4-year-old Pinus koraiensis, planted in open-top chambers at Changbai Mountain Station, received three different treatments [700 µmol(CO2) mol-1 = EC, control chamber = CC, and field = F]. Saturated net photosynthetic rate (PN) was 62 % higher in EC plants compared to CC and F plants as shown by PAR/PN response curves. Despite the increased PN, EC plants still showed decreased photosynthetic capacity when compared with CC and F plants at the same measurement CO2 concentration. EC plants had the highest stomatal conductance (gs) and ratio of intercellular to ambient CO2 concentration (Ci/Ca) compared with CC and F plants when measured at the same CO2 concentration. The Ci/Ca ratio was a sensitive indicator of stomatal behaviour, but not of photosynthesis. The responses of gs to EC did not correlate in magnitude or direction with responses of PN to EC. There was no significant difference in the number of stomata lines and stomata between EC and Ca. and Y. M. Zhou, S. J. Han.