Search

The SiC coating prepared on graphite substrate can effectively solve the corrosion and powder loss problems of graphite material in environments with high temperature and corrosive gas. In this paper, a SiC coating was prepared on the surface of graphite substrate. The deposition process parameters were adjusted and optimized to realize rapid manufacturing of high - performance SiC coating with the aim of providing theoretical basis and technical support for SiC coating’ application on the surface of graphite substrate. An industrial - grade chemical vapor deposition equipment was employed to prepare the silicon carbide coating on the surface of graphite substrates using methyl trichlorosilane (MTS) and H2 as raw materials. The effects of furnace pressure and sample position on the microstructure and thermal fatigue resistance of the coating were studied by analysis and testing methods such as scanning electron microscopy, X - ray diffractometer and vacuum thermal cycling. Results showed that when the furnace pressure was 2.0 kPa, a high - purity silicon carbide coating with single grain growth orientation could be prepared. As the furnace pressure increased, the deposition rate and thermal fatigue resistance of the coating both showed a non - monotonic change of first rising, then falling and then rising again. When the furnace pressure was 2.0 kPa, the silicon carbide coating had the highest deposition rate and the best thermal fatigue resistance. The coatings prepared with different sample positions were all pure SiC coatings, and the closer the substrate suspension position to the air distribution plate, the faster the coating deposition rate was and the better thermal fatigue resistance the coating showed. When the furnace pressure was 2.0 kPa and the sample position was 300 mm, a SiC coating with good thermal fatigue resistance could be quickly prepared.

Summary: Understanding how life history shapes genetic diversity is a fundamental issue in evolutionary biology, with important consequences for conservation. However, we still have an incomplete picture of the impact of life history on genome‐wide patterns of diversity, especially in long‐lived semelparous plants.Puya raimondii is a high‐altitude semelparous species from the Andes that flowers at 40–100 years of age. We sequenced the whole genome and estimated the nucleotide diversity of 200 individuals sampled from nine populations. Coalescent‐based approaches were then used to infer past population dynamics. Finally, these results were compared with results obtained for the iteroparous species, Puya macrura.The nine populations of P. raimondii were highly divergent, highly inbred, and carried an exceptionally high genetic load. They are genetically depauperate, although, locally in the genome, balancing selection contributed to the maintenance of genetic polymorphism. While both P. raimondii and P. macrura went through a severe bottleneck during the Pleistocene, P. raimondii did not recover from it and continuously declined, while P. macrura managed to bounce back.Our results demonstrate the importance of life history, in particular generation time and reproductive strategy, in affecting population dynamics and genomic variation, and illustrate the genetic fragility of long‐lived semelparous plants. [ABSTRACT FROM AUTHOR]

Euryodendron excelsum is in a monotypic genus Euryodendron , endemic to China. It has intermediate morphisms in the Pentaphylacaceae or Theaceae families, which make it distinct. Due to anthropogenic disturbance, E. excelsum is currently found in very restricted and fragmented areas with extremely small populations. Although much research and effort has been applied towards its conservation, its long-term survival mechanisms and evolutionary history remain elusive, especially from a genomic aspect. Therefore, using a combination of long/short whole genome sequencing, RNA sequencing reads, and Hi-C data, we assembled and annotated a high-quality genome for E. excelsum. The genome assembly of E. excelsum comprised 1,059,895,887 bp with 99.66% anchored into 23 pseudo-chromosomes and a 99.0% BUSCO completeness. Comparative genomic analysis revealed the expansion of terpenoid and flavonoid secondary metabolite genes, and displayed a tandem and/or proximal duplication framework of these genes. E. excelsum also displayed genes associated with growth, development, and defence adaptation from whole genome duplication. Demographic analysis indicated that its fluctuations in population size and its recent population decline were related to cold climate changes. The E. excelsum genome assembly provides a highly valuable resource for evolutionary and ecological research in the future, aiding its conservation, management, and restoration. [ABSTRACT FROM AUTHOR]

