[Effects of free air CO2 enrichment on rice canopy energy balance].

The change of crop canopy energy balance will affect crop growth and development and its water use efficiency. In this study, the FACE system (setup at at Anzhen, Wuxi, Jiangsu Province in 2001) was used to investigate the effects of FACE on rice canopy energy balance. The rice canopy microclimate observations were carried out from August 26 to October 13, 2001 when the rice crops were at the heading to maturing stage. The results showed that the maximum difference of rice canopy sensible and latent heat fluxes between ambient and FACE occurred at the same time of minimum air humidity, i.e., at about 14:00. From flowering to maturing stage, the maximum difference of rice canopy sensible and latent heat flux between FACE and ambient varied between 12-55 J.m-2.s-1 and -15(-)-65 J.m-2.s-1, respectively. The daytime total canopy sensible and latent heat fluxes of FACE were higher and lower than those of ambient, respectively, throughout flowering to maturing stage. The differences of daytime total canopy sensible and latent heat fluxes between ambient and FACE increased with the increase of net radiation above canopy during the same development stage, but decreased with the progress of the development stage. From flowering to maturing stage, the average difference of daytime total canopy latent heat flux between ambient and FACE was about 6.7%. FACE increased and decreased the ratio of daytime total canopy sensible and latent heat flux to daytime total net radiation above canopy, respectively, the ratio differences between FACE and ambient were 5.5%.