Negative Effects Of Ultraviolet Radiation Research Articles

Impacts of UV radiation on Bacillus biocontrol agents and their resistance mechanisms.

Bacillus biocontrol agent(s) BCA(s) such as Bacillus cereus, Bacillus thuringiensis and Bacillus subtilis have been widely applied to control insects' pests of plants and pathogenic microbes, improve plant growth, and facilitate their resistance to environmental stresses. In the last decade, researchers have shown that, the application of Bacillus biocontrol agent(s) BCA(s) optimized agricultural production yield, and reduced disease risks in some crops. However, these bacteria encountered various abiotic stresses, among which ultraviolet (UV) radiation severely decrease their efficiency. Researchers have identified several strategies by which Bacillus biocontrol agents resist the negative effects of UV radiation, including transcriptional response, UV mutagenesis, biochemical and artificial means (addition of protective agents). These strategies are governed by distinct pathways, triggered by UV radiation. Herein, the impact of UV radiation on Bacillus biocontrol agent(s) BCA(s) and their mechanisms of resistance were discussed.

Effect of Feeding Kiwifruit (Actinidia deliciosa) Extract on Survival Rate and Reproductive Organ Morphology of Fruit Fly (Drosophila melanogaster Meigen, 1830) Ultraviolet Light Irradiation

UV (ultraviolet) radiation is one of the radiations that are naturally emitted by the sun. As the result of climate changes, the earth's ozone layer changes and the UV light radiation to the earth's surface increases. The negative effect of UV radiation is increase due to the production of ROS (Reactive Oxygen Species) or free radicals in the body. UV radiation protection can be done by increasing the intake of antioxidant-rich foods as free radical inhibitors. Actinidia deliciosa or kiwifruit is a antioxidants-rich fruit including vitamin C. This research was carried out with Drosophila melanogaster as a animal model because it is easy to breed in the laboratory, has a short life cycle, and produces large numbers of eggs. Drosophila melanogaster or fruit flies are the most commonly used of animal models in the biomedical and pharmacological fields. This study aims to determine the effect of UV radiation on fruit fly survival at the larval, pupa, and imago stages and the morphology changes of male and female reproductive organs, as well as to determine the effect of feeding kiwi fruit extract on survival rate and morphology changes of male and female reproductive organs of UV irradiated fruit fly. This research was conducted by providing UV exposure treatment and without UV radiation treatment to fruit flies for 2 hours on banana and kiwi feed medium. Data analysis was carried out with the One Way Anova test followed by the Duncan test. The results showed that UV radiation could affect the survival and morphology of the reproductive organs of fruit flies. The survival rate in the control treatment was 58%, PK treatment 81%, PPUV treatment 45%, and PKUV treatment 47%.

Photoprotection Knowledge and Photoprotective Behavior of University Students: A Cross-sectional Study in Indonesia

Objective: Awareness regarding the negative effects of ultraviolet radiation are commonly neglected in Asian countries. This study sought to evaluate the ultraviolet radiation knowledge and photoprotective behaviors of university students in Indonesia. Methods: This observational cross-sectional was conducted at Pelita Harapan University, Indonesia. Results: A total of 89 (45.4%) medical students and 107 (54.6%) nonmedical students participated in this study. Their mean age was 21.03 ± 2.03 years, and 46.4% of them had Fitzpatrick type III skin. Medical students as well as older students exhibited a higher level of knowledge regarding photoprotection (P ≤ 0.05). Factors related to good photoprotective behaviors were sex, older age, and average expenditure on skincare. Further analysis revealed that a high level of knowledge regarding photoprotection was related to acceptable photoprotective behaviors (P = 0.01; odds ratio = 1.97; 95% confidence interval = 1.13–3.54). Conclusions: Knowledge regarding sun-related damage and practice of photoprotective behaviors were low among the participants. The results indicate that formal education and academic subjects should incorporate the topic of sun-related damage and promote the practice of photoprotective behaviors early on to increase awareness among populations.

