Synergistic effects of 13-year warming and nitrogen fertilization accelerating soil carbon destabilization in North China Plain farmland

C-MBC values compared to single-factor treatments and the CK. The WN treatment significantly reduced the cumulative PE by 3%, whereas single treatments increased it by 2-4%. Structural equation modeling identified soil total nitrogen (TN) and passive carbon pool size as the primary regulators of these contrasting effects. Our findings suggest that the long-term combination of warming and nitrogen fertilization could exacerbate soil carbon destabilization in farmland. Microbial metabolic shifts potentially serve as an important regulatory mechanism influencing agricultural soil carbon stocks under future climate warming.