Solar UV‐B radiation and ethylene play a key role in modulating effective defenses against Anticarsia gemmatalis larvae in field‐grown soybean

Solar UV‐B radiation has been reported to enhance plant defenses against herbivore insects in many species. However, the mechanism and traits involved in the UV‐B mediated increment of plant resistance are unknown in crops species, such as soybean. Here, we studied defense‐related responses in undamaged and Anticarsia gemmatalis larvae‐damaged leaves of two soybean cultivars grown under attenuated or full solar UV‐B radiation. We determined changes in jasmonates, ethylene (ET), salicylic acid, trypsin protease inhibitor activity, flavonoids, and mRNA expression of genes related with defenses. ET emission induced by Anticarsia gemmatalis damage was synergistically increased in plants grown under solar UV‐B radiation and was positively correlated with malonyl genistin concentration, trypsin proteinase inhibitor activity and expression of IFS2, and the pathogenesis protein PR2, while was negatively correlated with leaf consumption. The precursor of ET, aminocyclopropane‐carboxylic acid, applied exogenously to soybean was sufficient to strongly induce leaf isoflavonoids. Our results showed that in field‐grown soybean isoflavonoids were regulated by both herbivory and solar UV‐B inducible ET, whereas flavonols were regulated by solar UV‐B radiation only and not by herbivory or ET. Our study suggests that, although ET can modulate UV‐B‐mediated priming of inducible plant defenses, some plant defenses, such as isoflavonoids, are regulated by ET alone.     

Solar UV-B radiation affects below-ground parameters in a fen ecosystem in Tierra del Fuego, Argentina: implications of stratospheric ozone depletion

Stratospheric ozone depletion caused by the release of chlorofluorocarbons is most pronounced at high latitudes, especially in the Southern Hemisphere (including the so‐called ‘ozone hole’). The consequent increase in solar ultraviolet‐B radiation (UV‐B, 280–315 nm) reaching the earth's surface may cause a variety of alterations in terrestrial ecosystems. Most effects might be expected to occur above‐ground since sunlight does not penetrate effectively below‐ground. Here, we demonstrate that solar UV‐B radiation in a fen in Tierra del Fuego (Argentina), where the ozone hole passes overhead several times during the Austral spring, is causing large changes of below‐ground processes of this ecosystem. During the third and fourth year of a manipulative field experiment, we investigated root systems in these plots and found that when the ambient solar UV‐B radiation was substantially reduced, there was a 30% increase in summer root length production and as much as a threefold decrease in already low symbiotic mycorrhizal colonization frequency of the roots compared with plots receiving near‐ambient solar UV‐B. There was also an apparent shift toward older age classes of roots under reduced solar UV‐B. Such large changes in root system behaviour may have decided effects on competition and other ecological interactions in this ecosystem.     

UV‐B impairs growth and gas exchange in grapevines grown in high altitude

We previously demonstrated that solar ultraviolet‐B (UV‐B) radiation levels in high altitude vineyards improve berry quality in Vitis vinifera cv. Malbec, but also reduce berry size and yield, possibly as a consequence of increased oxidative damage and growth reductions (lower photosynthesis). The defense mechanisms toward UV‐B signal and/or evoked damage promote production of antioxidant secondary metabolites instead of primary metabolites. Purportedly, the UV‐B effects will depend on tissues developmental stage and interplay with other environmental conditions, especially stressful situations. In this work, grapevines were exposed to high solar UV‐B (+UV‐B) and reduced (by filtering) UV‐B (?UV‐B) treatments during three consecutive seasons, and the effects of UV‐B, developmental stages and seasons on the physiology were studied, i.e. growth, tissues morphology, photosynthesis, photoprotective pigments, proline content and antioxidant capacity of leaves. The +UV‐B reduced photosynthesis and stomatal conductance, mainly through limitation in gas exchange, reducing plant's leaf area, net carbon fixation and growth. The +UV‐B augmented leaf thickness, and also the amounts of photoprotective pigments and proline, thereby increasing the antioxidant capacity of leaves. The defense mechanisms triggered by + UV‐B reduced lipid peroxidation, but they were insufficient to protect the photosynthetic pigments per leaf dry weight basis. The +UV‐B effects depend on tissues developmental stage and interplay with other environmental conditions such as total radiation and air temperatures.     

