1 | INTRODUCTION
The Qinling Mountains are a natural boundary between China’s north and south stretching over 1,600 kilometers in east-west direction, which formed approximately during the Mesozoic and Cenozoic (Zhang, Cawood, Dong, & Wang, 2019). Due to most of the mountains are higher than 2000 meters and diversified topography, the mountains form an important boundary and are home to a diverse variety of wildlife, many of which are rare on earth. Recent phylogeographic and population genetic studies have showed that the Qinling Mountains probably served as a barrier for wild plants and animals, such as Paeonia (Yuan, Cheng, & Zhou, 2012; Xu et al., 2019), Sinopodophyllum hexandrum (Liu, Yin, Liu, & Li, 2014), Actinidia chinensis (Wang, Liao, & Li, 2018), and reptile (Yan, Wang, Chang, Ji, & Zhou, 2010; Huang et al., 2017). However, contrary to these studies, some other results suggested that the Qinling Mountains have no obvious impact on genetic structure (Zhan, Li, & Fu, 2009). This discrepancy may depend on the mechanisms by which the species survive and disperse, as well as how they respond to the surrounding environment.
Over the past few decades, habitat fragmentation occurred in the Qinling Mountains due to human’s large-scale forest logging, building of roads and urbanization. The habitat fragmentation has resulted in low genetic diversity and population structure not only for plants but also for other species, including golden snub-nosed monkey and giant panda (Huang et al., 2016; Ma et al., 2018). For most plants, habitat fragmentation often reduces gene flow and genetic diversity by disrupting the movement of seed (Sebbenn et al., 2011; Lander, Harris, Cremona, & Boshier, 2019; Ony et al., 2020). It was reported that seed dispersal play important roles in determining genetic variation patterns in fragmented landscapes (Browne & Karubian, 2018).
Cymbidium faberi is a terrestrial orchid enlisted in Appendix of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). It is a species with a distribution from Nepal, Northeast India to south of China, north to the Qinling Mountains (Flora of China Editorial Committee, 2009). It grows on rocky and scrubby slopes, usually in Quercus variabilis forests at altitudes of 700 – 3000 m. Like many other cymbidium species, C. faberi is a self-compatible allogamous species that depends on insect pollinators such as honeybees for seed production (Suetsugu, 2015). The dust-like seeds are often produced in huge numbers, and they usually lack endosperm and the embryo is undifferentiated. The empty space inside seeds and the trichomes on the endocarp make them well suited for wind dispersal (Arditti & Ghani, 2000; Gamarra, Ortúñez, Cela, & Merencio, 2018). Thus, topographic feathers such as the Andes seem not to have been much of a barrier to the dispersal of lowland epiphytic orchidsCycnoches (Perez-Escobar et al., 2017). However, a recent study of an epiphytic orchid found a seed dispersal barrier between northwestern and southeastern populations within Costa Rica (Trapnell et al., 2019).
To date, whether geological barriers such as the Qinling Mountains and habitat fragmentation in the areas have an impact on C. faberiremains unknown. Here, we analyzed 271 samples based on maternally inherited two chloroplast DNA sequences to evaluate the impact of Qinling Mountains and habitat fragmentation on genetic structure ofC. faberi . The aims of this paper are: (1) to assess the level of genetic variation and spatial genetic structure of C. faberi in the Qinling Mountains; (2) to explore the demographic history ofC. faberi in the Qinling Mountains; and (3) to try to explain the genetic structure based on species seeds dispersal ability and human activity that have influenced it.