Carbonate rock weathering substantially promotes soil microbial-derived carbon accumulation

Abstract Microbial-derived carbon (necromass) is crucial for long-term soil organic carbon (SOC) persistence, yet how carbonate rock weathering regulates its accumulation remains unresolved, despite the global prevalence and rapid weathering of carbonate rocks. Using global synthesis, regional sampling, and microcosms, we tested how carbonate rock weathering affects microbial-derived carbon. Globally, karst soils contained 43.4% more amino sugars and 57.6% more SOC than non-karst soils. Regionally, karst soils had 19.3% higher SOC-normalized amino sugars, 57.8% larger mineral-associated amino sugars, and more oxidized lignin signatures. Within karst soils, weathering rate was the strongest predictor of microbial necromass, and calcium fractions were associated with mineral-associated amino sugars. In microcosms, carbonate rock addition increased soil pH and calcium, shifted enzyme allocation toward oxidative processing of chemically complex native SOC, potentially facilitating microbial necromass formation. Carbonate rock addition also increased incorporation of 13C-labelled labile carbon into microbial necromass by 22–71%. Our findings identify carbonate rock weathering as a geogenic control linking microbial necromass formation with calcium-associated stabilization, highlighting the potential to leverage this weathering pathway to enhance SOC persistence.