Solar UV-B decreases decomposition in herbaceous plant litter in Tierra del Fuego, Argentina: potential role of an altered decomposer community

Tierra del Fuego, Argentina (55°S), receives increased solar ultraviolet‐B radiation (UV‐B) as a result of Antarctic stratospheric ozone depletion. We conducted a field study to examine direct and indirect effects of solar UV‐B radiation on decomposition of Gunnera magellanica, a native perennial herb, and on the native community of decomposer organisms. In general, indirect effects of UV‐B mostly occur due to changes in the chemical composition of litter, whereas direct effects during decomposition result from changes in decomposer organisms and/or differences in the photochemical breakdown of litter. We designed a full‐factorial experiment using senescent leaves that had received either near‐ambient or attenuated UV‐B during growth. The leaves were distributed in litterbags and allowed to decompose under near‐ambient or reduced solar UV‐B during the growing season. We evaluated initial litter quality, mass loss, and nutrient release of decomposing litter, and microbial colonization of both initial litter and decomposed litter. We found that litter that decomposed under near‐ambient UV‐B had significantly less mass loss than litter that decomposed under reduced UV‐B. The UV‐B conditions received by plants during growth, which did not affect mass loss and nutrient composition of litter, affected fungal species composition but in different ways throughout the decomposition period. Before the decomposition trial, Beauveria bassiana and Penicillium frequentans were higher under reduced UV‐B, whereas Cladosporium herbarum and pigmented bacteria were more common under the near‐ambient compared to the reduced UV‐B treatment. After the decomposition period, leaves that had grown under reduced UV‐B showed higher frequency of Penicillium thomii and lower frequency of Trichoderma polysporum than leaves that had grown under near‐ambient conditions. The UV‐B condition received during decomposition also affected fungal colonization, with Penicillium chrysogenum being more frequent in leaves that had decomposed under reduced UV‐B, while the other species were not affected. Our results demonstrate that, in this ecosystem, the effects of UV‐B radiation on decomposition apparently occurred mostly through changes in the fungal community, while changes in photochemical breakdown appeared to be less important.     

Insect perception of ambient ultraviolet-B radiation

Solar ultraviolet‐B radiation (UV‐B, 290–315 nm) has a strong influence on the interactions between plants and animal consumers. Field studies in various ecosystems have shown that the intensity of insect herbivory increases when the UV‐B spectral band of solar radiation is experimentally attenuated using filters. This effect of UV‐B on insect herbivory has been attributed to UV‐B‐induced changes in the characteristics of plant tissues, and to direct damaging effects of UV‐B photons on the animals. We tested for effects of UV‐B radiation on insect behaviour using field experiments with the thrips Caliothrips phaseoli. When placed in a ‘choice’ tunnel under natural daylight, these insects showed a clear preference for low‐UV‐B environments, and this preference could not be accounted for by differences between environments in total irradiance. These results provide the first evidence of ambient UV‐B photoperception in an insect, challenging the idea that animals are unable to detect variations in the narrow UV‐B component of solar radiation.     

