Effects of Elevated CO2 and Temperature on Flowering Times of Asteraceae Species
Johnston, A. and Reekie, E. 2008. Regardless of whether rising atmospheric carbon dioxide levels increase air temperature, flowering phenology will be affected. International Journal of Plant Science 169: 1210-1218.
In exploring this dual possibility, the authors examined the effects of elevated atmospheric CO2 concentration by itself (ambient and ambient + 330 ppm) as well as the combined effect of elevated CO2 and elevated air temperature (ambient + 1.5°C) on the flowering phenology of 22 species of plants in the family Asteraceae, which were grown under natural seasonally-varying temperature and daylength in separate compartments of a glasshouse in Wolfville, Nova Scotia, Canada.
The two researchers report that, "on average, elevated CO2 by itself advanced flowering by four days," while "increasing temperature as well as CO2 advanced flowering by an additional three days." They also found that "CO2 was more likely to hasten phenology in long- than in short-day species," and that "early- and late-flowering species did not differ in response to elevated CO2, but the combined effect of elevated CO2 and temperature hastened flowering more in early- than late-flowering species."
In light of their several findings, Johnston and Reekie concluded that, with respect to time of flowering in Asteraceae species, "the direct effect of CO2 on phenology may be as important as its indirect effect through climate change."