Observation of O:CO exchange ratio for net turbulent fluxes and its application to forest carbon cycles.

An average O:CO exchange ratio for net turbulent O and CO fluxes in a cool temperate deciduous forest in central Japan was obtained based on an aerodynamic method using continuous measurements of atmospheric O/N ratio and CO concentration. The average daily mean O:CO exchange ratio was 0.86 during summer, 2013, a value significantly lower than the 1.1 used as a globally averaged terrestrial biospheric O:CO exchange ratio in a CO budget analysis. Using the value of 0.86, along with the O:CO 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 O/CO 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 CO efflux observed using an open-flow soil chamber method. These results suggest that the simultaneous observation of O and CO concentrations in a forest has potential as a new tool to evaluate the forest CO budget. [ABSTRACT FROM AUTHOR]