An in vitro study of fixed and essential oils claimed to have photoprotective properties

Today, the negative effects of ultraviolet radiation on the skin are well known, so we know we should use protection whenever we are exposed to the sun. Sun protection products, therefore, form part of an overall strategy against photo-induced cancers. However, over several years, controversies have led to consumer mistrust of certain sun protection products containing organic filters, said to be allergens, endocrine disrupters or even responsible for coral bleaching. Taking advantage of the dismay this has caused in some consumers, internet sites have promoted plant oils and essential oils as natural solar filters to replace pharmaceutical sun creams. Using an in vitro method, we studied 15 fixed oils, one oily macerate, one butter, eight essential oils, and an essential wax, chosen among the substances most commonly mentioned on the internet. For each substance, we determined the sun protection factor (SPF) and UVA protection factor (PF-UVA), the universal references for protection level in the ultraviolet range. We demonstrated that these fixed oils and essential oils, for which we found SPF and PF-UVA values of only around 1, are totally devoid of any photoprotective properties. So as to avoid potential users suffering serious consequences, therefore, they should not be considered as sunscreens.

ДОСЛІДЖЕННЯ ЕКРАНУЮЧИХ ВЛАСТИВОСТЕЙ ТЕКСТИЛЬНИХ МАТЕРІАЛІВ ЩОДО ДІЇ УЛЬТРАФІОЛЕТОВОГО ВИПРОМІНЮВАННЯ

Study the possibility of using textile materials for shielding against the negative effects of ultraviolet radiation. Methodology. Theoretical and experimental researchs are based on the basic principles of textile materials science. The UV shielding ability of textiles was assessed by the UV protection factor (UPF). The UV protection factor was evaluated on a UV-Vis spectrophotometer (Cary 50, Varian, Australia) in accordance with AS / NZ 4399: 1996 in the wavelength range 280-400 nm. According to AS / NZ 4399: 1996, textiles are classified according to the value of the UV protection factor (UPF) as those that provide "excellent UV protection", "very good UV protection", "good UV protection", "does not protect against UV radiation." Results. The main sources of UV radiation are analyzed and the features of the conditions of human exposure when working indoors and outside are considered. It has been established that the degree of human exposure depends on the intensity of UV radiation, and can be reduced by using protective equipment. Flexible textile screens can be one of the effective means of protection against UV radiation. The advantages of textile screens are the possibility of their modification and the ability to create shielding products of various shapes. The level of protective properties of textile screens depends on many factors, namely: the chemical nature of the polymer of textile materials, structural characteristics, modification by certain substances, color, moisture, etc. The results of the study of the coefficient of protection against ultraviolet radiation of textile materials, depending on their color are presented. Scientific novelty. It is proved that the optical properties are not only important for the evaluation of appearance of the textile and garment aesthetic perception, they can control the shielding properties of the textile to the action of UV radiation. It was found that dark saturated colors of textile fabrics, all other conditions being equal, provide shielding properties at the level of "very good protection" compared to light unsaturated colors (the UPF level varies from 10 to 35 with increasing color saturation). Practical value. The possibility of using textile materials for UV protection has been confirmed.

Effect of ultraviolet radiation on the skin

The beneficial effect of ultraviolet radiation on our skin manifests itself in the synthesis of vitamin D. However, the detrimental effect of this radiation is much more severe. A longer duration of the effect of this radiation speeds up photoaging of skin depending on its phonotype. Symptoms of burning accompanied by tiredness, headaches, changes in temperature, skin damage observed testify to the negative effect of ultra-violet radiation. The unsuitable acquisition of measures of protection with SPF (Sun Protection Factor) numbers and their seasonal application presuppose the formation of wrinkles. This issue remains relevant today as well, because the results of ultraviolet radiation are diagnosed ever more often. They testify to careless skin care. The slightest skin redness, swelling or brownness is reaction of the skin to harmful ultraviolet radiation. The aim of the investigation was to examine the effect of ultraviolet radiation on skin. The investigation was carried out in virtual space on the Internet website www.apklausa.lt in 2021 (2 months). A total of 209 respondents took part in the investigation. The results and conclusions of the investigation are as follows: due to the nature of work, about half of the respondents were exposed to ultraviolet radiation the whole day or 3–4 hours a day. One the third of the respondents used the solarium procedures once per week, provided themselves with measures of protection in shops; however, they did not set great store by the protective effect of SPF filters. One the sixth of the respondents used measures of protection when their skin suffered serious damage.

Phenolic Compounds in Prevention and Treatment of Skin Cancers: A Review.

