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  • 1
    Electronic Resource
    Electronic Resource
    Effects of nitrogen deficiency on nitrate reductase, nitrate assimilation and photosynthesis in unicellular marine algae (1983)
    Springer
    Marine biology 77 (1983), S. 101-105 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nitrate reductase (NR) activity appeared in ammoniumgrown cultures of 5 species of marine algae, representing 4 classes, after a short period of nitrogen starvation. In nitrogen-limited chemostat cultures of Nannochloropsis oculata and Chlorella stigmatophora there was an inhibition of photosynthetic carbon fixation during nitrate assimilation. In these organisms, nitrate assimilation was light-dependent and inhibited by 3-(3′,4′-dichloro-)-1-1-dimethyl urea (DCMU). In N. oculata, an obligate autotroph, nitrite assimilation was dependent on light absolutely. Physiological changes that occur in these organisms during nitrogen deficiency enable them to assimilate nitrogen rapidly when it becomes available.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396306
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  • 2
    Electronic Resource
    Electronic Resource
    Assessing the organic phosphorus status of an Oxisol under tropical pastures following native savanna using 31P NMR spectroscopy (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 332-339 
    Details
    ISSN: 1432-0789
    Keywords: Soil phosphorus ; Organic P species ; 31P NMR spectroscopy ; Improved tropical pastures ; Acid savanna soils ; Earthworm casts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract 31P nuclear magnetic resonance (NMR) spectroscopy, P fractionation, and a P sorption experiment were used to follow the changes in P in the A horizons (0–10 cm) of acid savanna soils, Colombia, after little P fertilization and 15 years' continuous growth of a grass (Brachiaria decumbens) and a grass/legume (B. decumbens+Pueraria phaseoloides) pasture. Ready P supply as analyzed by Bray P was low under native savanna (1.3 mg kg-1 soil) and responded moderately on pasture establishment. Concurrently, the affinity of the soil for inorganic P declined slightly after pasture establishment. 31P NMR spectroscopy revealed that P associated with humic acids was dominated by monoester P followed by diester P. Smaller proportions were observed for phosphonates, teichoic acid P, orthophosphate, and pyrophosphate. P associated with fulvic acids had lower proportions of diester P and higher contents of orthophosphate. Under native savanna the reserves of labile organic P species (phosphonates and diester P including teichoic acid P) associated with humic and fulvic acids were 12.4 and 1.1 kg ha-1, respectively, and increased to 18.1 and 1.8 kg ha-1 under grass pasture, and to 19.5 and 2.3 kg ha-1 under grass/legume pasture. These data emphasize the importance of labile organic P species in the P supply for plants in improved tropical pastures, and further indicate that humic acid P in particular responds to land-use changes within a relatively short time-scale. Earthworm casts were highly abundant in the B. decumbens+P. phaseoloides plot and were enriched in labile organic P species. We conclude that earthworm activity improves the P supply in soil under tropical pastures by creating an easily available organic P pool.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335963
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  • 3
    Electronic Resource
    Electronic Resource
    Assessing the organic phosphorus status of an Oxisol under tropical pastures following native savanna using 31P NMR spectroscopy (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 332-339 
    Details
    ISSN: 1432-0789
    Keywords: Key words Soil phosphorus ; Organic P species ; 31P NMR spectroscopy ; Improved tropical pastures ; Acid savanna soils ; Earthworm casts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract 31P nuclear magnetic resonance (NMR) spectroscopy, P fractionation, and a P sorption experiment were used to follow the changes in P in the A horizons (0–10 cm) of acid savanna soils, Colombia, after little P fertilization and 15 years’ continuous growth of a grass (Brachiaria decumbens) and a grass/legume (B. decumbens+Pueraria phaseoloides) pasture. Ready P supply as analyzed by Bray P was low under native savanna (1.3 mg kg–1 soil) and responded moderately on pasture establishment. Concurrently, the affinity of the soil for inorganic P declined slightly after pasture establishment. 31P NMR spectroscopy revealed that P associated with humic acids was dominated by monoester P followed by diester P. Smaller proportions were observed for phosphonates, teichoic acid P, orthophosphate, and pyrophosphate. P associated with fulvic acids had lower proportions of diester P and higher contents of orthophosphate. Under native savanna the reserves of labile organic P species (phosphonates and diester P including teichoic acid P) associated with humic and fulvic acids were 12.4 and 1.1 kg ha–1, respectively, and increased to 18.1 and 1.8 kg ha–1 under grass pasture, and to 19.5 and 2.3 kg ha–1 under grass/legume pasture. These data emphasize the importance of labile organic P species in the P supply for plants in improved tropical pastures, and further indicate that humic acid P in particular responds to land-use changes within a relatively short time-scale. Earthworm casts were highly abundant in the B. decumbens+P. phaseoloides plot and were enriched in labile organic P species. We conclude that earthworm activity improves the P supply in soil under tropical pastures by creating an easily available organic P pool.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335963
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  • 4
    Electronic Resource
    Electronic Resource
    Spatial distribution of soft X-ray and EUV emission associated with a chromospheric flare of importance 1B on August 2, 1972 (1974)
    Springer
