Effect of disturbance and nutrient addition on native and introduced annuals in plant communities in the Western Australian wheatbelt

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.     

Comparison of the Precision Obtained in Counting Viable Bacteria by the Spiral Plate Maker, the Droplette and the Miles & Misra Methods

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.