How no-tillage and cropping systems shape soil organic carbon formation and stabilization over time: Evidence from a 16-year chronosequence

Soil organic carbon (SOC) plays a vital role in climate change mitigation, global food security, and soil health sustainability. While conservation tillage, particularly no-tillage (NT), has been empirically proven to enhance SOC, the temporal dynamics of SOC formation pathways remain poorly quantified across different cropping systems. Samples were collected from the surface layer in a long-term NT experiment (since 2001) that included two treatments: a) NT with continuous maize (Zea mays L.) (NTMM); b) NT with maize-soybean (Glycine max Merr.) rotation (NTMS). Plant- and microbial-derived C were quantified using lignin phenols and amino sugars as biomarkers to assess SOC formation pathway. Rock-Eval (RE) thermal analysis was used to assess SOC stability. SOC reached a relative steady-state after 13 years under both NTMS and NTMM. Although cropping systems influenced the fungal/bacterial ratio, they did not significantly alter the total microbial-derived C contribution to SOC in the steady-state (since 2014). Plant-derived C increased substantially, reaching 4.68 times (NTMS) and 5.97 times (NTMM) initial levels after 15 years. Microbial-derived C dominates SOC formation, while plant-derived C increases rapidly with SOC accumulation under long-term no-tillage systems. The increase of hydrogen index and residual C calculated from RE indicated that NT increased both the labile C pool that promoted crop growth and the stable C pool which benefited the long-term SOC sequestration. These findings shed light on the SOC formation and stabilization change over time in no-tillage and provide a stepping stone for understanding SOC sequestration mechanism under different cropping systems.