Amity L. Williams

Flowering phenology in a species‐rich temperate grassland is sensitive to warming but not elevated CO2

* Flowering is a critical stage in plant life cycles, and changes might alter processes at the species, community and ecosystem levels. Therefore, likely flowering-time responses to global change drivers are needed for predictions of global change impacts on natural and managed ecosystems. * Here, the impact of elevated atmospheric CO2 concentration ([CO2]) (550 micromol mol(-1)) and warming (+2 masculineC) is reported on flowering times in a native, species-rich, temperate grassland in Tasmania, Australia in both 2004 and 2005. * Elevated [CO2] did not affect average time of first flowering in either year, only affecting three out of 23 species. Warming reduced time to first flowering by an average of 19.1 d in 2004, acting on most species, but did not significantly alter flowering time in 2005, which might be related to the timing of rainfall. Elevated [CO2] and warming treatments did not interact on flowering time. * These results show elevated [CO2] did not alter average flowering time or duration in this grassland; neither did it alter the response to warming. Therefore, flowering phenology appears insensitive to increasing [CO2] in this ecosystem, although the response to warming varies between years but can be strong.

Influence of warming on soil water potential controls seedling mortality in perennial but not annual species in a temperate grassland

In a water-limited system, the following hypotheses are proposed: warming will increase seedling mortality; elevated atmospheric CO2 will reduce seedling mortality by reducing transpiration, thereby increasing soil water availability; and longevity (i.e. whether a species is annual or perennial) will affect the response of a species to global changes. Here, these three hypotheses are tested by assessing the impact of elevated CO2 (550 micromol mol(-1) and warming (+2 degrees C) on seedling emergence, survivorship and establishment in an Australian temperate grassland from autumn 2004 to autumn 2007. Warming impacts on seedling survivorship were dependent upon species longevity. Warming reduced seedling survivorship of perennials through its effects on soil water potential but the seedling survivorship of annuals was reduced to a greater extent than could be accounted for by treatment effects on soil water potential. Elevated CO2 did not significantly affect seedling survivorship in annuals or perennials. These results show that warming will alter recruitment of perennial species by changing soil water potential but will reduce recruitment of annual species independent of any effects on soil moisture. The results also show that exposure to elevated CO2 does not make seedlings more resistant to dry soils.

Flowering, seed production and seed mass in a species-rich temperate grassland exposed to FACE and warming

Long-term effects of climate change on plant communities must be mediated by reproductive and recruitment responses of component species. From spring 2003 until autumn 2006, we monitored flowering and seed-production responses to free air CO2 enrichment (FACE) and 2°C warming in a species-rich, nutrient-poor southern temperate grassland, by using the TasFACE experiment. There were no effects of either FACE or warming on the proportion of species flowering in any year. Flowering, seed production and seed mass were not significantly affected by FACE, warming or their interaction in most species. Some species, however, did respond significantly to simulated global changes. These responses generally were not governed by life history, but there were two distinct trends. First, warming increased the proportion of the population that flowered in perennial grasses but not in other species types. Second, flowering and seed production of both perennial woody dicots responded strongly to the interaction of FACE and warming, with Bossiaea prostrata producing most seeds in warmed FACE plots and Hibbertia hirsuta producing the most in unwarmed FACE plots. FACE increased seed mass 4-fold in the perennial C3 grass Elymus scaber (P < 0.01) but substantially reduced seed mass of the perennial C3 grass Austrodanthonia caespitosa (P < 0.02) and the perennial forb Hypochaeris radicata (P < 0.02), with the remainder of species unaffected. Our results indicate that warming and elevated CO2 had little effect on seed production in the temperate grassland ecosystem. The few significant affects there were, however, are likely to have substantial implications for community composition and structure.

Elevated CO2 and warming impacts on flowering phenology in a southern Australian grassland are related to flowering time but not growth form, origin or longevity

Flowering is a critical stage in plant life cycles, and changes in phenology might alter processes at the species, community and ecosystem levels. Therefore, likely flowering-time responses to global-change drivers are needed for predictions of global-change impacts on natural and managed ecosystems. Predicting responses of species to global changes would be simplified if functional, phylogenetic or biogeographical traits contributed substantially to a species’ response. Here we investigate the role of growth form (grass, graminoid, forb, subshrub), longevity (annual, perennial), origin (native, exotic) and flowering time in determining the impact of elevated [CO2] (550 μmol mol-1) and infrared warming (mean warming of +2°C) on flowering times of 31 co-occurring species of a range of species-types in a temperate grassland in 2004, 2005 and 2007. Warming reduced time to first flowering by an average of 20.3 days in 2004, 2.1 days in 2005 and 7.6 days in 2007; however, the response varied among species and was unrelated to growth form, origin or longevity. Elevated [CO2] did not alter flowering times; neither was there any [CO2] by species-type interaction. However, both warming and elevated [CO2] tended to have a greater effect on later-flowering species, with time to first flowering of later-flowering species being reduced by both elevated [CO2] (P < 0.001) and warming (P < 0.001) to a greater extent than that of earlier-flowering species. These results have ramifications for our predictions of community and ecosystem interactions in native grasslands in response to global change.