Abstract: Using turbulent data from Xilinhot National Climatological Observatory (Inner Mongolia) during March of 2010 and February of 2011, we analyzed the diurnal/seasonal variation of the net ecosystem carbon exchange (NEE) of a Stipa krylovii steppe, after data assessment and control. The results showed that the power spectrum and cospectrum in the inertial subrange could be expressed by the power law, and the power exponents were -2/3 and -4/3, respectively. 74% of the dataset could be classified as highquality data for further basic research, while 8% should be removed. At the diurnal scale, the NEE in the steppe showed distinctly different temporal patterns of single and double peaks, with stronger uptake in the morning. At the seasonal scale, the S. krylovii steppe was very low in carbon exchange during the cold winter, turned to be a weak sink when the temperature gradually rose in the spring, and reached its maximum in the June, the early summer. The steppe was constrained in carbon assimilation by the droughts in the months of July and August, and declined to be a weak sink when the steppe faded in the autumn. The annual cumulative carbon flux over the S. krylovii steppe in Inner Mongolia was -348 g CO₂·m^-2·a^-1. The net ecosystem exchange reached its maximum and minimum in June (daytime) and July (night), respectively. This research provided an enhanced understanding of carbon exchanges during the growing and nongrowing seasons in a temperate steppe, and would benefit the land surface process models and biogeochemical models on parameterizing and validation.

Key words: photosynthetic production, plant type, simulation model, light distribution, double cropping rice