Priming effect on plant-derived mineral-associated organic C in paddy soil: a three-source partitioning study with a dual-13C approach

Mineral-associated organic matter (MAOM) represents a large and stable soil carbon (C) pool, yet its response to fresh labile C inputs—a key driver of priming effects (PEs)— could lead to significant impacts on soil C cycling. Although PEs have been extensively studied across various ecosystems, a knowledge gap remains regarding the specific soil organic carbon (SOC) pools involved, particularly key MAOM fractions such as iron-associated organic carbon (Fe-OC). Therefore, we employed a dual-isotope labelling approach (using glucose at two contrasting ¹³C enrichments) to trace the mineralization of ¹³C-enriched Fe-OC (derived from rice litter) and native SOC in response to glucose addition under flooded conditions. When added individually, the mineralization of Fe-OC (16.1 %) was lower than that of glucose (67.0 %). Glucose addition suppressed mineralization of both Fe-OC (from 16.1 % to 10.4 % of Fe-OC present) and native SOC (from 0.90 % to 0.78 % of SOC), demonstrating a negative priming effect. The negative priming intensity was correlated with glucose mineralization rates, and the suppression of mineralization was stronger for Fe-OC than for SOC. Based on the added:native Fe-OC ratio, 84.6 % of the negative PE was attributed to a reduction in MAOM mineralization. Our findings demonstrate that MAOM exhibits high responsiveness to labile C inputs, with its suppressed mineralization representing an underlying mechanism that may facilitate carbon sequestration in C-rich hotspots within paddy soils.