Lithology modulates soil priming effect via resource limitations and bacterial community structure

Abstract The soil priming effect (PE), triggered by root exudate inputs that stimulates microbial activity and drives significant soil carbon (C) losses in terrestrial ecosystems. However, the influences of resource limitation and microbial communities shaped by distinct lithologies on soil PE remains unclear. Here, we conducted an incubation experiment to assess soil CO 2 emissions and PE in two contrasting soil types: calcium (Ca)‐rich karst soils derived from limestone and Ca‐poor non‐karst soils from clastic rock, both under similar climatic conditions. We added 13 C‐labelled glucose and glycine (containing nitrogen)—two prevalent root exudate compounds. We found positive PE in both soil types. Glycine, a simple nitrogen‐rich amino acid, induced a greater PE than glucose. After the addition of glucose and glycine, enzymatic responses differed between the two soil types. In non‐karst soils, β‐N‐acetyl‐glucosaminidase activity increased while the ratio of β‐D‐glucosidase to the sum of β‐N‐acetyl‐glucosaminidase and leucine aminopeptidase decreased—an extracellular‐enzyme signature commonly interpreted as indicative of nitrogen mining. In contrast, in karst soils, both β‐D‐glucosidase activity and the C:nitrogen‐cycling enzyme ratio increased, patterns commonly interpreted as microbial stoichiometry. In addition, non‐karst soils primed 166%–277% more organic C than karst soils. Notably, greater exchangeable Ca in karst soils was positively correlated with bacterial community diversity and network complexity, which in turn promoted more energy‐efficient bacterial resource acquisition and thereby reduced PE. In contrast, in non‐karst soils, greater short‐range‐ordered iron/aluminium oxide contents were correlated with simpler bacterial networks, leading to greater bacterial energy demands and amplifying PE. Our findings reveal that lithology driving geochemical constraints shape bacterial community structure and function, thereby modulating soil PE. In particular, we highlight the significance of Ca in promoting soil organic C accumulation in karst ecosystems by reducing PE through its regulation of bacterial processes. Read the free Plain Language Summary for this article on the Journal blog.