Land use changes accelerate the carbon (C) cycle, yet their impact on soil inorganic C (SIC), particularly pedogenic carbonates (PC), is often overlooked. Here, we investigated the response of soil C pools to land use changes in the Loess Plateau, and elucidated the PC formation mechanisms. For broader context, a global meta-analysis was conducted focusing on the joint response of soil organic C (SOC) and SIC to land use changes. Converting croplands to forests resulted in a trade-off between SOC gains and SIC losses at both local and global scales. The SIC loss in forests was primarily derived from lithogenic carbonate (LC, 16 Mg C ha-1). These LC losses were partly compensated by the neoformation of PC in soils at 40-100 cm depth. Converting croplands to orchards increased SIC stocks, primarily due to PC formation (23 Mg C ha-1). More than 51 % of the CO2 fixed during PC formation originated from microbial respiration. Organic fertilizers or plant residues input stimulated microbial activity, generating more CO2 and subsequently HCO3-. The HCO3-then formed PC in the presence of Ca2+ and Mg2+ in soil, which are prerequisites for PC formation. Organic fertilizer-derived Ca2+ and Mg2+ contributed to PC accumulation in orchards. In forests, the porous soil structure facilitated Ca2+, Mg2+, and HCO3-leaching into the deep soil layers, thereby generating more PC at 40-100 cm depth. This study revealed the instability of SIC, and first quantified soil CO2 fixed by land use-induced PC. To establish accurate carbon sink accounting methodologies, future research should clarify the contribution of SIC dynamics to atmospheric CO2 removal.