关键词: 有机碳, 稳定机制, 森林土壤, 迁移, 土壤类型, 黑碳

Abstract: The seed bank is a potential plant community and indicates orientation of plant community succession. Since the grazing ban policy was implemented, grassland utilization has been shifted from free grazing to hay-making. In this study, we assessed the impacts of clipping and grazing on soil seed bank composition (density, functional and species composition) and its similarity with aboveground vegetation. We established four different clipping treatments: no clipping control (CK), clipping at 15 cm high (M₁₅), at 5 cm high (M₅) and free grazing (GR) in a typical Stipa kryloviidominated steppe in Inner Mongolia. The seed bank was sampled with cutting ring and TTC method was used for testing seed viability. Viable seeds were counted and the Sorensen’s similarity between the species composition of soil seed bank and above ground vegetation was calculated. The results showed that soil seed bank density ranged from 6245.0±1351.9 to 8155.9±909.1 seeds per square meter across all treatments. The CK had a higher soil seed bank density than M₁₅. Of all the functional groups, perennial forbs had the highest soil seed bank density and accounted for around 55%-60% of the total seed bank density. Annual forbs accounted for 36%-43% of the soil seed bank density and showed significantly a higher seed density at GR than at M₁₅. From the individual species level, the seed density of Stipa krylovii and Allium bidentatum was significantly affected by clipping and grazing. Sorensen’s similarity index for CK, GR, M₅ and M₁₅ was 0.55, 0.58, 0.48 and 0.60, respectively. Our experiments indicated that seed bank in the Inner Mongolia typical steppe was highly sensitive to free grazing and clipping. Both clipping and grazing reduced the soil seed bank density, and thus were predicted to retard the restoration of the degraded Stipa krylovii natural steppe.

Key words: migration, forest soil, stabilization mechanism., black carbon, organic carbon, soil type