In this study, we developed a three-way carbon dioxide (CO2) flux-partitioning algorithm that separates net ecosystem exchange (NEE) into aboveground plant respiration (R-above), belowground root and soil respiration (R-below), and gross primary production (GPP). We applied this algorithm to a coupled dataset of continuous chamber-measured soil respiration and eddy covariance (EC)-measured NEE of CO2 in an oak-hickory (Quercus-Carya) deciduous broadleaf forest from 2006 to 2015. We found that on annual time scale, R-below dominated over R-above with the former accounting for 66.9-86.4% and the latter 13.6-33.1%, of the total ecosystem respiration (R-eco). The ratio of Rbelow to R-above varied seasonally, ranging from 1.77 to 7.25 in growing season, and 1.02 to 4.57 in non-growing season. The temperature sensitivity (E-0) of R-below was significantly higher than that of R-above, and E-0 of R-eco responded differently to air and soil temperature. Over the whole study period, annual mean R-above, R-below, and GPP were 243, 806, and 1170 g C m(-2), respectively, with annual R-eco accounting for 89.6% of GPP, of which 68.8% was lost as R-below and 20.8% lost as R-above, and leaving only 10% of the carbon fixation in ecosystems. These estimates, however, did not consider potential light inhibition of leaf respiration. If we accept the presence of light inhibition, then the daytime three-way partitioning method would underestimate annual R-above by 20.4% whereas the nighttime method would overestimate R-above by 23.9% and GPP by 4.7%, compared with estimates accounting for light inhibition in leaves.