Photosynthetically Active Radiation Treatment Research Articles

Comparative Study of Algal Responses and Adaptation Capability to Ultraviolet Radiation with Different Nutrient Regimes.

Frequent outbreaks of harmful algal blooms (HABs) represent one of the most serious outcomes of eutrophication, and light radiation plays a critical role in the succession of species. Therefore, a better understanding of the impact of light radiation is essential for mitigating HABs. In this study, Chlorella pyrenoidosa and non-toxic and toxic Microcystis aeruginosa were mono-cultured and co-cultured to explore algal responses under different nutrient regimes. Comparisons were made according to photosynthetically active radiation (PAR), UV-B radiation exerted oxidative stresses, and negative effects on the photosynthesis and growth of three species under normal growth conditions, and algal adaptive responses included extracellular polymeric substance (EPS) production, the regulation of superoxide dismutase (SOD) activity, photosynthetic pigments synthesis, etc. Three species had strain-specific responses to UV-B radiation and toxic M. aeruginosa was more tolerant and showed a higher adaptation capability to UV-B in the mono-cultures, including the lower sensitivity and better self-repair efficiency. In addition to stable μmax in PAR ad UV-B treatments, higher EPS production and enhanced production of photosynthetic pigments under UV-B radiation, toxic M. aeruginosa showed a better recovery of its photosynthetic efficiency. Nutrient enrichment alleviated the negative effects of UV-B radiation on three species, and the growth of toxic M. aeruginosa was comparable between PAR and UV-B treatment. In the co-cultures with nutrient enrichment, M. aeruginosa gradually outcompeted C. pyrenoidosa in the PAR treatment and UV-B treatment enhanced the growth advantages of M. aeruginosa, when toxic M. aeruginosa showed a greater competitiveness. Overall, our study indicated the adaptation of typical algal species to ambient UV-B radiation and the stronger competitive ability of toxic M. aeruginosa in the UV-radiated waters with severer eutrophication.

The inhibitory effects of the antifouling compound Irgarol 1051 on the marine diatom Skeletonema sp. across a broad range of photosynthetically active radiation.

The release of anthropogenic organic pollutants has resulted in extensive environmental risks to coastal waters. Among pollutants released, the most common antifoulant, Irgarol 1051, is an effective inhibitor of photosystem II of photoautotrophs; thus, the continuous release of this compound into surrounding seawater would potentially threaten marine algae. To investigate this, we grew the model marine diatom Skeletonema sp. at different concentrations of Irgarol 1051 and levels of photosynthetically active radiation (PAR). Irgarol did not affect the photochemical capacity when cells were incubated in the dark, but photochemical yields all significantly decreased, and relative inhibition by Irgarol increased once cells were exposed to even the lowest PAR, with lower photochemical yields observed under increased level of Irgarol. In addition, the rate of decrease in yield increased with Irgarol concentration but was unchanged among PAR treatments. The growth rates showed a similar pattern to photochemical yields, with lower values under higher Irgarol concentrations, but with no significant differences in the effect of Irgarol observed between the light levels employed. The ratio of repair to damage rates of PSII clearly shows that this ratio decreased with light intensity, largely due to increases in damage rates and that the PAR level at which repair balanced damage decreased under a high level of Irgarol. Our results suggest that the inhibitory effects of Irgarol become obvious after PAR exposure even at a relatively low light level, suggesting that Irgarol would affect phytoplankton throughout the daytime, and may therefore have a broad environmental risk, potentially limiting coastal primary production.

Evaluation of the photosynthetically active radiation (PAR) treatment as degreening method on ‘Okitsu’ Satsuma

ABSTRACT The aim of this work was to study the effect of postharvest light treatment as a potential degreening method on ‘Okitsu’ Satsuma mandarin (Citrus reticulata Blanco). Furthermore, a possible synergistic effect of light and ethephon treatment was also evaluated. For this, mature green fruit were harvested and treated. The treatments were: 1) exposing the fruit to increasing periods of time of photosynthetically active radiation (PAR); 2) the combination of a traditional ethephon degreening method with the most effective PAR treatment. The results show that 12 h and 24 h of PAR treatments were the most favourable to obtain the better effects of degreening, not affecting the rest of quality parameters. The combination of the 24 h of PAR and ethephon treatments was not effective to degreen the fruit. The present work is the first step in the approach to the study of PAR treatment as a degreening method on citrus and, according to the results, we consider it could be a promising degreening treatment on ‘Okitsu’ mandarin.

