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  • 15N transformations  (1)
  • Active transport  (1)
  • Competition  (1)
  • 1
    Electronic Resource
    Electronic Resource
    The effect of suppression treatments on the uptake of 15N by intercropped corn from labeled alfalfa (Medicago sativa) (1993)
    Springer
    Biology and fertility of soils 16 (1993), S. 221-226 
    Details
    ISSN: 1432-0789
    Keywords: Legume suppression ; Microbial pool ; 15N transformations ; Intercropped corn ; Alfalfa ; Medicago sativa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In greenhouse experiments, we examined the N transferred to intercropped corn from 15N-labeled alfalfa shoot residue and intact roots in an undisturbed soil system in response to two different suppression treatments and complete killing of alfalfa. The alfalfa treatments included complete killing (glyphosate only), glyphosate injury + cutting, and cutting only, with alfalfa shoot residue returned to the soil surface in all three treatments. Corn was planted in each pot following application of the treatments. When alfalfa was suppressed by glyphosate injury + cutting, corn had recovered 12% of the alfalfa N by 8 weeks of growth, but with cutting only, N recovery by corn was reduced to 4.0%. The completekill treatment resulted in 8% recovery by corn of alfalfa N. In all treatments, most of the alfalfa-N remained in the soil organic pool. A second experiment tested a cutting only treatment with 15N-labeled alfalfa residue returned to the soil surface. The 15N-labeled alfalfa residue contributed 4.1% of N to corn during the 8-week growth cycle. Twice as much 15N was found in the active microbial biomass pool in the two treatments with live intereropped plants compared to the monoculture treatments with complete killing (non-intercropped) and the control treatment of alfalfa regrowth only. An analysis of the change in the 15N content of the undisturbed alfalfa roots from just before the suppression until 8 weeks later suggested that approximately 80% of the root 15N was lost from the plant suppressed by cutting. This corresponds to 28% of the total N released from the alfalfa. The results suggest that the degree of legume suppression was a key factor in the availability of legume N to the second crop. When the two species were intercropped, more of the N available from legume residues went to plant uptake and microbial biomass and was not stabilized as quickly in the soil organic pool. Appropriate management schemes must be designed to increase N availability to the second crop without yield reduction. These studies suggest severe suppression is necessary; if successful, more of the N can be maintained in active pools.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00361412
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Assimilatory nitrate uptake in Pseudomonas fluorescens studied using nitrogen-13 (1981)
    Springer
    Archives of microbiology 129 (1981), S. 135-140 
    Details
    ISSN: 1432-072X
    Keywords: Pseudomonas fluorescens ; Assimilatory nitrate reduction ; Nitrate reductase ; Nitrate uptake ; Active transport ; Nitrogen-13 ; Short-lived isotope
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The mechanism of nitrate uptake for assimilation in procaryotes is not known. We used the radioactive isotope, 13N as NO3 -, to study this process in a prevalent soil bacterium, Pseudomonas fluorescens. Cultures grown on ammonium sulfate or ammonium nitrate failed to take up labeled nitrate, indicating ammonium repressed synthesis of the assimilatory enzymes. Cultures grown on nitrite or under ammonium limitation had measurable nitrate reductase activity, indicating that the assimilatory enzymes need not be induced by nitrate. In cultures with an active nitrate reductase, the form of 13N internally was ammonium and amino acids; the amino acid labeling pattern indicated that 13NO3 - was assimilated via glutamine synthetase and glutamate synthase. Cultures grown on tungstate to inactivate the reductase concentrated NO3 - at least sixfold. Chlorate had no effect on nitrate transport or assimilation, nor on reduction in cell-free extracts. Ammonium inhibited nitrate uptake in cells with and without active nitrate reductases, but had no effect on cell-free nitrate reduction, indicating the site of inhibition was nitrate transport into the cytoplasm. Nitrate assimilation in cells grown on nitrate and nitrate uptake into cells grown with tungstate on nitrite both followed Michaelis-Menten kinetics with similar K mvalues, 7 μM. Both azide and cyanide inhibited nitrate assimilation. Our findings suggest that Pseudomonas fluorescens can take up nitrate via active transport and that nitrate assimilation is both inhibited and repressed by ammonium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00455349
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Competition between sulfate-reducing and methanogenic bacteria for H2 under resting and growing conditions (1984)
    Springer
    Archives of microbiology 137 (1984), S. 26-32 
    Details
    ISSN: 1432-072X
    Keywords: Desulfovibrio ; Methanospirillum ; Methanobacterium ; Methanosarcina ; Hydrogen kinetics ; Competition ; Monod kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The basis for the outcome of competition between sulfidogens and methanogens for H2 was examined by comparing the kinetic parameters of representatives of each group separately and in co-culture. Michaelis-Menten parameters (V max and K m) for four methanogens and five sulfate-reducing bacteria were determined from H2-depletion data. Further, Monod growth parameters (μmax, K s, Y H2) for Desulfovibrio sp. G11 and Methanospirillum hungatei JF-1 were similarly estimated. H2 K m values for the methanogenic bacteria ranged from 2.5 μM (Methanospirillum PM1) to 13 μM for Methanosarcina barkeri MS; Methanospirillum hungatei JF-1 and Methanobacterium PM2 had intermediate H2 K m estimates of 5 μM. Average H2 K m estimates for the five sulfidogens was 1.2 μM. No consistent difference among the V max estimates for the above sulfidogens (mean=100 nmol H2 min-1 mg-1 protein) and methanogens (mean=110 nmol H2 min-1 mg-1 protein) was found. A two-term Michaelis-Menten equation accurately predicted the apparent H2 K m values and the fate of H2 by resting co-cultures of sulfate-reducers and methanogens. Half-saturation coefficients (K s) for H2-limited growth of Desulfovibrio sp. G11 (2–4 μM) and Methanospirillum JF-1 (6–7 μM) were comparable to H2 K m estimates obtained for these organisms. Maximum specific growth rates for Desulfovibrio sp. G11 (0.05 h-1) were similar to those of Methanospirillum JF-1 (0.05–0.06 h-1); whereas G11 had an average yield coefficient 4 x that of JF-1. Calculated μmax and V max/K m values for the methanogens and sulfidogens studied predict that the latter bacterial group will process more H2 whether these organisms are in a growing or resting state, when the H2 concentration is in the first-order region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00425803
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    Paper (German National Licenses)
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