Background: Subtropical China is a global center of biodiversity and one of the most important refugia worldwide. Mountains play an important role in conserving the genetic resources of species.Liriodendron chinenseis a Tertiary relict tree largely endemic to subtropical China. In this study, we aimed to achieve a better understanding of the phylogeographical pattern ofL. chinenseand to explore the role of mountains in the conservation ofL. chinensegenetic resources.Methods: Three chloroplast regions (psbJ-petA,rpl32-ndhF, andtrnK5’-matK) were sequenced in 40 populations ofL. chinensefor phylogeographical analyses. Relationships among chloroplast DNA (cpDNA) haplotypes were determined using median-joining networks, and genetic structure was examined by spatial analysis of molecular variance (SAMOVA). The ancestral area of the species was reconstructed using the Bayesian binary Markov Chain Monte Carlo (BBM) method according to its geographic distribution and a maximum parsimony (MP) tree based on Bayesian methods.Results: Obvious phylogeographic structure was found inL. chinense. SAMOVA revealed seven groups matching the major landscape features of theL. chinensedistribution area. The haplotype network showed three clades distributed in the eastern, southwestern, and northwestern regions. Separate northern and southern refugia were found in the Wu Mountains and Yungui Plateau, with genetic admixture in the Dalou Mountains and Wuling Mountains. BBM revealed a more ancient origin ofL. chinensein the eastern region, with a west–east split most likely having occurred during the Mindel glacial stage.Discussion: The clear geographical distributions of haplotypes suggested multiple mountainous refugia ofL. chinense. The east–west lineage split was most likely a process of gradual genetic isolation and allopatric lineage divergence when the Nanling corridor was frequently occupied by evergreen or coniferous forest during Late Quaternary oscillations. Hotspots of haplotype diversity in the Dalou Mountains and Wuling Mountains likely benefited from gene flow from the Wu Mountains and Yungui Plateau. Collectively, these results indicate that mountain regions should be the main units for conserving and collecting genetic resources ofL. chinenseand other similar species in subtropical China.

Cinnamomum camphora is a valuable broad-leaf tree indigenous to South China and East Asia and has been widely cultivated and utilized by humans since ancient times. However, owing to its overutilization for essential oil extraction, the Transplanting Big Trees into Cities Program, and over deforestation to make furniture, its wild populations have been detrimentally affected and are declining rapidly. In the present study, the genetic diversity and population structure of 180 trees sampled from 41 populations in South China were investigated with 22 expressed sequence tag-simple sequence repeat (EST-SSR) markers. In total, 61 alleles were harbored across 180 individuals, and medium genetic diversity level was inferred from the observed heterozygosity (Ho), expected heterozygosity (He), and Nei’ gene diversity (GD), which were 0.45, 0.44, and 0.44, respectively. Among the 41 wild populations, C. camphora had an average of 44 alleles, 2.02 effective alleles, and He ranging from 0.30 (SC) to 0.61 (HK). Analysis of molecular variance (AMOVA) showed that 17% of the variation among populations and the average pairwise genetic differentiation coefficient (F_ST) between populations was 0.162, indicating relatively low genetic population differentiations. Structure analysis suggested two groups for the 180 individuals, which was consistent with the principal coordinate analysis (PCoA) and unweighted pair-group method with arithmetic means (UPGMA). Populations grouped to cluster I were nearly all distributed in Jiangxi Province (except population XS in Zhejiang Province), and cluster II mainly comprised populations from other regions, indicating a significant geographical distribution. Moreover, the Mantel test showed that this geographical distance was significantly correlated with genetic distance. The findings of this research will assist in future C. camphora conservation management and breeding programs.

