What was done
Winter wheat was grown in open-top chambers and in field-tracking climatized enclosures located in The Netherlands at ambient (350 ppm) and elevated (700 ppm) CO2 to determine its response to elevated CO2 during the course of a growing season.

What was learned
In early spring, when low light and temperature characterized the growing environment, elevated CO2 had no apparent effect on plant biomass, even though it boosted midday photosynthetic rates by 19%.  In late spring, however, after irradiance and temperature had risen, elevated CO2 increased photosynthetic rates by 53% and influenced plant biomass as well.  By season's end, the CO2-induced photosynthetic stimulation had dropped to 27%, while grain yield and total biomass were 19% greater than that reported for plants grown at ambient CO2.  It is interesting to note, although total plant nitrogen concentration decreased by 5% due to atmospheric CO2 enrichment, there was no decline in grain nitrogen content.

What it means
This study indicates that as the CO2 content of the air rises, winter wheat will likely respond favorably by increasing photosynthesis, biomass and yield.  However, during the course of development, such increases will occur and accrue as temperatures and irradiance increase with the growing season.  Thus, CO2-induced growth enhancements are likely to be greater in environments, and during times, of high irradiance and temperature than they are in environments, and during times, of low irradiance and temperature.