Abstract: The Free-air CO2 Enrichment(FACE) system was used to investigate the effect of FACE on wheat canopy microclimate.The wheat canopy microclimate observations were carried out during elongation and mature stages.The results showed that the FACE extreme significantly reduced the wheat leaf stomatal conductance in upper,middle and lower leaves compared with the check by 28%,32%,and 26%(p<0.01)respectively.The maximum daytime mean temperature difference of the vegetation canopy between FACE and ambient reached at 1.58℃ in response to stomatal closure under E-CO2 at the flowering stage.The maximum daytime air temperature difference varied between 0.12 and 0.98℃ inside the canopy,and 0.03~0.7℃ at the canopy top.Whereas daytime air humidity inside the canopy was lower in FACE plot than in ambient plot.The maximum daytime air humidity difference between FACE and ambient varied between-0.3%～-7% at about 14:00.The net radiation above wheat canopy was not significantly affected by FACE.

Key words: FACE, FACE, Wheat, Microclimate, Stomatal conductance, Canopy temperature