Long-term light grazing facilitates topsoil carbon accumulation in desert steppes by disrupting preferential flow...

Grazing exerts a remarkable influence on soil water infiltration in arid regions. Compared with matrix flow featuring uniform infiltration, preferential flow rapidly transports limited precipitation and drives nutrient migration, thereby regulating the accumulation and spatial distribution of soil carbon and nitrogen. Nevertheless, the mechanisms by which grazing alters soil preferential flow and subsequently affects soil carbon and nitrogen dynamics remain poorly elucidated. This study was conducted in desert steppe, comparing soil carbon and nitrogen contents and preferential flow characteristics between long-term enclosed plots (10 years of grazing followed by 20 years of enclosure) and long-term lightly grazed plots (30 years) across three habitats: natural caragana shrub, planted caragana shrub and grassland. Results demonstrated that, relative to long-term enclosure, long-term light grazing mitigated the magnitude of preferential flow. Overall, light grazing significantly elevated the contents of soil organic carbon, easily oxidizable organic carbon, dissolved organic carbon, recalcitrant organic carbon, and soluble organic nitrogen in the topsoil. In enclosed plots, soil carbon and nitrogen levels were higher in the matrix flow zone than in the preferential flow zone, whereas an opposite pattern was observed in grazed plots, with an amplified discrepancy in carbon and nitrogen between the two zones. Long-term light grazing promotes topsoil carbon accumulation and alters carbon distribution patterns in desert steppe by reducing soil preferential flow intensity. These findings provide a sustainable approach for enhancing the carbon sink capacity of desert steppes while sustaining pastoral livelihoods.