Interactions between willows and insect herbivores under enhanced 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.

Field crop responses to ultraviolet-B radiation: a review

Elevated UV-B radiation did not affect decomposition rates of needles of two coniferous species in subtropical China

In a greenhouse study, plants of three monocotyledonous and five dicotyledonous species, which occur in a Dutch dune grassland, were exposed to four levels of ultraviolet-B (UV-B) radiation. UV-B levels simulated up to 30% reduction of the stratospheric ozone column during summertime in The Netherlands. Six of the plant species studied in the greenhouse were also exposed to enhanced UV-B irradiance in an experimental field study. In the field experiment plants either received the ambient UV-B irradiance (control) or an enhanced UV-B level simulating 15–20% ozone depletion during summertime in The Netherlands. The purpose of both experiments was to determine the response of the plant species to UV-B radiation and to compare results obtained in the greenhouse with results of the field experiment. Large intraspecific differences in UV-B sensitivity were observed in the greenhouse study. Total dry matter accumulation of monocotyledons was increased, while dry matter accumulation of dicotyledons remained unaffected or decreased. The increase in biomass production of monocotyledons at elevated UV-B was not related to the rate of photosynthesis but to alterations in leaf orientation. In the greenhouse study, UV-B radiation also affected morphological characteristics. Shoot height or maximum leaf length of five out of eight species was reduced. In the field study only one species showed a significantly decreased maximum leaf length at enhanced UV-B. Possible reasons for this discrepancy are discussed. The absorbance of methanolic leaf extracts also differed between species. UV absorbance of field-grown plants was higher than greenhouse-grown plants. In the greenhouse study, the highest UV-B level increased UV-B absorbance of some species. In the field study however, this stimulation of UV absorbance was not observed. In general, results obtained in the greenhouse study were similar to results obtained in the field study. Difficulties in extrapolating results of UV-B experiments conducted in the greenhouse to the field situation are discussed.

Field experiments and laboratory tests have shown multiple effects of enhanced ultraviolet-B (UV-B) radiation on cotton growth, development, and yield. Adverse effects include development of chlorotic and necrotic patches on leaves, reductions in total leaf area, plant height, photosynthesis, and yield. However, little work has been carried out to incorporate these experimental results into a simulation model and to estimate the effects of UV-B radiation under field conditions with varied environments and management practices. This study incorporates experimental results of UV-B effects on cotton crop into a cotton simulation model, GOSSYM, which is being used widely in various applications. In this work, first modules were modified to incorporate the effects of UV-B radiation on canopy photosynthesis, leaf area expansion, and stem and branch elongation. Then, the modified model was used to test the validity of model assumptions and algorithms on independent experimental data sets. Finally, preliminary studies were performed to simulate the effects of UV-B radiation in the field conditions at Stoneville, Mississippi using 30-year (1964-1993) climate data. Simulation results agreed well with experimental measurements, proving the validation of the model. Our results suggest that cotton lint yield declined with increased UV-B radiation. The reductions were 20% when UV-B irradiance was 12 kJ m^-2 under irrigated conditions. Similar reductions in yield were predicted at lower UV-B radiation (11 kJ m^-2) under rain-fed conditions. The modified model will be useful to simulate the impacts of UV-B radiation on cotton growth and yield under current and future climatic conditions and to suggest management options to mitigate the adverse effects.

Human alterations to natural systems have resulted in a loss of biological diversity around the world. Amphibian population losses have been more severe than those of birds and mammals. Amphibian population declines are likely due to many factors including habitat loss, disease, contaminants, introduced species and ultraviolet-B (UVB) radiation. The effect of UVB, however, varies widely among species and can vary within populations of the same species or at different life-history stages. This variation has often led to opposing conclusions about how UVB affects amphibians. We used meta-analysis techniques to explore the overall effects of UVB radiation on survival in amphibians. We also used recently developed factorial meta-analytic techniques to quantify potential interactions between UVB radiation and other stressors on amphibians. Ultraviolet-B radiation reduced survival of amphibians by 1.9-fold compared with shielded controls. Larvae were more susceptible to damage from UVB radiation compared with embryos, and salamanders were more susceptible compared with frogs and toads. Furthermore, UVB radiation interacted synergistically with other environmental stressors and resulted in greater than additive effects on survival when 2 stressors were present. Our results suggest that UVB radiation is an important stressor in amphibians, particularly in light of potential synergisms between UVB and other stressors in amphibian habitats.