Metabolite specific effects of solar UV-A and UV-B on alder and birch leaf phenolics

We measured the concentrations of ultraviolet (UV)‐absorbing phenolics varying in response to exclusion of either solar UV‐B or both solar UV‐A and UV‐B radiations in leaves of grey alder (Alnus incana) and white birch (Betula pubescens) trees under field conditions. In alder leaves 20 and in birch leaves 13 different phenolic metabolites were identified. The response to UV exclusion varied between and within groups of phenolics in both tree species. The changes in concentration for some metabolites suggest effects of only UV‐A or UV‐B, which band being effective depending on the metabolite. For some other metabolites, the results indicate that UV‐A and UV‐B affect concentrations in the same direction, while for a few compounds there was evidence suggesting opposite effects of UV‐A and UV‐B radiation. Finally, the concentration of some phenolics did not significantly respond to solar UV. We observed only minor effects on the summed concentration of all determined phenolic metabolites in alder and birch leaves, thus indicating that measuring only total phenolics concentration may not reveal the effects of radiation. Here, we show that the appropriate biological spectral weighting functions for plant‐protective responses against solar UV radiation extend in most cases – but not always – into the UV‐A region and more importantly that accumulation of different phenolic metabolites follows different action spectra. This demonstrates under field conditions that some of the implicit assumptions of earlier research simulating ozone depletion and studying the effects of UV radiation on plant secondary metabolites need to be reassessed.     

The effects of long-term elevated UV-B on the growth and phenolics of field-grown silver birch (Betula pendula)

The effects of long‐term elevated UV‐B radiation on silver birch (Betula pendula Roth) seedlings were studied over three growing seasons in an outdoor experiment in Finland started 64 days after germination. One group of seedlings was exposed to a constant 50% increase in UV‐B_CIE radiation, which corresponds to 20–25% of ozone depletion; another group received a small increase in UV‐A radiation and a third (the control group) received ambient solar radiation. Changes in growth appeared during the third growing season; the stems of the UV‐B treated seedlings were thinner and their height tended to be shorter compared with that of the control seedlings. In contrast, there were no UV‐B effects on biomass, bud burst, bud dry weights, leaf area, rust frequency index or chlorophyll concentrations in any of the summers. During the three‐year study, the flavonols were significantly increased by the elevated UV‐B only in the first growing season. The responses varied greatly among individual compounds; the most induced were the quercetin glycosides, while the main flavonols, myricetins, were reduced by the UV‐A control treatment. In the second summer phenolic acids, such as 3,4′‐dihydroxypropiophenone‐3‐glucoside, neochlorogenic acid and 5‐coumarylquinic acid, were increased by the UV‐B treatment. In the third year, the constitutive concentrations of phenolics were not affected by the UV‐B treatment.     

Impact of changes in natural ultraviolet radiation on pigment composition, physiological and morphological characteristics of the Antarctic moss, Grimmia antarctici

The impact of ambient ultraviolet (UV)‐B radiation on the endemic bryophyte, Grimmia antarctici, was studied over 14 months in East Antarctica. Over recent decades, Antarctic plants have been exposed to the largest relative increase in UV‐B exposure as a result of ozone depletion. We investigated the effect of reduced UV and visible radiation on the pigment concentrations, surface reflectance and physiological and morphological parameters of this moss. Plexiglass screens were used to provide both reduced UV levels (77%) and a 50% decrease in total radiation. The screen combinations were used to separate UV photoprotective from visible photoprotective strategies, because these bryophytes are growing in relatively high light environments compared with many mosses. G. antarctici was affected negatively by ambient levels of UV radiation. Chlorophyll content was significantly lower in plants grown under near‐ambient UV, while the relative proportions of photoprotective carotenoids, especially β‐carotene and zeaxanthin, increased. However, no evidence for the accumulation of UV‐B‐absorbing pigments in response to UV radiation was observed. Although photosynthetic rates were not affected, there was evidence of UV effects on morphology. Plants that were shaded showed fewer treatment responses and these were similar to the natural variation observed between moss growing on exposed microtopographical ridges and in more sheltered valleys within the turf. Given that other Antarctic bryophytes possess UV‐B‐absorbing pigments which should offer better protection under ambient UV‐B radiation, these findings suggest that G. antarctici may be disadvantaged in some settings under a climate with continuing high levels of springtime UV‐B radiation.     

