Why does elevated CO2 affect time of flowering? An exploratory study using the photoperiodic flowering mutants of Arabidopsis thaliana

Evidence is accumulating that the effect of CO2 on time of flowering involves interactions with photoperiod, but the basis for this interaction is unclear. Here, which components of the photoperiod flowering pathway account for this interaction in Arabidopsis thaliana were examined. 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. Leaf number at flowering and the number of days required for induction of flowering were determined. Elevated CO2 interacted with both the photoreceptors and the subsequent transduction reactions in the photoperiod pathway. The direction and magnitude of the effects varied with photoperiod. Elevated CO2 also affected flowering by increasing 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.