The effect of soil physical structure in soil carbon and nitrogen distribution under different land use types in typical forest grassland transition zone on Loess Plateau, China

Abstract Land use/vegetation cover change, reflecting a range of human land use practices, is the most prevalent and immediate influence on alterations in soil quality. The physical structure of soil is crucial for safeguarding soil carbon (C) and nitrogen (N), as it modulates the physical protection mechanisms and the distribution of these elements within the soil. Nevertheless, the impact of soil physical structure on soil C and N accumulation under different land use/vegetation cover in the same area remains unclear. This research collected soil samples from five land use types in the typical forest grassland transition zone of the Loess Plateau, including natural forests, artificial forests, shrubs, meadows, and farmland. We investigated the topsoil physical structure, soil C and N pools within aggregates, and driving factors in five land use types. Our results indicated that SOC of soil macroaggregates in natural forests, artificial forests, shrublands, and meadows was 16.4%, 23.7%, 8.6%, and 40.7% higher than in farmland. The MBC of soil macroaggregates in natural forests, artificial forests, shrublands, and meadows was 48.9%, 26.4%, 37.0%, and 18.8% higher than in farmland. Soil C and N storage and soil aggregate stability were the lowest in farmland soil ( p < .05). The changes in soil C and N in five land use types were markedly influenced by the C and N quantity contained in large aggregates with a size range of >0.25 mm. Soil MBC and MBN were closely related to soil enzymes. Environmental factors indirectly influence soil C and N storage through impacting soil properties and physical structure. These results emphasized the significance of soil physical structure in soil C and N content. When formulating land use policies, we should fully consider the effects of alterations in soil physical structure on soil C and N storage after vegetation cover changes. It is crucial to improve and enhance soil structure to maintain soil C and N nutrients and resist erosion.