Introduction

Arbuscular mycorrhizal (AM) fungi are important root symbionts found in the majority of terrestrial plant roots (van der Heijden et al., 2015). Arbuscular mycorrhizal fungi can have significant impacts on plant fitness (Klironomos et al., 2000), plant community composition (Hartnett & Wilson, 1999; van der Heijden et al., 2008) and ecosystem functioning (van der Heijden et al., 2015) – although in other cases, AM fungi have been found to colonize plant roots with few benefits for the plant (Cosme et al., 2018; Wang et al., 2021, 2022). Since the advent of modern sequencing techniques, the global diversity patterns of AM fungi have become increasingly well understood (Kivlin et al., 2011; Davison et al., 2015, 2018). Although many AM fungal species are distributed globally (Davison et al., 2015), others are confined to particular habitats or geographical regions (Veresoglou et al., 2013; Davison et al., 2016) and may show remarkable niche differentiation, in particular in relation to temperature and soil pH (Davison et al., 2021). However, for some major land areas, including the Arctic, AM fungal diversity and its drivers remain poorly understood (Öpik et al., 2013; Pärtel et al., 2017), even though AM fungal communities in the Arctic are distinct from those in other areas (Vasar et al., 2022).

As the Arctic regions are crucial for the storage of large portions of the Earth's carbon (C) stocks (Mack et al., 2004), it is important to understand the potential drivers of these stocks. Mycorrhizal fungi, including AM fungi, may contribute to C cycling and storage via impacts on plant photosynthetic rates, use of photosynthates, and C storage in their biomass (Read & Perez-Moreno, 2003; Godbold et al., 2006; Soudzilovskaia et al., 2015a,b; Deckmyn et al., 2020). Arctic regions are currently experiencing the globally highest rates of climate change (IPCC, 2014), so we urgently need to understand the general diversity and role of AM fungi in cold climates, and the environmental drivers of local AM fungal communities.

Compared to temperate environments, few studies exist on the regional species pool of AM fungi in Arctic environments, the relative abundance of taxa and the structuring of AM fungal communities along environmental gradients. The existing studies from the Arctic typically have relied on either spore morphological identification from soil samples (with some uncertainty about host plant identity), or root colonization quantification (bringing little information about AM fungal species diversity) (although see Appoloni et al., 2008; Öpik et al., 2013; Davison et al., 2018).

In a study along a latitudinal gradient in the Canadian Arctic, Olsson et al. (2004) found high AM fungal root colonization at the southernmost sites, but little to no colonization at the northernmost sites, despite the presence of putative AM plants. The most northern sites did, however, sustain a higher degree of non-mycorrhizal plants. A higher abundance of non-mycorrhizal and facultative mycorrhizal plants in harsh environments is a common pattern (Bueno et al., 2017). For the Arctic, several explanations have been proposed for the low prevalence of AM plants, as reviewed in Kytöviita (2005). One hypothesis attributes this pattern to history, because the Arctic ecosystem has evolved relatively recently and been deglaciated for only 3000–8000 yr. Another notion is that mycorrhizal associations with higher degradative abilities, such as ericoid mycorrhiza or ectomycorrhiza, will provide a larger benefit to plants, and therefore be more prevalent. Finally, Kytöviita (2005) proposes that the low prevalence of AM fungi might be a consequence of poor adaptation by AM fungi to nutrient uptake in cold environments. From the perspective of an Arctic plant, the costs for sustaining an AM fungal partner may then outweigh the benefits. With regards to AM fungal colonization of roots, several studies from the Arctic nonetheless have found colonization levels ranging from 11–36% root length colonized (Allen et al., 2006), through 27–51% root length colonized (Ormsby et al., 2007), to 37–85% root length colonized (Olsson et al., 2004). Newsham et al. (2017) studied 102 plants from 11 plant species, and found structures resembling AM fungi in 41 of the plant individuals.

