中文摘要：

采用空间代替时间的方法,对毛乌素沙地三种不同演替阶段的油蒿（Artemisia ordosica）群落（半固定沙地油蒿群落、具生物结皮的油蒿群落、油蒿＋本氏针茅群落）的群落特征及生物量、叶片气体交换过程、不同土层（0-10cm、10-20cm、20-40cm、40-60cm、60-80cm）土壤含水量、根系垂直分布等进行测定。结果表明：油蒿群落演替是油蒿与草本植物竞争、生物结皮发育、土壤发育以及土壤水分垂直变化等生物非生物因素综合作用的结果。随着油蒿群落演替的发展,群落物种数、草本层盖度和生物量、群落总盖度逐渐增加,而油蒿个体数、油蒿盖度、油蒿叶生物量以及生物土壤结皮盖度则先增加后减少,油蒿根系有向下分布的趋势,0-10cm土层逐渐以草本植物根系占优势。土壤水分是毛乌素沙地油蒿群落演替的主要驱动力,通过影响油蒿叶片气孔导度和净光合速率,以及根系垂直分布影响油蒿在群落中的竞争力。不同演替阶段油蒿群落土壤水分低值区不同,半固定沙地油蒿群落0-10cm和20-40cm土壤含水量最低,具生物结皮的油蒿群落10-20cm土壤含水量最低,而油蒿＋本氏针茅群落60-80cm土壤含水量最低。

英文摘要：

Space-time substitution was applied to evaluate the community characteristics,biomass,gas exchange process of leaf,soil moisture content of different layers（ 0-10 cm,10-20 cm,20-40 cm,40-60 cm and 60-80cm） with ECH2 O EC-TM,vertical distribution of roots and so on,under three different succession stages of Artemisia ordosica community（ A. ordosica community in semi-fixed dune,A. ordosica community with biological crusts and A. ordosica ＋ Stipa bungeana community）. The succession of A. ordosica community was the result of combination of abiotic and biotic factors such as the competition of A. ordosica and herbaceous,the development of biological crusts and soil,the vertical distribution of soil moisture,and so on. With the succession development of A. ordosica community,the number of species in community,herbaceous coverage,herbaceous biomass,total community coverage gradually increased,while the number of A. ordosica individuals,A.ordosica coverage,leaf biomass of A. ordosica and the coverage of biological crusts presented the trend of increase firstly and then decreased. The root distribution presented downward trend as the development of succession,while herb roots gradually dominated in the soil layer of 0-10 cm with the development of A. ordosica community. The proportion of A. ordosica fine roots collected at 0-40 cm depth in the semi-fixed,fixed dune with biological crusts,and A. ordosica ＋ Stipa bungeana community was 75. 69%,79. 10% and 42. 34%,respectively,but the fine roots distributed at 20-80 cm depth in A. ordosica ＋ Stipa bungeana community was 77.87%. Soil moisture was the main driving force for the succession of A. ordosica community in Mu Us Sandland,which could affect the competitiveness by influencing the net photosynthetic rate,stomatal conductance and root vertical distribution of A. ordosica. The low soil moisture content area was different during the succession processes. The soil moisture content of A. ordosica community in semi-fixed dune was the lowest in 0-10 cm and 20-40