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1

Digitale Medien

Ability of free-living cells ofBradyrhizobium japonicum to denitrify in soils (1989)

Breitenbeck, G. A. ; Bremner, J. M.

Springer

Biology and fertility of soils 7 (1989), S. 219-224

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ISSN: 1432-0789

Schlagwort(e): Soybean rhizobia ; Denitrification ; Nitrate ; Nitrous oxide ; Bradyrhizobium japonicum

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Summary Experiments to assess the ability of free-living cells of six strains of soybean rhizobia (Bradyrhizobium japonicum USDA 76, 94, 110, 122, 123, and 135) to denitrify nitrate in five soils showed that although some strains ofB. japonicum have the capacity to rapidly denitrify nitrate in soils under anaerobic conditions, it is unlikely that the numbers of soybean rhizobia commonly found under field conditions are sufficient to significantly influence either the extent or the products of denitrification in soil. It is our general conclusion that the advantages, if any, that the ability to denitrify conveys to rhizobia or to the rhizobia-legume symbiosis are not offset by increased losses of plant-available N when denitrifying strains of rhizobia are present as free-living cells in soil.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00709652

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2

Digitale Medien

Intrinsic antibiotic resistance and competition in fast- and slow-growing soybean rhizobia on a hybrid of Asian and US cultivars (1989)

Young, C. C. ; Chao, C. C.

Springer

Biology and fertility of soils 8 (1989), S. 66-70

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ISSN: 1432-0789

Schlagwort(e): Antibiotic resistance ; Bradyrhizobium japonicum ; Competition ; Rhizobium fredii ; Soybean nodulation

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Summary Six fast-growing soybean rhizobia (Rhizobium fredii) and thirteen slow-growing soybean rhizobia (Bradyrhizobium japonicum) were examined for resistance to 10 antibiotics. Axenic studies were carried out to determine the competitiveness of dual-strain inocula consisting of fast- and slow-growing rhizobia isolated from subtropical-tropical soils for nodule occupancy on a hybrid of Asian and US soybean cultivars. Nodule occupancy was determined by intrinsic resistance to erythromycin and neomycin. The results showed wide variability in resistance to 10 antibiotics for fast- and slow-growing rhizobia. The intrinsic antibiotic resistance of fast- and slow-growing rhizobia was extremely high against nalidixic acid (400 μg ml−1) and penicillin (200 μg ml−1). The competitive ability of inoculant strains for nodule occupancy varied for different combination sets and with the plant growing media. Our results show that fast-growing rhizobia nodulate a hybrid of Asian and US soybean cultivars. Fast-growing soybean rhizobia did not completely exclude nodulation by the slow-growing strains, which formed 0–79% nodules, depending on the strain used in the inoculum.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00260518

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3

Digitale Medien

Survival and potential denitrifying activity of Azospirillum lipoferum and Bradyrhizobium japonicum inoculated into sterilized soil (1989)

Steinberg, C. ; Gamard, P. ; Faurie, G. ; [weitere]

Springer

Biology and fertility of soils 7 (1989), S. 101-107

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ISSN: 1432-0789

Schlagwort(e): Azospirillum lipoferum ; Bradyrhizobium japonicum ; Denitrifying enzyme potential ; Gamma-sterilized soil ; Population dynamics ; Zea mays

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Summary Potential denitrifying activity and population dynamics of Azospirillum lipoferum (137C) and Bradyrhizobium japonicum (G2sp) inoculated into a γ-sterilized soil were studied for a period of 3 weeks. The denitrifying enzyme potential of soil inoculated independently with each bacterial species was strongly stimulated by the presence of a plant (Zea mays L.). Simultaneous inoculation of both bacteria also produced a higher denitrifying enzyme potential than simple inoculation. Even with double inoculation, the presence of a plant did not modify the evolution of the activity. The response of the population dynamics to these treatments followed a different pattern. The population dynamics of A. lipoferum was not affected by the presence of the plant or by the presence of B. japonicum. In contrast, the presence of both a plant and of A. lipoferum seemed to promote the growth of B. japonicum.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00292566

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4

Digitale Medien

Nodulation competition among Bradyrhizobium japonicum strains as influenced by rhizosphere bacteria and iron availability (1989)

Fuhrmann, J. ; Wollum, A. G.

