A large number of field studies have reported accelerations in flowering time among plant species over the last century. Shifts in flowering time can have major influences on 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 time, although the simultaneous effects of rising [CO2] are not well understood, along with the interactive effects of these two factors. In addition, experimental warming studies have not been able to fully explain the high degree of accelerations in flowering time observed in the field. 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 in a variety of Arabidopsis thaliana genotypes originating from multiple locations. In a first series of experiments, plants were grown at full preindustrial (270 ppm CO2, 20.0 °C) and full modern (380 ppm CO2, 21.3 °C) conditions, as well as with isolated increases in both [CO2] and temperature.
Results/Conclusions
Between preindustrial and modern conditions, the isolated effect of increasing [CO2] did not alter flowering times among Arabidopsis genotypes, while increasing temperature slightly delayed flowering. When both rising [CO2] and temperature were combined, these factors produced an unexpected acceleration in flowering time that mimicked observed shifts under field conditions. Thus, it is possible that an increase in both factors is required to explain the global trends in flowering time accelerations. To explain these responses at the whole-plant level, we found that the combined effects of rising [CO2] and temperature enhanced growth rates, while simultaneously stabilizing plant size at flowering, which produced accelerated flowering times at the modern condition.
In a second set of experiments, we found that between modern and future conditions (700 ppm CO2, 25.0 °C), further increases in temperature and [CO2] led to high variation in flowering time responses that included both accelerations and delays. If represented under field conditions, such responses would produce major selective pressures since genotypes functioned very differently at future versus modern conditions for flowering time. This suggests that developmental timing, especially within species, may become increasingly perturbed under future climate change scenarios.