[Effects of free-air CO2 enrichment on rice canopy microlimate]

In this study, the free-air CO2 enrichment (FACE) system (setup at at Anzhen, Wuxi, Jiangsu Province in 2001) was used to investigate the effects of FACE on rice canopy microclimate. 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 development stage. The results showed that FACE reduced the rice leaf stomatal conductance. The rice leaf stomatal conductance difference between FACE and ambient was larger among upper layer leaves than among lower layer leaves and at heading and milk filling stages than at maturing stage. FACE increased daytime rice canopy temperature but had little effect on nighttime rice canopy temperature. The daytime rice canopy temperature difference between FACE and ambient was larger at heading and milk filling stages than at maturing stage. From heading to flowering, the daily maximum rice canopy temperature difference between FACE and ambient reached 1.2 degrees C under fine weather condition. The average daytime rice canopy temperature from flowering to maturing stage was about 0.43 degree C. Daytime air temperature inside rice canopy was also affected by FACE. Daytime air temperature inside rice canopy was higher in FACE plot than in ambient plot. The value of daytime air temperature difference between FACE and ambient increased with the increase of solar radiation and varied with height. The maximum daytime air temperature difference between FACE and ambient varied between 0.47-1.2 degrees C and 0.37-0.8 degree C at middle of canopy and canopy height, respectively. Air humidity and nighttime air temperature inside rice canopy were not significantly affected by FACE. These results indicate that FACE reducing rice leaf stomatal conductance was the major cause of the increase of canopy temperature and inside canopy air temperature in FACE plot. The higher canopy temperature and inside canopy air temperature in FACE plot resulted in the earlier maturity of rice crop in FACE plot than that in the ambient plot.