Background The ephemeral flora of northern Xinjiang, China, plays an important role in the desert ecosystems. However, the evolutionary history of this flora remains unclear. To gain new insights into its origin and evolutionary dynamics, we comprehensively sampled ephemeral plants of Brassicaceae, one of the essential plant groups of the ephemeral flora. Results We reconstructed a phylogenetic tree using plastid genomes and estimated their divergence times. Our results indicate that ephemeral species began to colonize the arid areas in north Xinjiang during the Early Miocene and there was a greater dispersal of ephemeral species from the surrounding areas into the ephemeral community of north Xinjiang during the Middle and Late Miocene, in contrast to the Early Miocene or Pliocene periods. Conclusions Our findings, together with previous studies, suggest that the ephemeral flora originated in the Early Miocene, and species assembly became rapid from the Middle Miocene onwards, possibly attributable to global climate changes and regional geological events.

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Different organ morphologies determine the manner in which plants acquire resources, and the proportion of biomass of each organ is a critical driving force for organs to function in the future. Regrettably, we still lack a comprehensive understanding of root traits and seedling biomass allocation. Accordingly, we investigated and collected the seedling root morphological traits and biomass allocation of 50 annual ephemeral species to clarify the adaptation to environment. The findings of this study showed that there was a significantly negative correlation between root tissue density (RTD) and root diameter (RD) (p < 0.05), which did not conform to the hypothesis of the one-dimensional root economics spectrum (RES). On this basis, we divided 50 plant species into those rooted in dense or gravelly sand (DGS) or loose sand (LS) groups according to two soil conditions to determine the differences in root strategy and plant strategy between the two groups of plants. Our study revealed that the species rooting DGS tend to adopt a high penetration root strategy. However, the species rooting LS adopt high resource acquisition efficiency. At the whole-plant level, 50 species of ephemerals were distributed along the resource acquisition and conservation axis. Species rooting DGS tend to adopt the conservation strategy of high stem biomass fraction and low resource acquisition efficiency, while species rooting LS tend to adopt the acquisition strategy of high root and leaf biomass fraction and high resource acquisition efficiency. The research results provide a theoretical basis for the restoration and protection of vegetation in desert areas.

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Future increased precipitation in cold desert ecosystems may impact annual/ephemeral plant species that germinate in both spring and autumn. Our primary aim was to compare the life history characteristics of plants from spring-germinating (SG) and autumn-germinating (AG) seeds of Erodium oxyrhynchum. Plants in field plots with simulated increases in precipitation of 0, 30 and 50 % in spring and summer were monitored to determine seedling survival, phenology, plant size, seed production and biomass accumulation and allocation. Germination characteristics were determined in the laboratory for seeds produced by plants in all increased precipitation treatments. Increased precipitation in spring significantly improved survival of seedlings from SG and AG seeds, but survival was less for AG than SG. An increase in precipitation increased the number of seeds per plant for both SG and AG, but AG produced more seeds per plant than SG. With increased precipitation, percentage of dormant seeds from SG increased significantly, while that of AG decreased slightly. Our study suggests that with increased spring and summer rainfall AG will produce an increased number of nondormant seeds that could germinate in autumn and SG an increased number of dormant seeds that become part of the soil seed bank. However, ability of some seeds to germinate in autumn and others in spring will be maintained as long as soil moisture is limited in autumn.

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The leaf and soil stoichiometric characteristics and their relationships of two ephemeral plants (Hypecoum erectum and Euphorbia turczaninowii) and two ephemeroid plants (Ferula meyeri and Astragalus flexus) were analyzed in extreme desert environment. There was no significant difference among each soil factor in different sampling plots of each species. Soil nitrogen (N) content (0.18-0.22 mg . g-1) was far lower than soil phosphorus (P) content (1.58-1.62 mg . g-1), and the N/P only ranged 0.12-0.15, indicating a serious lack of soil N. N, P and N/P all represented significant difference among the four species, in which A. flexus had the highest values with 57.36 mg . g-1, 2.46 mg . g-1 and 23.43, followed by H. erectum with 34.05 mg . g-1, 1.98 mg . g-1 and 17.56, the values for E. turczaninowii were 27.07 mg . g-1, 1.87 mg . g-1 and 14.51, and the values for F. meyeri were 28.63 mg . g-1, 2.20 mg . g-1 and 13.10, respectively. N and P contents showed significant correlation of each species, while most soil factors did not show significant correlation with leaf stoichiometric values.

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Five new (1-5) and one known (6) jatrophane diterpenoid esters were isolated from the ethanol extract of the whole herb of Euphorbia turczaninowii. Their structures were established by extensive spectroscopic methods. The absolute stereochemistry of 3 beta,5 alpha,8 alpha,15 beta-tetraacetoxy-7 beta-benzoyloxyjatropha-6(17),11E-dien-9,14-dione (1) was confirmed by a single-crystal X-ray analysis coupled with the exciton chirality circular dichroism method. Compounds 1-6 were inactive when evaluated both in a mouse ear inflammation assay and for cytotoxicity against the B16 mouse melanoma cell line.

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