Effectiveness of Photoprotective Strategies in Three Mixotrophic Planktonic Ciliate Species

Mixotrophic ciliate assemblages often prevail in summer in the surface layers of lakes. During this time, they are potentially exposed to damaging levels of incident solar ultraviolet radiation (UVR) and need efficient photoprotective mechanisms to minimize the damage. Herein, we tested the algal-bearing species of Pelagodileptus trachelioides, Stokesia vernalis, and Vorticella chlorellata for how they handled stress under exposure to the artificial sunlight spectrum (i.e., UV treatment), just photosynthetically active radiation (PAR), or in the dark (i.e., control). In addition to measurements of their survival, changes in behavior, shape, and whether dark or photoenzymatic repair (PER) mechanisms are present, we measured the concentration of UV-absorbing compounds (i.e., mycosporine-like amino acids). In contrast to the response in the PAR and dark treatments, sublethal effects were observed in all species when exposed to UVR. A wavelength-specific test for P. trachelioides revealed that UV-B was especially lethal. These results suggest that the photoprotective mechanisms found in these ciliates are not sufficient to allow for their survival directly at the surface and that, accordingly, they need to shift their position further down in the water column.

Enhancement of the Production of Bioactive Microalgal Metabolites by Ultraviolet Radiation (UVA 365 nm).

Two marine microalgae, Nitzschia closterium and Isochrysis zhangjiangensis, treated for 9 days with photosynthetically active radiation (PAR), were subjected to 3 days of ultraviolet light band A at 365 nm (UVA365) followed by a 3 day post-UVA PAR treatment. Compared with the control that only had PAR treatment, UVA365 treatment significantly ( p < 0.05) increased the amounts of total xanthophylls in N. closterium and I. zhangjiangensis by up to 3.53- and 1.23-fold, respectively, after 3 days of UVA365 irradiation. In particular, UVA365 treatment markedly ( p < 0.05) increased two major bioactive xanthophyll pigments, fucoxanthin in N. closterium and diadinoxanthin in I. zhangjiangensis, by up to 1.97- and 1.52-fold, respectively. UVA365 treatment significantly ( p < 0.05) increased the accumulation of another bioactive microalgal metabolite, total mycosporine-like amino acids, in N. closterium and I. zhangjiangensis by up to 1.40- and 1.30-fold, respectively. UVA365 irradiation has potential as an efficient approach for enhancing the production of valuable microalgal metabolites.

Induction of phenolic compounds by UV and PAR is modulated by leaf ontogeny and barley genotype

We investigated the effect of leaf ontogeny and barley genotype on the accumulation of phenolic compounds (PhCs) induced by ultraviolet (UV) and photosynthetically active radiation (PAR). We hypothesized that different groups of PhCs are induced in leaves differing in ontogeny, and that this has consequences for protective functions and the need for other protection mechanisms. Generally, lower constitutive contents of PhCs (under conditions of UV exclusion and reduced PAR) were found in a UV-sensitive genotype (Barke) compared to a tolerant genotype (Bonus). However, UV and PAR induced accumulation of PhCs exceeded the constitutive amounts several fold. Specifically, lutonarin, 3-feruloylquinic acid, unidentified hydroxycinnamic acid and luteolin derivatives were markedly enhanced by high PAR and UV irradiances. Leaves developed during UV and PAR treatments had higher PhCs contents than mature leaves already fully developed at the onset of the UV and PAR treatment. UV and PAR treatments had, however, a minor effect on saponarin and unidentified apigenin derivatives which occur particularly in mature leaves of the tolerant genotype Bonus. In addition, high UV and PAR intensities increased the total content of xanthophylls (VAZ), while chlorophyll content was reduced, particularly in developing leaves. A redundancy analysis revealed positive associations between most of PhCs and VAZ and a negative association between total chlorophylls and carotenoids. Non-linear relationships between VAZ and lutonarin and other PhCs indicate that VAZ accumulation can compensate for the insufficient efficiency of anti-oxidative protection mediated by PhCs. Accordingly, we conclude that UV and PAR-induced accumulation of PhCs is affected by leaf ontogeny, however, this effect is compound-specific.

