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Grazing exerts a key role in nutrient cycling in grassland ecosystems, however, little is known about the effects of short-term enclosure on methane (CH(4)) fluxes in a semi-arid steppe biome like this of Inner Mongolia. CH(4) fluxes were measured in the Leymus chinensis (Trin) Tzvel. grassland using static chamber and gas chromatography (GC). Measurements were carried out twice per month over a growing season in 2004 at the two sites (one fenced since 1999 (UG99) and the other subjected to freely grazing (FG)). All CH(4) fluxes were positive, indicating that this grassland functioned as the active atmospheric CH(4) uptakes. During this period, the UG99 site (57.6 +/- 6.7 mu g Cm(-2) h(-1)) had significantly higher mean CH(4) uptake in comparison to the FG site (37.0 +/- 6.3 mu g C m(-2) h(-1)). A significant liner negative correlations between CH(4) uptake and soil moisture (0-5 cm) at the both sites were found (P <0.05). The results indicated that short-term enclosure was helpful to improve CH(4) uptake in this area.