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Three antigens were associated with the cell walls of pseudomonads. A highly antigenic, strain-specific antigen of high molecular weight and protein or lipoprotein in nature, occurred as an envelope around the cells. It could be washed off the cells closely associated with carbohydrate material but its antigenicity was not dependent on the carbohydrate present. Another antigen, common to all strains tested, was situated below the first antigen. This was less antigenic than the strain-specific antigen and was polysaccharide or lipopolysaccharide in nature. A second common antigen was the mucopeptide of the cell walls. This had an antigenicity similar to that of the second antigen and was dependent on both the carbohydrate and polypeptide components of the macromolecule. There appears to be some correlation between these findings and the structure of cell walls of pseudomonads are shown by electron microscopy. 相似文献
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To investigate factors affecting the ability of introduced species to invade natural communities in the Western Australian wheatbelt, five communities were examined within a nature reserve near Kellerberrin. Transect studies indicated that introduced annuals were more abundant in woodland than in shrub communities, despite an input of introduced seed into all communities. The response of native and introduced annuals to soil disturbance and fertilizer addition was examined. Small areas were disturbed and/or provided with fertilizer prior to addition of seed of introduced annuals. In most communities, the introduced species used (Avena fatua and Ursinia anthemoides) established well only where the soil had been disturbed, but their growth was increased greatly when fertilizer was also added. Establishment and growth of other introduced species also increased where nutrient addition and soil disturbance were combined. Growth of several native annuals increased greatly with fertilizer addition, but showed little response to disturbance. Fertilizer addition also significantly increased the number of native species present in most communities. This indicates that growth of both native and introduced species is limited by nutrient availability in these communities, but also that introduced species respond more to a combination of nutrient addition and soil disturbance. 相似文献
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The Spiral Plate Maker yielded counts of viable bacteria in pure suspensions that were at least as precise as those obtained under comparable conditions by the Droplette and Miles & Misra methods. A tendency of the Miles & Misra method to produce erroneous counts of Escherichia coli was demonstrated and the advantages of the mechanical method over established counting methods is discussed. 相似文献
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Abstract Assessment of the ecological risk posed to native vegetation from the development of shallow and saline water tables is considered an urgent task in southern Australia. Ecological risk can be defined as the product of the likelihood of an ecological effect and the consequences of that effect. At present, the likelihood of the development of a shallow water table is determined by hydrological modelling at the catchment scale, and this in itself is often equated to ecological risk. In contrast, the ecological consequences of secondary salinity are generally investigated at the patch scale. Translating ecological likelihood and the ecological consequences of risk across these scales has proved problematic, both conceptually and quantitatively. Here we argue that the consideration of ecological risk within the context of the patch‐ or catchment‐scale is based upon human perceptions of spatial units, rather than the ecological scales at which various processes determine vegetation dynamics. By focusing on the processes that determine vegetation dynamics, and the dimensions of these processes, both spatial and temporal scales can be built into conceptual frameworks that aim to understand vegetation change, such as frameworks of alternative stable states. We present an alternative conceptual framework of the ecological risk from secondary salinity based around using the rates of processes, such as salt accumulation in the soil or the frequency of waterlogging, at the scales at which these processes occur. This framework also integrates concepts of vegetation states and transitions between meta‐stable states and alternative stable states. 相似文献
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