Northern hardwood forests in formerly glaciated areas had been free of earthworms until exotic European earthworms were introduced by human activities. The invasion of exotic earthworms is known to dramatically alter soil physical, geochemical, and biological properties, but its impacts on soil microbiomes are still unclear. Here we show that the invasive earthworms alter soil microbiomes and ecosystem functioning, especially for nitrogen cycling. We collected soil samples at different depths from three sites across an active earthworm invasion chronosequence in a hardwood forest in Minnesota, USA. We analyzed the structures and the functional potentials of the soil microbiomes by using amplicon sequencing, high-throughput nitrogen cycle gene quantification (NiCE chip), and shotgun metagenomics. Both the levels of earthworm invasion and soil depth influenced the microbiome structures and the functional gene abundances. In the most recently and minimally invaded soils, Nitrososphaera and Nitrospira as well as the genes related to nitrification were more abundant than in the heavily invaded soils. By contrast, genes related to denitrification and nitrogen fixation were more abundant in the heavily invaded than the minimally invaded soils at various depths. Since denitrification can cause a nitrogen loss from the ecosystem, our results suggest the invasion of earthworms could influence the overall forest N cycling.

以前冰川地区的北部阔叶林一直没有蚯蚓，直到人类活动引入了外来的欧洲蚯蚓。众所周知，外来蚯蚓的入侵会极大地改变土壤的物理、地球化学和生物学特性，但其对土壤微生物组的影响仍不清楚。在这里，我们表明侵入性蚯蚓改变了土壤微生物组和生态系统功能，特别是对于氮循环。我们在美国明尼苏达州的阔叶林中通过活跃的蚯蚓入侵时间序列从三个地点收集了不同深度的土壤样本。我们通过使用扩增子测序、高通量氮循环基因定量（NiCE 芯片）和鸟枪法宏基因组学分析了土壤微生物组的结构和功能潜力。蚯蚓入侵水平和土壤深度都影响微生物组结构和功能基因丰度。在最近和最小入侵的土壤中，Nitrososphaera和Nitrospira以及与硝化作用相关的基因比在严重入侵的土壤中更为丰富。相比之下，与反硝化和固氮相关的基因在不同深度的严重入侵土壤中比最低入侵土壤中更丰富。由于反硝化会导致生态系统中的氮流失，我们的研究结果表明蚯蚓的入侵可能会影响整个森林氮循环。