青藏东缘若尔盖高寒草甸中小型土壤动物群落特征及季节变化

中小型土壤动物是生态系统的重要组成部分。为了查明高寒草甸生态系统的中小型土壤动物群落特征及其变化动态,2008至2009年间,利用定位观测方法对青藏东缘若尔盖高寒草甸的中小型土壤动物进行了5次调查。结果为:(1)捕获中小型土壤动物9318只,隶属于3门7纲88类;平均密度为39941.67 个/m²;大类群中,线虫纲(Nematoda)的个体数占总个体数的91.50%,蛛形纲(Arachnida)(主要为蜱螨目)、弹尾纲(Collembola)、寡毛纲(Oligochaeta)和昆虫纲(Insecta)分别占3.73%、2.55%、1.12%和1.07%;(2)土壤动物的群落密度、类群数、密度-类群指数、Shannon指数、Simpson指数和Pielou指数均有显著的季节差异(P<0.01或P<0.05),表明高寒草甸生态系统的中小型土壤动物群落多样性对季节变化具有高度敏感性;(3)线虫纲、蛛形纲、弹尾纲、寡毛纲和昆虫纲的密度变化趋势基本一致,并均有显著的季节差异(P<0.05);(4)各季节间的Sorensen群落相似性系数低于Morisita-Horn相似性系数,表明季节变化对群落物种组成的影响相对较强,对优势类群个体密度的影响相对较弱;(5)中小型土壤动物群落的类群数和密度,以及弹尾纲、寡毛纲和昆虫纲的密度均与温度有显著的负相关(P<0.01或P<0.05),线虫和蛛形纲的密度与温度和降水均有不显著的负相关(P>0.05)。研究结果表明若尔盖高寒草甸的中小型土壤动物群落组成和多样性具有明显的季节特征,而温度是影响其季节变化的最主要气候因素;另外,从温度、降水及其年间变化对中小型土壤动物的影响可知全球气候变暖在短期内将会对高寒草甸土壤动物群落产生不利的影响。

Dynamics of soil meso- and microfauna communities in Zoig(e)alpine meadows on the eastern edge of Qinghai-Tibet Plateau, China

Soil fauna play an important role in terrestrial ecosystems, directly or indirectly modulating the availability of resources for other species by changing biotic or abiotic materials. Knowledge of temporal variability of soil fauna is crucial to understanding soil community dynamics and food webs, especially in variable systems such as an alpine meadow ecosystem. A typical alpine meadow in Zoigê County grassland located on the eastern edge of Qinghai-Tibet Plateau, China, was studied to document the composition, diversity, and seasonal variations of soil meso- and microfauna communities in alpine grasslands. Six 50 m × 50 m plots were established using permanent markers. Five observations were conducted from July 2008 to October 2009 and six samples in size of 50 cm × 50 cm were investigated in each plot every time. Tullgren and Baermann's methods were used to extract 9318 soil meso- and microfauna individuals and these were classified into three phyla, seven classes, and 88 taxonomic groups. The mean density of the soi1 meso- and microfauna community was 39941.67 ind./m². Nematoda dominated, accounting for 91.50% of the individuals in the soil meso- and microfauna community; Arachnida (mainly Acarina), Collembola, Oligochaeta (mainly Enchytraeidae) and Insecta (mainly Diptera larvae and Coleoptera larvae) made up 3.73%, 2.55%, 1.12%, and 1.07%, respectively. The community individual density, taxonomic group, and diversity indexes of soil meso- and microfauna varied by season both intra- and inter-years, with minimum numbers of both individuals and taxonomic groups recorded in July and the maximum in October. Significant seasonal changes were recorded in community taxonomic groups, individual density, density-group indices, the Shannon and Pielou indices (P<0.01), and the significant change was also found with Simpson Index (P<0.05). The seasonal density change trends within the five major classes, Nematoda, Arachnida, Collembola, Oligochaeta and Insecta, were similar to each other, and had significant differences (P<0.05). The values of the Sorensen Index among the seasons were lower than the Morisita-Horn Index, implying the seasonal change has a relatively stronger influence on the taxonomic composition of the meso- and microfauna community than on the abundance of the dominant taxonomic groups. Pearson correlation analysis shows the taxonomic group (P<0.01) and individual density (P<0.05) of the community have a significantly inverse relationship to air and soil temperatures (depth 0-15 cm) but are not significantly related to monthly precipitation; the same results were found with the individual densities of Collembola, Oligochaeta and Insecta, but not to those of Nematoda and Arachnida. All results suggest the taxonomic composition and diversity of soil meso- and microfauna communities in an alpine meadow ecosystem on the eastern edge of Qinghai-Tibet Plateau have obvious seasonal characteristics; seasonal changes in temperature are the main factor influencing those changes. In addition, the effects of temperature and precipitation on the soil meso- and microfauna community also implies increased global temperatures will have adverse short-term effects on soil fauna in the alpine meadow ecosystem.