Abstract: The sensitivity of soil respiration to temperature is one of the uncertain factors affecting global warming. In order to understand the difference of this sensitivity in natural broadleaf forest and artificial coniferous forest with the exclusion of other factors’ influence, a laboratory simulation was conducted with the soil samples (0-10 cm) collected from a Quercus variabilis secondary forest and a Pinus taeda plantation in Jiangsu Province of Southeastern China. The samples were incubated in closedjars in laboratory at 5 ℃, 15 ℃, 25 ℃, and 35 ℃, respectively, and alkaliabsorption method was applied to measure soil respiration. Soil physical and chemical properties were also measured. The results showed that the sensitivity of soil respiration to temperature (Q₁₀ value) was larger in Q. variabilis secondary forest than in P. taeda plantation. At 5 ℃, 15 ℃, and 25 ℃, there was no significant difference in the amount of cumulative CO₂ released from soil respiration in the two forest stands, and the dynamic changes of soil CO₂ release were similar. At 35 ℃, the amount of cumulative CO₂ released from soil respiration was significantly higher in Q. variabilis secondary forest than in P. taeda plantation; while at 25 ℃, it was in adverse. The soil total carbon, nitrogen, calcium and phosphorus contents and C/N ratio were higher in Q. variabilis secondary forest than in P. taeda plantation. It was suggested that under the predicted global warming scenarios, natural broadleaf forests might release more CO₂ than artificial coniferous forests.

Key words: Northwest plateau of Hebei Province, Vegetation, Actual productivity, Converting farmland to forest and pasture land, Strategy