Soil respiration (Rs), the emission of CO2 from the soil surface, is one of major carbon fluxes from terrestrial ecosystems to the atmosphere, and is therefore an important component of the global carbon balance. Total respiration from soils is mainly comprised of both the heterotrophic respiration of microorganisms (soil bacteria, fungi, and fauna) and autotrophic respiration from roots and their associated mycorrhizae. While Rs has received considerable attention in recent decades, much less is known about the contribution of heterotrophic or autotrophic component to the total Rs. A large part of gross primary production is consumed in heterotrophic respiration, and published estimates of the contribution of heterotrophic respiration to total Rs vary greatly and ranged from 10% to 90%. As a result, precise assessment of the contribution of autotrophic respiration to the total Rs is important to understand the effects of global climate change and human management practices on carbon sequestration and cycling in terrestrial ecosystems. This study aimed to reveal seasonal changes of Rs and the contribution of root respiration to total Rs in a Cunninghamia lanceolata plantation in the Tianjiling Forestry Park (113°01′-113°02′ E, 28 °06′-28°07′ N) of Changsha, Hunan Province, China. A trenching method, in which the roots existing in a given area are severed at the plot boundary but not removed, was used to determine the contribution of root respiration to total soil CO2 efflux. The Rs rates were measured from January 2007to December 2008 by using infrared gas exchange analyzer of Li-Cor 6400-09. The results showed that the soil temperature at 5cm depth between trenched plots (without living roots) and control plots (with living roots) was not significant difference（P=0.987）, but soil moisture at 5cm depth between these two types of plots was significant difference（P=0.035）.The Rs rates in control plots increased from May to August and then decreased during autumn. A similar seasonal pattern of Rs process was found in the trenched plots, but the Rs rates in the trenched plots were lower than the controls, and the difference was significant in 2008（P＝0.021）. The rates of soil CO2 efflux within the trenched and control plots ranged 0.19-2.01 and 0.26-2.61μ mol?m-2s-1 respectively. The annual Rs in the trenched and control plots averaged 0.90 and 1.30μ mol?m-2s-1, respectively. The Rs rates were decreased 9.4%-59.7% with an annual value of 30.4% in trenched plots when compared with the control plots. There was a significant exponential relationship (R2＝0.882，P＝0.000) between Rs within the trenched plots and soil temperature. The Q10 value, representing the sensitivity of Rs to soil temperature was higher in the trenched plots (2.56) than the control plots (2.01). It was worth mentioning that great decreases of Rs within the trenched plots was suppressed in September 2008 due to natural distribution of precipitation and the variation of soil moisture in the study area.