Pedogenic carbonate formation by land use changes

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. © 2025 Elsevier B.V.