Abstract
In this study, we developed a three-way carbon dioxide (CO2) flux-partitioning algorithm that separates net ecosystem exchange (NEE) into aboveground plant respiration (Rabove), belowground root and soil respiration (Rbelow), 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, Rbelow dominated over Rabove with the former accounting for 66.9–86.4% and the latter 13.6–33.1%, of the total ecosystem respiration (Reco). The ratio of Rbelow to Rabove 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 (E0) of Rbelow was significantly higher than that of Rabove, and E0 of Reco responded differently to air and soil temperature. Over the whole study period, annual mean Rabove, Rbelow, and GPP were 243, 806, and 1170 g C m−2, respectively, with annual Reco accounting for 89.6% of GPP, of which 68.8% was lost as Rbelow and 20.8% lost as Rabove, 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 Rabove by 20.4% whereas the nighttime method would overestimate Rabove by 23.9% and GPP by 4.7%, compared with estimates accounting for light inhibition in leaves.