To date, few studies have investigated the diversity of AM fungi in the Arctic. As these studies are based mostly on soil samples taken from a mixed rhizosphere, there is some uncertainty about the link between AM fungal diversity and host plant identity. For example, Varga et al. (2015) used spore morphotyping from soil samples to find 18 spore morphospecies, and Greipsson et al. (2002) used trap-culturing and spore morphotyping to discover 11 morphospecies. Some DNA-based root and soil AM fungal data exist from Iceland, Svalbard and the Scandinavian Arctic (Appoloni et al., 2008; Öpik et al., 2013; Davison et al., 2015, 2018; García de León et al., 2018). Here, the species concept most frequently adopted is that of Virtual Taxa (VT; Öpik et al., 2010), for which most studies have shown moderate diversity of approximately 10–20 VT per area. For example, in Iceland, Norrbotten (Sweden), and Lapland (Finland), authors found species within the genera Glomeraceae, but also a few Acaulosporaceae, Claroideoglomeraceae and Diversisporaceae (Appoloni et al., 2008; Öpik et al., 2013; Davison et al., 2018; García de León et al., 2018). Of those identified to VT, the MaarjAM database showed that 9, 19 and 22 AM fungal VT have been found in these areas, respectively.

Overall, although studies suggest that the presence of AM fungal symbiosis is low in the Arctic at the level of both plant species (Allen et al., 2006; Newsham et al., 2017) and individuals (Newsham et al., 2017), cases of high root colonization by AM fungal structures have still been reported (Olsson et al., 2004; Ormsby et al., 2007), as have several species of AM fungi (Greipsson et al., 2002; Öpik et al., 2013). It thus appears that there is still much to learn about AM fungal diversity in the Arctic and how it relates to plant species identity.

A particular knowledge gap relates to the impact and relative importance of plant species identity in structuring AM fungal communities, and how the influence of plant species identity varies along environmental gradients (Helgason & Fitter, 2009; Vályi et al., 2016). Elevational gradients are convenient to address this topic, because they show strong variation in the abiotic and biotic environment (e.g. in temperature, resource availability and vegetation structure) at fine spatial scales (Körner, 2007). Simultaneously, AM fungal richness, root colonization and spore density have been found to decrease with increasing elevation (Gai et al., 2012). Even though many AM fungal species are able to colonize a large range of plant species, there is evidence that plant identity can leave a detectable imprint on AM fungal community composition (Vandenkoornhuyse et al., 2003; Hausmann & Hawkes, 2009; Sepp et al., 2019; Davison et al., 2020). Additionally, studies have found that elevational gradients may add a further signature to plant–AM fungal associations: Li et al. (2014) reported that AM fungal communities in two plant species were more similar at intermediate elevations than at low or high elevations, respectively. Whether Arctic AM fungal communities respond to such environmental gradients remains to be resolved.

In order to study how variation in environmental conditions and plant species identity influence the distribution of AM fungi within the High Arctic, we used an elevational gradient located in the Zackenberg valley, Northeast Greenland. We identified AM fungi by amplicon-sequencing the roots of 19 Arctic plant species, sampled at 18 locations along the elevational gradient. At each sampling location, we characterized the abiotic and biotic environment. We targeted the following questions:

1. What is the species richness and composition of AM fungal communities in the High Arctic?

2. What are the relative and joint impacts of elevation and plant species in explaining the presence, richness, composition and network structure of AM fungal communities?

3. How do the abiotic and biotic factors varying along elevation influence AM fungal occurrence, richness and community composition?

Based on global patterns in the structuring of mutualistic associations, we expected Arctic AM fungal species to be generalists (Schleuning et al., 2012), able to live in a broad range of habitats, to be globally widespread (Orme et al., 2006) and to lack unique adaptation to the Arctic or local environment (e.g. Öpik et al., 2006; Davison et al., 2015). Based on records from the MaarjAM database (maarjam.ut.ee), we expected to find the species richness to be in the range of 5–25 VT.

