若尔盖高寒草甸退化对中小型土壤动物群落的影响

土壤动物是陆地生态系统物质循环和能量流动的中心环节，也是生态系统演化的重要驱动因子。为了查明青藏东缘若尔盖高寒草甸生态系统退化过程对中小型土壤动物群落的影响，2008年7、10两月分别对若尔盖高寒草甸沼泽草甸、草原草甸和沙化草甸三个不同退化阶段的中小型土壤动物群落进行了调查。共分离到中小型土壤动物9450个，隶属于4门5纲12目70科104类；优势类群为线虫（Nematode），个体数占85.79%；蜱螨目（Arachnida）、弹尾目（Collembola）、寡毛纲（Oligochaeta）和昆虫纲（Insect）依次占8.73%、3.24%、1.32%和0.88%。群落密度、类群数、Margalef丰富度指数和密度-类群指数均在7、10两月份均随高寒草甸的退化而显著降低（p<0.01或p<0.05），10月份的差异更明显。Shannon-wiener多样性指数、Pielou均匀性指数和Simpson优势度指数无显著变化（p>0.05）。各主要类群个体数在群落中所占的比例呈波动性变化，但沙化可使蜱螨目的数量相对提高，而弹尾目相对下降。随退化程度的加重，三个退化阶段的Sorenson群落相似性逐渐降低，而Morisita-Horn相似性的变化则不同，说明高寒草甸的退化对中小型土壤动物群落物种组成的影响较大，对群落优势类群数量的影响较小。10月份的群落密度、多样性和群落相似性均高于7月份，表明群落结构组成受季节的影响；但是各退化阶段的Sorenson和Morisita-Horn季节相似性比较说明，季节变化对沙化草甸种类组成的影响大于草原草甸，对草原草甸群落优势类群数量的影响大于沙化草甸。个体密度和类群数的表聚性程度也随退化加重而降低。以上研究结果表明，高寒草甸的退化能够降低土壤动物群落的组成种类和结构复杂性，将会影响其生态服务功能。

Influence of degradation on soil meso-microfauna communities in Zoig? alpine meadow

Soil fauna plays an important role in nutrient cycling and energy flow, and is also an important driver of ecosystem succession. The Qinghai-Tibetan Plateau, with an area of 2.5 million square kilometers, and elevation of over 4,500 meters, has been called "the third polar area of the earth". The wetlands of the Qinghai-Tibetan Plateau are an important biodiversity area. The Zoigê Wetland, located on the eastern Qinghai-Tibetan Plateau, is a typical example of an alpine meadow. Since the 1950s, the Zoigê Wetland has degraded as a result of global change and human activity, and parts have become desert-like with little plant coverage. The effect of this degradation on the structure and diversity of the below-ground soil biota is unknown. To investigate the effects of degradation on the soil meso- and microfauna in Zoigê Alpine Meadow, three degradation stages (marsh meadow, grassland meadow and sand meadow) were selected, and examined in July and October, 2008. A total of 9,450 individuals were captured from the soil meso- and microfauna, and classified into 4 phyla, 5 classes, 12 orders, 70 families and 104 taxa. The community was found to be dominated by nematodes, accounting for 85.79% of the individuals. Other common taxonomic groups were Arachnida (8.73%), Collembola (3.24%), Oligochaeta (1.32%), and insects (0.88%). In both July and October, abundance, richness and diversity in soil meso- and microfaunal communities were observed to be significantly less (P<0.01 and P<0.05) for each degradation stage. Differences among the three degradation stages were more significant in October. No significant changes were recorded in the Shannon diversity index, Pielou's index, and Simpson's diversity index (P>0.05). Percentages in each taxonomic group varied, without an obvious trend. The sand meadow had a greater relative abundance of Arachnida to Collembola than did the marsh meadow or the grassland meadow. The Sorensen similarity index showed a decline as degradation progressed, but this was not observed with the Morisita-Horn similarity index. Degradation thus had a greater influence on composition of the soil meso- and microfaunal community than on individuals belonging to dominant taxonomic groups. Diversity was higher in October than in July, as indicated by the higher values obtained for the taxonomic groups, diversity index, Sorenson similarity index and Morisita-Horn similarity index. This suggested that seasonal change can influence the structure and composition of the soil community. Furthermore, seasonal similarities between the three meadow stages, as shown by the Sorenson and Morisita-Horn indices, indicated that seasonal changes have a greater effect on taxonomic composition in the sand meadow than in the grassland meadow. The opposite pattern was observed for the abundance of dominant taxonomic groups. A greater number of individuals and taxonomic groups were found in the surface layer of the soil as degradation increased. Serious degradation of alpine meadows can significantly reduce taxonomic diversity and structural complexity within these meso- and microfaunal soil communities. Clearly this influences the ecological functions of alpine meadows.