What was done
The authors "summarize the results of 60 studies reporting flowering-time responses (defined as the time to first visible flower) of both crop and wild species at elevated CO2."

What was learned
Springer and Ward state that "all possible responses have been observed both among species as well as within species, including accelerated, delayed and no change in flowering time in response to elevated CO2." However, they find that "flowering-time responses of wild species grown at elevated CO2 are much more evenly distributed, in that a similar number of studies report accelerated, delayed, or no change in flowering time, whereas crops primarily showed accelerated flowering (approx. 80% exhibited accelerated flowering)." They also report that "plants utilizing both the C3 and C4 photosynthetic pathways show altered flowering time with elevated CO2," but they say that "two crop species that account for a substantial portion of the world's agricultural production, soybean [a C3 crop] and maize [a C4 crop], do not show consistent patterns in the response of flowering time at elevated CO2."

The two researchers additionally determined that "studies performed within a genus also show a lack of consistent flowering-time response to elevated CO2," and that among only ten genotypes of a single well-studied species (Arabidopsis thaliana), "all possible flowering-time responses to elevated CO2, including delayed, accelerated and unaltered flowering times, were observed." Finally, they report that "a majority of multifactor studies that measured flowering time report no interaction between elevated CO2 and other environmental factors, such as temperature ... nutrient availability ... light ... and ozone," although they note that "a limited number of elevated CO2 studies do show significant interactive effects with other environmental factors."

What it means
Springer and Ward conclude that the studies they reviewed "clearly show that future increases in atmospheric CO2 will have major effects on the flowering time of both wild and crop species," but they say that "at this time it is not possible to account for the wide variation in flowering-time responses because knowledge of the underlying physiological and molecular mechanisms is incomplete."