity in tobacco (Nicotiana tabacum L.) leaves.

Carotenoids are important components of plant antioxidant systems, which protect photosystems from photooxidative destruction during ultraviolet-B (UV-B) exposure. The influence of carotenoids on total antioxidant capacity (TAC) of plants has rarely been studied. In this study, tobacco (Nicotiana tabacum L., 'K326') seedlings exposed to UV-B radiation were used in order to evaluate the effects of ambient levels of UV-B radiation on carotenoid accumulation. The aim was to investigate whether carotenoids could enhance TAC as a means of UV protection. Our results showed that leaf carotenoid content in the low UV-B exposure (+9.75 μW/cm2) plants was approximately 8% higher than that observed in control plants at 2-8 days of exposure. At high UV-B exposure (+20.76 μW/cm2), the carotenoid content increased rapidly after 1 day's exposure (10.41% higher than the control), followed by a return to the content as in control plants. Furthermore, carotenoid content positively correlated with TAC (P = 0.024). These results suggest that carotenoids have antioxidant properties and play an important role in the antioxidant system. UV-B exposure increased the carotenoid synthesis capability of plants. The plants could deplete the carotenoids to scavenge excess ROS at high UV-B radiation levels, which protects the tobacco plant from oxidative damage caused by UV-B stress.

Interactive effects of ultraviolet-B radiation and pesticide exposure on DNA photo-adduct accumulation and expression of DNA damage and repair genes in Xenopus laevis embryos

Pesticide use and ultraviolet-B (UVB) radiation have both been suggested to adversely affect amphibians; however, little is known about their interactive effects. One potential adverse interaction could involve pesticide-induced dysregulation of DNA repair pathways, resulting in greater numbers of DNA photo-adducts from UVB exposure. In the present study, we investigated the interactive effects of UVB radiation and two common pesticides (endosulfan and α-cypermethrin) on induction of DNA photo-adducts and expression of DNA damage and repair related genes in African clawed frog (Xenopus laevis) embryos. We examined 13 genes that are, collectively, involved in stress defense, cell cycle arrest, nucleotide excision repair (NER), base excision repair, mismatch repair, DNA repair regulation, and apoptosis. We exposed X. laevis embryos to 0, 25, and 50μg/L endosulfan or 0, 2.5, and 5.0μg/L α-cypermethrin for 96h, with environmentally relevant exposures of UVB radiation during the last 7h of the 96h exposure. We measured the amount of cyclobutane pyrimidine dimers (CPDs) and mRNA abundance of the 13 genes among treatments including control, pesticide only, UVB only, and UVB and pesticide co-exposures. Each of the co-exposure scenarios resulted in elevated CPD levels compared to UVB exposure alone, suggesting an inhibitory effect of endosulfan and α-cypermethrin on CPD repair. This is attributed to results indicating that α-cypermethrin and endosulfan reduced mRNA abundance of XPA and HR23B, respectively, to levels that may affect the initial recognition of DNA lesions. In contrast, both pesticides increased transcript abundance of CSA and MUTL. In addition, mRNA abundance of HSP70 and GADD45α were increased by endosulfan and mRNA abundance of XPG was increased by α-cypermethrin. XPC, HR23B, XPG, and GADD45α exhibited elevated mRNA concentrations whereas there was a reduction in MUTL transcript concentrations in UVB-alone treatments. It appeared that even though expression of XPC and CSA were induced by exposure to UVB or pesticides, XPA was the limiting factor in the NER pathway. Our results suggest that pesticides may increase the accumulation of UVB-induced DNA photo-adducts and one likely mechanism is the alteration of critical NER gene expression. The present study provides important implications for evaluating the combined risks of pesticide usage and potentially increasing UVB radiation in aquatic ecosystems.

Not just about sunburn--the ozone hole's profound effect on climate has significant implications for Southern Hemisphere ecosystems.

