Abstract: Soil is a major C pool， and it has a close link with atmospheric and biotic pools. Soil respiration is an important component in carbon cycle of terrestrial ecosystem. Soil respiration is the sum of heterotrophic respiration (soil fauna, bacteria and fungi) during decomposition of organic matter, and autotrophic (root) respiration. As an index of the metabolic activity of heterotrophic microbes and plant roots, soil respiration shows spatial heterogeneity. On a global scale, soil respiration showed a clear zone characteristic from tundra to equatorial ecosystems; soil respiration also showed a significant spatial variation under different vegetation, soil texture and landusing patterns and other factors in smallscale topography. In the desert, there is big variation in sand dune terrain conditions by the impact of changes in different parts of soil moisture, soil temperature, vegetation diversity, community appearance and characteristics of vegetation conditions. The previous study was emphasized on the effect of desertification on soil respiration and carbon balance studies，whereas spatial heterogeneity of soil respiration and its mechanism was inadequate. And studies for the quantitative assessment of soil respiration which reveals desertification of terrestrial ecosystem carbon cycle and its effect on global climate change has an important significance. In order to understand the controlling environmental factors of soil respiration in sand land, we studied daily variation of soil respiration and its relationship with air temperature, air humid and soil temperature in Horqin Sand Land. By using LI-6400 portable photosynthesis apparatus connected to soil chamber，soil respiration and environmental factors under different sand dune terrains(low land, windward slope, the top of the dune, leeward slope) and different vegetation conditions(Caragan microphylla and Setaria virdis) of the dune in a sand dune were measured in August 2010, with related affecting factors analyzed. The result indicates that the diurnal trend soil respiration showes the same change with an increase trend and the maximum in the morning，a decrease trend in the afternoon and the minimum before dawn．The change of soil respiration rate has a significant spatial heterogeneity.The range of change is in the following order：leeward slope(1.95±0.21μmolCO2·m-2·s-1)>the top of the dune(1.05±0.14μmolCO2·m-2·s-1)>windward slope(0.74±0.08μmolCO2·m-2·s-1) >low land(0.62±0.09μmolCO2·m-2·s-1）．The soil respiration of the sand land has a close relationship to the vegetation condition，Caragan microphylla(0.69±0.06μmolCO2·m-2·s-1)，Setaria virdis(0.86±0.11μmolCO2·m-2·s-1)．Diurnal change in soil respiration has a positive correlation with air temperature and a negative correlation with air humid and an positive correlation with soil temperature．An exponential model can be used to describe the relationship between soil respiration and soil temperature, with the sensitivity of soil respiration to temperature differing between different terrains and different vegetation types; and soil respireation controlled the rates of soil respireation and R2 is from 0.220 to 0.748. There is no difference in Q10 value of soil respiration under different terrains and different vegetation conditions of the dune.

Key words: soil respiration, dune topography, vegetation condition, soil temperature