Picea koraiensis is major silvicultural and timber species in northeast China, and its distribution area is an important transition zone for genus spruce migration. The degree of intraspecific differentiation of P. koraiensis is high, but population structure and differentiation mechanisms are not clear. In this study, 523,761 single nucleotide polymorphisms (SNPs) were identified in 113 individuals from 9 populations of P. koraiensis by genotyping-by-sequencing (GBS). Population genomic analysis showed that P. koraiensis was divided into three geoclimatic regions: Great Khingan Mountains climatic region, Lesser Khingan Mountains climatic region, and Changbai Mountain climatic region. Mengkeshan (MKS) population on the northern edge of the distribution area and Wuyiling (WYL) population located in the mining area are two highly differentiated groups. Selective sweep analysis showed that MKS and WYL populations had 645 and 1126 selected genes, respectively. Genes selected in the MKS population were associated with flowering and photomorphogenesis, cellular response to water deficit, and glycerophospholipid metabolism; genes selected in the WYL population were associated with metal ion transport, biosynthesis of macromolecules, and DNA repair. Climatic factors and heavy metal stress drives divergence in MKS and WYL populations, respectively. Our findings provide insights into adaptive divergence mechanisms in Picea and will contribute to molecular breeding studies.

Genome-wide single nucleotide polymorphism (SNP) markers were obtained by genotyping-by-sequencing (GBS) technology to study the genetic relationships, population structure, gene flow and selective sweeps during species differentiation of Picea wilsonii, P. neoveitchii and P. likiangensis from a genome-wide perspective. We used P. jezoensis and P. pungens as outgroups, and three evolutionary branches were obtained: P. likiangensis was located on one branch, two P. wilsonii populations were grouped onto a second branch, and two P. neoveitchii populations were grouped onto a third branch. The relationship of P. wilsonii with P. likiangensis was closer than that with P. neoveitchii. ABBA-BABA analysis revealed that the gene flow between P. neoveitchii and P. wilsonii was greater than that between P. neoveitchii and P. likiangensis. Compared with the background population of P. neoveitchii, the genes that were selected in the P. wilsonii population were mainly related to plant stress resistance, stomatal regulation, plant morphology and flowering. The genes selected in the P. likiangensis population were mainly related to plant stress resistance, leaf morphology and flowering. Selective sweeps were beneficial for improving the adaptability of spruce species to different habitats as well as to accelerate species differentiation. The frequent gene flow between spruce species makes their evolutionary relationships complicated. Insight into gene flow and selection pressure in spruce species will help us further understand their phylogenetic relationships and provide a scientific basis for their introduction, domestication and genetic improvement.

To evaluate the effects of donor ages on growth and stress resistance of 6-year-old seedlings propagated from 5-, 2000-, and 3000-year-old Platycladus orientalis donors with grafting, cutting, and seed sowing, growth indicators and physiological and transcriptomic analyses were performed in 6-year-old seedlings in winter. Results showed that basal stem diameters and plant heights of seedlings of the three propagation methods decreased with the age of the donors, and the sown seedlings were the thickest and tallest. The contents of soluble sugar, chlorophyll, and free fatty acid in apical leaves of the three propagation methods were negatively correlated with donor ages in winter, while the opposite was true for flavonoid and total phenolic. The contents of flavonoid, total phenolic, and free fatty acid in cutting seedlings were highest in the seedlings propagated in the three methods in winter. KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analysis of differentially expressed genes showed phenylpropanoid biosynthesis and fatty acid metabolism pathways, and their expression levels were up-regulated in apical leaves from 6-year-old seedlings propagated from 3000-year-old P. orientalis donors. In addition, hub genes analysis presented that C4H, OMT1, CCR2, PAL, PRX52, ACP1, AtPDAT2, and FAD3 were up-regulated in cutting seedlings, and the gene expression levels decreased in seedlings propagated from 2000- and 3000-year-old donors. These findings demonstrate the resistance stability of cuttings of P. orientalis and provide insights into the regulatory mechanisms of seedlings of P. orientalis propagated from donors at different ages in different propagation methods against low-temperature stress.