POLLINATION ECOLOGY OF SONNERATIA ALBA(SONNERATIACEAE)

摘要

Sonneratia alba J. Smith (Sonneratiaceae) is a seaward rare evergreen true euhaline mangrove tree species S. alba flowers for about two weeks during August. It is hermaphroditic, self-compatible and exhibit mixed breeding system which is primarily adapted for cross-pollination. It is typically anemophiious and the functional nectary in this species does not have any role in pollination since biotic vectors do not visit the flowers. High winds could effectively prevent the flight activity of insects.The flowers being large, distinct against the foliage, exposing the numerous stamens to air, the high pollen output per flower, high pollen-ovule ratio and the powdery pollen enable anemophily to be effective to set fruit in this plant species. The plantdespite having mixed breeding system, it shows fruit abortion to a significant level. This indicates that the plant might be selectively eliminating the growing offspring, especially those originating from selfing in order to allocate resources for thexenogamous fruits. The flowers produce numerous ovules but only 33% of them set seed in each fruit. The low natural fruit set rate is compensated by the high seed set rate. The seeds disperse following the decomposition of the fruit in tidal water. New plants emerge in the vicinity of parental sites only. The study suggests that the true mangrove, S. alba along with other seaward plant species such as Aegialitis rotundifolia and Ceriops tagal is important in building mangrove forest in seaward mangroveareas.