Fruit Polymorphyism With Reference To Its Ecological Adaptive Strategy In Diptychocarpus Strictus Of Ephemeral Plants

Diptychocarpus strictus is one of the few species which have heterocarpy on the same raceme in Cruciferae and an early spring ephemeral plant mainly distributed in Zhungaer Basin of China. This species have two kinds of morph, the purple-flowered morph and the white-flowered morph. The upper and lower flowers in a same raceme in this species develop into two kinds of siliques with different morphology and dehiscenting manner respectively. In this paper, we observed and compared the characteristics of seeds germination, phenology, the reproductive allocation, breeding system and the fruit-set and seed-set characteristics of two kinds of morph of this species, and discussed their survival strategies in the extreme environment of Zhungaer desert. The main results were as follow:1) The germination strategies and phenological characteristics: the germination of seeds showed obvious spatiotemporal differences, the sibling seeds could germinate in both spring and autumn. The plants grew rapidly and the life spans of the spring germinated plants (only about 70 days) are shorter than that of the autumn germinated plants (about 100 days).2) The breeding system characteristics: ① This species have two kinds of floral morphs, the purple-flowered morph and the white-flowered morph, and the flowers color is stably inherited. The ratio of the two morphs within a population is close to 1: 1. ② There are significant differences in the anther length of the longer stamens in the upper flowers of a raceme, and in the petal length and the style length of the lower flowers in a raceme between the two morphs. The parameters of morphological characters of the upper flowers in a raceme are bigger than those of the lower flowers. ③ The upper flowers have more pollen grains, higher P/O ratios, and larger ovule numbers than the lower flowers in the same raceme of the two morphs and the difference is significant between them, and there are significant differences in pollen grains per anther in the longer stamens of upper flowers in a raceme between the two morphs. Pollen grains per anther in the shorter stamens are more than those in the longer stamens of a same flowers and the difference is significant between them. ? The pollen longevity and the stigma receptivity are just overlapped; The period of highest pollen vigor is just that of the strongest stigma receptivity. Dynamic curves of pollen viability of the longer and the shorter stamens in the two morphs are similar to each other. At the beginning of anther dehiscing, the pollen vigor of both the longer and shorter stamens is over 90%. ⑤ There were few pollinators during the flowering span and self-pollen could germinate normally on the stigma. Fruit-set was 87.78% and 85.56% respectively under the treatments of no emasculation and bagging, and 94.44% and 90.00% under the condition of natural pollination in the two morphs, indicating that the breeding system of D. strictus belongs to facultative selfing.3) The reproductive allocation: The plants favored to allocate a greater proportion of resources to reproductive activities, the reproductive allocation of the spring and the autumn germinated plants could reach to about 65% and was higher than that of most annual plants and perennial plants, and the difference is significant between the spring and the autumn germinated plants of the purple-flowered morph, and not significant between them of the white-flowered morph.