Abstract: Gas exchange was measured for flag leaf of winter wheat in the flowering and dough stage under the free air CO2 enrichment(FACE) system.Photosynthetic parameters were also calculated by using a biochemical model.Research was conducted on the effect of the response curves and photosynthetic parameters with elevated CO2(550 μL·L-1).The results showed that the net photosynthesis rate,which increased with CO2 concentration in short term,decreased even disappeared in FACE rings both at flowering stage and dough stage.That means photosynthetic acclimation occurred in the flag leaf of winter wheat in FACE rings.There was not liner relationship between photosynthetic acclimation and N supply.SPAD and chlorophyll content in the flag leaf decreased with elevated CO2,which probably was main reason for photosynthetic acclimation.

Key words: FACE(Free Air Carbon dioxide Enrichment), FACE(Free Air Carbon dioxide Enrichment), Photosynthetic acclimation, Winter wheat, Flag leaf, Gas exchange measurement, SPAD, Chlorophyll