Role of Photosynthetically Active Radiation and Dark Conditions on the Repair of Ultraviolet-B Radiation-induced Damages in the Cyanobacterium Nostoc sp. Strain HKAR-2

Introduction: We have investigated the effects of ultraviolet-B (UV-B; 280-315 nm) radiation on Chl a, phycocyanin, allophycocyanin, photosynthetic efficiency and reactive oxygen species (ROS) generation in Nostoc sp. strain HKAR-2 and the role of photosynthetically active radiation (PAR) and dark on the repair processes.Methods: Samples were exposed to UV-B for 14h followed by PAR and dark treatment for 10h. Chl a, phycocyanin and allophycocyanin concentration and photosynthetic efficiency i.e., the photosynthetic quantum yield of PS II (Fv/Fm) were estimated. In vivo detection of ROS by fluorescence microscopy and spectroscopy was done using the fluorescent probe 2′,7′-dichlorodihydrofluorescein diacetate (DCFH).Results: Progressive decrease of 50% and 41% in survival rates of cyanobacterium was observed after 12 and 14h of exposure respectively and a significant increase in survival was observed during the recovery process in PAR and dark. Chl a, phycocyanin and allophycocyanin concentration decreased after 12h of UV-B exposure. Significant recovery of phycocyanin and allophycocyanin was observed in the samples placed on PAR. Fv/Fm decreased with time and 42% decrease was observed after 14h of exposure. Pronounced fluorescence intensity, due to produced ROS was observed after 14h of UV-B exposure. The significant decrease in DCF fluorescence was observed in the samples placed in PAR and dark.Conclusions: UV-B exposed cyanobacteria kept on PAR showed speedy recovery in comparison to those kept in dark. This indicates the possible role of repair processes such as photoreactivation in the repair of damage caused by UV-B to cyanobacterium. Hence, further studies are needed for the thorough understanding of repair processes in cyanobacteria in response to UVR.

Cellular Mycosporine-like amino acids protect photosystem II of the Dinoflagellate Scrippsiella sweeneyae from ultraviolet radiation damage

Photo-damage to photosystem II (PSII) from ultraviolet radiation (UVR) was determined using chlorophyll fluorescence in relation to sunscreen factors on the dinoflagellate Scrippsiella sweeneyae based on the cellular mycosporine-like amino acid contents (CMAAs, cell) and cell diameter (=light path, d). Three different CMAAs, cell were prepared by acclimating cells to three levels (30.8, 15.2, and 7.7Wm−2) of photosynthetically active radiation (PAR). PAR-acclimated cells were exposed to PAR (0.64Wm−2)+UVR (3.94W m−2=2.51Wm−2 UVB+1.43Wm−2 UVA) for 12min. High PAR (HL) and medium PAR (NDF1) treatments acclimated cells to induce shinorine and porphyra-334 (longer λmax at 333 and 334nm); whereas, the low PAR (NDF2) treatment acclimated cells to induce mycosporine-glycine and palythine (shorter λmax at 310 and 320nm). Absorption spectra for the individual MAAs were reconstructed using the λmax and CMAAs, cell and were summed to reconstruct the absorption of the total CMAAs, cell (m2cell−1) to estimate the sunscreen factor (S[λ]) at λmax. The highest S(λmax) was obtained for cells that acclimated to the highest PAR (highest CMAAs, cell and longest d); whereas, the lowest S(λmax) was obtained for cells acclimated to the lowest PAR (the lowest CMAAs, cell and the shortest d). CMAAs, cell contributed approximately 94%, whereas d contributed <6%, of the sunscreen factor (Sλmax). UVR-induced damage was indexed with a temporal decrease in the optimum quantum yield (Fv/Fm) in the Photosystem II. The highest damage was observed for cells acclimated to the lowest Sλmax (lowest CMAAs, cell and shortest d); whereas, the lowest damage was observed for cells acclimated to the highest Sλmax (highest CMAAs, cell and longest d). The CMAAs, cell mitigated most of the UVR-induced damage in photosystem II of the dinoflagellate S. sweeneyae.

