Abstract: By using eddy covariance method, this paper dealt with the power spectra and cospectra of turbulence under three atmospheric stability regimes, i.e., unstable, near neutral, and stable, in Horqin semi-arid sandy grassland. The power spectra of longitudinal and lateral velocities under the three atmospheric stability regimes were similar, and in accordance with the -2/3 law. The power spectra of vertical wind speed had no inertial sub-ranges under near neutral atmospheric stratification, which indicated that the three-dimensional sonic anemomcter didn’t totally capture the signal. Under the stable atmospheric condition, there were horizontal turbulence motions and molecular diffusions. Moreover, the power spectra of both CO₂ and H ₂O illustrated that the open-path eddy covariance system could satisfy the estimation of turbulence fluxes over canopy, and the peaks of the power spectra were shifted to the high frequency end. The cospectra of vertical wind speed with three scalars were similar, with the inertial subranges of cospectra becoming shorter from unstable to stable atmospheric conditions and conforming to the -4/3 law, which illustrated that the spatial separation of instruments didn’t affect the observed fluxes.

Key words: Myoporum bontioides, Plutella xylostella, Bioactivity, Flavonoids