Independent and interactive effects of rising [CO2] and temperature over the last century on flowering time in Arabidopsis ecotypes

Background/Question/Methods

Predicting the effects of global change on plant phenology is critical for understanding the functioning of future ecosystems since shifts in phenology can have major consequences for plant evolution, plant-pollinator interactions, and carbon accumulation within ecosystems. There has been a long-standing assumption that rising temperatures over the last century have led to faster plant growth rates, and ultimately earlier flowering, since plants may reach the size for reproductive maturity more quickly. Although a number of individual field studies report accelerated flowering times over the last century, large field surveys (100+ species) indicate that only 5-30% of species actually show a significant response in this direction, and some species even exhibit delayed flowering with warming. Generally, these studies only consider the role of increasing temperature, while ignoring the potential individual and interactive effects of rising [CO₂]. Here we delineated the effects of rising [CO₂] and temperature between preindustrial and modern periods on flowering time in field-collected ecotypes of Arabidopsis thaliana from diverse locations.

Results/Conclusions

We found that the isolated effects of increasing [CO₂] accelerated flowering times, while the addition of higher temperature actually eliminated this response. Consequently, the combined effects of rising [CO₂] and temperature offset one another, eliminating any changes in flowering times between full pre-industrial and modern conditions. The lack of flowering time shifts between the preindustrial and modern treatments occurred despite enhanced growth rates that occurred in response to both increased [CO₂] and temperature. Any potential accelerations in flowering time due to these higher growth rates was negated by a systemic increase in plant size at flowering among all ecotypes in response to simultaneous [CO₂] and temperature rise. Overall, we caution against assuming that shifts in flowering time are always driven by rising temperature, and show that major changes may be occurring within plants even under scenarios where flowering times are not affected. We conclude that rising [CO₂] should be considered along with temperature when explaining plant phenological responses to global change over the last century and into the future.