Springer

Biology and fertility of soils 7 (1989), S. 108-112

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ISSN: 1432-0789

Schlagwort(e): Bradyrhizobium japonicum ; Glycine max ; Soil inoculation ; Nodulation ; Rhizosphere ; Rhizobacteria

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Summary Bacteria isolated from the root zones of field-grown soybean plants [Glycine max (L.) Merr.] were examined in a series of glasshouse experiments for an ability to affect nodulation competition among three strains of Bradyrhizobium japonicum (USDA 31, USDA 110, and USDA 123). Inocula applied at planting contained competing strains of B. japonicum with or without one of eleven isolates of rhizosphere bacteria. Tap-root nodules were harvested 28 days after planting, and nodule occupancies were determined for the bradyrhizobia strains originally applied. Under conditions of low iron availability, five isolates (four Pseudomonas spp. plus one Serratia sp.) caused significant changes in nodule occupancy relative to the corresponding control which was not inoculated with rhizosphere bacteria. During subsequent glasshouse experiments designed to verify and further characterize these effects, three fluorescent Pseudomonas spp. consistently altered nodulation competition among certain combinations of bradyrhizobia strains when the rooting medium did not contain added iron. This alteration typically reflected enhanced nodulation by USDA 110. Two of these isolates produced similar, although less pronounced, effects when ferric hydroxide was added to the rooting medium. The results suggest that certain rhizosphere bacteria, particularly fluorescent Pseudomonas spp., can affect nodulation competition among strains of R. japonicum. An additional implication is that iron availability may be an important factor modifying interactions involving the soybean plant, B. japonicum, and associated microorganisms in the host rhizosphere.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00292567

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5

Digitale Medien

Relative efficiency, ureide transport and harvest index in soybeans inoculated with isogenic HUP mutants of Bradyrhizobium japonicum (1989)

Hungria, M. ; Neves, M. C. P. ; Döbereiner, J.

Springer

Biology and fertility of soils 7 (1989), S. 325-329

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ISSN: 1432-0789

Schlagwort(e): N2 fixation ; Soybeans ; Bradyrhizobium japonicum ; HUP mutants ; N transport ; Ureide ; Acetylene reduction assay (ARA)

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Summary Differences between isogenic uptake hydrogenase (HUP) mutants of Bradyrhizobium japonicum in terms of nodule efficiency, N2 fixation and N incorporation into various plant parts were studied in a monoxenic greenhouse experiment in order to confirm previous results with soybeans and beans inoculated with various HUP+ and HUP− strains. The HUP+ revertant PJ17-1 of a HUP− mutant (PJ17) of strain USDA DES 122 showed a completely restored relative efficiency (100% versus 78±2% for the HUP− mutant), higher nodule efficiency (N2 fixed per g nodules), higher ureide-N transport rates, higher N contents in pods and higher N harvest indices. All these observations confirm previous experiments with HUP+ and HUP− strains.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00257827

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6

Digitale Medien

Hydrogen metabolism and nitrogen fixation of soybean (Glycine max. L.) inoculated with different strains ofRhizobium spp. (1989)

Kimou, A. ; Drevon, J. J.

Springer

Biology and fertility of soils 7 (1989), S. 259-262

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ISSN: 1432-0789

Schlagwort(e): Hydrogenase ; Nitrogenase ; Nodulation ; Bradyrhizobium japonicum ; Rhizobium fredii ; Acetylene reduction assay (ARA)

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Summary Hydrogenase activities and N2-fixing capacities of soybean nodules (Glycine max. cv. Hodgson), inoculated with strains ofBradyrhizobium japonicum andRhizobium fredii from different geographical regions, were measured after 35 days of culture under controlled conditions. Of the strains tested, 47% induced nodules with bacteroids which recycled H2. The data obtained suggest that H2-recycling ability is not a major factor influencing early N2-fixation which depends essentially on the precocity and intensity of the initial nodulation.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00709658

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7

Digitale Medien

Development of magnetic anisotropies in ultrathin epitaxial films of Fe(001) and Ni(001) (1989)

Heinrich, B. ; Cochran, J. F. ; Arrott, A. S. ; [weitere]

