Solar Photosynthetically Active Radiation Research Articles

Twenty-Year Climatology of Solar UV and PAR in Cyprus: Integrating Satellite Earth Observations with Radiative Transfer Modeling

In this study, we present comprehensive climatologies of effective ultraviolet (UV) quantities and photosynthetically active radiation (PAR) over Cyprus for the period 2004 to 2023, leveraging the synergy of earth observation (EO) data and radiative transfer model simulations. The EO dataset, encompassing satellite and reanalysis data for aerosols, total ozone column, and water vapor, alongside cloud modification factors, captures the nuanced dynamics of Cyprus’s atmospheric conditions. With a temporal resolution of 15 min and a spatial of 0.05° × 0.05°, these climatologies undergo rigorous validation against established satellite datasets and are further evaluated through comparisons with ground-based global horizontal irradiance measurements provided by the Meteorological Office of Cyprus. This dual-method validation approach not only underscores the models’ accuracy but also highlights its proficiency in capturing intra-daily cloud coverage variations. Our analysis extends to investigating the long-term trends of these solar radiation quantities, examining their interplay with changes in cloud attenuation, aerosol optical depth (AOD), and total ozone column (TOC). Significant decreasing trends in the noon ultraviolet index (UVI), ranging from −2 to −4% per decade, have been found in autumn, especially marked in the island’s northeastern part, mainly originating from the (significant) positive trends in TOC. The significant decreasing trends in TOC, of −2 to −3% per decade, which were found in spring, do not result in correspondingly significant positive trends in the noon UVI since variations in cloudiness and aerosols also have a strong impact on the UVI in this season. The seasonal trends in the day light integral (DLI) were generally not significant. These insights provide a valuable foundation for further studies aimed at developing public health strategies and enhancing agricultural productivity, highlighting the critical importance of accurate and high-resolution climatological data.

Atmospheric dependence of the direct, diffuse, and global clear-sky conversion ratios between solar photosynthetic active irradiance and photon flux

The ratio of the global solar photosynthetic active radiation (PAR) photon flux (in μmol/m2s) to global solar PAR irradiance (in W/m2) is of interest to convert one into another. This ratio is usually considered as a constant value close to its extraterrestrial value, 4.55μmol/J. However, this ratio depends on the spectral composition of solar radiation at ground level and it is different for the diffuse and beam components of solar irradiance. Under clear-sky conditions, the three PAR ratios (global, beam and diffuse) are determined by the local atmospheric composition and the relative air mass. In this work, the SMARTS spectral irradiance model with MERRA-2 atmospheric inputs is used to evaluate the dependence of these ratios under clear-sky conditions with air mass, aerosol optical depth (AOD), precipitable water vapor and ozone column. The accuracy of the SMARTS beam spectral irradiance is previously assessed using local spectroradiometer measurements. The clear-sky ratios for the diffuse and direct components increase with increasing air mass, while the global ratio shows only a weak air mass dependence. The clear-sky ratios can be modeled with simple bi-variate linear models in air mass and AOD. These results can be used in similar climatic regions to convert PAR flux to PAR irradiance and vice versa with increased accuracy for the global, direct, and diffuse radiation under cloud-free conditions.

