Lakes cover large parts of the climatically sensitive Arctic landscape and respond rapidly to environmental change. Arctic lakes have different origins and include the predominant thermokarst lakes, which are small, young and highly dynamic, as well as large, old and stable glacial lakes. Freshwater diatoms dominate the primary producer community in these lakes and can be used to detect biotic responses to climate and environmental change. We used specific diatom metabarcoding on sedimentary DNA, combined with next-generation sequencing and diatom morphology, to assess diatom diversity in five glacial and 15 thermokarst lakes within the easternmost expanse of the Siberian treeline ecotone in Chukotka, Russia. We obtained 163 verified diatom sequence types and identified 176 diatom species morphologically. Although there were large differences in taxonomic assignment using the two approaches, they showed similar high abundances and diversity of Fragilariceae and Aulacoseiraceae. In particular, the genetic approach detected hidden within-lake variations of fragilarioids in glacial lakes and dominance of centric Aulacoseira species, whereas Lindavia ocellata was predominant using morphology. In thermokarst lakes, sequence types and valve counts also detected high diversity of Fragilariaceae, which followed the vegetation gradient along the treeline. Ordination analyses of the genetic data from glacial and thermokarst lakes suggest that concentrations of sulfate (SO42−), an indicator of the activity of sulfate-reducing microbes under anoxic conditions, and bicarbonate (HCO3−), which relates to surrounding vegetation, have a significant influence on diatom community composition. For thermokarst lakes, we also identified lake depth as an important variable, but SO42− best explains diatom diversity derived from genetic data, whereas HCO3− best explains the data from valve counts. Higher diatom diversity was detected in glacial lakes, most likely related to greater lake age and different edaphic settings, which gave rise to diversification and endemism. In contrast, small, dynamic thermokarst lakes are inhabited by stress-tolerant fragilarioids and are related to different vegetation types along the treeline ecotone. Our study demonstrated that genetic investigations of lake sediments can be used to interpret climate and environmental responses of diatoms. It also showed how lake type affects diatom diversity, and that such genetic analyses can be used to track diatom community changes under ongoing warming in the Arctic.

中文翻译：

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西伯利亚北极冰川湖和热岩溶湖表层沉积物中硅藻群落组成的遗传和形态学测定

湖泊覆盖了气候敏感的北极景观的大部分区域，并对环境变化做出快速反应。北极湖泊有不同的起源，包括占主导地位的热岩溶湖泊，这些湖泊规模小、年轻且充满活力，也包括大型、古老和稳定的冰川湖。淡水硅藻在这些湖泊中占主要生产者群落的主导地位，可用于检测对气候和环境变化的生物反应。我们在沉积 DNA 上使用特定的硅藻元条形码，结合下一代测序和硅藻形态，评估俄罗斯楚科奇西伯利亚林线交错带最东端的 5 个冰川湖和 15 个热岩溶湖中的硅藻多样性。我们获得了 163 种已验证的硅藻序列类型，并从形态上鉴定了 176 种硅藻。尽管使用这两种方法在分类学分配上存在很大差异，但它们显示出脆皮科和木耳科的相似的高丰度和多样性。特别是，遗传方法检测到冰川湖中脆弱类植物的隐藏湖内变异和中心 Aulacoseira 物种的优势，而 Lindavia ocellata 使用形态学占主导地位。在热岩溶湖中，序列类型和阀门计数也检测到脆皮科的高度多样性，它们沿着树线的植被梯度变化。对来自冰川湖和热岩溶湖的遗传数据的排序分析表明，硫酸盐 (SO42−) 的浓度是缺氧条件下硫酸盐还原微生物活动的指标，而碳酸氢盐 (HCO3−) 的浓度与周围植被有关，对硅藻群落组成有显着影响。对于热岩溶湖泊，我们还将湖泊深度确定为一个重要变量，但 SO42− 最好地解释了来自遗传数据的硅藻多样性，而 HCO3− 最好地解释了来自阀门计数的数据。在冰川湖中检测到更高的硅藻多样性，这很可能与更大的湖龄和不同的土壤环境有关，这导致了多样化和特有现象。相比之下，小的、动态的热岩溶湖泊居住着耐压的脆性类植物，并且与沿林线交错带的不同植被类型有关。我们的研究表明，湖泊沉积物的遗传调查可用于解释硅藻的气候和环境响应。它还展示了湖泊类型如何影响硅藻多样性，