Interactions of atmospheric CO2 and temperature affect flowering time in Arabidopsis thaliana ecotypes

Atmospheric CO₂ and mean global temperature have shown an alarming rate of increase since industrialization. To improve predictions of the future effects of global warming on plant fitness and productivity, an understanding of the effects of CO₂ by temperature interactions is necessary. We have studied how temporal variation in CO₂ and temperature has jointly affected the flowering phenology of Arabidopsis thaliana genotypes from the pre-industrial (270 ppm/25ºC) to the present (380 ppm/26.3ºC) period. We grew fifteen genotypes (n=10) using growth chambers under the following four treatments to simulate pre-industrial and present environments: 270 ppm CO₂ + 25/18ºC day/ night temperature (hereafter ‘L’); 270 ppm + 26.3/19.3ºC (hereafter ‘H’); 380 ppm + 25/18ºC and 380 ppm + 26.3/19.3ºC. On average, flowering time, aboveground biomass, leaf number and leaf area increased significantly between 380 ppm/L and 380 ppm/H treatments, but no differences were present between 270 ppm/L and 270 ppm/H treatments. Thus, plants grown at 380 ppm CO₂ responded more strongly to an increase in temperature (1.3ºC) than plants grown at 270 ppm. Between 270 ppm/L and 380 ppm/H, some genotypes exhibited a significant delay in flowering time, increased biomass, leaf number and leaf area, while others showed either an opposite response or changes that were not statistically significant. Responses of all the parameters tested revealed a significant three way (genotype×CO₂×temperature) interaction. Our results suggest that the rise in CO₂ and temperature (post-industrialization) and their interactive effects are sufficient to alter environmental selection regimes and cause significant developmental changes in many ecotypes.