DNA Barcoding the Canadian Arctic Flora: Core Plastid Barcodes (rbcL + matK) for 490 Vascular Plant Species

Accurate identification of Arctic plant species is critical for understanding potential climate-induced changes in their diversity and distributions. To facilitate rapid identification we generated DNA barcodes for the core plastid barcode loci (rbcL and matK) for 490 vascular plant species, representing nearly half of the Canadian Arctic flora and 93% of the flora of the Canadian Arctic Archipelago. Sequence recovery was higher for rbcL than matK (93% and 81%), and rbcL was easier to recover than matK from herbarium specimens (92% and 77%). Distance-based and sequence-similarity analyses of combined rbcL + matK data discriminate 97% of genera, 56% of species, and 7% of infraspecific taxa. There is a significant negative correlation between the number of species sampled per genus and the percent species resolution per genus. We characterize barcode variation in detail in the ten largest genera sampled (Carex, Draba, Festuca, Pedicularis, Poa, Potentilla, Puccinellia, Ranunculus, Salix, and Saxifraga) in the context of their phylogenetic relationships and taxonomy. Discrimination with the core barcode loci in these genera ranges from 0% in Salix to 85% in Carex. Haplotype variation in multiple genera does not correspond to species boundaries, including Taraxacum, in which the distribution of plastid haplotypes among Arctic species is consistent with plastid variation documented in non-Arctic species. Introgression of Poa glauca plastid DNA into multiple individuals of P. hartzii is problematic for identification of these species with DNA barcodes. Of three supplementary barcode loci (psbA–trnH, psbK–psbI, atpF–atpH) collected for a subset of Poa and Puccinellia species, only atpF–atpH improved discrimination in Puccinellia, compared with rbcL and matK. Variation in matK in Vaccinium uliginosum and rbcL in Saxifraga oppositifolia corresponds to variation in other loci used to characterize the phylogeographic histories of these Arctic-alpine species.准确鉴定北极植物物种，对于理解气候诱导下其多样性与分布的潜在变化至关重要。为实现快速物种鉴定，我们为490种维管植物（vascular plant）的核心质体条形码基因座（core plastid barcode loci）生成了DNA条形码（DNA barcode），该类群涵盖近半数加拿大北极植物区系，以及加拿大北极群岛植物区系的93%。rbcL与matK的序列获取率分别为93%与81%，且从腊叶标本（herbarium specimen）中获取rbcL序列的成功率高于matK，二者分别为92%与77%。基于联合rbcL+matK数据的距离法与序列相似性分析，可区分97%的属、56%的物种以及7%的种下类群（infraspecific taxa）。单属采样物种数与该属物种分辨率百分比之间存在显著负相关关系。我们针对采样量最大的10个属——薹草属（Carex）、葶苈属（Draba）、羊茅属（Festuca）、马先蒿属（Pedicularis）、早熟禾属（Poa）、委陵菜属（Potentilla）、碱茅属（Puccinellia）、毛茛属（Ranunculus）、柳属（Salix）、虎耳草属（Saxifraga）——详细阐述了其条形码变异特征，并结合系统发育关系与分类学背景展开分析。上述类群中核心条形码基因座的物种区分率从柳属的0%到薹草属的85%不等。多个类群的单倍型（haplotype）变异并不符合物种边界，其中包括蒲公英属（Taraxacum）：该属北极物种间的质体单倍型分布格局，与非北极物种中已报道的质体变异特征相一致。灰早熟禾（Poa glauca）的质体DNA渐渗（introgression）至哈特兹早熟禾（P. hartzii）的多个个体中，这使得利用DNA条形码鉴定这两个物种存在一定困难。针对早熟禾属与碱茅属的部分类群，我们额外扩增了3个辅助条形码基因座：psbA–trnH、psbK–psbI与atpF–atpH。相较于rbcL与matK，仅atpF–atpH提升了碱茅属的物种区分效果。越橘（Vaccinium uliginosum）的matK序列变异与对叶虎耳草（Saxifraga oppositifolia）的rbcL序列变异，分别与用于解析这些北极-高山物种系统地理历史的其他基因座的变异特征相一致。