• KOREAN JOURNAL OF CROP SCIENCE
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• v.35 no.2
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• pp.156-164
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• 1990

A field experiment was conducted to study both the distribution characteristics of photosynthetically active radiation (PAR) in the soybean canopy and their relationships with dry matter production. The soybean cultivars 'Hwanggeumkong' and 'Paldalkong' were sown with the spaces of 60$\times$15cm and 30$\times$15cm at Suwon on May 20 and on June 20 in 1989. The ratio of PAR to the total shortwave radiation was estimated by the empirical equation derived from sunshine hours and direct incoming radiation. The functional relationships between the PAR interception and the leaf area index were expressed as a function of Beer's law. The extinction coefficients(k) in the functions ranged from 0.77 to 0.92. The values of k were greater at higher planting density, but they were affected neither by planting dates nor by varieties. The reflection ratio of PAR($\alpha$) was determined by the exponential function as below; $\alpha$=$\alpha$p-($\alpha$p-$\alpha$o) exp(-kㆍLAI) where $\alpha$p was the reflectance at the maximum LAI and $\alpha$o was that of the bare soil. The ap ranged from 0.025 to 0.035 and $\alpha$o ranged from 0.11 to 0.12, respectively. The reflected PAR ranged from 0.049 to 0.064 and the transmitted PAR ranged from 0.168 to 0.340 until maximum dry weights were observed. The slope from the linear regression of dry matter on absorbed PAR, conversion efficiency, ranged from 1.30 to 2.3g MJ$^{-1}$ during the growing season until maximum dry weight was reached. The total dry matter yield above ground (TDM) increased with the increases in the conversion efficiency. TDM was higher in Hwanggeumkong than Paldalkong and higher in the space of 30$\times$15cm than 60$\times$15cm, Paldalkong showed higher harvest index than Hwanggeumkong. than Hwanggeumkong.

• The Korean Journal of Ecology
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• v.8 no.2
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• pp.99-107
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• 1985

Photosynthetically Active Radiation (PAR) affects the growth of plants as well as their photosynthetic rates. A mathematical model for intercepted solar radiation on the tilted leaf with any azimuth angle was established and the leaf orientation in which receives the maximum solar radiation was determined each month, during the growing season, and for an year. PAR was maximized at the leaf elevation of 50。~60。 in the winter, at that of 20。~40。. On the whole the leaves of tilt angle 0。~40。 received much radiation comparing with those of other tilt angles. The theoretical tendencies were compared with the distribution of leaf orientation measused practically. The average leaf elevation of maple tree was 17.0。$\pm$12.0。, and that of ginkgo was 29.8。$\pm$16.0。. Several results from other literatures support our suggestion that cumulative effevct of the relationships between surface normal vector and a vector pointing in the direction of the radiation determine the leaf orientation.

• The Korean Journal of Ecology
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• v.27 no.6 s.122
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• pp.363-367
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• 2004

Photosynthetically active radiation (PAR) beneath the forest canopy, understory species richness and diversity, and biomass were measured in a Larix leptolepis plantation seven years after thinning in Yangpyeong. Four different thinning intensities (control, $10\%,\;20\%\;and\;40\%$ stocking reduction) were applied in 1997. The current PAR values were lower than those measured four years after thinning, and PAR at the heavy thinning plots was significantly higher than that of other thinning intensities. A total of 23 species including 9 tall-trees and 14 shrubs were found for the high layer while a total of 82 species including 10 tall-trees, 29 shrubs, and 43 herbs for the low layer. Species richness and diversity generally increased with thinning intensities, and the trends were more evident for the low layer. Aboveground biomass significantly differed among thinning intensities for both shrubs and herbs. Also there was a negative correlation between biomass and the current number of stems per hectare. The current study suggested that the effects of thinning on light conditions at the forest floor, species richness and diversity and production of understory vegetation continued seven years after the treatment.