Several clinical studies have shown that exposure of skin to solar ultraviolet (UV) radiation causes adverse effects, such as inflammation, oxidative stress and DNA damage. As a result, different skin disorders can arise, among which are skin cancer, including non-melanoma skin cancer (NMSC) and melanoma (MM). Phenolic compounds are plant-derived secondary metabolites with a well-known antioxidant activity, able to counteract the negative effects of UV radiation. In this review, we discuss the effects of some selected phenols on NMSC and MM, demonstrating that they can be useful in the prevention and in the treatment of these types of tumors. Moreover, we report the mechanisms by which these phenols carry out their antitumor action. In vitro and in vivo studies have highlighted that many phenols are capable of inducing photoprotection, apoptosis and autophagy. They can also reduce DNA methylation, tumorigenesis, tumor incidence and proliferation. Moreover, we describe some examples of plant extracts, whose anticancer activity appears to be better than that of single phenols. A great concordance of results emerged, despite the differences in experimental methods. Therefore, the knowledge compiled here could provide the basis for conducting some well-organized clinical trials to validate the chemopreventive and the therapeutic potential of some phenolic compounds in patients with NMSC and MM.

Increasing Temperature Counteracts the Negative Effect of UV Radiation on Growth and Photosynthetic Efficiency of Microcystis aeruginosa and Raphidiopsis raciborskii.

High temperature can promote cyanobacterial blooms, whereas ultraviolet radiation (UVR) can potentially depress cyanobacterial growth by damaging their photosynthetic apparatus. Although the damaging effect of UVR has been well documented, reports on the interactive effects of UV radiation exposure and warming on cyanobacteria remain scarce. To better understand the combined effects of temperature and UVR on cyanobacteria, two strains of nuisance species, Microcystis aeruginosa (MIRF) and Raphidiopsis raciborskii (formerly Cylindrospermopsis raciborskii, CYRF), were grown at 24°C and 28°C and were daily exposed to UVA+UVB (PAR+UVA+UVB) or only UVA (PAR+UVA) radiation. MIRF and CYRF growth rates were most affected by PAR+UVA+UVB treatment and to a lesser extent by the PAR+UVA treatment. Negative UVR effects on growth, Photosystem II (PSII) efficiency and photosynthesis were pronounced at 24°C when compared to that at 28°C. Our results showed a cumulative negative effect on PSII efficiency in MIRF, but not in CYRF. Hence, although higher temperature ameliorates UVR damage, interspecific differences may lead to deviating impacts on different species, and combined elevated temperature and UVR stress could influence species competition.

HPT Türevi UV Absorblayıcıların PET İplik ve Kumaşların UV Dayanımı Üzerine Etkilerinin İncelenmesi

Morötesi (ultraviyole, UV) ışımanın tüm polimerler gibi tekstil malzemelerinin performansları üzerinde de olumsuz etkileri bulunmaktadır. Bu etkiler, dış ortam uygulamaları için üretilmiş ürünlerde daha da önem kazanmaktadır. UV ışımanın olumsuz etkisini azaltarak ürünlerin daha uzun süre kullanımını sağlayabilmek amacıyla UV absorblayıcı katkı maddeleri kullanılmaktadır. Bu katkı maddeleri masterbatch yöntemiyle, üretim sırasında lif yapısına katılarak tekstil ürünlerinin UV dirençleri arttırılabilinir. Polimerlerin açık hava koşullarındaki performanslarını belirleyebilmek amacıyla yapılan testlere dış ortam şartlandırma testleri denilmektedir. Bu testler, gerçek dış ortam şartlarında yapılabileceği gibi laboratuvar koşullarında dış ortam şartlarını simüle eden cihazlarında da gerçekleştirilebilinir. Laboratuvar ortamında yapılan testler hızlandırılmış yapay dış ortam şartlandırma testleri olarak adlandırılır. Açık hava uygulamarı için poliakrilonitril liflerinden yapılmış tekstil ürünleri yaygın olarak kullanılmaktadır. Ancak bu liflerin tedariklerinde çeşitli zorluklarla karşılaşılması ve maliyetlerinin yüksek olması bu tür uygulamalar için polietilen tereftalat (PET) liflerine olan ilgiyi arttırmaktadır. Bu çalışmada hızlandırılmış yapay dış ortam şartlandırma testleri, katkısız PET (referans PET) ve hidroksifenil triazin (HPT) türevi ticari bir katkı malzemesi olan Tinuvin 1577 ED ile UV ışımaya karşı direnci arttırılmış PET (katkılı PET) iplik ve bu iplikler kullanılarak dokunmuş kumaşlara 1000 saat süre ile uygulanmıştır. Her 250 saatte bir numunelerin kopma mukavemeti, kopma uzaması ve renk değişimi özellikleri kayıt edilmiştir. Şartlandırma testlerinden önce yapılan çekme deneyleri katkı maddelerinin PET ipliklerin kopma mukavemetlerini azaltıp, kopma uzaması değerlerini arttırdığını, dolayısı ile mekanik özellikler üzerinde olumsuz bir etkisinin olduğunu göstermiştir. Ancak 1000 saatlik dış ortam şartlandırma testlerinin sonunda bu katkı maddelerinin UV ışımanın PET iplik ve kumaşların mekanik özellik ve renk değişimi üzerindeki olumsuz etkisini belirgin bir oranda azalttığı tespit edilmiştir.

