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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 51 (2000), S. 0 
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Identifying ‘functional' pools of soil organic matter and understanding their response to tillage remains elusive. We have studied the effect of tillage on the enriched labile fraction, thought to derive from microbes and having an intermediate turnover time. Four soils, each under three regimes, long-term arable use without tillage (NT), long-term arable under conventional tillage (CT), and native vegetation (NV), were separated into four aggregate size classes. Particle size fractions of macro- (250–2000 μm) and microaggregates (53–250 μm) were isolated by sonication and sieving. Subsequently, densiometric and chemical analyses were made on fine-silt-sized (2–20 μm) particles to isolate and identify the enriched labile fraction. Across soils, the amounts of C and N in the particle size fractions were highly variable and were strongly influenced by mineralogy, specifically by the contents of Fe and Al oxides. This evidence indicates that the fractionation procedure cannot be standardized across soils. In one soil, C associated with fine-silt-sized particles derived from macroaggregates was 567 g C m−2 under NV, 541 g C m−2 under NT, and 135 g C m−2 under CT, whereas C associated with fine-silt-sized particles derived from microaggregates was 552, 1018, 1302 g C m−2 in NV, NT and CT, respectively. These and other data indicate that carbon associated with fine-silt-sized particles is not significantly affected by tillage. Its location is simply shifted from macroaggregates to microaggregates with increasing tillage intensity. Natural abundance 13C analyses indicated that the enriched labile fraction was the oldest fraction isolated from both macro- and microaggregates. We conclude that the enriched labile fraction is a ‘passive' pool of soil organic matter in the soil and is not derived from microbes nor sensitive to cultivation.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 52 (2001), S. 0 
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: It is generally accepted that particulate organic matter derives from plants. In contrast, the enriched labile fraction is thought by many to derive from microbes, especially fungi. However, no detailed chemical characterization of these fractions has been done. In this study, we wanted to assess the sources (plants or microbes; fungi or bacteria) and degree of microbial alteration of (i) three particulate organic matter fractions – namely the free light fraction (1.85 g cm−3), the coarse (250–2000 μm) and the fine (53–250 μm) intra-aggregate particulate organic matter fractions – and of (ii) three density fractions of fine-silt associated carbon – namely 〈 2.0, 2.0–2.2 (i.e. enriched labile fraction) and 〉 2.2 g cm−3– by analysing the amino sugars, by CuO oxidation analyses, and by 13C-, 1H- and 31P-NMR analyses. Macroaggregates (250–2000 μm) were separated by wet-sieving from a former grassland soil now under a no-tillage arable regime. The three particulate organic matter fractions and the three density fractions were isolated from the macroaggregates by a combination of density flotation, sonication and sieving techniques. Proton NMR spectroscopy on alkaline extracts showed that the enriched labile fraction is not of microbial origin but is strongly degraded plant material that is enriched in aliphatic moieties partly bound to aromatics. In addition, the enriched labile fraction had a glucosamine content less than the whole soil, indicating that it is not enriched in carbon derived from fungi. Decreasing yields of phenolic CuO oxidation products and increasing side-chain oxidation in the order coarse intra-aggregate particulate organic matter 〈 fine inter-aggregate particulate organic matter 〈 fine-silt fractions indicate progressive alteration of lignin as particle size decreases. The light fraction was more decomposed than the coarse inter-aggregate particulate organic matter, as indicated by (i) its larger ratio of acid-to-aldehyde of the vanillyl units released by CuO oxidation, (ii) the smaller contribution of H in carbohydrates to total extractable H as estimated by 1H-NMR spectroscopy, and (iii) a larger contribution of monoester P to total extractable P in the 31P-NMR spectra. In conclusion, the four fractions are derived predominantly from plants, but microbial alteration increased as follows: coarse inter-aggregate particulate organic matter 〈 light fraction ≈ fine inter-aggregate particulate organic matter 〈 enriched labile fraction.
