Ecosystem co2 flux over two years for a 200-year-old Chinese broad-leaved korean pine mixed forest

Long-term measurement of carbon metabolism of old-growth forests is critical to predict their behaviors and to reduce the uncertainties of carbon accounting under changing climate. Eddy covariance technology was applied to investigate the long-term carbon exchange over a 200 year-old Chinese broad-leaved Korean pine mixed forest of Forest Ecosystem Open Research Station of Changbai Mountains (128°28'E and 42°24' N, Jilin Province, P. R. China), Chinese Academy of Sciences, since August 2002. This paper reports the result on (1) Regulation of environmental factors on phase and amplitude of ecosystem CO2 uptake and release; (2) sink/source status on the data obtained with open-path eddy covariance system and CO2 profile measurement system from Jan. 2003 to Dec. 2004. Corrections due to storage and friction velocity were applied to the eddy carbon flux. The most significant difference between 2003 and 2004 were precipitation and temperature. The precipitation of 2004 was 707.3 mm and very close to 693.9 mm, the averaged value between 1982 and 2004, while the precipitation of 2003 was 538.4 mm. Atmospheric and soil temperature at 5 cm depth of 2004 were 0.7 and 0.5 C higher than that of 2003 separately. The forest was a net sink of atmospheric CO2 and sequestered - 449 gC m-2 during the study period, and -278 and -171 gC m-2 for 2003 and 2004 separately. FGPP and FRE over 2003 and 2004 were -1332, -1294 gC m-2. and 1054, 1124 gC m-2 separately. The seasonal trends of gross primary productivity (FGPP) and respiration (RE) followed closely with the change in LAI and temperature. The summer is the most significant season as far as ecosystem carbon balance is concerned. The 90 days of summer contributed 66.9, 68.9% of FGPP, 60.4 and 62.1% of RE of whole year. This study shows that old-growth forest can be strong net carbon sink of atmospheric CO