Ultraviolet Radiation Exposure, Risk, and Protection in Military and Outdoor Athletes.

Overexposure to ultraviolet radiation (UVR) from the sun is associated with deleterious health effects including, but not limited to, increased risk of skin cancers. Military personnel and those who participate in outdoor exercise or sports represent two potential populations at elevated risk of negative health consequences of UVR exposure due to large amounts of time spent outdoors, often in harsh UVR environments. Despite exposure to high and/or frequent doses of UVR in recreational and tactical athletes, adequate sun-protection practices are often disregarded or not well understood by many within these at-risk populations, resulting in heightened risk of negative UVR effects. The focus of this review is to examine the available literature regarding UVR exposure, risk of adverse health effects of UVR exposure, and sun protection practices in outdoor exercisers, athletes, and military personnel.

The antagonistic effect of UV radiation on warming or nitrate enrichment depends on ecotypes of freshwater macroalgae (Charophytes).

Increases in ultraviolet radiation (UVR), a negative global change factor, affect aquatic primary producers. This effect is expected to be modulated by other global change factors, and to be different for populations adapted to different environments. A common garden experimental approach using freshwater green macroalgae, the cosmopolitan charophyte species Chara hispida and C.vulgaris, allowed us to test whether the beneficial increases in water temperature (T) and nitrate concentration (N) mitigate negative UVR effects. Also, whether these interactions would be not only species-specific but also according to the origin of the population; therefore, two populations of each species were used: one from a coastal wetland and the other from a mountain lake. Two factorial-design experiments were performed: (i) the presence and absence of UVR×lower and higher T×four populations, and (ii) the presence and absence of UVR×lower and higher N×four populations. Response variables were: growth, morphometry, UVR-protective compounds, photosynthetic pigments, and stoichiometric composition. There were consistent response patterns in the key variables that represent different organization levels. Our main results showed that both warming and, to a lesser extent, the increase in nutrients ameliorated the negative effects of UVR on the molecular processes involved in acclimation to UVR, and that such a mitigating effect depended on the different phenotypic plasticity of each species and each ecotype. The coastal populations, being from a more variable environment, were more resilient than the mountain populations, mainly because of changes in growth and morphology.

Epidemiological features of the skin cancer

Background: The relevance of the study of oncological pathology of the skin is due to the annual increase of morbidity rate of skin cancer and significantly high mortality rate among patients. The research of epidemiological features of skin cancer will identify risk groups and those who need primary medical care.The basis for the research of the epidemiological features of skin cancer among the contingent of SIS – State Institution of Science “Research and Practical Centre of Preventive and Clinical Medicine” of the State Administrative Department (SIS “RPC PCM” SAD) is personalized information on patients that's stored in the database of the SIS since 1996. For the retrospective epidemiological analysis were used data from 2005 to 2014. The obtained results were compared with corresponding figures among patients from Kyiv and Ukraine.Results: The morbidity rate of melanoma and NMCS (Non-melanoma cancers of the skin) is higher than the corresponding figures of the population of Kyiv and Ukraine, despite the decline in the incidence of melanoma in 2014 by 14 % compared to the year 2013. The mortality rate of patients with skin cancer, mainly due to patients with melanoma, among the contingent of SIS is also higher than the corresponding figures of the population of Kyiv and Ukraine. The majority of patients with skin cancer were men of the 2nd period of middle age and elderly age. The highest morbidity rate of skin cancer was registered in age groups of 65–74 years old and 75 years old and older regardless of gender. The recurrence and prolongation of oncological process were registered among patients with melanoma in 2.3 %, and among patients with NMCS– 1.1 % annually.Conclusions: The obtained results showed a significant prevalence of skin cancer among the contingent of SIS compared with the morbidity rate of melanoma among the population of Kyiv and Ukraine. The analysis of epidemiological characteristics show the need for raising awareness of primary care physicians of the earliest clinical manifestations of skin cancer, raising patients awareness of the negative effects of ultraviolet radiation and solariums, the need for protection against ultraviolet irradiation, the use of methods of self-examination, timely reference to a doctor

Solar PAR and UVR modify the community composition and photosynthetic activity of sea ice algae.

