Abstract: 【Objective】 The effect of calcium on soil organic carbon (SOC) turnover was studied. 【Method】 Two Karst soils (terra fusca and rendzina) and a contrast soil (red soil) were selected (54 samples) for the study. Both sampling in field to analyze and laboratory incubation were done. The contents of four speciations of calcium and SOC were tested. Three typical samples from three soil types were used to conduct a 100d incubation experiment, and no adding exogenous substrate (CK), calcium carbonate addition (T2), both 14C-labeled organic substrate and calcium carbonate addition (T3) were designed. Mineralization of SOC and the content of different calcium speciations were measured during the incubation experiment. 【Result】 The result showed that the calcium speciation of exchangeable-Ca and bound to organic mater-Ca were more closely related with SOC. SOC mineralization was significantly affected by adding calcium carbonate. The increment of bound to organic matter-Ca in red soil, terra fusca and rendzina was 2.14%, 4.66%, 10.23%, respectively, and the priming effect of cumulative mineralization by adding calcium carbonate was in the order of red soil ＞ terra fusca ＞ rendzina (P＜0.05).【Conclusion】 It was concluded that SOC stability has differences in different soil types. The stability of SOC was in the order of rendzina＞ terra fusca ＞ red soil. Therefore, the soil type which is most beneficial to cumulate SOC is rendzina, the second is terra fusca and the last was red soil in Karst area.

Key words: Karst soil, calcium speciation, soil organic carbon, mineralization