中文翻译：

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海拔高度和植物物种特性共同塑造了北极高海拔地区多样化的丛枝菌根真菌群落

介绍

丛枝菌根 (AM) 真菌是在大多数陆生植物根系中发现的重要根系共生体（van der Heijden等人，2015 年）。丛枝菌根真菌可对植物适应性（Klironomos等人，2000 年）、植物群落组成（Hartnett & Wilson，  1999 年；van der Heijden等人，2008 年）和生态系统功能（van der Heijden等人，2015年）产生重大影响) – 尽管在其他情况下，已发现 AM 真菌在植物根部定殖，对植物几乎没有好处（Cosme等人，2018 年；Wang等人，2021 年、2022 年）。自现代测序技术问世以来，AM 真菌的全球多样性模式已得到越来越多的了解（Kivlin等人，2011 年；Davison等人，2015 年，2018 年）。尽管许多 AM 真菌物种在全球分布（Davison等人，2015 年），但其他物种仅限于特定的栖息地或地理区域（Veresoglou等人，2013 年；Davison等人，2016 年）并且可能表现出显着的生态位分化，特别是与温度和土壤 pH 值的关系（Davison等人., 2021 年）。然而，对于包括北极在内的一些主要陆地区域，AM 真菌多样性及其驱动因素仍然知之甚少（Öpik等人，2013 年；Pärtel等人，2017 年），尽管北极的 AM 真菌群落与其他地区不同其他领域 (Vasar et al ., 2022 )。

由于北极地区对于储存大部分地球碳 (C) 储量至关重要（Mack等人，2004 年），因此了解这些储量的潜在驱动因素非常重要。菌根真菌，包括 AM 真菌，可能通过影响植物光合速率、光合产物的使用和生物量中的碳储存来促进碳循环和储存（Read & Perez-Moreno，  2003 年；Godbold等人，2006 年；Soudzilovskaia等人., 2015a , b ; Deckmyn等人, 2020 )。北极地区目前正在经历全球最高的气候变化率（IPCC，  2014)，因此我们迫切需要了解 AM 真菌在寒冷气候中的一般多样性和作用，以及当地 AM 真菌群落的环境驱动因素。

与温带环境相比，北极环境中 AM 真菌的区域物种库、类群的相对丰度以及沿环境梯度的 AM 真菌群落结构的研究很少。北极的现有研究通常依赖于土壤样本的孢子形态学鉴定（寄主植物身份存在一些不确定性）或根定植量化（几乎没有提供有关 AM 真菌物种多样性的信息）（尽管参见 Appoloni等人，2008 年） ;Öpik等人，2013 年；戴维森等人，2018 年）。

在加拿大北极地区沿纬度梯度的一项研究中，Olsson等人。( 2004 ) 在最南端发现了高 AM 真菌根定植，但在最北端几乎没有定植，尽管存在假定的 AM 植物。然而，最北部的地点确实维持了更高程度的非菌根植物。恶劣环境中非菌根和兼性菌根植物的丰度较高是一种常见模式（Bueno等人，2017 年）。对于北极，AM 植物的低流行率提出了几种解释，正如 Kytöviita（2005 年）所回顾的那样). 一种假设将这种模式归因于历史，因为北极生态系统的演变相对较晚，冰川消融仅 3000-8000 年。另一个观点是，具有较高降解能力的菌根群落，如杜鹃花菌根或外生菌根，将为植物提供更大的益处，因此更为普遍。最后，Kytöviita ( 2005 ) 提出，AM 真菌的低流行率可能是 AM 真菌对寒冷环境中养分吸收的适应不良的结果。从北极植物的角度来看，维持 AM 真菌伙伴的成本可能会超过收益。关于根部的 AM 真菌定植，来自北极的几项研究仍然发现定植水平范围为 11-36% 的根长定植（Allen等人，2006 年），通过 27-51% 的根长定植（Ormsby等人，2007 年），到 37-85% 的根长定植（Olsson等人，2004 年）。Newsham等人。( 2017 ) 研究了 11 种植物的 102 种植物，并在 41 种植物个体中发现了类似于 AM 真菌的结构。