Dynamics of photosynthetic solar active radiation in Ukraine over 1986 - 2015

Photosynthetically active solar radiation (PSR) – solar radiation within the wavelength range of 380 ¼710 nm – forms a basis of plants' life that determines their photosynthesis. No measurements of photosynthetically active solar radiation (PSR) take place in Ukraine due to the lack of standard devices. Direct, scattered and total PSR is calculated via transition measurements and coefficients, whereas total PSR is measured via sunshine duration – using the indirect method. The purpose of the research is to determine PSR and its dynamics during specific months and the warm period of the year (April-October). The components of the radiation regime within the network of actinometric and meteorological observations in Ukraine for 1986 - 2015, 1986 - 1995, 1996 - 2005, 2006 - 2015 were obtained using mathematical statistics and climatological methods. In the course of the research changes in the PSR during specific months and the warm period over specific decades were determined. During the months of the warm period over 1986 -2015, direct, diffused, total PSR and total PSR calculated via sunshine duration tend to increase from the west, northwest or Ukrainian Carpathians to the southern steppe zone and Crimea. During the warm period over 1986 - 1995, the amount of direct PSR varies within 472 ¼ 891 MJ/m², diffused radiation – 887 ¼ 1156 MJ/m², total radiation – 1457 … 1917 MJ/m², total PSR calculated based on sunshine duration – 1621 … 2056 MJ/m²; over 1996 - 2005 the amount of direct PSR varies within – 469 … 1030 MJ/m², diffused – 802 … 1004 MJ / m², total – 1305 … 1973 MJ/m², total PSR calculated based on sunshine duration – 1654 … 2192 MJ/m²; over 2006 - 2015 the amount of direct PSR varies within 485 ¼ 1065 MJ/m², diffused radiation – 737 ¼ 951 MJ / m², total PSR – 1270 … 1977 MJ / m², total PSR calculated based on sunshine duration – 1649 … 2233 MJ / m². The increase in integrated direct solar radiation over 1996 - 2005 compared to 1986 - 1995, as well as over 2006 - 2015 compared to 1996 - 2005, led to an increase in direct PSR; the decrease in diffused solar radiation led to a decrease in diffused PSR; and ambiguous changes in the components of total solar radiation led to fluctuations in total PSR; increase in sunshine duration is accompanied by an increase in total PSR calculated based on sunshine duration. The research is relevant due to the factor of modern climate variability at the global and regional levels. The study of PSR changes is an urgent task of modern agrometeorology. It enables long-term effective planning of agricultural development.

A Model Combining Forest Environment Images and Online Microclimate Data Instead of On-Site Measurements to Predict Phytoncide Emissions

In the existing phytoncide-prediction process, solar radiation and photosynthetically active radiation (PAR) are difficult microclimate factors to measure on site. We derived a phytoncide-prediction technique that did not require field measurements. Visual indicators extracted from forest images and statistical analysis were used to determine appropriate positioning for forest environment photography to improve the accuracy of the new phytoncide-prediction formula without using field measurements. Indicators were selected from the Automatic Mountain Meteorology Observation System (AMOS) of the Korea Forest Service to replace on-site measured climate data and the phytoncide-prediction equation was derived using them. Based on regression analyses, we found that forest density, leaf area, and light volume above the horizon could replace solar radiation and PAR. In addition, AMOS data obtained at 2 m altitudes yielded suitable variables to replace microclimate data measured on site. The accuracy of the new equation was highest when the surface area in the image accounted for 25% of the total. The new equation was found to have a higher prediction accuracy (71.1%) compared to that of the previous phytoncide-prediction equation (69.1%), which required direct field measurements. Our results allow the public to calculate and predict phytoncide emissions more easily in the future.

Prediction of Natural Volatile Organic Compounds Emitted by Bamboo Groves in Urban Forests

Due to the COVID-19 outbreak, people in countries around the world including the United Kingdom, Denmark, Canada, and South Korea are seeking physiological and psychological healing by visiting forests as stay-at-home orders continue. NVOCs (natural volatile organic compounds), a major healing factor of forests, have several positive effects on human health. This study specifically researched the NVOC characteristics of bamboo groves. This study revealed that α-pinene, 3-carene, and camphene were observed to emit the most, and the largest amount of NVOC emitted was seen during the early morning and late afternoon within bamboo groves. Furthermore, NVOC emission was found to have normal correlations with temperature and humidity, and inverse correlations with solar radiation, PAR (photosynthetically active radiation), and wind speed. A regression analysis conducted to predict the effect of microclimate factors on NVOC emissions resulted in a regression equation with 82.9% explanatory power, finding that PAR, temperature, and humidity had a significant effect on NVOC emission prediction. In conclusion, this study investigated NVOC emission of bamboo groves, examined the relationship between NVOC emissions and microclimate factors, and derived a prediction equation of NVOC emissions to figure out bamboo groves’ forest healing effects. These results are expected to provide a basis for establishing more effective forest healing programs in bamboo groves.

