Terracing drives Chinese Loess Plateau toward carbon neutrality: Spatiotemporal interaction between land use...

Terracing enhances soil organic carbon (SOC) reserves and stability, serving as a key strategy for climate mitigation while enhancing soil quality and ecosystem functionality. However, the large-scale spatial impacts of long-term terrace modifications on SOC dynamics remain poorly quantified. Focusing on the extensively terraced Loess Plateau, this study investigated the impacts of three decades (1990-2020) of terrace modifications and land use transitions on SOC dynamics. Utilizing spatially explicit terrace distribution maps, multitemporal land use data, and high-resolution soil grids, we systematically evaluated structural changes in terrace systems and subtype conversions, while quantifying terrace-mediated SOC sequestration processes. Over the three decades, terrace coverage increased by 65.09 %, with accelerated expansion rates observed before 2010 particularly in Shanxi, Shaanxi, and Gansu provinces. Cultivated terraces consistently dominated the terrace landscape, followed by grassy terraces. Forest and other terrace types, though maintaining lower proportions, exhibited rapid expansion. Primary terrace sources included sloped cropland, forest, and grassland, with sloped cropland conversions representing the most extensive transformations. Crucially, slope-to-terrace conversion approximately doubled per-unit SOC storage capacity. Conversion of sloping cropland and grassland into terraces emerged as the primary contributors to SOC storage enhancement, with grassland-derived terraces predominantly emerging in Inner Mongolia, Ningxia, and Qinghai, while cropland conversions skewed eastward. While terrace expansion generally enhanced carbon sequestration, we identified localized SOC depletion clusters where land use adjustments reduced terrace vegetation cover. These findings provide actionable insights for optimizing terrace management to maximize SOC sequestration efficiency and inform climate-resilient land management policies.