THE CHARATERISTICS OF CO2 CONCENTRATION AND FLUX,TURBULENCE FLUXES IN THE NEAR SURFACE LAYER OVER THE WHEAT FIELD

The gradient of CO2 concentration, photosynthetically active radiation, netradiation, soil heat flux, profiles of wind speed, and air temperature and humidity were mea-sured above a wheat field during May and June 1985 at Beijing Agro-Ecosystems Experimental Station, Chinese Academy of Sciences. Fluxes of carbondioxide, sensible heat, latent heat and momentum were calculated by using the aerodynamic method. The obser-vation site, equipment, calibration techniques, and the errors associated with the mea-surement, and the computational procedures are described. The results show that the diurnal variations of the amplitude of CO2 concentration were 103.4 to 27.5, 87.5 to 27.3, and 69.8 to 11.5 ppm;the average CO2 concentrations were 345.3, 350.6 and 357.5 ppm for the photosynt hesis type, and 373.9, 369.7 and 362.1 ppm for the respiration type at 1m, 2m and 10m above surface, respectively, from May 14 to June 15. During the day, transfer direction of the CO2 fluxes and gradients was from air to cropcanopy, and atnoon(11 to 13 hour) the transfer rate reaches negative maximum value. Atnight, transfer of the CO2 fluxes and gradients was in the reversed direction and reaches positive maximum in the early morning(4 to 6 hour). There are strong correlation between CO2 flux and the netradiation(Rn) , available energy(H+LE) , photosynthetically active radiation and momentum flux.