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Industrial and engineering chemistry 12 (1940), S. 416-417 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Global change biology 2 (1996), S. 0 
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: An experiment was carried out to determine the effects of elevated CO2, elevated temperatures, and altered water regimes in native shortgrass steppe. Intact soil cores dominated by Bouteloua gracilis, a C4 perennial grass, or Pascopyrum smithii, a C3 perennial grass, were placed in growth chambers with 350 or 700 μL L−1 atmospheric CO2, and under either normal or elevated temperatures. The normal regime mimicked field patterns of diurnal and seasonal temperatures, and the high-temperature regime was 4 °C warmer. Water was supplied at three different levels in a seasonal pattern similar to that observed in the field.Total biomass after two growing seasons was 19% greater under elevated CO2, with no significant difference between the C3 and C4 grass. The effect of elevated CO2 on biomass was greatest at the intermediate water level. The positive effect of elevated CO2 on shoot biomass was greater at normal temperatures in B. gracilis, and greater at elevated temperatures in P. smithii. Neither root-to-shoot ratio nor production of seed heads was affected by elevated CO2.Plant tissue N and soil inorganic N concentrations were lower under elevated Co2, but no more so in the C3 than the C4 plant. Elevated CO2 appeared to increase plant N limitation, but there was no strong evidence for an increase in N limitation or a decrease in the size of the CO2 effect from the first to the second growing season. Autumn samples of large roots plus crowns, the perennial organs, had 11% greater total N under elevated CO2, in spite of greater N limitation.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 1 (1987), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The phenotype of a recently-described mutant (OVG), conditionally defective in chromosome partitioning and septal positioning, was originally thought to be due to a new gene (parD) mapping at 88.4 min. We have now shown that, in addition to the parD mutation, OV6 carries a gyrAam mutation and that this mutation is probably responsible for the gross phenotype of the mutant. We have cloned the gyrA gene, identified the GyrA protein, sequenced the gyrA gene and flanking genes, cloned and sequenced the gyrAam, mutation, and identified its truncated product, in addition, we have identified the transcriptional start point of the gyrA gene. The E. coli GyrA protein has extensive homologies with Gyrase proteins of other organisms and weak sequence homologies with some eukaryotic cytoskeletal proteins.
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  • 6
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Foliar and root symptoms are described for Australian lucerne yellows (ALuY), a disease common in Australian lucerne seed crops. A phytoplasma was detected in plants exhibiting symptoms, but not in symptomless lucerne plants. Oligonucleotide primers specific to the phytoplasma 16S-23S rRNA intergenic spacer region (SR) were used in polymerase chain reaction (PCR) assays on DNA extracted from lucerne plants with and without symptoms. Identical restriction fragment length polymorphism (RFLP) enzyme profiles were obtained for PCR products amplified from 10 yellows-affected lucerne samples. RFLP profiles obtained for four restriction enzymes were different from those of the tomato big bud (TBB) phytoplasma. ALuY phytoplasma PCR products were sequenced to determine phylogeny and were found to fall within the faba bean phyllody phytoplasma group, or phytoplasma group 16srII. Transmission electron microscopy revealed phytoplasmas in the phloem of yellows-affected plant samples, but not in symptomless plant samples. Fungal, bacterial and viral agents in the aetiology of Australian lucerne yellows were ruled out.
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 248 (1974), S. 514-515 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] During the course of experiments designed to study the presence of receptors for antigen-antibody complexes on tumour cells7, it was found that the mouse fibroblast cell line, A9, made rosettes to sheep erythrocytes which were not coated with antibody. Here we present experiments describing this ...
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  • 9
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 181 (1958), S. 1076-1076 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Fig. 1. Audiograms (a) for subject A, aged 21, and (b) for subject B, aged 28 years The remarkable feature of these audiograms (Fig. 1) is the appearance of distinct ripples covering the range of frequencies up to about 2,000 c./s. Further experiments showed (1) that the ripples were stable over a ...
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Gene 61 (1987), S. 189-198 
    ISSN: 0378-1119
    Keywords: Northem-blot analysis ; Q6/Q8 gene ; RNase protection ; Transcription ; exon ; intron ; recombinant DNA
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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