Climate scientists have concluded that stratospheric ozone depletion has been a major driver of Southern Hemisphere climate processes since about 1980. The implications of these observed and modelled changes in climate are likely to be far more pervasive for both terrestrial and marine ecosystems than the increase in ultraviolet-B radiation due to ozone depletion; however, they have been largely overlooked in the biological literature. Here, we synthesize the current understanding of how ozone depletion has impacted Southern Hemisphere climate and highlight the relatively few documented impacts on terrestrial and marine ecosystems. Reviewing the climate literature, we present examples of how ozone depletion changes atmospheric and oceanic circulation, with an emphasis on how these alterations in the physical climate system affect Southern Hemisphere weather, especially over the summer season (December-February). These potentially include increased incidence of extreme events, resulting in costly floods, drought, wildfires and serious environmental damage. The ecosystem impacts documented so far include changes to growth rates of South American and New Zealand trees, decreased growth of Antarctic mosses and changing biodiversity in Antarctic lakes. The objective of this synthesis was to stimulate the ecological community to look beyond ultraviolet-B radiation when considering the impacts of ozone depletion. Such widespread changes in Southern Hemisphere climate are likely to have had as much or more impact on natural ecosystems and food production over the past few decades, than the increased ultraviolet radiation due to ozone depletion.

Impact of increasing Ultraviolet-B (UV-B) radiation on photosynthetic processes

Increased UV-B radiation on the earth’s surface due to depletion of stratospheric ozone layer is one of the changes of current climate-change pattern. The deleterious effects of UV-B radiation on photosynthesis and photosynthetic productivity of plants are reviewed. Perusal of relevant literature reveals that UV-B radiation inflicts damage to the photosynthetic apparatus of green plants at multiple sites. The sites of damage include oxygen evolving complex, D1/D2 reaction center proteins and other components on the donor and acceptor sides of PS II. The radiation inactivates light harvesting complex II and alters gene expression for synthesis of PS II reaction center proteins. Mn cluster of water oxidation complex is the most important primary target of UV-B stress whereas D1 and D2 proteins, quinone molecules and cytochrome b are the subsequent targets of UV-B. In addition, photosynthetic carbon reduction is also sensitive to UV-B radiation which has a direct effect on the activity and content of Rubisco. Some indirect effects of UV-B radiation include changes in photosynthetic pigments, stomatal conductance and leaf and canopy morphology. The failure of protective mechanisms makes PS II further vulnerable to the UV-B radiation. Reactive oxygen species are involved in UV-B induced responses in plants, both as signaling and damaging agents. Exclusion of ambient UV components under field conditions results in the enhancement of the rate of photosynthesis, PS II efficiency and subsequently increases the biomass accumulation and crop yield. It is concluded that predicted future increase in UV-B irradiation will have significant impact on the photosynthetic efficiency and the productivity of higher plants.

Relations between Conspecific Density and Effects of Ultraviolet‐B Radiation on Tadpole Size in the Striped Marsh Frog

Global increases in ultraviolet-B radiation (UVBR) associated with stratospheric ozone depletion are potentially contributing to the decline of numerous amphibian species around the world. Exposure to UVBR alone reduces survival and induces a range of sublethal effects in embryonic and larval amphibians. When additional environmental stressors are present, UVBR can have compounding negative effects. Thus, examination of the effects of UVBR in the absence of other stressors may substantially underestimate its potential to affect amphibians in natural habitats. We examined the independent and interactive effects of increased UVBR and high conspecific density would have embryonic and larval striped marsh frogs (Limnodynastes peronii). We exposed individuals to a factorial combination of low and high UVBR levels and low, medium, and high densities of striped marsh frog tadpoles. The response variables were time to hatching, hatching success, posthatch survival, burst-swimming performance of tadpoles (maximum instantaneous swim speed following an escape response), and size and morphology of tadpoles. Consistent with results of previous studies, we found that exposure to UVBR alone increased the time to hatching of embryos and reduced the burst-swimming performance and size of tadpoles. Similarly, increasing conspecific density increased the time to hatching of embryos and reduced the size of tadpoles, but had no effect on burst-swimming performance. The negative effect of UVBR on tadpole size was not apparent at high densities of tadpoles. This result suggests that tadpoles living at higher densities may invest relatively less energy in growth and thus have more energy to repair UVBR-induced damage. Lower densities of conspecifics increased the negative effects of UVBR on developing amphibians. Thus, low-density populations, which may include declining populations, may be particularly susceptible to the detrimental effects of increased UVBR and thus may be driven toward extinction faster than might be expected on the basis of results from single-factor studies.

