Characteristics of energy and mass exchanges in the wheat field of Lhasa, Xizang (Tibet)

The experiment on energy and mass exchanges, which include CO2 flux, water evapotranspiration, sensible heat, net radiation and soil heat flux, was conducted in the wheat field of Lhasa, Xizang. The result was analyzed and compared with those obtained in the wheat fields of other two climatic regions. The canopy net photosynthesis rate in the Xizang Plateau is the largest in the three climatic regions. The canopy net photosynthesis rate increases linearly with the intensity of net radiation. But when the net radiation is greater than 700 W/m², the increasing rate of net photosynthesis begin to decrease. During a day, water use efficiency of the canopy net photosynthesis is the highest just after sunrise and the lowest just before sunset. The total daily energies of net radiation and evapotranspiration in the wheat field of Xizang (Tibet) are the largest in the three regions, but their intensities in the late afternoon are the lowest.