1 INTRODUCTION
Angiosperms can reproduce not only through sexual reproduction, but also
simultaneously with asexual reproduction. In asexual reproduction, the
clonal growth of the organisms is the most important pathway (Geremew et
al., 2018; Mandel et al., 2019; Sandén et al., 2020). It is estimated
that ~80% of angiosperms can engage in clonal growth
(Wang et al., 2010; Geremew et al., 2018; Wang et al., 2018a). Clonal
plants general occupy dominant positions in forests, grasslands,
wetlands, deserts, and other habitats, can expand their living space
through clonal growth, and exhibit more morphological plasticity through
clonal ramets. Meanwhile, clonal plants have a greater capacity to
utilize resources in adapting to heterogeneous environments, and play a
critical role in the maintenance of ecosystems (Kartzinel et al., 2015;
Van Drunen et al., 2015; Wang et al., 2018a). Therefore, the growth
characteristics and spatial structure of clonal plants have been a topic
of intense interest in ecology and evolution research (Chen et al.,
2016; Geremew et al., 2018; Wang et al., 2018a).
If the clonal plant has more buds, it would have relatively higher ratio
of clonal growth, as which is the basis of the germination and
development of ramets (Wang et al., 2016). Usually, clonal growth has
significant impacts on the spatial structures and level of diversity of
plant populations. Some researchers showed the clonal plants can form
spatially diverse genetic structures and different clonal diversity
plaques, at even smaller spatial scales (Wang et al., 2018a). Meanwhile,
asexual reproduction can decrease the level of genetic diversity of
population (Zhang & Zhang, 2006) and influence and determine the
adaptability of plants to specific environments during the evolutionary
process (van Drunen et al., 2015; Pirog et al., 2017). Nevertheless, the
spatial structures and diversity of clonal plants may be affected by
biological and abiotic factors such as habitat heterogeneity, growth
strategies, and seedling recruitment patterns (Kartzinel et al., 2015;
Sandén et al., 2020). So, analyzing spatial genetic structures and
clarifying the genetic patterns of different patches of clonal plants
might be of great significance for exploring the formation, maintenance,
and decline mechanisms of clonal plant populations (Kartzinel et al.,
2015; Wang et al., 2018b; Mandel et al., 2019).
The perennial herb Clintonia udensis of the genusClintonia Raf, which is widely distributed across Eastern Asia,
has two cytotypes that include diploid (2n = 14) and tetraploid (4n =
28) (Wang et al., 2008; Wang et al., 2010; Wang et al., 2011; He et al.,
2017). Although the diploid is continuously and extensively distributed
from Yunnan Province of South China to Heilongjiang Province in Northern
China, the tetraploid has only a limited presence in these areas,
encompassing the Jade Dragon Snow Mountains in Yunnan Province,
Shennongjia in Hubei Province, and the Hualongshan Mountains in Shaanxi
Province, which overlap or are adjacent to the diploid distribution
areas.
The morphological characteristics of C. udensis leaves, fruits,
inflorescences, and pollens presented complex diversity between
different populations; however, no significant differences were found
between the different ploidies. The seed size of this perennial herb is
significantly different between the diploid and tetraploid (Wang &
Zhao, 2007). Field investigations revealed that the color of the scape
in the diploid is brown, while that is green in the tetraploid (Bai et
al., 2009), and both the diploid and tetraploid have a hard rhizome.C. udensis not only asexually reproduces through axillary buds
but also generates seeds through sexual reproduction. In wild habitats,
diploids and tetraploids can generally produce seedlings and grow in
decayed fallen wood and moist mossy ground; thus, C. udensis is a
facultative plant (Liu et al., 2016).
However, the trade-off between the sexual reproduction and asexual
reproduction of plants is influenced by many factors. Changes in the
ratios between sexual reproduction and asexual reproduction in different
habitats are primarily determined by the modification of ecological
factors such as light, water, and temperature (Huang et al., 2018; Wang
et al., 2018; Alonso-Marcos et al., 2019; Wang et al., 2020). Under
harsher environments, the ratio of asexual reproduction is increased,
i.e. the occurrence and frequency of clonal plants might be higher under
stressed conditions (Van Drunen et al., 2015; Wang et al., 2018a; Ma et
al., 2019). In the Hualongshan Mountains, the diploid of C.
udensis grows mainly in areas at 2450 m on the south slopes, while the
tetraploid grows in areas at 1900 m on the north slopes which are
different from the diploid surroundings. The vertical distribution
pattern of different ploidies would be an ideal natural material for
studying the clonal growth characteristics, clonal structures, and
ecological adaptability of C. udensis .
According the previous study, it is an autotetraploid for the tetraploid
of C. udensis (Wang & Zhao, 2007). The doubled genome of
autoploid may imply higher potential and broader adaptability than its
ancestral diploid (Wan et al., 2018). Within the autotetraploid with
four same chromosomes, it can be expected to a certain extent having a
larger effective population size. Thus, the gene diversity level of
tetraploid should be higher than that of diploid (Brown et al., 2000; Li
et al., 2008; Wang et al., 2016). However, these were mainly obtained
from the inter-polyploidy of plants. For the intra-polyploidy, the
similar pattern would be occurred between different polyploid still is
uncertain.
In this study, we explored the clonal spatial structures of diploid and
tetraploid C. udensis populations of the Hualongshan Mountains
and verified the genetic diversity distribution pattern between
intra-polyploid through field investigations and Simple Sequence Repeat
(SSR) molecular markers. Our main aims were to: a) analyze the clonal
diversity, genetic differentiation, and spatial
clonal configurations of different
ploidies; and b) reveal rationales
for the differences in spatial structures between diploids and
tetraploids. These results are likely to further enhance our
understanding of the ecological adaptation characteristics of different
intra-ploidies, provide insights toward enriching the spatial structures
of clonal plants, and establish a foundation for elucidating the
adaptation mechanisms of clonal plants to their environments.