The Ecological Adaptive Strategies On Andromonoecious Sex System Of Two Apiaceae Species

Andromonoecy, i.e. presence of both staminate and hermaphrodite flowers on the same individuals, is observed in Ferula syreitschikowii K.-Pol. and Soranthus meyeri Ledeb., which are common early spring sabulicolous ephemeroid in the Guerbantonggut Desert of northwest China. In this paper, we demonstrated the sex ratios and resource allocation in these two species, as well as pollination characteristics and breeding system in F. syreitschikowii, and the specific objectives of the study was to give some theoretical evidence for exploring the ecological adaptive strategy of these two species to desert environment. The main results are as follows:1. There were significant differences between staminate flowers and hermaphrodite flowers of S. meyeri in characteristics of flower (P<0.01), and staminate flowers and hermaphrodite flowers of F. syreitschikowii differ significantly in those characteristics of flower, except for the length of filament(P>0.05). Biomass and pollen number in hermaphrodite flowers was significantly higher than that of staminate flowers.2. With the increasing of umbel order, the proportion of staminate flowers tends to increase, and the central flowers were more often male than peripheral flowers within an umbellet in the two species. Umbels of different orders flower in a sequence; the primary umbel blooms first, followed by those of higher orders. But there is substantial overlap of about 1.0 d in male and female phases among umbels of consecutive orders. Flowers in an umbellet flower from outer to inner, and all the flowers present male function first and then female function simultaneously. Flowers are protandrous at the lever of umbel and flower with the male and female phase separated by a quiescent, which can prevent self-pollination. The stage of anthesis and stigmatic receptivity was different between the two species3. The sex ratios are related to the resource allocation to male and female function, larger plants allocate more resources to their female function and the sex-ratio leans to be more female-biased, while smaller plants prone to invest more resource to their male functions and the sex-ratio leans to be more male-biased. Sex ratios are effected by environment factors in the two species, which is more evident in S. meyeri than that in F. syreitschikowii.4. The rewards offered to insects by hermaphrodite flowers differed in different sex-phase, which were pollen and nectar in male phase and only nectar in female phase. The tendency of the production of nectar at male and female phase of hermaphrodite flowers was similar, and there was no significant difference in cumulative nectar production between male and female phase of hermaphrodite flowers(P>0.05). Incets did not show distinct preference for different phase umbel (P>0.05), and the frequency of insets visit to male and female phase umbels has no difference(P>0.05). Furthermore, the number of umbels visited by insets in male and female phase during their foraging trip has no difference (P>0.05).5. P/O value of hermaphrodite flowers was 11151±337 in F. syreitschikowii, and dynamic tendency of pollen viability of staminate and hermaphrodite flowers was similar. Pollen longevity of two morph flowers was about 50-52 h, and the stage of stigmatic receptivity of hermaphrodite flowers was about 36-48 h. Hermaphrodite flowers produced fruits after self-pollination (geitonogamy) and cross-pollination, which results F. syreitschikowii is a mixed mating system. The fruit sets of cross-pollination are higher than those of self-pollination and hand-pollination with pollen from staminate flowers are higher than that from hermaphrodite flowers.It made reproductive success of these two species maximize by adjusting their sex ratio. By self-compatible and overlapping of flowering duration among umbels of consecutive orders, the lack of pollinators and low efficiency of pollination were complemented in F. syreitschikowii, which could ensure the reproductive success. The reproductive traits of the two species have significant ecological consequenceson in settling successfully, species persistence and population enlarged in Junggar Desert.