Managing eucalyptus trees in agroforestry systems: Productivity parameters and PAR transmittance

Agroforestry systems, in which trees and crops are cultivated in rotation, succession, or association with pastures, are alternatives for the sustainable implementation of agriculture. This study estimated the productive characteristics from eight years old eucalyptus trees in different agroforestry systems and transmission of photosynthetically active solar radiation (PAR). These were composed of a pasture of palisade grass (Urochloa brizantha “BRS Piatã”) and eucalyptus trees (Eucalyptus urograndis “GG100”) planted in April 2011 in single rows 15 m apart with 2 m in-row spacing, totaling 333 trees ha−1. In 2016, half of the trees were thinned, and the spacing was changed to 15 × 4 m. The two systems were then evaluated using an integrated crop-livestock-forestry system (agrosilvopasture with pasture renewal, ICLF) and an integrated livestock-forest system (silvopasture with no pasture renewal, ILF). Each system had 12 paddocks of 5000 m2. In ICLF, pasture was renewed in one-third of each replication of area (two paddocks) per crop year, where the grass was simultaneously sown with corn for silage. Pasture renewal was carried out in the 2013–2014, 2014–2015, 2016–2017, and 2017–2018 growing seasons. Data were collected in April 2016 and June 2019, when 110 trees were harvested to determine wood volume and 28 to gather wood rings and samples of the canopy, roots, and carbon content. These data were used to build the equations for estimating stem volume (m3 tree−1) and tree biomass (kg tree−1). Stem diameter at breast height (DBH, 1.3 m above the ground) and tree height (H) were measured in 10% of the trees in each plot to estimate stem volume and biomass; these were compared by t-test (5%). PAR was measured continuously from 2013 to 2019 at 70 cm aboveground with linear quantum sensors at the four ICLF positions across the tree line. Using these data, equations for volume = exp[(− -10.21 + 1.68 × ln(DBH)+1.29 × ln(H)] and biomass = exp[−3.88 + 2.41*ln(DBH)+0.62 × ln(H)] were built. The stem volume was greater in ICLF (225.7 m3 ha−1) than in ILF (215.2 m3 ha−1) (p = 0.0369). The total biomass was 148.3 Mg ha−1 for ICLF and 141.0 Mg ha−1 for ILF, with no significant differences between systems. The agroforestry systems accumulated 64.5 Mg ha−1 of carbon in tree biomass by eight years after system implementation. The basal area of trees in both agroforestry systems showed a strong relationship with the transmission of PAR to the pasture.

Characterizing the three-dimensional spatiotemporal variation of forest photosynthetically active radiation using terrestrial laser scanning data

The three-dimensional (3-D) spatiotemporal distribution of forest canopy photosynthetically active radiation (PAR) is a major determinant of within-crown variations of leaf photosynthesis and transpiration. However, it remains challenging to map the 3-D spatiotemporal distribution of PAR within and under the forest canopy due to the limited ability to capture the detailed 3-D structures of forest canopies.This study proposes a simple approach to estimate the 3-D spatiotemporal distribution of forest canopy PAR at a fine spatial resolution based on terrestrial laser scanner (TLS) data by characterizing difference in transfer of incident solar direct PAR and diffuse PAR and by considering the effect of the orientation angles of foliage elements on the 3-D distribution of direct PAR. Estimated PAR was validated using 10-minute PAR measurements from pyranometers at different locations within four forest plots, at which effective leaf area index (LAIe) ranged from 0.83–4.25. It showed that the proposed method captured 85% (N=2831, p<0.001) of the variations in the field pyranometer measurements. Furthermore, the proposed method was also applicable for estimating the vertical distribution of PAR (R2=0.95, N=15, p<0.001). Direct, diffuse, and total PAR exhibited similar vertical distributions changing with LAIe. It was shown that without differentiation of direct and diffuse PAR or ignoring effects of orientation angles of foliage elements may cause errors of about 20% in the estimated 3-D PAR distribution. Furthermore, the results indicated that the proposed method can be used to estimate the vertical distribution of PAR when the average neighbor point distance (NPD) is ≤20 cm. This proposed method will be usable for accurate separation of sunlit and shaded leaves and estimation of vertical distribution of PAR, which will benefit to reduce uncertainties in the estimation of terrestrial carbon fluxes and retrieval of vegetation structural and biochemical parameters.

