DNA barcoding evaluation and implications for phylogenetic relationships in Lauraceae from China

Lauraceae are an important component of tropical and subtropical forests and have major ecological and economic significance. Owing to lack of clear-cut morphological differences between genera and species, this family is an ideal case for testing the efficacy of DNA barcoding in the identification and discrimination of species and genera. In this study, we evaluated five widely recommended plant DNA barcode loci matK, rbcL, trnH–psbA, ITS2 and the entire ITS region for 409 individuals representing 133 species, 12 genera from China. We tested the ability of DNA barcoding to distinguish species and as an alternative tool for correcting species misidentification. We also used the rbcL+matK+trnH–psbA+ITS loci to investigate the phylogenetic relationships of the species examined. Among the gene regions and their combinations, ITS was the most efficient for identifying species (57.5%) and genera (70%). DNA barcoding also had a positive role for correcting species misidentification (10.8%). Furthermore, based on the results of the phylogenetic analyses, Chinese Lauraceae species formed three supported monophyletic clades, with the Cryptocarya group strongly supported (PP = 1.00, BS = 100%) and the clade including the Persea group, Laureae and Cinnamomum also receiving strong support (PP = 1.00, BS = 98%), whereas the Caryodaphnopsis–Neocinnamomum received only moderate support (PP = 1.00 and BS = 85%). This study indicates that molecular barcoding can assist in screening difficult to identify families like Lauraceae, detecting errors of species identification, as well as helping to reconstruct phylogenetic relationships. DNA barcoding can thus help with large-scale biodiversity inventories and rare species conservation by improving accuracy, as well as reducing time and costs associated with species identification.

樟科（Lauraceae）是热带与亚热带森林的重要组成类群，兼具重要的生态与经济价值。由于该科内各属与物种间缺乏明确的形态差异，樟科成为检验DNA条形码（DNA barcoding）在物种与属鉴定及区分中效能的理想研究对象。本研究针对中国境内12属133种共计409份样本，对5个广泛推荐的植物DNA条形码基因座——matK、rbcL、trnH–psbA、ITS2及完整ITS区——开展了评估。本研究验证了DNA条形码区分物种的能力，并将其作为纠正物种误鉴定的替代工具进行了测试。此外，本研究还通过rbcL+matK+trnH–psbA+ITS组合基因座，对受试物种的系统发育关系进行了探究。在单个基因区域及其组合中，ITS区段在物种鉴定（成功率57.5%）与属级区分（成功率70%）方面表现最优。DNA条形码在纠正物种误鉴定方面同样发挥了积极作用（校正率达10.8%）。此外，基于系统发育分析结果，中国樟科物种可划分为三个得到支持的单系支：厚壳桂类群（Cryptocarya group）获得极强支持（后验概率PP=1.00，自举支持率BS=100%）；包含鳄梨类群（Persea group）、月桂族（Laureae）及樟属（Cinnamomum）的支系同样得到较强支持（PP=1.00，BS=98%）；而琼楠属-新樟属（Caryodaphnopsis–Neocinnamomum）支系仅获得中等支持（PP=1.00，BS=85%）。本研究表明，分子条形码技术可助力樟科这类形态鉴定难度较高的类群的物种筛查、物种鉴定误差的检出，同时也有助于系统发育关系的重建。因此，DNA条形码可通过提升物种鉴定的准确性、缩短鉴定耗时并降低相关成本，为大规模生物多样性普查及珍稀物种保护工作提供有力支撑。