Abstract: Field observations of CH4 and CO2 concentration down soil profiles in the major grassland communities of Xilin River Basin of Inner Mongolia in 1999 indicate that the distribution of methane through the soil profile was different from that of carbon dioxide. Methane concentration decreased gradually with soil depth while the concentration of carbon dioxide showed a strongly increasing trend. On the other hand, methane concentration in the soil of meadow steppe, Leymus chinensis steppe and Stipa grandis steppe, a series driven by moisture gradients in Xilin River Basin, differed significantly with seasonal variation. Variation in the time scale of impacts may partially account for the result that there was no significant effect of grazing on CH4 and CO2 concentration in the grassland soil.

Key words: Inner Mongolia, Grassland, CH4, CO2