Liriodendron is a Tertiary period relic tree genus with a typical East Asian and North American disjunction distribution pattern. As an angiosperm base group of trees, Liriodendron provides a valuable resource for the study of evolution processes. Here, we reconstruct the phylogeny and population genetic structure of Liriodendron based on the restriction site-associated DNA sequencing (RAD-Seq) of a wide collection of individuals from 16 populations. Our results reveal a clear phylogenetic break between L. chinense and L. tulipifera and obvious genetic divergence between the eastern and western populations of L. chinense, which are consistent with the patterns of geographical distributions. The phylogeographic history and long-term geographical isolation of the genus may be responsible for this pattern. Furthermore, a closer relationship was found between L. tulipifera and the eastern populations of L. chinense, indicating the ancient phylogeny of L. chinense in this area. The results of this study will aid in the development of scientific strategies for the conservation and utilization of the Liriodendron germplasm.

Afforestation plays a critical role in ecosystem restoration and carbon sequestration. However, there continues to be insufficient knowledge about the long-term effects of different tree species on the forest soil in central subtropical China. In this study, five indigenous afforestation tree species commonly used in the region, including Bretschneidera sinensis, Liriodendron chinense, Schima superba, Phoebe bournei, and Cunninghamia lanceolata, were selected to explore their long-term effects on the forest soil. The soil’s physicochemical properties, organic carbon content, enzyme activity, and respiration were investigated. Our results revealed significant differences in the soil physicochemical properties, enzyme activity, organic carbon content, and soil respiration among the different tree species even with the same tree species types. Broad-leaved species, particularly L. chinense and P. bournei, exhibited superior soil physicochemical properties, higher amounts of organic carbon contents, enzyme activity, and soil respiration compared to coniferous species C. lanceolata. Notably, for the two studied evergreen tree species, P. bournei seemed to improve the forest soil quality more than S. superba. Hence, increasing the proportion of broad-leaved tree species may have a beneficial effect on the soil’s physicochemical properties and microecology. Furthermore, considering tree species’ compositions in afforestation will help to optimize soil quality and ecosystem health.

Cinnamomum camphora (L.) J.Presl is a representative tree species of evergreen broad-leafed forests in East Asia and has exceptionally high economic, ornamental, and ecological value. However, the excessive exploitation and utilization of C. camphora trees have resulted in the shrinking of wild population sizes and rare germplasm resources. In this study, we characterized 171 C. camphora trees from 39 natural populations distributed throughout the whole of China and one Japanese population. We investigated genetic diversity and population structure using genome-wide single-nucleotide polymorphism (SNP) identified by genotyping by sequencing (GBS) technology. The results showed the genetic diversity of the C. camphora populations from western China > central China > eastern China. Moreover, the Japanese population showed the highest diversity among all populations. The molecular variance analysis showed 92.03% of the genetic variation within populations. The average pairwise F_ST was 0.099, and gene flow Nm was 2.718, suggesting a low genetic differentiation among populations. Based on the genetic clustering analysis, the 40 C. camphora populations clustered into three major groups: Western China, Central China, and Eastern China + Japan. Eastern China’s population had the closest genetic relationship with the Japanese population, suggesting possible gene exchange between the two adjacent areas. This study furthers our understanding of the genetic diversity and genetic structure of C. camphora in East Asia and provides genetic tools for developing strategies of C. camphora germplasm utilization.

Liriodendron chinense (Hemsley) Sargent is a Class II protected plant in China as natural populations are on the verge of extinction. There is still a lack of systematic research on the genetic resources of its geographic populations. In this study, we used 20 pairs of SSR markers with high polymorphism to analyze a total of 808 L. chinense samples from 22 regions, and 63 Liriodendron tulipifera Linn samples from 2 regions were used as a comparison group. The results revealed a total of 78 alleles in L. chinense, and the average expected heterozygosity (He) was 0.558, showing a low level of genetic diversity. The degree of differentiation of L. chinense was high, with the differentiation coefficient (Fst) as high as 0.302, which is related to the low gene flow (Nm = 0.578). Based on the genetic structure, principal coordinate analysis (PCoA) and phylogenetic analysis of 24 Liriodendron spp. populations, L. chinense and L. tulipifera had obvious differentiation, while the differentiation between L. chinense geographic populations was very large and irregular. Inbreeding appears within the geographic populations, and the level of genetic diversity is very low. In order to protect the genetic diversity of L. chinense, in addition to protecting the existing population as much as possible, artificial cultivation should introduce materials from multiple populations.