Dependency of UVR-induced photoinhibition on atomic ratio of N to P in the dinoflagellate Karenia mikimotoi

To investigate the effects of Nitrogen (N):phosphorus (P) ratio and solar ultraviolet radiation (UVR) on the growth and photophosphorylation of oceanic phytoplankton, the effects of UVR and N:P ratio on K. mikimotoi were evaluated. K. mikimotoi cells were cultured in artificial seawater (ASW) under five different N:P ratios (1:1, 16:1, 50:1, 100:1 and 200:1) for 15 days (phase 1: 1–5 day; phase 2: 6–10 day; phase 3: 11–15 days). Next, K. mikimotoi cultures were exposed to photosynthetically active radiation (PAR), PAB (PAR + UV-A + UV-B) and PA (PAR + UV-A), respectively. Finally, K. mikimotoi cells grown under the Redfield ratio (16:1) had the largest growth rate (0.257day−1), highest pigment concentrations (chlorophyll a (Chla): 0.465 × 10− 5 μg cell−1, carotenoid (Caro): 0.249 × 10−5 μg cell−1) and maximum superoxide dismutase (SOD) activity (0.9 U × 10−6 cell−1) compared with those grown under other N:P ratios. The UV-absorbing compounds’ (UVabc) absorbance was largest at the N:P ratio of 50:1 during the range of 310–360 nm, with a relatively higher value at the N:P ratio of 16:1. UV intensity was positively correlated with photoinhibition. K. mikimotoi cells grown at the N:P ratio of 16:1 showed the smallest photoinhibition compared to those grown at other N:P ratios under the PAR treatment with the largest r:k ratio; similar results were found for both the PA and PAB treatments. The Redfield ratio of 16:1 is optimal for the growth and photophosphorylation of K. mikimotoi. The weakest UVR-induced photoinhibition at this ratio may be attributed to the highest photosystem II (PSII) repair rate and SOD activity.

English

Changes in the photosynthetically active radiation (PAR) levels to which a certain species are adapted can result in different plant growth responses. Thus, analytical and systematic studies on the mechanisms that plant species use to survive when subjected to changes in PAR are required. To address the lack of literature on this topic for Ananas comosus, this study aimed to evaluate the effects of different PAR levels on the growth of this species. A completely randomised experimental design was used consisting of subdivided plots containing a total of 1176 forest plants, including 1040 Sc (Schizolobium parahyba subsp. amazonicum), 96 Cg (Cordia goeldiana Huber), 40 Sw (Swietenia macrophylla King), and 13.000 An (Ananas comosus var. erectifolius) agricultural plant species. Seven treatments were established based on this combination of species. These treatments were installed using a completely randomised block design with split plots. Each plot measured 18 m x 24 m, and each treatment was replicated four times, resulting in a total of 28 plots and an experimental area of 12.096 m². After establishing the treatments, studies were conducted to evaluate the influence of different radiation levels on An plant growth. In this study, pluviometric precipitation data and mean percentage values (53, 64, 71 and 100%) of PAR (μmol m - ² s -1 ) were recorded. Over the period between 2003 and 2006, the number of leaves, the lengths of the leaves, and the number of An sprouts were measured every six months. The highest number of leaves was recorded in the treatments in which the plants were exposed to 64% PAR. The number of leaves in this treatment was similar to that in the 71% PAR treatment. However, the number of leaves decreased in the plants that were subjected to either the highest (100%) or the lowest (53%) level of PAR. The use of different PAR levels for An plants under cultivation conditions showed that the best growth rates of the leaves and shoots were associated with lower levels of PAR (53% and 64%). However, cultivation under full sunlight favoured a higher number of leaves. The fibre, leaf and mucilage production progressively increased until the third year of the experiment.

