Modelling soil carbon dynamics and persistence in tropical and subtropical environment

Soil carbon sequestration is a cornerstone of soil fertility, especially in tropical and subtropical regions, and critical for mitigating climate change. However, despite recent advances in understanding the effect of anthropogenic activities on soil carbon stocks (SOC), there is a lack of modelling studies describing soil carbons dynamics and persistence especially in tropical and subtropical environments. This study investigates SOC dynamics and persistence in three long-term conservation agriculture soils across Brazil’s diverse climatic zones: subtropical (Ponta Grossa), transitional (Londrina), and tropical Cerrado (Lucas do Rio Verde). Through a 30-month incubation experiment with varying carbon inputs (0, 6, 12, 24 Mg C ha⁻¹), we measured CO₂ emissions and SOC stocks. After, we used a three-pool feedback model to adjust CO₂ emission and SOC dynamics and used model fitted parameters to obtain carbon transit times and ages. We found that carbon persistence in the tropical Cerrado soils (carbon age ≈ 23.5 years in incubation) is lower compared to subtropical Ponta Grossa (carbon age ≈ 36 years in incubation).  Clay and silt content was more related to SOC dynamics than fertility attributes and carbon stability was similar in surface and deeper layers. This result indicates that soil carbon sequestration in deeper layers can be related to carbon translocation mechanisms, but not necessarily to differences in carbon composition or interactions with soil minerals. Our results shed light on carbon persistence in tropical and subtropical soils, supporting greenhouse gases mitigation strategies and more realistic projections of soil carbon stocks dynamics in Earth System Models.