• KOREAN JOURNAL OF CROP SCIENCE
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• v.27 no.4
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• pp.296-313
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• 1982

At a time when world population and food supply are in a delicate balance, it is essential that we look at factors to improve this balance. We can alter the environment to better fit the plant's needs, or we can alter the plant to better fit the environment. Improved technology has allowed us to increase the yield level. For moderately detrimental weather events technology has generally decreased the yield variation, yet for major weather disasters the variation has increased. We have raised the upper level, but zero is still the bottom level. As we concentrate the production of particular crops into limited areas where the environment is closest to optimum, we may be increasing the risk of a major weather related disaster. We need to evaluate the degree of variability of different crops, and how weather and technology can interact to affect it. The natural limits of crop production are imposed by important ecological factors. Production is a function of the climate, the soil, and the crop and all activities related to them. In looking at the environment of a crop we must recognize these are individuals, populations and ecosystems. Under intensive agriculture we try to limit the competition to one desired species. The environment is made up of a complex of factors; radiation, moisture, temperature and wind, among others. Plant response to the environment is due to the interaction of all of these factors, yet in attempting to understand them we often examine each factor individually. Variation in crop yields is primarily a function of limiting environmental parameters. Various weather parameters will be discussed, with emphasis placed on how they impact on crop production. Although solar radiation is a driving force in crop production, it often shows little relationship to yield variation. Water may enter into crop production as both a limiting and excessive factor. The effects of moisture deficiency have received much more attention than moisture excess. In many areas of the world, a very significant portion of yield variation is due to variation in the moisture factor. Temperature imposes limits on where crops can be grown, and the type of crop that can be grown in an area. High temperature effects are often combined with deficient moisture effects. Cool temperatures determine the limits in which crops can be grown. Growing degree units, or heat accumulations, have often been used as a means of explaining many temperature effects. Methods for explaining chilling effects are more limited.

• Korean Journal of Ecology and Environment
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• v.52 no.4
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• pp.333-339
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• 2019

The Red swamp crawfish Procambarus clarkii is native to the southern United States and inhibits all over the world including the United States, Asia, Africa and Europe. In Europe, it is known to disrupt ecosystems such as competition with native crayfish. In this study, habitats of red swamp crawfish were identified in Jiseok stream (15.5 km section) and Daecho stream (6.1 km section) of Youngsan river. A total 33 red swamp crawfish were captured. A female captured in Jiseok stream carried 215 newly hatched red swamp crawfish in her the burrow. As a result of the analysis of the habitat environment, the water temperature was ranged of 2.4~32.8℃, conductivity was 53.4~502.3 μS cm^-1 and DO was 0.74~22.64 mg L^-1. As a result of measuring HOBO, the temperature ranged from -9~48.1℃, showing a change of 57.1℃ throughout the year. The variation of the water temperature throughout the year from 2.9~33.9℃ was found to be 31℃. Red swamp crawfish have a high adaptability and a wide range of environmental resistance, and report a sharp increase in newly invaded areas, negatively affecting indigenous organisms. In addition, it can be used as a medium for the spread of diseases and parasites, so prompt investigation and research should be carried out.

• Korean Journal of Weed Science
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• v.4 no.1
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• pp.19-25
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• 1984

Emergence, growth of weeds and growth, yields of rice (cv. Sam Seung Byeo) were determined at different transplanting times and nitrogen levels. Dominant weed species were Cyperus difformis, Rotala indica, Monochoria vaginalis, Cyperus serotinus, Sagiitaria pygmaea, Scirpus hotarui, and Fimbristylis miliacea. Number of weeds was increased in earlier transplanting time and but decreased in high nitrogen level. Dry weight of weeds was decreased with increase of nitrogen level at early transplanting time (May 26) but increased at nitrogen 8 or 16㎏/10a, Plant height, dry weight, leaf area index, and yield of rice were decreased as transplanting time was delayed but increased as nitrogen level increased. Yield reduction of rice due to weed competition was increased in earlier transplanting time and decreased in high nitrogen level.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.5
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• pp.430-434
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• 2001

The algicidal activity of Shewanella (formerly Alteromonas) sp. SR-14 against diatom, Chaetoceros calcitrans was reported in our previous papers. In this study, the effect of Vibrio alginolyticus on the algicidal activity of Shewanelia sp, SR-14 was examined under the optimum algicidal conditions, i.e., temperature ($21\pm1^{\circ}C$), light intensity (4,000 lux), and light: dark cycle (12 hour: 12 hour). Shewanella sp. SR-14 grew well in the presence or the absence of V. alginolyticus in Conwy medium. Algal growth was only inhibited by Shewanella sp. SR-14. V. alginolyticus did not show the algicidal activity, Growth of C. calcitrans increased synergistically with growth of V. alginolyticus. When the initial inoculum of V. alginolyticus was only 1 log cycle higher than that of Shewanella sp. SR-14, the effect of V. alginolyticus on the algicidal activity of Shewanella sp. SR-14 was insignificant during incubation of mixed culture, i.e., two bacterial species and the alga. However, when V. alginolyticus dominated Shewanella sp. SR-14 by 3 log cycles of bacterial counts, it was found that the strain SR-14 could not inhibited growth of C. calcitrans up to 5 days of incubation.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.1
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• pp.39-45
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• 1997