Integration and scaling of UV‐B radiation effects on plants: from molecular interactions to whole plant responses

A process based model integrating the effects of UV‐B radiation to molecular level processes and their consequences to whole plant growth and development was developed from key parameters in the published literature. Model simulations showed that UV‐B radiation induced changes in plant metabolic and/or photosynthesis rates can result in plant growth inhibitions. The costs of effective epidermal UV‐B radiation absorptive compounds did not result in any significant changes in plant growth, but any associated metabolic costs effectively reduced the potential plant biomass. The model showed significant interactions between UV‐B radiation effects and temperature and any factor leading to inhibition of photosynthetic production or plant growth during the midday, but the effects were not cumulative for all factors. Vegetative growth were significantly delayed in species that do not exhibit reproductive cycles during a growing season, but vegetative growth and reproductive yield in species completing their life cycle in one growing season did not appear to be delayed more than 2–5 days, probably within the natural variability of the life cycles for many species. This is the first model to integrate the effects of increased UV‐B radiation through molecular level processes and their consequences to whole plant growth and development.     

Seasonal fluctuations in leaf phenolic composition under UV manipulations reflect contrasting strategies of alder and birch trees

Seasonal variation in leaf phenolic composition may be important for acclimation of plants to seasonal changes in their biotic and abiotic environment. For a realistic assessment of how plants respond to solar UV‐B (280–315 nm) and UV‐A (315–400 nm) radiation, seasonal variation in both environment and plant responses needs to be taken into account. This also has implications for studies concerning stratospheric ozone depletion and resulting increased UV‐B radiation, as other environmental variables and/or plant phenology could interact with UV radiation. To elucidate this, we established a field experiment using plastic films attenuating different parts of the solar UV spectrum. The concentration of individual phenolic compounds was measured during one growing season in leaves of grey alder (Alnus incana) and white birch (Betula pubescens) trees. Our results showed changes in concentration of, e.g. hydrolyzable tannins in birch that suggest an effect of UV‐A alone and e.g. chlorogenic acids in alder indicate a quadratic effect of UV‐B irradiance and both linear and quadratic effect for UV‐A in second‐degree polynomial fits. Further, there was interaction between treatment and sampling time for some individual metabolites; hence, the UV response varied during the season. In addition to the UV effects, three temporal patterns emerged in the concentrations of particular groups of phenolics. Possible implications for both sampling methods and timing are discussed. Moreover, our results highlight differences in responses of the two tree species, which are taken to indicate differences in their ecological niche differentiation.     

Functional acclimation to solar UV-B radiation in Gunnera magellanica, a native plant species of southernmost Patagonia

The ecosystems of Tierra del Fuego (in southern Patagonia, Argentina) are seasonally exposed to elevated levels of ultraviolet‐B radiation (UV‐B: 280–315 nm), due to the passage of the ‘ozone hole’ over this region. In the experiments reported in this article the effects of solar UV‐B and UV‐A (315–400 nm) on two UV‐B defence‐related processes: the accumulation of protective UV‐absorbing compounds and DNA repair, were tested. It was found that the accumulation of UV‐absorbing sunscreens in Gunnera magellanica leaves was not affected by plant exposure to ambient UV radiation. Photorepair was the predominant mechanism of cyclobutane‐pyrimidine dimer (CPD) removal in G. magellanica. Plants exposed to solar UV had higher CPD repair capacity under optimal conditions of temperature (25 °C) than plants grown under attenuated UV. There was no measurable repair at 8 °C. The rates of CPD repair in G. magellanica plants were modest in comparison with other species and, under equivalent conditions, were about 50% lower than the repair rates of Arabidopsis thaliana (Ler ecotype). Collectively our results suggest that the susceptibility of G. magellanica plants to current ambient levels of solar UV‐B in southern Patagonia may be related to a low DNA repair capacity.     

