Abstract: By using open top chamber, a field experiment was conducted to study the effects of elevated ozone concentration on the diurnal change of winter wheat photosynthesis at milking stage. At 13:00-15:00, the field environmental variables (photosynthetic active radiation, chamber temperature, and vapor pressure difference) were the menace to the winter wheat photosynthesis. Comparing with the control, fumigation with 100 and 150 nl·L^-1 of ozone led to the decrease of net photosynthetic rate by 6.3% and 11.1%, respectively (P<0.05). In treatment 100 nl·L^-1 of ozone, the stoma limit value, transpiration rate, stomatal conductance, and water use efficiency had a change trend basically in accordance with that in control; whereas in treatment 150 nl·L^-1 of ozone, the transpiration rate and stomatal conductance increased significantly before 11:00, but the water use efficiency was in adverse. At 13:00-15:00, the water use efficiency increased significantly in both cases. The above evidences indicated that under no environmental stress, the decrease of net photosynthetic rate could be attributed to the stomatal and non-stomatal limitation in treatments 100 and 150 nl·L^-1 of ozone, respectively. Under stressed environment, both 100 and 150 nl·L^-1 of ozone improved the winter wheat water use efficiency significantly, moreover, 150 nl·L^-1 of ozone induced a significant increase of intercellular CO₂ use efficiency.

Key words: Upper reaches of Yangtze River, Dark coniferous forest, Soil water, Infiltration