Land-use shapes the composition and stability of soil water-stable aggregates in a plateau agro-pastoral ecotone

Background: The northeastern Tibetan Plateau is a typical agro-pastoral ecotone that experiences frequent land-use changes. Maintaining stable soil aggregates in this region is key to protecting the environment and supporting food production on the Tibetan Plateau. Nevertheless, comparative data on soil aggregate composition and stability across diverse land-use types and soil depths in this region are currently limited. Methods: Herein, soil samples from 0-20 cm and 20-40 cm depths were gathered at 52 sites spanning four dominant land-use types in the northeastern Tibetan Plateau: grassland (GL), cropland (CL), orchard (OC), and planted forest (PF). The composition and stability of soil aggregates were assessed using the wet sieving method. Results: The results exhibited that silt and clay particles (SC, 2 mm) had relatively low mass proportions. Aggregate stability in the 0-20 cm layer ranked PF > GL > CL > OC, with PF and GL significantly more stable than OC. In the 20-40 cm layer, the highest aggregate stability was found in GL. Except for PF, aggregate stability varied little between different soil layers for other land-use types. Aggregate stability is positively associated with the contents of soil organic carbon, total nitrogen, and alkali-hydrolyzable nitrogen, underscoring the critical role of soil organic matter in regulating soil aggregation. Conclusions: The findings suggest that land-use type is a key determinant of soil structure in the northeastern Tibetan Plateau.