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  • Cell & Developmental Biology  (1)
  • Lolium perenne  (1)
  • Reference unit  (1)
  • 1995-1999  (3)
  • 1980-1984
  • 1
    Electronic Resource
    Electronic Resource
    The number of bacteria in the rhizosphere during plant development: relating colony-forming units to different reference units (1999)
    Springer
    Biology and fertility of soils 28 (1999), S. 285-291 
    Details
    ISSN: 1432-0789
    Keywords: Key words Chrysanthemum ; Rhizosphere ; Rhizobacteria ; Root age ; Reference unit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The number of bacteria was determined during the growth of chrysanthemum plants on young (tip) and old (base) root parts. We assessed if the same conclusions could be drawn on the dynamics of bacterial populations during plant development when different reference units were used to express the bacterial counts. The results indicated that the total number of bacteria on the base decreased significantly during plant development, when expressed per root length, per root fresh weight or per root surface. The number of bacteria on the tip only decreased significantly when expressed per root length. Using the unit of dry weight of adhering soil, contradictory results were obtained for both base and tip; in general, the number of bacteria increased significantly during plant development. Thus, different reference units may lead to different conclusions. Root surface seemed to be the best unit to use, but the use of this unit requires time-consuming measurements. Regression analyses indicated that the reference unit "root surface" was highly correlated with root fresh weight (R 2=93%). Thus, once this relation is determined, the less time-consuming unit can be measured in the experimental work. To analyse the data, the colony-forming units should be expressed per root surface. Besides bacterial numbers during plant development, we assessed whether the bacterial populations collected showed different growth rates on agar plates. The growth rates of bacteria from the tip and base and different development stages of the plants showed differences, indicating differences in the metabolic state of the collected populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050495
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  • 2
    Electronic Resource
    Electronic Resource
    Carbon and nitrogen allocation in Lolium perenne in response to elevated atmospheric CO2 with emphasis on soil carbon dynamics (1997)
    Springer
    Plant and soil 188 (1997), S. 299-308 
    Details
    ISSN: 1573-5036
    Keywords: elevated CO2 ; carbon partitioning ; nitrogen partitioning ; Lolium perenne ; microbial biomass ; mineralisation ; soil carbon dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effect of elevated CO2 on the carbon and nitrogen distribution within perennial ryegrass (L. perenne L.) and its influence on belowground processes were investigated. Plants were homogeneously 14C-labelled in two ESPAS growth chambers in a continuous 14C-CO2 atmosphere of 350 and 700 μL L-1 CO2 and at two soil nitrogen regimes, in order to follow the carbon flow through all plant and soil compartments. After 79 days, elevated CO2 increased the total carbon uptake by 41 and 21% at low (LN) and high nitrogen (HN) fertilisation, respectively. Shoot growth remained unaffected, whereas CO2 enrichment stimulated root growth by 46% and the root/soil respiration by 111%, irrespective of the nitrogen concentration. The total 14C-soil content increased by 101 and 28% at LN and HN, respectively. The decomposition of the native soil organic matter was not affected either by CO2 or by the nitrogen treatment. Elevated CO2 did not change the total nitrogen uptake of the plant either at LN or at HN. Both at LN and HN elevated CO2 significantly increased the total amount of nitrogen taken up by the roots and decreased the absolute and relative amounts translocated to the shoots. The amount of soil nitrogen immobilised by micro-organisms and the size of the soil microbial biomass were not affected by elevated CO2, whereas both were significantly increased at the higher soil N content. Most striking was the 88% increase in net carbon input into the soil expressed as: 14C-roots plus total 14C-soil content minus the 12C-carbon released by decomposition of native soil organic matter. The net carbon input into the soil at ambient CO2 corresponded with 841 and 1662 kg ha-1 at LN and HN, respectively. Elevated CO2 increased these amounts with an extra carbon input of 950 and 1056 kg ha-1. Combined with a reduced decomposition rate of plant material grown at elevated CO2 this will probably lead to carbon storage in grassland soils resulting in a negative feed back on the increasing CO2 concentration of the atmosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004233920896
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  • 3
    Electronic Resource
    Electronic Resource
    Em-tomography of section collapse, a non-linear phenomenon (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Microscopy Research and Technique 31 (1995), S. 311-316 
    Details
    ISSN: 1059-910X
    Keywords: EM-tomography ; Reconstructions ; Back projection ; Section collapse ; Distortion of Z dimensions ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Using back projection for reconstruction and tilt series of Epon or Lowicryl embedded and sectioned material, we demonstrated: (1) a reduction in thickness of 50% for Epon and 80% for Lowicryl sections, and (2) a non-uniform density distribution along the electron-optical axis in sections. The highest density was found at the vacuum exposed side of the section. The formvar side of the section showed a similar increase in density, but not to the same extent. Minimalization of electron exposure, even without pre-exposure, did not affect the reconstructed thickness, nor did it affect the non-uniform density distribution. However, parallax measurements showed that at 150K, collapse of Epon sections does not take place. For EM-tomography of plastic embedded material our findings imply that at the top and bottom portion of the sections the dimensions of the reconstructed structures are distorted, but that in the middle portion the dimensions are reliably retained. © 1995 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jemt.1070310409
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