迄今为止，很少有研究调查北极 AM 真菌的多样性。由于这些研究主要基于从混合根际采集的土壤样本，AM 真菌多样性与寄主植物身份之间的联系存在一些不确定性。例如，Varga等人。( 2015 ) 使用土壤样品的孢子形态分型发现 18 种孢子形态，Greipsson等人。( 2002 ) 使用陷阱培养和孢子形态分型发现了 11 种形态。一些基于 DNA 的根和土壤 AM 真菌数据存在于冰岛、斯瓦尔巴群岛和斯堪的纳维亚北极地区（Appoloni等人，2008 年；Öpik等人，2013 年；Davison等人., 2015 , 2018 ; García de León等人，2018 年）。在这里，最常采用的物种概念是虚拟分类群 (VT; Öpik et al ., 2010 )，大多数研究表明每个区域大约有 10-20 VT 的适度多样性。例如，在冰岛、Norrbotten（瑞典）和拉普兰（芬兰），作者发现了 Glomeraceae 属内的物种，还有一些 Acaulosporaceae、Claroideoglomeraceae 和 Diversisporaceae（Appoloni等人，2008 年；Öpik等人，2013 年；戴维森）等人，2018 年；García de León等人., 2018 年）。在那些被确定为 VT 的人中，Maarj AM数据库显示在这些地区分别发现了 9、19 和 22 AM 真菌 VT。

总体而言，尽管研究表明在北极地区，AM 真菌共生的存在在植物物种（Allen等人，2006 年；Newsham等人，2017 年）和个体（Newsham等人，2017 年）水平上都很低， AM 真菌结构的高根定植案例仍有报道（Olsson等人，2004 年；Ormsby等人，2007 年），AM 真菌的几种物种也是如此（Greipsson等人，2002 年；Öpik等人，2013 年）). 因此，关于北极的 AM 真菌多样性及其与植物物种特性的关系，似乎还有很多需要了解的地方。

一个特定的知识缺口涉及植物物种特性在构建 AM 真菌群落中的影响和相对重要性，以及植物物种特性的影响如何随环境梯度变化（Helgason 和 Fitter，  2009 年；Vályi等人，2016 年）。海拔梯度很容易解决这个问题，因为它们在精细的空间尺度上显示出非生物和生物环境（例如温度、资源可用性和植被结构）的强烈变化（Körner，  2007）。同时，已发现 AM 真菌丰富度、根系定植和孢子密度随着海拔升高而降低（Gai等人，2012 年）). 尽管许多 AM 真菌物种能够在大范围的植物物种中定殖，但有证据表明植物身份可以在 AM 真菌群落组成上留下可检测的印记（Vandenkoornhuyse等人，2003 年；Hausmann 和 Hawkes，  2009 年；Sepp等人., 2019 年；戴维森等人，2020 年）。此外，研究发现，海拔梯度可能为植物-AM 真菌关联增加进一步的特征：Li等人。( 2014) 报告说，两种植物中的 AM 真菌群落在中等海拔高度分别比在低海拔或高海拔处更相似。北极 AM 真菌群落是否对这种环境梯度有反应仍有待解决。

为了研究环境条件和植物物种特性的变化如何影响高北极地区 AM 真菌的分布，我们使用了位于格陵兰东北部扎肯伯格山谷的海拔梯度。我们通过对 19 种北极植物的根进行扩增子测序来鉴定 AM 真菌，这些植物在沿海拔梯度的 18 个位置采样。在每个采样点，我们都对非生物和生物环境进行了描述。我们针对以下问题：

1. 高北极地区 AM 真菌群落的物种丰富度和组成是什么？

2. 海拔和植物物种在解释 AM 真菌群落的存在、丰富度、组成和网络结构方面的相对和联合影响是什么？

3. 沿海拔变化的非生物和生物因素如何影响 AM 真菌的发生、丰富度和群落组成？

基于互惠关系结构的全球模式，我们预计北极 AM 真菌物种将成为多面手（Schleuning等人，2012 年），能够生活在广泛的栖息地，在全球范围内广泛传播（Orme等人，2006 年） ) 并且缺乏对北极或当地环境的独特适应性 (eg Öpik et al ., 2006 ; Davison et al ., 2015 )。根据 Maarj AM数据库 (maarjam.ut.ee) 的记录，我们预计物种丰富度在 5–25 VT 范围内。