Evidence is accumulating that the effect of CO₂ on time of flowering involves interactions with photoperiod, but the basis for this interaction is unclear. We examined which components of the photoperiod flowering pathway account for this interaction in Arabidopsis thaliana. Ten mutants deficient in particular loci in the photoperiod pathway, as well as the wild type, were grown under short and long days at either ambient or elevated CO₂. We determined leaf number at bud formation and the number of days required or induction of flowering.

Results/Conclusions

Elevated CO₂ had an effect on the blue light receptor, CRYPTOCHROME 2 under short days, and on the GIGANTEA gene under long days that increased the number of  leaves required for bud formation, and an effect on FLOWERING LOCUS T in both long and short days that reduced the number of leaves required. Elevated CO₂ also affected flowering by increasing the rate of leaf production. The net effect of elevated CO₂ on time of flowering varies because CO₂ has a complex array of effects on different elements of the developmental pathway leading to flower induction that may either hasten or delay flowering depending upon the influence of other environmental factors such as photoperiod.