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Background and aims: Subtropical seasonally dry forests from South America are now experiencing one of the highest rates of forest-cover change globally. These changes may affect the dynamics of soil organic carbon (SOC) including long-term stabilization processes, with profound consequences for the fertility and carbon storage of these ecosystems. Methods: In order to explore the effect of different land-use regimes on SOC dynamics, we determined the amount and quality of plant litter, the amount and quality (lignin and carbohydrate content) of SOC, and the soil basal respiration rates across seasonally dry Chaco forests of Argentina. Results: Changes in land-use regimes significantly reduced the amount of litter but not its quality. As a consequence, the SOC content was also reduced together with SOC quality. Unexpectedly, we found a higher CO release per SOC unit in soils with lower amount and quality of SOC. Conclusions: The results presented here show a clear effect of different land-use regimes on SOC dynamics through a reduction in the amount and quality of SOC. Additionally, we found that potential microbial activity is somehow disconnected from substrate quantity and quality, suggesting that the molecular structure of SOC is not significantly affecting long-term soil stabilization processes across these seasonally-dry ecosystems. [ABSTRACT FROM AUTHOR]