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 we report the impact of elevated [CO2] (550 mol mol-1) and warming (+2ºC) 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 3 out of 23 species. Warming reduced time to first flowering by an average of 19.1 days 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, nor 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.