| Members of Brassicaceae are one of the most important groups of ephemeral plants and a major component of the desert flora in the Junggar Basin. In this thesis, reproductive ecology of four early spring ephemeral species in Brassicaceae: Alyssum linifolium Steph. ex Willd.,A. dasycarpum Steph. ex Willd.,A. desertorum Stapf. and Lepidium perfoliatum L. was observed and analyzed, including the phenology, breeding system, reproductive allocation, the pattern of fruit set and seed set. Meanwhile, the diaspore characteristics and dispersal strategies of 24 ephemeral species and characteristic of mucilaginous seeds of 6 ephemeral species in Brassicaceae were studied both in field and indoor, the especial reproductive and life history strategies and the adaptation mechanism to the Junggar desert of the above species were discussed. The main results are as follows:1)Four species belonged to typical ephemeral plants which escaped from the hot and dry summer of the Junngar Desert. Seed germination of theirs was correlated with seasonal precipitation, the fruits matured fully between the below ten days of May and the above ten days of June. The life cycles of spring germinated plants were between 54d and 63d. In four species, and the reproductive growth period accounted for 2/3 of their life histories. This is an adaptive strategy of escaping from the high death risk of hot and dry summer in the Junngar Desert.2)The flowers of four species were bisexual, tetradynamous and the anthesis of each flower was about 1-2days. In four species, the anther dehisces of long stamen was earlier than that of short stamen, but pollen grains per anther were difference between the short and the long stamen in each flower. The dynamic curves of pollen viability in long and short stamen were similar. The pollen longevity and the stigma receptivity are just overlapped; the period of highest pollen vigor is just that of the strongest stigma receptivity. P/O value of four species were 150.96±33.40,400.64±37.23,303.58±53.00 and 528.52±96.94, respectively. The investigation results on pollination, pollen germination, and their fruit-set under the treatment of no emasculation and bagging in four species showed that the breeding system of four species can be regard as predominantly selfing. Four species allocated a high proportion of resources to reproductive activities and their reproductive allocation were higher than that of most annual and perennial plants with 67.37%,62.92%,57.96%,66.46% respectively. The inflorescence length correlated positively with its fruit numbers and the fruit-set of inflorescences on the top-branches was above 80% and higher than that on the sub-branches in four species. These suggested that the fruit-set may be limited by the resources in four species.3)Mucilagineous seeds can floated on water for 2-24h, increase in weight 8-29 times by absorbing water, holding water 7-18.5h in 6 ephemeral Brassicaceae species. Mucilagineous seeds could adhere to the soil surface after wetting. Seed mucilage is ecologically advantageous for seed dispersal, germination, seedling development and protection of seed.4)The fruits and seeds morphologic characters and the dispersal mode of 24 ephemeral Brassicaceae species in the Junggar Desert was conducted. The morphology of fruits and seeds, dispersal units and mode are multiform among species. The dispersal patterns of these species could be divided into two types: short-term dispersal and time-dispersal pattern, and belonged to"protection"and"escaping"strategies respectively. Part of these species prolonged dispersal time of seeds by spatio-temporal separation. These characteristics are adaptations to successful dispersal and settlement of the dispersal unit, resistance against drought, escaping from massive seed collection, formation of a long-term seed bank, and distribution of offspring over a large area, thus ensuring the continuation of the species and increasing the possibility of population growth in new habitats in the Junggar Desert.
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