Potential impact of climate change on selected agricultural crops in north-eastern Austria

The vulnerability and adaptation of major agricultural crops to various soils in north‐eastern Austria under a changing climate were investigated. The CERES crop model for winter wheat and the CROPGRO model for soybean were validated for the agrometeorological conditions in the selected region. The simulated winter wheat and soybean yields in most cases agreed with the measured data. Several incremental and transient global circulation model (GCM) climate change scenarios were created and used in the study. In these scenarios, annual temperatures in the selected region are expected to rise between 0.9 and 4.8 °C from the 2020s to the 2080s. The results show that warming will decrease the crop‐growing duration of the selected crops. For winter wheat, a gradual increase in air temperature resulted in a yield decrease. Incremental warming, especially in combination with an increase in precipitation, leads to higher soybean yield. A drier climate will reduce soybean yield, especially on soils with low water storage capacity. All transient GCM climate change scenarios for the 21st century, including the adjustment for only air temperature, precipitation and solar radiation, projected reductions of winter wheat yield. However, when the direct effect of increased levels of CO₂ concentration was assumed, all GCM climate change scenarios projected an increase in winter wheat yield in the region. The increase in simulated soybean yield for the 21st century was primarily because of the positive impact of warming and especially of the beneficial influence of the direct CO₂ effect. Changes in climate variability were found to affect winter wheat and soybean yield in various ways. Results from the adaptation assessments suggest that changes in sowing date, winter wheat and soybean cultivar selection could significantly affect crop production in the 21st century.     

Ambient ultraviolet radiation in the Arctic reduces root biomass and alters microbial community composition but has no effects on microbial biomass

We assessed the effects of ambient solar ultraviolet (UV) radiation on below‐ground parameters in an arctic heath in north‐eastern Greenland. We hypothesized that the current UV fluxes would reduce root biomass and mycorrhizal colonization and that these changes would lead to lower soil microbial biomass and altered microbial community composition. These hypotheses were tested on cored soil samples from a UV reduction experiment with three filter treatments (Mylar, 60% UV‐B reduction; Lexan, up to 90% UV‐B reduction+UV‐A reduction; UV transparent Teflon, filter control) and an open control treatment in two study sites after 3 years' manipulation. Reduction of both UV‐A and UV‐B radiation caused over 30% increase in the root biomass of Vaccinium uliginosum, which was the dominant plant species. UV reduction had contrasting effects on ericoid mycorrhizal colonization of V. uliginosum roots in the two sites, while it had no clear effects on fungal (ergosterol) or microbial biomass (measured both with fumigation–extraction and quantitative lipid biomarker analysis) in soil. However, principal component analysis of lipid biomarkers (phospholipid and glycolipid fatty acid profiles) showed that microbial community composition was altered by UV reduction. Although the UV responses were slight considering the large dose difference between the treatments (from near‐ambient to up to 90% UV‐B reduction), we cannot rule out the possibility that the recovery of ozone layer would change the below‐ground functioning of arctic ecosystems.     

紫外线-B辐射与3种植物幼苗的光合作用——光合作用对紫外线-B敏感性的比较

紫外线 - B辐射降低豌豆、大豆和黄瓜 3种植物幼苗的净光合作用速率 ( Pn)和表观量子效率 ( AQE) ,Pn和 AQE的减少幅度随紫外线 - B辐射时间的延长逐渐增大。 3种植物的光合作用对紫外线 - B辐射的敏感性依次为 :豌豆 >黄瓜 >大豆 ,光合作用光抑制的发生程度与光合作用对 UV- B辐射敏感性有内在联系。定量分析显示 ,光合作用光抑制的发生程度随UV- B辐射时间增加 ,是 UV- B辐射剂量的累积效应。     

Interaction of COP1 and UVR8 regulates UV‐B‐induced photomorphogenesis and stress acclimation in Arabidopsis