Effect of PAR and temperature on the photosynthesis of the Japanese alga, Ecklonia radicosa (Laminariales), based on field and laboratory measurements

:The effect of photosynthetically active radiation (PAR) and temperature on the photosynthesis of a Japanese brown alga, Ecklonia radicosa, was determined by using dissolved oxygen sensors and pulse-amplitude modulated (PAM) fluorometry. The effective quantum yield (ΦPSII) of the sporophytes, in a natural population in shallow water, showed a characteristic noontime decline that indicated the influence of high PAR. However, ΦPSII of sporophytes in deeper water (−10 to −20 m) did not appear to be affected and maintained relatively high values of ΦPSII. In laboratory measurements of ΦPSII, after 12 h of continuous low and high PAR (100 and 1000 μmol photon m−2 s−1), a relatively greater decrease in ΦPSII in the high PAR treatment was observed. Furthermore, despite an overnight dark acclimation, the maximum quantum yield (Fv/Fm) under the high PAR treatment did not fully recover. A net photosynthesis–irradiance (P-E) curve was generated at 20°C, which revealed low compensation and saturation irradiances (Ec and Ek) of 14 and 45 μmol photon m−2 s−1, suggesting adaptation to a low PAR environment. Results from experiments to determine the net/gross photosynthesis and dark respiration rates revealed that the maximal gross photosynthetic rates occurred at 27.5°C and were 5.18 μg O2 gww−1 min−1; whereas, the dark respiration rate increased exponentially with a mean value of 1.35 μg O2 gww−1 min−1 at 22°C. Fv/Fm was relatively stable at low temperature, and the highest value (0.73) occurred at 16.5°C. The field survey and laboratory experiments revealed that E. radicosa is well adapted to relatively low PAR and water temperatures typical of warm temperate coastal regions in Japan. The poor response to high PAR and the inability of sporophytes to fully recover overnight from high PAR exposure indicates that the vertical distribution of this species is driven by the PAR environment.

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.

Effects of solar radiation on pigmentation and induction of a mycosporine-like amino acid in two cyanobacteria, Anabaena sp. and Nostoc sp. ISC26

ABSTRACTThe effect of filtered natural solar radiation, including photosynthetically active radiation (PAR) and PAR+ultraviolet radiation (UVR), on pigmentation and synthesis of a UV absorbing ‘mycosporine-like amino acid’ (MAA) in two filamentous and heterocystous cyanobacteria, Anabaena sp. and Nostoc sp. ISC26 was studied over 3 days. In Anabaena sp. and Nostoc sp. ISC26, chlorophyll a (chl a) content decreased after 72 h to 5.45 ± 0.09 and 7.01 ± 0.54 μg mg−1 DW respectively under PAR treatments; and to 4.33 ± 0.22, 6.12 ± 0.04 μg mg−1 DW in PAR+UV treatments, as did carotenoids (Car) (2.68 ± 0.01, 2.93 ± 0.01 μg mg−1 DW) (PAR), (2.53 ± 0.01, 2.57 ± 0.05 μg mg−1 DW) (PAR+UV). A considerable increase was observed in the carotenoid:chlorophyll a (Car/Chl a) ratio as a result of carotenoid accumulation in the first 24 h and reduction of chlorophyll in the following days. A single MAA was isolated, purified by high performance liquid chromatography (HPLC) and identified as shinorine. Shinorine concentration increased significantly during 72 h specifically under PAR+UV (1270.8 ± 50.42, 2208.09 ± 73.04 nmol g−1 DW) in Anabaena sp. and Nostoc sp. ISC26, respectively, indicating an adaptation strategy of cyanobacteria against harmful solar short wavelength radiation especially in natural habitats.

Ultraviolet and photosynthetically active radiation can both induce photoprotective capacity allowing barley to overcome high radiation stress

