Abstract: In order to understand the accumulation and transformation of organic carbon in typical Karst soils, soil samples were collected from terra fusca and rendzina, and a 100day incubation experiment was conducted to study the accumulation and transformation of soil organic carbon under no exogenous substance addition (CK), ¹⁴Clabeled rice straw addition (T1), calcium carbonate addition (T2), and ¹⁴Clabeled rice straw + calcium carbonate addition (T3), taking soil microbial biomass carbon (MBC), basic respiration (BR), BR/MBC ratio (qCO₂), and MBC/SOC ratio as the indicators and with red soil as the contrast soil. During the mineralization of the organic carbon in test soils, both the BR and the qCO₂ followed the order of rendzina > terra fusca > red soil (P<0.05). Treatment T3 had the greatest effect in enhancing the stability of soil MBC. The changes of the soil microbial indicators differed significantly with test soils, and thus, using these indicators to measure the stability of soil organic carbon would be more credible.

Key words: Alternaria alternata, Erysiphe cichoracearum,  Bacillus pumilus, antagonistic activity.