The effects of increased photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) on species diversity, biomass and photosynthetic activity were studied in fast ice algal communities. The experimental set-up consisted of nine 1.44 m(2) squares with three treatments: untreated with natural snow cover (UNT), snow-free (PAR + UVR) and snow-free ice covered with a UV screen (PAR). The total algal biomass, dominated by diatoms and dinoflagellates, increased in all treatments during the experiment. However, the smaller biomass growth in the top 10-cm layer of the PAR + UVR treatment compared with the PAR treatment indicated the negative effect of UVR. Scrippsiella complex (mainly Scrippsiella hangoei, Biecheleria baltica and Gymnodinium corollarium) showed UV sensitivity in the top 5-cm layer, whereas Heterocapsa arctica ssp. frigida and green algae showed sensitivity to both PAR and UVR. The photosynthetic activity was highest in the top 5-cm layer of the PAR treatment, where the biomass of the pennate diatom Nitzschia frigida increased, indicating the UV sensitivity of this species. This study shows that UVR is one of the controlling factors of algal communities in Baltic Sea ice, and that increased availability of PAR together with UVR exclusion can cause changes in algal biomass, photosynthetic activity and community composition.

Combined impact of ultraviolet radiation and increased nutrients supply: a test of the potential anthropogenic impacts on the benthic amphipod Amphitoe valida from Patagonian waters (Argentina)

Experiments were conducted during the Austral Summer of 2014 to determine the effects of increased nutrient input and ultraviolet radiation (UVR) on the food consumption rate (FCR) and food preference in the amphipod Amphitoe valida. We collected specimens from the Patagonian coast (Argentina), from beaches close (Barrancas Blancas; BB) and further away (Cangrejales; C) from the Chubut River, which constitutes the potential source of eutrophication. Organisms were exposed to different radiation regimes (full radiation vs. PAR only) and fed with different macroalgae diets (i.e., from different geographical location and with different quality in terms on nutrient content). Males collected from C showed food compensation, consuming more food under low-nutrient diets, while no compensation was observed in males from BB. Regardless of their origin, UVR decreased the FCR when males where fed on ambient nutrient diets, but not when males fed on high-quality diets indicating that in the former case, individuals were in worse physiological conditions to cope with UVR; food quality, however, significantly counteracted the deleterious effects of UVR on FCR. Females collected from the two beaches showed similar FCR under high-nutrient diet and had no food compensation when fed in low-nutrient diets. Females were more vulnerable to UVR, since their FCR were lower when exposed to UV radiation independent of the diet. Our results show that under anthropogenic eutrophication and high solar UVR levels an increase in the nutrient input could favor only males of A. valida, by reducing the negative effects of UVR on their FCR. Nevertheless, these nutrient inputs might cause additional problems like anoxia, as a result of an unusual macroalgal growth, thus affecting amphipod’s survival.

Dissolved organic carbon ameliorates the effects of UV radiation on a freshwater fish

Anthropogenic activities over the past several decades have depleted stratospheric ozone, resulting in a global increase in ultraviolet radiation (UVR). Much of the negative effects of UVR in aquatic systems is minimized by dissolved organic carbon (DOC) which is known to attenuate UVR across the water column. The skin of many fishes contains large epidermal club cells (ECCs) that are known to play a role in innate immune responses and also release chemical alarm cues that warn other fishes of danger. This study investigated the effects of in vivo UVR exposure to fathead minnows (Pimephales promelas), under the influence of two sources of DOC: Sigma Aldrich humic acid, a coal based commercial source of DOC and Luther Marsh natural organic matter, a terrigenous source of DOC. Specifically, we examined ECC investment and physiological stress responses and found that fish exposed to high UVR, in the presence of either source of DOC, had higher ECC investment than fish exposed to high UVR only. Similarly, exposure to high UVR under either source of DOC, reduced cortisol levels relative to that in the high UVR only treatment. This indicates that DOC protects fish from physiological stress associated with UVR exposure and helps maintain production of ECC under conditions of UVR exposure.