Subtidal zonation of a cumacean Bodotria biplicata was investigated in the sandy shore surf zone of Dolsando, southern Korea. Three replicate samples were taken with a sledge net at three sites, such as the surface and bottom of 1 m depth and waters edge, at hourly intervals over the neap and spring tide cycles on January 1993 (n=225). B. biplicata, the most dominant cumacean in this area, exhibited peak density at the bottom while about $0.6\%$ of total catch was collected at the surface. Mean density during the neap tide cycle was slightly higher than that during the spring tide cycle. The depth of subtidal zone influenced the total catch of B. biplicata. The changes in density were related to the depth of subtidal zone rather than day-night cycle or ebb-flood tide. The results obtained in this study suggest that the diel vertical migration is not distinct. During both neap and spring tide cycles, B. biplicata attained a density maximum at the same level of about 90 cm below lower low water (LLW). It is likely, therefore, that this species performs shore- and seaward horizontal migration fortnightly. The speed and distance of migration may be directly related to the beach slope and tide range. Ontogenetic differences in subtidal distribution were observed. Juveniles and manca larvae tended to occur lower areas than the adults. Such differences may reduce intraspecific competition for diets.

• Korean Journal of Weed Science
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• v.12 no.3
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• pp.223-229
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• 1992

Very recently, the cultural pattern of paddy rice in Korea was transitted in a short period, and resulted as earlier in season and more in fertillizer application among others. Specially the weed emergence in paddy fields was drastically increased as affected by change of cultural pattern into early planting and into direct seeding methods. Of course, the direct-seeding in row seeding induced more weeds than in broad-cast direct -seeding. By maintaining the water level with saturation of the paddy surface induced more weeds, relatively more annual weeds than by deep in water level, respectively. Relatively more annuals in number of species and in emerged quantity comparing with perennials was caused by the shifting of cultural methods from transplanting to direct seeding. The severe weed competition damages were mainly resulted due to the shading by taller plant heights of weeds than crop during the whole growing seasons. Conclusively, accepting of direct seeding methods in paddy rice culture in Korea, the present bases for weed control methods ought to be naturally and effectively improved to meet the newly made weed problems.

• Journal of Korea Foresty Energy
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• v.20 no.2
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• pp.69-80
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• 2001

Larix kaemferi Carr. is one of main timber species in Korea that could be found in plantations and growing stands on all over the country The proper practice of thinning is one of very important techiques in silviculture, which greatly affects the quality and size of timber produced. Proper thinning period is considered to be important for maintaining stand growth before competition initiated. To investigate suitable thinning period, this study investigates the volume and radial growths of Larix kaemferi plantation in Mt. Worak located in the central part of Korea. The main findings and conclusions obtained from this study were as follow ; (1) The tree height curve equation for Larix kaemferi in Mt. Worak was calculated H=4.25783+0.80024D(H=Tree height, D=DBH). (2) To estimate tree volume for Larix kaemferi by DBH and tree height or only by DBH, regression equations were calculated as V=0.00147-0.002095D-0.000211H+0.00015D.H++$0.000744D^2$+$0.000008H^2$(V=Volume(($m^3$), H=Tree height(m), D=DBH(cm)), V=0.0000794-0.000512D+$0.000826D^2$. (3) The criteria of estimating thinning time of Larix kaemferi are the age when maximum tree height-MAI(mean annual increment) obtained and the age when annual DBH increments of dead trees decrease to below average. (4) The age of maximum tree height MAI was not significantly correlated with stocking. Therefore, it can not be used as a criterion for estimating thinning time of Larix kaemferi (5) The estimated thinning time equation of Larix kaemferi was obtained by regression analysis of the disk section collected from dead trees. The obtained equation is Y=0.2825+0.01752X(Y=Desirable thinning age, X=the sum total of nearest 4-trees interval(cm)). (6) General estimated thinning age of Larix kaemferi, which planted 3,086 stocks/ha, is concluded as 12 to 14 year.