Response of maize ( Zea mays L.) nitrate reductase to UV-B radiation

This article provides an overview of existing literature on the ultraviolet-B (UV-B) radiation effects on algae and cyanobacteria. We report on the effects of UV-B radiation to the growth and development, biomass, sensitivity, photosynthetic pigments, UV-B absorbing compounds, photosynthesis, protein and DNA damage, enzyme activity, nitrogen fixation and assimilation of nitrogen, protective mechanisms of algae and cyanobacteria, the accommodation of algae and cyanobacteria to environmental stress, and the effects to ecology system. Many of the studies show the dramatic effects of UV-B radiation; but typically these studies were conducted under conditions with supplemental UV-B irradiance that was higher than would ever occur outside experimental conditions or natural condition. A few of the studies reviewed used experimental conditions and supplemental UV-B irradiance that approached realism. Enhanced UV-B generally decreased chlorophyll content, whereas it increased UV-B absorbing compounds in many algae. Decrease in photosynthesis, particularly at higher UV-B doses, was due to both direct (effect on photosystem) and indirect (decrease in pigments) effects. The decreases in chlorophyll pigments and photosynthesis resulted in lower biomass. However, algae and cyanobacteria have evolved various avoidance and repair mechanisms to protect themselves against the damaging effects of UV radiation to acclimate to enhanced UV-B radiation. The review points to areas where further studies on the relationships among nitrogenase, Rubisco, antioxidase activity, signal, antioxidants, and free radicals under enhanced UV-B are needed to quantify the effects of UV-B radiation on algae and cyanobacteria. These studies are needed in order to develop dose response functions that can facilitate development of dynamic simulation models for use in UV-B and other environmental impact assessments.

The effects of ultraviolet-B (UV-B) radiation on water relations, leaf development, and gas-exchange characteristics in pea (Pisum sativum L. cv Meteor) plants subjected to drought were investigated. Plants grown throughout their development under a high irradiance of UV-B radiation (0.63 W m-2) were compared with those grown without UV-B radiation, and after 12 d one-half of the plants were subjected to 24 d of drought that resulted in mild water stress. UV-B radiation resulted in a decrease of adaxial stomatal conductance by approximately 65%, increasing stomatal limitation of CO2 uptake by 10 to 15%. However, there was no loss of mesophyll light-saturated photosynthetic activity. Growth in UV-B radiation resulted in large reductions of leaf area and plant biomass, which were associated with a decline in leaf cell numbers and cell division. UV-B radiation also inhibited epidermal cell expansion of the exposed surface of leaves. There was an interaction between UV-B radiation and drought treatments: UV-B radiation both delayed and reduced the severity of drought stress through reductions in plant water-loss rates, stomatal conductance, and leaf area.

BackgroundThe different wavelengths of solar radiation incident on earth [herein: Photosynthetically Active Radiation (PAR) , Ultra Violet-A (UV-A) and Ultra Violet-B (UV-B)] and their spectral balance not only have an impact on plants’ growth, morphology and physiology, but also are important for the quality and quantity of plant secondary metabolites.Material and methodsIn an outdoor study we addressed the effects of PAR intensity and UV-A and UV-B on the growth, yield, phenolic and flavonoid content, antioxidant activity and essential oil composition of Pelargonium graveolens L’Hér. The experiment was performed with split plots in a randomized complete block design with three replications. During the growth, two PAR intensities (ambient PAR and reduced PAR) and four UV treatments (ambient UV, enhanced UV-A, enhanced UV-B and enhanced UVA + B) were applied.ResultsHigh PAR intensity decreased the length and width of leaf, the height of plant and fresh weight of aerial parts, and increased the dry weight of aerial parts. Enhanced UV-B irradiation was associated with reduced plant height, leaf expansion and fresh and dry weight of aerial parts. Interestingly, the negative effect of UV-B radiation on morphology and growth of plant was largely alleviated by high PAR intensity. The amount of total phenols and flavonoids, antioxidant activity and essential oil production of P. graveolens strongly increased with the increase of UV-B irradiation and PAR. On the other hand, UV-A radiation did not significantly influence total phenol and flavonoid content, antioxidant activity and essential oil composition. Moreover, the combination of high PAR intensity and UV-B led to further increases in total flavonoid content and antioxidant capacity. Both high PAR intensity and enhanced UV-B increased the percentage of geraniol in essential oil, leading to a slight reduction of citronellol/geraniol ratio which is a marker of quality for rose geranium essential oil.ConclusionsOverall, we conclude that UV-B irradiation was associated to reduction of plant growth and yield, while, the adverse effect of UV-B irradiation on the plant was mitigated by high PAR intensity. On the other hand, both high PAR and enhanced UV-B boosted the production of phenols, flavonoids and essential oil. Considering that the lower citronellol/geraniol ratio is the most important indicator for the economic value of rose geranium essential oil, reducing citronellol/geraniol ratio under enhanced UV-B radiation and/or high PAR is likely to be favorable.