Occupational Exposure to Natural UV Radiation and Premature Skin Ageing

The skin is the part of the human body most vulnerable to ultraviolet (UV) radiation. The spectrum of the negative effects of UV radiation on the skin ranges from acute erythema to carcinogenesis. Between these extreme conditions, there are other common skin lesions, e.g.,photoageing. The aim of this study was to assess the skin for signs of photoageing in a group of 52 men occupationally exposed to natural UV radiation. There were 2 types of examinations: an examination of skin condition (moisture, elasticity, sebum, porosity, smoothness, discolourations and wrinkles) with a device for diagnosing the skin, and a dermatological examination. The results of both examinations revealed a higher percentage of skin characteristics typical for photoageing in outdoor workers compared to the general population.

Fitness costs and benefits of ultraviolet radiation exposure in marine pelagic copepods

Summary Life‐history theory predicts that organisms should allocate energy throughout their life such that they maximize their fitness. Copepod zooplankton are known to accumulate sunscreens (so‐called mycosporine‐like amino acids, MAAs) and antioxidant carotenoids to mitigate negative effects of ultraviolet radiation (UVR), but it is not well known how this affects their fitness. We followed cohorts of the marine copepod Acartia tonsa and assessed how fitness was affected by UVR exposure and a diet rich in UVR‐protective sunscreens. Several fitness components including somatic growth, egg quality and nauplii production (larvae) were negatively affected by UVR, whereas other components such as size at maturity, survival and length of life were not. Nauplii production through low egg quality was the most influential life‐history parameter that changed in response to UVR. There was interaction between fitness costs and food source. If copepods were fed a diet rich in UVR‐screening MAAs, they were able to maintain and even increase their fitness even though they were exposed to otherwise detrimental radiation. Levels of UVR‐protective carotenoids were low in the studied species and a meta‐analysis revealed that marine copepods in general have much lower – by an order of magnitude – levels of carotenoids than freshwater species, while levels of MAAs are similar between the two habitats. We conclude that allocation to different fitness components to some extent is plastic although egg quality is by far the most influential factor, and this is an example of how environmental variability affects overall fitness. Fitness costs associated with UVR exposure in the absence of UVR‐screening MAAs were present. Other costs such as costs for accumulating MAAs were not detected, and if present, they were outweighed by a stimulated fitness in combined UVR and MAA treatments challenging the common model that inducible defences (such as accumulation of MAAs) should come with a cost. Low levels of carotenoids in marine systems suggest high predation pressures on pigmented specimens. Accumulation of nonpigmented MAAs could hence be a key adaptation for surface‐dwelling marine zooplankton to maintain or even increase their fitness when exposed to detrimental radiation.

Interactive effects of vertical mixing, nutrients and ultraviolet radiation: in situ photosynthetic responses of phytoplankton from high mountain lakes in Southern Europe

Abstract. Global change, together with human activities, has resulted in increasing amounts of organic material (including nutrients) that water bodies receive. This input further attenuates the penetration of solar radiation, leading to the view that opaque lakes are more "protected" from solar ultraviolet radiation (UVR) than clear ones. Vertical mixing, however, complicates this view as cells are exposed to fluctuating radiation regimes, for which the effects have, in general, been neglected. Furthermore, the combined impacts of mixing, together with those of UVR and nutrient inputs are virtually unknown. In this study, we carried out complex in situ experiments in three high mountain lakes of Spain (Lake Enol in the National Park Picos de Europa, Asturias, and lakes Las Yeguas and La Caldera in the National Park Sierra Nevada, Granada), used as model ecosystems to evaluate the joint impact of these climate change variables. The main goal of this study was to address the question of how short-term pulses of nutrient inputs, together with vertical mixing and increased UVR fluxes modify the photosynthetic responses of phytoplankton. The experimentation consisted in all possible combinations of the following treatments: (a) solar radiation: UVR + PAR (280–700 nm) versus PAR (photosynthetically active radiation) alone (400–700 nm); (b) nutrient addition (phosphorus (P) and nitrogen (N)): ambient versus addition (P to reach to a final concentration of 30 μg P L−1, and N to reach N:P molar ratio of 31); and (c) mixing: mixed (one rotation from surface to 3 m depth (speed of 1 m 4 min−1, total of 10 cycles)) versus static. Our findings suggest that under ambient nutrient conditions there is a synergistic effect between vertical mixing and UVR, increasing phytoplankton photosynthetic inhibition and excretion of organic carbon (EOC) from opaque lakes as compared to algae that received constant mean irradiance within the epilimnion. The opposite occurs in clear lakes where antagonistic effects were determined, with mixing partially counteracting the negative effects of UVR. Nutrient input, mimicking atmospheric pulses from Saharan dust, reversed this effect and clear lakes became more inhibited during mixing, while opaque lakes benefited from the fluctuating irradiance regime. These climate change related scenarios of nutrient input and increased mixing, would not only affect photosynthesis and production in lakes, but might also further influence the microbial loop and trophic interactions via enhanced EOC under fluctuating UVR exposure.