Use of solar radiation in the improvement of spring canola (Brassica napus L., Brassicaceae) yield influenced by nitrogen topdressing fertilization

The objective of the present study was to quantify and evaluate the coefficients of interception, absorption, and use of photosynthetically active solar radiation (PAR), and its effects on grain yield (YLD) of spring canola influenced by N topdressing fertilization. Two experiments were performed in 2013 and 2014 using a randomized block design, with four replicates and five treatments of N: T1-T5 (10, 20, 40, 80, and 160 kg ha -1 , respectively). Plant, PAR, and meteorological variables were measured. The lower PAR interception efficiency (ei) occurred in treatment T1. The range of light extinction coefficient (k) was of the 0.55 to 1.09. PAR absorption efficiency (ea) ranged from 86 to 93%, while the PAR use efficiency (RUE) ranging from 1.2 to to 3.7 g m -2 MJ -1 . The mean N dose for maximum agronomic efficiency (MAE) for YLD was 99.3 kg ha -1 . The YLD varied according to N treatments and was influenced by RUE, dry matter accumulated until flowering (DMF), dry matter after flowering (DMAF) and total dry matter (TDM). Nitrogen fertilization affects the balance of PAR and, consequently, the canola yield.

Determining the K coefficient to leaf area index estimations in a tropical dry forest.

Vegetation indices are useful tools to remotely estimate several important parameters related to ecosystem functioning. However, improving and validating estimations for a wide range of vegetation types are necessary. In this study, we provide a methodology for the estimation of the leaf area index (LAI) in a tropical dry forest (TDF) using the light diffusion through the canopy as a function of the successional stage. For this purpose, we estimated the K coefficient, a parameter that relates the normalized difference vegetation index (NDVI) to LAI, based on photosynthetically active radiation (PAR) and solar radiation. The study was conducted in the Mata Seca State Park, in southeastern Brazil, from 2012 to 2013. We defined four successional stages (very early, early, intermediate, and late) and established one optical phenology tower at one plot of 20 × 20m per stage. Towers measured the incoming and reflected solar radiation and PAR for NDVI calculation. For each plot, we established 24 points for LAI sampling through hemispherical photographs. Because leaf cover is highly seasonal in TDFs, we determined ΔK (leaf growth phase) and Kmax (leaf maturity phase). We detected a strong correlation between NDVI and LAI, which is necessary for a reliable determination of the K coefficient. Both NDVI and LAI varied significantly between successional stages, indicating sensitivity to structural changes in forest regeneration. Furthermore, the K values differed between successional stages and correlated significantly with other environmental variables such as air temperature and humidity, fraction of absorbed PAR, and soil moisture. Thus, we established a model based on spectral properties of the vegetation coupled with biophysical characteristics in a TDF that makes possible to estimate LAI from NDVI values. The application of the K coefficient can improve remote estimations of forest primary productivity and gases and energy exchanges between vegetation and atmosphere. This model can be applied to distinguish different successional stages of TDFs, supporting environmental monitoring and conservation policies towards this biome.

OPTICAL PROPERTIES OF LAKE VENDYURSKOE

We conducted a field study on light conditions in a small boreal Karelian Lake Vendyurskoe over two years. Albedo of ice-covered lake varied from 0.9 to 0.1, and the euphotic zone depth exceeded 3.5 m during the melting stage. The Secchi disc depth changed from 2.5 m after ice-break to 3.7 m at the stage of early summer. The vertical distribution of the photosynthetically active solar radiation (PAR) attenuation coefficient for water Kw was characterized by high spatial (vertical) and temporal (seasonal and interannual) variability which can be connected with the dynamics of plankton cells. The highest values of Kw eached 2–2.8 m–1 in the upper 0.5 m layer of a water column, and decreased to 0.5–1.5 m–1 with increasing depth. The highest values of Kw were marked in the end of ice-covered period.

