干扰对生物土壤结皮及其理化性质的影响

生物土壤结皮作为荒漠地区特殊环境的产物，具有较强的抗风蚀、水蚀功能，也是干旱荒漠地区植被演替的重要基础。随着人类活动的加剧，生物土壤结皮也受到不同类型和不同程度的干扰，主要包括放牧、火烧、车辆碾压等形式。干扰对生物土壤结皮的影响主要表现在生物土壤结皮结构及盖度的变化、土壤理化性质的改变、土壤微生物数量及活性的变化等几个方面。放牧对土壤物理性质的影响还没有一致的结论，除了干扰的程度还与土壤含水量有关系。火烧虽然改善了土壤结构，但是破坏了地表植被的盖度，而且恢复比较困难，也加速了外界侵蚀的力度，对土壤化学性质也有显著影响。机械碾压的破坏力最强，且没有任何的积极意义。

Study on the Effects of Disturbances on the Physical and Chemical Properties of Microbiotic Crusts in Arid Areas

Microbiotic crusts are an important component of desert ecosystems, and they are important in stabilizing soils in arid and semi - arid regions. However, microbiotic crusts are sensitive to disturbances, and the disturbances to microbiotic crusts become more serious along with the increase of human activities in arid and semi - arid regions. These disturbances include livestock grazing and fire and mechanical compression. The distutbances can directly affect many aspects of the structure and function of mierobiotic crusts, including crust coverage, spedes composition and physical and chemical properties. Livestock grazing can reduce the coverage and species richness of microbiotic crusts, especially the lichens and mosses. Algae are much more tolerant to the disturbance of livestock grazing. Livestock grazing affects significantly the soil surface features but not the bulk density of sandy soils, and results in the decrease in OC, N and P contents in topsoil. Microbiotic crusts are generally killed by fires, resulting in loss of biomass and visible coverage, regeneration of mierobiotic crusts depends on the prefire composition and structure of the vascular plant communities, fire intensity and fire occurring frequency. Effects of mechanical disturbance are especially noticeable to erodible soils and large landforms.