• Journal of Korean Society of Forest Science
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• v.99 no.3
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• pp.397-403
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• 2010

This study was conducted to investigate the changes in soil temperature, soil moisture content, light availability (photosynthetically active radiation, PAR) and diameter growth in 46-year-old Korean pine (Pinus koraiensis Siebold et Zuccarini) plantation located in Gwangneung experimental forest after 4 years from thinning. Three different thinning intensities [control, 45%(T45), and 60%(T60) basal area reduction] were applied in 2004. Mean soil temperature and soil water content were $8.9^{\circ}C$ and 14.3% for control, $10^{\circ}C$ and 16.1% for T45 and $10.2^{\circ}C$ and 16.1% for T60, respectively. Mean soil temperature and moisture content were significantly different among the treatment plots (p<0.05). Mean PAR in control, T45 and T60 was 44, 143 and178 ${\mu}mol/m^2$/sec, respectively and the differences were also statistically significant among the treatment plots (p<0.05). Mean annual diameter growth in control, T45 and T60 was 0.4, 1.5 and 1.2 mm, respectively. Diameter growth of Pinus koraiensis was steadily increased after thinning in comparison to control. Consequently, the results suggested that soil temperature, soil moisture content and light availability were likely to last beyond the 4 years after thinning in this Korean pine plantation.

• ALGAE
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• v.29 no.1
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• pp.27-34
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• 2014

Availability of nutrients is known to influence marine primary production; and it is of general interest to see how nutrient limitation mediates phytoplankton responses to solar ultraviolet radiation (UVR, 280-400 nm). The red tide diatom Skeletonema costatum was cultured under nitrate (N)-limited and N-replete conditions and exposed to different solar irradiation treatments with or without UV-A (315-400 nm) and UV-B (280-315 nm) radiation. Its photochemical quantum yield decreased by 13.6% in N-limited cells as compared to that in N-replete ones under photosynthetically active radiation (PAR)-alone treatment, and the presence of UV-A or UV-B decreased the yield further by 2.8 and 3.1%, respectively. The non-photochemical quenching (NPQ), when the cells were exposed to stressful light condition, was higher in N-limited than in N-replete grown cells by 180% under PAR alone, by 204% under PAR + UV-A and by 76% under PAR + UV-A + UV-B treatments. Our results indicate that the N limitation exacerbates the UVR effects on the S. costatum photosynthetic performance and stimulate its NPQ.

• ALGAE
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• v.28 no.3
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• pp.281-288
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• 2013

Photosynthetic carbon fixation regulates air-sea $CO_2$ fluxes in the waters of coral reefs. However, little has been documented on the effects of solar UV radiation (UVR, 280-400 nm) upon photosynthetic behaviors of phytoplankton dwelling in these ecosystems. In order to evaluate the aforesaid, surface dwelling tropical coral reef phytoplankton assemblages collected from the South China Sea were exposed to solar radiation (i.e., photosynthetically active radiation [PAR] + UV radiation A [UVA] + UV radiation B [UVB], 280-700 nm; PAR + UVA, 320-700 nm; and PAR, 400-700 nm) under static or simulated-mixing conditions. Under the static condition, UVA and UVB significantly reduced the carbon fixation with the maximum of 22.4 and 15.3%, respectively; while lower UVR-related photosynthetic inhibition was observed in case of phytoplankton samples being subjected to mixing. At a moderate level of mixing (i.e., circulation time 80 min), the UVA and UVB caused inhibition were lowered by 52.1 and 79.6%, respectively. Based on this it could be stated that vertical mixing induced by winds and/or tides in the natural environments could reduce the inhibitory effect of solar UVR on phytoplankton productivity in the coral reefs water.

• Journal of Photoscience
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• v.9 no.2
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• pp.436-438
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• 2002

Since solar radiation contains wavelength essential for photosynthesis accompanying with near-UV light, UV-B effects on biological parameters and acclimation mechanisms are influenced by photosynthetically active radiation (PAR). Therefore, to elucidate near-UV shielding mechanism in higher plants, we cultivated cauliflower under usual solar radiation and increased UV-B from fluorescent lamps, two- or three-fold excess over continuously estimated UV-B dose in PAR during daytime, using computer regulated systems. Increased UV-B radiation had little effect on growth expressed as fresh weigh and leaf area. Water soluble low molecular weight compounds showing absorption in near UV region were enhanced according to the irradiated UV-B dose. One of compounds in cauliflower leaves was identified as chlorogenic acid. This was found to have no near-UV photosenSitizerable activity and is known to have an ability to scavenge a wide species of active oxygen. Another pro-oxidant compound that generates superoxide anion radical under near-UV irradiation was not induced by increased UV-B during cultivation, and identified as lumazine, a degradation product from folic acid.

