The Study On Reproductive Strategy Of Dimorphic Seed Of Borszczowia Aralocaspica

Borszczowia aralocaspica is an endemic species in the Central Asian deserts, with utricles and perianth coating the fruit and healing into berry-like dispersal units. In this paper, the dispersal units, seed morphs, germination characteristics, seed size and the pattern of fruit set of Borszczowia aralocaspica were observed and compared in field and indoor, and their reproductive and survival strategies were discussed in the extreme environment of desert in Xinjiang. The main results are as follow:(1) Borszczowia aralocaspica produces two types of dispersal units and utricles that differ in shape, size and seed colour. The dispersal units are green and fleshy when young and develop either into brown fruit which are big or strong, round, flat, and covered with extended bracteoles or into smaller or lighter black fruit which are lens-shaped with a glossy, smooth testa, covered with extended bracteoles.(2) The seeds of Borszczowia aralocaspica were germinated for 30d in incubators with thermoperiods of 5/15℃, 5/25℃and 15/25℃(dark 12h / light 12h). Brown seeds germinated rapidly and the germination percentages were all above 81%, while black seeds germinated slowly and had a low germination percentage. Cold stratification and scarification of covering layers (pericarp and seed coat) can significantly increase germination percentage of black seeds. Extending the storage time can also increase, but not significantly. This suggests that black seeds have non-deep physiological dormancy.(3) We discovered that the size, mass and germination percentage of the two type seeds were variable in different years. They all increased with increase of rainfull, and were: 2007 year>2008 year>2006 year. The result showed that the seeds were bigger and germination percentages were higher if rainfull was adequate in flowering and fruiting period.(4) The results also showed that Borszczowia aralocaspica had significant difference in the size of individuals in its natural population, and the size of individuals influenced the number and the proportion of different type seeds. The number of black and brown seeds, the total number of seeds all had significant change, and increased with the increase of plant size. The number of black seeds was higher than brown seeds in all three classes plants, but the proportion increased with the decrease of plant size. The change was significant in the year 2008, but not significant in the year 2007.