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  • bioassay  (3)
  • Astrophysics  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Allelopathic potential of vegetative and flowering ragwort (Senecio jacobaea L.) plants against associated pasture species (1994)
    Springer
    Plant and soil 164 (1994), S. 61-68 
    Details
    ISSN: 1573-5036
    Keywords: allelopathy ; aqueous extract ; bioassay ; leachate ; ragwort ; soil toxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The allelopathic effects of vegetative and flowering plants of the annual/biennial pasture weed Senecio jacobaea L. (ragwort) against Lolium perenne L. (perennial ryegrass) and four pasture legumes were investigated using a range of bioassays. Bioassays based on shoot and root leachates demonstrated detectable, although usually slight, allelopathic effects, and these did not usually differ between the two developmental stages of S. jacobaea. However, aqueous extract and tissue decomposition bioassays demonstrated stronger allelopathic effects, particularly for flowering plants, and this was in general agreement with toxicity assessments of soil collected from under S. jacobaea plants in the field. According to our study, flowering plants have the potential to weaken pasture through allelopathy, and decomposition of above-ground litter appears as the most likely mechanism facilitating this. The aqueous extract and tissue decomposition bioassays also revealed that L. perenne was less susceptible to S. jacobaea allelopathy than were the legumes, suggesting that encouraging a strong L. perenne component in pastures has potential for reducing the overall inhibitory ef S. jacobaea on pasture production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010111
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Comparison of osmotic and allelopathic effects of grass leaf extracts on grass seed germination and radicle elongation (1992)
    Springer
    Plant and soil 140 (1992), S. 315-319 
    Details
    ISSN: 1573-5036
    Keywords: allelopathy ; bioassay ; germination ; osmotic potential ; plant extract ; radicle elongation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The influence of osmotic effects of aqueous plant extracts on the results of allelopathy bioassays was investigated for four pasture grass species. It was found that allelopathic effects were substantially overestimated when osmotic effects were not taken into account. It is concluded that bioassays using aqueous plant extracts are more realistic when osmotically adjusted control values (with the same osmotic potential as the plant extract being tested) are used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010609
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Use of a comparative approach to identify allelopathic potential and relationship between allelopathy bioassays and “competition” experiments for ten grassland and plant species (1996)
    Springer
    Journal of chemical ecology 22 (1996), S. 933-948 
    Details
    ISSN: 1573-1561
    Keywords: Allelopathy ; bioassay ; Carduus nutans L. ; comparative approach ; correlative evidence ; forage plant ; grassland ; phytometer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Various allelopathy bioassays were used to evaluate the allelopathic potential of 10 grassland forage species against a common test (phytometer) species,Carduus nutans L. Aqueous extracts did not influenceC. nutans germination, although radicle elongation was often severely inhibited.C. nutans was strongly affected by shoot, but not root, leachates. Decomposing ground tissue had mixed effects, and often stimulated shoot production ofC. nutans. Calculation ofR 2 (coefficient of determination) values between these results, and the results of previous experiments investigating the effects of the same 10 species onC. nutans emergence and development in field plots and glasshouse competition experiments frequently revealed strong, statistically significant relationships. Our results therefore provide correlative evidence for the importance of allelopathy in field conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02029946
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  • 4
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    Massive Star Formation of the SGR a East H (sub II) Regions Near the Galactic Center (2010)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A group of four compact H II regions associated with the well-known 50 km/s molecular cloud is the closest site of on-going star formation to the dynamical center of the Galaxy, at a projected distance of approximately 6 pc. We present a study of ionized gas based on the [Ne II] (12.8 micron) line, as well as multi-frequency radio continuum, Hubble Space Telescope Pa alpha, and Spitzer Infrared Array Camera observations of the most compact member of the H II group, Sgr A East H II D. The radio continuum image at 6 cm shows that this source breaks up into two equally bright ionized features, D1 and D2. The spectral energy distribution of the D source is consistent with it being due to a 25 =/- 3 solar mass star with a luminosity of 8 +/- 3 x 10(exp 4) Solar luminosity . The inferred mass, effective temperature of the UV source, and the ionization rate are compatible with a young O9-B0 star. The ionized features D1 and D2 are considered to be ionized by UV radiation collimated by an accretion disk. We consider that the central massive star photoevaporates its circumstellar disk on a timescale of 3x (exp 4) years giving a mass flux approximately 3 x 10(exp -5) Solar Mass / year and producing the ionized material in D1 and D2 expanding in an inhomogeneous medium. The ionized gas kinematics, as traced by the [Ne II] emission, is difficult to interpret, but it could be explained by the interaction of a bipolar jet with surrounding gas along with what appears to be a conical wall of lower velocity gas. The other H II regions, Sgr A East A-C, have morphologies and kinematics that more closely resemble cometary flows seen in other compact H II regions, where gas moves along a paraboloidal surface formed by the interaction of a stellar wind with a molecular cloud.
    Keywords: Astrophysics
    Type: GSFC.JA.4829.2011 , The Astrophysical Journal; 725; 1429-1439
    Format: application/pdf
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  • 5
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    A Three Parsec-Scale Jet-Driven Outflow from Sgr A (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: The compact radio source Sgr A* is coincident with a 4x 10(exp 6) solar Mass black hole at the dynamical center of the Galaxy and is surrounded by dense orbiting ionized and molecular gas. We present high resolution radio continuum images of the central 3' and report a faint continuous linear structure centered on Sgr A*. This feature is rotated by 28 deg in PA with respect to the Galactic plane. A number of weak blobs of radio emission with X-ray counterparts are detected along the axis of the linear structure. In addition, the continuous linear feature appears to be terminated symmetrically by two linearly polarized structures at 8.4 GHz, approx 75" from Sgr A*. The linear structure is best characterized by a mildly relativistic jet-driven outflow from Sgr A*, and an outflow rate 10(exp 6) solar M / yr. The near and far-sides of the jet are interacting with orbiting ionized and molecular gas over the last 1-3 hundred years and are responsible for the origin of a 2" hole, the "minicavity", where disturbed kinematics, enhanced FeII/III line emission, and diffuse X-ray gas have been detected. The estimated kinetic luminosity of the outflow is approx 1.2 X 10(exp 41) erg/s which can produce the Galactic center X-ray flash that has recently been identified
    Keywords: Astrophysics
    Type: GSFC.JA.6609.2012
    Format: application/pdf
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