What was done
The authors grew two soybean cultivars - Ripley, which is semi-dwarf and determinate in growth, and Spencer, which is standard-size and indeterminate in growth - for two growing seasons in open-top chambers receiving atmospheric CO2 concentrations of ambient and ambient plus 300 ppm CO2 to study the effects of elevated CO2 on the growth and yield of these two contrasting cultivars.

What was learned
Averaged over both years, elevated CO2 increased photosynthetic rates in Ripley and Spencer varieties by 76 and 60%, respectively.  However, Spencer showed a greater degree of CO2-responsiveness to vegetative biomass production than did Ripley (132 vs. 65%, respectively).  Likewise, elevated CO2 enhanced seed yield in Spencer by 60% but by only 35% in Ripley.  Thus, Spencer, the standard-size indeterminate soybean cultivar, displayed greater responsiveness to atmospheric CO2 enrichment than did the semi-dwarf determinate variety.

What it means
In the agricultural research and development industry, numerous selection processes and field trials are carried out before seed of a particular crop variety is made available to commercial growers.  This study indicates that selection for favorable yield responses to atmospheric CO2 enrichment could well make a big difference to future farm productivity and profitability.  In this particular instance, for example, standard-size soybean cultivars, which display an indeterminate growth pattern, were shown to be likely to increase their yields faster than semi-dwarf cultivars, which display a determinate growth pattern, as the air's CO2 content continues to rise.  Hence, standard-size varieties should probably be favored in the future.