The studied vegetation types were shrubland CK16 (16-year-old Caragana korshinskii Kom.), shrubland CK26 (26-year-old C. korshinskii Kom.), shrubland AS (Armeniaca sibirica Lam.), natural grassland and artificial pasture. We investigated SOC stocks and measured soil carbon, in <0.25, 0.25–1, 1–2, 2–5 and 5–8 mm sized aggregates, and carbon fractions [humus (HS-C), humic acid (HA-C), fulvic acid (FA-C)] from CK shrublands, natural grassland and cropland.

The SOC stocks were the greatest for CK shrublands and natural grassland. Compared with cropland, shrubland CK caused increases in >2 mm sized aggregate C stocks. The 1–2, 2–5, 5–8 mm size aggregate C stocks were the highest in the natural grassland. HS-C was 1.4, 3.1, and 4.1 Mg ha−1 greater in shrubland CK16, shrubland CK26, and natural grassland, respectively, than in cropland.

Conversion to C. korshinskii shrublands and protection of natural grassland should be promoted to improve the contribution of vegetation to SOC sequestration.