What was done
In one experiment, the authors grew soybeans in insulated and non-insulated pots within open-top chambers that were maintained at ambient and twice-ambient concentrations of atmospheric CO2 for 12 or 24 hours per day to study the influence of daily CO2 exposure duration on soybean growth and yield.  In a second similar experiment, where plants received differential CO2 concentrations around the clock, soybeans were grown in pots or rooted directly in the ground to determine the effects of rooting environment and elevated CO2 on growth and yield.

What was learned
Elevated CO2 generally increased plant weight and yield components for both durations of daily CO2 exposure.  However, elevated CO2 only caused significantly greater increases in pod weight, number and stem weight.  Plants placed in insulated pots grew faster and larger than plants placed in non-insulated pots, but there were no significant interactions between CO2 and pot insulation.

In the second experiment, elevated CO2 generally decreased values of stomatal conductance, whereas plants grown in pots exhibited values of stomatal conductance that were nearly one-third greater than those of plants rooted in the soil.  However, pod and seed weight, seed number, and stem weight all increased to the same extent due to atmospheric CO2 enrichment, regardless of whether plants were rooted in the ground or placed in pots.

What it means
The authors determined that 12 hours of daily atmospheric CO2 enrichment was sufficient to elicit growth responses comparable to those achieved with 24 hours of daily CO2 enrichment.  Likewise, they found that soybeans grown in large pots displayed CO2-induced growth responses that were similar to those of plants rooted directly in the ground, even though naturally-rooted plants exhibited lower values of stomatal conductance.  Thus, as the CO2 content of the air rises, soybean plants growing in fields, as well as those growing in pots and containers, will likely display comparable increases in growth and yield.