Heterotrophic respiration,an important pathway releasing CO_2 into atmosphere,is largely influenced by soil temperature.Changes in heterotrophic respiration under climate change may lead to large uncertainties in estimation of ecosystem carbon store.As one of the most important terrestrial ecosystems,grassland cover approximately 40%of the global land surface and play a critical role in regulating global carbon balance.In order to examine the effects of global warming on soil heterotrophic respiration,soil samples were collected from Duolun County(42°02'N,116°17'E),Inner Mongolia,China,where field warming had been conducted for 4 years (2006-2009),and Kessler farm(34°59'N,97°31'W),Oklahoma,USA,where field warming was started from November 1996.Laboratory incubation results has shown that the content of soil organic carbon(SOC)in temperate grassland has not significantly decreased after several years successive field warming.The response of SOC decomposition to temperature change(Q_(10))has not been significantly affected by field warming.Soil carbon cycle in the context of global climate change is a complex phenomenon,requiring a further investigation.