Tillage effects on physical qualities of a vertisol in the central highlands of Ethiopia

Chlorofluorocarbons are mainly responsible for the depletion of stratospheric ozone layer which results in increase of UV-B radiation on earth’s environment and causing adverse effects on flora. In the present study we have investigated the effect of ultraviolet-B (UV-B) radiation on two cryptogamic plants (Xanthoria elegans and Bryum argenteum) growing at high altitude of central Himalayan region of India. These plants were naturally receiving UV-B radiation and were analyzed for photosynthetic pigments, UV-B absorbing compounds and phenolics. In the field experiments, both of these plants contain higher amounts of UV-B absorbing compounds and phenolics and no major changes in total chlorophyll and carotenoid under UV-B exposed conditions were recorded. B. argenteum contains higher amounts of total chlorophyll, carotenoids, UV-B absorbing compounds and phenolics than the X. elegans at the duration of 120 h. The maximum average UV-B irradiance was 4.38 Minimal Erythemal Dose per hour (MED/ h) at the experimental site while minimum average UV-B irradiance was 1.72 MED/ h. The UV-B absorbing compounds and phenolics provide protection to these plants against UV-B radiation. Key words : Total chlorophyll, high altitude, pigments, UV-B absorbing compounds, UV-B radiation.

Impacts of long-term enhanced UV-B radiation on bryophytes in two sub-Arctic heathland sites of contrasting water availability.

Anthropogenic depletion of stratospheric ozone in Arctic latitudes has resulted in an increase of ultraviolet-B radiation (UV-B) reaching the biosphere. UV-B exposure is known to reduce above-ground biomass and plant height, to increase DNA damage and cause accumulation of UV-absorbing compounds in polar plants. However, many studies on Arctic mosses tended to be inconclusive. The importance of different water availability in influencing UV-B impacts on lower plants in the Arctic has been poorly explored and might partially explain the observed wide variation of responses, given the importance of water in controlling bryophyte physiology. This study aimed to assess the long-term responses of three common sub-Arctic bryophytes to enhanced UV-B radiation (+UV-B) and to elucidate the influence of water supply on those responses. Responses of three sub-Arctic bryophytes (the mosses Hylocomium splendens and Polytrichum commune and the liverwort Barbilophozia lycopodioides) to +UV-B for 15 and 13 years were studied in two field experiments using lamps for UV-B enhancement with identical design and located in neighbouring areas with contrasting water availability (naturally mesic and drier sites). Responses evaluated included bryophyte abundance, growth, sporophyte production and sclerophylly; cellular protection by accumulation of UV-absorbing compounds, β-carotene, xanthophylls and development of non-photochemical quenching (NPQ); and impacts on photosynthesis performance by maximum quantum yield (F(v) /F(m)) and electron transport rate (ETR) through photosystem II (PSII) and chlorophyll concentrations. Responses were species specific: H. splendens responded most to +UV-B, with reduction in both annual growth (-22 %) and sporophyte production (-44 %), together with increased β-carotene, violaxanthin, total chlorophyll and NPQ, and decreased zeaxanthin and de-epoxidation of the xanthophyll cycle pool (DES). Barbilophozia lycopodioides responded less to +UV-B, showing increased β-carotene and sclerophylly and decreased UV-absorbing compounds. Polytrichum commune only showed small morphogenetic changes. No effect of UV-B on bryophyte cover was observed. Water availability had profound effects on bryophyte ecophysiology, and plants showed, in general, lower growth and ETR, together with a higher photoprotection in the drier site. Water availability also influenced bryophyte responses to +UV-B and, in particular, responses were less detectable in the drier site. Impacts of UV-B exposure on Arctic bryophytes were significant, in contrast to modest or absent UV-B effects measured in previous studies. The impacts were more easily detectable in species with high plasticity such as H. splendens and less obvious, or more subtle, under drier conditions. Species biology and water supply greatly influences the impact of UV-B on at least some Arctic bryophytes and could contribute to the wide variation of responses observed previously.

