Search

This Assessment Update by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) considers the interactive effects of solar UV radiation, global warming, and other weathering factors on plastics. The Assessment illustrates the significance of solar UV radiation in decreasing the durability of plastic materials, degradation of plastic debris, formation of micro- and nanoplastic particles and accompanying leaching of potential toxic compounds. Micro- and nanoplastics have been found in all ecosystems, the atmosphere, and in humans. While the potential biological risks are not yet well-established, the widespread and increasing occurrence of plastic pollution is reason for continuing research and monitoring. Plastic debris persists after its intended life in soils, water bodies and the atmosphere as well as in living organisms. To counteract accumulation of plastics in the environment, the lifetime of novel plastics or plastic alternatives should better match the functional life of products, with eventual breakdown releasing harmless substances to the environment. [ABSTRACT FROM AUTHOR]

This article explores the relationship between solar UV radiation, climate change, and plastic pollution. It highlights the role of UV-driven weathering in the degradation of plastics and the formation of harmful micro- and nanoplastic particles. The article emphasizes the need for global assessments of plastic dispersal, persistence, and weathering to consider these linkages. It also discusses the impact of the Montreal Protocol on plastic degradation and the potential effects of UV radiation and climate change on plastic pollution in the future. The article concludes by calling for further research and the development of new plastics with durability matching the functional life of products. [Extracted from the article]

The eight papers in this issue of I Photochemical & Photobiological Sciences i are authored by members and co-authors of the Environmental Effects Assessment Panel (EEAP) of the Montreal Protocol under the United Nations Environment Programme. In that first Assessment, Martyn emphasised the importance of evaluating the ways in which biological systems and the environment were being affected by depletion of stratospheric ozone and associated enhanced UV-B (280-315 nm) radiation at the Earth's surface. These papers assess the linkages between stratospheric ozone depletion and UV radiation, and climate change, with respect to the effects on the environment and human health. [Extracted from the article]

The UVR8 photoreceptor in Arabidopsis thaliana is specific for ultraviolet-B (UV-B; 280–315 nm) radiation and its activation leads to a number of UV-B acclimation responses, including the accumulation of flavonoids. UVR8 participates in a signaling cascade involving COP1 and HY5 so that the absence of any of these components results in a reduction in the ability of a plant to accumulate flavonoids in response to UV; Cop1 mutants show high dropouts and hy5-ks50 hyh double mutants show very low levels of flavonoids. The predominant phenolics in Arabidopsis thaliana are sinapic acid derivatives as well as non-aclyated quercetin and kaempferol di- and triglycosides containing glucose and rhamnose as glycosylated sugar moieties. How this flavonoid profile in Arabidopsis thaliana is affected by UV radiation, how rapidly these changes occur in changing UV conditions, and which components of the UV-B signalling pathway are involved in rapid UV acclimatization reactions is poorly understood. In the present study, we examined these questions by characterizing the flavonoid profiles of Arabidopsis thaliana signalling mutants and wild types grown under different UV levels of constant UV-B+PAR ratios and then transferring a subset of plants to alternate UV conditions. Results indicate that flavonoid accumulation in Arabidopsis thaliana is triggered by UV and this response is amplified by higher levels of UV but not by all compounds to the same extent. The catechol structure in quercetin seems to be less important than the glycosylation pattern, e.g. having 2 rhamnose moieties in determining responsivity. At low UV+PAR intensities the introduction of UV leads to an initial tendency of increase of flavonoids in the wild types that was detected after 3 days. It took 7 days for these changes to be detected in plants grown under high UV+PAR intensities suggesting a priming of PAR. Thus, the flavonoid profile in Arabidopsis thaliana is altered over time following exposure to UV and PAR, but the functional significance of these changes is currently unclear. [ABSTRACT FROM AUTHOR]

