Interactive effects of warming and drought on soil organic carbon sequestration and methane uptake in straw and biochar amended soils: Mechanisms and global implications

The interactive effects of warming and drought on soil carbon-methane feedback in straw- versus biochar-amended agricultural systems need more comprehensive quantification, despite their critical implications for climate-smart soil management. By integrating controlled incubation experiments with a global meta-analysis (105 observations), we revealed that drought suppressed CH4 uptake by 58.9% in carbon-amended soils through synergistic depletion of methanotrophic functional capacity (pmoA gene abundance) and microbial biomass carbon, while attenuating thermal sensitivity of methane uptake. Crucially, warming triggered opposing methane sink responses: it stimulated uptake in straw-amended soils (by 15.4%, CI: −0.348 to 0.656), yet collapsed methanotrophy in biochar systems (by −78.4%, CI: −1.167 to −0.401), mechanistically linked to thermal disruption of methanotroph community integrity and pmoA gene expression. Structural equation modeling further exposed biochar-induced vulnerability, where warming directly suppressed pmoA abundance (r = −0.691, p < 0.001), overriding its carbon stabilization benefits. Globally synthesized data unveiled paradoxical soil organic carbon dynamics under warming—short-term losses vs. long-term accruals—highlighting the imperative for decade-scale in situ validations. Our findings established an amendment-specific biogeochemical framework, demonstrating that straw and biochar follow divergent carbon-climate trajectories: the former enhanced methane sink resilience but risked soil organic carbon instability, while the latter traded carbon persistence for methanotrophic functional collapse. This work redefined climate-smart amendment strategies by embedding microbial metabolic gatekeeping into Earth system models, providing actionable pathways for sustainable agroecosystem management under accelerating climate extremes.