O2:CO2 exchange ratios observed in a cool temperate deciduous forest ecosystem of central Japan

Detailed observations of O-2:CO2 exchange ratios were conducted in a cool temperate deciduous forest located in central Japan. The exchange ratios of soil respiration and net assimilation were found to be 1.11 +/- 0.01 and 1.02 +/- 0.03 from soil chamber and branch bag measurements, respectively. Continuous measurements of the atmospheric O-2/N-2 ratio and the CO2 concentration, made inside the canopy during a summer season, indicated that the average exchange ratio was lower in the daytime (0.87 +/- 0.02) than in the nighttime (1.03 +/- 0.02) with a daily mean value of 0.94 +/- 0.01. The observed average daytime and nighttime exchange ratios were nearly consistent with the corresponding values obtained from a one-box canopy O-2/CO2 budget model simulation of net turbulent O-2 and CO2 fluxes between the atmosphere and the forest ecosystem. Our results suggest that the daily mean exchange ratios of the net turbulent O-2 and CO2 fluxes depend sensitively on the forest ecosystem processes.