Effects of meteorological conditions and plant growth stage on the accumulation of carvacrol and its precursors in Thymus pulegioides

The effects of meteorological conditions (temperature, rainfall, photosynthetically active solar radiation (PAR) and sunshine duration) and plant growth stages on the quantitative composition of a secondary metabolite – essential oil and its main compounds, in the carvacrol chemotype of Thymus pulegioides L. (Lamiaceae) cultivated in open ground were studied under the same micro-edaphoclimatic environmental conditions for six years. The essential oil was isolated by hydrodistillation, the analysis of monoterpenic phenol carvacrol and the biogenetic precursors (monoterpene hydrocarbons p-cymene and γ-terpinene) were carried out annually using GC-FID and GC-MS. In the carvacrol chemotype investigated in this study, the yield of essential oil varied from 0.72% to 0.98% (CV = 12%) at full flowering stage. Regression analysis showed a significant negative relationship between the amount of essential oil and both temperature and rainfall during T. pulegioides flowering (July) and the period from April (beginning of vegetation) to July, but a strong positive relationship with photosynthetically active solar radiation during April–July (beta = 0.658, p < 0.05). The percentage of carvacrol, p-cymene and γ-terpinene ranged between 16.88 and 29.29% (CV = 18%), 5.54–11.33% (CV = 23%) and 20.60–24.43% (CV = 6%) respectively. Regression analysis showed the significant positive relationship between the percentage of carvacrol and sunshine duration at the flowering stage (in July) (beta = 0.699, p < 0.05); while the negative relationship was established between the percentages of precursors of carvacrol and photosynthetically active solar radiation and sunshine duration. The accumulation of p-cymene, the percentage of which varied most strongly from all investigated chemical compounds, showed significant positive relationships with temperature and rainfall during the period April–July and temperature in July (beta = 0.617, beta = 0.439 and beta = 0.429 respectively, p < 0.05). The analysis of plant growth stages showed that the highest amount of essential oil in carvacrol chemotype of T. pulegioides accumulated at ripening/seed maturity stage. The percentage of carvacrol increased gradually from the stem elongation to the post-flowering/seed maturity stage, overtaking the full flowering stage by 22%. The highest carvacrol content in the T. pulegioides carvacrol chemotype coincided with the highest oil yield during the fruiting stage. The amount of essential oil was also measured at the second full flowering stage, because after cutting the aerial part of the plant at the full flowering stage T. pulegioides often bloom for a second time: the carvacrol chemotype accumulated by 21% lower yield of essential oil at this stage compared to the first flowering, however, only traces of carvacrol and its precursors were found at the second full flowering stage.

Leaf color is fine-tuned on the solar spectra to avoid strand direct solar radiation.

The spectral distributions of light absorption rates by intact leaves are notably different from the incident solar radiation spectra, for reasons that remain elusive. Incident global radiation comprises two main components; direct radiation from the direction of the sun, and diffuse radiation, which is sunlight scattered by molecules, aerosols and clouds. Both irradiance and photon flux density spectra differ between direct and diffuse radiation in their magnitude and profile. However, most research has assumed that the spectra of photosynthetically active radiation (PAR) can be averaged, without considering the radiation classes. We used paired spectroradiometers to sample direct and diffuse solar radiation, and obtained relationships between the PAR spectra and the absorption spectra of photosynthetic pigments and organs. As monomers in solvent, the spectral absorbance of Chl a decreased with the increased spectral irradiance (Wm(-2)nm(-1)) of global PAR at noon (R(2)=0.76), and was suitable to avoid strong spectral irradiance (λmax=480nm) rather than absorb photon flux density (μmolm(-2)s(-1)nm(-1)) efficiently. The spectral absorption of photosystems and the intact thallus and leaves decreased linearly with the increased spectral irradiance of direct PAR at noon (I dir-max), where the wavelength was within the 450-650nm range (R(2)=0.81). The higher-order structure of photosystems systematically avoided the strong spectral irradiance of I dir-max. However, when whole leaves were considered, leaf anatomical structure and light scattering in leaf tissues made the leaves grey bodies for PAR and enabled high PAR use efficiency. Terrestrial green plants are fine-tuned to spectral dynamics of incident solar radiation and PAR absorption is increased in various structural hierarchies.

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.