The ultraviolet‐B (UV‐B) portion of the solar radiation functions as an environmental signal for which plants have evolved specific and sensitive UV‐B perception systems. The UV‐B‐specific UV RESPONSE LOCUS 8 (UVR8) and the multifunctional E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) are key regulators of the UV‐B response. We show here that uvr8‐null mutants are deficient in UV‐B‐induced photomorphogenesis and hypersensitive to UV‐B stress, whereas overexpression of UVR8 results in enhanced UV‐B photomorphogenesis, acclimation and tolerance to UV‐B stress. By using sun simulators, we provide evidence at the physiological level that UV‐B acclimation mediated by the UV‐B‐specific photoregulatory pathway is indeed required for survival in sunlight. At the molecular level, we demonstrate that the wild type but not the mutant UVR8 and COP1 proteins directly interact in a UV‐B‐dependent, rapid manner in planta. These data collectively suggest that UV‐B‐specific interaction of COP1 and UVR8 in the nucleus is a very early step in signalling and responsible for the plant's coordinated response to UV‐B ensuring UV‐B acclimation and protection in the natural environment.     

Growth and physiological responses of cotton (Gossypium hirsutum L.) to elevated carbon dioxide and ultraviolet-B radiation under controlled environmental conditions

Better understanding of crop responses to projected changes in climate is an important requirement. An experiment was conducted in sunlit, controlled environment chambers known as soil–plant–atmosphere–research units to determine the interactive effects of atmospheric carbon dioxide concentration [CO₂] and ultraviolet‐B (UV‐B) radiation on cotton (Gossypium hirsutum L.) growth, development and leaf photosynthetic characteristics. Six treatments were used, comprising two levels of [CO₂] (360 and 720 µmol mol^?1) and three levels of 0 (control), 7.7 and 15.1 kJ m^?2 d^?1 biologically effective UV‐B radiations within each CO₂ level. Treatments were imposed for 66 d from emergence until 3 weeks after the first flower stage. Plants grown in elevated [CO₂] had greater leaf area and higher leaf photosynthesis, non‐structural carbohydrates, and total biomass than plants in ambient [CO₂]. Neither dry matter partitioning among plant organs nor pigment concentrations was affected by elevated [CO₂]. On the other hand, high UV‐B (15.1 kJ m^?2 d^?1) radiation treatment altered growth resulting in shorter stem and branch lengths and smaller leaf area. Shorter plants at high UV‐B radiation were related to internode lengths rather than the number of mainstem nodes. Fruit dry matter accumulation was most sensitive to UV‐B radiation due to fruit abscission. Even under 7.7 kJ m^?2 d^?1 of UV‐B radiation, fruit dry weight was significantly lower than the control although total biomass and leaf photosynthesis did not differ from the control. The UV‐B radiation of 15.1 kJ m^?2 d^?1 reduced both total (43%) and fruit (88%) dry weights due to smaller leaf area and lower leaf net photosynthesis. Elevated [CO₂] did not ameliorate the adverse effects of UV‐B radiation on cotton growth and physiology, particularly the boll retention under UV‐B stress.     

Differential response of radish plants to supplemental ultraviolet-B radiation under varying NPK levels: chlorophyll fluorescence, gas exchange and antioxidants

