Variations of Soil Organic and Inorganic Carbon Stock and Soil Aggregation due to Land Use Change to Urban Green Spaces of Arid Environment

ABSTRACT Physical protection by soil aggregates is a key mechanism for carbon sequestration and stabilization. Urban green spaces provide vital ecosystem services, including carbon storage; however, there is limited understanding of variation in soil aggregation and the related inorganic and organic carbon sequestration in response to anthropogenic land use changes in urban soils. Here, we compared the vertical distributions (0–100 cm) of soil organic carbon (SOC) and inorganic carbon (SIC) across cropland, grassland, woodland, and urban green spaces in a newly urbanized area of northwest China. Soil aggregate distribution, stability, and the related organic carbon (OC) and inorganic carbon (IC) contents in the topsoil were also examined. Compared to other land use types, urban green spaces exhibited the highest SIC stock (peaking at 4.91 kg m −2 in the 40–60 cm depth) but the lowest SOC stock (e.g., 0–20 cm: 0.90 kg m −2 vs. 1.43 – 2.00 kg m −2 in natural and agricultural ecosystems) across the entire soil depth, indicating pronounced SOC depletion during early urbanization. Urban green spaces had the lowest macroaggregate (> 0.25 mm, 11.11% and 5.92%, respectively) and mean weighted diameter (MWD, 0.15 and 0.12 mm, respectively) in the 0–20 and 20–40 cm soil depths. A significant correlation between bulk SOC and macroaggregate, aggregate‐associated OC contents suggested that aggregate disruption drives substantial SOC loss from macroaggregate, microaggregates (0.25–0.053 mm), and silt and clay fractions (< 0.053 mm). Soil total nitrogen content and the Normalized Difference Vegetation Index (NDVI) were key drivers of OC accumulation in all aggregate fractions and bulk soil. Collectively, urbanization‐induced conversion to green spaces exacerbates SOC loss via aggregate disruption. Strategic management of soil nitrogen and vegetation cover may mitigate this loss by stabilizing aggregate‐occluded OC, with critical implications for carbon sequestration in arid urban ecosystems.