Operational semi-physical spectral-spatial wheat yield model development

Abstract. Spectral yield models based on Vegetation Index (VI) and the mechanistic crop simulation models are being widely used for crop yield prediction. However, past experience has shown that the empirical nature of the VI based models and the intensive data requirement of the complex mechanistic models has limited their use for regional and spatial crop yield prediction especially for operational use. The present study was aimed at development of an intermediate method based on the use of remote sensing and the physiological concepts such as the photo-synthetically active solar radiation (PAR) and the fraction of PAR absorbed by the crop (fAPAR) in Monteith’s radiation use efficiency based equation (Monteith, 1977) for operational wheat yield forecasting by the Department of Agriculture (DoA). Net Primary Product (NPP) has been computed using the Monteith model and stress has been applied to convert the potential NPP to actual NPP. Wheat grain yield has been computed using the actual NPP and Harvest index. Kalpana-VHRR insolation has been used for deriving the PAR. Maximum radiation use efficiency has been collected from literature and wheat crop mask was derived at MNCFC, New Delhi using RS2-AWiFS data. Water stress has been derived from the Land Surface Water Index (LSWI) which has been derived periodically from the MODIS surface reflectance data (NIR and SWIR1). Temperature stress has been derived from the interpolated daily mean temperature. Results indicated that this model underestimated the yield by 3.45 % as compared to the reported yield at state level and hence can be used to predict wheat yield at state level. This study will be able to provide the spatial wheat yield map, as well as the district-wise and state level aggregated wheat yield forecast. It is possible to operationalize this remote sensing based modified Monteith’s efficiency model for future yield forecasting with around 0.15 t ha-1 RMSE at state level.

Effects of temperature, pH, and UV radiation on alkaline phosphatase activity in the terrestrial cyanobacterium Nostoc flagelliforme

Cyanobacteria produce phosphatases in response to phosphorus deficiency as some other autotrophs. However, little has been documented on the effects of key climate change factors, such as temperature rise and solar UV radiation (280–400 nm), on cyanobacterial alkaline phosphatase activity. Here, we found that the terrestrial cyanobacterium Nostoc flagelliforme showed higher activity of the enzyme with increasing temperature and pH levels, exhibiting maximal values at 45 °C and pH 11, respectively. However, when exposed to solar radiation in the presence of UV-A (320–400 nm) and UV-B (280–320 nm), significant reduction of the enzyme activity was observed at a photosynthetically active radiation (PAR) level of 300 W m−2 (1,450 μmol photons m−2 s−1), which is equivalent or lower than the noontime level of solar PAR at the organism's habitats. UV-A and UV-A + UV-B induced about 21 and 39 % inhibition of the enzyme activity in the 3-h exposures. The decrease in the activity of phosphatase can be attributed to the UV radiation-induced inactivation of the enzyme and indirectly to the UV radiation-induced production of reactive oxygen species.

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.

Photosynthetically active and UV radiation act in an antagonistic way in regulating buoyancy of Arthrospira ( Spirulina) platensis (cyanobacterium)

Buoyancy provided by gas vesicles has been suggested to play an important role in regulating vertical distribution and nutrient acquisition in cyanobacteria. However, little is known about how changes in UV radiation (UVR, 280–400 nm) would affect the buoyancy. We have shown here that the floatation activity of the economically important cyanobacterium Arthrospira platensis (D-0083) decreased with increased photosynthetic rates associated with increased photosynthetically active radiation (PAR), but it decreased less in the presence of UVR, which resulted in inhibitory effects. When the cells were grown under isoenergetic levels of solar PAR or UVR alone, they migrated downward under PAR but maintained buoyant under UVR. The buoyancy regulation of A. platensis depended on the exposed levels of PAR as well as UVR, which affected photosynthesis and growth in an antagonistic way. The buoyancy of A. platensis in water columns is likely to be dependant on diurnal photosynthetic performance regulated by solar radiation, and can hardly be considered as an active strategy to gain more energy during sunrise/sunset or to escape from harmful irradiation during the noon period.

The effects of shading on dioecious, pistillate Hydrilla verticillata (L.f.) Royle transplants from Lake Okeechobee, Florida, U.S.A.