Plants perceive ultraviolet-B (UV-B) radiation through the UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8), and initiate regulatory responses via associated signalling networks, gene expression and metabolic pathways. Various regulatory adaptations to UV-B radiation enable plants to harvest information about fluctuations in UV-B irradiance and spectral composition in natural environments, and to defend themselves against UV-B exposure. Given that UVR8 is present across plant organs and tissues, knowledge of the systemic signalling involved in its activation and function throughout the plant is important for understanding the context of specific responses. Fine-scale understanding of both UV-B irradiance and perception within tissues and cells requires improved application of knowledge about UV-attenuation in leaves and canopies, warranting greater consideration when designing experiments. In this context, reciprocal crosstalk among photoreceptor-induced pathways also needs to be considered, as this appears to produce particularly complex patterns of physiological and morphological response. Through crosstalk, plant responses to UV-B radiation go beyond simply UV-protection or amelioration of damage, but may give cross-protection over a suite of environmental stressors. Overall, there is emerging knowledge showing how information captured by UVR8 is used to regulate molecular and physiological processes, although understanding of upscaling to higher levels of organisation, i.e. organisms, canopies and communities remains poor. Achieving this will require further studies using model plant species beyond Arabidopsis, and that represent a broad range of functional types. More attention should also be given to plants in natural environments in all their complexity, as such studies are needed to acquire an improved understanding of the impact of climate change in the context of plant-UV responses. Furthermore, broadening the scope of experiments into the regulation of plant-UV responses will facilitate the application of UV radiation in commercial plant production. By considering the progress made in plant-UV research, this perspective highlights prescient topics in plant-UV photobiology where future research efforts can profitably be focussed. This perspective also emphasises burgeoning interdisciplinary links that will assist in understanding of UV-B effects across organisational scales and gaps in knowledge that need to be filled so as to achieve an integrated vision of plant responses to UV-radiation. [ABSTRACT FROM AUTHOR]

Exposure of plants and animals to ultraviolet-B radiation (UV-B; 280–315 nm) is modified by stratospheric ozone dynamics and climate change. Even though stabilisation and projected recovery of stratospheric ozone is expected to curtail future increases in UV-B radiation at the Earth's surface, on-going changes in climate are increasingly exposing plants and animals to novel combinations of UV-B radiation and other climate change factors (e.g., ultraviolet-A and visible radiation, water availability, temperature and elevated carbon dioxide). Climate change is also shifting vegetation cover, geographic ranges of species, and seasonal timing of development, which further modifies exposure to UV-B radiation. Since our last assessment, there has been increased understanding of the underlying mechanisms by which plants perceive UV-B radiation, eliciting changes in growth, development and tolerances of abiotic and biotic factors. However, major questions remain on how UV-B radiation is interacting with other climate change factors to modify the production and quality of crops, as well as important ecosystem processes such as plant and animal competition, pest–pathogen interactions, and the decomposition of dead plant matter (litter). In addition, stratospheric ozone depletion is directly contributing to climate change in the southern hemisphere, such that terrestrial ecosystems in this region are being exposed to altered patterns of precipitation, temperature and fire regimes as well as UV-B radiation. These ozone-driven changes in climate have been implicated in both increases and reductions in the growth, survival and reproduction of plants and animals in Antarctica, South America and New Zealand. In this assessment, we summarise advances in our knowledge of these and other linkages and effects, and identify uncertainties and knowledge gaps that limit our ability to fully evaluate the ecological consequences of these environmental changes on terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Dryland ecosystems cover nearly 45% of the Earth’s land area and account for large proportions of terrestrial net primary production and carbon pools. However, predicting rates of plant litter decomposition in these vast ecosystems has proven challenging due to their distinctly dry and often hot climate regimes, and potentially unique physical drivers of decomposition. In this study, we elucidated the role of photopriming, i.e. exposure of standing dead leaf litter to solar radiation prior to litter drop that would chemically change litter and enhance biotic decay of fallen litter. We exposed litter substrates to three different UV radiation treatments simulating three-months of UV radiation exposure in southern New Mexico: no light, UVA+UVB+Visible, and UVA+Visible. There were three litter types: mesquite leaflets (Prosopis glandulosa, litter with high nitrogen (N) concentration), filter paper (pure cellulose), and basswood (Tilia spp, high lignin concentration). We deployed the photoprimed litter in the field within a large scale precipitation manipulation experiment: ∼50% precipitation reduction, ∼150% precipitation addition, and ambient control. Our results revealed the importance of litter substrate, particularly N content, for overall decomposition in drylands, as neither filter paper nor basswood exhibited measurable mass loss over the course of the year-long study, while high N-containing mesquite litter exhibited potential mass loss. We saw no effect of photopriming on subsequent microbial decay. We did observe a precipitation effect on mesquite where the rate of decay was more rapid in ambient and precipitation addition treatments than in the drought treatment. Overall, we found that precipitation and N played a critical role in litter mass loss. In contrast, photopriming had no detected effects on mass loss over the course of our year-long study. These results underpin the importance of biotic-driven decomposition, even in the presence of photopriming, for understanding litter decomposition and biogeochemical cycles in drylands. [ABSTRACT FROM AUTHOR]