• Korean Journal of Ecology and Environment
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• v.33 no.4 s.92
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• pp.319-327
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• 2000

The feeding behavior of 1-year-old silver carp, Hypophthalmichthys molitrix (Val.) on phytoplankton species in a shallow hypertrophic lake was studied from 22 May to 18 September, 1997. Over the experimental period, the filter-pore sizes of the fish, the total biomass of the phytoplankton and the water temperature in each enclosure changed little with time. The fish biomass in each enclosure increased with time, while their percentage of weight gain correlated negatively to the stocking density, due perhaps to competition for prey. An analysis of gut contents of silver carp showed a strong similarity between the algal communities in the foregut and the water, and was significant for the fish enclosure with a low density (p<0.05). The presence of silver carp rarely suppressed the abundance of phytoplankton such as Oscillatoria, Anabaena and Melosira even at high ingestion levels. There were weak relationships between the IU values of each phytoplankton and the selectivity of fish on them (r = 0.001, p>0.5). There was no doubt that the silver carp fed unselectively when cyanobacteria populations were high, even though the selectivity index for diatoms was slightly higher than those for cyanobacteria, green algae and cryptomonads. Improvements in methodologies are needed to clearly understand and generalize the feeding behavior of silver carp.

• Korean Journal of Environmental Biology
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• v.18 no.4
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• pp.367-376
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• 2000

Euglenoids occurring in freshwaters are indicator organisms to be used for assessing water quality and applying to environmental education. One hundred sixty eight taxa of euglenoids belonging to three orders, four families and nine genera occur in various waters, especially in eutrophicated and polluted places in Korea. Members of Euglena and Strombomonas are abundant in urban drainages and old ponds, and those of Trachelomonas, Phacus, and Lepocinclis often occur in stagnant waters such as natural wetlands and old swamps. Population size of some euglenoids is significantly correlated to nitrogenous nutrients. Euglena caudata, E. doses, E. ehrenbergii, E. haemichromata, E. geniculata, E. viridis, Lepocinclis ovum, Strombomonas urceolata, Phacus trypanon, Trachelomonas hispida, and T volvocina cells in Korea bloomed in winter and spring, when other phytoplanktonic algae greatly decrease. Blooming of euglenoids indicates tolerance to pollutants and positive selection as a result of competition with other phytoplankton species. We developed a web site on green euglenoids (Yahoo. com: Science/ Biology/ Botany/ Phycology/ Biology of Green Euglenoids), which may be use d for cyber education of water environment. We also presented a method for assessing water quality using diversity and population size of euglenoids, which is considered to be suitable for environmental education of polluted waters.

• Food Science of Animal Resources
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• v.26 no.3
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• pp.402-409
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• 2006

Although microorganisms are, in fact, the most diverse and abundant type of organism on Earth, the ecological functions of microbial populations remains poorly understood. A variety of bacteria including marine Vibrios encounter numerous ecological challenges, such as UV light, predation, competition, and seasonal variations in seawater including pH, salinity, nutrient levels, temperature and so forth. In order to survive and proliferate under variable conditions, they have to develop elaborate means of communication to meet the challenges to which they are exposed. In bacteria, a range of biological functions have recently been found to be regulated by a population density-dependent cell-cell signaling mechanism known as quorum-sensing (QS). In other words, bacterial cells sense population density by monitoring the presence of self-produced extracellular autoinducers (AI). N-acylhomoserine lactone (AHL)-dependent quorum-sensing was first discovered in two luminescent marine bacteria, Vibrio fischeri and Vibrio harveyi. The LuxI/R system of V. fischeriis the paradigm of Gram-negative quorum-sensing systems. At high population density, the accumulated signalstrigger the expression of target genes and thereby initiate a new set of biological activities. Several QS systems have been identified so far. Among them, an AHL-dependent QS system has been found to control biofilm formation in several bacterial species, including Pseudomonas aeruginosa, Aeromonas hydrophila, Burkholderia cepacia, and Serratia liquefaciens. Bacterial biofilm is a structured community of bacterial cells enclosed in a self-produced polymeric matrix that adheres to an inert or living surface. Extracellular signal molecules have been implicated in biofilm formation. Agrobacterium tumefaciens strain NT1(traR, tra::lacZ749) and Chromobacterium violaceum strain CV026 are used as biosensors to detect AHL signals. Quorum sensing in lactic acid bacteria involves peptides that are directly sensed by membrane-located histidine kinases, after which the signal is transmitted to an intracellular regulator. In the nisin autoregulation process in Lactococcus lactis, the NisK protein acts as the sensor for nisin, and NisR protein as the response regulator activatingthe transcription of target genes. For control over growth and survival in bacterial communities, various strategies need to be developed by which receptors of the signal molecules are interfered with or the synthesis and release of the molecules is controlled. However, much is still unknown about the metabolic processes involved in such signal transduction and whether or not various foods and food ingredients may affect communication between spoilage or pathogenic bacteria. In five to ten years, we will be able to discover new signal molecules, some of which may have applications in food preservation to inhibit the growth of pathogens on foods.