Abstract: Characteristics of CO₂,water and heat fluxes of terrestrial ecosystems and related mechanisms involved provide insights into the coupling cycle of water and carbon and the model development.It′s necessary to investigate the characteristics of water and carbon fluxes for understanding the crop productivity and water use efficiency.In this study,we analyzed the diurnal changes of water and carbon fluxes at full heading time of winter2wheat in North China based on the eddy covariance technique.The results showed that there existed evident midday depression of CO₂,water vapor and canopy conductance under clear sky condition,as a result of photo-inhibition caused by strong radiation.The responses of CO₂ flux to photosynthetically active radiation could be expressed by Michaelis-Menten function,with apparent quantum yield 0.002997 mg/μmol photons and maximum potential of carbon flux 3.3494 mg/(m²·s).The water vapor flux and canopy conductance were significantly correlated with photosynthetically active radiation.However,at the same light condition,canopy conductance in afternoon was apparently smaller than that in the morning due to the feedback restrain of photosynthate,whereas water vapor flux in afternoon was much larger than that in the morning,resulting from the changes of air temperature and vapor pressure deficit.Note that water use efficiency in the morning was higher than that in the afternoon,because water vapor flux in afternoon was much larger than that in the morning,while no obvious difference exited for CO₂ flux between the morning and afternoon.

Key words: Cropland ecosystems, CO₂ flux, Water vapor flux, Canopy conductance, Diurnal changes, Winter-wheat

CLC Number: 

• S152.7