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作 者 ：张元明*,王雪芹

期 刊 ：生态学报 2010年 30卷 16期 页码：4484~4492

关键词：生物土壤结皮；形成过程；演替特征；微结构；荒漠地区；

Keywords:biological soil crust, formation process, successional characteristics, microstructure, desert area,

摘 要 ：中国科学院知识创新工程重要方向项目（KZCX2-YW-336）;国家自然科学基金资助项目(No.40771114)

Abstract:In arid and semi-arid lands, the vegetation cover is usually sparse or absent. Nevertheless, in open spaces among higher plants, the soil surface is generally covered by a community of highly specialized organisms, such as mosses, lichens, liverworts, algae, fungi, cyanobacteria, and bacteria. These communities are usually referred to biological soil crusts, or cryptogamic, cryptobiotic, microbiotic, microphytic soil crusts. Biological soil crusts, given their extraordinary abilities to survive desiccation and extreme high temperatures, high pH and high salinity, have been found in desert areas all over the world and may constitute as high as 70% of the living cover in some plant communities. They play a significant role in ensuring the proper functioning of desert ecosystem, such as involvement in the process of formation, stability and fertility of soil, prevention of soil erosion caused by wind or water, augment of vascular plant colonization, and stabilization of sand dunes. The biological soil crust resulting from the colonization of soil surface by communities of filamentous cyanobacteria were mainly dominated by Microcoleus, which occurs as a cluster of filaments surrounded by a gelatinous sheath. Other important taxa are Lyngbya, Anabaena and Xenococcus lyngbyge. At this developmental stage, the main contributors for sand fixation were changed from bacteria to filamentous cyanobacteria. Microscopic examination of this kind of crust revealed an intricate network of filamentous cyanobacteria and extracellular polymer secretions, which binds and entraps mineral particles and finer particles stick on the filament surface. These effects enhance soil cohesion and resistance to erosion. Two major mechanisms are suggested for maintaining sand surface stabilities: (1) the ability of exopolysaccharides from some microorganisms (mainly bacteria) to cohere sand particles, and (2) formation of network by the filamentous microbes and cryptogam (cyanobacteria, algae, lichen and moss). With the alternation of crust-related species from cyanobacteria, algae and lichen to moss, the main agents maintaining microstructure of biological soil crust changed accordingly from glutinous exopolysaccharides to filamentous algae and hyphae of lichen and moss. Generally, the development of biological soil crust can be divided into three phases: original succession phase (including soil microorganisms and soil enzymes), algae crust phase and lichen-bryophyte crust phase. The establishment of former phase crust serves as a basis for the next phase of crust succession. Under drought conditions, soil crust is brittle, and can be crushed easily when subjected to compressional or shear forces. When the surface crust is broken, the unconsolidated loose sand grains below the crust are exposed to wind, resulting in severe soil erosion. Under favorable environmental conditions, such as sufficient water supply and moderate temperature, the less developed biological soil crust may surpass the intermediate phase and develop into higher level biological soil crust.

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