Organic Material Reduced Positive Priming Effect in Continuous Cropping Soil by Regulating Microbial Community and Alleviating Nitrogen Restriction

ABSTRACT Background Long‐term continuous cropping alters soil physicochemical properties, causing nutrient imbalances and disruptions in microbial communities. However, the priming effect (PE) in long‐term continuous cropping systems remains poorly understood. Aims The objective of this study is to investigate the direction and magnitude of soil PE under varying organic amendments (quality and quantity) and mineral nitrogen (N) co‐inputs. Methods The soil of a long‐term continuous cropping tobacco field was collected and incubated for 32 days. Six treatments were designed: CK (no additions), mineral N, low 13 C glucose + mineral N, high 13 C glucose + mineral N, low 13 C straw + mineral N, and high 13 C straw + mineral N. This study investigated how organic amendments regulate soil PEs by mediating microbial nutrient limitation, community structure, and soil aggregation, based on measurements of carbon dioxide release, microbial biomass carbon (C) and N, extracellular enzyme activities, phospholipid fatty acid analysis, and aggregate stability. Results Mineral N addition reduced microbial N immobilization and soil aggregate stability, while stimulating soil organic matter (SOM) mineralization (positive PE). The addition of glucose or straw provides C sources and energy for microorganisms, stimulating soil microbial activity and enhancing community stability, whereas increased extracellular enzyme activities alleviate nitrogen limitation and improve soil nitrogen availability. The direction of PEs was determined by the carbon‐to‐nitrogen (C/N) ratio of external organic inputs and mineral nitrogen, with low C/N ratios inducing negative PEs and high C/N ratios producing positive PEs. Straw addition induced weaker PEs (both directions) than labile glucose, while enhancing fungal biomass ( K ‐strategists) to promote soil aggregation and aggregate stability, thereby facilitating soil organic carbon (SOC) sequestration (negative PE). Conclusions Excessive mineral‐N addition and deficient organic material inputs are key drivers of SOC loss in continuous cropping fields. The quality and quantity of the organic substrates regulate the magnitude and direction of the PEs, underscoring the importance of organic substrate inputs in the long‐term continuous cropping field.