Ormosia is a genus of the Fabaceae family that shows a distinct evolutionary history due to its typical Asian-American tropical disjunction distribution pattern. However, both its phylogeny and biogeographic mechanisms have not been fully resolved. In addition, Ormosia species have great economic and ecological potential in the wood and handicraft (using their attractive seeds) industries, reforestation, and folk medicine (due to their flavonoids, alkaloids, and terpenoids), making them highly valuable in research, especially from a genomic perspective. We report the genome assemblies of two common Ormosia species, Ormosia emarginata and Ormosia semicastrata, in South China, using both long and short sequencing reads. The genome assemblies of O. emarginata and O. semicastrata comprised 90 contigs with a total length of 1,420,917,605 bp and 63 contigs with a total length of 1,511,766,959 bp, respectively. Benchmarking Universal Single-Copy Orthologs (BUSCO) assessment revealed 97.0% and 98.3% completeness of the O. emarginata and O. semicastrata assemblies, respectively. The assemblies contain 48,599 and 52,067 protein-coding genes, respectively. Phylogenetic analyses using 1032 single-copy genes with 19 species indicated that they are closely related to Lupinus albus. We investigated genes related to plant hormones, signaling, the circadian rhythm, transcription factors, and secondary metabolites derived from the whole genome and tandem and proximal duplications, indicating that these duplications should play important roles in the growth, development, and defense of Ormosia species. To our knowledge, our study is the first report on Ormosia genome assemblies. This information will facilitate phylogenetic and biogeographic analyses and species breeding in the future. [ABSTRACT FROM AUTHOR]

Among relic species, genomic information may provide the key to inferring their long-term survival. Therefore, in this study, we investigated the genome of the Paleogene relic tree species, Bretschneidera sinensis , which is a rare endemic species within southeastern Asia. Specifically, we assembled a high-quality genome for B. sinensis using PacBio high-fidelity and high-throughput chromosome conformation capture reads and annotated it with long and short RNA sequencing reads. Using the genome, we then detected a trade-off between active and passive disease defences among the gene families. Gene families involved in salicylic acid and MAPK signalling pathways expanded as active defence mechanisms against disease, but families involved in terpene synthase activity as passive defences contracted. When inferring the long evolutionary history of B. sinensis , we detected population declines corresponding to historical climate change around the Eocene–Oligocene transition and to climatic fluctuations in the Quaternary. Additionally, based on this genome, we identified 388 single nucleotide polymorphisms (SNPs) that were likely under selection, and showed diverse functions in growth and stress responses. Among them, we further found 41 climate-associated SNPs. The genome of B. sinensis and the SNP dataset will be important resources for understanding extinction/diversification processes using comparative genomics in different lineages. [ABSTRACT FROM AUTHOR]

Feng Shui woodlands are naturally or artificially formed green areas in southern China. They are precious for maintaining ecosystem balance in modern semiurban environments. However, they are generally small and geographically isolated from each other, and the status of genetic diversity of the plant species within them has been almost neglected. Therefore, we studied the genetic diversity of the endangered Erythrophleum fordii in eight Feng Shui woodlands (a total of 1,061 individuals) in Guangzhou, a large city in southern China, using microsatellites. For comparison, one population with 33 individuals sampled in a nature reserve was also studied. Although our results indicate that significant demographic declines occurred historically in E. fordii, such declines have not resulted in consistent reductions in genetic variation over generations in Feng Shui populations in the recent past, and the levels of genetic variation in these populations were higher than or comparable to the genetic variation of the population in the nature reserve. In addition, our parentage and paternity analyses indicated widespread and potential long‐distance pollen flow within one Feng Shui woodland, indicating the presence of an unbroken pollination network, which would at least partially alleviate the genetic erosion due to habitat fragmentation and the unequal gene contributions of E. fordii parents to their progenies when favorable recruitment habitats are absent under most of the parent trees. Overall, our results suggest that E. fordii in Feng Shui woodlands may not be driven to extinction in the near future. Nevertheless, uncontrolled fast urban development with a lack of awareness of Feng Shui woodlands will cause the local extinction of E. fordii, which has already happened in some Feng Shui woodlands. [ABSTRACT FROM AUTHOR]