Abstract: The research on CO2 flux in forest system was one of the hot topics in global changes. The CO2  flux during growth season of natural broadleaved mixed forest in Xiaoxinganling mountains was analyzed, based on observed data continuously in 2008 by using openpath eddy covariance system. The results showed that the CO2 flux changed from -0.46 to 0.42 mg·m-2·s-1during the whole growth season. The maximum uptake occurred at 9 o’clock during June and the maximum efflux occurred at 5 o’clock during July. During daytime, the carbon uptake increased with the temperature increasing when it was below 26.63℃. On the contrary, it decreased with temperature increasing when it was above 2663℃. During nighttime, the maximum efflux occurred 13.50℃. In all, it showed that carbon assimilation was 212.32 g·m-2 during the whole growth season of natural broadleaved mixed forest in Xiaoxinganling mountains in 2008.

Key words:  CO2 flux, Broadleaved mixed forest, Eddy covariance method, Xiaoxinganling mountains