topic : Canopy CO2 exchange diurnal and seasonal variations
(Yoshiko KOSUGI, Kyoto Univ.)

I will next introduce the three years’ results of diurnal and seasonal variations in canopy CO2 exchange from 2002 to 2005, which is now also published in Agricultural and Forest Meteorology. At calm night, CO2 exchange occurs with not eddy but storage and advection flux, so eddy covariance method can not count all night time CO2 emission. We also observed storage flux but the advection flux is very difficult to observe.

So, we compare eddy flux shown with green line in this figure and eddy+storage flux which is shown with dark green line, and soil respiration rate shown in red line. In this figure, we omit low u* data

which usually showed severe underestimate of total gas exchange because of advection flux as this left figure. We can see that observed nighttime NEE and Fc were increased in wet season. Soil respiration usually only match about half of night time CO2 emission with total ecosystem respiration. So this comparison strongly suggests that nighttime CO2 efflux was underestimated even when the CO2 storage term is considered and high u*.