The Reproductive Ecology On Three Species Of Ephemeral Plants In Asteraceae

Epilasia hemilasia (Bge.) Clarke, Koelpina linearis Pall. and Hyalea pulchella (Ledeb.) C. Koch were three ephemeral species of Asteraceae which were distributed in Junggar desert. With the aid of the field investigation, fluorescence microscope, scanning electron microscope and biostatistics methods, phenology characteristics, breeding system, fruit pattern, reproductive allocation and fruit dispersal mechanism of them were studied in this thesis. We aimed at analyze life-history and reproductive strategies of these plants and their adaptation to desert environment. The main results show as follows:1) Phenological characteristics: Three species belonged to typical ephemeral plants escaping from droughty. Their plants could germinate and grow rapidly with melting snow and precipitation in early spring. The fruits of theirs became mature before the rigorous weather of summer. Their life-spans were only fifty to eighty days, and could be divided into three continuous stages: vegetative growth period, co-exist period of vegetative and reproductive growth and reproductive growth period. The proportion of reproductive growth was great in life history. Furthermore, the fruits of H. pulchellacan could germinate in autumn.2) Breeding system: ①The florets of capitulum could divide into ray and disk ones. Both kinds of florets were lingulate and fertile in E. hemilasia and K. linearis; but the florets of H. pulchella were tubulous, in which the ray ones were pink and sterile, while disk ones were white and fertile. The flowering duration of capitulum did not last for a long time. ②The breeding systems of three kinds of plants were mixed mating system. The P/O value of ray and disk florets were 460.53 ± 71.64 and 443.49 ± 87.88 respectively in E. hemilasia. While the P/O value of ray and disk ones were 300.15 ± 40.20 and 296.55 ± 50.13 respectively in K. linearis. But the P/O value of disk-florets in H. pulchella was 1260.50 ± 70.19. ③The abortion rates of pollen in three kinds of plants were quite low. The pollen abortion rates of ray and disk florets were 2.58 ± 0.67% and 5.63 ± 0.55% respectively in E. hemilasia. And the rates of ray and disk one were 0.47 ± 0.23% and 0.44 ± 0.35% respectively in K.linearis. But the abortion rate of disk-florets pollen was 4.56 ± 1.67% in H. pulchella. ④Dynamic curves of pollen viability in three kinds of plants were similar and pollen viabilities were highest at the beginning of flowering. The flowering durations of single floret were in highly accordance with the periods of higher pollen viability, the optimal period of stigma receptivity and the rush hour of insects visiting. These characters ensured the reality of pollination and reproduction success in a short time. ⑤Results of fruit sets under two treatments and the fluorescence microscope observation proved that there were autogamy and xenogamy in E. hemilasia and K. linearis, and H. pulchella needed pollination medium.3) Biomass allocation and fruit set characteristic: The individual size, biomass of reproductive organs, numbers and weights of achenes and the number of individual capitulum in all three kinds of plants all decreased with increasing density. But reproductive allocation had the reverse trend. Fruit sets of ray and disk florets in E. hemilasia and that of disk florets in K. linearis and in H. pulchella also decreased with the increasing density. However, fruit set of ray florets increased with increasing density in K. linearis.