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  • 1
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Halophila stipulacea beds in the northern Gulf of Elat (Red Sea) may be subdivided into three different sub-habitats, each harboring a distinct population of diazotrophs. Nitrogen (N2) fixation in the phyllosphere and in the rhizomes/upper-sediment niche was light dependent, suggesting its dependence on photosynthesis. N2 fixation in the phyllosphere was not affected by the addition of either glucose or 3-3,4-dichloro-phenyl-1,1-dimethyl-urea (DCMU), indicating that the diazotrophs involved carried out non-oxygenic photosynthesis. They may, thus, have been photosynthetic bacteria. N2 fixation in the rhizomes/upper-sediment niche, however, was greatly enhanced by the addition of glucose, but was suppressed in the presence of DCMU. This indicates that the diazotrophs involved here probably possess two photosystems (I and II) and may be Cyanobacteria. The anaerobic rhizosphere, in which fixation rates in light were very slow but were greatly enhanced by the addition of glucose, is probably populated by heterotrophic diazotrophs. Plant and sediment samples used in the present study were collected from the Gulf of Elat between 1990 and 1992.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The properties of the recently discovered extrasolar planets were not anticipated by theoretical work on the formation of planetary systems, most models for which were developed to explain our Solar System. Indeed, the observational technique used to detect these planets (measurement of ...
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Observations of the long-lived emission—or ‘afterglow’—of long-duration γ-ray bursts place them at cosmological distances, but the origin of these energetic explosions remains a mystery. Observations of optical emission contemporaneous with the burst of ...
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 89 (1985), S. 159-183 
    ISSN: 1573-5036
    Keywords: Marine algae ; Sea vegetables ; Thalassonomy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The outdoor cultivation of sea vegetables is carried out on a large scale in the Orient, mainly in Japan, China, Taiwan, Korea and the Philippines. Food crops are the most important among the sea vegetables cultivated, with Porphyra and Undaria being the more important in Japan and Laminaria in China. Eucheuma, an industrial crop containing the phycocolloid carrageenan, is cultivated in wide areas of the Philippines. The cultivation of the major food crops, which developed quickly over the past 30 years, is largely based on the results of research, especially with regard to seeding procedures, which have reached a certain level of sophistication. The major crops of sea vegetables are cultivated attached to ropes or nets located in a suitable site and habitat. Crops of limited economic value, however, are still cultivated by the old, primitive method of planting on stones on the ocean bed and other similar means. The location and timing of farming are selected with regard to the requirements of the plants for light, temperature, water movement, exposure to air (for the intertidal species),etc. Cultivation of seeding material of the three food crops and seeding of ropes and nets is carried out indoors under more or less controlled conditions. When the sporelings become established they are transferred to cultivation grounds in the ocean. When the plantlets grow too densely (in Laminaria) they have to be separated and replanted at the correct distances. This is done several weeks after transplantation to the ocean, when they are large and sufficiently strong. Eucheuma and other industrial crops are propagated vegetatively, using cuttings and fragments as planting material. Where seawater is lacking in nutrients, fertilizers are applied to guarantee a higher yield. The harvest is carried out manually, except for Porphyra, for which mechanical harvesters are used. Sea vegetables are attacked by pathogens that may cause severe damage to the crops. Diseases caused by improper growing conditions are also known. Grazers may also inflict losses. In all major crops the strains cultivated have been selected. In a few cases hybridization and other genetic techniques have been used to obtain domesticated varieties that can grow and yield far beyond the limits of their wild-type parents. Despite the fact that some mechanization has been introduced into the cultivation of sea vegetables, it is still by and large a highly labor-intensive enterprise. Nevertheless, it competes well with terrestrial crops in the Orient from the economic point of view. Interest in the cultivation of sea vegetables is widespread in the West and much experimental work aimed at its materialization has been underway during the lastca. twenty years.
    Type of Medium: Electronic Resource
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