Abstract: Net photosynthetic rate, transpiration rate and water utilization efficiency of 2-year-old cutting seedlings of different clones of Larix olgensis Henry growing in phytotron, were measured at different CO₂ concentration, and regressive analysis was done.The results showed that net photosynthetic rate and water utilization efficiency increased, while transpiration rate decreased, with the increasement of CO₂ concentration.But the parttern and intensity of CO₂ response of different clone were different.CO₂ compensation point of different clone of Larix olgensis Henry was different either.These diversity were the fundation of clone selection.CO₂ respones of net photosynthetic rate and water utilization efficiency had very important significance in clone selection, while CO₂ compensation point was senseless.Growth of larix olgensis Henry might become faster and its distribution area might become bigger in future higher CO₂ concentration condition.

Key words: Larix olgensis Henry, Physiological ecology characteristics, CO₂ response, Clone selection