[Objective] In calcareous soils, recent studies have found that soil-derived CO₂not only comes from the decomposition of soil organic carbon (SOC) but also from dissolution of soil inorganic carbon (SIC). Under straw addition, CO₂emission in calcareous soils comes from at least three sources, i.e., straw-C, endogenous SOC and SIC. Owing to technical limitations in source partitioning of CO₂, the effects of straw addition on SOC and SIC release are still not fully understood in calcareous soils. Therefore, this uncertainty needs urgent attention.[Method] We conducted a 32-week laboratory incubation experiment with ¹³C labeled maize straw under different straw rates in calcareous soils collected from farmlands of North China Plain. The effects of straw addition on CO₂ emission from SOC decomposition and SIC dissolution were investigated. The approach was based on using three-source mixing model(IsoSource) to differentiate three sources of CO₂(straw-C, SOC and SIC). Four treatments were set up, including no straw addition (CK), low rates of straw addition(S1, 9.6 t·hm^-2of maize straw amendment), medium rates of straw addition (S2, 28.8 t·hm^-2of maize straw amendment) and high rates of straw addition (S3, 48.0 t·hm^-2of maize straw amendment).[Result] As the incubation time progressed, the contribution of straw decomposition to soil CO₂ emission decreased. The contribution of straw decomposition to soil CO₂ emission increased with the increase of straw addition rates. For S1, S2 and S3 treatments, the soil CO₂ emission derived from straw, SOC and SIC was about 3:3:4, 5:2:3 and 6:2:2, respectively. S1 treatment decreased SOC decomposition by 9%, while S2 and S3 treatments increased SOC decomposition by 22% and 57%, respectively. The mineralization of straw and SOC increased SIC dissolution, and the degree of promotion increased with the amount added. The degrees of promotion for S1, S2 and S3 treatments were 368%, 561% and 652%, respectively.[Conclusion] Straw addition not only affected the release of SOC-derived CO₂, but also the release of SIC-derived CO₂. In calcareous soils, if the contribution of SIC dissolution to soil CO₂ emission is unaccounted for, it may lead to overestimation of SOC decomposition and affect the accuracy of priming effects evaluation.