What was done
The authors grew, from seed, well watered and fertilized plants of two closely related out-crossed genotypes of Arabidopsis thaliana (SG and CG) -- which were generated through artificial selection, where genotype SG was selected for high seed number at elevated CO2 over five generations, and where genotype CG was randomly selected and thus represents a nonselected control -- in 500-ml pots filled with a 1:1:1 mixture of vermiculate, gravel and Turface within controlled environment chambers maintained at atmospheric CO2 concentrations of 380 and 700 ppm, measuring time to visible flowering, number of leaves at flowering and total biomass at flowering, as well as foliar sugar concentrations. Then, in a subsequent experiment with the same growth conditions, they characterized the expression patterns of several floral-initiation genes.

What was learned
Springer et al. report that "SG delayed flowering by 7-9 days, and flowered at a larger size (122% higher biomass) and higher leaf number (81 more leaves) when grown at elevated versus current CO2 concentration," but that "flowering time, size and leaf number at flowering were similar for CG plants grown at current and elevated CO2." In addition, they say that "SG plants had 84% higher foliar sugar concentrations at the onset of flowering when grown at elevated versus current CO2, whereas foliar sugar concentrations of CG plants grown at elevated CO2 only increased by 38% over plants grown at current CO2." Last of all, they report that "SG exhibited changes in the expression patterns of floral-initiation genes in response to elevated CO2, whereas CG plants did not."

What it means
Noting that "delayed flowering increases production of vegetative resources that can be subsequently allocated to reproductive structures," the researchers go on to say that "such evolutionary responses may alter total carbon gain of annual plants if the vegetative stage is extended, and may potentially counteract some of the accelerations in flowering that are occurring in response to increasing temperatures." More generally, their results demonstrate the ability of elevated CO2 to alter the expression of plant genes in ways that may enable plants to take better advantage of the ongoing rise in the air's CO2 content.