Elucidating the mechanisms of warming-induced stability for soil organic C is one of the keys for evaluating the tendency of soil C sources /sinks in projected global warming models. Organic C densities in soil,and soil physical and biochemical fractions, under different warming scenarios in the Karst Plateau were investigated following a 4-yr continuous warming using infrared radiators, via density fractionation and acid hydrolysis. Six treatments were arranged: no warming ( ambient temp,CK) ; symmetric warming ( ambient + 2. 0℃ full year) ; and lowly,moderately,highly,and extremely asymmetric warming ( ambient + 2. 5℃ /1. 5℃,3. 0℃ / 1. 0℃,3. 5℃ /0. 5℃,and 4. 0℃ /0℃ in winter-spring /summer-autumn seasons,respectively; LAW,MAW,HAW,and EAW) . The moderately asymmetric warming was highly similar to a multi-year warming scenario in the study region. The results showed there were no significant differences in soil organic C densities in the surface layer ( 0-15 cm) among the warming treatments,with a range of 1. 95 kg·m~(-2) to 2. 02 kg·m~(-2) ,which is insignificantly different to the CK ( 1. 94 kg·m~(-2) ) . There were no significant differences in the C density of light and heavy fractions,and the recalcitrant heavy-fraction among the warming treatments,and between the warming and no warming treatments. The average recalcitrant C density of the light fraction in the warming treatments was 1. 18 times higher than the CK,with a significantly higher recalcitrant C density of the light fraction in the symmetric warming,and lowly and moderately asymmetric warming treatments,compared to that of the CK. The recalcitrant C density and recalcitrant C index of the light fraction showed a tendency to decrease as the asymmetry of warming increased under the five warming scenarios. Warming had negligible effects on the organic C density in soil,and soil physical and biochemical fractions in the subsurface layer ( 15-30 cm) . The results revealed that in the short-term,warming may increase the recalcitrance of non-protected C in the Karst Plateau soil. This is not necessarily an over-or underestimation of the effects of global warming on soil organic C density and the capacity of soil to protect C when subjected to symmetric warming,but may potentially overestimate the recalcitrance of organic C in the non-protected fraction of the surface layer ( 0- 15 cm) .