Abstract
The aerodynamical method for carbon dioxide flux measurement in the surface air layer of plant community under field condition is highly evaluated. This method, however, is rarely used because of its complexity in measuring technique and hard labour work in calculation. The authors developed the self recording instrument for this method.
The vertical turbulent flux of CO2(P0) in the surface air layer of plant community is represented by the following equation. (Thornthwaite and Holzman (1938), and Inoue (1957)).
P0=k2(u2-u1)(C2-C1)/(lnz2-d/z1-d)2
If we assumed that the zero plane displacement d is constant, the equation can be changed into
P0=K(Δu)(ΔC)
where
K=k2/(lnz2-d/z1-d)2
Consequently, P0 can be determined by putting directly both Δu and ΔC into a multiplier.
The zero plane displacement d changes with wind speed, but if the two heights of z1, z2 are selected properly, the error due to the change of the zero plane displacement is less than five per cent.
The ΔC is measured with a differential type infra-red gas analyzer (Horiba Co.) and Δu and d with five cup anemometer (Casella Co.).
As it takes more time to detect the CO2 concentration than the wind speed, the wind speed is recorded continuously on the endless tape with stereo tape recorder, and when the CO2 concentration is detected, the wind speed is play-backed and simultaneously the Δu and ΔC are put into the multiplier.
The examples of records were presented in Figs. 7 through 9.
