Ecological Adaptive Strategies Of Breeding System And Heterocarpy In Ephemeral Heteracia Szovitsii

Heteracia szovitsii is one of the common ephemeral Asteraceae species that germinates in early spring in the Junggar Desert, and it produces three morphs of achenes with different morphologies in one infructescence. To better understand how this species adapted to its desert habitat, the breeding systems, morphological and dispersal features, as well as germination and dormancy of three morphs of achenes were investigated and analyzed in this article, the main results are as follows:(1) There were differences among the three types florets of one capitula in floret numbers, length and width of ligules, length of stigma lobes, size of ovary, length of beaks, pappus and the pollen numbers of one floret. The anthesis of the capitula lasted 2.5~3 h and showed on a explosive flowering pattern.The life span of peripheral floret was longgest and central floret was shotest. There were autogamy and secondary pollen presentation during the flowering. Pollen longevity and stigma receptivity overlap; the period of highest pollen vigor was just the same as the peak of stigma receptivity. H. szovitsii was a facultative selfer, the selfing was autogamy, outcrossing depends secondary pollen presentation and insect pollination. Halictus sexnotatulus was the major pollinator and the time of visited was 2 h. The selfing of H. szovitsii insure its reproduction success , and outcrossing increase fitness of progeny.(2) Compared with central achenes, the pericarps of peripheral and intermediate achenes were thicker, darker in color, and contained a higher amount of phenolic compounds and more sclerenchyma, which could protect the embryo better and cause the seeds to be more dormant. Embryo mass of peripheral and intermediate achenes was greater than that of central achenes, and thus could produce larger and more competitive seedlings. After maturation, central achenes with pappus dispersed over a wide range, while peripheral and intermediate achenes with no pappus usually dispersed near the mother plant. The different number of heteromorphic achenes could spread the risk of dispersal and settlement for this species. The larger number of central achenes increases chance for their random dispersal, and this is favorable for exploiting a larger geographical range for the population. The lower number of peripheral and intermediate achenes could decrease sibling competition due to dispersal near the mother plant. Formation of heteromorphic achenes is a form of bet hedging that could spread the risk of mortality in the extreme environment of the Junggar Desert.(3) The three morphs of fresh achenes differed in level of dormancy, only central achenes germinated over a wide range of temperatures in both light and darkness, whereas peripheral and intermediate achenes did not germinate at all. The effect of light was different at different tempretures. With prolonging of dry storage at room temperature, the dormancy of central and intermediate achenes gradually became lower, and germination percentage increased, while none of peripheral achenes germinated. peripheral and intermediate achenes had deep innate dormancy. With prolonging of dry storage the embryo could germinate, the germination had singnificant difference compared to intact achenes, but the pericarp of central achenes was no effection on germination. Under the treatment of GA3, except the intact peripheral achenes, the embryo and intact achenes could be dormancy-broken, but different type of achene had different accelerate on dormancy breaking. So the degree of dormancy and mechanical resistance (to embryo growth) of three morphs of achenes were different.