中文摘要：

研究了黄土高原典型流域内不同植被下生物结皮的厚度、容重和抗剪强度等变化特征。结果表明：不同植被下黄土生物结皮的发育程度差异较大,表现在结皮的厚度、抗剪强度和容重几个指标上,总体发育程度顺序为：乔灌下结皮〉多年生草本下结皮〉一年生草本下结皮。随着生物结皮的发育和演替,结皮厚度增加,但增加幅度相对缓慢;结皮容重呈降低趋势,土壤孔隙结构得以改善;结皮抗剪强度不断增大,表明其控蚀效果相应增强。生物结皮的覆盖度和厚度均明显表现为：阴坡〉阳坡,而容重变化则相反,即阴坡〈阳坡;抗剪强度表现为阳坡略大于阴坡。说明坡向对生物结皮的发育具有显著影响。不同植被和坡向下生物结皮的发育特征出现差异,其水文生态功能理应有所不同,这在今后的研究中应予以重视。

英文摘要：

Biological soil crusts（BSC） are common features on soil surface in arid and semiarid regions,and play significant biological roles in these ecosystems.In order to determine the developmental characteristics of BSC in Liudaogou watershed in the wind-water erosion crisscross region on the Loess Plateau of China,the thickness,shear strength,and the bulk density of the BSC under different vegetation types and in different slope aspects were measured and taken as evaluation indices of crust＇s development.The results indicated that： there were great differences among these properties of BSC under different vegetation types,and the development degrees of BSC generally followed the order of the arbor and shrub vegetationperennial herbaceous plantsannual herbaceous plants in research area.With the development and succession of BSC,the crust＇s thickness increased gradually,but the increasing extent was very slow.Meanwhile,the bulk density of BSC notably decreased with the increase of crust＇s thickness,while the porosity and structure of soil was improved.The shear strength and thickness of BSC showed obviously positive correlation.With the increase of crust＇s shear strength,the effects of BSC on controlling erosion were enhanced.The formation and development of BSC was significantly affected by slope aspects.The crust＇s cover and thickness in the shady slope was significantly higher than that in the sunny slope,but the bulk density exhibited an opposite trend.Shear strength of BSC in the sunny slope was slightly greater than that in the shady slope.These were mainly caused by the light,soil moisture content and nutrient conditions in different slope aspects.Therefore,more attention should be paid to the ecological and hydrological functions of BSC determined by its development and succession stages in this area,which may be affected by vascular plants and slope aspects.