Abstract: The importance of microbial decomposition processes in soils subject to climate and planting type change has been recognized as a critical gap in our understanding of carbon balances between soils and the atmosphere.Autotrophic microbes, found abundantly in soil, have the ability to photosynthesize carbon by assimilating atmospheric carbon dioxide (CO₂). However, the distribution of autotrophic microbe-assimilated carbon in soil composition as well as in aggregate fractions of soil under different planting type is yet to be ascertained. Therefore, this study used continuous carbon isotope (¹⁴C-CO₂) labeling along with ex-situ simulated incubation experiments and chemical and physical fractionation of soil organic matter to examine the distribution characteristics of microbe-assimilated carbon in humus and aggregate fractions of soils obtained from three different planting type (rice paddy systems (P-R), paddy-upland rotation systems (P-U), and upland rice cultivation systems (U-C). Results showed that planting type has an effect on autotrophic microbial carbon fixation. Autotrophic microbes in rice paddy soils (P-R) had the maximum ability to fix carbon (w(¹⁴C-SOC) was 38.32 mg/kg, approximately two times that in P-U and U-C soils). In addition, the ¹⁴C content in active carbon pools (¹⁴C-DOC and ¹⁴C-MBC) present in P-R and P-U soils was considerably greater than that in U-C soils. Furthermore, autotrophic microbe-assimilated carbon entered the three soil humus components to varying extents, as follows:it primarily entered the humins, which comprises 67.7% of the humus. The assimilated carbon also entered the differently sized soil particles in aggregates, thereby sequestering the carbon. It primarily entered those aggregates with particle diameters ranging from 0.020 to 0.200 mm and from 0.200 to 2.000 mm. Of the three tested soils obtained from different land uses, the rice paddy soil exhibited the highest ¹⁴C-SOC content for each particle size.