The main objective of this study was to determine the effects of acclimation to ultraviolet (UV) and photosynthetically active radiation (PAR) on photoprotective mechanisms in barley leaves. Barley plants were acclimated for 7 days under three combinations of high or low UV and PAR treatments ([UV−PAR−], [UV−PAR+], [UV+PAR+]). Subsequently, plants were exposed to short-term high radiation stress (HRS; defined by high intensities of PAR – 1000 μmol m−2 s−1, UV-A – 10 W m−2 and UV-B 2 W m−2 for 4 h), to test their photoprotective capacity. The barley variety sensitive to photooxidative stress (Barke) had low constitutive flavonoid content compared to the resistant variety (Bonus) under low UV and PAR intensities. The accumulation of lutonarin and 3-feruloylquinic acid, but not of saponarin, was greatly enhanced by high PAR and further increased by UV exposure. Acclimation of plants to both high UV and PAR intensities also increased the total pool of xanthophyll-cycle pigments (VAZ). Subsequent exposure to HRS revealed that prior acclimation to UV and PAR was able to ameliorate the negative consequences of HRS on photosynthesis. Both total contents of epidermal flavonols and the total pool of VAZ were closely correlated with small reductions in light-saturated CO2 assimilation rate and maximum quantum yield of photosystem II photochemistry caused by HRS. Based on these results, we conclude that growth under high PAR can substantially increase the photoprotective capacity of barley plants compared with plants grown under low PAR. However, additional UV radiation is necessary to fully induce photoprotective mechanisms in the variety Barke. This study demonstrates that UV-exposure can lead to enhanced photoprotective capacity and can contribute to the induction of tolerance to high radiation stress in barley.

Photosynthetic performance of Anabaena variabilis PCC 7937 under simulated solar radiation

In vivo chlorophyll fluorescence analysis reflecting the photosystem II functionality was investigated in the cyanobacterium Anabaena variabilis PCC 7937 under simulated solar radiation in a combination with various cut-off filters (WG 280, WG 295, WG 305, WG 320, WG 335, WG 345, and GG 400) to assess the effects of photosynthetically active radiation (PAR), ultraviolet-A (UV-A), and ultraviolet-B (UV-B) radiations on photosynthesis. The photosynthetic activity (PA) was severely inhibited immediately after 10 min of exposure to high PAR, UV-A, and UV-B radiations compared with low PAR grown control samples. After 1 h of exposure, PA of 17.5 ± 2.9% was detected in the high PAR exposed samples compared with the control, while only a trace or no PA was observed in the presence of ultraviolet radiation (UVR). A recovery of PA was recorded after 2 h of the exposure, which continued for next 4, 8, 12, and 24 h. After 24 h of the exposure, PA of 57.5 ± 1.9%, 36.1 ± 11.7%, 23.5 ± 3.3%, 22.3 ± 5.2%, 20.8 ± 6.7%, 13.2 ± 6.6%, and 21.6 ± 9.5% was observed compared with the control sample in 400, 345, 335, 320, 305, 295, and 280 nm cut-off filters-covered samples, respectively. The relative electron transport rate, measured after 24 h exposure, showed also a disturbance in electron transfer between the two photosystems under the high PAR and UVR treatments relative to the control samples, suggesting the inhibition of photosynthesis. This study suggests that both high PAR and UVR inhibited the photosynthetic performance of A. variabilis PCC 7937 by damaging the photosynthetic apparatus, however, photoprotective mechanisms evolved by the organism allowed an immediate repair of ecologically important machinery, and enabled its survival.

Shade light interaction with salicylic acid in regulating growth of sun (alpine) and shade (prairie) ecotypes of Stellaria longipes

The possible involvement of salicylic acid (SA) in a typical growth response of plants to shade light was investigated using the model system Stellaria longipes L. Goldie. The prairie (shade) ecotype of S. longipes is from foothills grassland habitat where it grows under shrubs or among taller grasses. The plants of this ecotype responded, as expected, with increased growth under lower red to far-red (R/FR) ratio and reduced photosynthetically active radiation (PAR). By contrast, the alpine (sun) ecotype is from an open sunny habitat, where canopy shade is a non-factor. The plants of this ecotype failed to respond with increased growth under a lower R/FR ratio, but had increased growth under a reduced PAR level. To examine the possible role of SA in shade light-mediated growth, the two main components of shade light, R/FR ratio and PAR, were uncoupled, and a series of experiments were performed by measuring the endogenous SA content and the plant response to exogenous SA concentrations. Contrary to the alpine plants, the prairie plants had increased endogenous SA content and higher shoot biomass accumulation under a low R/FR ratio treatment compared with normal or high R/FR ratios. Both alpine and prairie plants responded to a low PAR treatment with a decrease in endogenous SA content and an increase in shoot biomass accumulation, but the magnitude of this response was higher in prairie plants. Based on the results of this study, we conclude that shoot SA content is differentially regulated by both R/FR ratio and PAR signals, and SA may contribute, in ecotype specific manner, to growth changes in plants subjected to changing light environments.

