Observation of O2:CO2 exchange ratio for net turbulent fluxes and its application to forest carbon cycles

Abstract

AbstractAn average O2:CO2 exchange ratio for net turbulent O2 and CO2 fluxes in a cool temperate deciduous forest in central Japan was obtained based on an aerodynamic method using continuous measurements of atmospheric O2/N2 ratio and CO2 concentration. The average daily mean O2:CO2 exchange ratio was 0.86 during summer, 2013, a value significantly lower than the 1.1 used as a globally averaged terrestrial biospheric O2:CO2 exchange ratio in a CO2 budget analysis. Using the value of 0.86, along with the O2:CO2 exchange ratio of 1.11 for the ecosystem respiration (RE) and 1.00 for the gross primary production (GPP), the net ecosystem production (NEP) measured with an eddy covariance method was separated into GPP and RE using a one‐box canopy O2/CO2 budget model. The estimated average daily‐mean GPP and RE values were consistent, within estimation errors, with those estimated from an empirical function of air temperature; the RE values were also comparable to the soil CO2 efflux observed using an open‐flow soil chamber method. These results suggest that the simultaneous observation of O2 and CO2 concentrations in a forest has potential as a new tool to evaluate the forest CO2 budget.