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Themeda triandra (kangaroo grass) is the most widespread plant species in Australia. Using herbarium specimens, we quantified awn-length variation across its distribution in relation to climate. We found that awn lengths were shortest around the eastern and southern coast of Australia (with short awns also concentrated in the Pilbara), increasing in length progressively inland and towards the north. There was a significant positive relationship between awn length and mean annual temperature. Further research is needed to understand why awn lengths vary, and how awn-length variation affects seed and seedling fitness in natural habitats. [ABSTRACT FROM AUTHOR]

A general prediction of ecological theory is that climate change will favor invasive nonindigenous plant species (NIPS) over native species. However, the relative fitness advantage enjoyed by NIPS is often affected by resource limitation and potentially by extreme climatic events such as drought. Genetic constraints may also limit the ability of NIPS to adapt to changing climatic conditions. In this study, we investigated evidence for potential NIPS advantage under climate change in two sympatric perennial stipoid grasses from southeast Australia, the NIPS Nassella neesiana and the native Austrostipa bigeniculata. We compared the growth and reproduction of both species under current and year 2050 drought, temperature and CO2 regimes in a multifactor outdoor climate simulation experiment, hypothesizing that NIPS advantage would be higher under more favorable growing conditions. We also compared the quantitative variation and heritability of growth traits in populations of both species collected along a 200 km climatic transect. In contrast to our hypothesis we found that the NIPS N. neesiana was less responsive than A. bigeniculata to winter warming but maintained higher reproductive output during spring drought. However, overall tussock expansion was far more rapid in N. neesiana, and so it maintained an overall fitness advantage over A. bigeniculata in all climate regimes. N. neesiana also exhibited similar or lower quantitative variation and growth trait heritability than A. bigeniculata within populations but greater variability among populations, probably reflecting a complex past introduction history. We found some evidence that additional spring warmth increases the impact of drought on reproduction but not that elevated atmospheric CO2 ameliorates drought severity. Overall, we conclude that NIPS advantage under climate change may be limited by a lack of responsiveness to key climatic drivers, reduced genetic variability in range-edge populations, and complex drought-CO2 interactions. [ABSTRACT FROM AUTHOR]

Ecological risk assessment is an important step in the production and commercialisation of transgenic plants. To date, however, most risk assessment studies have been performed on crop plants, and few have considered the ecological consequences associated with genetic modification of pasture species. In this study we compared the growth, yield, population dynamics and competitive ability of transgenic Trifolium subterraneum subsp. subterraneum cv. Leura (subclover) expressing a nutritive sunflower seed albumin ( ssa) gene with the equivalent non-transgenic commercial line in a glasshouse competition trial. Plants were grown in low-fertility soil typical of unimproved native southeastern Australian grasslands. We measured survivorship, seed production rate, seed germination rate, seed weight, dry weight yield and the intrinsic rate of population increase (λ) of plants grown in mixtures and monocultures over a range of densities (250 to 2000 plants m−2), and also determined intragenotypic and intergenotypic competition coefficients for each line. There were no significant differences between transgenic and non-transgenic plants in any of the measured variables except survivorship; transgenic plants had a significantly lower survival rate than non-transgenic plants when grown at high densities (p<0.01). However, density-dependent effects were observed for all measured variables, and in all models plant density affected the response variables more than the presence of the transgene. Based on these results, we conclude that the ssa gene construct appears to confer no advantage to transgenic T. s. subterraneum cv. Leura growing in mixed or pure swards under the fertility and density regimes examined in the trial. Our data also suggest that transgenic subterranean clover expressing the ssa gene is unlikely to exhibit a competitive advantage over associated non-transgenic commercial cultivars when grown in dense swards in low-fertility pastures. [ABSTRACT FROM AUTHOR]