Presents a study which investigated low pressure radio frequency inductive discharges sustained in Xe/I[sub2] mixtures for production of ultraviolet radiation from XeI at 253nm. Overview of the kinetics of Xe/I[sub2] discharges; Description of the experiment; Experimental results for excited state emission and absorption in Xe/I[sub2] discharges; Conclusions.

Ongoing changes in Earth's climate are shifting the elevation ranges of many plant species with non-native species often experiencing greater expansion into higher elevations than native species. These climate change-induced shifts in distributions inevitably expose plants to novel biotic and abiotic environments, including altered solar ultraviolet (UV)-B (280-315 nm) radiation regimes. Do the greater migration potentials of non-native species into higher elevations imply that they have more effective UV-protective mechanisms than native species? In this study, we surveyed leaf epidermal UV-A transmittance (TUVA) in a diversity of plant species representing different growth forms to test whether native and non-native species growing above 2800 m elevation on Mauna Kea, Hawaii differed in their UV screening capabilities. We further compared the degree to which TUVA varied along an elevation gradient in the native shrub Vaccinium reticulatum and the introduced forb Verbascum thapsus to evaluate whether these species differed in their abilities to adjust their levels of UV screening in response to elevation changes in UV-B. For plants growing in the Mauna Kea alpine/upper subalpine, we found that adaxial TUVA, measured with a UVA-PAM fluorometer, varied significantly among species but did not differ between native (mean D 6.0%; n D 8) and non-native (mean D 5.8%; n D 11) species. When data were pooled across native and nonnative taxa, we also found no significant effect of growth form on TUVA, though woody plants (shrubs and trees) were represented solely by native species whereas herbaceous growth forms (grasses and forbs) were dominated by non-native species. Along an elevation gradient spanning 2600-3800 m, TUVA was variable (mean range D 6.0-11.2%) and strongly correlated with elevation and relative biologically effective UV-B in the exotic V. thapsus; however, TUVA was consistently low (3%) and did not vary with elevation in the native V. reticulatum. Results indicate that high levels of UV protection occur in both native and non-native species in this high UV-B tropical alpine environment, and that flexibility in UV screening is a mechanism employed by some, but not all species to cope with varying solar UV-B exposures along elevation gradients. [ABSTRACT FROM AUTHOR]

