古尔班通古特沙漠不同地貌部位生物结皮的选择性分布

新疆古尔班通古特沙漠是我国最大的固定和半固定沙漠，其间广泛发育着以地衣植物为主的生物结皮，是除种子植物以外的固定沙面的重要生物因子。研究表明，生物结皮的分布对地貌部位有较强的选择性，生物结皮的不同发育阶段种类组成亦有较大的差别。沙垄顶部为流动或半流动沙丘，主要以微生物种类分布为主。沿沙垄顶部向两侧坡间延伸，开始出现发育较弱的藻结皮，脆而极易破损。从坡上部至坡中部出现发育充分的藻结皮，具有一定的抗机械能力，并在局部微地形凸起部位有地衣植物出现。沿坡中部至坡下缘部，逐渐开始发育有良好的地衣结皮。同时，在蛇麻黄等低矮灌木群落下已经发育有苔藓结皮。丘间低地是生物结皮最为丰富的部位，苔藓植物除分布于低矮灌丛下外，还在灌丛间形成面积不等的纯群，与发育良好的地衣结皮镶嵌分布。

Distribution Characteristics of Biological Crust on Sand Dune Surface in Gurbantunggut Desert, Xinjiang

The Gurbantunggut Desert, the largest fixed and semi-fixed desert in China, are covered by well-developed biological crust, which acted as one of the important biological factors for sand dune fixation in this desert. The results showed that the distribution of biological crust has selective characteristics on different surface of sand dune, and the species component varies according to different succession stages of biological crust. The microorganism crust mainly distribute on the surface of drifting or semi-drifting sand dunes. From the top of sand dune to slope area, there occurs the algae crust, which serves as the early stage of biological crust and is fragile to outside disturbance. From lower slope area to inter-dune area, the lichen crust, which is dominant type of biological crust in this desert, becomes rich and well-developed with a common color of black and gray. The inter-dune area posses the richest cover of biological crust comprised by both lichen and moss species. The moss crust mainly distributed under the canopy of small shrub such as Ephedra distachya.