| Boreal forest is the second largest biome on the earth, which lies in middle-high latitude of the northern hemisphere and where temperature increases strongly. Thus, boreal forest is an important research object in global climate change and carbon cycle. Larix gmelinii forest in Daxing'an Mountains of Northeast China is an important component of boreal forest. Long-term measurement of the CO2 fluxes between the vegetation and the atmosphere has facilitated the research on carbon cycle and its controlling mechanisms in boreal forest ecosystem and its response to global climatic change in the future. Based on two-year continuous CO2 exchange observation during growing seasons from 2007 to 2008 over Chinese boreal forest by eddy covariance method in northeast China, we analyzed diurnal and seasonal dynamics of gross ecosystem productivity(GEP), ecosystem respiration(Re) and net ecosystem CO2 exchange(NEE) and their controls. Major conclusions are summarized as follows:(1) The diurnal pattern of GEP could be expressed as one-humped curves with the maximum appeared at 9:00-10:00. The daily length of carbon sequestration from the atmosphere was reduced from 16 hours in June to 1.1 hours in October. GEP was the largest in July with the highest air temperature and precipitation during the whole growing seasons. Mean daily GEP in 2007 and 2008 were 19.45 g CO2·m-2·d-1 and 17.67g CO2·m-2·d-1, respectively. GEP had close linear relationship with both temperature and photosynthetically active radiation (PAR), and especially, the correlative coefficient for soil temperature at 5 cm depth was around 0.55. It indicated that temperature was a major limited factor in boreal forest ecosystem, and PAR was the basis of photosynthesis. Precipitation was enough in boreal forest ecosystem, which was not a limited factor.(2) The diurnal pattern of Re could be expressed as one-humped curves with the maximum appeared at 15:30-16:30. Re and its range in daytime were both larger than those in nighttime. Re was the largest in July and August during the whole growing seasons. Mean daily Re in 2007 and 2008 were 15.15 g CO2·m-2·d-1 and 14.11 g CO2·m-2·d-1. Re was mainly influenced by temperature, and the correlative coefficients with soil temperature (average R=0.492) were higher than those with air temperature (average R2=0.369). Temperature could explain about 34%-51% of seasonal dynamics of Re in Chinese boreal forest ecosystem.(3) The diurnal patterns of NEE could be expressed as one-humped curves with the maximum appeared at 9:00-10:00. The daily length of carbon sequestration from the atmosphere was reduced from 14 hours (5:00-19:00) in June to 9 hours (7:30-16:30) in October. Chinese boreal forest ecosystem was a carbon sink in June, July and August, while a carbon source appeared in September and October. Mean daily NEE in 2007 and 2008 were-1.45 g CO2·m-2·d-1 and-1.37 g CO2·m-2·d-1. NEE was mainly influenced by PAR, and the correlative coefficients were 0.558 and 0.494 in 2007 and 2008, respectively.(4) The intensity of carbon dioxide exchange during growing season in 2007 was stronger than that in 2008. The reason might result from higher mean air temperature (12.46℃in 2007 and 11.04℃in 2008) and higher mean photosynthetically active radiation (697μmol·m-2·s-1 in 2007 and 639μmol·m-2·s-1 in 2008).
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