Effects of solar PAR and UV radiation on tropical biofouling communities

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 402:31-43 (2010) - DOI: https://doi.org/10.3354/meps08455 Effects of solar PAR and UV radiation on tropical biofouling communities Sergey V. Dobretsov1, Louis Gosselin2, Pei-Yuan Qian3,* 1Marine Science and Fisheries Department, College of Agricultural and Marine Sciences, Sultan Qaboos University, Sultanate of Oman 2Department of Biological Sciences, Thompson Rivers University, Kamloops, British Columbia, Canada 3KAUST Global Partnership Program, Department of Biology, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR *Corresponding author. Email: boqianpy@ust.hk ABSTRACT: We investigated the effect of solar ultraviolet radiation (UVR) and photosynthetically active radiation (PAR) on the development of tropical micro- and macrofouling communities for 30 d. The experimental design involved 3 treatments: full spectrum (PAR+UVR), PAR only, and minimal light (reduced PAR and UVR). Terminal restriction fragment length polymorphism analysis demonstrated that different light conditions resulted in the formation of highly different microbial communities. The lowest densities of bacteria were found under the full spectrum treatment, while the lowest densities of diatoms were found in the minimal light treatment. Macrofouling communities consisted of 13 species and differed among light treatments. In the presence of UVR, communities had low species diversity, evenness, and richness, while in minimal light and PAR treatments, communities had high species diversity, evenness, and richness. Similarity percentage (SIMPER) analysis revealed that the tubeworm Hydroides elegans, the alga Ulva (Enteromorpha) sp., and the bivalve Perna viridis were the species responsible for most of the dissimilarities in macrofouling communities among treatments. While densities of H. elegans were similar in the PAR and minimal light treatments, this polychaete had higher growth rates under minimal light conditions. We conclude that UVR and PAR directly control the development of shallow micro- and macrofouling communities by inhibiting the recruitment and growth of sensitive species and promoting the growth of resistant species, but also that these forms of solar radiation influence the surface cues available to competent larvae by altering the development of the microbial community. KEY WORDS: Ultraviolet radiation · Visible light · Microbial communities · Biofilm · Biofouling · Community structure · Larval recruitment · Juvenile growth · South China Sea · Photosynthetically active radiation Full text in pdf format PreviousNextCite this article as: Dobretsov SV, Gosselin L, Qian P (2010) Effects of solar PAR and UV radiation on tropical biofouling communities. Mar Ecol Prog Ser 402:31-43. https://doi.org/10.3354/meps08455 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 402. Online publication date: March 08, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Acclimation of Red Sea macroalgae to solar radiation: photosynthesis and thallus absorptance

Thallus absorptance, daily courses of maximal quantum yields of chlorophyll fluores- cence of photosystem II (Fv/Fm) and electron transport rates (ETR) were determined in 3 macroalgae (Hypnea spinella, Rhodophyta; Sargassum vulgare, Phaeophyta; and Ulva lactuca, Chlorophyta) collected from a low nutrient supply (LNS) ecosystem (Red Sea, Gulf of Aqaba, Eilat, Israel). In addi- tion, U. lactuca grown previously in high nutrient supply (HNS) fishpond effluents was used to eval- uate the effect of nutrient enrichment on photosynthesis. Short-term (2 d) and mid-term (5 d) effects of both photosynthetically active radiation (PAR) and full solar irradiance (PAB: PAR+UVA+UVB) at 3 solar irradiance treatments (no neutral filters, no NF; 2 neutral filter layers, 2NF; and 4 neutral filter layers, 4NF simulating levels of irradiance at 5, 10 and 20 m depth respectively) were evaluated in algae incubated with running seawater. Significant effects of time (variation throughout the day) and irradiance (number of neutral filters) on both Fv/Fm and ETR were observed. Photoinhibition occurred at noon under the no NF (up to 40% decrease) and 2NF (up to 30% decrease) treatments; however, full recovery in all treatments was reached in the afternoon (dynamic photoinhibition) except in H. spinella. The highest maximum ETR was observed in the no NF treatment despite its strongest photoinhibitory effect. The decrease in Fv/Fm at noon was similar to or higher under the PAB than under the PAR treatment alone, depending on the species. Photoinhibition was lower and the maxi- mum ETR was higher in HNS than in LNS U. lactuca, indicating positive effects of nutrient supply on both photosynthesis and photoprotection. The maximum ETRs exhibited by different algae may be related to their zonation in the field and the resulting energy supply.