The accumulation of ultraviolet (UV)-absorbing compounds (flavonoids and related phenylpropanoids) in the epidermis of higher plants reduces the penetration of solar UV radiation to underlying tissues and is a primary mechanism of acclimation to changing UV conditions resulting from ozone depletion and climate change. Previously we reported that several herbaceous plant species were capable of rapid, diurnal adjustments in epidermal UV transmittance ( T), but how widespread this phenomenon is among plants has been unknown. In the present study, we tested the generality of this response by screening 37 species of various cultivated and wild plants growing in four locations spanning a gradient of ambient solar UV and climate (Hawaii, Utah, Idaho and Louisiana). Non-destructive measurements of adaxial T indicated that statistically significant midday decreases in T occurred in 49 % of the species tested, including both herbaceous and woody growth forms, and there was substantial interspecific variation in the magnitude of these changes. In general, plants in Louisiana exhibited larger diurnal changes in T than those in the other locations. Moreover, across all taxa, the magnitude of these changes was positively correlated with minimum daily air temperatures but not daily UV irradiances. Results indicate that diurnal changes in UV shielding are widespread among higher plants, vary both within and among species and tend to be greatest in herbaceous plants growing in warm environments. These findings suggest that plant species differ in their UV protection 'strategies' though the functional and ecological significance of this variation in UV sunscreen protection remains unclear at present. [ABSTRACT FROM AUTHOR]

Epidermal UV transmittance (TUV) and UV‐absorbing compounds were measured in sun and shade leaves of Populus tremuloides and Vicia faba exposed to contrasting light environments under field conditions to evaluate UV acclimation potentials and regulatory roles of photosynthetically active radiation (PAR) and UV in UV‐shielding. Within a natural canopy of P. tremuloides, TUV ranged from 4 to 98% and showed a strong nonlinear relationship with mid‐day horizontal fluxes of PAR [photon flux density (PFD) = 6–1830 µmol m−2 s−1]; similar patterns were found for V. faba leaves that developed under a comparable PFD range. A series of field transfer experiments using neutral‐density shade cloth and UV blocking/transmitting films indicated that PAR influenced TUV during leaf development to a greater degree than UV, and shade leaves of both species increased their UV‐shielding when exposed to full sun; however, this required the presence of UV, with both UV‐A and UV‐B required for full acclimation. TUV of sun leaves of both species was largely unresponsive to shade either with or without UV. In most, but not all cases, changes in TUV were associated with alterations in the concentration of whole‐leaf UV‐absorbing compounds. These results suggest that, (1) moderate‐to‐high levels of PAR alone during leaf development can induce substantial UV‐protection in field‐grown plants, (2) mature shade leaves have the potential to adjust their UV‐shielding which may reduce the detrimental effects of UV that could occur following sudden exposures to high light and (3) under field conditions, PAR and UV play different roles in regulating UV‐shielding during and after leaf development. [ABSTRACT FROM AUTHOR]

Studies were conducted on three herbaceous plant species growing in naturally high solar UV environments in the subalpine of Mauna Kea, Hawaii, USA, to determine if diurnal changes in epidermal UV transmittance (TUV) occur in these species, and to test whether manipulation of the solar radiation regime could alter these diurnal patterns. Additional field studies were conducted at Logan, Utah, USA, to determine if solar UV was causing diurnal TUV changes and to evaluate the relationship between diurnal changes in TUV and UV-absorbing pigments. Under clear skies, TUV, as measured with a UV-A-pulse amplitude modulation fluorometer for leaves of Verbascum thapsus and Oenothera stricta growing in native soils and Vicia faba growing in pots, was highest at predawn and sunset and lowest at midday. These patterns in TUV closely tracked diurnal changes in solar radiation and were the result of correlated changes in fluorescence induced by UV-A and blue radiation but not photochemical efficiency (Fv/Fm) or initial fluorescence yield (Fo). The magnitude of the midday reduction in TUV was greater for young leaves than for older leaves of Verbascum. Imposition of artificial shade eliminated the diurnal changes in TUV in Verbascum, but reduction in solar UV had no effect on diurnal TUV changes in Vicia. In Vicia, the diurnal changes in TUV occurred without detectable changes in the concentration of whole-leaf UV-absorbing compounds. Results suggest that plants actively control diurnal changes in UV shielding, and these changes occur in response to signals other than solar UV; however, the underlying mechanisms responsible for rapid changes in TUV remain unclear. [ABSTRACT FROM AUTHOR]

