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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Weed research 31 (1991), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: This study examined the effects of competition on the growth of Avena fatua, winter wheat and winter barley. Plants were sampled at frequent intervals from replacement series experiments at two contrasting sites in the U.K. A. fatua was much slower to establish than the two cereals, but thereafter exhibited a faster rate of growth. In monoculture, it took a considerable time for A. fatua to reach a size equal to that of the cereals, but by the end of the experiments it was the largest of the three species. The change-over from cereal dominance in mixtures to A. fatua tiominance was rapid, and in three cases coincided with cereal flag leaf emergence. In the fourth case, it appeared to coincide with the art of canopy height extension. At one site the rder of competitiveness at anthesis was A. fatua= barley〉wheat, and at the other site the order was A. fatua〉wheat〉barley. In order to explain and predict differences between years and sites, more studies are required on morphological development in relation to abiotic variables.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1939
    Keywords: Phenotypic plasticity ; Agrestal vs. ruderal ; Nutrient variability ; Marginal populations ; Solanum ptycanthum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To test if the high nutrient inputs of agroeosystems select for specialized agroecotypes or for phenotypic plasticity, Ontario populations of the northwardly migrating annual weed Solanum ptycanthum from ruderal (beach) and agricultural habitats were compared over a nutrient gradient. Temporal variation of total available nitrogen was determined in both types of habitats. As gene flow via seed contamination of tomato transplants from S. United States was detected, variation in response to nutrient (N) levels was also compared between agrestal populations from the northern (Ontario) and southern (Georgia) ends of the species range. Five families from six populations (two northern agrestal, two northern ruderal and two southern agrestal) were grown in the greenhouse at low, medium and high nutrient levels, and plant growth and traits associated with reproductive success measured. All populations displayed significant levels of plasticity in the majority of vegetative and reproductive traits. There were no detectable differences over the levels of nutrients tested between individuals sampled from northern agrestal and ruderal populations, even though variation in available nitrogen is greater in agroecosystems. Southern agrestal populations were genetically differentiated from the northern populations, and exhibited almost twice the overall plasticity of northern populations, measured by the Mahalanobis distance. Canonical discriminant analysis showed complete overlap in the northern populations over all nutrient levels, suggesting that colonization of new habitats is via a general-purpose genotype, rather than by selection for specialized agroeotypes.
    Type of Medium: Electronic Resource
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