A Preliminary Study On The Factors Affecting Seed Germination Characteristics Of Cercidiphyllum Japonicum(Cercidiphyllaceae)

Cercidiphyllum japonicum(Cercidiphyllaceae),a last remaining primitive plant in Cercidiphyllum and an endangered plants,only distributes in China and Japan because of human activities and population update is difficult.C.japonicum ranges from 1500 to2700 m,southwest China.Although the seed yield is very high,the seedlings are rare.To explore the reasons,we investigated the effects of temperature,storage methods and storage time,and litters on seed germination in Dafengding National Nature Reserve,Meigu,Sichuan Province,Our works not only provide a theoretical basis for the population update,but also provide a scientific support for the seed storage and breeding,as well as population restoration.The results are listed as follows:1.Seed characteristics of C.japonicumThe trapezoidal seeds of C.japonicum with wings are small.The seeds length and width(without wings)were 1.330 ± 0.059 mm and 1.943 ± 0.058 mm.The wing length and width were 3.585 ± 0.153 mm and 1.904 ± 0.059 mm,respectively.The thousand seed weight was only 0.3420 ± 0.0014 g.The water absorption rate of seeds which with very thin seed coat was 331.4% ~ 367.9%,and increased rapidly within 2 hours and then stabilized.Therefore,under the condition of sufficient water,it can rapidly absorb and expand and germinate.In addition,the seeds vigor could be maintained for 6 to 8months,so the low temperature in winter would not lead to the loss of seed vigor.2.Effects of temperature on the seed germination of C.japonicumThe temperature range of seed germination was from 10 ? to 30 ?,and at 25 ?,the germination rate was the highest(42.3%).Under the condition of 5 ? / 10 ?,the seeds only germinated(no cotyledons were displayed after the radicle broke through the seed coat),but failed to germinate normally.By contrast,it could germinate normally at14 ? / 17 ? and 18 ? / 20 ?,and the germination rate was the highest(34.3%)at18 ? / 20 ?,which is lower than that at 25 ?.There was a significant difference between the changing temperature and the constant temperature.The germination time of seeds was more than 20 days under the constant temperature conditions(except for25 ?),but the germination time was reduced to 15 days and 18 days at 14 ? / 17 ?and 18 ? / 20 ? respectively.Additionally,the survival rate of primary seedlings decreased from 63.3% after the first month to 0 % after the fourth month at the low temperature in winter.The results showed that the most suitable temperature for seed germination was 25 ?,and the seeds could sprout rapidly under the condition of variable temperature.The low temperature in winter was not suitable for the survival ofprimary seedlings.3.Effects of storage condition and time on the seed germination of C.japonicumAlthough the seeds of C.japonicum can not germinate in winter,it does not mean that it has lost its germinating ability.In order to study whether the seeds can germinate and the optimum storage conditions,five storage conditions(low temperature wet storage(-4 ? ~-2 ?),lower temperature wet storage(5 ? ~ 10 ?),low temperature dry storage(-4 ? ~-2 ?),lower temperature dry storage(5 ? ~ 10 ?),room temperature dry storage(10 ? ~ 15 ?)were set up.The seed germination experiment was carried out after storage for one,two,three and four months.The results showed that after the seeds were stored at low temperature and humidity in winter,the germination rate of seeds decreased from 34.7% after one month to 27.6% after four months,but the decrease was not significant,which indicated the seeds still had the ability to germinate and form seedlings under the appropriate temperature conditions.The germination rates of seeds stored at low temperature,lower temperature and room temperature and dry conditions were from 33.3%,31.3% and 29.6% after one month to 3.0%,4.7% and 0% after four months,respectively.The germination ability of the seeds decreased significantly with the passage of time,and the seeds stored at room temperature and dry conditions lost its germination ability after four months.Taking the germination rate and germination potential into consideration,the results showed that it is good for the long-term storage of the C.japonicum seeds at low temperature and wet storage conditions.4.Effects of litter on seed germination and primary seedling of C.japonicumThe seeds could germinate normally,when the thickness of litter cover was 0-3cm.At 0 cm,the seed germination rate was the highest(30.7%)and the root length was the longest(7.757 mm).With the litter cover thickness increase,the seed germination rate gradually decreased and the root length gradually reduced.Meanwhile the seed germination was delayed,and the time required for germination completion was increased.In addition,the seed did not germinate when they did not contact the soil on the surface of litter and the thickness of litter layer was 4 cm and 5 cm.Therefore,litter coverage will lead to the extension of seed germination,which is not conducive to occupy the niche.On the other hand,when the concentration of litter extract was higher(20 g/L?40g/L?80 g/L),it could inhibit the seed germination of C.japonicum.By contrast,the lowest concentration of litter extract(10 g/L)could promote the seed germination of C.japonicum and the germination rate was the highest(50.3%).Meanwhile,the highest concentration of litter extract not only showed a significant difference in the inhibition of seed germination,but also significantly inhibited the root length and stem length of primary seedlings.These results suggested that the litter of C.japonicum had allelopathic effects on its seed germination and the primary seedling growth.Considering the influence factors of seed germination and primary seedlings establishment in the process of C.japonicum population renewal,this study believes that low temperature in winter does not conducive to the survival of primary seedlings generated by seed germination,which may lead to the poor renewal of C.japonicum natural population;it is suitable for the storage of seeds under low temperature and wet conditions;seed germination and primary seedling establishment are susceptible to the double interference of physical and chemical factors of the litter.