高寒冻土区生物结皮对土壤理化属性的影响

生物结皮是高寒地区地被层的重要组分之一。其作为地表特殊的结构层，能够改变地表结构及土壤理化属性，从而影响冻土环境。迄今为止，关于青藏高原高寒生态系统中生物结皮对土壤理化属性的影响尚不清楚。以青藏高原高寒冻土区生物结皮为研究对象，初步研究了生物结皮的特征及其对土壤理化属性的影响。结果表明：生物结皮在高寒草甸退化过程中广泛发育，主要以藻结皮为主，其盖度可达37.3%~51.7%，结皮层平均厚度为12.6 mm。由于生物结皮的发育，高寒地区5~20 cm土层粉粒含量有所增加，但差异不显著，而结皮层土壤田间持水量相比于裸地表层（2 cm）增加了10%~40%，结皮层容重较裸地降低了30%；两种类型藻结皮均显著增加了结皮层及其下0~20 cm土层土壤有机质，而深色藻结皮增加了结皮层及其下0~20 cm土层土壤全氮含量，浅色藻结皮仅增加了结皮层土壤全氮含量，对其下0~20 cm土层土壤全氮含量没有显著影响；生物结皮对土壤pH没有显著影响；生物结皮是高寒生态系统植被退化过程中的关键环节。研究结果为揭示生物结皮在高寒生态系统中发挥重要生态功能提供依据。

The impact of the biological soil crusts on the frozen soil properties in the frozen ground region

BSCs （biological soil crusts）， as ubiquitous living covers on soil surface of the enclosure grassland in the frozen ground region of the Qinghai-Tibet Plateau. However， studies on the influence of biocrusts on soil properties in the frozen ground region were fresh. Objective of the paper was to determine the influence of the biological soil crusts on soil physicochemical properties of the surface forzen soil. Field investigation was conducted and physicochemical properties of two kinds of BSCs from this region was analyzed. The results showed that BSCs occupy 37.3%~51.7% of the soil surface and the cyanobacteria crust is dominant across the study area， with a thickness of up to 12.6 mm， which was higher than the hot arid desert regions. At the same time， BSCs increase the silt particle content of 5~20 cm， but the impact is not significant， while it had remarkable effect on water holding capacity and soil bulk density. Water holding capacity of the BSCs layers increased by 10.0%~40.0% compared to the bare soils， while soil bulk density of the BSCs layer was 30.0% lower than bare soils. Both types of BSCs （dark cyanobacteria crusts and light cyanobacteria crusts） remarkably increased soil organic carbon content （TOC） of BSC layer and 0~20 cm soil layers. While both BSCs have different impact on soil total nitrogen （TN） content， dark cyanobacteria crusts had significant increase on TN in the BSCs layers and below 20 cm soil layers， but light cyanobacteria crusts only increased BSCs layer TN had no impact on the below 20 cm soil layers. Meanwhile the BSCs have no significant impact on the soil pH. Biological crust is very important in the process of vegetation degradation in alpine ecosystem. The research results provide a theoretical basis for revealing the ecological functions of biological crust in alpine ecosystem.