| Pseudotsuga brevifolia is a member of the Pseudotsuga in the Pinaceae family,Due to its rare number,it is listed as a second-class protected plant in the country.Its trees have good adaptability in the karst hilltop area,but because of its excellent growth material,large amount of deforestation and slow growth,the distribution area is scattered.This study investigated the Southwest Guizhou to hechi of guangxi transition region and the distribution of the southern guangxi two Pseudotsuga brevifolia populations,through the age class structure,divided into static life table,survival curve and survival function curve drawing,reveal the Pseudotsuga brevifolia population structure and dynamic characteristics of the Pseudotsuga brevifolia in exploring karst area population growth status,development trend and maintaining mechanism,as to provide theoretical basis for species conservation protection,also the vegetation restoration of karst area in the future work is of great significance.Chloroplast genomes have simple structure,low molecular weight,slow evolution rate and large amount of genetic information,so they have unique advantages in species identification,gene transformation,phylogenetic evolution and so on.We sequenced and assembled the chloroplast genome,analyzed the basic structure of the genome,analyzed the comparative genomics of related species,reconstructed the phylogenetic tree of Pseudotsuga brevifolia based on the chloroplast genome data,and analyzed the phylogeny of the species.These studies have enriched the genomic database,and provided important data and theoretical references for phylogenetic research,molecular marker development,chloroplast transformation technology,and endangered status analysis and conservation recommendations.The results are as follows:(1)In both regions,the self-renewal ability was poor,and the number of young and old plants was small,and the number of young in southwest Guangxi was very small;The population in the two regions was in decline,and the population in the southwest of Guangxi was more serious.By survival curve analysis,the two areas of Pseudotsuga brevifolia populations are Deevey-Ⅱ type,the first Ⅴ the Southwest Guizhou to hechi of guangxi area population-level with the first Ⅸ Ⅵ age-Ⅹ species survive several drops fastest age class stage,mortality rate,the largest in southwest of guangxi Pseudotsuga brevifolia population level during the first Ⅳ-Ⅴ age population survive several drops fastest,mortality is the largest;According to the analysis of survival function curve,the characteristics of Chrysalis Pseudotsuga brevifolia population in the transition region from southwest Guizhou to Hechi of Guangxi are as follows: high early mortality rate and weak foundation;In the middle and late decline,the population viability is low,in a state of decline.The population of Chrysanthemum cuspidata in southwest Guangxi is in a state of decline,and the decline period is earlier than that of the former Chrysanthemum cuspidata population.(2)The chloroplast genome of Pseudotsuga brevifolia showed a typical four-body structure,with the total length of 122348 bp,66627bp for LSC,54863 bp for SSC,and 858 bp for IR.The total length GC content was37.64%,LSC GC content was 37.95%,SSC GC content was 39.64% and IR GC content was 37.06% of the total bases.The total number of genes in the chloroplast genome was 114,including 73 protein-coding genes,37 t RNA genes,4 r RNA genes and 8 introns.Structurally similar to most gymnosperms.(3)A total of 29 SSRs were detected in the chloroplast genome of P.brevifolia,and the single nucleotide sites were the most.62 pairs of forward repeats were detected in the chloroplast genome,accounting for77.5% of the total number of repeats,12 pairs of palindromic repeats were detected,and there were no reverse repeats or complementary repeats.A total of 20442 codons were encoded in it.The most frequently used codon was GAA encoding glutamic acid(Glu),the number of which was 850(4.16%),and the least used codon was GUG encoding methionine(Met),the number of which was only 1.Leucine(Leu)had the highest encoding rate,while cysteine(Cys)had the lowest encoding rate.(4)Based on the comparative analysis of the basic characteristics of chloroplast genomes from related species of the same family,we found that the length of chloroplast genomes was basically in the middle level,but the GC content of chloroplast genome was the lowest(37.64%),and the number of t RNA was the highest.Comparative analysis of chloroplast genome sequences showed that the IR region was more conserved in the coding region than in the non-coding region.The results of chloroplast genome rearrangement showed that the sections of P.brevifolia and P.sinensis,Picea asperata and Abies fanjingshanensis had the same arrangement and similar structure,indicating that the chloroplast genome of these species did not occur rearrangement.There were many partial sequence deletions,inversion and rearrangement in Pseudolarix amabilis,Pinus yunnanensis,Cathaya argyrophylla,Keteleeria davidiana,Tsuga chinensis,Tsuga longibracteata which were significantly different from those in P.brevifolia.The results of IR region expansion and contraction analysis showed that the distribution of genes in IR region was different from that of other species,and the distribution of other boundary genes had little difference,and there was no obvious expansion and contraction in IR region of P.short-leaved.(5)Phylogenetic trees reconstructed from different data sets indicate that the plants closest to the P.brevifolia are both the Larix decidua.Abies,Keteleeria,Pseudolarix,and Cerdus are all grouped into the same branch,indicating that these five genera are closely related,and the genus Chrysalis is closely related to this branch.In the common coding sequence,Pinus species and all other Pinaceae species are divided into two major clades,while Pinus and Picea constitute sister groups in the whole genome.It is speculated that the large variation or deletion of the coding sequence of gymnosperms may lead to the clustering differences of Pinus species in different datasets. |
