| Physocarpus amurensis belongs to Physocarpus of Rosaceae, which is a defoliate shrub. The genus Physocarpus includes approximately 20 species in the world, and the geographic distribution of this species is centred in North America in the world, only one species in China. P. amurensis distributed in China is an ancient relic species. It is not only excellent ornamental shrubs, but also officinal function. Now, the areas of distribution and the amount of population of this species in China are much less than the past. So it is believed gradually as an endangered plant and must try to protest it. Up to date, however, the study on the reproduction peculiarity and endangered mechanism of this species is still unknown. Therefore, P. amurensis, the object of our study, located on Mao Er Shan, Hei LongJiang province. This study focuses on these issues with respect to breeding characteristic of P. amurensis, for example, pollination, fruiting characteristics, break seed dormancy, clonal propagation in nature, and establish a rapid micropropagation system through tissue culture. The author has observed outdoors and experimented indoors in several years, and has made a systematic study on reproduction peculiarity of P. amurensis for the first time, and ascertain preliminarily endangered mechanism of this species, and then to bring forward scientific and effective measure for resumed and extended population, and to make a contribution for the protection of the endangered species. The conclusions are as follows:1. The flower period from early June to early July, about 26 days. The flower morphology was changed with the characteristic of stamen 28-33, pistil 2 and rare 3-4. Physocarpus amurensis can not self-pollination in nature, and sexual propagation need pollinator. Pollinators were small insect such as small bees, flies and ants, and so on, but the species and quantity were very sparse. Pollination efficiency was also low. The transformation rate of flowering to fruiting changed was 37.80% and the rate of seed bearing was 12.93% in nature. The proportion of single carpel and double carpel development to fruit attained respectively 64.18% and 35.82% of number of fruit set. The fruit and seed set percentage were so low, and the reason was ovule abortion. Ovule abortion principally related to the failure of pollination and lead to most ovule can not accomplish fertilization.2. The fruiting of P. amurensis was very low. It contained 1-8 seeds in per follicle. The fruit proportion with 1-2 seeds in per fruit was very high, and averaged 2.98 seeds per fruit. There were no significant differences (P>0.05) in the seed number among same and different maternal plant, and it means that the sexual reproduction of the maternal plant was nearly synchronous and the fruit growth was at the similar stage. But highly significant differences (P<0.01) in the seed weight among different maternal plant. The 1000-weightwas 1.38g, the water content in the seed averaged 10.33%, the seed vitality attain 87.78%;the germination experiment showed that there were no significant differences (.P>0.05) in the germination percentage among different maternal plant, germination percentage averaged 21.44%, but the seedling emergence rates was only 5.56% in the soil. Overall, the main cause for continuing and extending the population is in ferior capability of the low fruiting set and seedling emergence rates. Low seedling recruitment may be caused by low seed production as a consequence of pollinator limitation or if seed input is sufficient, by lack of favorable conditions or microsites for seedling establishment.3. Seed of P. amurensis can produce dormancy after the seed mature. Seed soaking in fresh water gave low germination percentage (28.33%) . In order to break dormancy, we used different methods. The best one was that treated with mixture solution (50mg/L GA3+ 4%KNC>3) for 72h, which gave 90% germination percentage. And the germination situation was improved significantly (PO.01) when treated by 100 or 200 mg/L GA3. The low temperature treatment for 28 days could promote obviously the germination percentage and germination situation. The sowing depth had a very important effect on germination, and germination percentage was apparent descendent when sowing depth was deeper.4. Maintenance of populations was mainly dependent on clonal propagation, and extremely rare seedlings in nature. We studied the clonal propagation characteristic. The architecture of rhizomes of P. amurensis essentially belongs to the aparse guerrilla linear system, the rhizomes with unawakened buds may survive a long time, the variations in diameters of rhizomata with length was parabola type;branching angle between rhizomes was comparative stabilization, usually were 30° and 70°. Clonal growth of P. amurensis was the results of long-term to fit environment, and clonal propagules, relative to seedlings, have a greater capacity to survive.5. Factors affecting the regeneration of P. amurensis were studied. Axillary bud from mature mother tree and tip bud from seedling was the best explants. For axillary bud, both MS medium and WPM medium could stimulate proliferation, but MS medium was more effective for shoot growth. d)WPM, supplemented with 0.01 mg/L TDZ was the best for axillary induction. ?MS, supplemented with 1.0 mg/L NAA and 1.0 mg/L BA was the best for proliferation. (3)MS, supplemented with 2.0 mg/L NAA and 0.6 mg/L BA was the best for strong growth. ?MS, supplemented with 0.1 mg/L IBA was the best for rooting. Plantlets were established in sterilized soil in a humidity chamber and transferred to field conditions with more than 65% survival. For tip bud from seedling, ? MS+BA 1.0 mg/L +NAA 1.0 mg/L, for tip bud germination;(D MS+BA 0.8 mg/L+NAA 0.4 mg/L, for shoot proliferation;(3) MS+IBA 0.5 mg/L +GA3 0.3 mg/L, for shoot elongation and strong. It induced abundance adventitious buds in the stage of shoot proliferation, but rates ofrooting were very low, and quality was very poor. So we studied outer test-tube root technology, the best treatment was 100 or 200 mg/L NAA soaked for 30min, transferred to field conditions with 93.1% and 88% survival, respectively.6. Threaten reason analysis: Quantities of the plants were exiguous, and natural regeneration of P. amurensis was difficult. Through field observation, we did not find the seedling under the natural population. At present, the areas of distribution of population were much less than the past. Population extended was limited highly because of babitat particularity (surrounded by rock, soil rareness) and biological characteristic of P. amurensis (clonal plant, maintenance of populations was mainly dependent on clonal propagation under the nature). Among Sexual reproduction, Ovule abortion principally related to the failure of pollination and lead to most ovule can not accomplish fertilization and farther induced the fruit and seed set percentage low. Seed holded dormancy characteristic, germination percentage was low (less than 30%), seedling emergency rate also was low (less than 6%). In addition, the seed was very small, germination condation (temperature, illumination, water and litter depth, et al) in the nature may be limit seed germination and seedling establishment. Large-scale habitat fragmentation or disappear maybe one of the main external factors to its endanger. All factors or interaction effect maybe lead to scant seedlings and poor natural regeneration.7. Implication for conservation of this endangered species: As the species has not effective pollen/seed dispersal mechanism. Ex-situ conservation is a significant means to protect endangered species and natural population. Due to its limited distribution and restricted population number, especially, deficiency of natural regeneration capability, must protest the species from ex-situ conservation. However, because the species is adapted to some special ecological conditions and may be sensitive to changes of environmental conditions, it is important to amplify the population size through ex-situ conservation to decrease or avoid the risk of extinction. |
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