Unraveling carbon mineralization patterns and mechanisms in conservation agriculture: A global synthesis and multi-point experiment

Abstract

The mineralization of soil organic carbon (SOC) profoundly impacts the efficiency of SOC sequestration, crucial for the long-term stable carbon (C) sequestration in soil. Despite its significance, systematic studies investigating the effects of three pillars of conservation agriculture (CA), i.e., no-till, residue retention (RR), and crop rotation (CR), on the mineralization of SOC remain scarce. To address the gap, we conducted a comprehensive analysis, collating data from 89 experimental sites worldwide and integrating with field experimental data sampled from 10 sites across China. Our study evaluated potentially mineralizable carbon (PMC) using first-order kinetic fitting, and specific PMC (SPMC, PMC/SOC) to elucidate patterns of SOC mineralization under CA and its moderation by climatic, environmental, and soil factors. The results showed a gradual decrease in PMC with the adoption of increasing numbers of CA pillars, with the full implementation reducing PMC by 35.1%. The impact of no-till on PMC and SPMC was not significant, while RR and CR significantly increased and decreased PMC by 21.0% and 27.3%, respectively. Notably, only CR significantly increased SPMC by 15.0%. The findings suggest that under CR, PMC exhibit reduced sensitivity to climatic and environmental changes and emphasizing higher environmental stability of SOC. Soil microbial indicators demonstrated direct and indirect positive regulatory effects on PMC, and SPMC is positively affected by MBC in addition to SOC, both of which indicate the vital role of soil microbes in regulating SOC mineralization. We proposed a conceptual model highlighting nonlinear relationship between stable SOC pool and SOC, emphasizing how the relationship between C sequestration and emission reduction can be optimized under CR. Further research should delve into understanding microbial pathways in SOC mineralization and their role in balancing mineralization and sequestration.