We examined the influence of short-term exposure of different UV wavebands on the fine-scale kinetics of hypocotyl growth of dim red light-grown cucumbers (Cucumis sativus L.) and other selected dicotyledonous seedlings to evaluate: (1) whether responses induced by UV-B radiation (280–320 nm) are qualitatively different from those induced by UV-A (320–400 nm) radiation, and (2) whether different wavebands within the UV-B elicit different responses. Responses to brief (30 min) irradiations with 3 different UV wavebands all included transient inhibition of elongation during irradiation followed by wavelength specific responses. Irradiations with proportionally greater short wavelength UV-B (37% of UV-B between 280 and 300 nm) induced inhibition of hypocotyl elongation within 20 min of onset of irradiation, while UV-B including only wavelengths longer than 290 nm (and only 8% of UV-B between 290 and 300 nm) induced inhibition of hypocotyl elongation with a lag of 1–2 h. The response to short wavelength UV-B was persistent for at least 24 h, while the response to long wavelength UV-B lasted only 2–3 h. The UV-A treatment induced reductions in elongation rates of approximately 6–9 h following exposure followed by a continued decline in rates for the following 15–18 h. Short wavelength UV-B also induced positive phototropic curvature in both cucumber and Arabidopsis seedlings, and this response was present in nph-1 mutant Arabidopsis seedlings defective in normal blue light phototropism. Reciprocity was not found for the response to short wavelength UV-B. The short wavelength and long wavelength UV-B responses differed in dose–response relationships and both short wavelength responses (phototropic curvature and elongation inhibition) increased sharply at wavelengths below 300 nm. These results indicate that different photosensory processes are involved in mediating growth and morphological responses to short wavelength UV-B (280–300 nm), long wavelength UV-B (essentially 300–320 nm) and UV-A. The existence of two separate types of hypocotyl inhibition responses to UV-B, with one that depends on the intensity of the light source, provides alternate interpretations to findings in other studies of UV-B induced photomorphogenesis and may explain inconsistencies between action spectra for inhibition of stem growth. [ABSTRACT FROM AUTHOR]

Ratios of chlorophyll fluorescence induced by ultraviolet (UV) and bluegreen (BG) radiation [F(UV)/F(BG)] were determined with a Xe-PAM fluorometer to test the utility of this technique as a means of non-intrusively assessing changes in the pigmentation and optical properties of leaves exposed to varying UV exposures under laboratory and field conditions. For plants of Vicia faba and Brassica campestris, grown under controlled-environmental conditions, F(UV-B)/F(BG) was negatively correlated with whole-leaf UV-B-absorbing pigment concentrations. Fluorescence ratios of V. faba were similar to, and positively correlated with (r2=0.77 [UV-B]; 0.85 [UV-A]), direct measurements of epidermal transmittance made with an integrating sphere. Leaves of 2 of 4 cultivars of field-grown Glycine max exposed to near-ambient solar UV-B at a mid-latitude site (Buenos Aires, Argentina, 34° S) showed significantly lower abaxial F(UV-B)/F(BG) values (i.e., lower UV-B epidermal transmittance) than those exposed to attenuated UV-B, but solar UV-B reduction had a minimal effect on F(UV-B)/F(BG) in plants growing at a high-latitude site (Tierra del Fuego, Argentina, 55° S). Similarly, the exotic Taraxacum officinale did not show significant changes in F(UV-B)/F(BG) when exposed to very high supplemental UV-B (biologically effective UV-B=14–15 kJ m-2 day-1) in the field in Tierra del Fuego, whereas a native species, Gunnera magellanica, showed significant increases in F(UV-B)/F(BG) relative to those receiving ambient UV-B. These anomalous fluorescence changes were associated with increases in BG-absorbing pigments (anthocyanins), but not UV-B-absorbing pigments. These results indicate that non-invasive estimates of epidermal transmittance of UV radiation using chlorophyll fluorescence can detect changes in pigmentation and leaf optical properties induced by UV-B radiation under both field and laboratory conditions. However, this technique may be of limited utility in cold environments where UV and low temperatures can stimulate the production of BG-absorbing pigments that interfere with these indirect measurements of UV-transmittance. [ABSTRACT FROM AUTHOR]

