Coupled geomorphic and climate-driven biogeochemical processes regulate soil organic carbon stocks in agricultural terraces

Agricultural terraces are among the most widespread human-made landforms. They profoundly reshape soil land-scapes and influence the carbon cycle, yet the extent and drivers of their impact remain highly uncertain. By inte-grating field observations from 14 well-drained terrace landforms across a climatic-geochemical gradient with adata synthesis, we show that changes in soil organic carbon (SOC) stocks after terracing are governed by two coupled C turnover-geomorphic processes: replacement of lost topsoil C at eroding positions and stabilization of buried SOC at depositional positions. Climate strongly modulates these processes by shaping soil geochemistry and plantproductivity, which in turn control SOC replacement and stabilization within terraces. Thus, terracing effects on SOC stocks shift from consistently positive in humid regions to mixed (positive and negative) outcomes in dry regions.This study establishes a framework for elucidating SOC dynamics in well-drained terrace systems and provides ascientific basis for targeted management strategies to enhance C sequestration in agricultural terraces globally.