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  • labile organic P  (2)
  • Cationic amphiphiles
  • 1
    ISSN: 1573-5036
    Keywords: ammonium ; labile organic P ; nitrate ; N mineralization ; phosphorus ; Plantago major L. ssp. pleiosperma ; soil nutrient availability ; soil nutrient pools ; spatial variation ; temporal variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract As part of a research project on the variation in life-history characteristics within a population of Plantago major L. ssp. pleiosperma, seasonal and spatial variability in the availability of macronutrients (N, P, and K) were examined on a small scale in the 0–25 cm soil depth at a primary beach plain site, embanked since 1966. On the basis of distinct differences, among other things, in plant biomass, an a priori division into three different types of microhabitat occurring in a mosaic distribution pattern was made: an overall low-lying area (subsite 1) with slightly elevated patches of 0.5 to 1.5 m in diameter (subsite 2) and rather large patches, 20 to 40 m in diameter, of sea buckthorn shrubs, with small and relatively open spots (subsite 3) in the transitional zone from lower area into scrub. All three subsite types were studied within a total area of approximately 2000 m2. Three methods of analysis were applied: an inventory survey (sampling once at the start of the growing season), an analysis of the seasonal variation (sampling at approximately monthly intervals during the period April-November), and an assessment of nitrogen mineralization potentials in the laboratory (sampling once at the beginning of the growing season). All three procedures clearly demonstrated the occurrence of differences in the availability of nutrients over very short distances, i.e. a pronounced spatial variability among subsites. Particularly the availability of N and P appeared to have increased at the subsites 2 and 3, when compared to subsite 1. This small-scale differentiation in soil properties has occurred in an essentially homogeneous parent material (e.g. in texture and carbonate content) over a period of about 20 years. Besides a spatial variability, statistically significant temporal fluctuations were observed in the availability of N, P, and K. Relative fluctuations of mineral N (as indicated by the range/mean ratio) were especially large at the subsites 2 and 3.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 127 (1990), S. 179-192 
    ISSN: 1573-5036
    Keywords: acid soils ; ammonium ; Calluna vulgaris ; Deschampsia flexuosa ; Erica tetralix ; heathland ecosystems ; labile organic P ; Molinia caerulea ; nitrogen mineralization ; nitrate ; nitrification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A survey was conducted over a range of 17 Dutch heathland locations, subdivided into 41 sites dominated by either dwarf-shrubs (Calluna vulgaris or Erica tetralix) or grass species (Deschampsia flexuosa or Molinia caerulea). Among the habitats of the dominant plant species relatively little differences in general soil properties were observed. The P status of Deschampsia sites was relatively high as well as the NO3 −-N concentrations in the 0–10 cm layer (FH included) at the grass-dominated sites. At sites with a dead or degenerating dwarf-shrub vegetation, NH4 +-N concentrations reached very high levels. Net production of nitrate was observed during incubation of intact 0–10 cm soil cores (FH-layer included) in the laboratory for all sites, even though in some instances, particularly at Calluna and Erica sites, no nitrate was initially measured. Generally, a higher nitrification rate was found for the grass-dominated sites, and for Deschampsia in particular. The net production of nitrate was highly significantly correlated with net N mineralization, being a reasonable predictor of nitrification in a simple regression model (R2=0.47; P〈0.001). Net nitrification was also significantly correlated with the NO3 −-N initially present at the start of the growing season (R=0.65; P〈0.001) and with the labile organic P content of the soil (R=0.65; P〈0.001). By including initial NO3 −-N and labile organic P, together with net N mineralization and pH, in a multiple regression model, net nitrate production could be predicted with a much higher precision (R2=0.75; P〈0.001). Although apparent nitrification was not significantly correlated with pH, the latter contributed significantly to the multiple regression equation for the prediction of the former. The influence of the labile organic P pool may act via its positive correlation with microbial biomass, thus more or less reflecting the potential mineralization/nitrifying capacity of a particular site.
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  • 3
    ISSN: 1434-193X
    Keywords: Cationic amphiphiles ; Transfection ; Pyridinium salts ; Vesicles ; Lipoplex ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Pyridinium amphiphiles have found practical use for the delivery of DNA into cells. Starting from 4-methylpyridine, a general synthesis has been devised for the production of pyridinium amphiphiles which allows variation in both the hydrophobic part and in the headgroup area of the compounds. By means of differential scanning microcalorimetry, zeta potential, particle size measurements and cryo electron microscopy, some characteristics of the pyridinium amphiphile/DNA complexes have been determined.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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