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• W196072396 abstract "Parthenium hysterophorus L. (parthenium weed) is a serious problem in the beef producing areas of central Queensland. It is also spreading into cropping areas, where it is a contaminant of grain, is causing increasing environmental damage, and is a significant human health concern. As a result of these factors it is considered one of the most significant and damaging weeds in Australia. Two known introductions of this weed into Australia have occurred, one in central Queensland and the other in south-east Queensland. The central Queensland population has been much more 'aggressive' and troublesome than the south-east Queensland population and some ecological differences between the two populations are thought to exist. The purpose of this research was to ascertain fundamental information about a range of aspects of the biology of this weed in Australia, including determining if there are any significant biological differences between P. hysterophorus plants firom the two populations currently present. Several experiments were conducted on the seed biology of P. hysterophorus. In laboratory germination studies it was found that the optimum temperature for germination of both populations of this species was between 22 and 25°C, while significant germination occurred over a wide range of temperatures (8 to 30°C). In further laboratory studies, it was found that relatively concentrated smoke water solutions inhibited the germination of this species. Glasshouse experiments demonstrated that the germination of native species was more heavily stimulated by aerosol application of smoke than was P. hysterophorus. Hence, it is possible that fire may be used as a pasture management tool in order to tip the ecological balance in favour of native pasture species. Experiments were conducted in order to determine the persistence of P. hysterophorus seeds in a variety of situations. A field study demonstrated that more than 70% of seeds buried 5 cm below the soil surface survived for at least 2 years, while surface-lying seeds survived for periods no longer than 6 months. This indicated that persistence of the weed's seeds may be increased if they are buried by some form of soil disturbance, such as flooding, cultivation or the activity of animals. Some innate seed dormancy was detected in a portion of freshly collected P. hysterophorus seeds, which was probably caused by water-soluble germination inhibitors being present in the seeds and their accessory structures (i.e. the diaspores). These chemicals first need to be leached from the diaspores before germination will occur, and this explains why significant germination of P. hysterophorus occurs in the field only after major rainfall events. The abundance and persistence of P. hysterophorus seeds in the soil seed bank at two sites in central Queensland was also investigated in glasshouse experiments. There was relatively little change in the abundance of P. hysterophorus seeds in the seed bank over a period of 18 months, another indication that the seeds are very persistent in the soil. The population of P. hysterophorus seeds in the top 3.5 cm of soil was also very large, with estimates between 1500 and 34000 seed m-2. depending on the level of infestation of the weed and the time of year. In fact, this weed accounted for between 47% and 87% of the total seeds present in the soil at the two study sites. During these experiments it was also observed that the emergence rate of P. hysterophorus seedlings was significantly faster than that of all other species present in the soil seed bank at these sites. This rapid emergence has also been noticed in the field and may be part of the reason why this weed is so aggressive and able to out-compete most other species found in these locations. The growth and phenology of P. hysterophorus was studied by growing plants from the two populations (i.e. central Queensland and south-east Queensland) together in a growth cabinet under conditions designed to imitate summer climatic conditions in Emerald, Brisbane, Armidale and Ballarat. It was found that plants grew and completed their life-cycle under all of these conditions. However, the plants grown under Emerald, Brisbane and Armidale conditions grew much faster and taller, and produced more seeds, than those grown under Ballarat conditions. It took the weed less than 60 days to reach maturity under Emerald conditions while over 100 days were required when the plants were grown in Ballarat conditions. Several differences were detected in the growth of P. hysterophorus plants from the two populations. In particular, plants from the central Queensland population grew much taller and were significantly larger than those from the south-east Queensland population, and this may be one reason why the former population has been more aggressive. There were also differences in seed size, seed mass, and proportion of seeds filled when plants from the two populations were compared. Hence, it does seem that these two populations, originating from separate introductions, should be regarded as two distinct 'biotypes'. Finally, experiments were conducted on the growth of P. hysterophorus under enhanced levels of atmospheric carbon dioxide (CO2) to determine whether the competitiveness of the weed might change in the future as a result of continued climate change. It was found that the P. hysterophorus plants grown at the elevated level of CO2 (480 ppm) were much taller and larger than those grown under present levels of CO2 (360 ppm). Parthenium hysterophorus plants were also grown in competition with Cenchrus ciliaris L. (buffel grass) at both of these CO2 concentrations. The dry weight of C. ciliaris plants in these experiments was about seven times greater than that of P. hysterophorus when they were grown at present CO2 concentrations. However, at the elevated concentration of CO2, the dry weight of P. hysterophorus was about the same as that of C. ciliaris. These findings, their role in the ascendancy of P. hysterophorus in the semi-arid areas of central Queensland, and their implications to the future management this weed in Australia are also discussed." @default.
• W196072396 created "2016-06-24" @default.
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• W196072396 date "2002-01-01" @default.
• W196072396 modified "2023-09-27" @default.
• W196072396 title "The biology of Parthenium hysterophorus L. in Australia" @default.
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