Responses of soil seed banks and soil microbial activity to grazing exclusion in cold semiarid grasslands

The soil seed bank (SSB) and soil microbial communities are among the most crucial drivers of belowground biodiversity in grasslands. Changes in components of soil biodiversity following protection from grazing were observed in cold, semiarid grasslands. To study these changes, soil samples were taken in an intensively grazed area and in an exclosure established 20 years prior to this study. In particular, changes in biodiversity components such as SSB and microbial activities in two soil depths (0-5 and 5-10 cm) were measured. Nonmetric dimensional scaling showed that after grazing removal, the SSB had changed. SSB density, richness, and diversity were higher in the ungrazed plots. The increase in SSB density and diversity in the exclosure may have been caused by the absence of direct adverse effects of grazing on the SSB, like trampling and plant consumption, or by reduced indirect effects, such as seed germination facilitation in canopy gaps created by grazing animals. The effect of grazing removal on basal respiration, substrate-induced respiration, and urease activity was highly significant (p < 0.01) and may be due to an increase in soil moisture after grazing exclusion. The effect of grazing removal on soil biological parameters was greater in the upper layer than in the deeper soil layer. This study shows that grazing exclusion can be a useful approach in restoring components of soil biodiversity.