Nonindigenous Plant Advantage in Native and Exotic Australian Grasses under Experimental Drought, Warming, and Atmospheric CO2 Enrichment

Abstract

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.

Elevated CO2maintains grassland net carbon uptake under a future heat and drought extreme

“…Most previous studies on the impact of eCO 2 associated with drought and/or elevated temperature did not report whole ecosystem responses, but primarily plant responses at various organizational levels. Generally, they show that eCO 2 alleviates the stress associated with drought and/or elevated temperature (4,16,18,(22)(23)(24)(25)(26)(27)(28), but some studies found inconsistent responses (29)(30)(31)(32)(33)(34)(35)(36). This variability could be linked with the seasonality of precipitation (35,37) or with the intensity and length of the imposed stress, because the effect of eCO 2 has been shown to be positive under moderate drought and negligible under severe stress when stomata are fully closed (14).…”

Why non-native grasses pose a critical emerging threat to biodiversity conservation, habitat connectivity and agricultural production in multifunctional rural landscapes

“…While eco-physiological distinctiveness is certainly a feature of NNGs, many have morphological and ecological similarities to native congeners or analogues (e.g., Godfree et al 2013), and there may be substitutability among grasses that would allow for a basic level of connectivity and resource provision to be maintained, even in invaded landscapes. Perhaps some trade-off species have a smaller impact on conservation value than others, in which case prioritising their use could help retain multi-value landscape elements.…”

“…This is particularly true when sympatric native species have similar morphological attributes (e.g., Godfree et al 2013), or when the production of floral parts has been affected by drought or overgrazing. For example, it is common for new populations of H. hirta, E. curvula, and especially Nassella spp., which are morphologically similar to Australian native Themeda, Cymbopogon, Poa, and Austrostipa species, to go unrecognised for many years.…”

“…5), key species of which have continental or sub-continental distributions (e.g., Themeda triandra). The potential range of many NNGs, especially those sourced from genetically diverse populations (Godfree et al 2013) or bred for enhanced fitness or niche breadth (e.g., Culvenor et al 2007;Lavergne and Molofsky 2007) is correspondingly large (Fig. 3c).…”

Invasive Species: Plants

“…Many invasive and native plants increase biomass production and fecundity under elevated [CO 2 ], a response known as the CO 2 fertilization effect (Godfree et al, 2013). Because trade-offs exist between acquisition of atmospheric CO 2 and water loss, altering [CO 2 ] changes physiological processes taking place in plant tissue, in turn altering plant growth and water use efficiency.…”