Minor long-term effects of ultraviolet-B radiation on methane dynamics of a subarctic fen in Northern Finland

The effects of elevated ultraviolet-B (UV-B) radiation on methane dynamics was studied in a natural fen in Northern Finland for three growing seasons (2003–2005). This is the first in situ study on the effects of elevated UV-B radiation on methane dynamics in a natural fen. The experimental setup consisted of 30 study plots (120 × 120 cm) that were randomly divided into three treatments: ambient control, UV-A control and elevated UV-B. The UV-B enhancements were 63, 37 and 21% above ambient during the growing seasons 2003, 2004 and 2005, respectively. Elevated UV-B did not affect net methane emission. Stable isotope composition of methane indicated that methane was produced by the acetate fermentation. Under elevated UV-B there was a slight increase in the concentrations of acetate and propionate but decrease in the oxalate concentration suggesting UV-B-induced changes in the belowground processes. The results emphasize the need for long-term field studies under moderately enhanced exposures to estimate whether the function and feedbacks of mire ecosystems change under increased UV-B radiation.

Research advances on the biological effects of elevated ultraviolet-B radiation on terrestrial plants

This review describes the effects of ultraviolet-B (UV-B) radiation on plant growth and development, photosynthesis and photosynthetic pigments and UV-B absorbing compounds. Moreover, plant ecosystem level responses to elevated UV-B radiation and interactions of UV-B radiation with abiotic and biotic factors were also involved. Results collected in this review suggest that approximately two-thirds terrestrial plant species are significantly affected by increase in UV-B radiation. The majority of evidences indicate that elevated UV-B radiation is usually detrimental but there exists tremendous variability in the sensitivity of species to UV-B radiation, and sensitivity also differs among cultivars of the same species.

Quantifying the metabolic cost to an Antarctic liverwort of responding to an abrupt increase in UVB radiation exposure

AbstractWe quantified the metabolic cost to the Antarctic leafy liverwort Cephaloziella varians of responding to an abrupt increase in ultraviolet B (UVB) radiation exposure in the natural environment at Rothera Point on the western Antarctic Peninsula (67 °34′S, 68 °07′W). The liverwort was protected from exposure to UVB radiation for 44 days with screens containing Mylar polyester, after which time its thalli, which are normally black in colour, had become green owing to reduced concentrations of an anthocyanidin, identified here as riccionidin A, in thallus tips. Thalli were then exposed to an abrupt increase in UVB radiation by removing the screens. The thalli became visibly darker within 48 h of the screens being removed, resynthesizing riccionidin A to the same concentration as that present in thalli outside screens during this period. Chlorophyll fluorescence measurements indicated that nonphotochemical quenching was higher in the thalli formerly under the screens than in those not previously covered with screens, but that Fv/Fm and photochemical quenching were the same in the two groups of thalli. We used data from aqueous phase oxygen electrode measurements to calculate an estimate for carbon fixation by C. varians during the 48 h after the screens were removed. Assuming a photosynthetic quotient for Antarctic bryophytes of 1, these analyses indicated that the minimum weight of carbon used to synthesize riccionidin A was equivalent to 1.85% of the carbon fixed by thalli during the 48 h after the abrupt increase in UVB radiation exposure.

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.

Differential response of leaf gas exchange to enhanced ultraviolet-B (UV-B) radiation in three species of herbaceous climbingplants

We measured diurnal changes in photosynthetic rate, transpiration rate, stomatal conductance and water use efficiency in three species of herbaceous climbing plants ( Luffa cylindrica, Trichosanthes kirilowii and Dioscorea opposita) exposed to two intensities of UV-B radiation: 3.0 μw cm −2 (R1) and 8.0 μw cm −2 UV-B (R2) radiation under ambient growth conditions. Responses differed per species and per treatment. In Luffa all values increased compared to the Control in both treatments, except for stomatal conductance in R2. In Trichosanthes photosynthetic rates and water use efficiency increased, while the transpiration rates decreased under both treatments, and stomatal conductance was lower in R1. In Dioscorea photosynthetic rates and water use efficiency decreased under both treatments, while the transpiration rates and stomatal conductance increased. The results suggested that to some extent increased UV-B radiation was beneficial to the growth of L. cylindrica and T. kirilowii, but detrimental to D. opposita.