The effect of shading on morphometric and meristic characteristics of dioecious, pistillate Hydrilla verticillata (L.f.) Royle was investigated in a large outdoor tank using water, sediment, and plants from Lake Okeechobee, Florida. These data were needed for a hydrologically integrated submersed aquatic vegetation model being developed to assess the effects of restoration activities on Lake Okeechobee. Plants were grown in peat sediment and lake water, under ambient temperature (27.0-30.8 °C) and photoperiod (13 L: 11D to 14 L: 10 D). Treatments were established by differentially shading plants with varying numbers of layers of fiberglass window screen. Photon flux density (PFD) measured 0.27 m above the sediment surface ranged from 8 to 154 μmole photons m -2 s -1 , or 1.1 to 21.6 % of average incident photosynthetically active solar radiation (PAR), based on percent transmittance in the tank and averaged continuous daytime measurements from a mid-lake PAR sensor. Plant characteristics examined included ash-free dry mass (AFDM), leaf, node, shoot, and branch numbers, leaf area, cumulative shoot length, and the number of leaves on the upper third of all shoots; all of which decreased linearly with decreasing PAR, and had statistically significant treatment effects. No statistically significant treatment effects were found for maximum shoot and mean and maximum internodal lengths, or when the number of leaves or branches on the upper third of all shoots were expressed as a percentage of their totals, indicating that significant treatment-induced internodal elongation and canopy formation had not occurred. Mean absolute and relative growth rates ofH. verticillata were estimated to be 11.6 ± 1.9 mg AFDM plant -1 d -1 (mean ± SE) and 0.04 ± 0.003 d -1 , respectively. Estimated photosynthetic PFDs for no net growth (NNG) was negative, with an upper 95 % confidence limit of 13 μmole photons m -2 s -1 , or 1.8 % of mean incident PAR for absolute, and 7 μmole photons m -2 s -1 , or 0.9 % of mean incident PAR for the mean relative growth rate. These results demonstrate that H. verticillata has a high growth rate and can grow in very low light, which may impart an important adaptive advantage given the poor light climate typical of much of Lake Okeechobee and many other disturbed, culturally hypereutrophic waterbodies.

Effects of solar UV and visible radiations on the spiral structure and orientation of Arthrospira (Spirulina) platensis (Cyanophyta)

P. Li and K. Gao. 2008. Effects of solar UV and visible radiations on the spiral structure and orientation of Arthrospira (Spirulina) platensis (Cyanophyta). Phycologia 47: 573–579. DOI: 10.2216/08-19.1Morphological characteristics of Arthrospira spp. are important for product quality and harvesting efficiency. Solar ultraviolet radiation (UVR) has been previously shown to break their spirals. To further explore the relationship of morphology and UVR, we examined the spiral length, helix diameter, helical pitch and orientation of A. platensis while exposing the cells to solar radiation with or without UVR. Although solar exposures initially led to breakage of the spirals, no significant difference was found among the treatments with or without UVR. During the long-term exposures to solar radiation, the spirals became more compressed in the outdoor strain (grown under sunlight for decades) but more loosened in the indoor strain [grown under artificial photosynthetically active radiation (PAR) for decades]. Spiral orientation was altered from the right- to left-handed only in the outdoor strain, with a frequency of less than 1%. Presence of UVR enhanced such an orientation change, and regrowing under indoor low PAR (UVR-free condition) reversed the orientation to right-handed. Structure of some membrane molecules was suggested to be altered by high solar PAR and UVR.

Global and direct photosynthetically active radiation parameterizations for clear-sky conditions

Estimation of clear-sky photosynthetically active solar radiation (PAR) is an important first step in calculating this solar spectral band under all sky conditions. This procedure is commonly used to derive incoming solar radiation from remote sensing data or using digital elevation models. We introduce a new parameterization to calculate instantaneous values of direct normal and horizontal global PAR components. The main goal was to limit the number of input parameters for PAR predictions to Ångström's turbidity coefficient, ground PAR-band albedo and atmospheric pressure (the latter two can be replaced by ground broadband albedo and site altitude). An important novel property of this parameterization is that it provides an analytical solution that provides integrated values along any time interval. Comparisons between calculated and measured values for different climatology sites demonstrate that the model can provide a good level of accuracy for instant, hourly and daily PAR estimates, with RMSE and MBE values of less than 4% and ±2%, respectively. The influence of turbidity parameters and ground albedo on model performance was also analyzed. The introduction of Ångström's turbidity coefficient and ground albedo should allow the use of the increasing worldwide aerosol information available and to consider sites affected by snow cover in an easy and fast way.