Current and projected increases in ultraviolet‐B (UV‐B; 280–315 nm) radiation may alter crop growth and yield by modifying the physiological and biochemical functions. This study was conducted to assess the possibility of alleviating the negative effects of supplemental UV‐B (sUV‐B; 7.2 kJ m^?2 day^?1; 280–315 nm) on radish (Raphanus sativus var Pusa Himani) by modifying soil nitrogen (N), phosphorus (P) and potassium (K) levels. The N, P and K treatments were recommended dose of N, P and K, 1.5 times recommended dose of N, P and K, 1.5 times recommended dose of N and 1.5 times recommended dose of K. Plants showed variations in their response to UV‐B radiation under varying soil NPK levels. The minimum damaging effects of sUV‐B on photosynthesis rate and stomatal conductance coupled with minimum reduction in chlorophyll content were recorded for plants grown at recommended dose of NPK. Flavonoids increased under sUV‐B except in plants grown at 1.5 times recommended dose of N. Lipid peroxidation (LPO) also increased in response to sUV‐B at all NPK levels with maximum at 1.5 times recommended dose of K and minimum at recommended dose of NPK. This study revealed that sUV‐B radiation negatively affected the radish plants by reducing the photosynthetic efficiency and increasing LPO. The plants grown at 1.5 times recommended dose of NPK/N/K could not enhance antioxidative potential to the extent as recorded at recommended dose of NPK and hence showed more sensitivity to sUV‐B.     

Functional significance and induction by solar radiation of ultraviolet-absorbing sunscreens in field-grown soybean crops

Colorless phenylpropanoid derivatives are known to protect plants from ultraviolet (UV) radiation, but their photoregulation and physiological roles under field conditions have not been investigated in detail. Here we describe a fast method to estimate the degree of UV penetration into photosynthetic tissue, which is based on chlorophyll fluorescence imaging. In Arabidopsis this technique clearly separated the UV-hypersensitive transparent testa (tt) tt5 and tt6 mutants from the wild type (WT) and tt3, tt4, and tt7 mutants. In field-grown soybean (Glycine max), we found significant differences in UV penetration among cultivars with different levels of leaf phenolics, and between plants grown under contrasting levels of solar UV-B. The reduction in UV penetration induced by ambient UV-B had direct implications for DNA integrity in the underlying leaf tissue; thus, the number of cyclobutane pyrimidine dimers caused by a short exposure to solar UV-B was much larger in leaves with high UV transmittance than in leaves pretreated with solar UV-B to increase the content phenylpropanoids. Most of the phenylpropanoid response to solar UV in field-grown soybeans was induced by the UV-B component (lambda 相似文献   

Testing for Effects of UV‐B Radiation on Anti‐Predator Behavior in Amphibians: A Critique and Some Suggestions

In a recent paper, Kats et al. (2000) reported three experiments intended to test for effects of UV‐B radiation (hereafter, UV‐B) on predator‐avoidance behaviors in three amphibian species. They introduced their study in the context of concern about increasing penetration of solar UV‐B to ground level, owing to loss of stratospheric ozone, and its possible effects on amphibian populations. Kats et al. concluded from their results: `ultraviolet exposure may have important sub‐lethal effects in amphibians that could adversely effect (sic) their fitness'. As Kats et al. cited field studies that apparently demonstrated lethal effects of ambient levels of UV‐B on amphibians, their conclusion that sub‐lethal effects may occur is not obviously contentious. Furthermore, their experiments appear to be based on accepted methods. Nevertheless, I contend that the conclusions drawn by Kats et al. are not justified by the results they reported. Here, I discuss some problems with their study and suggest some possible improvements for future studies.     

Photoinhibition by visible and ultraviolet radiation in the red macroalga Porphyra umbilicalis grown in the laboratory

Photosynthetic oxygen production and PAM fluorescence measurements were used to follow photoinhibition in the red macroalga Porphyra umbilicalis. Exposure to simulated solar radiation caused inhibition of the effective photosynthetic quantum yield from which the thalli partially recovered in the shade in subsequent hours. There were no significant differences between samples exposed to unfiltered radiation and those exposed to radiation from which increasing portions of UV radiation had been removed indicating that the thalli are well adapted to current levels of solar PAR and UV radiation. This notion was supported by the finding of high concentrations of UV screening pigments which were even enhanced by exposure to increased UV radiation. However, when exposed to (only) UV radiation about 50% higher than that encountered by the organisms in their natural habitat, the photosynthetic yield decreased slowly and did not show any recovery even when the degree of inhibition did not exceed 10%.