Abstract:

Characteristics of CO₂ flux were investigated by using the data collected from an open path eddy covariance system and an automatic weather gradient system in a 13-year-old Chinese fir plantation ecosystem in Huitong County, Hunan Province, in 2008. The results showed that there were pronounced diurnal and annual variations in CO₂ flux in the Chinese fir plantation. In clear days, mean duration of negative CO₂ fluxes decreased from summer, spring, autumn to winter, and the biggest mean daily carbon dioxide flux range and the earliest time of the average minimum carbon dioxide appeared in summer, followed by autumn, spring and winter. The Chinese fir plantation ecosystem had a negative monthly CO₂ flux that acted as a carbon sink except for January and February. The minimum accumulated monthly net carbon ecosystem exchange (maximum carbon sink) was -53.0 g C·m^-2 occurred in June. The annual net carbon ecosystem exchange amounted to -255.3 g C·m^-2. The CO₂ flux was closely related to several meteorological factors including photosynthetic active radiation, air temperature and soil temperature. The Michaelis-Menten model could be used to express the relationship between CO₂ flux and photosynthetic active radiation in daytime, however the model parameters varied apparently with different temperatures (P<0.05). The CO₂ flux at night showed an exponential relationship with soil temperature at 5 cm depth(P<0.05).

Key words: Chinese fir plantation, eddy covariance, CO₂ flux, photosynthetic active radiation, air temperature, soil temperature