Abstract
Following Inoue's (1957) suggestion the aerodynamic method of measuring the CO2 assimilation and/or respiration of plants over wide fields has been applied to a wheat field during a whole day in May of 1957. This method, which was first applied preliminarily to a paddy field in September of 1956, makes use of the aerodynamic relation of turbulent transfer as
P=(U2-U1)(C1-C2)/{2.303/klogZ2-d/Z1-d}
where U1, U2 and C1, C2 are the wind velocity and the absolute concentration of CO2 (for example, mg CO2 perliter air), k the Kármán's constant (0.4), d the zeroplane displacement, and P is the turbulent flux of CO2. The positive and negative values of P are respectively corresponding to the respiration and assimilation of plants over the field. The choice of the heights Z1 and Z2 must be adequate in order to the above equation be applied without the modifications due to the stability factors. The CO2 flux from the soil surface has been neglected by examining the small gradient of CO2 within the air layer amongst stalks. The assimilation rate in daytime and the respiration rate in night are reasonably shown in Table 1 aswell as the evapotranspiration and/or condensation rate χ of water vapor. A brief discussion of the apparent relationship between photosynthesis and evapotranspiration has been given.