Ultraviolet Radiation Reduces the Photoprotective Capacity of the Marine Diatom Phaeodactylum tricornutum (Bacillariophyceae, Heterokontophyta)

This study demonstrates that UV radiation (UVR) reduces the photoprotective capacity of the diatom Phaeodactylum tricornutum by affecting xanthophyll cycle (XC) activity. The short-term reduction of photosystem II (PSII) maximum efficiency of charge separation (F(v)/F(m)) in cells exposed to UVR could be explained mainly by a reduced photoprotective capacity under this condition. Phaeodactylum tricornutum cells acclimated to two different photosynthetically active radiation (PAR) intensities, high light (HL, 200 micromol quanta m(-2) s(-1)) and low light (LL, 50 micromol quanta m(-2) s(-1)), were exposed to saturating irradiance (1100 micromol quanta m(-2) s(-1)) in the presence (PAR + UVR) and absence of UVR (PAR). HL cells exhibited a greater reduction in F(v)/F(m) in PAR + UVR when compared with the PAR treatment that was related to a reduction in the de-epoxidation of XC pigments. In contrast, in LL cells, UVR did not considerably affect XC de-epoxidation even though the reduction in F(v)/F(m) was greater than in HL cells. The negative effect of UVR on photoprotection was more pronounced in HL cells because they synthesized more XC pigments than LL cells. This was confirmed when XC activity was blocked with dithiothreitol and when PSII repair was inhibited with chloramphenicol (CAP). The differential reduction of F(v)/F(m) between PAR + UVR and PAR treatments disappeared when XC was blocked in HL cells. A higher reduction and an incomplete recovery of F(v)/F(m) were observed in cells incubated with CAP in the presence of UVR. Such responses confirm that UVR had a negative effect on photoprotective mechanisms causing an enhancement of damage by PAR, especially in HL-acclimated cells in which heat dissipation is important for PSII regulation.

Response to short term ultraviolet stress in the reef-building coral Pocillopora capitata (Anthozoa: Scleractinia)

Coral reefs are impacted by a range of environmental variables that affect their growth and survival, the main factors being the high irradiance and temperature fluctuations. Specimens of Pocillopora capitata Verrill 1864 were exposed to photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) for 32 h under laboratory conditions. We examined lipid peroxidation (MDA), antioxidant enzyme activities (SOD, CAT, GPx and GST), chlorophyll a (Chl a), carotenoid pigments (CPs), mycosporine-like amino acids (MAAs), and expulsion of zooxanthellae. Our results revealed that corals exposed to UVR had relatively low levels of carotenoids and antioxidant enzyme activities compared to those exposed to PAR, as well as lower CPs/Chl a ratios. Although MAAs and CPs are rapidly produced as non-enzymatic antioxidants in response to UVR in corals, these were not sufficient, even in the dark phase of the experiment, to mitigate the damage caused by formation of reactive oxygen species (ROS), which caused breakdown of the symbiotic relationship between the zooxanthellae and the host animal to an extent 33 times greater than in the PAR treatment. In this study, it could be possible to distinguish that, parallel to the short-term adjustments, such as the amount of pigment in the algae or the sensitivity of the photosynthetic response reported in other species of coral, P. capitata exhibits at the enzymatic level a series of responses oriented to resist the effects derived from the propagation of ROS and, thus, to adapt to and maintain its reproductive capacity in shallow oceanic environments that commonly exhibit high UVR levels. Nevertheless, as a result of the inappropriate location of the artificial intercommunication structure of the Juluapan Lagoon with respect to the arrecifal area of study and therefore of the tides influence, other variables, such as the changes in short-term in turbidity, sediment inputs, nutrients, temperature and osmolarity, can act in combination and cause irreversible damage. The implementation of a management plan for the coralline reefs of the Mexican Pacific coast is required.