Soil respiration is one of the major carbon (C) fluxes between terrestrial ecosystems and the atmosphere and plays an important role in regulating the responses of ecosystem and global C cycling to natural and anthropogenic perturbations. A field experiment was conducted between April 2005 and October 2006 in a semiarid grassland in northern China to examine effects of topography, fire, nitrogen (N) fertilization, and their potential interactions on soil respiration. Mean soil respiration was 6.0% higher in the lower than upper slope over the 2 growing seasons. Annual burning in early spring caused constant increases in soil respiration (23.8%) over the two growing seasons. In addition, fire effects on soil respiration varied with both season and topographic position. Soil respiration in the fertilized plots was 11.4% greater than that in the unfertilized plots. Water- and plant-mediation could be primarily responsible for the changes in soil respiration with topography and after fire whereas the positive responses of soil respiration to N fertilization were attributable to stimulated plant growth, root activity and respiration. The different mechanisms by which topography, fire, and N fertilization influence soil respiration identified in this study will facilitate the simulation and projection of ecosystem C cycling in the semiarid grassland in northern China. (c) 2007 Elsevier Ltd. All rights reserved.