Abstract：
Human introductions have resulted in earthworms establishing in the Arctic, species known to cause cascading ecosystem change. However, few quantitative outdoor experiments have been performed that describe how these soil modifying earthworms are reshaping structures in tundra soils. In this study, we used three-dimensional (3-D) X-ray images of soil cores (approximately 10 cm diameter, 20 cm height, N = 48) to assess how earthworms (Aporrectodea sp. and Lumbricus sp.) affect soil structure and macropore networks in an outdoor mesocosm experiment that lasted four summers. Effects were assessed in both shrub-dominated (heath) and herb-dominated (meadow) tundra. Earthworms almost doubled the macroporosity in meadow soils and tripled macroporosity in heath. Interestingly, the fractal dimension of macropores decreased in response to earthworm burrowing in both systems, indicating that the presence of earthworms reduced the geometric complexity in comparison to other pore-generating processes active in the tundra. Observed effects on soil structure occurred along with a dramatically reduced soil moisture content, which was observed the first winter after earthworm introduction in the meadow. Our findings suggest that predictions of future changes in vegetation and soil carbon pools in the Arctic should include major impacts on soil properties that earthworms induce.
摘要：
人类的引进导致蚯蚓在北极建立，已知会导致级联生态系统变化的物种。然而,很少进行定量的室外实验来描述这些土壤改良蚯蚓如何重塑苔原土壤中的结构。在这项研究中,我们使用了土壤核心的三维（3-D）X射线图像（直径约10厘米，20厘米高,N=48），以评估蚯蚓（Aporrectodeasp。和Lumbricussp.)在持续四个夏天的户外介观实验中影响土壤结构和大孔隙网络。在灌木主导的（荒地）和草本主导的（草甸）苔原中都评估了效果。蚯蚓在草甸土壤中的大孔隙度几乎翻了一番，在健康中的大孔隙度增加了三倍。有趣的是,在两个系统中，大孔隙的分形维数随着蚯蚓的挖洞而降低，表明与苔原中活跃的其他孔隙生成过程相比，蚯蚓的存在降低了几何复杂性。观察到的对土壤结构的影响随着土壤水分含量的急剧下降而发生，这是在草地上引入蚯蚓后的第一个冬天观察到的。我们的发现表明，对北极植被和土壤碳库未来变化的预测应包括对蚯蚓诱导的土壤特性的重大影响。
