Root Exudates Shape Soil Organic Carbon Stabilization by Controlling Microbial Necromass Formation Under Long-Term Nitrogen Fertilization

Soil organic carbon (SOC) stabilization is largely governed by the accumulation of microbial necromass carbon, yet how stabilization is influenced by root exudation remains poorly understood, particularly under long-term nitrogen (N) fertilization. Here, we investigated SOC dynamics in paddy soil under long-term N fertilization (12 years, urea) at four application rates (0, 100, 200, and 300 kg N ha−1). We quantified root exudate inputs, microbial community composition, microbial necromass, and soil physicochemical properties to identify the primary drivers of SOC accumulation. Our results showed that SOC content increased progressively with N application rate and these changes were attributable to N-induced increases in root exudate inputs, alterations to microbial community structure, and enhanced accumulation of microbial necromass. Structural equation modeling further revealed that root exudates served as a critical linkage between N fertilization, microbial necromass accrual, and SOC stabilization. Taken together, our findings imply that long-term N fertilization enhances SOC accumulation by stimulating root exudate-driven microbial necromass accrual, highlighting the pivotal role of plant–soil interactions in regulating carbon dynamics in rice agroecosystems.