Springer

Applied physics 49 (1989), S. 473-490

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ISSN: 1432-0630

Schlagwort(e): 75.70

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract Ultrathin films, bcc Fe(001) on Ag(001), fcc Fe(001) on Cu(001) and Fe/Ni(001) bilayers on Ag, were grown by molecular beam epitaxy. A wide range of surface science tools were employed to establish the quality of epitaxial growth. Ferromagnetic resonance and Brillouin light scattering were used to extract the magnetic properties. Emphasis was placed on the study of magnetic anisotropies. Large uniaxial anisotropies with easy axis perpendicular to the film surface were observed in all ultrathin structures studied. These anisotropies were particularly strong in fcc Fe and bcc Fe films. In sufficiently thin samples the saturation magnetization was oriented perpendicularly to the film surface in the absence of an applied field. It has been demonstrated that in bcc Fe films the uniaxial perpendicular anisotropy originates at the film interfaces. In situ measurements indentified the strength of the uniaxial perpendicular anisotropy constant at the Fe/vacuum, Fe/Ag and Fe/Au interfaces asK us = 0.96, 0.63, and 0.3 ergs/cm2 respectively. The surface anisotropies deduced for [bulk Fe/noble metal] interfaces are in good agreement with the values obtained from ultrathin films. Hence the perpendicular surface ansiotropies originate in the broken symmetry at abrupt interfaces. An observed decrease in the cubic anisotropy in bcc Fe ultrathin films has been explained by the presence of a weak 4th order in-plane surface anisotropy,K 1∥S=0.012 ergs/cm2. Fe/Ni bilayers were also investigated. Ni grew in the pure bcc structure for the first 3–6 ML and then transformed to a new structure which exhibited unique magnetic properties. Transformed ultrathin bilayers possessed large inplane 4th order anisotropies far surpassing those observed in bulk Fe and Ni. The large 4th order anisotropies originate in crystallographic defects formed during the Ni lattice transformation.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00617014

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8

Digitale Medien

Ultrathin film magnetic research at the Naval Research Laboratory (1989)

Krebs, J. J.

Springer

Applied physics 49 (1989), S. 513-521

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ISSN: 1432-0630

Schlagwort(e): 75.70

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract Scientists at the Naval Research Laboratory have been using molecular beam epitaxy techniques to grow a variety of high quality magnetic transition metal (TM) films and superlattices having TM thicknesses in the 1–10 monolayer regime. The magnetic and structural properties of these samples have been studied with a wide variety of standard and spin-sensitive techniques, both in vacuo and, when suitably protected, in air. The magnetic behavior of the materials is strongly modified as the TM layers become ultrathin. This work is illustrated with examples involving ultrathin Fe layers on Ag(001), Fe/Ag(001) superlattices containing ultrathin Fe layers, and bcc Co on GaAs(110).

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00617018

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9

Digitale Medien

Magnetic surface anisotropy of transition metal ultrathin films (1989)

Bruno, P. ; Renard, J. -P.

Springer

Applied physics 49 (1989), S. 499-506

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ISSN: 1432-0630

Schlagwort(e): 75.30G ; 75.30T ; 75.70

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract In order to study the magnetic anisotropy of transition metal ultrathin films, we have performed tight-binding calculations including spin-orbit coupling. Beside the anisotropy energy these calculations also yield the orbital moment, which turns out to be much more anisotropic than in bulk materials. The effects of interfacial mismatch and roughness are discussed within phenomenological models. We also briefly review experimental results on the magnetic surface anisotropy (MSA) in transition metal ultrathin films. In some cases such as Au/Co/Au(111) sandwiches the MSA wins the competition with the shape anisotropy arising from the magnetostatic energy: below a critical thickness this leads to aperpendicular spontaneous magnetization. We show the effects of this crossover on the hysteresis loops and on the magnetoresistance, and the effects of interface roughness on the critical thickness.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00617016

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10

Digitale Medien

EXAFS study of the atomic structure of amorphous Tb20Fe80 (1989)

Robinson, C. J. ; Samant, M. G. ; Marinero, E. E.

Springer

Applied physics 49 (1989), S. 619-629

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ISSN: 1432-0630

Schlagwort(e): 75.50.K ; 75.70 ; 61.10.L ; 78.20.L ; 81.40

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract The atomic structure of amorphous Tb20Fe80 thin films has been studied by Extended X-ray Absorption Fine Structure (EXAFS) of both FeK and TbL III absorption edges. The local site geometry around Fe atoms shows predominantly Fe nearest neighbors with an Fe-Fe distance distribution centered on 2.50±0.02 Å and a coordination number of 9.1±1. In contrast, the radial structure function (RSF) obtained at the Tb edge is broad and asymmetric. The peak in the RSF corresponds to a Tb-Fe near neighbor distance of 2.94±0.1 Å with no evidence for Tb-Tb nearest neighbor coordination. The width and the shape of the RSF suggest that the Tb-Fe atomic environment is anisotropic and strained probably as a consequence of the growth process. This distorted atomic environment is suggested to be responsible for the magnetic anisotropy in these alloys. Thermal annealing at 200 °C leads to reduction inK u. We propose that this results from reordering of the Tb local environment such that the average structural anisotropy in the distribution is reduced. EXAFS data show that annealing at 400°C causes precipitation of bcc polycrystalline Fe. The addition of 7 at.% Au to the alloy prevents this recrystallization and preserves the amorphous state but does not prevent the structural relaxation which reducesK u at lower temperatures.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00616986

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