Pollination And Factors Affecting Seed Germination Of Physocarpus Amurensis

Physocarpus amurensis is an ancient relic species, and belongs to Physocarpus of Rosaceae, which is only one species in China. The habitat is severely threatened due to the factors of nature and history, the effects of human activity. Now, the areas of distribution and the amount of population of this species in China are much less than the past. This species has been listed as a member of the national gradeⅡrare and endangered plants. In addition, it is not only excellent ornamental shrubs, but also officinal function. So the plant has greatly significant the resource value and economy significance. In this paper, we studied the biology characteristic of pollen and stigma, breeding system, flowering phenology, flower visitors, and effect of different environment factor on seed germination of P. amurensis. Based on the above- mentioned studies, we analyzed the reproduction factors resulting in the endangering of Physocarpus amurensis and offered scientific theory basis in order to f protect the species. Conclusion as follow:P.amurensis was dichogamy and herkogamy. The life span of one flower and inflorescences were 5.1±0.23d, 8.4±0.98d, respectively. The flowering process for one flower of this species can be divided into six periods by the flower morphology and dehiscence: "flower bud", "Pre-dehiscence", "Initial dehiscence", "Full dehiscence", "End- dehiscence", and "Withering period". The pollen viability of was higher than 90% at the blooming day. Pollen viability was significantly decreased with the increasing of storage time under dry and wet conditions (P＜0.05). The pollen viability could last about three days under dry condition, significantly decreased from then, absolutely lost viability in sixth day. Pollen absolutely lost viability when stored only one day under wet condition. The stigma had receptivity when second day after blooming, and the receptivity could last about three days. Based on the results of pollen-ovule ratio (P/O) and emasculation, bagging, and artificial pollination studies, the breeding system of P. amurensis was outcrossing, self-incompatible, and demanded for pollinators. Pollen quantity and source significantly affected fruit abortion. There was evidence that lack of pollination and spontaneous self-pollination caused particularly high fruit abortion, which also indicated that apomixis and spontaneous self-pollination was unlikely. Fruit abortion was delayed after hand pollination, which suggests limitation by pollen quantity. Selfpollination caused earlier abortion than experimental cross-pollination within populations. The pollination extremely depended on insects under the natural condition, but the variety and quantity were very little, the visiting frequency of visitors was also extremely low. The effective pollinators were Apidae.P. amurensis seeds were very small and dispersed only short distance from the parent plants due to their morphological characteristics. Superficial seed dormancy was found. Seed germination required light, and light can promote it. The seeds can germinated when the seeds were incubated at 10-25℃, and seeds germinated most quickly and germination percentage was most high at 20℃. The sowing depth had a highly significant differences effect on seedling emergence (P＜0.01), the seedling emergence rates were most high (68.33%±6.01%) when seeds were buried in the surface of soil. Seedling emergence rates decreased with increasing soil depth and were 0 at 2 cm soil depth. The most suitable soil moisture content for seedling emergence was 40%, and emergence was most quickly and seedling emergence rates were most high, and mortality rates were also low. Seed germinated slowly and the configuration was bad when soil moisture content was in 20% and 30%, and seedling mortality rates reached 63.81±12.16% and 43.16±5.04%, respectively.We conclude that reproduction and dispersal of P. amurensis might be negatively affected by self-incompatible and sparse insect variety, low visiting frequency by visitors and pollen viability quickly declined as a result of wicked weather, other than dichogamy, pollen and stigma biology characteristic. The temperature and illumination could not be reasons for limiting seed germination in the nature, and soil moisture content and seed burial depth were the most crucial factor in determining seed germination and seedlings establishment.