大型土壤动物群落对短花针茅草原荒漠化过程的响应

Response of soil macrofauna to desertification in Stipa breviflora desert steppe

土壤动物是草地生态系统的重要组分,对维持草地生态系统结构与功能的稳定性具有重要作用,研究土壤动物群落对草地荒漠化的响应有助于揭示地下与地上生态过程的联系,全面认识荒漠化的本质。选取鄂尔多斯高原西部未荒漠化(Ⅰ)、轻度荒漠化(Ⅱ)、中度荒漠化(Ⅲ)、重度荒漠化(Ⅳ)及极重度荒漠化(Ⅴ)5种短花针茅荒漠草原生境,采用手拣法对大型土壤动物群落进行了野外调查。共获得1门2纲6目25个土壤动物类群,优势类群为蚁科和金龟子总科幼虫,常见类群8个。结果显示,短花针茅荒漠草原大型土壤动物群落具有温带草原土壤动物群落的基本特征。在荒漠化进程中,大型土壤动物群落优势类群(蚁科和金龟子总科幼虫)未发生变化,但群落总个体密度和类群数显著下降(P<0.01,P<0.01),群落香浓多样性、丰富度和均匀度降低(P<0.01,P<0.01,P<0.05),群落结构趋于简单。不同荒漠化生境土壤动物群落显示出明显的退化梯度,各土壤动物类群的分布揭示了它们对生境因子的偏好和响应模式的差异。短花针茅草原荒漠化对土壤动物垂直分布的影响具有由个体到类群、由表土层到下层的变化规律,但未改变土壤动物分布的表聚性。荒漠化导致的食物资源减少是蚁科动物个体密度变化的主要原因,轻度荒漠化(Ⅱ)最适宜蚁科动物生存,土壤全氮、有机质和地上生物量对步甲科和象甲科幼虫个体密度影响较大,重度荒漠化(Ⅳ)和极重度荒漠化(Ⅴ)生境将严重影响步甲科和象甲科幼虫的生存,但对金龟子总科和蜘蛛目动物个体密度影响不大。土壤动物与生境因子、生境及荒漠化进程之间的关系综合反应了草地生态系统退化过程。

Soil fauna is an important component of grassland ecosystems and plays a key role in maintaining the stability of ecosystem structure and functioning. Studying the response of soil fauna to desertification may reveal the ecological linkage between aboveground and belowground processes, and improve our understanding of the ecological consequences of desertification. A survey of the soil macrofauna community was conducted by hand sorting at No-desertification （ Ⅰ ）, Light- desertification （ Ⅱ ）, Moderate-desertification （ Ⅲ ）, Heavy-desertification （ Ⅳ ）, and Extreme- desertification （ Ⅴ ） habitats in Stipa breviflora steppe. A total of 25 fauna groups belonging to 6 orders, 2 classes and 1 phylum were found. The dominant groups were Formicidae and Scarabaeidae larvae with 8 common groups. Soil macrofauna communities in the Stipa breviflora steppe were similar to those in other areas in temperate prairies. As desertification progressed, the dominant groups （Formicidae and Scarabaeidae larvae ） did not change. However, the structure of soil macrofauna communities became simpler with total individual density and number of soil animal groups （P 〈 0.01, P 〈 0.01 ） ,biodiversity （P 〈 0.01 ）,richness （P 〈 0.01 ）and evenness indices （P 〈 0.05 ） decreasing significantly. Soil fauna communities and soil animal groups in different habitats along a degradation gradient showed different preferences and responses to habitat factors. Desertification in the Stipa breviflora steppe affected the vertical distribution of soil fauna, with first affected individuals and then groups. The first effects were seen in the top layers and later in the deeper layers of the soil, but the highest faunal abundances were found in the top soil layers. The Light-desertification （ Ⅱ ） habitat was most preferred by the Formicidae, but food shortage resulting from desertification led to a decrease in Formicidae abundance. Soil total nitrogen, organic matter and aboveground dry biomass were the main factors affecting individual densities of Carabidae and Curculionidae larvae, which did not survive in Heavy-desertification （ Ⅳ ） and extreme- desertification （ Ⅴ ） habitats. Desertification had little effect on the total individual density of Scarabaeidae and Araneida. The degradation of grassland ecosystems was reflected by the relations among soil fauna, habitat factors, and desertification.