Abstract: Biological soil crusts are prevalent in arid and semiarid regions, they are the complex mixtures of cyanobacteria, green algae, phycolichens, mosses, liverworts, fungi and bacteria. In order to understand the effect of biological soil crusts (BSCs) on seed emergence and seedling growth in loess region, we conducted field surveys and studied the impact of intact crusts, broken crusts and soil on seed emergence of 4 plant species including Pinus tabulaeformis, Caragana korshinskii, Hippophae rhamnoides and Pyrus betulifolia based on the field emergence experiment in Wuqi County, Shaanxi Province during the period from July to August 2009. The results reveal that the vegetation coverage was reduced significantly with the increase of BSCs coverage and thickness (P<0.01), and vegetation types were in an increase trend (P＞0.05). Seed emergence rate and emergence process were affected by plant species and crust types (intact crusts, broken crusts and soil) (P<0.01), and the interaction between the two affected slightly the seedling emergence (P＞0.05), but affected significantly the emergence process (P<0.01). The seed emergence rate under broken BSCs was higher than that under intact BSCs, but there was no significant difference with soil. Broken BSCs could increase plant biomass and rootshoot ratio of plants, but intact BSCs affected the plant biomass and rootshoot ratio depending on the types of seed.

Key words: biological soil crust, seed emergence, vegetation coverage, broken BSCs, Wuqi , County, the Loess plateau