Disentangling the effects of rising [CO2] and temperature on flowering time in Arabidopsis
Shifts in flowering time can have major consequences for plant evolution, plant-pollinator interactions, and carbon accumulation within ecosystems. There has been a major focus on understanding the effects of rising temperature on flowering times, whereas the simultaneous effects of rising [CO2] are often not considered. In addition, while many field studies report accelerations in flowering times over the last century, and experimental warming studies show this trend continuing into the future, these accelerations are not universal in that delays are also regularly reported. To address the possible reasons for these differences, we have experimentally delineated the individual and interactive effects of increasing [CO2] and temperature across preindustrial, modern, and future time periods on the flowering times and growth responses of 8 field-collected ecotypes of Arabidopsis thaliana from diverse locations.
Between preindustrial and modern conditions, increasing [CO2] accelerated flowering times, while increasing temperature slightly delayed flowering. When both were combined, these factors produced no change in net flowering time. Modern [CO2] greatly enhanced growth rates relative to preindustrial [CO2], but surprisingly, this did not translate into earlier flowering because plants grown at the modern treatment flowered at a larger biomass than at the preindustrial [CO2] treatment. These results suggest that increases in [CO2] may have played a role in altering flowering times over the last century, and indicate that major changes may be occurring within plants even when flowering times remains constant. Between modern and future conditions, further increases in temperature and [CO2] led to large variations in flowering time and plant size at flowering among ecotypes. Future [CO2] continued to accelerate growth rates across all ecotypes. Consistent increases in growth rates coupled with variable biomass at flowering explain the large degree of flowering time variation under future conditions, where relatively smaller ecotypes exhibited accelerated flowering times while larger ecotypes delayed flowering. This suggests that flowering times, especially within species, may become increasingly perturbed under future climate change scenarios.