    Solar physics 34 (1974), S. 349-375 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Soft-X-ray and extreme ultraviolet spectroheliographs carried by the OSO-7 (Orbiting Solar Observatory) have been used to record the development of XUV emission associated with a flare of importance 1b on August 2, 1972. Spatial resolution was 20″ and spectral resolution was adequate to select emission lines originating within well-defined ranges of electron temperature between 5 × 104 and 30 × 106K. The data show that heating only the pre-existing coronal material adjacent to the flare site cannot account for the soft X-ray emission measure observed during the event. The flare emission originating at T e ⩽ 2.3 × 106K exhibits an impulsive component coincident with an impulsive microwave event. This radiation appears to coincide spatially with Hα radiation emitted at that time and is centered on the neutral line separating magnetic fields of opposite polarity. One soft X-ray-emitting feature, estimated to have an initial electron temperature of 2–10 × 106K, forms during the impulsive phase immediately over the Hα flare. A second, arch-like feature observed at wavelengths near 1.9 Å and estimated to have T e≅30 × 106K is located approximately 35000 km above the Hα event. Both regions have lengths of about 27000 km but transverse dimensions small compared to the spatial resolution of the spectroheliograph, i.e., less than 14000 km. The region with highest electron temperature exhibits the greatest stability in position. This region cools to approximately 10 × 106K in 6 to 12 min which is compatible with cooling by conduction to the chromosphere. The best association with a dark surge is found in an emission line of Fe xiv.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00153673
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  • 5
    Electronic Resource
    Electronic Resource
    Ionization equilibrium in soft X-ray-emitting solar flares (1974)
    Springer
    Solar physics 36 (1974), S. 383-401 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Studies of the flare-produced line feature at 1.9 Å due to highly ionized iron show that it is emitted in conditions closely approximating steady-state ionization equilibrium. Calculations of the line flux per unit emission measure from time-dependent and steady-state ionization equilibria are compared with observed values during four flares in particular. Only for electron densities N e ⪞ 1010 cm-3 do the time-dependent equilibrium values give as good an approximation to the observed values as the steady-state equilibrium. This lower limit is compared with values of N e derived from analyses of the temperature decline in each of these events, and with estimates of N e given by other workers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00151209
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  • 6
    Electronic Resource
    Electronic Resource
    Polarization results of solar X-rays from OSO-7 (1974)
    Springer
    Solar physics 37 (1974), S. 429-435 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Polarization measurements of solar X-ray events that were obtained with an instrument on OSO-7 are presented. The results appear to be consistent with the results of Tindo et al. on the existence and magnitudes of polarization. A comparison with polarization predictions when X-rays are produced by radial beams of electrons gives two examples of deviations from such a model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152500
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  • 7
    Electronic Resource
    Electronic Resource
    Coronal temperatures and temperature gradients from OSO-7 spectroheliograms (1976)
    Springer
    Solar physics 47 (1976), S. 611-626 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Temperatures and temperature gradients for the outer corona are obtained from brightness gradients of EUV lines that were measured with the spectroheliograph on OSO-7. Brightness gradients show considerable deviations from isothermal model calculations that include collisional excitation and photoexcitation. A negative temperature gradient that gives both positive and negative ion abundance gradients appears to be able to account for the discrepancy. For λ284 of Fe xv, perhaps the strongest line from the outer corona, measurements during 1972 appear to be consistent with (i) a temperature near 2.3×106K near the equator at ϱ = 1.3±0.1 solar radii from the solar center; (ii) (ϱ/T) dT/dϱ values near -0.7 that extend from as low as ϱ = 1.2 to about ϱ = 1.8. Temperatures from strong lines of Fe xiv and Fe xvi indicate that variations of about ±0.2×106K exist along lines of sight where emission is appreciable. There appears to be some agreement between these results and temperature measurements from ion abundances in the solar wind and Doppler width of λ5303.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00154770
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  • 8
    Electronic Resource
    Electronic Resource
    Methods for the study of nitrogen assimilation and transport in grain legumes (1987)
    Springer
    World journal of microbiology and biotechnology 3 (1987), S. 3-22 
    Details
    ISSN: 1573-0972
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Description / Table of Contents: Résumé L'étude de l'assimilation et du transport de l'azote dans les légumineuses à graines est une nécessité préliminaire pour la sélection des cultivars destinés aux croisements visant à accroître la fixation de l'azote pour la croissance des plantes et le rendement en graines. Les méthodes employées pour ces études sont éparpillées dans la littérature et n'ont pas été suffisamment testées. Dans cet article, il est présenté une étude d'ensemble de méthodes fiables, particulièrement adaptées aux laboratoires des pays en voie de développement qui ne di sposent pas d'instrumentation sophistiquée et coûteuse. Il est notamment décrit un système simple et peu onéreux de flux continu pour mesurer la fixation de l'azote par réduction de l'acétylène, ainsi que des techniques pour déterminer la respiration des nodules, le dégagement d'hydrogéne et l'activité nitrate-réductase des plantes. Plusieurs techniques colorimétriques ont été adaptées à l'analyse de l'azote nitrique, aminé, uréidique et total, dans de faibles volumes de suc de xylème prélevé par saignée.
