Plant DNA barcode library for native flowering plants in the arid region of northwestern China

DNA barcoding is a well-established tool for rapid species identification and biodiversity monitoring. A reliable and traceable DNA barcode reference library with extensive coverage is necessary but unavailable for many geographical regions. The arid region in northwestern China, a vast area of about 2.5 million km(2), is ecologically fragile and often overlooked in biodiversity studies. In particular, DNA barcode data from the arid region in China are lacking. We develop and evaluate the efficacy of an extensive DNA barcode library for native flowering plants in the arid region of northwestern China. Plant specimens were collected, identified and vouchered for this purpose. The database utilized four DNA barcode markers, namely rbcL, matK, ITS and ITS2, for 1816 accessions (representing 890 species from 385 genera and 72 families), and consisted of 5196 barcode sequences. Individual barcodes varied in resolution rates: species- and genus-level rates for rbcL, matK, ITS and ITS2 were 79.9%-51.1%/76.1%, 79.9%-67.2%/88.9%, 85.0%-72.0%/88.2% and 81.0%-67.4%/84.9%, respectively. The three-barcode combination of rbcL + matK + ITS (RMI) revealed a higher species- and genus-level resolution (75.5%/92.1%, respectively). A total of 110 plastomes were newly generated as super-barcodes to increase species resolution for seven species-rich genera, namely Astragalus, Caragana, Lactuca, Lappula, Lepidium, Silene and Zygophyllum. Plastomes revealed higher species resolution compared to standard DNA barcodes and their combination. We suggest future databases include super-barcodes, especially for species-rich and complex genera. The plant DNA barcode library in the current study provides a valuable resource for future biological investigations in the arid regions of China.