Abstract: From January to December 2008, the CO₂ flux in a larch plantation (Larix gmeilinii) in Maoershan region of Shangzhi County, Heilongjiang Province was measured by eddy covariance method, and the diurnal changes of leaf photosynthetic rate were measured in growth season (from May to October). There existed differences in the net ecosystem exchange (NEE) of the plantation in different time periods under the effects of environmental factors. In the afternoon (12:00-24:00), the NEE changed more slowly with the variation of vapor pressure deficit (VPD) than in the morning (0:00-12:00); and in the morning, the light use efficiency was 0.6284 mol·mol^-1, 14% more than that in afternoon. The NEE increased with increasing temperature, and the increment in the morning was 50% higher than that in the afternoon (air temperature >15 ℃). These differences in responding to environmental changes led to 88% NEE implemented in the morning, and only 12% NEE implemented in the afternoon. The annual gross ecosystem productivity (GEP) in the morning took a percentage of 60%, and that in afternoon took 40%. These findings were supported by the observation at leaf level, i.e., on average of whole growth season, the leaf photosynthetic capacity in the morning was over 2-fold higher than that in afternoon. Generally, the annual NEE, ecosystem respiration (R_e), and GEP of the plantation in 2008 were 263-264 g C·m^-2, 718-725 g C·m^-2, and 981-989 g C·m^-2, respectively.

Key words: Larix gmelinii, eddy covariance method, carbon budget, leaf photosynthesis, Phyllostachys edulis invasion, soil fungi, community characteristic, broadleaf forest, Tianmu Mountain.