Tracing microbial-mineral pathways of soil priming under contrasting organic inputs using ¹³C labeling and NanoSIMS

Organic inputs can shift the soil priming effect and thereby alter the turnover of native soil organic carbon (SOC), yet the mechanisms linking microbial metabolism and mineral protection in the native SOC pool remain poorly resolved. Here, we conducted an incubation experiment using ¹³C-labeled organic inputs (glucose, straw, and biochar) with different bioavailability to elucidate microbial metabolic response and mineral association in the native SOC pool. Glucose and straw induced positive priming by favoring r-strategist microorganisms, which strengthened native SOC catabolism relative to the unamended control, with metabolic quotient (qCO₂) increasing by 171.1% and 27.7% and microbial turnover rate (MTR) increasing by 105.1% and 94.4%, respectively. Conversely, biochar shifted priming to negative, enriched K-strategist microorganisms, and decreased native qCO₂ by 45.5% and MTR by 4.1% relative to the unamended control, while showing the strongest anabolic incorporation of native SOC into microbial biomass and necromass among the three inputs. Nanoscale secondary ion mass spectrometry (NanoSIMS) showed fourfold higher mineral surface coverage by ¹³C in the biochar treatment than in the glucose or straw treatments, coinciding with 14.6% and 9.0% greater native mineral-associated organic carbon (MAOC) accumulation, respectively. Partial least squares path modeling (PLS-PM) further indicated that priming effect is governed by multiple synergistic pathways, in which bacterial metabolic regulation and mineral-mediated protection jointly determine the direction and magnitude of priming. Our findings emphasize the joint role of soil mineral and microbe in regulating soil priming through coordinated controls on native catabolism and anabolism, which has important implications for mitigating priming induced carbon (C) losses and enhancing soil C persistence.