J Syst Evol ›› 2021, Vol. 59 ›› Issue (6): 1139-1141.

• Editorial •

### Plant diversity and ecology on the Qinghai–Tibet Plateau

Jian-Quan Liu1, Jia-Liang Li1, and Yang-Jun Lai2

1. 1 Key Laboratory of Bio‐Resource and Eco‐Environment of the Ministry of Education, College of Life Sciences, Sichuan University, Chengdu 610065, China
2 State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany Chinese Academy of Sciences, Beijing 100093, China
• Received:2021-11-28 Accepted:2021-11-28 Online:2021-11-28 Published:2021-11-01

Abstract:

The Qinghai–Tibet Plateau (QTP) comprises a platform (sometimes called the Qinghai–Tibet Plateau sensu stricto), the Himalayas, and Hengduan Mountains (Liang et al., 2018; Mao et al., 2021). The latter two parts and adjacent highlands are also called the Pan-Himalaya. Numerous plants are distributed there with many endemic species, probably because of the high diverse landscapes created by continuous geological and climatic activities (Favre et al., 2015; Mao et al., 2021). As the well known biodiversity hotspot of the alpine plants in the world (Sun et al., 2017), many studies have been conducted on evolutionary origin and ecological adaptation of those species occurring in the QTP (e.g., Wen et al., 2014, 2019; Zhang et al., 2019). In the present special issue, we collected 15 related papers on this topic. Among them, two are invited reviews. Mao et al. (2021) provide a comprehensive review of evolutionary origin of species diversity on the QTP. Especially, they outlined major disputes and likely causes in this research topic, including circumscribing and naming the QTP, the QTP uplifts, dating of molecular phylogenetic trees, non-causal correlations between QTP uplifts and species diversification and the unified ice sheet. The authors also summarized genomic advancements related to high-altitude adaptation of both plants and animals. Tong et al. (2021) reviewed the reproductive strategies of animal-pollinated alpine plants on the QTP, involving pollination system, pollen limitation, self-pollination, and sexual system. In this region, 95.4% of animal-pollinated plants are pollinated by insects (i.e., bees, moths, butterflies, and flies) with only 4% by vertebrates (i.e., bats and birds). Self-pollination through self-compatibility shift from outcrossing has become an effective reproductive strategy to overcome pollen limitation in alpine plants. The other 13 research papers aimed to address origin and adaptation of alpine flora involving three major lines of evidence: genomics, ecology, and paleobotany. We hope that the collection of these papers will increase our understanding of the origin, speciation, and adaptation of alpine species on the QTP.

## 1 Genomics: Phylogeny, Speciation, and High-Altitude Adaptation

Because of the decreasing cost, it is becoming easy to obtain numerous homologous sequences to construct the high-solved and well supported phylogeny for diverse genera. Here, we collect three related case studies. A phylogenomic analysis using nuclear and plastome genes by Zhou et al. (2021) was conducted for the peonies (Paeoniaceae, Paeonia L.). Their results suggest that the Paeoniaceae is a relict and ancient lineage with a divergence from the close relatives in the late Cretaceous. The common ancestor of the extant peonies may have survived in the Pan-Himalaya during the ice ages. The further diversification evolved into two subgenera and seven sections that are widespread in the Northern Hemisphere. In addition, climatic oscillations since the late Pliocene promoted polyploidy speciation including both allotetraploids and autotetraploids. Ye et al. (2021) constructed phylogeny of two species-rich bamboo genera (Poaceae) in the Himalayas and Hengduan Mountains based on simplified genome sequences. They revealed the high discordance of gene topologies and extensive hybridization between identified lineages. They conclude that reticulate evolution seems to be common during species diversification of these two genera. Chen et al. (2021) constructed phylogeny and diversification of the subtribe Gentianinae (Gentianaceae) in the QTP and adjacent regions based on transcriptomes. Similarly, they found the inconsistent phylogenetic relationships of a few identified clades based on nuclear and plastome genes. Both hybridization and incomplete lineage sorting may account for these discordant relationships. Especially, they found many gene duplication events in several phylogenetic nodes. Therefore, hybridization and gene duplication might have together facilitated species diversification of this subtribe in the alpine regions of the QTP in addition to the previously assumed geographic isolation.

The diverse habitats of the QTP provide chances for fast species divergence and adaptive evolution. Similarly, in this issue, we publish three related works. Based on genomic data, Li et al. (2021b) examined the cryptic divergence in an alpine ginger Roscoea tibetica Batalin (Zingiberaceae) in Hengduan Mountains of the QTP. They identified two deeply diverged lineages. However, gene flow occurred because of the second contact of these two lineages after the initial divergence. For two aspens occurring in the high- and low-altitude regions, however, Li et al. (2021a) revealed continuous gene flow since the initial divergence. A clear hybrid zone was recovered in the contacting region of the two species. In addition, for the high-altitude species, many genes related to the high-altitude adaptation were found to experience positive evolution. Therefore, natural selection may also play an important role during the divergence history of these two species. Such a strong selection posted by the arid habitat of the QTP may also exist for the lower plants. Zhang et al. (2021) used transcriptome data to examine the adaptive evolution of one high-altitude algae. Compared with the closely related low-altitude algae, a few genes involved in the antioxidative response, DNA repair, and translational/post-translational modifications were found to show positive evolution in the high-altitude species, possibly because of strong abiotic stresses, for example, extensive UV-B radiation on the QTP. All of these case studies suggest that geographic isolation, natural selection (especially high-altitude stresses), and hybridization may have together promoted the speciation of plants occurring there.