Abstract: By using eddy covariance method and a open-path CO₂ analyzer placed on a tower in a tropical seasonal rain forest in Xishuangbanna (ChinaFLUX), the 10 Hz observation data of six microclimate variables including three dimensional direction wind speed (u, v, w), CO₂ concentration, H₂O concentration, and air temperature above the canopy of the forest were obtained, and the clear days in four typical months (January, April, July, and October) were selected to calculate the power spectrum and cospectrum of the variables to vertical velocity (w) at five periods of time in a day (morning, 08:00-11:30; noon, 12:00-15:00; afternoon, 15:30-19:00; night, 19:30-23:30; before dawn, 0:00-07:30), aimed to approach the high/low frequency responsivity of the variables above the canpy of tropical seasonal rain forest. Under the conditions of clear weather and good turbulence above the canopy in the tropical seasonal rain forest, the power spectrum slopes of the six variables in their inertial subrange followed -2/3 p
ower law, and their cospectral slopes in inertial subrange followed to -4/3 power law, indicating that the contribution of largescale motions to matter and energy transference above the canopy could satisfy the requirement of observing the responsivity in high and middle frequency signal areas. It was inferred that our sampling frequency of flux observation was reasonable, and our data obtained from the complicated topographical condition were valid and could be used as the actual flux figures in the further study.

Key words: Low light density, Long-term suboptimal temperature, Short-term low temperature, Photosynthesis, Growth speed, Cucumber