Substrate-specific priming of mineral-associated organic carbon in various cropland soils

Organo-mineral interactions are crucial for soil carbon sequestration, but the stabilization of mineral-associated organic carbon (MAOC) to fresh carbon inputs remains uncertain. Using ¹³C isotope tracing, we investigated the destabilization potential of contrasting carbon substrates (glucose versus oxalic acid) on MAOC persistence in three cropland soils (black, paddy, and loess soils). The cumulative CO₂ caused by glucose was much higher than that caused by oxalic acid in all three soils due to preferential substrate utilization. Substrate-specific priming effects (PE) of MAOC were observed across three soil types. Compared with the control, cumulative PE in glucose exhibited divergent responses, with positive PE in black (2.98 %) and loess (220.48 %) soils, but a negative PE in paddy soil (−33.2 %). Conversely, oxalic acid induced uniformly positive PE across all soils, with 121.66 % in black soil, 23.65 % in paddy soil, and 152.53 % in loess soil, respectively. Higher thermal stability, the highest ratio of MAOC to the specific surface area of muffled soil, and enriched aromatic C groups (CO, Ar–C–C(H)) in paddy soil MAOC corresponded to its higher stability, as evidenced by its resistance to glucose-induced priming. By contrast, oxalic acid universally stimulated MAOC destabilization via mineral chelation. Our findings demonstrate that carbon sequestration strategies in agroecosystems must account for both substrate properties and soil-specific mineral-organic associations to optimize MAOC stabilization.