Changes in understory plant composition and biodiversity declines in northeastern North American forests are widespread. Preserving species and ecosystem function requires appropriate identification and management of important stressors. Co-existence of stressors, among them earthworm invasions and white-tailed deer, make correct identification of mechanisms that cause diversity declines challenging. We used an established factorial experiment to assess survival and growth of native seedlings (Actaea pachypoda, Aquilegia canadensis, Cornus racemosa, Quercus rubra and Prenanthes alba) in response to presence/absence of deer and earthworms. We expected deer and earthworms to reduce seedling survival and biomass, and we evaluated potential pathways to explain this impact (soil N and P concentrations and pools, root architecture, and arbuscular mycorrhizal fungi [AMF] colonization). We developed structural equation models (SEM) to identify specific pathways through which earthworms and deer were impacting plant species with different life histories. Seedling survival was not affected by our treatments nor the plant and soil variables we tested. Actaea biomass was smaller in earthworm-invaded plots, and with larger total N pools. In contrast, both deer and earthworm treatments were associated with lower soil nutrient concentrations, and earthworm invaded plots had smaller N and extractable P pools. Actaea, Cornus, Prenanthes and Quercus seedlings had a lower proportion of fine roots in earthworm-invaded plots, while fine roots in Aquilegia made up a higher proportion of the root system. AMF colonization in Quercus was reduced in sites colonized by earthworms, but AMF in other species were unaffected. Our SEMs showed high correlation among soil variables, but because we do not know which variables are drivers of this change and which are the passengers, we can only conclude that they are changing together as deer and earthworms exert their respective influence. Different plant species responded in idiosyncratic ways to earthworm and deer effects on soil fertility, root architecture and limited effects on AMF colonization. While earthworm and deer-mediated changes to fine roots, soil nutrients, and AMF may lead to changes in plant performance over time, these changes rarely translated to lower plant performance in our seedlings.

中文翻译：

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蚯蚓和白尾鹿对根系、丛枝菌根和林木苗木性能的影响

北美东北部森林林下植物组成的变化和生物多样性的下降很普遍。保护物种和生态系统功能需要适当识别和管理重要的压力源。压力源的共存，其中包括蚯蚓入侵和白尾鹿，使得正确识别导致多样性下降的机制具有挑战性。我们使用既定的析因实验来评估本地幼苗（Actaea pachypoda、Aquilegia canadensis、Cornus Racemosa、Quercus rubra 和 Prenanthes alba）在鹿和蚯蚓存在/缺失时的存活和生长。我们预计鹿和蚯蚓会降低幼苗存活率和生物量，我们评估了解释这种影响的潜在途径（土壤 N 和 P 浓度和池、根结构、和丛枝菌根真菌 [AMF] 定植）。我们开发了结构方程模型 (SEM) 来确定蚯蚓和鹿影响具有不同生活史的植物物种的特定途径。幼苗存活不受我们的处理以及我们测试的植物和土壤变量的影响。Actaea 生物量在蚯蚓入侵的地块中较小，并且具有较大的总氮库。相比之下，鹿和蚯蚓处理都与较低的土壤养分浓度有关，蚯蚓侵入的地块具有较小的 N 和可提取 P 库。在蚯蚓侵染地块中，Actaea、山茱萸、Prenanthes 和 Quercus 幼苗的细根比例较低，而沉香的细根在根系中的比例较高。在蚯蚓定居的地方，栎属的 AMF 定居减少了，但其他物种的 AMF 不受影响。我们的 SEM 显示土壤变量之间具有高度相关性，但由于我们不知道哪些变量是这种变化的驱动因素，哪些是乘客，我们只能得出结论，随着鹿和蚯蚓发挥各自的影响，它们正在一起变化。不同的植物物种以特殊的方式对蚯蚓和鹿对土壤肥力、根系结构的影响以及对 AMF 定植的有限影响做出反应。虽然蚯蚓和鹿介导的细根、土壤养分和 AMF 的变化可能会导致植物性能随时间发生变化，但这些变化很少转化为我们幼苗中植物性能的降低。但因为我们不知道哪些变量是这种变化的驱动因素，哪些是乘客，我们只能得出结论，随着鹿和蚯蚓发挥各自的影响，它们正在一起变化。不同的植物物种以特殊的方式对蚯蚓和鹿对土壤肥力、根系结构的影响以及对 AMF 定植的有限影响做出反应。虽然蚯蚓和鹿介导的细根、土壤养分和 AMF 的变化可能会导致植物性能随时间发生变化，但这些变化很少转化为我们幼苗中植物性能的降低。但因为我们不知道哪些变量是这种变化的驱动因素，哪些是乘客，我们只能得出结论，随着鹿和蚯蚓发挥各自的影响，它们正在一起变化。不同的植物物种以特殊的方式对蚯蚓和鹿对土壤肥力、根系结构的影响以及对 AMF 定植的有限影响做出反应。虽然蚯蚓和鹿介导的细根、土壤养分和 AMF 的变化可能会导致植物性能随时间发生变化，但这些变化很少转化为我们幼苗中植物性能的降低。根结构和对 AMF 定植的有限影响。虽然蚯蚓和鹿介导的细根、土壤养分和 AMF 的变化可能会导致植物性能随时间发生变化，但这些变化很少转化为我们幼苗中植物性能的降低。根结构和对 AMF 定植的有限影响。虽然蚯蚓和鹿介导的细根、土壤养分和 AMF 的变化可能会导致植物性能随时间发生变化，但这些变化很少转化为我们幼苗中植物性能的降低。