Nitrate reduces the negative effect of UV radiation on photosynthesis and pigmentation in Gracilaria tenuistipitata (Rhodophyta): the photoprotection role of mycosporine-like amino acids

Barufi J.B., Mata M.T., Oliveira M.C. and Figueroa F.L. 2012. Nitrate reduces the negative effect of UV radiation on photosynthesis and pigmentation in Gracilaria tenuistipitata (Rhodophyta): the photoprotection role of mycosporine-like amino acids. Phycologia 51: 636–648. DOI: 10.2216/10.77.1Photoprotection of the agarophyte red alga Gracilaria tenuistipitata against ultraviolet radiation (UVR) was investigated in algae submitted for 1 week to photosynthetically active radiation (PAR, 260 μmol photons m−2 s−1) or PAR + UVR (UV-A, 8.13 W m−2 and UV-B, 0.42 W m−2) under different nitrogen concentrations: 0, 0.1, and 0.5 mM of NO3−. Photosynthetic pigments decreased during the time of the experiment mainly under low nitrogen supply and UVR. Incubation under high nitrogen supply (0.5 mM) sustained the photosynthetic levels over time. In contrast, mycosporine-like amino acids (MAAs) increased up to eightfold in the presence of UVR and 0.5 mM NO3−. Under PAR + UVR, maximal quantum yield was positively correlated to MAA abundance, whereas under PAR no correlation was found. The photosynthetic yield of algae cultivated during seven days under PAR + UVR was less affected by a 30-min exposure of high UVR (16 W m−2) and fully recovered after transferring to low PAR irradiances, whereas algae kept under PAR were more affected by UV exposure and no full recovery was observed. Growth rates decreased after three days in the presence of UVR and under low nitrate supply. However, these rates were similar when compared with treatments of PAR and PAR + UVR after seven days, with the exception of samples in 0 mM NO3−, indicating that the acclimation after one week's exposure is related to nitrate supply. In conclusion, the lowest negative effect of UVR on photosynthesis and growth rate in high N-supply-grown algae could be explained by the stimulation of photoprotection mechanisms, such as accumulation of MAAs. Photostimulation of MAA accumulation by UVR under high N supply was observed in G. tenuistipitata even after 20 years in culture without the induction of this photomorphogenic light signal.

Effects of ultraviolet radiation and nutrients on the structure-function of phytoplankton in a high mountain lake

The combined effect of high solar ultraviolet radiation (UVR) and nutrient supply in a phytoplankton community of a high mountain lake is analyzed in a in situ experiment for 6 days with 2 × 2 factorial design. Interactive UVR × nutrient effects on structural and functional variables (algal biomass, chlorophyll a (chl a), primary production (PP), maximal electron transport rate (ETR(max)), and alkaline phosphatase activity (APA)), as well as stoichiometric ones (sestonic N per cell and N:P ratio) were found. Under non-nutrient enriched conditions, no deleterious effects of UVR on structural variables, PP, photosynthetic efficiency and ETR(max) were observed, whereas only particulate and total APA were affected by UVR. However, percentage excreted organic carbon (%EOC), dissolved APA and sestonic C and P per cell increased under UVR, leading to a decrease in algal C:P and N:P ratios. After nutrient enrichment, chl a, total algal biomass and PP were negatively affected by UVR whereas %EOC, ETR(max) and internal C, P and N content increased. We suggest that the mechanism of algal acclimation to UVR in this high UVR flux ecosystem seems to be related to the increase of internal algal P-content mediated by physiological mechanisms to save P and by a stimulatory UVR effect on dissolved extracellular APA. The mechanism involved in the unmasking effect of UVR after nutrient-enrichment may be the result of a greater sensitivity to UVR-induced cell damage, making the negative UVR effects more evident.