The invasive potential of parthenium weed (Parthenium hysterophorus L.)in Australia

Thi Lan Thi Nguyen (2011). The invasive potential of parthenium weed (Parthenium hysterophorus L.)in Australia PhD Thesis, School of Agriculture and Food Sciences, The University of Queensland.

       
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Author Thi Lan Thi Nguyen
Thesis Title The invasive potential of parthenium weed (Parthenium hysterophorus L.)in Australia
School, Centre or Institute School of Agriculture and Food Sciences
Institution The University of Queensland
Publication date 2011-06
Thesis type PhD Thesis
Supervisor Professor Steve Adkins
Dr. Sheldon Navie
Dr. Doug George
Total pages 308
Total colour pages 10
Total black and white pages 298
Subjects 07 Agricultural and Veterinary Sciences
Abstract/Summary Parthenium weed (Parthenium hysterophorus L.) belonging to the Asteraceae family is described as an aggressive herbaceous weed of tropical and subtropical environments. It has the ability to dramatically reduce the productivity of pastures, as well as cause a range of allergy and respiratory diseases for both livestock and people. It has also become an important cropping weed and significantly disrupted native community biodiversity. In Australia, parthenium weed is currently one of the most important invasive weeds and is predominantly found in Queensland. Clearly, there is a need to understand thoroughly the effects of several environmental parameters upon the reproductive biology of parthenium weed, the effects of climate change variables upon the weed’s early growth, the mechanisms of the weed spread, seed persistence, and the impact of parthenium weed upon plant biodiversity. Insights into these aspects may allow us to model and hence, predict the invasion potential of parthenium weed and thereby, to manage the weed more effectively and successfully. Warm (35/28 ºC, day/night), as compared to cool growth conditions (25/18 ºC, day/night), advanced the developmental process of parthenium weed, speeding up its life cycle, its time to flowering and fruiting commencement, and promoting height attainment and biomass accumulation. This change of temperature also promoted the reproductive ability of the plant, increasing its seed production capacity, the filled seed percentage, promoting the proportion of dormant seeds and producing seed with the capacity to live longer in the soil seed bank. Under an elevated CO2 concentration (550 ppmv), coupled with a cooler (30/15 ºC, day/night), wetter soil condition (field capacity), the early plant growth of two biotypes (Clermont and Toogoolawah) was greatly promoted over that seen under the same conditions but under an ambient CO2 concentration (390 ppmv). However, growth was not significantly increased under elevated CO2 conditions when the early growth was under warm conditions (35/20 ºC, day/night). In addition, the species composition and the dynamics of the soil seed bank were studied at two sites (Moolayember Creek and Clermont) in central Queensland. Parthenium weed was significantly reducing the community diversity, the species richness, the Shannon-Weiner index and the evenness index. However, the impact of parthenium weed at the Moolayember Creek site was less than that seen at the two Clermont sub-sites. When considered over a 15 year period, the initially declining parthenium weed seed bank at the Moolayember Creek site had more recently plateaued. Unfortunately, very little improvement in the overall size of the seed bank of the palatable fodder plants had occurred there. At the Clermont sites, the parthenium weed seed bank was still increasing gradually in size. Furthermore, the seed bank of grass species remained extremely low and this site seemed to be unstable and undergoing a continued decline in biological quality. The spread of weed seed (including that of parthenium weed) on vehicles was studied over a three year period. Material washed off vehicles at off-road wash down facilities, taken from five sites in central Queensland, in each of the four seasons of the year showed that the average total number of viable seeds t-1 of dry sludge was ca. 67,000. A typical wash down facility was removing up to ca. 335,000 viable seeds from vehicles per week. Parthenium weed was present in the sludge at all five facilities, with an average of 1,340 seeds t-1 of dry sludge. A typical wash down facility was removing up to 4,000 viable parthenium weed seeds per week. Moreover, the viability of parthenium weed seeds in water was measured in distilled, river, and sludge water at temperatures ranging from 10 to 34 ºC and in solutions of different pH (4 to 9 of pH levels) at temperature ranging from 15 to 30 ºC, for between 0 to 45 days. The viability of parthenium weed seeds was still high after 45 days in distilled and river water especially when the temperature of those solutions was low. This viability of parthenium weed seeds was less in sludge water. The higher the temperature of the water and the longer the seeds were in the water, the lower the subsequent seed viability observed. Warmth elevated the rate of seed viability decline but seeds would be predicted to remain viable for up to 20 days in river water. For the viability of seeds in different pH solutions, the higher the temperature of the solution and the longer the seeds were in it, the lower was their viability but these outcomes did not depend upon the pH of the solution. Finally, the impact of parthenium weed upon botanical community diversity was assessed in areas infested with different densities of the weed (i.e. high, low and no parthenium weed) at a pastoral site in Kilcoy, Queensland, Australia. The importance value index and the relative density of native species were lowest at the high density of parthenium weed site and highest at the no parthenium weed site and the species diversity and the community evenness decreased as the parthenium weed infestation levels increased, both in summer and in winter, both in the above-ground community and in the soil seed bank. This study has shown that components of a changing climate, including elevated atmospheric CO2 concentration, warmer temperatures and drier soils are likely to promote the growth and reproductive capacity of parthenium weed, as well modify quality components of its seed. Such changes brought about by climate change would also aid the weed persistence in the environment, therefore promoting its longer-term invasive potential. In combination with these advantages, the spread of the weed’s seeds by vehicles and water is also likely to increase. The stimulation of growth and increased competitiveness of the weed will also lead to a greater suppression of native community biodiversity. All of these findings strongly suggest that the problems associated with parthenium weed will increase in Australia and around the world in the future.
Keyword parthenium weed
Parthenium hysterophorus
reproductive capacity
soil seed bank
weed seed spread
biodiversity
climate change
early growth
Additional Notes Colour pages xv, xvi, 22, 74, 105, 108, 123, 184, 204, 210 Landscape pages 126-129, 204, 249-258

 
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