[Short-term Mechanism of Warming-induced Stability for Organic Carbon in the Karst Plateau Soil].

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, 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 to 2.02 kg·m, which is insignificantly different to the CK (1.94 kg·m). 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).