    Abstract: Resumen El estudio de la asimilación y del transporte de nitrógeno en leguminosas de grano es un preámbulo necesario para la selección de cultivares obtenidos en programas de mejora que tengan como objetivo el incremento de la contribución de la fijación de nitrógeno a la producción de plantas y de semillas. Los métodos utilizados en dichos estudios estan dispersos en la literatura y no siempre se han comprobado lo suficiente. Este trabajo presenta un amplio conjunto de técnicas seguras, que se adaptan particularmente bien para su uso en laboratorios de países en desarrollo que carecen de instrumental caro y sofisticado. Se describe un sistema de flujo continuo para la medida de la fijación de N2 (reducción de acetileno) que utiliza componentes sencillos y baratos, tembién se describen técnicas para estimar la respiración de los nódulos, la evolución del hidrógeno y la actividad nitratò-reductasa de la planta. Se han adaptado varios métodos colorimétricos para el análisis del Nitrógeno total y del Nitrógeno combinado (en forma de aminas, amidas y derivados de la urea) contenidos en pequeños volumenes de savia bruta (xilema).
    Notes: Summary The study of nitrogen assimilation and transport in grain legumes is a necessary preliminary to selecting plant cultivars for breeding programs aimed at increasing the contribution of nitrogen fixation to plant production and seed yield. Methods used in such studies are spread widely throughout the literature and have not always been sufficiently tested. This paper presents a comprehensive set of reliable techniques particularly adapted for use in laboratories in developing countries which lack sophisticated and expensive instruments. A continuous flow system for the measurement of N2 fixation (acetylene reduction) using simple and inexpensive components is described, as are techniques for the estimation of nodule respiration, hydrogen evolution and plant nitrate reductase activity. A number of colorimetric techniques have been adapted for the analysis of nitrate-, amino-, amide-, ureide- and total-N in small volumes of xylem (bleeding) sap.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01090491
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  • 9
    Electronic Resource
    Electronic Resource
    OSO-7 results on coronal emission near 304 Å (1975)
    Springer
    Solar physics 43 (1975), S. 337-350 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The spectral composition and spatial distribution of equatorial coronal emission near 304 Å is examined. Spectral scans indicate that the predominant line is from Si xi. Comparisons of observations with calculations of intensity changes with altitude indicate that collisional excitation is important near the Sun but that photoexcitation becomes dominant beyond about 1.3 R ⊙ from the solar center. Observed and calculated intensities are in approximate agreement for abundances and electron densities that are within the range of observed values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152358
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  • 10
    Electronic Resource
    Electronic Resource
    On coronal Fe abundances and temperatures from XUV emission lines (1977)
    Springer
    Solar physics 53 (1977), S. 435-444 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Data obtained by the OSO-7 spectroheliograph on strong XUV lines of five, different Fe ions from the outer equatorial corona are presented. Interpretation of the data with a spherically symmetric model atmosphere gives average ion abundances for lines of sight at 0.3R ⊙ from the limb. Fe xvi is usually more abundant than Fe xv, xiv, xii and ix, but there are times when Fe xii is more abundant than the other ions. The deviation of measured relative abundances of Fe xii, xiv, and xvi from predictions of ionization equilibrium at one temperature seems to indicate that there are appreciable temperature variations along lines of sight. Element abundances are very uncertain since they appear to depend so heavily on likely but unknown density irregularities along lines of sight.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00160286
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