SUMMARY (1) The eddy-correlation technique was used to measure CO2 efflux from the floor of a deciduous forest. Midday values of CO2 efflux typically ranged between 0.30 and 0.45 mg m-2 s-1. These values were somewhat larger than those from previous chamber studies, which typically ranged from 0.2 to 0.3 mg m-2 s-1. (2) Daytime CO2 efflux from the canopy floor was correlated with air temperature. A suppression in CO2 effiux was observed late in the afternoon and a burst in CO2 efflux was observed near dusk, which was independent of temperature. (3) CO2 effiux from the floor of a deciduous forest was insensitive to changes in wind speed under the conditions studied. This insensitivity was probably due to the soil type and soil litter at the experimental site and the low wind speeds encountered near the forest floor. (4) The eddy-correlation technique seems to provide a promising means for measuring CO2 efflux from a forest or orchard floor. More work, however, is needed to examine the role of the dispersive term on subcanopy mass and energy exchange. Further examination into the mechanism causing the late afternoon suppression and early evening burst in CO2 efflux is also needed. The role of canopy water deficits or pressure fluctuations should be investigated as possible factors contributing to this suppression. Future studies of the early evening respiratory burst should include measurements of photosynthetic translocation to the roots.
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