中文摘要：

地表糙度是影响地表径流和侵蚀过程的重要属性．生物结皮在干旱半干旱区广泛分布，是地表糙度的影响因子之一．本文采用链条法测定了黄土丘陵区不同发育阶段生物结皮表面糙度特征，分析了不同发育阶段生物结皮表面糙度对坡向、土壤含水量和冻融作用的响应及其与各理化性质的相关性，初步探索了生物结皮对地表糙度的影响及其相关因素．结果表明：生物结皮显著改变地表糙度，随着生物结皮从藻结皮向藓结皮演替，其糙度先降低后增加，生物结皮发育形成10年以后，其表面糙度基本趋于稳定；研究区早期形成的藻结皮表面糙度较裸土降低47．0％，深色藻结皮（藓类盖度〈20％）较裸土降低20．4％，混生结皮（藓类盖度为20％一60％）和苔藓结皮（藓类盖度〉70％）表面糙度与深色藻结皮基本一致；坡向对发育10年以上的生物结皮表面糙度的影响不显著；土壤含水量影响地表糙度特征．研究区浅色藻结皮表面糙度随水分变化较为剧烈；随着生物结皮发育，深色藻结皮、混生结皮和苔藓结皮表面糙度随水分的变化趋于平缓．冻融增加了生物结皮表面糙度．浅色藻结皮经两次冻融后表面糙度增加29．7％；深色藻结皮、混生结皮和藓结皮表面糙度的影响需经过反复冻融才有所体现．生物结皮表面糙度与藓结皮盖度呈显著正相关（P〈0．1）．

英文摘要：

Soil surface roughness exerts profound influence on runoff and sediments yield from slopes. Biological soil crusts （BSCs） are ubiquitous living cover in the open spaces between plants in arid and semiarid ecosystems, which considerably impact the surface roughness. Aimed to deter- mine the effect of biological crusts on the surface roughness and its influence factors, this study in- vestigated the surface roughness of soil with BSCs at their different successional stages by using the chain method. Besides, the impacts of slope aspects, soil water content and freezing and thawing on surface roughness were also investigated. Then, the correlations between roughness and soil chemi- cal and physical properties were evaluated. The results showed that soil surface roughness decreased at the initial successional stage of BSCs but increased along with BSCs＇ development in the region. Soil roughness tended to be stabile since BSCs developed ten years later. The roughness was re- duced by 47.0% by the light eyanobacteria-dominated crust and 20.4% by the dark cyanobacteria- dominated crust （moss coverage 〈20% ） , compared with the bare soil. Soil moisture significantly impacted surface roughness. The surface roughness of BSCs changed obviously with soil moisture in the early development, but only slightly in their later succession. Freezing-thawing also affected surface roughness with BSCs. Roughness was more susceptible to freezing-thawing in the early development of BSCs, with an increase of 29.7% compared with the bare soil. The surface roughness of late successional BSCs exhibited a slight change only after repeated freezing-thawing. The surface roughness of BSCs showed a statistically significant relationship with the coverage of moss （P 〈 0.1）.