中文摘要：

通过野外调查并结合室内分析，研究了黄土丘陵区阴坡不同年限退耕地土壤生物结皮的盖度、厚度、容重、粘结力以及结皮土壤的有机质、养分含量等理化性质．结果表明，研究区耕地退耕后首先出现由降雨打击而形成的结构结皮，其后随退耕年限的延长，结皮生物逐渐迁入，与土壤复合逐步演化为生物结皮．生物接皮面积随着高等植被盖度的增加有降低的趋势；厚度随退耕年限的延长呈倒S型增加，退耕10年后，结皮厚度增加缓慢；容重随退耕年限的延长而减小．结皮的形成可显著增强土壤粘结力，结皮层粘结力随退耕年限的延长呈倒S型增长，结皮土壤有机质、全氮含量明显高于研究区耕地土壤，且随退耕年限的延长而增加；退耕10年后，结皮土壤有机质及全氮含量趋于稳定，结皮土壤全磷含量与农地耕层土壤相当．生物结皮的形成提高了土壤速效氮、磷、钾含量．研究区阴坡退耕地土壤结皮的形成大致可分为3个阶段：退耕1～4年为结皮初始形成期，5—10年为结皮快速发育期，10年以后为稳定期．

英文摘要：

Soil bio-crust （SBC） plays an important role in degraded ecosystem restoration. The field investigation and laboratory analysis of SBC on different year rehabilitated grasslands at the north slope of hilly Loess Plateau showed that after cropland shifted to rehabihtated grassland, rainfall- induced structural crust appeared firstly, and then, with the increasing year of rehabilitation, crust- forming microorganism gradually settled in, and SBC developed. The depth of SBC increased in inverse ＂S＂ shape with increasing year of rehabilitation. 10 years after rehabilitation, the increase of SBC depth slowed down, and soil bulk density decreased from 1.4 g · cm^-3 to 1.1 g · cm^-3. SBC formation improved soil cohesion significantly, and the latter was increased in inverse ＂S＂ shape with increasing year of rehabilitation. The organic matter and total nitrogen contents in SBC were obviously higher than those in cropland, and increased gradually with increasing year of rehabilitation but tended to be stable after 10 years of rehabilitation. The available N, P and K contents in SBC were also increased, but no significant difference of total phosphorus was found between SBC and cropland soil. The formation of SBC in test region could be classified into 3 stages, i. e. , the first stage named the beginning of the formation, which was from 1 to 4 years of grassland rehabilitation, the second stage named the rapid development period, which was from 5 to 10 years of the rehabilitation, and the third stage named stable period after 10 years of rehabilitation.