Characterization and Comparative Analysis of Complete Chloroplast Genomes of Three Species From the Genus Astragalus (Leguminosae)

Astragalus is the largest genus in Leguminosae. Several molecular studies have investigated the potential adulterants of the species within this genus; nonetheless, the evolutionary relationships among these species remain unclear. Herein, we sequenced and annotated the complete chloroplast genomes of three Astragalus species—Astragalus adsurgens, Astragalus mongholicus var. dahuricus, and Astragalus melilotoides using next-generation sequencing technology and plastid genome annotator (PGA) tool. All species belonged to the inverted repeat lacking clade (IRLC) and had similar sequences concerning gene contents and characteristics. Abundant simple sequence repeat (SSR) loci were detected, with single-nucleotide repeats accounting for the highest proportion of SSRs, most of which were A/T homopolymers. Using Astragalus membranaceus var. membranaceus as reference, the divergence was evident in most non-coding regions of the complete chloroplast genomes of these species. Seven genes (atpB, psbD, rpoB, rpoC1, trnV, rrn16, and rrn23) showed high nucleotide variability (Pi), and could be used as DNA barcodes for Astragalus sp. cemA and rpl33 were found undergoing positive selection by the section patterns in the coded protein. Phylogenetic analysis showed that Astragalus is a monophyletic group closely related to the genus Oxytropis within the tribe Galegeae. The newly sequenced chloroplast genomes provide insight into the unresolved evolutionary relationships within Astragalus spp. and are expected to contribute to species identification.

Using forage litter to improve soil degradation of pure Betula platyphylla forest in the Loess Plateau, China

The long-term growth of pure forest is an important issue that affects stability and sustainable development of ecosystem, while using forage litter as fertilizer or directly establishing tree-grass complex vegetation may be the most effective prevention way. This study took the artificial pure forests of Betula platyphylla, which were widely distributed in the Loess Plateau of China, as the object and conducted a 120-day decomposition incubation experiment of forest humus soil mixed with seven common leguminous forage litters to study the effects of forage litters in controlling the degradation of soil biological and chemical properties of pure forests. The results showed that: by adding forage litter to the soil of pure B. platyphylla forest, litters of Lespedeza bicolor and Onobrychis viciaefolia improved the soil quality obviously, followed by Astragalus adsurgens and Melilotus officinalis, while Medicago sativa lead to obvious deterioration, followed by Vicia villosa and Coronilla varia.