Data on the effect of vegetation and land use type on soil organic carbon (SOC) distribution in particle-size and density fractions in the subtropical forest region in China will improve our understanding of the C sequestration potential of those different vegetation-land use types. We quantified SOC in particle size (coarse, medium and fine) and density fractions (light and heavy) under four types of common forest vegetation-land uses: an evergreen broad-leaf forest, a pine forest, a managed chestnut forest and an intensively managed bamboo forest in subtropical China. The SOC in the 0–20 and 20–40 cm soil layers was the highest in the bamboo forest (31.6–34.8 g·C·kg⁻¹), followed by the evergreen broad-leaf forest (10.2–19.9 g·C·kg⁻¹), the pine forest (8.5–13.6 g·C·kg⁻¹) and the chestnut forest (6.3–12.2 g·C·kg⁻¹). The SOC was largely in the coarse fraction under the evergreen broad-leaf, pine and bamboo forests, while it was largely in the fine fraction in the chestnut forest, suggesting that SOC in the chestnut forest was likely more stable than that in the other forest vegetation-land use types. The SOC in the light fraction under the four forest vegetation-land use types ranged from 1.4 to 13.1 g·C·kg⁻¹ soil, representing 21%–37% of the total organic C; this suggests that the majority of the SOC was in the better protected, heavy fraction. We conclude that forest vegetation-land use type (and the associated management practices) influenced SOC distribution in particle size and density fractions in the studied subtropical forests in southeastern China.

Yeyong mustard is a mustard vegetable belonging to the Brassicaceae family and the Brassica genus. This study assembled, annotated, and analyzed the chloroplast genome of Brassica juncea L., aiming to clarify its systematic evolutionary relationship with other cruciferous plants. The study used the Illumina NovaSeq 6000 platform to sequence the entire chloroplast genome of leaf mustard, and systematically analyzed its genome structure, repeat sequences, nucleic acid diversity, and codon preferences using bioinformatics methods. At the same time, the phylogenetic relationships were constructed by combining the leaf chloroplast genome sequences of other cruciferous plants. The results showed that the chloroplast genome of leaf mustard had a total length of 153,490 bp and a GC content of 36.36%, exhibiting a typical tetrad structure; a total of 132 coding genes were annotated, including 87 mRNA genes, 37 tRNA genes, and eight rRNA genes, and no pseudogenes were found. Codon preference analysis shows that leucine (Leu) has the highest frequency of use, with 32 codons having a relative synonymous codon usage (RSCU) greater than 1, mostly ending in A or U; there are 37 scattered repetitive sequences and 315 simple repetitive sequences in the genome. Ka/Ks analysis showed that the chloroplast genes of leaf mustard were subjected to purification selection as a whole, while genes such as nadhF and petD showed positive selection, which is speculated to be related to adaptive evolution. The results of the phylogenetic analysis further confirm that the chloroplast genome of leaf mustard has a typical tetrad structure and is relatively conserved. It is most closely related to mustard greens in terms of evolutionary relationship, followed by Brassica plants such as nori and turnip, and is also closely related to Brassica plants such as European rapeseed. This study elucidated the conservative characteristics and evolutionary patterns of the chloroplast genome in mustard leaves, providing theoretical support for the phylogenetic research of the Brassicaceae family and the development and utilization of germplasm resources.

Background: Kenaf (Hibiscus cannabinus L.) is an important fiber crop belonging to the genus Hibiscus in the Malvaceae family. Research on its chloroplast genome holds significant importance for deciphering the evolutionary relationships of the Hibiscus species, developing genetic markers, and promoting kenaf (H. cannabinus) genetic breeding. Methods: Based on high-throughput sequencing technology, this study completed the sequencing and assembly of the kenaf (H. cannabinus) chloroplast genome. Results: (1) The kenaf (H. cannabinus) chloroplast genome exhibits a typical circular quadripartite structure with a total length of 163,019 bp, including a large single-copy region (LSC) of 90,467 bp, a small single-copy region (SSC) of 19,486 bp, and a pair of inverted repeat regions (IRa/IRb) of 26,533 bp each. The total GC content is 36.62%, among which, the IR region has the highest GC content (42.61%) and the SSC region the lowest (30.87%). (2) A total of 131 genes were annotated, including 85 mRNAs, 37 tRNAs, 8 rRNAs, and 1 pseudogene. Their functions cover photosynthesis (e.g., pet and atp family genes), self-replication (e.g., rpl, rps, and rpo family genes), and genes with unknown functions (e.g., ycf1 and ycf2). A codon usage bias analysis revealed that the relative synonymous codon usage (RSCU) value of the stop codon UAA is the highest (1.6329), and codons ending with A/U are preferentially used (e.g., GCU for alanine with RSCU = 1.778). (3) A repeat sequence analysis identified various interspersed repeat sequences (predominantly 30~31 bp in length, with a relatively high proportion in the 30~40 bp range, including forward and palindromic types) and simple sequence repeats (cpSSRs). Among them, single-base repeat SSRs account for the highest proportion (e.g., (A)8 and (T)9), and specific SSR primers were designed. (4) A comparative evolutionary analysis indicated that the Ka/Ks ratios (nonsynonymous substitution rate/synonymous substitution rate) of core chloroplast genes (e.g., rps2 and rpoC2) in kenaf (H. cannabinus) are all less than 1 (0.145~0.415), suggesting that they are under purifying selection. The collinearity similarity of chloroplast genomes between kenaf (H. cannabinus) and its closely related species reaches over 99.97%, and the IR region boundaries are relatively conserved. The phylogenetic tree shows that kenaf (H. cannabinus) clusters with closely related Hibiscus species with a 100% bootstrap value, indicating a close genetic relationship. Conclusions: This study provides basic data for the functional analysis of the kenaf (H. cannabinus) chloroplast genome, the phylogeny of Hibiscus, and the utilization of genetic resources.