| Poplar is one of the most widely used afforestation species in the world, and occupies the larg-est area of plantations in China. It is critically important to determine the carbon exchange as im-pacted by environmental factors at different time scales for managing poplar plantations to improve the productivity and carbon sequestration functionality. Net ecosystem exchange (NEE), gross eco-system production (GEP), ecosystem respiration (Re) that of the carbon exchange, and meteorologi-cal factors of a Populus×euramericana cv. "74/76" plantation located on the floodplain of Yong-ding River in Daxing District, Beijing, were measured by using an eddy covariance system and a microclimate measurement system from 2006 to 2009, respectively. Furthermore, soil respiration (Rs), was measured by a4-channel soil respiration measurement system (Li-8150, Li-Cor, NE) in the poplar plantation ecosystem from 2007 to 2009. The variations of NEE, GEP, Re, Rs and their re-sponses to environmental factors were analyzed and discussed in the paper.(1) The degree of energy closure was shown a better result in the data quality. It was 0.81,0.77, 0.78 and 0.73 at half-hourly scale that compared it was 0.95,0.87,0.92 and 0.81 at daily scale in the growing seasons from 2006 to 2009, respectively.(2) Annual NEE was-403.72,-372.74,-790.10 and-563.18 gCm-2yr-1from 2006 to 2009, re-spectively, which compared to-590.95,-640.62,-929.41 and -664.50 gCm-2yr-1 for the comulated NEE during the four growing seasons. The inter-annual variation of comulated during the growing seasons was more than that of total year.(3) The comulated GEP over the four growing seasons was 1270.46,1232.91,1568.81 and 1278.83 gCm-2yr-1 from 2006 to 2009, which was part of 1384.79,1319.30,1653.68 and 1380.05 gCm-2 yr-1 over the four total years, respectively. The ratio of comulated GEP over the four growing seasons to annual GEP was more than 90% in the four years.(4) Annual Re was 981.07,946.68,863.58 and 817.30 gCm-2 yr-1, and comulated Re during the four growing seasons was 679.51,592.41,639.41 and 614.34 from 2006 to 2009, respectively. The ratio of comulated Re during the four growing seasons to annual Re was 69.26%,62.58%,74.04% and 75.71%.(5) Annual Rs was 642.11,629.29 and 609.05 gCm-2yr-1from 2007 to 2009, respectively, and the ratio of annual Rs to annual Re was 67.83%,72.87%and 74.52%in the three years,.(6) The most significant pertinence associated with NEE was PAR, which can explain about 46.8%～67.7% of the variation at half-hourly scale in daytime during the growing seasons.(7) Ts5 was the most significant factor for Re at half-hourly scale at night over the growing seasons, while in the non-growing seasons, the most significant pertinence associated with Re was Ta at night.(8) Re was serious affected by disease and insect or drought stress, but it was obsolete for Rs. Re and Rs were mainly controlled by Ts5, but Rs was more responsive to Ts5 than Re. Re was more affected by vwc than Rs.
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