Cucumber plants (<i>Cucumis sativus</i> L. cv. Jinchun No 3) grown in a greenhouse were treated with three different biologically effective ultraviolet-B (UV-B) radiation levels: 1.28 kJ. m^-2 (CK), 8.82kJ.m^-2 (T1) and 12.6 kJ. m^-2 (T2). Irradiances corresponded to 8% and 21% reduction in stratospheric ozone in Lanzhou. Plants at three-leaf stage were irradiated 7 h daily for 25 days. The growth, stomata, flavonoid and ABA content in cucumber leaves exposed to 3 levels of UV-B radiation were determined in this paper. The results indicated that, compared with the control after 25 days UV-B radiation, RI of cucumber under T1 treatment is -18.0% and RI under T2 treatment is -48% mostly because of the reduce of leave area and dry weight accompanying with the increase of SLW; the rate of stomata closure under the treatments of T1 and T2 on the 6th day was up to respectively 70% and 89%, and amounted to 90% and 100% on the 18th day, and the guard cells in some stomata apparatus became permanent pores and lost their function at the same time; with the duration of UV-B radiation, the rise of the absorbance to ultraviolet light (305nm) showed the content increase of flavonoid; Abscisic acid (ABA) was determined by means of ELISA which showed that under the T1 treatment, the content of ABA was up to maximum to 510% higher than that of the control on the 21st day, meanwhile, under the treatment of T2, it was the highest on the 18th day to 680% of the control, and then had a decrease tendency on 21st day. The result still indicated that ABA accumulation could be induced by enhanced UV-B the radiation. The bigger was the dose of radiation, the higher was the accumulation of ABA. When intensity of UV-B radiation went beyond the degree of endurance of cucumber plants, ABA content descended then. Cucumber plants resist enhanced UV-B radiation by means of improving the contents of ABA and flavonoid. The increase of ABA content in cucumber leaves could lead to the stomata closure. Therefore, the changes of ABA content and absorbance, the rate of stoma closure in cucumber leaves were the adaptive mechanism to enhanced UV-B radiation.

Leaf and canopy photosynthetic characteristics of cotton ( Gossypium hirsutum) under elevated CO 2 concentration and UV-B radiation

Ultraviolet B (UVB) irradiation of the skin causes immunosuppression which is relevant to the induction of skin cancer. The mechanism of this immunomodulation is unclear but various regulatory molecules have been implicated, including cis-urocanic acid (cis-UCA) and the cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin 10 (IL-10). Whether ultraviolet A (UVA) induces similar changes has not been investigated fully. We studied the effect of in vivo UVB and long-wave UVA (UVA1) exposure on the induction of TNF-alpha, IL-10 and cis-UCA in human skin. Volunteers were irradiated with three minimal erythema doses (MED) of UVB or UVA1. At different times after irradiation, suction blisters were raised from irradiated and from non-irradiated (control) skin. The TNF-alpha and IL-10 protein concentration, and the percentage of cis-UCA in the blister fluid, were then determined. UVB irradiation of human skin led to a rapid and significant increase in TNF-alpha concentration in suction-blister fluid, with maximal values 6 h after irradiation (n = 6, P < 0.05). In contrast, UVA1 irradiation led to a decrease in TNF-alpha concentration in the suction-blister fluid compared with non-irradiated skin, with the lowest values 6 h after irradiation (n = 6, P < 0.05). Both UVB and UVA1 exposure of the skin induced a slight increase in IL-10 concentration. However, the increase in IL-10 was only significant after UVB irradiation (UVB, n = 6, P < 0.05; UVA, n = 7, P < 0.1). As previously shown, both UVB and UVA1 result in the photo-isomerization of trans-UCA and an increased percentage of cis-UCA was found in the suction-blister fluid. Thus the results show differential effects of UVB and UVA1 irradiation on the induction of immunoregulatory molecules, which may help to explain the variation in immune responses after UVB and UVA1 exposure of human skin.

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

Ultraviolet-B (UV-B) exposure in the course of litter decomposition may have a direct effect on decomposition rates via changing states of photodegradation or decomposer constitution in litter while UV-B exposure during growth periods may alter chemical compositions and physical properties of plants. Consequently, these changes will indirectly affect subsequent litter decomposition processes in soil. Although studies are available on both the positive and negative effects (including no observable effects) of UV-B exposure on litter decomposition, a comprehensive analysis leading to an adequate understanding remains unresolved. Using data from 93 studies across six biomes, this introductory meta-analysis found that elevated UV-B directly increased litter decomposition rates by 7% and indirectly by 12% while attenuated UV-B directly decreased litter decomposition rates by 23% and indirectly increased litter decomposition rates by 7%. However, neither positive nor negative effects were statistically significant. Woody plant litter decomposition seemed more sensitive to UV-B than herbaceous plant litter except under conditions of indirect effects of elevated UV-B. Furthermore, levels of UV-B intensity significantly affected litter decomposition response to UV-B (P<0.05). UV-B effects on litter decomposition were to a large degree compounded by climatic factors (e.g., MAP and MAT) (P<0.05) and litter chemistry (e.g., lignin content) (P<0.01). Results suggest these factors likely have a bearing on masking the important role of UV-B on litter decomposition. No significant differences in UV-B effects on litter decomposition were found between study types (field experiment vs. laboratory incubation), litter forms (leaf vs. needle), and decay duration. Indirect effects of elevated UV-B on litter decomposition significantly increased with decay duration (P<0.001). Additionally, relatively small changes in UV-B exposure intensity (30%) had significant direct effects on litter decomposition (P<0.05). The intent of this meta-analysis was to improve our understanding of the overall effects of UV-B on litter decomposition.