What was done
The authors grew soybeans for 21 days in controlled environments having atmospheric CO2 concentrations of approximately 360 (ambient) or 720 ppm and soil temperatures of 25 (ambient) or 30°C to study the interactive effects of these parameters on photosynthesis and growth.

What was learned
Elevated CO2 significantly increased whole plant net photosynthesis at both temperatures, with the greatest effect occurring at 30°C.  However, as time progressed, photosynthetic acclimation occurred; and this increase dropped from a 50% enhancement at 13 days into the experiment, to a 30% enhancement at its conclusion eight days later.  In spite of this acclimation, atmospheric CO2 enrichment significantly enhanced total dry weight at final harvest by 36 and 42% at 25 and 30°C, respectively, relative to controls grown at 360 ppm atmospheric CO2.

What it means
As the CO2 content of the air increases, soybean plants will likely increase their rates of net photosynthesis.  This direct physiological response to atmospheric CO2 enrichment typically increases carbohydrate production, thus allowing photosynthetically derived sugars to be transferred to growing sink tissues to increase overall plant biomass.  If air temperatures increase slightly in the future, soybean plants should exhibit even greater photosynthetic rates, due to the positive interaction between elevated CO2 and temperature, leading to even greater increases in biomass.