Broad-band UV-B radiation inhibited hypocotyl elongation in etiolated tomato (Lycopersicon esculentum Mill. cv. Alisa Craig) seedlings. This inhibition could be elicited by < 3 µmol m-2 s-1 of UV-B radiation provided against a background of white light (> 620 µmol m-2 s-1 between 320 and 800 nm), and was similar in wild-type and phytochrome-I-deficient aurea mutant seedlings. These observations suggest that the effect of UV-B radiation is not mediated by phytochrome. An activity spectrum obtained by delivering 1 µmol m-2 s-1 of monochromatic UV radiation against a white light background (63 µmol m-2 s-1) showed maximum effectiveness around 300 nm, which suggests that DNA or aromatic residues in proteins are not the chromophores mediating UV-B induced inhibition of elongation. Chemicals that affect the normal (photo)chemistry of flavins and possibly pterins (KI, NaN3 and phenylacetic acid) largely abolished the inhibitory effect of broad-band UV-B radiation when applied to the root zone before irradiation. KI was effective at concentrations < 10-4 M, which have been shown in vitro to be effective in quenching the triplet excited states of flavins but not fluorescence from pterine or singlet states of flavins. Elimination of blue light or reduction of UV-A, two sources of flavin excitation, promoted hypocotyl elongation, but did not affect the inhibition of elongation exerted by UV-B. KI applied after UV-B irradiation had no effect on the inhibition response. Taken together these findings suggest that the chromophore of the photoreceptor system involved in UV-B perception by tomato seedlings during de-etiolation may be a flavin. [ABSTRACT FROM AUTHOR]

UV-B radiation inhibits hypocotyl elongation in etiolated tomato (Lycopersicon esculentum Mill. cv. Alisa Craig) seedlings acting through a photoreceptor system with peak apparent effectiveness around 300 nm. In order to further characterize the response and gain insight into its potential ecological significance, the time-course of inhibition was measured and compared with the time-course of flavonoid accumulation in the same seedlings. When a background of strong (> 620 µmol m-2 s-1) white light (WL) was supplemented with low irradiance UV-B (∼ 3 µmol m-2 s-1), substantial (∼ 50%) inhibition of elongation occurred within 3 h of the light treatment. The magnitude of UV-B-induced elongation inhibition was similar in wild type (WT) and au-mutant seedlings, in spite of the large differences between genotypes in rate and temporal pattern of elongation. In comparison to the effect of UV-B on elongation, induction of flavonoid accumulation in WT and au seedlings undergoing de-etiolation was a much slower response. Several UV-absorbing compounds appeared to be specifically induced by light, and some of them accumulated faster under the WL + UV-B treatment than under WL alone. However, there was little or no detectable effect of WL on flavonoid levels until up to 3 h of treatment, and the specific UV-B effect was measurable only after 6 h of continuous treatment. Indeed, UV-B-screening properties of crude alcoholic extracts were not different between WL and WL + UV-B treatments until after 9 or 24 h. When the light treatments were applied to seedlings that were just breaking through the soil surface, UV-B was found to consistently retard seedling emergence. These results suggest that the rapid inhibition of elongation in de-etiolating seedlings is an evolved response to UV-B, which may serve to minimize seedling exposure to sunlight until protective pigmentation responses (triggered by WL and UV-B) have taken place in the seedlings' epidermis. [ABSTRACT FROM AUTHOR]