Photosynthesis, fluorescence, shoot biomass and seed weight responses of three cowpea ( Vigna unguiculata (L.) Walp.) cultivars with contrasting sensitivity to UV-B radiation

Current and projected increases in ultraviolet-B (UV-B) radiation (280–320 nm) may alter crop production. An experiment was conducted to study the influence of UV-B radiation on photosynthetic CO 2 assimilation, photosystem II (PSII) photochemistry, pigments, UV-B absorbing compounds, vegetative and reproductive growth responses of three cowpea cultivars, California Blackeye (CB)-5, CB-27, and Mississippi Pinkeye (MPE). Cowpea cultivars were subjected to four levels of biologically effective UV-B radiation of 0 (control), 5, 10 and 15 kJ m −2 d −1 from 8 days after emergence (DAE) to maturity of the crop in sunlit, controlled environment chambers. Increase in UV-B radiation caused a decrease in maximum light-saturated photosynthesis ( A max) in all the three cultivars, but the magnitude of decrease varied, 12% in MPE, 37% in CB-27, and 43% in CB-5 at 15 kJ of UV-B. The lower damaging effect of UV-B on A max in MPE was supported by a smaller decrease in maximum rate of Rubisco activity ( V cmax) coupled with higher levels of light-saturated rate of electron transport ( J max) compared to other sensitive cultivars, CB-5 and CB-27. The tolerance nature of MPE was further evidenced by less or no effect of UV-B on photosynthetic electron transport rate (ETR), photochemical quenching ( q P), and quantum yield of PSII photochemistry ( Φ PSII) compared to CB-5 and CB-27 across the UV-B treatments. Further, maximal electron transport rates (ETR max) estimated at saturated light substantially decreased with increase in UV-B in CB-5 and CB-27, while there was no or less influence on MPE. All cultivars showed linear relationship between Φ PSII and quantum yield of CO 2 fixation ( Φ C O 2 ) derived from light–response curves and internal-CO 2-response curves of chlorophyll a (Chl a) fluorescence. MPE maintained significantly higher concentration of UV-B absorbing compounds compared to the CB-5 and CB-27 across UV-B levels. Plants grown at elevated UV-B radiation produced significantly lower plant and seed dry weights in both the sensitive cultivars (CB-5 and CB-27) while the effect on MPE was minimal. This study revealed that the current and projected UV-B radiation could significantly decrease the growth and yield of sensitive cowpea cultivars, possibly caused by reduction in the photosynthetic efficiency of plants. In general, MPE showed more tolerance to UV-B radiation based on most of the parameters studied as compared to the CB-5 and CB-27.

Growth and physiological responses of an invasive alien species, Silene noctiflora, during two developmental stages to four levels of ultraviolet-B radiation

Few studies have considered the effects of ultraviolet-B (UVB) radiation during different developmental stages of plants, especially on invasive alien species. We studied growth and physiological responses of night-flowering catchfly (Silene noctiflora) to UVB radiation during 2 developmental stages. Silene noctiflora plants were grown under biologically effective UVB (UVBBE) radiation of 0, 4, 8, and 16 kJ·m−2·d−1 in controlled-environment growth chambers. Growth and physiological parameters of plants were measured during vegetative and reproductive stages. In general, enhanced UVB radiation reduced stem height and diameter, leaf area, and total dry matter. It also decreased leaf weight ratio, leaf area ratio, stomatal number, net CO2 assimilation, water use efficiency, and chlorophyll concentration but increased specific leaf weight, epidermal cell size, transpiration, UV-absorbing compounds, and epicuticular wax. Plants were taller and had higher chlorophyll, UV-absorbing compounds, and wax but lower ethylene evolution in the reproductive stage than in the vegetative stage. Overall, S. noctiflora plants were damaged by a four-fold increase of UVB radiation, as was apparent from reduced total seed yield. They acclimated under ambient UVB and a two-fold increase of UVB in their reproductive stage. These results mean that this plant may remain an invasive species under increased UVB radiation.

