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  • 1
    Electronic Resource
    Electronic Resource
    Extractability of labelled microbial biomass N by electro-ultrafiltration and CaCl2 extraction (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 314-320 
    Details
    ISSN: 1432-0789
    Keywords: Nitrogen mineralization ; Microbial biomass ; Soil drying ; Extractable organic N ; 15N isotope dilution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A laboratory soil incubation and a pot experiment with ryegrass were carried out in order to examine the extractability of microbial biomass N by using either 10-mM CaCl2 extraction or the electro-ultrafiltration (EUF) method. The aim of the experiment was to test the hypothesis whether the organic N (Norg) extracted by EUF or CaCl2 from dried soil samples represents a part of the microbial biomass. For the laboratory incubation a 15N-labelled Escherichia coli suspension was mixed with the soil. For the pot experiment a suspension of 15N-labelled bacteria was applied which had previously been isolated from the soil used. Soil samples of both treatments, with and without applied bacterial suspension, were extracted by EUF and CaCl2. The extractability of applied microbial biomass was estimated from the difference in extractable Norg between the two treatments. In addition, the N isotopic composition in the upper plant matter, in the soil, and in organic and inorganic N fractions of EUF and CaCl2 extracts was analysed. Both experiments showed that the applied microbial biomass was highly accessible to mineralization and thus represented potentially mineralizable N. However, this mineralizable N was not extractable by CaCl2 or by the EUF method. It was, therefore, concluded that the organic N released on soil drying and which was thus extractable was derived from the non-biomass soil organic matter. The result suggests that both extraction methods may provide a suitable index for mineralizable N only in cases where the decomposable organic substrates are derived mainly from sources other than the living soil biota.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335960
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Extractability of labelled microbial biomass N by electro-ultrafiltration and CaCl2 extraction (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 314-320 
    Details
    ISSN: 1432-0789
    Keywords: Key words Nitrogen mineralization ; Microbial biomass ; Soil drying ; Extractable organic N ; 15N isotope dilution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A laboratory soil incubation and a pot experiment with ryegrass were carried out in order to examine the extractability of microbial biomass N by using either 10-mM CaCl2 extraction or the electro-ultrafiltration (EUF) method. The aim of the experiment was to test the hypothesis whether the organic N (Norg) extracted by EUF or CaCl2 from dried soil samples represents a part of the microbial biomass. For the laboratory incubation a 15N-labelled Escherichia coli suspension was mixed with the soil. For the pot experiment a suspension of 15N-labelled bacteria was applied which had previously been isolated from the soil used. Soil samples of both treatments, with and without applied bacterial suspension, were extracted by EUF and CaCl2. The extractability of applied microbial biomass was estimated from the difference in extractable Norg between the two treatments. In addition, the N isotopic composition in the upper plant matter, in the soil, and in organic and inorganic N fractions of EUF and CaCl2 extracts was analysed. Both experiments showed that the applied microbial biomass was highly accessible to mineralization and thus represented potentially mineralizable N. However, this mineralizable N was not extractable by CaCl2 or by the EUF method. It was, therefore, concluded that the organic N released on soil drying and which was thus extractable was derived from the non-biomass soil organic matter. The result suggests that both extraction methods may provide a suitable index for mineralizable N only in cases where the decomposable organic substrates are derived mainly from sources other than the living soil biota.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335960
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    The central role of microbial activity for iron acquisition in maize and sunflower (2000)
    Springer
    Biology and fertility of soils 30 (2000), S. 433-439 
    Details
    ISSN: 1432-0789
    Keywords: Key words Iron chlorosis ; Iron reduction ; Ferrireductase ; Microbial activity ; Phytosiderophore
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Maize (Zea mays L.) and sunflower (Helianthus annuus L.) grown on a calcareous soil showed poor growth and/or were chlorotic in spite of abundant Fe in the roots. It has been hypothesized that microbial siderophores chelate Fe (III) in the soil, and that in this form Fe is transported towards the root apoplast. On the calcareous soil, total and apoplastic root Fe concentrations were high, probably because of a high apoplastic pH depressing Fe (III)-reductase activity and thus the Fe2+ supply to the cytoplasm. On the acidic soil, total and apoplastic root Fe concentrations were low, probably because of a low apoplastic pH favouring Fe (III) reduction, hence plants showed no Fe-deficiency symptoms. The main objective of the present work was to investigate the role of microbial soil activity in plant Fe acquisition. For this purpose, plants were grown under sterile and non-sterile conditions on a loess loam soil. Plants cultivated under non-sterile conditions grew well, showed no Fe-deficiency symptoms and had fairly high Fe concentrations in the roots in contrast to plants grown in the sterile medium. Low root and leaf Fe concentrations in the axenic treatments indicated that the production of microbial siderophores was totally suppressed. Accordingly, sunflowers were severely chlorotic and this was associated with very poor growth, whereas in maize only growth was drastically reduced. In maize under sterile conditions, root apoplastic and total Fe concentrations were not as low as in sunflowers, which may have indicated that phytosiderophores produced in maize partly sustained Fe acquisition, but due to poor growth were not as efficient in supplying Fe as microbial activity under natural conditions. It may be therefore assumed that in natural habitats soil microbial activity is of pivotal importance for plant Fe acquisition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050021
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
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