Hypocotyl elongation responses to ultraviolet-B (UV-B) radiation were investigated in glasshouse studies of de-etiolated seedlings of a long-hypocotyl mutant (lh) of cucumber (Cucumis sativus L.) deficient in stable phytochrome, its near isogenic wild type (WT), and a commercial cucumber hybrid (cv. Burpless). A single 6- or 8-h exposure to UV-B applied against a background of white light inhibited hypocotyl elongation rate by ca 50% in and WT seedlings. This effect was not accompanied by a reduction in cotyledon area expansion or dry matter accumulation. Plants recovered rapidly from inhibition and it was possible to stimulate hypocotyl elongation in plants exposed to UV-B by application of gibberellic acid. In all genotypes inhibition of elongation was mainly a consequence of UV-B perceived by the cotyledons; covering the apex and hypocotyl with a filter that excluded UV-B failed to prevent inhibition. These results indicate that reduced elongation does not result from assimilate limitation or direct damage to the apical meristem or elongating cells, and strongly suggest that it is a true response to UV-B. The fact that UV-B influences used were very low in relation to total visible light, and the similarity in the responses of lh and wild-type plants, are consistent with the hypothesis that UV-B acts through a specific photoreceptor. It is argued that, given the weak correlation between UV-B and visible-light levels in most natural conditions, the UV-B receptor may play an important sensory function providing information to the plant that cannot be derived from light signals perceived by phytochrome or blue/UV-A sensors. [ABSTRACT FROM AUTHOR]

Mixtures and monocultures of wheat (Triticum aestivum) and wild oat (Avena fatua), a common weedy competitor of wheat, were exposed to enhanced solar UV-B radiation simulating a 20% reduction in stratospheric ozone to assess the timing and seasonal development of the UV-B effects on light competition in these species. Results from two years of field study revealed that UV-B enhancement had no detectable effect on the magnitude or timing of seedling emergence in either species. End-of-season measurements showed significant UV-B inhibition of leaf insertion height in wild oat in mixture and monoculture in the second year (irrigated year) but not in the first year (drought year). Leaf insertion height of wheat was not affected by UV-B in either year. The UV-B treatment had no detectable effect on monoculture or total (combined species) mixture LAI but did significantly increase (5-7%) the fractional contribution of wheat to the mixture LAI after four weeks of growth in both years. In addition, the UV-B treatment had subtle effects on LAI height profiles with early season mixtures showing significant reductions in wild oat LAI in lower canopy layers in both years while mid-season Year 2 mixtures showed significant reductions in wild oat LAI in upper canopy layers. The changes in canopy structure were found to significantly increase (6-7%) the proportional simulated clear sky canopy photosynthesis and light interception of wheat in mixture. These findings, and others, indicate that the effects of UV-B enhancement on competition are realized very early in canopy development and provide additional support for the hypothesis that UV-B enhancement may shift the balance of competition between these species indirectly by altering competitive interactions for light. [ABSTRACT FROM AUTHOR]

As well as guiding pollinators to the centre of flowers, areas of the corolla that absorb UV radiation may help to protect floral reproductive parts from solar UV radiation that would otherwise be reflected onto them. In their recent article, 'Floral pigmentation has responded rapidly to global change in ozone and temperature', Koski et al. 1 compared herbarium specimens collected between 1941 and 2017 to investigate whether the size of the UV-absorbing area in the centre of flowers (called 'bullseyes', UV proportion, or UVP) has changed relative to the size of the flower over this period. The article, and a subsequent feature 2 , describe an increase in UVP of ∼ 2% per year across all taxa examined. However, the study's main conclusion that this trend can be partially related to changes in ozone and temperature does not withstand close examination. Robson et al. comment on a recent study suggesting that reductions in atmospheric ozone may have driven changes in floral pigmentation. [ABSTRACT FROM AUTHOR]