Larval amphibians seek warm temperatures and do not avoid harmful UVB radiation

Habitat use by animals often reflects the balance between conflicting demands such as foraging and avoiding predation. Environmental stressors such as temperature can also affect habitat use in many organisms, particularly in ectothermic animals. For example, warm, shallow thermal regimes in ponds can optimize growth and developmental rate of amphibian larvae but may also expose larvae to potentially harmful levels of ultraviolet B (UVB) radiation. Thus, optimally, amphibians seeking sunlight for thermoregulation must balance this behavior while limiting their exposure to harmful UVB radiation. We conducted a series of laboratory and field experiments to test the hypothesis that larval amphibians avoid UVB by selecting microhabitats with lower exposure to UVB. We then quantified habitat use of the larvae of 4 amphibian species using field transects in 3 ponds with different UVB transmission. Tadpoles did not avoid UVB radiation in laboratory or field experiments and preferred warmer temperatures in laboratory thermal gradients regardless of UVB exposure. The majority of anuran larvae were observed in water less than 10‐15 cm deep in field surveys, whereas salamander larvae were most often observed in deeper, cooler water. The similarity in habitat use across different sites and the lack of evidence of UVB avoidance in choice tests suggest that larval anuran amphibians may be exposed to harmful levels of UVB radiation due to habitat choice behaviors that have been established over evolutionary time. Levels of UVB radiation at the earth’s surface have recently increased due to stratospheric ozone depletion. Thus, long-term selection pressures such as thermoregulation may override the relatively recent selection pressure of increased UVB radiation. Key words: Ambystoma macrodactylum, Bufo boreas, ephemeral pond, habitat use, Pseudacris regilla, Rana cascadae, selection pressure, thermoregulation, ultraviolet B radiation, UVB avoidance. [Behav Ecol]

UV-B effects on the nutritional chemistry of plants and the responses of a mammalian herbivore

Stratospheric ozone depletion has caused ground-level ultraviolet-B (UV-B) radiation to rise in temperate latitudes of both hemispheres. Because the effects of enhanced UV-B radiation on the nutrition of food consumed by mammalian herbivores are unknown, we measured nutritional and chemical constituents of 18 forages and related changes to in vitro dry matter digestibility. We also measured intake and in vivo digestibility of Pacific willow (Salix lasiandra) and alfalfa (Medicago sativa L.) by blue duikers (Cephalophus monticola). Forages were irradiated for 3 months with ambient (1x) or supplemental (1.6 x) UV-B radiation representing a 15% ozone depletion for Pullman, Washington, USA. Enhanced UV-B radiation had minimal and inconsistent effects on the nutritional content, in vitro dry matter digestibility, and protein-binding capacity of forages. However, flavonoid compounds increased in seven of the 13 forbs and woody dicots that were evaluated. Flavonoids were found to decrease only in yarrow (Achillea millefolium). When offered simultaneously, blue duikers preferred 1x and 1.6 x UV-B irradiated plants of alfalfa equally, but ate 26% less willow grown under 1.6 x UV-B radiation. However, when fed to duikers in separate feeding experiments, total dry matter intake and in vivo digestibility of dry matter, fiber, protein, and apparent energy did not differ between alfalfa and willow grown under 1x and 1.6 x UV-B radiation. We conclude that expected increases in UV-B radiation from ozone depletion would have minimal effects on intake and digestion of ruminant herbivores.

Effects of UV‐B radiation on seed yield of Glycine max and an assessment of F1 generation progeny for carryover effects

Glycine max (L.) Merr plants were grown outdoors in potted sand exposed to elevated ultraviolet-B (UV-B) radiation provided by filtered fluorescent lamps to determine the effects of UV-B on seed yield and UV-B-induced carryover effects in the F1 generation. Increased UV-B radiation had no detectable effects on reproductive parameters except for a reduction on seed number per plant and an increase in the number of unseeded pods per plant and dry weight of unseeded pods per plant in the field supplemental UV-B experiment. Studies on carryover effects in the greenhouse progeny growth trial also showed no effect of parental treatment with UV-B on biomass production, and most symbiotic-N traits and plant metabolite measured. However, the concentrations of N in nodules and starch in roots were significantly increased in the F1 generation progeny from elevated UV-B radiation relative to their F1 counterparts from ambient radiation. Assessing the effects of seed size on plant growth and symbiotic function in the F1 progeny showed that total biomass, dry matter yield of individual organs (leaves, stems, roots and nodules), total plant N and fixed-N rose with increasing seed size. Seed concentration of flavonoids was also enhanced with increasing seed size. These findings suggest that subtle changes did occur in the F1 generation progeny of parental plants exposed to elevated UV-B with potential to accumulate with further exposure to elevated UV-B radiation.