Comparison of the floral trait and scent from two sympatric desert spring flowering Brassicaceae herbs

Mt. Kalamaili Nature Reserve is a famous nature reserve of desert ungulates in China. Desert spring flowering plants are an important part of the desert vegetation in this reserve and an excellent source of forage for herbivorous wild animals. Chorispora sibirica and Dontostemon elegans are the two kinds of Brassicaceae desert spring-flowering herbs that are widely sympatrically distributed on the gravelly desert in this region. To compare the differences in the floral characteristics and scent between the two desert herbs, we observed and measured the floral characteristics of the two species in the field and collected and analyzed the composition of their volatile floral scent. The results showed that: 1) both desert herbs showed typical entomophilous flower traits, such as a larger corolla diameter, bright colors, and a strong floral fragrance. The two herbs exhibited significant differences in the main floral characteristics, especially in their corolla color and diameter, petal width, and stamen length. 2) A total of 41 volatiles were isolated and identified from the floral scents of the two desert herbs, mainly terpenoids. Among them, (Z)-β-Ocimene was the main component of the floral scent of C. sibirica, while the highest amounts of α-pinene and phenylacetaldehyde were detected in the floral scent of D. elegans. The principal component analysis indicated that there is obvious interspecific variation in the chemical composition of the floral scents among the two desert herbs. The two sympatric desert herbs can attract their pollinators through obvious floral characteristics and scents in spring, to promote their own outcrossing, which may increase the offspring’s fitness. Shared pollinators may use this difference between the two species to distinguish between them and then separately pollinate each species to ensure the interspecific reproductive isolation between the two species, maintaining the species diversity in this region; this would be significant for the conservation of wild animals in this region.