Aboveground and belowground contributions to ecosystem respiration in a temperate deciduous forest

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.

Automated summary

A three-way carbon dioxide flux-partitioning algorithm was developed and applied to a dataset of an oak-hickory deciduous broadleaf forest. The algorithm successfully separated net ecosystem exchange into aboveground plant respiration, belowground root and soil respiration, and gross primary production. It was found that belowground respiration dominated over aboveground respiration on an annual time scale, and the temperature sensitivity of belowground respiration was higher than that of aboveground respiration.