Abstract: [Objective] The nrDNA and cpDNA were used to determine the genetic differentiation between Haloxylon ammodendron and H. persicum, two species with sympatric distribution in China. The species discrimination ability of each single fragment and its combination of two genes was compared. In addition, we investigated the degree of ecological niche divergence and its impact on species evolution. Our study could provide important basic information for the understanding of phylogeny and phylogeography of H. ammodendron and H. persicum.[Method] We sampled 30 H. ammodendron and H. persicum individuals from the southern Gurbantunggut Desert. We performed sequence analyses using two nuclear gene sequences (ITS2, ITS1-ITS4) and three cpDNA non-coding regions (trnS-trnG, rps4 and trnV). The distance method (based on Kimura 2-parameter model) was used to analyze genetic differentiation of the two species. Bayesian method were employed to explore molecular phylogeny among individuals. Four method (genetic distances, phylogenetic trees, BLAST, and character-based method) were employed to examine the species discrimination ability of each single fragment and its combination of two genes. On this basis, we used ecological niche analysis software to calculate the ecological niche divergence of H. ammodendron and H. persicum.[Result] 1) For H. ammodendron and H. persicum, the total length of the two combined ITS sequences was all 1 117 bp, the average content of G + C was 34.74% and 34.82%, and the number of information sites accounted for 2.33% and 1.43%, respectively. The total length of the three combined cpDNA non-coding regions are all 2 344 bp, and the average content of G + C was 59.62% and 59.39%, and information sites accounted for 0.68% and 0.43%, respectively. 2) Two distinct clades of H. ammodendron and H. persicum was detected in the two phylogenetic trees. 3)Based on ITS and cpDNA sequences, the minimum interspecific genetic distance of the two species was greater than the maximum intraspecific genetic distance, and an obvious interspecific and intraspecific barcoding gap was found. The sequences combination of ITS and cpDNA can therefore be used as DNA barcode for identification of H. ammodendron and H. persicum. 4) Regarding the species discrimination rate, as calculated by the four method showed:the rate of each single ITS fragment and its combination was all 100%; for trnS-trnG, trnV and its combination, the rate was all 100%; for rps4 and its combination of trnS-trnG or trnV, the identification rate was all 0%. The sequence combinations of trnS-trnG+trnV+rps4 was 100%. 5) The observed values of ecological niche parameters (D-value and I-value) and the simulated values of the identity test were concentrated around 0.65 and 0.90 respectively, indicating a similar ecological niche in H. ammodendron and H. persicum.[Conclusion] Using ITS and cpDNA sequences, we revealed a clear genetic differentiation and molecular phylogeny relationship between individuals of H. ammodendron and H. persicum. Both the ITS and cpDNA sequence combinations could be used as DNA barcode sequences to identify H. ammodendron and H. persicum. There was no evidence for an ecological niche differentiation between H. ammodendron and H. persicum, and ecological factors did not play a significant role in the divergence and evolution of the two species, and the two species were likely to have similar evolutionary history. The conclusion of this study provide an important theoretical basis and data support for studying the phylogenetics, genetics and evolution of H. ammodendron and H. persicum.

Key words: Haloxylon ammodendron, Haloxylon persicum, interspecific differentiations, ITS sequences, cpDNA sequences, molecular phylogenetic relationships, ecological niche differentiation