Soil pH Amelioration Fosters Persistent Carbon Sinks Through Mineral Stabilization and Aggregate Protection

The stability of soil organic carbon (SOC) is fundamental to the integrity of agricultural carbon credits but remains challenging to verify and predict. A persistent methodological challenge lies in isolating the specific effect of soil pH amelioration from confounding factors like organic matter inputs. Here, by applying bivariate linear mixed-effects modelling to a global synthesis of 180 field trials, we quantitatively disentangled the effects of pH amelioration on SOC components across a stability continuum from bulk soils to aggregate fractions. The results showed that pH amelioration enhanced bulk SOC stocks by 18%-20%, with mineral-associated organic carbon and microbial necromass carbon significantly increasing by 11%-15% and 12%-19%, respectively. Simultaneously, pH amelioration restructured soil architecture toward enhanced aggregate stability, preferentially enriching carbon within microaggregates (by up to 44% in alkaline soils). Structural equation modelling confirmed that this process is hierarchically driven by pH-induced shifts in microbial biomass and aggregate stability. The pH amelioration-shared increment in particulate organic carbon and mineral-associated organic carbon tended to attenuate with prolonged experimental duration, while that in microbial necromass carbon remained invariant. Across organic substitution types, pH amelioration under manure substitution significantly increased all carbon components, while straw substitution exhibited a weaker pH amelioration-shared effect on particulate organic carbon increment compared to biochar and manure. Our findings suggest that pH amelioration is a fundamental process that engineers persistent carbon sinks by directing carbon flow into mineral-stabilized and physically protected pools. This work repositions precision pH management as an essential ecological engineering strategy and provides a mechanistic foundation for transitioning carbon credit protocols from stock-based accounting to stability-centric verification.