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

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.