The Adaptive Significance Of Hermaphrodite-gynomonoecy And Seed Dormancy In Eremurus Anisopterus

Eremurus anisopterus (Kar. et Kir) Regel.(Xanthorrhoeaceae, Liliaceae s.l.) is a perennial, early-spring ephemeral herb. In China, this species is distributed only on the fixed and/or semi-fixed sand dunes of the Gurbantunggut Desert of Xinjiang Uyghur Autonomous Region. At the beginning of the reproductive growing season of E. anisopterus, there are two kinds of plants with different sizes, and which can be divided in to hermaphroditic and gynomonoecious plants. Lower flowers of the racemes of gynomonoecious plants developed abnormally with their stamens undeveloped, but middle and upper flower were perfect flowers. Thus, this species has a hermaphrodite-gynomonoecious sexual system. The relationship between the sexual system and plant size, the floral traits of pistillate and perfect flowers, floral allocation, pollinator preferences and pollen movement of the two flower morphs, and seed dormancy and germination were explored in field and indoor studies, and the adaptive significance of hermaphrodite-gynomonoecious sexual system and seed dormancy of this species was determined. The main results were as follows:(1) Whether the pistillate flowers occurrs or not and it’s number was positively correlated with plant size in investigated populations of E. anisopterus. The composition of flowers within the raceme changes from perfect flowers into a combination of pistillate flowers and perfect flowers with increasing of plant size of E. anisopterus. However, the number of hermaphroditic plants was significantly greater than gynomonoecious plants in investigated populations, and the number of perfect flowers was also significantly greater than pistillate flowers within the raceme. These results indicate that the occurrence and the number of pistillate flowers are size-dependent. The pistillate flowers of gynomonoecious plants are functionally female flowers with sterile anthers, but hermaphroditic plants don’t produce pistillate flowers. There were no differences in petal mass among the perfect flowers of hermaphroditic plants and the perfect flowers and pistillate flower of gynomonoecious plants, but the androecium mass of perfect flowers of hermaphroditic plants was significantly higher than that of pistillate flowers of gynomonoecious plants. There were no differences of gynoecium mass between the pistillate and perfect flowers within gynomonoecious plants. Perfect flowers produced smaller but larger number of ovules and seeds, while pistillate flowers produce fewer but larger ovules and seeds. These results suggest that pistillate flowers compensate for the loss of male function through better seed quality. The presence of two flower types in gynomonoecious plants is advantageous because it permits flexible allocation of resources to male and female reproductive functions.(2) The flowering order within the raceme of E. anisopterus is from the bottom to the top. Bees are the main pollinators of this species and they usually visit flowers sequentially upward on the raceme. In gynomonoecious plants, bees preferred to visit perfect flowers, which were also capable of partial self-fertilization. Perfect flowers received a higher proportion of intra-plant pollen (geitonogamy) than pistillate flowers. However, pistillate flowers largely depended on insect-mediated pollination, indicating that pollen limitation was more severe in pistillate flowers than in perfect flowers. Plants with greater numbers of pistillate flowers received more outcross pollen, suggesting that the occurrence of pistillate flowers largely reduced geitonogamy in the gynomonoecious plants. These results are consistent with the outcrossing-benefit hypothesis for gynomonoecy.(3) The freshly-matured seeds of E. anisopterus have small underdeveloped embryos when they disperse in summer (June), but the underdeveloped embryos began to grow rapidly when the temperatures decreased in autumn and completed their grows before germination (radicle emergence). Fresh seeds did not germinate during the first month of incubation in light and darkness over a range of temperatures. These indicated seeds of this species have morphophysiological dormancy (MPD). After>12weeks incubation at5/2℃both embryo growth and germination occurred, showing that they have a complex level of MPD. Since both afterripening and GA3increase germination, seeds have intermediate complex MPD. The ecological advantage of dormancy being broken by a combination of afterripening and cold stratification and of embryo growth occurring at low temperatures is that seeds can germinate and seedling emergence in early spring as soon as the soil becomes moist. This pattern of dormancy can provide for the successful establishment and population expansion of this species in the desert, which maybe an adaptative strategy to the variable environment in Gurbantunggut Desert.