The Reproductive Ecology On Astragalus Flexus

The flowering phenology, breeding system, pollination biology, fruit set and seed set and fruit dispesal was investigated in Astragalus flexus Fisch., which is a perennial ephemerals species distributing widely in the Guerbantonggut Desert, Xinjiang, China from April, 2006 to June, 2007. The main results as follows:1) In both of the years, the annual periodic flowering phenologies were revealed. the flowering phenology were similar, population began to flower in the end of April or at the beginning of May. The flowering amplitude curves of inflorensence were steady, the number of opened flowers per day was 2, and the duration of inflorensence was both about 11d, a single flower spaned 1d. There was a sigmificant difference of flowering phenology between two years, the duration of 2006 flowering phenology was 29d, the peak flowering remained 20d; the duration of 2007 was 14d, and the peak flowering remained 7d only. Perhaps it was influenced by factors of environments in different years, and the flowers were opened at right time. And low temperature or big winds will lead the plants without anthesis. The flowering phenology of individuels was determined by the number of inflorescence, more inforescences will lead the phenology longer. Then the flowering phenology of this species was influenced by environment of desert, while this species can end it by hereditary feature.2) The breeding system was determined. This species was protandry and delayed selfing. The flowers were all hermaphrodite, the position of stigma was higher than that of anthers in bud, with the length of style, fused stamens and free stamen were 0.73cm, 0.57cm and 0.50cm, respectively, so the flowers were herkogamy now; the styles and stamens grew at different speed, the speed of stamens growth was faster; anthers dihisense 12h before vexilla opened, and after vexilla opened, the stigmatic receptivity was appeared with the length of style, fused anthers and free anther were 2.97cm, 2.91cm and 2.71cm, so it was protandry. And at that time, the flowers were still herkogamy, stigma could receive the pollen grains by outcrossing. but at the end of anthesis, the flowers turned to brown, there were no chances for outcrossing, if the flower had not been visited, the fused anthers pushed the pollen within the keel onto the stigma at the end of anthesis; on the other hand, the manual pollination of outcrossing and selfing set fruits, too. So this species was delayed selfing and provided reproductive assurance. P/O ratio and OCI indicated that the breeding system was facultative xenogamy, need pollinators. So, this species will govern a shift of floral features toward delayed autonomous selfing to assure reproduction and the production of offspring.3) The pollination syndrome of A. flexus was melittophily. Anthophora atricilla Eversmann and Psithyrus sp. were the pollinators. Most of them visited flowers at 11:00 and 19:00, the number in 10min was 6. When the pollinators arrived, they visited the base of inflorescence firstly, and did not visit the unopened ones; Nectar secretion started immediately after vexillum opened, then the highest rate of secretion occurred around 13:00. After 14:00, the production of nectar decreased considerably, ceasing at about 19:00. And the flower has tripping mechanism, and tripping occurred as the staminal column was released under pressure of the pollinating vector as it alighted on the wing-petals and forages on the intrastaminal nectary at the base of the vexillum. These indicated that this species could attract polliators by effective pollination syndrome when the environment of desert influenced the pollinators'actions.4) Fruit set was higher at the base of infructescence, and reach 40.00% at the 7th flower; the fruit set of upper flowers was low, the highest was 20.00%. But the fruit set of the 3rd flower was only 13.33%. The seed set was higher at the base of fruit; the highest seed set was at the centre of fruit, at 11st seed set reached 63.33%. So we guessed that fruit set and seed set were limited by the resources in this species, and plnats were selective seed abortion and fruit abortion for assure some of fruits and seeds mature and dispersal. It is ecologically adavantageous for ensuring the continuation of the species and increasing the possiblility of population growth in desert environment.