Abstract: Soil seed bank is the material basis for natural regeneration of vegetation; the spatial heterogeneity of soil seed bank is of important significance for understanding the mechanism of population reproduction and regeneration. Based on field survey and geostatistics method, this paper studied the spatial heterogeneity of soil seed bank in four differentlydegraded grasslands and its relationship with the ground vegetation of Stellera chamaejasme population in the northern slope of Qilian Mountains, Northwest China. Our results showed that the semivariogram models of soil seed bank in the four degraded grassland gradients were nonlinear, showing aggregated distribution. With the aggravation of grassland degradation, the density and range of soil seed bank increased, the sill and structure proportion showed the trend of “U” type, and the spatial heterogeneity of 76.88%-93.75% was caused by the spatial autocorrelation. Furthermore, in both the nodegradation and heavydegradation grasslands, the relationship between ground vegetation density and seed bank density of S. chamaejasme population showed a significant positive correlation; in the light and moderatedegradation grasslands, such relationship did not exist. In the process of grassland degradation, the spatial distribution of soil seed bank was mainly affected by structural factors such as ground vegetation, while grazing and other disturbance factors to a certain extent reduced the spatial autocorrelation.

Key words: UV, photosynthesis, SA, Ulva prolifera