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.