• Ocean Science Journal
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• v.41 no.4
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• pp.235-244
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• 2006

Determining 'photosynthetically active radiation' (PAR) is a key part of calculating phytoplankton productivity in a biogeochemical model. We explore the daily and seasonal variability in the ratio of PAR irradiance to total irradiance that occurred at Ieodo Ocean Research Station (IORS) in the East China Sea under clear-sky conditions in 2004 using a simple radiative transfer model (RTM). Meteorological data observed at IORS and aerosol optical properties derived from Aerosol Robotic Network observations at Gosan are used for the RTM. Preliminary results suggest that the use of simple PAR irradiance-ratio values is appropriate in calculating phytoplankton productivity as follows: an average of $0.44\;({\pm}0.01)$ in January to an average of $0.48\;({\pm}0.01)$ in July, with average daily variabilities over these periods of about $0.016\;({\pm}0.008)$ and $0.025\;({\pm}0.008)$, respectively. The model experiments demonstrate that variations in the major controlling input parameters (i.e. solar zenith angle, precipitable water vapor and aerosol optical thickness) cause PAR irradiance ratio variation at daily and seasonal timescales. Further, increases (>0.012) in the PAR irradiance ratio just below the sea-surface are positively correlated with high solar zenith angles and strong wind stresses relative to those just above the sea-surface.

• Journal of Practical Agriculture & Fisheries Research
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• v.25 no.4
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• pp.84-89
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• 2024

Light is an important component among which plays a crucial role in determining the production and quality of fruit trees. Since the disturbance of light directly leads to reduced photosynthetic efficiency, their damage can be increased especially in fruit trees such as Japanese apricots with a short growing time. In this study, we investigated how the effects of shading condition can affect the production and quality of Japanese apricots according to increased damages by light disturbance in the main orchard complex. The average photosynthetically active radiation (PAR) level in Japanese apricots was rapidly dropped as the shading time was increased compared to the control (304 μmol/m²/s) and the PAR level decreased to 142 μmol/m²/s after shaded for eight hours. The maximum photosynthetic efficiency, with a PAR value of 900 to 1,000 μmol/m²/s, corresponds to the time period without shading and the time period with 2 hours of shading, and these times range from 11 a.m. to 3 p.m. And the time period for shading for 4 hours was from 1:00 p.m. to 2:00 p.m., and under conditions of shading for 6 and 8 hours, the effect was a low amount of light. There was no difference in the weight of Japanese apricots during 2 hours shading time, however, it was significantly reduced as shading time were increased. The difference of the acid content and L/D ratio was not significant on shading time, but the SSC was decreased as times going on. In conclusion, our results indicate that the shading for more than 2 hours make negative effects to decrease the weight and SSC and the yield and affects directly to drop in fruit quality.

• Ocean and Polar Research
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• v.40 no.4
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• pp.281-288
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• 2018

The transmission of solar light according to the distribution of chromophoric dissolved organic matter (CDOM) was measured in the Pacific Arctic Ocean. The Research Vessel Araon visited the ice-covered East Siberian and Chukchi Seas in August 2016. In the Arctic, solar [ultraviolet-A (UV-A), ultraviolet-B (UV-B), and photosynthetically active radiation (PAR)] radiation reaching the surface of the ocean is primarily protected by the distribution of sea ice. The transmission of solar light in the ocean is controlled by sea ice and dissolved organic matter, such as CDOM. The concentration of CDOM is the major factor controlling the penetration depth of UV radiation into the ocean. The relative CDOM concentration of surface sea water was higher in the East Siberian Sea than in the Chukchi Sea. Due to the distribution of CDOM, the penetration depth of solar light in the East Siberian Sea (UV-B, $9{\pm}2m$; UV-A, $13{\pm}2m$; PAR, $36{\pm}4m$) was lower than in the Chukchi Sea (UV-B, $15{\pm}3m$; UV-A, $22{\pm}3m$; PAR, $49{\pm}3m$). Accelerated global warming and the rapid decrease of sea ice in the Arctic have resulted in marine organisms being exposed to increased harmful UV radiation. With changes in sea ice covered areas and concentrations of dissolved organic matter in the Arctic Ocean, marine ecosystems that consist of a variety of species from primary producers to high-trophic-level organisms will be directly or indirectly affected by solar UV radiation.