Abstract. Earthworm invasion in North American forests has the potential to greatly impact soil microbial communities by altering soil physicochemical properties, including structure, pH, nutrient availability, and soil organic matter (SOM) dynamics. While most research on the topic has been carried out in northern temperate forests, little is known on the impact of invasive earthworms on soil microbial communities in the boreal forest, a region characterized by a slower decay of organic matter (OM). Earthworm activities can increase OM mineralization, altering nutrient cycling and biological activity in a biome where low carbon (C) and nitrogen (N) availability is typically limiting microbial and plant growth. Here, we characterized and compared microbial communities of earthworm-invaded and non-invaded soils in previously described sites across three major soil types found in the Canadian boreal forest using a space-for-time approach. Microbial communities of forest floors and surface mineral soils were characterized using phospholipid fatty acid (PLFA) analysis and metabarcoding of the 16S rRNA gene, for bacteria and archaea, and ITS2 region for fungi. In forest floors, the effects of earthworm invasion were minor. In mineral soil horizons, earthworm invasion was associated with higher fungal biomass and greater relative abundance of ectomycorrhizal fungi. Oligotrophic bacteria (Acidobacteriota and Chloroflexi) were less abundant in invaded mineral soils, where Gram(+) : Gram(−) ratios were also lower, while the opposite was observed for the copiotrophic Bacteroidota. Additionally, earthworm-invaded mineral soils harboured higher fungal and bacterial species diversity and richness. Considering the important role of soil microbial communities for ecosystem functioning, such earthworm-induced shifts in their community composition are likely to impact nutrient cycling, as well as vegetation development and forest productivity at a large scale as the invasion progresses in these boreal systems.

中文翻译：

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蚯蚓入侵的北方森林土壤拥有独特的微生物群落

摘要。北美森林中的蚯蚓入侵有可能通过改变土壤理化特性（包括结构、pH 值、养分可用性和土壤有机质 (SOM) 动态）来极大地影响土壤微生物群落。虽然大多数关于该主题的研究都是在北部温带森林中进行的，但人们对入侵蚯蚓对北方森林土壤微生物群落的影响知之甚少，北方森林是一个以有机物 (OM) 腐烂速度较慢为特征的地区。蚯蚓活动可以增加 OM 矿化，改变生物群落中的养分循环和生物活动，在这些生物群落中，低碳 (C) 和氮 (N) 可用性通常会限制微生物和植物的生长。这里，我们使用空间换时间的方法，对加拿大北方森林中发现的三种主要土壤类型的先前描述地点的蚯蚓入侵和未入侵土壤的微生物群落进行了表征和比较。使用磷脂脂肪酸 (PLFA) 分析和 16S rRNA 基因的元条形码（细菌和古细菌以及真菌的 ITS2 区域）对森林地面和地表矿质土壤的微生物群落进行了表征。在森林地面，蚯蚓入侵的影响很小。在矿质土壤层中，蚯蚓入侵与较高的真菌生物量和较高的外生菌根真菌相对丰度有关。贫营养细菌（Acidobacteriota 和 Chloroflexi）在侵入的矿质土壤中数量较少，其中 Gram(+) : Gram(−) 比率也较低，而对于嗜酸性拟杆菌门则观察到相反的情况。此外，蚯蚓入侵的矿质土壤具有更高的真菌和细菌物种多样性和丰富度。考虑到土壤微生物群落对生态系统功能的重要作用，这种由蚯蚓引起的群落组成变化可能会影响养分循环，以及随着这些北方系统的入侵进展，大规模的植被发育和森林生产力。