白三叶(Trifolium repens)入侵对城市草坪生态系统土壤动物的影响

土壤动物是土壤生态系统中十分活跃的生物类群之一，也是城市草坪生态系统的重要组成部分。由于外来植物白三叶入侵，草坪土壤动物可能受到直接或间接的影响，进而改变城市草坪生态系统功能及过程。研究白三叶入侵对城市草坪生态系统土壤动物的影响，可为进一步了解外来植物入侵机制及城市草坪的建植养护提供理论依据。采用野外调查的试验方法对4种不同入侵程度下城市草坪的土壤动物群落特征和土壤理化性质进行了研究。结果如下：4种不同入侵程度的草坪样地共捕获土壤动物30099只，隶属于19目43科，其中小杆科、线蚓科和跳虫科为优势类群；土壤动物个体数量和类群数量整体表现为中度入侵 > 轻度入侵 > 对照 > 重度入侵，符合中度干扰假说；土壤动物个体数量和类群数量的季节动态主要表现为夏秋较高，冬春较低。CCA分析显示，土壤理化因子中铵态N对土壤动物影响相对较小，可能与白三叶改善了草坪土壤的供N水平并使其不成为土壤动物分布的限制因子有关；同时，土壤理化因子对土壤动物优势类群影响较小，而主要影响常见和稀有类群。总体而言，一定程度的白三叶入侵增加了土壤动物群落的多样性，但当达到重度入侵时，白三叶形成单优群落，减少了植物多样性，进而使土壤动物可获得的生活资源减少，土壤动物群落多样性呈下降趋势；白三叶入侵后通过改变土壤理化性质，影响到土壤动物常见和稀有类群，并最终改变草坪土壤动物的群落结构。

Effects of Trifolium repens invasion on soil animals in an urban turf ecosystem

Soil animals are not only one of most active components of the biome in soil ecosystems, but also are an important part of urban turf ecosystems. The invasion of Trifolium repens L. may result in direct or indirect undesirable impacts on both turfgrass growth and the below-ground soil fauna, which somewhat alter the functions and processes of urban turf soil ecosystem. Therefore, research on the responses of soil fauna to the invasion of T. repens could not only help us to further understand the mechanisms of exotic plant invasion in urban turf ecosystems, but also to provide a practical and theoretical basis for turf establishment and maintenance. In this study, we analyzed the soil animal community structures and the soil physicochemical properties in four sampling areas with varying invasion intensities of T. repens using field investigation methods. A total of 30099 individual soil animals, belonging to 19 orders and 43 families, were collected. Among these soil animals, the dominant families present were Rhabditidae, Enchytraeidae, and Poduridae. The number of soil animal individuals and groups were significantly different and showed the following order among the four sampling areas:moderate invasion > mild invasion > control > severe invasion. This phenomenon is consistent with the intermediate disturbance hypothesis. Furthermore, we found that the number of soil animal individuals and groups was higher in summer and autumn than in spring and winter. A canonical correspondence analysis indicated that ammonium nitrogen concentration was not the environmental limitation factor for soil fauna distribution, which presumably resulted from the nitrogen fixation ability of T. repens. Our results also showed that soil physicochemical factors mainly affected common and rare groups of soil fauna, but had little influence on the dominant groups. In summary, our results demonstrated that the invasion of T. repens with a mild degree increased the diversity of soil fauna. With the increase of invasion intensity, the turf was gradually dominated by T. repens and the plant diversity decreased, which led to a shortage of available resource for soil fauna and resulted in a decline in soil animal community diversity. We hypothesized that the invasion of T. repens would influence the quantity and structure of common and rare groups of soil fauna, and would ultimately affect the community characteristics of soil animals by changing soil physicochemical properties.